Elastic seismic response of moment resisting framed structures with soil-structure interaction

The present study analyses effects of soil-structure interaction (SSI) on the elastic response of moment resisting framed reinforced concrete structures founded on embedded raft in an elastic half-space to accelerograms compatible to design spectra conforming to diverse geology. Most structures are designed to remain elastic under design basis earthquake and are expected to exhibit inelasticity but no collapse under maximum credible earthquake. Moreover machine foundations subjected to harmonic excitations are supposed to respond in an elastic manner during its routine use. Hence there is a need to understand elastic response of structure-soil systems. The effect of SSI is to increase natural period and damping of the structure-soil system. Structure-to-soil stiffness ratio is the most significant parameter influencing extent of inertial SSI effects and has been selected as a metric of SSI and smaller values denote closeness to fixed-base structures. It is observed that SSI leads to reduced design forces in structures subjected to either harmonic excitation or ensembles of spectrum compatible design basis earthquakes. The results are expressed as response spectra plots which are quite familiar to structural engineers.