Evan C. Bentz

Civil Engineering, University of Toronto, Canada
E-mail: bentz@ecf. utoronto. ca


In the design of concrete structures, the engineer is tasked with selecting structural geometry, mem­ber sizes and reinforcement details to ensure that the applied loads to which the structure is subjected can be safely carried to the foundation. For design against axial load and moment there is essentially global unanimity concerning the relationships that should be used to achieve this design. Specifically, the well-known rules of engineering beam theory or “plane sections remain plane” as originally explained by Robert Hooke are used; see Figure 1 (Hooke, 1678). This simple, general and accurate theory allows the engineer to design a member with confidence even when confronted with unusual geometry or new materials.

In contrast to the agreement that exists for flexural design, the mechanisms of shear resistance and provisions based on these mechanisms have not yet reached international consensus. In some jurisdictions purely empirical methods are used while others use more theoretically derived methods of various complexity and understandability. While the use of different methods in different places is not of direct concern, that these different methods produce transverse reinforcement requirements that vary by as much as a factor of six suggests that engineers’ understanding of shear is far behind their understanding of flexure.

Fig. 1. Robert Hooke’s figure demonstrating that Fig. 2. Different modes of shear failure modelled in

plane sections remain plane published in 1678. Canadian code.


M. Pandey et al. (eds), Advances in Engineering Structures, Mechanics & Construction, 67-80.

© 2006 Springer. Printed in the Netherlands.

As shown in Figure 2, shear forces in beams are modelled in the Canadian code (CSA, 2004) with either a strut-and-tie model, suitable for short shear spans or a sectional model suitable for longer shear spans. As the strut-and-tie provisions of the 2004 concrete design code are largely unchanged from the 1994 standard, they will not be described further in this document. The sectional provisions of the 2004 concrete design code, on the other hand, have changed significantly and this paper will summarize the development and use of these provisions. In the author’s opinion, the new shear provisions of the 2004 standard represent a breakthrough in the modelling of shear behaviour and should help foster international discussion towards the generation of a consensus on shear behaviour.