Lap length,Development length, Lapping Zone, crank bar

1. Lapping length
2.Development Length (Ld)
3.Lapping Zone
4.Crank bar
5. Chair
6. Jackle

1. Lapping length (as per IS 456)

# In Tension Zone 
a. For flexural tension : Ld or 30D (where, Ld= development length &D= Dia of rebar in mm)
b. For Direct tension : 2Ld or 30D (where, Ld= development length &D= Dia of rebar in mm)

# In Compression Zone
Lap length= Development length  Ld , But not Less than 24D


Note: if diffrent diameter are to be spiced lap length is calculated on the basis of smaller dia bar.

# Lap length as per Concrete mix (Acc to Nominal Mix)
M15 (1:2:4)= 40D
M20 (1:1.5:3)= 45D (for column) ,60D (for Beam) & 60D (for Slab)

2. Development Length Ld

Ld= 40 D or 41 D

3. Lapping Zone

# Column
Lap zone= L/2

# Beam
Compression Zone= L/3 (centre)
Tension Zone=L/4 (Beam column Junction)

4. Crank Bar
Crank bar is provide to resist negative B.M on Slab Which is always on column junction (i.e provide end part of slab )
Length of Crank = 0.42D (where D= Effective depth of Slab in mm i.e. depth after deduct Clear cover)