Abstract

The requirement for the seismic analysis of cable-stayed bridges under spatially varying loads is not well defined in the bridge design codes around the world. The Canadian Highway Bridge Design Code briefly stipulates that it is the responsibility of the designer to check the effect of the spatially varying loads while no details are provided. Given this, the objective of this study is to evaluate the seismic performance of cable-stayed bridges using multi-support excitation. For the purpose of the study, Quincy Bayview Bridge located in Illinois, USA is selected for the analysis. Ten ground motion acceleration time-histories obtained from earthquakes in the US, Japan, and Taiwan are used as initial seismic excitation to be applied on the bridge. They are then converted to displacement time-histories and applied at each support by considering the phase delay of the wave traveling from one support to another. The seismic analysis using multi-support excitation shows that significant vertical deck displacement is produced, which is generally ignored in the analysis of cable-stayed bridges under uniform excitation. The response curve for the vertical deck displacement vs wave velocity demonstrates that a resonance-like condition is triggered at relatively low velocity. A mathematical formula is developed to account for the potential of resonance for the displacement of the deck in the vertical direction. Furthermore, a time delay factor of 0.72 is proposed to estimate the critical seismic wave velocity that would trigger the resonance. In addition, the results from this study indicate that attention is required for
the bridge response in the direction orthogonal (e.g., vertical direction) to the direction of the seismic loading (e.g., horizontal direction), while multi-support excitation should be considered for this purpose.