Computing the Effects of Vertical Ground Motion Component on Performance Indices of Bridge Sliding-Rubber Bearings

In this study, the effects of the vertical ground motion component (VGMC) of near-fault records on the structure as well as sliding-rubber bearings have been investigated. For this purpose, a highway bridge with sliding-rubber hybrid isolators was modeled and analyzed to evaluate the effect of VGMC on the performance of the structure and isolators. Numerical study on the bridge was conducted under two conditions: (1) with only two horizontal seismic components and (2) with three seismic components (including the VGMC). For this purpose, finite element model of the structure was developed in OpenSees software and then subjected to nonlinear dynamic analysis using 29 different ground motion records. The results showed that maximum shear and axial force in the isolator elements and axial force of the column and mid-span moment in the bridge undergo significant increase under all seismic excitations. Due to the absence of self-restoring force in the studied isolator, the permanent and maximum deck displacement increased during some of the earthquake records, and in a few cases, the permanent displacements of the deck were particularly significant. The axial forces of the isolators on the base and abutment were found to be correlated with the spectral acceleration at the period of vibration mode effective in vertical direction.