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UBC Theses and Dissertations

Effect of multi-directional ground motions on the performance of lead-rubber isolators in base-isolated bridges Kedarisetti, Ashritha


Seismic Isolation is an effective design approach widely used in the seismic design of bridges. Understanding the behaviour of isolation systems and their effects on the overall seismic performance of bridges under different types of ground motions is important. Studies reveal that the isolation systems are effective even in the presence of vertical ground motion components, however, they have a significant influence on the demands incurred on the isolators. This study aims to investigate the effect of multi-directional ground motions on the behaviour of lead rubber isolators in base-isolated bridges. The influence of multi-directional ground motions on the isolator deformation, axial force, and overturning moment demands are studied. This thesis also attempts to understand the damping, hysteresis, and particle motion of the isolators. Influence of vertical eccentric load and the impact of the orientation of ground motions on the critical displacement response of isolators which have not been extensively studied in the existing literature are also explored. A 3-span bridge isolated with lead rubber bearings at abutments and piers is modelled in Seismostruct. Two suites consisting of 16 and 7 sets of ground motions are selected for the study. Three sets of incremental dynamic analyses with scaling factors ranging from 1 to 5 are carried out. The results obtained indicate that though the demands on the isolators are high in the presence of vertical ground motions, the isolators perform well. The axial force and overturning moment demand on the isolators exceed their capacities when the intensity of the ground motions is high, i.e., higher scaling factors. However, further research is recommended to determine the effect of this exceedance on the performance of isolators and their anchoring systems. The orientation of ground motions influences the critical displacement response of the isolators and this has to be taken into consideration while designing isolations systems. The observations on the damping and hysteresis characteristics of the isolators shed light on the potential areas of research to understand these systems better.

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