lapping of bars | Lapping zone in beam and column as per IS codes | IS 456:2000 | IS 13920:1993 | SP 34 - 1987

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Lapping of bar:


Lapping of bar: Additional length of bar required to transfer stress from one bar to another bar.



Points to be considered while lapping: as per (IS 456:2000 & SP 34 - 1987)

1. Lapping should be avoided for bars whose diameter is greater than 36mm. For larger diameter bars welding is preferable. In cases where welding is not practicable, additional spirals should be provided around lapping.
2. Lap length including anchorage value of hooks for bars in flexural tension shall be Ld  or 30Ø whichever is greater. The straight length of the lap shall not be less than 15Ø or 200mm
3. The lap length in compression shall be equal to the development length in compression or 24Ø whichever is greater.
4. When bars of two different diameters are to be spliced, the lap length shall be calculated on
the basis of diameter of the smaller bar.
5. Lapping should be avoided in tension zone.
6. Stirrups should be provided at closer distances in lapping zone.


Lapping zone in column: as per (IS 13920:1993)
1. Lapping is always provided at mid – height of column.
2. Lapping should be provided at alternate bars.
3. Lapping should not be provided parallelly.
4. Lapping should be at a distance of L/4 from supports.
5. Lapping is avoided in tension zone.

Lapping zone of column

Enlarged portion of mid - height of column
 
Enlarged portion near support


Typical example of column with cranked bar provided in lapping zone:
Lapping Zone in Beam: as per (IS 13920:1993)

1. Lapping is avoided at mid span for bottom bars of beam because of large deflections at mid span.
2. For top bars of beam lapping is done at the center of the beam i.e at a distance of L/3 at the center.
3. For bottom bars of beam lapping is done at a distance of  L/4 from the inner face of column on both sides as mentioned in below figure.



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