Civil Engineering Reference
In-Depth Information
predicting an optimum number for each job, especially as the particular skills of the
construction team also greatly influence the actual rate of output. In general terms,
however, within any sector of the construction industry there is a recognisable trend:
output increases as more units of labour are taken on but not at a constant rate. To
understand why such a phenomenon occurs within any firm in the short run, we
have to analyse in detail the law of diminishing (marginal) returns.
Table 7.1
Diminishing returns: a hypothetical case in construction
In the first column, we give the number of workers used per week on a project. In the
second column, we give their total product; that is, the output that each specified
number of workers can produce in terms of square metres. The third column gives the
marginal product. The marginal product is the difference between the output possible
with a given number of workers minus the output made possible with one less worker.
For example, the marginal product of a fourth worker is 20 square metres, because with
four workers 140 square metres are produced, but with three workers only 120 are
produced; the difference is twenty.
Total product
(output in sq. m per week)
Marginal physical product
(in sq. m per week)
Input of labour
0
1
0
20
20
40
60
20
10
10
2
3
4
60
120
140
150
5
6
7
8
160
165
163
5
-2
DIMINISHING RETURNS
The concept of diminishing marginal returns applies to many different situations.
If you buckle a seat belt over your body in a car, a certain amount of additional
safety is obtained. If you add another seat belt some more safety is obtained, but not
as much as when the first belt was secured. When you add a third seat belt, again
safety increases but the amount of additional safety obtained is even smaller. In a
similar way, the
u-values
- a measure of heat loss - related to glazing do not decline
steadily as you add more panes of glass within a window unit. The u-values typically
associated with single, double and treble glazing are 5.7, 2.8 and 2.0 respectively.
Therefore, assuming the wall construction and other factors remain constant, going
from single to double glazing improves the u-value by 2.9, while adding a third pane
of glass only improves the u-value by 0.8.
