The bond stress between a reinforcement bar and concrete: is it theoretically predictable?

Abstract

In reinforced concrete, a good bond between the reinforcement and the concrete is required for an optimal interaction of these two materials. In the present contribution, an attempt is made to lay down the factors influencing the value of the ultimate bond stress τdu in a formula by a theoretical approach. The stress condition in the concrete around the bar is described by means of the model of a thick-walled cylinder subjected to an internal radial compression σ′. Once one has determined the pressure σ′ that causes failure of the concrete, τdu can be calculated using Coulomb's failure condition. Factors influencing this failure of the concrete are (among other things) the presence of a stress gradient, the contribution of the concrete on either side of the contact length between steel and concrete, and the form of the test piece (form factor). © 1988 RILEM.