simplified analytical model of a covered queen-post-truss ...analysis using staad software...
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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
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
-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 – 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.