A Comparative Study on Seismic Analysis of Regular, Plan and Vertical Irregular G+12 RC Structure

Abstract

Due to urbanization and less availability of construction land, the engineers are planning for multi-storied construction. In this study, a multi-storied (G+12) RC building is considered for earthquake analysis by using previous earthquake data i.e., the analytical method used for this work is response spectrum analysis. When the multistorey building constructions comes into the practice there are various possibility of failure of the structures, either it might be due to gravity loading or might be due to lateral pressures i.e., Earthquake or wind loads. If the structures are not analysed and designed for the above-mentioned loading conditions as per the IS codal specifications, a severe damage might be observed. So, in this study, the analysis is performed for gravity loadings and by using the previous earthquake analytical data, “Response Spectrum Analysis” method is used for the earthquake analysis. There is various finite element approach software are available in the market, for this study ETABS (version 21) is used for analysing the structure. In this study totally 5 models are used they are plan regular, regular and vertical irregular building are considered and the results for all of these are discussed in the coming chapters.

Introduction

This study investigates how structural irregularities affect the seismic behavior of multi-story reinforced concrete (RC) buildings. Irregularities in plan or elevation often cause stress concentrations and torsional effects, increasing vulnerability during earthquakes. Stiffness irregularities, mass distribution, and vertical geometry are particularly critical, with stiffness having the greatest influence on dynamic response. Risk-based retrofitting strategies, such as shear walls, can improve structural resilience by enhancing strength and stiffness while reducing lateral displacement.

Methodology:

• A 12-story commercial RC building (25 × 30 m plan, 40.2 m height) was modeled with different configurations: regular, plan-irregular, and vertical-irregular (L-shape).

• Material: M30 concrete, Fe550 steel; columns: 600×900 mm, beams: 300×450 mm, slab: 150 mm.

• Response spectrum analysis per IS 1893-2016 evaluated base shear, storey shear, storey drift, and storey displacement in X and Y directions.

Results:

• Storey Drift: Maximum drift occurred in irregular structures in both X and Y directions.

• Storey Shear: Irregularities caused slight increases in shear (up to ~5.81%) in some directions, while regular structures showed minor decreases (~8.5%).

• Storey Displacement: Irregular buildings exhibited substantially higher displacements—up to 23.42% in X and 22.02% in Y—compared to regular structures.

Conclusion

The comparative analysis for plan regular, plan irregular and vertical irregular structures are made by channelized graphs and tabular columns and the discussion w.r.t results are discussed in the chapter 4 and the conclusions for those results and discussions are derived here: 1) Analysis of RSA method using ETABS has provided a comprehensive understanding of the building\'s response to particularly during seismic events. 2) As per the analytical results, the comparison between plan regular, plan irregular and vertical irregular buildings, the results of plan irregular showed 22.02% displacement w.r.t Y-direction is higher than plan regular building and w.r.t vertical irregular building, it showed 5.62%. Hence it can conclude that keeping the requirement of the architectural considerations, can be suggested to consider vertical irregular structure. 3) As per the analytical results, the comparison between plan regular, plan irregular and vertical irregular buildings, the results of plan irregular showed 1.76% displacement w.r.t X-direction is higher than plan regular building and w.r.t vertical irregular building, it showed 23.42%. Hence it can be concluded that is keeping the requirement of the architectural considerations, this can be suggested to consider vertical irregular structure. 4) As per the analytical results, the comparison between plan regular, plan irregular and vertical irregular buildings, the results of plan irregular showed 8.52% shear w.r.t X-direction is lesser than plan regular building and w.r.t vertical irregular building, it showed higher 4.3%. Hence it can be concluded that keeping the requirement of the architectural considerations, it can be suggested to consider vertical irregular structure. 5) As per the analytical results, the comparison between plan regular, plan irregular and vertical irregular buildings, the results of plan irregular showed 5.81% shear w.r.t Y-direction is higher than plan regular building and w.r.t vertical irregular building, it showed higher 4.63%. Hence it can be concluded that keeping the requirement of the architectural considerations, it can be suggested to consider irregular structure. 6) As per the analytical results, the comparison between plan regular, plan irregular and vertical irregular buildings, the results of plan irregular showed drift w.r.t X-direction is higher than plan regular building and w.r.t vertical irregular building, it showed lesser. Hence it can be concluded that keeping the requirement of the architectural considerations, it can be suggested to consider irregular structure. 7) As per the analytical results, the comparison between plan regular, plan irregular and vertical irregular buildings, the results of plan irregular showed drift w.r.t Y-direction is higher than plan regular building and w.r.t vertical irregular building, it showed lesser. Hence it can be concluded that keeping the requirement of the architectural considerations, can be suggested to consider irregular structure. All the models were analysed in ETABS using the response spectrum method. In comparison with plan regular, plan irregular, and vertical irregular buildings, the plan regular building showed better performance than the other two types. However, considering architectural requirements, the plan irregular building proved to be safer with respect to storey shear, storey drift, and storey displacement. Therefore, it can be concluded that, taking into account economy, structural safety, stability, and overall requirements, the plan irregular building can be suggested as the final choice.

References

[1] Al-Sabaeei, Mohammed Sadeq, K. R. Dabhekar, and I. Khedikar. \"State of art on seismic comparison of different types (V, diagonal and X) of bracings on different shapes of buildings (L, H, Tand rectangular) with response spectrum method.\" Materials Today: Proceedings (2023). Vol. 04, issue 0.5, pp 1061 [2] Arvindreddy, R. J., and M. Fernandes. \"Seismic analysis of RC regular and irregular frame structures.\" Int. Res. J. Eng. Techno 2 (2015): 44-47. Vol. 8, issue 9, pp.3423-3426 [3] Chaudhary, Krishna Prasad, and Ankit Mahajan. \"RSA of irregular shaped high-rise buildings under combined effect of plan and vertical irregularity using csi ETABS.\" IOP Conference Series: Earth and Environmental Science. Vol. 889. No. 1. IOP Publishing, 2021. [4] Divya, Rachakonda, and K. Murali. \"Comparative analysis of behaviour of horizontal and vertical irregular buildings with and without using shear walls by ETABS software.\" Materials Today: Proceedings 52 (2022): Vol. 8, issue 9, pp.471-476 [5] Haque, Mohaiminul, et al. \"Seismic performance analysis of RCC multi-storied buildings with plan irregularity.\" American Journal of Civil Engineering 4.3 (2016): Vol. 03, No.02, pp.68-73. [6] Krishnan, R., and V. L. Sivakumar. \"A comparative study of geometry and locations of shear walls on regular and irregular RC structures by using response spectrum analysis.\" Indian J Sci Techno 16.30 (2023): Vol. 8, issue 9, pp. 2358-2364. [7] Mukundan, Hema, and S. Manivel. \"Effect of vertical stiffness irregularity on multi-storey shear wall-framed structures using RSA. \" International Journal of Innovative Research in Science, Engineering and Technology 4.3 (2015): 1186-1198. [8] Prathap, G. Vamshi, and D. Radha. \"Comparative Analysis of Behaviour of Horizontal and Vertical Irregular Buildings with and Without Using Shear Walls by ETABS Software.\" Journal of Engineering Sciences (2023). Vol.02, issue 03, pp.91-96 [9] Shelke, Ravindra N., and U. S. Ansari. \"Seismic analysis of vertically irregular RC building frames.\" International Journal of Civil Engineering and Technology 8.1 (2017): 155-169. [10] Sowmya, G. S., and Vinod Kundaragi. \"Comparison Of Conventional and Flat Slabs Using RSA Method for Symmetric and Asymmetric Commercial Building Using E Tabs.\" (2020). [11] IS 456 (2000), \"Plain and Reinforced Concrete-Code of Practice\", Bureau of Indian Standards, New Delhi, India. [12] IS 875-Part 1 (1987), \"Code of Practice for Design Loads (Other than Earthquake) for Buildings and Structures. Part 1 Dead Loads Unit Weights of Building Materials and Stored Materials\", IS, New Delhi, India. [13] IS 875-Part 2 (1987), \"Code of Practice for Design Loads (Other than Earthquake) for Buildings and Structures. Part 2 Imposed Loads”, IS, New Delhi, India. [14] IS 1893-Part 1 (2016), \"Criteria for Earthquake Resistant Design of Structures. Part 1-General Provisions and Buildings\", IS, New Delhi, India. [15] Textbook; Earthquake Resistant Design of Structures by Pankaj Agarwal and Manish Shrikhande.

Copyright

Copyright © 2025 Murulinaik G R, Chetan Gonni S. 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.