Effect of inelastic soil structure interaction on distribution of seismic vulnerability in special moment frame RC structures

A complete nonlinear SSI model of a structural system on soft soil including an inelastic moment frame resting on a foundation on nonlinear Winkler springs is developed in this study. Various RC frames differing in height from 3 to 9 stories are studied. For each building a suit of 10 consistent earthquakes are selected and scaled. Each frame accompanied by its flexible base is analyzed under its associated earthquakes and the averages of its maximum responses are calculated. Story shear forces and plastic hinge rotations of beams and columns are determined. The results show that while the total hinge rotations decrease in each moment frame due to SSI, the plastic hinge rotations at the lower stories increase compared with when no SSI is taken into account. Thus distribution of vulnerability changes and the lower stories become more seismically vulnerable when the true flexible-base response is determined.