### 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.

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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 👇

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 😄.