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Increased use of timber bridges in the U.S. transportation system has required additional research to improve the current design methodology of these bridges. For this reason, the U.S. Forest Service, Forest Products Laboratory (FPL), and the Federal Highway Administration have supported several research programs to attain the objective listed above. This report is a result of a study sponsored by the FPL, with the objective of determining how highway truckloads are distributed to girders of a glued-laminated timber bridge. The American Association of State Highway and Transportation Official (AASHTO) load and resistance factor design (LRFD) Bridge Design Specification provides live-load distribution provisions for glued-laminated girder timber bridges that were used in previous AASHTO Specifications. The AASHTO live-load distribution provisions were reviewed in this report. Field-test results were used to review the current AASHTO LRFD glued-laminated timber girder bridge-design specifications and to validate analytical results obtained by finite-element analyses. With the validated analytical models, parametric studies were performed to determine the worst-case live-load distribution factors that can be used to calculate the design moment and shear for glued-laminated timber girders. Simplified live-load distribution equations that can be used to determine these distribution factors were developed and are provided in this report. These equations take into account how load is distributed to the bridge girders, considering the effects of span length, girder spacing, and clear width of the bridge.
Increased use of timber bridges in the U.S. transportation system has required additional research to improve the current design methodology of these bridges. For this reason, the U.S. Forest Service, Forest Products Laboratory (FPL), and the Federal Highway Administration have supported several research programs to attain the objective listed above. This report is a result of a study sponsored by the FPL, with the objective of determining how highway truckloads are distributed to girders of a glued-laminated timber bridge. The American Association of State Highway and Transportation Official (AASHTO) load and resistance factor design (LRFD) Bridge Design Specification provides live-load distribution provisions for glued-laminated girder timber bridges that were used in previous AASHTO Specifications. The AASHTO live-load distribution provisions were reviewed in this report. Field-test results were used to review the current AASHTO LRFD glued-laminated timber girder bridge-design specifications and to validate analytical results obtained by finite-element analyses. With the validated analytical models, parametric studies were performed to determine the worst-case live-load distribution factors that can be used to calculate the design moment and shear for glued-laminated timber girders. Simplified live-load distribution equations that can be used to determine these distribution factors were developed and are provided in this report. These equations take into account how load is distributed to the bridge girders, considering the effects of span length, girder spacing, and clear width of the bridge.
In order to promote and increase the use of timber bridges in our nations transportation systems, the United States Department of Agriculture (USDA) and the Forest Products Laboratory funded research to develop design criteria to improve the design of glued-laminated timber bridges. This project is part of this research and is directed towards developing, and/or making recommendations for, acceptable live load deflection criteria, which are based on the actual structural performance of these types of bridges. Specifically, the relationship between live load deflection and the condition of the asphalt wearing surface is of particular interest. To accomplish this, eight glued-laminated timber girder bridges and four longitudinal glued-laminated timber deck bridges were selected for testing. The performance of the bridges was investigated under live loading and analyzed in conjunction with the condition of the wearing surfaces gathered from field inspections. Testing involved loading the structures with fully loaded tandem axle dump trucks and gathering global and differential deflection data. Field tests revealed that the majority of the asphalt wearing surface deterioration was primarily the result of differential deflections.
This report presents a comprehensive analysis of the design, construction, inspection, and maintenance of timber bridges.
"This synthesis will be useful to bridge engineers and others concerned with the design and structural evaluation of highway bridges. Information is presented on various approaches currently used to calculate the distribution of wheel loads among the supporting members in bridge superstructures."--Avant-propos.
The live load distribution factor (DF) equations provided by AASHTO-LRFD for the decked precast/prestressed concrete (DPPC) girder bridge system do not differentiate between a single or multilane loaded condition. This practice results in a single lane load rating penalty for DPPC girder bridges. The objective of this project is to determine DF equations which accurately predict the distribution factor of the DPPC girder bridge system when it is only subjected to single lane loading. Eight DPPC girder bridges were instrumented. Each bridge was loaded with a single load vehicle to simulate the single lane loaded condition. The experimental data was used to calibrate 3D FE models and 2D grillage models of the DPPC girder bridge system. The calibrated models were used to conduct a parametric study of the DPPC girder bridge system subjected to a single lane loaded condition. Two sets of new equations that describe the single lane loaded distribution factor for both shear and moment forces of these bridges are proposed and compared with AASHTOLRFD DF equations.