Vibration
Vibration Mitigation
The response of a site to a vibration source is very site specific, and it is almost always preferable to perform a measurement survey of the site. Base Isolation (mounting a building on a resilient foundation) is commonly assumed to be the most appropriate solution to vibration problems. Alternative vibration control options, directed at the source, propagation path and receiver should also be considered. The range of options may provide viable cost effective alternatives to Base Isolation, and may in some cases be used as supplementary measures to a Base Isolation proposal. No significance should be attached to the order of the alternative options listed, and the list is not exhaustive.
At Source - Industrial
- isolate source
- undertake maintenance on plant
- alter design of plant
- adopt different work practice
- procure new plant
Railway
- smoother running surface
- alter vehicle unsprung mass
- alter line speed
- resilient rail fixings, booted sleepers, track ballast mats or a floating track slab
Highway
- improve quality of running surface
- remove potholes refit loose manhole covers
Propagation Path
- increase propagation path, site building or sensitive parts far away from the source
- trenches in path between source and building
- concrete wall built into the ground between source and receiver (Impedance Wall)
- ground treatment to stiffen a layer of soil (Wave Impedance Block)
At Receiver
- Rearrangement of plan (e.g. locate building far from source, switch location of car parks and landscaping into nearby areas)
- Reconsider use of site (commercial may be less sensitive than residential)
- Avoid floor resonance with dominant peaks in ground vibration spectrum (de-tune)
- Solid ground bearing slabs may be preferential to suspended slabs (e.g. bungalows in place of two storey dwellings)
- Unavoidable resonances targeted at frequencies of least Human sensitivity, usually requires high frequency
(bandwidth may be broad, increasing risk of tuning with source)
- Low natural frequency floors may avoid tuning with source (also a narrower bandwidth),
but a risk of footfall induced vibration (see ISO 10137:1992)
- A floor may constructed on isolators off a floor below (floating floor)
- Isolate sensitive areas (box-within-a-box)
- Isolate individual items of sensitive equipment
- A dynamic system added to the primary system (Dynamic Vibration Absorber), to neutralise motion
(at a specific frequency, where de-tuning cannot be achieved)
- Select structural form for optimum damping (e.g. concrete in preference to steel)
- Constrained layer floor damping treatments
- Foundations taken into strata with less vibration, decouple from soil near surface
- Sensitive equipment on ground rather than suspended floors, or equipment on foundation
bearing deep in soil, and decoupled from building or soil near surface
- Deploy traditional structural materials in a way that achieves a rigid body mount frequency
comparable to that obtained with Base Isolation
- Increase path length of vibration source to increase damping
(e.g. suspend floors from tops of columns rather than supported from columns directly off the ground)
- Irregular construction patterns and discontinuities in the construction
- Heavier forms of construction
- Increase background noise levels to mask intrusive noise
- Active vibration control using electromechanical or hydraulic actuators
(unlikely to be a viable option in all but special circumstances)