Shear Area of Reinforced Concrete Circular Cross-section Members

The shear strength of reinforced concrete members without shear reinforcement is related to the shear stress carried by the concrete effective shear area. For rectangular sections the effective shear area represents the area corresponding to the effective depth. However, for circular sections this area is not as readily defined. Different empirical proposals have been suggested recently but no analytical solution exists so far in literature. In this work the effective shear area of circular sections has been derived purely analytically. The ratio of the effective shear area to gross section area was expressed as a function of the neutral axis depth for different values of the concrete cover. For a typical value of neutral axis depth, it was shown that the effective shear area ranges between 0.6 and 0.8 times the sections gross area depending on the depth of the concrete cover. Thus, an average value of 0.7 seems to be a reasonably accurate value for design purposes and, moreover, it is in good agreement with other recent proposals.