Mohammad DAVOODI - Assistant Professor, De pt. of Geotechnical Earthquake Engineering, IIEES, Tehran, Iran
Mani SADJADI - Research Associate in D ept. of Geotechnical Earthquake Engineering, IIEES, Tehran, Iran

Generally, in order to evalua te the seismic demand of structures, it is assu med that the structure is located on a rigid soil. However, wi th 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 rol es in the design of structures. This paper addresses the effects of Peak Ground Velocity to Peak Ground Acceleration ratio (PGV/PGA) of near-faul t ground motions as a compound intensity index that can describe the frequency characteristics of groun d motion on response of various soil-structure SDOF systems. A total 49 near-field ground motions records w ere 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).ParametricU studies between PGV/PGA ratio of pulse-like ground motions andS maximumh relative displacement (Umax ) indicate that with increase in structure-to-soil stiffness ratios(S ), earthquakes with higher PGV/PGA ratio produce greater responses. Moreover, increasing in slender r atios ( h) and decreasing in mass ratios (m ) result in the responses of soil-structure SDOF systems become greater in all structure-to-soil stiffness ratios.

Soil-Structure Interaction, SDOF System, Strong Ground Motion, PGV/P GA Ratio