Experimental Study on Dynamic Bond Behavior between Reinforcement and Concrete under Fire.

Bond failure is a crucial element in ascertaining the failure mechanisms of reinforced concrete (RC) structures. The investigation pertaining to the dynamic loading's impact on bond efficacy remains a lacuna within scholarly discourse. Therefore, 138 eccentric pull-out half-beam specimens have been fabricated to probe the intricate degradation mechanisms underlying the bond-slip phenomena between concrete and reinforcement when subjected to high-temperature transients. Initially, a series of experiments were conducted on half-beam specimens possessing different reinforcement diameters and embedded lengths. Subsequently, the transient temperature changes within the bond segment were recorded, and this was pursued by the execution of eccentric pull-out tests. Second, the bond stress-strain curves under transient temperature were measured. The experimental findings revealed that the bond strength peaked at 101°C and showed an upward trend up to 302°C. Beyond this temperature, however, the bond strength exhibited a decline. Specifically, at a target temperature of 400°C, the bond strength increased by 18.1% and 9.3% compared to values at 20°C and 200°C, respectively. In contrast, it decreased by 23.2% and 41.3% in comparison to values at 600°C and 800°C. Additionally, as the reinforcement diameter increased, there was a decrease in bond strength, while the ultimate failure force increased. Finally, a methodology for evaluating bond strength under dynamic temperature was introduced, and a semiempirical constitutive model was formulated, taking into account the interplay between different heating rates. The constitutive model underwent validation through temperature computations, proposing a bending moment calculated methods, thus affirming its accuracy under fluctuating temperature scenarios. [ABSTRACT FROM AUTHOR]