Schedule Compression and Time-Cost Trade-Off - Construction Project Scheduling and Control - page 242

These factors impact both productivity and cost. The impact on productivity will
affect duration of the activity and the cost of labor and equipment resources.

Productivity and Cost Multipliers

The scheduler can divide the year, in a certain location, into time segments (inter-
vals of 10 days, or months, for simplicity in this discussion), assigning productivity
and cost multipliers for each segment. The base productivity and cost can be “nor-
mal,” “average,” or “optimum.” It does not matter, as long as the multipliers are
estimated with respect to the base numbers. For example, if we consider January as
base for productivity and cost in location X (100%), then we compile productivity and
cost multipliers for other months (or time periods) based on past records and future
expectations. Let's suppose that we compiled this table:

Cost Multiplier a (CM) Month Productivity Multiplier (PM)

January 1.00 1.00

February 1.00 1.00

March 1.10 0.90

April 1.05 0.90

May 0.95 0.95

June 0.85 1.05

July 0.75 1.10

August 0.70 1.20

September 0.85 1.10

October 1.00 1.00

November 1.10 0.90

December 1.00 0.95

a The cost impact from the productivity change is included under the productivity
multiplier only. For more accurate results, the cost multiplier should be broken
into three multipliers—for labor, equipment, and materials—but for the sake of
simplicity and to demonstrate the concept, we will keep it as one multiplier.

Now, when a schedule is created based on base productivity and cost, it has to be
recalculated:

Adjusted duration = ∑ Dur i ∕PM i

(8.1)

Adjusted cost = ∑ Cost i ∗ CM i

(8.2)

For example, if an activity is scheduled to start on May 27 and it has 12 days'
duration (with base productivity), the adjusted duration will be distributed between
May and June. We don't know exactly how long this activity will take, but based
on Productivity multipliers 12 days. The

portion in May will be 5 days (May 27 through 31), but we need to calculate the
portion in June, X :
From equation 8.1:

< 1.00, we expect the total duration to be >

Base Duration = Adjusted Duration ∗ Productivity Multiplier