P-I and End Rotation Effects on the Influence of Mechanical Properties of Elastomeric Isolation Bearings

Seismic isolation systems constitute an accepted and simple technique for earthquake protection of structural systems and sensitive components. This approach has considerable potential in preventing the structures and their equipment from earthquake destruction. For predicting the behavior of an isolation bearing, Haringx's theory is usually employed. According to this theory, the mechanical properties of an elastomeric isolation bearing can be predicted and described. Many investigators have proposed a nonlinear, mechanical model for multilayer elastomeric bearings. However, in previous theoretical and experimental studies, the effects of initial rotation at the ends of the bearings have been neglected. In this study, Haringxas 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 have been considered for modeling the elastomeric isolation bearing: (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. 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 have also been presented. Examples are presented to demonstrate the validity of the development method in predicting the mechanical properties of elastomeric bearings with specified geometric parameters. The results of this study have shown that initial rotation as a boundary condition will change the mechanical properties of the laminated rubber bearings.