Post-Fire Residual Capacity of Reinforced Concrete Beam

Abstract

Incidents of fire are in increasing trend in developing countries. Exposure to fire may lead to a decrease in load carrying capacity and stiffness of a reinforced concrete (RC) structure. The degree of damage is related to the fire intensity in terms of temperature and duration of fire. Assessment of the residual capacity of a fire-damaged RC structure is difficult since there is no direct method to identify the extent of damage in the structural member. Sustained high temperature on a RC beam surface leads to progressive heating of the inner layers of concrete. Consequently, reinforcement bars get exposed to excessive high temperature which reduces the strength of rebars. In this article, an attempt was made to determine the post-fire residual capacity of a RC beam subjected to fire using finite element (FE) model. For this, FE models of 4 (four) RC beams with different clear cover thickness and depth subjected to fire were developed. After model validation, these were used to determine the residual capacity of RC beams exposed to fire for a duration of 30 min to 4 h. Results show that exposure to fire reduces the residual capacity and stiffness of a RC beam significantly. The nature of failure of a RC beam may become brittle after exposure to fire for longer period. Effect of increased clear cover on the residual capacity of the RC beam was found insignificant. Comparing the post fire residual capacity of RC beams obtained from FE analysis and simplified method showed that simplified method may overestimate the residual capacity of RC beams when they are exposed in fire for long duration.