Effect of Vertical Irregularities in Stiffness Due to Seismic Activity

This research investigates the effect of vertical irregularities in stiffness on the seismic and blast performance of reinforced concrete (RC) multi-storey buildings with and without girders. Using ETABS software, analytical models were developed for G+6, G+9, G+12, G+15, G+20, and G+25 structures to assess their response under seismic and 100 kg TNT blast loading conditions at varying distances (10 m, 15 m, and 20 m). The study evaluates parameters such as storey displacement, storey drift, base shear, and stiffness, following the provisions of IS 1893 (Part 1): 2016. Results revealed that buildings with vertical stiffness irregularities exhibited increased displacement and drift, particularly in upper storeys, indicating higher vulnerability under dynamic loads. Conversely, structures with girders showed improved stiffness, reduced drift, and better stability, demonstrating their role in enhancing overall seismic and blast resistance. Moreover, increasing the standoff distance significantly reduced base shear and displacement. The findings highlight the necessity of maintaining proper stiffness distribution and girder placement to ensure structural integrity and safety in earthquake- and blast-prone regions. This study provides practical insights for optimizing structural design to achieve performance-based, code-compliant, and resilient buildings.