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What is Wire Chair?Accessories used with the placement of reinforcing mesh or mat, which elevates the mat above the surface of the formwork and keep the reinforcement mesh at their place during reinforcement bar fixing and concreting. The wire chair should be strong enough to withstand load of labors that carry out fixing steel bars and concreting operation, in addition to make sure that designated concrete cover is properly executed.
Fig.1: Chairs used to support reinforcement mat
Types of Wire Chair for Concrete ConstructionThere are three major type of wire chair which include goalpost type continuous wire chair, individual wire chair, and lattice type continuous wire chair. These are discussed in the following sections:
1. Goalpost Type Continuous Wire ChairGoalpost type continuous wire chair is manufactured from three longitudinal equally sized continuous steel bars as can be observed from Figure 2. The use of three bars is to make sure that the chair can withstand design loads.
Fig.2: Goalpost Type Continuous Wire ChairThe space of supporting steel bar of goalpost type continuous wire chair shall be 100mm. Normally, the height of this type of chair range from 30mm to 200mm, and 400mm for large design loads. Finally, it is possible to manufacture goalpost continuous wire chair using greater bar sizes based on demands.
Fig.3: Goalpost Continuous Wire Chair
2. Individual Wire ChairIndividual wire chair is commonly used for the case where there is no bottom reinforcement off which to support a continuous chair for instance it can be employed to support top reinforcement in cantilever slab where bottom reinforcement may not be present. It is specified that, protective layer of plastic shall be applied to individual wire chair leg. The layer need to be extended about 40mm as from the bottom of the leg as illustrated in Figure 4.
Fig.4: Protective layer used for the leg of individual wire chairThe height of individual wire chair ranges from 75mm to 200mm, and the length of linked legs range from 175mm to 300mm.
Fig.5: Individual high chair used in the fixation of reinforcement bars of slab
3. Lattice Type Continuous Wire ChairThis type of chair, as shown in Figure 6, is manufactured from three longitudinal steel wires with equal sizes to be able to resist the design load. The interval between supporting wire shall be maximum 200mm and the size of the top steel bar should be 5mm. it should be bear in mind that chair with considerably smaller bar sizes will not be acceptable. The height of lattice type continuous wire chair ranges from 50mm to 200mm. similar to goalpost type continuous wire char, lattice type continuous wire chair with greater height with greater bar diameter can be manufactured based on the demand.
Fig.6: Lattice Type Continuous Wire Chair