Steps in Construction Scheduling

Planning  & Scheduling

Planning: Process of choosing the method and order of work

Scheduling: Process of determining the interrelationship of associated timings of operations.

Steps in Construction Scheduling

• Splitting of the project into work activities
• Determining logic relationships/interrelationships between activities.
• Construction of Network Diagrams.
• Assigning durations to work activities.
• CPM Calculations resulting in start times, finish times and float calculations of activities.
• Marking of critical Path
• Construction of Bar Charts / Time phased diagrams.

Activity

• An element of work performed during the course of a project. Or
  • An amount of work that can be identified so that we know what it involves and can recognize, when it starts and finishes.
• An activity normally has an expected duration, an expected cost, and expected resource requirements
  

Network Diagrams

• Any schematic display of the logical relationship of project activities.
• Always drawn from left to right to reflect project chronology.
• Usually a combination of arrows and nodes.

Mainly of two types:

1. Arrow Diagram
2. Node Diagram / Precedence Diagram
   

Arrow Diagrams

• Activities shown by Arrows. Relationship between activities shown by nodes / events.
• Length of arrows does not obey any scale.
• Start-to-finish relationships.
• Dummies.
• Numbering of nodes / events.
• Milestones

Activity Durations

• Activity duration is forecasted by any of the several means, including:
  1. Check Past Records.
  2. Check Standards and / or cost guides, if available.
  3. Ask the workers, who will do it
  4. make an educated guess
• Any time units may be allotted to activity durations like days, hours, weeks, months, shifts, etc.
• In CPM, a single duration is forecasted for an activity.
• In PERT (Program Evaluation & Review Techniques), 3 durations are forecasted for an activity and mean taken by weighted average method. Then, Project’s Duration or any Event Completion Time is calculated by probability distribution.
  

CPM Calculations

• Calculates the following for each activity

EST = Earliest Starting Time

EFT = Earliest Finishing Time

LST = Latest Starting Time

LFT = Latest Finishing Time

TF = Total Float

FF = Free Float

• Total Float is Maximum time for which an activity can be delayed without delaying the project.
• Free Float is maximum time for which an activity cane be delayed without delaying the start of proceeding activity.
• Total Float = Free Float + Interfering Float
  

Critical Path

• The path (or paths) in the network diagram, from start to finish, on which all the activities have zero total and free floats, is called Critical Path.
• It is the longest path (or paths) from start to finish in a net work diagram.
• It gives minimum normal time to complete a project.
• It is usually marked by double lined arrows in a network diagram.
  

SINGLE SPAN BRIDGE PROJECT

    (ACTIVITY  DESCRIPTION)

Node Diagrams

• Activities shown by Nodes, relationship between Activities shown by arrows or links.
• Easier to construct.
• Generally no need of dummies. Instead dummies used only to give single start or finish.
• CPM Calculations similar to Arrow diagrams.
  

Bar Chart

• Gives Pictorial Representation of Activities.
• Activities begin at EST and show their EFT, FF, TF, Durations, etc.
• Arrows at the relative ends to show dependency.
• Status Line Concept
• Unable to show complete interdependency between Activities.
• Time-scaled Network Diagrams show complete interdependency between Activities.

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