减隔震连续梁桥非经典阻尼问题与地震响应简化分析

Simplified analysis of seismic response for an Isolated continuous girder bridge with non-classical damping

针对减隔震连续梁桥地震响应简化分析面临的非经典阻尼问题,以铅芯橡胶支座为例,对比直接积分结果与强迫解耦后的模态时程结果以研究非经典阻尼的影响,并利用线性滞回阻尼特性建立由减隔震装置等效阻尼比计算结构模态阻尼比的方法,在此基础上采用基于反应谱的简化方法计算地震响应,并与非线性时程结果进行比较。分析结果表明:减隔震装置产生的集中阻尼改变结构整体阻尼分布特性,非经典阻尼对结构地震响应的贡献随等效模态阻尼比增加而增大;将减隔震装置等效线性化后,再用反应谱方法按等效线性模型计算结构的地震响应,所得桥墩内力和主梁位移都不一定是可能的最大值,计算结果偏于不安全。

In order to analyze seismic response of an isolated continuous girder bridge,taking lead rubber bearing(LRB) for example,direct integration method of time-history and modal method of time-history after forced uncoupling were employed to study the effect of non-classical damping on the seismic response,structural modal damping ratios were obtained from equivalent damping ratios of isolators according to linear hysteretic damping model,then compared with the non-linear time history analysis,simplified analysis based on response spectra method was adopted to calculate the seismic response.The results indicated that non-classical damping produced by seismic isolation devices changes the overall damping characteristics of structure and its contribution to structural seismic response rises with increase in equivalent modal damping ratio,and the seismic response obtained using simplified analysis after equivalent linearization of isolators is not safe for the lower estimation of pier forces and the main beam displacements.