Generally, a contractor has three options in accelerating a construction schedule: working longer hours, increasing the number of workers, or creating an additional shift of workers.
Although there has been a significant amount of research conducted on scheduled overtime on constructional labor productivity, little information exists addressing the labor inefficiency associated with working a second shift. University of Wisconsin researchers have come up with a formula and table to estimate the productivity loss of a second shift. Their conclusion is that small amounts of well organized shift work can serve as a very effective response to schedule acceleration. Based on the data analyzed, the researchers determined that the productivity loss and percentage shift work could be expressed as follows:
Productivity Loss = 0.22052 + 0.07152 ln (% shift work expressed as a decimal).
Figure three is a graphical representation of the equation and table four shows the productivity multiplier of shift work depending on the amount of shift work. For example, assume the project has a budgeted man hour requirement of 30,000 hours. Due to increased scope changes the contractor employs a second shift. The total number of shift hours is 6,000 hours, or 20% shift work.
Inserting the 20% shift work into the formula as a decimal:
Productivity loss = 0.22052 + 0.07152 ln (0.2) = 0.1054
Multiplying the productivity loss by the total project hours spent in shift work (6,000 hours on the second shift and overlapping with 6,000 on the first shift equals 12,000 hours):
Efficiency loss = 12,000 hours x 0.1054 = 12,600 hours of productivity lost.
The equation can be used as a beginning point for negotiations between owners and contractors for adjustments due to an owner-initiated schedule acceleration and compression. The formula also allows a contractor to select the most cost effective option (i.e., over-manning, over-time and shift work) when schedule acceleration is required. The positive effects of shift work on productivity makes it the preferable option in place of over?time or over?manning. The major source of labor inefficiency in shift work stems from overlapping the first and second shift, thus the authors recommend to overlap supervision of the two shifts by asking the supervisors of the first shift to stay longer and the supervisors of the second shift to arrive earlier. They also recommend, if at all possible, to assign completely different tasks at different locations to the second shift workers than those of the first shift.
Journal of Construction Engineering and Management, March 2008. Awad S. Hanna, Impact of Shift Work on Labor Productivity for Labor Intensive Contractor.