CRITICAL PATH METHOD: CPM

CRITICAL PATH METHOD: CPM

The Critical Path Method (CPM) is a project management technique used to plan and manage complex projects. It helps project managers identify the most critical tasks and determine the shortest possible duration for completing a project. CPM is particularly useful for projects with numerous interdependent activities and tasks. Here's a detailed explanation of CPM:

Definition: CPM is a mathematical algorithm and graphical representation used for project scheduling. It identifies the sequence of tasks that must be completed on time to prevent project delays and calculates the earliest start and finish times for each task, as well as the total project duration.

Description:

1. Task Identification: The first step in CPM is to identify all the tasks or activities required to complete the project. Each task should have a clear description and a defined duration.
2. Sequence of Activities: Next, you establish the relationships between the tasks. Some tasks can only begin once others are completed (dependent tasks), while others can occur simultaneously (independent tasks). This creates a network diagram, often represented using the Activity-On-Node (AON) method.
3. Estimate Durations: Assign time estimates for each task based on historical data, expert judgment, or other estimation techniques. This includes estimating the optimistic, pessimistic, and most likely duration for each task, which is used for probabilistic analysis (PERT analysis).
4. Critical Path Calculation: Using the network diagram and task duration estimates, CPM calculates the earliest start and finish times for each task and identifies the critical path. The critical path is the longest sequence of dependent tasks that determine the overall project duration. Any delay in tasks on the critical path will directly impact the project's completion date.
5. Float or Slack: CPM also calculates the float or slack time for non-critical tasks. Float represents the amount of time a task can be delayed without delaying the entire project. Tasks on the critical path have zero float, while non-critical tasks have positive float.
6. Monitoring and Control: Throughout the project, project managers use the CPM schedule to track progress, identify potential delays, and take corrective actions to keep the project on track.

Working Procedure:

1. Task List: Identify all project tasks and create a list with descriptions and durations.
2. Network Diagram: Create a network diagram, either manually or using project management software that shows the dependencies between tasks.
3. Duration Estimates: Estimate the time required for each task and input these estimates into the network diagram.
4. Critical Path Calculation: Calculate the earliest start and finish times for each task, and identify the critical path.
5. Float Calculation: Calculate the float for non-critical tasks.
6. Project Schedule: Use the information from steps 4 and 5 to create a project schedule that includes start and finish dates for each task.
7. Monitoring and Control: Continuously monitor the project's progress, making adjustments as needed to ensure tasks are completed on time.

Examples: Let's consider a simple construction project:

• Task 1: Excavate the site (4 days)
• Task 2: Pour foundation (5 days)
• Task 3: Build walls (7 days)
• Task 4: Install roof (3 days)
• Task 5: Interior finishing (6 days)
• Task 6: Landscaping (2 days)

Dependencies:

• Task 1 must be completed before Task 2 can start.
• Task 2 must be completed before Task 3 can start.
• Task 3 must be completed before Task 4 can start.
• Task 3 and Task 4 can be done simultaneously.
• Task 4 must be completed before Task 5 can start.
• Task 5 must be completed before Task 6 can start.

 

Problem: Construction of a New Office Building

A construction company has been contracted to build a new office building for a client. The project involves various tasks, and the client has set a strict deadline for completion. The construction company needs to determine the most efficient schedule for completing the project to ensure it meets the deadline while minimizing costs and delays.

Tasks and Durations:

1. Site preparation (3 days)
2. Foundation excavation (5 days)
3. Foundation pouring (7 days)
4. Framing and structural work (10 days)
5. Roofing and exterior finishes (8 days)
6. Interior construction (12 days)
7. Plumbing and electrical installation (9 days)
8. HVAC installation (6 days)
9. Flooring and finishing touches (7 days)
10. Landscaping and exterior work (4 days)

Dependencies:

• Task 1 must be completed before Task 2 can start.
• Task 2 must be completed before Task 3 can start.
• Task 3 must be completed before Task 4 can start.
• Task 4 must be completed before Task 5 can start.
• Task 4 and Task 5 can be done simultaneously.
• Task 5 must be completed before Task 6 can start.
• Task 6 must be completed before Task 7 can start.
• Task 7 and Task 8 can be done simultaneously.
• Task 8 must be completed before Task 9 can start.
• Task 9 must be completed before Task 10 can start.

Using the Critical Path Method (CPM), let's solve this problem:

1. Create a Network Diagram: Draw a network diagram that represents the project's tasks and their dependencies.
2. Duration Estimates: Assign the estimated durations to each task as mentioned above.
3. Critical Path Calculation: Calculate the earliest start and finish times for each task. Identify the critical path, which is the longest path of dependent tasks.
4. Float Calculation: Calculate the float or slack for non-critical tasks.

Here are the results of the CPM analysis:

• The critical path is: Site preparation (3 days) -> Foundation excavation (5 days) -> Foundation pouring (7 days) -> Framing and structural work (10 days) -> Roofing and exterior finishes (8 days) -> Interior construction (12 days) -> Plumbing and electrical installation (9 days) -> Flooring and finishing touches (7 days) -> Landscaping and exterior work (4 days).
• The total project duration, based on the critical path, is 65 days.
• Non-critical tasks have varying amounts of float, indicating how much they can be delayed without impacting the project's completion date. For example, HVAC installation has 6 days of float, which means it can be delayed by up to 6 days without affecting the project's overall timeline.

Using the CPM analysis, the construction company can now create a project schedule that ensures the critical tasks are completed on time to meet the client's deadline. They can also use the float information to manage non-critical tasks more flexibly while staying within the overall project duration. This approach helps optimize the construction project, minimize delays, and ensure successful project completion.