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