Project Management Part 5 Project Scheduling

Topic Outline: Project Scheduling Identifying relationships among activities Project network diagrams Identifying critical paths and critical activities Determining activity slack times Gantt charts Project scheduling exercise Other precedence relationships Management of project schedules

Identifying Activity Relationships In addition to estimating activity time duration and cost, relationships among activities must also be identified Relationships: What task immediately precedes this task? What task immediately follows this task? What tasks can be done concurrently? These are referred to as precedence relationships The main relationship for scheduling is ‘what task immediately precedes the current task,’ which is referred to as the immediate predecessor task

Project Network Diagrams Network diagrams show the precedence relationships among activities It’s easier to understand these relationships graphically Network diagrams help to understand the flow of work in a project Network diagrams are a useful tool for project planning and control, as well as for scheduling One (perhaps exaggerated) claim is that the network represents ¾ of the planning process

2 Versions of Network Diagrams Activity-on-Arrow (AOA) networks –also called Arrow Diagramming Method (ADM) –simpler for projects with many dependencies –emphasizes events; milestones can be easily flagged –sometimes requires dummy activities Activity-on-Node (AON) networks –also called Precedence Diagramming Method (PDM) –easier to draw for simple projects –emphasizes activities –no dummy activities

Activities vs. Events Activity – a chunk of work that is part of the project; an activity may be broken down into multiple subactivities Event – a significant point in time during the project, such as a milestone event; an event could be the time at which an activity is completed or the time at which related concurrent activities have all completed Dummy Activity – an artificial activity with zero time duration that only shows a precedence relationship among activities

Activity-on-Arrow (AOA) Networks b c d e f g Activity Predecessor m n r s _ _ m, n n m r n s k j k j j k or Dashed lines are called dummy activities

12 Excavate & pour footings Pour foundation Install drains Project Network for House Construction (AOA network) Install rough electrical & plumbing Pour basement floor Install cooling & heating Erect frame & roof Lay brickwork Lay storm drains Install drywall Lay flooring Install finished plumbing Install kitchen equipment Paint Finish roof Install roof drainage Finish grading Finish floors Pour walks; Landscape Finish electrical work Finish carpeting

Project Network Example Task Pred. Dur. a -- 4 g c,d 1 b -- 3 h e 4 c a 3 i f 5 d a 2 j e,g 6 e b 6 k h,i 1 f b 4 Draw AOA and AON networks

Activity-on-Arrow (AOA or ADM) Network (Initial Network)

Activity-on-Arrow (AOA or ADM) Network (Final Network) a b d c g j k i h f e

Activity-on-Node (AON or PDM) Network

A project has the following activities and precedence relationships: Predecessor Predecessor Activity Activities a -- f c,e b a g b c a h b,d d a i b,d e b j f,g,h Draw AOA and AON networks Project Network Example

Activity on Arrow (Initial Network)

Activity on Arrow (Final Network) a b c d e f g h i j

Activity on Node

Critical Path path – any route along the network from start to finish Critical Path – path with the longest total duration This is the shortest time in which the project can be completed. Critical Activity – an activity on the critical path *If a critical activity is delayed, the entire project will be delayed. Close attention must be given to critical activities to prevent project delay. There may be more than one critical path.

Critical Path Brute force approach to finding critical path: 1.identify all possible paths from start to finish 2.sum up durations for each path 3.largest total indicates critical path (This approach is inefficient, but is instructive)

b = 2 d = 4 g = 9 h = 9 f = 8 c = 5 a = 6 k = 6 j = 7 i = 4 e = 3

Slack Times EST—Earliest Start Time –Largest EFT of all predecessors EFT—Earliest Finish Time –EST + duration for this task LFT—Latest Finish Time –Smallest LST of following tasks LST—Latest Start Time –LFT – duration for this task Slack—LFT – EFT or LST – EST

Computing Slack Times Task = duration slack = xxxx ESTEFT LSTLFT

Slack Times Example Task Pred. Dur. a -- 4 g c,d 1 b -- 3 h e 4 c a 3 i f 5 d a 2 j e,g 6 e b 6 k h,i 1 f b 4 For each task, compute ES, EF, LF, LS, Slack

Start Finish a=4 slack= b=3 slack= c=3 slack= d=2 slack= e=6 slack= f=4 slack= g=1 slack= h=4 slack= i=5 slack= j=6 slack= k=1 slack= Task=dur slack=xxx ESTEFT LFTLST

Gantt Charts The main purpose of a Gantt chart is to display the schedule of activities They are easy to understand They are flexible in that you can also show other information on the chart, such as resources required, who is responsible, critical activities, percent complete, etc. All project management software packages will create Gantt charts

Gantt Chart Activity abcdefghiabcdefghi Time (weeks)

Project Scheduling Exercise DynaTech Equipment Corp. case Divide into small groups Read case (5 minutes) Assignment:(40 minutes) –List the immediate predecessors and WBS number for each activity –Draw project network diagram (lowest level) –Draw Gantt chart –Determine project completion time

Other Precedence Relationships The typical precedence relationship between two activities is that when the first activity has finished, then the second activity can start. In this case the first activity is called the immediate predecessor of the second activity. This is referred to as a Finish-to-Start linkage. Other precedence relationships, or linkages, are also possible. Lead and lag times are also possible.

Other Precedence Relationships Finish-to-Start Linkage (FS) Start-to-Start Linkage (SS) Finish-to-Finish Linkage (FF) Start-to-Finish Linkage (SF) Activity 1 Activity 2 Activity 1 Activity 2 Activity 1 Activity 2 Activity 1 Activity 2 Lead and Lag Times Lead (-) and Lag (+) times are expressed as part of the immediate predecessor notation. So 1FS+3 listed for the immediate predecessor of Activity 2 means that Activity 1 is the predecessor with a Finish- to-Start linkage and a 3-day lag time after Activity 1 finishes before Activity 2 can start. 1FS-3 means that Activity 2 can start 3 days before Activity 1 finishes. 1FF+3; 1SF-5; 1SS+4

Management of Project Schedules Meeting project deadlines is often the most important goal in project management Careful scheduling of project activities is critical to meeting the project due date Effective project managers should have a good understanding of the issues involved in activity scheduling