Effect of bond, aggregate interlock and dowel action on the shear strength degradation of reinforced concrete

The macroscopic shear strength contribution of concrete in reinforced concrete members is supported by dowel action, aggregate interlocking across tension-shear cracks and the tensile stress field that becomes mobilised in concrete through reinforcement concrete bond. The mechanics of this relationship are explored in this paper for the benefit of improved understanding of the degradation of shear strength in reinforced concrete as a function of imposed deformation demand. The mathematical formulation uses the non-linear smeared crack/smeared reinforcement approach to consider plane stress states in reinforced concrete elements. The critical modelling assumption in assessing the concrete contribution to shear resistance was the representation of force transfer from bar to concrete, which requires establishing equilibrium both at crack locations as well as in a global sense. The significance of this modelling approach on the overall shear strength was evaluated by the comparison of computed results with those obtained from the conventional model, wherein concrete participation is lumped artificially under the so-called `tension-stiffeningʹ property. From this comparison the parametric dependence of tension stiffening on bar diameter, crack spacing and bond properties is illustrated. Through the mathematical formulation it was possible to identify and highlight the effect that compression softening of the concrete struts has on the contribution of the web reinforcement to shear resistance, which represents yet another source of globally observed strength degradation. The proposed model was verified by comparison with experimental results and was subsequently used for parametric investigation of the associated design problem.