修正Clough滞回模型下的地震力调整系数

Seismic force modification factors for structures with modified-Clough hysteretic model

采用反向加载时刚度退化的修正克拉夫(Modified-Clough,MC)滞回模型,计算了单自由度体系(SDOF)在四类场地下各74～106条地震波输入后的弹塑性动力时程响应,得到了不同自振周期、延性、阻尼比和后期刚度系数等参数组合下的地震力调整系数R。结果表明,影响R的决定性因素是结构的延性,延性越大R越大;阻尼比、后期刚度对R的影响是第二位的,而且只在短周期范围内比较明显。对R谱的横轴做标准化处理后,较好地保留了R谱在特征周期处的峰值特征,并提出了R的计算公式。为了分析耗能能力、刚度退化的影响,将延性和耗能能力作为两个独立变化的因素,分析了理想弹塑性(EPP)、剪切滑移(SSP)和无任何耗能能力的双线性弹性(BIL)模型下的R谱,与MC滞回模型下的R谱一起相互之间进行了对比。结果表明,在延性保持相同的情况下耗能能力在中长周期结构中对地震力调整系数几乎没有影响,这一结论对美日等国近几年引入一些注重延性而不单纯看重耗能能力的细部构造提供了理论解释。在中等周期范围内,刚度退化的MC结构比EPP结构的强度需求反而要小。

Based on an elasto-plastic time-history earthquake analysis of a single degree of freedom system （SDOF） , the seismic force modification factor R of the modified-Clough （MC） model, which can be employed to represent structures that exhibit stiffness degradation when subjected to cyclic loading, is investigated. A total of 370 earthquake records from 4 sites are employed to calculate the structure response and the factor R for different structure periods, ductility, damping ratios and the post-yield stiffness ratios. It is found that the most important factor in determining R is the ductility, while both damping and the post yield stiffness have a minor effect in the short period range. The R spectra are normalized by using the characteristic period Ts of the ground motion to maintain the peak behavior near Tg. Simplified formulae are proposed for the R spectra. Three other hysteretic models, including elastic perfectly- plastic （EPP） , shear-slipped （SSP） and bilinear elastic （BIL） , are analyzed to examine the effect of energy- dissipating capacity and stiffness degradation on the R spectra, and the results, together with the R spectra for MC model, are compared. It is found that the energy dissipating capacity has nearly no effect on the R spectra in the middle-to-long period range. This provides an explanation on the recent American practice that emphasizes more on the ductility than on the energy dissipating capacity. Comparison between EPP and MC models indicates a smaller strength requirement for the latter model within medium periods.