近断层脉冲型地震动对基础隔震结构水平向减震系数的影响分析

Study on horizontal seismic reduction factor of base-isolated structure subjected to near-fault pulse-like ground motions

水平向减震系数是基础隔震设计的重要参数之一。为研究近断层脉冲型地震动对水平向减震系数的影响,以单自由度体系为研究对象,基于反应谱法,给出单自由度体系的水平向减震系数计算公式,考虑近断层影响,分析不同方法中水平向减震系数的差异;以多自由度体系为研究对象,选取36条近断层脉冲型地震动,同时剔除其中的主脉冲成分,得到36条非脉冲型地震动,将这72条地震动作用于多层基础隔震结构,基于时程分析法,对比了在脉冲和非脉冲型地震动作用下的水平向减震系数变化规律,并分析脉冲周期、场地类别和断层距对水平向减震系数的影响。研究结果表明:现行方法虽有一定的合理性,但是难以准确考虑近断层脉冲型地震动对水平向减震系数的影响。随着地震动强度的增大,水平向减震系数呈先减小后增大的趋势,相同地震动强度下,近断层脉冲型地震动作用下结构的水平向减震系数更大,变化幅度更大。近断层脉冲型地震动对水平向减震系数有放大作用,水平向减震系数的放大系数随着近断层地震动脉冲周期的增大,呈整体增大的趋势。当断层距较小时,水平向减震系数的放大效应更为显著,而与场地类别无明显关系。在近断层基础隔震结构设计中,水平向减震系数的放大系数建议取1.50。

Horizontal seismic reduction factor is an important parameter in base isolation design. In order to study the influence of near-fault pulse-like ground motion on the horizontal seismic reduction factor, single-degree-of-freedom system was selected as the research object, and the calculation formula for horizontal seismic reduction factor of single-degree-of-freedom system was established based on the response spectrum method. The difference of horizontal seismic reduction factor obtained from different calculation methods was analyzed. Meanwhile, multi-degree-of-freedom system was also selected as the research object, 36 near-fault pulse-like ground motions were selected, and 36 non-pulse-like ground motions were generated by removing the main pulse component from the 36 near-fault pulse-like ground motions. These 72 ground motions were used for multi-storey base-isolated structures. Based on the time history analysis method, the variations of the horizontal seismic reduction factors obtained from pulse and non-pulse-like ground motions were compared, and the influences of pulse period, site type and fault distance on the horizontal seismic reduction factors were analyzed. The results show that the current calculation methods are reasonable, but it is difficult to accurately consider the influence of near-fault pulse-like ground motion on the horizontal seismic reduction factor. With the increase of ground motion intensity, the horizontal seismic reduction factor decreases and then increases. For the same ground motion intensity, the horizontal seismic reduction factor of the structure under near-fault pulse-like ground motions is larger and the change is faster. The horizontal seismic reduction factor tends to amplify under near-fault pulse-like ground motion. With the increase of pulse period of near-fault pulse-like ground motion, the amplification coefficient of horizontal seismic reduction factor increases accordingly. The amplification effect of horizontal seismic reduction factor is more significant with a small fault distance. But the amplification factor of horizontal seismic reduction factor has non-significant relation with the site type. It is suggested that the value of amplification factor of the horizontal seismic reduction factor is taken as 1.50 in the near-fault isolation design.