Reinforced Beams in Flexure and Minimum Reinforcement

In this section, we examine with some detail the existing approaches to the failure of beams in bending. In general, it is accepted that strongly reinforced beams that fail by steel yielding are mostly fracture – insensitive. So, structures of this type have not been much investigated from the viewpoint of fracture mechanics. However, there are situations in which fracture plays a role; two extreme cases have been investigated by various authors: (1) failure of concrete in compression for normally reinforced concrete, and (2) failure of lightly reinforced beams.

The first type of failure, which was investigated by Hillerborg (1990), will be discussed in Section 10.5.12, mainly to show that even if normally reinforced beams are not sensitive to fracture in tension, they do show size effect due to fracture in compression. Investigations on the second case tremendously expanded in recent years. They will be discussed now.