Stirrup Effectiveness in Reinforced Concrete Beams with Axial Force

A study of the effectiveness of web reinforcement in reinforced concrete beams subject to axial forces is reported, involving the testing of 60 simply supported reinforced concrete T-beams and eight restrained reinforced concrete T-beams. The primary variables were axial force, the amount of web reinforcement, the concrete strength, and the shear span to depth ratio. Secondary variables were the web reinforcement yield point and the amount of flexural reinforcement. Measurements were made of applied loads, deflections, web reinforcement strain, and diagonal tension crack width. The effectiveness of the web reinforcement was found to be unaffected by the presence of axial forces. The design procedures for beams with web reinforcement contained in the ACI Building Code, ACI 318-63, were found to be conservative. Relationships are proposed which more closely reflect the variation of ultimate shear strength with variation of relevant parameters.