Effect of behavioral parameters of base isolators on the seismic response of the bridge to near-fault ground motions

Abstract

The current study examined the effectiveness of considering the nonlinear behavior of lead rubber bearings (LRBs) on the response of seismically isolated bridges. Also, the effect of the vertical component of the strong ground motion on the critical buckling capacity of LRBs was studied. 3D modeling of a seismically isolated bridge with nonlinear time history analysis under near-fault ground motion was applied. The results showed lack of consideration of the cavitation, post-cavitation and strength degradation behavior in tension and force softening under compression produces a large axial force and small axial displacement in LRBs and axial force-deformation appears to be perfectly linear. The results revealed that the average maximum base shear force in the bridge piers increased by 116% and 29.8% in the longitudinal and transverse direction respectively in comparison with the simple modeling. It also increased the average maximum displacement of bridge pier about 113% in the longitudinal direction and 31% in the transverse direction. Simplifying the LRBs modeling led to produces smaller stress and base shear forces of the bridge columns relative to actual conditions. Since the AASHTO regulation requires a seismically isolated bridge substructure to remain in the linear range, so in the bridges with a simplified model of LRBs, the nonlinear behavior of some columns of isolated bridges will be ignored under strong near-fault ground motion.