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Importance of perfect lapping of steel bars in RCC construction works

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The overlapping of steel bars in several concrete mix should be perfect in R.C.C construction works since splicing of steel is applied to transmit all the stresses from one bar to another bar.

The length of the lapping varies in several concrete mixes as different concretes contain various crushing strength.

In job site, a steel bar is provided with a length 6 to 12 meter. Therefore, when the length is over 12 m, the steel bar should be overlaid in order that the splice length of the steel bar is dependent on the followings :-

1. The diameter of the steel bar to be applied.
2. Amount of stresses formed in the bars.
3. The type of concrete to be utilized (M15, M20 etc.)

Assume, there is a column with a height 200 ft, and it is not possible to provide a 200 ft long one single bar at the site, therefore, the bar should be overlapped to attain the total length of the column.

OVERLAPPING RESTRICTION:

1. The lapping should not be arranged over 36 mm diameter bars as those diameter bars can’t transmit the stresses from one bar to another bar and also the alignment of the column bar is also changed with the lap on these bars.

2. The lapping of the steel bars is not also arranged in high shear force zones and it should be arranged at that zone where shear force will be minimum.

LAPPING OF SEVERAL CONCRETE MIX:

Normally, there are three types of zone like compression zone, neutral zone and tension zone. In various zones, various splice length of the steel bars are provided. In R.C.C construction, 3 types of concrete mix M15, M20, and M25 are commonly used.

Also Read: Importance of Mild Steel Bars in Cement Concrete

IN M15 CONCRETE MIX: In M15 grade of concrete, the ratio of concrete mix is 1 : 2: 4, it signifies that 1 part of cement, 2 part of sand and 4 part of aggregates.

Tension zone : Compression Zone.
Fe 250 – 55 Ø - Fe 250 – 45 Ø
Fe 415 – 57 Ø - Fe 415 – 47 Ø
Fe 500 – 68 Ø - Fe 500 – 57 Ø

Tension zone is formed at the bottom of the Beam, Slab etc and the compression zone is developed at the top. In the tension zone, steel bars combat elongation etc.

IN M20 CONCRETE MIX: In M20 grade of concrete, the ratio of concrete mix is 1 : 1.5: 3, it signifies that 1 part of cement, 1.5 part of sand and 3 part of aggregates.

Tension zone : Compression Zone.
Fe 250 – 46 Ø - Fe 250 – 37 Ø
Fe 415 – 47 Ø - Fe 415 – 38 Ø
Fe 500 – 57 Ø - Fe 500 – 46 Ø

IN M25 CONCRETE MIX: In M25 grade of concrete, the ratio of concrete mix is 1 : 1 : 2, it signifies that 1 part of cement, 1 part of sand and 2 part of aggregates.

Tension zone : Compression Zone.
Fe 250 – 39 Ø - Fe 250 – 32 Ø
Fe 415 – 41 Ø - Fe 415 – 33 Ø
Fe 500 – 49 Ø - Fe 500 – 39 Ø

Here Ø denotes the diameter of the bar. Suppose, a steel bar Fe 500 and concert mix M25 are used in concrete. The diameter of the bar is 10 mm. The splice length of the steel bar should be 49 x 10 = 490 mm when the bar remains in tension zone and 39 x 10 = 390 mm when the bar remains in the compression zone.

Importance of perfect lapping of steel bars in RCC construction works