Appendix B BS 6472 weightings
B1 Values for continuous and impulsive vibration
Human discomfort values for continuous vibration have been extensively researched and published in BS 6472 (1984 and 1992), ISO 2631.2-1989 and AS 2670.2-1990, which form the basis of this guideline. References and a bibliography identifying the research studies are included in each of these standards.
In general, the standards and the reference studies on which they are based use frequency-weighted vibration values to evaluate and assess the likely effects of vibration on building occupants. The shape of the weighted rms acceleration curve used for this purpose is shown in Figure B1.1 for z-axis vibrations. A similar curve for x- and y-axis vibrations is shown in Figure B1.2. The minimum of the weighted z-axis rms vibration curve (i.e. 0.005 m/s2 or 54 dB re 10-6m/s2) corresponds approximately to the threshold of perception of continuous z-axis vibration for most people.
Figure B1.1 Weighted z-axis vibration rms acceleration-Curve 1 (Source: BS 6472-1992)
The 'threshold of perception' weighted rms acceleration curves shown in Figures B1.1 and B1.2 can also be expressed as equivalent weighted peak vibration velocity curves. This is illustrated in Figure B1.3 for z-axis vibration, again with the minimum value of the curve corresponding approximately to the threshold of perception (0.14 mm/s or 103 dB re 10-6 mm/s). A similar curve for x- and y-axis vibrations is shown in Figure B1.4.
Figure B1.2 Weighted x- and y-axis vibration rms acceleration (Source: BS 6472–1992)
Figure B1.3 Weighted z-axis vibration peak velocity—Curve 1 (Source: BS 6472–1992)
Figure B1.4 Weighted x- and y-axis vibration peak velocity (Source: BS 6472–1992)
On the basis of these 'threshold of perception' curves, the standards relate the degree of response (complaint levels or incidence of 'adverse comment') from building occupants in terms of multiples of the base-weighted vibration value (i.e. the curves) according to the type of occupancy, period of day and type of vibration (i.e. continuous or impulsive). The criteria set out in Tables 2.2 and 2.4 have been established by applying the BS 6472-1992 multiplication factors (Table B1.1) to the limiting value in the acceleration curve for the z-axis (i.e. 0.005 m/s2 from Figure B1.1). To assist in determining the criteria at all frequencies, Table B1.2 presents the numerical values of the base curves presented in Figures B1.1 to B1.4.
Table B1.1 Multiplying factors used to specify satisfactory magnitudes of building vibration with respect to human response
| ||Multiplying factors|
|Place||Time||Continuous vibration||Impulsive vibration|
|Critical working areas (e.g. hospital operating theatres, precision laboratories)||day||1||1|
Source: BS 6472–1992
In general, a doubling of vibration magnitudes (corresponding to an increase of 6 dB in vibration acceleration or velocity) represents an appreciable change in response. As indicated by Figure B1.5, for example, an increase of 6 dB in vibration represents approximately a doubling in the percentage of people that perceived vibration in a survey of people living near a railway line in Japan (Nelson, 1987).
Figure B1.5 Reported responses to train vibration levels (Source: Nelson, 1987)
Table B1.2 Vibration values for the base curves in Figures B1.1 to B1.4
|Frequency Hz ||z-axis vibration values ||x- & y-axis vibration values |
|rms acceleration m/s2 (Figure B1.1) ||Peak velocity mm/s (Figure B1.3) ||rms acceleration m/s2 (Figure B1.2)||Peak velocity mm/s (Figure B1.4)|
B2 Vibration dose for intermittent vibration
B2.1 Key scientific studies
Griffin and Whitham (1980) investigated the effects of duration on the discomfort produced by impulsive whole body vibration for durations of up to 32 seconds. The results indicated that discomfort was dependent on the duration of exposure, and that motions containing high peak values should be evaluated by using the root mean quad approach set out in Section 2.4 of this guideline.
Howarth and Griffin (1988) conducted experiments to determine the manner in which annoyance caused by railway-induced building vibration depended on the frequency of occurrence of train vibration events. They also investigated how annoyance depended on the magnitude of the vibration. Their experiments confirmed that the relationship between the number of train vibration events and the magnitude of the vibration could be used to predict conditions causing similar annoyance, and confirmed that the root mean quad VDV approach was consistent with observations. These results formed the basis of the vibration dose concept presented in BS 6472-1992.
B2.2 Acceptable values for vibration dose
The approach adopted in BS 6472 for assessing intermittent or complex vibration is to calculate a vibration dose (using the root-mean-quad approach), and to relate that vibration dose, in terms of relative acceptability, to the corresponding vibration doses for exposure to continuous vibration.
BS 6472 presents acceptable vibration doses for residences only. However, since vibration dose is proportional to preferred values of continuous vibration, the VDVs for other areas of occupancy (e.g. offices, workshops) are inferred from Table 2.2 to yield the doses set out in Table 2.4.
B2.3 Alternative calculation of vibration dose using rms velocity
The root-mean-quad approach is presented in BS 6472-1992 for the calculation of vibration dose from rms acceleration. The following analysis illustrates the derivation of a simplified procedure for determining eVDV from the rms velocity value, rather than an rms acceleration value.
- Over the frequency range of 8 to 80 Hz, z-axis velocity requires no frequency weighting in order to determine annoyance or disturbance response (no weighting over frequency range 2-80 Hz for x- and y-axis vibration). At frequencies below 8 Hz, the use of unweighted velocity is more strict than the requirements of BS 6472.
B3 Approximate frequency weightings of base curves (1-80 Hz)
The frequency weightings in Table B3.1 are approximated from the base curves in Figures B1.1 to B1.4 to give an approximate quantification of the relative effects of different vibration frequencies on human annoyance or complaints about interference with activities.
Table B3.1 Approximate frequency weightings of base curves (1-80 Hz)
Values taken from Table 3 of BS 6841-1987
1 Weighting defined in BS 6841-1987
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