Simplified Analytical Model of a Covered Queen-Post-Truss Timber Bridge

Transcription

1 Simplified Analytical Model of a Covered Queen-Post-Truss Timber Bridge Fouad Fanous, Douglas Rammer & Terry Wipf, Bridge Engineering Center Forest Product Laboratory

2 Study Scope 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

3 Bridge Descriptions Moxely Bridge 3

4 Views of the Moxley Bridge Elevation View Plan View

5 Field Measured Timber Dimensions 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

6 Bridge Schematics Strain Gage Locations

7 Front Axel 4,700 lbs. Back Axel 11,440 lbs. Distance between axels 176 inches

8 Analysis using STAAD Software

9 Displacement (in) Measured and Calculated Deflection East Truss West Truss Staad results Truck Position (ft)

10 Micro strain Strain Compaison Sensor 4813 Sensor 4805 Analytical 4813 & 4805 Distance of front axle from south abutment (ft)

11 Micro strain Strain Comparison Cont Sensor 4785 Sensor 4819 Analytical 4785 & Distance of front axle from south abutment (ft)

12 Micro strain Strain Comparison Cont Sensor 1966 Sensor 4817 Analytical 4817 Analytical Distance of front axle south abutment (ft)

13 Micro strain Strain Comparison Cont Sensor 4782 Sensor 4789 Analytical 4782 Analytical Distance of front axle from south abutment (ft)

14 Micro strain Strain Comparison Cont Sensor 4811 Sensor 4810 Analytical 4810 Analytical Distance of front axle from south abutment (ft)

15 Micro strain Strain Comparison Cont Sensor 4816 Analytical Distance of front axle from south abutment (ft)

16 Data Collection Method Source of Discrepancies

17 Source of Discrepancies Cont. Members Conditions and Dimensions Load Distribution Irregularities Present in the Bridges Geometric Irregularities Material Properties

18 Summary & Conclusions Finite element Joint Eccentricities Material Properties Analyze the as built structure

19 Acknowledgement 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. Douglas Wood Allison Lunde Graduate Students