A vector‐valued ground motion intensity measure for base‐isolated buildings in far‐field regions

Necmettin Güneş
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Abstract

In this study, the effects of the spectral acceleration at the superstructure first‐mode period on the isolator displacement are investigated for far‐field ground motions. For this purpose, two different base‐isolated models are subjected to 165 far‐field ground motions. It is demonstrated that considering the spectral acceleration at the superstructure first‐mode period, besides that at the effective period, improves the estimation accuracy of isolator displacement. ASCE 7‐22 modifies the scaling period range to consider the superstructure first mode period and proposes the new period range from the superstructure first‐mode period to the 1.25 times effective period. In the ASCE 7‐22, the same weight factor is used for the whole period range. However, the present study shows that adding the superstructure first‐mode related period range with appropriate weight factor to the effective period‐based scaling range decreases the dispersion of isolator displacement in the nonlinear response history analyses (NRH). Then, to overcome the spectral shape effects on the fragility curves, a vector‐valued intensity measure parameter is obtained by combining spectral acceleration at the effective period and reduced spectral acceleration at the superstructure first‐mode period. The optimum contribution factor for the spectral acceleration at the superstructure first‐mode period is defined as the ratio of the superstructure first‐mode period to the effective period. The article shows that the proposed parameter is efficient and sufficient to be used as an intensity measure for far‐field ground motions. Furthermore, regression analysis results indicate that this vector‐valued intensity measure parameter correlates well with the isolator displacement. Further, the article shows that using the proposed IM parameter in the fragility curves makes the collapse margin ratio of these curves less sensitive to the spectral shape of the selected ground motions.
远场区域基底隔离建筑物的矢量值地动强度测量方法
在本研究中,研究了上部结构第一模态周期的频谱加速度对远场地面运动中隔振器位移的影响。为此,对两种不同的基座隔震模型进行了 165 次远场地面运动试验。结果表明,除有效周期外,考虑上部结构第一模态周期的频谱加速度可提高隔震器位移的估算精度。ASCE 7-22 修改了缩放周期范围以考虑上部结构一模周期,并提出了从上部结构一模周期到 1.25 倍有效周期的新周期范围。在 ASCE 7-22 中,整个周期范围使用相同的权重系数。然而,本研究表明,在基于有效周期的缩放范围内添加与上部结构首模相关的周期范围并配以适当的权重系数,可降低非线性响应历史分析(NRH)中隔震器位移的离散性。然后,为了克服脆性曲线上的频谱形状效应,通过结合有效周期的频谱加速度和上部结构第一模态周期的减小频谱加速度,得到一个矢量值强度测量参数。上部结构首模周期频谱加速度的最佳贡献系数定义为上部结构首模周期与有效周期之比。文章表明,所提出的参数是有效的,足以用作远场地动的强度测量。此外,回归分析结果表明,该矢量值烈度测量参数与隔震层位移有很好的相关性。此外,文章还表明,在脆性曲线中使用所提出的 IM 参数可使这些曲线的坍塌裕度比对所选地面运动的频谱形状不那么敏感。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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