Civil and Construction Engineering Iowa State University

Simplified Analytical Model of a Covered

Queen-Post-Truss Timber Bridge

Fouad Fanous, Douglas Rammer & Terry Wipf

Iowa State University, Bridge Engineering Center

Forest Product Laboratory

Civil and Construction Engineering Iowa State University

Objective • Develop a simple analytical model

• Approximately predicts behavior

• Assist in load rating calculations

• Include as built characteristics – eccentric connections, splice joints, material properties, etc.

Finite Element Analysis • Development of 2-D and 3-D finite element models for each bridge

Selected Bridges • Indiana & Vermont

• Burr-Arch and Queen-Post Truss Bridges

Recommendation • From comparison of displacement and strain values of field and analytical – recommend

appropriate modeling approach

Study Scope

Bridge Descriptions

3

Moxely Bridge

Civil and Construction Engineering Iowa State University

Views of the Moxley Bridge

Plan View

Elevation View

Civil and Construction Engineering Iowa State University

Structural Member Width (in.) Height (in.)

Bottom & Top Chords 9 9

Floor Beam 5 9 ½

Verticals 9 9

Diagonals 4 9

Tension Rods 1 in. diameter

Field Measured Timber Dimensions

Bridge Schematics – Strain Gage Locations

Front Axel 4,700 lbs.

Back Axel 11,440 lbs.

Distance between axels

176 inches

Civil and Construction Engineering Iowa State University

Analysis using STAAD Software

-0.06

-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0 20 40 60 80

Dis

pla

ce

men

t (i

n)

Truck Position (ft)

East Truss

West Truss

Staad results

Measured and Calculated Deflection

Civil and Construction Engineering Iowa State University

-50

-40

-30

-20

-10

0

10

20

30

0 20 40 60 80

Mic

ro s

train

Distance of front axle from south abutment (ft)

Sensor 4813

Sensor 4805

Analytical 4813 & 4805

Strain Compaison

Civil and Construction Engineering Iowa State University

-2

0

2

4

6

8

10

12

14

16

0 20 40 60 80

Mic

ro s

tra

in

Distance of front axle from south abutment (ft)

Sensor 4785

Sensor 4819

Analytical 4785 & 4819

Strain Comparison –Cont.

Civil and Construction Engineering Iowa State University

-35

-30

-25

-20

-15

-10

-5

0

5

0 20 40 60 80M

icro

str

ain

Distance of front axle south abutment (ft)

Sensor 1966

Sensor 4817

Analytical 4817

Analytical 1966

Strain Comparison –Cont.

Civil and Construction Engineering Iowa State University

-50

-40

-30

-20

-10

0

10

0 20 40 60 80M

icro

str

ain

Distance of front axle from south abutment (ft)

Sensor 4782

Sensor 4789

Analytical 4782

Analytical 4789

Strain Comparison –Cont.

Civil and Construction Engineering Iowa State University

-150

-100

-50

0

50

100

150

200

0 20 40 60 80

Mic

ro s

tra

in

Distance of front axle from south abutment (ft)

Sensor 4811

Sensor 4810

Analytical 4810

Analytical 4811

Strain Comparison –Cont.

Civil and Construction Engineering Iowa State University

-20

0

20

40

60

80

100

120

0 20 40 60 80

Mic

ro s

trai

n

Distance of front axle from south abutment (ft)

Sensor 4816

Analytical 4816

Strain Comparison –Cont.

Source of Discrepancies

Data Collection Method

Source of Discrepancies – Cont.

Members Conditions and Dimensions

Load Distribution

Irregularities Present in the Bridges

Geometric Irregularities

Material Properties

Summary & Conclusions

Finite element

Joint Eccentricities

Material Properties

Analyze the as built structure

Acknowledgement

Douglas Wood

Allison Lunde

Graduate Students

Civil and Construction Engineering Iowa State University

This study is part of the Research, Technology and Education portion of the National Historic

Covered Bridge Preservation (NHCBP) Program administered by the Federal Highway

Administration. The NHCBP program includes preservation, rehabilitation and restoration of

covered bridges that are listed or are eligible for listing on the National Register of Historic Places;

research for better means of restoring, and protecting these bridges, development of educational

aids; and technology transfer to disseminate information on covered bridges in order to preserve

the Nation's cultural heritage.

This study is conducted under a joint agreement between the Federal Highway Administration -

Turner Fairbank Highway Research Center, and the Forest Service - Forest Products Laboratory.

Federal Highway Administration Program Manager - Sheila Rimal Duwadi, P.E.

Forest Products Laboratory Program Manager - Michael A. Ritter, P. E.