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Bar bending schedule (BBS) of RCC beam. (Type-1) / How to calculate the cutting length & weight of rebar's in RCC beam.

 Let us calculate the cutting length & weight of rebars in the RCC beam as shown in the below-given drawing.








Given data:

Beam width = 300mm.

Beam depth = 550mm.

Clear span = 4500mm. = 4.5m.

Top reinforcement = 16mm ∅ - 2nos.

Bottom rebar 1st layer = 20mm ∅ - 2nos.

Bottom rebar 2nd layer = 16mm ∅ - 2nos.

Stirrup at zone-1 = 8mm∅ @ 125c/c

Stirrup at zone-2 = 8mm∅ @ 150c/c. 

Clear cover = 30mm.

Spacer bar = 25mm∅

Development length Ld = 50d


Calculation:

A. Cutting length:

1. Bottom layer-1 bar:

Cutting length of the main bar

= [clear span + (2nos. × development length) - ( 2nos. × 90° bend)]

= [4500mm. + (2nos. × 50d) - ( 2nos. × 2d)]

= [4500mm. + (2nos. ×50 × 20mm.) - ( 2nos. × 2× 20mm.)]

= [ 4500mm. + 2000mm - 80mm.]

= 6420mm.


2. Bottom layer-2 bar:

Cutting length of the bar

= [clear span + (2nos. × development length) - ( 2nos. × 90° bend)]

= [4500mm. + (2nos. × 50d) - ( 2nos. × 2d)]

= [4500mm. + (2nos. ×50 × 16mm.) - ( 2nos. × 2× 16mm.)]

= [ 4500mm. + 1600mm - 64mm.]

= 6036mm.


3. Top bar:

As the dia. of top bar = dia of 2nd layer bar,

The cutting length will be the same i.e. = 6036mm.


4. Spacer bar:

The cutting length 

= [beam width - (2nos. × clear cover) +10mm]

= [300mm.- ( 2nos. × 30mm.) + 10mm.]

= 250mm.


5. Stirrup bar:

The cutting length of the stirrup bar

= [{2nos. ×  (a +b )} + (2nos.× hook length) -  ( 3nos. × 90° bend) - (2nos. ×135° bend )]



Where,

  a = {beam width - (2 × cover)} 

     = {300mm. - (2 × 30mm.)}

     = 240mm.


 b = {beam depth - (2 × cover)}

     = {550mm. - (2 × 30mm.)}

     = 490mm.


The cutting length of the stirrup

= [{2 nos. × (240mm. + 490mm.)} + (2nos ×10d ) - (3 nos. × 2d ) - (2 nos. × 3d) ]


To know, why we take bend deductions, Go through the article 👇

👀.  What are bend deductions for different angles in reinforcement bars?


Note:  Here, hook length is taken as 10d.

 = [{2 nos.×730mm.} + (2nos. ×10 × 8mm) - ( 3 nos. × 2 × 8mm ) - ( 2 nos. × 3 × 8 mm.)]

= [1460mm. + 160 mm - 48mm - 48mm.]

= [1620mm. - 96 mm.]

= 1524 mm i.e. 1.524 m.


B. No. of bars:

1. Stirrups for zone-1:

No. of stirrups

= 2 sides × [{( clear span of the beam /3) ÷ stirrup spacing } + 1]

= 2 sides ×[{( 4500mm. /3) ÷ 125mm. } + 1]

= 2 sides × [{1500mm. ÷ 125mm. } + 1]

=  2 × [12 +1]

= 2× 13 nos.

= 26 nos.


2. Stirrups for zone-2:

No. of stirrups

= [{( clear span of the beam /3) ÷ stirrup spacing } -1]

= [{( 4500mm. /3) ÷ 150mm. } - 1]

= [{1500mm. ÷ 150mm. } - 1]

= [10 -1]

= 9 nos.

The total no. of the stirrup.

= stirrups in [zone-1 + zone-2]

= [26nos. + 9nos.]

= 35 nos.

Note:

As we have added 2nos. of stirrups in zone-1, we have to deduct 1no. from zone-2.


3. Spacer bar:

The no of spacer bars

= [{clear span ÷ 1000mm. } + 1]

= [ {4500mm ÷ 1000mm. } + 1]

= [4.5 +1]

= 5.5nos. 

By rounding off = 6 nos.


To know what is a spacer bar, Go through the article 👇

👀.  What is a spacer bar in a beam?-purpose, spacing & its cutting length.


Now, let us prepare a BBS table for the RCC beam.

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.

Bottom bar-1.

20

2

6.42

12.84

2.466

  31.663

2.

Bottom bar-2

16

2

6.036

12.072

1.578

  19.049

3.

Top bar

16

2

6.036

 12.072

1.578

  19.049

4.

Spacer bar

25

6

0.25

1.5

3.854

    5.781

5.

Stirrup bar

8

35

1.524

53.34

0.395

  21.069

4.

       Total weight of bars =

  96.611

5.

         Add 3% wastage =

 2.898    

6.

The grand total wt. of rebar's =

 99.51

 


To know, how to calculate the weight of rebars per RMT., Go through the article 👇

❤.  How to calculate the weight of reinforcement bars?


Continued 👉 Part-2👇

👀.  Bar bending schedule (BBS) of a continuous beam. (Type-2)


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


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