Seismic Performance of Regular and Irregular High-Rise Buildings: Influence of Geometrical Configuration on Structural Response

Abstract

This research investigates the comparative seismic performance of regular and irregular high-rise building geometries using ETABS software. Five building configurations—square, rectangular, L-shaped, C-shaped, and T-shaped—were analyzed under dynamic loading conditions as per relevant Indian Standards. Key structural parameters such as storey displacement, storey drift, base shear, time period, and frequency were evaluated to assess stability and load resistance.Results indicate that regular configurations, particularly square-shaped buildings, perform better due to symmetrical stiffness and uniform mass distribution, resulting in reduced displacement and drift. Irregular structures, especially L and T shapes, exhibit higher torsional effects and stress concentration, leading to increased lateral response.The study highlights the significant impact of building geometry on seismic behavior and structural efficiency. The findings provide practical guidance for optimizing high-rise building design in earthquake-prone regions, ensuring improved safety, serviceability, and overall structural performance while balancing architectural requirements.

Introduction

High-rise buildings are increasingly constructed in urban areas due to rapid urbanization and limited land availability. However, in earthquake-prone regions these tall structures are vulnerable because of their height, slenderness, and complex dynamic behavior. Earthquakes can cause large ground motions that lead to excessive inter-storey drift, torsional effects, and even structural collapse. Ensuring seismic safety is therefore essential to protect human lives, infrastructure, and economic stability.

Buildings are generally classified as regular or irregular based on their geometry, mass distribution, and stiffness. Regular buildings have uniform structural properties, resulting in more predictable seismic behavior. In contrast, irregular buildings have variations in plan shape, vertical configuration, or mass distribution, which create complex seismic responses. Common plan irregularities include L-, T-, and C-shaped buildings, while vertical irregularities include soft storeys, setbacks, and sudden stiffness or mass changes. These irregularities often produce torsional effects, stress concentrations, and larger displacement and drift during earthquakes.

Modern architectural demands often encourage irregular building shapes for aesthetic and functional reasons, but such configurations reduce seismic resilience. Studies have shown that irregular buildings experience higher torsion, uneven load distribution, and greater structural demand compared with regular buildings. As a result, advanced analysis methods such as response spectrum or time-history analysis are required to accurately evaluate their behavior.

Seismic design philosophy focuses on strength, stiffness, ductility, and energy dissipation to ensure that buildings can resist earthquake forces without collapse. International design codes such as IS 1893 (India), Eurocode 8, ASCE 7-16, and FEMA 356 provide guidelines for identifying irregularities and performing seismic analysis. Although these codes emphasize dynamic analysis for irregular structures, they often rely on simplified assumptions and may not fully capture the complex nonlinear behavior of irregular high-rise buildings.

Irregularities are mainly classified into plan irregularities, vertical irregularities, and mass/load distribution irregularities. These irregularities significantly influence seismic response parameters such as natural frequency, base shear, storey drift, displacement, and torsional effects. Irregular buildings typically exhibit higher drift, uneven shear distribution, and concentrated damage patterns compared to regular buildings.

The present study investigates the effect of plan irregularity on seismic performance by modeling five reinforced concrete buildings—square, rectangular, L-shaped, C-shaped, and T-shaped—using ETABS software. All models have identical height, materials, and loading conditions but different plan configurations. Seismic analysis is performed using response spectrum analysis based on IS 1893 (2016). Results indicate that irregular shapes such as T- and rectangular plans experience higher displacement and shear, while L- and C-shaped buildings show irregular structural behavior due to asymmetry. The study demonstrates that building geometry plays a crucial role in seismic performance and must be carefully considered during design.

Conclusion

1) The study establishes that building geometry plays a crucial role in determining the seismic performance of high-rise structures under dynamic loading conditions. 2) Regular-shaped buildings, especially square configurations, exhibit better structural stability with lower storey displacement, reduced drift, and uniform base shear distribution due to symmetrical mass and stiffness. 3) Irregular geometries such as L-, C-, and T-shaped buildings show higher lateral displacement, increased torsional effects, and stress concentration, particularly at upper storeys. 4) Dynamic characteristics, including time period and flexibility, vary with geometry, with irregular buildings demonstrating comparatively higher vulnerability during seismic excitation. 5) For improved safety and serviceability in seismic-prone regions, regular building configurations are preferable, while irregular structures require additional strengthening measures and careful structural optimization.

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Copyright

Copyright © 2026 Mr. Amol Pandharinath Sahane, Mr. Keshav Raghunath Kale. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.