Earthquake resistance performance of laminated and lead core rubber bearings

Abstract

Base isolation has been used in many classes of civil engineering structures to reduce the damage from earthquake attacks. The main idea behind this innovative technique is to shift the fundamental natural frequency of the structure to a value much lower than the dominant frequency of the earthquake. In this work, dynamic characteristics of a five-storey benchmark model isolated with laminated rubber bearings (LRB) and Lead core rubber bearings (LCRB) under Kobe and El-Centro ground motions were examined using a shaking table. The earthquake resistant performance of LRB and LCRB isolators was evaluated. The first natural frequency of the model was reduced from 4.7Hz for the unisolated model to 2.9 and 1.7 Hz for the LRB and LCRB isolated models, respectively. It was observed that maximum floor accelerations were significantly reduced with the addition of an LRB or LCRB isolation system regardless of the ground motion input. However, the LRB was identified to be :more effective than LCRB in reducing accelerations and model relative displacements, and therefore, provided a better protection of the superstructure and its contents. On the other hand, the LCRB produced smaller base and floor displacements, and hence can ensure structural stability better than the LRB. This property of LCRB stems from high damping and stiffness of the lead core.