Q: What is welded wire reinforcement?
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.
Welded wire reinforcement is an efficient, economical, and viable option for all large-scale concrete reinforcement applications.
Q: Is welded wire reinforcement a new product?
No. Actually, welded wire reinforcement has been around since John Perry invented a machine to weld wires into large sheets in 1901, 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 1906.
Q: What type of projects are good candidates for welded wire reinforcement?
There are many types of projects that are good candidates for welded wire reinforcement. The most common type of project would involve these large-scale construction elements: walls, slabs, footings, columns, beams, and girders. Representative project types where welded wire reinforcement can be best implemented include:
- Precast box culvert and precast pipe
- Parking garages
- Sound walls
Q: Is designing in welded wire reinforcement difficult and time consuming?
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).
Q: Is welded wire reinforcement a proprietary product?
No. Welded wire reinforcement is a mild steel reinforcement required to conform to the ASTM A1064 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 A1064 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.
Q: Conventional reinforcing bars have standard sizes. Does welded wire reinforcement have standard sizes?
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.
Q: What are the production limitations of welded wire reinforcement sheets (length, width, area of steel)?
Welded wire reinforcement sheets can be produced in a variety of lengths, widths and wire sizes. Each welded wire reinforcement facility has their own range of production based on their manufacturing equipment being utilized. The following is a list of general parameters used in producing welded wire reinforcement sheets:
- Maximum length: approximately 50 feet for sheets, up to 600 feet for rolls
- Maximum width: approximately 12 feet
- Typical range of wire sizes: 0.014 in2 to 0.31 in2
- Wire Spacing: 2” minimum, unlimited maximum
Q: Are there standard sheets of welded wire reinforcement or is everything custom made?
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.
Q: Is there a specific terminology used for the welded wire reinforcement product?
Welded wire reinforcement is typically referred to as a “mat” or a “sheet”, with the terms “WWR mat” and “WWR sheet” being used interchangeably. Welded wire reinforcement is also produced in continuous runs such that the finished product is furnished in “rolls”.
Q: Is there a size relationship requirement for deformed wires being welded together?
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 A1064.
If the structural design does not rely upon welded intersections, then there is no wire size relationship requirement. Per ASTM A1064, 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.
Q: ACI 301 currently requires a 12" support spacing for wire sizes smaller than D4.0 / W4.0. What are the Wire Reinforcement Institute's (WRI) recommendations for support spacing of welded wire reinforcement?
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.
Q: Can welded wire reinforcement be manually welded (stick welded)?
Manual welding of welded wire reinforcement is permitted as noted in several ASTM Standard Specifications, including:
- C1577 (precast monolithic concrete box sections)
- C478 (precast concrete manhole sections)
- C76 (reinforced concrete culvert for storm drain and sewer pipe)
- C507 (reinforced concrete elliptical culvert).
Other instances of manual welding may be permitted by the licensed design professional, as noted in ACI 318-19 Section 26.6.4.
Q: How is the welding done, and how is weld integrity confirmed?
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 A1064 as the governing material specification, which is also referenced in ACI 318-19.
Q: If a design is to rely on a welded intersection for development or curtailment purposes, how strong does the weld need to be so that it is considered “structural?”
By way of the ACI 318-19 reference to ASTM A1064, the required weld strength shall not be less than 35 ksi x nominal area of the larger wire at the intersection. This is also referenced in ACI 318-19 R220.127.116.11 and confirmed during manufacture.
Welded Wire Reinforcement Uses FAQs
Q: What methods of corrosion protection are available for welded wire reinforcement?
Welded wire reinforcement can be:
- Hot-dipped galvanized
- Comprised of stainless steel wires
The applicable material specifications are ASTM A884, ASTM A1060, and ASTM A1022.
Q: With wires welded in an orthogonal pattern, is there any design advantage derived from potential “two-way” interactive flexural behavior?
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.
Q: Is welded wire reinforcement permitted for use as flexural reinforcement in beams, walls, and structural slabs?
ACI 318-19 Table 18.104.22.168(a) allows the use of ASTM A1064 welded wire reinforcement as flexural, axial, and/or shrinkage and temperature reinforcement in all conventional beam, wall, and structural slab applications.
Welded wire reinforcement is not used as flexural, axial, and/or shrinkage and temperature reinforcement in special seismic systems (special moment frames and special structural walls).
Q: Is welded wire reinforcement permitted for use as transverse reinforcement in special seismic systems?
ASTM A1064 welded wire reinforcement is permitted as transverse reinforcement in special moment frames and special structural walls per ACI 318-19 Table 22.214.171.124(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.
Q: For the purposes of simplifying design with welded deformed wire reinforcement, can the engineer ignore potential contribution from the welded intersections despite the intersections being present?
Yes. In fact, save for instances where perimeter/edge welded wires might be depended upon for development or curtailment as a designer’s option, the ACI 318 standard treats welded deformed wire reinforcement the same as reinforcing bars: familiar rules for straight-line development length, lap splice, and hook development are applicable.
Q: In Section 126.96.36.199.3 of ACI 318-19, the standard states that, for non-stirrup applications, a maximum spacing of 16” for welded intersections in the direction of calculated stress is applicable. What if I want to specify reinforcement in welded deformed wire reinforcement mat form, but only need structural wires in one direction and not the other? Do I still need to satisfy the spacing requirement for what are essentially non-structural wires?
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 188.8.131.52.3.
ACI 318-19 Sections 184.108.40.206 and 220.127.116.11.1 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.