Postfire Anchorage Behavior of Hooked Bars in Reinforced Concrete Beam-to-Column Joints

Many RC structures experience fire during their service life, after which the evaluation of their postfire performance becomes necessary. Exposure to elevated temperatures due to fire influences the mechanical properties of concrete and steel reinforcement as well as the anchorage of steel in concrete. This paper investigated the effects of heat exposure on the anchorage of 90° hooked bars in RC beam-column joints. Twenty full-scale RC specimens were fabricated with different bar diameters, amounts of transverse reinforcement, and spacings of hooked bars. The specimens were subjected to flexural loading that induced tensile forces in the hooked bars at ambient temperature, either in unheated conditions or after exposure to maximum nominal temperatures of 500°C and 750°C. The results indicated that the tensile load-carrying capacity of hooked bars decreased by as much as 52% and 22% due to exposure to a maximum nominal temperatures of 750°C and 500°C, respectively. The residual strength was well correlated with the remaining compressive strength of concrete at the core of the column. Equations are proposed for estimating the maximum pull-out force and the postfire development length of hooked bars.