The column lap splice location must be selected from the structural analysis and approved reinforcement detailing. A column is not always a pure compression member: bending, seismic actions and frame behaviour can put longitudinal bars into tension. For ductile seismic frames, IS 13920:2016 adds specific requirements for splice location, splice percentage and transverse confinement. This article focuses on those seismic detailing requirements; ordinary lap length calculations are covered separately in our column lap length article.
What Is Lapping in Column?
A column lap splice overlaps two longitudinal bars so that force can be transferred through bond with the surrounding concrete. The required length depends on the calculated bar stress, concrete and steel properties, bar diameter, bond conditions and the governing code. Because a frame column can be subjected to combined axial load and bending, do not assume every column bar is always in compression. Use the design stress state and approved bar-bending schedule.
Why Is Lapping Zone Important in Columns?
The lapping zone in column determines where the overlaps should be placed to minimize structural weakness. Incorrect lapping can cause cracks, poor load transfer, and even failure at critical points. Proper lapping ensures uniform stress transfer between bars, structural safety and serviceability, compliance with IS 456:2000 and other building codes, and economic reinforcement detailing. A column carries high axial loads; hence, the position of lapping directly affects its performance and stability.
Column Lap Splice Location in Ductile Seismic Frames
For columns detailed under IS 13920:2016, lap splices of longitudinal bars are permitted only in the central half of the clear column height. They must not be placed inside the beam-column joint or within a distance of 2d from the face of the beam, where d is the relevant member depth as defined by the code. Not more than 50 percent of the bar area may be spliced at one section. These are seismic ductile-detailing provisions and must not be generalized to every column in every design situation.
For non-seismic or other design cases, splice position still depends on the force and moment distribution, governing code and structural drawings. Mid-height is not an automatic rule for all short or long columns, and a site team must not shift a splice without the structural designer’s approval.
Lap Length in Column as per IS Code
IS 456:2000, Clause 26.2.5.1, bases lap length on the development length for the relevant stress condition. For compression splices, the lap length is the development length in compression but not less than 24 times the nominal bar diameter. For flexural-tension and direct-tension splices, the code gives different requirements based on development length and minimum multiples of bar diameter. A column under combined axial load and bending may have bars in tension; therefore, do not select the compression rule simply because the member is called a column. Calculate the splice for the actual design action and apply any additional IS 13920 requirements.
Rules and Guidelines for Lapping in Columns
Apply the splice rules of the design code and project drawings. For ductile seismic columns detailed to IS 13920:2016, no more than 50 percent of longitudinal bar area may be spliced at one section; lap splices must lie in the permitted central region and be confined with closed links over the full splice length at the specified spacing. Cover, tie arrangement, link hooks, lap length and splice staggering must all match the approved details. Do not assume a fixed 40 mm cover or 1.3 lap-length offset is suitable for every column and code condition.
Types of Lapping in Column
1. Straight Lapping
The most common method where two bars overlap in a straight line for a required lap length. Suitable for compression members.
2. Cranked Lapping
Bars are bent or cranked before overlapping to increase the bond and anchorage. This is mainly used when the space is limited or in sloped members.
3. Welded Lapping
Bars are joined by welding instead of overlapping. It provides a strong connection but is costlier and requires skilled labor.
4. Coupler Connection
Modern high-rise structures often use mechanical couplers instead of lapping. They provide 100% strength transfer and avoid congestion of steel in heavily reinforced columns.
Common Mistakes in Lapping Columns
Common mistakes include lapping all bars at the same height, providing insufficient lap length, lapping near the beam-column junction, using corroded or unclean steel bars, improper binding, or ignoring staggered laps. Each of these errors can significantly reduce the column’s compressive and load-bearing capacity.
Practical Example of Lapping Zone in Column
Do not choose a lap position by applying a fixed distance such as “middle 1,000 mm” to every storey. First determine the clear column height and design actions; then check the applicable splice-location restrictions, joint exclusion zones, splice percentage and confinement provisions. For a ductile column under IS 13920:2016, the central-half rule and the required distance from the beam face govern. The lap length must be calculated for the bar stress condition and specified materials. The structural drawings should show the exact splice zone, lap length, stagger and link detailing.
Advantages of Proper Lapping Zone
Proper lapping enhances column stability and strength, ensures better load transfer between reinforcement bars, reduces stress concentration, improves durability, and minimizes crack formation. It also maintains continuity of reinforcement without using costly alternatives. Correct lapping detailing simplifies site work and reduces steel wastage.
When to Use Couplers Instead of Lapping
Mechanical couplers may be specified where lap splices are prohibited, impractical or cause reinforcement congestion. For ductile columns designed to IS 13920:2016, lap splices are not used for longitudinal bars larger than 32 mm; the specified mechanical splice must satisfy the relevant product standard and project acceptance requirements. Couplers do not automatically provide “full strength” unless their type, installation and test/qualification requirements are verified.
FAQs About Lapping Zone in Column
What is the minimum lap length for columns?
Under IS 456:2000, the compression lap is based on the development length in compression and must not be less than 24 times the bar diameter. Additional seismic detailing requirements may govern for ductile frames. The final value must be calculated for the actual stress condition and confirmed in the approved drawings.
Where should lapping not be done in a column?
For ductile seismic columns detailed to IS 13920:2016, lap splices are restricted to the central half of clear column height and must be kept out of the beam-column joint and the prohibited distance from the beam face. For other cases, location must follow the structural analysis and approved drawings; “mid-height” is not a universal instruction.
Can all bars in a column be lapped at the same level?
No, only 50% of the bars should be lapped at a single section to maintain column strength.
What happens if lapping is not properly done?
Improper lapping can lead to cracks, bond failure, and structural collapse under high loads.
Can we weld bars instead of lapping?
Yes, welding or mechanical couplers can be used as alternatives to lapping, especially for larger diameter bars or high-stress zones.
Conclusion
The lapping zone in column is a critical aspect of reinforced concrete construction. A properly designed and executed lap ensures safe stress transfer, durability, and compliance with structural codes. Always follow IS 456:2000 guidelines for lap length and placement, avoid congested or highly stressed areas, and ensure that laps are staggered. For heavy or high-rise structures, mechanical couplers can replace lapping for improved performance and reliability.