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Steps in Construction Scheduling

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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

Possible Drafting Styles of Arrow DiagramsUse of a dummy Activity

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)

Single Span Bridge Activity Project Description

Example Network Single Span Bridge Project Activities

Summary of Network Calculations

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.

Arrow Diagram & Precedence Diagram Correspondence

Sub Activities, Redundant Links Examples

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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