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Selection of plastic rebar chairs Before using the plas […]
Selection of plastic rebar chairs
Before using the plastic bar chairs, the users must make sure the thickness of the concrete cover is regulated in the design. In case, there is no instruction in the design, the user must refer to the current regulations. The selection of plastic spacer should be implemented in the following sequence:
1. Identify the type of structure
In general, most of all concrete spacers can be used in various structures and installation positions. However, some spacers are specially designed with certain advantages for a particular type of structure. Consequently, a selection of the right spacer will bring the advantage in the technical aspect, the convenience in construction, and reduce the cost for the project as well. Some types of plastic spacer are designed for bottom mesh, top mesh, steelwork of columns/wall, the beam ends…
2. Identify the surface supporting the bar chairs
The load-bearing capacity of the foundation or formwork is decisive to the selection of the bar chair. In general, if the surfaces supporting the bar chairs are firm formwork or bedding concrete, the bar chairs will contact their supporting surfaces on the minimum areas. This is the common design for plastic bar chairs of the type “ A-shaped”, ”H shapes”, circular shape, rectangular-shaped…
In the case where the supporting surface is not firm, such as soil, stone base, we must use the bar chairs with their base areas large enough to distribute the load during the construction onto the ground and ensure the bar chair as well as the rebar they are supporting, will not be settled.
3. Identify the layer of mesh
For supporting the bottom mesh layer, we can use any kind of plastic bar chair with a suitable height. However, if using the bar chair for the upper mesh layer, we should consider using the bar chair with a large base, such as a cone-shaped bar chair, which will avoid their turning over during the concreting work.
Some rebar chair products are designed for both bottom and top mesh.
4. Determine the binding requirement with steel rebar
The plastic spacers directly bind the steel rebar with the elastic clip details. Depend on the requirement, the user will decide whether to use the plastic spacer with a clip or not.
To the reinforcement cage of footings, beams, slabs are placed on the bar chairs and shall not be moved during the construction, we do not need to use the bar chair with clips. However, in case that the reinforcement cage of structures is removable, such as bore pile, precast structures…or they can be displaced during the construction by the equipment, workers…the user should select the spacer with clip to ensure them will not be lost during the construction.
5. To determine the concrete cover thickness
This is the main parameter of the bar chair product. The height of bar chairs is commonly designed with the interval of 5 or 10mm, depending on the product type.
6. To identify the rebar diameter
The bar chair is generally designed for a range of diameters from small to large. The user must select the right diameter of the bar chair, especially with the clip-on bar chair. The bar chairs with the wrong diameter of the clip will not able to fit the steel bars during installation.
Installation of plastic bar chair
1. Check the steel rebars have been correctly installed and completed.
2. Check the right bar chair products for each structure.
3. To the reinforcement of beam or slab
Raise the steel cages for a gap between steel and formwork, then place the bar chairs underneath; Adjust the bar chairs' position to ensure good contact with the supporting surface.
4. To the rebar of column or wall
Determine the height, spacing suitable for installation of the plastic spacer; adjust the wheels by turning them to the right position to obtain good contact with the formwork.
5. If using the clip-on or wheel rebar chairs, the user pushes the bar chairs into the steel rebar or vice versa until the steel rebar reaches the inside face of the bar chairs.
6. The distance of the rebar chairs will comply with the requirement of the designer.
Taizhou Saiweiyue Mould & Plastic Co., Ltd is a company who are specialized in making plastic rebar chair moulds, here viewing some of the injection moulds we made before.
If you have any project on plastic injection moulds, welcome to contact SWY MOULD with email ([email protected]) or WhatsApp/Wechat (+86 157 5766 8880).