Now, let us go through 7 basic rules while lapping the rebars in columns.
1. Lap length diameter:
For eg., if the upper bar of 16mm dia. is lapped with a lower bar of 20mm dia., and if the lap length is taken as 50d, then
Lap length 50d = 50 × 16mm = 800mm. 👈correct
Lap length 50d = 50 × 20mm = 1000mm 👈 incorrect
2. Lapping zone :
3. Staggered bar :
All the bars that are lapped should be staggered within zone B as shown in the above drawing. In any case, not more than 50% of rebars should be lapped in the same level. If all the column bars are lapped at the same level, it leads to the failure of the column.
4. Stirrup spacing :
The spacing of the stirrups in the lapping zone should be minimum when compared to the regular column c/c stirrup spacing.
If the designed regular spacing for the column stirrup is 175 c/c, then the spacing of stirrups in the lapping zone maybe 150 c/c or 125 c/c as according to the column design.
5. Welding the rebar :
As per IS code, if the bar diameter is greater than or equal to 36mm, then you should consider welding those bars instead of lapping. If welding is not possible, then you can lap these bars with an additional spiral of 6mm bar at the splice length.
6. Joggle length :
J = 6 ×Diameter of rebar
= 6 × 20mm = 120mm.
7. Rebar placing:
When we tye the rebars in the lapping zone, the joggled part of the bar should be placed over the inner surface of the bottom bar (as shown in the above drawing ) to get a uniform clear cover from the concrete surface.
If you tye the joggled portion of the rebar over the outer surface of the bottom bar, then the lapping zone invades the concrete cover area provided for the bars.
All information in good manner
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