Cutting Length Of Bent-Up Bars In Slab
As a site engineer, you need to calculate the cutting length of bars according to the slab dimensions and give instructions to the bar benders.
For a small area of construction, you can hand over the reinforcement detailing to the bar benders. They will take care of cutting length. But beware, that must not be accurate. Because they do not give importance to the bends and cranks.
They may give some extra inches to the bars for the bends which is totally wrong. So it is always recommended that as a site engineer, calculate the cutting length yourself.
In this article, we will discuss how to calculate the length of reinforcement bars of the slab. Let’s start with an example.
Example:
Where,
- Diameter of the bar = 12 mm
- Clear Cover = 25 mm
- Clear Span (L) = 8000
- Slab Thickness = 200 mm
- Development Length(Ld) = 40d
Calculation:
Cutting Length = Clear Span of Slab + (2 x Development Length) + (2 x inclined length) – (45° bend x 4) – (90° bend x 2)
Inclined length = D/(sin 45°) – dD/ (tan 45°) = (D/0.7071) – (D/1)= (1D – 0.7071D)/0.7071= 0.42 D
As you can see, there are four 45°bends at the inner side (1,2,3 & 4) and two 90° bends ( a,b ).
45° = 1d ; 90° = 2d
Cutting Length = Clear Span of Slab + (2 X Ld) +(2 x 0.42D) – (1d x 4) – (2d x 2) [BBS Shape Codes]
Where
- d = Diameter of the bar.
- Ld = Development length of bar.
- D = Height of the bending bar.
In the above formula, all values are known except ‘D’.
So we need to find out the value of “D”.
D = Slab Thickness – (2 x clear cover) – (diameter of bar)
= 200 – (2 × 25) – 12
= 138 mm
Now, putting all values in the formula
Cutting Length = Clear Span of Slab + (2 x Ld) +(2 x 0.42D) – (1d x 4) – (2d x 2)
= 8000 + (2 x 40 x 12) +(2 x 0.42 x 138) – (1 x 12 x 4) – (2 x 12 x 2)
∴ Cutting Length = 8980 mm or 8.98 m.
So for the above dimension, you need to cut the main bars 8.98 m in length.
FAQ
How to calculate cutting length of bent up bar?
Cutting Length of top bar= Clear span of beam + development length (Ld) on 2 sides – clear cover on 2 ends. Cutting Length of bottom bar= Clear span of beam + development length (Ld) on 2 sides – clear cover on 2 ends
What is the length of a bent up bar bent at 45 degrees?
The length of the bent-up bar for 30°, 45°, and 60° are 0.3D, 0.45D, and 0.6D respectively
How to calculate bend deduction length of bar?
For example, if the diameter of the rebar is 12 mm, then the deduction for a 45-degree bend would be 12 mm (1 x 12 mm). This means that the length of the rebar needed for the bend would be 12 mm shorter than the length required for a straight section of the same rebar
How to calculate bar length?
Calculate the Length of Bar. Number of Bars = Opposite Length / Spacing + 1 , Number of Stirrups = Actual Length / Spacing + 1. Total Length of Bar = Length of Bar x Number of Bars. Check the Diameter of Bar
What is 0.42 d in crank bar?
∴ For 45-degree cranked or bend up bar, the inclined length of crank = 0.42 d
What is the distance between bars in a slab?
The maximum diameter of bar used in slab should not exceed 1/8 of the total thickness of slab. Maximum spacing of main bar is restricted to 3 times effective depth or 300 mm whichever is less. For distribution bars the maximum spacing is specified as 5 times the effective depth or 450 mm whichever is less
