Isolated Footings in BBS

Isolated footings are used to support individual columns and distribute the load to the soil. The Bar Bending Schedule (BBS) for isolated footings includes calculations for bottom reinforcement, top reinforcement, and side reinforcement if required.

Components of Isolated Footing Reinforcement

  • Main Reinforcement: Bars placed at the bottom of the footing to resist tensile stresses.
  • Distribution Reinforcement: Bars placed perpendicular to the main reinforcement to distribute the load evenly.
  • Side Reinforcement: Provided for deep footings if necessary.

Example of Isolated Footing BBS

Given:

    Footing size: 2m x 2m x 0.5m
    Cover: 50mm
    Main bar diameter: 16mm
    Distribution bar diameter: 12mm
    Spacing of bars: 150mm c/c

Step 1: Calculate Number of Bars

    Effective dimensions = Total dimension - 2 x Cover
    Effective length = 2000mm - 2 x 50mm = 1900mm
    Effective width = 2000mm - 2 x 50mm = 1900mm
    
    Number of main bars = (Effective width / Spacing) + 1
                       = (1900 / 150) + 1 = 13 bars
    Number of distribution bars = (Effective length / Spacing) + 1
                               = (1900 / 150) + 1 = 13 bars

Step 2: Calculate Bar Length

    Length of each main bar = Effective length + 2 x Cover
                           = 1900 + 2 x 50 = 2000mm or 2m
    
    Length of each distribution bar = Effective width + 2 x Cover
                                   = 1900 + 2 x 50 = 2000mm or 2m

Step 3: Total Steel Quantity

    Total length of main bars = Number of main bars x Length of each main bar
                             = 13 x 2 = 26m
    
    Total length of distribution bars = Number of distribution bars x Length of each distribution bar
                                      = 13 x 2 = 26m

Best Practices

  • Ensure adequate cover to protect reinforcement from corrosion.
  • Follow design specifications for bar spacing and diameter.
  • Maintain proper alignment of bars during construction.

By accurately preparing the BBS for isolated footings, construction teams can ensure material optimization and structural safety.




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