Effect of Horizontal Geometric Irregularity on a High Rise RC Structure

The seismic performance of reinforced concrete (RC) structures is highly sensitive to their geometric configuration, both in plan and elevation. Among these, horizontal geometric irregularity— manifested in forms such as L-shaped, T-shaped, and Ushaped plans, re-entrant corners, diaphragm discontinuities, and torsional eccentricities—has been repeatedly identified as a major factor contributing to structural vulnerability during earthquakes. In India, where several regions fall under Seismic Zones III, IV, and V as per IS 1893:2016 (Part 1), the consequences of such irregularities can be severe if not addressed in the design stage. Irregular plan layouts alter the stiffness and mass distribution, often creating a mismatch between the centre of mass (CM) and centre of rigidity (CR). This results in significant torsional effects, stress concentrations, and non-uniform displacement patterns. Post-earthquake damage surveys, such as those following the 2001 Bhuj earthquake, have shown that irregular buildings suffered disproportionate damage compared to their regular counterparts. The current study aims to evaluate the seismic response of horizontally irregular RC buildings in compliance with Indian Standards, using analytical modelling and performance assessment techniques. By comparing regular and irregular configurations, the research seeks to provide practical recommendations for achieving torsional stability and improved seismic resilience.