Inferring target reliability index of reinforced concrete beams in a standard fire situation according to Brazilian standards

Abstract Since there is no consensus in the literature on the target reliability index values of reinforced concrete structures in a fire situation, this article aims to present a methodology for inferring the implicit target reliability index range for reinforced concrete beams in a standard fire situation from the prescriptions of Brazilian standards. The limit state function used in the analysis compares the resisting bending moment and the applied bending moment on the structures, which are based on a reinforced concrete beam with representative characteristics for typical residential buildings in Brazil. Because of the aforementioned limit state function, in order to generate a target reliability index interval, it was considered a variation in the nominal cover value of the beams and a variation on the load ratio applied to them. The former variation is important because the cover is the variable that most influences the resistance of the beams in a fire situation, while the second variation is important because it is a variable that can cause changes in the applied bending moment of the structures. In this way, using a developed computational tool, based on the FORM Method, the reliability of the beams with fire resistance time greater than the Required Fire Resistance Time (TRRF in Portuguese) defined by standard is evaluated by the analytical method allowed by the Brazilian standard. In this context, a target reliability index interval was possible to be inferred for these structures ranging from 0.32 to 1.52. This interval, which represents the reliability for the TRRF of 60 minutes, can be divided according to the nominal value of the cover or the aggressiveness class of the beam’s environment and corresponds to a 6% to 37% probability of failure, which can be understood as conservative reliability.