Handling and Lifting Requirements

The below graph shows the relationship between mat size, placement method, and installation cost. Smaller mats, due to their light weight, can be placed manually by hand. From the graph, the smaller the mat the higher the labor cost. The limit for manually placed mats is around 18 ft where the labor cost is the lowest. Mechanical placement (equipment, cranes, etc.) is needed for larger mats. The graph shows the minimum length is around 18 ft. The longer the mat the more economical it is to place. The maximum length is based on fabricating limits, bar sizes used, and transportation issues.

British Cement Association."Economic Assembly of Reinforcement ,"Bennet, D. and MacDonald, L.

Shipping

Welded wire reinforcement is shipped in bundled quantities not exceeding 150 sheets per bundle. The bundles are securely fastened together to prevent movement during shipping and handling. Each bundle shall be tagged bearing the name of the manufacture, description of the material, and other information as may be required by the purchaser. Bundle sizes are usually determined by the weight of the bundle or the requirements of the customer. Most bundles weigh between 2,000 and 5,000 pounds. Bundle weights are usually related to the customer's equipments unloading capacity. Bundles are then placed into stacks on the truck. The number of bundles in each stack is related to the overall height of the truck. Typical height is eight feet above the bed of the truck. The number of stacks on a truck is depended on the size of the sheet and the size of the truck. Customer may request dunnage (4x4 wood post) every 3 to 4 feet under the welded wire reinforcement to facilitate unloading with a forklift.

Nested & Un-Nested

Sometime bundles are assembled by flipping alternate sheets, allowing the sheets to "nest". Nesting increases the number of sheets per bundle by 33% and provides additional stability within the bundle.

Loading & Unloading

Welded Wire Reinforcement maybe lifted on and off a truck using a crane, forklift, or other lifting equipment. Loading and unloading material with a crane requires lifting eyes. Lifting eyes are lengths of wire passing completely through to the underside of the bundle and brought back up to the top and twisted around 3 to 4 times to form an eye. Lifting eyes are located in the bundle to limit deflecting and bending in the center of the bundle. Typically there are four lifting eyes per bundle located along the outside edge of the sheet. Loading and unloading material with a forklift requires the welded wire reinforcement to be supported by dunnage. Dunnage raises the welded wire reinforcement off the bed of the truck allowing forklifts to unload the trucks without damaging the material.

Storage

Store welded wire reinforcement in a protected area to limit the potential for injury and surface deterioration caused by prolonged exposure to conditions that accelerate the oxidation of steel. Prior to placement of concrete, all reinforcement shall be free of materials that may adversely affect or reduce bond. Rust, surface irregularities, mill scale or a combination of all three will not be cause for rejection. Material will be accepted as being satisfactory without cleaning or brushing provided the minimum dimensions, cross sectional area, and tensile properties of the reinforcement specimen meet the physical requirements for the size and grade of steel specified.

Supports/Accessories

WWR Supports

Project specifications should indicate the requirements for properly supporting the reinforcement. Various types of supports for WWR are commercially available. The types of supports include wire and welded wire supports, individual high chairs with plates, bolsters with plates, all-plastic supports, concrete blocks, and others. Individual high chairs or bolsters without plates may be used with a firm sub-base or mud mat.

Position of Reinforcement and Cover

The proper position for the steel reinforcement is a decision based on the design itself and is controlled by the intended function of the steel. When one layer of reinforcement is used, then it should be located at or above the mid-depth of the slab. Some architects/ engineers require that the single layer be placed 2 inches below the top surface of the slab. In thicker slabs, the reinforcement must be low enough so that it will not interfere with saw cutting. Others recommend that the layer be placed at one-third the depth below the top surface. Any of these locations can be the appropriate choice, depending on the design concept — for example, whether the slab is reinforced for crack control, or is reinforced for structural reasons, or designed for shrinkage-compensating concrete. When one layer of reinforcement is used, it should not be allowed to be below mid-depth. In general, positioning at one-third the depth below the surface is sufficient.

When two layers of reinforcement are used, the question of cover applies to both layers. The upper layer should be placed at least 1 inch below the top surface of the slab. The specified depth of any saw cut must also be considered and the upper layer placed below that saw cut. In the case of the lower layer, when the concrete slab is placed on a well-constructed base course (normally graded, compacted and porous), many who design floors consider 1-1/2˝ of clear cover below the steel to be adequate. Additional cover should not be necessary unless the governing building code requires a bottom cover of up to 3 inches.

Common Support Types

Slab on Grade Base Conditions on Selection of Supports

Most manufacturer’s brochures will indicate the base surfaces required for their products. The ACI Committee 360 report recommends a graded granular fill, appropriate for compaction and trimming, as the base material for slabs-on-grade. Gravel bases, when compacted, fit this description. Compacted granular fill allows a greater variety of supports for consideration due to the inherent strength and stability of gravel. The so-called sand cushion (a few inches of uniformly graded sand) is usually not stable or stiff, and thus demands the use of supports with base plates or concrete blocks. The supports must not penetrate the base (subgrade) during the construction process because the specified position of the reinforcing steel could be changed and its beneficial effect diminished. When polyethylene sheeting is used under a slab, the selected supports must not puncture the sheeting. Other materials may be required under a slab due to special circumstances or conditions. For example, the floors in cold storage or freezer warehouses are usually placed upon insulation boards. The selected supports must not penetrate the insulation board.

Spacing and Strength of Supports

Generally supports are spaced 2 to 6 (or more) feet apart, depending on the stiffness and weight of the WWR being supported. Between the supports, the reinforcement must not deflect or sag excessively. While there are no criteria for limiting this deflection, the reinforcement must not deflect beyond any required clearances. There is limited information available on requirements for support spacings for welded wire reinforcement. There are several factors to consider before determining support spacings. These factors include the diameter and spacing of the reinforcement (larger wire diameters with wider support spacings will allow workers to step through rather than on the reinforcement); and general recognition of any construction loads that will be applied before and during concrete placement. The welded intersections of WWR provide a very rigid sheet of reinforcement. The suggested spacings of supports in Table 1 may be used for estimating and construction. However, the preceding factors should be considered.

Source for this website page: - The WRI Institute Publication Tech Facts - TF 702-R-03

Placing Plans