The seismic design of the tall building requires determining the expected lateral drift and the internal forces in the structural elements. In the analysis, it is common for the structure engineer to consider a fixed base structure which means that the foundations and the underlying soil strata are assumed to be infinitely rigid. This assumption is not
Proper since the underlying soil in the near field always consists of soft soil layers that posses different properties and may drastically affect the seismic motion before hitting the structure foundation. Moreover, it is highly expected the soft soil layers will posses nonlinear behavior when subjected to high strain level in case of strong seismic excitations. During the structure vibration, the mutual interaction with the near field soil strata, the foundation and the structure itself will lead to different structure behavior from the fixed base assumption.
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