Effect of lead core heating on the seismic performance of bridges isolated with LRB in near‐fault zones

Abstract

SUMMARY In this paper, the effect of lead core heating and associated strength deterioration on the seismic response of bridges isolated with lead rubber bearings (LRB) is investigated as a function of the characteristics of the isolator and near fault ground motions with forward rupture directivity effect. Furthermore, the ability of bounding analyses to provide a design envelope for maximum isolator force and maximum isolator displacement is verified. For this purpose, a series of nonlinear dynamic analyses are conducted for LRB isolated bridges where both deteriorating and non‐deteriorating force‐deformation relationship of LRB were employed. The analyses are performed for both simulated and recorded ground motions. It is found that while the temperature rise in the lead core generally increases with increasing magnitude and number of near fault ground motion velocity pulses, it decreases with larger distances from the fault. It is also found that bounding analysis method provides conservative (envelope) estimates of maximum isolator displacement and maximum isolator force for design purposes that fulfill its intended purpose. Copyright © 2012 John Wiley & Sons, Ltd.

Use of Bounding Analyses to Estimate the Preformance of a Seismically Isolated Structure

“…As a result, a new research area emerged to assess the efficiency of existing design approach, which provides envelopes for response quantities of LRBs, compared to actual behavior of isolators. However, yet, there are only a few studies that utilized the model proposed by Kalpakidis and Constantinou [4,5] to scrutinize the effect of lead core heating on the response of LRBs [6][7][8][9][10]. Among these, Ozdemir et al [6] investigated the response of LRBs in a seismic isolated bridge by a parametric study.…”

“…Authors studied the effects of isolation period and characteristic strength to weight ratio on lead core heating of LRBs through comparisons with the results obtained from bounding analyses. Ozdemir and Dicleli [7] studied lead core heating effect on the hysteretic behavior of LRBs subjected to both simulated and recorded near-fault ground motions for a single-degree-of freedom (SDOF) system. Parameters considered by the authors were number of cycles, distance from fault rupture and magnitude of motion.…”

Lead core heating in lead rubber bearings subjected to bidirectional ground motion excitations in various soil types

“…In the literature, there are only a few research studies that considered deteriorating force‐deformation relation of LRBs in the analysis of seismic isolated structures . In their study, Ozdemir et al .…”

“…Authors revealed that bounding analyses conducted with non‐deteriorating representations for LRBs lead to overestimated isolator displacements compared with the ones obtained by considering the deteriorating representation for LRBs. In another study conducted by Ozdemir and Dicleli , the temperature‐dependent behavior of LRBs was studied rigorously considering the effect of ground motion characteristics when lead core heating is of concern. They compared response quantities of isolated bridges for both deteriorating and non‐deteriorating representations of LRBs.…”

“…The performed analyses were focused on the effects of distinct near‐field ground motion parameters such as the number, intensity, and period of the velocity pulse (or magnitude and distance from fault). The study of Ozdemir and Dicleli revealed that isolator displacements are overestimated as magnitude and the number of pulse increases and distance from the fault decreases (characteristics of high seismicity) when temperature‐dependent behavior of LRBs is not considered. However, both of the studies discussed earlier did not consider the coupling in both orthogonal horizontal directions by applying ground motions unidirectionally.…”