CROSS Safety Report
Floor vibration in a gym
Vibration within the floor structure of a second floor gym gives rise to concern of structural resonance and possible fatigue of structural members.
Key Learning Outcomes
For clients and building owners:
- Vibration from installations with dynamic equipment such as gyms may restrict the re-use of some existing buildings
- Seek professional advice to be assured that any vibration is a serviceability and not a structural safety concern
For architects and designers:
- Consider the response to dynamic loading when planning and designing floors including for facilities such as gyms and dance venues
For civil and structural engineers:
- Consider dynamic response early in the structural design process and seek specialist advice if the analysis and design are beyond your competency
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A reporter is a member of a gym and is concerned about the resonant response in the steel structure due to the treadmills on the second floor. There have not been any structural problems identified, although the oscillations are felt throughout the floor.
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Expert Panel Comments
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Humans are very sensitive to vibration and often find it uncomfortable at magnitudes that are not of concern to the integrity of the structure. If the amplitudes are low, the stresses will be low and there should be no fatigue. However, steel structures can be prone to fatigue, particularly when they have not been designed or fabricated with dynamic loading in mind and are subjected to regular dynamic loads. Building owners do need to be assured that any vibration relates to comfort criteria rather than structural safety.
SteelConstruction.info (developed by BCSA, Steel for Life and the SCI acting in partnership) provides guidance on floor vibrations, their sources, consequences, assessment and design considerations. They confirm that even walking-induced vibrations can be a problem:
'The most common source of vibration that can cause nuisance in building applications is human activity, usually walking. Although small in magnitude, walking-induced vibrations can cause a nuisance to people working or living in the building, especially to the use of sensitive equipment or to those engaged in motion-sensitive activities, e.g. surgery. Naturally, the problem is more acute for more vigorous types of human activity such as dancing and jumping and therefore designers of buildings featuring a gymnasium or dance studio should take extra care to limit the vibrations in the rest of the building.'
The reporter has very helpfully highlighted the need for detailed structural surveys and assessments, when repurposing buildings, to understand how the building works under the new loading conditions, and not just for any change in static loads. Calculation of responses to dynamic loads are not the norm in design checks of existing buildings but engineers should recognise where a new use may bring about vibration which requires assessment. As an example, mixed-use developments with gyms and residential accommodation may require stringent assessment. The response of some structures to dynamic loads can be a very complex matter which requires specialist input which may well be outside the competence of many engineers. Some structures, including for example some lighter structures, can behave very adversely and be completely unacceptable to occupants when subjected to particular dynamic loadings. Modifications may be required to some repurposed structures to render them acceptable in use to occupants. In the extreme, fatigue or other failure of the structure is of course possible.
There have been cases of floor collapses due to vigorous dancing although generally these have been due to over-loading rather than fatigue.