Bar Bending Schedule - Importance | advantages | Preparation


What is Bar Bending Schedule (BBS)?

Bar bending schedule is a list of reinforcement bars in a tabular form giving the particulars of bars, the shape of bending with sketches, length of each, total length and total weight. Usually, for each type of RCC work a schedule of bars is usually prepared. With the help of BBS the requirements of different sizes and lengths of bars may be known and maybe arranged and bent-up during the time of construction. It gives information about
  1. Particular of size and type of bars
  2. The shape of bending with a sketch if any
  3. Number of sets or numbers of bars of each set
  4. Length of each and total length in running meter
  5. Weight per unit length and total weight.


Importance of Bar Bending Schedule

As we know the cutting and bending of steel bar is done by labour at the site. The labour working on site are not so technically sound so it is difficult to explain them with the help of drawing. There are chances of wrong cutting and bending of steel. With the help of BBS, it is very easy to explain to them because in BBS shape and cutting length of bars is given. A supervisor can easily guide the labours and required work can be done by them as per structural design requirement and specification.
Advantages of Bar Bending schedule
  1. There is faster execution of work at the site with the help of BBS, which reduces construction cost and time.
  2. BBS reduces reinforcement wastages in cutting.
  3. BBS helps in improving quality control at the site.
  4. It helps in stock management at the site.
  5. It helps in auditing of reinforcement and provides a check on theft.
  6. It helps in the fast preparation of bills of construction works.
  7. It helps in the estimation of steel quantity.
How to prepare a bar bending schedule

BBS should contain the following Details
  1. Description of bar
  2. Shape and bending dimension
  3. Numbers of bar same types
  4. Length of bar
  5. The total length of the bar
  6. Diameter of bar
  7. Weight  
  8. Total weight

Most of the details discussed above are given in the drawing. We have to calculate the cutting and bending length and total weight which we can calculate as follows:

The length of one hook may be taken as 9D and the total length of the straight bar hooked at both ends may be taken as L + 18D




For 45°cranked or bent up bar

The additional length for one bent up is = difference in length of hypotenuse and base
                                   
                                                                =   d/sin45°- d

                                                                =   d(1/0.707 - 1)

                                                               =   d(1.42 - 1)

                                                               =  0.42d = 0.45d ( approx)

For two bent ups additional length is equal to 2 × 0.45d = 0.9d where d is the vertical distance between the centre of the upper and lower arms of the bent up bars, which is equal to a total depth of beam or slab minus bottom and top cover.


For 30°cranked or bent up bar

Inclined length of crank = d/sin30° = 2d

the horizontal length of crank =  d/tan30 = 1.73d
The extra length required for one crank = 2d-1.73d = 0.27d = 0.3d(say)
For a bar cranked at both ends at 30 the additional length is equal to 2 × 0.3d = 0.6d

Overlap or Lap Length at joint

For lap, length read - What is Lap Length?


Length of Hook and Total Length of Bar for different shape


Length of Bent -up bar for 30°, 45°, and 60°












PERCENTAGE OF REINFORCEMENT ACCORDING TO CONCRETE volume:
1. Lintel, Slab                              -      0.7 to 1%
2. Beams                                      -      1.0  to  2.0%
3. Columns                                  -      1.0  to 5%
4.  Foundation raft, footing etc.   -      0.5 to 8%

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Also, Read -
1. How to calculate unit weight of steel bar
2. Difference Between One way and Two way Slab

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