Local bond-slip model between steel bars and concrete after exposure to high temperatures

The impact of high-temperature exposure on the residual bond behavior between deformed steel bars and concrete is a critical aspect that affects their composite interaction and the load-bearing capacity of reinforced concrete (RC) members after fire events. This paper presents an analytical method to predict the residual bond behavior and failure modes of steel bars embedded in concrete after exposure to high temperatures. The concrete cover is modeled as a thick-walled cylinder with the inner surface under uniform pressure. During the loading process, the concrete cover is divided into two portions: an intact outer portion and a cracked inner portion. The material properties of both steel and concrete, along with the tension-softening characteristics of the cracked inner portion, are well-defined in the analytical method. Simplified equations are developed to estimate the maximum radial stresses, residual bond strength and interfacial slip parameters, which together define the bond-slip relationship at the steel bar-to-concrete interface after high-temperature exposure. The accuracy and validity of these simplified equations are extensively verified by comparing the predictions obtained from these simplified equations with corresponding analytical results, experimental data from the literature and the load-displacement curves predicted by the proposed finite element model.