Fragility analysis of hillside buildings designed for modern seismic design codes

Summary The structural configurations of hillside buildings are significantly different than those observed on flat terrain. To study the effect of often observed structural configurations of hillside buildings, collapse fragility of regular “flat land (FL)” and irregular “split‐foundation (SF)” and “step‐back (SB)” buildings is studied using incremental dynamic analysis. The effects of building height, seismic zone, and near‐ and far‐field sites on collapse fragility are investigated. It is observed that SF and SB hillside buildings exhibit significant torsional effects at the storey just above the uppermost foundation level. In case of FL buildings, collapse occurs due to the flexural failure of beams and columns. On the other hand, in SF and SB buildings, the collapse occurs due to the combined effects of shear failure of short columns and flexural failure of beams and columns in the storey just above the uppermost foundation level. In general, SF buildings are observed to be the most vulnerable, whereas FL buildings are the least vulnerable. It is observed that high‐rise SF and SB buildings show unacceptably high probability of collapse at maximum considered earthquake, in Seismic Zone V and for the near‐field site in Seismic Zone IV.