Planning in dynamic environment; linked bar chart

Need for planning in a dynamic environment

A project works in an environment that keeps changing: prices of material and labour, exchange rates, government policy, weather, technology, availability of funds and the needs of the client. Without planning, the project would be run by guesswork. Planning is necessary because it:

• forecasts the likely changes and prepares alternatives in advance;
• sets objectives and a baseline so that deviations can be measured;
• allocates scarce resources properly and avoids idle time and shortages;
• coordinates many parties (client, consultant, contractor, suppliers);
• allows quick re-planning when a change occurs, by updating the schedule and resources;
• reduces risk, delay and cost overrun.

Linked bar chart as a planning tool

A linked bar chart is a bar chart in which the bars are joined by arrows (links) that show the dependence between activities: the finish of a predecessor is linked to the start of its successor. It therefore combines the simple view of a bar chart with the logic of a network.

Example: a small building project (time in weeks).

                 0   4   8   12  16  20  24  (wk)
                +------------------------
A Site clearing |#>                      
B Excavation    | ##>                    
C Foundation    |   ###>                 
D Plinth beam   |      ##>               
E Walls+columns |        #####>          
F Roof slab     |             ###>       
G Plumb/electric|             ###>       
H Plastering    |                ###>    
I Floor,doors   |                   ###> 
J Painting      |                      ##
                +------------------------

Reading: the arrow > means the successor starts when the predecessor finishes. The project takes 24 weeks. Roof (F) and plumbing (G) run in parallel after walls (E), and plastering (H) waits for both. Since F and G have equal durations, no activity has any float, so all are critical: for example, a delay in E, F or G pushes H, I and J and the completion date.

Justification: the chart is easy to prepare and read, shows the start, finish and duration of each activity, and its links show which activities control the others, so it is suitable for planning and for explaining the schedule to site staff.

Limitations

• Becomes crowded and unclear when the number of activities is large.
• Does not clearly show the critical path or the float of each activity.
• Does not show the uncertainty of durations (no probability).
• Difficult to revise: a change needs redrawing.
• Shows only simple finish-to-start dependence; resources and costs are not shown.