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The Standards & Industrial Research Institute of Malaysia (SIRIM) publishes specifications for steel and welded steel fabric.
The appropriate Malaysian and also British Standards are given in the tables beside:
|Specification for Cold Reduced Mild Steel Wire for The Reinforcement of Concrete|
|Specification for Welded Steel Fabric for The Reinforcement of Concrete|
MS 144 and MS 145 stipulate the minimum requirement for characteristic yield strength of welded fabric:
|Grade||Min. Characteristic Strength (N/mm2)|
Ribbed Fabric has been widely used as reinforcement for concrete structures in Malaysia and many developed countries.
Advantages of ribbed fabric are :
- Higher bond and anchorage characteristics of its ribbed wire.
- Ribbed wire is cold-rolled produced
- the rolling process give rise to uniform plastic flow in the material. The results - more consistent properties and better ductility.
- Crack widths in concrete elements are controlled to the minimum because force is well distributed through bond effect of ribbed wire as compared to plain wire.
Metex Steel Fabric is manufactured with automatic welding machines to develop a weld shear stress of 250 N/mm2. This weld is achieved by a controlled combination of pressure, electric current and time to develop a fusion of wires without reducing tensile properties of the wire. Our latest high technology mesh welding machine is capable of doing triple tier welding as shown in the Figure 02.
Once Metex Fabric is embedded in concrete, the anchorage of the fabric necessary to develop tensile stresses within the wire is achieved by the embedded of the cross wire. With the weld shear stress referred to above, one weld will achieve at least half of the specified characteristic yield stress of the wire. Hence the bond between the wire surface and the concrete can be regarded as additional anchorage and the tensile stresses can be developed in shorter lengths than those required by smooth bars.
An embedded of two welds will develop at least the yield strength of the wire.
Tension lap length should be at least equal to the design tension anchorage length necessary to develop the required stress in the reinforcement.
The length should be at least 25% more than the compression anchorage length. In the detailing of steel fabric, two cross welds are provided to transfer the stresses. In sidelaps of one-way slabs, half yield strength laps with overlap of only one cross weld are acceptable. This is commonly used in top (negative) reinforcement.
Full yield strength lap should always be provided when lap length is not specified.
End anchorage in the form of hooks and bends should only be used to meet specific design requirements.
BS 8110 Clause 7.4 Surface Condition states:
Reinforcement should not be surrounded by concrete unless it is free form mud, oil, paint, retarders, loose rust, loose mill scale, snow, ice, grease or any other substance which can be shown to affect adversely the steel or concrete chemically, or reduce the bond. Normal handling prior to embedment in the concrete is usually sufficient for the removal of loose rust and scale from reinforcement.
Loose rust is removed during handling and shaking of reinforcement. It is not advisable to strike the reinforcement.
Any surface rust which remains on the fabric is not harmful and will increase the bond and anchorage properties of fabric. Wire brushing is unnecessary and may reduce the bond on plain steel wire.
Overhang refers to the distance between the tip of the wire and the first weld joint. Overall dimensions, spacing of the wires and where the usage of the fabric will determine the overhang provided.
The uses of Metex Fabric may be applied with advantage including almost any purpose where a load is to be carried, where material is to be contained, or where a surface is required to be fire-resisting or waterproof.
Examples are :
Roofs and Floors
Bins and Bunkers
Wharves and Jetties
Our technical staff will be pleased to discuss your particular application with you.
The following points will be of assistance when placing Metex Fabric:
- For rectangular meshes, make sure that the Fabric is placed with the main wires in the correct direction, normally in the direction of the shorter span. On some occasions, they are placed in the directions of the longer span, therefore the drawings should be followed exactly.
- It is important that the Fabric is given the correct cover as shown on the plan. Any increase in the cover decreases the effective depth of the slab and reduces its strength. Insufficient cover will not protect the reinforcement from rusting.
- As the final strength of a slab is determined to a major degree by the correct location of the reinforcement it is advisable to position the Fabric on supports. Small pre-cast concrete blocks are suitable as spacers under the bottom layer in suspended slabs or in ground slabs where only one layer of fabric is used. Where Fabric is to be placed in the top of the slab for cantilever reinforcement, or to provide against negative moments, bar chairs of wire or plastic, or short lengths of bar of Fabric bent into a hurdle shape should be used to support the top layer.
- When using Metex Fabric in rolls for ground slabs, secure the free end of the roll by dog spikes or weighting.
- When the unrolling has been carried out sufficiently far enough for cutting, place a plank lightly against the unrolled portion to spikes or weighing.
- Cutting is easily done by using bolt cutters.