Steel Reinforcing in Concrete

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.

Concrete Rebar Markings / Notation
Concrete Rebar Markings / Notation
#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

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.

Photo of steel reinforcing installed prior to concrete pour
Photo of steel reinforcing installed prior to concrete pour
Article Updated: September 4, 2021

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