and welcome back to this series of lectures on principles of construction management and
in the last couple of lectures we have been talking about planning and scheduling in construction
projects today we will concentrate on what is called resource leveling and allocation
now construction schedules as we know are either time oriented or they can be resource
oriented in our discussion so far we have mostly talked about concepts related to time
oriented scheduling today of course as i have mentioned we will talk about resource allocation
resource leveling and those concepts which are resource oriented scheduling concepts
now what is resource scheduling estimation of activity times and project durations using
network diagrams assuming that there is no cap or there is no constraint on the availability
of resources that is what we have been doing if you recall those in earlier example we
are probably going to do it again today that we estimate the quantum of work have a number
for the productivity of the labour or equipment and try to come up with the time that is required
to complete that activity so we almost assume that there is no constraint on the availability
of the resources as such but in real life projects there are resource constraints such
as shortage delayed delivery competing demands it may happen that you may have a set of resources
but there are different activities in the project which demand the use of that resource
you may have only ten laborers or ten workers and there may be five activities which demand
labour or demand workers to complete them we have to decide as construction managers
which activities would take precedence over the others and so on so there are various
situations because of which we need to do resource allocation we have to decide or prioritize
which activities will be taken up first which may be postponed to a later time
resource planning and allocation plays an important role in managing construction projects
now lets look at the principles involved in deploying resources to activities in a project
and the resulting implications through a very simple illustrative example we have talked
of this project before when we considered a simple project having just the activities
a b c and d with precedences as given a and b are independent and can be started right
at the word go c depends on a and d depends on b this is the man days requirement as far
as each of these activities is concerned now we also said that a and c require labor of
similar expertise let us say t one and b and d require labor of another expertise which
is t two what we tried to talk about was that if we allocate lets say ten numbers of t one
expertise labor and ten numbers of t two expertise labor how will the project planning be done
now once we assume that there are ten workers with t one expertise available to us ten workers
of t two expertise available to us we can find out that the time required to complete
this project is fifty days for activity a twenty days for activity b thirty days for
c and twenty days for d this is nothing but this number here which is man days divided
by the number of laborers
now what this assumes is that the labor supply or the availability of labor whether it is
t one or t two is constant over the entire duration of the project representing this
project on an activities on arrow network we can find out that if a is done in fifty
days c is done in thirty days b is done is twenty and twenty the earliest that the project
can be completed is eighty days because this path is now the critical path this can be
done in forty days in this representation what we have assumed is that as far as the
labor with t one expertise is concerned as far as the labor with t two expertise is concerned
both of them are employed to the fullest extent right from the word go till the project is
completed so ten numbers of workers with t one expertise work from day one to day eighty
even the project is completed initially for some time they work on activity a and then
they work on activity c in this case we have assumed that the activity b starts at the
earliest that it can and these people who have an expertise in t two work initially
on b and then on d and then everybody goes home
this part of course can actually be completed not necessarily starting with zero but anywhere
in this region provided it is not going beyond the eighty day limit when a and c will get
completed now this approach which assumes a constant deployment of labor has its own
problems uniform availability of resources is neither possible nor desirable moreover
it is not advisable as well few obvious reasons could be mobilizing sufficient funds during
the initial stages of the project may not be possible in most projects most of the construction
activities happen during the middle stages of project and hence it is recommended to
have a gradual increase in the deployment of resources in the initial stages and gradually
decrease it after meeting the peak demand which essentially happens during the middle
of the project we have talked about the s curve and its relevance as far as project
progress is concerned there are lots of reasons why most projects follow this s curve in the
initial part it is not only the mobilization of the funds but it is also the learning experience
availability of front all these kind of issues make it very difficult to achieve a progress
which can be sustained all the time but having done that additional experience of learning
it is much easier to gradually increase the resources reach a peak level and then (( )) it
off
similarly towards the end of the project it is very difficult to have the entire work
force working at that project there will be a smaller and smaller areas which will be
available there will be smaller and smaller amounts of work which will be left and therefore
it makes no sense it will be very difficult for a uniform progress to be maintained what
i am essentially saying is if we differentiate this total progress with respect to time what
we will get is a progress curve so this is our rate at which the project moves and if
the project moves gradually in the beginning reaches a peak at the middle stages of project
and then goes to zero once again what we will get as the cumulative progress is what is
given in blue now this is precisely the kind of deployment of labor that we would like
to actually see rather than the constant deployment as we have seen in the previous slide what
this slide shows is an alternative way of having employed the labor for completing the
five hundred or three hundred man days of work it really shows the deployment at different
points in time and the rest of it i am sure you can figure out
now coming to our main discussion today which is resource planning and scheduling there
are two aspects to our discussion one is resource leveling and the other is resource allocation
leveling deals with distribution of resources within the fixed project duration and allocation
deals with availability of resources under a constraint so coming to the first part which
is resource leveling that is the process of allocating resources among various activities
such that the peak requirement of resources is reduced with a constraint on time and the
underlying assumptions in resource leveling are only one type of resource is considered
throughout the project and activities already underway should be completed first what i
would like you to recall is that activities are of two types lets say critical activities
and non critical activities critical activities are those which must follow one after another
without any gap without any gap means there is no float and at the completion of these
critical activities the project is completed so basically the last activity to be completed
has to be a critical activity that is by definition
now along with the critical activities there is a set of non critical activities with whatever
dependences they may have critical activities also have their dependence on non critical
activities but there is some float there is some (( )) independence in deciding when a
non critical activity is done so the whole idea of resource leveling is to make sure
that the resources that are used in non critical activities are not spread out over the project
is sporadically it should not happen that over a period of time i need a resource here
then i need it here then i need it here if possible i would like to build these resources
such that they are used here and here so that this particular resource can be brought to
site only for this duration and be let go provided of course that this is for non critical
activities in the case of critical activities there is something which we may not be help
much
so with this background in mind let us move forward and try to understand the steps involved
in the resource leveling process identification of critical activities arrangement of activities
on the time axis based on their early state dates determining the total number of resources
required on each day by adding the resource requirements of individual activities planned
for that day and the resource profile determined as a chart called the resource aggregation
or resource loading chart as we do a simple example these things will become clear repeat
steps two and three with activities being plotted using the latest start dates comparing
the two resource charts that is that determined in step three and four and finding out an
acceptable resource profile between the two extremes eliminating the peaks and values
in the resource distribution this is done by arranging non critical activities within
their float which obviously means that the duration of the project is not compromised
let us go through a simple example to understand this concept let me once again reiterate that
what the steps essentially have told us is that a non critical activity can start and
finish as is shown here if this is my earliest starting date for that particular activity
this is the duration of that activity this becomes my earliest finishing time for this
activity however without compromising the duration of the project this activity can
also be scheduled in this time frame where the duration of the project remains the same
and this is my last starting date or the latest starting date this becomes my latest finishing
date this we get from the backward pass and this is what we get from the forward pass
and remember that the activity can be scheduled anywhere between these two extremes that is
within e s t and l s t if the activity starts anywhere in this region it will get completed
anywhere in this region and this will not compromise the length of the project so that
is precisely the kind of thought process that goes on in leveling of resources so lets understand
this a little bit better through this example which gives us the seven activities as shown
their dependences and i have already the network for you so this here is the durations of all
these activities a requires thirteen b requires five c requires five d requires twelve e requires
two and f requires five lets say days to complete g requires ten and this number here in the
bracket is the resources so in this case as a simple example we are saying that this number
here represents the number of workers which is required to complete this activity we must
remember that as far as this example is concerned we are also going to assume that a requires
two workers means it requires a team of two workers it cannot be done or it cannot be
started unless there are two people available further it cannot be accelerated by putting
more people on the activity
so with this understanding and assumptions let us try to find out what can we do with
the resource allocation algorithm which we have just learnt so the earliest and latest
occurrence of the events are shown in the notes and they have been obtained by the forward
pass and the backward pass i am sure you know how to do it a can start at zero and therefore
this node here which is node tow the earliest it can be reached is thirteen this node five
can be reached earliest depending upon the maximum of these three nodes which are converging
on this and so on so we find out that activities a d and g are critical and the project duration
is thirty five days so this is the first step we find that a d and g are critical activities
they are highlighted by a form arrow and we find that the project can be completed in
thirty five days
now let us try to do the next step which is scheduling these activities on the time access
this representation schedules these activities in the earliest start times so a obviously
starts here finishes at thirteen d which follows this is completed here g is completed here
and this is thirty five days as far is b is concerned you will recall from the diagram
that it depends on a and therefore can be started as soon as a is completed and the
same thing is valid for activity c so these activities start here on lets say thirteen
and are completed at whatever times depending on their durations and we reach these points
as is shown here now on this if we superimpose what is the kind of resources that we need
on each day we find that as far as this point is concerned that is as far as the first thirteen
days are concerned only activity a can be done no other activity can be done which means
that a which needs a team of two persons is the only activity going on as far as this
project is concerned and our deployment is only two workers now coming to day fourteen
we have the possibility of activity d b and c being carried out d requires two b requires
three and c requires four workers and therefore the deployment required as far day fourteen
is concerned is nine this continues till such time as activity c is finished once c finishes
we have activity f which may start and so on what we need is to do find out on a given
day what are the activities that are going on and find out what is the demand for the
labor on that particular day so we find that beyond this point only activity g is going
on and that requires four people and that is what we have so towards the end of the
project we have only people working on activity g right upto the end of the project
this is a scenario for starting all the activities on their earliest starting times now if we
represent this labor deployment on the time axes this is what we get so we have two people
here increases to nine here goes to eight five drops to two and then goes back to four
what we have to see is whether this is the most desirable form of labor deployment or
not in order to be able to do that let us try something else let us try to schedule
the activities so that they start at their latest starting times what we are trying to
do is to ensure that g which is the last activity and depends on the completion of activity
e and completion of activity f is not delayed because this is my critical path in order
for this to happen we must make sure activity b starts here activity e starts here c starts
here and f starts here that is precisely what is their latest starting times so now with
this algorithm or with this thought process let us try to then find out what is our labor
deployment this is what the numbers you will get from here to here it will be all twos
then it goes to six nine eight and goes back to four
representing this on the time axis in a manner that we did the last times as well we find
that we have possibly a slightly better situation we have two six nine eight and four now the
point is can we do something better than that now let us do yet another reiteration with
the same example so let us try to do another reiteration and try to see if we can remove
the peaks further and reschedule our non critical activities but what we must remember is we
must remain within the floats of these activities now with this thought in mind that we will
use the floats and try to reschedule the activities let us do this reiteration in this one what
we are saying is that activity c and f which is here are starting at their earliest starting
times which is somewhere here and b and e are starting at their latest starting times
and with this if we do the resource aggregation we find the numbers to be given as they are
at the bottom
this is the graphical representation of the resource profile that we get when we have
chosen to start one set at the earliest starting times and one set at the latest starting times
now before we compare these three resource curves i must point out that here we find
that the peak demand of resources has reduced from nine to eight now this picture here shows
the comparison that we have this was when the activity is started on their earliest
staring times this what we have when we have the activities starting at the latest starting
times and this is what we have when we did the combination of e s t and the l s t for
the different activities personally to me this seems to be the best alternative that
we have so far we can try another you can work out more examples or more combinations
with b e and c f separated what we have done is b and e have been taken to both start at
the same time b and e have followed each other c and f have followed each other as soon as
the previous one was completed so as soon as b was completed e was started as soon as
c was completed f was started we can separate these two activities because we can say that
b we will start at the earliest time and e we will start at the latest time
so if we do these kind of combinations we will probably be able to generate more resource
aggregation curves and then make a judgment on which is the most desirable form it may
also be governed by availability and so on and that is the next topic of discussion today
that is allocations of resources under a constraint regime now coming to the discussion on resource
allocation under a constraint the resource allocation is performed when the availability
of resources is constraint due to limited availability of resources some activities
have to be necessarily delayed the basic objective is to find out which of the activities can
be delayed and finally arrive at the shortest possible time to complete the project satisfying
the resource constraints this may or may not result in the delay of the project
in as much as we will try to ensure that the project is not delayed by finding out the
critical activities trying to make sure that the critical activities are not starved of
resources at times it may become impossible to avoid and that is something which we have
to deal with and if we plan enough we are able to flag these issues in advance now as
far as the steps which are involved in resource allocation these are the following identify
the critical activities in the network allocate resources day wise if at any time the resource
requirement exceeds availability then allocation of resources to activities should follow the
following rules rule one resource allocation get the first preference rule two ongoing
activities should not be stopped in the middle rule three allocate resources to activities
that have the least earliest starting time and rule four if two activities have the same
e s t then allocate the resources to the activity that has a lesser float please note that activities
may be rescheduled due to resource allocation which may result in activities that become
critical once we are playing around or shifting the non critical activities their starting
points their scheduling that may lead to a change in the critical path and that is something
which has to be constantly kept in mind it should be ensured that the above is accounted
for in making a decision based on the above rules this change in the critical activities
should always be there as a governing principle when we are trying to do the reallocation
of resources
now lets look at an illustrative example for this lets consider the same example and which
the project takes thirty five days to complete normally now we will assume that the maximum
availability of resources on a given day is eight so recall that the maximum resources
that we had in a lot of our simulations that we ran was nine determine if there is any
delay in the project completion again we would carry out this first exercise and find out
that a d and g are critical activities with the project duration of thirty five days through
the forward and the backward pass now this here shows a graphical representation of the
activities is starting at e s t with the float the float is what we have added to the previous
diagram and this is our resource aggregation diagram and we note that till day thirteen
activity a that has a resource requirement of only two is carried out and that is not
a problem because the maximum available resources is eight
now on day fourteen however the resources need to be allocated to activities d b and
c if they have to start on their respective e s ts now the total resource requirement
on day fourteen therefore turns out to be nine which is exceeding the available limit
of eight so we have to find out which of these activities needs to be supported how should
the resources be allocated and for that we go to the rules that we have just gone through
if we look at this tabular representation of the rules we have activities d b and c
competing for the resources the resource requirements for these activities is two three and four
respectively and we write down whether these activities are critical or not whether they
are ongoing or not what is the earliest starting time of these activities what is the float
now based on this we have to assign the priorities so in this particular case activity d is the
clear winner in the first round because it is a critical activity so it gets priority
number one but it has a requirement of only two resources now since more resources are
available basically the competing activities are b and c
now which of this gets a priority would be determined by the float in this case and in
this case c has a lower float and therefore gets a priority two and b having a higher
float is left behind that is it is allowed to delay that is activities d and c will be
scheduled together constituting six resources and activity b will be delayed please note
that even though we are consuming only six resources we cannot start b because it requires
three and we have only two available moving on this situation will continue till day eighteen
only when it comes to day nineteen we have a situation where activities d b e and f compete
for resources and in that case we draw this table and find out the priority of allocation
we find that d b f and e is the ranking d is on the top because it is a critical activity
the next is b because it has the earliest starting point and between e and f f is taking
precedence because it has a lower float
now this allocation of resources shall be followed till activities b and f are completed
and on day twenty four activities d and e have a total resource requirement of five
which is within the permissible limit and therefore activity e which was delayed but
it has also been completed within its float so what it shows is that all preceding activities
that is a b c d e and f would be completed by day twenty five so required resources or
the needed resources for the activity g which is a critical activity can easily be allocated
towards the end of the project and this is what we will have activity g will be allocated
with the required resources of four and the project will be completed within the scheduled
time of thirty five days
so what we have seen in this example is that there is a delay in the start of activities
b and e due to the resource limitation of eight but these activities are completed within
their float time and the project has not been delayed at the end having done this example
the way we did it let me review with an assignment that would be the resource allocation if the
limited number was seven we worked with the example of eight in fact in our example when
we did the resource leveling at that time also in one of the iterations we found that
we could complete the project with the maximum allocation of eight workers i would like you
to compare these two scenarios and do this exercise if the number was seven will the
resource limitation of seven result in a delay of the project and finally will there be any
change in the critical activities due to this revised maximum on the available resources
these three questions are left to you as a food for thought we will try to come back
and discus them if possible at later point in time and here is the list of references
as usual which will help you better understand the discussion that we have had today and
i will look forward to see you in a later class
thank you