What is Lap Length?
Important Point
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 also required when the bar diameter has to be changed along the length (as is sometimes done in columns).Branding
The purpose of ‘Lap’ is to transfer the axial force effectively from the terminating bar into the connecting bar with this same line of action in the junction.
This invariably introduces stress concentrations at this surrounding concrete. These effects should be minimized by
- Using proper splicing techniques.
- Keeping these lapping locations away from sections with high flexural/shear stresses. and
- Staggering the locations of splicing at the individual bars of a group (as typically in a column).
When splicing in such situations becomes unavoidable, special precautions need to be employed, such as
- Increasing the length of the lap length (In lap splices and lap welding)
- Using spirals or closely-spaced stirrups around the length of the stirrups.
Also, read: What Is Guniting, Set Guniting Systems , Advantage, Disadvantage
Type of Lapping Method:
- The lapping of bars (lap splice)
- Welding of bars (welded splice)
- Mechanical connection.
What is Development Length?
The development length is defined as the length of the bar required on either side of the section under consideration. To develop the required stress in steel at that section through a bond.
The calculated tension or compression in any bar at any section shall be developed on the peach side -of the section by an appropriate development length or end anchorage or by a combination thereof. as per IS code 456-2000, Page-42, Cl. 26.2
The preceding discussion suggests this concept of development length of a reinforcing bar.
The development length is defined as the length of embedment necessary into developing the full tensile strength of this bar, controlled by either pullout or splitting.
With reference to as per below fig, the moment, and therefore the steel stress, is evidently maximum in point a (neglecting the weight of the beam) and zero at the supports.
If the bar stress is f, at a, then the total tension force Abl, must be transferred from the bar to this concrete in the distance 1 by bond forces.
To fully develop this strength of the bar, the distance one must be at least equal to the development length of this bar, established by tests.
In the beam of as per above fig, if the actual length /is equal to or greater than the development length Id, no premature bond failure will occur.
The beam will fail at bending or shear rather than by bond failure. This will be so even when, in the vicinity of cracks, local slip may have occurred over small regions along this beam.
It is seen that the main requirement for safety against bond failure is this: the length of the bar, from any point of given steel stress (L or at most f) to it’s nearby free end, must be at least equal to its development length.
If this requirement is satisfied, this magnitude of the nominal flexural bond force along the beam, as given by Eq. (as below), is of only secondary importance, since the integrity of this member is ensured even in this face of possible minor local bond failures.
U = V/JD
However, if this actual available length is inadequate for full development, special anchorage, such as by hooks, must be provided.
Also, read: Trapezoidal Footing Formula with Calculation
Difference Between Lap Length and Development Length
| SR.NO. | DEVELOPMENT LENGTH | LAP LENGTH |
| 1 | Length of reinforcement bar required to transfer load or stress developed in a reinforcement bar into the concrete. | Length of reinforcement bar required to completely transfer load or stress from one bar to another bar |
| 2 | It is denoted by Ld | It minuteness the continuity in the structure |
| 3 | It is always provided at the end of beam, column, or slab | It is provided when the length of bars ends. |
| 4 | It is also useful for providing grip & support & doesn’t allow slipping | It is transferred to continuity and also transfers stees from one bar to another bar. |
| 5 | This is bound between concrete and reinforcement. | This is a bond between reinforcement and reinforcement. |
Lap Length
The lap length is the length provided to overlap two rebars in order to safely transfer load from one bar to another bar and alternative to this is to provide mechanical couplers. It is also known as lap splices.
Lap Length Vs. Development Length in Reinforced Concrete
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.
How to Calculate Lap Length and Development Length?
Generally, the development length is 41d where d is the diameter of the bar. For direct tension, the lap length should be 2 Ld or 30d whichever is greater is considered. In this case, the straight length of the lapping bar shall not be less than 15d or 20cm.
Lap Splice Length Requirements for Rebar
1 Lap Splices. but not less than 12 inches (305 mm). The length of the lapped splice shall be not less than 40 bar diameters. Computed stress in reinforcement due to design loads, psi (MPa).
Development Length Calculation Methods
In the case of bundled bars in contact, the development length is given by that for the individual bars and increased as follows:
- 10% for two bars in contact.
- 20% for three bars in contact.
- 33% for four bars in contact.
Lap Length in Construction Standards
So the second bar is kept closely to the first bar and overlapping is done. This amount of overlapping between two bars is called “lap length”. Lapping is usually done where minimum bending stress is encountered. In general, lap length is 50d which means 50 times the bar diameter, if both bars are of same diameter.
Lap Length Formula
1. Lap length For flexural tension = L x d or 30 x d (The greater value among the two values calculated is taken.) 2. Lap length For direct tension = 2 x L x d or 30 x d (The greater value among the two values calculated is taken.)Jun 4, 2021
Lapping Length
What Is Lap Length? Lap length is the overlapping length of two bars side by side which gives the required design length. In RCC structure, if the length of a bar is not sufficiently available to make the design length, lapping is done. Suppose we need to construct a building of 20 m in height.
What Is 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.
What Is Lap Length and Development Length?
Lapping length can be defined as the length that is needed for overlapping of two steel bars so they act like a single bar. Development length is defined as the length of the steel reinforcement from one element to another element needed to transfer stresses.
What Is Development Length?
The term “development length” signifies the bar length that must be present for the stress to be transferred successfully into the concrete. For concrete and steel, it is the length of the bar that must be implanted into the material to generate enough tension to provide the appropriate bond strength.
What Is the Lap Length for Welding the Reinforcement Bars?
Lap splicing is done by overlapping the bars and wiring them together. The length of lap splices can reach 60 inches for 1-inch bar diameter, and more than 100 inches for 1.5-inch bar diameter [5].
What Is the Minimum Lap for Rebar?
What is the minimum lap length? For direct tension, the straight length of the lapping bar shall not be less than 15d or 20 cm. While in the case of compression lapping should not be less than 24d.
What Is the Development Length of Steel Reinforcement?
Development length is the bar length required to transfer stress/load from steel bar to concrete. In comparison, Anchorage length is provided if adequate development length can’t be provided inside the fixed end/support. It is usually considered as 8 times of bar diameter.
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