Utilising confinement reinforcement for shear resistance in reinforced concrete structures

Common transverse reinforcement of reinforced concrete members with circular cross-section consists of round ties or spirals. Its purpose in members that are not subjected to significant shear loading is to provide proper confinement for concrete, and eliminate buckling of the longitudinal reinforcement bars. If spirals are to be used as both shear enabler and confiner for reinforced concrete beams then, under combined action of moment and shear, spirals will be required to provide or contribute to proper shear resistance. Hence, a proper assessment for spiral shear contribution is required. The validity of concepts which underline current methods for shear design used in design codes will be investigated in this paper, especially for beams with the shear configuration, which violates basic code rules on forming a truss. A simplified sectional model based on sectional crack analysis and a corresponding approach in assessing the shear contribution of spiral shear reinforcement are presented. A method for evaluating the shear capacity of beams with spirals has also been proposed.