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Terry Collins
Sustainability consultant
Asked a question last year

What is the diffrence between lap length and development length?

What is the diffrence between lap length and development length?

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Lap length:

The reinforcement bars come in certain lengths. This length may not be sufficient.

For example,

In tall buildings, there may arise a situation where the length of the rebar in the column may not be sufficient. To meet the need, we will have to overlap the existing rebar with a new one. The length to which they are overlapped is called Lap length. Lap length should be provided in such a way that the load is transferred safely to the new bar. Here transfer is from steel to steel.

Development length:

What is the diffrence between lap length and development length?

The bond between steel and concrete is very crucial for the performance of a structure. The length of a member required to develop the full bond is called the anchorage length. The bond is measured by bond stress. In the above diagram, you can see the difference between a beam with and without development length.

Wilma Caldwell
Architectural technologist

Development Length

At the point when you have a reinforcement bar that is not required to convey the tensile forces, then the tension is zero at that section. At that point, you should build up the bar further with the grip between the steel and concrete that makes it a continuous structure. Presently we need to give this development length in such a case that we don’t. At that point, the bar doesn’t have any restrain, and we realize that if a part doesn’t have any restrain, then it doesn’t resist any forces. So this is the idea of development length.

Lap Length

At the time of placing steel for RC structures, if the length of the bar required to make a design length is insufficient, then the lapping of the bars is done.

Lap length is the min length that should be provided if two bars are joined together such that forces can be transferred safely.

LAP LENGTH IN TENSION.

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 should be greater than 15d or 20 cm.

LAP LENGTH IN COMPRESSION:

The lap length in compression should be equivalent to the development length in compression figured but be greater than 24d.

FOR DIFFERENT DIAMETER BARS:

Bars of different dia are to be fastened, and then the lap length is to be calculated with reference to smaller die bar.

Lap length is the length that is provided by overlapping the bars over each other so that they can easily transfer the load from one member to another.

acc. to IS456 lapping should not be done for bars greater than 32 mm dia bars

And acc. to IS 13920, the lapping should not be done for bars greater than 36mm dia bars and for joining couplers or welding should be done.

whereas,

development length is the length, which is provided by inserting reinforcement inside concrete so that is can provide enough strength against the tension forces applied to the bars. It is also called as anchorage length.

Dennis Holt
Entry level engineer

In case of Reinforced cement concrete (Rcc),
Lap length: when the bar of required length is not available for providing reinforcement in that case the extra length of overlapping required for transfer of load easily and to act as unison.it13 is lap length.
Development length: it is the extra embedded length. It is required for the development of bond and transfer the force from steel to concrete and make the structure continuous at junctions like beam and column.

For different diameters bars lap length, why lap length is calculated with reference to smaller dia ?
Smaller dia may be given less length and bigger dia give higher length
Why we take smaller dia to calculate lap length?

A “lap� or splice is designed to transfer the force from.one bar to the next in line. It stands to reason that the maximum force that needs to be transferred is limited by the smaller bar. Hence the lap is calculated for the smaller bar

Henry Newman
Water resource engineer

lap length is required when bars placed short of their required length (due to nonavailability of longer bars) need to be extended. lap length is to be provided to safely transfer the load.

Development length is provided to transfer the load from steel to concrete. It is also known as anchorage length.