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What is Chair Reinforcement in Building Construction ?


Chair Bar Guidelines for Reinforcement

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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