A Novel Experimental Approach for Evaluating Residual Capacity of Fire Damaged Concrete Members

Reinforced concrete structures exposed to fire retain significant residual capacity due to better fire resistance properties of concrete, and future re-use of the structure is generally possible. Nonetheless, fire induced degradation can result in a permanent loss of strength and serviceability. An accurate evaluation of residual capacity is necessary for taking informed decisions on future use and need for repairs in fire damaged concrete structures. This paper proposes a novel three-stage experimental approach for evaluating residual capacity of fire damaged concrete members. The approach comprises of evaluating response in three sequential stages, namely, during pre-fire exposure condition; during fire exposure comprising of heating and cooling phases of fire, followed by complete cool down of the member to ambient temperature; and then finally during post-fire exposure condition. This approach is applied to evaluate residual capacity of four concrete beams subject to different fire scenarios and load levels. Results indicate that fire damaged concrete beams retain significant residual capacity even after exposure to heating duration lasting beyond their prescriptive fire rating. Furthermore, decay (cooling) rate of fire exposure impacts extent of post-fire residual capacity retained in reinforced concrete beams. Also, increasing load level present prior to, and during fire exposure (including extended cool down) lead to a greater reduction in stiffness than residual capacity of fire damaged concrete beams. Finally, relatively large post-fire deflections occur in fire damaged concrete beams which adversely impact their serviceability limit state. The proposed approach can form the basis to conduct standardized tests for determining residual capacity of fire damaged concrete members.