Abstract In this study, a new damping reduction equation is proposed to obtain reasonable estimates of the actual nonlinear responses of seismic isolated structures (SIS) subjected to near fault ground motions (NFGM) with forward-rupture-directivity effect, using equivalent linear analysis (ELA) procedure. For this purpose, first, a set of 29 NFGM are selected and grouped according to their site soil classification. Then, the average response spectra of the NFGM are plotted and a smoothed design response spectrum for each set of ground motions are obtained. Next, nonlinear time history analysis (NLTHA) and ELA of SIS are performed for the selected ground motions. Subsequently, the average of the isolator displacements calculated from the NLTHA are obtained for each set of NFGM considered in the analyses. Then, the damping reduction factor required to obtain an isolator displacement equal to the average isolator displacements obtained from the NLTHA of SIS is back calculated via the ELA procedure. Next, the variation of the damping reduction factor is plotted as a function of various combinations of the parameters considered in this research in dimensionless form and nonlinear regression analyses are performed to formulate the damping reduction equation. The isolator characteristic strength, post elastic period, the corner period of the response spectrum and peak ground acceleration are found to affect the damping reduction factor and hence, the displacements obtained from ELA. The proposed damping reduction equation is found to yield more reasonable estimates of the actual nonlinear responses compared to those available in the literature and design codes.

中文翻译：

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近断层地震动作用下隔震结构等效线性分析的阻尼折减方程

摘要 在这项研究中，提出了一个新的阻尼减少方程，以使用等效线性分析来合理估计地震隔离结构 (SIS) 受到具有前向断裂方向性效应的近断层地震动 (NFGM) 的实际非线性响应 ( ELA) 程序。为此，首先，根据场地土壤分类选择并分组 29 种 NFGM。然后，绘制 NFGM 的平均响应谱，并获得每组地面运动的平滑设计响应谱。接下来，对选定的地震动进行非线性时程分析 (NLTHA) 和 SIS 的 ELA。随后，为分析中考虑的每组 NFGM 获得从 NLTHA 计算的隔离器位移的平均值。然后，通过 ELA 程序反向计算获得与从 SIS 的 NLTHA 获得的平均隔振器位移相等的隔振器位移所需的阻尼减少系数。接下来，将阻尼折减系数的变化绘制为本研究中考虑的各种参数组合的无量纲形式的函数，并进行非线性回归分析以制定阻尼折减方程。发现隔离器特征强度、后弹性周期、响应谱的拐角周期和峰值地面加速度会影响阻尼减少因子，从而影响从 ELA 获得的位移。