环境激励下基础隔震结构的主要动力特性研究

Investigation on main dynamic characteristics of base-isolated structures under ambient excitation

通过对两栋基础隔震建筑在环境激励下的振动测试,运用随机子空间识别法和有理分式多项式法分别识别了结构的模态频率、振型和模态阻尼比。识别结果表明在环境激励下,基础隔震结构的基本频率远大于设计计算多遇地震工况下的基本频率;等效黏滞阻尼比很小,与未隔震结构的阻尼比相当,可以将基础隔震结构视为经典的比例阻尼系统。进一步以其中一栋为研究对象,以识别的模态参数作为修正基准,采用多目标优化的方法反演了环境激励下隔震层的实际水平等效刚度,结果表明其值为多遇地震下计算刚度取值的10.9倍。最后,基于反演的实际隔震层的水平等效刚度对结构的初始有限元模型进行了修正,并对修正后的模型进行了数值分析,分析结果与实际测试结果的对比表明修正后的模型可以更好地反映基础隔震结构在环境激励下的动力特性。

Ambient vibration tests were conducted on the two base-isolated buildings.Modal frequencies,mode shapes and modal damping ratios were identified using stochastic subspace identification（SSI） and rational fraction polynomial（RFP） methods.The identified results show that under ambient excitation,fundamental frequencies of these two base-isolated structures are much larger than the values under frequently occurring earthquake level.And the equivalent viscous damping ratio is as low as the value of non-isolated structure,so base-isolated structures can be considered as classical proportional damping system under ambient excitation.Furthermore,taking one of the two buildings as study case,identified modal parameters were used as the updating benchmark and the actual equivalent horizontal stiffness of isolation layer was estimated inversely using the multi-objective optimization method.The results show that the actual stiffness value is 10.9 times of that in the design case under frequently occurring earthquake level.Finally,the preliminary finite element model were updated based on the inversely estimated stiffness of the isolation layer and the updated model was analyzed numerically.Comparison of the results between analysis and test indicates that the updated model can represent the dynamic characteristics of the base-isolated structure under ambient excitation more reliably.