HOW TO CALCULATE THE QUANTITY OF STEEL IN COLUMN (BBS)
EXAMPLE:
We have a column. The height of the column is 3 m and having a
crosssectional area is 500 x 400 mm. Six bars are going to use having a
diameter of 16 mm. The diameter of the stirrup is 8 mm and having a
spacing @ 150 mm and @200 mm at L/3 respectively.
GIVEN DATA:
Height = 3 meter
Cross section = 500 x 400 mm
No of vertical bars = 6 nos.
the diameter of the vertical bar = 16 mm.
Diameter of stirrup = 8 mm.
stirrups center to center spacing = @150 or @ 200 mm.
SOLUTION:
The calculation was to proceed in two steps.
·
Longitudinal bars calculation
·
Cutting length of stirrups
STEP 1: LONGITUDINAL BARS CALCULATION
Length of 1 Rod = H + Ld
H = Height
Ld = development length (50d)
Length of 1 Rod
= 3000mm + 50d (where d is dia of the bar)
= 3000 + 50(16)
= 3000 + 800
= 3800mm or 3.8m
Total length
The length one vertical bar is 3.8m. as we have six vertical bars
= 6 x 3.8
Total length = 22.8 m bar of 16mm needed
STEP 2: CUTTING THE LENGTH OF RECTANGULAR STIRRUPS
The crosssectional area of the column is 500 mm x 400 mm
Take it has,
500mm is side A
400mm is side B
Minimum clear cover to the reinforcement: 15 mm to the bars in slabs,
25 mm to bars in beams and
columns. In
large columns, say
450 mm in thickness, the
cover should be
40 mm.
SIDE A

SIDE B

A =500 – 2 Side clear cover
A = 500 – 2 x clear
cover
A = 500 – 2 x
40
A = 500 – 80
A = 420 mm

B =400 – 2 x Top
& Bottom cover
B = 400 – 2 x clear cover
B = 400 – 2 x 40
B = 400 – 80
B = 320 mm

NO OF STIRRUPS REQUIRED
As mentioned spacing @ 150 mm and @200 mm at L/3 respectively.
Formula = L/3 +1
L/3= 3000/3
=1000 mm or 1 m
NO OF STIRRUPS NEEDED IN TOP ZONE
=1000 / 150
= 6.67 nos say 7 nos
NO OF STIRRUPS NEEDED IN BOTTOM ZONE
=1000 / 150
= 6.67 nos say 7 nos
NO OF STIRRUPS NEEDED IN MID ZONE
= 1000/200
=5 nos
TOTAL STIRRUPS NEEDED
= 7+5+7 =19 nos
Formula = 19 +1=20 nos
NO OF STIRRUPS REQUIRED = 20 nos
CUTTING LENGTH OF ONE STIRRUP
Formula:
Cutting Length of Stirrups = Perimeter of Shape + Total hook length –
Total Bend Length
Perimeter Of Shape
Perimeter of Rectangle = 2 ( length + breadth)
Perimeter of Square = 4 x side length
Perimeter of circle or Circumference of Circle = 2πr = πd
(r= radius, d= Diameter of Circle)
Total hook Length
1 Hook length = 9d or 75mm
Total Bend Length
45° Bend length = 1d
90° Bend length = 2d
135° Bend length = 3d (Remember, d = Diameter of Bar)
Cutting Length of rectangular Stirrup = 2 ( length + breadth) + 2 numbers of hooks – 3 numbers of 90° bends
– 2 numbers of 135° bends
= 2(a+b) + 2(9d) – 3(2d) – 2 (3d)
= 2(500+400) + 2(9x8) – 3(2x8) – 2(3x8)
= 2(900) + 2(72) – 3(16) – 2(24)
= 1800 + 144 – 48 – 48
=
1848mm say as 1.84m
We have a total of 20 nos of stirrups, which are going to use,
Total length
= 20 x 1.84
= 36.8 m long 8 mm bar
CUTTING THE LENGTH OF
RECTANGULAR STIRRUPS = 36.8 m
RESULT:
TOTAL LONGITUDINAL BARS (6 nos) = 22.8 m bar of 16mm
CUTTING THE LENGTH OF RECTANGULAR STIRRUPS =
36.8 m of 8mm
As we know the formula for weight calculation of steel bar for 1 meter
is = D^{2}/162
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