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Project Management (a quick tutorial) - - Schedule Logic

Schedule Logic and Schedule Management

There are several methods used to develop and manage schedules.  Each method has advocates.  We will outline two schedule methodologies:

  1. Critical Path Method (CPM)
  2. Critical Chain Project Management (CCPM)
Critical Path Method (CPM)

Set up the schedule with adequate time for each task.  Identify task durations and the relation (dependency) between tasks.  Add buffers to allow for unknown situations.  Set key milestones.  Identify the critical path.  Monitor the critical path and drive the team to maintain each critical milestone. 

Advantages of the Critical Path Method:

  1. Easy project organization – each task is started as soon as possible
  2. Clear focus – the tem can be focused on the critical elements, driving them to completion.
  3. Less schedule management effort – set the schedule and revise infrequently, revise it only as required.  The goal is to maintain the total schedule adjustments below the total buffer so that the project milestones are achieved.
  4. It's the default - scheduling programs typically default to the critical path method

Disadvantages of the Critical Path Method:

  1. Schedules allow, and in some cases promote, inefficiencies
  2. Projects schedule with CPM typically have longer project timelines


Critical Chain Project Management (CCPM)

The Critical Chain Method for schedule management was developed by Eliyahu Goldratt and is outlined in his book Critical Chain.  In this method, task durations are established based on the resources required to complete each task.  The goal is to focus project management on the critical resources.  This method requires all resources to be flexible in task start times and requires all resources to dedicate their effort to the efficient completion of their assigned task.  Critical Chain tasks are monitored and managed aggressively.

With traditional project management methods, 30% of the lost time and resources are
typically consumed by wasteful techniques such as bad multi-tasking,
Student syndrome, In-box delays, and lack of prioritization.

Harvey Maylor, Project Management


Critical Chain Schedule Development and Management Process:

Set up the schedule with the minimum time scheduled for each task.  Identify the critical resources and establish the critical chain.  Add buffers as required to protect the critical chain.  Set key milestones.  Monitor the critical chain and use the buffers selectively, though team collaboration.  Drive the team to maintain each critical milestone. 

The critical Chain process requires the strategic development of buffers:

  1. Project buffers    (to protect key milestones)
  2. Feeding buffers   (to protect the critical chain)
  3. Resource buffers (to protect against resource limitations)

Advantages of the Critical Chain Method:

  1. Shorter project time
  2. CCPM aggregates the safety time added to many subtasks into project buffers to protect project milestones
  3. Resource capability is evaluated with schedules based on resource availability

Disadvantages of the Critical Chain Method:

  1. Requires the Project Manager to promote the CCPM process to the project team.  CCPM is often misunderstood requiring PM leadership and support.  (Team education is often required)
  2. Constant project management / team effort to adjust tasks durations based on actual task need.
  3. Team members must be flexible in task start times.
  4. Resources must be flexible in task start times
  5. Once the task starts the resources must dedicate their effort to the efficient completion of their task.
  6. Constant PM / Team interaction is required to manage the project buffers and avoid the waste of project safety time


Comparison between Critical Path and Critical Chain Project Management

In project management, the critical chain is the sequence of both precedence- and resource-dependent terminal elements that prevents a project from being completed in a shorter time, given finite resources. If resources are always available in unlimited quantities, then a project's critical chain is identical to its critical path.


Key Differences between Critical Path and Critical Chain:

Critical Path
Project Management (CPM)

Critical Chain
Project Management (CCPM)

Project progress and health is managed by reviewing individual task performance against time and cost budgets.

Project progress and health is managed by reviewing the consumption rate of the buffers.

The critical chain is developed against the apparent optimum solution.  The optimum solution is reviewed and revised as the project is developed.

Determining the absolute optimum is difficult – if not impossible.  In CCPM the schedule flows with project evolution, always protecting the project constraints.

each task is started as early as possible

each task is started as late as possible

schedule milestones are fixed

schedule milestones are protected with buffers



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Construction Management Southeast Kansas

What is Project Management?

Project management is the process of planning, organizing, securing, and managing resources to achieve project goals.

What is a Project?

A project is a temporary work effort with a defined beginning and end, undertaken to meet specific goals and objectives. Projects are designed to bring about beneficial change or added value.

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What is Construction Project Management?

Construction Project Management is project management that applies to the construction sector.  Construction Project Management includes the overall planning, coordination and control of a project from inception to completion aimed at meeting a client’s requirements in order to produce a functionally and financially viable project.

What is Construction Management?

Construction managers plan, coordinate, budget, and supervise ...

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