Overlapping of Steel in The Different Grade of Concrete
The acceptable overlapping of the steel in the different concrete mix is very important because in the construction of ( R.C.C ) overlapping of the steel bars is very necessary.
Before going to determine the overlapping of steel let’s clear the given simple concepts.
Why Overlapping is provided. ?
The lapping of the rebar is Most important because splicing of the rebar is provided to transfer the stresses from 1 bar to other bar. The length of the overlapping is different in different concrete mixes because all concrete has not the same strength it has different strength.
Steel present in market in the specific length means 12m. If the length of the steel is used in construction more than ( 12meter ) then desirable or given by designer overlapping length will be provided to transfer the load safely.
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In the construction of ( R.C.C ) structure if the required length of the steel is not available during placing of steel then overlapping is done. Usually overlapping length is between 40 to 60d where “d” is the dia of steel. but if overlap length is not given 50d value is assumed for example if dia of the bar is 16mm then overlapping length= 50x 16 = 800mm
Overlapping Is depends on
Overlapping is depending on these factor that is given below

Tension Zone

Compression Zone

Rebar size

Concrete cover

Grade of concrete
1 . Tension Zone
In tension zone the overlapping is provided at the ends where shear force is 0. The overlapping is provided in the minimum shear force area.
2 . Compression Zone
In compression zone the overlapping should be provided at the center where shear force is 0.
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3 . Rebar size
The overlapping is depending on the rebar size it means if the dia of the steel is more than the overlapping length will be more while if the size of steel is less than the length of overlapping will less. For example, the overlapping for ( 12mm ) dia steel will be if we assume the overlapping formula 50d the overlapping length will be 50 x 12 = 600mm. While for greater dia of the steel 16mm the overlapping length will be 50 x 16 = 800 mm
4 . Concrete Cover
Overlapping is also depending on the concrete cover
5 . Grade of Concrete
If the grade of the concrete is good, then length of overlapping is less for example in ( M15 ) the overlapping is 55d while in ( M20 ) the overlapping is 46d.
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Suppose pillar having a height 60m. So at the side, we don’t have a 60m long 1 single bar we must overlape the steel to get the total length of column.
Overlapping of Different Concrete Mix
we have 3 zones that is Compression Zone, Tension zone & Neutral zone. In different zones, there is different splice length of the steel is use. In construction of ( R.C.C ) there is mostly 3 types of the concrete mix is used that is M15, M20, & M25.
Overlapping in ( M 15 ) Concrete Grade
M 15 concrete mix the material is used in the ( 1 : 2 : 4 ) proportion it means one part of cement, second part of sand and four part of aggregates.
Tension Zone 

S.No 
Steel Type 
Overlapping 
1 
Fe250 
55d 
2 
Fe415 
57d 
3 
Fe500 
68d 
Compression Zone 

S.No 
Steel Type 
Overlapping 
1 
Fe250 
45d 
2 
Fe415 
47d 
3 
Fe500 
57d 
Tension is the creating at the bottom of the Beam, Slab & the compression is create at the top. In the tension zone steel is used to resist elongation.
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Where d is the diameter of the bar. Suppose we are using the steel bar Fe 250 & concert mix M15. The diameter of the bar is 20mm. By using the formula, the splice length of the steel bar will be 55 x 20 = 1100mm & if the bar is in tension zone & 45 x 20 = 900mm if the bar is in the compression zone.
Overlapping in ( M 20 ) Concrete Mix
M 20 concrete mix the material is used in the ( 1 : 1.5 : 3 ) proportion it means one part of cement, 1.5 part of fine aggregate and three part of coarse aggregates.
Tension Zone 

S.No 
Steel Type 
Overlapping 
1 
Fe250 
46d 
2 
Fe415 
47d 
3 
Fe500 
57d 
Compression Zone 

S.No 
Steel Type 
Overlapping 
1 
Fe250 
37d 
2 
Fe415 
38d 
3 
Fe500 
46d 
Where d is the diameter of the bar. Suppose we are using the steel bar Fe 250 & concert mix M20. The diameter of the bar will be 20mm. By using the formula, the splice length of steel bar will be 46 x 20 = 920mm & if the bar is in tension zone & 37 x 20 = 740mm if the bar is in the compression zone.
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Overlapping in ( M 25 ) Concrete Mix
M 25 concrete mix the material is used in the ( 1 : 1 : 2 ) proportion it means one part of cement, one part of fine aggregate & two part of coarse aggregates.
Tension Zone 

S.No 
Steel Type 
Overlapping 
1 
Fe250 
39d 
2 
Fe415 
41d 
3 
Fe500 
49d 
Compression Zone 

S.No 
Steel Type 
Overlapping 
1 
Fe250 
32d 
2 
Fe415 
33d 
3 
Fe500 
39d 
Where d is the diameter of bar. Suppose we are using the steel bar Fe 250 & concert mix M25. The diameter of the bar will be 20mm. By using the formula, the splice length of steel bar will be 39 x 20 = 780mm and if the bar is in tension zone & 32 x 20 = 640mm if the bar is in the compression zone.
Overlapping Limitations
The overlapping will not be used if the dia of the steel is more than 36mm because those diameter steel doesn’t transfer the stresses from 1 steel to other steel & further the aligning of the column steel is also affected overlapping of the steel should not be used in high shear force zones & it should be used at that zone where shear force will be less.
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