The Influence of Input Motion Scaling Strategies on Nonlinear Ground Response Analyses of Soft Soil Deposits

A key issue for the estimation of ground shaking is the proper selection of input motions at the seismic bedrock. At the same time, the effect of the input motion scaling strategy on structural response is typically studied disregarding the presence of the soil deposit. In this work, different soft soil deposits are selected by varying the shear wave velocity profiles and the depth to the seismic bedrock, modelling the soil behaviour through a nonlinear constitutive model implemented into a fully coupled FE code. Seven input motions are retrieved for several selection strategies in conjunction with two seismic intensity levels. Hence, more than 300 one-dimensional ground response analyses are performed. The results of the analysed cases, which are presented in terms of spectral response at ground surface and amplification factors, indicate that: (i) the use of an advanced elasto-plastic soil constitutive model accounts for nonlinear ground response effects, including higher site amplification in the mid-period range and deamplification of the peak ground accelerations; (ii) the different scaling strategies lead to comparable mean values of the amplification factors, and (iii) the variability of the amplification factors is significantly reduced when the scaling strategy seeks the compatibility with the target spectrum over a specified period range. The research will aid the prediction of local seismic site response over large areas, particularly in the absence of the fundamental period of a structure and facilitate its use in general recommendation for quantifying and reducing uncertainty.

Automated summary

The selection of input motions at the seismic bedrock is crucial for estimating ground shaking. However, the effect of input motion scaling strategy on structural response is commonly studied without considering the presence of the soil deposit. In this study, different soft soil deposits were modeled using a nonlinear constitutive model, and more than 300 ground response analyses were conducted. The results showed that using an advanced elasto-plastic soil constitutive model accounted for nonlinear ground response effects, different scaling strategies led to comparable mean values of amplification factors, and variability of amplification factors was significantly reduced when the scaling strategy was compatible with the target spectrum over a specified period range.