Golshan POURSAFFARI - M.Sc. Graduate, IIEES, Tehran, Iran
Hossein JAHANKHAH - Assistant Professor, IIEES, Tehran, Iran

Adjacent structures affect seismic response of each other through connecting soil. Regarding population growth and urban structures density, the cross interaction of adjacent structures, well-known as structure-soil-structure interaction (SSSI), has received attentions in recent decades. Soil-structure interaction (SSI) studies showed that, as a general trend, possibility of unexpected damage is decreased by introducing base flexibility in seismic structural design. In these studies, it appeared that both dynamic properties such as dynamic damping and stiffness, called as dynamic impedance, as well as foundation input motion (FIM), of an isolated structure, change by the SSI effects. Moreover, the structure has influence on seismic motion of its surroundings, up to a distance of ten times the foundation length (Gueguen et al., 2002). Similarly, if a structure is constructed near the said structure, the nearby motion will change additionally. Thus the structures have influence on dynamic properties and input motion of each other. Gueguen et al. (2002) has shown that the effect of soilstructure interaction on nearby motion decreases as the distance increases. In contrast, finding critical distance betweenadjacent structures is not as simple as the case of the SSI because of the complexity of the SSSI. On the other hand, since adjacent structures have strong effects on each other, both favorable and unfavorable, study of the critical distance seems to be necessary. Previously, SSI has been studied using direct and indirect methods. In indirect method, with the use of superposition concept, the problem is studied in two phases. I) Kinematic interaction, changing Free Field Motion (FFM) to FIM as a result of stiffness contrast between foundation elements and soil, and II) Inertial interaction, changing in dynamic properties, i.e. dynamic impedances, of structure caused by structure and foundation masses. Since kinematic interaction usually decreases horizontal component of FIM in SSI, in conservative approach, its effects are not considered in common designs and it has been less studied. However, kinematic interaction by creation of rotational components during earthquake can cause considerable effects on seismic response of structures and can be so destructive. Jahankhah et al. (2013) proposed simplified equations, for practical design, in which both horizontal and rotational FIMs are integrated in a single horizontal component called Net Horizontal FIM.

Structure-soil-structure interaction (SSSI), Kinematic interaction, Numerical analysis, Parametric study,Transfer function (TF), Critical distance