To minimise the discomfort of standing people caused by vibration of a floor, it is necessary to know how their sensitivity to vibration depends on the frequency of the vibration. This study was designed to determine how the discomfort of standing people exposed to horizontal and vertical vibration depends on vibration frequency over the range 0.5 to 16 Hz. Using the method of magnitude estimation, sixteen subjects judged the discomfort caused by fore-and-aft, lateral, and vertical sinusoidal vibration at each of the sixteen preferred one-third octave centre frequencies from 0.5 to 16 Hz at each of nine magnitudes. Subjects also reported the main cause of their discomfort.Equivalent comfort contours were constructed, reflecting the effect of frequency on subject sensitivity to vibration acceleration. With horizontal vibration, at frequencies between 0.5 and 3.15 Hz the discomfort was similar when the vibration velocity was similar, whereas at frequencies between 3.15 Hz and 16 Hz the discomfort was similar when the vibration acceleration was similar. At frequencies less than 3.15 Hz, the subjects experienced problems with their stability, whereas at higher frequencies vibration discomfort was mostly experienced from sensations in the legs and feet. With vertical vibration, discomfort was felt in the lower-body and upper-body at all frequencies. The frequency weightings in current standards for predicting the vibration discomfort of standing persons have been greatly influenced by the findings of studies with seated subjects: the weightings are consistent with the experimentally-determined frequency-dependence of discomfort caused by vertical vibration but inconsistent with the experimentally-determined frequency-dependence of discomfort caused by horizontal vibration. The results suggest that the responses of seated and standing people are similar for vertical vibration, but differ for horizontal vibration, partly due to greater instability in standing persons.
When standing and exposed to vibration in trains, passengers and crew may seek support by leaning on a surface or holding a bar or a handle that alters the transmission of vibration to their bodies. The effects of such contact on the discomfort caused by vibration have not been previously investigated.This study was designed to investigate the effects of postural supports on the discomfort caused by fore-and-aft and lateral whole-body vibration in the frequency range 0.5 to 16 Hz. Using the method of magnitude estimation, 12 standing male subjects judged the discomfort caused by five magnitudes of sinusoidal vibration at six frequencies (
The discomfort of standing people experiencing steady-state vibration can be predicted from the root-mean-square of the frequency-weighted acceleration, but alternative methods are advocated for evaluating motions containing transients. Using the method of magnitude estimation, 20 standing subjects estimated the discomfort caused by octave-bandwidth random vibrations at two centre frequencies (1 and 8 Hz) in each of three directions (fore-and-aft, lateral, and vertical). For motions having seven different crest factors (i.e. the ratio of the peak to the r.m.s. value), the vibration magnitude required for similar discomfort, and a method predicting this equivalence, was determined.
Few studies have compared the discomfort caused by vibration in different directions, and few have investigated the vibration discomfort of standing people. This study was designed to compare the discomfort experienced by standing people exposed to sinusoidal vibration in the fore-and-aft, lateral, and vertical directions. Using the method of magnitude estimation, 12 subjects estimated the discomfort caused by 4-Hz sinusoidal vibration at 10 different magnitudes. At 4 Hz, subjects were less sensitive to lateral vibration than to fore-and-aft vibration (K y /K x =0.71), and more sensitive to vertical vibration than to horizontal vibration (K z /K x =1.95; K z /K y =2.77).Previous findings showing how the discomfort of standing people depends on the frequency of fore-and-aft, lateral, and vertical vibration were used to define frequency weightings that reflect relative sensitivity to vibration in each direction. The frequency weightings differ from those appropriate for seated people, and differ from the weightings for standing people in current standards that were mostly derived from understanding of the discomfort of seated people. HighlightsShows how direction of vibration affects the vibration discomfort of standing people.Shows vibration discomfort is different in seated and standing people.Standards for predicting vibration discomfort of seated and standing people can be improved.
Few studies have investigated discomfort caused by multi-axis vibration and none has explored methods of predicting the discomfort of standing people from simultaneous fore-and-aft, lateral, and vertical vibration of a floor. Using the method of magnitude estimation, 16 subjects estimated their discomfort caused by dual-axis and tri-axial motions (octave-bands centred on either 1 Hz or 4 Hz with various magnitudes in the fore-and-aft, lateral, and vertical directions) and the discomfort caused by single-axis motions. The method of predicting discomfort assumed in current standards (square-root of the sums of squares of the three components weighted according to their individual contributions to discomfort) provided reasonable predictions of the discomfort caused by multi-axis vibration. Improved predictions can be obtained for specific stimuli, but no single simple method will provide accurate predictions for all stimuli because the rate of growth of discomfort with increasing magnitude of vibration depends on the frequency and direction of vibration. Practitioner summary (<50 words)Useful estimates of the vibration discomfort of standing people can be obtained from the root-sums-of squares of the floor acceleration in each of the three directions (fore-andaft, lateral, and vertical) if the three components are frequency-weighted according to the dependence of discomfort on the frequency of vibration in each axis.
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