Abstract
A proposed adequation of NBR 6118, Item 7.4, related to shear strength of reinforced concrete beams is presented with aims to application on circular cross-section. The actual expressions are most suitable to rectangular cross-section and some misleading occurs when applied to circular sections at determination of VRd2, Vc and Vsw, as consequence of bw (beam width) and d (effective depth) definitions as well as the real effectiveness of circular stirrups. The proposed adequation is based on extensive bibliographic review and practical experience with a great number of infrastructure elements, such as anchored retaining pile walls, where the use of circular reinforced concrete members is frequent.
Highlights
Reinforced concrete circular cross-section beams are often used in infrastructure works, such as retaining structures for excavations (Figure 1)
The application of the Brazilian Standard expression for circular cross-section beams presents some problems, such as: (a) the applicability of the expression used for the determination of VRd2, the shear strength design related to the concrete failure by diagonal compression; (b) the definition of the value of bw for the calculation of Vc, the parcel of shear force resisted for complementary mechanisms to truss; (c) doubts related to the efficiency of circular stirrups in shear strength when determining Vsw, the portion of the shear force resisted by shear reinforcement
For calculation of Vsw, part of the shear force resisted by the transverse reinforcement, the model proposed by Merta [4], is quite complex, because it considers the geometry of the circular stirrups properly
Summary
Reinforced concrete circular cross-section beams are often used in infrastructure works, such as retaining structures for excavations (Figure 1). The application of the Brazilian Standard expression for circular cross-section beams presents some problems, such as: (a) the applicability of the expression used for the determination of VRd2, the shear strength design related to the concrete failure by diagonal compression; (b) the definition of the value of bw for the calculation of Vc, the parcel of shear force resisted for complementary mechanisms to truss; (c) doubts related to the efficiency of circular stirrups in shear strength when determining Vsw, the portion of the shear force resisted by shear reinforcement. It is a simplified procedure that allows visualization of the orientation of the tangential stresses in the cross section
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