Gantt chart; resource allocation and smoothing

Gantt chart

A Gantt chart is a bar chart in which each activity is a horizontal bar on a time scale; the bar is filled in as work progresses, so that planned and actual progress are seen together. It is used for scheduling and monitoring.

Example (days): A excavation (3 days, 4 men), C foundation (3 days, 2 men, after A) and B fencing and store (2 days, 2 men, independent). = shows work done up to the status at the end of day 3.

                  0 2 4 6 (day)
                 +------
A Excavation     |===|  
C Foundation     |   ###
B Fencing, store |== |  
                 +------
                     ^ status (day 3)

Resource allocation

Resource allocation is the assignment of the available manpower, machines and materials to the activities of the schedule. The daily requirement of every activity (early start schedule) is added to get a resource aggregation chart, drawn as a resource histogram. If the demand is uneven or higher than the supply, the schedule is adjusted. Two cases occur:

1. Resource levelling or smoothing (time-limited) - the project duration is fixed; activities are shifted within their float to get a smooth demand.
2. Limited resource allocation (resource-limited) - the amount of resource available is fixed; activities are delayed, even beyond their float, so the duration may increase.

Resource smoothing

Smoothing is the adjustment of non-critical activities within their total float to remove peaks and valleys of the histogram without changing the project duration or the critical path.

In the example the critical chain is A-C (6 days); B has a float of 4 days. Early start histogram (B on days 1-2):

  6 |# #         
  5 |# #         
  4 |# # #       
  3 |# # #       
  2 |# # # # # # 
  1 |# # # # # # 
    +------------
     1 2 3 4 5 6  day
     6 6 4 2 2 2  men

Peak = 6 men. Starting B on day 4 (inside its float) gives:

  4 |# # # # #   
  3 |# # # # #   
  2 |# # # # # # 
  1 |# # # # # # 
    +------------
     1 2 3 4 5 6  day
     4 4 4 4 4 2  men

The peak falls from 6 to 4 men; total man-days (22) and the completion time (6 days) are unchanged. Benefits: steady employment, less hiring and firing, better use of equipment.