In dynamic analysis and design of structures in general, it is assumed that the soil under the foundation is rigid and the effect of soil-structure interaction is neglected. Seismic design spectra of building codes have also calculated with the same assumption. Soil-structure interaction changes the dynamic response of a structure and can have a positive or negative effect on the performance of structures. In this study the effect of soil-structure interaction on the average response spectrum is calculated using the substructure method. The equations of motion of structures resting on flexible soils are derived and decomposed into its modal components as an extension of the kashida; TEXT-ALIGN: justify; TEXT-KASHIDA: 0%; TEXT-INDENT: 14.2pt; MARGIN: 0in 0in 0pt; unicode-bidi: embed; DIRECTION: ltr" Keywords : Soil-structure interaction, 0in; MARGIN: 0in 64.35pt 0pt 0in; mso-add-space: auto" dir=rtl
