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 a square-inch. W16 refers to the area of the transverse wires in 100ths of a square-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

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.

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