地震动速度脉冲对不同高宽比基础隔震结构抗震性能的影响

为研究近断层地震动的速度脉冲对基础隔震结构地震反应的影响，建立了不同高宽比的传统抗震及基础隔震框架结构有限元模型，选取了6条具有向前方向性效应和滑冲效应速度脉冲的实际近断层强震记录作为结构基础输入地震动，对8个模型进行了非线性动力时程分析，对比分析了传统抗震及基础隔震框架结构模型的层间位移角、支座位移和基底剪力等反应。结果表明：在近断层速度脉冲型地震动作用下，随着结构高宽比的增加，基础隔震结构的层间位移角和基底最大剪力逐渐增加，而隔震支座位移有先增大后减小的趋势，且随着地震动峰值速度与峰值加速度比值的增大，隔震支座位移也逐步增大；基础隔震对高宽比小于3的结构具有较好的减震效果，且高宽比越小其减震效果越好，但是当结构高宽比为4时，基础隔震效果较差；近断层地震动的速度脉冲对基础隔震结构底部楼层的不利影响会导致结构出现倒塌破坏。

Effects of velocity pulse of ground motion on seismic capacity of base-isolated structures with different height-to-width ratios

The influence of velocity pulse characteristics of near-fault ground motions on the seismic response of base-isolated structures was investigated in this paper. The analysis models of traditional seismic frame structures and corresponding base-isolated structures with different height-to-width ratios were established by using finite element software. Six ground motion records with forward directivity velocity pulse and fling step velocity pulse were selected as the seismic input at foundation of structures, and eight structures were analyzed by nonlinear dynamic time-history analysis. The comparative analysis is carried out on parameters of the structure responses such as the inter-story drifts, bearing displacement and base shear force. Under the velocity pulse-like ground motions, the inter-story drifts and the base shear of base-isolated structures gradually increase when the height-to-width ratio increases but the displacements tend to increase first and then decrease, and the displacement of isolation layer increases with the ratio of peak velocity to peak acceleration of the input ground motions. The base-isolated structures with the height-to-width ratio less than 3 have better vibration reduction capacity under velocity pulse-like ground motions. The smaller the height-to-width, the better the vibration reducing effect, and conversely, the seismic capacity of base-isolated structures is poor if the height-to-width ratio of the structure is 4.The adverse effect of velocity pulse of near-fault ground motion on the response of lower part of the base-isolated structure may even lead to collapse damage on the structure.