Lap length is one of the important terms in the reinforcement. This is usually confused with another important term called development length and anchorage length.
During the placement of steel in a Reinforced concrete structure, if the required length of the single bar might fall short. To get the desired design length, the lapping of two bars side by side is done.  An alternative to this is to provide mechanical couplers.

The overlapping of the steel is very important in R.C.C works because splicing of steel is used to transfer all the stresses from one bar to another bar. The length of the lapping is different in different concrete mixes because different concrete having a different crushing strength.

1- The lapping is not provided above 36 mm diameter bars because those diameter bars doesn’t transfer the stresses from one bar to another bar and also the alignment of the column bar is also affected by providing the lap on these bars.

2- The lapping of the steel bars also not provided in high shear force zones and it should be provided at that zone where the shear force will be minimum.

In M 15 Concrete Mix: In M 15 we use the concrete mix 1 : 2: 4 means 1 part of cement, 2 part of sand and 4 part of aggregates.

Tension zone        Compression Zone

Fe 250 – 55 ∅              Fe 250 – 45 ∅

Fe 415 – 57 ∅               Fe 415 – 47 ∅

Fe 500 – 68 ∅              Fe 500 – 57 ∅

In M 20 Concrete Mix:  In M 20 we use the concrete mix 1: 1.5 : 3 means 1 part of cement, 1.5 part of sand and 3 part of aggregates.

Tension zone        Compression Zone

Fe 250 – 46 ∅              Fe 250 – 37 ∅

Fe 415 – 47 ∅               Fe 415 – 38 ∅

Fe 500 – 57 ∅              Fe 500 – 46 ∅

In M 25 Concrete Mix: In M 25 we use the concrete mix 1 : 1: 2 means 1 part of cement, 1 part of sand and 2 part of aggregates.

Tension zone        Compression Zone

Fe 250 – 39 ∅              Fe 250 – 32 ∅

Fe 415 – 41 ∅               Fe 415 – 33 ∅

Fe 500 – 49 ∅              Fe 500 – 39 ∅

Where ∅ is the diameter of the bar? Suppose we are using a steel bar Fe 500 and concert mix M25. The diameter of the bar will be 10 mm. By using the formula, the splice length of the steel bar will be 49 x 10 = 490 mm and if the bar is in tension zone and 39 x 10 = 390 mm if the bar is in the compression zone.