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Uppal 1
Recent Research on Railroad Timber Bridges and Their Components
A. Shakoor Uppal
Transportation Technology Center, Inc.
a subsidiary of the Association of American Railroads
P.O. Box 11130 55500 DOT Road
Pueblo, Colorado 81001 USA
Abstract:
An overview of some of the research related to the railroad timber bridges and their components
undertaken over the past few decades is presented. This overview involves the surveys and workshops
that were held to determine the research needs and the publications that described the status of research in
progress, the field tests on bridges, laboratory tests on bridge components, the analytical work, and
miscellaneous other pertinent research work.
The paper concludes that although field testing of bridges has provided a greater understanding of
their behavior under train loading, further evaluation is desirable for more closely determining the actual
forces carried by the individual components. The allowable longitudinal shear stresses given in the
American Railway Engineering and Maintenance of Way Association (AREMA) Manual for Railway
Engineering Chapter 7 could to be reviewed in light of the results of the full-scale tests on timber bridge
ties and timber bridge stringers. Field tests have demonstrated that the methods of strengthening of timber
bridges currently employed work to varying degree of effectiveness. Specially-engineered wood products
offer promise for upgrading existing timber bridges because of their higher strength and other qualities.
Regular inspection and proper evaluation followed by timely and adequate maintenance program could
extend the useful service life of many existing railroad timber bridges for several years. The paper also
concludes that the use of NDE techniques for determining the strength properties and decay in wood
should be further investigated.
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Uppal 2
INTRODUCTION
Timber bridges, or trestles as they are often called, have existed since the beginning of the railroads in
North America. They have been faster and more economic to construct for relatively short spans (Exhibit
1). Because of maintenance economics and limitation on span lengths, many have been replaced with
steel or concrete structures. Nevertheless, there are still a large number of trestles in service today forming
a significant part (approximately 29 percent) of the railroad bridge inventory. As the timber bridges age
and are subject to ever-increasing axle loads, railroads want to assure their continuing safe performance
under traffic. The outcome of the past research is being re-examined and new areas of research are being
explored, and various methods of economically maintaining and strengthening are being re-evaluated in
order to find ways to extend their service life.
Wipf et al. (1995) conducted a literature review on testing of timber railway bridges in a report
funded by the Association of American Railroads (AAR). This was primarily an extension of the same
effort. The Wipf report outlined the field and laboratory testing performed and it also cited various
surveys conducted to establish research needs, status of research including those on that highway bridges
applicable to railroad bridges, theoretical work, and other pertinent miscellaneous studies.
OBJECTIVES
The primary objective of this paper is to present a brief overview of some of the railroad timber bridge
research performed during the past few decades and to highlight the salient findings of this research. The
secondary objective is to cite the research needs established through various publications, surveys, and
workshops, and to describe the areas of research previously identified that are either underway or remain
in need of research.
This paper is a summary of a report which is divided into the following five sections:
• Surveys, Workshops, and Publications Determining Research Needs and Describing Research
Status
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• Field Tests on Bridges
• Laboratory Tests on Bridge Timber Components
• Analytical Work
• Miscellaneous Research Work
SURVEYS, WORKSHOPS, AND PUBLICATIONS
DESCRIBING RESEARCH STATUS AND DETERMINING RESEARCH NEEDS
Wipf et al. (1997), Foutch (1989), Foutch et al. (1994), and Jones (1997) cited the results of the literature
reviews, surveys, and workshops to determine research needs. Wipf listed 22 research projects out of 118
potential projects ranging from materials, preservatives, construction, and maintenance to economics.
Foutch found that the two highest rated short-term projects involved the development of methods for
determining the ultimate shear, bearing, and bending strength for both new and existing timber bridges.
Other short-term projects that received moderate support were the study of load path for existing bridges
through field testing and the development of nondestructive techniques for evaluation of strength and
remaining life of existing bridges. Jones summarized the previous research in fatigue of timber stringers
by Lewis, the AAR and Tsai and Ansell.
Other research
A brief description was given on the status of several research projects in progress at different times as
reported by Magee (1967), Freas (1967), Bohannan (1968), Oliva (1990), GangaRao (1990), Crews
(1994), and Ritter et al. (1998, 1994). Some of the research projects pertinent to timber bridges are stated:
• Stresses in components of timber trestles
• Different softwood and hardwood species for bridge components
• Glued laminated and stressed laminated construction
• Preservative treatments of timber
• Nondestructive evaluation (NDE) techniques for timber
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FIELD TESTS ON BRIDGES
Nine railroad timber bridges were tested under train loading and at varying train speeds to study their
dynamic performance. Exhibit 2 is a photograph of timber trestle under dynamic testing. The University
of Manitoba; as reported by Uppal, et al. (1990) and Graham (1993), tested three of the bridges. Iowa
State University carried out five tests on three more of the bridges, as reported by Wipf et al. (1993,
1997). Colorado State University performed tests on the remaining three bridges as reported by
Gutkowski et al. (1999) and Robinson et al. (1998). All but the first three tests were performed for the
Association of American Railroads (AAR). The following general inferences were drawn from the
findings of some of the tests:
• The load deflection behavior of the bridge span was fairly linear, in contrast to the nonlinear
behavior of bridge approaches and that of the normal track section.
• The ballast deck span was comparatively stiffer than the similar open-deck one (Exhibit 3). The
bridge spans were stiffer than the approaches, which in turn were stiffer than the track sections.
The vertical loads measured by shear circuits at crawl speeds compared closely to those obtained
from wayside scales.
• Typical load and displacement versus time plots for the open deck timber bridge in Exhibit 4 are
shown in Exhibits 5 and 6, respectively.
• For both the open deck and the ballast deck spans, the dynamic load factors and the dynamic
displacement factors increased with increase in train speed.
• The maximum dynamic displacement factors (i.e., the ratio of dynamic to static displacements)
for the open deck was found to be 1.19 and that for the ballast deck was found to be 1.57.
• The differences in deflections of spaced stringers versus packed stringers of a chord were small.
• The individual stringers in a chord did not behave as a unit. This situation appears to increase
with lowering of bridge condition. However, stringer deflections were successively more
consistent for glued laminated stringers chords and ballast deck spans.
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• There was an insignificant amount of continuity over deflections between the stringers in two
adjacent open deck spans.
• The dynamic performance of a timber bridge depends very much on the condition of its material,
the condition of fasteners, and the bearing of the its components.
• The methods of strengthening that were tested in the field -- the use of helper stringers on the
outside of the existing chords and between the existing chords (Ritter et al., 1994), replacement of
chord made out of the solid sawn stringers with those made out of the glued laminated stringers
(Ritter et al., 1995), and the conversion of an open deck to a ballast deck -- all work to increasing
degrees of effectiveness. The choice of the method depends on many factors including the
existing condition, future life expectancy, and cost of the strengthening (Exhibit 7 a and b).
• Modulus of elasticity (MOE) values for the bridge spans determined by ultrasonic techniques fall
within the range of those established by the conventional methods.
• The structural modeling is required to predict response. However, this modeling is complex and
expensive because of the variables involved.
• Exhibit 8 is a photograph of a stress laminated deck test bridge. From the tests on the stress
laminated deck slab span, the following general additional inference was drawn:
− The measured deflections at midspan showed a decrease in deflection with an increase of the
test train speed.
− Exhibits 9 and 10 show longitudinal and transverse deflections for different train speed. The
deflections measured in the transverse direction indicated that the stress laminated deck slab
behaved like an orthotropic plate with loads being resisted both in the longitudinal and the
transverse directions.
Field Monitoring and Testing
Field monitoring and testing on about two dozen highway bridges have been reported by GangaRao et al.
(1991) of West Virginia University, Ritter et al. (1995, 1996), Wacker et al. (1984, 1992, 1995, 1996),
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Hislop et al. (1996), Kainz (1996), Hilbrich (1996, 1997), and McCutcheon (1992) of the United States
Department of Agriculture (USDA) Forest Products Laboratory. As illustrated in Exhibit 11, the bridges
were either stress laminated or a combination of stress laminated and glued laminated construction.
Different species of softwood and hardwood were used, treated with different preservatives, and made of
different cross sections such as slab, tee, and box sections. The bridges were monitored over periods of
two to five years. All were performing well with minor or no serviceability deficiencies, except three
bridges that had developed slight sags due to the vertical creep. Exhibits 12 and 13 show displacement
profiles at various longitudinal and transverse sections, respectively, with an applied displacement of 1
inch.
Exhibit 14 illustrates three configurations for stressed-timber decks: basic, box section, and T-section.
Tests by GangaRao also indicated the following::
• The measured live load deflections and strains were consistently less than those that were
calculated in the design process.
• The bar force levels remained above or near 50 percent of the initial jacking level, which means
that the ability of the stressing bars to maintain compressive force on bars is satisfactory.
• The loss of camber was evident on all monitored bridges and was substantially larger than
anticipated.
• The environment had little detrimental effect on the bridges tested.
LABORATORY TESTS ON BRIDGE TIMBER COMPONENTS
Bridge Ties
Soudhki et al. (1991) and Madsen (1995) carried out static and dynamic tests on Douglas fir bridge ties.
Soudhki et al
The purpose of the tests conducted by Soudhki was to determine the axle load distribution and
longitudinal shear strength using large size shear specimens and fatigue life of ties. The test setup was
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similar to tie supports in service (see Exhibit 15). Some of the inferences drawn from the tests were as
follows:
• The axle load distribution per tie was at least 25 percent and 30 percent of the axle load for bridge
ties with support girders spaced at 8 feet and 7 feet, respectively. A 14-inch on-center spacing of
ties produced a stiffer deck where the axle load distribution is more spread than in a 16-inch tie
spacing. Further, the use of tie pads resulted in a concentration of the axle load distribution.
Exhibit 16 shows the setup for bridge tie load distribution tests and Exhibit 17 plots the typical
axle load distribution data per tie for beams at 8 feet and ties at 14 inches on-center with no tie
pad.
• The ultimate shear ranged from a minimum of 650 psi to 930 psi. The length of shear region did
not effect the ultimate shear stress. The failure of the shear specimens was by radial and
tangential splitting along the shear region. See Exhibits 18 and 19 for shear test setup and typical
load for shear strain curves.
• Eight bridge ties were dynamically tested in four-point loading. The total load varied from 30
kips (125 psi) to 95 kips (396 psi) and there was no failure at 5 million cycles to failure at 675
cycles, respectively. Exhibit 20 depicts timber bridge ties applied load versus number of cycle to
failure.
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Madsen
The objective of the tests conducted by Madsen was to establish realistic estimate of bridge tie actual
shear strength. The test setup is shown in Exhibit 21. A total of 400 ties (200 new and 200 removed from
a bridge after more than 30 years of service) were tested with different amounts of overhang. Some of the
findings of these tests were as follows:
• The shear capacity of the bridge ties was higher than the bending capacity when tested with
overhangs, but about equal when tested in flush end condition. The overhanging ends of ties
almost doubled the shear capacity.
• When the ties were dapped, they lost 24 percent of their original bending capacity but did not
cause a similar loss in the shear capacity.
• The difference in bending capacity of treated and untreated ties was 7 percent. This is not
explicitly recognized in the current design codes.
• The shear capacity of timber was much greater than shown in the present building codes. The
allowable shear stress could safely be 200 psi. Exhibit 22 illustrates the timber bridge tie shear
strength in the flush condition and Exhibit 23 shows bending strength.
Timber Stringers
Chow
Chow et al. (1997) conducted static tests of old stringers, the survivors of a much larger population of in-
service stringers. The objectives of the Chow tests were to conduct ultimate static bending strength tests
on full-size railroad bridge stringers and to determine if it is possible to justify the increase in the
allowable stress through these tests. The test setup is shown in Exhibit 24. The results are shown in
Exhibits 25 and 26. An average maximum shear stress value and the average maximum bending stress
value at failure were found to be 270 psi and 300 psi for Douglas fir, respectively; and 3,500 psi and
4,000 psi for southern pine, respectively. The mode of failure of all lengths of stringers was in shear or in
a combination of shear and tension.
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Uppal 9
Fry et al.
Fry et al. (1999) reported both static and dynamic tests on new stringers of timber bridges. The objective
of the tests conducted by Fry were to develop stress range versus number of cycle of loading (S-N) curves
for timber similar to those used for steel to determine the remaining fatigue life of beams. This ongoing
program involves tests on southern pine, Douglas fir, and glued laminated stringers. The test setup is
shown in Exhibit 27. To date, static tests on southern pine are complete and dynamic tests on southern
pine are complete. The specimens tested so far failed in shear. The static tests resulted in an average
maximum shear stress of 355 psi. Preliminary indications from the dynamic tests are that a longitudinal
shear stress value of 100 psi or more for design could be safely used for yellow pine stringers. Exhibit 28
illustrates timber stringer shear stress versus number of cycles.
Pellerin and Peterson et al.
Pellerin (1995) and Peterson et al. (1999) have successfully used in-laboratory and in-place NDE
techniques for determining the strength properties and deterioration in wood members.
Tsai and Ansell
Tsai and Ansell (1997) indicated that the failure life is largely species-independent when normalized by
static strength. Their report also indicates that moisture has detrimental effect on fatigue life not only in
reducing the fatigue life but also in accelerating the fatigue damage process.
Rammer and Lebow
Investigations by Rammer and Lebow (1997) indicated that the shear strength of green, solid sawn
Douglas fir beams is not constant but varies with the size of beam. Larger beams have lower shear
strength.
Triantafillou
Triantafillou�s (1991) study showed that fiber-reinforced plastic sheets bonded to wood beams could
substantially increase its shear capacity and that this cost- and work-efficient reinforcement could be
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Uppal 10
applied with minor influence on the aesthetics of wood. Exhibit 29 shows test details of wood beams
reinforced with carbon fiber plastics (CFP). Exhibit 30 shows typical load versus midspan deflection
diagrams for wood beams reinforced with fiber reinforced plastic (FRP) in shear.
Johns and Madsen
Johns and Madsen�s (1982) extensive work on the duration of load effect on lumber inferred that the load
duration phenomenon has proved to involve a definite stress effect, with differing behavior for different
levels of applied stress. It was suggested that a 2-year loading time be used as the basis for published
allowable stresses instead of the 10-year period presently used.
Gutkowski et al.
Laboratory load tests were conducted by Gutkowski et al. on full-size specimens replicating the main
elements of three-, two-, and single-span bridge chords. Initial results, shown in Exhibit 31, indicated
modest difference in the midspan displacement between deck case; thus, lack of continuity at supports.
The models used did not closely predict the measured values mainly because of the support movements.
Other Research
Tests conducted especially on engineered wood products by various researchers indicate that much higher
allowable design stresses could be used for these products as opposed to the solid sawn timber. These
products also indicated far less variability in strength properties, and offer greater choices of forms and
span lengths and better preservative treatment. Though the use of the especially engineered wood
products thus far has been limited in railroad bridges, they have performed well in varying climatic
conditions. Exhibit 32 is a comparison of allowable shear stresses for several species of wood.
ANALYTICAL WORK
Uppal et al. (1998), Rammer and Lebow (1997), Triantafillou (1991), Oliva et al. (1990), Fry et al.
(1999) and Johns and Madsen (1982) all reported analytical work related to timber bridges.
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Uppal 11
Uppal et al.
Uppal et al. used a multi-degree of freedom vehicle-bridge model for predicting the load at wheel-rail
interfaces, vertical displacements, and accelerations at midpoints of a ballast deck and open deck timber
bridge span (see Exhibits 33 and 34). Despite its limitations, this model has offered a means of
comparison with the experimental values and of carrying parametric studies. Exhibit 35 shows a
comparison between measured and predicted displacement versus time plots. The model could be
enhanced to include the stresses in members and several other features.
Rammer and Lebow
Rammer and Lebow developed a mathematical relationship between beam shear and ASTM shear block
strength, including a stress concentration factor for the re-entrant corners of shear block.
Triantafillou
Triantafillou's analytical work showed a level of effectiveness for fiber reinforced plastic (FRP)
reinforcement. The report also discussed how FRP reinforcement was maximized when fibers were
placed in the longitudinal direction and the height of externally bonded sheets was just a little higher than
a limiting value, beyond which FRP precedes wood failure.
Oliva et al.
Oliva et al.(1990) used a commercial finite element computer program with orthotropic plate modeling
capabilities that accurately predicted the behavior of stress-laminated bridge decks. The two analytical
techniques used were capable of providing satisfactory simulation of actual stressed deck behavior as
measured experimentally. Exhibit 36 provides FPL deck and pre-stressing details.
Johns and Madsen
Johns and Madsen treated the duration of load effect as a visco-elastic, limited ductility fracture
mechanics model involving two creep parameters and one strength parameter. They generated a family of
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Uppal 12
curves for different levels of applied stress versus lifetime as a function of percentage of short-term
strength applied. Exhibit 37 shows the numerical results for constant stress.
MISCELLANEOUS WORK
Laine et al.
A study by Laine et al. (1996) showed that the plate compression fatigue was neither a problem, nor a
major contributing factor in the deterioration of creosote-treated red oak cross ties under 33-kip or 39-kip
wheel loading.
Jimenez et al.
Jimenez et al. (1999) reported on gage widening and degradation of different types of ties (e.g., hardwood
and softwood ties, reconstitutes ties, glued laminated ties, parallel strand laminated ties) with different rail
anchoring arrangements under service tests on a loop at the Facility for Accelerated Service Testing
(FAST) located at the Transportation Technology Center near Pueblo, Colorado. Exhibit 38 provides the
calculated gage widening rate in Section 7, 5-degree curve with 4 inches superelevation at FAST.
Uppal and Otter, Muchmore, and Verna
Uppal and Otter (1998) gave an outline of methodologies for strengthening and extending life of existing
railroad bridges and Uppal (1990) illustrated the use of laminated timber (i.e., glued laminated and stress
laminated timber) in railroad bridges. Muchmore (1983) described the properties of treated wood as a
structural material and stated that wood is an economical and practical structural material for many short
span bridges when properly treated to prevent early decay deterioration. Verna et al. (1990) described the
benefits and detriments of timber as a material for bridge construction.
Other Sources
The AREMA Manual for Railway Engineering, Chapter 7, �Timber Structures� provides for design and
construction of railroad timber bridges or trestles. The following materials provide excellent guidelines
for design, construction, and maintenance of wood bridges:
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Uppal 13
• Wood Handbook: Wood as an Engineering Material, Forest Products Laboratory
• Timber Bridge Design, Construction, Inspection and Maintenance,� Forest Products Laboratory
• �Structural Behavior of Timber, � Timber Engineering Ltd.
• "Final Report - Structural Monitoring of Stress-Laminated Timber Bridges in West Virginia,"
West Virginia University
CONCLUSIONS
During the past few decades, a fair amount of research on timber has been carried out. Exhibit 39 is a
photograph of a timber railroad bridge. Work that is considered to be more pertinent to railroad bridges
has been discussed in this report. Based on this brief overview of the literature, the following concluding
remarks are made:
• Although the field testing of bridges has provided a better understanding of their behavior under train
loading, still more tests are desirable for more closely determining the actual forces carried by the
individual components.
• The allowable longitudinal shear stress values given in the AREMA Manual, Chapter 7 could to be
reviewed in light of the results of full-scale tests on timber bridge ties and timber bridge stringers.
• Field tests have demonstrated that methods of strengthening of timber bridges work to varying
degrees of effectiveness. The choice of the method to be employed depends on many factors
including condition, future life expectancy, and cost.
• The conversion of an open deck to a ballast deck has shown advantages.
• The use of the specially-engineered products of wood such as glued laminated, parallel strand
laminated and stressed laminated timbers offer promise in upgrading and life extension of the existing
railroad timber bridges. They possess higher allowable design stresses as opposed to the solid sawn
timber of the same species, can have far less variability in strength properties, and can offer greater
choices of forms and span lengths, and better preservative treatment.
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Uppal 14
• With regular inspection and proper evaluation followed by timely and adequate maintenance
program, the useful service life of many existing railroad timber bridges can be extended by several
years.
• Repairing/reinforcing wood members using fiber-reinforced plastic should be further investigated in
view of the need for prolonging the life of the existing timber bridges.
• Use of NDE techniques for determining the strength properties and for determining decay in wood
may be beneficial. This may offer an effective way of finding internal defects in wood without using
of test drilling.
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Uppal 15
Exhibit 1. A Timber Trestle under a Curved Track
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Uppal 16
Exhibit 2. Timber Trestle under Dynamic Testing
Exhibit 3. Relative Stiffness of Timber Bridges Spans, Bridge Approach and Track
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Exhibit 4. Open Deck Timber Bridge
Exhibit 5. Loads at Wheel/Rail Interfaces versus Time ODB Site, Midpoint of Span S2, Test Train Number 2, 30 mph
Exhibit 6. Vertical Displacement versus Time ODB Site, Midpoint of Span S2, Test Train No. 2, 30 mph
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Uppal 18
Re
lati v
e D
isp
lace
me
nt
(in
)
T im e (se c) T im e (se c)
S tri nger 5 S tri nger 6S tri nger 7 S tri nger 8
Exhibit 7a. Replacement of Solid Sawn Timber Deck with Glue Laminated Deck
-0. 7
-0. 6
-0. 5
-0. 4
-0. 3
-0. 2
-0. 1
0
0.1
Rel
ativ
e D
ispl
acem
ent
(in)
0 2 4 6 8 10 12 14 16 Tim e (sec) Ti m e (sec)
S tri nger 5 S tri nger 6 S tri nger 7
1995 D ataR evenue S ervi ce Trai n4 ply sol id saw n chord7 3/4" x 16 1/4" stri ngers
S tri nger 5
0018413b
S tri nger 6S tri nger 7 S tri nger 8
1996 D ata1-6axl e locom otive, 3 hoppers4 ply gl ue-l am inat ed chord6 3/4" x 18" st ri ngers
Exhibit 7b. Conversion of Open Deck to Ballast Deck
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Uppal 19
Exhibit 9. Longitudinal Displacements � Stress Laminated Deck
Exhibit 8. Stress Laminated Deck Test Bridge
Exhibit 10. Transverse Displacements � Stress laminated Deck
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Uppal 20
Exhibit 11. FPL Deck and Pre-stressing Details
Exhibit 12. Displacement Profiles at Various Longitudinal Sections with an Applied Displacement of 1 inch
Exhibit 13. Displacement Profiles at Various Transverse Sections with
an Applied Displacement of 1 inch
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Exhibit 14. Configurations for Stressed-timber Decks: (a) Basic;
(b) Box Section; and (c) T-section
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Exhibit 15. Setup for Dynamic Tests on Timber Bridge Ties
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Exhibit 17. Typical Axle Load Distribution Data Per Tie for Beams at 8 feet and Ties at 14 inches On-center with No Tie Pad
Exhibit 16. Setup for Bridge Tie Load Distribution Tests
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Uppal 24
c.
b.
Exhibit 18. Shear Test Setup: (a) Typical Specimen, (b) Schematic
Representation, (c)Test Setup, and (d) Schematic Representation
d.
a.
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Uppal 25
Exhibit 19. Typical Load � Shear Strain Curves for Shear Test
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Exhibit 20. Timber Bridge Ties Applied Load Versus Number of Cycle to Failure
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Exhibit 21a. Test Setup for Dynamic Tests � Timber Bridge Ties with and without End Overhang
Exhibit 21b. Dynamic Test on Timber Bridge Ties in Progress
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Exhibit 23. Timber Bridge Ties � Bending Strength
Exhibit 22. Timber Bridge Ties � Shear Strength, Flush Condition
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Exhibit 24a. Test Setup for Static Tests on Timber Stringers in Progress
Exhibit 24b. Schematic of Test Setup
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Exhibit 26. Percentage Exceeding Ultimate Shear Stresses
Exhibit 25. Percentage Exceeding Ultimate Bending
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Exhibit 27. Test Setup for Dynamic tests on Timber Stringers (Two Stringers Tested Simultaneously per Test Frame x Two Frames)
10
100
1000
0.1 10 1000 105 107 109
8" x 16" Solid-Sawn, Creosote-Treated Southern PineAll Shear Failures and Run-Outs
(regression calculations consider "TAMU 98/99 Shear Failures" only)
AAR 1967 Shear Failures
AAR 1967 Run-Outs
TAMU 98/99 Shear Failures
TAMU 98/99 Run-Outs
TAMU 98/99 Ongoing Tests
95% Lower Confidence Limit
y = 327.44 * x^(-0.045107) R= 0.81887
Puls
atin
g S
hea
r S
tres
s A
mpli
tude
∆V
max
(p
si)
No. Pulsating Load Cycles (N)
95% Lower Confidence Limit
∆V95%
= 239 N (-0.045)
Exhibit 28. Timber Stringers Shear Stress versus Number of Cycles
1191/ exh.doc
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Uppal 32
c) Experimental Testing Apparatus
Exhibit 29. Test Details of Wood Beams Reinforced with CFP
a. Geometry of Wood Beams Tested
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b. Beam Designs Used in Experimental Program
Exhibit 30. Typical Load Versus Midspan Deflection Diagrams for Wood Beams Reinforced with FRP in Shear
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Exhibit 32. Comparison of Allowable Shear Stresses
Species of Timber Shear parallel to grains (psi)
Softwood 60-85
Hardwood 80-145
Glue-laminated (Softwood) 90-165
Parallel-strained Laminated (softwood) 175-290
Exhibit 31. Laboratory Tests on 3-, 2- and 1-Span Timber Bridge Chord
Far Inside
Near Inside
Near Inside
Far Inside
Measured Displacement Predicted Displacement
4 Stringers
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Exhibit 33a. Idealized Vehicle Model
Exhibit 33b. Idealized Train � Location of Wheels on Chord Segments
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Exhibit 34a. Relationship between Displacement Under ith
Wheel and Its Neighboring Nodal Points j and j+1
Exhibit 34b. Vehicle � Bridge Interaction Relationship
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Exhibit 35. Comparison between Measured and Predicted Displacement Versus Time, ODB Span S2, Test Train No. 2 at 30 mph
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Exhibit 36a. FPL Deck and Pre-stressing Details. (ML89 5804)
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Exhibit 36b. Comparison of Analytical Results and Experimental Longitudinal Deck Displacement Profiles along the Deck Center Line for the Deck with
Continuous Laminae, without Steel Channels, and with Rods on 2-foot Centers Deck Span was 24 ft, and the Transverse Stressing was at 50 lb/in
2. The Comparison Shown is for
a Point Load at Center at Midspan. (ML89 5824)
Exhibit 36c. Comparison of Analytical Results and Experimental Transverse Deck Displacement Profiles at Midspan for the Deck with Continuous Laminae,
without Steel Channels and with Rods on 2-foot Centers Deck Span was 24 ft, and the Transverse Stressing was at 100 lb/in
2 (compared with Fig. 16(a)
at 50 lb/in2). The Comparisons shown are for a Point Load at Center at Midspan
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Exhibit 37. Time Relationship: Numerical Results for Constant Stress (1psi = 6.89 kPa)
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Exhibit 38. Calculated Gage Widening Rate in Section 7, 5-degree, 4-inch Superelevation Curve
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Exhibit 39. Railroad Timber Bridge
(C) AREMA (R) 2000
Uppal 43
Bibliography
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Atlanta, GA.
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Department, Colorado State University, Fort Collins, CO, December 1998.
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Components in Strengthening Timber Bridges," TD 97-026, Association of American
Railroads, July 1997.
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Conference, Vancouver Canada, May 1991.
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in Civil Engineering, ASCE, May 1997.
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Engineering, CSCE, December 1990.
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