Theoretical Model of Bond Strength Considering Rib Spacing and Concrete Softening Behavior

A series of pullout bond tests were conducted on rebar with two different rib spacings and various concrete formulations to assess the bonds between high-strength rebar and concrete. The effect of varying the rib spacing on the bond strength was investigated, as was the bond mechanism between rebar and concrete. A bilinear softening constitutive model was used to describe the softening behavior of concrete in the cracked zone. A theoretical calculation model for bond strength was established that takes into account the effects of concrete in cracked and noncracked zones. The influence of different radial displacement distributions in the cracked zone on the calculation results was also investigated. The computational model was validated by comparing its results with the experimental data. The model’s accuracy was found to be highest when the radial displacement distribution in the cracked zone aligns with the equivalent elasticity hypothesis. Using this hypothesis to ensure a sufficient safety margin is recommended. An analysis of bond strength between reinforcement and concrete at different transverse rib spacings was performed using the proposed model, which showed that the reduction in bond strength is minimal when this spacing is less than d. However, this reduction accelerates and then slows down as the spacing increases; when it reaches 2d, the bond strength approaches that of plain round bars embedded in concrete.