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.
| BAR SIZE | DIAMETER | AREA |
|---|---|---|
| #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.
