Abstract
The existence of local soft interlayer can significantly amplify or attenuate the ground motion and thus might influence the lagged spatial coherency between spatially varying earthquake ground motions. A target site with a local soft interlayer was assumed first, and then two numerical examples were set. In example 1, linear soil behavior was considered and a large amount of quasi-stationary spatially varying earthquake ground motions were generated by combining the one-dimensional wave propagation theory and the classical spectral representation method. The influence regularity of varying shear wave velocity, buried depth, and thickness of the soft interlayer on the characteristics of lagged spatial coherency was investigated. In example 2, non-linear soil behavior was taken into account and fully non-stationary spatially varying earthquake ground motions were thus generated by using time-varying transfer function and spectral representation method. An overall evaluation was carried out to shed light on the differences of characteristics of spatial coherency between non-linear soil and linear soil cases. It showed that: (i) As the shear wave velocity of interlayer declines and as the buried depth and thickness increase, remarkable reduction of spatial coherency showed up; (ii) the reduction of lagged spatial coherency caused by varying buried depth may be more inclined to concentrate in the lower frequency range; (iii) the non-linear soil behavior can cause greater further reduction of lagged spatial coherency in comparison with linear soil behavior, especially in the higher frequency range; (iv) the troughs of lagged spatial coherency curve tend to be located in the variation range of vibration frequency of time-varying spectral ratio.
Highlights
To incorporate the influence of non-linear soil behavior into the simulation of fully non-stationary spatially varying earthquake ground motions (SVEGMs) and based on the assumption that the soil property is linear at each minute time interval, the authors obtained time-varying soil properties by using a numerical site response analysis and substituted time-varying shear modulus and damping ratio data into the classical transfer function, and time-varying transfer function was established (Detailed information can be found in Refs. [51,52]): H =
Mean lagged spatial coherencies for non-linear soil and linear soil cases and corresponding time-varying spectral ratios under varying shear wave velocity of soft interlayer are shown in Figure 10, and tm is the time interval with respect to the lowest value of shear modulus
By using two numerical examples and based on previously established time-varying transfer function model incorporating the influence of soil non-linearity, the influence regularity of the properties of soft soil interlayer on the lagged spatial coherency between spatially varying earthquake ground motions was studied in the present paper, where the variation trend of lagged coherency loss with the shear wave velocity, thickness, and burial depth of soft soil interlayer was mainly focused on and relevant analyses were presented
Summary
The spatial variation of ground motions is moving researchers and engineers’ focus toward the seismic response characteristics of large-scale or extended structures [1,2,3,4,5,6,7,8,9,10,11] and engineering site [12,13,14] under spatially varying earthquake ground motions (SVEGMs). A lot of studies were performed on the influence of site conditions on the spatial coherency [26,33,34,35,36,37] In general, these studies were on the basis that the soil property was linear and/or the shear modulus of soil layers were regularly increasing as depth, and underlying soft soil interlayer or non-linear soil behavior was not taken into account. In example 1 (linear soil case), by combining the 1D wave propagation theory with classical spectral representation method (SRM), numerous quasi-stationary SVEGMs in horizontal out-of-plane, horizontal in-plane, and vertical in-plane directions were simulated for the target site, where varying shear wave velocity, buried depth, and thickness of the soft interlayer were considered. Mean lagged spatial coherency between SVEGMs under each circumstance above mentioned was estimated, and a series of comparisons were conducted
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