8. Project Time Management

Transcription

1 8. Project Time Management Project Time Management closely coordinated Two basic approaches -bottom-up (analytical) -top-down (expert judgement) Processes required to ensure timely completion of the project Work packages are decomposed into schedule activities PTM Processes 1. Define Activities what are activities to produce deliverables 2. Sequence Activities what are dependencies among activities 3. Estimate Activity Resources what and how many resources needs each activity work packages are decomposed into schedule activities such that the project objectives will be met. List (not hierarchy) of activities 4. Estimate Activity Durations how many work period needs each activity 5. Develop Schedule analysing activities, resources and constraints to create the project schedule 6. Control Schedule controlling changes to the project schedule Approved schedule is is a time baseline. Without realistic dates, project is unlikely to be finished as scheduled - Control account for planning future work without associated work packages. Management control point. - Planning package for planning future known work without detailed schedule activities. - Work package the lowest WBS level. - Schedule activities the lowest planning level Not the deliverable rather work todo.

2 Project Time Management cd. 1 Sequence Activities Dependencies: identifying and documenting logical dependencies among activities. Support the latter development of a realistic schedule Mandatory physical limitations, hard logic, prototypes needed; inherent in nature of work being done Discretionary defined by pm team; best practices or unusual aspects of project soft logic, External relationship between project activities and non-project activities (company policies, procurement, etc.) - Project Management software often used - 2 methods to construct the diagram: PDM - Precedence Diagramming M. ADM - Arrow Diagramming M. PDM more popular But needs 4 types of dependencies ADM - simpler but may need dummy activities Begin Begin FINISH-START The most common e.g. Installation-tests START-START e.g. concrete deliverypouring fundamentals FINISH-FINISH e.g. final works -cleaning START-FINISH (the rarest overlapping ) e.g. disassembly of scaffolding - elevation End End What are arrows? What are nodes?

3 Project Time Management cd. 2 Develop Schedule Program Evaluation and Review Technique (PERT)- Determining start and finish dates for project activities. Often iterates as more information are available Two categories of time constraints: - imposed dates on activities starts/finishes e.g. Start/Finish No Later Than... (contract, restrictions) - key events/milestones for completing deliverables by specified date (initially requested+expected may be interfaces with work outside the project) Some of the Develop Schedule Techniques uses weighted average duration to calculate project duration differs from CPM by using mean (expected value) instead of most-likely estimate in CPM Schedule Network Analysis generates the schedule with different methods calculates early/late start/finish dates / eliminates loops and open ends. Critical Path Method (CPM) single early/late start and finish date for all activities. based on specified, sequential network and single duration estimate. calculates float to determine flexibility and shows critical path. Schedule Compression look to shorten the schedule without affecting scope crashing cost and schedule trade-offs to determine greatest amount of compression for least incremental cost often results in higher costs fast tracking performing activities in parallel that normally would be sequenced often results in re-work and usually increases risk

4 Project Time Management cd. 3 Brief introduction to CPM/time Critical Path Method Two important definitions: Float: the amount of time an activity can be delayed without delaying the entire project. Calculated by the difference between Early and Late Start/Finish. Critical path is the longest path, the duration of the project and identifies activities without float (critical activities) that need monitoring Algorithm: how to draw the network diagram (PDM) 1. Not too long list of activities (max 10-15) 2. Every activity is to be described like this (indicating ES/EF early start/finish and LS/LF late start/finish) 3. Every activity in the list needs duration, predecessors and dependency 4. Draw the network 5. Two passes - forward and backward Forward: put earliest start and finish dates on forks put MAXIMAL dates of coming Final earliest finish = final latest finish Backward: put latest finish and start dates on forks put MINIMAL dates of returning Calculate float for every activity (LS-ES or LF - EF) Remember: only 1 start, only 1 finish of the network ES duration EF Activity name LS float LF

5 Project Time Management cd. 4 Brief introduction to PERT (Program Evaluation and Review Technique) The whole difference to CPM results from other treatment of the estimation of each activity duration, which is considered as random variable with known distribution (beta), defined by three estimates: o optimistic, m most probable, p - pessimistic. Thus for each activity we calculate Duration (expected value) Standard Deviation: Variance (how unsure we are with duration): μ = σ = 2 σ o + 4 m + p 6 p o 6 2 p o 6 = μ project = μ critical σ project = σ ( critical 2 ) μ ± 1σ μ ± 2σ μ ± 3σ 68,26% activity duration estimates 95,45%... 99,73%... You can draw the network like in CPM using expected value, but knowing more on the whole project, incl. some risk estimations

6 Project Time Management cd. 5 Control Schedule Determining the current status of the project schedule Influencing factors which create schedule changes Determining that schedule has changed Different forms of schedule have different purposes Schedule Updates Revisions change schedule baseline a.k.a. rebaselining Important issue to network diagram: Projects can have more than 1 critical path (increased risk) and can involve dummy tasks DIFFERENT FORMATS OF PROJECT SCHEDULE ALWAYS: CALENDARS BASED data date = as-of date = time now date BAR CHART (summary or detailed with dependencies) MILESTONE CHART NETWORK DIAGRAM (time-scaled)