a Karbakhsh - Dept. of Civil Eng., University of Malaya (UM), Malaysia
i Othman - Dept. of Civil Eng., University of Malaya (UM), Malaysia
K. A. Malek - Rubber Research Institute, Malaysian Rubber Board, Selangor, Malaysia

Seismic isolation system is an accepted and simple technique for earthquake protection of structural systems and sensitive components. This approach appears to have considerable potential in preventing earthquake damage to structures and their internal equipments. For predicting the behaviour of an isolation bearing, the Haringx’s theory is usually employed. According this theory, the mechanical properties of an elastomeric isolation bearing have been predicted and described by many investigators so far and they have proposed a nonlinear, mechanical model for multilayer elastomeric bearings. However, in past theoretical and experimental studies, the effects of initial rotation in the ends of bearings have been neglected. In this study, the haringx’s theory is extended and an analytical method is presented by considering the initial rotations of the upper and lower ends of multilayer rubber bearings, as new boundary conditions. Three boundary conditions including: 1) equal rotation at the bottom and top end of a bearing, 2) rotation only at the bottom end and 3) rotation only at the top end of a bearing have considered for modelling the elastomeric isolation bearing. According to these boundary conditions, variations of the lateral displacement and interior rotation of the laminated rubber bearings are obtained. The variations of horizontal stiffness, internal bending moment and interior shear force of the bearing also have been presented. Examples are presented to demonstrate the validity of the development method in predicting the mechanical properties ofelastomeric bearings with specified geometric parameters. The results of this study have brilliantly shown that initial rotation as a boundary condition will change the mechanical properties of the laminated rubber bearings.

base isolation, laminated rubber bearing, elastomeric bearing, stabilityanalysis