How to calculate steel quantity from drawing

How to Calculate Steel Quantity from Drawing | BBS of Slab | Steel Quantity Calculation8 min read

How to Calculate Steel Quantity From Drawing?

Data requires for estimation of steel quantity:

1) Plan of Section or Element. (Slab, Beam, Column & Foundation)

2) Section and Elevation Details.

3) All dimensions must be clear and co-related.

Read More: Building Construction Step by Step Process


General Guidelines To Be Followed In Preparing BBS

  • The bars are required to be grouped together for each of the structural units, For e.g. beam, etc.
  • In a building structure, the Listing of bars should be done floor to floor.
  • For cutting and bending operations, schedules should be provided separately in the form of A4 sheets and should not a part of the detailed reinforcement drawings.
  • The form of bar, fabric schedule, and the shapes of the bar used should be according to BS 8666.
  • It is always preferable that bars should be listed in numerical order in the schedule for better understanding.
  • The bar mark reference on the label which is attached to a bundle of bars refers seperately and uniquly to a specific group of defined length, size, shape, and type used on the job.
  • This is very crucial as a bar mark reference can then state to a class of bar characteristics. Similarly, it also helpful in the case of steel fixers and laborers can keep track of the type and number of bars needed to complete a specific work.

Slab Steel Calculation Formula

slab section
Slab Section
How to Calculate Steel Quantity from Drawing
Slab Reinforcement Details

Let, us take one example of a slab for steel estimation.

Following Quantity, we have to calculate from drawing.

  • Cement Concrete for Slab.
  • Centering and Shuttering for Slab.
  • Weight of 12mm dia. Bars.
  • Weight of 8mm dia. Bars.
  • Prepare Bar Bending Schedule.

(Note:  Weight of Steel bars 12mm – @ 0.9 kg / m

                                              8 mm – @ 0.4 kg/m,


Steel Quantity Calculation Estimation Sheet

Sr. No.Item DescriptionNo.Length (m)WidthHeightQuantity
1Cement Concrete for Slab (1:1.5:3):
L = 4 + 0.23 + 0.23 = 4.46 m14.463.460.121.85 cu m
B = 3 + 0.23 + 0.23 = 3.46

(See drawing in to in dimension (without the wall) of the slab is given 3 m x 4 m. For calculating Quantity of slab concrete we have to calculate out to out the dimension of the slab.)

2 Centering & Shuttering for Slab:            
  Bottom 1 4.00 3.00   – 12.00 cu m
  Sides 2 4.46   – 0.15 1.34 cu m
  ( Take 30mm Extra Above
Slab Thickness)
2 3.46   – 0.15 1.04 cu m
          Total 14.38 cu m

(Formwork Quantity is calculated in a square meter. There is one bottom portion and 4 side shuttering. For bottom we have in to in dimension of slab 3m x 4m. For Side formwork, there is 2 different dimensions, 2 with 4 m side and 2 with 3 m sides. For the total length we have to add wall width of both sides to get the total length.)

Read More: Estimation of a Building with Plan

How to Calculate Steel Quantity from Drawing


312 mm dia main Steel bars @ 150 mm c/c Alternate bent up.      
 L = 3 + 0.23 + 0.23 + (2 x 9 x 0.012) – (2 x 0.05)      
 L = 3.58 (Straight Length) (For finding out nos. of the bar we have to calculate the straight length of the main bar without adding extra length due to bent up)
 Span = 4 + 0.23 + 0.23 – (2 x 0.05)
          = 4.36 m
      
 No. of Bars = (4.36/0.15) + 1
                     = 30 nos.
      
 Extra Length of Bent up:      
How to calculate steel quantity from drawing
X – Value
 Extra Length = 0.45 X      
 X = 0.12(Slab Thickness) – 2 x 0.02 (Top & Bottom Cover) – 0.012/2(Harf dia top) – 0.012/2( Half dia bottom)      
 X = 0.12- 2 x 0.02 – 0.012/2 – 0.012/2 = 0.068 m      
 L = 3.58 + 0.45X
L = 3.58 + 0.45 x 0.068
3.61
30 3.61 @0.90 97.47 kg

(In case of bent up bars are provided on both sides, we have to add 0.45 X twice in length)

4 8 mm dia. Distribution steel @ 180 mm  c/c            
  Bars at Bottom:            
  Hook Length = 9d
                         = 9 x 0.008
                         = 0.072 < 0.075
( Mini. Hook length = 0.075)
           
  L = 4 + 0.23 + 0.23 + 2 x 0.075(Both side hook(9d)            
  L = 4.51 m            
  Width of Slab = 3 + 0.23 + 0.23 – 2 x 0.05 (Both Side Cover)
= 3.36 m
           
  No. of Bars = (3.36 / 0.18) + 1 = 20 nos.            
  Bars at Top:            
  Width of Slab at one end for
bent up at Top
           
  L= 0.23 +  0.45 – 0.068 – 0.05(cover)            
(When bent up bar bent to top at the end of the bar, there is also distribution steel is provided. we have to add these bars in total distribution steel bar nos.)
  L = 0.562 m            
  Nos. of Bars at one End:
= (0.562/0.18) + 1
= 5 nos.
           
  Nos. of bars at both side
 = 2 x 5 = 10
           
  Total Bars = 20 + 10 + 30 30 4.51 @ 0.40 54.12 kg

BBs for Slab


Steel Quantity Calculation Excel Sheet

Free Download Above Excel Sheet

How to Calculate Steel Quantity from Drawing | BBS of Slab | Steel Quantity Calculation

How to Calculate Steel Quantity from Drawing



FAQs:

How to Calculate Steel Quantity

Longitudinal steels
Calculate the total length of longitudinal bars which equal to the height of column plus laps for footing multiply number of longitudinal bars.
Convert this length in kgs. This can be easily done by multiplying cross-section area of steel with total length by the density of steel which 7850 kg/m3

Steel Quantity Calculation

(Cutting length) main bar: formula = (l) + (2 x ld) + (1 x 0.42d) – (2 x 1d), where l = clear span of the slab, ld = development length which is 40 d (where d is diameter of bar), 0.42d = inclined length (bend length), 1d = 45° bends (d is diameter of bar) first calculate the length of “d“.


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