Effect of Soil Type on the Analytical Fragility Curves of Low-Rise RC Medium Ductility Frames

These days، the probabilistic evaluation of seismic structural damages and loss estimation through fragility functions has become more popular. The fragility functions for new structures are developed by the analytical methods in which the probabilistic behavior of structures is estimated by nonlinear analysis of structures with real EQ time history records. Therefore، type of records and method of record selection may affect the estimated fragility curves of structures. In this paper، the effect of the soil type on the fragility curve of low-rise RC medium ductility frames is studied. For this reason، three 1، 2 and 3 story RC medium ductility frames were considered and the fragility curve of these frames were estimated by probabilistic method and conducting time history analysis by EQ records obtained from four types of soils in the Iranian code of practice for seismic resistant design of buildings. The results have shown that the soil type has significant effect on the fragility function of frames. In general، the probability of failure of frames in fragility functions increased by increasing of soil type from hard to soft soil. These results contradicted with the philosophy of equal safety for different type of building design by the same code. Therefore more improvement in the design code needs to be conducted in order to incorporate similar safety in different soils.