Chair bars refer to a small supporting structure that is used to lift or support the reinforcing steel bars (rebars) in the slab off the ground so that they can be properly positioned within the concrete.
Purpose of chair bars in slab
- Lift and support the reinforcing steel bars off the ground.
- Maintain the correct positioning and spacing of the rebars within the concrete slab.
- Ensure that the rebars are held in place during pouring and do not sink to the bottom of the slab.
- Allow the concrete to flow around and encase the rebars, providing additional strength to the structure.
- Prevent cracking and other structural issues that could occur if the rebars were not properly supported and positioned.
Parts of chair bars
Base: The bottom part of the chair that rests on the ground or the formwork of the slab.
Legs: The vertical components that connect the base to the top of the chair.
Top: The horizontal part of the chair that supports the rebar.
Spacers: Optional components that can be attached to the legs of the chair to provide additional support and maintain the correct spacing between the rebars.
According to IS 456 cl.12.3.2 (paragraph 3), the chairs used for supporting reinforcement bars should meet the following requirements:
- The chairs should be placed at a max spacing of 1m.
- the minimum diameter of the chair bar should be at least 12mm.
The chairs should be stable and not tip over during the concrete pouring process.
Checklist for civil site engineers for the checking of chair bars
- Ensure that the spacing between the chairs does not exceed 1 meter as per IS 456.
- Check that the chairs are stable and properly supported on the ground or formwork.
- Check that the chairs are not displaced or moved during the concrete pouring process.
- Check the size of chair bars i.e. it should not be less than 12mm.
