Seismic Evaluation of an Elevated Highway Bridge in a Low Seismic Region – a Case Study

This paper presents the results of the seismic evaluation of an elevated seven-span bridge with tall piers in western Pennsylvania. The bridge was modeled using the SEISAB software, and the analysis used modal superposition method. Various modeling strategies related to piers, abutments, expansion joints, fixed joints, rocker bearings, and hanger supports were studied. Several modeling options were made to capture different behavior responses under seismic loading conditions. The force and displacement demands are compared, and an assessment is made with respect to the potential for damage based on the analysis results. The result of the study shows that for the level of earthquakes expected in the region, columns will not be overstressed. Furthermore, the analysis results show that displacements of the superstructure should not be of concern in light of the fact that there is sufficient bearing seat width and that concrete pedestals have been added in front of the bearing supports to presumably prevent the walking off of the bearing from the support. The study concludes that considering the low level of earthquakes expected in PA, the potential for collapse of the superstructure due to bearing support failure is negligible. The paper contributes to better understanding of the behavior of tall and elevated highway bridges in low seismic regions. The results of the study reinforce the view that decisions on seismic retrofit of such bridges in low seismic regions should not be based on column tie spacing.

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