Civil Engineering Reference
In-Depth Information
vibration. There are similar regulations
in the x and z directions. To obtain
exposure limits for reduced comfort,
subtract 10 dB. For exposure limits to
avoid tissue damage, add 6 dB.
Laboratory studies have confirmed that vibrations between 3 and 5 Hz are likely to be
physically uncomfortable at an acceleration level of approximately 0.1 g, to be painful
and distressing at intensities of about 1 g, and to cause injuries if the acceleration exceeds
2 g. These findings form the main background for the present ISO standards for vibration
(see Figure 13.9) (Mackie et al., 1974; Gruber, 1976).
Hansson et al. (1976) studied exposure to whole-body vibrations of 44 industrial truck
drivers. He found that using ISO Standard 2631 for exposure limits (ISO, 1997), 6 of the
industrial truck drivers presented a risk to health if exposure lasted for 8 hours. Vibration
was fatiguing and reduced the work capacity of the drivers in two thirds of the trucks
studied (according to ISO standards).
Large and heavy trucks exposed the drivers to lower frequencies than did small and
light trucks. Obviously, the vibration characteristics of similar machines vary
considerably, depending upon the design. Hansson et al. (1976) concluded that
manufacturers and designers of trucks are not always well informed about the
implications of different design alternatives on whole-body vibration.
FIGURE 13.9
The resonant
frequencies of different parts of the
body of a seated driver.
