Conversions of in-pound units to metric units.

To convert square inches to millimeters square, multiply by 645 (then round to whole numbers). To convert inches to millimeters, multiply by 25.4 (then round to whole numbers).

WWR is what the industry today refers to for all styles of Welded Wire Reinforcement. Every change takes a transition period. For instance, in much of WRI's literature, WWR is often referred to as fabric or mesh or WWF, which imply light reinforcing materials. However, this industry is continuing to grow into what we call the structural WWR market. Future ASTM standards, e.g., Volume 01.04--Steel Reinforcement--will reflect this change of wording, from fabric and mesh to reinforcement.

With further changes to heavier wire and the structural WWR market tonnage increasing each year, structural reinforcement describes the product much more accurately. To be more specific, anytime an engineer uses a moment capacity similar to the one published as Mu in ACI 318, Chapter 9 (even for slabs on ground), it flags the fact that the reinforcement is structural or primary reinforcement. One can even apply the area of steel of a WWR style, e.g., 6x6-W1.4xW1.4 in the ACI equation, which yields an ultimate moment capacity of 16% of the cracking moment (Mcr) of a 4"slab.

Some will continue to call out the old but still common wire sizes today as 6 gage (W2.9), or 8 gage (W2.1) or 10 gage (W1.4). Those wire sizes in a 6x6 style are less than 42 #/100sf and some will refer to them as fabric or mesh. [Incidentally, the call-outs in parentheses are the areas of the wire multiplied by 100.] However, as mentioned above, all steel reinforcement areas can be classified as structural or primary reinforcement. Therefore, with the 3 wire sizes noted above, as well as the many sizes over a W4, i.e., W4 wires, each direction on 6 x 6 spacings yields a weight of 58#/100sf--and other wire spacings can be specified as structural WWR. By the way much of our industry produces wire sizes up to W or D 20 (1/2"diameter) and some have the capability to produce W or D 31 (5/8"diameter) and even W or D 45 (3/4"diameter).

The WWR industry can furnish a greater variety of wire spacings than what many are aware of, and areas of steel can match the design professional's requirements more accurately. The typical range of spacings--2, 3, 4, 6, 12, 16 & 18 inches (these occur in tables in the current WRI Manual of Standard Practice)--can be greatly expanded. Sheets of WWR reinforcement have been furnished with 24-, 36-, 48- and even 60-inch spacings. It depends on the application and the size of wires specified. Call WRI member producers for their ability to meet your specific reinforcement needs.

Here is a list of uses for structural WWR in reinforced concrete construction:

For cast in place concrete buildings.

WWR has been, and will continue to be, designed into slabs on ground (for both structural and crack control reinforcement), supported slabs, walls (for both foundations and structural shear walls) and shear reinforcing for column ties and beam/girder stirrups. Confinement reinforcement in concrete columns, at beam/column joints and confinement ties around boundary elements in concrete structures requiring design-basis earthquake detailing and concrete piles and caissons.

For cast in place bridge structures.

WWR is designed in foundations, piers and pier caps, may also be used in bridge girders, decks, approach slabs, median barriers and retaining walls. WWR may also be specified in concrete piling, CIP bridge railing, deck and highway paving overlays. Corrosion resistant WWR (coated or stainless steel) may be specified when snowmelt chemicals are used.

In precast concrete.

WWR is used in architectural panels, beams/girders, box beams and tees for floors, deck structures and pre-topped or post-topped slabs on single and double tees, as well as I-beams used in parking structures. Precast concrete sewer pipe, box culverts and related sewer components, as well as the 3-sided precast bridge market, are all reinforced with WWR, as are underground utilities, such as electrical boxes, telephone boxes, etc. These markets and other precast applications almost exclusively use WWR reinforcement and account for more than a third of the total tonnage of WWR produced annually for construction.

For prestressed concrete structures.

WWR shear reinforcement is used in bridge I-girder web reinforcement and for prefabricated rapid replacement bridge decks constructed on prestressed and /or precast bridge structures. There are other P/PC structural highway components, i.e. bridge rails, median barriers and soundwalls, that rely on WWR reinforcement.

Walls and Slabs.

Structural WWR is a growing presence in many more tilt-up wall panels, today, and is specified for structural slab reinforcement in the many distribution centers being built every day around the world. Slab on Ground Foundations are specified with WWR as the structural slab reinforcement on expansive soils. Composite metal deck supported slabs use WWR for the reinforcement above the flutes of the decks.

There are many shrinkage compensating slabs on ground that require steel reinforcement to handle tensile stresses when the slab expands and to hold the slab in position when it shrinks. WWR is a first choice reinforcement for many of these applications.

Interstate highways, state roads and airport paving have WWR reinforcement. It can compete very well with the continuously reinforced concrete pavement (CRCP) concept.

Many tunnel liner projects, whether units are precast or cast in place, use WWR reinforcing.

Structural welded wire reinforcement is used for tiebacks on retaining walls, as well as related earthwork reinforcement for reinforced soil embankments.

Various codes and standards do not give advice on spacing of supports for WWR?

WRI's Tech Fact—TF 702-2R—does have guidelines for support spacing based on many years of experience. This TF can be downloaded from the WRI Publications of this site. Simply stated:

The above guidelines for WWR support spacings can be used for supported concrete slabs, whether formed or placed on composite metal decks.

• Spacing of supports for WWR with wire sizes larger than W or D9 could be increased over the spacings shown depending on the construction loads applied.
  
  
• Consider additional rows of supports when permanent deformations of WWR sheets occur. On the other hand, spacing of supports may be increased provided supports are placed and properly positioned just as concrete is being screeded.

Speaking of supports for WWR, there are many types of supports made specifically for WWR. The TF 702-2R has photos of some of them. The same companies that sell rebar supports will usually handle those shown in the TF as well. Call the WRI if you would like references to any specific support and manufacturer of same.

It is a misnomer to think that ductility of WWR is less than conventional reinforcing. It is an old belief that says wire has low ductility. Some research by a number of universities has not only proven the high strength characteristics of WWR, but that equal or greater strains and elongations are achievable compared with conventional reinforcing. As a reference, see ACI 318-02, Chapter 11 on shear reinforcement. In reality, there is more stretch or maximum strength with WWR before fracture than most know about. There is a test in ASTM A 370 (A4.4.2) for measuring total elongation in the elastic plus plastic range before fracture. WRI has documentation available that shows strains of 6-14% with various sizes of cold-worked, low carbon wires (W3 to D12). Also, ASTM Standards require tests with welds in the center of gauge lengths. For a reference on this data, see WRI's Manual of Standard Practice, WWR-500.

Got a question? Get An Answer. If you have a question on how to use WWR or where to find more information email us at wirereinforcementinstitute.org, or write or call us at:

WRI
942 Main Street
Suite 300
Hartford, CT 06103
Phone: 800-552-4974
Fax: 860-808-3009

To see a list of questions others have asked, please go to Questions.