Table of Contents
In this article, we will discuss Lap Length Vs Development length.
1. Lap Length
Lap length can be defined as the length that is provided so as to allow the overlapping of two reinforcement bars thereby ensuring safe and efficient transfer of load from one bar to another.
When the reinforcement bars are placed; the length of a single reinforcement bar may not be sufficient.
In such a case, the required design length is achieved by overlapping two bars.
The lap length is thus provided to allow such lapping of the reinforcement bars side by side.
In other words, the length of overlap between the two reinforcement bars is the lap length.
Lap length may also be provided when the diameter of the reinforcement bar has to be changed along the length, particularly during the reinforcement of columns.
Such a process of overlapping the reinforcement bars side by side so as to obtain the desired design length is known as lapping.
The primary objective of providing the lap is to ensure efficient transfer of axial force from the terminating bar to the new connected bar along the same line of action in the junction.
When the two reinforcement bars have an equal diameter; the lap length can be calculated using the following formula:
Lap Length = 50 x D
Where,
D = diameter of the reinforcement bars
In case, the diameters of the reinforcement bars are not equal then the lap length is calculated using the value of the bar with a smaller diameter.
2. Development length
Development Length is provided to share the load from steel to concrete. Development Length is also named anchorage length.
According to IS 456:2000, the calculated tension or compression in any bar at any section shall be designed on each side of the section by keeping the proper development length or by an end anchorage. So that the member won’t be slipped out from the support.
Such length will be given in a continuous beam, cantilever slabs, and other critical joints (beam-column). It will be added as a bend where the restraining member is slim like an end beam as shown below (Ld).
3. Lap Length Vs Development length
The lap length vs development length is as follows:
| S.No | Lap Length | Development Length |
| 1. | Lap length is to be provided to safely transfer the load. | Development Length is provided to share the load from steel to concrete. |
| 2. | Lap Length is also known as splice length. | Development Length is also named anchorage length. |
| 3. | If the rebar needs to be expanded beyond that limit then enough lap length is to be given to safely transfer the load. | According to IS 456:2000, the calculated tension or compression in any bar at any section shall be developed on each side of the section by giving proper development length or by an end anchorage. So that the member won’t be slipped out from the support. |
| Read Also: IS Codes for Civil Engineering |
