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Bar bending schedule (BBS) of a simply supported beam. (Type-3) / How to calculate the cutting length & weight of rebar's in simply supported beam.

  Part- 2   👈 Back   

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






Given data:

Beam width = 300mm.

Beam depth = 450mm.

Column width = 300mm.

Clear span L = 4000mm. = 4m.

Top  bar= 16mm ∅ - 2nos.

Top bent-up bar = 16mm ∅ - 2nos.

Bottom reinforcement = 25mm ∅ - 2nos.

Stirrup = 8mm∅ @ 150c/c

Clear cover = 30mm.

Development length Ld = 45d


Calculation:

A. Cutting length:

1. Bottom  bar:

Cutting length of the bottom bar

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

= [4000mm. + (2nos. × 45d) - ( 2nos. × 2d)]

= [4000mm. + (2nos. × 45 × 25mm.) - ( 2nos. × 2× 25mm.)]

= [ 4000mm. + 2250mm - 100mm.]

6150mm.

= 6.15m.


2. Top bar:

Cutting length of top bar

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

= [4000mm. + (2nos. × 45d) - ( 2nos. × 2d)]

= [4000mm. + (2nos. × 45 × 16mm.) - ( 2nos. × 2× 16mm.)]

= [ 4000mm. + 1440mm - 64mm.]

= 5376mm.

= 5.38m.

 

3. Bent-up bar or crank bar

Cutting length of the bent-up (crank) bar

= [clear span + ( 2nos. × development length ) + (2 nos.× extra crank length) - {(2nos.× 90° bend) + (4nos.× 45° bend)}]

= [4000mm + ( 2nos. × 45d ) + ( 2nos. × 0.42D ) - {(2 nos.× 2d ) + (4nos.× 1d )}]


Note:

 1. As the crank bar is bent at 45°, the resulting slope length will be 0.42D extra as it represents the hypotenuse of a triangle.

 2. There are 2nos. of 90° bend & 4 nos of 45° bend as shown in the below drawing. 



 

   Cutting length of the crank bar

  = [4000mm + ( 2 × 45 × 16mm.) + ( 2nos. × 0.42D ) - {(2nos.× 2 × 16mm.) + (4nos.× 1 × 16mm.)}]




Here, D

     = [beam depth + bar diameter - {( top & bottom clear cover) + (top & bottom stirrup dia.)}]

     = [ 450mm. + 16mm. - {(2nos × 30 mm.) + ( 2nos. × 8mm.)}]

     = [ 450mm. + 16mm. - 76mm.]

     = 390mm.


Cutting length of the bent-up (crank) bar

 = [4000mm + (2 × 45 × 16mm.) + (2nos. × 0.42 × 390mm.) - {(2nos.× 2 × 16mm.) + (4nos.×16mm)}]

= [4000mm + (1440mm.) + (327.6mm.) - {64mm. + 64mm}]

= [ 5767.60 mm. - 128mm.]

= 5639.6mm.

= 5.64m.


Important note: If you are curious to know, why the extra crank length is taken as 0.42D  in the above formula, you can click here.


4. Stirrup:

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) - (2 × 1/2 × stirrup dia.)} 

     = {300mm. - (2 × 30mm.) - ( 2 × 1/2 × 8mm.)}

     = {300mm. - (60mm.) - (8mm.)}

     = 232mm.


 b = {beam depth - (2 × cover) - (2 × 1/2 × stirrup dia.)} 

     = {450mm. - (2 × 30mm.) - ( 2 × 1/2 × 8mm.)}

     = {450mm. - (60mm.) - (8mm.)}

     = 382mm.


The cutting length of the stirrup bar

= [{2 nos. × (232mm. + 382mm.)} + (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.


The cutting length of the stirrup

 = [{2 nos. × 614mm.} + (2nos. ×  10 × 8mm) - ( 3 nos. × 2 × 8mm ) - ( 2 nos. × 3 × 8 mm.)]

 = [1228mm. + 160 mm - 48mm - 48mm.]

 = [1388mm. - 96 mm.]

 = 1292 mm i.e. 1.292 m.



B. No. of stirrups

No of stirrups in beam

 =  [{ clear span of the beam  ÷ stirrup spacing } + 1]

 =  [{ 4000mm. ÷ 150mm. } + 1]

 =   [26.66 +1]

 = 27.66 nos.

By rounding off = 28 nos.

Now, let us prepare a BBS table for the simply supported 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

25

2

6.15

12.30

3.853

 47.39  

2.

Top bar

16

2

5.38

10.76

1.578

 16.98

3.

Bent-up bar

16

2

5.64

11.28

1.578

  17.80

4.

Stirrup bar

8

28

1.292

36.176

0.395

  14.29

5.

       Total weight of bars =

  96.46

6.

         Add 3% wastage =

    2.89

7.

The grand total wt. of rebar's =

 99.35

 


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

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