Performance Evaluation of RC Elements Under Standard Fire Exposure Using Finite Element Analysis Approach

Reinforced concrete (RC) structural elements are usually designed for fire exposure by evaluating the fire resistance ratings (FRRs). FRRs are quantified by experimental tests, numerical simulations, and using guidelines available in codes and standards. In the Indian context, IS 456, IS 1642 and NBC (vol 1, part 4) mention guidelines for FRRs for RC structures under fire. These guidelines are based on comprehensive experimental testing on isolated/individual elements subjected to standard fire scenarios. They are prescriptive and typically yield FRRs as a function of clear cover and cross-section dimensions. They do not explicitly account for critical considerations such as load ratio, boundary conditions, material properties, etc. Given the rapidly evolving high-rise building stock in India, the aforementioned limitations need detailed investigation. In this context, the current study develops a finite element (FE) analysis-based FRR quantification framework for RC elements (beams and columns) designed using Indian Codes. The FE analysis is based on structural fire analysis in the OpenSees code using a 1-D beam-column element formulation. An experimental validation study is included to demonstrate the accuracy and efficacy of the FE analysis framework. Comprehensive response history analysis (temperatures and deflection histories) is conducted on the RC elements under fire conditions. Also, parametric studies are performed on the influence of cross-section, load ratio, boundary conditions, and clear cover on FRRs of RC elements. Furthermore, comparison studies on the FE analysis-based FRRs vs. FRRs as per Indian codes are presented.