Comparative Seismic Performance of Reinforced Concrete Buildings with Different Plan Irregularities Using Response Spectrum Analysis

The rapid urbanization of metropolitan regions has resulted in increasing demand for architecturally complex structures possessing functional and aesthetic irregularities. Although plan irregular configurations provide flexibility in architectural planning, they significantly influence the seismic response of reinforced concrete structures. Earthquake-induced forces are highly sensitive to structural geometry, stiffness distribution, mass irregularity, and torsional characteristics. Numerous post-earthquake investigations have demonstrated that irregular buildings experience substantially higher damage levels compared with geometrically regular structures due to stress concentration and uneven lateral force distribution. The present study investigates the seismic performance of four reinforced concrete building configurations, namely Regular Rectangular, L-Shaped, T-Shaped, and U-Shaped plans. A G+15 reinforced concrete moment-resisting frame is modeled and analyzed using ETABS software in accordance with IS 1893 (Part 1): 2016 provisions. Response Spectrum Analysis is adopted to evaluate structural response under earthquake loading. Critical performance parameters including maximum storey displacement, storey drift, fundamental time period, base shear, and torsional response are examined and compared. The results demonstrate that plan irregularity significantly affects seismic behavior. The U-shaped and T-shaped configurations exhibit greater lateral displacement and torsional vulnerability, whereas the regular configuration provides more uniform force distribution and improved seismic stability. The study highlights the importance of considering plan irregularity during the conceptual design stage and recommends suitable structural measures to mitigate adverse seismic effects in irregular buildings.