Details about overlapping length in RCC
Definition of overlapping or lap length in RCC - Because of the limited length of bar, laping of bars are necessary in a member having in excess of 12m in length or where length of bar is needed in excess of 12m.
Lap Length:- It belongs to the length of bar necessary to transmit the stress securely.
Alternatively, the lap length can be defined as follow :-
Lap Length:- Overlapping Length or Lap Length is required for retaining the continuation of bars for transmitting the load from one bar to another bar securely. It is based on the grade of concrete, grade of steel and dia. of bar.
Reason for providing Lap Length - Normally, reinforcement steel is fabricated with a standard length of 12m. When it is required to arrange a length in excess of 12m at the time of construction, the bars are lapped to keep continuation in the reinforced structures.
This lap length differs in several RCC structures and normally remains among 30d (d=bar diameter) to 55d based on the design and grade.
Desired Lap Length in Column - With adherence to IS Code 456-2000 overlapping length should not be under 75mm. There should be no lapping in tensile zone of construction members. For column, normally 24d – 40d is provided where ‘d’ denotes dia of bar.
Some vital points to be considered for Column Lap Length:
• Lapping should be arranged at the center of column since bending moment at mid point is zero so it is recommended to lap at mid point.
• Lapping of bars should be arranged successively. Lap should not be provided at equivalent point as there is chance for buckling.
• Lateral ties should be placed narrowly in Lapping zone.
• Because of maximum stress, lap can’t be done at column/beam/slab joint. Lapping should not be provided at L/4 distance from top and bottom of the slab.
How Much Lap Length should be provided in beam. For beam, 24d is normally applied for compression zone and 45d for tensile/tension zone.
How Much Lap Length should be provided in Slab. For slab, length 50d is applied where ‘d’ stands for dia of bar.