Development of the 2004 Canadian Standards Association (CSA) A23.3 shear provisions for reinforced concrete Evan C. Bentz and Michael P. Collins Abstract: This paper describes the development of the 2004 Canadian Standards Association (CSA) A23.3 shear design provisions for reinforced and prestressed concrete structures. These methods are similar to the 1994 standard in providing a simplified and general shear design method. They differ from previous standards by providing a direct link between these two methods and simple equations for the calculation of β and θ used in the general method rather than providing these values in a table. The paper explains the basic assumptions behind the new shear provisions, provides a derivation of the new equations, and compares designs made with the new equations to designs obtained from previous standards. In general, the new shear provisions require slightly less shear reinforcement than that required by the previous standard. The new general method is significantly easier to use, particularly with spreadsheets. Key words: shear, building codes, reinforced concrete, size effect, structural design. Résumé : Cet article décrit le développement des dispositions de la norme CSA A23.3 2004 quant à la conception anticisaillement des structures en béton armé et précontraint. Ces méthodes sont similaires à celles de la norme 1994 en ce qu’elles fournissent une méthode de conception anticisaillement simplifiée et générale. Elles diffèrent cependant de celles des normes antérieures en fournissant un lien direct entre ces deux méthodes et en fournissant des équations simples pour le calcul de β et de θ utilisés dans la méthode générale plutôt que de fournir ces valeurs dans un tableau. L’article explique les hypothèses à la base de ces nouvelles dispositions anticisaillement, fournit une dérivée des nouvelles équations et compare les conceptions réalisées en utilisant les nouvelles équations aux conceptions obtenues en se servant des normes antérieures. Règle générale, les nouvelles dispositions anticisaillement exigent légèrement moins de renforcement anticisaillement que ce qui est requis par l’ancienne norme. La nouvelle méthode générale est beaucoup plus simple à utiliser, particulièrement avec des tableurs. Mots clés : cisaillement, codes du bâtiment, béton armé, effet d’échelle, conception des structures. [Traduit par la Rédaction] Bentz and Collins 534 Introduction In the creation of complex concrete structures, the number of individual members that must be designed to resist applied loads can be extremely large. As an example, Fig. 1 shows two large concrete buildings in downtown Toronto, each with well over 1000 structural elements that must all safely transfer moment, axial load, and shear towards the foundation. To design members for moment and axial loads, the well-known rational theory of “plane sections remain plane” is used, allowing the engineer to design with confidence, even when faced with complex reinforcement geometry or new materials. In contrast, the lack of a universally agreed upon model for shear behaviour has meant that many codes of practice still rely on purely empirical equations to estimate the shear force required to cause a member to fail in shear. With the increased use of new materials and the ability to analyze, and therefore use, geometry of increased complexity, it becomes important for the engineer to understand basic shear behaviour to see the limits of the code equations. Basing the shear design equations on a simple and rational model most easily allows that understanding: the engineer can use the equations themselves to learn about behaviour as many students have done with flexure and axial load through the years. In Canada, the Canadian Standards Association (CSA) 1984 Design of concrete structures for buildings (CSA 1984) and 1994 (CSA 1994) Design of concrete structures require- ments have provided two independent methods for shear design. The first is called the “simplified method,” which is derived from the empirical methods of the American Con- crete Institute (ACI) code (ACI Committee 318 2005), and the second is a rationally based shear design method called the “general method” (Rahal and Collins 1999). Despite the advantages of being based on a rational theory, the general method can be sufficiently complex to use, particularly with spreadsheets, that many engineering offices are forced by necessity to use it less often than they may wish. Thus, shear design in Canadian concrete buildings is often performed with Can. J. Civ. Eng. 33: 521–534 (2006) doi:10.1139/L06-005 © 2006 NRC Canada 521 Received 7 June 2005. Revision accepted 5 January 2006. Published on the NRC Research Press Web site at http://cjce.nrc.ca on 15 June 2006. E.C. Bentz 1 and M.P. Collins. Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, ON M5S 1A4, Canada. Written discussion of this article is welcomed and will be received by the Editor until 30 September 2006. 1 Corresponding author (e-mail: bentz@ecf.utoronto.ca). Can. J. Civ. Eng. Downloaded from www.nrcresearchpress.com by East China Jiaotong University on 09/16/19 For personal use only.