Influence of low temperature exposure time on the mechanical properties of a lead rubber bearing

This study investigates the change in hysteretic properties of lead rubber bearings (LRBs) exposed to low temperatures for several exposure times. For this purpose, a full-scale LRB was conditioned at temperatures of -20°C, -10°C and, 0°C for 3, 6 and, 24 hours and subjected to displacement-controlled cyclic motions at loading frequencies of 0.1 Hz and 0.5 Hz. During the cyclic tests, various levels of shear strain were applied to the isolator, including 50%, 100%, and 134%. Recorded force-displacement curves were analyzed to quantify the variations in hysteretic properties. Based on these findings, the accuracy of existing equations for estimating the amplification of mechanical properties was evaluated. It was found that the existing formulas do not account for the effect of exposure time on LRB characteristics at low temperatures. Consequently, new formulations were developed to provide more accurate predictions of these changes that account for both the effects of low temperatures and exposure time. Additionally, this study investigated the contribution of the lead core to modification in post-yield stiffness after low-temperature exposure for a different set of isolators. Four distinct LRBs were tested for this purpose, all different from the isolator examined in the tests involving varying exposure durations. Tests were performed on both large- and small-size LRBs, with and without lead cores, at a frequency of 0.1 Hz and a rubber shear strain of 100%, following conditioning at 0°C, -10°C, and -20°C for 24 hours. Force-displacement loops recorded during the tests were used to compute the hysteretic properties of bearings with and without a lead core.