What are floor vibrations and why are they important?

The term ‘vibrations’ when applied to floors refers to the oscillatory motion experienced by the building and its occupants during the course of normal day-to-day activities.

This motion is normally vertical (up and down), but horizontal vibrations are also possible. In either case, the consequences of vibrations range from being a nuisance to the building users to causing damage to the fixtures and fittings or even (in very extreme cases) to the building structure.

The severity of the consequences will depend on the source of the motion, its duration and the design and layout of the building.Floor vibrations are generally caused by dynamic loads applied either directly to the floor by people or machinery. 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.Machinery-induced vibrations are best dealt with at source through the provision of isolating mounts or motion arresting pads.

Machines installed in factories tend to produce the most severe vibrations due to their size and the nature of their operation. However, floor vibration is rarely a problem in most factories, since it is accepted by the workforce as part of the industrial environment.

Once constructed, it is very difficult to modify an existing floor to reduce its susceptibility to vibration, as only major changes to the mass, stiffness or damping of the floor system will produce any perceptible reduction in vibration amplitudes.

It is important therefore that the levels of acceptable vibration be established at the concept design stage, paying particular attention to the anticipated usage of the floors. The client must be involved in this decision, as the specified acceptance criteria may have a significant impact on the design of the floor and the cost of construction.