Abstract
Base isolation is a means of reducing the transmission of vibration into buildings and was first used in the 1960s. Since then many buildings have been mounted on springs of various types in order to reduce the effects of ground-borne vibration from roads and railways. For most applications, the building rests on steel springs or laminated rubber bearings. A typical objective is a reduction in vibration transmission of at least 10 dB for frequencies above 10 Hz, but, while difficult to verify, such performance is probably rarely ever achieved.
Current practice suggests that the choice of spring type has a significant effect on the efficiency of the vibration isolation, as well as having implications on the cost and implementation of the system. However, there remain unanswered a number of fundamental questions concerning the specification and design of isolation bearings for buildings. For example, what is the most appropriate stiffness of the bearings for a given application and to what extent is damping an important part of a good system?
This paper reviews current methods of predicting isolation performance and introduces an alternative model which aims to model more fully the behaviour of base-isolated buildings. The benefits of a power-flow approach in assessing isolation performance are also discussed and it is argued that this enables a more appropriate measure of performance to be defined than one based on vibration amplitudes alone.
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