软土地基上高层隔震结构模型振动台试验研究

Shaking table test on high-rise isolated structure on soft soil foundation

通过对高层隔震结构模型在刚性地基和软土地基条件下进行对比振动台试验,研究软土地基上高层隔震结构的地震反应特性和隔震效果。采用叠层剪切型土箱以减小边界影响,采用粉质黏土作为模型土,考虑基底压力的相似,采用高宽比为4的5层钢框架作为上部隔震结构模型,设计了软土地基上高层隔震结构、非隔震结构以及刚性地基上隔震、非隔震结构的振动台试验模型。试验结果表明:土-结构相互作用(SSI)效应对隔震结构的影响程度较非隔震结构轻;SSI效应显著降低了隔震结构模型的自振频率、增加了体系的阻尼;软土地基上隔震结构能够有效减轻结构的地震反应,但是相对于非隔震结构的加速度反应比值增大,隔震效果降低;SSI效应可能增加也可能减小隔震结构的地震反应,不仅与地震动类型有关还与输入地震动强度相关;软土地基上高层隔震结构基础输入地震动与自由场地震动在反应谱水平上基本一致,采用自由场地震动确定基础输入地震动是可行的,且偏于安全,而非隔震结构基础输入地震动则与地基更深层的地震动接近。

In order to investigate the seismic behavior and isolation effectiveness of a high-rise isolated structure on soft soil foundation,the shaking table tests of a high-rise isolated model on rigid and soft soil foundation were conducted.A laminar shear soil container was fabricated to minimize the boundary effects.With the similitude of the soil pressure,five-story steel frame models of aspect ratio 4,either with or without rubber bearings,supported by a pile group,and seated on a silty clay deposit,were subjected to different strong ground motions.From the results,it is found that soil-structure interaction（SSI） effects on high-rise isolated structure models are not as important as those in unisolated counterpart.Due to SSI,the natural frequency of the isolated model system is obviously reduced,and damping ratio largely increased.The efficiency of the presented isolation system on soft soil is confirmed.However,the ratio of peak acceleration of the isolated model to the unisolated one on soft soil is increased,with the isolation effectiveness reduced relatively.SSI can increase or decrease the seismic response of high-rise isolated model,depending on not only the type but also the intensity of the earthquake motion.It is also observed that the acceleration response spectrum of the foundation input motion agrees well with that of the free-field motion for the isolated structure.While,for the unisolated one,it is close to those of the ground motions at greater depths of soil.