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Bar bending schedule (BBS) of a sunshade. (Type-2) / Calculating the cutting length & weight of reinforcement in a chajja.

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Let us make BBS of the Chajja or RCC sunshade as shown below.



 

Given data:

Length of chajja = 1000mm.

Width of chajja = 600mm.

Chajja thickness (front) = 75mm.

Lintel beam width = 230mm.

Lintel beam depth = 400mm.

Main bar ( gun bar) = 10∅ @ 150c/c.

Distribution bar = 8∅ @ 150 c/c.

Clear cover of chajja =20mm.

Lintel beam cover = 25mm.


Calculation:

A. Cutting length:

1. Cutting length of the main bar (gun bar):




Cutting length of the gun bar

= [ (ab + bc + cd + de + ef + fg +gh + hi) - (6nos. × 90° bend. + 1no. × 135° bend.)]

Where,

ab = [chajja thickness - (2nos. × cover) ]

     = [75mm. - ( 2nos. × 20mm.) ]

     = 35mm.


bc = [ (chajja width - chajja cover) + (beam width - beam cover)]

     = [ (600mm. - 20mm.) + (230mm. - 25mm.)]

     = [ 580mm. + 205mm.]

     = 785mm.


cd = [ chajja thickness - chajja cover - beam cover]

      = [ 75mm. -20mm. - 25mm.]

       = 30mm.


de = [ beam width - (2nos.× cover) ]

    = [ 230mm. - (2nos.× 25mm.) ]  

    = 180mm.


 ef = [ beam depth - (2nos.× cover) ]

    = [ 400mm. - (2nos.× 25mm.) ]  

    = 350mm.


  fg = de = 180mm.


  gh = ef = 350mm.


hi = hook length

     = 12d = [12 × 10mm.]

     = 120mm.

Now, the cutting length of the gun bar

= [ (35mm. + 785mm. + 30mm. + 180mm. +350mm. + 180mm. + 350mm. + 120mm.) - (6nos. × 2 ×       10mm. + 1no. ×3 × 10mm.)]

= [ 2030mm.- 150mm.]

= 1880mm.

= 1.88m.


2. Cutting length of distribution bar

= [ chajja length - (2nos.× sunshade cover)] 

= [ 1000mm. - ( 2nos. × 20mm.)]

= 960mm.

0.96m.


B. No. of bars:

1. No. of main bars/gun bars.

= [{chajja length - (2nos. × cover)} ÷ c/c distance ] +1

= [{1000mm. - (2nos. × 20mm.)} ÷ 150mm. ] +1

= [ {960mm.}  ÷ 150mm. ] +1

= 6.4 +1

7.4

By rounding off = 8 nos.


2.  No. of distribution bars

= [{chajja width - cover - main bar dia} ÷ c/c distance ] +1

= [{600mm. - 20mm. - 10mm} ÷ 150mm. ] +1

= [ {570mm.}  ÷ 150mm. ] +1

= 3.8 +1

4.8

By rounding off = 5 nos.


If you want to know, how to prepare BBS of lintel beam, Go through the article👇

💁 ° How to calculate the cutting length & make BBS of the Lintel bar.


Now, let us prepare a BBS table for the Chajja or sunshade.

Sl. No.

Type of Bar

Dia.

in mm.

Nos.

Length

in m.

Total length

in m.

Weight

in Kg/m.

Total

 bar wt.

in kg.

1.

Main bar.

10

8

1.88

15.04

0.612

   9.20

2.

Distribution bar.

8

5

0.96

4.80

0.395

   1.90 

3.

       Total weight of steel bars =

 11.10

4.

         Add 3% wastage =

    0.33

5.

The grand total wt. of rebar's in chajja =

 11.43

 

Thank you for going through these calculation steps. Have a good day 😄.



 


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