and welcome back to our lectures on principles of construction management today we will continue
with our discussion on planning and scheduling what we had done in the last class was to
construct a network based on the information given in this table and we had made this network
similarly for another example when there were five activities in the project we had constructed
this network based on the precedences given now what we will do today is to have a general
discussion on some of the resources that are required for the planning of a construction
project so we will talk of quantification of workload
that is in man days or man hours so at the end of it what we are given is a quantum of
work whether it is cubic meters of excavation or pouring a certain volume of concrete or
erecting a certain tonnage of steel or whatever that is so we have to convert that workload
to the workload in order to get an estimate of the time involved then we have to identify
the resources we have to identify the equipment we have to identify the labour and so on we
may have to also make judgments on whether to employ this equipment or that equipment
or maybe employ no equipment at all only then we can arrive at some kind of an estimate
of the time which is required to complete the project
then its also the matter of allocation of resources that is how much resources is allocated
to a certain project most of the time the project manager is not working with infinite
resources so there is a finite resource whether its in terms of manpower its in terms of equipment
its terms of materials so the decision has to be made how to allocate the resources at
given point in time at one point in time it may be deemed or it may be felt that there
is one activity which needs a particular source more than the other and finally we need to
keep in mind the fact that all this effort is being done to figure out or to understand
what are the implications of this exercise in the cost of the project
so having said that lets try to move forward and go to an illustrative example which consists
of lets say four activities abc and d with the following interdependencies and estimate
of the quantum of work in this case we have already done the first step that is we have
converted the quantum of work to the man days so in this case there are activities abc and
d a and b can be started without any dependence on each other and c depends on a and d depends
on b and lets further assume that the activities a and c require labour with t one expertise
and activities b and d require labour with t two expertise and we are talking only in
terms of labour deployment so this project is such that it requires only
workers but workers having an expertise in certain area it could be for example carpentry
and masonry we have added this information on expertise in the same table and now we
have a and c which is one set of activities which required t one and we have b and d which
require t two and the man days estimates for a and c is five hundred and three hundred
for b and d it is two hundred and two hundred so if we move forward and we make an assumption
that we will deploy ten workers with expertise t one and ten workers with expertise t two
which is given here what do we get this assumption was necessary in order that we are able to
get the times required to be able to complete these activities
so if we divide this man days by the number of workers its elementary arithmetic that
we can say that well this activity can be done in fifty days this can be done in twenty
days thirty days in twenty days what we have to understand is that dividing this man days
by the number of people who are working is a simplistic approach and what we are saying
is that the efficiency of the workers is not being taken into account the learning that
happens over the period of time after all we are talking of fifty days so what the kind
of productivity of the worker is in the initial phases need not be the same as in the final
phases so given those kind of simplifying assumptions
this basically just gives us a estimate of the time so now if we move forward from here
and try to draw the activities on arrow network which we have seen last time this is what
we will get this network shows the activities and the estimated man days for each activity
so activity a is one two activity b is one three they can be started independently c
can be started only after a has finished that is activity two four and similarly we have
activity d which is three four which can be started only after b has finished and with
these numbers indicating the estimate of the man days we move forward and complete this
network which now gives us the times which we have also calculated earlier
so lets not bother about what is written in this squares because thats something which
we will talk about later we can complete activity a in fifty days and see which starts after
fifty days we can complete it in another thirty days and therefore the project can be completed
in eighty days as far as a and c is concerned similarly b and d can be completed in twenty
and twenty which is forty days so what is effectively happening is that if we plot time
here and activity a here what we are saying is that this is going to take fifty days b
can be started immediately and it will take twenty days c can be started only after a
is completed and its going to take another thirty days and d can be started after b has
finished so its going to be here so its forty so of course lets not bother about the scale
this should be fifty here so that brings me to fifty this comes to forty and this is where
my eighty is so this is one rough representation assuming that we are starting b at the earliest
possible time that it could have been started this is not really necessary and thats what
we are trying to see from this example later on so effectively what we are saying as far
as this discussion is concerned is that the project needs eighty days for completion with
this kind of deployment of manpower what was the deployment of manpower we have put ten
workers for a ten workers for b and the same workers which were working for a after completion
of a moved to c and the completion of b these workers move to activity d
we also find from this small chart that bd is not a critical activity of course critical
activities there is a technical definition and we will talk about it in the next class
but its very obvious that b and d even if they get delayed a little bit here and there
it will not affect the project so long as they can be completed within the eighty days
that is the time that is being taken by the activities a and c to complete so if now we
move forward and try to studies different case what we do is that we reduce the allocation
with t two expertise that is the workers working for activities b and d to be extend lets say
make the five that the path bd now also takes eighty days
so what we know is this ten remains where it is but this five is reduced from ten earlier
we were working with ten people even for b and d but now we are going to put lets say
five people so what happens as a result of this reallocation the times taken for a and
c dont change but the times taken for b and d they become forty each so what this results
in is something like this that a and c can be completed in eighty days as earlier and
b and d also now takes eighty days so going back to our earlier representation what is
happening is that if i have a taking fifty days b now taking forty days c is starting
at the end of a and taking thirty days and d is starting at the end of completion of
b and taking forty days now we have this eighty day deadline where
both a and c and b and d are getting completed at the same time so what effectively has happened
is the project is still being running in eighty days but there is a reduction in the manpower
of expertise t two so this was an illustrative example as to how we can change the resources
allocated to certain activities and try to engineer the duration of that activity but
at the same time not compromising on the duration of the project
now we can do another example where we try to enhance the allocation to a and c and try
to reduce the project duration to forty days now where is this forty coming from its coming
from the fact that b and d could be completed with ten people in forty days so now what
we want to see is is it possible to complete a and c also in forty days by just enhancing
the manpower and thats what we are trying to do we are trying to allocate additional
manpower to activities a and c that is being increased by ten to twenty and what we have
now is that a and c are getting completed in twenty five and fifteen days and this makes
it forty and this was what the original allocation was and we are still at forty
so going back to that network we have now a and c having forty days and b and d also
getting completed in forty days so going back to that chart representation that we have
if we have this time what we are doing is a has now been shortened to twenty five b
is taking twenty days which is just a little less than that c is starting after twenty
five which is somewhere here and going to fifteen days and d is starting just after
the completion of is also getting completed but project is getting completed in forty
days so this is what we have achieved by enhancing
the allocation to activities a and c so what we see is that the project duration is reduced
to forty days using additional resources what we have to think is how does this affect the
total cost of the project what we have to consider is both the direct and indirect costs
and that is something which we are leaving as a food for thought for the present and
we will address this issue at some point in time later on in this course now lets move
on to an another example lets talk in terms of an example of a project which involves
daily floor cleaning of a two hundred square meter house the option one is to do a manual
operation using the simplest of tools and tackles and from experience we know that the
task can be done in two hours every day and the cost is three hundred indian rupees
so now we are invoking experience to determine the time in the previous case we had invoked
experience but it was not obvious because we did not even have the actual work involved
but we had given only the man days involved so in this case we are saying that experience
tells us that it can be done in two hours every day and the cost is three hundred rupees
and therefore the monthly cost is nine thousand rupees if we were to now do this operation
using a vacuum cleaner and obviously the vacuum cleaner will have an operator so we have to
consider the cost of both of these and again by experience we know that the tasks can now
be completed in thirty minutes thats half an hour instead of two hours and the cost
is hundred rupees for the labour so in the previous case when it was two hours
we had taken a labour cost of thee hundred now if it is half an hour instead of seventy
five we are taking a cost of hundred for the simple reason that here it was lets say unskilled
labour but in the case of operating an equipment the kind of labour involved could be different
and therefore we have enhanced the cost involved as far as labour is concerned so therefore
the total cost per month is thee thousand which is the labour cost and we have to include
the equipment costs so now how do we determine the equipment cost we have to lets say find
the cost of the vacuum cleaner which is lets say forty eight thousand and the service life
is two years with no salvage value we also say that there is a maintenance cost
involved of one thousand rupees per month so the total cost as far as equipments is
concerned would be lets say two thousand rupees a month which is basically purely depreciation
we take forty eight thousand distributed over twenty four so we get two thousand and we
have a maintenance cost which is one thousand and my total equipment cost is three thousand
and therefore the overall cost is three thousand for equipment and three thousand for labour
which is six thousand per month as against the nine thousand in option a
so what we have to think about is the availability of labour is something which is very very
important in calculating the labour cost and in fact the labour cost is often governed
more or less by the availability of labour so if there is shortage of labour the labour
cost will keep going up the cost of the equipment initial and maintenance so through this example
what i have tried to do is to illustrate how it can be integrated into a decision making
process what we have to also think is is it rational to choose only on the basis of relative
total cost what are the other possible yardsticks and if those yardsticks can be found we would
probably be able to make a more rational and a educated decision
so some of those things could be quality and safety in a country or in a situation where
labour is cheaply available so the labour intensive construction may be economical but
what we have to make sure or also understand that there could be issues in terms of quality
and safety as far as safety is concerned there may be situations where it is difficult almost
impossible sometimes to have a worker working depending on what kind of regulations and
specifications are there it may have to be an equipment which has to be sent in to be
able to carry out a particular construction activity in which case regardless of the cost
of equipment we have to really opt for that working with only labour has the problem with
quality also at times because different people have different competence levels and its difficult
to ensure uniform quality which is so much easier to achieve if we are working with equipments
now mechanization of course has also given a quantum leap to capability that is we are
now able to think of and execute projects which were simply not possible earlier because
it was not possible to carry out those activities manually so lets try to take one more example
where the project involves the excavation of a thirty meter by thirty meter raft foundation
to a depth of two meters with the earth to be transported up to thirty meters from the
edge and the completion time is given to be ten days
so option a if we talk of manual operation the total quantity of excavation is very clear
the total quantity of excavation is thirty into thirty into two which is eighteen hundred
cubic meters we have to convert this quantum of work to man days using productivity information
we have to convert the man days information to the number of labourers used or workers
required to ensure that the task is completed in ten days and assuming a wage rate calculate
the cost of the excavation so these are basically the steps involved in calculating the cost
of this project using manual labour alone so if we try to do that the quantity of excavation
is given man hours per unit lets say two hours per unit in this case the unit is a cubic
meter and therefore to do eighteen hundred cubic meters we need thirty six hundred man
hours and assuming eight hours per unit days of work and the days required to complete
the work is four hundred fifty and for the task to be completed in ten days we need forty
five workers and now for these forty five workers the total cost at lets say three hundred
sixty eight which is given in the standards are given in regularly published documents
the total cost of excavation turns out to be one hundred sixty five thousand six hundred
rupees for eighteen hundred cubic meters if we do this operation manually
one way of looking at these numbers could be that if we take this to be lets say hundred
and eighty thousand then what that means is that a hundred eighty thousand rupees is being
taken to do an excavation of eighteen hundred cubic meters so basically what we are looking
at is the hundred rupees per cubic meter is the rate of the excavation this weight does
not include contractor profits it does not include water charges or power charges or
whatever the miscellaneous charges that may be applicable to a particular site but that
gives you some insight into these numbers now lets continue and try to do this operation
mechanically using excavators and dumper trucks so the quantity excavation doesnt change eighteen
hundred determine the time required to carry out the excavation using one excavator and
assume that there will be two trucks which will be employed to transport the earth in
order to determine the cost we need to know the initial cost of the excavator or the truck
or we could find out the cost of engaging this equipment at the site for the period
estimated then find out the cost of consumables for the excavator and the trucks and determine
the labour cost associated with the operators of these equipment and we will have the total
cost of excavation carried out mechanically so for that for an eighteen hundred cubic
meter excavation lets assume that the productivity of the excavator is thirty cubic meters per
hour so what we are looking at is sixty hours of equipment use its not man hours in this
case its more like equipment hours so it means that sixty hours is when the equipment should
be running and if we assume that the equipment transfer eight hours a day we have that number
of days required to complete the project as seven point five now if we assume that this
seven point five is something like eight so we say that the time of completion is eight
days then the number of labourers or the operators required every day is six because we are having
a excavator and two trucks which are operating each of them has two people the cost of the
equipment that is the excavator is six thousand five hundred rupees a day and for eight days
this turns out to be fifty two thousand similarly the cost of the tipper which has been taken
to be eighteen hundred per day for eight days and two tippers is twenty eight thousand eight
hundred the cost of labour at seven hundred rupees per day for six people working eight
days is thirty three thousand six hundred to this cost we must add twenty centimeters
to be leveled manually that is what is being considered in this case because using an excavator
it is not sometimes possible to get a very plain surface
so that last twenty centimeters that is ten percent of the cost will have to be brought
from option a and that cost is sixteen thousand five hundred and sixty so if we do that the
total cost of work involved is a hundred and fourteen thousand four hundred as against
about a hundred and sixty five thousand which was the cost that we got for purely manual
operation so with this we have kind of completed a comparison of carrying out an excavation
of eighteen hundred cubic meters but we must remember that its an open excavation its a
free excavation with no encumbrances and we have made assumptions in terms of productivities
in terms of what is the labour requirement to do every cubic meter of the work and in
the case of equipment the productivity which we have taken to be thirty cubic meters per
hour so with this we come to an end of the discussion today so these are the reference
books which will help you understand the subject better and before we close the discussion
today i would like to leave you with the thought that what we have assumed in the discussion
when we are talking about twenty labourers here and ten labourers there in the first
example what we have said is that over a period of time the labour deployment remains constant
now is this the best way of deploying labour that is right from the word go till the end
of the project it is the same number of people which are working so we took it to be twenty
we took it to be five ten and so on but we made an assumption that all of them will be
working throughout the project this is something which we have to think about because it may
not be possible to begin your work with this kind of a labour force so what is more realistic
is to have a smaller amount of labour in the beginning go to a peak and then gradually
reduce the labour force so that the total work is completed in still the same time so
with this thought i look forward to seeing you once again
thank you