Shear and Diagonal Tension - Design of Reinforced Concrete - page 233

Figure 8.8 Two situations where end shear reduction is not permitted.
7. Various tests of reinforced concrete beams of normal proportions with sufficient
web reinforcing have shown that shearing forces have no significant effect on the flexural
capacities of the beams. Experiments with deep beams, however, show that large shears
will often keep those members from developing their full flexural capacities. As a result,
the Code requirements given in the preceding paragraphs are not applicable to beams
whose clear spans divided by their effective depths are less than four or for regions of
beams that are loaded with concentrated loads within a distance from the support equal to
the member depth and that are loaded on one face and supported on the opposite face.
Such a situation permits the development of compression struts between the loads and the
supports. For such members as these, the Code in its Appendix A provides an alternate
method of design, which is referred to as “strut and tie” design. This method is briefly de-
scribed in Appendix C of this text. Should the loads be applied through the sides or bot-
tom of such members, their shear design should be handled as it is for ordinary beams.
Members falling into this class include beams, short cantilevers, and corbels. Corbels are
brackets that project from the sides of columns and are used to support beams and girders,
as shown in Figure 8.9. They are quite commonly used in precast construction. Special
web reinforcing provisions are made for such members in Section 11.8 of the Code and
are considered in Section 8.12 of this chapter.
Figure 8.9 Corbel supporting beam reaction.