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Construction industry

When the earth moves

   

Shock-resistant constructions. Buildings which return to their original shape after an earthquake. 'Shock-absorbers' which damp the energy impacting at sensitive points in buildings. These and other anti-earthquake technologies are at the heart of many research projects.

     
   
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Europe is far from safe from seismic risks, and not only in the traditionally vulnerable areas (Italy, Greece, Balkans, Turkey), but also in countries with a 'dormant seismicity', such as Portugal. As to the rest of the world, the list of regions at risk would be too long to enumerate. Hence the importance of the work currently being undertaken by the Seismic and Vibration Isolation research group in developing innovative protection systems based on dissipation phenomena.

Flexibility
There are three distinct categories of quake-proofing methods. The first covers techniques designed to make constructions more flexible. 'The main aim is to protect people by raising the collapse threshold,' explains Claude Dumoulin, an engineer with Bouygues, one of the project partners. 'But a building which is deformed by an earthquake does not return to its original shape. These methods, which are among the oldest and least expensive, are not ideal.' In Europe's high-risk areas, constructors are legally bound to respect certain technical standards for this category of anti-seismic design.

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The ELSA laboratory at the Joint Research Centre in Ispra has a unique installation for simulating structural resistance to earthquakes. It uses hydraulic rams to subject prototype buildings to forces of the order of 100 tonnes. These tests are of value in validating the resistance standards adopted by the European building industry (Eurocodes).

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Elasticity
The second approach is based on elasticity, designing buildings which are able to return to their original shape after deformation. Some nuclear plants, for example, are built on rubber mattresses which filter the shocks coming from the ground. 'Attempts are currently under way to perfect this technique which is used for particularly sensitive buildings, such as oil refineries, chemical plants, hospitals, civil security and police buildings, and bridges,' explains Mr Dumoulin. 'A number of key buildings in Italy are already equipped with "shock absorbers" of this kind.' But the mattress technique is not without its drawbacks. In the event of a seismic shock, the 'floating' building can move a great deal, leading to the violent rupture of the solid structures to which it is linked, such as pipes.

Shock absorbers

Researchers are also studying the concept of shock-absorbing or damping mechanisms which are able to absorb and disseminate the energy impacting at a building's sensitive points. The devices being studied are either of the metal-based, elasto-plastic variety or rubber- or oil-based viscous shock absorbers. Used in combination with the mattress technique, these help reduce the building's movement.

These developments in seismic isolation are mainly designed to protect particularly strategic constructions. 'These technologies could be extended to other large buildings and to apartment blocks, as in Japan or California,' points out Georgios Katalagarianakis. 'We must look at ways of reducing their cost to achieve a more favourable risk-investment ratio.' 'The regulations must also take full account of these new devices in order to make it easier for the construction industry to use them,' adds Mr Dumoulin.

     
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