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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