During placing the steel in RC structure if the required length of a bar is not sufficiently available to make a design length then lapping is done.
Lap length is the minimum length that must be provided if two bars are joined together such that forces can be transferred safely.
Lap length of reinforcement bars:
- Flexural tension – Ld or 30d whichever is greater.
- Direct tension – 2Ld or 30d whichever is greater.
- Lap length in compression shall be equivalent to the development length in compression computed but not less than 24d.
- Different diameter are to be spliced, the lap length is calculated on the basis of smaller diameter bar.
- Lap splices should not be used for the bars having larger dia than 36mm.
- Lap length for Columns – 45d.
- Lap length for Beams – 60d
- Lap length for Slabs -60d.
- Example for if we need to lap 20mm dia column bars, we have to provide a minimum lap of 45 * 20 = 900mm.