Cloaking theory could help to protect buildings from quakes

Mathematicians at Manchester University have developed a theory that could be used to protect buildings from earthquakes.

The theory suggests that it may be possible to protect buildings from vibrations by elastodynamically cloaking certain components with pressurised rubber so that the structure is not affected by powerful waves, such as those generated by an earthquake.

Cloaking has previously been thought of as a theoretical technology that could enable objects to become invisible to certain parts of the electromagnetic spectrum.

Manchester University’s Dr William Parnell said: ‘Since a perfect cloak is practically impossible in principle for a variety of reasons, we could say that cloaking — in this instance — is a significant reduction in how much the waves are scattered from an object as compared with the uncloaked object.

‘The aim was to try to produce a cloak for a special type of wave — an anti-plane shear wave — by using “pre-stress” rather than using specially engineered metamaterials, which are the common method for cloaking.’

Pre-stressing involves intentionally introducing permanent internal stresses into a structure in order to improve a material’s performance in certain conditions.

Parnell said: ‘Cloaking works by exploiting anisotropy, or directional dependence, and inhomogeneity, or spatial dependence, of material properties, thus permitting them to be guided in a specified manner.’

The research has focused solely on the relatively simple anti-plane shear waves, but Parnell is now turning his attention to Love waves, which could be of practical importance.

Parnell said: ‘Long-term earthquake protection is a potential area of application but it would be hard to say at this time exactly what this would entail.’

No practical experiments have been done to date, but Parnell believes his theory could provide an important step in the right direction. He is considering some small-scale practical experiments to test his research.

There are a wide range of current engineering solutions to protect buildings from earthquakes. However, these are often expensive to implement, such as the tuned mass damper in the Taipei 101 skyscraper in Taiwan, which cost $4m (£2.5m).