Calculating the cutting length of rebar is essential for determining the amount of reinforcement required for various structural elements like beams, columns, slabs, and footings. Here are the steps to calculate the cutting length of rebar for different types of bends and shapes:
Basic Steps for Calculating Cutting Length
- Identify the Shape of the Rebar:
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- Straight bar
- Bent bar (L-shape, U-shape, etc.)
- Stirrups or ties
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- Gather the Required Measurements:
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- Lengths of straight segments
- Angles and radii of bends
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- Use Standard Formulas for Bends:
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- For each bend, the additional length due to the bend (bend allowance) must be considered
1. Straight Bar:
The simplest case is a straight bar with no bends.
Cutting Length=Total Length of the Bar
Example:
- Length of the bar: 6 meters
Cutting Length=6 meters
2. L-Shape Bar (90-degree bend):
For a bar with a single 90-degree bend, we need to account for the bend allowance.
Given:
- Lengths:
A=500 mm, B=600 mm
- Diameter (D): 12 mm
Bend Allowance Calculation:
The bend allowance for a 90-degree bend is calculated using the formula:
Bend Allowance=π×D/2
Bend Allowance=π×12/2=18.85 mm
Total Cutting Length:
Cutting Length=A+B+2×Bend Allowance
Cutting Length=500+600+2×18.85=500+600+37.7=1137.7 mm
3. U-Shape Bar:
For a bar with two 90-degree bends (U-shape):
Given:
- Lengths: A=300 mm, B=400 mm, C=300 mm
- Diameter (D): 12 mm
Bend Allowance Calculation:
Same as above, for each 90-degree bend:
Bend Allowance=18.85 mm
Total Cutting Length:
Cutting Length=A+B+C+2×Bend Allowance
Cutting Length=300+400+300+2×18.85=300+400+300+37.7=1037.7 mm
4. Stirrups:
Stirrups are closed loop bars with multiple bends. Typically, they have 4 corners (90-degree bends).
Given:
- Lengths: A=200 mm, B=300 mm
- Diameter (D): 10 mm
Bend Allowance Calculation:
Same as above, for each 90-degree bend:
Bend Allowance=π×102=15.7 mm
Total Cutting Length:
Cutting Length=2×(A+B)+4×Bend Allowance
Cutting Length=2×(200+300)+4×15.7
Cutting Length=2×500+62.8=1000+62.8=1062.8 mm
5. Bent-Up Bar:
For bars bent up at an angle (commonly 45 degrees in beams):
Given:
- Lengths: A=1000 mm, B=1000 mm
- Inclination Angle: 45 degrees
- Diameter (D): 16 mm
Bend Allowance Calculation:
The bend allowance for a 45-degree bend is:
Bend Allowance=π×D/4
Bend Allowance=π×164=12.57 mm
Hypotenuse Calculation:
For the bent portion, calculate the hypotenuse of the right triangle:
Bent Length=Sqrt (Sq(A)+Sq(B))
Bent Length=1414.2 mm
Total Cutting Length:
Cutting Length=Bent Length+2×Bend Allowance
Cutting Length=1414.2+2×12.57=1414.2+25.14=1439.34 mm
Conclusion
These calculations ensure that you consider the additional length required due to bends, ensuring accurate cutting lengths for different shapes of rebar. Always refer to local codes and standards for specific requirements and modifications.
