Skewed highway bridges.

PDFTech ReportRC-15412006-0413Highway bridgesBridge designSkew bridgesFinite element methodFactor analysisMichiganMichigan. Dept. of TransportationFu, GongkangChun, Pang-joWayne State University. Center for Advanced Bridge EngineeringNTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and StructuresNTL-HIGHWAY/ROAD TRANSPORTATION-DesignUS Transportation CollectionMany highway bridges are skewed and their behavior and corresponding design analysis need to be furthered to fully accomplish design objectives. This project used physical-test and detailed finite element analysis to better understand the behavior of typical skewed highway bridges in Michigan and to thereby develop design guidelines and tools to better assist in routine design of these structures.It is found herein that the AASHTO LRFD Bridge Design Specifications' distribution-factor analysis method is generally acceptable but overestimates the design moment for the typical Michigan skewed bridge spans analyzed herein and sometimes underestimates the design shear. Accordingly, a modification factor for possible shear underestimation based on detailed finite element analysis is recommended for routine design. Furthermore, the AASHTO specified temperature load effect is found to be relatively significant, compared with live load effect and should receive adequate attention in design. On the other hand the influence of warping and torsion effects in the analyzed typical Michigan skewed bridges is found to be small and negligible for the considered cases of span length, beam spacing, and skew angle. Based on these findings, the AASHTO distribution-factor analysis method is recommended to be used beyond the MDOT current policy of 30O skew angle limit for refined analysis, provided that the recommended modification factor C is applied and if the structure type, span length, beam spacing, and skew angle are within the ranges of the analyzed spans covered in this report.An analytical solution for skewed thick plate modeling the concrete bridge deck is also developed in this research project, which can be furthered into an analytical solution for the bridge superstructure. When implemented in a software program, the analytical solution will serve routine design better than the distribution factor method and the finite element analysis method, without a constraint to the skew angle or a requirement for complex input such as element type, shape, size, etc. required for finite element analysis