Title: A New Shear Design Model for Circular RC Members considering Shear Flow and Deviation Effects

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Publication: CIA

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Date: 2/13/2011

Abstract:
The shear bearing behaviour and the state of stresses in circular RC members are investigated. The shear flow is analytically derived from the equilibrium conditions of slender spatial bars and the coupling of bending moments and shear forces assuming the validity of the Bernoulli-Hypothesis. It is supplemented by radial deviation forces that act inside the section plane and perpendicular to the circular stirrups, ensuring equilibrium and interacting with the inclined compressive struts. Starting from the notion that stirrups act like rings under internal pressures, shear flow and deviation forces are coupled to a consistent mechanical model. Their stresses exceed the ones in rectangular sections by up to about 35%. Similar extents apply to the concrete stresses in the inclined shear struts. Thus, capacities of the tensile and of the compressive shear struts evidently decrease. An efficiency factor is introduced to account for such decreases. Because of its mechanical basis, the model is applicable to a variety of international codes to generalise their application to the analysis of circular sections. Numerical FE investigations and experimental data are presented for qualitative and quantitative verification of the model. Comparisons of stress distributions and ultimate shear bearing capacities show good agreement with the presented model.