MECHANICS OF CONCRETE PARTICIPATION IN CYCLIC SHEAR RESISTANCE OF RC

In conventional design of shear-dominated reinforced concrete elements shear resistance is assumed to comprise reinforcement and concrete co ntributions. Because the design code assumes these contributions to be uncoupled and independent of the load history, the estimated nominal shear strength of reinforced concrete is insensitive to the number and intensity of imposed load cycles. However, in accordance with recent experimental evidence, the concrete contribution to shear resistance d egrades with increasing ductility demand, thereby rendering the estima ted nominal shear strength conservative for low levels of deformation, and increasingly unconservative for larger imposed displacements. Thi s paper attempts to establish the parametric relationship between shea r strength and deformation demand through a nonlinear analytical model of cyclic plane-stress states in reinforced concrete. The formulation establishes tensorial, constitutive, and equilibrium relations, all e xpressed in terms of average stresses and strains. The model was used to conduct a parametric investigation of several design variables. The rate of strength degradation and ductility capacity were used to gaug e the parametric sensitivity of the problem. It was found that the cal culated concrete shear contribution degraded with increasing deformati on demand and was enhanced by an increase in the level of axial load a nd the amount of transverse reinforcement. A simplified design equatio n was developed from the analytical results to express the dependence of the concrete contribution term on the intensity of imposed deformat ion demand.