Effects of isolation on the seismic response of bridges designed for two different soil types

Abstract

The objective of this study was to investigate the effect of lead rubber isolators on the seismic response of bridges designed according to current codes for two different soil conditions: hard and medium type soils, in order to assess their applicability for the design of new bridges or retrofit of existing ones. The study was conducted for two levels of earthquake, one corresponding to a return period of 50 years and a service limit state, the other with a return period of 1,000 years and a failure limit state. Twenty one subduction earthquake records on the two types of soil were used to evaluate the linear and nonlinear dynamic response of a set of bridges designed for this purpose with and without base isolation. The response parameters evaluated are the maximum relative displacement on top of the piers, the maximum pier distortion, the maximum shear forces in the piers and the ductility demands for the isolators. The results presented are the average of these maxima for the various earthquakes. This study is an expansion of a previous one in which the seismic response of 36 bridges considering models with and without base isolators, structures with linear base isolators and bridges with nonlinear isolators. The results of this study confirm the conclusions previously obtained and show that the isolation can have beneficial effects even for bridges located in medium soil types.