ATTENUATING LATERAL VIBRATION SOURCES

Vibration is often characterised and detailed in simplistic terms in the vertical axis. Similarly, many isolation calculations continue to be carried out on the assumption that systems operate in a single degree of freedom (SDOF). While this is often the most crucial direction to consider in lightweight structures with responsive floorplates, this ignores vibration generated and carried in lateral axes, for example from ground-borne rail sources where the energy can be significant. This paper is focussed on base-isolated buildings, but similar principles can apply to box-in-box or MEP isolation. Specifying vibration isolation bearings to control vibration in lateral directions is more complex. Care must be taken when calculating the lateral SDOF natural frequency as the lateral isolation system is not gravity-loaded. Designs should be sympathetic to this and must respect limits on movement required by the project structural engineer. Treating the vertical and lateral axes independently can easily lead to designs which are overly stiff in the vertical plane. Furthermore, when considering the global building response, coupling between the vertical and lateral axes should be considered. This paper discusses this in more detail and how to balance the acoustic requirement with the structural. Case studies are discussed which include preventing lateral structural movement of the core under wind loading, safeguarding against lateral forces in blast/seismic scenarios and resiliently supporting facades.