Question

1. Based on your observation of the reinforced beam’s tensile strength vs. the unreinforced beam, why do we use steel in most structural concrete?

Answer 1

A beam when subjected to transverse loads (that is acting perpendicular to the axis of the beam) bend downwards. The top fibers of the beam are under compression while bottom fibers are under tension.

When such a beam is made of cement concrete and loads are applied as above, cracks would develop on the bottom side. This is because concrete is very weak in tension but good in compression. With the increase of the load, the cracks would proceed upwards causing ultimate collapse of the beam.

To increase the strength of the concrete, reinforcements are provided in those regions of the beam where it is weak in strength that is on the tension region. Such a beam is said to be of reinforced cement concrete. When such a beam is loaded as above and when tension is developed at the bottom fibers, it is transferred to the steel reinforcements from concrete if there is good bonding between them. Since steel is good in compression as well as in tension, it is able to take these tensile loads. Thus, the overall tensile strength of concrete is increased in this manner.

Thus, by adding steel reinforcements in those regions of concrete structural members where they are subjected to tension, the strength is increased and they can take higher loads without collapse.