Assessment of soil amplification effects on the seismic vulnerability of irregular reinforced concrete buildings of varying heights

Earthquakes pose a significant threat to structures in seismically active regions. It is, therefore, important to understand the factors that influence the vulnerability of buildings. The seismic performance of buildings is significantly influenced by soil amplification, which depends upon the soil type and ground motion characteristics. In addition, building height and geometric configuration, especially for asymmetric structures such as L-shaped buildings, play a crucial role due to the different stiffness, flexibility, and torsional effects. This present study investigates the impact of soil amplification and ground motion characteristics on the seismic vulnerability of unsymmetrical L-shaped buildings of varying heights by considering five different soil profiles (3 homogeneous and 2 layered) and five different ground motions (two far-field and three near-field). Reinforced concrete moment-resisting frame buildings exhibit significant nonlinear behavior under strong seismic excitation, which must be accurately captured to assess their seismic performance. In this study, the pushover and time history analysis have been performed to estimate the seismic response of the building in terms of base shear, roof displacement, and demand ductility. Finally, fragility analysis has been conducted to estimate the probability of damage, damage index, seismic vulnerability index, and recovery time of the building considering the amplified ground motion effects caused by various soil profiles. The analysis reveals that near-field ground motions significantly amplify ground motion which results in increased roof displacement values (up to 211%), collapse damage (up to 37%), damage index (up to 162%), seismic vulnerability index (up to 189%) and recovery time (up to 383 days) of the building compared to far-field motions. Soil amplification effects are most significant in low-rise buildings, while with increasing building height of unsymmetrical, vulnerability rises due to torsional effects. Layered soil profiles in Silchar and Turkey increase the vulnerability of low-rise buildings, whereas homogeneous clay soil poses greater risks for high-rise buildings. This study highlights the need for Indian Standard (IS) codes to incorporate soil-specific amplification factors and building height considerations, offering practical recommendations to improve seismic design practices for unsymmetrical buildings.