Effect of concrete cover on the bond-slip behavior between steel section and concrete in SRC structures

The concrete cover is one of the key factors affecting the bond performance of steel reinforced concrete (SRC) structures. The main objective of this paper was to study the effect of concrete cover on the bond-slip behavior between steel section and concrete in SRC structures. Firstly, push-out tests on SRC specimens were conducted and the failure modes, bond stress-slip curves as well as strain distribution of the specimens were investigated. The experimental results indicated that the bond strength of steel section encased in concrete could be significantly improved by increasing the concrete cover due to the enhancement in the concrete confining effect. As the concrete cover increased from 90 mm to 170 mm, the initial bond stress, ultimate bond stress, and residual bond stress increased by 76.9%, 46.6%, and 97.2%, respectively. The concrete cover also had a considerable impact on the initial and residual slips between the steel section and concrete. Further, nonlinear finite element models of push-out tests were established and verified against the test results. The numerical results demonstrated that there were three shear mechanisms including chemical adhesion, static friction, and sliding friction performing differently at each loading stage. Finally, a parametric study was carried out based on the verified FE models. Four cracking patterns of the concrete surface were observed with the variation of the ratio of concrete cover to the clear distance between the flange tip and the web side surface of concrete.