PERT / CPM:RESOURCE SCHEDULING IN NETWORK

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VirtualUniversity of Pakistan

OperationsResearch (MTH601)

RESOURCESCHEDULING IN NETWORK

In scheduling projects usingPERT or CPM, we have assumedthat the only constraintfor an activity is to

fixthe starting date andthe finishing date. An activity may be started as soon as all its predecessors havebeen

completed.Thus we have an early startschedule for all the activities. In such scheduling procedures it is assumed

thatthe resources required to perform activities are available to any unlimited extent or atleast sufficient resources

areavailable for the activity to be started sometime betweenearliest and latest startdates. But we comeacross

situationswhere the project managershave to face the problem of limited or fixed resourceslike manpower

availabilities, machine availabilities and capitalmobilization. Activities, whichoccur on parallel pathsthrough

network, may compete for thesame resource.

Recentlyconsiderable work is in progress in developing heuristic programmesfor solving large

combinatorial problems, A heuristic can be defined as a guide or method of reducing search in a problem-solving

situations. It gives a rule of thumb.Businessmen employ heuristics quiteoften for their problems. As an example we

considerthe classic management rule, "Handle only exceptional problemsand let the subordinatesdecide on routine

matters" as a heuristic. Sometime a simple rule of thumb may not be enough, butother rules are also to particular

problem is referred to as 'heuristic programme'requiring a computer for complex problems. A number of different

heuristicprogrammes for schedulingprojects with limitedresources have beendeveloped recently. These

programmesare classified in any one of the two following forms.

Resource leveling programmes: These programmesseek an attempt to reducepeak resourcerequirements

andsmooth out period to periodassignments with a restriction on project duration. In otherwords, in these

programmesthe resource requirements(manpower or money power) arekept at a constant level by altering

thestart time of the different activities. But at the same time,the project duration andthe sequence arenot

violated.

Resource allocation programmes: These programsmake an attempt to allocatethe availableresources

(manpower, machine hours, money) to project activites and to find the shortest projectschedule consistent

withfixed resource limits. Thefollowing articles deal withthese types of heuristicprogrammes.

Resourceleveling program: Resource leveling programmes aremost appropriate to situationswhere we maintain a

relatively stable employment levels andutilize the resources at a more constant rate. If thelevels change eitherway

theexpenses are involved in hiring, training, firing, unemployment insuranceand so on. The activityslack is a

measure of flexibility in the assignment of activity start times. We mayuse activity slack as a means to smoothing

peakresource requirements. Theprocedure involves preparing an early-start early-finish schedule forthe project on

timescale and then plotting a resource-loading chart forthe schedule. The activitesare shifted suitably to reducethe

peakresource requirements withoutviolating the sequence andpreserving the finishdate.

ResourceAllocation: In many cases the schedulingproblem does not involveonly smoothing of requirementsbut

also allocation of resources. Almost thereare some constraints, which may be in the form of limitedmen, machines

or finance. The various activities have to work at theiroptimum taking into considerations theserestrictions.

Theresource-leveling model could be modified to give us the desiredresults. The constraint of the fixed

duedate would have to be removed and concentrate on pushing down the triggerlevels until peakrequirements are

allunder resource limits. If the limits are confining, the jobs will be pushed to the right, thereby delayingthe project

duedate on the schedule graph.The constraints cannot be based both on project duedate and resourcelimits.

Resourcesare allocated on a period-by-periodbasis to accommodate someavailable job, aftertheir

predecessorshave been completed. Theessential elements aredetermining which jobs are to be scheduled and

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