Everything You Need To Know To Find The Best Rebar Welded Wire Mesh

Welded wire reinforcement is a prefabricated reinforcement for structural concrete comprised of orthogonally arranged high-strength steel wires.  Wires are cold-worked to incremental sizes up to and including 5/8” diameter (equivalent to a #5 rebar), then fused together using a machine-controlled electric resistance welding process that is governed by ASTM standards.  Modern welding equipment and production methods allow for a high level of customization during manufacture, with variability in wire size, spacing, and length possible on a given WWR mat to suit project-specific requirements.  Welded wire reinforcement mats can also be pre-bent by the manufacturer to conform to the spatial geometric form of particular structural elements. 

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Welded wire reinforcement is an efficient, economical, and viable option for all large-scale concrete reinforcement applications.

No. Actually, welded wire reinforcement has been around since John Perry invented a machine to weld wires into large sheets in , at a time when he was looking for a way to make fencing. He started to advertise welded wire reinforcement as reinforcement for concrete in .

No. The design process is relatively the same as designing with conventional rebar and the main difference takes place once the design engineer calculates the required areas of steel and before the area of steel is converted into conventional reinforcing bars. At this point, the required areas of steel are then converted into the specified spacing and wire sizes used in a welded wire reinforcement sheet.

WWR is a mild steel, high-strength reinforcement for structural concrete that is recognized in code and design standards published by the American Concrete Institute (ACI), the American Association of State Highway and Transportation Officials (AASHTO), and the American Railway Engineering and Maintenance-of-Way Association (AREMA).

No. Welded wire reinforcement is a mild steel reinforcement required to conform to the ASTM A Standard Specification. All welded wire reinforcement manufacturers are all held to this common standard.
 
While it is feasible for one welded wire reinforcement producer to pursue different markets or applications than its competitors, or for one producer to have slightly different internal processes and/or automated welding equipment than its competitors, the reinforcement itself must always be compliant with the ASTM Specification’s requirements, and this is confirmed through ASTM A certification and testing measures.
 
Welded wire reinforcement is a manufactured product in the same sense that rebar is, and as such should not be subject to unique proprietary-like scrutiny on the basis of its inherent pre-assembly.

Reinforcing bars are typically produced to eleven pre-defined sizes.  In contrast, the range of wire sizes used in welded wire reinforcement production is roughly 300, with wires produced in cross-sectional area increments of one-tenth of a square inch.  Combine this with the fact that the welded wire reinforcement mat geometries themselves are capable of being produced with varying lengths, widths, and wire spacings, and the result is a WWR product that is highly customizable to suit a project or application’s specific needs. 

All manufacturers carry what are referred to as standard sheets, which are those configured to suit project applications that have longstanding construction industry demand. The range of standard sheets offered from one producer to the next will typically vary slightly, depending on regionally-driven demand.

With that said, because of the capabilities of modern welding equipment, the production of project-specific welded wire reinforcement sheet configurations is increasingly common for both precast and cast-in-place concrete applications. Designers are not limited to a standard sheet size or wire diameter.

If the structural design is relying upon welded intersections for the purposes of development or curtailment, then, yes, there exists a wire size relationship: the smaller wire must have a cross-sectional area at least 40% that of the larger wire per ASTM A. 

If the structural design does not rely upon welded intersections, then there is no wire size relationship requirement. Per ASTM A, the welded wire reinforcement producer is still required to verify that welded intersections exhibit a weld shear strength of 800 pounds. This is typically for basic transport, handling, and placing purposes.

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The ACI 301 mandated support spacing does not guarantee conformance with a project's specified acceptable tolerance, nor does it allow for alternative support patterns or methods that would achieve conforming results.

Support spacing should be derived on a case-by-case basis with due consideration for attributes such as the reinforcement itself (type, size, and spacing), the intended function/performance of the reinforced concrete element, the selected chair/bolster type, and the substrate upon which the support rests, to name a few.

Pre-established tolerances - whether through a combination of ACI 318 and ACI 117 requirements or through a design professional's project-specific requirement - should govern placement of welded wire reinforcement fabric. Refer also to TF 702 in the WRI technical document library.

The WRI always encourages close collaboration between a project's contractor and design professional of record to ensure appropriate placement criteria and procedures.

Welding is carried out by automated welding machines using a controlled electrical fusion process.  Unlike manual stick welding characterized by the depositing of a consumable electrode, electrical fusion welding is predicated on welded parts (two wires) being pressed together to allow the flow of electricity across the contact interface, resulting in the material being fused together.  This process is acknowledged in ACI 318-19 Section R26.6.4.

Confirmation of weld integrity is carried out as part of the material’s certification process during manufacture, with ASTM A as the governing material specification, which is also referenced in ACI 318-19.

Design codes do not recognize any two-way interaction that might exist as a result of orthogonally-arranged welded wire reinforcement. In structural engineering practice, reinforcement for each primary direction is essentially analyzed separately, independent of the presence of welds, with the only exception being those instances in which perpendicular perimeter/edge welded wires are depended upon for development or curtailment.

ASTM A welded wire reinforcement is permitted as transverse reinforcement in special moment frames and special structural walls per ACI 318-19 Table 20.2.2.4(a), but the welds themselves are not permitted to be relied upon for resistance to any stresses. As such, for welded wire reinforcement used in seismic applications, bond and anchorage of the reinforcement must be derived from wire surface deformations and hooked wire curtailments only, with any potential contribution by welded intersections ignored/disregarded.

The need for “single-direction” welded deformed wire reinforcement mats is very common.

It is noteworthy that ACI 318-19 acknowledges treatment of welded deformed wire reinforcement in a manner identical to individual loose deformed bars and deformed wires when welded intersections are either absent or are not intentionally-positioned for tensile development or curtailment.  With this treatment established, and in light of modern welded wire manufacturing capabilities, it is difficult to find a technical justification for a broadly-applied prescriptive maximum spacing of welded intersections as is done in Section 20.2.1.7.3.   

ACI 318-19 Sections 25.4.6.4 and 25.5.3.1.1 outline the common scenario in which the absence of intentionally-positioned welded intersections in turn requires calculation of welded deformed wire reinforcement development length and lap splice length, respectively, to be based on the same equations that are used for individual (loose, non-welded) deformed bars and deformed wires.  In essence, these ACI 318 provisions direct the designer to disregard any contribution a welded intersection might make to bond and development, and have the designer instead base these attributes on the deformed wire surface's contribution alone. 

We encourage designers and contractors to continue to take advantage of the highly-customizable welded deformed wire reinforcement mat arrangements capable of being produced by modern automated welding equipment.  This includes “single-direction” welded wire reinforcement mats characterized by structural deformed wires in one direction and perpendicular non-structural wire positioned as required in the other direction.

Contact us to discuss your requirements of Concrete Reinforcing Steel Mesh. Our experienced sales team can help you identify the options that best suit your needs.

thejack...let's clarify a couple of things...

First, fiber is not a reinforcement. It is a concrete mix enhancement. It does not substitute for reinforcing steel, even though its manufacturers would like you to believe otherwise. It does enhance both the compressive and tensile properties of the concrete mix, but it does not prevent drying shrinkage cracking. In fact, the cracks may end up slight farther apart but ultimately wider than without the fiber enhancement.

Reinforcing steel, including wire mesh, does not prevent cracks in concrete. It only serves to hold the cracks closer together when the do occur (and they will occur unless you are using shrinkage compensating cement).

Which is better? You've already been given a few of the pros and cons. As paddingtongreen noted, most concrete placement crews don't know how to work properly with wire mesh. He's exactly right about standing on the mesh and trying to pull it up. If you don't believe it, put on a pair of lace up boots, leave the laces untied. Reach down and pull up on both sets of boot laces at once. Hmmm...couldn't pick yourself up, huh?

Wire mesh has a few advantages. One is that it is closely spaced to allow reinforcement in lateral shear and tension to overlap; thus helping them both. Another is that it requires less labor to place than conventional rebar. The problem is that most concrete placement crews think it solves all concrete ills and the only thing they have to do is put it somewhere in the concrete. Not true.

To be effective, wire mesh needs to be in the MIDDLE 1/3 of the cross section. Most often it is in the bottom 1/10 of the cross section, where it is worthless.

I prefer wire mesh mats, rather than rolled wire mesh. Those can be dropped in from the top during placement, or can be support on chairs without the waviness.

If you use conventional rebar, use the smallest rebar you can get (#3 or 4) and space it close together. Put it in the middle 1/3 of the slab cross section.

Preventing cracking in concrete has a lot more to do with selecting the right mix design and proper placement, finishing, and saw-cutting than it has to do with reinforcement.

Make sure you use the largest coarse aggregate practicable for the placement. Don't use a pump mix to place a driveway...you don't need to in most cases. Make sure that the water-cement ratio is kept as low as possible, given the placement constraints. Use a water reducing admixture if necessary.

Sawcut the joints in as close to square sections as possible and make the sawcuts the same day as placement. If you wait until the next day, some cracks have already formed, whether you see them or not. Joints should be spaced no more than 36 times the concrete thickness in inches (for instance, a 4" thick slab should have joints at no more than [(4*36)/12] or 12 feet.

Another critical component is thickness control of the concrete. You commonly see requirements for flatness in the 1/4" in 10 feet range (we won't get into Ff or Fl numbers). That's great from the topside...what about the subgrade. While you're making the concrete flat on top, it can vary in thickness because of poor subgrade control that will promote cracking. Make sure the subgrade is as flat as possible and don't allow any quick transitions of more than say 1/2" in 4 feet. Remember, a 4" floor slab should have a thickness variation of no more than -1/4", +3/8", under ACI tolerances.

A slab on grade with light loading really needs no reinforcing if you follow good concrete placement, finishing, jointing and curing techniques. If you're in a cold climate, follow cold weather concreting recommendations...if you're in a hot climate, follow hot weather concreting recommendations.

For a residential driveway, I prefer wire mesh and fibers.

On my personal driveway is used wire mesh and fibers. I used psi concrete with 5% air entrainment. The only exception was the section on the sidewalk and the apron. There, no steel reinforcement was allowed to provide easier access/replacement for utilities since the bedrock was 4' down and frost depth was 5'.

Where I am now, if your contractor is using one of the better suppliers, they will not deliver anything less than psi with 5% air for a driveway or patio. You can get a small producer to deliver it to a contractor. Some contractors will not pour without fibers and leave the choice of steel reinforcement(bars or mesh) up to the specifier/customer.

When you want the higher strength for micro-cracking, especially with higher strengths, fibers serve a purpose in with higher cement contents and water requirements. The cost added is minimal. If you have some control over the contractor or on-site observation, mesh can be very effective and is compatible with sawed joints if it is placed in the bottom 2/3 of the slab.

Toad - make sure they save the cut-offs from the mesh, since they make great cages (2' diameter by 6' high) for tomatoes since the mesh is about 6' wide.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.