层间隔震结构模型降阶和优化分析

Model reduction and parameter optimization of story isolation structure

基于模态综合理论,对层间隔震结构的多质点计算模型进行了降阶分析,推导了1个新型的两质点模型。与常规的两质点模型相比较,本模型中下部质点的质量为隔震层下部子结构的第1阶模态质量而不是总质量,并且下部质点所受的地震作用要考虑下部子结构的第1阶振型参与系数。与常规两质点模型相比较,提出的模型在预测顶部加速度和基底剪力方面与多质点全模型的计算结果更为接近,尤其是在预测基底剪力方面。据此,基于底部剪力均方值最小评价指标对隔震层的优化参数给出了解析解。进一步的,考察了隔震层设置位置对层间隔震结构减震效果的影响,分析表明,当隔震层位置处于原结构的下部时,对顶层加速度和基底剪力有较明显的减震效果,随着隔震层所处楼层的提升,减震效果逐渐减弱,因此隔震层的位置应优先安装在结构的中下部。

Based on modal synthesis theory, the multi-degree-of-freedoms （MDOF） computational model of story isolation structure can be reduced to a novel two-degree-of-freedoms （2DOF） model. Compared with the traditional 2DOF model, the lower lumped mass of the presented 2DOF model is the first-order modal mass instead of total mass of the lower substructure below the isolation story. Besides, the first-order modal participation coefficient of the lower substructure should be considered when calculating equivalent seismic load acting on the lower particle of the proposed 2DOF model. Numerical analysis shows the predicted top-story acceleration and base shear force by the proposed 2DOF model agree better with that by the MDOF model, especially on the base shear force aspect. Then, according to the performance index of the minimum base shear force variance, the optimal parameters of iso- lation story are derived theoretically. In addition, the influence of placement of isolation story on the vibration re- duction effect of story isolation structure is also investigated. Numerical results show that, when the isolation story is placed at the lower part of the structure, the top story acceleration and base shear force are mitigated significantly. With the increase of isolation story height, the vibration reduction effect attenuates gradually. Therefore, the isola- tion story is recommended to be placed at the mid and lower part of the structure.