Civil Engineering Reference
In-Depth Information
Then,
→
12 = 5 ∗ 0
.
95 +
X
∗ 0
.
85
X
= 8
.
53 days
Total adjusted duration = 5 + 8
.
53 = 13
.
53 days
In other words, this activity, when started on May 27, would be expected to take
1.53 days more than it would if it were performed in January. This is not as bad as
performing it in July (12∕0
14 days).Onthe
other hand, it would take less than 12 days if it were performed in March or November
(12∕1
.
75 = 16 days) or August (12∕0
.
70 = 17
.
91 days).
Keep in mind that unit price is inversely proportioned to duration:
.
1 = 10
.
Crew cost
(
$ per day
)
Crew production
(
units per day
)
Unit price
(
$ per unit
)=
Ideally, we would like to do this activity when productivity is at its maximum
(i.e., duration is at its minimum) and cost is at its minimum. This may be possible
and simple if we are talking about one activity. But in the panoramic view of project
scheduling, with hundreds or thousands of activities spread over several months or
years, we should not focus on the local optimal (activity) solution but, rather, on
the global optimal (project) solution. It will take several iterations because, in each
iteration, activities' durations change when productivity multipliers are applied. This
will trigger shifts in the start and finish dates of succeeding activities, which may push
them into different productivity multiplier zones, and so on. For more details, see
papers coauthored by the author in the reference section
13
.
After finding the “optimum” schedule, it is a good idea for the scheduler to con-
duct a sensitivity analysis: if the project start is delayed or moved earlier by 1 day or one
unit of time, what would be the impact on the completion date and cost? Such an anal-
ysis is important because it will help the project management assess different scenarios,
including the possibility of change orders, weather delays, and other factors. It is like
many of us who experiment with the optimum time to leave home in the morning
and arrive at our workplace, in order to have the shortest driving time. A delay of 10
minutes in departure may mean arriving 30 minutes later.
Tip Box 8.5
It may amaze you to find out the cost savings from optimizing the project's start point
and activities' durations. It is the responsibility of the general contractor to explore
the optimum schedule and inform the owner of that schedule and the alternatives.
13
Four papers written by Dr. Ahmed Senouci and Dr. Saleh Mubarak (2012, 2013), listed in the reference
section.
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