Theoretical model for the bond-slip relationship between ribbed steel bars and confined concrete

This paper conducts a theoretical research into bond-slip relationship between ribbed steel bars and concrete. According to whether the concrete is cracked or not, the ascending part of the bond-slip curve is divided into two sections which are calculated by two different mechanical models. Based on the wedging action mechanism, the slip is introduced as displacement boundary conditions into the model, which is the main innovation of this study. The boundary conditions of the model are changed by the changing slip, so the bond stress values corresponding to all levels of slip are obtained. According to the rebar geometrical parameters specified in National Standard GB1499-2007, the spacing of the adjacent ribs is fitted as a linear function of the rebar diameter. Then characteristic slip with the rib spacing as the main parameter is adopted in this study. Also, a negative exponential function is proposed for the descending part of the bond-slip curve. Specially, parameters of slipping path are therefore suggested for engineering applications. Comparison between calculated values and test results shows that the theoretical model can reasonably predict the local bonding problems with different steel bar diameters and concrete strength grades.