Seismic fragility of reinforced concrete buildings on hill slopes and performance of existing seismic irregularity descriptors

The present study investigates the seismic risk of four prevalent typologies of reinforced concrete sloping ground buildings constructed in hilly terrains, namely split-foundation (SF), stepback (SB), stepback setback (SBSB), and flatland (FL) buildings, designed as per provisions of Indian codes. These selected, designed buildings were subjected to bidirectional seismic excitation using 22 ground motion records for nonlinear dynamic analysis. The seismic risk of SF, SB, SBSB, and FL buildings is evaluated using probabilistic seismic demand models, seismic fragility functions, seismic drift hazard curves, mean annual exceedance probabilities, and collapse margin ratio (CMR). Results demonstrate that the seismic risk of SB and SBSB typologies is similar and less than that of the SF and FL buildings. From the CMR, the study found that the application of seismic provisions in the Indian standards resulted in satisfactory, safe seismic performance of the sloping ground buildings at the 10 % and 2 % probability of exceedance in 50 years. Further, sloping ground buildings typically have coupled structural irregularities (both plan and vertical), characterizing their seismic behaviour. Numerous descriptors exist in the literature for assessing the level of seismic irregularity in irregular buildings, including sloping ground buildings, based on their geometry or fundamental dynamic properties. In the final part, the paper evaluates the applicability and efficacy of existing irregularity descriptors in quantifying the seismic risk of sloping ground buildings by correlating the seismic risk to the irregularity descriptors. It is found that the existing descriptors are poorly correlated with the seismic risk of sloping ground buildings.