Vibration

Sound is essentially vibration in air, so the topic is familiar to us. From a noise control perspective, it's critical to understand how it is generated and propagated.

Vibration in structures, the ground and from machinery may effect humans and it's usually with that in mind that it causes concern.

Ground borne vibration from construction, transportation etc may cause cosmetic or structural damage to buildings or causes disturbance to occupants of the buildings. It may also cause re-radiated noise in buildings.

Occupational vibration may cause damage or task impairment to people at work, typically from hand-arm vibration (power tools etc) or whole-body (vehicles, platforms etc) vibration.

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Building Damage


BS 7385-2:1993 Evaluation and measurement for vibration in buildings. Guide to damage levels from groundborne vibration gives guidance on the levels of vibration above which building structures could be damaged. The standard states that there is a major difference between the sensitivity of people in feeling vibration and the onset of levels of vibration which damage the structure. Furthermore it states that cracking commonly occurs in buildings whether they are exposed to vibration or not. For residential buildings, the standard states that for cosmetic damage (cracking in plaster work etc.) to occur, a peak particle velocity of some 15 mm/s is necessary at a vibration frequency of 4 Hz; this rises to 20 mm/sec at 15 Hz, and thereafter the limit rises to 50 mm/s at 40 Hz and above. The Association of Noise Consultant's (ANC) document "Measurement and Assessment of Groundborne Noise and Vibration" states that these limits apply to the maximum of the vibration levels in the three mutually perpendicular axes and that minor structural damage can occur at levels around twice the above limits and major damage can occur at levels around four times the above limits.




Disturbance


The most commonly used standard for environmental vibration assessment is BS 6472-1:2008 Guide to evaluation of human exposure to vibration in buildings. Vibration sources other than blasting. Most often it is used to assess railway vibration.

It sets out an unusual parameter known as the vibration dose value (VDV) or estimated vibration dose value (eVDV). Separate Day and Night-time periods apply.




Occupational


Occupational exposure to vibration can be divided into

  • Hand-arm vibration (HAV) comes from the use of hand-held power tools and is the cause of significant ill health (painful and disabling disorders of the blood vessels, nerves and joints).
  • Whole-body vibration (WBV) is transmitted through the seat or feet of employees who drive mobile machines, or other work vehicles, over rough and uneven surfaces as a main part of their job. Large shocks and jolts may cause health risks including back-pain.

National health & safety legislation enacts the the European Directive Physical Agents directive. This sets out maximum vibration exposure limits and action levels for both hand-arm and whole-body vibration. Exposing unprotected workers to levels above the maximum limit is deemed to be unacceptable; whereas levels in excess of the action levels triggers various duties for both employers and employees.