In this work, a shear capacity model of reinforced concrete members with circular cross section transversely reinforced with circular hoops has been developed. The proposed model is based on the truss analogy by adding a concrete contribution term to the capacity of the shear reinforcement.
An additional deviatoric shear resisting mechanism of hoops - present solely in members with curved transverse reinforcement - was identified and expressed analytically. It is explained by the fact that a curved reinforcing bar under tension induces compression in radial direction as well. The component of this compressive force in the direction of external shear could thus be considered as an additional shear enhancing mechanism of the hoops. Its magnitude is expressed through the friction force that is present between the concrete and steel after the section is cracked and the bond partially destroyed. The concrete shear capacity has been derived by a parameter study and by applying a curve fit on the database of circular members without shear reinforcement. With the application of a strength degradation coefficient proposed so far in literature, the members shear capacity under cyclic load with increasing ductility has been expressed.
The proposed model has been compared with a recently proposed model and it was found that it predicts reasonably well the shear capacity of circular sections under cyclic load. By applying the strength reduction factors a sufficiently conservative design equation could be obtained suitable for incorporation in codes.