HOW TO CALCULATE THE QUANTITY OF STEEL IN COLUMN (BBS)

The quantity of steel calculation in the column is very easy and simple just need you little concentration. For your better understanding just look at this example.

Example:

suppose we have a column. The height of the column is 4 m and having a cross-sectional area is 300 x 400 mm and having a 40 mm of clear cover. 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  = 4 meter

Cross section = 300 x 400 mm

Clear cover  = 40 mm.

No of vertical bars  = 6 no’s.

The diameter of the vertical bar = 16 mm.

Diameter of stirrup = 8 mm.

stirrups center to center spacing = @150 or @ 200 mm.

BBS of Column =?

Solution:

The calculation was to proceed into two steps.

  1. vertical bars calculation
  2. Cutting length of stirrups

Step 1: Vertical Bar calculation

Length of 1 bar = H + Ld

#Where

Ld = development length

h = Height of column

Length of 1 bar

= 4000 mm + 40d   <where d is dia of bar>

= 4000 + 40 x 16

= 4000 + 640

= 4640 mm  or  4.640 m Ans..

The length one vertical bar is 4.640 m. we have total bar six bars,





Total length

= 6 x 4.640

= 27.84 m long vertical bar is required.

 

Step 2: Cutting the length of stirrups

The cross-sectional area of the column is 300 mm x 400 mm

A is the vertical cross-section area of the stirrup

B is a horizontal cross-section area of the stirrup

 

Calculation of length A

A = Horizontal Distance – 2 Side clear cover

A = 300  – 2 x clear cover

A = 300  – 2 x 40

A = 300  – 80

A = 220 mm

 

The length of B

B = Vertical distance –  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

No of stirrups

= 4000/3

=1333.3 mm or  1.33 m

Formula = L/3 / spacing + 1

(no of stirrups in end zone)

=1333.3 / 150

= 8.8 nos say 9 nos

There are total two zones of 150 mm spacing and one zone of 200 mm spacing.

=  2 x 9

= 18 nos (at end zones)

 

At Mid Zone

=1333.3 / 200

= 6.6 nos say 7 nos

Total no of stirrups

= 18 + 7

= 25 nos



Cutting length of one stirrup

Formula:

= (2 x A) + (2 x B) + hook – bend

Cutting length

= (2 x A) + (2 x B) + 2 x10d – 5 x 2d

# where

hook = 10d

bend = 5 x 2d  (we have 5 bends in one stirrup)

d =  is diameter of bar

= (2 x 220) + ( 2 x 320) + 2 x 10 x 8 – 2 x 5 x 8

= 440 + 640 + 160 – 80

= 1160 mm or 1.16 m

We have a total 25 nos of stirrups, which are going to use,

Total length

= 25 x 1.16

= 29 m long 8 mm bar.

 

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