Chapter 7 Flashcards
Network diagrams
shows project activities or tasks and their logical relationships
also shows events (instants in time; start of an activity)
2 construction methods of network diagrams
- AON mode (activity on mode)
2. AOA mode (activity on arrow)
AON mode
- each activity (work package or task) in project is represented by a node
- project represented as arrows and nodes (arranged in sequence as specified by immediate predecessors)
2 types of dependency relationships
- mandatory
- sequence of 2 actions can’t be reversed
- dependency can’t be eliminated - discretionary
- sequence is a matter of choice
- dependency can be eliminated (and activities overlapped to speed up process = fast tracking)
creating a project network
created using list of activities from Work Breakdown Structure and their predecessors
What happens when a delay occurs in one of the activities on the critical path?
the whole project is delayed
Early times: early start and early finish
earliest that activities can be started (ES) and finished (EF)
- ES depends on the EF of its predecessor
- do not consider potential constraints
Late times: late start and late finish
latest allowable times an activity can start (LS) and finish (LF) without delaying project completion
- LF depends on the LS for its successor
Total slack
amount of allowable deviation between the latest an activity must take place and the earliest it can take place
–> how much an activity can be delayed without delaying the whole project
Critical path
- has no or the least slack
- the time a project takes is dependent of the critical path
- it is the longest path
activities on the critical path
critical activities
free slack
the time an activity can be delayed without delaying the start of any successor activity
Alternative precedence relationships: Start-to-start (SS)
Start second task ___ days after first task starts
Alternative precedence relationships: Start-to-finish (SF)
Finish second task ___ days after first task starts
PDM (Precedence Diagramming Method)
shows the kinds of relationships in a project
- Start activity when predecessors are only partially completed
- Start activity n days after start of predecessor
- Start activity n days after predecessors are completed
- Finish activity n days after finished predecessor
Alternative precedence relationships: Finish-to-start (FS)
_______ day lag between predecessor and successor
Start second task ___ days after first task finishes
Alternative precedence relationships: Finish-to-finish (FF)
finish second task ___ days after first task finishes
–> mostly used with zero lag where activities must end on the same day
Time Constrained Project
- A project that must be completed by an
imposed date - Time is fixed, resources are flexible
–> sometimes resources are required to ensure project meets schedule
Resource Constrained Project
- A project in which the level of resources available cannot be exceeded
- Resources are fixed, time is flexible
- -> inadequate resources will delay the project
- Resource levelling (or smoothing) involves attempting to even out demands on resources by using slack (delaying non critical activities) to manage resource utilisation.
Resource allocation
assigning resources to activity
Workload (and formula)
amount of work imposed on resource
working days/year) x (productive working hours/day
Resource Loading
amount of particular resource needed to conduct all allocated activities
Loading for particular resources depends of
- amount of resource needed by project activities
2. start and finish dates of those activities
Resource levelling
alter schedules of project activities such that the resultant workload for a required resource is somewhat uniform throughout the project
–> do this by adding slack
Downside to splitting activities into pieces and schedule them at different times
can lead to wasted time and longer activity duration
Laddering
continue to the next component before entire design is complete
Managing multi-project resource schedules
- create project offices or departments to oversee the scheduling of resources across projects
- Use a project priority queuing system: first come, first served for resources
- centralise project management: treat all projects as a part of a “mega project”
- apply Critical Chain Methods to all project scheduling
- outsource projects/project sections to reduce the number of projects handled internally
Problems with multi-project resource schedules
- Overall project slippage
- delay on one project creates delays for other projects - inefficient resource application
- the peaks and valleys of resource demands create scheduling problems and delays for projects - resource bottlenecks
- shortages of critical resources required for multiple projects cause delays and schedule extensions
Criticism of network methods
- they incorporate assumptions and yield results that are sometimes unrealistic
- activities and duration require periodic modification
- failing of networks are actually inadequacies in project definition
Variability of Activity Duration
- Activity duration is not a single, deterministic value
- there is a range of possible durations for most activities
Sensitivity of a network
the likelihood that the original critical path(s) will change once the project is initiated
the sensitivity of a network is the function of
- the number of critical paths
- amount of slack across near critical paths
- the uncertainty of the time duration of activities, on and along the critical path
advantage of networks
they clearly display the interdependencies of project activities and show the scheduling impact that activities have on each other
