Calculating the cutting length of the crank bar in a slab / Cutting length of bent-up bar in a slab.

 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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