What is Chair Reinforcement in Building Construction ?

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Chair Bar Guidelines for Reinforcement (As per IS Code)

1. Purpose of Chair Bars

• Chair bars are used to hold the reinforcement bars in position during construction to prevent displacement while pouring concrete.
• They ensure the required spacing is maintained between the top and bottom reinforcement bars as per design specifications.

2. Spacing of Chair Bars

As per IS 456:2000 – Plain and Reinforced Concrete Code of Practice:

• Chair bars should be spaced at nominal 1000 mm centers, unless specified otherwise.
• For heavily reinforced slabs or where vibration may cause displacement, spacing can be reduced to 600-800 mm.

3. Diameter of Chair Bars

As per IS 2502:1963:

• The diameter of a chair bar is recommended as hc/50, where hc is the clear cover.
• The diameter should not be less than 12 mm.

4. Height of Chair Bars

• The height of chair bars should correspond to the spacing between the top and bottom reinforcement layers.
• Ensure the top reinforcement is not displaced during concreting by securely tying the chair bars to the reinforcement mesh.

5. Reinforcement Bars in Slabs and Rafts

As per IS 456:2000 – Section 26.5.2.1:

• T1 & T2: Top reinforcement bars provided for tensile stress.
• B1 & B2: Bottom reinforcement bars provided for flexural stress.
• Clear Cover:
  • 20-25 mm for slabs.
  • 40-50 mm for rafts (depending on exposure conditions).

6. Checklist for Site Engineers

• Ensure chair bars are placed at specified intervals and properly tied to the reinforcement mesh.
• Verify diameter and height of chair bars comply with the structural design and IS code.
• Inspect alignment and spacing of reinforcement bars before and after placing chair bars.

Additional Notes

• Avoid using makeshift or improper chair bars to prevent uneven spacing.
• For large-scale projects, consider pre-fabricated spacers for better precision and faster work.
• Regular inspection ensures durability and strength of the structure.

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