Last Updated on June 18, 2020 by Admin
The critical path method (CPM), or critical path analysis (CPA), is an algorithm for scheduling a set of project activities. It is commonly used in conjunction with the program evaluation and review technique (PERT). Read more to know about the Critical Path Method for construction and CPM for project management.
In construction, the critical path method is a project management technique that identifies critical path activities in stages. The CPM approach to project scheduling includes splitting a project into multiple job tasks, displaying them in a flow chart, and calculating the duration for each task and the overall project duration based on the individual tasks.
CPM – Critical Path Method
The critical path method (CPM) is a popular scheduling technique in the construction industry due to its simplicity and effectiveness.
It generates a graphical view of a project and calculates how much time and resources are required to complete each activity. It also determines critical activities requiring attention so that the project can be completed on time.
Without proper scheduling, no construction project would be completed on time. The foundation of that project schedule should typically be made up of the tasks that are essential to keep the project moving. That brings us to the Critical Path Method which is widely used in the construction industry.
Utilizing the Critical Path Method might be a little intimidating at first blush, but it’s simple at its core – plus utilizing it’s a great way to make projects more efficient.
While smaller construction jobs allow for spontaneous planning, bigger projects require construction project management. The construction critical path method (CPM) is a tool that many project managers use, often with their construction management software, to help figure out the best steps to take to finish a job efficiently. This critical path method, otherwise known as critical path scheduling, is one of the most frequently used construction planning techniques.
CPM for project management uses a network diagram to graphically illustrate the major activities of a construction project and to show the links between activities. CPM assigns each activity a single fixed duration.
What Is Critical about Critical Path Method?
What’s Needed in CPM
CPM is constructing a model of the project. Therefore, project managers and superintendents need to have a few essential information points for CPM for project management.
- List of Activities. They need to have a list of all activities required to complete the project. Managers typically will use a work-breakdown structure to be able to list all of the activities and when they need to be completed.
- The Work-Breakdown Structure is a breakdown of a project into smaller components. These smaller components are organized by hierarchy, or what needs to be completed first.
- The project managers or superintendents must have the duration of each activity. This is important in determining the overall schedule. While using PERT, they should be able to get a reasonably accurate estimate for the total length of each part.
- Project managers or superintendents must consider the various dependencies between activities. In construction, there are specific tasks that MUST happen before other tasks because it would be impossible to start them without it. These are dependencies and need to be considered when planning the project.
- Milestones and Deliverables. In order to know when a task or activity is complete, the project manager must know when the project should end and what the end looks like. Also, many subcontractors are paid based on their deliverables so knowing what the deliverable would look like is essential for many factors.
With all of these in mind and the tips to using CPM and PERT, it should be easier to understand what goes into CPM scheduling and visuals.
What is the Critical Path Method For construction?
The critical path method (CPM) is the most commonly used technique for scheduling in construction. It is sometimes referred to as critical path scheduling because it mainly calculates the minimum time needed to complete a construction project alongside the possible start and end times for the different activities.
A lot of construction texts and experienced project managers reference the critical path method as the only practical and usable scheduling procedure. There is also a myriad of computer programs and algorithms for critical path scheduling available that can effectively and efficiently handle projects with multiple activities.
The concept of the critical path method is best illustrated in a project graph (in the old days), or by computer programmes that perform the needed calculations without referencing a graph. The project graph visually represents the web of jobs in a construction project and their relationships with each other.
A coding system must be established to identify each construction job required to complete the entire project, that must be accompanied by the length of time needed to accomplish the job, and its immediate prerequisite tasks.
Each job is plotted on the graph as a circle with its coding details and other pertinent data (dates, etc.). Arrows are used to connect the circles (jobs) indicating the sequence relationships. The circles and arrows are depictions of what we refer to as a project network.
Six Basic Steps In Building a CPM
1. Identify the Activities
Start by developing a list of activities for the project, normally obtained from the work breakdown structure or the project scope and details. Sequence and duration will be added in subsequent steps. Activities are tagged by name, coding, accounting string, or other identifier and must have a duration or target date in the case of milestones.
2. Determine the Activities’ Sequence
A complete and thorough understanding of the sequence of the activities is needed to prepare and connect the list of activities prepared in the previous step. The project or construction manager needs to understand the activities that are linked or related so that they can show the proper connections in the schedule. Contractors sometimes fail to identify these relationships, causing delays and other problems during project execution.
3. Create the Network
The CPM evolves from summarizing all defined activities and showing the interdependencies between them. All critical work sequences need to be linked with logical coordination and planning. The CPM format should be based on calendar days as a main planning unit. A CPM schedule should avoid using working days, as such an approach is more likely to lead to confusion and errors.
4. Estimate Activity Completion Time
Using previous experience, project time estimates for how long it will take to complete activities for a single resource unit.
5. Identify the Critical Path
The critical path is the longest duration path through the network. Activities located on this path cannot be delayed without delaying the project. Because of its impact on the entire project, critical path analysis is an important aspect of project planning. The path for each activity can be identified using these parameters:
- ES—Early Start: Earliest time to start a predetermined activity, given that prior activities must be completed first.
- EF—Early Finish: Earliest finish time for the activity.
- LF—Late Finish: Latest time the activity must be completed without delaying the entire project.
- LS—Late Start: Latest start date that the activity must be started without delaying the project.
The critical path is the path through the project network in which none of the activities have been delayed—that is, the path for which ES=LS and EF=LF for all activities in the path. A delay in the critical path delays the project.
6. Update the CPM Diagram as Needed
As a project is being developed, you can update the critical path. Analyzing a new critical path may be possible when entering all the duration times of activities already completed. A new path might be possible and alternative solutions can be presented to either accelerate the project or continue working as projected. Sometimes it also is necessary to incorporate changes and extra tasks that were not part of the original critical path.
Advantages of Using the Critical Path Method
The CPM for project management increases visibility by allowing everyone on the project to understand how the individual tasks fit together and how they affect the overall project’s duration.
By dividing a large project into a series of smaller tasks, management and oversight are easier, and delays (critical or non-critical) are readily identifiable.
However, the critical tasks will need to be supervised with more attention than others to fully realize the increased efficiency and cost controls that the Critical Path Method provides.
Establishing a critical path schedule is just the beginning. The CPM schedule will need to be updated and monitored regularly to ensure its effectiveness.