First step to
rate analysis is the estimation of labour, materials, equipments and
miscellaneous items for particular quantity of reinforced concrete.
The second
step is to determine the component of structure for which the RCC rate analysis
is required, as the quantity of reinforcement steel varies with slabs, beams,
columns, foundation, RCC Roads etc., though the quantity of other materials
like sand, coarse aggregate and cement remain the same with the same mix design
(mix proportion) of concrete. Labour rates for reinforcement work changes with
type of structural component as the quantity of reinforcement steel changes.
The Quantity of materials like sand, cement and coarse aggregates vary with mix
design such as M15 (1:2:4), M20 (1:1.5:3), M25, M30 etc..
Here we will see the rate
analysis for lm3 of reinforced concrete.
1.Estimation of materials:
Material
estimation include sand, cement, coarse aggregate and steel for a
particular mix design. Let us consider a mix design of 1:1.5:3 for
our estimation practice. The dry volume of total materials required is
considered as 1.54 times the wet volume of concrete, due to voids present in
sand and aggregates in dry stage. Therefore, for our calculation, we will
consider the total volume of materials required as 1.54 m3 for 1 m3 of wet
concrete.
a) Bags of cement required:
Volume of cement required
for l m3 of Concrete =
1x1.54
------------ =0.28 cum
1+1.5 + 3
1 Bag of Cement -50 Kg
Cement Density=1440 Kg/Cum
Volume of one Bag cement=(50/1440)=0.0347 Cum
No of cement Bags required=
0.28/0.0347 = 8.07 bags of cement.
Volume of sand required =1.5x1.54
------------ =0.42 cum of sand
1+1.5 + 3
Volume of Coarse Aggregate
= 3 x1.54
------------
1+1.5 + 3
=0.84 cum of Coarse aggregate
Quantity of steel required depends on components of structure, i.e.
slabs, beams, columns, foundations, roads etc. To estimate the steel required,
there are two methods.
First method
is, when we have the drawing available, we can calculate the total weight of
steel required divided by total volume of concrete for different components.
This will give us the weight of reinforcement steel per cubic meter of
concrete.
Second method
is assuming the percentage of reinforcement for different components. Following
are the percentage of reinforcement steel generally required per different
components. Its values can vary from structure to structure, and can be assumed
from past experiences of similar structure.
• For
slabs = 1.0 % of concrete volume.
• For
Beam = 2 % concrete volume.
• For
column = 2.5 % of concrete volume.
• For
RCC Roads= 0.6 % of concrete volume.
Lets take example of RCC Column, where reinforcement required
is 2.5% of concrete volume, weight of steel required will be
2.5
-------- X 7850 =196.25 Kg
100 X 1
Labours
required are presented in terms of days required by particular labour to
complete its work for the given quantity of concrete. Following are the various
labours required:
a) Mason: As per
Standard Schedule of Rates and Analysis of Rates, One mason is required for
0.37 days.
b) Labours: One
Unskilled labours required for 3.5 days.
c) Water
carrier: One water carrier required for 1.39 days.
d) Bar
Bender: Bar bender requirement depends on weight of reinforcement. Lets
consider one bar bender required for 100 kg of steel as for 1 day.
e) Mixer
Operator: One mixer operator required for 0.0714 days.
f) Vibrator
Operator: One vibrator operator required for 0.0714 days.
Equipment and
other charges, such as water charges, miscellaneous items, tools and tackles
etc can be assumed as some percentage of total cost of materials and labours.
Lets say it as 7.5%.
Contractor's
profit depends on place to place, organization to organization and work to
work. It varies from 10 - 20%. For our case lets assume it as 15% of total cost
of materials, labours and equipments.
We have
calculated the quantity of every item in above 1-3 steps. For rate analysis of
RCC, we need to multiply each quantity with their rates to get the amount for
every item of work. Rates vary from place to place and time to time. It is
advisable to assume local rates or standard rates of the place.
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