Citation
Assessment of the Cimarron Narrow-Gauge Railroad Bridge

Material Information

Title:
Assessment of the Cimarron Narrow-Gauge Railroad Bridge
Creator:
Van Otterloo, Bradley Dean
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
Publication Date:
Language:
English
Physical Description:
xix, 293 leaves : illustrations ; 28 cm

Subjects

Subjects / Keywords:
Narrow gauge railroads -- Colorado -- Curecanti National Recreation Area ( lcsh )
Railroad bridges -- Colorado -- Curecanti National Recreation Area ( lcsh )
Railroad bridges -- Inspection ( lcsh )
Pins (Engineering) ( lcsh )
Narrow gauge railroads ( fast )
Pins (Engineering) ( fast )
Railroad bridges ( fast )
Railroad bridges -- Inspection ( fast )
Colorado -- Curecanti National Recreation Area ( fast )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 291-293).
Thesis:
Civil engineering
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Bradley Dean Van Otterloo.

Record Information

Source Institution:
|University of Colorado Denver
Holding Location:
Auraria Library
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
436917414 ( OCLC )
ocn436917414
Classification:
LD1193.E53 2009m V36 ( lcc )

Full Text
ASSESSMENT OF THE CIMARRON NARROW-GAUGE
RAILROAD BRIDGE
by
Bradley Dean VanOtterloo
B.S., University of Colorado Denver, 2004
A thesis submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
2009


This thesis for the Master of Science
degree by
Bradley Dean VanOtterloo
has been approved
by
Stephan A. Durham


VanOtterloo, Bradley Dean (M.S., Civil Engineering)
Assessment of the Cimarron Narrow-Gauge Railroad Bridge
Thesis directed by Professor Kevin L. Rens
ABSTRACT
Since the introduction of the National Bridge Inspection Standards (NBIS) in
1970, bridge inspectors have relied heavily on visual evidence to evaluate the
conditions of bridges across America. Inspections of bridges that contain unique
features or fracture critical members (FCMs) are accompanied by more in-depth
investigations using non-destructive testing (NDT) and stmctural modeling using
finite element models (FEMs). For pin-connected bridges, particular areas of interest
which can be aided by NDT are the connection pins at the joints of the structure.
NDT is used to identify hidden features and flaws within a connection pin that are
largely obscured by other connecting members. A FEM can be used to investigate
the structural capacity of other structural elements on pin-connected bridges. This
thesis details the visual assessment, NDT evaluation, and structural modeling of a 19th
century, pin-connected railroad bridge near the town of Cimarron, Colorado.
Visual assessment of the Cimarron Railroad Bridge in 2005, pinpointed areas
of the bridge that needed to be rehabilitated and indicated a concern about the


conditions of the connection pins of the structure. Ultrasonic tests were completed on
the bridge on two separate occasions, using different testing methods, in 2006 and
2008. The results of the ultrasonic tests indicated that hidden boundary conditions
and potential defects of pins are most easily recognizable when more intensive
ultrasonic scanning is completed across a test surface. In addition, results also
showed that a satisfactory connection at the area of testing can greatly influence the
interpretation of testing results. Out of all of the connection pins that were tested,
72% of the pins indicated shoulders concealed by other structural members, and 14%
of the pins were found to have potential subsurface flaws. A finite element model
(FEM) of the bridge showed that the maximum combined stress ratio of all of the
structural members was 93%. Recommended rehabilitation measures for the bridge
include repairing and replacing elements of the bridge, as well as monitoring the
bridge at regular intervals.
This abstract accurately represents the content of the candidates thesis. I recommend
its publication.
Signed
/Kevin L. Rens
/
/


DEDICATION
I dedicate this thesis to my parents, Jim and Kathy VanOtterloo, for if it
werent for their love and continued support throughout all of my years of attending
school, I feel none of my achievements would have been possible. In addition, I
dedicate this thesis to Dr. Kevin Rens and Dr. Fred Rutz, for giving me the
opportunity to work on this project and guiding me through to its completion.


ACKNOWLEDGEMENT
Many people assisted with this research project. First and foremost, I would
like to acknowledge my advisor and graduate committee chair from the University of
Colorado Denver, Dr. Kevin Rens. I would also like to acknowledge my graduate
committee member and assistant professor at the University of Colorado Denver, Dr.
Fred Rutz. Both Kevin and Fred organized and initiated this research project from
the very beginning and presented me with the opportunity to work with them and
apply the research toward a thesis. They both graciously donated their time and effort
into helping me collect data and prepare the findings necessary for this thesis.
In addition, the cooperation of the National Park Service, Curecanti National
Recreation Area, is gratefully acknowledged. In particular, Forest Frost,
Archeologist; Shawn Cigrand and Brett Simms, Climbing Rangers; and David Kane,
Safety Officer for the vital assistance they provided. Appreciation is also extended to
the University of Colorado Denver graduate students Paul Mischo, who conducted the
predecessor ultrasonic study, and Juliette Hidahl, who researched much of the Denver
& Rio Grande railroad history.


CONTENTS
Figures.....................................................................xi
Tables......................................................................xvii
Chapter
1. Overview............................................................... 1
1.1 Introduction........................................................... 1
1.2 Background to Railroad Bridge Inspections at Cimarron.................. 3
1.3 Purpose................................................................ 5
1.4 Organization........................................................... 5
2. Cimarron Narrow-gauge Railroad Bridge.................................. 7
2.1 Historical Background.................................................. 7
2.2 Location of the Cimarron Railroad Bridge...............................15
2.3 Summary Description of the Cimarron Railroad Bridge................17
2.4 Visual Condition Assessment Summary....................................19
3. National Bridge Inspection Standards...................................27
3.1 Establishment of the National Bridge Inspection Standards..............27
3.2 Use of Ultrasound as a Non-destructive Test............................29
4. Ultrasonic Non-destructive Testing.....................................30
4.1 Ultrasonic Testing Introduction........................................30
vii


4.2 Pulse-echo Ultrasonic Testing Technique................................31
4.3 Ultrasonic Testing Considerations......................................31
4.4 Advantages and Disadvantages of Ultrasonic Testing.....................36
4.5 Ultrasonic Flaw Detector...............................................37
4.6 Ultrasonic Flaw Detector Data Files....................................38
5. Cimarron Railroad Bridge Ultrasonic Testing............................41
5.1 Overview...............................................................41
5.2 2006 Laboratory Control Ultrasonic Testing.............................41
5.3 2006 Laboratory Control Ultrasonic Testing Results.....................44
5.4 2006 Field Ultrasonic Testing Approach.................................46
5.5 2006 Field Ultrasonic Testing Results..................................47
5.6 2006 Field Ultrasonic Testing Observations.............................54
5.7 2006 Field Ultrasonic Testing Conclusions..............................55
5.8 2008 Field Ultrasonic Testing Approach.................................56
5.9 2008 Field Ultrasonic Testing Results..................................58
5.10 2008 Field Ultrasonic Testing Observations.............................63
5.11 2008 Field Ultrasonic Testing Conclusions..............................65
5.12 Comparison between 2006 and 2008 Field Ultrasonic Testing Results......66
5.13 2008 Laboratory Control Testing........................................67
5.14 2008 Laboratory Control Ultrasonic Testing Results.....................69
5.15 Combined Field Ultrasonic Testing Results..............................70
viii


5.16 Problems Interpreting Ultrasonic Test Results......................73
5.17 Recommendations for Improving Ultrasonic Testing Results...........74
6. Structural Analysis................................................75
6.1 Structural Analysis Modeling using STAAD...........................75
6.2 STAAD Model Layout.................................................75
6.3 STAAD Model Loads..................................................77
6.4 STAAD Model Load Combinations......................................86
6.5 STAAD Model Results................................................86
7. Conclusions........................................................92
7.1 Conclusions from Visual Condition Assessment.......................92
7.2 Conclusions from Ultrasonic Testing................................92
7.3 Conclusions from Structural Analysis Modeling......................94
7.4 Recommendations for Preservation...................................96
Appendix
A. Photographs.......................................................100
B. Original Drawing and Reference Drawings...........................125
C. 2006 Laboratory Photographs and Ultrasonic A-scan Data............137
D. 2006 Field Ultrasonic A-scan Data.................................147
E. 2008 Field Ultrasonic A-scan Data.................................166
F. 2008 Laboratory Ultrasonic A-scan Data............................191
G. STAAD.Pro 2007 Input File.........................................195
IX


H. STAAD.Pro 2007 Output File....................................203
References..........................................................291
x


LIST OF FIGURES
Figure
2.1 Original Cimarron Timber Truss and Trestle........................ 9
2.2 Replacement Railroad Bridge Drawing...............................10
2.3 Cimarron Narrow-gauge Railroad Bridge.............................11
2.4 Marrow Point Dam..................................................12
2.5 Curecanti National Recreation Area Railroad Exhibit...............13
2.6 Cimarron Railroad Bridge on Display...............................14
2.7 D&RG Train on Display.............................................15
2.8 Cimarron Map......................................................16
2.9 West End of Cimarron Railroad Bridge..............................18
2.10 Weathered Timber Ties.............................................20
2.11 Bent Lower Chord Eyebars..........................................21
2.12 Bent Lower Chord Laced Channels and Cross Bracing Bar.............22
2.13 Cracked Lower Chord Laced Channel.................................22
2.14 Bent Lower Chord Cross Bracing....................................23
2.15 West Support Pier.................................................24
2.16 Paint Chipping and Minor Rusting of Bridge........................25
2.17 Pin Connection....................................................26
xi


4.1 Influence of Defect Size on Ultrasonic Display.........................33
4.2 Influence of Defect Orientation on Ultrasonic Display..................33
4.3 Influence of Transducer Location on Ultrasonic Display.................34
4.4 Influence of Shadow Effects on Ultrasonic Display......................34
4.5 Influence of Defect Distance on Ultrasonic Display.....................35
4.6 Influence of Signal Strength on Ultrasonic Display.....................35
4.7 Ultrasonic Testing Flaw Detector.......................................37
4.8 Sample Epoch III Flaw Detector Data File...............................40
5.1 2006 Laboratory Test Pins..............................................42
5.2 2006 Laboratory Testing on Sample Pin..................................43
5.3 Railroad Bridge Pin Referencing Schematic..............................48
5.4 Single Reflection Encountered during 2006 Field Testing................50
5.5 Secondary Reflection Encountered during 2006 Field Testing.............51
5.6 Possible Flaw Encountered during 2006 Field Testing....................52
5.7 Poor Ultrasonic Connection during 2006 Field Testing...................53
5.8 Single Ultrasonic Scan Field of View...................................57
5.9 Multiple Ultrasonic Scans Field of View................................57
5.10 Secondary Reflection Encountered during 2008 Field Testing.............62
5.11 Possible Flaw Encountered during 2008 Field Testing....................63
5.12 2008 Laboratory Test Pin...............................................67
5.13 2008 Laboratory Testing on Sample Pin..................................68
xii


6.1 Isometric View of STAAD Model......................................76
6.2 Dead Load D Applied to the STAAD Model.............................78
6.3 Dimensions and Weight of Boxcar #3132..............................79
6.4 Weight of Caboose #0577 ...........................................80
6.5 Live Load LI Applied to STAAD Model................................81
6.6 Live Load L2 Applied to STAAD Model................................82
6.7 Wind Load W1 Applied to STAAD Model................................83
6.8 Wind Load W2 Applied to STAAD Model................................84
6.9 Snow Load S Applied to STAAD Model.................................85
6.10 Strong Axis Bending Moment Diagram from the STAAD Model............87
6.11 Strong Axis Shear Diagram from the STAAD Model.....................88
6.12 Axial Stress Diagram from the STAAD Model..........................88
6.13 Displaced Shape from the STAAD Model...............................89
6.14 Combined Stress Ratios of the STAAD Model..........................90
6.15 Combined Stress Ratios of the ST AAD Model.........................91
A.l Information Sign..................................................101
A.2 View of the Railroad Bridge Exhibit Looking Southwest.............101
A.3 View of the Railroad Bridge Exhibit Looking Southwest.............102
A.4 View of the Railroad Bridge Exhibit Looking West..................102
A.5 View of the Railroad Bridge Exhibit Looking Northwest.............103
A.6 View of the Railroad Bridge Exhibit Looking East..................103
xiii


A.7 View of the Railroad Bridge Exhibit Looking East................104
A.8 View of the East Support of the Bridge...........................104
A.9 View of the Supporting Members of the Bridge....................105
A. 10 View of the Supporting Members of the Bridge....................106
A.l 1 View of the East Support of the Bridge..........................107
A. 12 View of the East Support of the Bridge..........................108
A.13 View of Locomotive #278.........................................109
A. 14 View of Tender...................................................109
A. 15 View of Boxcar #3132.......................................... 110
A. 16 View of Caboose #0577...........................................110
A. 17 View of the East End Frame of the Bridge.........................111
A. 18 View of the West End Frame of the Bridge.........................Ill
A. 19 View of the West End Frame of the Bridge .......................112
A.20 View of an Upper Chord Connection at the West End Frame..........112
A.21 View of an Upper Chord Connection Pin............................113
A.22 View of the East Support Pinned Connection.........................113
A.23 View of the East Support Pinned Connection.........................114
A.24 View of the East Support Pinned Connection Roller Bearings.........114
A.25 View of a Latticed Lower Chord Member at the East Support..........115
A.26 View of a Bracing Connection at the East Support...................115
A.27 View of the East Support Pinned Connection ........................116
xiv


A.28 View of the East Support Pinned Connection.......................116
A.29 View from Behind East Support Pinned Connection..................117
A.30 View of the East Support Pinned Connection Roller Bearings.......117
A.31 View of the West Support Pinned Connection.......................118
A.32 View of a Bracing Connection at the West Support.................118
A.33 View of a Bracing Connection at the West Support.................119
A.34 View of the West Support Bearing on the Pier.....................119
A.35 View of the West Support Connection Pin..........................120
A.36 View of a Lower Chord Latticed Member on East End of the Bridge..120
A.37 View of a Lower Chord Connection on East End of the Bridge.......121
A.38 View of a Lower Chord Connection on East End of the Bridge.......121
A.39 View from Behind a Lower Chord Connection........................122
A.40 View from Underneath a Lower Chord Connection....................122
A.41 View of the Lower Chord Eyebars Looking West.....................123
A.42 View of the Lower Chord Eyebars Looking East.....................123
A. 43 View of Bent Eyebars near the West Support.......................124
B. 1 Denver & Rio Grande Railroad Construction Drawing.................126
B.2 As-built Sketches.................................................128
B.3 Drawing of Locomotive #278........................................134
B.4 Drawing of Tender.................................................134
B.5 Drawing of Boxcar #3132...........................................134
xv


B.6 Drawing of Caboose #0577......................................135
B.7 Drawing of Boxcar Series #3000 through #3749..................135
B.8 Denver & Rio Grande Western R. R. Drawing L-70..................136
xvi


LISTS OF TABLES
Tables
4.1 Ultrasonic testing factors and the influence on testing results............32
4.2 Advantages and disadvantages to using ultrasound...........................36
5.1 2006 Laboratory ultrasonic testing results for Pin A.....................44
5.2 2006 Laboratory ultrasonic testing results for Pin B.....................44
5.3 2006 Laboratory ultrasonic testing results for Pin C.....................45
5.4 2006 Field ultrasonic testing results....................................49
5.5 2008 Field ultrasonic testing results for Pin SL8..........................59
5.6 2008 Field ultrasonic testing results for Pin NL8..........................59
5.7 2008 Field ultrasonic testing results for Pin SL7..........................59
5.8 2008 Field ultrasonic testing results for Pin NL7..........................60
5.9 2008 Field ultrasonic testing results for Pin SL6..........................60
5.10 2008 Field ultrasonic testing results for Pin SL0..........................60
5.11 2008 Field ultrasonic testing results for Pin NL0..........................61
5.12 Comparison of 2006 and 2008 field ultrasonic testing results............66
5.13 2008 Laboratory ultrasonic testing results.................................69
5.14 Combined field ultrasonic testing results..................................71
C. 1 Results from test Pin A...................................................138
xvii


C.2 Results from test Pin B..................................................141
C. 3 Results from test Pin C..................................................144
D. 1 Results from Pins SL8 and NL8..........................................148
D.2 Results from Pins SL7 and NL7..........................................149
D.3 Results from Pins SL6 and NL6..........................................150
D.4 Results from Pins SL5 and NL5..........................................151
D.5 Results from Pins SL4 and NL4..........................................152
D.6 Results from Pins SL3 and NL3..........................................153
D.7 Results from Pins SL2 and NL2..........................................154
D.8 Results from Pins SL1 and NL1........................................ 155
D.9 Results from Pins SLO and NLO..........................................156
D. 10 Results from Pins SU8 and NU8..........................................157
D. 11 Results from Pins SU7 and NU7..........................................158
D. 12 Results from Pins SU6 and NU6..........................................159
D.13 Results from Pins SU5 and NU5..........................................160
D. 14 Results from Pins SU4 and NU4..........................................161
D. 15 Results from Pins SU3 and NU3..........................................162
D. 16 Results from Pins SU2 and NU2..........................................163
D. 17 Results from Pins SU1 and NU1..........................................164
D.18 Results from Pins SUO and NUO..........................................165
xviii


E. 1 Results from Pin SL8....................................................167
E.2 Results from Pin NL8....................................................171
E.3 Results from Pin SL7....................................................175
E.4 Results from Pin NL7....................................................178
E.5 Results from Pin SL6....................................................181
E.6 Results from Pin SLO....................................................184
E. 7 Results from Pin NLO....................................................188
F. 1 Results from laboratory control pin.......................................192
xix


1.
Overview
1.1 Introduction
Within the United States, many bridges remain in service despite increased
demands on the structures and deterioration to their components. The construction
costs required to repair, strengthen, or replace existing bridges in today's
infrastructure is continually increasing, and, in turn, bridges are subjected to
compromising situations for which they were not originally intended. According to
the American Society of Civil Engineers 2009 Report Card for America's
Infrastructure, bridges overall within the United States were ranked as being mediocre
in terms of their current conditions and capabilities [ASCE, 2009]. As it stands this
year, more than 26% of the nation's bridges are classified as being functionally
obsolete or are considered to be structurally deficient, meaning that either the nature
of the bridges makes them more susceptible to failure if not properly inspected and
maintained or the bridge is not up to date with current design and operation codes
[ASCE, 2009; FHWA, 2004]. For this reason, assessing the current structural
condition of these bridges and determining their structural capacities are essential to
their continued use.
1


The structural condition of a bridge is most often determined visually by
completing a thorough inspection of the all of the components of the bridge. During
visual inspection, bridges are checked for conformity and completeness against
construction drawings. All of the bridge components are evaluated for signs of
movement, corrosion, cracking, or other signs of aging and deterioration. During
visual inspection any comments regarding the structure and any recommendations
about are reported.
When a bridge contains members that are critical to the stability, also known
as fracture critical members (FCMs) or elements that are hard to assess visually, more
in-depth inspection practices are used to assess the bridges condition. In these
instances, special non-destructive tests are used to gather additional information about
surface or subsurface conditions of the bridge components. These in-depth
inspections can help detect deterioration and defects which are not evident, but can
affect the intended performance of a bridge. For this reason, it is important to
complete additional tests on bridges where material quality, decay, and any other
uncertainties regarding the bridge structural capacity could influence the continued
use of the bridge [Sparks, 2007],
If the structural capacity of a bridge or element is in question, evaluation of
the structure or component using computer aided modeling can help provide accurate
2


and detailed answers. Structural analysis using a computer generated model can be
used to determine the current load carrying capacity and loading distribution for a
multitude of loading scenarios. The results from structural modeling can be easily
checked against the latest design codes to help pinpoint weaknesses which need to be
strengthened or replaced. Although structural modeling can be a very labor intensive
and precision oriented procedure, it is oftentimes necessary to provide a complete
understanding of the behavior of a structure or structural component, when
modifications or changes to a structure are being proposed.
1.2 Background to Railroad Bridge Inspections at Cimarron
In 2005, the University of Colorado Denver (UCD) contracted with the U.S.
National Park Service (NPS) to conduct a preservation study for the train-related
resources of the Curecanti National Recreation Area in Cimarron, Colorado. The
town of Cimarron, Colorado was once a depot for the Denver & Rio Grande (D&RG)
Railroad through the Black Canyon of the Gunnison River, and, as a result, a great
deal of railroad heritage has been stored and displayed throughout the town. At the
time of the preservation study, the NPS had intentions to rehabilitate and protect the
historical train resources. One resource of particular importance was a 19th century,
pin-connected, wrought iron railroad bridge.
3


The Cimarron Railroad Bridge, as it is called, is the sole surviving structure of
the D&RG Railroad through the Black Canyon. The railroad bridge serves as an
exhibit within the recreation area, displaying 19lh century steel construction and
preserved rolling stock from the narrow-gauge railroad era. As part of the
preservation study, a physical assessment of the Cimarron Railroad Bridge was
completed, along with recommendations for the preservation of the bridge [Jones et
al, 2005],
A year following the preservation study, additional inspection practices were
completed on the railroad bridge to more accurately determine the structural
condition of the bridge. Paul Mischo, UCD graduate student, completed ultrasonic
tests on all 36 pins connecting the bridge at the joints. The primary objectives of the
ultrasonic tests were to locate potential flaws existing in the pins or wear on the pins
which could not be seen during the visual inspection performed during the
preservation study of 2005 [Mischo, 2007]. Uncertainties surrounding the results
from 2006 ultrasonic tests indicated that additional ultrasonic tests should be
completed on the bridge pins in order to appraise the condition of the pins [Mischo,
2007]. More extensive ultrasonic tests were completed on 7 of the pins in 2008. The
results of the 2008 ultrasonic tests were applied to the results from 2006 to clarify
uncertainties and to definitively determine the structural condition of the pins.
4


1.3 Purpose
The purpose of this thesis is to present and discuss the findings of a structural
assessment, ultrasonic inspections of the pins and structural modeling of the wrought
iron railroad bridge located in Cimarron, Colorado, as well as to recommend actions
for preservation of the bridge.
1.4 Organization
This thesis is organized into 7 chapters. The first chapter presents an
introduction to bridge inspections and the inspections completed on the Cimarron
Railroad Bridge. Chapter 2 describes the historical background, features, and general
condition of the railroad bridge. Chapter 3 reviews the history of the National Bridge
Inspection Standards and the use of ultrasound in bridge inspections. Chapter 4 deals
with ultrasonic testing theory and provides an introduction to the principles of
ultrasonic testing. Chapter 5 presents the data of trial ultrasonic tests completed in a
laboratory and field ultrasonic tests completed on the railroad bridge pins, along with
interpretations of the results. Chapter 6 discusses structural analysis modeling of the
railroad bridge and results from the structural analysis model. Finally, Chapter 7
reports conclusions from the ultrasonic testing and structural modeling of the railroad
bridge and gives recommendations for caring for the bridge.
5


Supplemental information for the thesis is presented in appendices.
Additional photographs taken on location between 2005 and 2008 are displayed in
Appendix A. Original design drawings for the bridge and informational drawings for
the locomotive and rolling stock are displayed in Appendix B. Photographs and
Laboratory control ultrasonic testing data collected in the 2006 study are included in
Appendix C. Field ultrasonic testing data collected at Cimarron in 2006 and 2008 are
presented in Appendices D and E respectively. Laboratory control data collected in
the 2008 study is included in Appendix F. The input computer code developed to
model the railroad bridge using structural analysis software is provided in Appendix
G. And, the output results of the structural analysis software are included in
Appendix H.
6


2.
Cimarron Narrow-Gauge Railroad Bridge
2.1 Historical Background
In the late 19th century, the D&RG Railroad Company sought the construction
of a railroad line through the Black Canyon of the Gunnison River in western
Colorado. The proposed railroad line would continue west from the bustling town of
Gunnison and connect with the small town of Cimarron [Jones et al, 2005], The
railroad line would become part of the D&RG circle tour, a route which transported
passengers and cargo through some of the most rugged and scenic country in the
West. Construction of the railroad line through the canyon was expected to be very
hazardous and costly given the terrain of the canyon, but the construction of the
railroad line was deemed necessary despite the risks [Jones et al, 2005]. Access to
the coalfields north of Delta was of interest to the D&RG Railroad Company. There
was also a great desire to capitalize on the large amount of wealth and agriculture
being transported from the nearby San Juan mining districts [Jones et al, 2005]. In
addition to agriculture and the mining industry, the scenic grandeur of the railroad
line was thought to have great potential to enhance tourism in the area [NPS, 2006].
A narrow-gauge track was selected for the railroad line. Not only would the
narrow-gauge track require less cutting and filling of the canyon cliffs, which would
7


be less expensive, the narrow-gauge railroad tracks would make navigation of the
tight curves and steep grades of the canyon more efficient and manageable [Jones et
al, 2005]. By August 1881, the 35 mile (56 kilometer) stretch of narrow-gauge track
connecting Gunnison and Cimarron was well under construction. And, in August
1882, the first Denver & Rio Grande train passed through the upper reaches of the
Black Canyon of the Gunnison and into the railroad depot of Cimarron [NPS, 2006].
Along the stretch of railroad track and located just outside of the Cimarron
depot was a timber truss and trestle combination which crossed over the Cimarron
River. The railroad bridge near Cimarron was one of seven bridges that were used by
D&RG trains to traverse the canyon along the route [Jones et al, 2005]. Figure 2.1,
shows the original wood truss and trestle which was constructed in 1882.
8


Figure 2.1 Original Cimarron Timber Truss and Trestle.
Photo courtesy of the Ted Kierscey Collection.
[The Narrow Gauge Circle, 2006].
Nine years following completion of the railroad line, the timber bridge near
Cimarron was replaced with another bridge structure, presumably comprised of
wrought iron. The replacement railroad bridge, which consisted of 4 spans, was
assembled onsite in Cimarron in 1891. All four of the spans used came from other
locations on the D&RG railroad line around Colorado, a fact attested to by notes on
the surviving construction drawings [D&RG, 1891]. Figure 2.2 shows the layout of
the longest span of the replacement bridge installed at Cimarron in 1891. The note
attributed to this span of the bridge reads as follows:
9


119-1/3 deck pin connected span built when D&R.G.R.R. was under
management of A.T. & S.F. Railroad. Two spans: formerly bridge No.
231A and 243A second division, Denver & Rio Grande Railroad.
Used here the old span now piled near Nathrop Station without
change [D&RG, 1891],
The production date of the longest span or the company that built the bridge span is
unknown.
i .t ----------1*i---
i f.i I . . .........i I I

:tl' RbConstiiuctiox op Bbhigb^290.5'Div.
Figure 2.2 Replacement Railroad Bridge Drawing.
Portion of original construction drawing titled Reconstruction of Bridge
329 C. 3rd Div. Denver & Rio Grande Railroad. [D&RG, 1891].
10


Up until 1949, train traffic continued through the canyon until the popularity
of the automobile as the main mode of transportation forced the railroad line to
discontinue service. Figure 2.3 shows the final train pulling into Cimarron depot just
prior to decommission of the railway. After 1949, much of the surrounding narrow-
gauge railroad track was removed, and the 6 other bridges throughout the canyon
were disassembled.
Figure 2.3 Cimarron Narrow-gauge Railroad Bridge.
A final train crosses the narrow-gage railroad bridge at Cimarron,
Colorado, prior to the removal of track in 1949. [Photo used with
permission from Denver Public Library; Western History Dept.; Otto
Perry; OP-7965].


In 1962, the wrought iron railroad bridge served as a temporary haul road for
assistance in construction of the nearby Morrow Point Dam, shown in Figure 2.4
[Jones et al, 2005].
Figure 2.4 Marrow Point Dam.
Double curvature concrete arch dam built by the U.S. Bureau of
Reclamation and completed in 1968.
In 1963, a culvert for the Cimarron River was laid underneath the railroad
bridge. In the process of backfilling around the corrugated steel pipe, large rock fill
buried the western 1/3 of the bottom chords of the truss [Jones et al, 2005], The NPS
decided to create an exhibit utilizing the existing bridge in 1974, shown in Figure 2.5.
During that time, a 19th century locomotive engine, associated stock cars and a
12


caboose were located on the bridge for display, and the approach spans were removed
from either end of the railroad bridge [Jones et al, 2005]. In 1976, the bridge was
entered into the National Registrar of Historic Places [USBR, 1976].
Figure 2.5 Curecanti National Recreation Area Railroad Exhibit.
The largest span of the existing Cimarron Railroad Bridge was used for
display while the other spans of the bridge were removed. Note the rock
fill which covered up the bottom portion of the truss on the west end of the
bridge. Photo courtesy of the NPS.
In 1984, a flood through Cimarron Canyon washed out a roadway erected
beside the railroad bridge and the culvert beneath the bridge. It was discovered at that
time that several of the lower chord members of the bridge were damaged and bent,
13


which is presumed to be attributed to the previously mentioned backfilling operation
[Jones et al, 2005], Today, the Cimarron Railroad Bridge still stands just outside of
the Cimarron campground, as part of the Curecanti National Recreational Area
Railroad Exhibit, shown in Figures 2.6 and 2.7. For additional photographs of the
Cimarron Railroad Bridge and informational drawings regarding the bridge and the
train components on top of the bridge, refer to Appendices A and B respectively.
Figure 2.6 Cimarron Railroad Bridge on Display.
The Cimarron Railroad Bridge sits on display as the sole surviving
structure of the Denver & Rio Grande Railroad through the Black Canyon
of the Gunnison. [Jones et al, 2005].
14


Figure 2.7 D&RG Train on Display.
Rolling stock displayed atop the Cimarron Railroad Bridge, giving a
glimpse into the past when the railroad was active.
2.2 Location of the Cimarron Railroad Bridge
The Cimarron Railroad Bridge is located approximately 20 miles (32
kilometers) east of Montrose, off of U.S. Highway 50 near the town of Cimarron,
Colorado. The railroad bridge crosses over the Cimarron River in Cimarron Canyon,
just north of town, along the access road to Marrow Point Dam Figure 2.8 shows a
map of Cimarron and the location of the Cimarron Railroad Bridge.
15


AT i Cimarron Railroad Bridge
i V/ !;[ />/ /(/ ;/ // /. '/ ft (f
1 * Marrow Point Dam Road ^ a i / a if i h.!
// if
Vi
Cimarron River
f
/?
R
Sqauw Creek
JSll
Campground
, Mi // \
V !!
I: H
:i U
to Montrose
Vi
\v/
\(
H v
w

Visitor center
Picnic area
\\ \ \\
US Higway 50-
if
\ \\ 'Vx -=;
V \\\>
\ %
i] NX
Maintenance
AREA
to Gunnison
Figure 2.8 Cimarron Map.
[Adapted from NPS, 2006].
to Marrow
Point Dam
16


2.3 Summary Description of the Cimarron Railroad Bridge
The railroad bridge at Cimarron was a pin-connected Pratt deck truss. The
dimensions of the railroad bridge, as measured from the centerlines of the connection
pins was a span of 119 feet and 4 inches (36.4 meters), a width of 12 feet and 0 inches
(3.7 meters), and a depth of 19 feet and 6 inches (5.9 meters) [Jones et al, 2005].
Timbers ties, spaced at 1 foot and 0 inches (0.3 meter) were attached to the top of the
bridge and supported a pair of narrow-gauge rails. Beneath the timber ties sat the
upper chords of the bridge, which were pairs of back-to-back connected channels.
Also beneath the timber ties were two S sections, located approximately below each
of the narrow-gauge rails [Jones et al, 2005]. The S sections bear on built-up plate
girders serving as floor beams which frame into the vertical members of the truss.
Vertical members of the bridge consisted of latticed back-to-back channels
[Jones et al, 2005]. The vertical members were supported at the lower chord pins by
W section struts. The load-carrying bottom chords consisted of pin-connected
eyebars. There were built-up members, similar to the verticals, in the end bays of the
bottom chords [Jones et al, 2005]. Lateral cross bracing bars were present between
top and bottom chords of the bridge. The west supports of the bridge were anchored
to the stone masonry pier below creating a pinned-type connection. The east
supports, also anchored to stone masonry, consisted of roller bearings intended to
accommodate thermal expansion and contraction and movements due to live load
deflections [Jones et al, 2005]. A total of 36 pins held the bridge together at each of
17


the main truss connections. Figure 2.9 displays the pin-connected structural elements
of the west end of the bridge.
Figure 2.9 West End of Cimarron Railroad Bridge.
Structural members of the pin-connected railroad bridge at Cimarron.
Structural components of the railroad bridge appeared to have been produced
using wrought iron, and not steel. While metallurgical testing would be necessary to
confirm this, the fact that the structure pre-dates 1890, when many bridge fabricators
changed from use of wrought-iron to steel, suggests that the bridge was of wrought
iron construction [Jones et al, 2005]. The minimal amount of rust found on the
structure also suggests wrought iron components. In comparison to steel, wrought
iron has the tendency to corrode at a much slower rate [Jones et al, 2005]. For the
18


purpose of this thesis, all structural components of the bridge were assumed to be
wrought iron.
2.4 Visual Condition Assessment Summary
The first step in evaluating the railroad bridge at Cimarron was to complete a
visual inspection of the components of the bridge. During the visual inspection, the
conditions of the bridge elements were observed for defects or deterioration which
could influence the functionality of the structure. A summary of the visual condition
of the bridge elements follows:
General condition of the railroad bridge: The bridge was in good condition,
considering the age of the structure. The bridge contained some bent members,
chipped and worn off paint could be found over the entire structure, and some
minor rust was observed. One bottom chord member at an end bay was found to
be cracked, but can be easily repaired.
Ties: All timber ties along the bridge were weathered to some degree as shown in
Figure 2.10. The timber ties had water stains on them when viewed from beneath
the bridge and were soft from exposure to the elements [Jones et al, 2005].
19


Figure 2.10 Weathered Timber Ties.
Photograph courtesy of David Kane, NPS.
Deck wrought iron members: Good condition [Jones et al, 2005].
Upper chord structural members: Good condition [Jones et al, 2005],
Vertical and diagonal structural members: Good condition [Jones et al, 2005].
Bottom chords: Some of the lower chord eyebars and cross bracing members
were bent as shown in Figure 2.11 and Figure 2.12. One lower chord member
was bent and cracked as illustrated in Figure 2.12 and Figure 2.13. It is presumed
that damage to lower chords of the bridge occurred during backfilling operations
20


in 1963 (refer to Figure 2.5 on page 13 for an illustration of this)
[Jones et al, 2005]. Members can be repaired or replaced.
Figure 2.11 Bent Lower Chord Eyebars.
Photograph courtesy of David Kane, NPS.
21


Figure 2.12 Bent Lower Chord Laced Channels and Cross Bracing Bar.
Photograph courtesy of David Kane, NPS.
Figure 2.13 Cracked Lower Chord Laced Channel.
Photograph courtesy of David Kane, NPS.


Bottom diagonal bracing rods: Some bracing rods were bent downward, but can
be repaired [Jones et al, 2005]. Figure 2.14 illustrates that the bent rods
(presumably caused by rock fill embankment).
Figure 2.14 Bent Lower Chord Cross Bracing.
[Jones et al, 2005].
Pinned supports on west end: Good condition [Jones et al, 2005].
Roller nests at east bearings: Good condition, however show no sign of
movement in recent years [Jones et al, 2005].


Piers: Some minor damage and deterioration to limestone and granite blocks
below the supports. On the west abutment, one of the limestone capstones is
missing as shown in Figure 2.15 [Jones et al, 2005]. Piers can be repaired.
Figure 2.15 West Support Pier.
Granite and Limestone support pier underneath the Cimarron Railroad
Bridge. Note the capstone on the upper right of the pier is missing.
[Jones et al, 2005].
Paint: Good condition. Some minor chipping has occurred across all across the
structure (presumably caused by exposure to the elements). More severe chipping
has occurred along the lower chord members which were once buried under rock
24


fill embankment [Jones et al, 2005]. Small spots of rust are visible on the
structure at locations where paint coating has chipped, as shown in Figure 2.16.
Paint coating and rust spots are repairable. The composition of the paint is
unknown; further testing of the paint would need to be performed to inspect for
the presences of lead within the paint.
Figure 2.16 Paint Chipping and Minor Rusting of Bridge.
Photograph courtesy of David Kane, NPS.
Pins: Only the pin ends can be observed visually. Majority of pins hidden
surface area and volume was hidden underneath eye bars and other connecting
elements, as illustrated by Figure 2.17. No signs of cracks or deterioration to pin
ends. Additional investigation on pins is recommended [Jones et al, 2005].
25


Figure 2.17 Pin Connection.
Photograph courtesy of David Kane, NPS.
26


3.
National Bridge Inspection Standards
3.1 Establishment of the National Bridge Inspection Standards
The United States Secretary of Transportation developed the National Bridge
Inspection Standards (NBIS) for highway bridges following the 1967 collapse of the
State Highway 35 Bridge (Silver Bridge) in West Virginia. The collapse of the Silver
Bridge, which killed 46 people and injured 9 others, prompted national concern about
the conditions of bridges around the United States [NTSB, 1970], To help return
confidence to travelers within the United States, Congress enacted the NBIS into law
as part of the Federal-Aid Highway Act of 1970. The establishment of the NBIS
created uniform standards for bridge inspections, frequencies of bridge inspections,
and the qualifications of inspecting officials. In addition to inspections, the Act also
assigned funding to reinforce or replace deficient bridges across the nation [FHWA,
2004],
Despite efforts to keep the NBIS up to date with advances in research and
technology, periodic and unforeseen bridge collapses continued to occur within the
United States, each of which caused significant revisions to the NBIS. The 1983
collapse of the Interstate 95 Bridge (Mianus River Bridge), in Connecticut, which
caused a section of the bridge deck to plummet into the river and killed 3 people,
27


raised concern over corrosion and fatigue of steel connections [NTSB, 1984], As a
result, the NB1S were revised to incorporate more rigorous and stringent inspection
procedures for fracture critical structures [FHWA, 2004], The 1987 collapse of
Interstate 90 in New York State, where scouring washed soil away from underneath
one of the supporting bridge piers and fatally injured 10 people, brought new
concerns regarding underwater bridge foundations [NTSB, 1988], From this
collapse, bridge inspections were adjusted to include periodic underwater inspection
of all structures at risk and susceptible to scour damage [FHWA, 2004],
The collapse of the Interstate 35W Bridge in Minnesota in 2007, which caused
multiple spans of the bridge to fall into the Mississippi River and killed 13
individuals, has not officially evoked revision to the bridge inspection standards.
However, following the collapse, the Federal Highway Administration, issued an
immediate re-inspection of all steel deck truss bridges with fracture critical members
[FHWA, 2007], And, findings from the collapse of the I-35W, has sparked
investigations regarding overloaded bridges and bridges with under-designed gusset
plate connections [FHWA 2008, FHWA 2008].
28


3.2 Use of Ultrasound as a Non-destructive Test
Revisions to the NBIS in 1988 mandated that all bridges containing FCMs or
unique or special features receive additional attention to supplement routine visual
inspections [FHWA, 1988]. As a result of these revisions, non-destructive testing
techniques, such as ultrasound, have been used in the inspection of bridges where in-
depth investigations of critical features were necessary. The simplicity and reliability
of ultrasound makes it a preferred practice to use during bridge inspections.
Ultrasonic tests can provide onsite information regarding the subsurface conditions of
tested material and w ill not harm the testing material during the performance of the
test. The results from ultrasonic tests can be used to interpret the presence of surface
failures and deteriorations, such as fatigue cracking and corrosion, or can be used to
detect internal flaws to a material, such as a void or an inclusion [Kubba, 2008].
29


4.
Ultrasonic Non-destructive Testing
4.1 Ultrasonic Testing Introduction
Ultrasonic testing uses mechanically generated pressure waves to measure the
soundness of a homogeneous material. During an ultrasonic test, a transducer is
acoustically coupled to a testing material using a viscous coupling medium. Typical
materials used as coupling mediums are water, oil, glycerin, or grease. The
transducer transmits ultrasonic pulses in the frequency range of 1 MHz to 20 MHz
through the testing material at a prescribed velocity [Kubba, 2008]. Ultrasonic pulses
travel through the testing material until a discontinuity or material boundary reflects
the signal back to an acoustically coupled receiver. The receiver transforms the
reflected ultrasonic pulses into electrical energy, where material boundaries and any
discontinuities can be displayed [FHWA 2004].
Ultrasonic pulses are most commonly displayed in a graph-type format,
referred to as an A-scan, where the horizontal axis represents distance traveled by the
signal and the vertical axis represents signal amplitude of the returned ultrasonic
pulse. Within an A-scan display, the amplitude and position of a signal reflection is
30


directly proportional to the size and location of the discontinuity within the test
material [FHWA, 2004],
4.2 Pulse-echo Ultrasonic Testing Technique
Pulse-echo ultrasonic testing is a technique wherein a single transducer is
acoustically coupled to one side of testing material. The transducer serves both as a
transmitter and a receiver, sending ultrasonic pulses through the test material and
collecting them when they are reflected and returned to their point of origin [Nelligan,
2008], Either a straight-beam transducer or an angled-beam transducer can be used
during pulse-echo ultrasonic testing. A straight-beam transducer will transmit
ultrasonic signals perpendicular to a testing surface and an angled-beam transducer
will transmit ultrasonic signals at a specific angle into the testing surface. Straight-
beam transducers allow for straightforward detection of material discontinuities
directly beneath a testing surface, where angled-beam transducers require the use of
geometry to detect discontinuities [FHWA 2004].
4.3 Ultrasonic Testing Considerations
When performing an ultrasonic test there are many factors to keep in mind
which can influence the appearance of a displayed ultrasonic reflection. Some of the
factors involve the direction and strength of the signal that is being transmitted, and
others are linked to the composition of the testing material and the type of
31


discontinuity encountered. Table 4.1 describes the common variables which can
influence an ultrasonic test and the effects these variables have on display results.
Table 4.1 Ultrasonic testing factors and the influence on testing results.
[Adapted from FHWA, 2004],
Testing Variable Influence on Display Results
Ultrasonic Signal Strength Influences amplitude of the reflections displayed.
Transducer Coupling and Material Testing Surface Influences the quantity and quality of ultrasonic signal which can be passed into a testing material.
Direction and Location of Ultrasonic Signal Transmission Influences the potential for discontinuities to be encountered by the ultrasonic signal and the angle at which the discontinuities will be encountered.
Size and Orientation of Material Discontinuities (surface boundaries or other) Influences the reflection capability of the ultrasonic signal.
Number of Material Discontinuities (surface boundaries or other) Influences the reflection capability of the ultrasonic signal.
Material composition Influences the capacity of the signal to pass through a testing material and not attenuate.
Figure 4.1 through Figure 4.6 display some ultrasonic testing scenarios and
illustrate a few of the variables listed earlier.
32


A-SCAN ULTRASONIC SIGNAL DISPLAY
transducer
(at pin center)
Pin Defects
X
field of View
Pin
I
j
Figure 4.1 Influence of Defect Size on Ultrasonic Display.
The amplitude of the defect displayed is directly proportional to the size of
the defect encountered by the ultrasonic signal.
[Adapted from FHWA, 2004],
il NEAR-FIELD BACK \
11 NOISE WALL !
! insufficient Surface ij ;
5) Areato Reflect | j
if. Ultrasound |l !
W*w*i*^
A-SCAN ULTRASONIC SIGNAL DISPLAY
Figure 4.2 Influence of Defect Orientation on Ultrasonic Display.
The orientation of the defect will affect the amount of ultrasonic signal
capable of being reflected and displayed. [Adapted from FHWA, 2004].
33


A-SCAN ULTRASONIC SIGNAL DISPLAY
Transducer
(a t bottom of pin)
Pin Defects . _
\
\
\
' Pin
i________
I
.1'
Field of View
Figure 4.3 Influence of Transducer Location on Ultrasonic Display.
The location of the transducer and the discontinuities within the ultrasonic
signal field of view will influence the display.
[Adapted from FHWA, 2004],
NEAR-FIELD
Noise
First
i Defect
Back
Wall
Second Defect
Shadowed by
First Defect
: / "RET DEFECT , j
A-SCAN ULTRASONIC SIGNAL DISPLAY
Pin
Transducer
(A T PIN CENTER) -
Pin Defects
i
r
Jv
/
r
r
b i
'! !
Field of View
Figure 4.4 Influence of Shadow Effects on Ultrasonic Display.
A small defect located directly behind large defect will be shadowed by
the largest defect and not displayed. [Adapted from FHWA, 2004],
34


A-SCAN ULTRASONIC SIGNAL DISPLAY
Transducer
(at pin CENTER)
Pin Defects
Pin
Field of View x
Figure 4.5 Influence of Defect Distance on Ultrasonic Display.
The location of the defect will affect the strength of the ultrasonic signal
which is available to be reflected and displayed. Ultrasonic signal will
diminish and disperse as it travels through a testing material. Note the
amplitude loss between the reflections. [Adapted from FHWA, 2004].
Near-field
noise
Insufficient Signal Strength to Display Defect Weak Back WALL Reflection
AywAj tf
A-SCAN ULTRASONIC SIGNAL DISPLAY
Figure 4.6 Influence of Signal Strength on Ultrasonic Display.
Low Signal strength or poor transducer connections will influence the
visibility of signal reflections. [Adapted from FHWA, 2004].
35


4.4 Advantages and Disadvantages of Ultrasonic Testing
When using ultrasound to acquire additional information about a testing
material there are some advantages and disadvantages to keep in mind prior to
performing tests. The advantages and disadvantages of the ultrasonic testing are
described in Table 4.2.
Table 4.2 Advantages and disadvantages to using ultrasound.
[Adapted from FHWA, 2004],
Advantages
" ' 'I' --L-MII.-.--- L-
Ultrasonic testing can require only
single-sided access to a material to be
an effective non-destructive test.
Ultrasound can be used to acquire
thickness and distance information in
addition to detecting flaws.
Minimum surface preparation is
required to perform a test.
Testing results can be interpreted to
determine sizes and locations of
surface and subsurface discontinuities
within a test specimen of tested
material.
Disadvantages
Test specimens that have rough
surfaces will contain heavy near field
noise in the A-scan display.
Testing surfaces must be accessible
to the transducer.
Multiple defects present within a test
specimen may be disguised when
testing because of shadow effects.
Defects oriented parallel to the
ultrasound transmission may go
undetected.
Defects located outside of the field
of view of the ultrasonic signal will
not be detected on an A-scan display.
36


4.5 Ultrasonic Flaw Detector
The ultrasonic tests completed for this thesis were conducted using an Epoch
III, Model 2300 Flaw Detector and a 2.5 MHz straight-beam transducer produced by
Panametrics, Inc. The Epoch III Flaw Detector features a fully alphanumeric data
logger that stores A-scan waveforms with setup information. Capabilities of the
Epoch III flaw detector include thickness measurement, detection of discontinuities
and flaws, and material classification of a tested material. Figure 4.7 shows the
Epoch III flaw detector unit.
Figure 4.7 Ultrasonic Testing Flaw Detector.
The Epoch III ultrasonic testing machine with an attached straight-beam
transducer.
37


4.6 Ultrasonic Flaw Detector Data Files
Data files collected by the Epoch III flaw detector are presented in the A-scan
format. There are 10 major divisions which separate the horizontal axis of the
graphing display which allow for distance calculations of the reflected ultrasonic
signal and a graduated scale attached to the vertical axis which can be used for visual
reference of the signal amplitude. Accompanying a graphical display of the
ultrasound signal is a listing of parameters which are used during the transmission of
the signal which contribute to the display. Figure 4.8 shows a sample data file
recorded by the Epoch III flaw detector while pointing out some of the important
parameters referenced in the data file. Short descriptions of the important parameters
used to display the ultrasonic signal are described below.
Sensitivity is used to adjust the ultrasonic signal strength between a range of 0
and 100.0 decibels. The sensitivity level used during testing will affect the
amplitude which ultrasonic signal reflections are displayed [Panametrics, 2004].
Velocity is the programmed material constant, between 0.0250 and 0.6000 inches
per microsecond (655 and 15240 meters per second), which is used for distance
calculations. Ultrasound travels at different velocities through different materials.
By adjusting the material velocity, ultrasonic signal reflections can be displayed at
their precise distances [Panametrics, 2004].
38


Range is the setting used to adjust the distance displayed by the data file. By
adjusting the range value, a user can determine how much of an ultrasonic signal
reflection (or multiple signal reflections) will be displayed. Range can be
adjusted from 0.038 inch (1 millimeter) up to 200 inches (5000 millimeters)
[Panametrics, 2004],
Pulsar Level is the parameter used to adjust the penetration power of the
reflected ultrasonic signal based on the size of material being tested. Pulsar levels
range from Low (100 volts) to High (400 volts). The high pulsar setting will
provide penetration power for testing thick materials and the low pulsar setting is
ideal for near surface resolution when testing thin materials [Panametrics, 2004].
Damping Level is used to adjust the penetration power of the reflected ultrasonic
signal, similar to the pulsar level (mentioned above). Damping levels can be
adjusted from 50-ohm to 400-ohm. The highest damping setting will provide
penetration power for testing thick materials and the lowest damping setting is
ideal for near surface resolution when testing thin materials [Panametrics, 2004].
39


Figure 4.8 Sample Epoch III Flaw Detector Data File.


5.
Cimarron Railroad Bridge Ultrasonic Testing
5.1 Overview
As mentioned in Section 2.4, Visual Condition Assessment Study, the visual
inspection of the pins within the Cimarron Railroad Bridge resulted in insufficient
information to categorize the condition of the pins. This prompted the need to
conduct a more in-depth investigation on the pins. In order to gain more information
about the pins, onsite ultrasonic testing was completed. Two series of tests were
completed on the pins during 2006 and 2008. The procedures used for each of the
series of tests as well as the results are presented within.
5.2 2006 Laboratory Control Testing
Prior to the completion of ultrasonic tests in the field in 2006, a set of trial
bridge pins were fabricated and tested [Mischo, 2007]. The purpose of the test was to
gain familiarity with the Epoch III flaw' detector and its capabilities. Dimensions of
the trial pins were selected to mimic the assumed shape of railroad bridge pins at
Cimarron. For the tests, 3 straight pins were fabricated using 2-3/4-inch (70
millimeters) diameter steel rods cut into 6 inch (152 millimeters) lengths with
1/10-inch (2.5 millimeter) threads machined into both ends, as shown in Figure 5.1.
41


Mock damage was inflicted on each of the pins to simulate conditions that might be
experienced in the field. Perpendicular cuts of varying depths were placed in one of
the pins (referred to as Pin A) to mimic a fracture of the pin, and J /16-inch (1.5
millimeter) and 1/8-inch (3 millimeter) diameter holes of were drilled into the other
two pins (referred to Pin B and Pin C respectively) to imitate a void that might exist
within a pin [Mischo, 2007],
Ir-
6 i1! - >
m * < a
Figure 5.1 2006 Laboratory Test Pins.
Laboratory tests pins B, A, C are presented from left to right.
[Mischo, 2007].
Ultrasonic tests were completed in each of the test pins in attempt to verify the
length of the pins and detect the mock damage of the pins. Petroleum jelly couplant.
42


a straight-beam transducer, and the pulse-echo method of testing were used to take
axial ultrasonic scans on one end of each of the test pins. Scans were performed
directly in front of each of the areas of inflicted damage on the pins [Mischo, 2007],
Figure 5.2 shows an illustration of a laboratory test completed in 2006. A complete
listing of all of the data files and photographs recorded during the 2006 laboratory
control testing procedure are presented in Appendix C.
Figure 5.2 2006 Laboratory Testing on Sample Pin.
[Mischo, 2007],
43


5.3 2006 Laboratory Control Testing Results
A summary of results obtained from the 2006 laboratory control tests
completed by Paul Mischo are presented in Table 5.1 through Table 5.3.
Table 5.1 2006 Laboratory ultrasonic testing results for Pin A.
[Adapted from Mischo, 2007].
Location of Ultrasonic Scan Results
Center of Pin No flaws detected. Back wall detected.
Cut Equal to Thread Depth No flaws detected.
Cut 1/16-inch Below Thread Depth Weak indication of flaw.
Cut 1/8-inch Below Thread Depth Moderate indication of flaw.
Cut 3/16-inch Below Thread Depth Strong indication of flaw.
Between Cuts No Haws detected.
Table 5.2 2006 Laboratory ultrasonic testing results for Pin B.
[Adapted from Mischo, 2007].
Location of Ultrasonic Scan Results
Center of Pin No flaws detected. Back wall detected.
1/16-inch Dia. Hole Equal to Thread Depth No flaws detected.
1/16-inch Dia. Hole 1/16-inch Below Thread Depth No flaws detected.
1/16-inch Dia. Hole 1/8-inch Below Thread Depth No flaws detected.
1/16-inch Dia. Hole 3/16-inch Below Thread Depth Weak indication of flaw.
Between 1/16-inch Dia. Holes No flaws detected.
44


Table 5.3 2006 Laboratory ultrasonic testing results for Pin C.
[Adapted from Mischo, 2007].
Location of Ultrasonic Scan Results
Center of Pin No flaws detected. Back wall detected.
1/8-inch Dia. Hole Equal to Thread Depth No flaws detected
1/8-inch Dia. Hole 1/16-inch Below Thread Depth No flaws detected
1/8-inch Dia. Hole 1/8-inch Below Thread Depth Weak indication of flaw
1/8-inch Dia. Hole 3/16-inch Below Thread Depth Weak indication of flaw
Between 1/16-inch Dia. Holes No flaws detected
Results from the laboratory testing of Pins A, B. and C, indicated that the far
wall of each of the test pins could be located consistently. Axial ultrasonic scans
performed using a straight-beam transducer could detect the presence of mock flaws
in each of the test pins with varying degrees of effectiveness. All mock damage that
was shielded from the ultrasonic signal by the threads of the pins during testing could
not be detected on any of the test pins. Axial cuts inserted across pin A could be
located at depths as little as 1/16-inch (1.5 millimeter) beyond the threads of the pin.
And, holes within a pin could only be detected reliably at depths of 3/16-inch (3
millimeter) beyond the threads of the pin. From these tests results, it was concluded
that the bridge pins on the Cimarron Railroad Bridge could be tested with reasonable
accuracy with for the presence of flaws using a straight-beam transducer.
45


5.4 2006 Field Ultrasonic Testing Approach
In 2006, ultrasonic tests were completed on all 36 of the pins connecting the
Cimarron Railroad Bridge [Mischo, 2007]. Under the supervision of climbing
rangers from the NPS, and with the assistance of climbing harnesses, a lanyard, and
horizontal lifeline set up across the bridge, each of the pins were visually observed
and axially scanned using ultrasound.
In order to facilitate good onsite ultrasonic measurements on the pins,
considerable effort was placed into reconditioning the ends of the pins prior to
completing tests. A grinder and a grinding wheel were used to remove paint and
create smooth surfaces along the ends of the pins where ultrasonic tests could be
completed. By creating a smooth surface, the amount of ultrasound sensitivity
required to complete the tests would be minimized, thus, making results easier to
interpret for discontinuities [Mischo, 2007],
Prior to testing, the transducer and flaw detector were calibrated against a test
member on the bridge in order to establish the material velocity required for testing.
During testing, one ultrasonic test was completed on the ends of each of the pins.
Using a straight-beam transducer and the pulse-echo technique, each of the pins was
tested along one end in order to confirm the boundaries of the pins and to identify any
discontinuities within the pins [Mischo, 2007]. Petroleum jelly was used as a
46


couplant to affix the transducer of the flaw detector to the testing surface of each of
the pins. Following testing, all pin ends were painted with a matching paint to
prevent rust from forming. All of ultrasonic data files recorded during the 2006 field
ultrasonic testing are presented in Appendix D.
5.5 2006 Field Ultrasonic Testing Results
Results of the pulse-echo ultrasonic tests completed on the railroad bridge
pins in 2006 are shown in Table 5.4. Tabular results display the types of reflections
encountered during ultrasonic testing for each of the pins across the entire structure.
The blacked out fields of the table indicate the types of results obtained for individual
pin that was tested. For simplicity in displaying the testing results, each of the pins
in the table are referenced according to their location on the bridge. Pins are
numbered from 0 to 8, going from east to west, to indicate the frame of the bridge on
which the pin was located. Additionally, pins are referenced with an S or an N to
indicate either the south (S) or north side (N) of the bridge that the pin was located
on, and pins are referenced with a U or a L to specify if the pin was part of an upper
chord (U) or lower chord (L) connection [Mischo, 2007]. Figure 5.3 shows a
simplified schematic of the railroad bridge for referencing of the bridge pins.
47


Frame 0
Figure 5.3 Railroad Bridge Pin Referencing Schematic.
[Adapted from Mischo, 2007].
48


Table 5.4 2006 Field ultrasonic testing results.
Types of reflections observed from the 2006 ultrasonic tests completed on
the pins of the railroad bridge at Cimarron, Colorado.
[Adapted from Mischo, 2007].
49


A summary of the results of the 2006 field ultrasonic testing, according to the
type of reflections observed, are categorized as follows:
9 of 36 (25%) of the ultrasonic scans contained only a single reflection at the
location of the end of the pin (referred to as far wall), as displayed by Figure 5.4.
The single reflections present in the ultrasonic scans indicate that there are not
boundary changes to the shape of the pin. No flaws could be definitively detected
in any of these pins.
ID>SL5 PEAK ii
Figure 5.4 Single Reflection Encountered during 2006 Field Testing.
Only a single reflection can be seen in the A-scan display of Pin SL5,
indicating that the boundary conditions of the pins are constant all of the
way to the far wall of the pin. [Mischo, 2007].
50


15 of 36 (42%) of the ultrasonic scans contained a secondary reflection ranging
from 2.5 to 3.5 inches (63.5 to 88.9 millimeters) from the far wall of the pin.
These supplemental reflections (referred to as secondary reflections) indicate that
the boundaries of the pins are changing near the ends of these pins. An
illustration of a secondary reflection encountered during 2006 field testing is
shown in Figure 5.5.
ID>NU? PEAK 23.00m
Figure 5.5 Secondary Reflection Encountered during 2006 Field Testing.
Multiple ultrasonic reflections can be seen in the A-scan display of Pin
NU7, indicating that the boundary conditions of the pins change near the
far wall of the pin. [Mischo, 2007].
51


6 of 36 (17%) of the ultrasonic scans contained a reflection in addition to a far
wall reflection or a secondary reflection, as displayed in Figure 5.6. The
unintended reflections found in the scan results indicate a possible flaw within
these pins, such as a corrosion crack between connection members or a void or
inclusion within the material.
ID>HL6 PEAK 26.50m
Figure 5.6 Possible Flaw Encountered during 2006 Field Testing.
The A-scan display for Pin NL6 shows a possible flaw in the pin at
approximately 8 inches (203.2 millimeters) from the near wall of the pin.
[Mischo, 2007],
52


12 of 36 (33%) of the railroad bridge pins did not have any visible reflections
within the ultrasonic scans, as shown in Figure 5.7. The absence of reflections in
the ultrasonic scan point to a connection problem between the transducer and
testing surface.
ID>NL2 PEAK 26,75m
Figure 5.7 Poor Ultrasonic Connection during 2006 Field Testing.
The A-scan display for Pin NL6 shows a possible flaw in the pin at
approximately 8 inches (203.2 millimeters) from the near wall of the pin.
[Mischo, 2007],
53


5.6 2006 Field Ultrasonic Testing Observations
From the 2006 field ultrasonic testing results, it was determine that there was
an inconsistency in the types of reflections recorded for the pins across the structure.
Results of the tests show that 10 of the 36 pins contained only a single reflection in
their displayed results, whereas 14 of the 36 pins contained secondary reflections in
their displayed results. For this reason, it is believed that the shapes of the pins may
be more complex than originally thought and contain changes in their diameter.
Ultrasonic scans from the 2006 field ultrasonic testing also show that there
was low signal amplitude recorded during many of the individual tests. This was
demonstrated by the fact that 12 of the 36 pins contained no visible signs of
reflections and could not be interpreted for the presence of flaws. The low signal
amplitude of the A-scans was most likely attributed to a poor connection between the
transducer and the testing surface of the pin. The petroleum jelly used as a coupling
medium had lost its viscosity and had become runny from the warm outside
temperatures during the tests. Surface irregularities on the ends of the pins prevented
the transducer from coming into good contact with the testing surface, and without
the required viscosity of the couplant, the ultrasonic signal could not be transmitted
into the pins effectively.
54


Results of the 2006 field ultrasonic testing demonstrated that the surface
conditions of the pins can have an effect on the recorded ultrasonic signal as well.
Because the testing surfaces of the pins were not fully smooth prior to testing, a
portion of the transmitted ultrasonic signal was reflected back to the transducer before
entering into the test material. As a result, a large signal reflection, referred to as near
field noise, was created at the beginning of the each of the A-scan displays. Near
field noise can influence the interpretation of reflections at the beginning of the
ultrasonic display, but does not have an effect on the transmission of the ultrasonic
signal through the test specimen.
5.7 2006 Field Ultrasonic Testing Conclusions
Following the 2006 field ultrasonic testing study, a more extensive
investigation of the bridge pins was necessary to fully understand the conditions of
the bridge pins. The single axial ultrasonic scans on the bridge pins yielded
inconsistent and uncertain results regarding the current shape and condition of the
pins. In order to better interpret the results, multiple measurements across the testing
surface of the pin needed to be performed to provide additional information about the
subsurface conditions of the pin and a more viscous couplant needed to be considered
to provide effective transmission of the ultrasonic signal.
55


5.8 2008 Field Ultrasonic Testing Approach
In 2008, a second series of ultrasonic testing was completed on 7 of the 36
railroad bridge pins. The purpose of the second series of ultrasonic tests was to gain
additional information which could be used to more accurately quantify the condition
of the pins. The 7 pins selected for ultrasonic testing were located on the lower
chords of the bridge in close proximity to the bridge supports. With the supervision
of a safety officer from the NPS, and with the assistance of climbing harnesses and
ladders, each of the pins was axially scanned using ultrasound.
Multiple axial ultrasonic scans were completed on one end of each of the
selected pins. Measurements of the tested pins were made using a tape measure to
verify the ultrasonic findings. Scans were taken around the perimeter of the pin, at
approximately the 3 o'clock, 6 oclock, 9 o'clock, and 12 oclock positions, as well as
at the center of the pins. A minimum of five ultrasonic scans were completed at each
of the pins tested. The purpose of completing multiple axial scans was to increase the
field of view which would be used to analyze the conditions of the pins. Figure 5.8
and Figure 5.9 illustrate the field of view concept with regards to ultrasonic
inspection. The figures depict the differences in the testing approach between the
2006 and 2008 field testing studies respectively.
56


Transducer
(AT ONE LOCATION ONLY)
Field of View
- Pin
+ -
! v Si /
/!
Pin Defect
END VIEW SIDE VIEW
SINGLE ULTRASONIC SCAN
Figure 5.8 Single Ultrasonic Scan Field of View.
Illustration of the field of view obtained when completing a single
ultrasonic scan on a test material. Note that the defect was missed when
only the single ultrasonic scan was completed.
Transducer
(at multiple locations)
Field of view -
-Pin
a \
id i++-1 ji
is \ t / T
a;-~~
V
x:
-t-;; =tf
'! at
r
/
Pin Defect-
END VIEW SIDE VIEW
MUL TIPLE UL TRASONIC SCANS
Figure 5.9 Multiple Ultrasonic Scans Field of View.
Illustration of the field of view obtained when completing multiple
ultrasonic scans on a test material. Note that more of the pin interior and
barrel can be observed when completing multiple ultrasonic scans.
For this series of tests, the pulse-echo technique and a straight-beam
transducer were used for consistency. The same material velocity as prescribed for
the 2006 ultrasonic tests was also used for consistency. Ambient temperatures at the
time of testing were conducive to using petroleum jelly as the coupling medium
57


between the transducer and the testing surfaces; therefore, it was used during testing.
Supplemental coupling mediums were on hand, if needed. No additional
reconditioning of the pins was performed prior to testing. The surface conditions of
the pins remaining from the preceding tests, with paint intact, were deemed to be
sufficient to perform the next set of ultrasonic tests without additional surface
preparation to the pins. All of ultrasonic data files recorded during the 2008 field
ultrasonic testing are presented in Appendix E.
5.9 2008 Field Ultrasonic Testing Results
Results of the pulse-echo ultrasonic tests completed on the bridge pins in 2008
are shown in Tables 5.5 through 5.11. The blacked out fields of the tables indicate
the types of results obtained for the individual pin that was tested. Similar to the field
ultrasonic testing presented earlier (refer to Table 5.4 on page 48) each of the pins are
referenced according to location on the bridge. In addition to pin location, each of the
pins is also referenced by the location at which the ultrasonic test was completed on
the end of the pin. Numbers (1-12) which follow the pin identification, designate the
position along the perimeter of the pin at which the ultrasonic scan was performed,
similar to the positions on the face of a clock. And, a letter C following the pin
identification designates an ultrasonic scan taken either at or toward the center of the
pin. For example, an ultrasonic test performed on Pin NL7 at the 6 oclock position
and also near the center, would be identified as Pin NL7 6C
58


Table 5.5 2008 Field ultrasonic testing results for Pin SL8.
Table 5.6 2008 Field ultrasonic testing results for Pin NL8.
Table 5.7 2008 Field Ultrasonic Testing Results for Pin SL7.
59


Table 5.8 2008 Field ultrasonic testing results for Pin NL7.
Table 5.9 2008 Field ultrasonic testing results for Pin SL6.
Table 5.10 2008 Field ultrasonic testing results for Pin SL0.
Pin ID Single Reflection Only Shoulder and Far End Reflection Possible Flaw Inconclusive Data
SL0 3
SL0 6
SL0 6C
SLO 9
SL0IOC
SLO 12
| SLO 12C
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Table 5.11 2008 Field ultrasonic testing results for Pin NLO.
Pin ID
Single
Reflection
Only
Shoulder
and Far End
Reflection
Possible
Flaw
Inconclusive
Data
A summary of the results of the 2008 field ultrasonic testing, according to the
type of reflections observed, are described below:
7 of 7 (100%) of the ultrasonic scans contained secondary reflections within the
A-scan display of the results The secondary reflection, indicate changes in the
boundary conditions in each of the pins at the observed locations. Depending
upon the position where the ultrasonic scan was performed, the secondary
reflections ranged from being heavily detectable in the A-scan display results to
only being slightly detectable. In general the most readily visible signs of
secondary reflections in the results occurred around the perimeter of the pins. An
illustration of secondary reflection encountered during 2008 field testing is shown
in Figure 5.9.
61


ID-3L? C
Figure 5.10 Secondary Reflection Encountered during 2008 Field Testing.
Multiple ultrasonic reflections can be seen in the A-scan display of Pin
SL7 C, indicating that the boundary conditions of the pins change near
the far wall of the pin. Note that the far wall reflection is stronger than
secondary reflection, indicating that more of the ultrasonic signal
encountered the far wall during testing.
3 of 7 (43%) of the ultrasonic scans contained reflections in addition to a far wall
reflection or a secondary reflection. These reflections indicate that a possible
flaw could exist within the pin. Figure 5.10 shows an example of a pin with a
possible flaw.
62



Figure 5.11 Possible Flaw Encountered during 2008 Field Testing.
The A-scan display for Pin SL8 3 shows a possible flaw in the pin at
approximately 1/3 of the length of the pin, measuring for the tested
surface.
5.10 2008 Field Ultrasonic Testing Observations
From the 2008 field ultrasonic testing results, it was observed that there was a
pattern in the recorded data regarding the boundary conditions of the pins. All of the
railroad bridge pins tested had secondary reflections within their display results which
were verifiable at multiple testing locations on each of the pins. Based on the
consistency that the secondary reflections were observed, it is highly likely that the
63


pins contain shoulders. Onsite measurements on one of the railroad bridge pins
completed in 2008 indicated that the pins on the bridge change from 3 inches
(76 millimeters) in diameter on the ends of the pins up to 3-1/2 inches
(88.9 millimeters) in diameter near the center of the pins. It is uncertain if the pins
are encased in sleeves at each of the connections, so the presence of shoulders on the
pins could not be definitely confirmed.
Ultrasonic scans from the 2008 field ultrasonic testing also show that the
coupling medium used to connect the transducer to the testing surfaces was effective
in producing a strong ultrasonic signal transmission. The weather conditions
encountered during 2008 testing caused the petroleum jelly to remain in its viscous
state, making it well-suited for use in ultrasonic testing against the rough surfaces of
the bridge pins. And, as a result of the good connection between the transducer and
the testing surfaces of the pins, moderate to high signal amplitude were recorded in
each of the individual ultrasonic tests. Having moderate or high signal amplitude for
the presentation of the results allowed for more distinct clear interpretations of the
A-scan displays.
Because no additional reconditioning was performed on the bridge pins prior
to field ultrasonic testing, the same amount of near field noise could be seen in the
A-scan display results for each of the individual tests. The viscosity of the petroleum
64


jelly coupling medium had little or no effect in reducing the presence of the near field
noise during 2008 field ultrasonic tests.
5.11 2008 Field Ultrasonic Testing Conclusions
From the 2008 field ultrasonic testing study, a more comprehensive
understanding of the railroad bridge pins was obtained. The multiple axial ultrasonic
scans performed on the pins provided additional information about the subsurface and
boundary conditions of the pins. And. the increased fields of view observed during
the tests were an effective measure in pinpointing surface conditions of the pins and
possible flaws. Results from the 2008 field ultrasonic testing helped to clarify
discrepancies surrounding the implied shape of the railroad bridge pins. The
consistency of the secondary reflections that were observed during testing, heavily
suggest that the pins change size toward the ends of the pins, and are not a single
diameter. From results of the 2008 field ultrasonic tests completed, it is interpreted
that all of the railroad bridge pins contain shoulders.
65


5.12 Comparison between 2006 and 2008 Field Ultrasonic Testing Results
In comparing the 2006 and 2008 ultrasonic studies completed, there were
discrepancies in the inteipretations of the types of results encountered for a number of
the railroad bridge pins. The increased fields of view observed for the railroad bridge
pins within the 2008 field ultrasonic study allowed for a more accurate evaluation the
7 pins tested, and, as a result, the pin interpretations from the 2008 field ultrasonic
study deviated from the results of the 2006 field ultrasonic study. Table 5.12 shows a
comparison of the observed results from both of the ultrasonic studies.
Table 5.12 Comparison of 2006 and 2008 field ultrasonic testing results.
Pin ID 2006 Field Ultrasonic Testing Results 2008 Field Ultrasonic Testing Results
SL8 Single Reflection Only Secondary Reflections with a Possible Flaw
NL8 Inconclusive Data Secondary Reflections
SL7 Inconclusive Data Secondary Reflections
NL7 Secondary Reflections Secondary Reflections
SL6 Single Reflection Only Secondary Reflections
SL0 Single Reflection Only Secondary Reflections
NL0 Secondary Reflections Secondary Reflections with a Possible Flaw
66


5.13 2008 Laboratory Control Testing
Following the completion of the field ultrasonic tests in 2008, a control
railroad bridge pin with a shoulder was fabricated and tested. The purpose of the test
was to evaluate the capacity of the Epoch III flaw detector to identify a shoulder on a
mock railroad bridge pin. Results from the laboratory control testing would be used
to provide evidence for the results of the 2006 and 2008 field ultrasonic studies. For
the laboratory test a bridge pin with a shoulder was fabricated using a 1-11/16-inch
(42.9 millimeter) diameter by 18-inch (457 millimeter) long steel rod. On one end of
the rod a shoulder was machined down to a diameter of 11/16-inch (17.5 millimeters)
at a distance of 1 -inch (25 millimeter) in from the end of the rod. An illustration of
the test pin with a machined shoulder is shown in Figure 5.11.
Figure 5.12 2008 Laboratory Test Pin.
67


Ultrasonic tests were completed on the test pin in attempt to verify the length
of the pin as well as to detect the machined shoulder of the pin. Petroleum jelly
couplant, a straight-beam transducer, and the pulse-echo method of testing were used
to take axial ultrasonic scans on the end of the pin, opposite the machined shoulder.
Scans were performed at three locations at the end of the test pin between the center
and the perimeter of the pin. See Figure 5.12 for an illustration a laboratory test
completed in 2008. A complete listing of all of the data files and photographs
recorded during the 2008 laboratory control testing procedure are presented in
Appendix F.
Figure 5.13 2008 Laboratory Testing on Sample Pin.
68


5.14 2008 Laboratory Control Testing Results
A summary of results obtained from the 2008 laboratory control tests are
presented in Table 5.13.
Table 5.13 2008 Laboratory ultrasonic testing results.
Location of Ultrasonic Scan Results
Center of Pin Weak Indication of Pin Shoulder.
Midway Between Pin Center and Pin Perimeter Moderate Indication of Pin Shoulder.
Perimeter of Pin Strong Indication of Pin Shoulder.
Results from the laboratory testing of a sample pin with a machined shoulder
indicated that the shoulder at the far end of the pin could be observed at all scanned
locations opposite from the shoulder. The strength of the ultrasonic reflections
obtained at the location of the pin shoulder were directly proportional to the amount
of surface area of the pin shoulder in front of the transducer at the time of testing. For
this reason, ultrasonic scans completed on the test pin, at the perimeter of the pin,
yielded stronger reflections from the pin shoulder when compared to ultrasonic scans
completed on the test pin, at the center of the pin. The results of the 2008 laboratory
tests reinforces the argument that secondary reflections observed in the field testing
results are shoulders on the pins.
69


5.15 Combined Field Ultrasonic Testing Results
Combined results of the pulse-echo ultrasonic tests completed on the bridge
pins in 2006 and 2008 are shown in Table 5.14. The table represents an interpretation
of the 2006 and 2008 ultrasound testing results. Information gathered about the pins
from the 2008 tests was used to reevaluating the ultrasonic scans of the pins
completed in 2006 and to definitively asses the conditions of the pins.
70


Table 5.14 Combined field ultrasonic testing results.
Types of reflections observed from the 2006 [adapted from Mischo,
2007] and 2008 ultrasonic tests completed on the pins of the Cimarron
Railroad Bridge.
Pin ID Far End Reflection Only Shoulder Reflection Only Shoulder and Far End Reflection Possible Flaw Inconclusive Data
SL8
NL8
SL7
NL7
SL6
NL6
SL5
NL5
SL4
NL4
SL3
NL3
SL2
NL2
SL1
NL1
SLO
NLO 1
SU8
NU8 mmmm
SU7
NU7
SU6
NU6
SU5
NU5
SU4
NU4
SU3
NU3
SU2
NU2 i i
SUl
NU1
SUO
NU0
71


A summary of the results of the ultrasonic testing, according to the type of
reflections observed, are described as follows:
6 of 36 (17%) of the ultrasonic scans contained only a single reflection at a
location indicative of either a pin shoulder or far wall. No flaw could be
definitively detected in any of these ultrasonic scans.
26 of 36 (72%) of the bridge truss pins presented additional information
regarding hidden pin dimensions. Multiple reflections in the results indicate the
presence of shoulders on the pins at a distance of 2.5 to 3.5 inches (63.5 to 88.9
millimeters) from the far wall of those pins.
5 of 36 (14%) of the ultrasonic scans on the bridge pins contained reflections (in
addition to shoulder and/or far wall reflections). These reflections could indicate
a possible flaw within these pins. Likely scenarios for these reflections include
corrosion around the pin, cracks in the pins due to high shearing stresses, voids or
inclusions within the pins, or wear grooves forming across the barrels of the
bridge pins.
4 of 36 (11%) of the bridge pins did not have any visible reflections within the
ultrasonic scans. The absence of reflections in the ultrasonic scans point to a
connection problem between the transducer and testing surface.
72


5.16 Problems Interpreting Ultrasonic Test Results
Accurate interpretations of the ultrasonic testing results during the 2006 and
2008 ultrasonic testing studies performed on the Cimarron Railroad Bridge were
hindered for the following reasons:
The irregular surface conditions of the pins during both series of tests created near
field noise at the beginning of each of the A-scan displays which could not be
analyzed for the presence of flaws
Thin couplant used during the first series of ultrasonic tests was difficult to work
with and conducted ultrasound poorly. This contributed to difficulty interpreting
the A-scan display results from the field ultrasonic tests completed in 2006.
The single scan ultrasonic tests that were completed in 2006 could only be
interpreted for the presence of flaws within the limitations of the single scan field
of view. Potential flaws outside of the single scan field of view could not be
detected.
The exact shapes of the pins were unknown. Onsite measurements of the pins and
A-scan display results point toward the existence of shoulders on the pins, but the
presence of shoulders could not be definitively confirmed on all of the pins.
73


5.17 Recommendations for Improving Ultrasonic Testing
Based on lessons learned from the 2006 and 2008 series of ultrasonic tests
performed the following list of recommendations was made in order to improve
ultrasonic tests on bridge pins performed in the future:
Thoroughly recondition of the end surface of the pins prior to testing. A smoother
end surfaces will reduce the amount of near-field noise displayed in A-scan
results.
Complete ultrasonic tests on the far sides of the bridge pins as well as on the near
sides. Additional ultrasonic tests on the far sides of the pins will help to confirm
potential flaws and reduce uncertainties in the results.
Use a couplant with a viscosity appropriate for the surface conditions of the tested
material. A viscous couplant should be used for rougher surface conditions
because it will fill in voids between the transducer and testing material better than
thin couplant.
Take multiple ultrasonic scans from different locations around the surface of the
pin to increase the field of view of the testing results.
74


6.
Structural Analysis
6.1 Structural Analysis Modeling using STAAD
Structural Analysis modeling of the Cimarron Railroad Bridge was completed
using the STAAD.Pro 2007 structural analysis software. Modeling of the bridge was
completed to determine the loading and response relationship between the train
components and the bridge, as well as the effects of live, wind and snow loads on the
bridge. In addition, the model was created to determine the effects to the bridge in
the event that cracked lower chord end bay member fails. Combined stresses (axial
and moment) from the model for each of the loading conditions were used to evaluate
the current structural condition of the bridge.
6.2 STAAD Model Layout
A 3-dimensional finite element model (FEM) comprising isotropic beam
elements was used to simulate the laterally braced, pin-connected, Pratt truss railroad
bridge. Using the photographs taken onsite (presented in Appendix A), and as-built
drawings of the bridge superstructure (presented in Appendix B), the required
dimensions and connection details for the bridge were interpreted and applied to the
structural model. Standard American structural steel shapes and bars were used in the
model to represent the wrought iron structural members of the bridge. Material
75


properties of wrought iron, including a yield strength of 25 kips per square inch (172
megapascals) were used to characterize the strength of the structural members
[Hatfield, 2001]. Pinned and roller structural supports were applied to the model,
similar to the supports seen in the field, and element member releases were created in
the model to simulate the pinned connections of the bridge. A cracked member with
reduced cross sectional area was applied to the FEM at the location of the end bay
lower chord member that was witnessed to be cracked in the field. The overall
dimensions of the model as measured between nodes within the model are 119 feet
and 4 inches (36.4 meters) for the span, 12 feet and 0 inches (3.7 meters) for the
width, and 19 feet and 6 inches (5.9 meters) the height. A visual representation of
railroad bridge model created using STAAD is shown in Figure 6.1. The entire
STAAD input file used to define the FEM is presented in Appendix G.
76


6.3 ST A AD Model Loads
Prior to completing any structural analysis on the railroad bridge, all of the
loads applied to the bridge needed to be estimated for the FEM. Based on the
environment of the bridge, it was determined that dead load, live load, snow load, and
a wind loads act on the bridge. The procedures for calculating and applying loads to
the FEM are described for each of the load scenarios.
The dead load (D) loading condition of the railroad bridge consisted of three
components. The weight of the wrought iron structural members, the weight of the 6
inch by 8 inch (15 centimeter by 20 centimeter) wood railroad ties, and the weight of
the railroad tracks. Weights for the wrought iron structural members did not need to
be calculated for the FEM. A gravity load command was used within the model to
account for the self weights of each of the structural elements. The weights of the
timber ties on top of the bridge were estimated to be 10 pounds per foot (146 newtons
per meter), and were distributed according to tributary width to the upper chord
members of the bridge and the top main load bearing members (S sections) of the
bridge. The weights of the railroad tracks across the bridge were estimated to weigh
60 pounds per yard (292 newtons per meter), and were applied to the model across
the top main load bearing members (S sections) of the bridge. The dead load loading
condition D applied to the model is illustrated in Figure 6.2.
77


Figure 6.2 Dead Load D Applied to the STAAD Model.
Dead loads of the model account for the weight of the wrought iron
structural elements, the weight of wooden ties, and the weight of wrought
iron track.
Multiple live load scenarios were added to the FEM to simulate the forces of
the train cars acting on the bridge. The first live load (LI) loading condition of the
railroad bridge corresponded to the weights of all of the train cars acting on the bridge
at their present day locations on the structure. The weights of both the train
locomotive and the tender were pulled from an information drawing, L-70, which was
created by the D&RG Western R.R and is presented in Appendix B. The weight of
the locomotive, listed at 69,110 pounds (307,417 newtons), was distributed according
to mass between its 10 wheels and applied to the top main load bearing members
(S sections) at the location of the locomotive. The weight of the tender, calculated to
be 20,175 pounds (89,743 newtons) when unloaded of coal and water, was distributed
78


evenly between its 8 wheels and applied to the top main load bearing members at the
location of the tender. The weight of the boxcar was taken to be the printed weight
on the side of the boxcar, as showrn in Figure 6.3.
Figure 6.3 Dimensions and Weight of Boxcar #3132.
Production dimensions, weight, and capacity stenciled on the side of the
boxcar.
The listed weight of the boxcar. 22,700 pounds (100,975 newtons), w-as distributed
evenly between its 8 wheels and applied to the top main load bearing members at the
location of the box car on the bridge. The weight of the caboose was also taken to be
the printed weight on the side of the car, as shown in Figure 6.4.
79


Figure 6.4 Weight of Caboose #0577.
Production weight stenciled on the side of the caboose.
The listed weight of the caboose, 18,900 pounds (84,071 newtons), was distributed
evenly between its 8 wheels and applied to the top main load bearing members at the
location of the caboose on the bridge. An illustration of the forces from the live load
loading condition LI applied to the model is illustrated in Figure 6.5.
80


Figure 6.5 Live Load LI Applied to the STAAD Model.
Live loads of the model account for the weight of the locomotive, tender,
boxcar, and caboose.
The second live load (L2) loading condition of the railroad bridge
corresponded to a scenario in which the locomotive would be detached from the rest
of the train and pulled off of the bridge. For this loading condition the weights of all
of the train cars acting on the bridge were again applied to the model. In addition,
longitudinal static friction forces were applied to the model to simulate the affects
pulling on the locomotive with its wheels locked in place. A static friction coefficient
of 0.7 was used to calculate the friction forces between the locomotive wheels and
railroad track [Sullivan, 1988]. Since it is unknown if the locomotive will roll if
pulled, it was conservative to apply these friction forces to the FEM for this loading
condition. Figure 6.6 shows the forces from the live load loading condition L2
applied to the model.
81