In this article, we will continue the topic of PERT and CPM and discuss about network constructiion.
Rules of network construction:
There are number of rules in connection with handling of events and activities of project network that should be followed :
[i] Try to avoid arrows that cross each other
[ii]Use straight arrows.
[iii]No event can occur until an activity preceding it has been completed
[iv] An event cannot occur twice i.e. there must be no loops
[v]An activity succeeding an event cannot be started until that event has occurred .
[vi]Use arrows from left to right .Avoid mixing two directions, vertical and standing arrows may be used if necessary .
[vii]Dummies should be introduced only if it is extremely necessary.
[viii]The network has only one entry point called the start event and one point of emergence called the end or terminal point.
NUMBERING THE EVENTS[FULKERSON’S RULE]
[i]Event numbers should be unique
[ii]Event numbering should be carried out on a sequential basis from left to right
[iii] The initial event which has all outgoing arrows with no incoming arrows is numbered as 1
[iv] Delete all arrows emerging from all numbered events .This will create at least one new start event out of preceding events
[v]Number all new start events 2,3 and so on Repeat this process until the terminal event without any successor activity is reached .Number the terminal node suitably.
*The head of an arrow should always bear a number higher than one assigned to the tail of the arrow.
CONSTRUCTION OF NETWORK
Example Construct a network for each of the projects whose activities and their precedence relationships are given below:
Soln: A,B,C are concurrent activities as they start simultaneously .B becomes predecessor of activities E and F.
In the next article, we will talk about Time Analysis for a project, which forms an important part of scheduling calcuations questions in GATE Mechancal Engineering.