How to Find Lap Length in Column Beam and Slab
The Civil Engineering
This is about Civil Engineering, Quantity Surveying, Land Surveying and AutoCAD Civil 3D Knowledge base learning hub
What is Lap Length?
Lap Length is required, When bars are placed too short, they must be extended to the required length.
Lap length is the length provided to overlap two rebars (reinforcement) in order to safely transfer load from one bar to another bar and an alternative to this is to provide mechanical couplers. It is also called lap splices.
The purpose of ‘Lap’ is to transfer the axial force from the terminating bar into the connecting bar with this same line of action (lateral) in the junction. This inevitably introduces stress concentrations at this surrounding concrete. These effects can be minimized by
When splicing becomes necessary in such situations, special precautions need to be taken., such as
Overview:
When manufacturing reinforcement steel bars, engineers typically make them 12 meters long so they can be easily transported.
However, in the case of reinforced concrete structures, larger beams, columns and slabs often need to be made.
In such a case, the reinforcement bars have to be overlapped to get the required length.
Usually, such overlapping of reinforcement bars is done where the magnitude of the bending stress is least.
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 the event that reinforcement bars do not have equal diameters, then the lap length is calculated using the value of the bar with a smaller diameter. Calculate Lap Length in Column Beam & Slab
a. Lap Length in Tension:
For the lap length in tension, the following formula can be used to calculate the lap length including the anchorage value of the hooks,
1. For flexural tension,?Lap length = L x d or 30 x d?(The greater value among the two?values calculated is taken.)
2. For direct tension,?Lap length = 2 x L x d or 30 x d?(The greater value among the two?values calculated is taken.)
领英推荐
Where,
L = development length
In such a case, the straight lapping length of the reinforcement bars must be greater than 200mm or 15 x d. Calculate Lap Length in Column Beam & Slab formula
b. Lap Length in Compression??
For the lap length in compression, we can use the same value for the development length as well.
However, in no case, the lap length can be less than?24 x d.
Why Do We Provide Lap Length of Rebar ???
Reinforcement steel is generally manufactured for 12 meters in length. During construction, when reinforcement is needed for a longer length than 12 meters, the bars are lapped to maintain continuity in the reinforced structures. The lap length varies in different RCC structures and generally lies between 30d (d=bar diameter) to 55d depending on the design and grade. Calculate Lap Length in Column Beam & Slab
Importance of Providing Lap Length??
The lap length is necessary for reinforced concrete structures to transfer tensile and compressive loads from one reinforcement bar to another by means of shear or skin friction.
If the lap length is not sufficient, the load transfer mechanism may be disrupted and lead to the failure of the entire structure. Lapping Zone of Column beam slab footing
Also, when the lap length provided is insufficient to reinforce concrete, the reinforcement bars may split, causing cracks in the concrete.
Thus, the lap length is necessary for?reinforced concrete structures.
What will happen if we don’t Provide Lap Length??
As we know that lapping should be provided between two rebars in order to safely transfer shear forces from one bar to the next bar, if we don’t provide lap length between two rebars the load is not safely transferred from one bar to the next bar, causing structure will be failed, if not failed it cause cracking, and permanent collapsing of a structure. For preventing any cracking, structure failure, and permanent collapsing, lapping should be provided in steel when we placed Steel in the RCC structure. Common Lap Length as per IS 456
Lap Length As Per IS 456:
Generally,?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. Common Lap Length as per IS 456
For Reading Complete Article please visit:
More Related Articles: