WELDED WIRE FABRIC

Welded wire fabric, often referred to as "wire mesh," comes in rolls and sheets. These must be cut to tit your individual application. The individual sections of fabric must be tied together, or "lapped," to form a continuous sheet of fabric.

Specifications and designs are usually used when wire fabric is being lapped. However, as a rule of thumb, one complete lap is usually sufficient with a minimum of 2 inches between laps. Whenever the rule of thumb is not allowed, use the end lap or side lap method.

In the end lap method, the wire mesh is lapped by overlapping one full mesh measured from the end of the longitudinal wires in one piece to the end of longitudinal wires in the adjacent piece. The two pieces are then tied at 1 1/2-foot centers with a snap tie. In the side lap method, the two longitudinal side wires are placed one alongside and overlapping the other and then are tied with a snap tie every 3 feet.

REINFORCING STEEL

Before placing reinforcing steel in forms, all form oiling should be completed. As mentioned earlier, oil or other coating should not contact the reinforcing steel in the formwork. Oil on reinforcing bars reduces the bond between the bars and the concrete. Use a piece of burlap to clean the bars of rust, scale, grease, mud, or other foreign matter. A light film of rust or mill scale is not objectionable.

Rebars must be tied together for the bars to remain in a desired arrangement during pouring. Tying is also a means of keeping laps or splices in place. Laps allow bond stress to transfer the load from one bar, first into the concrete and then into the second bar.

Methods of Tying

Several types of ties can be used with rebar. Some are more effective than others. The views in figure 7-20 illustrate the six types used by the Seabees: (A) snap, or simple, tie, (B) wall tie, (C) double-strand tie, (D) saddle tie, (E) saddle tie with twist, and (F) cross, or figure-eight, tie. As a Builder, you will probably be concerned only with the snap

Figure 7-20.-Types of ties.

and saddle ties. However, as a professional, you should be familiar with all six types.

SNAP, OR SIMPLE, TIE.- The snap, or simple, tie (view A of figure 7-20) is simply wrapped once around the two crossing bars in a diagonal manner with the two ends on top. The ends are then twisted together with a pair of side cutters until they are very tight against the bars. Finally, the loose ends are cut off. This tie is used mostly on floor slabs.

WALL TIE.- The wall tie (view B of figure 7-20) is made by taking one and one-half turns around the vertical bar, then one turn diagonally around the intersection. The two ends are twisted together until the connection is tight, then the excess is cut off. The wall tie is used on light vertical mats of steel.

DOUBLE-STRAND SINGLE TIE.- The double-strand tie (view C) is a variation of the simple tie. It is favored in some localities and is especially used for heavy work.

SADDLE TIE.- The wires of the saddle tie (view D) pass half way around one of the bars on either side of the crossing bar and are brought squarely or diagonally around the crossing bar. The ends are then twisted together and cut off.

SADDLE TIE WITH TWIST.- The saddle tie with twist (view E) is a variation of the saddle tie.

The tie wire is carried completely around one of the bars, then squarely across and halfway around the other, either side of the crossing bars, and finally brought together and twisted either squarely or diagonally across. The saddle tie with twist is used for heavy mats that are to be lifted by crane.

CROSS, OR FIGURE-EIGHT, TIE.- The cross, or figure-eight, tie (view F) has the advantage of causing little or no twist in the bars.

CARRYING WIRE.- When tying reinforcing bars, you must have a supply of tie wire available. There are several ways you can carry your tie wire. One way is to coil it to a diameter of 18 inches, then slip it around your neck and under one arm (figure 7-21). This leaves a free end for tying. Coil enough wire so it weighs about 9 pounds.

Another way to carry tie wire is to take pieces of wire about 9-inches long, fold them, and hook one end in your belt. Then, you can pull the wires out as needed. The tools you use in tying reinforcing bars include a 6-foot folding rule, side cutters, leather gloves, 50-foot tape measure, and a keel crayon, either yellow, red, or blue.

Figure 7-2l.-Carrying tie wire.

Figure 7-22.-Devices used to support horizontal reinforcing.

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