Shear strength of prestressed concrete beams without web reinforcement**

Using the theory of plasticity, coincident upper and lower bounds for the ultimate shear load are determined. The materials are assumed to be rigid, perfectly plastic, the tensile strength of the concrete being neglected. The unrealistic assumption of unlimited concrete ductility is amended by introducing an empirical effectiveness factor on the compressive strength. The solution, which gives the shear strength as a function of the shear-span ratio and the longitudinal reinforcement strength, is compared with the results of a test series, and excellent agreement is found. The dependence of the effectiveness ratio upon various factors, principally the concrete strength, is discussed by comparing it with a number of shear tests reported in the literature.