Bar Bending Schedule (BBS)

         Bar Bending Schedule is a very important knowledge an engineer should have and it is even more important for the site engineers. Basically, Bar bending schedule is used to obtain the quantity of rebar in a construction.  BBS includes the cutting length of rebar, size of rebar, bending of rebar and total quantity of rebar.
        BBS is a very important document which needs to be included in the Running Bill (Interim Payment certificate) prepared by the contractor. Hence BBS is generally prepared by the contractors engineer and approved by the consultants. However in big projects such as hydropower the BBS is prepared by the District Resident Engineer from consultant. It is better to prepare BBS during the site is running and when needed. BBS provides the total quantity of rebar used and it is updated in every IPC. BBS also helps the barbenders to prepare the rebar which needs to be installed. It is very user friendly and can be understood easily.
             Basically BBS contains following columns:-
1)     Shape of Bar
2)     Diameter of Bar
3)     Number of Bars
4)     Cut Length of Bar
5)     Total Length of Bar
6)     Unit Wt. of Steel (KG/m)
7)     Weight of Bars.
                
           Below is the sample format of a BBS.
                

                                                               Fig: - Bar Bending Schedule 
    

                                                    Fig:- Rebar Drawing of Water Tank

                As we can see above is a sample of  BBS of a water tank. It contains all the details for the quantity calculation. In the second column we can see the shape of rebar which needs to be cut with all the dimension. This helps the workers on how to bend the rebars. Then there is information on the cutting length of rebar and diameter of the rebar to be used and also the number of rebars to cut. The we can see the unit weight which differs according to the diameter of the rebar. We can also see the total weight of the rebars.
                             The main thing the engineer should know to prepare BBS is to read the rebar arrangement drawing. We can see the bends and hooks provided in the ends of the rebars, it's length depends upon the size of rebars and strength of rebar. IS 2502: 19631 Table II gives the bend and hook length. Normally in building : -
    Bend Length = 9D 
    Hook Length = 5D
    where D= Diameter of Rebar. 
                    Lap length is another important thing to know for preparing the rebar and we also need to know the lapping position of rebars in all type of structures. Notes on lapping position will be described in the next blog ut the basic thing is lapping of rebar is done always against the bending moment diagram. Lapping length can be obtained from the code IS 456:2000. It depends upon the size and strength of rebar. Generally these informations are provided in the general notes which is included in the structural drawing. Hence engineer should carefully study the drawing and contents.

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