Stability Analysis of Laminated Rubber Bearings Using New Boundary Conditions

Base isolation is, in recent times, an accepted design philosophy as an earthquake resistant strategy for structural systems and sensitive instruments. Predicting the behavior of laminated rubber bearings, usually obtained from Haringx’s theory which considers lateral displacement and rotation angle in a rubber column has been developed by many researchers. They have proposed a nonlinear, mechanical model for multilayer elastomeric bearings. However, in past theoretical and experimental studies, the effects of rotation in the lower and upper ends of bearings have been neglected. In this study, an analytical method is presented and formulated by considering the initial rotations of the upper and lower ends of multilayer rubber bearings, as new boundary conditions. Three boundary conditions including equal rotation at the bottom and top end of a bearing, rotation lone at the bottom end and finally rotation only at the top end of a bearing have considered for modeling and analyzing a rubber 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 investigated. Examples are presented to demonstrate the validity of the development method in predicting the mechanical properties of laminated elastomeric bearings with specified geometric parameters. The results of this study have brilliantly shown that initial rotation as a boundary condition will change the mechanical behavior of the laminated rubber bearings.