Steel is a high-strength material compared to concrete.
The useful strength of ordinary reinforcing steel in tension as well in
compression, i.e. the yield strength, is of the order of 10 times the
compression strength of common structural concrete, or of the order of 100
times its tensile strength. On the other hand, steel is a high-cost material as
compared with concrete.
The two materials are best used in combination if the
concrete is made to resist the compression stresses. Thus, in reinforced-concrete
beams the resists the compression force, longitudinal steel bars are located
close to the tension face to resist the tension force, and frequently
additional steel are disposed that they resist the inclined tension stresses
which are caused by the shear force in the webs of beams.
However, reinforcement is also used for resisting
compression forces primarily where it is desired to reduce the cross-sectional
dimension of compression members, as in the lower floor columns of multistory
buildings. Even such necessity is not exist, a minimum amount of reinforcement
is placed in all compression members to safeguard them against the effects of
small accidental bending moments which might crack and even fail an unreinforced
member.
