Analysis of dynamic interaction and response in multispan girder bridges subjected to near-fault earthquakes

Abstract

This study delves into the separation and collision behavior of multi-span bridges with plate rubber bearings, focusing on the influence of seismic excitation period and vertical/horizontal acceleration (V/H) ratio during near-fault earthquakes. Employing the modal superposition approach, a four-span bridge model is scrutinized to understand the dynamic interaction between its components under seismic forces. The main girder, supports, and piers are simplified into beam, spring, and rod elements, respectively, to analyze vertical movements and collisions. Different bridge positions are evaluated for separation using the transient wave function, and the vertical impact force during collisions is assessed via the indirect modal method. It emerges that bridge separation is likely when excitation periods align with the bridge's natural frequency, especially for multi-span structures. These bridges also demonstrate a 25–110% increase in vertical collision forces compared to double-span bridges under various excitation periods, surpassing V/H= 2/3 standard. Theoretical energy-based calculations corroborate these observations.