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Abstract
The discomfort of standing people experiencing steady-state vibration can be predicted from the root-mean-square (rms) 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 rms value), the vibration magnitude required for similar discomfort, and a method predicting this equivalence, were determined. The rms method (with an exponent of 2) and the root-mean-quad method (exponent of 4) tended to, respectively, underestimate and overestimate the discomfort of high-crest factor motions. The optimum evaluation method had an exponent of about 3.0 for 1-Hz motions and 3.5 for 8-Hz motions. Current standards do not provide reliable indications of when vibration discomfort can be predicted by an rms measure.
Statement of Relevance: Current standards recommend alternatives to the root-mean-square method (exponent of 2.0) for predicting the discomfort caused by transient vibration. The alternatives include the root-mean-quad or vibration dose value (exponent of 4.0) and peak values. An exponent of 2.0 underestimates, but an exponent of 4.0 slightly overestimates, the discomfort of transients experienced by standing people. Peak values are not appropriate.
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Acknowledgements
This study was conducted with the support of Société Nationale des Chemins de fer Français (SNCF), Paris, France. The assistance of Cedric Gallais is gratefully acknowledged.