SSI in steel frames subjected to near-fault earthquakes

Modern seismic codes are usually associated with far-field earthquakes and generally neglect soil-structure interaction, assuming that omission of this phenomenon leads to conservative results. This study investigates the effect of soil-structure interaction on the inelastic response of two-dimensional steel frames subjected to near-fault earthquakes, which have been recorded near to seismic faults with reverse and strike-slip mechanisms. In order to achieve this, thirty-six planar moment resisting steel frames which have been designed for seismic and vertical loads according to European codes are examined under the action of sixty near-fault pulse-like records. Simplified soil-structure interaction is carried out using springs and dashpots to simulate the flexibility of soil at the soil-foundation interface and adopting the effective properties of soil. Seismic response parameters, such as, interstorey drift ratios, maximum floor accelerations and inelastic displacement ratios are numerically determined by dynamic inelastic analyses. After a comprehensive statistical analysis, empirical expressions for these parameters in terms of the number of storeys of structures, the type of fault mechanism as well as the consideration or not of soil-structure interaction are obtained. Critical examination of the results indicates that the flexibility of soil strongly affects the seismic response of steel frames. Furthermore, it is concluded that the structural response parameters under consideration are noticeably influenced by the type of fault mechanism.