RESPONSE ANALYSIS METHOD CONSIDERING HEAT-MECHANICS INTERACTION BEHAVIOR OF LEAD RUBBER BEARINGS

Abstract

 When seismically isolated buildings are exposed to strong long-period and long-duration ground motions, seismic isolation devices such as Lead Rubber Bearings (LRBs) can be subjected to larger and more cyclic deformations than anticipated in conventional structural design. In an LRB, seismic input energy is absorbed as hysteresis energy of a lead plug and finally transformed into thermal energy. The large and multiple cyclic deformations of the LRB generate a large amount of heat, causing high temperature in the lead plug. The resulting deterioration of damping characteristics, which encompasses complex thermal and mechanical phenomena, may adversely affect a seismically isolated building's response. There are two important requirements when simulating the heat-mechanics interaction behavior of an LRB. The first is to evaluate the temperature rise of the lead plug due to the energy absorption, and the second is to evaluate the change of mechanical properties it causes.
 This paper describes a response analysis method considering the heat-mechanics interaction behavior of an LRB. A heat conduction analysis applying the difference method and the configuration of a simple analytical model are proposed. A relationship between the temperature and the yield stress of the lead plug is also proposed based on a simulation analysis of conventional experimental results. The effects of absorbed energy distribution in the calculation of the temperature rise of the lead plug for the analysis are investigated, as well as the effects on the evaluation of the equivalent temperature of the lead plug. Simulation analysis results using the proposed method are compared to conventional experimental one, the validity of the proposed method regardless of the size of the LRB is verified, and an arrangement of lead plug and loading condition is proposed.
 The proposed analysis method is applied to evaluate the heat-mechanics interaction behavior of the LRB. This method is useful for damage evaluation of seismically isolated buildings using LRBs under multi-cyclic deformation caused by long-period and long-duration ground motions.