Concrete and steel
reinforcing work together beautifully in reinforced concrete structures. The
advantages of each material seem to compensate for the disadvantages of the
other. For instance, the great shortcoming of concrete is its lack of tensile
strength; but tensile strength is one of the great advantages of steel.
Reinforcing bars have tensile strengths equal to approximately 100 times that
of the usual concretes used.
The two materials
bond together very well so there is little chance of slippage between the two,
and thus they will act together as a unit in resisting forces. The excellent bond
obtained is due to the chemical adhesion between the two materials, the natural
roughness of the bars, and the closely spaced rib-shaped deformations rolled on
the bar surfaces.
Reinforcing bars are
subject to corrosion, but the concrete surrounding them provides them with
excellent protection. The strength of exposed steel subject to the temperatures
reached in fires of ordinary intensity is nil, but the enclosure of the
reinforcement in concrete produces very satisfactory fire ratings. Finally,
concrete and steel work well together in relation to temperature changes
because their coefficients of thermal expansion are quite close to each other.
For steel the coefficient is 0.0000065 per unit length per degree Fahrenheit,
while it varies for concrete from about 0.000004 to 0.000007 (average value 0.0000055).
