Civil Engineering: A Very Short Introduction (Very Short Introductions) by David Muir Wood

Author:David Muir Wood [Wood, David Muir]
Language: eng
Format: mobi
Publisher: Oxford University Press
Published: 2012-09-26T16:00:00+00:00

20. The skyscraper known as Taipei 101 contains a tuned mass damper in the form of a gold-painted sphere of steel plates hung from steel cables and connected to the building through shock absorbers. Its natural frequency matches that of the building itself and helps to improve structural response under wind or earthquake loading

Earthquakes in developing countries tend to attract particular coverage. The extent of the damage caused is high because the enforcement of design codes (if they exist) is poor. The earthquake in Haiti in January 2010 was a magnitude 7 quake with horizontal ground accelerations up to about 45 per cent of earth’s gravity. It demolished schools, houses, offices, hospitals, government buildings, parliament, bridges, power stations, and water supply structures. It inevitably had a devastating effect on the life of all people in the country. Estimates of the death toll vary hugely – the number killed was probably between 50,000 and 100,000. The Loma Prieta earthquake in San Francisco in October 1989 was of slightly higher magnitude 7.1; 37 people were killed and there was damage to buildings and infrastructure but at a greatly reduced scale by comparison with Haiti. The geological fault ruptures for the two quakes were broadly similar but there were strongly contrasting effects. California has long had very detailed requirements for the design of all sorts of structures to survive earthquake loading, which are regularly updated after every earthquake occurrence, and these requirements are strictly enforced. The majority of the damage in Haiti was the result of poor construction and the total lack of any building code requirements.

Almost every major earthquake in any part of the world produces some effects that had not been directly anticipated in the development of the building codes for that or other areas. For example, the magnitude 6.8 Kobe earthquake of January 1995 combined the usual horizontal shaking (peak ground accelerations as high as about 90 per cent of earth’s gravity) with unusually high levels of vertical shaking (peak vertical accelerations up to about 46 per cent of earth’s gravity). The peaks of horizontal and vertical acceleration do not necessarily coincide. But if they do, a bridge which feels only about half its usual weight (because the ground is dropping away) is givensynchronous lateral excitationi10 a sideways kick. The most striking image from the Kobe earthquake is of the elevated Hanshin highway on its elegant piers which had all toppled sideways. This led to changes in the design codes in Japan and elsewhere to require allowance for such devastating combinations of ground motion.

The earthquake in Haiti is just one of many earthquakes in developing countries where the enforcement of codes is not considered important and the exigencies of daily life are challenge enough without having to worry about building to resist more or less infrequent earthquakes. There is a challenge to developed countries to design building styles which, while only subtly different from traditional styles, nevertheless improve the chances of earthquake survival. Heavy mud or tile roofs on flimsy

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