United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Timber Bridge

Information

Resource Center

Research

Paper

FPL–RP–552

Field Performance of

Timber Bridges

9. Big Erick's

Stress-Laminated Deck Bridge

James A. Kainz

James P. Wacker

Martin Nelson
Abstract

The Big Erick’s bridge was constructed during September

1992 in Baraga County, Michigan. The bridge is 72 ft long,

16 ft wide, and consists of three simple spans: two stresslaminated deck approach spans and a stress-laminated box

center span. The bridge is unique in that it is one of the first

known stress-laminated timber bridge applications to use

Eastern Hemlock sawn lumber and a combination of stresslaminated decks and a stress-laminated box in a single

bridge. Performance of the bridge was monitored for

35 months, beginning at the time of installation. Monitoring

involved gathering and evaluating data relative to the moisture content of the wood components, the force level of

stressing bars, and the behavior of the bridge under staticload conditions. In addition, comprehensive visual inspections were conducted to assess the overall condition of the

structure. Based on field evaluations, the bridge is performing well, with only minor serviceability deficiencies.

November 1996

Kainz, James A.; Wacker, James P.; Nelson, Martin. 1996. Field

performance of timber bridges—9. Big Erick’s stress-laminated deck

bridge. Res. Pap. FPL–RP–552. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory. 24 p.

A limited number of free copies of this publication are available to the

public from the Forest Products Laboratory, One Gifford Pinchot Drive,

Madison, WI 53705–2398. Laboratory publications are sent to more than

1,000 libraries in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the

University of Wisconsin.

The United States Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, sex,

religion, age, disability, political beliefs, and marital or familial status. Persons with disabilities who require alternative means of communication of

program information (braille, large print, audiotape, etc.) should contact

the USDA Office of Communications at (202) 720–2791. To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture,

Washington, DC 20250, or call (800) 245–6340 (voice), or (202) 720–1127

(TTD). USDA is an equal employment opportunity employer.

Acknowledgments

We express our sincere appreciation to the following from the

USDA Forest Service, Forest Products Laboratory, who contributed to this project: Mike Ritter, Paula Hilbrich Lee,

Lola Hislop, Maureen Mathias, and Kim Stanfill–McMillan

for assisting with data collection, data analysis, and report

preparation; Vyto Malinauskas and Earl Geske for developing

and fabricating load cells; and the Information Services Team

for assistance in preparing this report.

Contents

Page

Introduction................................................................1

Background................................................................1

Objective and Scope.....................................................3

Design, Construction, and Cost .....................................3

Design ...................................................................3

Construction ...........................................................5

Cost ......................................................................9

Evaluation Methodology...............................................9

Moisture Content.....................................................9

Bar Force................................................................9

Load Test Behavior..................................................9

Condition Assessment ............................................11

Results and Discussion...............................................11

Moisture Content...................................................11

Bar Force..............................................................11

Load Test Behavior................................................12

Condition Assessment ............................................18

Conclusions .............................................................22

References ................................................................23

Appendix—Information Sheet......................................24
Field Performance of Timber Bridges

9..Big Erick’s Stress-Laminated Deck Bridge

James A. Kainz, General Engineer

James P. Wacker, General Engineer

Forest Products Laboratory, Madison, Wisconsin

Martin Nelson, Area Forest Manager

Michigan Department of Natural Resources

Baraga County, Michigan

Introduction

In 1988, the U.S. Congress passed legislation known as the

Timber Bridge Initiative (TBI) (USDA 1995). The objective

of this legislation was to establish a national program to

provide effective and efficient utilization of wood as a structural material for highway bridges. Responsibility for the development, implementation, and administration of a program

based on the goals of the TBI legislation was assigned to the

USDA Forest Service. The Forest Service established three

primary program areas to effectively implement and administer this program: demonstration bridges, technology transfer,

and research. The demonstration bridge program and technology transfer are administered through the Timber Bridge

Information Resource Center (TBIRC) in Morgantown, West

Virginia. As part of the demonstration bridge program,

TBIRC has been awarding annual grants for demonstration

bridges on a competitive basis since 1989. Funds are

awarded for the design and construction of demonstration

timber bridges with innovative designs and those that use

locally available underutilized wood species. The TBIRC

also maintains a technology transfer program to provide

assistance and state-of-the-art information related to all

aspects of timber bridges. Responsibility for the research portion of the TBI program was assigned to the USDA Forest

Service, Forest Products Laboratory (FPL). The FPL established a broad research program to conduct a variety of timber bridge studies under laboratory and field conditions, including a nationwide bridge monitoring program. Through

the bridge monitoring program, FPL is able to collect, analyze, and distribute information on the field performance of

timber bridges to provide a basis for validating or revising

design criteria and further improving efficiency and economy

of timber bridge design, fabrication, and construction.

This report is ninth in a series that documents the field performance of timber bridges included in the FPL national

timber bridge monitoring program. It describes the development, design, construction, and field performance of the Big

Erick’s bridge located in Baraga County, Michigan.

Table 1—Factors for converting English units of

measurement to SI units

English unit

Conversion

factor SI unit

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

square foot (ft2

) 0.09 square meter (m2)

pound (lb) 4.448 Newton (N)

lb/in2

 (stress) 6,894 Pascal (Pa)

The bridge is a 72-ft-long, single-lane, three-span structure,

consisting of stress-laminated deck approach spans and a

stress-laminated box center span. (See Table 1 for metric

conversion factors.) Built in 1992, the Big Erick’s bridge

was funded through a competitive grant from the TBIRC and

matching funds from the Michigan Department of Natural

Resources. The bridge is one of the first known applications

that uses Eastern Hemlock lumber, a locally underutilized

secondary softwood species, in a stress-laminated configuration. The bridge is also the first known application where a

stress-laminated deck is combined with a stress-laminated

box. An information sheet on the Big Erick’s bridge is

provided in the Appendix.

Background

The Big Erick’s bridge is located in Baraga County, approximately 20 miles northeast of L’Anse, in the western

Upper Peninsula of Michigan (Fig. 1). The bridge is owned

by the Michigan Department of Natural Resources (MI–

DNR) and is part of a state forest gravel road that provides

access to the Huron River valley for recreation, private residences, logging traffic, and fire control equipment. The

estimated average daily traffic for this section of the road is

approximately 30 vehicles, of which 30 percent is logging

traffic.
2

The original Big Erick’s bridge was constructed in 1957 by

the MI–DNR Fire Division to provide access for administrative vehicles, fire equipment, and logging trucks. This

bridge was 20 ft wide and consisted of two 20-ft-long approach spans and a 32-ft-long center span (Fig. 2). Beneath

two layers of timber plank deck, the approach spans were

supported by untreated sawn lumber stringers and the center

span was supported by steel stringers. Failure of the deck

material in 1980 alerted MI–DNR officials to structural problems with the bridge. After the decking material was repaired, an annual inspection in 1989 revealed cracked and

decayed wood stringers on the approach spans. Several

options were examined to repair or replace the structure. As a

result of uncertainty regarding the extent of rehabilitation

required to restore full-load capacity, replacement of the

bridge was deemed the most feasible solution.

As a result of the high volume of public recreation in the

area, the MI–DNR chose a timber bridge as a replacement to

blend with the natural aesthetics of the area. The Upper Peninsula Resource Conservation and Development Council was

contacted to submit a proposal for partial funding for a replacement demonstration timber bridge under the Forest

Service demonstration program. As part of this proposal, a

preliminary bridge design was developed, consisting of two

stress-laminated decks and one stress-laminated box. Eastern

Hemlock was selected as a primary material for the bridge

because it is an underutilized, locally grown species in the

Upper Peninsula of Michigan. The proposal was submitted

in January 1991 to the TBIRC for inclusion under the Timber Bridge Initiative (USDA 1995). After review by a selection panel, funds were awarded and final design of the replacement bridge was initiated. During the final design phase

of the project, FPL was contacted to monitor the new Big

Erick’s timber bridge. As a result, FPL and MI–DNR developed a mutually agreeable monitoring plan that was initiated

at installation.

Figure 1—Location maps for the Big Erick’s bridge.

Figure 2—Big Erick’s bridge prior to replacement

(1980).
3

Objective and Scope

The objective of this project was to evaluate the field performance of the Big Erick’s bridge for 35 months, beginning

at bridge installation. The project scope included data collection and analysis related to the wood moisture content,

stressing bar force, bridge behavior under static truck loading, and general structure performance. The results of this

project will be considered with similar monitoring projects

to improve design and construction methods for future stresslaminated bridges.

Design, Construction,

and Cost

The design and construction of the Big Erick’s bridge was a

cooperative effort involving several agencies and individuals.

An overview of the design, construction, and cost of the

bridge superstructure is presented.

Design

Design of the Big Erick’s bridge was completed by a consulting engineer retained by MI–DNR. The design geometry

provided for three simple spans with a total length of 72 ft

and a width of 16 ft. The structure consists of two 20-ft-long,

stress-laminated deck approach spans and one 32-ft-long,

stress-laminated box center span (Fig. 3). The span lengths

were designed to match existing reinforced concrete abutment

and pier configurations, because the substructure was in serviceable condition. Each span was also designed for construction as preassembled half-width panels to improve transportation and on-site assembly.

Aside from those design aspects related to stress laminating,

the bridge design was in accordance with the American

Association of State Highway and Transportation Officials

(AASHTO) Standard Specifications for Highway Bridges

(AASHTO 1989) for a single lane of AASHTO HS25–44

truck loading. Design criteria for stress laminating were

different for the deck and box spans and are discussed in

detail in the following sections on approach span design and

center span design. Common to both stress-laminated designs was the use of 0.625-in. coarse, right-hand thread, high

strength steel bars, which comply with the requirements of

ASTM A722 (ASTM 1988) and provide a minimum

ultimate tensile strength of 150,000 lb/in2

.

Design of the bridge rail and curb system was based on

AASHTO static-load requirements for vehicular and pedestrian traffic. The bridge rail and curb consisted of two 5.125-

by 6-in. glued-laminated (glulam) timber rails and a 6- by

12-in. sawn lumber curb with 6- by 12-in. sawn lumber

scupper blocks. The rail and curb were attached to 8.75- by

10.5-in. glulam posts, spaced 6 ft on center along the edges

of the bridge (Fig. 3, Guardrail and Anchorage).

For protection from deterioration, all steel components, including stressing hardware, stressing bars, and anchorage

plates, were galvanized in accordance with AASHTO M111

(AASHTO 1990). All wood components were preservative

treated with creosote in accordance with American Wood

Preservers’ Association (AWPA) Standard C14 (AWPA

1990). To protect pedestrians from direct contact with creosote-treated lumber, the glulam rails were covered with

CCA-treated dimension lumber facia boards. In addition, a

2.75-in. asphalt wearing surface was specified for the bridge

and approach roadway as a means of protecting the deck

surface from the premature deterioration resulting from direct

exposure to traffic and the elements.

Approach Span Design

The stress-laminated deck approach spans were identical in

design and configuration. Design criteria for stress laminating

were based on a newly developed Forest Service design procedure (Ritter 1990). Each span was 20 ft long, 16 ft wide,

and 11 in. deep (Fig. 3). The laminations consisted of 2- by

11-in. Eastern Hemlock sawn lumber that was surfaced on

one side to provide uniform thickness. Eastern Hemlock was

not available in 20-ft lengths; therefore, butt joints were used

in the decks. Butt joints were spaced across the width and

length at intervals of eight laminations and 4 ft, respectively

(Fig. 4). Design values for the Eastern Hemlock laminations

were based on the National Design Specification for Wood

Construction (AFPA 1988) for lumber visually graded

No. 1, in accordance with Northeastern Lumber Manufacturing Association (NELMA) rules (NELMA 1986). The tabulated design values for the Eastern Hemlock species combination were 1,300 lb/in2

 for bending strength, 1,200,000 lb/in2

for modulus of elasticity (MOE), 85 lb/in2 for shear strength,

and 550 lb/in2 for compression strength perpendicular to

grain. All design values were adjusted with the appropriate

wet-use factors, and laminations were specified to be at or

less than 19 percent moisture content prior to preservative

treatment and bridge installation.

The stressing system for the stress-laminated decks utilized

nine high strength steel bars per span that were inserted

through predrilled holes at the center of the laminations

(Fig. 3, Section A-A). The bars were spaced 2 ft on center,

starting 2 ft from the span end. Each bar required a tensile

force of 26,400 lb to provide 100-lb/in2 interlaminar compression between the laminations. Bar tension was trans- ferred into the deck using a discrete plate anchorage system,

consisting of 6- by 12- by 0.875-in. bearing plates and a

2- by 5- by 1-in. anchor plate with a hexagonal nut (Fig. 3

Guardrail and Anchorage).

Center Span Design

Design requirements for the stress-laminated box center span

were based on standard design criteria adopted by West Virginia Department of Highways (WV–DOH 1989). The span

is 32 ft long, 16 ft wide, and 22.5 in. deep (Fig. 3). The box

configuration consisted of Southern Pine glulam webs and

Eastern Hemlock sawn lumber flanges. Glulam webs were

8.75 in. wide and 22.5 in. deep, except for the two center

webs that were 5.125 in. wide and 22.5 in. deep. Glulam

design was based on material properties for combination

24F–V3, as specified by the American Institute of Timber
4

Figure 3—Design configuration of the Big Erick’s bridge.
5

Construction (AITC) Standard Specifications for Structural

Glued Laminated Timber for Softwood Species (AITC

1987). Tabulated design values were 2,400 lb/in2

 for bending

strength, 1,800,000 lb/in2 for MOE, 200 lb/in2 for shear

strength, and 560 lb/in2 for compression strength perpendicular to grain. All design values were adjusted by appropriate

wet-use factors per AITC requirements. The sawn lumber

flanges, 7 in. deep, were the same species and grade of Eastern Hemlock as was used for the approach spans. Butt joints

in the sawn lumber flanges were specified at an interval of

one butt joint every four adjacent laminations, spaced 4 ft

longitudinally (Fig. 4).

The stressing system for the center span consisted of 30 high

strength steel bars placed in pairs, 3.5 in. from the top and

bottom of the glulam beams (Fig. 3, Section B-B). The bars

were spaced 2 ft on center, starting 2 ft from the span ends,

and were placed through the center of the top and bottom

sawn lumber flange. A tensile force of 16,800 lb was required

in each bar to provide 100 lb/in2

 of interlaminar compression. Bar tension was transferred into the box using a discrete plate anchorage system, consisting of 6- by 10- by

0.875-in. bearing plates and 2- by 5- by 1-in. anchor plates

with a hexagonal nut (Fig. 3, Guardrail and Anchorage).

Construction

Construction of the Big Erick’s bridge was completed by

MI–DNR personnel and local prison labor in the summer

and fall of 1992. Construction extended over several months

and was completed in two phases: assembly and installation.

Assembly

As previously mentioned, the bridge was designed for preassembly in half-width sections at a location other than the

bridge site. The process began with the harvesting and milling of Eastern Hemlock sawn lumber in the Upper Peninsula

of Michigan. The material was then airdried and stored outside for approximately 5 months prior to preservative treatment (Fig. 5). During this period, the glulam beams were

manufactured in Wisconsin. Following drying and manufacture, all sawn lumber and glulam members were prefabricated

(cut and drilled) and sent to Indiana for pressure preservative

treatment with creosote. When the preservative treatment was

completed, the material was shipped to Baraga, Michigan,

for assembly. During 3 weeks in July 1992, the sawn lumber

and glulam beams were assembled into half-width panels.

The approach span deck assembly was initiated by placing

the laminations edgewise on temporary supports and nailing

them together. Bars were then inserted through predrilled

holes (Fig. 6). The center span box assembly proceeded in a

similar manner. The exterior web was placed on temporary

supports, and the bottom flange was nailed to the web. The

next web was placed adjacent to the bottom flange, and the

top flange was nailed in place. After the top and bottom

flanges were in place, the bars were inserted through the predrilled holes (Fig. 6). Both assembly processes continued

until 8-ft-wide panels were completed. After each panel was

assembled, bearing plate anchorage systems were installed on

all the bars. The stressing bars were then tensioned along the

length of the half-width panel to a design load of 26,400 lb

for the approach spans and 16,800 lb for the center span.

Figure 4—Butt-joint configuration used with Eastern Hemlock deck laminations for the (a) approach spans

and (b) center span on the Big Erick’s bridge. A butt joint was placed transverse to the span in every

(a) eighth lamination on the stress-laminated decks and (b) fourth lamination on the stress-laminated box.

Longitudinally, butt joints in adjacent laminations were separated by 4 ft.
6

The stressing was accomplished with a hydraulic jacking

system, which consisted of a hydraulic pump, a single hollow core jack, and a stressing chair (Fig. 7) (Wacker and

Ritter 1992). After all panels were assembled and stressed, a

second design load stressing was completed August 26,

1992, approximately 1 month after the initial stressing. The

panels were then loaded on two flatbed trailers and

transported to the bridge site in preparation for bridge

installation (Fig. 8).

Installation

After demolition and removal of the existing bridge superstructure, an assessment of the reinforced concrete substructure revealed that the west abutment had sustained freezethaw damage. To remedy the problem, the damaged part

of the west abutment was removed, and the remaining

portion of the abutment was capped with new concrete. The

remainder of the substructure was structurally adequate, and

the complete substructure was coated with a sealer prior to

the new bridge installation. Wood sleeper blocks, measuring

12.5 by 5.75 in., were added at the center span piers to raise

the new bridge to the existing roadway grade. After the addition of neoprene bearing pads, additional modifications were

not made to the abutments or piers.

When the substructure work was completed, the assembled

half-width panels were lifted into place with a large overhead

crane (Fig. 9). After the half-width panels were placed, each

panel was connected to the adjacent panel with high strength

steel couplers on the stressing bars (Fig. 10). After all bars

were coupled, stressing bars were partially tensioned to bring

the half-width panels into contact. Full-design bar force was

then introduced into the bridge by utilizing two separate sets

Figure 5—Eastern Hemlock lumber for the Big Erick’s

bridge awaiting preservative treatment.

Figure 6—Prefabrication of the stress-laminated deck

(top) and stress-laminated box (bottom) in half-width

panels at an outdoor work site.

Figure 7—High strength steel bars were tensioned

using a single hydraulic jack, electric pump, and

steel chair.

Figure 8—Prefabricated half-width panels arriving at

the bridge site prior to installation.
7

of hydraulic equipment. The MI–DNR crew began at opposite ends of each span and stressed each bar along the length

of that span (Fig. 11). On the center span, each set of bars

(top and bottom) was tensioned before moving along the

span length to the next set of bars. After all bars were fully

tensioned, the stressing process was repeated to ensure that

the stress level was uniform and at the required design level.

After bar stressing, the bridge was attached to the substructure. The two approach spans were connected by steel angles,

concrete anchors, and lag bolts located in the corners, at the

abutments, and underneath the deck at the piers. The center

span was connected by drift pins driven through the end of

each glulam web to the sleeper block on the concrete pier.

Following substructure attachment, the timber curb and rail

system was installed. As a result of expected pedestrian

traffic from the adjoining campground, CCA-treated lumber

facia boards were installed over the creosote rail members and

a roofing sealer was applied to the curb. The asphalt wearing

surface was applied approximately 2 weeks after bridge installation. The completed bridge is shown in Figure 12.

Figure 10—Connection betwen half-width panels

was achieved by placing couplers on adjacent

bars and stressing the entire deck together.

Figure 11—Two sets of deck stressing equipment

were used to tension the stressing bars after deck

placement.

Figure 9—Placement of half-width panels with an

overhead crane.
8

Figure 12—Completed Big Erick’s bridge: side view (top), end view (bottom).
9

Cost

Total cost of the Big Erick’s bridge superstructure was

$66,157 and included fabrication, materials, labor, and construction. As a result of the different design methodologies

used in this three-span bridge, costs for each span type were

tabulated separately and are summarized in Table 2. The cost

per square foot is based on the total cost of the span divided

by the total deck area of that span. The $75/ft2 for the center

span was almost twice the $43/ft2 for the approach spans.

The increased center span cost is attributable to the greater

quantity of material and longer installation time. The increased material cost of the center span is the result of using

glulam timber for the webs; two rows of plates, bars, and

nuts; and two layers of flange decking material.

Evaluation Methodology

To evaluate the structural and serviceability performance of

the Big Erick’s bridge, MI–DNR contacted FPL for assistance. Through mutual agreement, a 3-year bridge monitoring plan was developed by the FPL and implemented

through a Cooperative Research and Development Agreement

with MI–DNR. The plan included performance monitoring of

the deck moisture content, stressing bar force, static-load test

behavior, and general bridge condition. During the installation of the bridge, FPL representatives visited the bridge site

to install instrumentation and train MI–DNR personnel in

the data collection process for moisture content and bar force

measurements. Static-load tests and general bridge condition

assessments were conducted by FPL representatives during

site visits. The evaluation methodology employed procedures and equipment developed by FPL and used on similar

structures (Ritter and others 1991).

Moisture Content

To characterize changes in moisture content, an electricalresistance moisture meter was used to obtain wood moisture

content readings on a monthly basis. Moisture meter measurements were taken by MI–DNR personnel from the sawn

lumber in the west approach span and were assumed to be

representative of overall bridge moisture content. The west

span was chosen because of safety concerns in accessing other

bridge locations. Measurements were obtained in accordance

with ASTM D4444–84 (ASTM 1990) by driving the moisture pins into the underside of the deck at depths of 2 to

3 in., recording the moisture content value from the unit,

then adjusting the moisture content value for temperature and

wood species, if necessary.

Bar Force

To monitor stressing bar force, two calibrated load cells were

placed on each span of the Big Erick’s bridge at the time of

bridge installation. The cells were placed on the stressing

bar, between the bearing and anchorage plates, to monitor bar

forces based on the strain variations in the load cell

(Fig. 13). Load cell measurements were obtained by

MI–DNR personnel with a portable strain indicator on a

biweekly basis for the first year, and monthly thereafter. The

measurements were then converted to force levels, based on

laboratory load cell calibrations, to determine the tensile

force in the bar. Approximately midway through the monitoring period, the load cells were unloaded and adjusted for

zero balance shift. At the conclusion of the monitoring

period, the load cells were removed, adjusted for zero balance

shift, and recalibrated in the laboratory. In addition, hydraulic stressing equipment was used at the site visits during the

monitoring period to verify bar force levels obtained from the

load cells.

Load Test Behavior

To determine load behavior of the Big Erick’s bridge, two

static-load tests were conducted during the monitoring

period. The first load test was completed on two separate

occasions; the approach spans were tested 2 months after

bridge installation and the center span was tested 11 months

after installation. A second and final load test was completed

35 months after bridge installation and included tests on all

three spans.

The static-load test consisted of positioning a fully loaded

truck separately on each span and measuring the resulting

deflections along the transverse midspan of the loaded span.

For both load tests, the truck was positioned for three transverse load cases on each span (Fig. 14). The first load case

centered the vehicle over the longitudinal centerline; the

second load case located the vehicle adjacent to the upstream

curb; the third load case located the vehicle adjacent to the

Table 2—Final costs of bridge superstructure

Deck Cost (US$)

Span

area

(ft2) Materials Labor Total

Per

ft2

Approacha 640 12,390 15,391 27,781 43

Center 512 24,909 13,467 38,376 75

a

Costs are based on total costs for west and

 east spans.

Figure 13—One of six load cells installed on stressing

bars to measure changes in bar force.
10

downstream curb (Fig. 15). Longitudinal vehicle placement

differed, depending upon the span length and vehicle configuration. Measurements of bridge deflections were taken prior

to testing (unloaded), for each load case (loaded), and at the

conclusion of testing (unloaded). Measurements of bridge

deflections from an unloaded to loaded condition were obtained by hanging calibrated rules on the underside of the

deck and reading values with a surveyor’s level. The accuracy of this method for repetitive readings is estimated to be

±0.04 in.

Load Test 1A

The first load test was November 19, 1992, and involved

approach span testing only. The test vehicle was a loaded,

three-axle dump truck with a gross vehicle weight of

54,760 lb (Fig. 16). The vehicle was positioned longitudinally, with the tandem rear axles bisecting the midspan with

the front axle off the bridge. The truck faced west when testing the west span and east when testing the east span. Data

points were transversely positioned along the midspan of

each approach span at an interval of 2 ft, beginning at the

longitudinal bridge centerline. It should be noted that the

data points were not directly below the vehicle wheel lines

during load case 1.

Load Test 1B

Load test 1B involved the center span only and was completed August 23, 1993,—9 months after the sawn lumber

approach spans were tested. The test vehicle was a loaded,

three-axle dump truck with a gross vehicle weight of

Figure 14—Transverse load cases

(looking west) used for all static-load

tests on the Big Erick’s bridge.

Figure 15—Transverse load test cases used for all

spans: (top) load case 1, centered on roadway; (middle)

load case 2, adjacent to upstream curb; (bottom) load

case 3, adjacent to downstream curb.
11

57,92 lb (Fig. 16). The vehicle was positioned longitudinally, facing east, so that the centroid of the vehicle aligned

with the midspan. Data points were set at the centerline of

each glulam beam at midspan.

Load Test 2

The final load test was completed July 18, 1995, and included testing on all three spans. The test vehicle was a

loaded, three-axle dump truck with a gross vehicle weight of

53,420 lb (Fig. 16). The vehicle was positioned longitudinally on each span in the same positions used for load tests

1A and 1B. Data points were located for the approach spans

at a transverse spacing of 1.5 ft so that the points aligned

with the vehicle wheel lines. Data points for the center span

were the same as those used for load test 1B.

Analytical Assessment

At the conclusion of load testing, the approach span behavior

was modeled for load test and AASHTO HS 25–44 loading

using an orthotropic plate computer program developed at

FPL. The center span was not modeled.

Condition Assessment

The general condition of the bridge was assessed on four

separate occasions during the monitoring period. Condition

assessments were performed by FPL personnel at bridge installation and during load testing. The assessments involved

visual inspections, measurements, and photographic documentation of the condition of the bridge. Items of specific interest included geometry, camber, wood condition, wearing

surface, and stressing system.

Results and Discussion

Performance monitoring of the Big Erick’s bridge extended

for 35 months, beginning in September 1992. Results and

discussion of the performance data follow.

Moisture Content

The average trend in electrical resistance moisture content

readings is shown in Figure 17. Readings taken at the beginning of the monitoring period indicate an average moisture content of approximately 33 percent. During the monitoring period, an overall decrease in moisture content was

observed, with seasonal changes of ±2 percent. At the end of

monitoring, moisture content was approximately 28 percent,

a 5-percent decrease. The laminations remained within

±3 percent of the fiber saturation level for Eastern Hemlock,

which is generally assumed as 30 percent but can range from

25 to 30 percent (FPL 1987).

Bar Force

The average trend in bar force, starting at the third stressing,

is shown in Figure 18. At the third stressing, all bars were

tensioned to the design level of 100 lb/in2, or 26,400 lb for

the approach spans and 16,800 lb for the center box. After

2 months, all three spans lost 40 to 50 percent of the design

bar force and the bars were retensioned. Eleven months after

installation, all three spans lost 50 to 60 percent of the design bar force and were tensioned again. Approximately

2 weeks after this fifth bar tensioning, the bar force stabilized

at approximately 70 percent of the design bar force, then decreased slowly for the remainder of the monitoring period. At

the conclusion of monitoring, bar force values were 14,800 lb

Figure 16—Load test truck configurations and axle loads

for load tests 1A, 1B, and 2. All vehicle track widths,

measured center–to–center of the rear tires, were 6 ft.

Figure 17—Average trend in electrical resistance

moisture content readings.
12

for the west span, 8,700 lb for the center span, and 12,500 lb

for the east span, which is 45 to 55 percent of the design bar

force. With each bar tensioning, the rate of bar force loss

decreased, although the overall amount of bar force lost between stressings remained relatively equal.

The bar force loss was probably the result of three factors:

stress relaxation, prefabrication methodology, and crushing of

the timber laminations. The majority of bar force loss was

the result of stress relaxation, a time-dependent phenomenon

caused by the long-term compressive force of the steel bars

acting on the wood microstructure. The rate of stress relaxation was greater on the Big Erick’s bridge when compared

with other stress-laminated bridges and was probably the result of the high moisture content in the timber laminations.

An additional factor affecting bar force loss was the prefabrication methodology of completing two of the recommended bar

tensionings on partial-width sections. This methodology

diminished the positive effects of repetitive tensionings, because the bars were not full width until the third tensioning.

Another plausible cause of bar force loss was crushing of the

exterior laminations on the approach spans. Crushing was

observed under the bearing plates during construction and the

monitoring period. The rate of crushing and the corresponding bar force loss decreased with each subsequent bar tensioning. This is discussed in detail in the Condition Assessment

section.

The observed bar force on the center and approach spans behaved similarly, as displayed in Figure 18. The center and

approach spans have different bar force design values; therefore, percentage of bar force loss was used for comparison. All

spans exhibited similar bar force losses of 40 to 50 percent

before the fourth stressing, 50 to 60 percent prior to the fifth

stressing, and 45 to 55 percent at the end of monitoring.

These similarities between the approach spans and the center

span suggest that stress-laminated decks and boxes, built

from comparable materials, perform alike when subjected to

the same environmental conditions.

Load Test Behavior

Results of the static-load tests and analytical assessment of

the Big Erick’s bridge are presented. For each load case,

transverse deflection measurements are given at the midspan

of each span as viewed from the east end (looking west). No

permanent residual deformation was measured at the conclusion of the load testing, and there was no detectable movement at bridge supports. At the time of load tests 1A and

1B, the average bridge prestress was approximately

100 lb/in2. For load test 2, the bridge prestress was

approximately 56 lb/in2 in the west span, 52 lb/in2 in the

center span, and 47 lb/in2 in the east span.

Load Test 1A and 1B

Transverse deflections for load test 1A and 1B with the locations and magnitudes of the maximum measured deflections

are shown in Figure 19. For each of the three load positions

on the west and east approach spans, the deflections are typical of the orthotropic plate behavior observed for other stresslaminated decks (Ritter and others 1990). For the west span,

the maximum measured deflection was 0.45 in. for load

case 1 and 0.49 in. for load cases 2 and 3. For the center

span, the maximum measured deflection was 0.31 in. for

load case 1, 0.37 in. for load case 2, and 0.35 in. for load

case 3. On the east span, the maximum measured deflection

was 0.37 in. for load case 1 and 0.43 in. for load cases 2

and 3. As shown in Figure 19, the approach span maximum

measured deflections occurred virtually in the same locations

for each load case with minor variations, which are within

Figure 18—Average trend in bar force, starting at the

third bar tensioning for (a) west, (b) center, and

(c) east spans.
13

Figure 19—Transverse deflection measured at midspan (looking west) for load tests 1A and 1B. Bridge

cross-sections and vehicle cases are presented to aid interpretation only and are not to scale.
14

the measurement error. However, deflections on the east span

were 12 to 18 percent less than deflections on the west span.

The difference in measured deflection was most likely the result of differences in the sawn lumber laminations between

the two decks, because wood naturally has material property

variations, even in the same grade. Deflections for the center

span were less than the approach spans as a result of the differences in design and cross section.

Assuming uniform material properties, symmetric loading,

and accurate deflection measurements, the bridge deflections

for load cases 2 and 3 should be a mirror image. Load tests

1A and 1B of the measured deflections for load case 2 and a

mirror image of load case 3 are displayed in Figure 20. As

shown, there are slight deflection variations near the longitudinal centerline, but the deflections are essentially the same.

The variations may be due to eccentricities in the loading or

errors within the accuracy of the measurement methods.

Load Test 2

Load test 2 transverse deflections for the west, center, and

east spans are shown in Figure 21. As with load test 1, the

deflections are typical of the orthotropic plate behavior observed on stress-laminated decks. For the west span, the

maximum measured deflection was 0.47 in. for load case 1

and 0.51 in. for load cases 2 and 3. The maximum measured

deflection for the center span was 0.28 in. for load case 1,

0.35 in. for load case 2, and 0.31 in. for load case 3. On the

east span, the maximum measured deflection was 0.39 in. for

load case 1 and 0.49 in. for load cases 2 and 3. As with the

first load test, the approach spans maximum measured deflections are in the same locations and east span deflections for

load case 1 are again 12 to 18 percent less than load case 1

deflections on the west span. However, load cases 2 and 3

approach span deflections are virtually overlapping. The

variation in measured deflections between load cases and load

tests was probably a result of a combination of prestress and

material property differences between the decks. The prestress

effect describes the decrease of transverse stiffness when the

amount interlaminar compression in the deck decreases (see

Analytical Assessment). The west and east approach spans

were load tested at prestress levels of 56 and 47 lb/in2

,

respectively; therefore, the east span had a lower transverse

stiffness during load testing. A combination of a stiffness decrease caused by prestress effect and material property differences described in the load test 1 section, yields similar deflection results for load test 2, load cases 2 and 3. The

deflection differences observed in load case 1 were probably a

result of a smaller prestress effect for the concentric loading.

Measured deflections for load case 2 and a mirror image of

load case 3 are given in Figure 22. As with load test 1, deflection curves for each span are similar except for minor

variations. These variations were probably the result of

measurement errors during load testing and are within the accuracy of the measurement method.

Load Test Comparison

A comparison of the load case deflection for load tests 1 and

2 is shown in Figure 23. For each respective load case,

Figure 20—Comparison of approach span measured

deflections for load tests 1A and 1B, showing the

actual deflection of load case 2 and the mirror

image of load case 3 (looking west).
15

Figure 21—Transverse deflection measured at midspan (looking west) for load test 2. Bridge cross-sections

and vehicle cases are presented to aid interpretation only and are not to scale.
16

Figure 23—Comparison of the measured deflections for

load tests 1 and 2 (looking west).

Figure 22—Comparison of approach span measured

deflections for load test 2, showing the actual

deflection of load case 2 and the mirror image

of load case 3 (looking west).
17

Figure 23—con.
18

deflections for the two load tests are similar. On the approach

spans, the slight increases in deflection observed during

load test 2 were attributable to decreases in the prestress

(discussed in Analytical Assessment). For the center span,

the measured deflections decreased on load test 2 compared

with load test 1. The decrease in deflection was probably due

to the 3,200-lb lighter load applied at load test 2. In addition, prestress factors probably played a smaller role for the

center span because the glulam beam webs were full span.

As expected, the center span stress-laminated box displayed

less deflection under similar loading than did the stresslaminated deck approach spans. The difference in measured

deflection for the center span compared with the approach

spans was 0.20 in. for all load cases. The smaller deflection

indicates that the center span configuration could have been

extended to a longer span than was built.

Analytical Assessment

Analytical assessment was completed only for the approach

spans. Results of the measured deflections compared with the

predicted bridge response based on orthotropic plate analysis

are shown in Figure 24 for load test 1 and Figure 25 for load

test 2. As shown, the predicted response was similar to the

measured response with minor variations. The differences at

the bridge edges were expected because the curb and railing

do provide some stiffness, which was not accounted for in the

analysis. Other variations were relatively minor and within

the measurement reading error.

For further analysis, the same analytic parameters used for the

load tests were used to determine the predicted response of an

AASHTO HS 25–44 truck for load cases 1 and 3. (Load

case 2 is a mirror image of load case 3.) Figure 26 displays

the predicted response at the respective bar force levels for

load tests 1A and 2. For load tests 1A and 2, the theoretical

maximum deflection obtained for the HS 25–44 truck occurred in load case 3. The theoretical maximum deflections for

load test 1A were 0.46 in., or 1/490 for the west span and

0.39 in., or 1/578 for the east span. For load test 2, the

maximum theoretical deflection was 0.54 in., or 1/417 for

the west span and 0.49 in., or 1/460 for the east span. Deflections computed using AASHTO recommended design procedures for the specified MOE were 0.66 in., or L/340 on the

approach spans and 0.61 in., or L/610 on the center span.

Assuming constant bridge properties, the same theoretical

bridge deflection would normally be expected for the same

AASHTO HS 25–44 loading used for each load test. However, it has been determined that a decrease in interlaminar

compression in stress-laminated bridges with butt joints results in a decrease in longitudinal bridge stiffness (Oliva and

others 1990). The differences in the theoretical deflections for

the two load tests were attributable to an approximate 15- to

20-percent decrease (15 percent west and 20 percent east) in

longitudinal bridge stiffness for load test 2 as a result of the

decreased level of interlaminar stress from 100 lb/in2

 for load

test 1A to 56 lb/in2 on the west span and 47 lb/in2 on the

east span for load test 2.

Condition Assessment

Condition assessment of the Big Erick’s bridge indicated

that structural performance was good, but serviceability deficiencies were noted. Inspection results for specific items

follow.

Geometry

Width measurements taken on all spans indicate that the center span was rectangular, but each approach span midspan

width was narrower than that at the abutments, commonly

referred to as an hourglass shape (Ritter and others 1995).

Approach span midspan widths were approximately 1.5 in.

narrower than at the abutments. The shape was probably attributable to deck restraints at the abutments and piers that

did not allow for transverse movement at these locations following the third stressing. Eleven months after installation,

the connections were removed to allow free transverse

movement. A second contributing factor was the use of a

single hydraulic jack during the stressing process. An hourglass shape has appeared on other similar bridges that were

stressed with a single hydraulic jack. The hourglass shape

does not affect bridge strength, but it does make alignment of

rails and curbs difficult and is not aesthetically pleasing.

Camber

Table 3 displays the camber measurements taken 11 months

after installation and the end of monitoring period. During

24 months, camber loss of 0.60 in., 0.72 in., and 0.36 in.

was measured for the west, center, and east spans, respectively. These losses were most likely a result of creep that

was accelerated by the high moisture content of the timber

laminations. Although camber does not affect bridge

strength, perceptions of bridge safety are affected by noticeable sag that will occur with extensive creep. Initial measurements were not taken after the bridge was installed; therefore, the amount of camber loss that was due to short-term

bridge dead load is unknown.

Wood Condition

Inspection of the wood components of the bridge showed no

signs of deterioration. Minor checking was evident on the

end grain of the rail posts that were exposed to rapid wet–dry

cycles. This checking could have been alleviated through the

use of a sealer on the post end grain. In several locations on

the curb and railing system, vehicle damage was observed

(Fig. 27). In some cases, the damage has broken the preservative envelope and could cause premature deterioration.

The south-side exterior laminations on the stress-laminated

approach spans were also surface checked and distorted as a

result of rapid wet–dry cycling. Some railing system bolts

and washers were crushed into the timber laminations,

probably a result of bolt over tightening at installation. At

the conclusion of monitoring, preservative staining and dripping were observed on the concrete abutments and piers and

several bar anchorages (Fig. 12). In addition, a light grey

coating on exposed bridge members could indicate an excess

of preservative treatment that is migrating to the surface and

combining with dust from the approach roadway.
19

Figure 24—Comparison of the approach span measured deflections for load test 1 and the theoretical deflection based

on orthotropic plate analysis (looking west).
20

Figure 25—Comparison of the approach span measured deflections for load test 2 and the theoretical deflection

based on orthotropic plate analysis (looking west).
21

Wearing Surface

The asphalt wearing surface was observed to be in poor condition at the conclusion of the monitoring period. Large

transverse cracks were observed at the piers and at the west

abutment. At the west pier, transverse cracking has heaved

1 to 2 in. above the roadway grade. Longitudinal rutting was

also observed along two vehicular wheel lines in the asphalt

on the bridge and the approach roadway, which varied from

0.5 to 1.5 in. in depth. The rutting is most severe at the center span (Fig. 28). Rutting was first observed 11 months after

bridge installation and increased during the monitoring period. The heaving and rutting were probably caused by a

poor asphalt mix and will cause rain water to remain on the

deck for extended periods. This condition also tends to trap a

substantial quantity of gravel and other debris on the surface

from the unpaved road. The debris accumulations could lead

to premature deterioration of the wearing surface.

Stressing System

The stressing bar anchorage system has performed adequately. No measurable distortion in the bearing plates was

observed, and the exposed steel stressing bars, hardware, and

anchorage plates showed no visible signs of corrosion or

other deterioration. There was no apparent crushing of the

Figure 26—Maximum theoretical deflection at approach span midspan for AASHTO HS 25–44 truck loading

at 100 lb/in2

 (both spans), 52 lb/in2 (west span), and 47 lb/in2 (east span).

Table 3—Camber measurements

Camber measurements (in.)

Span Design

11 months

after

installation

November

1992

End of

monitoring

July 1995

Creep loss

during

monitoring

West 0.625 0.60 0.00 0.60

Center 1.00 0.90 0.18 0.72

East 0.625 0.18 –0.18 0.36
22

bearing plates into the Southern Pine glulam exterior laminations of the center span. However, crushing of the Eastern

Hemlock laminations on the approach spans was first observed during bridge construction and continued progressively until the end of monitoring (Fig. 29), and seems to

have contributed to short-term bar force loss after bar tensioning. This crushing occurred even though the bearing plates

were properly designed, based on published values for compression perpendicular to grain adjusted for wet-use conditions. This indicates that the published design values for

compression perpendicular to grain may not be representative

of the material for use in this application. The use of a treatable hardwood species, such as oak or maple, on the outer

laminations has been shown to perform well without crushing problems (Ritter and others 1995).

Conclusions

After 35 months in service, the Big Erick’s bridge is performing satisfactorily and should provide many years of

acceptable service. Based on extensive bridge monitoring, we

make the following observations and recommendations:

• The sawn lumber components of the Big Erick’s bridge

were initially installed at 33-percent moisture content.

The average trend in moisture content indicates that

changes are occurring slowly, with an average decrease of

5 percent during the monitoring period. The high moisture content contributed to bar force and camber loss during the monitoring period. It is expected that the moisture

content will gradually decrease and lamination dimensional change should be expected. Future bridges constructed of this type should utilize laminations with moisture content at or below 19 percent.

• Following the final design bar tensioning, two additional

bar tensionings were required due to rapid loss of bar

force. The decrease in bar force was primarily attributable

to transverse stress relaxation in the wood laminations

with additional effects from crushing of the approach span

exterior laminations near the bar anchorages. It is anticipated that the bridge will require retensioning in the near

future. In addition, as the moisture content decreases, the

bar force will also decrease until an equilibrium moisture

content is reached. Therefore, bar force should be checked

annually and retensioned as necessary until it reaches a

constant level.

• Load testing and analysis indicate that all three spans of

the Big Erick’s bridge are performing in a linear elastic

manner, and the approach spans exhibit orthotropic plate

behavior when subjected to truck loading. HS25–44 truck

loading conditions produced maximum deflections of 0.46

and 0.39 in. for the west and east approach spans at

100 lb/in2

and 0.56 in., and 0.49 for the west and east

approach spans at 57 and 47 lb/in2, respectively. These

deflections correspond to values of L/490, L/578, L/417,

and L/460, based on the center–center of bearing span

length.

Figure 27—Vehicle damage to curb and rail system

observed during a site visit near the end of the

monitoring period.

Figure 28—Rutting of asphalt wearing surface

measured at the center span during a site visit for

load test 2.

Figure 29—Visible crushing of approach span, Eastern

Hemlock lumber lamination, observed after the

removal of the bearing plate at the final site visit.
23

• Width measurements taken on all spans indicate that

although the center span is rectangular, each approach

span midspan width is narrower than the width at the

abutments, which is referred to as an hourglass shape. The

hourglass shape is probably the result of the attachment of

the span ends after the third bar tensioning, which prevented transverse movement at the abutments and piers

during subsequent bar tensionings. For future bridges, attachments to the abutments and/or piers should be made

only at the underside of the longitudinal centerline to allow for transverse movement or after the bridge reaches bar

force equilibrium.

• Camber measurements of the stress-laminated decks and

box indicate that the camber decreased during 24 months

of monitoring. At the conclusion of monitoring, the west

span is approximately straight between supports, the center span has a vertical camber of approximately 0.2 in.,

and the east span has a slight sag of approximately 0.2 in.

• Wood checking is evident in the exposed end grain of the

bridge rail posts. It is likely this would not have occurred

if a sealer had been placed over end grain at the time of

construction. In addition, preservative treatment has

dripped and stained the concrete abutment and piers.

• The asphalt wearing surface has longitudinal ruts and

heaving at the piers, which contribute to increased standing water and debris on the surface of the bridge. These

conditions could lead to premature deterioration of the

wearing service.

• The use of high moisture content Eastern Hemlock sawn

lumber on the outside laminations of the approach decks

adversely affected the performance of the bar anchorages.

The wood crushing observed was approximately 0.75 in.

underneath the bearing plates. The inclusion of hardwood

laminations for the two exterior laminations would have

greatly enhanced the bar anchorage performance.

• Prefabrication of stress-laminated timber bridges saves

on-site construction time by allowing installation of the

bridge in sections by an overhead crane. However, bar

tensioning prior to installation on the prefabricated halfwidth panels adversely affects the bar force performance.

When using prefabrication, additional bar tensionings

should be planned when full-width bars are installed.

References

AASHTO. 1989. Standard specifications for highway bridges

14th ed. Washington, DC: American Association of State

Highway and Transportation Officials.

AASHTO. 1990. Standard specifications for transportation

materials and methods of sampling and testing. Vol. 1: Specifications. Washington, DC: American Association of State

Highway and Transportation Officials. 877 p.

AITC. 1987. Standard specifications for structural glued laminated timber of softwood species. AITC 117–87–Design. Vancouver, WA: American Institute of Timber Construction. 28 p.

AFPA. 1988. Design values for wood construction; a supplement to the 1986 edition of the national design specification.

Washington, DC: National Forest Products Association. 40 p.

ASTM. 1988. Standard specification for uncoated, high strength

steel bar for prestressing concrete; ASTM A722–86. Philadelphia, PA: American Society for Testing and Materials. 3 p.

ASTM. 1990. Use and calibration of hand-held moisture meters;

ASTM D 4444–84. Philadelphia, PA: American Society for

Testing and Materials. 6 p.

AWPA. 1990. Standards. Woodstock, MD. American Wood

Preservers’ Association. 200 p.

FPL. 1987. Wood handbook: Wood as an engineering material.

Agric. Handb. 72 (rev). Washington, DC: U.S. Department of

Agriculture; 466 p.

NELMA. 1986. Grading rules for northeastern lumber.

Cumberland Center, ME: Northeastern Lumber Manufacturing

Association.

Oliva, M. G.; Dimakis, A.G.; Ritter, M.A.; Tuomi, R.L. 1990.

Stress-laminated wood bridge decks: experimental and analytical evaluations. Res. Pap. FPL–RP–495. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products

Laboratory. 24 p.

Ritter, Michael A. 1990. Timber bridges: design, construction,

inspection and maintenance. EM 7700–8. Washington, DC:

U.S. Department of Agriculture, Forest Service, Engineering

Staff. 944 p.

Ritter, M.A.; Geske, E.A.; Mason, L. [and others]. 1990.

Performance of stress-laminated bridges. Wood Design Focus.

1(3): 12–16.

Ritter, M.A.; Geske, E.A.; McCutcheon, W.J. [and others].

1991. Methods for assessing the field performance of stresslaminated timber bridges. In: Marcroft, Julian, comp. Proceedings, 1991 international timber engineering conference; 1991

September 2–5; London, United Kingdom. High Wycombe,

United Kingdom: Timber Research and Development Association: 319–326. Vol. 3.

Ritter, M.A.; Wacker, J.P.; Duwadi, S.R. 1995. Field performance of stress-laminated timber bridges on low-volume roads.

In: Proceedings, 6th international conference on low-volume

roads; 1995 June 25–29; Minneapolis, MN. Washington, DC:

National Academy Press: 2: 347–357.

USDA. 1995. The timber bridge initiative, fiscal year 1995

status report. Radnor, PA: U.S. Department of Agriculture,

Forest Service, State and Private Forestry, Northeastern Area.

Wacker, J.P.; Ritter, M.A. 1992. Field performance of timber

bridges: 1. Teal River stress-laminated deck bridge. Res. Pap.

FPL–RP–515. Madison, WI: U.S. Department of Agriculture,

Forest Service, Forest Products Laboratory. 19 p.

WV–DOH. 1989. West Virginia department of highways standard bridge plans: stressed timber bridge type B. Morgantown,

WV: West Virginia Department of Highways.
24

Appendix—Information Sheet

General

Name: Big Erick’s bridge

Location: Baraga County, Michigan

Date of Construction: September 1992

Owner: Michigan Department of Natural Resources

Design Configuration

Number of Spans: 3 (simple)

Structure Type:

 Approach Spans:Stress-laminated decks with butt joints

 Center Span: Stress-laminated box with glulam webs

and sawn lumber butt-jointed flanges

Butt-Joint Configuration:

Approach Spans:1 in 8 transverse laminations with joints

in adjacent deck laminations

separated 4 ft longitudinally

 Center Span: 1 in 4 transverse laminations with joints

 in adjacent deck flange laminations

separated 4 ft longitudinally

Total Length (out–out): 72 ft

Skew: None

Span Lengths (out–out): 20 ft (approach spans); 32 ft

(center span)

Span Lengths (center–center bearings): 18.8 ft (approach

spans); 31 ft

(center span)

Bearing Lengths: 0.75 by 6 in. on full width neoprene

pads; each span overhangs 3 in. at

each end

Width (out–out): 16 ft

Width (curb–curb):14 ft

Number of Traffic Lanes: 1

Design Loading: AASHTO HS25–44

Wearing Surface Type: Asphalt pavement;

2- to 2.5-in. thickness

Material and Configuration

Deck/Flange Laminations:

Species: Eastern Hemlock

Size (actual): 2 by 11 in. (approach spans);

2 by 7 in. (box flanges)

Grade: No. 1 (not visually graded)

Moisture Condition:Approximately 34 percent

at installation

Webs:

Species: Southern Pine

Size (actual): 80.75 by 22.5 in.

Beam Designation: 24F–V3

Moisture Condition:Approximately 13 percent

average at installation

Rails:

Species: Southern Pine

Size (actual): 5.125 by 6 in., spliced at piers

Beam Designation: 24F–V3

Posts:

Species: Southern Pine

Size (actual): 8.75 by 10.5 in.

Beam Designation: 24F–V3

Curb and Scupper:

Species: Eastern Hemlock

Size (actual): 6 by 12 in., spliced at piers

Grade: No. 1 (not visually graded)

Preservative Treatment: Creosote

Stressing Bars:

Type: High strength steel threaded bar with coarse

right-hand thread, conforming to ASTM A–722

Diameter: 0.625 in.

Number:

Approach Spans: 18

Center Span: 30

Design Force: 26,400 lb, sawn lumber end spans

16,800 lb, center box span

Spacing: 24 in. center–center, beginning

2 ft from span ends

Anchorage Type and Configuration:

Anchor plate and nut: 2 by 5 by 1 in.

Approach Spans: 6- by 12- by 0.875-in. bearing plates

Center Span: 6- by 10- by 0.875-in. bearing plates