HOW TO CALCULATE STEEL QUANTITY FOR SLAB? - BAR BENDING SCHEDULE
Hii before going to calculate bar bending schedule for slab you should know to find your slab is whether one-way slab or two-way slab. If not its ok we will guide through this
One
Way Slab |
Ly/Lx
> 2 |
Two
Way Slab |
Ly/Lx
< 2 |
In one-way slab, Main bars are provided in a shorter direction (Cranked bars) and distribution bars are provided in a Longer direction (Straight bars).
in Two-way slab Main bars (cranked bars) are provided in both directions.
Q/A 79 |
Distribution bars: These bars are straight bars.
Main bars: These bars are cranked bars. Main bars are cranked at an angle of 45 Degree with the length of 0.42D
therefore,
D = Depth of Slab - Top cover – Bottom cover
Extra Bars: The extra bar is provided at the bottom of Cranked bars to maintain the framework of the slab. The length of Extra bar is L/4
.
OK We Think You Got A Clear Picture Of Slab Reinforcements Now Take Look Of This Detailing
GIVEN DATA FOR FLOOR SLAB 1
SIZE OF FLOOR SLAB 1
Length= 2950mm
Breadth= 6000mm
Beam size = 225x300mm
Main bars are 12 mm in diameter @ 150 mm centre to centre spacing
Distribution bars are 8 mm in diameter @ 150 mm centre to centre spacing. (Main Bar & Distribution Bar Difference)
Top and Bottom Clear Cover is 25 mm
Thickness of Slab – 150 mm
Therefore, To Find Its One Way Or Two Way Slab
Lx = 2950mm (shorter span)
Ly = 6000mm (Larger span)
Ly/Lx= 6000/2950 = 2.033
One
Way Slab |
Ly/Lx
> 2 |
Hence its one-way slab
So, We need to find
· Main bar for shorter span
· Distribution bar for longer span
· Top bar for main rod on both sides for critical structure
LCETED TRIVIA
1. Main reinforcement bar is normally used at the bottom of the slab.
Distribution bars are placed on the top of the main bar.
2. Main bar is used in shorter direction but distribution bar is used in longer span.
3. Higher dimension bar is used as main reinforcement bar.
Lower dimension bar is used as distribution bars.
4. Main reinforcement bar is used to transfer the bending moment to beams.
Distribution bars are used to resist the shear stress, and cracks developed at the top of the slab
STEP 1
Find Cutting Length Of Main Bars For Floor Slab 1
Length Of Main Bars = (depth of beam/2) + (width of beam/2) + (1 x inclined length) – (45° bend x 2) + length of shorter span + width of beam + (0.3 x intermediate slab length)
Inclined length = 0.42D
D = Slab thickness – 2 side clear cover (top cover + bottom cover)
D = 150 – (2 x 25) = 100mm
Inclined length = 0.42 x 100 = 42mm
45° bend = 1d
d = diameter of bar
45° bend = 1 x 12 = 12mm
Intermediate slab
L = 3100mm
Therefore,
Length Of Main Bars = (300/2) + (225/2) + (1 x 42) - (12 x 2) + 2950 + 300 + (0.3 x 3100) = 4730.5
Cutting length Of Main Bars for floor slab 1= 4.8m
STEP 2
No Of Bars Required For Cutting Main Bars
No of bars = (opp length/spacing) + 1
Opposite length of bar = 6000
Spacing = 150mm c/c as per given details
= (6000/150) + 1
No of bars = 41 nos
STEP 3
Total Length Of Bar Required For Main Bars Of Floor Slab 1
= no of bar x total length of bar
= 41 x 4.80 = 196.8m = 197m
Total length of bar required for main bars of
Floor Slab 1 =197m of 12mm rod
STEP 4
Find Cutting Length Of Distribution Bars For Floor Slab 1
Length of distribution bars = (breadth of beam/2) + length of longer span + (breadth of beam/2)
Length of distribution bars = (225/2) + 6000 +(225/2) = 6225mm
Length of distribution bars = 6.225m
STEP 5
No Of Bars Required For Cutting Distribution Bars
No of bars = (opp length/spacing) + 1
Opposite length of bar = 2950
Spacing = 150mm c/c as per given details
= (2950/150) + 1
= 20.6666666667 = 21 nos
No of bars = 21nos
STEP 6
Total Length Of Bar Required For Distribution Bars Of Floor Slab 1
= No Of Bar X Total Length Of Bar
= 21 x 6.225 = 130.725m
Total length of bar required for distribution bars of Floor Slab 1 = 131m of 8mm rod
STEP 7
Top Bar (Extra): Top Bars Are Provided At The Top Of Main Bar As Critical Length (L/4) Area
Number of top bars = (Lx/4) / spacing + 1
Number of top bars = ((2950/4) / 150) + 1 =5.91 = 6 nos of bars x 2 sides = 12 nos
Number of top bars = 12 nos of bars
STEP 8
Total Length Of Bar Required For Top Bars Of Floor Slab 1
Length of top bars = Length of Distribution Bars
Cutting Length Of top Bars = 6.225m
Total length of top bars = 6.225 x 10 = 27.25m
Total length of top bars of Floor Slab 1= 63 m of 8mm rod
GIVEN DATA FOR FLOOR SLAB 2
SIZE OF FLOOR SLAB 1
Length= 3100mm
Breadth= 6000mm
Therefore,
Lx shorter span = 3100mm
Ly larger span = 6000mm
Beam size = 225x300mm
Main bars are 12 mm in diameter @ 150 mm centre to centre spacing
Distribution bars are 8 mm in diameter @ 150 mm centre to centre spacing. (Main Bar & Distribution Bar Difference)
Top and Bottom Clear Cover is 25 mm
Consider Development length as 40 d
Thickness of Slab – 150 mm
Therefore, To Find Its One Way Or Two Way Slab
Lx = 3100mm (shorter span)
Ly = 6000mm (Larger span)
Ly/Lx= 6000/3100 = 1.93
Two Way Slab |
Ly/Lx
< 2 |
Hence its Two-way slab
So, We need to find
· Main bar for shorter span
· Main bar for longer span
· Top bar for main rod on both sides for critical structure
STEP 1
Find Cutting Length Of Main Bars For Floor Slab 2 (A2-B2 direction)
Length Of Main Bars (A2-B2) = (depth of beam/2) + (width of beam/2) + (1 x inclined length) – (45° bend x 2) + length of span + width of beam + (0.3 x intermediate slab length)
Inclined length = 0.42D
D = Slab thickness – 2 side clear cover (top cover + bottom cover)
D = 150 – (2 x 25) = 100mm
Inclined length = 0.42 x 100 = 42mm
45° bend = 1d
d = diameter of bar
45° bend = 1 x 12 = 12mm
Intermediate slab
L = 3000mm
Therefore,
Length Of Main Bars (A2-B2) = (300/2) + (225/2) + (1 x 42) - (12 x 2) + 3100 + 300 + (0.3 x 3000) = 4580.5
Cutting length Of Main Bars for floor slab 2= 4.6m
STEP 2
No Of Bars Required For Cutting Main Bars
No of bars = (opp length/spacing) + 1
Opposite length of bar = 6000
Spacing = 150mm c/c as per given details
= (6000/150) + 1
No of bars = 41 nos
STEP 3
Total Length Of Bar Required For Main Bars Of Floor Slab 2
= no of bar x total length of bar
= 41 x 4.6= 188.6m = 190m
Total length of bar required for main bars of
Floor Slab 2 =190m of 12mm rod
STEP 4
Find Cutting Length Of Main Bars For Floor Slab 2 (C2-D2 direction)
Length Of Main Bars (C2-D2) = (depth of beam/2) + (width of beam/2) + (1 x inclined length) – (45° bend x 2) + length of span + (width of beam/2)
Inclined length = 0.42D
D = Slab thickness – 2 side clear cover (top cover + bottom cover)
D = 150 – (2 x 25) = 100mm
Inclined length = 0.42 x 100 = 42mm
45° bend = 1d
d = diameter of bar
45° bend = 1 x 12 = 12mm
Intermediate slab
L = 3000mm
Therefore,
Length Of Main Bars (C2-D2) = (300/2) + (225/2) + (1 x 42) - (12 x 2) + 6000 + (225/2) = 6393m
Cutting length Of Main Bars for floor slab 2= 6.4m
STEP 5
No Of Bars Required For Cutting Main Bars
No of bars = (opp length/spacing) + 1
Opposite length of bar = 3100
Spacing = 150mm c/c as per given details
= (3100/150) + 1
No of bars = 21.6666666667 = 22
STEP 6
Total Length Of Bar Required For Main Bars Of Floor Slab 2
= no of bar x total length of bar
= 22 x 6.4= 140.8m = 141m
Total Length Of Bar Required For Main Bars Of
Floor Slab 2 =141m Of 12mm Rod
STEP 7
Top Bar (Extra) (A2-B2): Top Bars Are Provided At The Top Of Main Bar As Critical Length (L/4) Area
Number of top bars = (Ly/4) / spacing + 1
Number of top bars = ((6000/4) / 150) + 1 = 11 nos of bars x 2 sides = 22 nos
Number of top bars = 22 nos of bars
Top Bar (Extra) (C2-D2): Top Bars Are Provided At The Top Of Main Bar As Critical Length (L/4) Area
Number of top bars = (Lx/4) / spacing + 1
Number of top bars = ((3100/4) / 150) + 1 =6.16 = 7 nos of bars x 2 sides = 14 nos
Number of top bars = 14 nos of bars
.
STEP 8
Total Length Of Bar Required For Top Bars Of Floor Slab 2 (A2-B2)
Length of top bars = Length of Opposite Bars (C2-D2)
Cutting Length Of top Bars = 3.325m
Total length of top bars = 3.325 x 14 = 46.55m
Total length of top bars of Floor Slab 2= 47 m of 8mm rod
Total Length Of Bar Required For Top Bars Of Floor Slab 2 (C2-D2)
Length of top bars = Length of Opposite Bars (A2-B2)
Cutting Length Of top Bars = 6.225m
Total length of top bars = 6.225 x 14 = 87.15m
Total length of top bars of Floor Slab 1= 88m of 8mm rod
RESULT,
FLOOR SLAB 1,
Main Bars = 185m Of 12mm Rod
Distribution Bars = 131m Of 8mm Rod
Top Bars = 63m Of 8mm Rod
FLOOR SLAB 2,
Main Bars = 190m of 12mm rod
Main Bars = 141m Of 12mm Rod
Top Bars = 88 m of 8mm rod (A2-B2)
Top Bars = 47m of 8mm rod (C2-D2)
TOTAL
12mm rod required = 516m
8mm rod required = 329m
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