VARIATION IN RESPONSE OF A BRIDGE SEISMICALLY ISOLATED WITH LRBS UNDER THE EFFECT OF LOW AMBIENT TEMPERATURE

In this paper, the change in response parameters of a seismically isolated bridge, namely maximum isolator displacement (MID) and shear force (MSF), is studied when the ambient temperatures drops to (-30⁰C) from 20⁰C.Isolation system of the analyzed bridge is assumed to be composed of lead rubber bearings (LRBs).First, the LRB was subjected to cyclic loading after a conditioning period of 24 hours at both temperatures.Test results were used to validate the success of analytical model used to idealize the deteriorating hysteretic behavior of the LRB.Then, verified analytical representation of LRB was utilized in nonlinear response history analyses in order to measure the variation in MID and MSF in the bridge model under the effect of bidirectional seismic excitations at 20⁰C and -30⁰C.Two distinct group of ground motions, that constitute characteristics of both near-field and largemagnitude-small-distance records, were used in the analyses.Results showed that MIDs obtained for LRB properties of 20 o C are about 20% larger than the ones obtained for -30 o C, in an average sense.Furthermore, average MSF obtained for near-field ground motions at 20 o C and -30 o C are identical.However, for large-magnitude-small-distance ground motions, MSF of -30 o C is almost 25% larger than that of 20 o C.