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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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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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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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 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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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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• 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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• 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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Exhibit 1. A Timber Trestle under a Curved Track

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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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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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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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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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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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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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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

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Bibliography

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(C) AREMA (R) 2000

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(C) AREMA (R) 2000