All about civil construction knowledge- PARAM VISIONS

How to calculate rebar cutting length in a beam with lapping? / Calculating the cutting length of rebar's for lapping in a beam.

Let us calculate the cutting length of the top & bottom bar of a beam as shown below.






Given data:

Beam width = 300mm.

Beam depth = 550mm.

Column width = 400mm.

Effective length L1= 6m = 6000mm.

Effective length L2 = 5.5m. = 5500mm.

Top reinforcement = 20mm ∅ - 2nos.

Bottom  reinforcement = 25mm ∅ - 2nos.

Clear cover = 30mm.

Development length Ld = 50d.

Lapping length = 50d.


Calculation:

A. Cutting length:

1. Bottom bar:

 Total length of the bottom bar

= [L1 + L2+ (2nos. × development length) - (2nos. × 1/2 × column width) - ( 2nos. × 90° bend)]

= [6000mm. + 5500mm. + (2nos. × 50d) - (2nos. × 1/2 × 400mm.)  - ( 2nos. × 2d)]

= [6000mm. + 5500mm. + (2nos. ×50 × 25mm.) - (2nos. × 1/2 × 400mm.)- ( 2nos. × 2× 25mm.)]

= [ 11500mm. +  (2500mm.) - (400mm.)- ( 100mm.)]

13,500mm.

= 13.50m  > 12m.

The total length (13.50m.) is greater than the available bar length(12m.). Hence there will be lapping in the bar.


Before proceeding further, Go through the article 👇

👀. Where to provide lapping in beam reinforcement?

So that you will understand the correct position of lapping in the beam & the basic rules of lapping.


a. Cutting length of the part-1 of the bottom bar

= [L1 + (development length) + (half of lap length ) - (1/2 × column width) - ( 1no × 90° bend)]

= [ 6000mm. + (50d) + ( 1/2 × 50d) - (1/2 × 400mm.) - ( 2d)]

= [ 6000mm. + (50 × 25mm  ) + ( 1/2 × 50 × 25mm. ) - (1/2 × 400mm.) - ( 2 × 25mm.)]

= [ 6000mm. + (1250mm  ) + ( 625mm. ) - ( 200mm.) - (50mm.)]

= 7625mm.

= 7.625m.


b. Cutting length of the part-2 of the bottom bar

= [L2 + (development length) + (half of lap length ) - (1/2 × column width) - ( 1no × 90° bend)]

= [ 5500mm. + (50d) + ( 1/2 × 50d) - (1/2 × 400mm.) - ( 2d)]

= [ 5500mm. + (50 × 25mm  ) + ( 1/2 × 50 × 25mm. ) - (1/2 × 400mm.) - ( 2 × 25mm.)]

= [ 5500mm. + (1250mm  ) + ( 625mm. ) - ( 200mm.) - (50mm.)]

= 7125mm.

= 7.125m.


Check:

[Total length of bar + lap length ] = [cutting length of (part-1 + part-2)]

[13500mm + 50d] = [7625mm. +7125mm.]

[13500mm. + 50 × 25mm.] = 14750mm.

14750mm = 14750mm.  



2. Top bar:

 Total length of the top bar

= [L1 + L2+ (2nos. × development length) - (2nos. × 1/2 × column width) - ( 2nos. × 90° bend)]

= [6000mm. + 5500mm. + (2nos. × 50d) - (2nos. × 1/2 × 400mm.)  - ( 2nos. × 2d)]

= [6000mm. + 5500mm. + (2nos. ×50 × 20mm.) - (2nos. × 1/2 × 400mm.)- ( 2nos. × 2× 20mm.)]

= [ 11500mm. +  (2000mm.) - (400mm.)- ( 80mm.)]

13,020mm.

= 13.02m  > 12m

The total length (13.02m.) is greater than the available bar length(12m.). Hence there will be lapping in the bar.


a. Cutting length of the part-1 of the top bar 

= [L1 +( L2/2) + (development length) + (half of lap length ) - (1/2 × column width) - (90° bend)]

= [ 6000mm. + (5500mm.÷ 2) + (50d) + ( 1/2 × 50d) - (1/2 × 400mm.) - ( 2d)]

= [ 6000mm. + (2750mm.) + (50 × 20mm  ) + ( 1/2 × 50 × 20mm. ) - (1/2 × 400mm.) - ( 2 × 20mm.)]

= [ 6000mm. + (2750mm.) + (1000mm  ) + ( 500mm. ) - ( 200mm.) - (40mm.)]

= 10,010mm.

= 10.010m.


b. Cutting length of the part-2 of the top bar 

= [( L2/2) + (development length) + (half of lap length ) - (1/2 × column width) - (90° bend)]

= [ (5500mm.÷ 2) + (50d) + ( 1/2 × 50d) - (1/2 × 400mm.) - ( 2d)]

= [ (2750mm.) + (50 × 20mm  ) + ( 1/2 × 50 × 20mm. ) - (1/2 × 400mm.) - ( 2 × 20mm.)]

= [(2750mm.) + (1000mm  ) + ( 500mm. ) - ( 200mm.) - (40mm.)]

= 4,010mm.

= 4.010m.


Check:

[Total length of bar + lap length ] = [cutting length of (part-1 + part-2)]

[13020mm + 50d] = [10010mm. +4010mm.]

[13020mm. + 50 × 20mm.] = 14,020mm.

14,020mm = 14,020mm.  


Thank you for going through these calculation steps. Have a good day 😄.

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