Column lapping zone as per IS code is explained one by one in this tutorial as follows
1. Why need to do a lap in the steel bar?
-Standard manufactured length of the bar is 12 meter, if we
need more length than 12m have to lap the bar
-For work like column steel, beam etc on-site, not possible
to use directly 12 m bar so as per requirement we need to cut the bar and lap
as per need
-Lap is not provided bar diameter more than 36mm
2. What is the lap length/overlapping zone?
-The objective of the lap is to safely transfer the load or stress
from one bar to another bar
-Lap length provided for maintaining the continuity of bars
in structure
3. How much lap length should be provided in a column?
-As per is 456 2000 lapping length should not be less than
75mm
- Generally, we take 24d to 56d lapping length where d-diameter
of bar and this distance is depending on grade of steel, grade of concrete and
diameter of steel, we are using in column
4. Why lapping is provided in the centre?
-Lapping should be provided at the centre of the column
because bending moment at the midpoint is zero so try to lap at this height
-Due to maximum stress at the top we can’t provide lap at
column beam slab joint
-As per IS Code length from top of column, beam bottom x/4 and from slab top, x/4 distance lapping is not provided because it is tension zone, Maximum Bending moment is experiences
-At centre x/2 distance lapping is provided, this x/2 distance is Lapping Zone in Column where we can provide lapping in staggered form.
Photo shows Bending Moment diagram of Column
5. Why we are providing lap in staggered form?
-lapping should not be be given at same point because
buckling may occur in column
-Lateral ties should be provided closely paced in lapping
zone
-Staggered lapping means all bars should not be lapped at
same level max. 50% bars which can be lap one level
-lapping length staggered centre to centre distance of the
lap is not less than 1.3 times of lap length Ld (50x Dia of bar), that is 1.3xLd
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