Citation
Column action buckling of conventionally sheathed stud walls

Material Information

Title:
Column action buckling of conventionally sheathed stud walls
Creator:
Marxhausen, Peter
Publication Date:
Language:
English
Physical Description:
xiii, 154 leaves : ; 28 cm

Subjects

Subjects / Keywords:
Walls ( lcsh )
Buckling (Mechanics) ( lcsh )
Sheathing (Building materials) ( lcsh )
Buckling (Mechanics) ( fast )
Sheathing (Building materials) ( fast )
Walls ( fast )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 152-154).
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Peter Marxhausen.

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:
57662378 ( OCLC )
ocm57662378
Classification:
LD1190.E53 2004m M37 ( lcc )

Full Text
COLUMN ACTION BUCKLING OF CONVENTIONALLY
SHEATHED STUD WALLS
by
Peter Marxhausen
B.S. Colorado State University
A thesis submitted to the
University of Colorado at Denver
in partial fulfillment
of the requirements for the degree of
Masters of Science
Civil Engineering
2004


Marxhausen, Peter Dietrich (M.S., Civil Engineering)
Column Action Buckling Of Conventionally Sheathed Stud Walls
Thesis directed by Associate Professor Judith Stalnaker
ABSTRACT
Sheathing materials such as plywood, oriented strand board (OSB), drywall, and
fiberboard are commonly attached to one or both sides of load-bearing stud walls in
residential and commercial construction. There is no consensus among structural
engineering professionals as to which of these sheathing materials provides
protection against weak-axis buckling of the load-bearing wood studs. Plywood is
generally accepted as providing the necessary bracing, but codes do not specifically
state which of the other sheathing materials are acceptable for bracing studs against
compression buckling.
This study involves testing of 8 feet tall by 4 feet wide stud wall specimens
sheathed with OSB both sides, OSB one side, drywall one side, diywall both sides,
Thermo-Ply one side, fiberboard one side, and no sheathing. The allowable load
according to the wood specification for a braced wall specimen is 9.55 kips. Each
one of the specimens failed at more than 2.9 times the allowable load; i.e., each
sheathing material provided a factor of safety of at least 2.9 against weak axis
buckling. Therefore, each of the materials, when properly attached, was capable of
resisting weak axis stud buckling. Specimens with drywall on one or both sides had
a higher ultimate load than specimens with oriented strand board on one side. The
drywall specimens also exhibited ductility as crushing of the wood plate occurred.
This abstract accurately represents the content of the candidates thesis. I
recommend its publication.
Signed___
Ju
m


CONTENTS
Figures..............................................................viii
Tables...............................................................xiv
Chapter
1. Introduction......................................................1
2. Analysis of Existing Structures...................................5
2.1 Sylvestor Place (1995)............................................7
2.2 Ridgeglen Way (1985).............................................12
2.3 West Hampden Place (1976)....................................... 17
2.4 East 6th Avenue (1937)...........................................22
2.5 South Prince Street (1890).......................................26
3. Experimental Testing............................................ 30
3.1 T esting Machine................................................ 31
3.2 Load T ransfer Apparatus.........................................34
3.3 Testing Specimens............................................... 42
3.3.1 Timber...........................................................42
3.3.2 Sheathing Materials..............................................44
IV


3.3.2.1 Gypsum............................................................44
3.3.2.2 Oriented Strand Board............................................ 46
3.3.2.3 Thermo-Ply........................................................47
3.3.2.4 Fiberboard...................................................... 49
3.3.3 Fasteners..........................................................50
3.3.4 Attachments........................................................52
3.3.4.1 Stud to Plate.....................................................52
3.3.4.2 Gypsum to Studs...................................................52
3.3.4.3 Oriented Strand Board to Studs....................................56
3.3.4.4 Thermo-Ply to Studs...............................................57
3.3.4.5 Fiberboard to Studs...............................................58
3.3.4.6 No Sheathing......................................................58
3.4 Analysis Calculations..............................................59
3.5 F astener Strength.................................................65
4. T esting Results............'.....................................66
4.1 Data............................................................. 66
4.2 Photographs........................................................81
4.3 Photograph Index/Narration........................................100
5. Discussion........................................................112
5.1 Factor of Safety Against Buckling.................................112
5.2 Expected Performance of Various Sheathing Materials...............114
v


5.3 Performance of Fasteners
120
5.4 Recommended Further Studies..................................121
5.5 Conclusion.............;.....................................122
Appendix
A. Masters Thesis Proposal......................................124
B. Testing Schedule Proposal....................................130
C. Memorandum of Understanding..................................133
D. Laboratory Testing Receipt...................................136
E. Summary of Hours, Miles, and Costs...........................137
F. ER-1439 Thermo-Ply...........................................138
G. ER-5905 Oriented Strand Board................................140
H. ER-1874 Gypsum Board.........................................147
References.........................................................152
vi


FIGURES
Figure
2.1- Study Home No. 1 Framing Plan.............................10
2.2 - Front of Home.............................................11
2.3 - Rear of Home..............................................11
2.4 - Study Home No. 2 Framing Plan.............................15
2.5 - Front of Home.............................................16
2.6 - Rear of Home..............................................16
2.7 - Study Home No. 3 Framing Plan.............................20
2.8 - Front of Home.............................................21
2.9 - Rear of Home..............................................21
2.10 Study Home No. 4 Framing Plan............................24
2.11 Front of Home............................................25
2.12 Rear of Home.............................................25
2.13 - Study Home No. 5 Framing Plan............................28
2.14 Front of Home............................................29
2.15 Rear of Home.............................................29
3.1- MTS 907.57.................................................33
vii


3.2 - MTS Base
3.3- MTS Top Head..............................................33
3.4- MTS Controller............................................33
3.5 Elevation of the Load Transfer Apparatus..................39
3.6 - Section of the Load Transfer Apparatus....................40
3.7 Elevation of the Testing Set-Up...........................41
3.8 - 16d Common Nail...........................................51
3.9 - 8d Common Nail............................................51
3.10 - Roofing Nail.............................................51
3.11-Wallboard Screw............................................51
4.1- Average Ultimate Load.....................................70
4.2 - Gross Youngs Modulus.....................................71
4.3 - Average Ultimate Strain...................................72
4.4 - Load vs. Displacement: OSB, Drywall, and No Sheathing.....73
4.5 - Load vs. Displacement: Specimen Type 1....................74
4.6 - Load vs. Displacement: Specimen Type 2....................75
4.7 - Load vs. Displacement: Specimen Type 3....................76
4.8 - Load vs. Displacement: Specimen Type 4....................77
4.9 - Load vs. Displacement: Specimen Type 5....................78
4.10 - Load vs. Displacement: Specimen Type 6...................79
4.11 - Load vs. Displacement: Specimen Type 7...................80
vm


4.12- 1A (1).............................................82
4.13- 1A (2).............................................82
4.14- 1A (3).............................................82
4.15- IB (1)........'....................................82
4.16- IB (2).............................................83
4.17- 1C (1).............................................83
4.18- 1C (2).............................................83
4.19- 1C (3).............................................83
4.20 -2A(1)..............................................84
4.21- 2A (2).............................................84
4.22- 2A (3).............................................84
4.23- 2A (4).............................................84
4.24- 2B(1)..............................................85
4.25- 2B (2).............................................85
4.26- 2C(1)..............................................85
4.27- 2C (2).............................................85
4.28- 2C (3).............................................86
4.29- 2C (4).............................................86
4.30 -3A(1)............................................. 86
4.31- 3A (2).............................................86
4.32- 3A (3).............................................87
IX


87
4.33 3A (4)
4.34- 3A (5).............................................87
4.35- 3A (6).............................................87
4.36 -3B(1)...............................................88
4.37- 3B (2).............................................88
4.38- 3B (3).............................................88
4.39- 3B (4).............................................88
4.40 -3C(1)...............................................89
4.41- 3C (2).............................................89
4.42- 3C (3).............................................89
4.43 -3C (4)..............................................89
4.44- 3D (1).............................................90
4.45- 3D (2).............................................90
4.46- 3D (3).............................................90
4.47- 3D (4).............................................90
4.48- 3D (5).............................................91
4.49- 3D (6).............................................91
4.50- 4A(1)..............................................91
4.51- 4A (2).............................................91
4.52- 4A (3).............................................92
4.53 -4B(1)...............................................92
x


92
4.54- 4B (2)
4.55- 4C(1)...............................................92
4.56 -4C (2)...............................................93
4.57 -4C (3)...............................................93
4.58 -4C (4)...............................................93
4.59-5A(1).................................................93
4.60 5A (2)..............................................94
4.61-5A (3)................................................94
4.62 - 5A (4)..............................................94
4.63 -5B(1)................................................94
4.64-5B (2)................................................95
4.65 5B (3)..............................................95
4.66- 5C(1)...............................................95
4.67- 5C (2)..............................................95
4.68- 5C (3)..............................................96
4.69 5C (4)..............................................96
4.70-6A(1).................................................96
4.71 6A (2)..............................................96
4.72-6B(1).................................................97
4.73 - 6B (2)..............................................97
4.74 -6C(1)................................................97
xi


4.75 - 6C (2)...............................................97
4.76- 7A(1)................................................98
4.77- 7A (2)...............................................98
4.78- 7A (3)...............................................98
4.79- 7B(1)................................................98
4.80- 7B (2)...............................................99
4.81 -7C(1).................................................99
4.82- 7C (2)...............................................99
4.83- 7C (3)...............................................99
5.1 Gypsum Behavior......................................117
5.2 - OSB Behavior.........................................118
xii


TABLES
Tables
4.1- Testing Results Summary.....................................69
5.1- Average Ultimate Load and Factor of Safety..................113
5.2 - Anticipated and Actual Performance Rank.....................114
xm


1.
Introduction
Timber has established itself as the material of choice for single family construction,
multifamily residential construction three stories and less, small commercial
construction and manufactured housing. Load-bearing walls are typically comprised
of 2-inch nominal columns, called studs, spaced at 12 to 24 inches on center. The
axial load-bearing capacity of these studs is a function of anticipated load duration,
service moisture conditions, service temperatures, and stability against buckling.
Studs used for conventional framing are traditionally 2x4 (2 nominal inches deep and
4 nominal inches wide) or 2x6 (2 nominal inches deep and 6 nominal inches wide).
All methods used for column buckling analysis are dependent on determination of
the weak axis, which will control the calculated buckling load. Relatively short,
relatively strong, or heavily braced columns will not buckle, rather they will crush at
their material compressive strength load. Timber wall framing, unless used as a
trimmer, knee wall, or cripple wall, is generally tall enough that Euler buckling
action controls the allowable design load. Fully unbraced 2x4 or 2x6 studs will
buckle in the weak (2-inch nominal) direction. If the studs are adequately sheathed
or braced along their weak axis, buckling will occur in the strong (4-inch nominal)
1


direction. If the studs are adequately braced along both axes, short column action
and a crushing failure is anticipated.
From personal contacts in the practice of engineering and graduate work, the author
has encountered a wide range of opinions regarding what is required to brace studs
against both lateral torsional and column action compression buckling. Some
opinions encountered are as follows:
Only plywood or oriented strand board can brace columns in the weak
direction drywall is like having nothing at all.
Drywall is adequate to brace columns in the weak direction.
Without knowing what is required by code to brace studs, assuming drywall
is acceptable but Thermo-Ply is not seems reasonable.
Sheathing needs to be applied to both sides to consider a stud braced in the
weak direction.
Sheathing needs to be applied to only one side of studs to consider the stud
braced in the weak direction.
If plywood or oriented strand board is applied to both faces and adequately
fastened, composite action occurs and the stud can be considered short and
crushing will occur prior to buckling.
2


Fastener failure will occur before strong axis buckling can occur and the stud
will consistently fail in the weak direction.
Thermo-Ply is adequate to brace studs in the weak direction but fiberboard is
not.
Fiberboard is adequate to brace studs in the weak direction but Thermo-Ply is
not.
Opinions regarding bracing requirements vary from material to material, fastening
method to fastening method. Preliminary investigations, including code research and
phone conversations with the American Wood Council, did not generate any
complete documentation as to what is required or standard practice to brace studs
against compression buckling. Preliminary calculations indicate the design capacity
of a single stud can vary nearly 1,000% dependent upon assumptions made whether
a stud is completely unbraced or plywood both sides would sufficiently brace a
column to justify the short column assumption using the full Fc value of the wood.
This study investigated the effects of various lateral bracing on the capacity of axial
loaded stud walls. The study included full scale, destructive testing of 8 feet tall by 4
feet wide, 2x4 stud walls with studs spaced at 16 inches on center. The stud walls
were tested with various sheathing materials used in modem residential and
commercial construction. This study also investigated the framing of five residential
3


structures constructed in various decades to evaluate the design assumptions of past
engineers and home builders.
4


2. Analysis of Existing Structures
Five existing residential structures were studied to accurately evaluate the use of
conventional sheathing used historically to brace stud walls against buckling. The
residential structures studied were all constructed utilizing 2x4 studs at 16 inches on
center for the load-bearing walls. The residences were all constructed within the last
115 years using conventional framing methods. All five homes are within the Metro
Denver area and were either newly constructed or subjected to significant remodels
or renovations between 1994 and 2003 such that the 1997 and newer Uniform
Building Code (UBC, 1997) loading provisions are appropriate.
The analysis of each homes load path is on the following pages and is followed by a
roof framing plan with dimensions and two photographs taken of the home. The
homes highlight cases where bracing other than oriented strand board or plywood
was used to brace the studs in the weak direction. The applied load per stud,
calculated by the Uniform Building Code (UBC, 1997) requirements, in various stud
walls in these homes ranges from 503 to 1629 pounds per stud. For studs not
properly braced in the weak direction, the allowable load per stud is 484 pounds
based on the National Design Specification (NDS, 2001) requirements. In each of
the homes investigated, the applied load per stud exceeds the allowable load of 484
5


pounds. This finding illustrates that sheathing materials such as fiberboard and
drywall are being used by engineers and/or contractors as elements that can supply
protection against weak-axis buckling, although no code could be found that states
that these elements can be used for this purpose.
6


2.1 Sylvestor Place (1995)
The house at 54 Sylvestor Place was constructed in 1995 in Douglas County by
David Weekley Homes. The author purchased this home in 2002 after initially
encountering the home through a clients requested inspection.
Code Required Loading = 30 psf snow load
40 psf floor live load
10 psf wall dead load
12 psf roof dead load
12 psf floor dead load
In framing region one (Shown in Figure 2.1) the first floor interior load-bearing wall
supports the second floor framing, first floor mono trusses, second floor wall, and
second story trusses. This 9-foot tall load-bearing 2x4 stud wall is braced in the
weak direction with /2-inch drywall applied to both faces. The studs are spaced at 16
inches on center. The linear load on this wall can be calculated as follows:
2nd floor trusses = ((23-3 truss span / 2) + 12 eave) x (30 psf SL + 12psf DL)
= 530.25 plf
1st floor trusses (15-8 truss span / 2) x (30 psf SL + 12psf DL)_ 329 plf
2nd floor framing = (12-0 joist span / 2) x (40 psf SL + 12 psf DL) = 252 plf
7


2nd floor wall = 9-0 height x 10 psfDL = 90 plf
Wall linear load=2nd floor trusses +lst floor trusses +2nd floor framing + 2nd floor wall
= 530.25 plf + 329 plf + 252 plf + 90 plf
- 1,201.25 plf
Stud load = Wall linear load x stud spacing
- 1,201.25 x (16/(12/ft))
= 1,602 pounds per stud
A wall in region 2 is braced with Thermo-Ply. For this wall, The first floor exterior
load-bearing wall supports the second floor framing, second floor exterior wall and
second story mono/hip trusses. This 9-foot tall load-bearing 2x4 stud wall in the
garage is braced in the weak direction with structural grade Thermo-Ply on the
exterior face only with no finish on the interior. The studs are spaced at 16 inches on
center. The linear load on this wall can be calculated as follows:
2nd floor trusses = ((10-0 truss span / 2) + 12 eave) x (30 psf SL + 12 psfDL)
= 252plf
8


2nd floor framing = (1 -4 joist spacing / 2) x (40 psf SL + 12 psf DL)
= 35 plf
2nd floor wall = 9-0 height x 10 psf DL = 90 plf
Wall linear load = 2nd floor trusses + 2nd floor framing + 2nd floor wall
= 252 plf + 35 plf + 90 plf
= 377 plf
Stud load = Wall linear load x stud spacing
- 377 x (16 /(127ft))
= 503 pounds per stud
9


STUDY HOME #1
ADDRESS: SYLVESTOR PLACE, DOUGLAS COUNTY
YEAR BUILT: 1995
SIZE: 2293 SF
BRACING: THERMO-PLY & DRYWALL
O 5 10 20 30'
ONE AND TWO STORY
44*3"
Figure 2.1- Study Home No. 1 Framing Plan
10


Figure 2.3 Rear of Home
11


2.2 Ridgeglen Way (1985)
The house at 474 Ridgeglen Way was constructed in 1986 in Douglas County by
Mission Viejo. The author of this paper purchased the home in 2000.
Code Required Loading = 30 psf snow load
40 psf floor live load
10 psf wall dead load
12 psf roof dead load
12 psf floor dead load
In framing region one (Shown in Figure 2.4) The first floor interior load-bearing wall
supports the second floor framing. This 8-foot tall load-bearing 2x4 stud wall is
braced in the weak direction with 5/8-inch drywall on the garage face and 14-inch
drywall on the interior face. The studs are spaced at 16 inches on center. The linear
load on this wall can be calculated as follows:
2nd floor framing = (32-0 total joist span / 2) x (40 psf SL + 12 psf DL) = 832 plf
Wall linear load = 2nd floor framing
= 832 plf
12


Stud load = Wall linear load x stud spacing
= 832 x (16/(127ft))
= 1,109 pounds per stud
In framing region two the first floor exterior load-bearing wall supports the second
floor framing, second floor exterior wall and second story trusses. This 8-foot tall
load-bearing 2x4 stud wall in the garage is braced in the weak direction with
structural grade Thermo-Ply type sheathing on the exterior face only with no finish
on the interior. The studs are spaced at 16 inches on center. The linear load on this
wall can be calculated as follows:
2nd floor trusses = ((23-0 truss span / 2) + 12 eave) x (30 psf SL + 12 psf DL)
= 525 plf
2nd floor framing = (l-4 joist spacing / 2) x (40 psf SL + 12 psf DL) = 35 plf
2nd floor wall = 9-0 height x 10 psf DL = 90 plf
Wall linear load = 2nd floor trusses + 2nd floor framing + 2nd floor wall
= 525 plf + 35 plf + 90 plf
= 650 plf
13


Stud load = Wall linear load x stud spacing
= 650 x (16 / (127ft))
= 867 pounds per stud
14


STUDY HOME #2
ADDRESS: R1DGEGLEN WAY, DOUGLAS COUNTY
YEAR BUILT: 1986
SIZE: 1581 SF
BRACING: THERMO-PLY Sc DRYWALL
O 5' 10' 20 30'
Figure 2.4 Study Home No.2 Framing Plan
15


Figure 2.5 Front of Home
Figure 2.6 Rear of Home
16


2.3 West Hampden Place (1976)
The house at 11452 West Hampden Place was constructed in 1976 in Jefferson
County. The author encountered the home through a significant remodel in 2002
where the habitable space was nearly doubled.
Code Required Loading = 30 psf snow load
40 psf floor live load
10 psf wall dead load
12 psf roof dead load
12 psf floor dead load
In framing region one (Shown in Figure 2.7) the first floor interior load-bearing wall
supports the second floor framing. This 8-foot tall load-bearing 2x4 stud wall is
braced in the weak direction with /2-inch drywall applied to both faces. The studs
are spaced at 16 inches on center. The linear load on this wall can be calculated as
follows:
2nd floor framing = (27-0 joist span / 2) x (40 psf SL + 12 psf DL) = 702 plf
Wall linear load = 2nd floor framing
= 702 plf
17


Stud load = Wall linear load x stud spacing
= 702 x (16 / (127ft))
= 936 pounds per stud
In framing region two the first floor exterior load-bearing wall supports the second
floor framing, second floor exterior wall and second story trusses. This 8-foot tall
load-bearing 2x4 stud wall is braced in the weak direction with fiberboard on the
exterior face and drywall on the interior face. No drywall was present in the storage
room and rear of garage. The studs are spaced at 16 inches on center. The linear load
on this wall can be calculated as follows:
2nd floor trusses = ((27-0 truss span / 2) + 12 eave ) x (30 psf SL + 12 psf DL)
= 609 plf
2nd floor framing = (13-6 joist span / 2) x (40 psf SL + 12 psf DL) = 351 plf
2nd floor wall = 8-0 height x 10 psf DL = 80 plf
Wall linear load = 2nd floor trusses + 2nd floor framing + 2nd floor wall
= 609 plf+351 plf + 80 plf
= 1,040 plf
18


Stud load = Wall linear load x stud spacing
= 1,040 x( 16/(127ft))
= 1,387 pounds per stud
19


STUDY HOME #3
ADDRESS: W. HAMPDEN PLACE, JEFFERSON COUNTY
YEAR BUILT: 1976
SIZE: 2447 SF
BRACING: FIBERBOARD & DRYWALL
O 5 10' 20' 30'
Figure 2.7 Study Home No.3 Framing Plan
20


Figure 2.9 Rear of Home
21


2.4 East 6th Avenue (1937)
The house at 6375 East 6th Avenue was constructed in 1937 in Denver County. The
author encountered the home through a minor remodel in 2002 where the garage was
expanded and the kitchen was remodeled.
Code Required Loading = 30 psf snow load
40 psf floor live load
10 psf wall dead load
12 psf roof dead load
12 psf floor dead load
In framing region one (Shown in Figure 2.10) the first floor interior load-bearing
wall supports the second floor framing and second story rafter framing. This 9-foot
tall load-bearing 2x4 stud wall is braced in the weak direction with Vi-inch drywall
applied to both faces. The studs are spaced at 16 inches on center. In 1937 it is
likely that the finish was lath and plaster on the walls. The remodel investigation
found that a significant length of the wall had gypsum wallboard installed at an
unknown date for an unknown reason. The linear load on this wall can be calculated
as follows:
22


2nd floor rafters = (26-0 truss span / 2) x (30 psf SL + 12 psf DL) = 546 plf
2nd floor framing = (26-0 joist span / 2) x (40 psf SL + 12 psf DL) = 676 plf
Wall linear load = 2nd floor rafters + 2nd floor framing
= 546 plf + 676 plf
= 1,222 plf
Stud load = Wall linear load x stud spacing
= 1,222 x (16 /(127ft))
=1,629 pounds per stud
23


Figure 2.10 Study Home No.4 Framing Plan
24


Figure 2.11 Front of Home
25


2.5 South Prince Street (1890)
The house at 5493 South Prince Street was constructed in 1890 reportedly in
Jefferson County. In the mid-1900s the home was relocated to the South Santa Fe
corridor in Arapahoe County. Due to the reported Light Rail expansion along the
Santa Fe corridor the home was relocated to South Prince Street in downtown
Littleton. The author was involved with the most recent foundation design and the
addition to the sides and rear.
Code Required Loading = 30 psf snow load
40 psf floor live load
10 psf wall dead load
12 psf roof dead load
12 psf floor dead load
In framing region one (Shown in Figure 2.13) the first floor exterior load-bearing
wall supports the second floor framing, second floor exterior wall, and second stoiy
rafters. This 9-foot tall load-bearing 2x4 stud wall is braced in the weak direction
with Vi-inch drywall applied to the inside face and dimensional siding on the
exterior. The studs are spaced at 16 inches on center. In 1890 it is likely that the
finish was lath and plaster on the walls. The remodel investigation found that some
26


portions of the wall had gypsum wallboard installed at an unknown date for an
unknown reason. The linear load on this wall can be calculated as follows:
2nd floor rafters = ((20-6 truss span / 2) + 12 eave) x (30 psf SL+12 psf DL)
= 472.5 plf
2nd floor framing = (10-3 joist span / 2) x (40 psf SL + 12 psf DL) = 266.5 plf
2nd floor wall = 4-0 height x 10 psf DL = 40 plf
Wall linear load = 2nd floor rafters + 2nd floor framing + 2nd floor wall
=472.5 plf + 266.5 plf + 40 plf
=779 plf
Stud load = Wall linear load x stud spacing
= 779 plf x (16 / (12/ft))
=1,039 pounds per stud
27


STUDY HOME #5
ADDRESS: S. PRINCE STREET, ARAPAHOE COUNTY
YEAR BUILT: 1890
SIZE: 1262 SF
BRACING: DRYWALL/PLASTER
0 5 10 20 30
TWO STORY
Figure 2.13 Study Home No.5 Framing Plan
28


Figure 2.14 Front of Home
Figure 2.15 Rear of Home
29


3. Experimental Testing
Preliminary calculations indicated that the allowable axial load for an eight foot tall
stud braced in the weak direction was approximately 2.2 kips per stud. One kip is
equal to 1,000 pounds. With four studs per 4 by 8 panel, the calculated allowable
axial load per panel was approximately 8.8 kips. Past experience and research with
timber construction has indicated that the ultimate bending stress of 2x timber has
been nearly 2.5 to 3 times that of the allowable stress. Using this same ratio of
ultimate stress to allowable stress factor for the axial capacity indicated that the
ultimate axial capacities for the testing specimens may reach 26.4 kips per panel. If
the sheathing fastening schedule in the test specimens was such that shear transfer
could develop along the material-to-sheathing interface, both the gross area and
section modulus could be significantly increased. Assuming some shear transfer
could occur, it was anticipated that axial loads on the test specimen with oriented
strand board applied to both sides could potentially reach 35 to 40 kips.
The laboratory at the Denver Campus of the University of Colorado did not have
equipment capable of generating 40 kips of load to a 4 by 8 panel. Efforts to
conceive a home-constructed testing apparatus failed due to budgetary concerns and
apprehension about result accuracy.
30


3.1 Testing Machine
The University of Colorado Boulder Campus structures laboratory has a 1,000,0000
pound (one million pound or also called one-thousand kip) test machine that can be
configured to constant strain or constant load application. Based on the maximum
opening dimension of the machines heads, its ultimate load capacity, and its
sensitivity to measure load to the nearest 10 to 100 pounds, the machine was capable
of conducting the experiments. Arrangements were made to lease time on this testing
machine.
The testing machine is a 1,000,000 pound Material Testing System (MTS) model
number 907.57. The 15-foot tall load frame with adjustable cross head is MTS
model number 311.51. The load frame consists of four 9-inch diameter structural
pipes/hydraulic cylinders that the load cell can slide up and down. Once the desired
height of the top load cell/head is attained using a separate hydraulic system for
raising and lowering, the top head is locked in place onto the four aforementioned
pipes. The load cell contained in the 12-inch diameter cylinder top head is a MTS
model number 311.51 1,100 kip special. The four 9-inch diameter pipes extend
through the first floor and basement where they are anchored in a deep foundation.
The machines loading ability is obtained from a 12-inch hydraulic piston that is
located near the floor level. This hydraulic piston is pressurized from a large
31


electrically powered hydraulic pump located in the laboratory basement. The main
hydraulics controller is MTS model number 442.11 with a load range of 100 kips and
a piston stroke range of 5 inches. The main hydraulic pump is MTS Hydraulic
Power Supply model number 506.81 with an operating pressure of 150 psi to 3000
psi. A pressure of 3000 psi was used for our experiments. The software used to
record the data was National Instruments Labview 6i running on a Windows 95
operating system. Figures 3.1 to 3.4 on the next page are views of the testing
machine.
32


Figure 3.1 MTS 907.57 Figure 3.2 MTS Base
33


3.2 Load Transfer Apparatus
A 4-foot by 8-foot by 4-inch panel cannot be loaded between two 12-inch diameter
testing heads and be expected to model a uniform linear load across the top and
bottom edge of the panel. No appropriate load transfer device was available at the
University of Colorado or had been used in the past. Therefore the load transfer
apparatus had to be custom designed and fabricated prior to testing.
A measurement taken at the initial site visit showed that the MTS machine could
open to a maximum clearance of 10 feet between the bottom load piston and top
head. During the testing phase this measurement proved inaccurate as the top head
was raised to a clear height of nearly 11 feet. Nevertheless, it was believed that the
design of the load transfer apparatus was constrained to a depth limitation of no more
than 12 inches. Another clear design consideration was that the load transfer
apparatus would have to be anchored to heavy duty MTS eye bolts such that the
apparatus and the specimens did not become projectiles at failure loads.
Preliminary calculations indicated that heavy timber beams could be used along the
top and bottom edge to transfer the single piston load to the panel edge. Strength
demand of the proposed designed was governed by the ultimate load of the stud,
estimated to be 10 kips at a cantilever length of 21 inches. The 21-inch cantilever
length was obtained by one-half of the panel (48/2 = 24) minus one-fourth of the
34


testing head diameter (12/4 = 3). Through hand calculation of deflections, it was
quickly discovered that end stud deflections could exceed Vz-inch with any practical
size of available heavy timber. A 3/8-inch end deflection times two for the top and
bottom apparatus would yield approximately a %-inch strain difference between the
inner and outer studs. A %-inch strain difference between adjacent studs would be
unacceptable as the inner two studs would reach their ultimate load before the outer
studs became relatively loaded. Other possible problems, including durability,
proposed attachments to the testing machine, and apparatus stability led to the
rejection of heavy timber as the load transfer apparatus.
Next steel was evaluated as a possible material for the apparatus. Hand calculations
of 6-inch deep wide flange sections indicated they were significantly stiffer than the
heavy timber option. Another advantage to using steel was that it was durable in
nature and could be reused repeatedly for numerous tests. Eye-bolts could be
fastened to the steel to tie the beam to the MTS machine for stability at failure load.
Eye-bolts could also be utilized to hang the upper apparatus from the top head for
easier removal of failed specimens and installation of new ones.
To optimize the shape selection, the testing set-up was modeled in finite element
computer model. A 48-inch long 6-inch deep wide flange beam was modeled along
the bottom with a fixed reaction at mid-span. Four unbraced 2x4s were modeled at
35


equal spacing across the beam and a same size steel beam was modeled across the
top with a concentrated point load at mid-span. For model stability, a horizontal
roller reaction had to be provided at the left end of the top beam to prevent racking.
A trial run of approximately 10 kips on unbraced studs revealed that the inner studs
reached their Euler buckling load while the outer studs were at relatively low stress
levels.
Numerous iterations were performed using the heaviest 6-inch deep wide flange
available, then trying a W8xl0 wide flange section, then a W8x40. Each of the trials
yielded similar results that small deflections at the apparatus ends significantly
reduced the load transfer to the outer studs. From a practical standpoint, a W8x40, at
a weight of 160 pounds for a 4-foot length, is as heavy a section that can be lifted
and manipulated by two people on a ladder. Increasing the depth to 12 inches with a
similar limit of weight of 160 pounds still could not provide the stiffness required to
model a uniform linear load. The closest trial to the ideal model was a W 12x96 that
had a difference in load between the inner and outer studs of approximately 10%.
Thus the rigid beam concept was abandoned.
On the third iteration of the design, the concept of creating a uniform load was
abandoned and focused on using basic statics to devise a concept that would provide
four equal point loads, one for each stud. The beam adjacent to the piston was
36


designed to support two stub columns that coincided with the geometric center
between the outer two stud bays. Because the load application point was halfway
between the stub columns, the loads on the stub columns were equal and half that of
the applied load. The stub columns were then connected to a continuous transfer
beam that applied two equal loads to each of the end studs. When modeled, analysis
of this configuration showed that the continuous transfer beam developed moment
transfer between the center two studs, thus the center studs would still be expected to
fail prior to the outer studs, with an 8% greater load. The model was revised one last
time to apply a hinge in the center of the transfer beam. The hinge installation was
the key and equal load could be applied to all four stud at limit states.
Hollow structural sections (HSS) were selected for the beams due to their torsional
stability, greater capacity in weak axis bending, and their capacity to provide twice
the web strength compared to a wide flange beam. An HSS 6x3xl/4 was selected for
the transfer beam size and an HSS 5x3xl/4 was selected for the beam adjacent to the
piston. The transfer beam required 1-inch by 1-inch by 1/8-inch angles spaced 4.5
inches apart to keep the specimens centered on the apparatus and to keep them from
sliding out at ultimate failure. A 10-inch square by %-inch thick plate was welded to
the HSS at the contact area between the apparatus and the piston/head to keep the
apparatus from rolling off the head. Eye-bolts were bolted to the beam adjacent to
37


the piston to enable attachment to the testing machine; most critical was the head
attachment so the apparatus wouldnt fall once the specimen failed.
To fabricate the testing apparatus, shop drawings had to be generated indicating
material specifications, dimensions, and weld locations. (See Figures 3.5-3.7.) A
local steel fabricator, General Iron and Steel, was chosen due to a preexisting work
relationship. At the time of fabrication, General Iron and Steel called stating they
were out of % thick wall tubes and wished to substitute 3/8 wall. The thicker wall
created a greater moment of inertia and thus greater stiffness that was not
objectionable, thus the change was accepted.
38


Figure 3.5 Elevation of the Load Transfer Apparatus
39


SECTION A-A
SCALE: 1 = V-0"
Figure 3.6 Section of the Load Transfer Apparatus
40


\Y(
CROSS HEAD/
TOP CYLINDER
,Y/
!
/is
1
iil
LOAD APPUCATIOR/
BOTTOM CYLINDER
TESTING SET-UP
SCALE: 1/2" = 1'-0"
Figure 3.7 Elevation of the Testing Set-Up
41


3.3 Testing Specimens
The testing specimens were constructed of 2x4 studs sheathed with conventional
sheathing materials used in modem residential and commercial construction.
3.3.1 Timber
All studs utilized in testing were 2x4 nominal studs. Dressed dimensions for the
2x4s were 1-1/2 inches by 3-1/2 inches. All studs were pre-cut stud grade
measuring 92-5/8 long and purchased at Home Depot. Due to the volume of
materials required, multiple trips to the local Home Depot were required. The initial
purchase consisted of green ink stamped Hem-Fir stud grade 2x4s, graded by
Western Wood Products (WWP) and produced by Stimson Lumber Company. The
Stimson Lumber Company is a forest products processing plant based in Portland,
Oregon. Stimson owns and manages approximately 420,000 acres of forest, and has
14 manufacturing facilities in four states. Each stud also contained KDHT within the
grading stamp that indicates Kiln Dried Heat Treated. Each stud was hand
selected from store bundles. Studs were rejected at the time of purchase if they had
any of the following defects:
Not straight along either axis more than Vi inch.
Any wane along the middle third of the length.
Any wane at the ends deeper than 3/8 inch.
42


Face splits or checks deeper than % inch.
Impact damage from shipping or packaging.
Loose or open knots greater than 5/8 inch along the middle 75%. Studs with
in tact knots were not rejected regardless of location.
At times the stud reject pile became too large to handle and a return trip on the next
day was required. Unintentionally, a mix of black ink stamped studs that were
Douglas-Fir Larch entered the selection. These different grade studs were not
noticed until the day of testing; however, the difference was caught and noted for
each specimen.
The 2001 National Design Specification (NDS, 2001), Table 4A; Base Design
Values for visually Graded Dimension Lumber (2-4 thick) for these studs are as
follows:
Hem-Fir; Stud Grade:
Fb = 675 psi
Fc = 800 psi
Fcx = 405 psi
Fv = 150 psi
E = 1,200,000 psi
43


Douglas Fir-Larch; Stud Grade:
Fb = 700 psi
Fc = 850 psi
Fc_l = 625 psi
Fv= 180 psi
E = 1,400,000 psi
3.3.2 Sheathing Materials
Each of the sheathing materials was code and field researched to determine what
materials and manufacturers were commonly used.
3.3.2.1 Gypsum
The gypsum drywall used in construction of the specimens was purchased from the
Home Depot and was ToughRock Yz gypsum board manufactured by Georgia-
Pacific. ToughRock, a trade name for this product, was found to be similar to
most gypsum drywall in that the boards were dimensionally stable, noncombustible,
and had a gypsum core encased with paper. Toughrock specifically uses recycled
paper for the faces and long edges. ToughRock gypsum board is manufactured
specifically for interior walls and ceilings. The drywall came in 4-foot by 8-foot
sheets with tapered edges. Because the stud wall panels were 95-5/8 tall when
44


constructed (92-5/8 + 1l/zn + 1 'A = 95-5/8), approximately Vz of drywall had to
be trimmed from the top or bottom edge using a utility knife and straight edge. The
Georgia-Pacific manufactured gypsum conformed to the following standards as
published by their product literature:
ASTM C36 (physical properties)
ASTM Cl396
Federal Standard SS-L-30d, Type III, Grade R
CSA-A82.27-M
ICBO requirements
Physical Properties of Vz Gypsum Wallboard per Georgia-Pacific:
Nominal Width ...4-0 +/- 2/32
Nominal Thickness ....O-O 1/2+/- 1/64
Standard Length 8-0 +/-% (L< 16avail.)
Nominal Weight per square foot ....2.0 psf
Minimum Flexural Strength Parallel ....40 pounds (ASTMC473)
Minimum Flexural Strength Perpendicular... ....110 pounds (ASTMC473)
R-Value ....0.45
Minimum Nail Pull Resistance .... 80 pounds
Minimum Hardness ....15 pounds
Effective Stiffness (El) Typical Range ...1,500 to 4,000 lb*in2/in
45


Modulus of Rupture Machine Direction........750 psi (ASTM C36)
Modulus of Rupture Cross Direction..........260 psi (ASTM C36)
Compressive Strength (70F 50%RH)...........350 psi
Water Absorption (2-hour immersion).........10% of weight (ASTM C473)
Thermal Coefficient of Linear Expansion.....9.3X10"6 in/in F
3.3.2.2 Oriented Strand Board
Oriented strand board (OSB) is a mat-formed, layered construction panel made with
flakes, strands, or wafers harvested from small diameter, round wood logs and
adhered together under pressure and heat. Oriented strand boards strength mainly
comes from the larger pieces of wood fiber, interweaving of the wood
strands/wafers, and various degrees of orientation of the strands/wafers in the surface
layers. Oriented strand board utilized for specimen construction was 7/16-inch thick
and was manufactured by Louisiana Pacific, Ltd. The processing plant for the
specimens was number 457 which is Louisiana Pacifics Swan Valley plant in
Manitoba, Canada. All oriented strand board used was stamped with a manufacturer
date of June 2003 and was APA (American Plywood Association) span rated
sheathing for 24/16 with exterior type adhesive. The 7/16-inch thick panels were
stamped compliant with HUD-UM-40C standard and APAs performance rated PRP-
108 standard.
46


3.3.2.3 Thermo-Ply
Thermo-Ply is a laminated fibrous sheathing board that has been code-approved as a
weather resistive barrier complying with Section 1402.1 of the 1997 Uniform
Building Code (IBC,2000). The long fibers are treated with water-resistant and
weather-resistant plies and pressure laminated using water-resistant adhesive.
Thermo-Ply, which is manufactured by Ludlow Coated Products in Constantine,
Michigan, is manufactured in three grades: Standard (green), Structural (red), and
Super Strength (blue). The Standard grade is not rated for structural application and
is 0.078 inches thick. The Structural grade, also called Stormbrace, consists of
panels with a 0.115-inch nominal thickness with facings of polyethylene or foil. The
Structural grade, which was the grade selected for this experiment, had a
polyethylene face. Thermo-Ply is manufactured in numerous sizes, however at the
retail level only a 48-inch by 108-inch panel size could be located. The Super
Strength panels, which were not tested, are identical to the Structural grade except
they are 0.137 inches thick.
Thermo-Ply lists approvals from HUD/FHA, BOCA, ICBO, and SBCCI. The ICBO
Evaluation Service has evaluated the panels for shear load in ER-1439 (ICBO,
2001). This document can be found in the appendix. Per this report, Thermo-Ply
must be installed vertically over wood studs with all joints backed by blocking or
studs. The report also states that Structural grade Thermo-ply can be used for a
47


Limited Load-bearing Exterior Wood Stud Wall if the assembly consists of 5/8-
inch Type-X gypsum wallboard on the interior face, Thermo-Ply on the exterior face,
wood studs at 16-inches on center, brick veneer, and a maximum height of 8 feet.
The assembly may be used provided allowable bearing loads do not exceed the
following:
1. 1.8 kips per 2x4 stud.
2. Design stress of 0.78 f c per section 2307.3 of the UBC.
3. Design stress up to 51 % of Fc or Fci permitted for the stud grade and
species.
Thermo-Ply is a thin sheathing and susceptible to out-of-plane warping if improperly
installed. To properly install all three grades the first fastener should be installed in
the upper left with subsequent fasteners installed to the lower left. Fastening should
start next at the upper edge of the second stud from the left and proceed down the
length of the stud. This pattern should continue for all four studs. If a fastener is
installed at each comer without following the aforementioned pattern, gaps or
rippling is likely to occur.
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3.3.2.4 Fiberboard
Fiberboard, also called structural fiberboard, also called asphalt impregnated
sheathing, has been used as a moisture barrier for several decades and has gained
code approvals for use as an acceptable method for bracing walls against in-plane
shear. Fiberboard has various approvals for use as a moisture barrier and as a
structural element for the design of in-plane shear through the following codes:
1997 Uniform Building Code (UBC, 1997)
2000 International Residential Code (IRC, 2000)
2000 International Building Code (IBC, 2000)
Fiberboard has numerous manufacturers and sizes, however at the retail level only 4-
foot by 9-foot Temple Fiber Brace could be located. Temple Fiber Brace is
Mi-inch thick and made from southern pine lignocellulosic wood fibers from sawmill
residue. The fibers develop a bond through interfelting of the fibers with natural
asphalt and then the faces and edges are coated with asphalt to provide strength and
water protection. Fiberboard in general has a density of 21 to 25 pounds per cubic
foot or approximately 0.96 pounds per square foot. The tensile strength of Temple
fiberboard is 200 psi with an insulation value of R=1.22. Fiber Brace complies
with ANSI/AHA A194.1 and ASTM C208. Fiberboard is required to be installed in
a vertical direction from the sill to the top plate.
49


For comparison of products, the ICBO allowable shear in fiberboard braced walls is
only 20% less than oriented strand board fastened per the schedule used for this
experiment.
3.3.3 Fasteners
The basis for the fasteners used for each sheathing type is discussed below in Section
3.3.4. All fasteners used were manufactured by Grip Rite. All bright common and
roofing nails Grip Rite manufactures comply with ASTM FI667 specifications.
Fasteners used are shown on the next page in Figures 3.8-3.11.
50


Figure 3.10- Roofing Nail
51


3.3.4 Attachments
Each framing attachment and sheathing attachment was researched through the
building codes, the manufacturer specifications, and standard construction practice.
3.3.4.1 Stud to Plate
The studs were all fastened to a single sole plate and a single top plate with two 16d
common face nails. This fastening schedule is in conformance with the 2000
International Residential Code (IRC, 2000) Table R602.3(I) Fastener Schedule for
Structural Members and the 1997 Uniform Building Code (UBC, 1997) Table 23-
n-B-1 Nailing Schedule. To provide consistent nailing of the sill plate and sole
plate for the specimen, a template was fabricated to center the 16d nails across the
stud width and to locate each 16d nail 3/4-inch from each face of the specimen. Each
specimen was constructed using two axes of symmetry in that there was no specific
top or bottom. The 16d nails were shiny metallic gray, 3-1/2 inches long, had a
11/32-inch diameter head, and had a 5/32-inch shank diameter.
3.3.4.2 Gypsum to Studs
Gypsum board (drywall) can be fastened with glue, nails, or screws. The Gypsum
Association and Georgia-Pacific recommend installing drywall in accordance with
the publication GA-216 Recommended Specifications for the Application and
52


Finishing of Gypsum Board (Gypsum Association, 1996). Drywall that is V2 thick
or greater may be fastened to studs at 16 inches or 24 inches on center. For this
testing procedure we used studs at 16 inches on center to more accurately reflect a
standard load-bearing wall construction. Various sources were found that
recommended specific attachment of drywall to framing:
Gypsum Association Publication GA-216 (Gypsum Association,1996):
Gypsum should be nailed with a minimum nail length of 1.375 inches at 8
inches on center. Publication footnote is Also refer to local code
requirements. Gypsum should be screwed with a minimum screw length of
1 inch at 16 inches on center. Publication footnote is Also refer to local
code requirements.
Gypsum Association Publication GA-235-01 (Gypsum
Association,2001):
To test a 4x8 specimen for wind load in accordance with ASTM E330
fasteners (nails or screws) shall be installed at 8 inches on center.
1997 Uniform Building Code (UBC, 1997):
Section 2511 of the code states that supports, fasteners, and spacing shall
comply with Table 25-G. Table 25-G, for vertical installation, states that
nails shall be installed at 8 inches on center to all supports using 5d cooler or
wallboard nails. Table 25-G, for vertical installation and studs at 16 inches on
53


center, states that screws shall be installed at 16 inches on center to all
supports using number 13 gage, 1-3/8-inch long, 19/64-inch head screws.
1997 Uniform Building Code shear wall provisions (UBC, 1997):
Table 25-1 of the Code states that unblocked, Vi-inch, gypsum wallboard shall
be fastened to studs using 5d cooler or wallboard nails at 7 inches on center at
all supports. No alternative for screws is provided.
2000 International Residential Code (IRC, 2000):
Table R602.3(l) Fastener Schedule for Structural Members states that Vi-
inch gypsum sheathing shall be fastened with 1-1/2-inch galvanized roofing
nails or staples, 6d common nails, or 1-1/4-inch type W or S screws. All
fasteners shall be installed at 4-inches on center at the edges and 8 inches on
center at intermediate supports.
ICBO Evaluation Report ER-1874 (ICBO, 2001):
Table 2 on page 3 of the report specifies installation instructions for blocked
and unblocked shear walls using 5d common nails and Number 6 1 %
screws for various thicknesses of gypsum wallboard. If 5d common nails are
used, studs are allowed to be 24 inches on center and nails should be installed
at 7 inches on center at all supports. If Number 6 1V4 screws are used,
studs are allowed to be 16 inches on center and screws should be installed at
8 inches on center at the edges and 12 inches on center in the field.
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The decision was made to use screws over nails as screws are gaining more
popularity with the advent of high speed, cordless drills. Screws, in general, required
a greater on center spacing than that chosen for oriented strand board and thus may
provide insight to the effect of fastener spacing on buckling performance. Screws
also were more easily installed without damaging the drywall, unlike a missed
hammer strike while installing nails.
A variety of fastening schedules was available for the gypsum once screw type
fasteners were selected. Twelve-inch spacing on all framing supports was selected
for various reasons. One reason is that the fastener spacing was consistent on all
four studs to promote a possible failure at any stud location. Another reason is that
12 inches was no more than twice that of the 6-inch spacing selected for the oriented
strand board to which the comparison is being made. Twelve inches was not
stringent to meet code requirements for shear walls, but was in compliance with
fastening requirements for interior finishes and industry standard practice.
Screws used were 1-5/8-inch coarse thread drywall screws manufactured by Grip
Rite Fasners. The drywall screws had an 11/32-inch diameter bugle type head
that was recessed approximately 1/32 inches below the face paper. All screws were
driven with a 16-Volt cordless drill with a specialty drywall Phillips bit. The screws
55


were gumnetal gray, 1-9/16 inches long, had 9 threads per inch, 3/32-inch shank
diameter, and 5/32-inch outer thread diameter.
3.3.4.3 Oriented Strand Board to Studs
Per the 1997 Uniform Building Code (UBC, 1997) Table 23-II-I-1 Allowable Shear
for Wind or Seismic forces in pounds per foot for Wood Structural Panel Shear
Walls 7/16-inch oriented strand board is an approved structural sheathing. For
7/16-inch nominal thick panels with 1-1/2 inch minimum nail penetration into the
framing an 8d common or galvanized box nail may be used with a maximum spacing
of 6 inches on center at all panel edges and 12 inches on center along intermediate
framing members (field). Per the codes Table 23-II-B-l Nailing Schedule Vi-inch
and less thick wood sheathing may be nailed to framing members with 6d common
nails with a maximum spacing of 6 inches on center at all panel edges and 12 inches
on center along intermediate framing members (field).
The 2000 International Residential Code (IRC, 2000) Table R602.3(l) Fastener
Schedule for Structural Members indicates that 5/16-inch to Vi-inch thick wood
sheathing may be nailed to framing members with 6d common nails at with a
maximum spacing of 6 inches on center at all panel edges and 12 inches on center
along intermediate framing members (field).
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This study utilized hammer driven 8d common nails at a spacing of 6 inches on
center at all panel edges and 12 inches on center along intermediate flaming
members (field). The 8d nails were metallic gray, 2-5/16 inches long, had a 9/32-
inch diameter head, and a 1/8-inch shank diameter.
3.3.4.4 Thermo-Ply to Studs
The ICBO approval report (ICBO, 2001) requires that the Structural grade Thermo-
Ply be fastened to the studs using Number 16 gage staples or large flat-head Number
11 gage 1-1/4-inch galvanized roofing nails. Fastener installation is required to be at
3 inches on center at panel edges and 6 inches on center at intermediate supports
(field). For non-structural applications where the Thermo-Ply is being installed as a
moisture barrier, the above-mentioned fasteners may be installed at 6 inches on
center at all panel edges and 12 inches on center at intermediate supports (field).
The Technical Specifications for Thermo-Ply Sheathing authored by Ludlow
(Ludlow, 2002) are consistent with the ICBO fastener requirements for installation.
For this experiment hammer driven roofing nails were chosen over staples as the
fastener of preference.
This study utilized hammer driven roofing nails at a spacing of 3 inches on center at
all panel edges and 6 inches on center along intermediate flaming members (field).
57


The roofing nails were shiny metallic gray, 1-3/8-inch long, had a 3/8-inch diameter
head, and a 1 /8-inch diameter shank.
3.3.4.5 Fiberboard to Studs
Temple recommends installing Fiber Brace with 11 gage galvanized 1-1/2-inch
roofing nails with a 7/16-inch head at 3 inches on center at the edges and 6 inches on
center in the field. Alternatively, 16-gage staples can be used with the
aforementioned spacing. The 2000 International Residential Code (IRC, 2000)
Table R602.3(l) Fastener Schedule for Structural Members and the 1997 Uniform
Building Code (UBC, 1997) Table 23-II-J Allowable Shears for wind or seismic
loading on Vertical Diaphragms of Fiberboard Sheathing Board Construction for
Type V Construction Only have the same requirement for fastening.
This study utilized hammer driven roofing nails at a spacing of 3 inches on center at
all panel edges and 6 inches on center along intermediate framing members (field).
The roofing nails were shiny metallic gray, 1-3/8-inch long, had a 3/8-inch diameter
head, and a 1 /8-inch diameter shank.
3.3.4.6 No Sheathing
The specimens with no sheathing were braced with a 107 inch Simpson CS22
diagonal strap in each direction on one face. This strap was nailed with 3-10d
58


Simpson nails at the comers to the top and bottom plate only. No nails were
installed into the studs that would potentially affect bracing condition. The steel
straps were required to give the wall lateral stability to limit sudden or extreme
racking.
3.4 Analysis Calculations
All mathematical analysis of studs and studs column capacities was performed in
accordance with the 2001 National Design Specification (NDS, 2001) published by
the American Forest and Paper Association and the American Wood Council. The
analysis was undertaken so that approximate failure loads were known before
selecting the testing equipment. Also, these calculations could be compared to the
actual failure loads.
The allowable capacity of a stud is determined by multiplying the allowable
compression (Fc) by the area of the section. The Fc value for a given piece of
timber is calculated by multiplying the tabulated compression design value (Fc) by
the load duration value (Cd), the wet service factor (Cm), the temperature factor (Ct),
the size factor (Cf), the incising factor (CO, and the column stability factor (Cp).
This is outlined in NDS Table 4.3.1: Applicability of Adjustment Factors for Sawn
Lumber.
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Fc = Fc x Cd x Cm x Ct x Cf x Ci x Cp
The tabulated value for Fc in Part 2 of the 2001 NDS Code for Hem-Fir Stud grade is
800 psi. The area of a nominal 2x4 stud is 1.5 x 3.5 = 5.25in2. For this
experiment, the sustained temperatures did not exceed 150F, the timber moisture
content did not exceed 19%, and the studs were not pressure treated or incised so Cm,
Ct, and C; were equal to one.
Timber has an inherent ability to endure greater loads when the load is relatively
short term or transient. Similarly timber strength is inherently reduced when the
loads are of a long-term or permanent nature. The load duration factor, Cd reflects
this material property. An adequate Cd value for very transient loading such as
seismic or wind lasting 10 minutes or less is considered to be 1.6. The average
length of testing time of the specimen was over 12 minutes and was a relatively static
load. An adequate Cd value for relatively short term loading such as a construction
load lasting 7 days or less is 1.25. Because the construction loading duration factor
was more conservative in nature Cd equal to 1.25 was used, thus:
CD= 1.25
Per the Size Factor Cf adjustment table in Part 2 of the NDS Code a 2x4 has a Cf
equal to 1.15, thus:
CF= 1.15
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Per 3.7.1 of the 2001 NDS Code, the column stability factor is defined as follows:
Cp =
(3.7-1)
Where:
and...
and...
Where...
Fc* = Fc x CD x Cf
= 800 psi x 1.25 x 1.15
= 1150 psi
c = 0.8 for sawn lumber
FcE = (KcExE)/(le/d)2
Kce = 0.3 for visually graded lumber
E = 1,200,000 psi per Table 4A Part 2 NDS
le = 92.625
d = 1.5 for unbraced condition
d = 3.5 for braced or sheathed condition
Solving Cp for an unbraced condition yields:
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Cp = 0.08068
Solving Cp for a braced condition yields:
CP = 0.39529
Solving for Pub = the allowable load for the unbraced weak direction:
Pub = A x Fc
= A x Fcx Cd x Cm x Q x Cf x Q x Cp
= 5.25in2 x 800 psi x 1.25 x 1.0 x 1.0 x 1.15 x 1.0 x 0.08068
= 487 pounds per stud
Ppanel = P pounds per stud x 4 studs per panel
= 487 pounds x 4
= 1,948 pounds per panel
Solving for Pb = the allowable load for the braced weak direction:
Pb = AxFc
= A x Fc x Cd x Cm x Ct x Cf x Ci x Cp
= 5.25in2 x 800 psi x 1.25 x 1.0 x 1.0 x 1.15 x 1.0 x 0.39529
= 2,387 pounds per stud
62


Ppanel = P pounds per stud x 4 studs per panel
= 2,386 pounds x 4
= 9,546 pounds per panel
Through past engineering experience and research, it has been observed that
allowable stress design in wood construction typically yields approximately a 2.8
factor of safety between the calculated allowable load and the ultimate failure load.
To predict the ultimate load of the studs only (not any composite action) the above
allowable panel loads were multiplied by 2.8 as follows:
Unbraced: Ppanel ultimate = Ppanel x 2.8
= 1,948 pounds x 2.8
= 5,454 pounds
Braced: Ppanel ultimate ~ Ppanel x 2.8
= 9,546 pounds x 2.8
= 26,728 pounds
Alternatively, an analysis of weak direction buckling by the Euler Buckling method
yields the following:
PCT = 7i2 EI/L2
= 7t2 1,200,000 psi x 0.984375 in4 / 92.625 in2
63


=1,358 pounds per stud
Ppanel = Per pounds per stud x 4 studs per panel
= 1,358 pounds x 4
= 5,435 pounds per panel
= 99.6% of above predicted ultimate value
An analysis of strong direction buckling by the Euler Buckling method yields the
following:
PCT = 7t2 El / L2
= 7T2 x 1,200,000 psi x 5.359375 in4 / 92.625in2
= 7,398 pounds per stud
Ppanel = Per pounds per stud x 4 studs per panel
= 7,398 pounds x 4
= 29,594 pounds per panel
= 110.7% of above predicted ultimate value
64


3.5 Fastener Strength
From the compression buckling provisions outlined in Steel Structures: Design and
Behavior (Salmon and Johnson, 1997), the load required to brace a single column
from buckling is described as Q. For analysis of a stud wall sheathing fasteners:
PCT = 7i2 El / L2
= 7i2 1,200,000 psi x 0.984375in4 / 92.625 in2
=1,358 pounds per stud
Kideal = (P X Per) / L
= (4 x 1,358 pounds) / 92.625 in
= 58.64 pounds / in
Where P = 4 from chart on page 504
Q Kideal X A
= 58.64 pounds / in x 1
= 59 pounds
Where A = 1 from multiplying rejection criteria of Vi by 2
The drywall screws are capable of developing the 59-pound reaction required.
65


4. Testing Results
In general the testing was successful. As anticipated, initial tests uncovered
problems with stabilizing the load transfer device during loading that were easily
addressed.
4.1 Data
The data recorded by the computer was load versus displacement at intervals of
every one second. The computer program tabulated the raw data in a spreadsheet
generating nearly 60,000 data points.
Individual testing results were rejected when there was a testing machine failure or
testing apparatus failure. Specimens 3A (drywall on one side) and 5C-1 (Thermo-
Ply) were rejected because the load transfer apparatus twisted on both load heads,
rotating the specimens into a double-helix shape prior to failure. Specimen 3A was
the first specimen to twist which occurred on the first testing day. Subsequent tests
incorporated nylon straps tied to the large pipe columns that resisted the twisting
load. Specimen 5C-1 broke loose from the straps near the ultimate load on the final
day of testing. Specimen 5C-2 represents the testing once the straps were re-secured.
Specimen 4C (drywall both sides) was rejected due to the testing machines loss of
66


load after 5 minutes of testing, then an unexpected immediate strain of 1 to 2 inches
causing shock loading to the wall and audible pops in the timber and drywall. The
load implemented during this jump was not recorded, however, it was enough to
question whether internal failure or damage had occurred. Specimen 4C failed at
approximately 87% of the calculated average of the specimens 4A and 4B.
Including specimen 4C would have skewed the averages such that drywall on both
faces would be expected to fail before drywall applied to one side.
This data was organized, tabulated and averaged on the following pages. The
following tables and figures were created:
Table 4.1
Figure 4.1
Figure 4.2
Figure 4.3
Testing Results Summary. This sheet contains a summary of each
specimens performance.
Average Ultimate Load. Results are plotted in a bar graph in
increasing ultimate load.
Gross Youngs Modulus. Results are in the same specimen order as
the Average Ultimate Load bar graph. Note the trend that stiffness
corresponds to increasing ultimate load.
Average Ultimate Strain. Results are in the same specimen order as
the Average Ultimate Load bar graph. No pattern or correlation is
evident.
67


Figure 4.4 Load vs. Displacement: OSB, Drywall, and No Sheathing. Graphs show displacement for all specimen types.
Figure 4.5 Load vs. Displacement: Specimen Type 1. Type 1 is oriented strand board on one side.
Figure 4.6 Load vs. Displacement: Specimen Type 2. Type 2 is oriented strand board on both sides.
Figure 4.7 Load vs. Displacement: Specimen Type 3. Type 3 is drywall on one side.
Figure 4.8 Load vs. Displacement: Specimen Type 4. Type 4 is drywall on both sides.
Figure 4.9 Load vs. Displacement: Specimen Type 5. Type 5 is Thermo-Ply on one side.
Figure 4.10 Load vs. Displacement: Specimen Type 6. Type 6 is no sheathing
Figure 4.11 Load vs. Displacement: Specimen Type 7 Type 7 is fiberboard on one side.
68


o
vO
I h e i I Max Load (kips) Max Stress (hsi) Max A (inches) Max. Strain (in/in) Strain Rate (in/min) Strain at Pmax (in/in) Duration (minutes) Gross Young's Modulus (ksi) Failed Stud 2*2nd from Ea*t 2nd from W* 4W*st Buckling Typ* Buckling Direction Buckled Toward Sheathing Side? Test Date Test Time Test Order
1 1A 39.99 1 904 0.92 0 00961 0 11 0.00912 8.75 208.909 3 & 4 SAB NORTH NA 10/6/2003 9:31 AM 6
1 1B 38.16 1.017 0.90 0.00942 008 0.00828 10.72 219.552 1 SAB NORTH NA 10/6/2003 12:05 PM 12
1 1C 45.21 2 153 0.79 0 00828 0.06 0.00780 12.50 273.157 3 & 4 SAB NORTH NA 10/6/2003 2:44 PM 17
2 2A 33.67 1 603 1.34 0.01392 0.05 0.01228 26.05 130 542 NA SAB NORTH YES 9/15/2003 9:26 AM 1
2 2B 31.35 1.493 0.84 0.00875 0.08 0.00834 990 178989 1 SAB NORTH YES 10/6/2003 12:55 PM 13
2 2C 39 43 1 877 0.93 0.00973 0.09 0.00824 10.85 227.909 3 & 4 SAB SOUTH YES 10/13/2003 11:51 AM 22
3(bad) 3A 2015 1.340 1 05 001093 0.06 0.00725 1708 184 979 2 WAB SOUTH NA 9/15/2003 10:28 AM 3
3 3B 32 91 1.567 0.88 0.00918 0.06 0.00910 1403 172.210 1 &2 WAB NORTH NA 10/6/2003 9:03 AM 5
3 3C 36.72 1.748 1.13 0 01178 0.06 0.01164 17 80 150146 1 & 2 SAB EAST YES 10/6/2003 2:14 PM 16
3 30 45.53 2.168 1 03 0.01076 0.07 0.01021 15.38 212 385 1 &2 SAB NORTH NO 10/13/2003 9:32 AM 18
4 4A 39 99 1.904 0.71 0 00744 0.10 0.00741 7.32 256.928 NA SAB NORTH NA 10/6/2003 8:39 AM 4
4 4B 37.64 1.793 0.78 0.00811 0.06 0.00690 12.32 259 684 1 &2 SAB NORTH NA 10/6/2003 1:18 PM 14
4(bad) 4C 33.89 1.614 0.96 0.01004 0.09 0.00782 11.33 206.384 3 SAB NORTH NA 1CV13/2003 10:04 AM 19
5 5A 33.15 1.579 1.16 0.01205 0.06 0.01089 18.70 144.904 1 & 2 SAB SOUTH NO 10/6/2003 10:19 AM 8
5 5B 27.61 1.315 063 0.00653 0.08 0.00627 743 209 786 2 SAB SOUTH NO 10/6/2003 11:19 AM 10
5(bad) 5C-1 29.95 1 426 0.99 0.01026 0.08 0.01007 11.65 141.672 NA SAB NA NA 10/13/2003 10:52 AM 20
5 5C-2 31.64 1 507 1.04 0.01081 0.17 0 00676 6.13 172010 3 SAB NORTH NO 10/13/2003 11:13AM 20
6 6A 9.52 0.453 0 47 0 00489 0.10 0 00259 483 174 826 1 WAB EAST NA 9/15/2003 10:13AM 2
6 6B 8.30 0 395 0.44 0 00463 0.05 0.00264 835 149.483 1 WAB WEST NA 10/6/2003 9:49 AM 7
6 6C 6.93 0.330 0.69 0.00720 0.08 0 00380 8.15 86 859 1 WAB EAST NA 10/13/2003 11:35 AM 21
7 7A 36.64 1.745 1.08 0.01128 0.06 0.00948 17.10 183.995 3 SAB SOUTH NO 10/6/2003 10:51 AM 9
7 7B 31.10 1.481 1 00 001037 0.06 0.00976 11.75 151.695 3 & 4 SAB NORTH YES 10/6/2003 11:39 AM 11
7 7C 33.96 1.618 1.17 001222 0.09 0.01123 13.02 144.159 3 & 4 SAB NORTH NO 10/6/2003 1:44 PM 15
AVERAGE AVERAGE NORTH=13 YES=5
1222 2.267 SOUTH=5 NO=6
Sheathing Average Median Std. Dev. Average Median Std. Dev. Average Median Std. Dev.
Type UK. Load Uit. Load UK. Load Strain Strain Strain E E E
1 OSB Both Sides 41.12 39 99 366 0 87 0.90 0.07 233.87 219.55 34.43
2 OSB One Side 34 81 33 67 4.16 1.04 093 0.26 179.15 178 99 48 68
3 Drywall One Side 38.39 3672 6.47 1 01 1.03 0.13 178.25 172.22 31.56
4 Drywall Both Sides 38.82 37 64 3.08 0.75 0.78 0.13 241.00 256 93 30.01
5 Thermo Ply One Side 30.80 29 95 2.78 0.94 0.99 027 175 57 144 90 38 43
6 No Sheathing 8.25 8.30 1 29 0 53 0.47 0 14 137 06 149.48 45.28
7 Fiberboard One Side 33.91 33 98 2.77 1.08 1.08 009 159.95 151.70 21.16
Table 4.1 Testing Results Summary


45.00
40.00
_ 35.00
1/T
J- 30.00
o 25.00
(u
-1 20.00
o>
| 15.00
MM
§ 10.00
5.00
0.00
No Thermo Ply Fiberboard OSB One Drywall One Drywall Both OSB Both
Sheathing One Side One Side Side Side Sides Sides
Material
Figure 4.1 Average Ultimate Load


<0
a
v>
3
3
a
o
250.00
200.00
150.00
100.00
(A
O)
c
o 50.00
>-
0.00
24dbfl0
132ifl6
i
u
No
Sheathing
Thermo Ply
One Side
Fiberboard
One Side
OSB One
Side
Material
Drywall
One Side
Drywail
Both Sides
OSB Both
Sides
Figure 4.2 Gross Youngs Modulus


K)
(/)
O
C
(0
k.
4-
(0
a>
4-*
(0
E
1.20
No Thermo Ply Fiberboard OSB One Drywall One Drywall Both OSB Both
Sheathing One Side One Side Side Side Sides Sides
Material
Figure 4.3 Average Ultimate Strain


Load (kips)
45.00
u>
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30
Strain (inches)
Figure 4.4 Load vs. Displacement: OSB, Drywall, and No Sheathing


Strain (inches)
Figure 4.5 Load vs. Displacement: Specimen Type 1


Strain (inches)
Figure 4.6 Load vs. Displacement: Specimen Type 2


Strain (inches)
Figure 4.7 Load vs. Displacement: Specimen Type 3


Strain (inches)
Figure 4.8 Load vs. Displacement: Specimen Type 4


Strain (inches)
Figure 4.9 Load vs. Displacement: Specimen Type 5


Strain (inches)
Figure 4.10 Load vs. Displacement: Specimen Type 6


Figure 4.11 Load vs. Displacement: Specimen Type 7


4.2 Photographs
The following photographs shown in Figures 4.12 to 4.83 were taken during testing
along with video taping. In general each specimen had a photograph taken of the
set-up prior to load application, and then one to three photographs taken of key
failure modes. Following the photographs is a Figure narration describing each
photos contents. The photographs are identified by their construction type, testing
order (A, B, or C), and the last number in parenthesis indicates the series number for
a specific specimen.
81


Figure 4.12 1A (1)
Figure 4.13 1A (2)
82


Figure 4.18 1C (2)
Figure 4.19-1C (3)
83


Figure 4.20 2A (1) Figure 4.21 2A (2)
84


85


Figure 4.28 2C (3) Figure 4.29 2C (4)
Figure 4.30 3A (1) Figure 4.31 3A (2)
86


87


Figure 4.36 3B (1)
Figure 4.37-3B (2)
Figure 4.38-3B (3)
Figure 4.39 3B (4)
88