Stability Tests of Prestressed Concrete Through-Girder Pedestrian Bridge under Lateral Impact - Phase 2

Project summary:

This project addresses a practical form of pedestrian bridge construction known as the Prestressed Concrete Through-Girder bridge, in which two prestressed concrete bridge girders support a deck on the bottom flanges. This system is easy to construct, economical, and durable, but questions have been raised regarding the ductility of these girders and the stability of the assemblage upon vehicle impact. These bridges are non-redundant simple span systems that could collapse upon impact if the girders respond in a non-ductile manner, or if the assemblage becomes unstable. This project is the second phase of a study on the ductility and stability of prestressed concrete through-girder bridges. (The research activities for the first phase comprise analyses of typical girder cross-sections and bridge assemblages. )

Two issues regarding the prestressed concrete through-girder pedestrian bridge system were investigated. The first issue concerned the ductility of prestressed concrete girders in these bridges because the section that is typically used may be considered to be over-reinforced according to AASHTO LRFD Bridge Specifications. Response of the section, including neutral axis location, strand stress at ultimate capacity, and moment capacity, predicted by AASHTO Standard and AASHTO LRFD Specifications are compared with the sectional response determined from nonlinear strain compatibility analyses. Modifications were proposed to the AASHTO LRFD procedure to rectify the errors in predicting sectional response.

The second issue that was investigated concerns the strength and stability of prestressed concrete through-girder pedestrian bridges when subjected to impact by over-height vehicles. Three-dimensional finite element models of entire bridges and subassemblages were used to evaluate the strength, stiffness, and ductility characteristics of the bridge system and connection details. Accurate representation of the bridge details in the finite element models were assured by utilizing experimentally determined load-deformation characteristics for the connections. Results showed that significant improvements in the lateral load-deflection behavior of the bridge system could be obtained by implementing alternate connection schemes, and that concrete side-walls should be provided at girder ends.