chapter (estimating)
TRANSCRIPT
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hapter Six
ESTIMATING
6.1 ESTIMATING
An estimating is trial to judge the value size, cost etc or to forecast of what a job or
service is expected to cost. Normally it is generally based on similar works or projects
taken up in the past, making necessary amendments especially for the cost materials
and wages. The total cost of a work is made up of the cost of various individual
elements. The estimating of the total cost consists of
!i" #stimating the cost of the $ndividual #lements of the %ost.
!ii" &uilding up the total cost, taking into consideration each individual
element of the cost concerned.
The cost of various individual elements may be under the work section of
!i" 'reliminaries ( which shall include insurance, progress photographs
report, warning sign, lamps, signboard, watchman, and etc.
!ii" )ain work ( which shall include building, roads, water tanks, bridge, tower,
and etc.
!iii" $nternal services ( which shall include air conditioning, fire extinguisher,
electrical installation, sprinkler
!iv" #xternal works ( which shall include electrical mains comprise of
capital*service charge, sewerage, water supply, special foundations, site
work, surface drainage, road and paths, fencing and gates.
!v" Advertisement
!vi" +upervision
!vii" )iscellaneous!viii" 'rofessional fees ( which shall include surveyor, designer.
!ix" %ontingencies ( it is a sum entered to allow for possible additional work or
dayworks assume it was -/ of the total cost estimated.
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6.2 OBJECTIVES OF ESTIMATING
The main objectives of estimating are as follows
gives prior indication of the economic viability of a particular project
to make a decision whether to proceed the project or not due to its cost
an estimate helps establish data for the purpose of comparing
estimating may help a new design to reduce the cost of the project, when the original
design is found uneconomical.
6.3 STAGES OF ESTIMATING
Traditional civil engineering projects can be divided into six stages
i" $dentification,
ii" Appraisal,
iii" 2efinition,
iv" Approval,
v" $mplementation and
vi" 3peration.
Figure 6.3 : Variati! I! T"pe O# E$ti%ate &ith Cha!ge$ I! 'r(e)t Stage$
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Preliminaryestimate
Appraisal
estimates
Proposal
estimate
Approvedestimate
Post-contract
estimate
Achieved
estimate
Pre-tender
estimate
Time
Operation
Implementation
Approval
Definition
Appraisal
Identification
ProjectStage
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5igure 0.- shows the se6uence of these project stages and indicates the types of
estimate used in each stage.
Preliminary estimate ( an initial estimate at the earliest possible stages.&ased on crude indication of the project size or
capacity, to be used in planning stage.
Appraisal estimate ( should include all costs which be charged against the
project in order to provide best estimate off anticipated
total cost.
Proposal estimate ( based on a conceptual design and design study
specifications.
Approved estimates ( proposal estimate was modified due to client7s view
Pre-tender estimate ( a refinement of the approved estimate based on the
definitive design work using the information provided in
the tender documents. At this stage the estimate
should reflect the total capital cost of the project and all
the charges and fees and allowances or contingency
for the client7s risk.
Post-contract estimate ( a further refinement of the pre(tender estimate
Achieved cost ( actual costs of the job in order to review performance
and provide data for future projects.
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6.* T+'ES OF ESTIMATING TEC,NI-E
The five common estimating techni6ues are summarised as follows (
G/0a/ ( a simple estimating techni6ue which based on existence of data
from similar projects.
Fa)tria/ ( a techni6ue used widely on process plants where the key
components can be easily identified and priced and all other works
are calculated as factors of these components.
Ma!hur ( works is estimated in total man(hours and cost in conjunction with
plant and material costs.
!it rate ( based on bill of 6uantities, where the 6uantities if work are defined
and measured in accordance with standard method of
measurement.
Operati!a/ ( based on all the constituents operations necessary to construct
the works and estimating the labour, plant and materials costs
together with the overheads.
Table 0.8 shows the five estimating techni6ues in terms of their project data
re6uirements and estimating data re6uirements.
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Ta0/e 6.* : Mai! E$ti%ati!g Te)h!iue$ A! Their 4ata 5euire%e!t$
4ATA5E-I5EMENTS
ESTIMATING TEC,NI-E
G/0a/ Fa)tria/ Ma!hur$ !it rate Operati!a/
'roject data %ompletiondate
9ocation
+ize*capacity
%ompletiondate
9ocation
9ist of maininstalledplant items
%ompletiondate
9ocation
:uantities
+implemethod
statement
;ey dates
%ompletiondate
9ocation
&: !at leastmain items"
%ompletiondate
)aterials
:uantities
)ethodstatement
'rogram
&asic #stimating
2ata
'otential
'roblems,
eneralinflationforecasts
)arkettrends
$nflationindices
Achievedoverallcosts ofsimilarprojects!ade6uatelydefined"
>eneralinflationforecasts
)arkettrends
$nflationindices !forhistoricalprices"
#stablishedfactorialestimatingsystem
eneralinflationforecasts
)arkettrends
$nflationindices
?istoricalunit rates forsimilar workitems
'reliminaries
)aterialscosts
9abour ratesandproductivity7s
'lant costsandproductivities
3verheadcosts
)aterialscostsforecasts
9abour rateforecasts
'lant capitalandoperatingcostsforecasts
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6. CONSTITENTS OF ESTIMATE
The price of an item of work is made up of the following components (
%ost of materials ( calculate the materials re6uired for the item of work and
allow for waste and delivery to site.
%ost of labour ( this is very uncertain factor, the output of labour varies
considerably accordingly to place of works, weather
condition, heights etc.
%ost of tools and plants ( the cost should include
initial cost of machine
interest on capital cost
the economic life span of machine
maintenance
cost of transporting machine to site
number of hours machine is operated in one year
consumption of machines fuel cost
driver*foreman unskilled workers ( wages
output of machine
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6.6 &O57E4 E8AM'9ES
Exa%p/e 6.6.1 E$ti%ati!g O# Ex)aati! &r;$ 3 hr
The labour time costs 3 hr
9abour cost of excavating 1 m-of rock including 1@/ profit
F
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Exa%p/e 6.6.1.a E$ti%ati!g O# Ex)aati! &r;$
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Exa%p/e 6.6.2 E$ti%ati!g O# Fr%r;
=sing 9a0ur a! Materia/ C!$ta!t$, prepare estimation cost for fixing one !1" piece
-mm x -mm heavy duty car porch tile with 4mm thick of cement and total cost ofthe proposed car porch tiles project abiding on data below. The project duration is
expected to be two !4" days and re6uires two !4" skilled workers and two !4" unskilled
workers.
2ata
1. Dhite horse heavy duty tile !-mmx-mm" F
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4. Ce%e!t
a" vol. of cement F .- x .- x .4
F .1Bm-
Total vol. of cement F @ x .1BF 1.-C@m-
%ost of cement F !1.-C@ x 4Bbag" x rm1@.
F