Reconnaissance studies performed after destructive earthquakes have shown that seismic performance of existing buildings, especially constructed on weak soils, is significantly low. This situation implies the negative effects of soil-structure interaction on the seismic performance of buildings. In order to investigate these effects, 40 existing buildings from Turkey were selected and nonlinear models were constructed by considering fixed-base and stiff, moderate and soft soil conditions. Buildings designed before and after Turkish Earthquake code of 1998 were grouped as old and new buildings, respectively. Different soil conditions classified according to shear wave velocities were reflected by using substructure method. Inelastic deformation demands were obtained by using nonlinear time history analysis and 20 real acceleration records selected from major earthquakes were used. The results have shown that soil-structure interaction, especially in soft soil cases, significantly affects the seismic response of old buildings. The most significant increase in drift demands occurred in first stories and the results corresponding to fixed-base, stiff and moderate cases are closer to each other with respect to soft soil cases. Distribution of results has indicated that effect of soil-structure interaction on the seismic performance of new buildings is limited with respect to old buildings.

A large-scale seismic performance assessment study based on 98 precast buildings, constructed in the high seismicity region of western Turkey, was performed. Structural properties of buildings were obtained from the design projects and then verified by site investigations. Statistical evaluations of inventory buildings have shown that stiffness and ductility capacity of existing buildings are insufficient. This situation indicates that structural deficiencies emphasized in recent earthquakes are not site specific, but wider and common. Seismic performance of precast buildings was estimated using two different demand spectrums and two different calculation methods. Demand spectrums were constructed by considering site-specific properties of the target region and properties of weak soil sites. Seismic performance of buildings was estimated using the capacity spectrum method and the equal displacement approach. Results of these methods indicate that damage distributions are significantly amplified by...