Critical Path Networks



Critical Path Networks

Question 1 a

i)

PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method) are two techniques that provide network-based precedence relations and interdependence of activities.

b)

i)

In above figure, the elimination of activity 3 would mean that both activities 2 and 4 would be identified as being between nodes 1 and 3. However, if activity 6 is introduced, the unique designations for activity 2 (node 1 to 2) and 4 (node 1 to 3) will be preserved. Furthermore, if the problem in part (a) is changed so that activity 5 cannot start until both 3 and 4 are completed but that 6 can start after 4 alone is completed, the order in the new sequence can be indicated by the addition of a dummy activity 8. In general, activities may be necessary to meet the requirements of specific computer scheduling algorithms, but it is important to limit the number of such dummy link insertions to the extent possible.

ii)

Any activity with a float of zero is critical. Note here that, as a check, all float values should be >= 0 and that these float values are the same as those derived by the package. The float figures derived are known as also known as total float. As in the above example a "chain" of successive activities (in this case 2, 4 and 6) share the same float and this is common with total float. It is the delay possible for an activity if all preceding activities start as early as possible whilst all subsequent activities start at their earliest time - an equivalent (and easier) definition is the delay possible in an activity if it starts at its earliest time and all subsequent activities start at their earliest time.

With regard to calculating free float we have that convenient formulae are:

free float for activity i = min[earliest start time for j | j an immediate successor of i] - earliest start time for i - completion time for i

Activity Free float

2 0

4 0

iii)

Bar Charts are the most simple and easiest way to produce a scheduling form in the construction industry. It is widely used due to its simplicity and multiple adaptations to numerous events. A bar charts is formed with a list of activities, specifying the start date, duration of the activity and completion date of each activity, and then plotted into a the project time scale. The detailed level of the bar chart will depend on your project complexity and the intended use of the schedule.

A variation of the bar chart schedule, is the linked bar chart. Using a linked bar chart, the activities and subsequent items are linked with arrows and lines, specifying the sequence and order of preceding activities. The previous activities are linked one to another to demonstrate that one activity must be completed before the other activity can start.

Bar charts are useful and commonly used to detect the amount of resources needed for one particular project. Adding the resources vertically will produce what is called the resource ...