近断层地震动下公路桥梁铅芯橡胶支座变形发热及性能退化效应研究

Deformation, heating and performance degradation of lead rubber bearings for highway bridges under near fault ground motions

铅芯橡胶支座(LRB)是目前应用广泛的桥梁减隔震装置,地震中LRB往复变形会引发热量累积及温度升高,进而导致滞回耗能、特征强度和刚度的降低等力学性能方面的变化并威胁桥梁地震安全。以《公路桥梁铅芯隔震橡胶支座》(JT/T 822—2011)中22种型号的圆形LRB为对象,建立40个不同周期的单支座隔震结构模型,通过输入普遍适用于交通运输领域结构抗震设计和研究的40组水平双向近断层地震动记录进行非线性动力时程分析,研究了考虑铅芯发热与否对LRB的位移、温度、特征强度和滞回耗能等因素的影响,还讨论了铅芯温度增量和特征强度降低率与近断层地震动的关系,建立了支座位移延性系数、剪应变和特征强度与重量之比(Q_d/W)的拟合关系式。结果表明:对于中长周期(1.5~3 s)隔震体系,在近断层地震动下内部铅芯温度升高、特征强度下降现象明显,其温度增量在50℃~80℃,特征强度降低20%~40%,不考虑铅芯发热会低估15%左右的位移反应。

Lead-rubber bearings(LRBs) are extensively used seismic isolators in bridges. The cyclic deformation of LRBs under earthquake can cause heating accumulation and temperature rising. As a result, variations of mechanical properties of LRBs including dropping of hysteretic energy dissipation, characteristic strength and stiffness threaten seismic safety of bridges. Here, according to the code of the lead rubber bearing isolator for highway bridge(JT/T 822—2011), 22 types circular LRBs were taken as objects to establish 40 single bearing isolation structure models with different periods. 40 bilateral near-fault ground motion records suitable to transportation field structure aseismic design were input into models to perform nonlinear dynamic time history analyses. Effects of lead core heating on LRBs’ displacement, temperature, characteristic strength and hysteretic energy dissipation were studied. In addition, relations among increment of lead core temperature, characteristic strength reduction rate and near-fault ground motion were discussed to establish fitted relation expressions among bearing displacement ductility coefficient, shear strain and Q_d/W. Results showed that for the isolated systems with medium-long periods(1.5~3 s) under near fault ground motion, lead core temperature rising and characteristic strength dropping are obvious, the increase in lead core temperature is 50 ℃-80 ℃, characteristic strength drops 20%-40%;displacement responses of LRBs can be under-estimated by 15% not considering lead core heating.