Thumb rules
refers to an easily learned process or standard based on practical experience
rather than theory. It is not intended to be strictly accurate or reliable for
every situation.Thumb rules give us the quick decisions at construction field.
It provides with the rules of mathematical formula and broad ideas whenever
needed. As a engineer, we have to be practical and quick in the field of
construction. Basically,thumb rule is the guide for civil engineers for
predictable results. It can vary to some percent but it will give a general
idea as well.When we compare to get the result, the units in the thumb rules
are not the same. Therefore, never consider units when performing the thumb
rule.There are several thumb rules that we apply in construction. Here I am
discussing the most frequently used thumb rules on the site.
Thumb rule to calculate the Concrete Volume with respect to area:
Example:-
Lets consider ,
Plan Area = 45 x 25 =1125SFT
The plan area is 1125 SFT then the total volume of concrete required = 1125 x 0.038 m3 = 42.75 m3
Thumb rule to calculate the Steel quantity required for Slab,
Beams, Footings & Columns:
For
Residential buildings -
4.5Kgs - 4.75 Kgs /SFT
For
Commercial buildings - 5.0Kgs -
5.50 Kgs/SFT
For more accurate
results you can also use BN Datta recommendations:-
As per B N Datta, the
Steel quantity used in different members of the building can be calculated
easily using the following recommendations.
Examples:
FOR
SLAB:
How to calculate the
steel quantity of slab having the Length, width, and depth of the slab is 6m x
5m x 0.15m
Step
1: Calculate the
Volume of Concrete
Total Volume of Concrete
for above given Slab is 6 x 5 x 0.15 = 4.5
Step
2: Calculate the
steel quantity using formula
As per the above table, the steel quantity of slab is 1% of the total volume of concrete utilized.
Thumb rule to calculate Steel quantity of above slab = Volume of Concrete x Density of Steel x % of Steel of Member
Steel
quantity required for above slab = 4.5 x 7850 x 0.01 = 353 Kgs
FOR
COLUMN:
How to calculate the
steel quantity of column having the Length, width, and height of the slab is
1.2m x 0.3m x 4.2 m
Step
1: Calculate the
Volume of Concrete
Total Volume of Concrete
for above given column is 1.2 x 0.3 x 4.2 = 1.512
Step
2: Calculate the steel
quantity using formula
As per the above table, the steel quantity of column is 2.5% of the total volume of concrete utilized.
Thumb rule to calculate Steel quantity of above slab = Volume of Concrete x Density of Steel x % of Steel of Member
Steel quantity required for above slab = 1.512 x 7850 x 0.025 = 297 Kgs
Similarly , you can calculate for Beam and Footings.
Thumb rule to calculate the Shuttering area:
Shuttering costs 15-18%
of the total construction of the building. Shuttering is framed to bring the
concrete in Shape and giving a desired mould in terms of quality.
Thumb rule to calculate
the shuttering required is 6 times the quantity of concrete or 2.4 times of
Plinth area.
Suppose, the concrete
quantity is 0.8 m3, then the shuttering area required is 0.8 x 6
= 4.8
Components
of Shuttering:-
Components of Shuttering
are shuttering ply, battens and nails.
Shuttering Ply Quantity
calculation:
The shuttering Ply has a
length, width & depth of 2.45 x 1.22 x 0.012
The No. of Shuttering
Ply sheets = 0.22 times of Shuttering
Suppose, the area of
shuttering required = 4.8
Then the Shuttering Ply
required = 0.22 x 4.8 = 1.056
Battens Quantity Calculation:
Battens have different
widths but we usually use shuttering batten having a length & width of 75mm
x 40mm.
Batten Quantity = 19.82
x No. of Ply Sheets
if the construction
requires 32 Ply sheets, the total quantity of Battens are 19.82 x 32 = 634
Battens
Thumb rule for Shuttering oil
Quantity:
Shuttering oil is used to de-frame or de-assemble from the
concrete easily.
Total required Shuttering oil is = 0.065 x
Total Area of Shuttering
(or)
For every 15 m2 of shuttering 1 litre of
shuttering oil is consumed.
Example :
15m2is total area of shuttering, then Shuttering oil
required = 0.065 x 15 = 0.975 litres
Nails & Binding Wire
Quantity in Shuttering:
75gms of Nails are
used for 1m2 of Shuttering
75gms of Binding wire
is consumed for every 1m2 of Shuttering.
Example:
15m2 is total area of shuttering, then Binding
wire required = 75 x 15 = 1125gms
Plastering Quantity Thumb Rule:
Cement Masonry Quantity Thumb Rule:
Brickwork Thumb rule:
Thumb rule for Cement, Sand, Coarse Aggregate Quantity in Different grades of Concrete :
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