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Floor vibrations induced by human walking were investigated in a reinforced concrete structure. Six experimental floor structures were built in laboratories with the same dimensions and boundary conditions. Subjective tests were performed to assess the vibration serviceability of the floor structures. First, the subjects were asked to walk across a floor and then to rate the intensity of the vibrations, acceptability, and serviceability of the floors. In the second part of the tests, the subjects were seated on a chair placed in the middle of the floor and asked to rate floor vibrations when the walker passed the subjects. Floor vibrations induced by human walking were analyzed using peak acceleration, root mean square (r.m.s.) acceleration, and the vibration dose value (VDV), and four weighting functions (Wb, Wk, Wg, and Wm) were applied. Significant differences in the measured floor vibration were found across the floor structures, larger floor vibration lead to greater perceived vibration intensity, lower acceptability and serviceability. The Wb and Wk were found to be more applicable than Wg and Wm to explain perception of floor vibration. It was observed that the impact noise induced by walking did not influence the evaluation of floor vibration

The inclination of a backrest may be expected to alter the vibration transmitted to the body and the associated vibration discomfort. This study examined the influence of backrest inclination on the discomfort arising from whole-body vertical vibration when sitting in a rigid seat with a backrest inclined at 0? (upright), 30?, 60? and 90? (recumbent). Equivalent comfort contours were determined over the frequency range from 1 to 20 Hz and over the magnitude range from 0.2 to 2.0 ms 2 r.m.s. relative to the discomfort caused by 8-Hz vertical vibration at 0.4 ms-2 r.m.s. When sitting with the backrest inclined to 60? or 90?, there was less discomfort around 5 and 6.3 Hz than when sitting with the upright backrest. Around 16 and 20 Hz there was greater discomfort when sitting with the backrest inclined to 30?, 60?, and 90? than when sitting with the upright backrest. The reductions in discomfort at the lower frequencies may be associated with increased postural support and changes in the biodynamic responses of the body when reclined. Increased transmission of vibration to the head may explain the greater discomfort at high frequencies when sitting reclined. It is concluded that different methods of vibration evaluation are appropriate when evaluating vibration with upright and inclined backrests.

Vibration of the back is a potential source of discomfort for car passengers, with vibration in the x-axis (i.e. fore-and-aft with an upright backrest) often dominant. This study investigated how vibration discomfort depends on both the frequency of x-axis backrest vibration and the inclination of the backrest. Twelve subjects seated with a rigid backrest inclined by 0, 30, 60, or 90 degrees rated the discomfort caused by x-axis backrest vibration at 11 frequencies (between 2.5 and 25 Hz) at 9 levels (from about 3 to 24 dB above the absolute threshold in 3 dB steps) relative to the discomfort caused by 0.15 ms-2 r.m.s. 8-Hz x-axis backrest vibration. The subjects also rated the discomfort caused by 9 levels of 8-Hz x-axis backrest vibration relative to the discomfort caused by 2.0 ms-2 r.m.s. 8-Hz x-axis (i.e. vertical) vibration of the hand. The vibration acceleration of the backrest required to cause discomfort tended to be least at 8 Hz with the upright backrest and at 10 or 12.5 Hz with the backrest inclined by 30?, 60?, or 90?. At frequencies from 4 to 8 Hz, about 30 to 40% less acceleration was required to cause discomfort with the upright backrest than with the inclined backrests. It is concluded that frequency weighting Wc is appropriate for predicting vibration discomfort caused by x-axis vibration of an upright backrest, but that another frequency weighting (e.g. Wb) would be more appropriate for inclined backrests.

Models of the vertical apparent mass of the human body are mostly restricted to a sitting posture unsupported by a backrest and ignore the variations in apparent mass associated with changes in posture and changes in the magnitude of vibration. Using findings from experimental research, this study fitted a single degree-of-freedom lumped parameter model to the measured vertical apparent mass of the body measured with a range of sitting postures and vibration magnitudes. The resulting model reflects the effects of reclining a rigid backrest or reclining a foam backrest (from 0 to 30 degrees), the effects of moving the hands from the lap to a steering wheel, the effects of moving the horizontal position of the feet, and the effects of vibration magnitude (from 0.125 to 1.6 ms–2 r.m.s.). The error between the modelled and the measured apparent mass was minimised, for both the apparent masses of individual subjects and the median apparent masses of groups of 12 subjects, for each sitting posture and each vibration magnitude. Trends in model parameters, the damping ratios, and the damped natural frequencies were identified as a function of the model variables and show the effects of posture and vibration magnitude on body dynamics. For example, contact with a rigidbackrest increased the derived damped natural frequency of the principal resonance as a result of reduced moving mass and increased stiffness. When the rigid backrest was reclined from 0 to 30°, the damping decreased and the resonance frequency increased as a result of reduced moving mass. It is concluded that, by appropriate variations in model parameters,a single degree-of-freedom model can provide a useful fit to the vertical apparent mass of the human body over a wide range of postures and vibration magnitudes. When measuring or modelling seat transmissibility, it may be difficult to justify an apparent mass model with more than a single degree-of-freedom if it does not reflect the large influences of vibration magnitude, body posture, and individual variability.

Building vibration produced by external sources (e.g. road and rail traffic) and internal sources (e.g. domestic equipment and footfalls) is usually within the frequency range 1 to 80 Hz. The excitation of structures by wind or waves can induce horizontal motion at frequencies less than 1 Hz. This paper reviews guidance on the measurement, evaluation and assessment of human exposure to horizontal motion over the frequency range 0.063 to 1.0 Hz as provided in British Standard 6611 (1985) and the equivalent International Standard 6897 (1984). The guidance is compared with standards applicable to exposure to vibration at higher frequencies. It is concluded that BS 6611 and ISO 6897 do not adequately allow for the effects of exposure duration or for differences in the effects of motion on different tasks. Acceleration limits for buildings proposed in BS 6611 and ISO 6897 for the worst 10 minutes of a wind storm with a return period of 5 years or more are similar to satisfactory magnitudes in BS 6472-1 (2008) and BS 6841 (1987) for 10-minute daily exposures. Mean thresholds for the perception of motion in BS 6611 and ISO 6897 are a little higher than those in ISO 2631-1 (1997), BS 6472-1 (2008), and BS 6841 (1987). The acceleration magnitudes expected to impair task performance in BS 6611 and ISO 6897 are lower than the magnitudes impairing hand control in BS 6841. Possible revisions to BS 6611 and ISO 6897 are discussed.

Although many rail travellers use portable computers while travelling, the train environment has not been influenced by the desire to operate computers. Some trains provide power points and tables for portable computers, but an optimal design also requires understanding of how typing is disturbed by train motion. There are numerous studies of typing in static conditions and many studies of the interference of activities by vibration, but there have been few studies of the effects of vibration on typing. In the few studies previously conducted, the differing methods of measuring performance make it difficult to compare results.An experimental study has been performed to understand the effects of vibration magnitude, vibration frequency and vibration direction on typing performance. With 12 seated subjects in each condition, the effects on typing performance of five vibration magnitudes (0.63, 0.80, 1.00, 1.25 and 1.6 ms-2 r.m.s.) of 30-s periods of sinusoidal vibration at each of twelve frequencies (0.50, 1.00, 1.25, 1.60, 2.00, 2.50, 3.15, 4.00, 5.00, 6.30, 8.00, 10.00 Hz) were determined for each of the three translational axes (x-, y-, and z-axis) of whole-body vibration. Performance was evaluated by three measures: (a) the total number of data entries in 30 s, (b) the number of typing errors, and (c) a subjective estimate of typing difficulty. The results are presented in tabular and graphical form.Subjective estimates of typing difficulty varied with the magnitude, frequency, and direction of the vibration. Lateral vibration, especially in the range 1.6 to 6.3 Hz, created the greatest difficulty. Vertical vibration caused least difficulty. There were no statistically significant effects of vibration on typing speed or typing accuracy, probably because extra effort was used to counteract the vibration disturbance.

Vibration experienced in transport and in buildings can yield discomfort or annoyance if the vibration exceeds the threshold for vibration perception. Knowledge of thresholds makes it possible to determine which frequencies and directions of low magnitude vibration give rise to perception. The effect vibration frequency (2 to 315 Hz) on absolute thresholds for the perception of whole-body vibration has been determined experimentally with 12 seated persons for each of the three axes of excitation (fore-and-aft, lateral and vertical). The frequency-dependence of the thresholds differed between the three axes. At frequencies, greater than 10 Hz, sensitivity was greatest for vertical vibration. At frequencies less than 3.15 Hz, sensitivity was greatest to fore-and-aft vibration. In all three axes, the acceleration threshold contours at frequencies greater than 80 Hz were U-shaped, suggesting the same psychophysical channel mediated high frequency thresholds for fore-and-aft, lateral and vertical vibration. It is shown that the frequency-dependence of absolute thresholds for the perception of whole-body vibration are not consistent with the frequency weightings used in current standards.

A social survey questionnaire has been developed to determine human responses to vibration in residential environments. The overall aim was to produce a robust methodology for obtaining responses that could be combined with vibration measurements so as to investigate dose-response relationships for vibration in residential buildings. The vibration considered included that from sources outside the control of residents (e.g., road, rail, industrial, construction). This paper describes the development of the questionnaire and explains its structure and content. A review of social surveys and field and laboratory studies of vibration and noise is included. Methods of analysing responses obtained to the questionnaire are summarised.

BACKGROUND: It is commonly assumed that motion sickness caused by moving visual scenes arises from the illusion of self-motion (i.e., vection).HYPOTHESES: Both studies reported here investigated whether sickness and vection were correlated. The first study compared sickness and vection created by real and virtual visual displays. The second study investigated whether visual fixation to suppress eye movements affected motion sickness or vection. METHOD: In the first experiment subjects viewed an optokinetic drum and a virtual simulation of the optokinetic drum. The second experiment investigated two conditions on a virtual display: a) moving black and white stripes; and b) moving black and white stripes with a stationary cross on which subjects fixated to reduce eye movements. RESULTS: In the first study, ratings of motion sickness were correlated between the conditions (real and the virtual drum), as were ratings of vection. With both conditions, subjects with poor visual acuity experienced greater sickness. There was no correlation between ratings of vection and ratings of sickness in either condition. In the second study, fixation reduced motion sickness but had no affect on vection. Motion sickness was correlated with visual acuity without fixation, but not with fixation. Again, there was no correlation between vection and motion sickness. CONCLUSIONS: Vection is not the primary cause of sickness with optokinetic stimuli. Vection appears to be influenced by peripheral vision whereas motion sickness is influenced by central vision. When the eyes are free to track moving stimuli, there is an association between visual acuity and motion sickness. Virtual displays can create vection and may be used to investigate visually induced motion sickness.