Tuesday, June 2, 2009

Types of Ties for Concrete Rebar Reinforcement

Tie wire is used to hold rebar in place to ensure that when concrete is placed the bars do not shift out of position. Sixteen gauge wire is used to tie reinforcing bars. About 12 pounds (5.4 kg) of wire is required to tie an average ton of bars.

A number of different types of ties can be used with reinforcing bars; some are more effective than others. The illustration shows six types of ties that are identified according to the letters of the alphabet used to show individual ties.

* SNAP, OR SIMPLE, TIE. (view A) — The snap, or simple tie 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 cutoff. This tie is used mostly on floor slabs.

* WALL TIE. (view B) — The wall tie 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. (view C) — The double-strand tie is a variation of the simple tie. It is favored in some localities and is especially used for heavy work.

* SADDLE TIE. (view D) — The wires of the saddle tie 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. (view E) — The saddle tie with twist 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. (view F) — The cross, or figure-eight, tie has the advantage of causing little or no twist in the bars.

Lapping reinforcement in concrete

All forms of steel reinforcement must be lapped in accordance with AS 2870 requirements. The overlaps should be held together with tie wire.
Trench mesh laps; Where trench maps are joined end to end, they need to be overlapped by at least 500 mm. Where they overlap at T or L intersections the overlap should be the width of the trench mesh

Reinforcing bar lap; Reinforcing bar laps need to be overlapped by at least 500 mm

Square mesh lap; Square mesh lap has to be overlapped by at least 225 mm