Since concrete is a material that performs well under compressive loads, but performs poorly under tensile loading, steel is added to the concrete. The steel, which performs well under tensile loading, addresses this concern; it makes the concrete stronger and prevents cracking. Steel reinforcing is also used to tie different concrete elements together; for instance, to tie a concrete beam to a concrete column.

Welded Wire Reinforcement

Welded Wire Reinforcing, abbreviated WWR or WWF (Welded Wire Fabric), is generally used for reinforcing floor slabs. This type of reinforcing is made from a series of bars that run perpendicular to each other - in a grid layout. The bars are welded together to form a "sheet".

The nomenclature for specifying welded wire fabric is: WWR 8 x 6 - W12 x W16. The 8 refers to the longitudinal wire spacing, the 6 refers to the transverse spacing. W12 refers to the area of the longitudinal wires in 100ths of an inch. W16 refers to the area of the transverse wires in 100ths of an inch. In the bold example above, the reinforcement has longitudinal wires that are 0.12 square inches at 8" spacing; the transverse wires are 0.16 square inches at 6" spacing.

Steel Reinforcing Bars (Rebar)

Steel reinforcing bars are designated in 8ths of an inch. For instance a #5 bar has a diameter of 5/8". In addition, the bars are marked with the symbol of the production mill, the type of steel used, and the grade of steel.

Rebar Designation

Bar SizeDiameterArea
#33/8" = 0.375"0.11 sq in
#41/2" = 0.50"0.20 sq in
#55/8"= 0.625"0.31 sq in
#63/4" = 0.75"0.44 sq in
#77/8" = 0.875"0.60 sq in
#81" = 1"0.79 sq in
#91 1/8" = 1.125"1.00 sq in
#101 1/4" = 1.25"1.27 sq in
#111 3/8" = 1.375"1.48 sq in
#141 3/4" = 1.75"2.41 sq in
#182 1/4" = 2.25" 3.98 sq in
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Photo of Concrete Reinforcing Steel

Photo of steel bar reinforcing and welded wire reinforcing

More Information

The Concrete Reinforcing Steel Institute has a more detailed description of rebar markings, which also includes Canadian marking standards.

Concrete Reinforcing Manufacturers

Concrete Reinforcing

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