Dynamics & Vibration Research Group

Base isolation is a means of reducing the transmission of ground-borne vibration into buildings. It enables construction on sites previously deemed unacceptable for certain purposes due to high levels of vibration, for example from nearby roads and railways.

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? Such parameters may have a significant effect on the efficiency of the vibration isolation, as well as having implications on the cost and implementation of the system.

Current research at Cambridge aims to improve the methods of predicting isolation performance in order to objectively evaluate the alternative types of isolation bearing.

Project Details

Since the construction of a block of flats over St James' Park Station, London in 1965, numerous buildings have been built on springs. Examples include office towers, concert halls, hotels and hospitals.



Figure 1: London Metropole utilises rubber bearings

Although many different types of isolation bearing have been suggested and tried for buildings, the choice for modern buildings essentially lies between steel springs and rubber bearings. However, developments in the bearings themselves have not been matched by developments in the underlying theory. A means is still required to evaluate objectively the various types of bearing, in essence, to answer the question: which is best, steel or rubber?

Predictions of isolation performance are often based on simple models whereby the isolated building is represented as a rigid mass supported on a spring and some form of damping element.



Figure 2: The single-degree-of-freedom model

Such models are very limited since they fail to describe some of the major features of a building's dynamic behaviour. Models currently being developed at Cambridge aim to capture the essential characteristics of a base-isolated building in order to gain a better understanding of isolation performance. The flexibility of the building, the behaviour of its foundation and the nature of the vibration source are all important factors.



Figure 3: An alternative model of a base-isolated building

In addition to the development of theoretical models, experimental work is being undertaken in order to develop a better measure of isolation performance and compare theory with practice.

Relevant/Recent Publications

• Talbot, JP. 'On the performance of base-isolated buildings: a generic model', PhD dissertation, University of Cambridge, 2001.
• Talbot, JP and Hunt, HEM. 'On the performance of base-isolated buildings', Building Acoustics, vol.7(3), 2000.

Principal Investigator & Researchers

• Dr. H. E. M. Hunt
• James Talbot

Funding Body

• EPSRC (1 Oct. 1998 - 30 Sept. 2001)