As the ground response analysis serves an integral part of site specific seismic hazard study to obtain design ground motion, a proper and accurate estimation should be of prime importance. The paper presents a study on the effect of trapped soft and stiff soil layer on equivalent linear ground response analysis implemented in computer program STRATA. For this purpose, the concept of normally stiff and inversely stiff soil profiles have been introduced. The study clearly indicates the higher impact of a trapped soft soil layer profile, i.e., inversely stiff soil profile with soft layer, in comparison with trapped stiff layer profile, i.e., inversely stiff profile with stiff layer. For low to moderate ground motions, as the depth of the trapped soft layer increases, peak amplification and peak frequency reduces, and for high intensity input ground motion, significant reduction only in the peak frequencies is observed. On the other hand, as the depth of trapped stiff soil layer increases the outcome of ground response analysis remain quite similar. Peak transfer function, peak frequency, peak spectral ratio and peak spectral acceleration are found to exhibit a COV ≤ 60 to 100% for all combinations of IS-Soft profiles, whereas, IS-Stiff profiles exhibit a maximum COV ≤ 15 to 25% for all the considered input ground motions. Computed normalized-root mean square error (Norm-RMSE) values also clearly indicate the higher deviations in the ground response analysis for different combinations of trapped soft soil profiles, from that of normally stiff profile, whereas, trapped stiff layer profiles show lower deviations in the Norm-RMSE values. The profiles with trapped soft layer exhibit a Norm-RMSE value ≤0.8, whereas, trapped stiff layer profiles exhibit a Norm-RMSE value ≤0.2, which clearly demonstrate the large deviations in the outcome of ground response analysis in case of trapped soft layer profiles.

中文翻译：

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被困的软硬土层对地震现场响应分析的影响

由于地面响应分析是特定地点地震危险性研究中不可或缺的一部分，可用于获取设计地震动，因此正确而准确的估算至关重要。本文提出了对困软土层和刚性土层对计算机程序STRATA中实现的等效线性地面响应分析的影响的研究。为此目的，引入了通常为刚性和反刚性的土壤剖面的概念。该研究清楚地表明，与被困的刚性层剖面（即具有刚性层的反刚性剖面）相比，被困的软土层剖面（即具有软层的反刚性剖面）的影响更大。对于低到中等的地面运动，随着捕获的软层深度的增加，峰值放大率和峰值频率会降低，对于高强度输入地面运动，仅观察到峰值频率显着降低。另一方面，随着被困硬土层深度的增加，地面响应分析的结果仍然非常相似。对于IS-Soft配置文件的所有组合，发现峰传递函数，峰频率，峰光谱比和峰光谱加速度的COV≤60至100％，而IS-Stiff曲线的最大COV≤15至25％所有考虑的输入地面运动。计算出的归一化均方根误差（Norm-RMSE）值也清楚地表明，对于滞留软土剖面的不同组合，地面响应分析与正常刚度剖面的偏差较大，而滞留硬层剖面在水平方向的偏差较小。 Norm-RMSE值。