Energy based time equivalent approach for evaluating fire resistance of reinforced concrete beams

The current prescriptive approaches for evaluating fire resistance of reinforced concrete beams under standard fire exposure have a number of drawbacks and do not provide realistic performance assessment. As an alternative, time equivalent concept can relate the severity of design fire exposure to that of standard fire exposure. However, the current empirical formulae for evaluating such time equivalency are mainly derived for protected steel members and may not be applicable for reinforced concrete members. This paper presents an energy-based time equivalency method for evaluating the fire resistance of reinforced concrete beams under design fire scenarios. The proposed method is based on the principle of equivalent energy, and estimates fire resistance based on the equivalency between standard and design fire exposures. The validity of the method is established by comparing the predictions from the proposed approach with those from existing methods (equivalent area method and empirical formulae) and with nonlinear finite element analysis. The applicability of the proposed approach to design situations is illustrated through a numerical example. It is shown that the proposed energy based method is capable of predicting equivalent fire resistance under design fire scenarios with an accuracy that is sufficient for practical purposes.