Useful information on reinforcement lapping zone & lapping length in column
This construction video tutorial provides detail information on reinforcement lapping zone and lapping length for column.
A lap is essential when two pieces of reinforcing bar (rebar) are overlapped to create a constant line of rebar. The length of the lap is dependent on the concrete strength, the rebar grade, size, and spacing.
The purpose of providing lap is to transfer load from one bar to another bar aside from maintaining continuity. The placement of lap is influenced by the bending moment of the column.
Lap length means the length of the overlap of bar require to safely transfer stress from one bar to another. Lap length differs according to tension and compression zones and mostly depends on grade of concrete and steel. Development length stands for the length of the bar required to transfer stress from steel to concrete.
Rebars in column are lapped at around 5 feet from the story.
As indicated by I.S. 13920 Vertical bars of Columns should have been lapped in regular zone (Mid-height ) only and it should be staggered i.e. not in excess of 50% of bar should be lapped at one section. Besides, minimum clear vertical distance among lapped bars should have been 0.25 times lap length.
To gather more clear conception, go through the following video tutorial.
Video Source: Deepak Kumar