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.
|#3||3/8" = 0.375"||0.11 sq in|
|#4||1/2" = 0.50"||0.20 sq in|
|#5||5/8"= 0.625"||0.31 sq in|
|#6||3/4" = 0.75"||0.44 sq in|
|#7||7/8" = 0.875"||0.60 sq in|
|#8||1" = 1"||0.79 sq in|
|#9||1 1/8" = 1.125"||1.00 sq in|
|#10||1 1/4" = 1.25"||1.27 sq in|
|#11||1 3/8" = 1.375"||1.48 sq in|
|#14||1 3/4" = 1.75"||2.41 sq in|
|#18||2 1/4" = 2.25"||3.98 sq in|
Photo of Concrete Reinforcing Steel
The following photo shows a complex reinforcing condition at an edge of slab. This installation is complete and ready for the concrete pour. Shown in the photo are reinforcing bars (both candy-cane shaped and straight), welded wire reinforcement, and sheer studs mounted to the steel deck.
The Concrete Reinforcing Steel Institute has a more detailed description of rebar markings, which also includes Canadian marking standards.