Citation
Structural health monitoring of a cable stayed pedestrian bridge with interferometric radar

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Title:
Structural health monitoring of a cable stayed pedestrian bridge with interferometric radar
Creator:
Bennett, Paul James
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
Publication Date:
Language:
English
Physical Description:
1 electronic file. : ;

Subjects

Subjects / Keywords:
Cable-stayed bridges ( lcsh )
Interferometers ( lcsh )
Cable-stayed bridges ( fast )
Interferometers ( fast )
Genre:
non-fiction ( marcgt )

Notes

Abstract:
Due to an aging infrastructure inside the United States and advances in technology, innovative structural health monitoring methods are emerging. Both short and long term health monitoring of structures can yield valuable data which can be used to determine the condition and capacity of the structure. Much research has been performed in the area of long term health monitoring (defined as monitoring where the instruments are left for days, months or years) but short term monitoring is an emerging field. This document focuses on short term monitoring utilizing an instrument that is new to North America as of 2009. The subject instrument is the "IBIS-S" system which uses local interferometric radar to monitor structural movement wirelessly and in a non-contact manner. As this system is lightweight and wireless it is easy to quickly deploy, without interrupting the use of the structure, and allows the user to begin collecting data under live loads within hours. Outside of Europe, little research and verification of interferometric radar technology has been conducted on structures. This thesis presents interferometric radar theory, development and application as it relates to cable stayed bridges, particularly towards monitoring the health of the cables and overall natural frequencies of the bridge. It will be shown that interferometric radar can successfully be used to monitor the tension force and health of the cables as well as the global frequencies of the bridge. A protocol for monitoring the cables and the overall natural frequency for the City and County of Denver's cable stayed pedestrian bridge where 16th street crosses the Platte River is presented. Through the use of interferometric radar, baseline data was established for the subject bridge and it was determined that the fundamental frequency of the bridge is below the 3 Hz recommendation set forth in AASHTO standard.
Thesis:
Thesis (M.S.)--University of Colorado Denver. Civil engineering
Bibliography:
Includes bibliographic references.
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Paul James Bennett.

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Source Institution:
|University of Colorado Denver
Holding Location:
|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
860838661 ( OCLC )
ocn860838661

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Full Text
STRUCTURAL HEALTH MONITORING OF A CABLE STAYED PEDESTRIAN BRIDGE
WITH INTERFEROMETRIC RADAR
by
PAUL JAMES BENNETT
B.S. University of Nevada Reno, 2000
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
2012


2012
PAUL JAMES BENNETT
ALL RIGHTS RESERVED


This thesis for the Master of Science degree by
Paul James Bennett
has been approved for the
College of Engineering
by
Kevin L. Rens, Chair
Fredrick R. Rutz
Rui Lui
Chengyu Li
November 16, 2012


Bennett, Paul James (M.S., Civil Engineering)
Structural Health Monitoring of a Cable Stayed Pedestrian Bridge with Interferometric
Radar
Thesis directed by Professors Fredrick R. Rutz and Kevin L. Rens
ABSTRACT
Due to an aging infrastructure inside the United States and advances in
technology, innovative structural health monitoring methods are emerging. Both short
and long term health monitoring of structures can yield valuable data which can be used
to determine the condition and capacity of the structure. Much research has been
performed in the area of long term health monitoring (defined as monitoring where the
instruments are left for days, months or years) but short term monitoring is an emerging
field. This document focuses on short term monitoring utilizing an instrument that is new
to North America as of 2009.
The subject instrument is the IBIS-S system which uses local interferometric
radar to monitor structural movement wirelessly and in a non-contact manner. As this
system is lightweight and wireless it is easy to quickly deploy, without interrupting the
use of the structure, and allows the user to begin collecting data under live loads within
hours. Outside of Europe, little research and verification of interferometric radar
technology has been conducted on structures. This thesis presents interferometric radar
theory, development and application as it relates to cable stayed bridges, particularly
towards monitoring the health of the cables and overall natural frequencies of the bridge.
It will be shown that interferometric radar can successfully be used to monitor the
tension force and health of the cables as well as the global frequencies of the bridge. A
protocol for monitoring the cables and the overall natural frequency for the City and
County of Denvers cable stayed pedestrian bridge where 16th street crosses the Platte
River is presented. Through the use of interferometric radar, baseline data was


established for the subject bridge and it was determined that the fundamental frequency
of the bridge is below the 3 Hz recommendation set forth in AASHTO standard.
The form and content of this abstract are approved. I recommend its publication.
Approved: Fredrick R. Rutz
IV


DEDICATION
This thesis is dedicated to my incredibly supportive wife, Melissa, and my two
daughters, Hannah and Amelia, without whom this thesis and my graduate work never
could have happened thank you for your unwavering support. Additionally, I dedicate
this work to my father, Alan, who sacrificed so much in life to teach me about work ethic
and a belief that I can accomplish anything in life. I also would like to dedicate this
thesis to my Lord and Savior Jesus Christ who is my all in all and who has given me the
drive and discipline to succeed.
v


ACKNOWLEDGEMENTS
First, I would like to thank Dr. Richard Ziernicki and Knott Laboratory for funding
my graduate education and employing me, as well as Olson Instruments for graciously
loaning me their instrument and expertise. Second, I would like to thank Dr. Rui Liu who
was a tremendous help in this research. Third, I would like to thank Dr. Fredrick Rutz
and Dr. Kevin Rens for their support and guidance through this process.
VI


TABLE OF CONTENTS
CHAPTER
I. INTRODUCTION.............................................................1
Introduction.....................................................1
Scope and Objective of Thesis....................................2
Outline of Thesis................................................3
II. LITERATU RE REVIEW........................................................4
Introduction.....................................................4
History and Concept of Radar ....................................7
How IBIS Works..................................................10
Limitations of IBIS-S System ...................................15
IBIS Software...................................................17
Historic Use of Radar on Infrastructure ........................18
Historic Use of Radar on Cable Stayed Bridges...................19
Predicting Tensile Force in Cables Based on Fundamental Frequency .19
Effect of Vibrations on Pedestrian Bridges .....................19
Summary ........................................................28
III. THEORETICAL ANALYSIS ....................................................29
Overview........................................................29
Three Dimensional CAD Model ....................................29
SAP 2000 Model..................................................30
vii


General Bridge Construction
30
Support Conditions ....................................32
Bridge Fundamental Frequency ................................35
Conclusions .................................................35
IV. LABORATORY WORK ....................................................37
First Laboratory Experiment .................................37
Setup of First Experiment (Cable Test).......................37
Results of First Experiment (Cable)..........................39
Conclusions from First Experiment (Cable)....................43
Second Laboratory Experiment (Steel Channel).................43
Setup of Second Experiment (Steel Channel) ..................43
Results of Second Experiment (Steel Channel).................45
Conclusions from Second Experiment (Steel Channel)...........46
V. FIELDWORK ...........................................................47
Setup .......................................................47
Setup Comparisons ...........................................50
Testing and Results..........................................51
Cable Vibration Measurement .................................51
Global Bridge Vibration Measurement..........................56
Summary and Conclusions......................................56
viii
VI. DISCUSSION
57


Introduction..................................................57
Cable Calculations............................................57
Global Bridge Vibration Discussion ...........................61
General Bridge Construction ..................................67
Pedestrian Bridge Application of Work.........................67
Recommendations for City and County of Denvers Cable Stayed
Pedestrian Bridge at 16th Street Over The Platte River........68
Summary and Conclusions.......................................69
VII. CONCLUSIONS AND RECOMMENDATIONS......................................70
Conclusions ..................................................70
Recommendations...............................................70
Future Work...................................................71
REFERENCES.................................................................72
APPENDIX
A. Construction Documents for The City and County of Denvers Pedestrian Bridge -
16th Street Over The Platte River..........................................74
B. First Laboratory Test Cable Test ....................................131
C. Second Laboratory Test Channel Test..................................144
D. Field Measurement of Cable Vibration on Cable Stayed Pedestrian Bridge at 16th
Street over the Platte River..............................................156
IX


LIST OF TABLES
TABLE
4.1 Results of Lab Testing for Tensile Force Determination in Cable...........41
5.1 Measured Fundamental Natural Frequency of Bridge Cable by Cable Position (Hz)
55
6.1 Cable Force Determination.................................................59
6.2. Corrected Cable Force Determination, Based on 5th Mode...................60
x


LIST OF FIGURES
FIGURE
2.1 Suspension bridge population in the 20th century...........................5
2.2 Martin Olav Sabo cable stayed pedestrian bridge...........................6
2.3 Electromagnetic spectrum...................................................8
2.4 Ideal radar reflector......................................................9
2.5 Interferometric radar concept.............................................11
2.6 IBIS line of sight measurement...........................................12
2.7 Radar read out on PC......................................................13
2.8 Accuracy vs. SNR..........................................................14
2.9. Concept of range bins.....................................................16
2.10 Effects of cable sag on fundamental frequency............................22
2.11 Effects of cable sag on higher vibration modes...........................23
2.12 Effects of cable bending stiffness on fundamental frequency..............25
2.13 Effects of cable bending stiffness on fundamental frequency for higher modes ....26
3.1 Three dimensional view of bridge...........................................29
3.2 Three dimensional view of bridge...........................................30
3.3 Subject Bridge............................................................32
3.4 Bridge end bearing conditions.............................................33
3.5 Midspan support...........................................................34
3.6 Close in view midspan support.............................................34
XI


3.7 First mode shape from sap mode..........................................35
4.1 Cable in MTS equipped with accelerometer.................................38
4.2 Graph of calculated vs. actual cable force...............................42
4.3 Drawing of channel.......................................................44
4.4 Channel Testing in MTS...................................................44
5.1 Subject cable stayed bridge..............................................48
5.2 Radar setup in field.....................................................49
5.3 Accelerometer installed on cable on subject bridge.......................53
6.1 Radar plot of underside of bridge........................................61
6.2 Frequency domain plot of underside of bridge, data for seven floor beams overall. 62
6.3 Frequency domain plot of floor beam vibration on underside of bridge.....63
6.4 Frequency domain plot of south tower vibration...........................64
6.5 Frequency domain plot of north tower vibration...........................65
6.6 Frequency domain plot of north railing...................................66
6.7 Mode shape plot from Matlab.............................................67
xii


LIST OF EQUATIONS
EQUATION
2.1. Relative Displacement Equation...........................................11
2.2 Tension Force in Cable...................................................20
2.3 A non-dimensional characteristic parameter that reflects the influence of the sag-
extensibility on the cable natural frequencies................................20
2.4 A non-dimensional parameter which represents the effect of cable bending stiffness
on the natural frequencies of cable vibration.................................24
2.5 Fundamental bending frequency of cable stayed bridge......................27
2.6 Minimum fundamental frequency of bridge in the vertical direction.........28
2.7 Prescriptive weight of supported structure, including only dead load.....28
xiii


LIST OF SYMBOLS
SYMBOL
A Cross sectional area of cable
d The objects relative change in position
E Modulus of elasticity of cable material
/ Fundamental frequency in the vertical direction
fe Fundamental bending frequency
fn Fundamental frequency of member or structure
g Acceleration due to gravity
H Cable force in chord direction
I Moment of inertia of cable cross section
i Cable chord length
L Length of the main span
Le Effective cable length
m Mass per unit length of cable
n Mode number
T Axial Tension Force on Cable
W Weight of supported structure, including only dead load
Acp The change in radar phase
X The radar wavelength
X2 A non-dimensional characteristic parameter that reflects the influence of the sag-
extensibility on the cable natural frequencies
71 Mathematical constant
P Cable mass per unit length
XIV


E, A non-dimensional parameter which represents the effect of cable bending
stiffness on the natural frequencies of cable vibration
co-i Calculated fundamental frequency based on the taut string theory
co1s Fundamental frequency based on Ren et. als theoretical work which considers
cable sag
xv


CHAPTER I
INTRODUCTION
Introduction
Radar has long been used to track the movement of objects or masses across
large distances. This includes aircraft, sea vessels, precipitation, and vehicles.
Regarding static objects, such as structures, radar has been successfully used to locate
hidden objects. An example of this is the process of locating reinforcing steel in
concrete or underground utilities utilizing ground penetrating radar (GPR).
More recently radar has been used by satellites to monitor movement of soil/land
masses to an accuracy of several meters (IBIS-S Controller User Manual July 2010).
With time and technology, the accuracy of radar has greatly increased to the point where
it is now feasible to monitor very small movements. In the 1990s, an Italian corporation
known as Ingegneria Dei Sistemi, or IDS translated Systems Engineering -
partnered with the University of Florence to research the possibility of utilizing radar to
monitor earth movement to a higher degree of precision (i.e. millimeters (mm))
(25.4mm=1.0 inches) (Farina et al, 2011). IDS and the University of Florence were
successful in applying radar technology in monitoring land subsidence and slope
stability, particularly in mining applications (Farina et al, 2011). In this application, a
semi-permanent radar station is set up to focus on a particular slope (Farina et al, 2011).
IDS technology for monitoring slope stability has successfully been used in Europe for
over a decade (Farina et al, 2011).
In the late 1990s, Farrar et. al presented that radar could be used to monitor
movement in structures (Farrar et. al 1999). IDS and the University of Florence have
also researched radar applications on structures, namely monitoring small movements in
structures or structural members. Through all this research, IDS has developed a
1


system entitled Image By Interferometric Survey (IBIS) which utilizes radar to monitor
deflections in structural members with a precision of up to 1/100 mm (0.000394 inches).
The IBIS system is a non-contact, non-destructive, rapidly deployable system that has
positive implications for the structural health monitoring community. Both the benefits
and limitations of the IBIS instrument are discussed in this thesis. As it relates to
structures, the IBIS system has been used in Europe for approximately 10 years.
Inside of North America few IBIS systems exist and the few systems that do exist
are privately owned and operated by the mining industry to monitor slope stability.
Olson Instruments Inc. (Olson) of Wheatridge, Colorado currently has the only privately
held, for-hire, IBIS system in North America. Olson has graciously agreed to help
sponsor this thesis in the spirit of increasing the body of knowledge of the structural
health monitoring community.
Scope and Objective of Thesis
Because of its superior accuracy there are many potential IBIS applications in
structures. However, many such applications are still being researched. The primary
objective of this thesis is to explore, via laboratory and field experiments, an application
of IBIS technology to cable stayed bridges. Of particular interest is a pedestrian bridge
owned by the City and County of Denver, Colorado. A method to monitor the health of
the cables and overall bridge health with IBIS technology was developed and
implemented. The scope of this thesis is limited to one bridge and to vibration
monitoring on that bridge. Recommendations for future bridge health monitoring are
provided herein.
Outline of Thesis
This thesis presents the results of theoretical and experimental testing in which
interferometric radar technology is used to monitor the structural health of a cable stayed
2


pedestrian bridge. Chapter Two presents a review of available literature regarding
interferometric radar and its use on structures, including cable stayed bridges. Chapter
Three presents the results of a Finite Element Analysis (FEA) theoretical determination
of a particular cable stayed bridges fundamental frequency. Chapter Four presents the
results of laboratory experiments in which interferometric radar was used to determine
the tension force in a cable based on the fundamental frequency of vibration and an
attempt was made to determine the tension force in a steel channel through the use of
interferometric radar. Chapter Five presents the results of field work wherein
interferometric radar, an alternate instrument, and an accelerometer were used to
monitor vibrations in a cable stayed pedestrian bridge and the results of all three
instruments were compared. Chapter Six contains discussion and conclusions reached
as a result of the work in the previous four chapters as well as a testing protocol for the
subject pedestrian bridge. Chapter Seven presents final conclusions and
recommendations.
3


CHAPTER II
LITERATURE REVIEW
Introduction
The concept of a cable suspended bridge (a bridge in which smaller vertical
suspender cables that support the deck, hang from a larger catenary shaped cable
which anchors to the earth) has been around for centuries as historians note remote foot
bridges constructed with vines and ropes. However, the concept of a cable stayed
bridge a bridge in which the cables are diagonal, putting the bridge deck into
compression, and the cables attach to a structurally critical tower or mast is a more
recent (past 400 years) development.
The oldest known cable stayed bridge design concept dates back to a design
completed by the Venetian engineer Faustus Verantius in 1607 (Podolny 1999). The
oldest known constructed cable stayed bridge dates back to a 32 Meter (M) (105 Feet)
long span completed by Loscher in 1784 (Podolny 1999). The oldest known cable
stayed bridge in the United States is a still intact steel bridge located in Texas and was
designed by E.E. Runyon (Historic American Engineering Record 1968).
The concept of cable stayed bridges did not become common in place in the United
States until approximately 40 years ago. As can be seen in Figure 2.1, the use of cable
stayed bridges in new construction in the United States continued to increase until the
mid 1990s. The increased use of cable stayed bridges is due both to their aesthetic
appeal and their cost effectiveness for moderate bridges.
4


30
Figure 2.1 Suspension bridge population in the 20th century.
(Copyright 1999 by The McGraw-Hill Companies, Podolny, Walter, Jr., P.E. (1999). Section 15,
cable suspended bridges, Structural Steel Designers Handbook, Third Edition, ed.
Brockenbrough, R.L, Merritt, F.S., Image reproduced with permission from The McGraw-
Hill Companies)
With an increase in the number of cable stayed bridges in the United States in
the past 40 years there becomes a need for the development of structural health
monitoring techniques for cable stayed bridges. In contrast to a suspension bridge
wherein the failure of one of hundreds of suspender cables is likely not catastrophic, the
failure of a cable in a cable stayed bridge has a higher likelihood of being catastrophic.
For instance, consider the Martin Olav Sabo cable stayed pedestrian bridge in
Minneapolis, Minnesota (Figure 2.2) constructed over a light rail and highway in 2007
with a main clear span of 67 M (220 feet) which had a serious failure on February 19,
2012 that led to the closure of the bridge. The failure, involved the failure of two cables
which caused a portion of the bridge deck to deflect which in turn caused an increase in
loading on adjacent connections causing concern or a progressive collapse. Reportedly,
the cables failed due to a fatigue failure, induced by wind born vibrations, in a diaphragm
plate that connected to the bridge tower (WJE 2012). Many engineers have suspected
5


that the failure was caused by fatigue stresses that were induced by excessive vibrations
in the bridges cables as members of the community had expressed concern over
excessive vibrations. It is unknown to this engineer what type of structural health
monitoring program was in place for this bridge but perhaps closer monitoring of cable
vibrations and global vibrations would have predicted fatigue failure.
Figure 2.2 Martin Olav Sabo cable stayed pedestrian bridge.
(Copyright 2009 by John A. Weeks III, http://www.johnweeks.com/cablestay/pages/ped07.html,
Image used by kind permission from John A. Weeks III)
Much research exists regarding the structural health monitoring of cable stayed
bridges and a fundamental part of any such health monitoring plan involves vibration
monitoring. However, most, if not all, current vibration monitoring instruments require
persons to physically access the cables in order to obtain measurements which usually
results in temporary bridge closure. The purpose of this thesis is to explore the use of
radar technology for monitoring structural health in cable stayed bridges this concept
allows data to be gathered without closure of the bridge and in a non-contact manner.
6


History and Concept of Radar
The word radar, a noun in the English language, stems from an acronym developed
in the U.S. Navy RAdio Detection And Ranging (RADAR). As the name implies, radar
technology relies upon the use of radio waves to detect the location (range) of mass. On
the electromagnetic spectrum, radar is a subarea of the microwave region having a
range of frequency between 0.3 and 300 GHz (Figure 2.3). Radar technology has been
around for over 100 years but it wasnt until World War II when its use became
widespread and wide known as it was found very useful to track both enemy and ally
ship and aircraft locations and movements.
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Figure 2.3 Electromagnetic spectrum.
(http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html, Image Courtesy of Advanced
Light Source,
Lawrence Berkeley National Laboratory)
8


Radar is an invisible wave which, like any waveform, when emitted will reflect -or
bounce back- from objects in its way. Metallic objects are a particularly good reflector.
The quality of the reflection is dependent upon both the material and the angles inherent
to the object. An ideal radar reflector is a metallic object in the shape of an open
pyramid where the radar is directed at the inside of the pyramid this shape forces all
incoming waves to be reflected back towards their source (Figure 2.4).
Figure 2.4 Ideal radar reflector.
In a real world scenario, the rather sharp angle created at the point where an
aircrafts tailfin joins the fuselage is a good reflector of radar. With this basic knowledge
of radar one can view Lockheed Martins stealthy, nearly radar invisible, F117 aircraft
and come to understand the purpose of the oblique angles and out of plumb tail fins.
In order to locate or track the movement of an object, a radar emitter sends out radar
waves with a known frequency, amplitude, and wave length. An antenna is engineered
and setup to receive the radar waves. Due to the Doppler Effect, the reflected waves
9


have a different wavelength, frequency, phase and amplitude from the initial signal (IDS
2008). Utilizing the change in the waveform it is then possible to determine how far
away the object is and by this information one can track the relative movement
(displacement) of an object.
How IBIS Works
IDS IBIS system utilizes radar technology to detect small movements in structures or
structural members. The subject IBIS instrument, one that is licensed by the Federal
Communications Commission for use in the United States, emits microwaves at a
Continuous Wave Step Frequency (CWSF) of 17.1-17.3 MHz with a wavelength of
approximately 18mm (0.71 inches)(IDS 2010). The frequency and wavelength have
importance as they determine the size of object that can be detected, the maximum
measurable defection, and the minimum distance two objects must be separated by a
concept known as range bins for which further discussion is presented below.
IBIS utilizes a form of radar known as interferometric radar. In most radar
applications the amplitude change in the reflected wave form is used to determine the
location of the desired object. However, interferometric radar utilizes the change in
phase of the reflected wave to determine position. By monitoring the phase change, a
more accurate measurement of movement is possible (Figure 2.5).
10


First acquisition at time = T,
Transmitting
Antenna
Receiving
Antenna
Phase 1: cpl . Ill I III

Transmitting
Antenna
Receiving
Antenna
Phase 2: d oc cp2 cpi
Figure 2.5 Interferometric radar concept (adapted from IDS 2010).
An objects change in position is given by the equation 2.1 shown below.
Where: d = Objects relative change in position
A = Radar wavelength
A 7T= Mathematical constant
Inside of the interferometric radar technology are two concepts; Synthetic
Aperture Radar (SAR) and Real Aperture Radar (RAR). IDS manufactures a system for
long term monitoring of slopes and structures (IBIS-L) and a system for short term health
monitoring (IBIS-S). The instrument used in this research is the IBIS-S system. In a
static setup the IBIS-S relies upon RAR technology which, in contrast to a typical two
dimensional (2D) SAR image, results in a one dimensional (1D) view (Dei et al, 2009).
d =------- A (p
4 n
Equation 2.1 Relative Displacement Equation (Gentile 2008).
11


Due to the 1D limitation it is critical to understand that the displacement
measured is the objects relative movement in the line of radar. As the radar head is
rarely, if ever, pointed directly along the expected plane of movement (vertical in the
instance of a beam deflecting downward), the measured displacement is not actual
displacement (Figure 2.6). However, due to the superior accuracy of IBIS, vertical
displacement will produce a change in the measured distance and utilizing basic
trigometric principles one can calculate the actual displacement.
Figure 2.6 IBIS line of sight measurement (adapted from Gentile 2008).
From a hardware standpoint, the IBIS system is fairly simple. It consists of a
radar head or sensor that has two antennas. One antenna sends a signal and the other
12


receives. The radar head sits atop a traditional tripod that is leveled prior to use. Two
cables connect to the back of the sensor. One cable is used to power the system and
the other is used to send data to a personal computer (PC). Any PC system with the
proper software and a Universal Serial Bus port (USB) can be used to receive data.
The IBIS system has six available sets of antennas. Each antenna forms a
different shaped radar cone which results in a different field of view. For example, one
antenna produces a narrow focused cone and another produces a wide shallow cone.
While the IDS provided manuals give data on each of the antennas there are no known
publications which educate the user on which antennas are best for certain applications.
In the Field Work section of this paper more is presented on how an individual chooses
an antenna for a given application.
Once the IBIS system is assembled and powered, the user can view the radar
feedback on the PC. The radar feedback is presented on a plot with distance on the X
axis (in meters) and a signal to noise ratio (SNR) plotted on the Y axis (see Figure 2.7
for an example).
Profile
13


The stronger the SNR the more accurate the instruments output is. Thus, strong
peaks on the plot (high SNR) are necessary for the structural member(s) of interest. On
the low end, SNR ratios of 20 give an accuracy of 0.1mm (0.00394 inches) (IDS 2010).
On the high end, SNR ratios of 60 and higher give an accuracy of 0.005mm (0.00020
inches)(see Figure 2.8). Even with the low SNR ratios, a high degree of accuracy is
available.
(Copyright 2010 by IDS, IBIS-S Controller V 02.02.000 User Manual Rev. 1.1, July 2010, Image
used by kind permission from IDS)
Certain types of structural members are good natural reflectors of radar. These
include steel members with geometry changes such as L, C and W shaped members.
Steel cables are typically good reflectors. Typical plate steel and smooth rods are not
good reflectors of radar. Concrete and wood are not typically good reflectors of radar.
For applications where the user cannot achieve good reflections the user may be
required to install a reflector as shown in Figure 2.4.
In order for the user to have confidence as to what peaks correlate to which
structural members, a laser distance meter is a necessary tool. By placing the distance
14


meter on the IBIS and aiming at desired structural elements, the user can quickly
determine which peaks relate to which member(s). For the purpose of determining the
distance to smaller diameter cables, a distance meter with a live video feed and
crosshairs is necessary to ensure the laser is reflecting from the correct cable. For the
purposes of this thesis, a Leica DISTO D5 instrument (a laser distance meter which has
a range of up to 200 M (650 Feet) and an accuracy of 1mm (0.0394 Inches)) was used.
Thus, as long as the user has confidence in the objects each radar peak corresponds to
the user can collect displacement data on multiple structural elements at the same time.
For instance, one technique involves viewing the underside of a bridge, looking parallel
to the structure, allowing the user to collect displacement data for all cross
frames/members at the same time with one setup and one instrument.
In a typical static/tripod type of setup the IBIS system produces a 1D image. Due
to the static setup and CWSF, range bins are created in which the radar cannot
distinguish the difference between objects that are within a certain distance of each
other along the path of the wave propagation (see Figure 2.9). The range bin distance
for the IBIS-S system available in North America is 0.75 M (2.46 Feet); that is to say that
the instrument cannot differentiate between objects closer than 0.75 M (2.46 Feet) to
each other on a given radial distance from the instrument. Dei et al. (2009) have
successfully explored monitoring techniques, monitoring torsional motion, wherein the
instrument is mounted and moved slowly along a rail to produce a 2D, SAR image that is
not limited by range bins.
15


Figure 2.9 Concept of range bins.
(Copyright 2010 by IDS, IBIS-S Controller V 02.02.000 User Manual Rev. 1.1, July 2010, Image
used by kind permission from IDS)
IBIS can sample at a rate of 200Hz (100Hz Nyquist Frequency) permitting the user to
obtain accurate data when monitoring vibrations. The 200Hz sampling rate also permits
the user to see higher order natural frequencies and mode shapes in most structures
and cables.
Limitations of IBIS-S System
The IBIS system is limited to objects that are further than 0.75 M (2.46 Feet) apart
from each other. In addition to this limitation, IBIS 18mm (0.71 Inches) wavelength
requires that the object be larger than 18mm (0.71 Inches) in order that the waves do not
pass over the object. The implication of these limitations is that IBIS cannot practically
be used to monitor the tensile force in cables that have a diameter of less than 18mm
(0.71 Inches) (although a limitation of 25.4mm (1.00 inches) cable diameter is typically
recommended).
16


IBIS 18mm (0.71 Inches) wavelength also presents a dilemma for larger deflections. If
the deflections in the member exceed 18mm (0.71 Inches), then certain portions of the
radar waves will pass over the object resulting in incorrect data. For cables with low
tensile forces that are constantly excited by ambient conditions (wind, traffic) this proves
to be a problem. However, this problem can be overcome by mounting onto the cable,
or beam, a reflector that is much larger than the 18mm (0.71 Inches) wavelength -
obviously this would require access to the cable (which may not always be possible).
Benefits of IBIS are that its results are reportedly unaffected by weather conditions
and it typically requires no contact with the structural members so that monitoring can
occur while the structure is in use.
IBIS Software
IDS IBIS system is supplied with an outdoor rated laptop computer which features
hardware drivers to connect to and collect data from the radar head. However, any
personal computer can be used; the user does not have to use the supplied laptop. Also
provided with the IBIS system is MatLab-based post processing software. After the field
data- referred to as a mission- is complete, the user can launch the post processing
software and begin processing the gathered data (displacement data as a function of
time) for each point of interest. The post processing software is surprisingly simple to
use and is quite powerful. In particular, the software performs a Fourier Transform
function (which takes displacement data that was acquired in the time domain and plots
it in the frequency domain) after which the displacement, velocity and acceleration can
call be viewed in both the time and frequency domains.
IBIS MatLab based software also has the capability to determine mode shapes and
to form a movie that depicts the structures movement over time this is done in a click
of a button. These capabilities allow the user to process and view their data in the field
17


and within minutes form an opinion on the accuracy of the data as well as the behavior
of the structure.
Historic Use of Radar on Infrastructure
Radar has long been used to inspect roadways and structures through the use of
Ground Penetrating Radar (GPR). In contrast to IBIS use of interferometric radar
technology, GPR utilizes conventional radar technology to ascertain information. GPR
use in the United States began in the 1970s with its use on roadways, including bridge
decks, and its use has expanded to investigation of: buried utilities, voids below
roadways, pavement thicknesses, depth to bedrock and determination of deteriorated
areas of bridge decks, all utilizing high frequency microwaves of 0.5 to 1 GHz (Morey,
1998; Maser, 1994; Alongi etal, 1992, Scullion etal, 1992).
Today, GPR is still used for all of the above and its use has further expanded to
buildings and bridges. GPR is used to locate steel rebar and strands in mildly reinforced
concrete and pre/post stressed concrete, respectively. Tallini et al, successfully showed
that GPR can be used to determine foundation type and to investigate the quality (depth
and bulbs) of micropiles (Tallini et al, 2004)
As it pertains to interferometric radar, research indicates that the technology has
been successfully used to monitor the structural health of wind turbines (Pieraccini et al,
2008), buildings (Luzi et al, 2008), towers and culverts (Beben, 2011). Other research
involves multiple IBIS systems working together to measure torsion in structures (Dei et
al, 2009). Much research has also been dedicated to utilizing IBIS technology in the
monitoring of slope stability (see Pieraccini et al., 2001).
18


Historic Use of Radar on Cable Stayed Bridges
As previously mentioned, Farrar et. al explored the application of radar to monitor
movement in structures this included bridges (Farrar, et. al, 1999). Since that time
many groups including Pieraccini et al, Gentile, Dei et al have successfully
undertaken the monitoring of bridges with IBIS technology (Gentile 2008, Pieraccini et
al., 2001). These individuals have been successful in monitoring both
deflections/vibrations in bridge members as well as determining global natural
frequencies and mode shapes of the bridges. These bridges included cable stayed
bridges.
Specifically regarding the structural health of cables in the cable stayed bridges there
is very little published literature. In 2010 Gentile theorized that IBIS technology could be
used to monitor the health of cables in cable stayed bridges via monitoring changes,
over time, in the natural frequency of the member (Gentile 2010). Further, Gentile relied
upon previous research which determines the tension force in a cable based on the
cable properties and measured natural frequency. Over time, changes in the cables
frequency would indicate there is a change in the tension force which could indicate
deterioration in the cable or overall changes in the load paths in the bridge as a whole.
Predicting Tensile Force in Cables Based on Fundamental Frequency
The earlier work that Gentile did relied upon work done by Mehrabi in 2006
(Mehrabi 2006). Mehrabi indicates that the tension force in a cable member can be
determined by relying upon a taut string model which is represented by equation 2.2
(Mehrabi 2006):
19


T = 4pLe1()2
n
Equation 2.2 Tension Force in Cable (Ren et al).
Where: T = Axial tension force on cable
fn = Fundamental frequency of member or structure
n= Mode number
Le= Effective cable length
P = Cable mass per unit length
As the name implies, applying the taut string theory to cables assumes the cable
is taut. However, in many instances cables in cable stayed bridges are not taut. Such is
the case for the bridge that is the subject of this thesis. Both the degree of sag and the
bending stiffness of cables effect their fundamental frequency and changes the accuracy
of Equation 2.2 above. Ren et al sought to quantify the effect of bending stiffness and
sag on the taut string theory equation and their work indicates that indeed unacceptable
errors in predicted tensile force can occur due to cable sag and stiffness (Ren et. al,
2007). Ren et. al. performed a theoretical analysis on the effect of cable sag and in that
analysis they introduce a non-dimensional term (A2), shown in Equation 2.3 below,
which is an important characteristic parameter that reflects the influence of the sag-
extensibility on the cable natural frequencies (Ren et. al, 2007).
20


a2=(
mgl 2EAl
~HLe
Equation 2.3 A non-dimensional characteristic parameter that reflects the
influence of the sag-extensibility on the cable natural frequencies.
Where: E=
A=
Modulus of elasticity of cable material
Cross sectional area of cable
Le= Effective cable length
H= Cable force in chord direction
i = Cable chord length
m= Mass per unit length of cable
/t2= A non-dimensional characteristic parameter that reflects the influence of the
sag-extensibility on the cable natural frequencies
G= Acceleration due to gravity
When utilizing the first mode, Ren et al conclude that for A2 values greater than
1.0, large amounts of error exist (20% when A2 equates to 5.48, for example) (Ren et. al,
2007). This phenomena is shown graphically in Figure 2.10 below wherein coi is the
calculated fundamental frequency based on the taut string theory and co1s is the
fundamental frequency based on Ren et. als theoretical work which considers cable sag
(Ren et. al, 2007).
21


Figure 2.10 Effects of cable sag on fundamental frequency.
(Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations:
International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008,
Determination of Cable Tensions Based on Frequency Differences, Ren, Wei-Xin; Liu, Hao-Liang;
Chen, Gang; Page 176, Figure 2, used with kind permission from Inderscience Enterprises
Limited.)
Ren et als work went on to analyze the effect of cable sag on higher modes of
vibration and the results are very useful in this thesis work. Specifically, Ren et al
performed theoretical analysis for higher vibration modes and showed that the effects of
cable sag become negligible for higher vibration modes. A plot showing the variation of
A2 for different vibrations modes is shown in Figure 2.11 below. Note that in Figure
2.11, the y label on the y axis is a variable that represents different curve functions,
each of which contain the natural frequencies of the symmetric in-plane modes of a
sagged cable. On the same note, the jBI/2 label on the x axis is the algebraic roots
22


(1st, 2nd, 3rd, etc.) to the equation represented by variable y which represent
corresponding (1st, 2nd, 3rd, etc.) mode shapes.
Figure 2.11 Effects of cable sag on higher vibration modes.
(Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations:
International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008,
Determination of Cable Tensions Based on Frequency Differences, Ren, Wei-Xin; Liu, Hao-Liang;
Chen, Gang; Page 177, Figure 3, used with kind permission from Inderscience Enterprises
Limited.)
Ren et. al. conclude that when A2=300, the discrepancy between the first three
symmetric natural frequencies of the sagged cable obtained from their theoretical
equation and those of the taut-string cannot be neglected, but the sagged cable
frequency and taut-string frequency become very close after the fourth symmetric
vibration mode (3.5pi on Figure 2.11). Ren et al continue with lab and field work which
prove their theories. Ren et als work has significance for those in the structural health
monitoring community that work on cable stayed bridges since, prior to this work, cable
sag on many bridges introduced unacceptable errors in the calculated cable tension
23


forces. In order to remove the error associated with cable sag, one must determine the
fourth, or higher, cable vibration mode. The only drawback to this method is that
associated with determining the higher modes of vibration. The process of determining
the higher modes of vibration relies upon field work and review of power density plots
and sometimes during that process certain modes can be missed.
Ren et als work also looked at the effect of cable bending stiffness on the results
of the taut string theory. Ren et als work analyzes the cable as a simply supported
beam with an axial tension force and they introduce a non-dimensional parameter £
which represents the effect of cable bending stiffness on the natural frequencies of cable
vibration. £ is defined in equation 2.4 below (Ren et. al, 2008).
Equation 2.4 A non-dimensional parameter which represents the effect of cable
bending stiffness on the natural frequencies of cable vibration.
Where: E= Modulus of elasticity of cable material
1= Moment of inertia of cable cross section
T= Axial Tension Force on Cable
i = Cable chord length
£ = A non-dimensional parameter which represents the effect of cable bending
stiffness on the natural frequencies of cable vibration
Ren et al prepared a plot of £ versus natural frequency which is shown in Figure
2.12 below where co1 is the calculated fundamental frequency based on the taut string
theory and co1s is the fundamental frequency based on Ren et. als theoretical work
which considers cable stiffness (Ren et. al, 2007). Essentially, Ren et. al. concluded that
for lower values of £ (less than 50), the cable bending stiffness cannot be neglected but
for higher values (more than 50) cable bending stiffness can be neglected (Ren et. al,
24


2007). Also, the lower values of £ effect the results of the taut string theory for higher
order frequencies as shown in Figure 2.12.
Figure 2.12 Effects of cable bending stiffness on fundamental frequency.
(Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations:
International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008,
Determination of Cable Tensions Based on Frequency Differences, Ren, Wei-Xin; Liu, Hao-Liang;
Chen, Gang; Page 180, Figure 4, used with kind permission from Inderscience Enterprises
Limited.)
25


Figure 2.13 Effects of cable bending stiffness on fundamental frequency for
higher modes.
(Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations:
International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008,
Determination of Cable Tensions Based on Frequency Differences, Ren, Wei-Xin; Liu, Hao-Liang;
Chen, Gang; Page 180, Figure 5, used with kind permission from Inderscience Enterprises
Limited.)
In summary, Ren et. als work shows that when predicting cable tension based
on fundamental frequency utilizing the taut string theory, that cable sag effects the
results of the taut string theory for lower vibration modes but for higher vibration modes
the error is negligible (Ren, et. al, 2007). In contrast Ren et. al showed that the effect of
cable bending stiffness on the results of the taut string theory effect the higher frequency
modes more so than the lower modes (Ren, et. al, 2007).
Effect of Vibrations on Pedestrian Bridges
In their book, Vibration Problems in Structures, Bachmann et. al. indicate that
95% of pedestrians walk at rates between 1.65 and 2.35Hz (Bachmann, et.al, 1995).
Most structural engineers are aware that as the forcing frequency approaches the
fundamental frequency of the structure resonance can occur. It is for these reasons that
26


modern pedestrian bridge codes limit the natural frequency of pedestrian bridges. For
the subject bridge, the applicable bridge code 1997 AASHTO Guide Specifications for
Design of Pedestrian Bridges indicates that for pedestrian bridges the fundamental
frequency in the vertical direction must be above 3Hz, and the fundamental frequency in
the lateral direction must be above 1.3Hz (AASHTO 1997). Steel footbridges, such as
the subject one, are more susceptible to vibration problems due to pedestrians
(Bachman et. al, 1995). Work done by Wiss et al. indicates that the most severe
response in pedestrian bridges occurred when the fundamental frequency of the bridge
is closest to 2Hz (Wiss et al 1974).
Bachmann et al. present a basic empirical equation relating the fundamental
frequency of cable stayed bridges to their span length (Bachmann et.al, 1995). This
equation is presented in Equation 2.5 below (Bachmann et.al, 1995).
110
L
Equation 2.5 Fundamental bending frequency of cable stayed bridge (Bachmann
et al, 1995).
Where: L = Length of the main span
fe = Fundamental bending frequency
AASHTO 1997 indicates that if an analysis of the bridges fundamental frequency
in the vertical direction is not evaluated then the bridge may be proportioned to satisfy
the following criteria in equations 2.6 and 2.7:
27


1 80
/ >2.861n()
W
Equation 2.6 Minimum fundamental frequency of bridge in the vertical direction
(AASHTO 1997)
or
W> 180e(-35/)
Equation 2.7 Prescriptive weight of supported structure, including only dead load
(AASHTO 1997).
Where: / =Fundamental frequency in the vertical direction
W= Weight of supported structure, including only dead load
Summary
In summary, there are numerous cable stayed bridges inside of the United States
and those bridges require structural health monitoring. It is critical to design those
bridges to prevent fatigue failures which can occur due to excessive vibrations. A proper
health monitoring program can identify a loss of stiffness or excessive vibrations via
monitoring the global natural frequency of the bridge and the natural frequencies of the
cables. Equations exist which can correlate the tension in cables to the measured
natural frequency.
Radar technology has been around for decades but it has only been in the past 10
years that this technology has been used for structural health monitoring purposes. By
using interferometric radar technology, IDS has developed an instrument that can
monitor vibrations in cable stayed bridges in a non-contact manner.
28


CHAPTER III
THEORETICAL ANALYSIS
Overview
In order to have baseline data to compare field testing results to, a theoretical
Finite Element Analysis (FEA) was performed for the bridge of interest- the City and
County of Denvers cable stayed pedestrian, 16th Street over the Platte River. Utilizing
construction documents for the subject bridge, a three dimensional Computer Aided
Drafting (CAD) model was created. Next, the CAD model (a .dxf file) was imported into
SAP 2000 and the theoretical global fundamental frequency of the bridge was
determined.
Three Dimensional CAD Model
The subject bridge has a fairly complex geometry as is typical for cable stayed
bridges. In particular, the bridge is crowned vertically with the highest point being the
middle support; the towers are swept in three dimensions; and, the geometry is not
symmetrical about the center support. Utilizing elevations and dimensions from the
bridges original construction drawings, shown in Appendix A, the three dimensional
CAD model was created using AutoCAD software. Figures 3.1 and 3.2 below show
three dimensional CAD views.
29


Figure 3.2 Three dimensional view of bridge.
SAP 2000 Model
General Bridge Construction
Construction drawings (See Appendix A) for the subject bridge were obtained
and through inspection of the bridge it was concluded that the bridge was built in
substantial conformance with the construction documents regarding dimensions and
materials used.
Structurally, the bridge is fairly simple. The bridge features a decay resistant
wood decking (spanning perpendicular to the length of the bridge) that transmits gravity
loads to wolmanized wood stringers that span approximately 3.96 M (13 feet) (parallel to
the length of the bridge) and bear upon steel floor beams that span approximately 6.10
M (20 feet) (perpendicular to the length of the bridge). The steel joists attach at either
end to two main 40.64 Centimeter (CM) (16 inch) diameter steel tubes, or girders. The
steel tubes constitute the main gravity carrying element. The steel tubes rest upon
30


bearing pads near both ends of the bridge and at their midspan the tubes bear upon a
perpendicular built up steel member which attaches to the towers and the towers
transmit that load to a cast in place mildly reinforced concrete foundation. A photograph
of the bridge is shown below in Figure 3.3. The main tubes span approximately 31.70 M
(104 feet) between supports and gain significant support from cables. The cables are
25.4 mm (1 inch) diameter Class A structural steel strands (manufactured in accordance
with ASTM A586). The cable properties, as provided by the manufacturer (WireCo) are
as follows:
Tensile Capacity = 55,338 Kilograms (KG) (61 tons)
Weight per Unit Length = 30.65 Newtons/M (2.1 Ibs/ft)
Modulus of Elasticity = 1.66*1011 Pascals (Pa) (24,000 Kips per Square Inch (ksi))
Cross Section Area = 3.87 CM2 (0.60 in2)
The cables connect to the tube via a welded plate connection and the cables
connect to the plate via a pin ended connection. At their tops, the cables connect to
40.64 CM (16 inch) diameter steel tube masts via a similar connection.
31


s
Figure 3.3 Subject bridge.
Support Conditions
The subject bridge features cantilevers, approximately 3.05 M (10 feet) long on
the west end and 20 feet long on the east end, at both ends. Through inspections, it
was noted that the supports nearest the ends of the bridge are both roller bearing
supports as evidenced by the loose and slotted vertical bolts and the elastomeric
bearing pads shown in Figure 3.4 below.
32


Figure 3.4 Bridge end bearing conditions.
The bearing at the middle of the bridge was determined to be consistent with a
pin ended condition. This is evidenced by the main supporting tubes which bear upon
the aforementioned perpendicular built up steel member, as shown in Figures 3.5 and
3.6 below, via a welded steel plate that has limited moment capacity.
33


Figure 3.5 Midspan support.
Figure 3.6 Close in view midspan support.
The built up perpendicular steel section transmits the gravity loads from the main
tubes to the towers, or masts, via a bolted connection as shown in Figure 3.6. The
34


towers, or masts, are supported via a moment resistant connection at their base as
shown in Figure 3.6.
Bridge Fundamental Frequency
Through the FEA analysis it was concluded the global fundamental frequency of
the bridge is 3.39 Hz. In accordance with AASHTO recommendations, all the frequency
determinations in SAP 2000 were determined utilizing un-factored self-weights. The
SAP model was edited multiple times in order to determine its sensitivity to cable force
and individual element boundary conditions and no change in the fundamental frequency
or first mode shape occurred. This is due to a 7.16 M (23.5 foot) long steel framed
cantilever that exists on the east end of the bridge. The cantilever dominates the first
mode shape and that cantilever is unaffected by cable tension force as no cables
connect to that portion of the bridge. The first mode shape from the SAP model can be
seen in Figure 3.7 below.
Conclusions
In summary, the fundamental frequency of the bridge was determined to be 3.39
Hz in SAP 2000 software and the first mode shape was found to be dominated by the
east end cantilever section. Changes in the boundary conditions of individual elements
and the cable tension forces resulted in no change in the fundamental first mode shape
due to the dominance of the east end cantilever. The east end cantilever dominance is
35


consistent with field observations which are discussed in the Field Work portion of this
thesis.
36


CHAPTER IV
LABORATORY WORK
First Laboratory Experiment
Setup of First Experiment (Cable Test)
Bearing in the mind that one of the primary purposes of this thesis is to determine
if IBIS technology can be accurately used to measure the natural frequency of cables, a
laboratory experiment was designed and implemented. The first phase of the laboratory
experiment involved purchasing a 1.25 inch diameter cable (wire rope) with looped ends
and fixing the cable in UC Denvers (UCD) Material Testing System (MTS), stretching
the cable to a known tensile load, striking the cable with a rubber mallet to induce free
vibration and measuring the vibration motion with three instruments (see Figure 4.1 for
an image of the lab setup). The three instruments used were the subject IBIS-S system
(sampling at a rate of 100Hz Nyquist Frequency), a programmable accelerometer (GP1
Programmable Accelerometer manufactured by Sensr, sampling at a rate of 50 Hz
Nyquist Frequency and set at a g range of +/- 2.5g) and a non-contact instrument
manufactured by DynaTension (Model P1000) which measures the frequency of
vibration in cables. Loading was applied in 8.90 Kilonewton (KN) (2 Kips) (1Kip=1000
Pounds) increments starting at 0 KN (0 Kips) and going through to 115.65 KN (26 Kips).
Ten readings were taken with the P1000 and the results were averaged for a final value.
A minimum of four cable strikes were conducted with the accelerometer and the data
from those strikes were included in the Fourier analysis. A minimum of four cable strikes
were carried out with the IBIS instrument and that data was used in IBIS post
processing MatLab based fourier analysis.
37


The P1000 instrument has certain limitations based on cable tension, diameter
and length. Due to these limitations the P1000 could only be used to measure tension
forces above 44.48 KN (10 kips) in the laboratory setting. Due to the g range limitations
the accelerometer cut off certain portions of data early in the vibration after the cable
was struck. In the laboratory setting no limitations on the IBIS system were
encountered; this is certainly one advantage of IBIS technology, along with the fact that
the user does not need to have access to the cables as is required with traditional
instruments.
Once the fundamental frequency for the cable was found for each load case with
each of the three instruments, the fundamental frequency was utilized in the taut string
38


equation (Equation 2.2) to calculate the cable force. Since the cable had no sag during
the test Equation 2.2 was relied directly upon with no correction for sag extensibility.
Results of First Experiment (Cable)
From the 44.48-115.65 KN (10-26 Kip) range the IBIS system results and the
P1000 results proved to be very close this finding is encouraging. The data can be
seen in tabular form in Table 4.1 and graphically in Figure 4.2. The accelerometer
provides the user with acceleration as a frequency of time. Utilizing the Fourier
Transform function in Microsoft Xcel, the time domain data was plotted in the frequency
domain in order to view the peaks (natural frequencies) in the data. In Table 4.1 below
the findings from each of the three instruments are presented and it can be seen that all
three instruments are providing similar values reinforcing the confidence in IBIS results.
Based on these findings it can be concluded that IBIS technology can successfully be
used to measure frequency of vibration in cable stayed members with a diameter of
25.4MM (1 inch) or larger.
After the lab work was completed the data was incorporated into Mehrabis
tension equation. Mehrabis equation is a function of cable length and being that the
length term in the equation is squared, the equation is highly sensitive to cable length.
Due to the laboratory setup with looped cable ends, the exact effective length of the
cable is not exactly known. Further, during initial loading 0-44.48 KN (0 to 10 Kips) the
cable stretched substantially (over25.4MM -1 inch); thus, the cable length substantially
changed during this region. Given these observations it is no surprise that the subject
equation does not fit the data well from 0-44.48 KN (0-10 Kips). The important finding is
that all three instruments provide close data; there has been plenty of previous research
on the application of Mehrabis tension equation and that is not the purpose of this
research. After 44.48 KN (10 Kips) -once cable slack/loss was mostly removed-
39


Mehrabis tension equation proved to be fairly accurate (+/- 5%) as can be seen in
review of the data in Table 4.1.
Frequency domain plots from Microsoft Excel of each cable force increment
measured are shown in Appendix B and on those plots the reader can view the peak
which corresponds to the measured natural frequency. The figures shown in Appendix
B include frequency domain plots from IBIS MatLab based post processing system in
which the reader can view the peak which corresponds to the measured natural
frequency.
40


Table 4.1 Results of Lab Testing for Tensile Force Determination in Cable.
Actu al Fore e (Kips ) fn Me as ured with IBIS fn Measu red with P1000 fn Measure d with accelero meter Tension Force Based on IBIS (Kips) Tension Force Based on P1000 (Kips) Tension Force Based on Accel er ometer (Kips) % Accur acy IBIS % Accuracy P1000 % Accuracy Accelero meter
2.00 17.96 0.00 17.63 2.90 30.92
4.00 23.94 0.00 23.53 5.14 - - 22.24 - -
6.00 27.86 0.00 27.98 6.97 - - 13.87 - -
8.00 32.27 0.00 31.35 9.35 - - 14.40 - -
10.00 36.32 35.66 35.11 11.84 11.41 - 15.54 12.38 -
12.00 37.30 37.54 37.74 12.49 12.65 12.78 3.90 5.13 6.13
14.00 40.09 40.00 40.38 14.42 14.36 14.63 2.95 2.51 4.33
16.00 42.40 42.10 42.63 16.14 15.91 16.31 0.84 -0.58 1.90
18.00 44.55 44.40 44.73 17.81 17.69 17.96 -1.05 -1.73 -0.24
20.00 46.95 46.69 47.02 19.78 19.56 19.84 -1.09 -2.23 -0.79
22.00 48.80 48.82 48.93 21.37 21.39 21.49 -2.93 -2.85 -2.38
24.00 50.54 50.92 50.78 22.93 23.27 23.14 -4.69 -3.13 -3.70
26.00 52.50 52.62 52.64 24.74 24.85 24.87 -5.10 -4.62 -4.54
41


30
25
20
15
10
5
0
0 10 20 30
Applied Tension Force (Kips)
Tension Based on IBIS
Tension Based on P1000
Tension Based on
Accelerometer
Tension Readout on MTS
Figure 4.2 Graph of calculated vs. actual cable force.
42


Conclusions from First Experiment (Cable)
Based on the laboratory results from the cable test it was concluded that the
IBIS-S system can successfully be utilized to measure the fundamental frequency of
tension members such as wire rope and structural steel strands. It was also concluded
that for higher tension loads, once a majority of the slack has been removed, Mehrabis
tension equation can successfully be applied. Thus, it is shown that by using
interferometric radar, the fundamental frequency and tension force in cables can be
determined in a non-contact remote manner.
Second Laboratory Experiment (Steel Channel)
Setup of Second Experiment (Steel Channel)
After experiencing success with IBIS in measuring the natural frequency in
cables the idea came to try the same experiment with a rigid steel member. In
particular, tension members in steel truss bridges are of interest. A change in the
natural frequency of a steel truss member could indicate decay in the member or its
associated welds is occurring. In order to physically fit a steel member into the MTS a
rather large steel member (C10x15.3 A36 steel, as shown in Figure 4.3 was chosen.
The steel member was put under tension loads ranging from 2.22 to 177.93 KN (0.5 to
40 Kips) (Figure 4.4). The steel member was struck with a rubber mallet and the
vibration was measured with IBIS and an accelerometer that was mounted to the
channel. Again, the accelerometer data was imported into Microsoft Xcel and the time
domain data was plotted in the frequency domain in order to view the peaks (natural
frequencies) in the data. Due to the limitations of the accelerometer data was only
collected under tension loads up to and including 44.48 KN (10 Kips) with the
accelerometer.
43


2" DIA HOLE, TYP
Figure 4.3 Drawing of channel.


Results of Second Experiment (Steel Channel)
Initially the accelerometer data displayed errors and it was realized the
accelerometer was not well adhered to the channel and was moving independently of
the channel as evidenced by shifts in the acceleration data in the frequency domain.
Thus, the experiment was repeated. The results of this experiment were counter
intuitive in that the accelerometer data indicate a decrease in natural frequency as the
tension load increased. Further, the IBIS data and the accelerometer data did not
correlate well. Through reviewing the data it became apparent that over a large increase
in axial load (88.96KN (20 Kips) for instance) the natural frequency did not change
drastically and as the axial load got higher, increments in axial load resulted in smaller
changes in the natural frequency indicating a non-linear relationship exists between the
two. It was also noted that the channel sustained plastic deformation around the holes
that secured the channel to the MTS. It is likely that due to the relatively large stiffness
of the channel, when compared to typical truss bridge tension members, the natural
frequency is not a good indicator of the tension force.
Frequency domain plots from Microsoft Excel of each channel force increment
measured are shown in Appendix C and on those plots the reader can view the peak
which corresponds to the measured natural frequency. Appendix C includes frequency
domain plots from IBIS MatLab based post processing system in which the reader can
view the peak which corresponds to the measured natural frequency.
45


Conclusions from Second Experiment (Channel)
In summary, the results of this experiment were counter intuitive (the
accelerometer data indicated a decrease in natural frequency as the tension load
increased) and the IBIS data and the accelerometer data did not correlate well. Based
on the results from the second experiment it was concluded that interferometric radar
cannot be utilized to measure the fundamental frequency in steel channels with a C
shape until further research is conducted. It is possible that the material yielding and
stress concentration at the connection points negatively affected the experiment.
46


CHAPTER V
FIELD WORK
Setup
Setting up IBIS in the field is very simple and intuitive. Setup simply involves
setting up and leveling a tripod followed by attaching the radar head and connecting to
the PC via a USB cord. In order to gather data on the global bridge movement setup is
fairly simple; particularly for steel framed bridges with cross members or cross frames.
For the subject bridge (Figure 5.1) steel W cross beams are spaced 3.96 M (13 feet) on
center. The 90 degree bend at the web/flange connection on W sections is a great
reflector of radar. In this instance the user sets up the IBIS as close to one abutment or
the other as reasonably possible and aims the radar head along the length of bridge as
shown below in Figure 5.2. As long as the cross beams are at least 0.75 M (2.46 feet)
apart (for range bin reasons) this setup allows the user to collect displacement data on
all visible cross members at once. For the purposes of monitoring vibrations, the subject
of this thesis, it is not critical to input the geometry of the bridge into the IBIS software.
Inputting the bridge geometry and radar head angle/position is necessary if the user
desires actual displacement data (refer to Figure 2.6 for explanation on how IBIS
measures line of sight movement, not vertical displacement).
47


Figure 5.1 Subject cable stayed bridge.
48


Figure 5.2 Radar setup in field.
Once setup and turned on, the user must determine which peaks on the radar
display correspond to which structural elements. This is easily done with a laser
distance meter which is positioned on the radar head. By documenting the position of
49


each member and its corresponding radar peak the user can easily view the data at a
later time and correctly understand/apply the data.
For the purposes of monitoring vibration in cables the positioning of the IBIS
system is not as straightforward. Firstly, the user desires a location in which multiple
cables can be viewed at once. For the subject bridge the maximum number of cables
that can be viewed at once are three. However, the user must take care to insure that
the cables are at least 0.75 M (2.46 feet) apart along the line of sight. Depending on the
position of the IBIS it is quite possible that along the line of sight the cables could fall
within the same range bin. An example of this is a setup where the IBIS is aimed
directly perpendicular to the length of the bridge/cables in this instance all the cables
are in the same vertical plane. One might think that an ideal setup is at the end of the
bridge looking down the length of the cables such that the cables will be more than 0.75
M (2.46 feet) apart along the line of sight. However, depending on the bridge geometry
and construction, this setup would likely result in viewing vertical masts on the bridge
and could possibly result in the first cable blocking the view of the additional cables. An
ideal setup for a cable stayed bridge, when monitoring the cables, is one in which the
instrument is located near the end of the bridge, looking down the length of the bridge,
and the instrument is aimed such that no other bridge elements are in the field of view.
In some instances the user can setup near the middle of the bridge and look upwards
(Gentile, 2010). However, it is recognized that once a bridge is in service it is not very
realistic to setup near the middle of the bridge due to the waterway or roadway.
Setup Comparisons
Setup and data were obtained both by setting up the instrument on the bridge
deck (near the masts) and by setting up the instrument on the ground, isolated from the
bridge vibrations. The data gathered from the setup on the bridge was noted to
50


sometimes exclude lower vibration modes which is possibly due to the instrument
vibrating in-sync with the bridge. For this reason all subsequent setups were conducted
from the ground so as to isolate the instrument from the vibrations. It should be noted
that the vibrations on the subject bridge are very notable with large deflections (on the
order of one CM (2.54 inches). Thus, for bridges that are larger and more stiff
(automotive bridges) it may be possible to successfully monitor vibrations from the
bridge deck itself; future research is needed on this topic.
Testing and Results
Cable Vibration Measurement
The subject bridge contains a total of 12 cables. According to the engineer of
record (EOR) the top four cables were originally tensioned to 17.79 KN (4 Kips) each
and the remainder of the cables were tensioned to sufficiently bring the bridge deck into
the desired shape and alignment; thus, the original tension is only known in 4 of the 12
cables. A DynaTension P1000 instrument, an accelerometer and the IBIS instrument
were used to measure the natural frequency in each of the 12 cables. Six samples per
cable were taken with the P1000 and the results were averaged. With the
accelerometer, a minimum of 2000 data points were collected and utilized in the Fourier
analysis and this process was repeated and the results averaged. Wth the IBIS,
measurements were taken for each cable with a minimum of 2000 data points and this
process was repeated and the results averaged.
The results from the DynaTension meter are counterintuitive due to the relatively
high frequencies reported by the instrument. It was theorized that the DynaTension
meter was reporting higher mode shapes but review of the accelerometer data does not
show good correlation for higher mode shapes and as such it was concluded the
DynaTension meter data was erroneous. An attempt to repeat the measurements with
51


the DynaTension meter was made but after several attempts the exercise was
abandoned due to the DynaTension meter not working correctly. Further, even if the
DynaTension meter was successfully reporting higher mode shapes, the instrument has
no way of letting the user know which mode shape he or she is collecting data on. Since
Merhabis cable force determination equation is a function of both the natural frequency
and mode shape, the DynaTension meter is not helpful for determining the force in the
cable since the user has no way of knowing which mode he or she is measuring. The
DynaTension meter results are shown in Table 5.1 below.
It took several attempts to collect valuable data with the accelerometer (see
Figure 5.3 for a photograph of the accelerometer in use). After processing the
accelerometers field data from the initial attempts it was realized errors must have
occurred as the data had no clear peaks in the frequency domain. Based on permanent
shifts in the accelerometer data when viewed in the time domain it was realized the
instrument was vibrating independently of the cables and it was physically slipping
downward on the cable due to poor attachment. Thus, the experiment was repeated by
better securing the instrument to the cables. During the initial attempts to collect cable
vibration data with the accelerometer it was thought the cables needed to be struck into
free vibration with a rubber mallet as was done in the laboratory cable experiment.
However, after securely affixing the instrument the data still did not appear correct in the
time domain in fact the only data that appeared correct was the initial data collected
prior to striking the cable for the first time. Thus, it was concluded the bridge has
enough vibration on its own (movement in the bridge and its cables is visible under no
pedestrian loads which is a result of ambient environmental conditions such as minor
wind loads) and there is no need to strike the cables. Once the experiment was
repeated without striking the cables the data appeared very correct in both the time and
52


frequency domains and the data proved to be repeatable as the experiment was
conducted twice. The final accelerometer data was determined to be accurate due to its
appearance, intuitiveness, alignment with IBIS data, and the finding that cables in
similar (mirror) positions on opposite sides of the bridge was very close to each other.
The frequency data for each cable found from the accelerometer is shown in Table 5.1
and the frequency domain plots of the data for each cable are shown in Appendix D.
Figure 5.3 Accelerometer installed on cable on subject bridge.
It also took several attempts to gather usable cable data with the IBIS instrument.
This was largely due to the learning curve encountered in trying to find the optimal setup
position and in determining which radar peaks corresponded to which cables. Once the
optimum setup position was found for each set of cables, data was gathered quickly.
With a couple exceptions, the IBIS and accelerometer data correlated well (within 1/100th
of a Hz). In the instances where the two dont correlate well (error of 0.60 Hz) no real
logical conclusion was achieved. In these instances the experiment should be repeated
53


with both instruments in order to validate data, however this was not possible due to IBIS
availability constraints. Nonetheless, there were multiple instances where the IBIS
instruments data correlated very well with the accelerometer data and as such it was
concluded the IBIS instrument can successfully be used to monitor the fundamental
frequency in cables. The results of the IBIS measurements are shown in Table 5.1.
Both the accelerometer and IBIS frequency domain plots for the cables show
smaller peaks at 1.67 and 1.98 Hz in multiple instances. The smaller peaks are
consistent with global mode shapes. After review of the plots it was concluded that for
the bottom (shorter cables with greater tension force) no smaller peaks existed and due
to the large tension force in the cables and the cables close proximately to the center
(fixed) support, the global mode shape was not visible. For the middle cables, a
consistent small peak between 1.95 and 2.00 Hz was visible which is consistent with the
measured global fundamental frequency of the bridge as discussed below. For the
upper (longest) most cables a consistent small peak at approximately 1.66 Hz was
observed. As no global mode shape at 1.66 Hz was observed, this peak was not
expected and is not readily explainable. In the instances where the 1.66 peak was
observed, no peak was observed at 1.98 with the accelerometer. However, in the same
instances where a peak was observed at 1.66 with the IBIS instrument, a peak was
observed at 1.98 which is an indication the first global mode shape is observable with
IBIS but not with the accelerometer in some instances.
54


Table 5.1 Measured Fundamental Natural Frequency of Bridge Cable by Cable
Position (Hz).
NE Top NE Middle NE Bottom NW Bottom NW Middle NW Top sw Top SW Middle SW Bottom SE Bottom SE Middle SE Top
IBIS 2.22 3.80 5.21 6.03 3.46 2.44 2.14 3.77 6.62 6.12 4.05 2.72
Accelerometer 2.24 3.42 5.42 6.00 3.52 2.44 2.24 3.17 7.08 5.85 4.00 2.73
P1000 16.74 23.1 24.47 23.47 22.52 17.15 17.16 25.2 21.58 23.45 22.85 15.75
55


Global Bridge Vibration Measurement
In order to determine the bridges global fundamental frequency the IBIS
instrument was setup under the bridge and vibration data on multiple cross beams was
gathered. This experiment was repeated numerous times and from both sides of the
bridge as the center foundation prohibited viewing of all the cross members at once.
The data gathered indicate that the cross members lowest vibration mode occurs at a
peak of 1,98Hz consistently and as such it was concluded the fundamental frequency of
the bridge is 1.98Hz.
Summary and Conclusions
In summary, field testing indicates that inteferometric radar can successfully be
used to monitor the global bridge natural frequency, mode shape and the individual
bridge elements (cables, masts, railing) fundamental frequencies.
56


CHAPTER VI
DICSUSSION
Introduction
Within this section of the thesis, the theoretical, laboratory and field testing
results are combined to determine the success of utilizing interferometric technology to
monitor cable stayed bridges. Further, the cable tension forces, and global bridge
frequencies are determined.
Cable Calculations
As significant sag (more than 1 foot in some instances) was observed in the
cables on the subject bridge it was considered if the taut string theory could be utilized to
determine the tension force in the cables. As the cables were noted to be very flexible it
was determined unlikely that the cables bending stiffness would affect the results of the
taut string theory. Nonetheless, Ren et als research was utilized to determine if the
cable bending stiffness or sag were going to significantly affect the taut string theory
results.
The force in each cable was determined utilizing Merahbis equation and the
measured frequency and that tension data is shown in Table 6.1. Also, the non-
dimensional parameters set forth in Ren et. als work were calculated for each cable in
order to determine the accuracy of the taut string theory for each of the cables. As
discussed previously, Ren et al concluded that when A2 exceeds 1.0 for the first mode,
the cable sag can be neglected and when £ is greater than 50, the cable stiffness can
be neglected. In Table 6.1 it can be seen that £ is greater than 50 in every instance,
thus the cable stiffness was neglected. The A2 term was calculated less than 1.0 in all
but three cases and in one of the three cases the term was 1.32 which corresponds to a
57


relatively small error. For the two cases where the A2 term greatly exceeds 1.0, error in
the calculated tension force exists (likely on the order of 10%). In order to better
calculate the tension force in those two cases, a higher mode shape should be used.
For those two instances, the 5th mode was used, the tension force was corrected and
that corrected data is shown in Table 6.2. In comparing the corrected data in Table 6.2 it
is noted that the calculated tension force based on the 5th mode is quite different than
that calculated from the first mode. Given that the corrected tension force should only
be approximately 10% different between the two methods it was concluded that the 5th
mode was incorrectly determined and repeated attempts to re-analyze the data did not
yield better results. Thus, the data from Figure 6.1 was relied upon recognizing that in
some instances an error of approximately 10% likely exists.
It can be seen that the cable forces are relatively consistent across the bridge for
similar cables in similar positions. The only exception is one lower cable that has a
substantially higher (40% higher) tension force. As the IBIS and accelerometer data
compare well for that cable and multiple samples were taken it was determined the data
was accurate. One possible explanation is simply that the subject cable had to have a
higher tension force during construction in order to obtain the desired shape of the
bridge.
58


Table 6.1 Cable Force Determination.
Effecti ve Length (Feet) Cable Actual Length (Feet) fn Measur ed with IBIS fn Measur ed with acceler ometer Tension Force Based on IBIS (Kips) Tension Force Based on Accelerom eter (Kips) £ term from Ren et al /t2 term from Ren et al.
106.6 NETop 108.8 2.22 2.24 6.59 6.71 127.92 2.67
70.2 NE Middle 71.6 3.80 3.42 19.32 15.65 144.17 0.05
36.1 NE Bottom 36.8 5.21 5.42 36.32 39.30 101.61 0.00
99.4 NW Top 101.4 2.44 2.44 7.97 7.97 131.06 1.32
63.3 NW Middle 64.6 3.46 3.52 16.02 16.58 118.39 0.07
31.5 NW Bottom 32.1 6.03 6.00 48.65 48.16 102.64 0.00
99.4 SE Top 101.4 2.72 2.73 9.90 9.97 146.10 0.69
63.6 SE Middle 64.9 4.05 4.00 21.94 21.41 139.30 0.03
31.8 SE Bottom 32.4 6.12 5.85 50.11 45.79 105.17 0.00
106.3 SW Top 108.4 2.14 2.24 6.13 6.71 122.93 3.31
70.5 SW Middle 71.9 3.78 3.17 19.12 13.44 144.08 0.05
36.4 SW Bottom 37.1 6.62 7.08 58.63 67.06 130.28 0.00
59


Table 6.2 Corrected Cable Force Determination, Based on 5th Mode
Cable Length fn Measured Tension Force
(Feet) with accelerometer Based on Accelerometer, 5th Mode (Kips)
NETop 127.9 7.08 2.68
SW Top 144.2 7.56 3.06
60


Global Bridge Vibration Discussion
As seen in the cable data in Appendix D, global peaks in the cable data were
also observed at 1.98Hz which confirms these conclusions. While gathering data on the
cables it was possible to also gather data on the bridge masts and railing and both those
items were also found to have a first global mode at 1,98Hz again confirming the
conclusion that the bridges first global mode is 1.98Hz. The results of the floor beam,
mast and tower data are shown in Figures 6.1 through 6.6. One particular floor beam
displayed a smaller peak at 1,67Hz which is consistent with that observed on certain
cables.
Profile
Figure 6.1 Radar plot of underside of bridge (peaks correspond to floor beams).
61


2011.07.30-11.33.01-global1
Figure 6.2 Frequency domain plot of underside of bridge, data for seven floor
beams overlaid (Note: all members display peak at 1.986 Hz which was determined
to be the first global natural frequency of the bridge).
62


Figure 6.3 Frequency domain plot of floor beam vibration on underside of bridge
(Note: this member displays peaks at 1.67 (which correlates to cable vibration
data) and 1.98 Hz which corresponds to the measured global bridge natural
frequency of 1.98Hz).
63


2012.03.13-09.50.43-dynS-000001-Surv
frequency [Hz]
Figure 6.4 Frequency domain plot of south tower vibration (Note: This Tower
displays a peak at 1.94 Hz which is very close the measured global bridge natural
frequency of 1.98Hz).
64


frequency [Hz]
Figure 6.5 Frequency domain plot of north tower vibration (Note: This Tower
displays a peak at 1.98 Hz which matches the global bridge natural frequency of
1.98Hz; Smaller peaks after peak at 1.98 Hz correspond to other global bridge
mode shapes; Peak at 9.86 Hz which corresponds to the first local natural
frequency of north tower).
65


2012.03.13-10.22.27-dynS-00000Q-Surv
frequency [Hz]
Figure 6.6 Frequency domain plot of north railing (Note: This Tower displays a
peak at 1.98 Hz which corresponds to the measured global bridge natural
frequency of 1.98Hz).
Other peaks observed in the global survey was a large peak (the largest) at
2.64Hz and the next largest peak was at 3.3Hz which corresponds very closely with the
SAP model output which indicated the fundamental frequency was 3.39Hz. The
discrepancy between the SAP model and the field data is not readily explainable by this
engineer and would require more research.
The MatLab based post processing used by IBIS has the ability to take all of the
cross member time domain deflection data and overlay it simultaneously to create an
animation of the bridges motion and to determine the mode shape. This process was
completed and the deflected shape corresponds with that gathered from SAP in that the
66


two cantilevered ends, especially the east end, dominate the first mode shape (see
Figure 6.7 below).
Figure 6.7 Mode shape plot from Matlab.
When inspecting the bridge it was noted that the vibrations were very noticeable
and during time spent on the bridge pedestrians would routinely stop and ask if the
bridge was supposed to vibrate in the manner which it is. These findings are consistent
with Wiss et als work which indicates that the most severe and noticeable vibration in
pedestrian bridges occurs at a frequency of 2Hz (the subject bridge vibrates at 1.98Hz).
Pedestrian Bridge Application of Work
As can been seen in the above work, the fundamental frequency of the subject
bridge violates the AASHTO criteria which the bridge was designed with in regards to
the 3.0Hz limitation for the fundamental frequency. It is unknown to this engineer as to
whether or not the engineer of record performed calculations/models to check the bridge
for vibrations both vertically and laterally as should have been done. The scope of this
thesis is vertical vibrations; no investigation of lateral vibrations was conducted.
67


A quick check of Bachmann, et.als empirical equation for fundamental frequency
of cable stayed bridges shows that their equation either does not apply well to
pedestrian bridges or to bridges with multiple spans (Bachmann, et.al, 1995). Applying
their equation to the subject bridge indicates a fundamental frequency of 3.47Hz. It is
interesting that Bachmann et als equation (which is intended to be used for cable stayed
bridges) is rather close to the SAP model output of 3.39Hz and that one of the modes
measured in the field was at 3.3Hz. However, as the lowest mode measured in the field
was 1,98Hz it was determined this is coincidental.
Recommendations for City and County of Denvers Cable Stayed Pedestrian
Bridge at 16th Street Over The Platte River
It is recommended that the subject bridge be monitored for signs of fatigue.
Others have undertaken a bridge health monitoring protocol, index and baseline data for
the bridge. Through time spent on the bridge it was noted that the fasteners that secure
the decking to the structure often are backing out which result in not only loose deck
planks but protruding screws which are a trip hazard. It is likely that the loose screws
are a result of fatigue failure. Now that baseline data is available, the fundamental
frequency of the bridge, cables and masts can be checked annually, or bi-annually, and
any changes would warrant further investigation into potential decay or loss of stiffness.
The costs associated with trying to stiffen the bridge would be large and may not be
justified. The most economic method of solving the vibration problem would involve a
tuned mass damper system which is quite costly. Further, this thesis excludes an
evaluation of the bridges lateral fundamental frequency but such an analysis should be
performed and its quite possible that problems exist in the lateral direction as well.
68


Summary and Conclusions
In summary, the cable vibration data can be used to determine the tension force
in each of the cables. The global fundamental frequency of the subject bridge was
determined to be approximately 1.98Hz. The force in each of the cables is shown in
Table 6.1. The discrepancy between the SAP model and the field data is not readily
explainable by this engineer and would require more research which is outside the
scope of this thesis. It was concluded the AAHSTO empirical equations regarding
fundamental frequency are not accurate for cable stayed bridges. The subject bridge
violates AASHTO limitations for the fundamental frequency in the vertical direction. The
consequence of the low fundamental frequency will likely be premature fatigue failure of
one or more bridge elements. Future monitoring of the bridge should include vibration
monitoring.
69


CHAPTER VII
CONCLUSIONS AND RECOMENDATIONS
Conclusions
In summary, this thesis shows that interferometric radar can successfully be used
to determine the fundamental frequency of bridges and their individual elements. The
use of such radar has clear advantages in regards to ease of use, not needing direct
access to the bridge, and large amounts of data in short amounts of time. For these
reasons it is determined that interferometric radar is a good tool that can be used to
monitor the structural health of bridges and other structures.
Vibration data from cables on cable stayed bridges can be used to determine the
tension force in the cables. In many instances the taut string theory can be used and no
correction for cable stiffness and sag is needed. However, in the case where correction
is needed, higher vibration mode data can be used to determine the tension force more
accurately.
It was concluded the AAHSTO empirical equations regarding fundamental
frequency are not accurate for cable stayed bridges.
Recommendations
Regarding the City and County of Denver Bridge, 16th Street over the Platte, the
fundamental frequency of the bridge is below 3.0Hz which is an AASHTO violation and
this is of concern. Potential premature fatigue failure exists as a result of the low
fundamental frequency (1.98Hz). The noticeable vibrations in the bridge and the 1.98Hz
finding are consistent with Wiss et als work which indicates that the most severe and
noticeable vibration in pedestrian bridges occurs at a frequency of 2Hz. Now that
baseline data is available, the fundamental frequency of the bridge, cables and masts
70


can be checked annually, or bi-annually, and any changes would warrant further
investigation into potential decay or loss of stiffness.
Future Work
Future work should be completed in order to better determine if interferometric
radar can be used to determine the tension force in axially loaded steel members.
This thesis excludes an evaluation of the subject bridges lateral fundamental
frequency but such an analysis should be performed and its quite possible that
problems exist in the lateral direction as well.
Future research into the AASHTO empirical equations for limitations on
pedestrian bridge weight and fundamental frequency should be conducted.
Further research into the accuracy of the SAP model, and the apparent
discrepancy between field data, for the subject bridge should be considered.
71


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73


APPENDIX A
Construction Drawings
74


Table of Contents Page
Title Sheet 2
General Notes and Sheet Index 3
Summary of Approximate Quantities 4
Survey Control Plan 5
Utility Drawing 6
General Layout Plan 7
Construction Sequence 8
Hydraulic Information 9
Contractor Access Plan 10
Pedestrian Bridge Detour Plan 11
Pedestrian Bridge Detour Sign Details 12
Erosion Control Plan 13
Bridge General Plan 14
General Elevations and Grade Profile 15
Structural General Notes and Criteria 16
Bridge Plan and Deck Plan 17
East Abutment 18-20
West Abutment 21-23
Bridge Elevation 24
Partial plan 25
Pier Details 26
Bridge Details 27-33
Bridge Deck Details 34
Bridge Railing Details 35
Electrical Site Plan 36
Bridge Lighting Plan 37-38
Tabulations and Schedules 39
Landscape Cover Sheet 40
Layout Plan 41-42
Grading Plan 43-44
Abutment 45-46
Site Details 47-50
Planting Plan 51-52
Planting Details 53
Irrigation Details 54-56
75


~n|
05

CITY AND COUNTY OF DENVER
DEPARTMENT OF PUBLIC WORKS
TRANSPORTATION D VISSON/CIT Y ENGINEERING
16TH STREET PEDESTRIAN BRIDGE
OVER THE SOUTH PLATTE RIVER
CONTRACT NO. CE10563
STRUCTURE NO. D-02-PR-068
DRAWING NO. 133-5.9
D02PR068&052O02000J
KL&A, Inc. Structural Engineers The Lund Partnership, Inc. Crail Engtaws Clanton and Associates £l*Ctr<0l/Ligating Engtnetrs McLaughlin Water Engineers, Ltd. CTC-GEOTEK -
4412 W. Eisenhower Blvd. Lovelcnd CO 8Q537 970-667-2426 fox 970-667-2493 contact: Thomos W. Hortmonn, P.E. Oouglas Rutledge. PM 12265 W, Bayaud Avenue Suite U0 Lakewood. CO 80228 303-989-1461 fox 303-989-4094 contact: Jamie Pesicko, P.E. 4699 Nautilus Court South Suite 102 Boulder CO 80.301 303-530-7229 fox 303-530-7227 contact: Noncy Clgnton, P.E. 12596 West Bayaud Avenue Suite 200 Lakewood, CO 8D228 303-458-5550 fox 303-480-9766 contact John Pflaum, P.E. 155 South Navajo Oenver. CO 80223 i IT T^I x 303-698-1050 fox 303-698-1053 j 11\ If*/ contact: Roy M. Reed
- MAYi2 2OT^^^^


'vl
SHEET INDEX
SHr ptsamm
General Notes:
General Drawings:
GO.O Co^er Sheet and Signatures
GUO GeneraI Notes, Sheet Index &
Abbreviations
G1.1 Summary of Approximate Quantities
G1.2 Survey Control Plan
Gt.2.1 Utility Drawing
GU3 General Layout
G1.4 Construction Sequence
G1.5 Hydraulic Information
GI.6 Contractor Access Plon
GI. 7 Bike/Ped/Accessible Detour Plan
GJ. 7.1 Sign Details
Gf.8 Erosion Control Plan
Bridge General Drawings:
BID Bridge General Plon
B1.1 Bridge General Elevations & Section
Bridge Structural:
SJ.O Structural Notes and Criteria
S2.!. 1 Bridge Plon
52.1.2 East Abutment Plan
52.1.3 Longitudinal Section @ East Abut.
$2.1.4 East Abutment Sections
S2-I.5 West Abutment Plan,
Typical Bridge Section
SHT. NO DWG NO. DESORPTION
Bridge Electrical:
35 E1.0 Electrical Site Plon
36 EU Bridge Lighting Plan -
37 E1.2 Bridge Lighting Plan -
38 E1.3 Schedules & Detiols
39 NOT USED
Landscape:
40 L 1.0 Landscape Cover Sheet
41 LU1 West Side Layout PLon
42 LI.2 West Side Groding Plan
43 LI.3 West Side Abutment
44 LI.4 East Side Layout Plan
45 LI.5 East Side Groding Plan
46 L1.6 East Side Abutment
47 L2.1 Site Details
48 L2.2 Site Details
49 L23 Site Details
50 L2.4 Site Details
51 L3.1 East Side Planting Plan
52 L3.2 West Side Planting Plan
53 L3.3 Planting Details
54 L4.1 Irrigation Plans
55 L4.2 Irrigation Details
56 L4.3 Irrigation Details
Stuctural Abbreviations
21 S2.1.6 Longitudinal Section @ West Abut. AB8RCY OiriNtDON iswrv. nnxmi
22 52.1.7 West Abutment Section AS. M
23 S3.11 Bridge Elevation ear Cr
24 S3.1.2 Partial Plan & Bridge Details BOO
25 S4.1.0 Pier Details BTttu ftttNf
26 S4.!. 1 Bridge Details am CONST
27 28 54.1.2 54.1.3 Bridge Details Bridge Details KTiVt nioiTj' SCOT SL SirNN Ss
39 30 S4.1.4 S4.15 Bridge Detoils Bridge Details a CLP/ soc sb. 5WPI SUP! 5HCH r/ijr, T.0. appal fop tfiieO. V&bftrss
31 S4.1.6 Bridge Details £W> upsnsTo*
32 54.1.7 Bridge Detiols nan/ horfMfflaJ VZF1
33 55./. 7 Deck Details joint
34 S5.2.1 Roiling Details uv jcol
a ha Y 12 2003
_ I. The Contractor shall call (he Utility Notification Center of Colorado (UNCCJ at
1 -800-922-1987 for utility locations at least seven business days, not including
the day of the initial contact, prior to digging or beginning construction
2. The type, size, location ond number of above-ground ond underground
utilities or facilities is not known or represented in these documents or project
specifications. No guarantee is made os to the true size, location or number of
such utilities or facilities. It sholl be the responsibility of the Contractor to verify
the existence or location of all underground utilities dr facilities within the Omits
of the work. The omission from, or the inclusion of, utility or facility focotions
on the drawings is not to be considered os the nonexistence of, or o definite
location of, existing underground utilities or facilities.
3. The Contractor shall be responsible for the safety of those associated with
the work, pedestrians ond the general public throughout the duration of the
contract.
- City of Denver Street Occvponcy Permit
Contact: Permit Desk, (303) 446-3759
Denver Wastewater Management Building
2000 W. 3rd Avenue, first Floor
Note: There may be oddilionol permits which are required but which ore not
listed.
7. The Contractor sholl notify oil adjacent ond affected property owners and
users of relevant impacts caused by the work at least three weeks prior to
undertaking any work. The Contractor shot! coordinate all work with alt adjacent
and offected property owners and property users, prior to undertaking the work.
Every reasonable effort shall be mode by the Contractor to accommodate offected
property owner's and users occess to and use of their properties.
8. The contractor shall be allowed only limited occess through Commons Pork to
access the construction zone on the east side of the Ptatte River. Commons Park
is the area bounded by 15th Street, Utile Raven Street, 19th Street, ond the
Platte River. The Contractor shot/ be allowed to drive lightweight vehicles only (no
< The Contender shall obtain cl his expense and al no expense to the project, hemier lhm common pickop twek) through Commons Part on existing concrete
paths between Little Raven Street ond the construction zone. Absolutely no heavy
equipment or vehicles (such os dump trucks or concrete trucks) will be allowed
on these paths or through Commons Pork. The paths that the Contractor wiU be
allowed to use are those that provide the most direct access to the construction
zone, white providing the minima! impact to the Bike/Ped Detour. Absolutely no
traffic will fie allowed off of the existing concrete paths. Any route that is used
for this occess to the work zone shat! be approved by the Engineer prior to its
use. The Contractor shot! at alt times exercise extreme core to protect all existing
features In Commons Pork, and the Contractor shaft be solely responsible to
repair and restore any damage to any item caused by the Contractor's
operations, including, but not. limited to, paths, landscaping, and the irrigation
system. Safety of the Public shaft be of paramount importance to the Contractor,
ond the Contractor shot! ensure that the work ond. worksite shall be safe for the
Public at all limes. When he is using them, the Contractor sholl close to the
Public paths that the Contractor utilizes for occess through Commons Park, ond
extreme core sholl be token at ail times to ensure the safety of any .persons
utilizing the designated Bike/Ped/Accessibte Detour. No separate payment will be
made for any of (he provisions required by this note, including, but not limited
to, repair ond restoration of ony domoged items in Commons Pork ond closure
of paths and maintaining sofety of the Public, ond oil costs sholl be considered
incidental to the work.
9. The contractor shall be responsible for taking ond distributing meeting
minutes for all construction progress meetings. Costs for taking and distributing
meeting minutes shall not be paid for separately but sholl be included in the
price paid for Item 626, Mobilization.
10. Urban Drainage is expected to hove completed the construction of o new
river control structure on the east side of the river near the bridge by
approximately April 15, 2003. Vie contractor sholl ensure that this new control
structure is not domoged by his operations, ond any damage done by the
contractor shall be repaired at the contractor's expense.
The contractor is notified of the following information ond shot! indude ot his
expense the coordination of.
o. Anticipated fill over the Bike Trail at the west abutment left from Urban
Drainage contractor.
b. Anticipated culverts, fill, ond other miscellaneous items olong the west river
bank left from Urban Drainage contractor. Culverts and fit! may be added to or
modified to build causeway for crone access.
c. Acquisition of Bike/Ped detour from the Urban Drainage contractor os specified
in drawings and contract documents.
11. See the notice on sheet no. J regarding necessary qualifications of (he fabricator and other members of the
project team. On the bid dole, the contractor shat! include with his bkJFJetter-which states the name of the steet
fabricator, and as of February /. 2003 that steet fabricator sholl have been certified by the American Institute of
II permits which are necessary to perform the work except those to be obtained
by the City ond County of Denver (See General Note 6).
5. The Contractor shall satisfy all requirements of each Permit. The Contractor
sholl inform himself of oil Permit requirements prior to bidding. Costs for
obtaining oil Permits ond for adhering to alt Permit requirements sholl not be
paid for separately, but shall be included in the work.
6. The Owner hos obtained the following permit. A copy of this permit
included in the appendices to the project special provisions. The Contractor
is required to adhere to the requirements of this permit throughout the
duration of the project. The permit that the City has obtained is:
- Section 404 Permit, Nationwide Permit Number 14
Corps file No. 200180801
US Army Corp of Engineers
Terry McKee
" .(303) 979-4120
The Contractor is oho responsible for obtaining ond adhering
to the following permits and clearances for the 16th Over
the Platte Bridge Over the South Platte River project:
- City or Denver Parks ond Recreation
Construction and Access Permit
Contact: Jim hnono, (720) 810-1539
Contractor must adhere to ail Permit
requirements, including bicycle detour requirements
ond insurance requirements. The "Application for
Porks and Recreation Construction ond Access
Permit is included as an oppendix to the project
special provisions.
- Denver Wastewater Management Division Sewer Use
and Drainage Permit, with Erosion Control" checked
off.
Contact: Permit Desk, (303) 446-3759
Denver Wastewater Management Building
2000 W. 3rd Avenue, First Floor
Sheet Revisions
(>
()
o
c>
< )
16th Street Pedistrian Bridge General Notes and Sheet Index
Designer: Si'uclure D-02-PR066
Deloiler: Numbers
Sheet Subset: Subset Sheets: Cl.O of 12
xKL&A Inc.
4412 W. Eisenhower Blvd.
i Loveland, Colorado
\ PM970)657-2426
1 FAX: (970^67-2493

CITY AND COUNTY OF DENVER
DEPARTMENT OF PUBUC WORKS
3ii West Col-ax Aeue, Suite 201
'^J Denver, Colorado 50204
Pitooe: 720-513-4500 FAX: 720-913 *54.3
As Constructed
Project No./Code
PZ00298^068/CE10563
Sheet NurrSef


SUMMARY OF QUANTITIES
Nj
oo
CO
Hem Description Est. Quant. Unit Constructed Quantity
_ Rose Rid Schedule A
203-01A Utility location and PothoBna i is
203-01 Erosion Control i LS
250-01 Monitorha Technician 20 HR
250-02 Environmental Health & Safety Manoaemenl 1 LS HR
250-03 Health & Safely Officer 8
508-01 3300 SF
508-02 Wood Puri'ns 1700 IF
509-01 120,000 18
509-02 120.000 LB
509-03 Structural Steel (Field Point) 1 LS
512-01 4 EA
514-01 Pedestrian Paifino (0 Bridae) 500 FT
520-01 Bridait Cable Assembly. Fit tines fk Installation 1$
(45 CY)
613-01 Electrical Construction Is
625-01 Construction Surveying 1 LS
626-01 Mobilization i LS
630-01 Construction Zone Traffic Control 1 LS
630-02 (Bike/Ped Detour)
Construction Zone Traffic Control 1 LS
630-03 Construction Zone Traffic Control (Floaaina) too HR













Notes:
* Includes 83,150 to of Structural Steel supplied by the City and Counfy of Denver.
Pie City and County of Denver to provide 504 Bn. ft. (83,150 lbs) of 16", Schedule 100
pipe. This pipe is stored by the owner at the City Yard, booted at the comer of 53rd.
and Quebec Street Contractor is responsible tor loading and shipping the material to
fabricator's shop, at no additional cost to the project. See project special provisions,
revision cl section 509, steel structures. _
haSmW 1 2 2Q1
Item Description Est. Quon Unit Constructed Quantity
_ Hem
201-0! Cleorina and Grubbing 1 LS
202-01 Removal of Concrete Sidewalk 2,500 SF
203-015 Unclassified Excavation 1 LS
207-01 Toosoil. Pre-Amendtd. Imported and Placed 240 CY
210-01 1 LS
212-01 Native Seed Mix 1 12.SQL SF
212-02 Native Seed Mix 2 680 SF
212-03 Blue Grama Seed 2 LB
212-04 Sodded Turf 150 SF
212-05 Rockless Drainage System 1 LS
214-01 Pooufus saraenln. Plains Cottonwood, 2" cal 3 EA
214-02 214-03 Pamirs Americano. Wild Plum, 5 oat. 12 EA
Rhus Trifoboto. Three-Leaf Sumac, 5 aal. 90 EA
214-04 Quercus GambetF, Gambol Oak, 5 qaL B EA
214-05 Boulebua Gracilis. Blue Grama Grass. 5 col 249 EA
214-06 Euonvmus Fortunei 'Colorotos2 1/4"Pols 800 EA
214-07 Grovel Mulch with Fabric 455 SF
214B-01 Landscape Maintenance One Year 1 LS
216-01 Soil Retention Covering (NokMal) 475 sr
412-01 4 Wide Concrete Landscape Border 45 IF
412-02 8" Wide Concrete Landscape Border 39 LF
412-03 3' Wide Concrete Landscape Wad 20 IF
412-04 Concrete Pavement. Type A 2,559 SF
412-05 Concrete Povemenl, Type B 1955 SF
412-06 Concrete Pavement, Type C 170 SF-
412-08 Rumble Strip Pavement 34 SF
421-02 Sandstone Pavement 200 SF
421-07 19 LF
421-04 Sandstone Eld WoH 1 LS
506-01 Riprco (River's Edae) 125 :'Y










Item Description Est. Quon Unit Constructed Quantity
- Bose Bid Schedule 8 Hem
507-01 Grouted Rubble Sloped Bovina 15 CY
514-03 Guardrail an Stone Curb (East Side) 17 If
601-01 Concrete Waft at Romo 20 CY
623-01 Irrigation East and West Banks I LS


- Add Alternate No. 1 item
412-01 4 We Concrete Landscape Border 25 IF
412-05- Concrete Pavement, Type B 1925 SF
412-07 Concrete Curb at Romp 98 LF
514-01 Guard Roil on Ramp Well (West Side) 90 If

- Add Alternate No. 2 Item
421-01 Resetting of Exislina Slone Starrs 1 LS
514-02 Handrail at Stars (West Side) 27 LF
514-05 Custom Bench 1 LS

- Add Alternate No. J Item
514-04 Picket Fence Beneath Bridae 65 LF





' Notice:................ -............
On the bid date, the contractor shall include with his bid o letter which stales the name of
the steel 'fabricator, and that steel fabricator shall have been certified by the American
institute of Steel Construction, (A1S.C.) In the catagory of either Complex Steel Building
StmcturesfCbd) or Major Steel Bridges (Cbr) as of February 1, 2003. Furthermore, the
fabricator shah maintain the A.ISC. Cbd. and/or Cbr certification throughout the duration of
. the project A copy of the current certification shall be included with the letter.
Also, the technical specifications for this project delimeate special requirements for individuals
performing irrigation installation, bndscoping, landscape maintenance, aad stone masonry work.
Also, structured steel coating application shall be performed under the supervision of o Notional
Asociolbn of Corrosion Engineers (HA.C.E.) 'Certified Cooling Inspector provided by the
contractor (the cost of providing the Certified Coating Inspector shall be included in Hem 509,
structural steel (fabricated)). Also, special requirements are required of the subcontractor and
personnel responsible for the bridge cabk assembly. Aft of Ihest special requirements ore
found in the technical specifications. The contractor mV be required to provide these quafi/ied
personnel or subcontractors, the contractor shall designate to the city, in writing, aH of these
qualified personnel and subcontractors, including resumes, o minimum of one week prior to the
pre-construction conference. If the contractor attempts to provide unqualified personnel or
subcontractors, they sM be rejected, and the contractor shall replace the rejected personnel
or subcontractors with qualified personnel or subcontractors, at no additional cost to the
project.
KL&A Inc.
4412 W. Eisenhower 8
Love!cn Ph70)657-2426
FAX: (970)667-2493
As Constructed 16th Street Pedestrion Bridge Summary of Approximate Quantities
Hi Revisions: 0
Reused Deeper. EM flurrtwj D-02PR068
Peloiler:
Sheet Sd>? hts: Gi.1 o) 12
Project No./Code
PZG029ft_06S/CE 10563
3addl




J.
J.
00
o
LEGEND
FPC 9 FOUND 1 1/ STAMPED "(
cp A INDICATES l
o l 1
SSMH WCTCA7ES :
STUH @ INDICATES !
WUH 1 I
SN INDICATES 1
lp^-41 INDICATES 1
et INDICATES !
wv tX INDICATES
1GVIX INOICATES 1
INDICATES F
INDICATES -
-o- INDICATES (
% INDICATES 1
INOICATES 1
O' INDICATES 1
BtSS nr firAswre
BEARINGS SHOWN HEHEOK ARE BASED UPON THE COfFERLK OF W SBSET AS 8EWC Ha'47'OO'W
Jf ^1** w we Vita / acsm land hue survey cf portions cf blows 3 and a toceiner
WIH PORTIONS OF VACATED SIXTEENTH STREET. KASSEKKAKS ADOrtlCW TO DENVER OTT AH} COUHTY
OF DENVER, COLORADO'' REVISED MARCH 20, 2001. BY COWAN ENONEERHS & SURVCTNO WC.
BmaaiAfix no. s, elevation sibmi. navo ss m 3* brass cap
wcscre BASE OF TRMBUtSSCN UHE TOWER AT THE NORTHERLY CODER CF ISTM STREET AND
GUNNELL COURT. STAMPED '5*.
£ PROPERTY ONES SHOWN KSSCW ARC BASED ON IKE ALTA SURVEY PREP ABED BY CCWH
ENSNEERWG A SURVEYING, 1NCL (REVISED G3/2Q/Wi
u, Jj*.lmiTIES SH0W! WREDN CONTAJf ONLY GENERAL SffOmWN AS JO TSR DSCUTOCN.
JJ£W£gAf LOCATHX THE QTY AND COUNTY CF DENVER AND THE UNO PWHRSHP NfL
Offfi^LY DESCLHUS, AND ASSUMES HO UAEUTT FOR IKE UNERCRCU UXATICN IK EsSlEHCE OF
WCU5!i!& K0T uuiTED TO STORM, SWTARYSOSEH WTJR Uwt IfSSfrVBCm AMO
TOEPHONE. ELECTRIC. GAS OR CABLE LOCATIONS. SEE CENERALNCJES ' 'MWTSAW
.L,^nRACT0R SHULVERIFY location of farmer's WO GARODElYS pfqm and ail other
UTILITIES WO FACILITIES PRIOR TO CCNHEHCINS KTN CCNSIRUCTKfL THE eWIEACTOR UUst PROTECT
j^iPBJER^ANO eABOORTS PPEUNE AM) WE WATER WAT FLOWS WROXS IT JLT ALL TntES
0^J5 CONSTRUCTION. THE PIPE WHICH CARRIES THE WTCH THROUGH THE fftOfCT KUST8E
Rft^GULY LOCATED 6T THE CONTRACTOR PfKW TO COBGNONG WH AHYODSl CMSISUCBON
ACTMTES ON THE PRCUCCT. ALSO, THE CONTRACTOR MUST VESJFY 7HAT NONE CF WSOTCIRJMOi
JSTS?? BWUHNC THE PAD AM) USING WE CRAKE) WB1 DAMAGE THE PFE C DITCH IN
AAJY ^AY. THIS VERIFICATION SHALL BE'SU8UJTTED TO THE OTT PROS TO BEQHHHG THE Joa wo
^"f-BEDONE BY A COLORADO REOSIERED PROfTSSCKAL ENGNEBb WO SHALL WCUOE
CALCULATIONS AND DRAWNGS SEALES BY THE COLORADO FEGS7D ffiDFBSCNAL BMHEER.
S£??^S S*RCfS PIPELINE SUPRJE5 WATER TO IKE CHERCKEE TO4ER PLANT FCR
)5H 7X2 PUNT- WE SUPPLY OF THE WATER 5 CWTISAL TO THE OPERATORS
?,5S/??f?.PLANT- M0 Of PROVWWG COUNC WATER WGWO SHUT DOW TW PLANE.
cauotgfaiujre cf arcrwaTY to oowovw Denver. would tle axiRAciat cause failure cf
2A 10 J2E POWER PLANT, THE DENVER WATER CEPARTtfEHT *11 RAVE TO SUPPLY POTABLE
WATER AND THE CONTRACTOR MU. BE CHARGED FOR 1WS THESE COSTS, WOULD THEYOCOE. SHALL
k bcrns soar ffr we ccnvucib*. ww none of the costs to re ecfireeriKewater
THE COST OF TREATED WATER FOR 2*HOURS IS ESTIMATED TO BE tH^OaCft HONE CF Ks WORK.
llSJPi? TME REl OF THE FARMER'S AND GARDENER'S RICH, NCR TTE VBTOATXW
EE'S? AY ^ COU3RAO REOSIERED PSOFESSCNAL EVCM2S. SHALL BE PAID FOR SfffflMELY
SVT AU, Cf THIS YORK SHALL BE IN CUBED IN WE PRICE PAID FCR tTOI B2S, MOETOZATOL
INDICATES EVERGREEN
WITH TRUNK SITE
CONCRETE WAU.
J?H*£L 51 BE. 49
... 36r IN 516a. lO
INV. 36* OUT CN) 5167! 97
CHAIN UM< FENCE
8' PVC PIPE
CALL (JTTUTY NOTIFICATION
CENTER OF COLORADO
}800-92^-1987
CALL 2 BU9NESS OATO IN AOW
BEFORE YOU OIB. GRADE. OR ttCAV)
FOR THE MARKING OF UNDERGROUND
MEMBER UTUTIES.
Sheet Revisions
cn^ no motes (te rbgition vlu
(0*0 pfc>t> a
. CfTYAND COUNTY OF DENVER
CEPARnEKT OP PU8UC KORKS
333 West Goffox Avenue, Suite 20T
Denver, Colorado 8020+
Wioms 720-913-4500 FAX; 770-913-4543
As Constructed 16TH STREET PEDESTRIAN BRIDGE UTILITY DRAWING Project No./Code
Ko Revtsions:
PZ00298ub6S/CEt0S63
Revised: Designer. N ZAMCHKOWSKIT StnicJure Numbers D02PRO 58
DetaDen
VoM;
Sheet Subset GENERAL Subsets leets G1.2.1 of 12 Sheet Number S,


LEGEND
FPC FOUND 1 1/4 YELLOW PLASTIC CAP STAMPED 'COWAN EJ4G 1802"
CP A INDICATES LP.I, SURVEY CONTROL POINT INDICATES UTILITY BOX (ELEC., TELE.. A.C.)
SSMH INDICATES SANITARY SEWER MANHOLE
STMH INDICATES STORM SEWER MANHOLE
WMK @ INDICATES WATER MANHOLE
SH - INDICATES SIGN
U>^-& a INDICATES LIGHT POLE (W/ OR W/OUT GUY IMRE) INDICATES STORM GRATE/ CATCH BASN
wv tx INDICATES WATER VALVE
1GVEX 0 INDICATES IRRIGATION GATE VALVE INDICATES PIPE
INDICATES V CHAIN L
' WROUGHT IRON FENCE
iiJLTfca SWE RACK
iw.-jj. CONCRETE WALL
CAU. UT1UTY NOTIFICATION
CENTER OF COLORADO
t-BG0-922-1937
CALL 2 BUSINESS DAYS IN ADVANCE
BEFORE YOU DIG, GRADE, OR EXCAVATE
FOR THE MARKING OF UNDERGROUND
MEMBER UTILITIES.
Sheet Revisions
L_J -V-
CO
TT"
CD
TT
BASS OF BEARINGS
BEASNSS SHOW HEREON ARE BASED UPON THE CENTERLINE OF HIM STREET AS BEING N+WWW
AS aWW ON THE "ALTA / ACSH LAND TIM SURVEY OF PORTIONS OF 8L0(XS 3 AND A TOGEIHER
WTH PCRTKHS OF VACATED SIXTEENTH STREET. KASSEFtMAN* ADDITION TO DENVER CTTY AND COUKIY
CF EBAER. COLORADO" REVISED MARCH 20, 200), BY COWAN ENONEEHNC ft SURVEYNC. INC.
gNfHUAfitt
OTY CF CNWS BENCHMARK NO. MS, ELEVATION 5IQIL2!, NAM) 88 BAIUN. T BRASS CAP R
CONCRETE BASE OF ISANSflSSON LffiE TOKR AT WE NORTHERLY BWBl CF 15W STREET HO
CH£LL COURT. STAMPED *8S'.
2. WE IITlIfO SHOIH HEREON CONTAIN ONLY GENERAL INFORMATION AS 10 THEE CESCTBPTtON.
NATURE AND LOCATION. THE OTY AM) COUNTY Of DENVER AND THE LUND PARTNERS1, HC,
SPRESLY 9ESCLA1M5, AND ASSUMES NO UABlfTY FOR THE UNDERGROUND LOCATION OR BCSTENCE CF
UHJTIES WCUJDtNCL BUT NOT LIMITED TO, STORM, SAMTASY SEWJL WATER MAIN LWES/STUBOUTS AM)
TELEPHONE. ELECTRIC, GAS OR CABLE LOCATIONS. SEE GENERAL NOTES.
A QW3UCICR 9iML W3WY LOCATION CF PARSER'S AND CHOOtJtS flFOME HO ALL OWES
VTUTES AND FAd/TES FROR TO OOUEXQNG WH COSTRUCBCK THE COfTOOCfi MUST PROTECT
THE FARMER* AH) GARDOCl* FFEUKE AH) DC WATER THAT FLOWS 1KTQUGH IT AT ALL HUES
OURNG CONSTRUGTKN. THE PIPE WHKH CARRIES THE DTTCH TIfiOUGH THE PROECTIUST BE
WTSCAU.Y LOCATED BY THE CW1RACTCH PHCR ID CGMMEKCWC MTH ANY OTHER CCNS1RUCTKN
ACTMTES ON IK PRCkECT. ALSO, THE COfTRACTCfi MUST WWY THAT NONE OF HS CONSTRUCTION
ACmtIES (WOJJOUW BUUWC THE PAD AND USHO THE CRANE1 NIL DAMAGE THE PPE OR fflTCH N
ANY WAY. THIS WRFICATtOK SHALL BE 9JBHTTTED TO THE CTTY PSOR TO BEGlNNM WE VOUC AND
SHALL K DONE BY A COLORADO REGISTERED PROFESSIONAL ENSICEIL AND SU1L MCUJOE
CALOJIATICHS AH) DRAWINGS SEALED BY THE COLORADO FEGSTERED pROFESSONAl ENGMEER.
THE FABER* AND CAROOOl* PFELiNE SUPPLES WATER TO DC CHEROKEE POHER PLANT FDR
COCUNC PURPOSES WTHH THE PLANT. THE SUPPLY Of THS WATER B CRTTCAL TO THE OPERATIONS
OF THE POWER PLANT. HO FAJLUC CF PS0VC046 COOUNC WATER WOULD SHUT DOW THE PUNT.
CAUSHC FAILURE OF ELECT? CJTY TO OOWTOW DENVER. SHOLU) THE CONTRACTOR CAUSE FALURE OF
TUIST TO REAOJ Tt£ POWER PLANT, WE DENVER WA2R DEPARTMENT ALL HATE TO SUPPLY POTABLE
WATER, HO WE CONTRACTOR W. BE CHARS FOR TMS. THESE COSTS, SHOULD MY CCQJR. SHAU.
ec sent SOLELY BY THE CONTRACTOR. WITH HOC CF THE CQSfS TO BE 0OBC BY R£ PROECT
WE COST CF TREATED WATER FOR 24-HOURS IS ESTIMATED TO BE |H,SOaoa NOC X WB WORK.
HaUHNG THE TED LOCATION X THE FARMER'S AM) GARDENER* OTTCH, NX WE VEMFSCATTCM
PROVIDED 8Y THE COLORADO REGISTERED PR0FESSX3NAL ENGHEER, 9VLL BE PAID FOR SEPERATELY,
BUT ALL X THIS VOW SHALL BE HOLLOED IN THE PRICE PAD Ft* ITEM 626, UffiUZATWL
BURLINGTON NORTHERN SANTA FE RAILROAD CO.
TO BE ACQUIRED BY WE CITY AND COUNTY X
DENVER PRIOR TO CONSTRUCTION
STORM MANHOLES AND INLETS LOCATED T-ltf
WST X FENCE INDICATES APPROXIMATE
LOCATION X STORM LINE.
16TH STREET PEDESTRIAN BRIDGE GENERAL LAYOUT PLAN
Designer. NZAMCHKOWSKY Structure Numbers 002-PR0 63
Water
Sheet Subset GENERAL Vi J \i' Siijset Sheets G U of 12 ! U "" 1 1
Project No./Code
PZ00298_068/CE10563


NOTICE: THE BRIDGE ERECTION SEQUENCE THAT TEE CQNTRACTQRELECTS
TO UTILIZE, EVEN IF IT IS THE SEQUENCE SHOWN IN THESE DRAWINGS AND
DOCUMENTS, AS WELL AS DETAILS OF ANY ASSOCIATED FALSEWORK, SHALL
BE SUBMITTED BY THE CONTRACTOR TO THE CITY OF DENVER. ALSO, ITEMS
REFERENCED IN THE BRIDGE CONSTRUCTION SEQUENCE" NOTES, INCLUDING
NOTES 6, 8, AND 29, SHALL BE SUBMITTED BY THE CONTRACTOR ALL OF
THESE SUBMITTALS BY THE CONTRACTOR TO THE CITY OF DENVER MUST
\ BE SEALED BY A COLORADO REGISTERED PROFESSIONAL ENGINEER
\ THE COSTFOR THESE SUBMITTALS BY THE CONTRACTOR SHALL BE
^ INCLUDED IN THE PRICE PAID FOR ITEM 509-02,
y STRUCTURAL STEEL (ERECTION), AND THESE SEALED SUBMITTALS
' k SHALL BE PROVIDED TO THE CITY AT NO ADDITIONAL COST
, TO THE CITY OR TO THE PROJECT.
i } Bridge Constajctiw Sequence Plan
W av m0G3^
BRIDGE CONSTRUCTION SEQUENCE:
THE FOLLOWING OUTLINE IS A POSSIBLE SEQUENCE OF
CONSTRUCTION OPERATIONS, BASED ON THE ASSEMBLY OF THREE
BRIDGE SECTIONS AND THE USE OF A SINGLE CRANE TO RAISE
THE ASSEMBLED SECTIONS OF BRIDGE AND SWING THEM INTO
THEIR FINAL POSITION. THIS SEQUENCE IS AN OlfTLINE ONLY, IT
DOES NOT INCLUDE ALL OF THE DETAIL REQUIRED FOR A
COMPLETE CONSTRUCTION PLAN. THE CONTRACTOR IS
RESPONSIBLE FOR ALL CONSTRUCTION MEANS AND METHODS, AND
MAY USE AN ALTERNATIVE SEQUENCE OF CONSTRUCTION
OPERATIONS AT ITS DISCRETION:
1. OBTAIN NECESSARY PERMITS.
2. ENSURE THAT BIKE/PED DETOUR IS INTACT.
3. MOBILIZE. SET UP TEMPORARY FACILITIES.
4. PREPARE AND SUBMIT CONTRACTORS ERECTION PLAN AND PLAN
FOR TEMPORARY CONSTRUCTION.
5. CONSTRUCT TEMPORARY RAMP AND CAUSEWAY FOR CRANE
ACCESS.
6. CONSTRUCT CRANE PAD IF NEEDED.
a. NOTE: CONTRACTOR SHALL BE RESPONSIBLE FOR SELECTION OF
CRANE, CRANE PAD LOCATION, ENGINEERED PAD DESIGN (BY A CO
REGISTERED P.E. AND SUBMITTED FOR INFORMATION/REVIEW) AND
CONSTRUCTION OF CRANE PAD.
b. TEMPORARY EARTH RETAINING STRUCTURES MAY BE REQUIRED .
AT BASE OF CRANE PAD IN VICINITY OF RIVER BANK.
< CONTRACTOR'S CRANE PAD DESIGN SHALL INCLUDE DESIGN OF
' TEMPORARY RETAINING STRUCTURES, AS NECESSARY.
/ c. CRANE PAD MAY BE CONSTRUCTED OF EARTHEN FILL OR
STRUCTURAL MATERIALS SUCH AS CONCRETE. STEEL OR TIMBER.
EARTHEN FILL, IF USED, SHALL BE CLEAN MATERIAL, FREE OF
TRASH OR TOXIC MATERIALS.
d. IF PILES OR DRILLED PIERS ARE USED FOR CONSTRUCTION OF
CRANE PAD. CONTRACTOR SHALL EXERCISE CARE TO PREVENT
DAMAGE TO UNDERGROUND UTILITIES AND EXISTING CONSTRUCTION.
7. MOBILIZE CRANE.
8. PREPARE ASSEMBLY AREA FOR DELIVERY Of BRIDGE SECTIONS
ON WEST BANK OF RIVER.
a. SEE PLAN FOR APPROXIMATE LOCATION OF ASSEMBLY AREA
b. GRADE ASSEMBLY AREA AS REQUIRED TO CREATE SUITABLE
WORK AREA. EARTHEN FILL, IF USED. SHALL BE CLEAN MATERIAL,
FREE OF TRASH OR TOXIC MATERIALS.
c. CONTRACTOR SHALL BE RESPONSIBLE FOR SELECTION OF,
DESIGN AND CONSTRUCTION OF TEMPORARY FALSEWORK, DUNNAGE
. DEADMEN, GUY SYSTEMS, MUD SILLS, OR OTHER TEMPORARY
FACILITIES NEEDED FOR ASSEMBLY. DESIGN OF ANY TEMPORARY
FACILITIES, IF NEEDED, SHALL BE DONE 8Y A COLORADO LICENSED
P.E. AND SHALL BE SUBMITTED FOR INFORMATION OR REVIEW.
9. o. PREPARE EXISTING PILE CAP FOR INSTALLATION OF CENTER
PIER.
b. SEE BRIDGE CONSTRUCTION DRWAINGS FOR WORK REQUIRED AT
CENTER PIER.
10. PLACE CENTER PIER.
J J. PREPARE ABUTMENTS FOR INSTALLATION OF BRIDGE
SUPERSTRUCTURE.
a. SEE BRIDGE CONSTRUCTION DRAWINGS FOR WORK REQUIRED AT
ABUTMENTS.
12. DELIVER AND ERECT CENTER BRIDGE CABLE MASTS.
13. DELTrER BRIDGE StVHON No.i flivu/un ,u
AND ASSEMBLE BRIDGE SECTION No. I
o. COORDINATE DELIVERY SEQUENCE AND SCHEDULE WITH FIELD
ASSEMBLY OPERATIONS.
b. COMPLETE ALL BOLTED AND WELDED PERMANENT STRUCTURAL
CONNECTIONS BEFORE MOVING BRIDGE SECTION INTO PLACE
c. INSTALL ALL TEMPORARY STRONGBACKS, BRACING GUYINC OR
OTHER TEMPORARY OEMS REQUIRED TO MAINTAIN STABILITY OF THE
BRIDGE STRUCTURE SECTION NO. I WHILE BEING HOISTED INTO
FINAL POSITION.
d. PROVIDE TEMPORARY TRAFFIC CONTROL AND FLAGMEN AS
REQUIRED ON ALL IMPACTED PUBLIC WAYS, INCLUDING BIKE PATHS
DURING MATERIAL DELIVERY AND ASSEMBLY. PROVIDE A
TEMPORARY TRAFFIC CONTROL PLAN FOR OWNER'S REVIEW AND
OBTAIN STREET OCCUPANCY PERMIT PRIOR TO MOBILIZATION. (SEE
GENERAL NOTE 4 ON SHEET 2.)
14. ERECT SECTION No. I
o. INSTALL ALL TEMPORARY STRONGBACKS. BRACING, GUYING OR
OTHER TEMPORARY ITEMS REQUIRED TO MAINTAIN STABILITY OF THE
BRIDGE SECTION UNTIL CABLES ARE INSTALLED,
b. COMPLETE ALL BOLTED STRUCTURAL CONNECTIONS
15. INSTALL CENTER (4) CABLES. AND ADJUST CABLE TAKE-UPS
TO REMOVE SELFWEIGHT DEFLECTION OF PIPE TO FINAL
ELEVATIONS.
16. DELP/ER BRIDGE SECTION No.2 AND/OR COMPONENTS TO SITE
AND ASSEMBLE BRIDGE SECTION No. 2
17. ERECT SECTION No. 2
18. DELP/ER, ASSEMBLE, AND ERECT SECTION No. 3
19. INSTALL REMAINING (8) CABLES.
20. ADJUST CABLE TAKE-UPS, (8 CENTER CABLES ONLY) TO
REMOVE SELFWEIGHT DEFLECTION OF PIPE.
o. COMPLETE ALL STRUCTURAL CONNECTIONS AT ABUTMENTS
21. INSTALL DECK PURLINS '
22. INSTALL DECK, RAILING, LIGHTING, AND ELECTRICAL WORK.
23. ADJUST CABLE TAKE-UPS, (8 CENTER CABLES ONLY) TO
REMOVE DEAD LOAD DEFLECTION IN BRIDGE DECK.
24. ADJUST CABLE TAKE-UPS, (4 CABLES AT ABUTMENTS) TO
PROVIDE POST-TENSION LOAD SPECIFIED IN CONSTRUCTION
DOCUMENTS.
25. ADJUST CABLE TAKE-UPS, (8 CENTER CABLES ONLY) TO
REMOVE ALL SELFWEIGHT AND DEADLOAD DEFLECTION IN BRIDGE
DECK.
26. APPLY PINAL PAINT
27. DEMOBILIZE CRANE.
28. REMOVE ALL TEMPORARY CONSTRUCTION.
a. REMOVE ALL FILL MATERIALS. REGRADE SITE TO ORIGINAL
GRADE.
29. DEMOBILIZE AND REMOVE ALL TEMPORARY FACILITIES,
a. REMOVE BIKE/PED DETOUR. SIGNAGE AND BARRIERS.
NOTE: WHETHER THIS CONSTRUCTION SEOUENCE IS USED OF NOT
THE CONTRACTOR IS COMPLETELY RESPONSIBLE FOR THE STABILITY
AND INTEGRITY OF THE CRANE PAD, AND ASSEMBLY AREA. ANY
TEMPORARY FACILITIES CONSTRUCTED FOR STABILITY, SUCH AS
FALSEWORK, DUNNAGE, DEADMAN, GUY SYSTEMS. MUD SILLS
imaS, OR RETAINING STRUCTURES. SHALL BE DESIGNED AND
SEALED BY A CO LICENSED ENGINEER, AND THE SEALED
CALCULATIONS AND DETAIL DRAWINGS SHALL BE SUBMITTED TO THE
CITY FOR INFORMATION OR REVIEW, AT NO COST TO THE PROJECT
As Constructed 16th Street Pedestrian Bridge Construction Sequence Project No./Code
No Revisions: PZ00298^0S8/CE10563
Rrtsal: Des'qner: MB Structure Numbers D-02-PR058

Vo.fi: Subset nsets: G1.4 of 12 Sheet Number 7
Sheet Revisions
CID
CD
KLScA Inc.
4412 W. Eisenhower BWd.
Loveland, Colorado
Ph*970)667 -2425
FAX: 1970)667-2492
CITY AND COUNTY OF DENVER
DEPARTMENT OF PUBLIC WORKS
333 West Colloi Avenue. Suite 70'
Denver, Colorado 80204
Phone: 720-9(3-4500 FAX: 720- 913 -^5*3


327G15B.OWG (MWE) A1-Q16.001P (ORACLE) 500136
LOW CHORD AT W. ABUTMENT'
ELEVATION = 518159
LOW CHORD AT E. ABUTMENT
ELEVATION = 5182.16
WEST ABUTMENT
G>
Bridge Elevation
SCALE :
1" = 20 -0"
VIEW LOOKING DOWNSTREAM
WATERWAY AREA (FT2)
0 500 1000
5182
5180
5178
5176
5174
5172
5170
5168
5166
5164
100 YR
50 Yf
21

YR

&

EAST ABUTMENT
NOTES:
1. FLOOD FLOW AND ELEVATION DATA FOR THE SOUTH PLATTE RIVER
AT 16TH STREET IS AS FOLLOWS:
RFTURN FRFOUENCY
100-YEAR
50-YEAR
10-YEAR
FI OW fCFS)
22,300
17,900
8,800
CALCULATED WSFL
5179.9
5178.3
5173.8
2. FLOOD ELEVATIONS ARE BASED ON 1988 NAVD DATUM.
3. HYDRAULIC ANALYSES AND RESULTS ARE DOCUMENTED IN
"FLOODPLAIN ANALYSIS REPORT FOR SOUTH PLATTE RIVER AT
COMMONS PARK", BY McLAUOHLIN WATER ENGINEERS, LTD. (MWE)
DATED JUNE 1998, AND UPDATED BY A SUPPLEMENTAL LETTER
REPORT PREPARED BY MWE FOR KL&A, INC., DATED JULY 25, 2002*
VELOCITY (FT/SEC)
I Rfff/.

STAGF-ARFA-VELOCITY CURVES AT BRIDGE SITE
e>
Hydraulic Information
SCALE : AS SHOWN
As Constructed 16th Street Pedestrian Bridge Hydraulic Information l Proje&sw^Code
No Revisions: PZ00298_068/CE10563
Revised: Designer Structure Numbers 0-02PR068 953 CD 07/17/02

Void: Sheet Subset: Subsel * >tieet$: Gt.5 of 12 Sheet Number 8
Sheet Revisions
ae3.4SB.ssso t*z- aos.tB
CITY AND COUNTY OF DENVER
DEPARTMENT OF PUBUC WORKS
333 West Ccl/an Avenue. Suite 201
Denver, Cotorodo 80204
Phone: 720-313-4500 FAX: 720-913-4543
TRANSPORTATIONAIVISION


L


Full Text

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STRUCTURAL HEALTH MONITORING OF A CABLE STAYED PEDESTRIAN BRIDGE WITH INTERFEROMETRIC RADAR by PAUL JAMES BENNETT B.S. University of Nevada Reno, 2000 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Master of Science Civil Engineering 2012

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2012 PAUL JAMES BENNETT ALL RIGHTS RESERVED

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ii This thesis for the Master of Science degree by Paul James Bennett has been approved for the College of Engineering by Kevin L. Rens, Chair Fredrick R. Rutz Rui Lui Chengyu Li November 16, 2012

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iii Bennett, Paul James (M.S., Civil Engineering) Structural Health Monitoring of a Cable Stayed Pedestrian Bridge with Interferometric Radar Thesis directed by Professors Fredrick R. Rutz and Kevin L. Rens ABSTRACT Due to an aging infrastructure inside the United States and advances in technology, innovative structural health moni toring methods are emerging. Both short and long term health monitoring of structures can yield valuable data which can be used to determine the condition and capacity of the structure. Much research has been performed in the area of long term health monitoring (defined as monitoring where the instruments are left for days, months or year s) but short term monitoring is an emerging field. This document focuses on short term monitoring utilizing an instrument that is new to North America as of 2009. The subject instrument is the IBIS-S system which uses local interferometric radar to monitor structural movement wirelessly and in a non-contact manner. As this system is lightweight and wireless it is easy to quickly deploy, without interrupting the use of the structure, and allows the user to begin collecting data under live loads within hours. Outside of Europe, little research and verification of interferometric radar technology has been conducted on structures. This thesis presents interferometric radar theory, development and application as it relates to cable stayed bridges, particularly towards monitoring the health of the cables and overall natural frequencies of the bridge. It will be shown that interferometric radar can successfully be used to monitor the tension force and health of the cables as well as the global frequencies of the bridge. A protocol for monitoring the cables and the overall natural frequency for the City and County of Denvers cable stayed pedestrian bridge where 16th street crosses the Platte River is presented. Through the use of interferometric radar, baseline data was

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iv established for the subject bridge and it was determined that the fundamental frequency of the bridge is below the 3 Hz recommendation set forth in AASHTO standard. The form and content of this abstract are approved. I recommend its publication. Approved: Fredrick R. Rutz

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v DEDICATION This thesis is dedicated to my incredibly supportive wife, Melissa, and my two daughters, Hannah and Amelia, without whom this thesis and my graduate work never could have happened thank you for your unwavering support. Additionally, I dedicate this work to my father, Alan, who sacrificed so much in life to teach me about work ethic and a belief that I can accomplish anything in life. I also would like to dedicate this thesis to my Lord and Savior Jesus Christ who is my all in all and who has given me the drive and discipline to succeed.

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vi ACKNOWLEDGEMENTS First, I would like to thank Dr. Richard Ziernicki and Knott Laboratory for funding my graduate education and employing me, as well as Olson Instruments for graciously loaning me their instrument and expertise. Second, I would like to thank Dr. Rui Liu who was a tremendous help in this research. Third, I would like to thank Dr. Fredrick Rutz and Dr. Kevin Rens for their support and guidance through this process.

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vii TABLE OF CONTENTS CHAPTER I. INTRODUCTION ........................................................................................................ 1 Introduction ................................................................................................ 1 Scope and Objective of Thesis ................................................................. 2 Outline of Thesis ....................................................................................... 3 II. LITERATURE REVIEW ............................................................................................ 4 Introduction ................................................................................................ 4 History and Concept of Radar .................................................................. 7 How IBIS Works ...................................................................................... 10 Limitations of IBIS-S System .................................................................. 15 IBIS Software .......................................................................................... 17 Historic Use of Radar on Infrastructure .................................................. 18 Historic Use of Radar on Cable Stayed Bridges ..................................... 19 Predicting Tensile Force in Cables Based on Fundamental Frequency 19 Effect of Vibrations on Pedestrian Bridges ............................................. 19 Summary ................................................................................................ 28 III. THEORETICAL ANALYSIS .................................................................................. 29 Overview ................................................................................................. 29 Three Dimensional CAD Model .............................................................. 29 SAP 2000 Model ..................................................................................... 30

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viii General Bridge Construction ....................................................... 30 Support Conditions ..................................................................... 32 Bridge Fundamental Frequency ............................................................. 35 Conclusions ............................................................................................ 35 IV. LABORATORY WORK ......................................................................................... 37 First Laboratory Experiment ................................................................... 37 Setup of First Experiment (Cable Test) ................................................... 37 Results of First Experiment (Cable) ......................................................... 39 Conclusions from First Experiment (Cable) ............................................. 43 Second Laboratory Experiment (Steel Channel) ..................................... 43 Setup of Second Experiment (Steel Channel) ........................................ 43 Results of Second Experiment (Steel Channel) ...................................... 45 Conclusions from Second Experiment (Steel Channel) ........................... 46 V. FIELD WORK ........................................................................................................ 47 Setup ...................................................................................................... 47 Setup Comparisons ................................................................................ 50 Testing and Results ................................................................................ 51 Cable Vibration Measurement ................................................................ 51 Global Bridge Vibration Measurement .................................................... 56 Summary and Conclusions ..................................................................... 56 VI. DISCUSSION ........................................................................................................ 57

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ix Introduction ............................................................................................. 57 Cable Calculations .................................................................................. 57 Global Bridge Vibration Discussion ........................................................ 61 General Bridge Construction .................................................................. 67 Pedestrian Bridge Application of Work ................................................... 67 Recommendations for City and County of Denvers Cable Stayed Pedestrian Bridge at 16th Street Over The Platte River .......................... 68 Summary and Conclusions ..................................................................... 69 VII. CONCLUSIONS AND RECOMMENDATIONS .................................................... 70 Conclusions ............................................................................................ 70 Recommendations .................................................................................. 70 Future Work ............................................................................................ 71 REFERENCES ............................................................................................................... 72 APPENDIX A. Construction Documents for The City and County of Denvers Pedestrian Bridge 16th Street Over The Platte River ................................................................................... 74 B. First Laboratory Test Cable Test ......................................................................... 131 C. Second Laboratory Test Channel Test ................................................................ 144 D. Field Measurement of Cable Vibration on Cable Stayed Pedestrian Bridge at 16th Street over the Platte River .......................................................................................... 156

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x LIST OF TABLES TABLE 4.1 Results of Lab Testing for Tensile Force Determination in Cable ........................... 41 5.1 Measured Fundamental Natural Frequency of Bridge Cable by Cable Position (Hz) .............................................................................................................................. .......... 55 6.1 Cable Force Determination ...................................................................................... 59 6.2. Corrected Cable Force Determination, Based on 5th Mode .................................... 60

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xi LIST OF FIGURES FIGURE 2.1 Suspension bridge population in the 20th century ..................................................... 5 2.2 Martin Olav Sabo cable stayed pedestrian bridge ..................................................... 6 2.3 Electromagnetic spectrum .......................................................................................... 8 2.4 Ideal radar reflector .................................................................................................... 9 2.5 Interferometric radar concept ................................................................................... 11 2.6 IBIS line of sight measurement ............................................................................... 12 2.7 Radar read out on PC .............................................................................................. 13 2.8 Accuracy vs. SNR .................................................................................................... 14 2.9. Concept of range bins ............................................................................................. 16 2.10 Effects of cable sag on fundamental frequency ..................................................... 22 2.11 Effects of cable sag on higher vibration modes ..................................................... 23 2.12 Effects of cable bending stiffness on fundamental frequency ................................ 25 2.13 Effects of cable bending stiffness on fundamental frequency for higher modes .... 26 3.1 Three dimensional view of bridge ........................................................................... 29 3.2 Three dimensional view of bridge ........................................................................... 30 3.3 Subject Bridge .......................................................................................................... 32 3.4 Bridge end bearing conditions .................................................................................. 33 3.5 Midspan support ....................................................................................................... 34 3.6 Close in view midspan support ................................................................................ 34

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xii 3.7 First mode shape from sap mode ............................................................................ 35 4.1 Cable in MTS equipped with accelerometer ............................................................ 38 4.2 Graph of calculated vs. actual cable force ............................................................... 42 4.3 Drawing of channel .................................................................................................. 44 4.4 Channel Testing in MTS ........................................................................................... 44 5.1 Subject cable stayed bridge ..................................................................................... 48 5.2 Radar setup in field .................................................................................................. 49 5.3 Accelerometer installed on cable on subject bridge ................................................. 53 6.1 Radar plot of underside of bridge ............................................................................. 61 6.2 Frequency domain plot of underside of bridge, data for seven floor beams overall 62 6.3 Frequency domain plot of floor beam vibration on underside of bridge ................... 63 6.4 Frequency domain plot of south tower vibration ...................................................... 64 6.5 Frequency domain plot of north tower vibration ....................................................... 65 6.6 Frequency domain plot of north railing ..................................................................... 66 6.7 Mode shape plot from Matlab ................................................................................... 67

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xiii LIST OF EQUATIONS EQUATION 2.1. Relative Displacement Equation.. 2.2 Tension Force in C able 2.3 A non-dimensional characteristic parameter that reflects the influence of the sagextensibility on the cable natural frequencies. 2.4 A non-dimensional parameter which represents the effect of cable bending stiffness on the natural frequencies of cable vibration.. 2.5 Fundamental bending frequency of cable stayed bridge.. 2.6 Minimum fundamental frequency of bridge in the vertical direction....28 2.7 Prescriptive weight of supported structure, including only dead load.

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xiv LIST OF SYMBOLS SYMBOL A Cross sectional area of cable d The objects relative change in position E Modulus of elasticity of cable material f Fundamental frequency in the vertical direction ef Fundamental bending frequency nf Fundamental frequency of member or structure g Acceleration due to gravity H Cable force in chord direction I Moment of inertia of cable cross section l Cable chord length L Length of the main span Le Effective cable length m Mass per unit length of cable n Mode number T Axial Tension Force on Cable W Weight of supported structure, including only dead load The change in radar phase The radar wavelength 2 A non-dimensional characteristic parameter that reflects the influence of the sagextensibility on the cable natural frequencies Mathematical constant Cable mass per unit length

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xv A non-dimensional parameter which represents the effect of cable bending stiffness on the natural frequencies of cable vibration w1 Calculated fundamental frequency based on the taut string theory w1s Fundamental frequency based on Ren et. als theoretical work which considers cable sag

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1 CHAPTER I INTRODUCTION Introduction Radar has long been used to track the movement of objects or masses across large distances. This includes aircraft, sea vessels, precipitation, and vehicles. Regarding static objects, such as structures, radar has been successfully used to locate hidden objects. An example of this is the process of locating reinforcing steel in concrete or underground utilities utilizing ground penetrating radar (GPR). More recently radar has been used by satellites to monitor movement of soil/land masses to an accuracy of several meters ( IBIS-S Controller User Manual July 2010) With time and technology, the accuracy of radar has greatly increased to the point where it is now feasible to monitor very small movements. In the 1990s, an Italian corporation known as Ingegneria Dei Sistemi, or IDS translated Systems Engineering partnered with the University of Florence to research the possibility of utilizing radar to monitor earth movement to a higher degree of precision (i.e. millimeters (mm)) (25.4mm=1.0 inches) (Farina et al, 2011). IDS and the University of Florence were successful in applying radar technology in monitoring land subsidence and slope stability, particularly in mining applications (Farina et al, 2011). In this application, a semi-permanent radar station is set up to focus on a particular slope (Farina et al, 2011). IDS technology for monitoring slope stability has successfully been used in Europe for over a decade (Farina et al, 2011). In the late 1990s, Farrar et. al presented that radar could be used to monitor movement in structures (Farrar et. al 1999). IDS and the University of Florence have also researched radar applications on structures, namely monitoring small movements in structures or structural members. Through all this research, IDS has developed a

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2 system entitled Image By Interferometric Survey (IBIS) which utilizes radar to monitor deflections in structural members with a precision of up to 1/100 mm (0.000394 inches). The IBIS system is a non-contact, non-destructive, rapidly deployable system that has positive implications for the structural health monitoring community. Both the benefits and limitations of the IBIS instrument are discussed in this thesis. As it relates to structures, the IBIS system has been used in Europe for approximately 10 years. Inside of North America few IBIS systems exist and the few systems that do exist are privately owned and operated by the mining industry to monitor slope stability. Olson Instruments Inc. (Olson) of Wheatridge, Colorado currently has the only privately held, for-hire, IBIS system in North Amer ica. Olson has graciously agreed to help sponsor this thesis in the spirit of incr easing the body of knowledge of the structural health monitoring community. Scope and Objective of Thesis Because of its superior accuracy there are many potential IBIS applications in structures. However, many such applications are still being researched. The primary objective of this thesis is to explore, via laboratory and field experiments, an application of IBIS technology to cable stayed bridges. Of particular interest is a pedestrian bridge owned by the City and County of Denver, Colorado. A method to monitor the health of the cables and overall bridge health with IBIS technology was developed and implemented. The scope of this thesis is limited to one bridge and to vibration monitoring on that bridge. Recommendations for future bridge health monitoring are provided herein. Outline of Thesis This thesis presents the results of theoretical and experimental testing in which interferometric radar technology is used to monitor the structural health of a cable stayed

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3 pedestrian bridge. Chapter Two presents a review of available literature regarding interferometric radar and its use on structures, including cable stayed bridges. Chapter Three presents the results of a Finite Element Analysis (FEA) theoretical determination of a particular cable stayed bridges fundamental frequency. Chapter Four presents the results of laboratory experiments in which interferometric radar was used to determine the tension force in a cable based on the fundamental frequency of vibration and an attempt was made to determine the tension force in a steel channel through the use of interferometric radar. Chapter Five presents the results of field work wherein interferometric radar, an alternate instrument, and an accelerometer were used to monitor vibrations in a cable stayed pedestrian bridge and the results of all three instruments were compared. Chapter Six contains discussion and conclusions reached as a result of the work in the previous four chapters as well as a testing protocol for the subject pedestrian bridge. Chapter Seven presents final conclusions and recommendations.

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4 CHAPTER II LITERATURE REVIEW Introduction The concept of a cable suspended bridge (a bridge in which smaller vertical suspender cables that support the deck, hang from a larger catenary shaped cable which anchors to the earth) has been around for centuries as historians note remote foot bridges constructed with vines and ropes. However, the concept of a cable stayed bridge a bridge in which the cables are diagonal, putting the bridge deck into compression, and the cables attach to a structurally critical tower or mast is a more recent (past 400 years) development. The oldest known cable stayed bridge design concept dates back to a design completed by the Venetian engineer Faustus Verantius in 1607 (Podolny 1999). The oldest known constructed cable stayed bridge dates back to a 32 Meter (M) (105 Feet) long span completed by Loscher in 1784 (Podolny 1999). The oldest known cable stayed bridge in the United States is a still intact steel bridge located in Texas and was designed by E.E. Runyon (Historic American Engineering Record 1968). The concept of cable stayed bridges did not become common in place in the United States until approximately 40 years ago. As can be seen in Figure 2.1, the use of cable stayed bridges in new construction in the United States continued to increase until the mid 1990s. The increased use of cable stayed bridges is due both to their aesthetic appeal and their cost effectiveness for moderate bridges.

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5 Figure 2.1 Suspension bridge population in the 20th century. (Copyright 1999 by The McGraw-Hill Companies, Podo lny, Walter, Jr., P.E. (1999). Section 15, cable suspended bridges, Structural Steel Designers Handbook, Third Edition, ed. Brockenbrough, R.L, Merritt, F.S., Image repr oduced with permissi on from The McGrawHill Companies) With an increase in the number of cable stayed bridges in the United States in the past 40 years there becomes a need for the development of structural health monitoring techniques for cable stayed bridges. In contrast to a suspension bridge wherein the failure of one of hundreds of suspender cables is likely not catastrophic, the failure of a cable in a cable stayed bridge has a higher likelihood of being catastrophic. For instance, consider the Martin Olav Sabo cable stayed pedestrian bridge in Minneapolis, Minnesota (Figure 2.2) constructed over a light rail and highway in 2007 with a main clear span of 67 M (220 feet) which had a serious failure on February 19, 2012 that led to the closure of the bridge. The failure, involved the failure of two cables which caused a portion of the bridge deck to deflect which in turn caused an increase in loading on adjacent connections causing concern or a progressive collapse. Reportedly, the cables failed due to a fatigue failure, induced by wind born vibrations, in a diaphragm plate that connected to the bridge tower (WJE 2012). Many engineers have suspected

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6 that the failure was caused by fatigue stresses that were induced by excessive vibrations in the bridges cables as members of the community had expressed concern over excessive vibrations. It is unknown to this engineer what type of structural health monitoring program was in place for this bridge but perhaps closer monitoring of cable vibrations and global vibrations would have predicted fatigue failure. Figure 2.2 Martin Olav Sabo cable stayed pedestrian bridge. (Copyright 2009 by John A. Weeks III, http:// www.johnweeks.com/cablestay/pages/ped07.html, Image used by kind permission from John A. Weeks III) Much research exists regarding the structural health monitoring of cable stayed bridges and a fundamental part of any such health monitoring plan involves vibration monitoring. However, most, if not all, current vibration monitoring instruments require persons to physically access the cables in order to obtain measurements which usually results in temporary bridge closure. The purpose of this thesis is to explore the use of radar technology for monitoring structural health in cable stayed bridges this concept allows data to be gathered without closure of the bridge and in a non-contact manner.

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7 History and Concept of Radar The word radar, a noun in the English language, stems from an acronym developed in the U.S. Navy RAdio Detection And Ranging (RADAR). As the name implies, radar technology relies upon the use of radio waves to detect the location (range) of mass. On the electromagnetic spectrum, radar is a subarea of the microwave region having a range of frequency between 0.3 and 300 GHz (Figure 2.3). Radar technology has been around for over 100 years but it wasnt until World War II when its use became widespread and wide known as it was found very useful to track both enemy and ally ship and aircraft locations and movements.

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8 Figure 2.3 Electromagnetic spectrum. (http://www.lbl.gov/MicroWorlds /ALSTool/EMSpec/EMSpec2.html, Image Courtesy of Advanced Light Source, Lawrence Berkeley National Laboratory)

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9 Radar is an invisible wave which, like any waveform, when emitted will reflect or bounce backfrom objects in its way. Metallic objects are a particularly good reflector. The quality of the reflection is dependent upon both the material and the angles inherent to the object. An ideal radar reflector is a metallic object in the shape of an open pyramid where the radar is directed at the inside of the pyramid this shape forces all incoming waves to be reflected back towards their source (Figure 2.4). Figure 2.4 Ideal radar reflector. In a real world scenario, the rather sharp angle created at the point where an aircrafts tailfin joins the fuselage is a good reflector of radar. With this basic knowledge of radar one can view Lockheed Martins stealthy, nearly radar invisible, F117 aircraft and come to understand the purpose of the oblique angles and out of plumb tail fins. In order to locate or track the movement of an object, a radar emitter sends out radar waves with a known frequency, amplitude, and wave length. An antenna is engineered and setup to receive the radar waves. Due to the Doppler Effect, the reflected waves

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10 have a different wavelength, frequency, phase and amplitude from the initial signal (IDS 2008). Utilizing the change in the waveform it is then possible to determine how far away the object is and by this information one can track the relative movement (displacement) of an object. How IBIS Works IDS IBIS system utilizes radar technology to detect small movements in structures or structural members. The subject IBIS instrument, one that is licensed by the Federal Communications Commission for use in the United States, emits microwaves at a Continuous Wave Step Frequency (CWSF) of 17.1-17.3 MHz with a wavelength of approximately 18mm (0.71 inches)(IDS 2010 ). The frequency and wavelength have importance as they determine the size of object that can be detected, the maximum measurable defection, and the minimum distance two objects must be separated by a concept known as range bins for which further discussion is presented below. IBIS utilizes a form of radar known as interferometric radar. In most radar applications the amplitude change in the reflected wave form is used to determine the location of the desired object. However, interferometric radar utilizes the change in phase of the reflected wave to determine position. By monitoring the phase change, a more accurate measurement of movement is possible (Figure 2.5).

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11 4 d Figure 2.5 Interferometric radar concept (adapted from IDS 2010). An objects change in position is given by the equation 2.1 shown below. Equation 2.1 Relative Displacement Equation (Gentile 2008). Where: d= Objects relative change in position = Radar wavelength =Change of Phase as shown in Figure 2.5 = Mathematical constant Inside of the interferometric radar technology are two concepts; Synthetic Aperture Radar (SAR) and Real Aperture R adar (RAR). IDS manufactures a system for long term monitoring of slopes and structures (IBIS-L) and a system for short term health monitoring (IBIS-S). The instrument used in this research is the IBIS-S system. In a static setup the IBIS-S relies upon RAR technology which, in contrast to a typical two dimensional (2D) SAR image, results in a one dimensional (1D) view (Dei et al, 2009).

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12 Due to the 1D limitation it is critical to understand that the displacement measured is the objects relative movement in the line of radar. As the radar head is rarely, if ever, pointed directly along the expected plane of movement (vertical in the instance of a beam deflecting downward), the measured displacement is not actual displacement (Figure 2.6). However, due to the superior accuracy of IBIS, vertical displacement will produce a change in the measured distance and utilizing basic trigometric principles one can calculate the actual displacement. Figure 2.6 IBIS line of sight measurement (adapted from Gentile 2008). From a hardware standpoint, the IBIS system is fairly simple. It consists of a radar head or sensor that has two antennas. One antenna sends a signal and the other

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13 receives. The radar head sits atop a traditional tripod that is leveled prior to use. Two cables connect to the back of the sensor. One cable is used to power the system and the other is used to send data to a personal computer (PC). Any PC system with the proper software and a Universal Serial Bus port (USB) can be used to receive data. The IBIS system has six available sets of antennas. Each antenna forms a different shaped radar cone which results in a different field of view. For example, one antenna produces a narrow focused cone and another produces a wide shallow cone. While the IDS provided manuals give data on each of the antennas there are no known publications which educate the user on which antennas are best for certain applications. In the Field Work section of this paper more is presented on how an individual chooses an antenna for a given application. Once the IBIS system is assembled and powered, the user can view the radar feedback on the PC. The radar feedback is presented on a plot with distance on the X axis (in meters) and a signal to noise ratio (SNR) plotted on the Y axis (see Figure 2.7 for an example). Figure 2.7 Radar read out on PC.

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14 The stronger the SNR the more accurate the instruments output is. Thus, strong peaks on the plot (high SNR) are necessary for the structural member(s) of interest. On the low end, SNR ratios of 20 give an accuracy of 0.1mm (0.00394 inches) (IDS 2010 ). On the high end, SNR ratios of 60 and higher give an accuracy of 0.005mm (0.00020 inches)(see Figure 2.8 ). Even with the low SNR ratios, a high degree of accuracy is available. Figure 2.8 Accuracy vs. SNR. (Copyright 2010 by IDS, IBIS-S Controller V 02.02.000 User Manual Rev. 1.1, July 2010 Image used by kind permission from IDS) Certain types of structural members are good natural reflectors of radar. These include steel members with geometry changes such as L, C and W shaped members. Steel cables are typically good reflectors. Typical plate steel and smooth rods are not good reflectors of radar. Concrete and wood are not typically good reflectors of radar. For applications where the user cannot achieve good reflections the user may be required to install a reflector as shown in Figure 2.4. In order for the user to have confidence as to what peaks correlate to which structural members, a laser distance meter is a necessary tool. By placing the distance

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15 meter on the IBIS and aiming at desired structural elements, the user can quickly determine which peaks relate to which member(s). For the purpose of determining the distance to smaller diameter cables, a distance meter with a live video feed and crosshairs is necessary to ensure the laser is reflecting from the correct cable. For the purposes of this thesis, a Leica DISTO D5 instrument (a laser distance meter which has a range of up to 200 M (650 Feet) and an accuracy of 1mm (0.0394 Inches)) was used. Thus, as long as the user has confidence in the objects each radar peak corresponds to the user can collect displacement data on multiple structural elements at the same time. For instance, one technique involves viewing the underside of a bridge, looking parallel to the structure, allowing the user to collect displacement data for all cross frames/members at the same time with one setup and one instrument. In a typical static/tripod type of setup t he IBIS system produces a 1D image. Due to the static setup and CWSF, range bins are created in which the radar cannot distinguish the difference between objects that are within a certain distance of each other along the path of the wave propagation (see Figure 2.9). The range bin distance for the IBIS-S system available in North America is 0.75 M (2.46 Feet); that is to say that the instrument cannot differentiate between objects closer than 0.75 M (2.46 Feet) to each other on a given radial distance from the instrument. Dei et al. (2009) have successfully explored monitoring techniques, monitoring torsional motion, wherein the instrument is mounted and moved slowly along a rail to produce a 2D, SAR image that is not limited by range bins.

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16 Figure 2.9 Concept of range bins. (Copyright 2010 by IDS, IBIS-S Controller V 02.02.000 User Manual Rev. 1.1, July 2010 Image used by kind permission from IDS) IBIS can sample at a rate of 200Hz (100Hz Nyquist Frequency) permitting the user to obtain accurate data when monitoring vibrations. The 200Hz sampling rate also permits the user to see higher order natural frequencies and mode shapes in most structures and cables. Limitations of IBIS-S System The IBIS system is limited to objects that are further than 0.75 M (2.46 Feet) apart from each other. In addition to this limitation, IBIS 18mm (0.71 Inches) wavelength requires that the object be larger than 18mm (0.71 Inches) in order that the waves do not pass over the object. The implication of these limitations is that IBIS cannot practically be used to monitor the tensile force in cables that have a diameter of less than 18mm (0.71 Inches) (although a limitation of 25.4mm (1.00 inches) cable diameter is typically recommended).

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17 IBIS 18mm (0.71 Inches) wavelength also presents a dilemma for larger deflections. If the deflections in the member exceed 18mm (0.71 Inches), then certain portions of the radar waves will pass over the object resulting in incorrect data. For cables with low tensile forces that are constantly excited by ambient conditions (wind, traffic) this proves to be a problem. However, this problem c an be overcome by mounting onto the cable, or beam, a reflector that is much larger than the 18mm (0.71 Inches) wavelength obviously this would require access to the cable (which may not always be possible). Benefits of IBIS are that its results are reportedly unaffected by weather conditions and it typically requires no contact with the structural members so that monitoring can occur while the structure is in use. IBIS Software IDS IBIS system is supplied with an outdoor rated laptop computer which features hardware drivers to connect to and collect data from the radar head. However, any personal computer can be used; the user does not have to use the supplied laptop. Also provided with the IBIS system is MatLab-bas ed post processing software. After the field datareferred to as a missionis complete, the user can launch the post processing software and begin processing the gathered data (displacement data as a function of time) for each point of interest. The post processing software is surprisingly simple to use and is quite powerful. In particular, the software performs a Fourier Transform function (which takes displacement data that was acquired in the time domain and plots it in the frequency domain) after which the displacement, velocity and acceleration can call be viewed in both the time and frequency domains. IBIS MatLab based software also has the capability to determine mode shapes and to form a movie that depicts the structures movement over time this is done in a click of a button. These capabilities allow the user to process and view their data in the field

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18 and within minutes form an opinion on the accuracy of the data as well as the behavior of the structure. Historic Use of Radar on Infrastructure Radar has long been used to inspect roadw ays and structures through the use of Ground Penetrating Radar (GPR). In contrast to IBIS use of interferometric radar technology, GPR utilizes conventional radar technology to ascertain information. GPR use in the United States began in the 1970s with its use on roadways, including bridge decks, and its use has expanded to investigation of: buried utilities, voids below roadways, pavement thicknesses, depth to bedrock and determination of deteriorated areas of bridge decks, all utilizing high fr equency microwaves of 0.5 to 1 GHz (Morey, 1998; Maser, 1994; Alongi et al, 1992, Scullion et al, 1992). Today, GPR is still used for all of the above and its use has further expanded to buildings and bridges. GPR is used to locate steel rebar and strands in mildly reinforced concrete and pre/post stressed concrete, respectively. Tallini et al, successfully showed that GPR can be used to determine foundation type and to investigate the quality (depth and bulbs) of micropiles (Tallini et al, 2004) As it pertains to interferometric radar, research indicates that the technology has been successfully used to monitor the structural health of wind turbines (Pieraccini et al, 2008), buildings (Luzi et al, 2008), towers and culverts (Beben, 2011). Other research involves multiple IBIS systems working together to measure torsion in structures (Dei et al, 2009). Much research has also been dedicated to utilizing IBIS technology in the monitoring of slope stability (see Pieraccini et al., 2001).

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19 Historic Use of Radar on Cable Stayed Bridges As previously mentioned, Farrar et. al explored the application of radar to monitor movement in structures this included bridges (Farrar, et. al, 1999). Since that time many groups including Pieraccini et al, Gentile, Dei et al have successfully undertaken the monitoring of bridges with IBIS technology (Gentile 2008, Pieraccini et al., 2001). These individuals have been successful in monitoring both deflections/vibrations in bridge members as well as determining global natural frequencies and mode shapes of the bridges. These bridges included cable stayed bridges. Specifically regarding the structural health of cables in the cable stayed bridges there is very little published literature. In 2010 Gentile theorized that IBIS technology could be used to monitor the health of cables in cable stayed bridges via monitoring changes, over time, in the natural frequency of the member (Gentile 2010). Further, Gentile relied upon previous research which determines the tension force in a cable based on the cable properties and measured natural frequency. Over time, changes in the cables frequency would indicate there is a change in the tension force which could indicate deterioration in the cable or overall changes in the load paths in the bridge as a whole. Predicting Tensile Force in Cables Based on Fundamental Frequency The earlier work that Gentile did relied upon work done by Mehrabi in 2006 (Mehrabi 2006). Mehrabi indicates that the tension force in a cable member can be determined by relying upon a taut string model which is represented by equation 2.2 (Mehrabi 2006):

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20 2 2)(4 n f LTn e Equation 2.2 Tension Force in Cable (Ren et al). Where: T = Axial tension force on cable nf= Fundamental frequency of member or structure n= Mode number Le= Effective cable length = Cable mass per unit length As the name implies, applying the taut string theory to cables assumes the cable is taut. However, in many instances cables in cable stayed bridges are not taut. Such is the case for the bridge that is the subject of this thesis. Both the degree of sag and the bending stiffness of cables effect their fundamental frequency and changes the accuracy of Equation 2.2 above. Ren et al sought to quantify the effect of bending stiffness and sag on the taut string theory equation and their work indicates that indeed unacceptable errors in predicted tensile force can occur due to cable sag and stiffness (Ren et. al, 2007). Ren et. al. performed a theoretical analysis on the effect of cable sag and in that analysis they introduce a non-dimensional term ( l2), shown in Equation 2.3 below, which is an important characteristic parameter that reflects the influence of the sagextensibility on the cable natural frequencies (Ren et. al, 2007).

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21 eHL EA H mg 2 2)( Equation 2.3 A non-dimensional characteristic parameter that reflects the influence of the sag-extensibility on the cable natural frequencies. Where: E= Modulus of elasticity of cable material A= Cross sectional area of cable Le= Effective cable length H= Cable force in chord direction l = Cable chord length m= Mass per unit length of cable 2= A non-dimensional characteristic parameter that reflects the influence of the sag-extensibility on the cable natural frequencies G= Acceleration due to gravity When utilizing the first mode, Ren et al conclude that for l2 values greater than 1.0, large amounts of error exist (20% when l2 equates to 5.48, for example) (Ren et. al, 2007). This phenomena is shown graphically in Figure 2.10 below wherein w1 is the calculated fundamental frequency based on the taut string theory and w1s is the fundamental frequency based on Ren et. als theoretical work which considers cable sag (Ren et. al, 2007).

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22 Figure 2.10 Effects of cable sag on fundamental frequency. (Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations: International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008, Determination of Cable Tensions Based on Frequen cy Differences, Ren, Wei-Xin; Liu, Hao-Liang; Chen, Gang; Page 176, Figure 2, used with kind permission from Inderscience Enterprises Limited. ) Ren et als work went on to analyze the effect of cable sag on higher modes of vibration and the results are very useful in this thesis work. Specifically, Ren et al performed theoretical analysis for higher vibration modes and showed that the effects of cable sag become negligible for higher vibration modes. A plot showing the variation of l2 for different vibrations modes is shown in Figure 2.11 below. Note that in Figure 2.11, the y label on the y axis is a variable that represents different curve functions, each of which contain the natural frequencies of the symmetric in-plane modes of a sagged cable. On the same note, the 2/ I label on the x axis is the algebraic roots

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23 (1st, 2nd, 3rd, etc.) to the equation represented by variable y which represent corresponding (1st, 2nd, 3rd, etc.) mode shapes. Figure 2.11 Effects of cable sag on higher vibration modes. (Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations: International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008, Determination of Cable Tensions Based on Frequen cy Differences, Ren, Wei-Xin; Liu, Hao-Liang; Chen, Gang; Page 177, Figure 3, used with kind permission from Inderscience Enterprises Limited. ) Ren et. al. conclude that when l2=300, the discrepancy between the first three symmetric natural frequencies of the sagged cable obtained from their theoretical equation and those of the taut-string cannot be neglected, but the sagged cable frequency and taut-string frequency become very close after the fourth symmetric vibration mode (3.5pi on Figure 2.11). Ren et al continue with lab and field work which prove their theories. Ren et als work has significance for those in the structural health monitoring community that work on cable stayed bridges since, prior to this work, cable sag on many bridges introduced unacceptable errors in the calculated cable tension

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24 EI T forces. In order to remove the error associated with cable sag, one must determine the fourth, or higher, cable vibration mode. The only drawback to this method is that associated with determining the higher modes of vibration. The process of determining the higher modes of vibration relies upon field work and review of power density plots and sometimes during that process certain modes can be missed. Ren et als work also looked at the effect of cable bending stiffness on the results of the taut string theory. Ren et als work analyzes the cable as a simply supported beam with an axial tension force and t hey introduce a non-dimensional parameter which represents the effect of cable bending stiffness on the natural frequencies of cable vibration. is defined in equation 2.4 below (Ren et. al, 2008). Equation 2.4 A non-dimensional parameter which represents the effect of cable bending stiffness on the natural frequencies of cable vibration. Where: E= Modulus of elasticity of cable material I= Moment of inertia of cable cross section T= Axial Tension Force on Cable l = Cable chord length = A non-dimensional parameter which represents the effect of cable bending stiffness on the natural frequencies of cable vibration Ren et al prepared a plot of versus natural frequency which is shown in Figure 2.12 below where w1 is the calculated fundamental frequency based on the taut string theory and w1s is the fundamental frequency based on Ren et. als theoretical work which considers cable stiffness (Ren et. al, 2007). Essentially, Ren et. al. concluded that for lower values of (less than 50), the cable bending stiffness cannot be neglected but for higher values (more than 50) cable bending stiffness can be neglected (Ren et. al,

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25 2007). Also, the lower values of effect the results of the taut string theory for higher order frequencies as shown in Figure 2.12. Figure 2.12 Effects of cable bending stiffness on fundamental frequency. (Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations: International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008, Determination of Cable Tensions Based on Frequen cy Differences, Ren, Wei-Xin; Liu, Hao-Liang; Chen, Gang; Page 180, Figure 4, used with kind permission from Inderscience Enterprises Limited. )

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26 Figure 2.13 Effects of cable bending stiffness on fundamental frequency for higher modes. (Copyright Emerald Group Publishing Limited 0264-4401, Engineering Computations: International Journal for Computer-Aided Engineering and Software, Volume 25, No.2, 2008, Determination of Cable Tensions Based on Frequen cy Differences, Ren, Wei-Xin; Liu, Hao-Liang; Chen, Gang; Page 180, Figure 5, used with kind permission from Inderscience Enterprises Limited. ) In summary, Ren et. als work shows that when predicting cable tension based on fundamental frequency utilizing the taut string theory, that cable sag effects the results of the taut string theory for lower vibration modes but for higher vibration modes the error is negligible (Ren, et. al, 2007). In contrast Ren et. al showed that the effect of cable bending stiffness on the results of the taut string theory effect the higher frequency modes more so than the lower modes (Ren, et. al, 2007). Effect of Vibrations on Pedestrian Bridges In their book, Vibration Problems in Structures, Bachmann et. al. indicate that 95% of pedestrians walk at rates between 1.65 and 2.35Hz (Bachmann, et.al, 1995). Most structural engineers are aware that as the forcing frequency approaches the fundamental frequency of the structure resonance can occur. It is for these reasons that

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27 L fe110 modern pedestrian bridge codes limit the natural frequency of pedestrian bridges. For the subject bridge, the applicable bridge code 1997 AASHTO Guide Specifications for Design of Pedestrian Bridges indicates that for pedestrian bridges the fundamental frequency in the vertical direction must be above 3Hz, and the fundamental frequency in the lateral direction must be above 1.3Hz (AASHTO 1997). Steel footbridges, such as the subject one, are more susceptible to vibration problems due to pedestrians (Bachman et. al, 1995). Work done by Wiss et al. indicates that the most severe response in pedestrian bridges occurred when the fundamental frequency of the bridge is closest to 2Hz (Wiss et al 1974). Bachmann et al. present a basic empirical equation relating the fundamental frequency of cable stayed bridges to their span length (Bachmann et.al, 1995). This equation is presented in Equation 2.5 below (Bachmann et.al, 1995). Equation 2.5 Fundamental bending frequency of cable stayed bridge (Bachmann et al, 1995). Where: L = Length of the main span ef= Fundamental bending frequency AASHTO 1997 indicates that if an analys is of the bridges fundamental frequency in the vertical direction is not evaluated then the bridge may be proportioned to satisfy the following criteria in equations 2.6 and 2.7:

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28 ) 180 ln(86.2 W f )35.0(180feW Equation 2.6 Minimum fundamental frequency of bridge in the vertical direction (AASHTO 1997) or Equation 2.7 Prescriptive weight of supported structure, including only dead load (AASHTO 1997). Where: f=Fundamental frequency in the vertical direction W= Weight of supported structure, including only dead load Summary In summary, there are numerous cable stayed bridges inside of the United States and those bridges require structural health monitoring. It is critical to design those bridges to prevent fatigue failures which can occur due to excessive vibrations. A proper health monitoring program can identify a loss of stiffness or excessive vibrations via monitoring the global natural frequency of the bridge and the natural frequencies of the cables. Equations exist which can correlate the tension in cables to the measured natural frequency. Radar technology has been around for decades but it has only been in the past 10 years that this technology has been used for structural health monitoring purposes. By using interferometric radar technology, IDS has developed an instrument that can monitor vibrations in cable stayed bridges in a non-contact manner.

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29 CHAPTER III THEORETICAL ANALYSIS Overview In order to have baseline data to compare field testing results to, a theoretical Finite Element Analysis (FEA) was performed for the bridge of interestthe City and County of Denvers cable stayed pedestrian, 16th Street over the Platte River. Utilizing construction documents for the subject bridge, a three dimensional Computer Aided Drafting (CAD) model was created. Next, the CAD model (a .dxf file) was imported into SAP 2000 and the theoretical global fundamental frequency of the bridge was determined. Three Dimensional CAD Model The subject bridge has a fairly complex geometry as is typical for cable stayed bridges. In particular, the bridge is crowned vertically with the highest point being the middle support; the towers are swept in three dimensions; and, the geometry is not symmetrical about the center support. Utilizing elevations and dimensions from the bridges original construction drawings, shown in Appendix A, the three dimensional CAD model was created using AutoCAD software. Figures 3.1 and 3.2 below show three dimensional CAD views. Figure 3.1 Three dimensional view of bridge (purlins not shown for clarity sake). Cables Floor beams

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30 Figure 3.2 Three dimensional view of bridge. SAP 2000 Model General Bridge Construction Construction drawings (See Appendix A) for the subject bridge were obtained and through inspection of the bridge it was concluded that the bridge was built in substantial conformance with the construction documents regarding dimensions and materials used. Structurally, the bridge is fairly simple. The bridge features a decay resistant wood decking (spanning perpendicular to the length of the bridge) that transmits gravity loads to wolmanized wood stringers that span approximately 3.96 M (13 feet) (parallel to the length of the bridge) and bear upon steel floor beams that span approximately 6.10 M (20 feet) (perpendicular to the length of the bridge). The steel joists attach at either end to two main 40.64 Centimeter (CM) (16 inch) diameter steel tubes, or girders. The steel tubes constitute the main gravity carrying element. The steel tubes rest upon Cables

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31 bearing pads near both ends of the bridge and at their midspan the tubes bear upon a perpendicular built up steel member which attaches to the towers and the towers transmit that load to a cast in place mildly reinforced concrete foundation. A photograph of the bridge is shown below in Figure 3.3. The main tubes span approximately 31.70 M (104 feet) between supports and gain significant support from cables. The cables are 25.4 mm (1 inch) diameter Class A structural steel strands (manufactured in accordance with ASTM A586). The cable properties, as provided by the manufacturer (WireCo) are as follows: Tensile Capacity = 55,338 Kilograms (KG) (61 tons) Weight per Unit Length = 30.65 Newtons/M (2.1 lbs/ft) Modulus of Elasticity = 1.66*1011 Pascals (Pa) (24,000 Kips per Square Inch (ksi)) Cross Section Area = 3.87 CM2 (0.60 in2) The cables connect to the tube via a welded plate connection and the cables connect to the plate via a pin ended connection. At their tops, the cables connect to 40.64 CM (16 inch) diameter steel tube masts via a similar connection.

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32 Figure 3.3 Subject bridge. Support Conditions The subject bridge features cantilevers, approximately 3.05 M (10 feet) long on the west end and 20 feet long on the east end, at both ends. Through inspections, it was noted that the supports nearest the ends of the bridge are both roller bearing supports as evidenced by the loose and slotted vertical bolts and the elastomeric bearing pads shown in Figure 3.4 below.

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33 Figure 3.4 Bridge end bearing conditions. The bearing at the middle of the bridge was determined to be consistent with a pin ended condition. This is evidenced by the main supporting tubes which bear upon the aforementioned perpendicular built up steel member, as shown in Figures 3.5 and 3.6 below, via a welded steel plate that has limited moment capacity.

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34 Figure 3.5 Midspan support. Figure 3.6 Close in view midspan support. The built up perpendicular steel section transmits the gravity loads from the main tubes to the towers, or masts, via a bolted connection as shown in Figure 3.6. The

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35 towers, or masts, are supported via a moment resistant connection at their base as shown in Figure 3.6. Bridge Fundamental Frequency Through the FEA analysis it was concluded the global fundamental frequency of the bridge is 3.39 Hz. In accordance wi th AASHTO recommendations, all the frequency determinations in SAP 2000 were determined utilizing un-factored self-weights. The SAP model was edited multiple times in order to determine its sensitivity to cable force and individual element boundary conditions and no change in the fundamental frequency or first mode shape occurred. This is due to a 7.16 M (23.5 foot) long steel framed cantilever that exists on the east end of the bridge. The cantilever dominates the first mode shape and that cantilever is unaffected by cable tension force as no cables connect to that portion of the bridge. The first mode shape from the SAP model can be seen in Figure 3.7 below. Figure 3.7 First mode shape from sap model. Conclusions In summary, the fundamental frequency of the bridge was determined to be 3.39 Hz in SAP 2000 software and the first mode shape was found to be dominated by the east end cantilever section. Changes in the boundary conditions of individual elements and the cable tension forces resulted in no change in the fundamental first mode shape due to the dominance of the east end cantilever. The east end cantilever dominance is East Cantilever

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36 consistent with field observations which are discussed in the Field Work portion of this thesis.

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37 CHAPTER IV LABORATORY WORK First Laboratory Experiment Setup of First Experiment (Cable Test) Bearing in the mind that one of the primary purposes of this thesis is to determine if IBIS technology can be accurately used to measure the natural frequency of cables, a laboratory experiment was designed and implemented. The first phase of the laboratory experiment involved purchasing a 1.25 inch diameter cable (wire rope) with looped ends and fixing the cable in UC Denvers (UCD) Material Testing System (MTS), stretching the cable to a known tensile load, striking the cable with a rubber mallet to induce free vibration and measuring the vibration motion with three instruments (see Figure 4.1 for an image of the lab setup). The three instruments used were the subject IBIS-S system (sampling at a rate of 100Hz Nyquist Frequency), a programmable accelerometer (GP1 Programmable Accelerometer manufactured by Sensr, sampling at a rate of 50 Hz Nyquist Frequency and set at a g range of +/2.5g) and a non-contact instrument manufactured by DynaTension (Model P1000) which measures the frequency of vibration in cables. Loading was applied in 8.90 Kilonewton (KN) (2 Kips) (1Kip=1000 Pounds) increments starting at 0 KN (0 Kips) and going through to 115.65 KN (26 Kips). Ten readings were taken with the P1000 and the results were averaged for a final value. A minimum of four cable strikes were conducted with the accelerometer and the data from those strikes were included in the Fourier analysis. A minimum of four cable strikes were carried out with the IBIS instrument and that data was used in IBIS post processing MatLab based fourier analysis.

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38 Figure 4.1 Cable in MTS equipped with accelerometer. The P1000 instrument has certain limitati ons based on cable tension, diameter and length. Due to these limitations the P1000 could only be used to measure tension forces above 44.48 KN (10 kips) in the laboratory setting. Due to the g range limitations the accelerometer cut off certain portions of data early in the vibration after the cable was struck. In the laboratory setting no limitations on the IBIS system were encountered; this is certainly one advantage of IBIS technology, along with the fact that the user does not need to have access to the cables as is required with traditional instruments. Once the fundamental frequency for the cable was found for each load case with each of the three instruments, the fundamental frequency was utilized in the taut string

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39 equation (Equation 2.2) to calculate the cable force. Since the cable had no sag during the test Equation 2.2 was relied directly upon with no correction for sag extensibility. Results of First Experiment (Cable) From the 44.48-115.65 KN (10-26 Kip) range the IBIS system results and the P1000 results proved to be very close this finding is encouraging. The data can be seen in tabular form in Table 4.1 and graphically in Figure 4.2. The accelerometer provides the user with acceleration as a frequency of time. Utilizing the Fourier Transform function in Microsoft Xcel, the time domain data was plotted in the frequency domain in order to view the peaks (natural frequencies) in the data. In Table 4.1 below the findings from each of the three instruments are presented and it can be seen that all three instruments are providing similar values reinforcing the confidence in IBIS results. Based on these findings it can be concluded that IBIS technology can successfully be used to measure frequency of vibration in cable stayed members with a diameter of 25.4MM (1 inch) or larger. After the lab work was completed the data was incorporated into Mehrabis tension equation. Mehrabis equation is a function of cable length and being that the length term in the equation is squared, the equation is highly sensitive to cable length. Due to the laboratory setup with looped cable ends, the exact effective length of the cable is not exactly known. Further, during initial loading 0-44.48 KN (0 to 10 Kips) the cable stretched substantially (over 25.4MM -1 inch); thus, the cable length substantially changed during this region. Given these observations it is no surprise that the subject equation does not fit the data well from 0-44.48 KN (0-10 Kips). The important finding is that all three instruments provide close data; there has been plenty of previous research on the application of Mehrabis tension equation and that is not the purpose of this research. After 44.48 KN (10 Kips) once cable slack/loss was mostly removed-

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40 Mehrabis tension equation proved to be fairly accurate (+/5%) as can be seen in review of the data in Table 4.1. Frequency domain plots from Microsoft Excel of each cable force increment measured are shown in Appendix B and on those plots the reader can view the peak which corresponds to the measured natural frequency. The figures shown in Appendix B include frequency domain plots from IBIS MatLab based post processing system in which the reader can view the peak which corresponds to the measured natural frequency.

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41 Table 4.1 Results of Lab Testing for Tensile Force Determination in Cable. Actu al Forc e (Kips ) fn Meas ured with IBIS fn Measu red with P1000 fn Measure d with accelero meter Tension Force Based on IBIS (Kips) Tension Force Based on P1000 (Kips) Tension Force Based on Acceler ometer (Kips) % Accur acy IBIS % Accuracy P1000 % Accuracy Accelero meter 2.00 17.96 0.00 17.63 2.90 30.92 4.00 23.94 0.00 23.53 5.14 22.24 6.00 27.86 0.00 27.98 6.97 13.87 8.00 32.27 0.00 31.35 9.35 14.40 10.00 36.32 35.66 35.11 11.84 11.41 15.54 12.38 12.00 37.30 37.54 37.74 12.49 12.65 12.78 3.90 5.13 6.13 14.00 40.09 40.00 40.38 14.42 14.36 14.63 2.95 2.51 4.33 16.00 42.40 42.10 42.63 16.14 15.91 16.31 0.84 -0.58 1.90 18.00 44.55 44.40 44.73 17.81 17.69 17.96 -1.05 -1.73 -0.24 20.00 46.95 46.69 47.02 19.78 19.56 19.84 -1.09 -2.23 -0.79 22.00 48.80 48.82 48.93 21.37 21.39 21.49 -2.93 -2.85 -2.38 24.00 50.54 50.92 50.78 22.93 23.27 23.14 -4.69 -3.13 -3.70 26.00 52.50 52.62 52.64 24.74 24.85 24.87 -5.10 -4.62 -4.54

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42 Figure 4.2 Graph of calculated vs. actual cable force.

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43 Conclusions from First Experiment (Cable) Based on the laboratory results from the cable test it was concluded that the IBIS-S system can successfully be utiliz ed to measure the fundamental frequency of tension members such as wire rope and structural steel strands. It was also concluded that for higher tension loads, once a majority of the slack has been removed, Mehrabis tension equation can successfully be applied. Thus, it is shown that by using interferometric radar, the fundamental frequency and tension force in cables can be determined in a non-contact remote manner. Second Laboratory Experiment (Steel Channel) Setup of Second Experiment (Steel Channel) After experiencing success with IBIS in measuring the natural frequency in cables the idea came to try the same experiment with a rigid steel member. In particular, tension members in steel truss bridges are of interest. A change in the natural frequency of a steel truss member could indicate decay in the member or its associated welds is occurring. In order to physically fit a steel member into the MTS a rather large steel member (C10x15.3 A36 steel, as shown in Figure 4.3 was chosen. The steel member was put under tension loads ranging from 2.22 to 177.93 KN (0.5 to 40 Kips) (Figure 4.4). The steel member was struck with a rubber mallet and the vibration was measured with IBIS and an accelerometer that was mounted to the channel. Again, the accelerometer data was imported into Microsoft Xcel and the time domain data was plotted in the frequency domain in order to view the peaks (natural frequencies) in the data. Due to the limitations of the accelerometer data was only collected under tension loads up to and including 44.48 KN (10 Kips) with the accelerometer.

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44 Figure 4.3 Drawing of channel. Figure 4.4 Channel testing in MTS.

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45 Results of Second Experiment (Steel Channel) Initially the accelerometer data displayed errors and it was realized the accelerometer was not well adhered to the channel and was moving independently of the channel as evidenced by shifts in the acceleration data in the frequency domain. Thus, the experiment was repeated. The results of this experiment were counter intuitive in that the accelerometer data indicate a decrease in natural frequency as the tension load increased. Further, the IBIS data and the accelerometer data did not correlate well. Through reviewing the data it became apparent that over a large increase in axial load (88.96KN (20 Kips) for instance) the natural frequency did not change drastically and as the axial load got higher, increments in axial load resulted in smaller changes in the natural frequency indicating a non-linear relationship exists between the two. It was also noted that the channel sustained plastic deformation around the holes that secured the channel to the MTS. It is likely that due to the relatively large stiffness of the channel, when compared to typical truss bridge tension members, the natural frequency is not a good indicator of the tension force. Frequency domain plots from Microsoft Excel of each channel force increment measured are shown in Appendix C and on those plots the reader can view the peak which corresponds to the measured natural frequency. Appendix C includes frequency domain plots from IBIS MatLab based post processing system in which the reader can view the peak which corresponds to the measured natural frequency.

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46 Conclusions from Second Experiment (Channel) In summary, the results of this experiment were counter intuitive (the accelerometer data indicated a decrease in natural frequency as the tension load increased) and the IBIS data and the accelerometer data did not correlate well. Based on the results from the second experiment it was concluded that interferometric radar cannot be utilized to measure the fundamental frequency in steel channels with a C shape until further research is conducted. It is possible that the material yielding and stress concentration at the connection poi nts negatively affected the experiment.

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47 CHAPTER V FIELD WORK Setup Setting up IBIS in the field is very simple and intuitive. Setup simply involves setting up and leveling a tripod followed by attaching the radar head and connecting to the PC via a USB cord. In order to gather data on the global bridge movement setup is fairly simple; particularly for steel framed bridges with cross members or cross frames. For the subject bridge (Figure 5.1) steel W cross beams are spaced 3.96 M (13 feet) on center. The 90 degree bend at the web/flange connection on W sections is a great reflector of radar. In this instance the user sets up the IBIS as close to one abutment or the other as reasonably possible and aims the radar head along the length of bridge as shown below in Figure 5.2. As long as the cross beams are at least 0.75 M (2.46 feet) apart (for range bin reasons) this setup allows the user to collect displacement data on all visible cross members at once. For the purposes of monitoring vibrations, the subject of this thesis, it is not critical to input the geometry of the bridge into the IBIS software. Inputting the bridge geometry and radar head angle/position is necessary if the user desires actual displacement data (refer to Figure 2.6 for explanation on how IBIS measures line of sight movement, not vertical displacement).

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48 Figure 5.1 Subject cable stayed bridge.

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49 Figure 5.2 Radar setup in field. Once setup and turned on, the user must determine which peaks on the radar display correspond to which structural elements. This is easily done with a laser distance meter which is positioned on the radar head. By documenting the position of

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50 each member and its corresponding radar peak the user can easily view the data at a later time and correctly understand/apply the data. For the purposes of monitoring vibration in cables the positioning of the IBIS system is not as straightforward. Firstly, the user desires a location in which multiple cables can be viewed at once. For the subject bridge the maximum number of cables that can be viewed at once are three. However, the user must take care to insure that the cables are at least 0.75 M (2.46 feet) apart along the line of sight. Depending on the position of the IBIS it is quite possible that along the line of sight the cables could fall within the same range bin. An example of this is a setup where the IBIS is aimed directly perpendicular to the length of the bridge/cables in this instance all the cables are in the same vertical plane. One might think that an ideal setup is at the end of the bridge looking down the length of the cables such that the cables will be more than 0.75 M (2.46 feet) apart along the line of sight. However, depending on the bridge geometry and construction, this setup would likely result in viewing vertical masts on the bridge and could possibly result in the first cable blocking the view of the additional cables. An ideal setup for a cable stayed bridge, when monitoring the cables, is one in which the instrument is located near the end of the bridge, looking down the length of the bridge, and the instrument is aimed such that no other bridge elements are in the field of view. In some instances the user can setup near the middle of the bridge and look upwards (Gentile, 2010). However, it is recognized that once a bridge is in service it is not very realistic to setup near the middle of the bridge due to the waterway or roadway. Setup Comparisons Setup and data were obtained both by setting up the instrument on the bridge deck (near the masts) and by setting up the instrument on the ground, isolated from the bridge vibrations. The data gathered from the setup on the bridge was noted to

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51 sometimes exclude lower vibration modes which is possibly due to the instrument vibrating in-sync with the bridge. For this reason all subsequent setups were conducted from the ground so as to isolate the instrument from the vibrations. It should be noted that the vibrations on the subject bridge are very notable with large deflections (on the order of one CM (2.54 inches). Thus, for bridges that are larger and more stiff (automotive bridges) it may be possible to successfully monitor vibrations from the bridge deck itself; future research is needed on this topic. Testing and Results Cable Vibration Measurement The subject bridge contains a total of 12 cables. According to the engineer of record (EOR) the top four cables were originally tensioned to 17.79 KN (4 Kips) each and the remainder of the cables were tensioned to sufficiently bring the bridge deck into the desired shape and alignment; thus, the original tension is only known in 4 of the 12 cables. A DynaTension P1000 instrument, an accelerometer and the IBIS instrument were used to measure the natural frequency in each of the 12 cables. Six samples per cable were taken with the P1000 and the results were averaged. With the accelerometer, a minimum of 2000 data points were collected and utilized in the Fourier analysis and this process was repeated and the results averaged. With the IBIS, measurements were taken for each cable with a minimum of 2000 data points and this process was repeated and the results averaged. The results from the DynaTension meter are counterintuitive due to the relatively high frequencies reported by the instrument. It was theorized that the DynaTension meter was reporting higher mode shapes but review of the accelerometer data does not show good correlation for higher mode shapes and as such it was concluded the DynaTension meter data was erroneous. An attempt to repeat the measurements with

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52 the DynaTension meter was made but after several attempts the exercise was abandoned due to the DynaTension meter not working correctly. Further, even if the DynaTension meter was successfully reporting higher mode shapes, the instrument has no way of letting the user know which mode shape he or she is collecting data on. Since Merhabis cable force determination equation is a function of both the natural frequency and mode shape, the DynaTension meter is not helpful for determining the force in the cable since the user has no way of knowing which mode he or she is measuring. The DynaTension meter results are shown in Table 5.1 below. It took several attempts to collect valuable data with the accelerometer (see Figure 5.3 for a photograph of the accelerometer in use). After processing the accelerometers field data from the initial attempts it was realized errors must have occurred as the data had no clear peaks in the frequency domain. Based on permanent shifts in the accelerometer data when viewed in the time domain it was realized the instrument was vibrating independently of the cables and it was physically slipping downward on the cable due to poor attachment. Thus, the experiment was repeated by better securing the instrument to the cables. During the initial attempts to collect cable vibration data with the accelerometer it was thought the cables needed to be struck into free vibration with a rubber mallet as was done in the laboratory cable experiment. However, after securely affixing the instrument the data still did not appear correct in the time domain in fact the only data that appeared correct was the initial data collected prior to striking the cable for the first time. Thus, it was concluded the bridge has enough vibration on its own (movement in the bridge and its cables is visible under no pedestrian loads which is a result of ambient environmental conditions such as minor wind loads) and there is no need to strike the cables. Once the experiment was repeated without striking the cables the data appeared very correct in both the time and

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53 frequency domains and the data proved to be repeatable as the experiment was conducted twice. The final accelerometer data was determined to be accurate due to its appearance, intuitiveness, alignment with IBIS data, and the finding that cables in similar (mirror) positions on opposite sides of the bridge was very close to each other. The frequency data for each cable found from the accelerometer is shown in Table 5.1 and the frequency domain plots of the data for each cable are shown in Appendix D. Figure 5.3 Accelerometer installed on cable on subject bridge. It also took several attempts to gather usable cable data with the IBIS instrument. This was largely due to the learning curve encountered in trying to find the optimal setup position and in determining which radar peaks corresponded to which cables. Once the optimum setup position was found for each set of cables, data was gathered quickly. With a couple exceptions, the IBIS and accelerometer data correlated well (within 1/100th of a Hz). In the instances where the two dont correlate well (error of 0.60 Hz) no real logical conclusion was achieved. In these instances the experiment should be repeated

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54 with both instruments in order to validate data, however this was not possible due to IBIS availability constraints. Nonetheless, there were multiple instances where the IBIS instruments data correlated very well with the accelerometer data and as such it was concluded the IBIS instrument can successfully be used to monitor the fundamental frequency in cables. The results of the IBIS measurements are shown in Table 5.1. Both the accelerometer and IBIS frequency domain plots for the cables show smaller peaks at 1.67 and 1.98 Hz in multiple instances. The smaller peaks are consistent with global mode shapes. After review of the plots it was concluded that for the bottom (shorter cables with greater tension force) no smaller peaks existed and due to the large tension force in the cables and the cables close proximately to the center (fixed) support, the global mode shape was not visible. For the middle cables, a consistent small peak between 1.95 and 2.00 Hz was visible which is consistent with the measured global fundamental frequency of the bridge as discussed below. For the upper (longest) most cables a consistent small peak at approximately 1.66 Hz was observed. As no global mode shape at 1.66 Hz was observed, this peak was not expected and is not readily explainable. In the instances where the 1.66 peak was observed, no peak was observed at 1.98 with the accelerometer. However, in the same instances where a peak was observed at 1.66 with the IBIS instrument, a peak was observed at 1.98 which is an indication the first global mode shape is observable with IBIS but not with the accelerometer in some instances.

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55 Table 5.1 Measured Fundamental Natural Frequency of Bridge Cable by Cable Position (Hz). NE Top NE Middle NE Bottom NW Bottom NW Middle NW Top SW Top SW Middle SW Bottom SE Bottom SE Middle SE Top IBIS 2.22 3.80 5.216.033.462.442.143.776.62 6.12 4.052.72 Accelerometer 2.24 3.42 5.426.003.522.442.243.177.08 5.85 4.002.73 P1000 16.74 23.1 24.4723.4722.5217.1517.1625.221.58 23.45 22.8515.75

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56 Global Bridge Vibration Measurement In order to determine the bridges global fundamental frequency the IBIS instrument was setup under the bridge and vibration data on multiple cross beams was gathered. This experiment was repeated numerous times and from both sides of the bridge as the center foundation prohibited viewing of all the cross members at once. The data gathered indicate that the cross members lowest vibration mode occurs at a peak of 1.98Hz consistently and as such it was concluded the fundamental frequency of the bridge is 1.98Hz. Summary and Conclusions In summary, field testing indicates that inteferometric radar can successfully be used to monitor the global bridge natural frequency, mode shape and the individual bridge elements (cables, masts, railing) fundamental frequencies.

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57 CHAPTER VI DICSUSSION Introduction Within this section of the thesis, the theoretical, laboratory and field testing results are combined to determine the success of utilizing interferometric technology to monitor cable stayed bridges. Further, the cable tension forces, and global bridge frequencies are determined. Cable Calculations As significant sag (more than 1 foot in some instances) was observed in the cables on the subject bridge it was considered if the taut string theory could be utilized to determine the tension force in the cables. As the cables were noted to be very flexible it was determined unlikely that the cables bending stiffness would affect the results of the taut string theory. Nonetheless, Ren et als research was utilized to determine if the cable bending stiffness or sag were going to significantly affect the taut string theory results. The force in each cable was determined utilizing Merahbis equation and the measured frequency and that tension data is shown in Table 6.1. Also, the nondimensional parameters set forth in Ren et. als work were calculated for each cable in order to determine the accuracy of the taut string theory for each of the cables. As discussed previously, Ren et al concluded that when l2 exceeds 1.0 for the first mode, the cable sag can be neglected and when is greater than 50, the cable stiffness can be neglected. In Table 6.1 it can be seen that is greater than 50 in every instance, thus the cable stiffness was neglected. The l2 term was calculated less than 1.0 in all but three cases and in one of the three cases the term was 1.32 which corresponds to a

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58 relatively small error. For the two cases where the l2 term greatly exceeds 1.0, error in the calculated tension force exists (likely on the order of 10%). In order to better calculate the tension force in those two cases, a higher mode shape should be used. For those two instances, the 5th mode was used, the tension force was corrected and that corrected data is shown in Table 6.2. In comparing the corrected data in Table 6.2 it is noted that the calculated tension force based on the 5th mode is quite different than that calculated from the first mode. Given that the corrected tension force should only be approximately 10% different between the two methods it was concluded that the 5th mode was incorrectly determined and repeated attempts to re-analyze the data did not yield better results. Thus, the data from Figure 6.1 was relied upon recognizing that in some instances an error of approximately 10% likely exists. It can be seen that the cable forces are relatively consistent across the bridge for similar cables in similar positions. The only exception is one lower cable that has a substantially higher (40% higher) tension force. As the IBIS and accelerometer data compare well for that cable and multiple samples were taken it was determined the data was accurate. One possible explanation is simply that the subject cable had to have a higher tension force during construction in order to obtain the desired shape of the bridge.

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59 Table 6.1 Cable Force Determination. Effecti ve Length (Feet) Cable Actual Length (Feet) fn Measur ed with IBIS fn Measur ed with acceler ometer Tension Force Based on IBIS (Kips) Tension Force Based on Accelerom eter (Kips) term from Ren et al 2 term from Ren et al. 106.6 NE Top 108.8 2.22 2.24 6.59 6.71 127.92 2.67 70.2 NE Middle 71.6 3.80 3.42 19.32 15.65 144.17 0.05 36.1 NE Bottom 36.8 5.21 5.42 36.32 39.30 101.61 0.00 99.4 NW Top 101.4 2.44 2.44 7.97 7.97 131.06 1.32 63.3 NW Middle 64.6 3.46 3.52 16.02 16.58 118.39 0.07 31.5 NW Bottom 32.1 6.03 6.00 48.65 48.16 102.64 0.00 99.4 SE Top 101.4 2.72 2.73 9.90 9.97 146.10 0.69 63.6 SE Middle 64.9 4.05 4.00 21.94 21.41 139.30 0.03 31.8 SE Bottom 32.4 6.12 5.85 50.11 45.79 105.17 0.00 106.3 SW Top 108.4 2.14 2.24 6.13 6.71 122.93 3.31 70.5 SW Middle 71.9 3.78 3.17 19.12 13.44 144.08 0.05 36.4 SW Bottom 37.1 6.62 7.08 58.63 67.06 130.28 0.00

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60 Table 6.2 Corrected Cable Force Determination, Based on 5th ModeCable Length (Feet) fn Measured with accelerometer Tension Force Based on Accelerometer, 5th Mode (Kips) NE Top 127.9 7.08 2.68 SW Top 144.2 7.56 3.06

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61 Global Bridge Vibration Discussion As seen in the cable data in Appendix D, global peaks in the cable data were also observed at 1.98Hz which confirms these conclusions. While gathering data on the cables it was possible to also gather data on the bridge masts and railing and both those items were also found to have a first global mode at 1.98Hz again confirming the conclusion that the bridges first global mode is 1.98Hz. The results of the floor beam, mast and tower data are shown in Figures 6.1 through 6.6. One particular floor beam displayed a smaller peak at 1.67Hz which is consistent with that observed on certain cables. Figure 6.1 Radar plot of underside of bridge (peaks correspond to floor beams). Typical location of floor beam

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62 Figure 6.2 Frequency domain plot of underside of bridge, data for seven floor beams overlaid (Note: all members display peak at 1.986 Hz which was determined to be the first global natural frequency of the bridge).

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63 Figure 6.3 Frequency domain plot of floor beam vibration on underside of bridge (Note: this member displays peaks at 1.67 (which correlates to cable vibration data) and 1.98 Hz which corresponds to the measured global bridge natural frequency of 1.98Hz). 1.98 Hz 1.67 Hz

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64 Figure 6.4 Frequency domain plot of south tower vibration (Note: This Tower displays a peak at 1.94 Hz which is very close the measured global bridge natural frequency of 1.98Hz).

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65 Figure 6.5 Frequency domain plot of north tower vibration (Note: This Tower displays a peak at 1.98 Hz which matches the global bridge natural frequency of 1.98Hz; Smaller peaks after peak at 1.98 Hz correspond to other global bridge mode shapes; Peak at 9.86 Hz which corresponds to the first local natural frequency of north tower). 9.86 Hz

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66 Figure 6.6 Frequency domain plot of north railing (Note: This Tower displays a peak at 1.98 Hz which corresponds to the measured global bridge natural frequency of 1.98Hz). Other peaks observed in the global survey was a large peak (the largest) at 2.64Hz and the next largest peak was at 3.3Hz which corresponds very closely with the SAP model output which indicated the fundamental frequency was 3.39Hz. The discrepancy between the SAP model and the field data is not readily explainable by this engineer and would require more research. The MatLab based post processing used by IBIS has the ability to take all of the cross member time domain deflection data and overlay it simultaneously to create an animation of the bridges motion and to determine the mode shape. This process was completed and the deflected shape corresponds with that gathered from SAP in that the

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67 two cantilevered ends, especially the east end, dominate the first mode shape (see Figure 6.7 below). Figure 6.7 Mode shape plot from Matlab. When inspecting the bridge it was noted that the vibrations were very noticeable and during time spent on the bridge pedestrians would routinely stop and ask if the bridge was supposed to vibrate in the manner which it is. These findings are consistent with Wiss et als work which indicates that the most severe and noticeable vibration in pedestrian bridges occurs at a frequency of 2Hz (the subject bridge vibrates at 1.98Hz). Pedestrian Bridge Application of Work As can been seen in the above work, the fundamental frequency of the subject bridge violates the AASHTO criteria which the bridge was designed with in regards to the 3.0Hz limitation for the fundamental frequen cy. It is unknown to this engineer as to whether or not the engineer of record performed calculations/models to check the bridge for vibrations both vertically and laterally as should have been done. The scope of this thesis is vertical vibrations; no investigation of lateral vibrations was conducted. East Cantilever West Cantilever

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68 A quick check of Bachmann, et.als empirical equation for fundamental frequency of cable stayed bridges shows that their equation either does not apply well to pedestrian bridges or to bridges with multiple spans (Bachmann, et.al, 1995). Applying their equation to the subject bridge indicates a fundamental frequency of 3.47Hz. It is interesting that Bachmann et als equation (which is intended to be used for cable stayed bridges) is rather close to the SAP model output of 3.39Hz and that one of the modes measured in the field was at 3.3Hz. However, as the lowest mode measured in the field was 1.98Hz it was determined this is coincidental. Recommendations for City and County of Denvers Cable Stayed Pedestrian Bridge at 16th Street Over The Platte River It is recommended that the subject bridge be monitored for signs of fatigue. Others have undertaken a bridge health monitoring protocol, index and baseline data for the bridge. Through time spent on the bridge it was noted that the fasteners that secure the decking to the structure often are backing out which result in not only loose deck planks but protruding screws which are a trip hazard. It is likely that the loose screws are a result of fatigue failure. Now that baseline data is available, the fundamental frequency of the bridge, cables and masts can be checked annually, or bi-annually, and any changes would warrant further investigation into potential decay or loss of stiffness. The costs associated with trying to stiffen the bridge would be large and may not be justified. The most economic method of solving the vibration problem would involve a tuned mass damper system which is quite co stly. Further, this thesis excludes an evaluation of the bridges lateral fundamental frequency but such an analysis should be performed and its quite possible that problems exist in the lateral direction as well.

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69 Summary and Conclusions In summary, the cable vibration data can be used to determine the tension force in each of the cables. The global fundamental frequency of the subject bridge was determined to be approximately 1.98Hz. The force in each of the cables is shown in Table 6.1. The discrepancy between the SAP model and the field data is not readily explainable by this engineer and would require more research which is outside the scope of this thesis. It was concluded the AAHSTO empirical equations regarding fundamental frequency are not accurate for cable stayed bridges. The subject bridge violates AASHTO limitations for the fundamental frequency in the vertical direction. The consequence of the low fundamental frequency will likely be premature fatigue failure of one or more bridge elements. Future monitoring of the bridge should include vibration monitoring.

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70 CHAPTER VII CONCLUSIONS AND RECOMENDATIONS Conclusions In summary, this thesis shows that inte rferometric radar can successfully be used to determine the fundamental frequency of bridges and their individual elements. The use of such radar has clear advantages in regards to ease of use, not needing direct access to the bridge, and large amounts of data in short amounts of time. For these reasons it is determined that interferometric radar is a good tool that can be used to monitor the structural health of bridges and other structures. Vibration data from cables on cable stayed bridges can be used to determine the tension force in the cables. In many instances the taut string theory can be used and no correction for cable stiffness and sag is needed. However, in the case where correction is needed, higher vibration mode data can be used to determine the tension force more accurately. It was concluded the AAHSTO empirical equations regarding fundamental frequency are not accurate for cable stayed bridges. Recommendations Regarding the City and County of Denver Bridge, 16th Street over the Platte, the fundamental frequency of the bridge is below 3.0Hz which is an AASHTO violation and this is of concern. Potential premature fatigue failure exists as a result of the low fundamental frequency (1.98Hz). The noticeable vibrations in the bridge and the 1.98Hz finding are consistent with Wiss et als work which indicates that the most severe and noticeable vibration in pedestrian bridges occurs at a frequency of 2Hz. Now that baseline data is available, the fundamental frequency of the bridge, cables and masts

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71 can be checked annually, or bi-annually, and any changes would warrant further investigation into potential decay or loss of stiffness. Future Work Future work should be completed in order to better determine if interferometric radar can be used to determine the tension force in axially loaded steel members. This thesis excludes an evaluation of the subject bridges lateral fundamental frequency but such an analysis should be performed and its quite possible that problems exist in the lateral direction as well. Future research into the AASHTO empirical equations for limitations on pedestrian bridge weight and fundamental frequency should be conducted. Further research into the accuracy of the SAP model, and the apparent discrepancy between field data, for the subject bridge should be considered.

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72 REFERENCES Alongi, T., Clemena, G.G., Cady, P.D., (1992). “Condition evaluation of concrete bridges relative to reinforcement corrosion”, SHRP Report SHRP-S/FR-92-105, Vol 3, Washington D.C. American Association of State Highway and Transportation Officials (AASHTO). (1997). Guide specifications for design of pedestrian bridges, 1st Edition, Washington DC. Beben, D. (2011). “Application of the interferometric radar for dynamic tests of corrugated steel plate (Csp) culvert”, NDT&E International, 44, 405–412. Dei, D., Massimiliano, P, A., Fratini, M., A., Atzeni, C., and Bartoli, G. (2009). “Detection of vertical bending and torsional movements of a bridge using a coherent radar”, NDT&E International, 42, 741–747. Farrar, C.R., Darling, T.W., Migliorini, A., Baker, W.E., (1999). “Microwave interferometer for non-contact vibration measurements on large structures”, Mechanical Systems and Signal Processing Vol. 13, 241-253. Farina, P., Leoni, L., Babboni, F., Coppi, F., Mayer, L., Ricci, P., (2011). “IBIS-M, an innovative radar for monitoring slopes in open-pit mines”, Proceedings, Slope Stability 2011: International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, Vancouver, Canada, (September 18-21, 2011) Gentile, C., (2008). “Radar-based measuremen t of deflections on bridges and large structures” Department Of Structural Engineering, Politecnico Di Milano, Italy. Gentile, C., Bernardini, G. (2008). “Output-only modal identification of a reinforced concrete bridge from radar-based measurements”, NDT&E International, 41, 544– 553. Gentile, C., (2010). “Application of microwav e remote sensing to dynamic testing of stay-cables”, Remote Sensing 2010, 2, 36-51. Historic American Engineering Record (1968). “Bluff dale suspension bridge, spanning paluxy river at county route 149, bluff dale, erath county, TX”, http://www.loc.gov/pictures/item/tx0762/. IDS (2008). “IBIS, a ground based microwave interferometer with imaging capabilities for the remove measurement of displacements and vibrations”, Ingegneria Dei Sistemi S.p.A., Pisa, July. IDS (2010). “IBIS-S Controller V 02.02.000 User Manual Rev. 1.1”, Ingegneria Dei Sistemi S.p.A., Pisa, July. Luzi, G., Crosetto, M., Monserrat, O., and Gonzalez, A., (2008). “ A Radar Technique For Evaluating The Vibration State Of Buildings ”, Institute of Geomatics Av. Carl

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73 Friedrich Gauss, 11 Parc Mediterrani de la Tecnologia E-08860, Castelldefels, Barcelona. Maser, K.R., (1994). “Highway speed radar for pavement thickness evaluation”, Proceedings of the Fifth International Conference on Ground Penetrating Radar, Vol 2 of 3, June 12-16, Kitchener, Ontario, Canada 423-432. Mehrabi, A.B., (2006). “In-service evaluati on of cable-stayed bridges, overview of available methods, and findings”, Journal of Bridge Engineering 2006, 28, 14711482. Morey, R., (1998). “Ground penetrating radar for evaluating subsurface conditions for transportation facilities”, Synthesis of Highway Practice 255 National Cooperative Highway Research Program, Transportation Research Board National Academy Press. Pieraccini, M., Luzi, G., and Atzeni, C. (2001). “Terrain mapping by ground-based interfermoetric radar”, IEEE Transactions On Geoscience And Remote Sensing Vol. 39, No. 10, October. Pieracini, M., Parrini, F., Fratini M., Atzeni, C., and Spinelli, P., (2008). “In-service testing of wind turbine towers using a microwave sensor”, Renewable Energy, 33, 13– 21. Podolny, Walter, Jr., P.E. (1999). “Section 15, cable suspended bridges”, Structural Steel Designers Handbook, Third Edition, ed. Brockenbrough, R.L, Merritt, F.S., McGraw-Hill, Inc., New York, 15.1-15.100. Ren, W., Liu, H., Chen, G., (2007). “Determination of cable tensions based on frequency differences”, Engineering Computations: International Journal for Computer-Aided Engineering and Software 25, 2, 172-189. Scullion, T., Lau, C.L., Chen, Y., (1992). “Implementation of the texas ground penetrating radar system”, Report No. FHWA/TX-92/1233-1 Texas Department of Transportation. Tallini, M., Giamberardino, A., Ranalli, D., Scozzafava, M., (2004). “GPR survey for investigation in building foundations”, Tenth International Conference on Ground Penetrating Radar 21-24 June, 2004, Delft, The Netherlands, 395-397. Wiss, J.F., Parmelee, R.A. (1974). “Human Perception of Transient Vibrations”, Proceedings of American Society of Civil Engineers (A.S.C.E.),100, ST4, 773. Wiss, Janney, Elstner Associates, Inc. (2012). “Martin olav sabo pedestrian bridge cable diaphragm plate fracture investigation”, www.scribd.com/doc/98690035/sabobridge-report, June 28, 2012

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74 APPENDIX A Construction Drawings

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131 APPENDIX B First Laboratory Test – Cable Test Figure B1 Laboratory cable measured with accelerometer, 2 kips tension force. Figure B2 Laboratory cable measured with IBIS, 2 kips tension force. 17.63 HZ 17.96 HZ

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132 Figure B3 Laboratory cable measured with accelerometer, 4 kips tension force. Figure B4 Laboratory cable measured with IBIS, 4 kips tension force. 23.53 HZ 23.94 HZ

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133 Figure B5 Laboratory cable measured with accelerometer, 6 kips tension force. Figure B6 Laboratory cable measured with IBIS, 6 kips tension force. 28.22 HZ 27.86 HZ

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134 Figure B7 Laboratory cable measured with accelerometer, 8 kips tension force. Figure B8 Laboratory cable measured with IBIS, 8 kips tension force. 31.35 HZ 32.27 HZ

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135 Figure B9 Laboratory cable measured with accelerometer, 10 kips tension force. Figure B10 Laboratory cable measured with IBIS, 10 kips tension force. 35.11 HZ 36.32 HZ

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136 Figure B11 Laboratory cable measured with accelerometer, 12 kips tension force. Figure B12 Laboratory cable measured with IBIS, 12 kips tension force. 37.74 HZ 37.30 HZ

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137 Figure B13 Laboratory cable measured with accelerometer, 14 kips tension force. Figure B14 Laboratory cable measured with IBIS, 14 kips tension force. 40.38 HZ 40.09 HZ

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138 Figure B15 Laboratory cable measured with accelerometer, 16 kips tension force. Figure B16 Laboratory cable measured with IBIS, 16 kips tension force. 42.63 HZ 42.40 HZ

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139 Figure B17 Laboratory cable measured with accelerometer, 18 kips tension force. Figure B18 Laboratory cable measured with IBIS, 18 kips tension force. 44.73 HZ 44.55 HZ

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140 Figure B19 Laboratory cable measured with accelerometer, 20 kips tension force. Figure B20 Laboratory cable measured with IBIS, 20 kips tension force. 47.02 HZ 46.95 HZ

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141 Figure B21 Laboratory cable measured with accelerometer, 22 kips tension force. Figure B22 Laboratory cable measured with IBIS, 22 kips tension force. 48.93 HZ 48.80 HZ

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142 Figure B23 Laboratory cable measured with accelerometer, 24 kips tension force. Figure B24 Laboratory cable measured with IBIS, 24 kips tension force. 50.78 HZ 50.54 HZ

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143 Figure B24 Laboratory cable measured with accelerometer, 26 kips tension force. Figure B25 Laboratory cable measured with IBIS, 26 kips tension force. 52.64 HZ 52.50 HZ

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144 APPENDIX C Second Laboratory Test – Channel Test Figure C1 Laboratory cable measured with accelerometer, 0.5 kips tension force. Figure C2 Laboratory cable measured with IBIS, 0.5 kips tension force.

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145 Figure C3 Laboratory cable measured with accelerometer, 1 kips tension force. Figure C4 Laboratory cable measured with IBIS, 1 kips tension force.

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146 Figure C5 Laboratory cable measured with accelerometer, 1.5 kips tension force. Figure C6 Laboratory cable measured with IBIS, 1.5 kips tension force.

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147 Figure C7 Laboratory cable measured with accelerometer, 2 kips tension force. Figure C8 Laboratory cable measured with IBIS, 2 kips tension force.

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148 Figure C9 Laboratory cable measured with accelerometer, 2.5 kips tension force. Figure C10 Laboratory cable measured with IBIS, 2.5 kips tension force.

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149 Figure C11 Laboratory cable measured with accelerometer, 3 kips tension force. Figure C12 Laboratory cable measured with IBIS, 3 kips tension force.

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150 Figure C13 Laboratory cable measured with accelerometer, 3.5 kips tension force. Figure C14 Laboratory cable measured with IBIS, 3.5 kips tension force.

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151 Figure C15 Laboratory cable measured with accelerometer, 5 kips tension force. Figure C16 Laboratory cable measured with IBIS, 5 kips tension force.

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152 Figure C17 Laboratory cable measured with accelerometer, 10 kips tension force. Figure C18 Laboratory cable measured with IBIS, 10 kips tension force.

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153 Figure C19 Laboratory cable measured with IBIS, 15 kips tension force. Figure C20 Laboratory cable measured with IBIS, 20 kips tension force.

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154 Figure C21 Laboratory cable measured with IBIS, 25 kips tension force. Figure C22 Laboratory cable measured with IBIS, 30 kips tension force.

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155 Figure C23 Laboratory cable measured with IBIS, 35 kips tension force. Figure C24 Laboratory cable measured with IBIS, 40 kips tension force.

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156 APPENDIX D Field Measurement of Cable Vibration on Cable Stayed Pedestrian Bridge at 16th Street over the Platte River

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157 Figure D1 Field cable measured with accelerometer, northeast top. Figure D2 Field cable measured with IBIS, northeast top 2.24 HZ 1.66 HZ

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158 Figure D3 Field cable measured with accelerometer, northeast top, fifth mode. Figure D4. Field cable measured with accelerometer, northeast middle. 3.42 HZ 2.00 HZ 7.08 HZ

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159 Figure D5 Field cable measured with IBIS, northeast middle. Figure D6 Field cable measured with accelerometer, northeast middle, fifth mode. 16.75 HZ

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160 Figure D7 Field cable measured with accelerometer, northeast bottom. 5.42 HZ

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161 Figure D8 Field cable measured with IBIS, northeast bottom. Figure D9 Field cable measured with accelerometer, northeast bottom, fifth mode. 25.20 HZ

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162 Figure D10 Field cable measured with accelerometer, northwest bottom. Figure D11 Field cable measured with IBIS, northwest bottom. 6.00 HZ

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163 Figure D12 Field cable measured with accelerometer, northwest bottom, fifth mode. Figure D13 Field cable measured with accelerometer, northwest middle. 3.52 HZ 2.00 HZ 21.58 HZ

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164 Figure D14 Field cable measured with IBIS, northwest middle.

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165 Figure D15 Field cable measured with accelerometer, northwest middle, fifth mode. Figure D16 Field cable measured with accelerometer, northwest top. 2.44 HZ 1.66 HZ 19.29 HZ

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166 Figure D17 Field cable measured with IBIS, northwest top. Figure D18 Field cable measured with accelerometer, northwest top, fifth mode. 8.30 HZ

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167 Figure D19 Field cable measured with accelerometer,southwest top. 2.24 HZ 1.66 HZ

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168 Figure D20 Field cable measured with IBIS, southwest top. Figure D21 Field cable measured with accelerometer, southwest top, fifth mode. 7.56 HZ

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169 Figure D22 Field cable measured with accelerometer,southwest middle. 3.17 HZ 2.00 HZ

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170 Figure D23 Field cable measured with IBIS, southwest middle. Figure D24 Field cable measured with accelerometer, southwest middle, fifth mode. 17.19 HZ

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171 Figure D25 Field cable measured with accelerometer,southwest bottom. 7.08 HZ

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172 Figure D26 Field cable measured with IBIS, southwest bottom. Figure D27 Field cable measured with accelerometer, southwest bottom, fifth mode. 24.27 HZ

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173 Figure D28 Field cable measured with accelerometer,southeast bottom. Figure D29 Field cable measured with IBIS, southeast bottom. 5.85 HZ

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174 Figure D30 Field cable measured with accelerometer, southeast bottom, fifth mode. Figure D31 Field cable measured with accelerometer,southeast middle. 4.00 HZ 2.00 HZ 20.45 HZ

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175 Figure D32 Field cable measured with IBIS, southeast middle. Figure D33 Field cable measured with accelerometer, southeast middle, fifth mode. 17.57 HZ

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176 Figure D34 Field cable measured with accelerometer,southeast top. 2.73 HZ 1.66 HZ

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177 Figure D35 Field cable measured with IBIS, southeast top. Figure D36 Field cable measured with accelerometer, southeast top, fifth mode. 8.45 HZ