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Lap Length / Lapping Length Of Steel Bars

Lapping is very important for reinforcement usually done to increase the length of bar. In this article, I will discuss lap length with example.


Read: What Is Development Length Of Bar?

What Is Lap Length?

During placing the steel in RC structure if the required length of a bar is not sufficiently available to make a design length then lapping is done. Lapping means overlapping of two bars side by side to achieve required design length. (Refer to below image)

LAP LENGTH

Suppose, we need to build a 100 feet tall column. But practically 100 ft long bar is not available and it is also not possible to cage. Therefore we need to cut the bars in every second story. Now, we need to transfer the tension forces from one bar to the other at the location of discontinuity of bar. So we have to provide the second bar closed to the first bar that is discontinued and overlapping is to be done. The amount of overlapping between two bars is known as lap length.

In case of RCC structure, if the length of reinforcement bars need to be extended, splicing is used to join two reinforcement bars for transferring the forces to the joined bar.

Lap Length Formula:

Lap length in Tension:

The lapping length including anchorage value of hooks shall be

1. For flexural tension – Ld or 30d whichever is greater.

2. For direct tension – 2Ld or 30d whichever is greater.

The straight length of lapping shall not be less than 15d or 20 cm.

Lap length In Compression:

The lapping length in compression shall be equivalent to the development length in compression computed but not less than 24d.

For Different Diameter Bars:

In case of bars having different diameter are to be spliced, the lapping length is calculated on the basis of smaller diameter bar.

Lap Splices:

Lap splices should not be used for the bars having larger dia than 36 mm. In that case, welding should be done. But if welding is not practicable then lapping may be permitted for the bars larger than 36 mm dia. Additional spirals should be provided around the lapped bars.

Lapping length For Concrete Of 1:2:4 Nominal Mix:

Lap length in tension (for plain Grade-1 MS bar) including anchorage value is 58d. So eliminating the anchorage value the lap length = 58 – 2*9d = 40d

where 9d = hook allowance of bars up to 25 mm and k=2

Lap length for compression bar is equal to the value of development length calculated i.e 43.5d.

Lap length Of Column, Bem & Slab (M20 Concrete):

Columns – 45d

Beams – 60d

Slabs – 60d.

So if we use 20 mm dia column bars, we have to provide a minimum lap of 45 * 20 = 900 mm.

Also Read – Reinforcement Details In Beams And Slabs
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Comments ( 21 )

  1. I have already subscribed. And I used to raed your all pages . Its very knowledgeable one. Give or updates more pictures so that we can more imagine it.

  2. loweh elvis fonyuy
    May 15, 2017 at 12:37 pm

    i missed out on developing length, remainder please.

  3. I have missed your development length Pls update

  4. But some other constructions like metro in Hyderabad, laping one over another by use threading.there how to design.

  5. Pls suggest how to remove the production of each labour engage in construction activities

  6. I have already subscribed. And I used to raed your all pages . Its very knowledgeable one. Give or updates more pictures so that we can more imagine it.

  7. Lap length of steel in M35 grade of concrete

  8. is there different lapping lengths for different mixes of concrete, if so let me know??

  9. Do lap length differ if the grade of concrete changes?

  10. Why lapping is not allowed when dia of bar exceeds 35mm?

  11. Manish Kumar Singh
    January 31, 2018 at 3:42 am

    Sir please tell about these…
    When two different size of bars are spliced then lap length shall be calculated on the basis of smaller dia. Why ?

  12. is there a lapping length calculation difference using by welding the bar or just simply tying with tie wire?

  13. very helpfull information i am getting

  14. Pls tell me..
    Mini. Lap lenght for teinfo. Bar according to as per irc112-2011

  15. this website is actually very important and i have used it for many years!

  16. For laps in distribution reinforcement whether same formula to be followed at par with main reinforcement?

  17. Sir pls tell about these..
    Steel structure beam,column, slab lapping formula

  18. This website is very helpful and supportive for me and my work. Thanks for developing team…

  19. Can you tell the tolerance limit in lap length

  20. I want how to calculate collum latteral length

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