LONG-TERM PERFORMANCE EVALUATION OF HIGH DAMPING RUBBER BEARINGS BY ACCELERATED THERMAL OXIDATION TEST

摘要

High damping rubber (HDR) bearings are widely accepted as a base isolator in buildings and bridges in the world. It is well known that rubber materials change their properties when exposed to degradation factors including oxygen, ultraviolet, ozone, temperature, acid, and humidity. Among them, thermal oxidation is the predominant degradation factor for HDR in the built environments. In this study, based on the deterioration characteristics resulted from accelerated thermal oxidation tests of HDR bearings, a simple formula is derived to predict the variation of the equivalent shear stiffness of an HDR bearing. The long-term seismic performance of a base-isolated continuous steel bridge is evaluated by considering aging of HDR bearings. Using the simple formula, the equivalent stiffness and equivalent damping ratio of HDR bearings is calculated based on the size of bearing, an average temperature of the construction site, and various aging times up to 100 years. The results show that the equivalent shear stiffness of HDR bearing increases due to aging, which will cause the seismic force on the bridge to increase. The maximum stiffness change found in this study is about 14% of the initial stiffness. However, the most part of the change occurs soon after bearing installation.