Effects of Soil-Structure Interaction on Response of Structures Subjected to Near-Fault Earthquake Records

Near-fault ground motions have notable characteristics such as velocity time histories containing large-amplitude and long-period pulses caused by forward directivity effects and acceleration time histories with high frequency content. These specifications of near-fault earthquake records make structural responses to be different from those expected in far-fault earthquakes. In this paper, using moving average filtering, a set of near-fault earthquake records containing forward directivity pulses are decomposed into two parts having different frequency content: a Pulse-Type Record (PTR) that possesses long period pulses, and a relatively high-frequency Background Record (BGR). Studying the structural response to near-fault records reveals that elastic response spectra for fixed-base systems, in contrast to their response to ordinary earthquakes, show two distinct local peaks related to BGR and PTR parts. Also, the effect of Soil-Structure Interaction (SSI) on response of structures subjected to this type of excitations is investigated. Generally, the SSI effect on the response of structures is studied through introducing a replacement single-degree-of-freedom system with longer period and usually higher damping. Since this period elongation for the PTR-dominated period range is greater than that of the BGR-dominated one, the spectral peaks become closer in the case of soil-structure systems in comparison to the corresponding fixed-base systems