Analysis of the strength and stability of prestressed concrete through-girder pedestrian bridges under vehicular impact

Prestressed concrete through-girder bridge systems are a practical form of pedestrian bridge construction, in which reinforced concrete floor beams and the bridge deck are supported at the bottom flange of two prestressed concrete girders. Questions had been raised regarding two issues: (1) ductility of girder sections used in these bridges (Mn/DOT Type 63 section) and (2) strength and stability of the bridge system when subjected to lateral vehicular impact.; A nonlinear strain compatibility analysis of the Mn/DOT Type 63 section was performed in order to identify the design procedures that accurately predict the section behavior. Response of the section predicted by the AASHTO Standard and AASHTO LRFD Specifications was compared with the sectional response determined from the strain compatibility analyses. Based on the analysis results, modifications were proposed to the procedure used by the LRFD Specifications in order to rectify the errors in predicting the sectional response.; The behavior of a representative prestressed concrete through-girder bridge system under lateral impact loads was evaluated through finite element analyses integrated with laboratory tests. Three series of laboratory tests were conducted on representative bridge details and subassemblages to determine strength, stiffness, and ductility characteristics of critical elements under representative load configurations. The load-deformation characteristics obtained from the laboratory tests of the components and connection regions were then incorporated into 3-D finite element models to investigate the performance of the entire system.; The static finite element analyses, which included both the material and geometric nonlinearities, indicated significantly different bridge response depending on whether or not the flexibility of the girder supports was included in the models. The analyses also revealed that the type of load transfer mechanism among the bridge components depended on whether the girders were loaded at the exterior or interior face. Results from these analyses also showed that the lateral load and deformation capacities of the bridge system could be improved by (1) providing connectors between the bridge deck and girders, and (2) tying the floor beams and two girders with steel rods running through floor beams.