EVALUATION OF THE EFFECT OF PGV/PGARATIO OF STRONG GROUND MOTIONS ONRESPONSES OF SOIL STRUCTURE SDOFSYSTEMS

Generally, in order to evaluate the seismic demand of structures, it is assumed that the structure is located on a rigid soil. However, with increasing the soil flexibility there will be significant variations in the structural response, i.e. the effects of Soil-Structure Interaction (SSI). Furthermore, in the near-field zone, pulse-like motions play crucial roles in the design of structures. This paper addresses the effects of Peak Ground Velocity to Peak Ground Acceleration ratio (PGV/PGA) of near-fault ground motions as a compound intensity index that can describe the frequency characteristics of ground motion on response of various soil-structure SDOF systems. A total 49 near-field ground motions records were selected which have been classified into two categories: first, records with a strong velocity pulse, (i.e. forward-directivity); second, records with a residual ground displacement (i.e. fling-step). Parametric studies between PGV/PGA ratio of pulse-like ground motions and maximum relative displacement (U ) indicate that with increase in structure-to-soil stiffness ratios(S), earthquakes with higher PGV/PGA ratio produce greater responses. Moreover, increasing in slender ratios (h) and decreasing in mass ratios (m) result in the responses of soil-structure SDOF systems become greater in all structure-tosoil stiffness ratios