Let us now calculate the cutting length of a crank bar (bent-up bar) from the below-given data.
Given data:
Clear span between the columns = 3500mm.
Slab thickness = 150 mm.
Clear cover = 25mm.
Rebar diameter d = 12mm.
Development length Ld = 40d
If sometimes development length is not given in the drawing, you can assume it as 40d for the slab.
Cutting length of the crank bar
= {clear span +( 2nos. × development length )+(2 nos.× extra crank length) - [2nos.× 90° bend + 4nos.× 45° bend]}
= {3500mm +( 2×40d) +( 2 × 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 diagram.
= {3500mm + (2 × 40 × 12mm ) + ( 2 ×0.42D ) - [2nos. ×2 ×12mm + 4nos.× 1×12mm.]}
Here, D = slab thickness - ( top & bottom clear cover + bar diameter )
= 150mm - (2nos × 25 mm. +12mm )
= 150mm - 62 mm
D = 88 mm.
Total Cutting length
={ 3500 mm + 960mm +(2 × 0.42 × 88mm) - [ 48mm + 48mm ]}
= {3500 mm + 960mm + 73.92 mm - 96mm}
= 4533.92 mm - 96 mm
=4437.92 say 4438 mm.
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.
Thank you for going through this article❤. Have a good day😄
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