Network Techniques for Project Management
Project Planning and Network Scheduling Techniques
Project scheduling involves the systematic application of techniques to manage the activities required during the development of a project. Effective scheduling is carried out before the project begins and typically includes:
- Identifying the tasks to be completed.
- Estimating the duration of each task.
- Allocating necessary resources, primarily personnel.
- Determining the sequence and timing of activities.
Once the project is underway, continuous monitoring and control are essential to ensure the plan remains realistic and effective. This often requires revisions based on actual progress and unexpected developments.
Importance of Project Planning
Effective project planning ensures that project deliverables are achieved:
- Within the approved budget.
- Within the specified time constraints.
- At the required level of quality.
Key Project Scheduling Techniques
The three fundamental techniques for project planning and control are:
- Gantt Chart – A visual tool that represents tasks against time, making it easier to track progress and deadlines.
- Critical Path Method (CPM) – A technique used to identify the longest sequence of dependent activities, helping managers focus on tasks critical to timely completion.
- Program Evaluation and Review Technique (PERT) – A probabilistic model that accounts for uncertainty in activity durations, useful for complex projects with many interdependent tasks.
All three methods enable managers to monitor progress and costs against planned resource budgets, thereby improving efficiency and reducing risks of delay or cost overruns.
Gantt Chart
Gantt charts, also known as Bar Charts, are one of the earliest and simplest tools for project scheduling and tracking. Their use began during the Industrial Revolution in the late 1800s, when industrial engineer Henry Gantt developed them to improve factory efficiency. Today, Gantt charts remain widely used across industries, including in energy management projects, construction, IT, and manufacturing.
What is a Gantt Chart?
A Gantt chart is a horizontal bar chart that represents project tasks against a time scale. Each task is shown as a horizontal bar, where the length of the bar indicates the expected duration of the task.
- Activities are listed along the left-hand side.
- Time scale is displayed along the top or bottom of the chart.
- Each task is represented by a bar or line that reflects its duration.
- Dependencies between activities may also be shown.
- At review points, bars can be shaded to indicate the actual work completed.
- A vertical marker (cursor) shows the current status, making it clear which tasks are ahead or behind schedule.
Key Features of Gantt Charts
- Graphical and easy to understand – Simple to read and interpret, even for non-technical stakeholders.
- Quick to update – Changes in schedule can be adjusted visually.
- Effective for smaller projects – Works best where tasks are limited, and interdependencies are relatively few.
- Progress tracking – Activities can be overprinted or shaded progressively to show the percentage completed.
Advantages and Limitations of Gantt Charts
Advantages:
- Simplest and fastest method of formal project planning.
- Provides a clear visual timeline of project activities.
- Helps in tracking progress against the plan.
Limitations:
- Duration is clearly represented, but task sequences and interdependencies are not as well shown compared to network techniques like CPM or PERT.
- Less effective for complex projects with numerous tasks and relationships.
In summary, Gantt charts are a powerful yet simple project planning tool, particularly effective for projects with limited activities and straightforward scheduling requirements.
Critical Path Method (CPM)
The Critical Path Method (CPM) was developed by DuPont to address the challenge of shutting down chemical plants for maintenance and restarting them efficiently. It is a project management technique designed for complex projects involving multiple activities, some of which must be performed sequentially, while others can be executed in parallel.
CPM models project activities and events as a network, making it easier to identify dependencies, estimate timelines, and highlight critical tasks that determine the overall project duration.
- Activities are represented as nodes in the network.
- Events that signify the beginning or end of activities are represented by arcs or lines connecting the nodes.
Steps in CPM Project Planning
- Specify the individual activities – List all activities in the project. This forms the foundation for sequencing and estimating durations.
- Determine the sequence of activities – Identify dependencies and list immediate predecessors for each activity to construct the CPM network diagram.
- Draw the network diagram – Once activities and their sequences are defined, the network is drawn (originally as an Activity-on-Node network).
- Estimate activity completion times – Use past experience or historical data to estimate the time required for each activity. (Note: CPM assumes fixed activity durations and does not account for variations.)
- Identify the critical path – The critical path is the longest-duration path through the network. Activities on this path cannot be delayed without affecting the entire project schedule. This makes critical path analysis a key element of project planning.
- Update the CPM diagram – As the project progresses, actual completion times are recorded. The network may be updated to reflect changes, and a new critical path may emerge if project requirements shift.
Benefits of CPM
- Provides a clear graphical view of the project.
- Predicts the total time required to complete the project.
- Highlights critical activities that directly affect project timelines.
- Distinguishes between critical and non-critical tasks, allowing better resource allocation.
Limitations of CPM
- Assumes deterministic activity durations and does not consider variations or uncertainties in task completion times.
- Best suited for routine, well-defined projects with minimal uncertainty.
- Less effective for innovative or highly uncertain projects where completion times can fluctuate significantly.
In summary: CPM is a valuable technique for planning and controlling complex projects with well-defined activities, but its reliance on fixed time estimates limits its effectiveness in projects with high uncertainty.
Program Evaluation and Review Technique (PERT)
The Program Evaluation and Review Technique (PERT) is a network-based project management tool that incorporates uncertainty in activity completion times. It was developed in the late 1950s by the U.S. Navy for the Polaris missile project, which involved thousands of contractors.
Unlike deterministic methods, PERT recognizes that activity durations are not always fixed and may vary. By considering multiple time estimates, PERT helps managers deal with uncertainty, making it especially useful for large, complex, and research-oriented projects.
Key Concepts in PERT
- Activity: A task that must be performed.
- Event (milestone): Marks the completion of one or more activities.
- Precedence rule: An activity cannot start until all its predecessor activities are complete.
- Network representation: In PERT, activities are shown as arcs (lines), while milestones are represented as nodes (circles), usually numbered sequentially.
Characteristics of PERT
- Provides a structured basis for planning and forecasting.
- Ensures optimal use of resources to meet time and cost targets.
- Gives management visibility and control over “one-of-a-kind” projects, as opposed to routine operations.
Steps in the PERT Planning Process
- Identify activities and milestones – Define all required project tasks and the key events that mark progress.
- Determine activity sequence – Establish the order of activities, identifying dependencies among tasks.
- Construct the network diagram – Draw a flowchart showing the sequence of serial and parallel activities.
- Estimate activity times – For each activity, three time estimates are made:
- Optimistic time (OT) – Minimum time if everything goes well.
- Most likely time (MT) – Best realistic estimate under normal conditions.
- Pessimistic time (PT) – Maximum time if significant delays occur.
- From these, the expected time is calculated using a weighted average formula.
- Determine the critical path – The longest path through the network that defines the project’s minimum completion time.
- Update the network – Replace estimates with actual data as the project progresses. Delays may require resource adjustments, and the critical path may shift.
Benefits of PERT
- Provides an expected project completion time.
- Calculates the probability of finishing before a target date.
- Identifies critical path activities that directly affect completion.
- Highlights activities with slack time, allowing resource reallocation.
- Defines start and end dates for activities.
Limitations of PERT
- Requires significant time and labor for setup and maintenance.
- Reduces upper management’s decision-making ability due to complexity.
- Estimates may lack ownership and accuracy.
- Relies on limited historical data for time-cost estimates.
- Assumes unlimited resources, which may not be realistic.
- Can become overly detailed and complex for practical use.
PERT vs. CPM: Key Differences
|
Aspect |
PERT |
CPM |
|
Nature |
Probabilistic
(uncertainty considered) |
Deterministic
(fixed estimates) |
|
Time Estimates |
Three:
optimistic, most likely, pessimistic |
Single
(normal) time estimate |
|
Distribution |
Beta distribution
for activity time, normal distribution for project duration |
Fixed, no
probability distribution |
|
Application |
R&D and
high-uncertainty projects |
Construction
and resource-driven projects |
|
Progress Tracking |
Based on
milestones |
Based on
percent completion |
|
Use of Dummy Activities |
Yes |
Yes |
Summary
PERT is best suited for research, development, and innovative projects where time estimates are uncertain, while CPM is better for construction and routine projects where activity times can be predicted more accurately.
Network Re-planning Techniques
In project management, unforeseen challenges often require adjustments to schedules and resources. Network re-planning techniques are methods used to revise and optimize project networks to ensure effective utilization of resources and timely completion of projects. Two major techniques are based primarily on resource considerations:
1. Resource Leveling
Resource leveling aims to smooth out fluctuations in manpower or resource requirements over time. The objective is to eliminate peaks and valleys in resource usage while minimizing idle time.
- Ideally, this is achieved without altering the project’s end date.
- In practice, however, resource leveling often extends the project schedule and may increase costs.
2. Resource Allocation
Resource allocation focuses on finding the shortest possible critical path given the constraints of available or fixed resources.
- This technique redistributes resources to optimize project duration.
- A limitation is that employees may not always be technically qualified to handle multiple activities simultaneously.
Constraints in Re-planning
Not all PERT/CPM networks allow easy rescheduling of resources. Project managers must carefully reallocate resources to reduce the critical path duration, provided that slack time was not deliberately planned as a safety margin.
Additional Methods to Reduce Project Duration
Besides resource reallocation, several strategies can be applied to shorten project timelines:
- Elimination of some project components (reducing scope).
- Addition of extra resources (labor, equipment, budget).
- Parallelization of activities (overlapping tasks).
- Shortening activities on the critical path.
- Accelerating early activities to create downstream flexibility.
- Shortening the longest activities to reduce bottlenecks.
- Shortening the easiest activities where feasible.
- Increasing work hours per day (e.g., overtime or additional shifts).
Key Considerations
- In an ideal situation, project start and end dates are fixed, and all work must be completed within the agreed time frame and scope.
- If scope reduction becomes necessary to meet deadlines, the contractor faces serious risks, including:
- Project cancellation.
- Failure to meet performance expectations.
Summary
Network re-planning techniques like resource levelling and resource allocation help managers adapt to resource constraints, but they often come with trade-offs in time, cost, and scope. Effective use of these techniques requires balancing resource availability with project goals while minimizing risks.
FAQ's
Who developed the Gantt chart?
The Gantt chart was developed by Henry Gantt in the late 1800s to improve factory efficiency.
Who developed CPM?
CPM was developed by DuPont for scheduling plant maintenance projects.
Why was PERT developed?
PERT was developed in the 1950s by the U.S. Navy for the Polaris missile project involving thousands of contractors.
What is network re-planning techniques?
These are methods used to revise project schedules and resources when constraints or delays occur, ensuring optimal completion.
What other methods can reduce project duration?
Methods include adding resources, parallelizing tasks, shortening critical activities, or increasing daily work hours.
