Lap Length of Column, Beam and Slab

When the size of bars are short from their required length then lap length is necessary. When the diameter of the bar has to change along the length then the lap length is also required.

Purpose of using Lap Length

It is used to spread the axial force from the terminating bar to the connecting bar with the action in the junction. The effect of stress concentration should be minimized by using the splicing techniques, to keep the lapping locations away from the sections by the shear stresses.

Lap length according to the Indian Standard 456

The development length is 41d where d is the diameter of the bar. The lap length should be 2 Ld or 30d for direct tension. In this case, the straight length of the lapping bar should not be less than 15d or 20cm.

1. Type of lapping method
2. Lapping of bars
3. Welding of bars
4. Mechanical connection

Lapping of Bars

Lap splice is overlapped over a certain length and after that the axial force has to transfer from the terminating bar to the connecting bar through the mechanism of bond with the surrounding concrete.

Welding of Bars and Mechanical Connection

Welded splices and mechanical connection are suitable for large diameter bars. Welding splices need a special system to prevent the possibility of loss in strength because of welding heat. According to te indian standard code the design strength of welded splice should be limited to 80 percent of the design strength of the bar for the tension splices.

Lap Length of Column

The bars shall not be less than 12 mm in diameter. The minimum number of longitudinal bars provided at a column should be four in the rectangular columns and six in the circular columns.

The spacing of longitudinal bars should not exceed 300 mm.

Lap Length for Beams

The diameter of reinforcing bars should not overcome one-eighth of the total thickness of the slab.

The steel reinforcement at slabs should not be less than 0.15 percent of the total cross-sectional area. However, when high strength welded wire fabric is used, this value may be reduced to 0.12 percent.

Lap Length for Slabs

When the depth of the web at a beam overcomes 750mm, the side face reinforcement should be provided with the two faces. The total area of reinforcement should not less than 0.1 percent of the web area. It shall be spreaded equally on two faces at a spacing and it will not exceed 300 mm or web thickness.

The reinforcement in beams should be taken around the outermost tension and compression bars. The lap length for Beams is 60d.

Length of Lapping

Lap length is called the amount of overlap between the two bars. When stress of minimum bending is encountered then lapping is completed.

Sum Up

In this article we discuss Lap length, Purpose of using lap length, Type of lapping method, and Lap length of column, beam and slab. If readers like this article please share your valuable feedback with us.

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Lap Length of Column, Beam and Slab