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Bar Bending Schedule [BBS] Estimate Of Steel In Building Construction

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Introduction to Bar Bending Schedule [BBS]

Bar bending schedule commonly known as BBS is one of

the most important terms in Civil Engineering. Because it
plays a vital role in building construction.  Like other
building materials estimation of steel is also required for
constructing a building and here BBS comes with an easy
solution. Bar bending schedule provides the
reinforcement calculation and some other important
details such as bar mark, bar diameter, bar shape, cutting
length, number of bars, the weight of the bar, the total
weight of steel etc. So that we can order the required
amount of steel in advance.

Bar Bending Schedule [BBS]

Before dealing with the BBS, it’s very important to learn

the basics of Bar bending schedule. The below-
mentioned table is a  kick-start guide for learning Bar
bending schedule from scratch.

S.No. Particulars Result

1. Standard Length of the Steel 12m or 40′

Bar
(Bars are sold at standard
Length)

2. Weight of Bar
D2/162
for length = 1m
(were D =
Dia of Bar)

Ex: If the length of the bar is 12m 7.40Kgs

with 10mm Dia then,

Weight of bar =
D2/162Therefore for length 1m
= 1m x D2/162

= 1 x 102/162 = 0.61 KgsFor

length 12m = 12 x 102/162

= 7.40Kgs

3. Density of Steel 7850Kg/m3

1- Hook Length or Cutting length of Stirrups

The hook length is commonly provided for stirrups in

beams and ties in columns. In general, Hooks are added
at the two ends of the rebar in stirrups or ties.

Hook Length = 9d (d is dia of the bar)

Below image makes you clear why the Hook length = 9d

From above fig, length of hook = [(Curved Portion) + 4d]

= [(4d+d)+4d] = 9d

Hook Length = 9d [d is Diameter of the Bar]

Example Calculation considering stirrup with the

hooks at ends

For a clear understanding, look at the below image for

calculation of the total length of stirrup the with two hooks
at ends.

total Cutting Length of stirrup or tie = Total length of Bar +

2 x Hook Length (Two hooks)

Total Cutting Length = L+2(9d)

Therefore Total Cutting  length = L+18d (d is the

Diameter of a bar)

Hope, now you are clear with the Hook length calculation.

2- Bend Length

The Bend length calculation is different for Cranked bars

(bent up bars) and bends at corners. The bars are usually
cranked in Slabs and bars are bent at corners in Stirrups
or ties.

(i) Bend Length calculation in Cranked Bars

As  Shear stress is maximum at supports in Slab. To

resist these stresses we usually crank the bars at the
ends of supports in the slab. The below figure describes
the bent up bar in Slab. To calculate the bend length the
below procedure is followed.

From the above figure as the bar is bent at an angle

θ0 the additional length (la) is introduced.

Where, la = l1 – l2–(i)

Tanθ = D/l2 ; Sinθ  = D/l1

Hence  l1  = D/Sinθ and l2 = D/tanθ

Therefore from (i)  :- la = D/Sinθ – D/tanθ

Giving different θ values as 300 , 450, 600  results different

additional length  la values as below.

θ0 D/
Sinθ
D/
tanθ  la =D/Sinθ – D/tanθ

300 D/0.500 D/0.573 0.27D

450 D/0.707 D/1.000 0.42D

600 D/0.866 D/1.732 0.58D

900 D/1 0 1D

1350 D/0.707 D/-1 2.42D

The additional length is added to the total length of the

bar if the bars are cranked at a certain angle.

Example Calculation considering Bent up bar in Slab

(Cranked bar)

To keep the crank bar in position, an extra bar of length

(L/4) is provided below the crank bar as shown in the
below figure.

Therefore, the total length of bar = L+0.42D+0.42D+

(L/4)+(L/4) = 1.5L+0.84D

Remember D = Depth of Slab-Top Cover-Bottom

cover 

(ii) Bend Length calculation when bars are bent at

corners

The important standards used while calculating the bend

length at corners

1- 45° Bend length = 1d

2-  90° Bend length = 2d

3- 135° Bend length = 3d

Here, ‘d’ = Diameter of bar

Example Calculation considering stirrup with the

bends at corners

From above fig, There are 3 bends which are bent at an

angle of 900 and two bends are bent at an angle of 1350

Total bend length = 3 x 900 Bend length + 2 x 1350 Bend

length = 3 x 2d + 2 x 3d = 12d = 12 x 8 = 96mm

below table represents the total length of bar calculation

for different types of bar shapes.

Total
Bar Length of Total Bend Total Length
Shapes Hooks Length of Bar

Straight Two Hooks

No bend l + 18d
Bar = 9d + 9d

= 18d

Bent Up Two Hooks

One bend
l + 18d +
at one = 9d + 9d
bent at an
0.42D
End = angle 45

only 18d**d=Dia. =
0.42DRemember
D = Depth of
Slab-Top Cover-
Bottom cover

Double Two Hooks

Two bends
l + 18d +
Bent up = 9d + 9d
bent at an
0.42D + 0.42D

Bar = 18d angle 450 =l+18D+0.84D

Overlap Two Hooks

No bends Overlap
of bars = 9d + 9d
Length

= 18d =(40d to
45d)+18d

3- Overlap Length / Lap Length in Reinforcement

The standard length of Rebar is 12m. Suppose the height

of the column is 20 m. To provide this requirement, two
bars of length 12m and 8m are overlapped (joined) with
overlap length.

Overlap Length for compression members (columns)

= 50d

The Overlap Length for tension members (beams) =

40d

[d is the Diameter of the bar]

Have You seen the below picture on your top floor of the
building? We generally project some length of Bar on the
last floor i.e., 50D. It is used for further construction
purpose. (Constructing a new floor)

How to Prepare Bar Bending Schedule

To understand clear, Here we considering the below

structural member RCC Column and preparing a BBS +

BBS of Column

Structural Member Column

(3mx0.3mx0.3m)

Bar Marking 1. Main Bars

2. Stirrups (Longitudinal bars)

Dia of Bar 1. Main Bars = 16mm ;

2. Stirrups

(Longitudinal bars) = 8mm

No. of Bars used 1. Main bars = 4

2. Stirrups = 30

Cutting length 1. Main bars = 4.6m

2. Stirrups = 1.44m

Total Length of bar 1. Main bars = 18.4m

2. Stirrups = 43.2m

Weight of Steel bar 1. Main bars = 29Kgs

2. Stirrups =17Kgs

Calculation part of the above table

No. of Bars calculation

Main bars = 4

To calculate the No. of longitudinal bars adopt spacing

between bars is 0.1m

No. of Longitudinal bars = Length of column / Spacing =

3/0.1 = 30bars

Longitudinal bars = 30

Cutting length calculation:

Main bars = 3m + 50d + 50d = 3 + 50×0.016 + 50×0.016

= 4.6m

Stirrups:

Hook length = 9d + 9d = 18d = 18×0.08=1.44m

Bend length =3 x 900 Bend length + 2 x 1350 Bend length

= 3 x 2d + 2 x 3d = 12d = 12 x 8 =0.096m

= l +hook length + bend length = 0.3+0.3+0.3+0.3

+0.144+0.096=1.44m

Hence for Main Bars = 4.6m ; Longitudinal bars = 1.44m

Total Length of Bars:

The total length of Main bars =  No. of Main bars x length

of one bar

= 4 x 4.6 = 18.4m

The total length of the Longitudinal bars=No. of

longitudinal bars x length of one bar

=30×1.44=43.2m

SOCIAL LINKS
Weight of steel bar:

Weight of steel bar for 1m = 1m x D2/162

     
Total weight of Main bars = 18.4 x 162/162 = 29Kgs
8.5M 1.9M 1.1M 1.1M 20.9K 28.4K

Total weight of longitudinal bars = 43.2 x 82/162 =17Kgs

  
13.6K
Total weight of steel bar required to do BBS of above
column = 46Kgs
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