A Review on Plan Irregularity and Importance Factor Criteria

Abstract

Due to India’s high population density, a significant shortage of land for both residential and commercial purposes has been observed. In response, the construction of taller buildings with increased land coverage and enhanced aesthetic appeal has been undertaken by engineers. However, the structural stability of such architecturally unique buildings is often compromised due to their unconventional designs. In this review paper, an extensive evaluation of previous research studies related to enhancing the stability of these structures has been presented. Conclusive outcomes have been identified through a detailed examination of existing literature, forming the foundation for the stated research objectives. Technical insights and strategies have been compiled to address stability-related concerns in future designs. Emphasis has been placed on establishing practical recommendations for continued investigation in this field. With these findings, a framework for improving the structural resilience of modern architectural buildings has been proposed in upcoming research work.

Introduction

1. Plan Irregularity in Multistorey Buildings

Plan irregularity refers to the horizontal displacement of vertical structural elements (like columns or walls) from their typical alignment. Causes include foundation settlement, design intent, or construction tolerances. Excessive displacement can compromise structural stability, especially in seismic conditions, necessitating strict control and assessment throughout design and construction.

Indian Standards Recommendations

Out-of-plane offsets disrupt load paths and reduce seismic safety. IS codes mandate that for higher seismic zones (III, IV, V), lateral drift must remain under 0.2%, and offset irregularities should be avoided or minimized using expert guidance. Indian Standards provide configuration guidelines for such cases.

2. Importance Factor (IS 1893:2016)

The importance factor accounts for the critical function of structures during earthquakes. Ordinary buildings use a factor of 1.0, while hospitals, schools, and emergency facilities use higher values (1.2–1.5) to ensure functionality post-disaster. It directly affects base shear calculations, increasing structural resilience, and aligns India’s seismic design with global standards.

3. Literature Review Summary

A wide range of studies from 2012 to 2024 examined seismic behavior of regular vs. irregular structures, highlighting key findings:

• Irregularities (mass, stiffness, geometric) lead to increased base shear, displacement, and storey drift.

• Plan shapes like L, C, and H show greater seismic vulnerability due to uneven load distribution.

• Dynamic methods (Response Spectrum, Time History Analysis) are more accurate than static methods for assessing irregular buildings.

• Seismic Zones: Buildings in Zone V experience the highest deformation, displacement, and demand for reinforcement.

• Tools used: ETABS, STAAD Pro, and SAP2000 were frequently employed for seismic analysis.

• Code Comparisons: Transition from IS 1893:2002 to IS 1893:2016 and 2023 showed improved precision, safety, and cost efficiency.

• Design recommendations: Shear walls, belt walls, braced frames, and symmetrical mass distribution help reduce irregularity effects and improve seismic performance.

Conclusive Themes Across Studies

• Structural irregularities significantly impact seismic performance.

• Zone V poses the greatest risk and requires stricter design interventions.

• Updated Indian codes (IS 1893 series) offer enhanced guidance for addressing irregularities.

• Effective modeling and refined analysis methods (especially dynamic) are critical.

• Regular configurations and strategic use of shear walls improve safety and resilience.

Conclusion

A noticeable gap in the existing literature has been identified concerning the impact of out-of-plane offsets in multistorey buildings subjected to seismic forces. The influence of this factor on a building’s structural behavior and earthquake performance is considered significant for design purposes. In order to formulate effective mitigation strategies, further investigation into this parameter will be required. Development of design guidelines must be prioritized to minimize its adverse effects on structural response. From the detailed literature review, a set of conclusions has been drawn to emphasize the core findings and outline the required steps forward: 1) A comprehensive analysis of plan irregularities in multistory buildings in both directions has to be undertaken for lateral force assessment. 2) Compliance of different importance factors as prescribed in Indian standards should be checked. 3) Use of actual geotechnical data relevant to the proposed site has been advised to enhance the reliability of structural analysis. 4) Seismic zonal conditions in dual structural systems are to be investigated thoroughly for accurate seismic response predictions. 5) Evaluation of lateral drift limits in accordance with codal provisions has deemed essential for structural integrity. The feasibility of constructing buildings with out-of-plane configurations is intended to be assessed, with particular emphasis on identifying maximum allowable limits under site-specific soil conditions, making it a cornerstone for future research developments.

References

[1] V. Shiva Kumar, M. Manoj Kumar, (2019), “Response of Multi-Storeyed Buildings Having Vertical Irregularities using ETABS”, International Journal of Innovative Technology and Exploring Engineering (IJITEE), ISSN: 2278-3075, Volume-8 Issue-12, pp. 536-540. DOI: 10.35940/ijitee.L3418.1081219 [2] Prashanth Kumar N, Dr. Y. M. Manjunath, (2018), “Seismic analysis of vertically geometric irregular structures”, International Journal of Scientific Development and Research (IJSDR), ISSN: 2455-2631, Volume 3, Issue 5, pp. 510-516. [3] T. M. Prakash , B. G. Naresh Kumar, Punith N., Mallamma, (2017), “Seismic Analysis of Multi-Storeyed Building Having Vertical Irregularities Using Pushover Analysis”, International Journal of Innovative Research in Science, Engineering and Technology, ISSN(Online) : 2319-8753, Vol. 6, Issue 5, pp. 9340-9347. [4] Sudarshan Kulkarni, (2016), “Effect of Floating Columns in Multi Storey Building of Regular and Irregular Plan”, International Journal of Engineering Research & Technology, ISSN No: 2394-3696, Volume 4, Issue 08, pp 1-4. [5] Poonam, Anil Kumar and Ashok K. Gupta, (2012), “Study of Response of Structurally Irregular Building Frames To Seismic Excitations”, International Journal of Civil, Structural, Environmental and Infrastructure Engineering Research and Development (IJCSEIERD) ISSN 2249-6866, Vol.2, Issue 2 (2012) 25-31. [6] Isha Patel (2024), A Critical Review and Comparative Study of IS 1893: 2016 and IS 1893: 2023 (Part 1 and 2) with Practical Applications in Seismic Design. IJIRT/Volume 11/Issue 1/ISSN: 2349-6002/IJIRT 165930 /Page no. 2103-2107. [7] M. T. Raagavi, Dr. S. Sidhardhan (2021), A Study on Seismic Performance of Various Irregular Structures. (IJRES) ISSN: 2320-9364/ISSN: 2320-9356/Volume 9/ Page no. 12-19 [8] Umamaheswara Rao Tallapalem, Nurulla Shaik, Gopi Pagidimarry (2019), Analysis of Multi-Storey Building in Different Seismic Zones of India. IJRIAT/ Vol.7/ E-ISSN: 2321-963/Page no 488-494. [9] Biyyala Sai Ramesh, G. Swathi (2022), Comparison and analysis of regular and irregular configuration of Multi-Storey building in various seismic zones and various type of soil. IJARST ISSN No. 2457-0362/Vol.12/Page 43-50. [10] Nilesh Choudhary, BD Yadav, Jaydev Kumar Mahato (2022) Comparative Study of Regular and Irregular RC Structure in Different Seismic Zones and Soil Types. Earth & Environment Science Volume 5-Issue 4 ISSN: 2639-7455, pp 148-160. [11] Sarthak Jain, Dr J N Vyas (2023) Analytical Study of Irregular RC Structure in Severe Seismic Zone as per is 1893:2016- A Literature Review. IJRPR, Volume 4, Issue no 11 / ISSN 2582-7421/Page no 752-757 [12] Purushottam Dewangan & Tushar Saxena (2018) Seismic Analysis of Regular & Irregular Structures and its Comparison. IRJET Volume: 05 Issue: 09/ e-ISSN: 2395-0056/ p-ISSN: 2395-0072/Page no 785-790 [13] Siva Naveen E, Nimmy Mariam Abraham, Anitha Kumari SD (2019) Analysis of Irregular Structures under Earthquake Loads. ELSEVIER Procedia Structural Integrity 2452-3216/ Page no 806–819 [14] Varun Vijayvargiya, Dr. J N Vyas (2020) Comparative Analysis Of Vertically Irregular Structures In Different Seismic Zones. GJAETS ISSN 2349-0292/ Page no 11-31 [15] Rajeev Chauhan, et. al. (2021) Seismic Analysis of Regular and Irregular Configuration of Building. IJERA ISSN: 2248-9622/ Vol. 11/Issue 12/ Page no 47-57 [16] Md. Sabbir Hossain, S.K. Singh (2022) Comparative analysis of irregular RCC buildings in different zones. ICASF IOP Conf. Series: Earth and Environmental Science 1110 (2023) 012035 Page no 1-10 [17] Ravindra N. Shelke, U. S. Ansari (2017) Seismic Analysis Of Vertically Irregular Rc Building Frames. IJCET ISSN-0976-6308 and ISSN-0976-6316 /Volume 8/Issue 1/ Page no 155–169 [18] Rajgure Kalyani, Banarase Mayur (2018) Effect of Zone Factor on Seismic Performance of Multi-Storied RC Frame. IJERA/ISSN: 2248-9622/Vol. 8/Issue5 (Part –III) Page no 32-39 [19] Puppala Sesha Pavani, M.Sai Narashima Rao (2020) Seismic Evalution Of Irregular Structure Using Staad Pro. IRJET Volume: 07/ Issue: 07/e-ISSN: 2395-0056/ p-ISSN: 2395-0072/Page no 4398-4404 [20] M Rame Gowda, Soumya Antinamath (2022) Seismic Analysis of Vertical Geometric Irregular RC Frames with Respect to Different Seismic Zones using ETABS. IJERT/ISSN: 2278-0181/Vol. 11/Issue 09 Page no 232-238 [21] Arun R. Et al, K. Suhana, L. Saicharan Reddy (2019) Seismic base shear variation between regular and irregular RCC structure in various zones by STAAD PRO. ISSN: 2454-132X/Volume 5/Issue 2 Page no 853-859 [22] Maitrey Jambhulkar, Dr. Ashwini Tenpe (2024) Investigation of the Impact of Different Earthquake Zones on Irregular Plan Buildings Managed by Belt Wall. IJRASET ISSN: 2321-9653/Volume 12/Issue V/ Page no 5678-5683 [23] S. Natarajan, S. Veeraragavan (2016) A Review on Analysis and Design of Shear Walls in High Rise Irregular Building. 6 IJSETR/ ISSN 2319-8885/Vol.05/Issue.05/Page no 808-815 [24] Kavita Verma, Ahsan Rabbani (2018) Analysis Of G+6 Building In Different Seismic Zones of India Using Method of Static Analysis. IJCRT/ IJCRT1813113/Volume 6/Issue 2/ISSN: 2320-2882 Page no 265-272 [25] Sukumar V, Dr. D. C. Haran Pragalath (2016) A Role of Importance Factor In Seismic Design Of Indian Buildings. Scientific AMM ISSN: 1662-7482/Vol. 857/Page no 71-77.

Copyright

Copyright © 2025 Salim Shaikh, Chetan Gurjar. 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.