Some amount of rebar is left for future construction. This extra rebar will be needed for tying bars of column. This extra length of rebar is called lap length. Lap length is the overlapping length of two bars side by side which gives required design length. In RCC structure if the length of a bar is not sufficiently available to make design length, lapping is done.
The maximum length of rebar available in the market is usually 12m, so we need to join two bars of 12m to get required length of long bars.
The lap length varies from member to member.
Lap length for tension members = 40d.
Lap length for compression members = 50d.
Where, d = Diameter of bars.
The lap length including anchorage value of hooks shall be
1. For flexural tension – Ld or 30d whichever is greater.
2. For direct tension – 2Ld or 30d whichever is greater.
The straight length of lapping shall not be less than 15d or 20cm.