Stress-Softening Behavior of High-Damping Rubber Bearings at Low Temperatures

Abstract

High-damping rubber (HDR) bearings exhibit obvious initial stress hardening at lower ambient temperatures and stress softening under cyclic loading. The phenomenon of stress softening is usually referred to as the Mullins effect, which is often considered to be influenced by the rubber composition, the vulcanization profile used to manufacture the bearing, and the past strain history. The Mullins effect is temperature dependent and is larger at lower temperatures. In addition, the stiffness of HDR bearings decreases at a higher inner temperature caused by the self-heating of HDR materials under cyclic loading. Hence, the stress softening is attributed to the coupled temperature and Mullins effects. It is necessary to clarify the coupled temperature and Mullins effects on the mechanical behavior of HDR bearings to introduce them as seismic isolation devices for bridges in cold and earthquake-prone regions. In this study, a random polymer (RP) model was developed with consideration of the coupled temperature and Mullins effects for HDR bearings at low temperatures. The parameters of the RP model were identified using the hysteresis loops of HDR bearings in the cyclic loading and hybrid simulation tests with a temperature-controlled loading system at low temperatures. The accuracy of the RP model was verified by comparing the numerical seismic responses of a bridge isolated with HDR bearings using the proposed model with hybrid simulation results.