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# Overlapping of Steel Bar in Different Concrete Mix

## Overlapping of Steel in Different Grade of Concrete:

The acceptable overlapping of steel in the different concrete mix is very important because in the construction of RCC overlapping of steel bars is very necessary.

Before going to determine the overlapping of the steel lets clear the given simple concepts.

### Why overlapping is provided?

The lapping of the rebar is very important because splicing of rebar is provided to transfer the stresses from one bar to other bar. The length of the overlapping is different in different concrete mixes because all concrete has not same strength it has different strength.

Steel present in market in a specific length means 12 m. If the length of 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.

In construction of RCC structure if the required length of 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 the steel. but if overlap length is not given 50d value is assumed for example if dia of bar is 16 mm then overlapping length= 50x 16 = 800mm

#### Overlapping depends on:

Overlapping is depending on these factor that is given below:

• Tension Zone
• Compression Zone
• Rebar size
• Concrete cover
##### Tension Zone:

In tension zone the overlapping is provided at the ends where shear force is zero. The overlapping is provided in minimum shear force area.

##### Compression Zone:

In compression zone the overlapping should be provided at the center where shear force is zero.

##### Rebar size:

The overlapping is depending on the rebar size it means if the dia of 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 = 600 mm. While for greater dia of steel 16 mm the overlapping length will be 50 x 16 = 800 mm

##### Concrete Cover:

Overlapping is also depending on concrete cover

If the grade of concrete is good, then length of overlapping is less for example in M15 the overlapping is 55d while in M20 the overlapping is 46d.

Suppose pillar having a height 60 m. So at the side, we don’t have a 60 m long one single bar we must overlap the steel to get the total length of the column.

###### Overlapping of Different Concrete Mix:

we have three zones that is Compression Zone, Tension zone and Neutral zone. In different zones, there is different splice length of the steel is use. In construction of RCC there is mostly three types of concrete mix is used that is M15, M20, and M25.

Overlapping in M 15 Concrete Grade:

M 15 concrete mix the material is used in the 1 : 2 : 4 proportion it means 1 part of cement, 2 part of sand and 4 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 creating at the bottom of the Beam, Slab and the compression is create at the top. In the tension zone steel is used to resist elongation.

Where d is the diameter of the bar. Suppose we are using a steel bar Fe 250 and 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 and if the bar is in tension zone and 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 1 part of cement, 1.5 part of fine aggregate and 3 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 a steel bar Fe 250 and concert mix M20. The diameter of the bar will be 20 mm. By using the formula, the splice length of the steel bar will be 46 x 20 = 920 mm and if the bar is in tension zone and 37 x 20 = 740 mm if the bar is in the compression zone.

Overlapping in M 25 Concrete Mix:

M 25 concrete mix the material is used in the 1 : 1 : 2 proportion it means 1 part of cement, 1 part of fine aggregate and 2 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 the bar. Suppose we are using a steel bar Fe 250 and concert mix M25. The diameter of the bar will be 20 mm. By using the formula, the splice length of the steel bar will be 39 x 20 = 780 mm and if the bar is in tension zone and 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 steel is more than 36 mm because those diameter steel doesn’t transfer the stresses from one steel to other steel and further the aligning of the column steel is also affected overlapping of steel should not be used in high shear force zones and it should be used at that zone where shear force will be less.