Why is Reinforcement in Concrete Important?

One of the main disadvantages of concrete is its very low tensile strength that is practically exceeded at low levels of load. This results in cracking of the concrete surfaces that in turns leads to aesthetical problems (large deflection of beams or slabs) for the serviceability limit state as well as structural integrity problems at the ultimate limit state. On the other hand, reinforcing steel has rather high tensile strength and a symmetrical material constitutive law under tension and compression. However, a rebar alone that is subjected to compression fails prematurely due to buckling. For this reasons, use of reinforcement in a RC section leads to effective structural behaviour as reinforcing steel works effectively under tension and concrete works effectively under compression and confines the compression reinforcement. Figure 1 shows the Bending Moment Diagram of a continuous beam under vertical loads as well as the locations where reinforcing steel should be placed.