Details of bar bending schedule & it's formulas
Definition of Bar Bending Schedule or BBS
It belongs to a method of cutting and bending reinforcement bars into shapes recommended by a structural engineer.
It comprises a detailed list that demonstrates the location, mark, type, size, length, number and bending details of every bar in a reinforcement drawing concerning a structure. The method of listing is known as scheduling.
BBS contains the followings :-
- Member identification
- Bar Mark
- Shape of bending
- Diameter of bar
- Length of every bar
- Total numbers of bars
- Total length
Process to create a BBS
Recognition of members (steel bars)
Every type of bar generally contains a bar mark/designation.
Counting every type of bar
Counting can be done manually for a small concrete structure.
To workout the numbers of bars for a big slab structure, it is required to determine the width, clear cover and c/c (center to center) spacing among bars.
Numbers of bars = (width of concrete - 2 x clear cover)/c/c spacing between bars.
Computation of the length of Rebar
The entire length of every member bar is computed. The development length or anchorage length should also be included.
Computation of unit weight of individual bar
The unit weight of individual bar is generally computed with the following formula :-
Unit of weight of bar with diameter D = D^2/162 kg/m
Computation of total weight
With the use of following formula, the total weight of required steel is determined :-
Weight of bar = (Numbers of bars x Length x Unit Weight) kg
Elementary formula for bar bending schedule
Crank of length
Crank length = 1 x D
Inclined bar length = 0.42 x D
Hook Length = 6 x D
Angle = 45 degree
Length of the bending bar = 16 x D
Lapping length of the compression bar
L = 50 x D
Lapping length of the tension bar
L = 40 x D
Hook length in stirrup
Hook Length = 12 x D
In the above formulas, D denotes diameter of the bar.