The effect of soil on seismic performance analysis of reinforced concrete structures

 In the FEMA-P695 report, there is an applied method for evaluating the collapse of structures designed by seismic regulations under the most severely expected earthquake, in which the collapse of special concrete frames without considering the effect of soil-structure interaction is studied. In this study, soil-structure interaction analysis is used directly to evaluate the seismic performance of buildings. For this purpose, 4 and 8-storey reinforced concrete buildings with special bending frame system, on medium (D) and soft (E) soils classified according to ASCE7-10, have been modeled and analyzed by Opensees software. Incremental dynamic analysis has been used to accurately evaluate the collapse performance of the frames for both rigid base and flexible base. The results of the analysis show that the soil- structure interaction, especially with softer soil and increasing the number of building floors, can play a key role in the behavior of building frames including increasing system period, reducing floor drift, increasing performance and changing probability collapse of the structure. On the other, the results at first glance show an increase in the probability of collapse for frames placed on flexible supports at the same spectral acceleration, but using the modified flexible fragility curve, it is observed that the soil-structure interaction reduces the likelihood of collapse. Therefore, not considering the soil-structure interaction leads to unrealistic evaluation of the performance of structures.