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International Research Journal of Engineering and Technology (IRJET)

e-ISSN: 2395-0056

Volume: 12 Issue: 12 | Dec 2025

p-ISSN: 2395-0072

www.irjet.net

Seismic Strengthening of RCC Multi-Storey Building Frames introducing Bracing Systems Arup Saha Chaudhuri1, Susmita Nandi2, Indranil Pal3 and Md. Toshif Alam4 1Professor, Dept. of Civil Engineering, Techno Main Salt Lake, Kolkata, India 2, 3, 4PG Students, Dept. of Civil Engineering, Techno Main Salt Lake, Kolkata, India

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Abstract - The goal of this study is to strengthen RCC building initially designed and constructed for Seismic Zones II / III but now reclassified under Seismic Zone III / IV respectively because of modified seismic hazard assessments. Therefore, these buildings need to be strengthened introducing vertical steel or damper bracings as retrofit to improve lateral load resistance and structural performances. This study examines the structural performances of G+6, G+12 and G+15 storeyed RCC buildings for seismic zone up gradation. The existing buildings need to strengthen to withstand higher seismic forces because of the areas reclassified from Zone III / II to Zone IV / III respectively. Square-Hollow-Section (SHS) normal bracing members and fluid viscous damper bracing members are introduced in these case studies. For analysis and comparison, we are using the STAAD.Pro and ETABS software packages that contrast the structural behaviors before and after the retrofitting. In comparison to the original design, the results exhibit that the installation of vertical bracing systems greatly improves the safety of beams and columns by increasing their resistance to seismic forces. Mainly the beam column joint moments are drastically reduced thus column and beam designs are becoming safer. The results of these studies demonstrate that the RCC buildings’ structural stabilities are significantly increased by the addition of vertical bracing systems making it more earthquake-resistant in the future. This study for high-seismic-risk areas will improve structural engineering's sustainability and safety. Key Words: Seismic zone upgrade, Structural retrofitting, Rehabilitation, Increasing rigidity and damping

INTRODUCTION

With the increasing frequency and intensity of seismic events, the seismic vulnerability of existing Reinforced Cement Concrete (RCC) buildings has become a major concern. Many structures those were originally designed and constructed under lower seismic classifications are now found to be underprepared due to updated seismic hazard assessments. Particularly in India several regions have been reclassified from Seismic Zone II / III to Zone III / IV respectively, demanding urgent retrofitting interventions to enhance structural safety. One of the most effective and economically viable methods for retrofitting is the introduction of steel bracing or damper bracing systems. These bracings significantly enhance the lateral stiffness and strength of structures, thereby improving their seismic performances. This paper presents a comprehensive study on strengthening of RCC multi-storey buildings, particularly G+6 and G+12 storey buildings using steel bracings and that for G+15 storey building using fluid viscous damper bracings. The study aims to analyze and compare the structural behavior before and after retrofitting under seismic conditions. Mazzolani (Federico M.) introduced the concept of using removable steel Eccentric Braces (EBs) and Buckling Restrained Braces (BRBs) for seismic retrofitting. These systems are not only strong and elastic but also lightweight making them suitable for enhancing the seismic performance of existing structures without requiring major reinforcements. BRBs, in particular, have shown high ductility and stable inelastic response in laboratory tests, providing comprehensive improvements in lateral stiffness, strength and displacement capacity. Studies by D. Aniello, M. Della Corte and G. Mazzolani have reinforced the importance of these bracing systems in effectively reducing storey drifts and ensuring quick installation with minimal disruption to occupants. Similarly, Rajeev Kishan Pandey and Massumi & Tasnimi have demonstrated that steel X-bracings can significantly improve the ductility and energy dissipation capacity of low-ductile RCC frames. Ameena Muhammed A, Ifthana M N, Minnu Kurian, Shilpa Sajil and Merin Mathew (2023) have analyzed the seismic performance of a G+12 RCC residential building in Zones III and IV using ETABS 2018. Six scenarios are studied: unbraced and braced with X, V, Inverted V, K, and Diagonal systems, placed at mid and corner bays. Parameters like lateral displacement, storey drift and base shear have been evaluated. All bracing systems have improved performance, but K-type bracing is the most effective, reducing lateral displacement by 85% and storey drift by 79% in both directions. The study has concluded K-bracing significantly enhances stiffness and seismic resistance. Anes Babu, Dr. Chandan Kumar Patnaikuni, Dr. K.V.G.D. Balaji, and B. Santhosh Kumar (2017) studied the seismic performance of a G+9 RCC building using ETABS 2015 by analyzing three models: without bracing or shear wall, with various steel bracings (X, Chevron, Diagonal, V) and with a shear wall. Evaluated across seismic zones II to V, the study assessed storey displacement, drift, and shear. Results showed Chevron bracing was most effective in zones II and III, while X bracing excelled in zones IV and V. Kasai et. al. (2001), Lee & Taylor (2001), Uetani et. al. (2003), Chen, Li and Cheang (2010) used fluid viscous damper bracings for seismic resistance of tall buildings. Usage of bracing has improved stiffness and reduced drift significantly, proving to be an efficient and economical retrofitting solution.

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