# Time cost relationship and project crashing reasons

### Module 3 : Project Crashing and Resources

Crashing is reducing project time by expending additional resources . The project total time-cost relationship can be determined by adding up the direct cost . The time costs relation is then analyzed by regression analysis to obtain the Keywords: Construction project; Critical path method; Trade-off analysis; Crashing. Keywords: Project Management, Critical Path, Crashing, Time-Cost Trade-Off 1. the cause why a p roject is essential; seizing project necessities, . Plot the time-cost trade-off graph by linear interpolation between the.

### Network analysis - cost/time tradeoff

Project duration can often be reduced by assigning more labor to project activities, in the form of overtime, and by assigning more resources material, equipment, and so on.

However, additional labor and resources increase the project cost. Thus, the decision to reduce the project duration must be based on an analysis of the trade-off between time and cost. Project crashing is a method for shortening the project duration by reducing the time of one or more of the critical project activities to less than its normal activity time.

This reduction in the normal activity time is referred to as crashing. Crashing is achieved by devoting more resources, usually measured in terms of dollars, to the activities to be crashed. This network is repeated in Figure Although this sample network encompasses only single-activity time estimates, the project crashing procedure can be applied in the same manner to PERT networks with probabilistic activity time estimates.

We will assume that the times in weeks shown on the network activities are the normal activity times.

For example, 12 weeks are normally required to complete activity This cost is referred to as the normal activity cost. This new estimated activity time is known as the crash time, and the cost to achieve the crash time is referred to as the crash cost.

Dividing the total crash cost by the total allowable crash time yields the crash cost per week: The linear relationships between crash cost and crash time and between normal cost and normal time are illustrated in Figure The objective of project crashing is to reduce project duration while minimizing the cost of crashing. Since the project completion time can be shortened only by crashing activities on the critical path, it may turn out that not all activities have to be crashed.

However, as activities are crashed, the critical path may change, requiring crashing of previously noncritical activities to reduce the project completion time even further. Suppose the home builder needed the house in 30 weeks and wanted to know how much extra cost would be incurred to complete the house by this time. The normal times and costs, the crash times and costs, the total allowable crash times, and the crash cost per week for each activity in the network in Figure We start by looking at the critical path and seeing which activity has the minimum crash cost per week.

Activity will be reduced as much as possible.

The table shows that the maximum allowable reduction for activity is 5 weeks, but we can reduce activity only to the point where another path becomes critical. When two paths simultaneously become critical, activities on both must be reduced by the same amount. If we reduce the activity time beyond the point where another path becomes critical, we may be incurring an unnecessary cost. This last stipulation means that we must keep up with all the network paths as we reduce individual activities, a condition that makes manual crashing very cumbersome.

For that reason we will rely on the computer for project crashing; however, for the moment we pursue this example in order to demonstrate the logic of project crashing.

## 7 Reasons to crash your schedule

It turns out that activity can be crashed by the total amount of 5 weeks without another path becoming critical, since activity is included in all four paths in the network.

When meeting a fixed deadline Projects require change and changes however formal and appropriate your change control processes have a habit of adding more time into the plan. So what happens when your necessary and obligatory changes start adding more time to your fixed date project? You have two choices: I know that many project managers are given a fixed date to deliver by but with this often has some flexibility especially if the compulsory changes that add more time are requested by the project sponsor.

When you are delayed Delays early in the project necessarily have an impact on later work. You might consider crashing your schedule as a way to make up for some of the lost time. When the team is needed on other work And now we reach the reasons that are to do with resources. Your project simply might not be the most important thing happening in the business right now.

Your team might be needed on other projects — or at least a particular subject matter expert might be. Crashing your schedule is one way to free up certain resources more quickly.

You could look at crashing a workstream so that your critical resources are available for other tasks or projects. When another resource is free Sometimes the opposite happens — more resources suddenly become available. Ooo, more people for your project.