Impact of irregularities on seismic fragility of reinforced concrete structures

Earthquakes are a significant cause of damage to buildings and pose a serious threat to human life, particularly when structures have irregularities which affect their ability to resist seismic forces. The present study evaluates the performance of irregular reinforced concrete buildings under seismic loading. Nonlinear static analysis (pushover analysis) was conducted in accordance with the procedures prescribed by the Applied Technology Council (ATC-40) and Federal Emergency Management Agency (FEMA-356). Models were developed and analysed using ETABS software, focusing on buildings with plan symmetric and asymmetric configurations along with vertical irregularities like stiffness, mass, and combination of both stiffness + mass. This study compares vertically regular and irregular buildings by introducing different types of irregularities, which intern helps in understanding the behaviour of those buildings during earthquake. The behaviour of these buildings under seismic loading was evaluated through key parameters including base shear, lateral displacement, bending moments and storey shear forces for critical corners in the structural system. Results indicated that the buildings with combined stiffness and mass irregularities exhibit the most critical seismic behaviour, showing higher displacements and lower base shear capacity compared to other configurations. To mitigate this critical seismic response, shear walls were provided at different locations for buildings with different structural configurations.