PSI - Issue 70

Abhishek Badalia et al. / Procedia Structural Integrity 70 (2025) 121–128

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1. Introduction The primary goal of seismic retrofitting is to satisfy seismic safety regulations (Pohoryles et al., 2022). A key distinction between designing new structures and retrofitting existing ones is that all planning and construction activities in renovations must be based on the characteristics and constraints of the existing structure. Over the past 15 years, India has seen several moderate to large earthquakes, making it one of the most earthquake-prone nations in the world (Bhattacharya et al., 2014). Approximately 50 –60% of India’s land area is susceptible to seismic activity of various intensities, lots of existing structures lack seismic safety regulations and need retrofitting (Castro et al., 2018; Jain, 1998). Braces are inclined members, commonly known for their lateral force resisting properties when added to the building frame (Youssef et al., 2007). The bracing systems can be grouped according to their location in the reinforced concrete frames as internal or external and according to their connection style as eccentric or concentric bracing system (Nateghi-A, 1995; Poudel and Suwal, 2020). The brace arrangement in Reinforced Concrete (RC) frames is designed to enhance structural performance and durability through controlled deformations. Bracing systems are designed to withstand lateral loads in the modified frame beams and columns, which support vertical loads. This load distribution maximizes the structure's overall load-bearing capability (Rahimi and Maheri, 2018). There are two strategies in seismic retrofitting: 1) Structural level or Global level retrofitting method, which includes two primary approaches that are conceptually adopted and implemented in practice. The first, known as the conventional method, aims to enhance the structure’s capacity to withstand earthquake -induced forces, which include options like adding shear walls, infill walls or steel braces. The second, referred to as the unconventional approach, focuses on reducing the seismic forces acting on the structure by modifying the demand including options such as base isolation and supplemental dampers etc. 2) Member level or Local retrofitting method; where conventional methods focus on enhancing seismic resistance of structures, member level retrofit approach is to upgrade the strength of members (Desai, 2010; Navya and Agarwal, 2016). The most popular technique for increasing the strength of individual members is jacketing, which involves adding concrete, steel, or fibre-reinforced polymer jackets to confine concrete columns, beams, joints, and foundations. This method is more economical than structure-level retrofitting. On a global basis of resisting earthquake loads, shear walls are commonly used in RC framed buildings, whereas steel bracing is most often used in steel structures. This study presents a conventional retrofitting strategy using braces, focusing on evaluating an optimistic brace configuration for a mid-rise symmetrical building, which is 10 stories high. 2. Significance This study offers crucial information about how selective steel bracing retrofits might improve the seismic resistance of reinforced concrete (RC) frames. The experimental and analytical studies highlight the revolutionary effect of bracing systems on structural performance, as evident by the reported decrease in inter-story drift, decreased base shear, and regulated deformation patterns. When compared to their unbraced counterparts, the retrofitted frames continuously demonstrated greater energy dissipation, enhanced ductility, and decreased damage concentration, according to results presented in past studies. The findings from this study support the use of steel bracing as an economical, performance-driven intervention. It includes a broad review of recent and early age techniques used in retrofitting RC structures with steel braces and validates the outcomes of earlier research with a model-based study. The analysis results confirm that steel braces improve lateral stiffness and facilitate a more transparent load path distribution, allowing beams and columns to effectively concentrate on vertical loads while braces withstand seismic lateral stresses. All things considered, this study offers useful information for the planning and execution of retrofit plans for already-existing RC buildings, especially in seismically active areas. 3. Need for Retrofitting Seismic retrofitting for existing buildings may be necessary due to factors such as non-compliance with code guidelines, updates in codes and design practices, and revisions of codal provisions. These factors can result in deficiencies in the design or construction of structures (Ranganadhan and Paul, 2015). Reasons for retrofitting also include seismic zone upgrades, aging and strength degradation, structural modifications, changes in the building's use, etc. The main goal of seismic retrofit is public safety, and different structural and material survivability levels are