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Overlapping of Steel Bar in The Different Concrete Mix

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.

Overlapping of Steel in The Different Grade of Concrete

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 12-m. If the length of the steel is used in construction more than ( 12-meter ) 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 60-d where “d” is the dia of steel. but if overlap length is not given 50-d value is assumed for example if dia of the bar is 16-mm then overlapping length= 50x 16 = 800-mm

Overlapping Is depends on

Overlapping is depending on these factor that is given below

  1. Tension Zone

  2. Compression Zone

  3. Rebar size

  4. Concrete cover

  5. 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 ( 12-mm ) dia steel will be if we assume the overlapping formula 50-d the overlapping length will be 50 x 12 = 600-mm. While for greater dia of the steel 16-mm 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 55-d while in ( M20 ) the overlapping is 46-d.

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Suppose pillar having a height 60-m. So at the side, we don’t have a 60-m 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 20-mm. By using the formula, the splice length of the steel bar will be 55 x 20 = 1100-mm & if the bar is in tension zone & 45 x 20 = 900-mm 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 20-mm. By using the formula, the splice length of steel bar will be 46 x 20 = 920-mm & if the bar is in tension zone & 37 x 20 = 740-mm 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 20-mm. By using the formula, the splice length of steel bar will be 39 x 20 = 780-mm and if the bar is in tension zone & 32 x 20 = 640-mm 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 36-mm 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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About Raja Junaid Iqbal

Hi My name is Raja Junaid Iqbal and i am Land Surveyor by Profession but I've specialized in the field of Q,S and land development. As Professional Surveyor I engaged my self in all over the Gulf since 14 years.

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