Civil Engineering Reference
In-Depth Information
Mackie (1974) pointed out that it is not only the amount of physical energy that can
greatly influence the discomfort of vibrations; there are also several psychological
factors, including the following:
1. The nature of the task. For example, riding in a recreational boat is usually associated
with pleasure, although the same magnitude vibrations would be perceived as very
stressful in an industrial environment.
2. The person's degree of training or familiarity with the task. For example, a skilled
horseback rider can compensate for much of the vibration by rhythmically contracting
certain muscles. Likewise, an industrial worker can compensate for some of the
movements of a vibrating forklift truck or piece of industrial machinery. There are
also individual differences in sensitivity to vibration; heavy individuals suffer more
from vibration than do light individuals.
3. The presence of other stressors acting in combination. For example, vibration in
combination with noise produces a greater level of stress than vibration alone or noise
alone (Poulton, 1979). This will affect the physiological arousal of the individual,
which in turn has implications for the performance level (Figure 13.10).
In addition to the discomfort effects of vibration, there are several reputed health effects,
such as various spinal, anal-rectal, and gastrointestinal disorders (Fothergill and Griffin,
1977). However, these have been difficult to verify in research. Most of the evidence
comes from epidemiological investigations of truck drivers and heavy equipment
operators (Seidl and Heide, 1986). A large U.S. study of truck drivers
FIGURE 13.10
Yerkes-Dodson's law
can be used to illustrate the additive
