Thirteen full-size reinforced concrete panels were tested to determine the behavior of reinforced concrete elements subjected to membrane shear. The panels were designed to study three variables: 1) the percentage of reinforcement, 2) the ratio of transverse-to-longitudinal steel, and 3) the load path. The resulting load-deformation responses in the rest panels were correctly predicted by a softened truss model. This rational model satisfies the three fundamental principles of the mechanics of materials: materials: 1) stress equilibrium, 2) strain compatibility and 3) the constitutive laws of materials. Three constitutive. laws previously established from membrane elements subjected to biaxial tension-compression were applied to membrane elements subjected to shea,: It was found that the constitutive law of reinforcing bars must be modified by a factor that takes into account the ''kinking'' of the reinforcing bars. Membrane elements subjected to shear may fail in four modes: 1) under-reinforced, 2) partially under-reinforced in longitudinal steel 3) partially under-reinforced in transverse steel, or 4) over-reinforced. These four failure modes are also correctly predicted by the softened truss model.
