Schedule Compression and Time-Cost Trade-Off - Construction Project Scheduling and Control - page 234

This action increased the direct costs by $40 and decreased the indirect
costs by $120. The total impact on the cost is a net savings of $80.
We now have two paths that tie at 24 days' duration: ABEH and ACEH.
We can compress a shared activity (A, E, or H) or a combination of unshared
activities (B and C). We choose activity E and compress it from 6 days to 5 days
at a cost of $50.

Cycle 2
Path Duration (days)

ABEH 24 24 23

ACEH 25 24 23

ACFH 23 22 22

ACFG 24 23 23

ADG 23 23 23

The direct costs increase by $50, and the indirect costs decrease by
$120. This results in a net decrease of $70 in the total cost.
Now we have four paths that tie at 23 days' duration: all but ACFH. We can
compress a shared activity (A) or a combination of unshared activities (plenty
of options exist). We choose activity A and compress it from 5 days to 4 at a
cost of $100 11 . Activity A is now completely crashed.

Cycle 3
Path

Duration (days)

ABEH 24 24 23 22

ACEH 25 24 23 22

ACFH 23 22 22 21

ACFG 24 23 23 22

ADG 23 23 23 22

With this action, we spent an extra $100 in direct costs and saved $120
in indirect costs. The total cost decreased by $20 (we are still saving money,
but the rate is decreasing).
Now we need to compress the same four paths using the least-cost com-
bination. After a simple mathematical inspection of the table, we find the
best combination to be C, D, and E, with a total combined cost of $140.

11 If activity A could be crashed by more than 1 day, we could have crashed it to the limit, since it is part of
any path on the network. This means any day cut from activity A would automatically mean a day cut from
the entire schedule.