PSI - Issue 60

Sarmili Swain et al. / Procedia Structural Integrity 60 (2024) 553–563 Sarmili Swain / Structural Integrity Procedia 00 (2024) 000 – 000

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that existing RC buildings, which have been in use for over a decade, were originally designed to withstand only gravity loads (Oggu.P, 2022) . As cities grow and urban areas become more densely populated, various factors come into play that influence the frequency, severity, and consequences of secondary hazards (like vehicle accident, explosion, electric spark, etc.,). Fire poses a significant and unpredictable event to civil infrastructure throughout its serviceable life. It can originate as a primary event (such as a gas cylinder leakage or electrical short-circuit) or be triggered as a secondary event following other hazards (like earthquakes or explosions). Among various incidents, fire hazards are the most prevalent in structures, and they can potentially lead to fire-induced progressive collapse. In recent years some incidents that occurred due to progressive collapse are terrorist attack on World Trade Centre, New York on 11th September 2001 (Bazant.Z.P, 2002) , and High-rise fire on Plasco Building, Iran on 19th January 2017 (Shakib.H, 2020) . Progressive collapse refers to the catastrophic failure of a building caused by the local failure of a load bearing structural component, which initiates a chain reaction leading to the widespread collapse of the entire structure. Typically, unforeseen events like vehicle accidents or explosions can lead to the collapse of load-bearing elements (such as columns and beams), disrupting the distribution of loads and results in the transfer of excessive forces to adjacent components. Moreover, there is a significant risk of fire engulfing the structural components, weakening them and potentially causing a cascading failure of the building ’ s integrity at an earlier stage. Taking into account these various factors, the vulnerability of reinforced concrete (RC) structures becomes a major concern, highlighting the need for mitigation through proper design, construction, and regular maintenance practices. Considering the fore-mentioned issues, in recent past considerable number of experimental and numerical studies presented in literatures are focused on investigating progressive collapse in conjunction with the effects of elevated temperatures on reinforced concrete (RC) structures. Akshay et al. (Radadiya.A, 2017) analyzed a 10-storey symmetry RC building with four different cases and concluded that demand capacity ratio (DCR) in beam and columns are exceeding the allowable limit for all the cases indicating the building having high potential of progressive collapse. Rasool et al. (Ahmadi.R, 2016) carried out an experiment on 3/10 scale sub assemblage and proposed a macro model to estimate collapse behaviour of RC sub assemblages under middle column removal. Kodur et al. (Kodur V, 2008) developed a numerical model for predicting the behaviour of RC beam subjected to fire to understand heat transfer and strength analysis by establishing moment-curvature relationship as function of time. Ahmad (Shehada. A, 2021) provided a numerical model using fiber element approach and compared the result with ten reported database tests of reinforced concrete building by column removal scenario. Marjanishvili (Marjanishvili.S, 2004) illustrated the four different analytical approaches to deal with progressive collapse that includes linear static, nonlinear static, linear dynamic and nonlinear dynamic analysis. Sushil (Bhoite.S.M, 2020) evaluated demand capacity ratio of a beam and ratio of member force to its strength of a RC building with different trials. This existing literature primarily focused on assessment of the structural integrity of gravity load designed buildings and its resistance to fire in terms of time separately. However, there are chances of buildings getting exposed to fire during critical damage of structural component due to any eventuality like explosion or any accident. Therefore, there is a need to investigate the structural integrity of buildings during initiation of progressive collapse mechanism coupled with exposure to fire load scenarios. This clearly envisages the structural resistance of building components expressed by means of bending moments and shear forces in terms of exposure time and elevated temperature. Therefore, in this study an attempt has been made to investigate progressive collapse mechanism initiated by column removal scenarios (in accordance with GSA guidelines) coupled with simultaneous application of fire load scenarios (0, 30, and 60 minutes) for all structural components as per Euro codes (EN 1991-1-2 2002 and 1992-1-2 2004). Hence, a hypothetical G+3(ground + three floors) multistoried RC building frame designed for gravity loads (as per IS456:2000) has been considered to assess the building ’ s vulnerability, thereby contribute to estimate its structural integrity. 2. Modelling & Analysis The hypothetical G+3(ground + three floors) multi-storeyed RC building frame represented by ordinary moment resisting frame (OMRF) are designed for gravity loads in accordance with IS 456:2000 as shown in Fig.1. The detailed specifications of the building configuration with corresponding loads considered during design are outlined in Table 1 and Table 2.