Evaluation of Seismic Performance for Bridges Isolated with Lead-Rubber Seismic Isolator Bearing

Abstract

Lead rubber bearing (LRB) is the most developed and the most common seismic isolator in the world that can reduce 60- 80 percent of the seismic force to structures. Isolators are applied in bridge design to achieve maximum energy absorption (relative to the period in isolated buildings). Therefore, isolators with high damping should be used. In this regard, lead rubber seismic isolators, abbreviated LRB, have the inherent properties of 30 percent (independent of vibration frequency, temperature and environmental conditions). The objective of isolation in bridges is very different from building. In a building, isolators are installed to reduce the energy forces exerted on the superstructure in order to reduce stress on structural elements. However, seismic isolators are installed to protect the elements under the isolator (abutments and bases) to reduce the transmitted energy, and displace superstructures (deck) to substructures (abutments and bases). This study introduces lead rubber bearing (LRB) and its advantages compared to elastomeric bearings. Then, the design for replacement of those bearings in four important bridges in the country with seismic isolators, and its impact on reducing the stress on bases and abutments are discussed.