Effects of Heating and Load History on the Behavior of Lead-Rubber Bearings

Keywords: Lead-rubber bearings (LRB).  Lead core heating.  Cumulative travel.  Elevated temperature.  Mechanical properties.  Numerical simulations.  Predictions.  Finite element (FE) analyses.  Reduced scale testing.  Dynamic response.  Peak seismic response.  Seismic isolation systems.

Abstract: This report presents a comprehensive investigation of the effects of lead core heating and cumulative travel on the behavior of lead-rubber bearings.  A literature review and an experimental study of the effects of temperature on the mechanical properties of lead are presented.  A theory for predicting the temperature rise of the lead core in lead-rubber bearings (LRB) subjected to lateral motion is developed based on principles of mechanics.  The theory reduces the complex three-dimensional (3D) thermo-mechanical problem into a numerically solvable initial value problem on the history of temperature of the core and the strength of the bearing.  The accuracy of the theory is verified through comparison to experimental results and results of finite element (FE) analysis of several bearings.  The theory is then used to establish principles of similarity and scaling that can be used in reduced scale testing of lead-rubber bearings.  Furthermore, a model of the behavior of lead-rubber bearings that can be incorporated in dynamic response history analysis programs is described and validated through experiments.  Studies on the dynamic response of seismically isolated structures using the proposed model demonstrate the importance of accounting for the effects of lead core heating in calculating the peak seismic response of seismically isolated structures.