What is Lapping Zones for Column and Beam | lapping Zones | Lceted -lceted LCETED INSTITUTE FOR CIVIL ENGINEERS

## Jun 2, 2021

A lap is when two pieces of reinforcing bar (rebar) are overlapped to create a continuous line of rebar. The length of the lap varies depend on concrete strength, the rebar grade, size, and spacing.

Lapping Zones for Beams and Columns

What is Lapping Zone for Columns:

Consider a column as shown in fig below. Let L be the length of the column under consideration. At a distance of L / 4 from both ends of the column, there is a tension zone. In such a zone, lapping should not be provided as this zone is subject to tension.

At the centre of the column, the bending moment is equal to zero, which indicates that the centre of the column is under minimum pressure. For this reason, it is desirable to provide lapping in this section of the column. Thus, the pressures in the middle of the column can be transferred efficiently and smoothly from one reinforcement bar to another.

What is Lapping Zone for Beams:

In the case of a beam, the upper part (top part) of the beam is subject to contraction, while the lower part (bottom part) of the beam is subject to both compression and tension. For this reason, the top reinforcement bar of the beam must be provided to the left of the middle of the beam. In this section, it is desirable to provide lapping so that the beam is not subjected to a negative moment in between.

On the other hand, to strengthen the bottom, it is useful to provide lapping at the ends of the beam. Lapping can also be provided at a distance of L / 4 from the face of the column but it must be noted that this is not the midpoint of the beam. It should also be noted that joints should not be given to lapping.

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