What Is Lap Length? Lap Length of Column, Beam, and Slab

In this article, we will describe the lap length of some popular structural members such as column, beam, and slab.

Let’s get started!

First, let’s get some idea about what is lap length!

What Is Lap Length?

The standard size of the reinforcement bar is 12 meters. This is the length of the reinforcement bar that we get from the factory.

When we construct structural members more than 12-meter length, we needed to overlap two reinforcement bars together to uniformly distribute the load. This overlap length is known as lap length.

The primary aim of the lap length is to safely transfer the axial force effectively from the terminating bar into the connecting bar with the same line of action in the junction.

Lap Length of Column:

Lap length of column = 45d.

Where d is the diameter of the reinforcement bar.

Here are points to remember while calculating the lap length of the column.

• The reinforced bars shall not be less than 12 millimetres in diameter.
• The minimum number of longitudinal reinforced bars provided at a column shall be 4 in rectangular columns and 6 in circular columns.
• The spacing of longitudinal reinforced bars measured along the periphery of the column shall not exceed 300 millimetres.

Lap Length of Beam:

Lap length for Beam = 60d

Some key points to remember while calculating the lap length of a beam:

1. In case of the web at a beam exceeds 750 millimeters, side face reinforcement shall be provided along with the two faces.
2. The total area of such reinforcement should be not less than 0.1 percent of the web area and shall be distributed equally on two faces at a spacing not exceeding 300 millimeters or web thickness, whichever is less.
3. The transverse reinforcement in beams shall be taken around the outer-most tension and compression bars. In T-beams and I-beams, such reinforcement shall pass around longitudinal bars located close to the outer face of the flange.

Lap Length of Slab:

Lap length for Slab = 60d.

Some important points to remember while calculating lap length of slab:

1. The diameter of reinforced bars shall not exceed 1/8th of the total thickness of the slab.
2. The mild steel reinforcement in both directions at slabs shall not be less than 0.15 percent of the total cross-sectional area of the concrete slab. However, this value may be decreased to 0.12 percent when high-strength deformed bars or welded wire fabric are utilized.

Note: In some construction, lap length is considered 1 meter irrespective of diameter.