Introduction
This Technical Guidance Note is an introduction to the assessment of floor vibrations. Since the advent of lighter structures that have longer spanning elements within them, the built in dampening effect buildings have had historically has become less pronounced. Despite this, floor vibration can be an overlooked criterion during the design process. This can lead to expensive remedial works being carried out on structures after they have been built, as occupants complain of discomfort due to excessive movements and vibrations.
It should also be noted that floor vibrations can in some cases have a detrimental effect on the integrity of the structure. This usually occurs when there is a continuous long term vibration inducing load, such as a piece of machinery that is causing a dynamic response within the structure. This can then lead to a fatigue based failure of the supporting structure. This scenario however is rare as vibrations from such machinery would have to match the harmonic of the supporting structure, which is unlikely. Also, it is usually the building's occupants that generate vibrations and as their sense of comfort deteriorates, the cyclical movements within the structure drop to the point where fatigue induced failure cannot occur.
The assessment of floor vibration concerns how the mass of its supporting structure moves when subjected to an imposed load. This is determined by ascertaining the natural frequency of the supporting structure to the floor, which is stated in Hz (cycles per second). Once that is calculated it is then possible to assess how the structure will move when subjected to various types of imposed loading.