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Wednesday, January 27, 1999 Published at 18:16 GMT


Surviving earthquakes

Buildings in the background in Colombia remain standing

Amid the rubble of Armenia some buildings remained standing - earthquake proof structures designed to withstand the force of nature.

Much of the Colombian city was devastated by the earthquake, measuring six on the Richter Scale from less than 32km (20 miles) beneath the surface.

[ image: Computer simulations help engineers: Red is damage, blue is undamaged]
Computer simulations help engineers: Red is damage, blue is undamaged
Hundreds, if not thousands of homes, were destroyed but a few passed the test they had been designed for - and are still standing.

Zygmunt Lubkowski, from the international structural engineering company Ove Arup and Partners, says there are a number of factors in Colombia which could have added to the destruction brought by the country's largest earthquake this century.

He said: "If we design to modern codes of practice and ensure buildings are constructed properly we can prevent the loss of life that has been seen in Colombia.

"In Third World countries, people build their own houses. It's no wonder these buildings fall down.

"This is why there is so much damage. It's either old structures, structures designed to outdated codes or no code at all and badly built structures."

[ image: Survivors in the Armenian rubbble]
Survivors in the Armenian rubbble
Protecting a building against earthquakes does not come cheap. It can add 5% to the cost of construction.

But there are relatively simple design techniques for strengthening the resistance of normal homes such as 'tying' walls and roofs together with metal pins.

During an earthquake walls shake while the roof remains static until the movement of the walls causes the roof to fall.

When 'tied' the roof moves with the walls to minimise the damage.

Mr Lubkowski, a geo-seismic engineer, said: "For most people the bottom line is a building they will get out of alive. If you can prevent the roof caving in you have a better chance of that."

Other buildings - power stations or multi-storey office blocks - need much more sophisticated methods to stand up to an earthquake.

They include:

  • Fusing the structural system

    The force of an earthquake is channelled to a specific part of the building so although that part of the building will need repair, it will protect the rest of the building from damage.

  • Friction pendulum bearings

    The construction is built on a number of bearings which, are composed of a bearing and a concave dish. When the earthquake strikes, the protection system pushes upwards reducing the force striking the building.

Mr Lubkowski said: "Bearings can put up the cost of a building by 5%.

"But if you get a large enough earthquake during the lifetime of that building it will cost a lot more to repair or re-build it."

Earthquakes can also cause differing damage depending on a series of factors from the depth of origin - the Colombian one was close to the surface in geological terms - to intensity.

In Mexico 1985 all the quake's energy was released in such a way that only buildings above 10 to 15 storeys were damaged.

Japan and California, both rich areas sitting in earthquake zones, are leading the way in using state-of-the-art quake-proofing techniques.

But Mr Lubkowski adds: "No matter how good the design a building still needs to be constructed properly - and earthquakes are unpredictable."

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