Shear Flow Zone in Rectangular RC Members Subjected to Pure Torsion


This paper presents the results of a research program that focused on experimental examination of the shear flow zone in reinforced concrete members subjected to pure torsion. The thickness of the shear flow zone was measured using embeddable strain gage units developed especially for this purpose. The performance and the reliability of these units were first assessed experimentally. Four full-size RC square beams reinforced with various ratio of steel reinforcement and concrete cover thicknesses were tested. Results indicate that when maintaining section dimensions constant, the torsional capacity is influenced by the cover thickness. The actual shear flow zone is smaller than that predicted using ACI's formula but larger than that predicted by existing theories. In addition, the cracking torque is significantly larger than ACI's prediction. The measured compressive strain distribution in concrete struts was rather parabolic indicating some influence by the steel reinforcement. In this paper, a new definition for the shear flow centerline was introduced, more accurate formula for predicting the cracking torque is proposed, and the phenomenon of concrete cover spalling is discussed.


Civil, Architectural and Environmental Engineering

Keywords and Phrases

Cover spalling; Cracking torque; Embeddable strain gages; Reinforced concrete; Shear flow zone; Torsion

Document Type

Article - Conference proceedings

Document Version


File Type





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Publication Date

01 Dec 2001

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