Comparative Seismic Analysis of Symmetric and Asymmetric RCC Buildings Using ETABS Under Equivalent Static Method

Abstract

This study presents a comparative seismic analysis of symmetric and asymmetric RC buildings using the Equivalent Static Method as specified in IS 1893:2016. Two G+5 Storey RC buildings, one with a regular rectangular plan and the other with an L-shaped asymmetric configuration, were modeled and analyzed in ETABS software. Identical material properties, loadings, and structural dimensions were maintained for both models to isolate the impact of plan geometry. Key seismic response parameters that were studied included base shear, Storey shear, Storey drift, and Storey displacement. These parameters were evaluated under seismic loads applied in both X and Y directions. Results showed that the asymmetric structure experienced moderately higher responses, with an 8.13% increase in base shear and up to a 10.02% increase in top Storey displacement compared to the symmetric counterpart. Despite these increases, all values remained within the permissible limits outlined in IS 1893:2016. The findings emphasize the influence of plan irregularity on lateral seismic response and support the need for more advanced dynamic analyses in future studies

Introduction

1. Background

• Urban growth has increased construction of multi-storey RC buildings, even in seismic zones.

• Geometry, especially structural symmetry, plays a critical role in seismic resistance.

• Asymmetric buildings are more prone to torsion and irregular deformations during earthquakes.

2. Objective

To evaluate and compare the seismic response of symmetric and asymmetric (L-shaped) G+5 RC buildings using the Equivalent Static Method as per IS 1893:2016, modeled in ETABS.

3. Methodology

• Two models (Symmetric and Asymmetric) were created with identical structural specs:

  • Floor height: 3.5 m, Beam: 300×450 mm, Column: 450×600 mm, M30 Concrete, Fe500 Steel.

• Seismic zone: IV; Analysis done for EQX and EQY directions.

• Parameters evaluated:

  • Base Shear

  • Storey Shear

  • Storey Drift

  • Storey Displacement

4. Key Results

? Base Shear

• Higher in Asymmetric:

  • EQX: +8.13%

  • EQY: +1.98%

  • Due to plan irregularity causing torsion and increased lateral load.

? Storey Shear

• Asymmetric model showed:

  • 128.1 kN (8.13%) more shear in X-direction.

  • 29.4 kN (1.98%) more in Y-direction.

  • Higher forces especially near the base confirm torsional amplification.

? Storey Drift

• Maximum drift observed at 3rd storey in both models.

• Asymmetric building had:

  • +2.06% drift in X

  • +7.61% in Y

  • Still within IS 1893:2016 limits, but indicates greater deformation risk in non-structural elements.

? Storey Displacement

• Top storey displacement:

  • +3.69% increase in X-direction

  • +10.02% increase in Y-direction for Asymmetric model

• Suggests reduced lateral stiffness and increased flexibility in asymmetric configuration.

Conclusion

A comparative analysis of seismic performance of symmetric and asymmetric RC buildings using equivalent stative method as per IS 1893:2016 was concluded in this study. Modeling and analysis were done in ETABS software, maintaining consistent geometric, material, and loading parameters for both structures to solely concentrate the results for Plan configuration (Symmetry). The results demonstrate that: • The asymmetric building consistently exhibited higher base shear, Storey drift, and Storey displacement across both seismic directions (EQX and EQY). • The increase in base shear ranged up to 8.13%, and top Storey displacement showed a maximum increase of 10.02%, indicating that irregularity amplifies lateral seismic response. • Despite the increased response in the asymmetric model, all critical parameters remained within the permissible limits defined by IS 1893:2016, confirming the adequacy of the Equivalent Static Method for regular low-rise structures. Thus, while plan asymmetry affects seismic performance, its impact remains moderate in Mid-rise buildings under static analysis. However, attention to configuration during planning remains essential, particularly for performance-critical structures in high seismic zones.

References

[1] IS 456:2000, Plain and Reinforced Concrete – Code of Practice, Bureau of Indian Standards, New Delhi, India, 2000. [2] IS 875 (Part 1 & 2):1987, Code of Practice for Design Loads (Other Than Earthquake) for Buildings and Structures, Bureau of Indian Standards, New Delhi, India, 1987. [3] IS 1893 (Part 1):2016, Criteria for Earthquake Resistant Design of Structures, Bureau of Indian Standards, New Delhi, India, 2016. [4] A. K. Jain, Reinforced Concrete Limit State Design, 7th ed., New Delhi, India: Nem Chand & Bros., 2012. [5] T. Jayakrishna, K. Murali, P. Satish, and J. Seetunya, \"Seismic analysis of regular and irregular multi-storey buildings by using STAAD-Pro,\" International Journal of Civil Engineering and Technology (IJCIET), vol. 9, no. 1, pp. 431–439, Jan. 2018. [Online]. Available: http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=9&IType=1 [6] E. Ahmad, L. Khatua, K. C. Sethi, M. Villagómez-Galindo, A. Upadhyay, and K. Pathak, “Comparative seismic analysis of symmetrical and asymmetrical G+7 structures using STAAD.Pro: insights into performance and material efficiency,” Asian Journal of Civil Engineering, vol. 26, pp. 1495–1509, 2025. [Online]. Available: https://doi.org/10.1007/s42107-025-01262-6 [7] D. R. Deshmukh, A9. K. Yadav, S. N. Supekar, A. B. Thakur, H. P. Sonawane, and I. M. Jain, \"Analysis and design of G+19 storied building using STAAD-Pro,\" International Journal of Engineering Research and Application (IJERA), vol. 6, no. 7, pp. 17–19, Jul. 2016. [Online]. Available: http://www.ijera.com [8] R. Bento and A. Simões, \"Seismic performance assessment of buildings,\" Buildings, vol. 11, no. 10, p. 440, Sep. 2021. [Online]. Available: https://doi.org/10.3390/buildings11100440

Copyright

Copyright © 2025 Ishaan Trikha. 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.