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Standing up to disaster

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Earthquakes present an avoidable threat, provided well-established construction principles are followed

At 8.46am local time on 26 January this year, the Gujarat region of India was devastated by an earthquake.

The energy released was 1,000 times more powerful than the atomic bomb dropped on Hiroshima.

Regardless of the advances in seismic engineering, buildings simply cannot withstand such magnitude of force. But in the comparable 1994 Northridge earthquake in Los Angeles, fewer than 60 people died, whereas more than 30,000 lives were lost in Gujarat. The 500-fold difference comes down to the differential application of scientific principles.

Andy Thompson of Arup Advanced Technology and a member of the UK Earthquake Engineering Field Investigation Team (EEFIT), working under the auspices of the Institute of Structural Engineering, refutes the idea that earthquakes are natural phenomena beyond our control.He points out that India has good building codes (the current version of the Indian Seismic Design Code, IS1893: 1986, is similar to the American UBC) and has some of the finest structural engineers in the world.

'We've known since the 1970s how to design for earthquakes, ' he says. 'The 1971 San Fernando earthquake in California was a real milestone in earthquake engineering - many things were learnt.' Yet 30 years later, an earthquake devastated Gujarat.

Why?

It is important to realise that Gujarat was not razed to the ground.

Buildings remained standing - even in the epicentral region at Bhuj. The buildings that survived were government buildings that had adhered to the building code, old buildings built in the Raj period with walls up to a metre thick, and - belying the fact that money buys safety - shanty buildings which had the flexibility and lightness simply to float on top of the ground motion.

Ahmedabad, the capital of Gujarat, was built on thick deposits of alluvium. Says Thompson: 'Any time you get ground shake with soft soil, the taller buildings resonate with the movement and tend to collapse, ' unless they are designed and constructed for earthquake forces with no soft storeys (those are relatively stiff structures, with flexible lower storeys - like a rigid tower block resting on piloti). In earthquakevulnerable areas, these design features cost lives.

'What happens in any seismic event is displacement-demand on a structure - this seismic demand should be distributed evenly over the length of the structure, ' he says. 'If, however, it is concentrated at one level - if it is quite stiff at the top and flexible at the bottom - you're going to get all the rotation at the junction.

The consequence of soft storeys in Gujarat was that buildings just collapsed at the knees.'

In Gujarat, even if buildings had not been constructed or designed strictly within the code, some remained standing because they were built with care from blockwork. The villages that 'were shaken to bits'were made from random rubble with mud or cement mortar. When the tremor hit, they disintegrated and, in many places, the streets were just too narrow for people to escape.

Good detailing has life-saving importance in designing buildings to withstand earthquakes. Structural design is not about man defying the natural world, but about assimilation: understanding, harnessing and channelling destructive forces.

'When you are designing for earthquakes you have to assume some degree of damage - the key is to put this damage in the right place, ' says Thompson. 'Damage zones can help the designer by limiting the amount of force that the structure attracts.' He likens it to bending metal: after a large initial force is applied to start the bending, the metal gets to a point where it takes a constant force to continue to bend it.

At this point, the metal attracts no additional force. 'If you get a building to that level, it doesn't attract any more force from the earthquake. The key is to ensure that damage occurs in very specific spots.'

So how easy has it been for the EEFIT team to translate their experience of building in relatively rich California to an area such as Gujarat?

Thompson is fully aware that specialised knowledge alone is not enough to change the landscape of earthquake-hit zones.

'Avoiding simple things such as soft storeys, making the building symmetrical and providing good detailing would be a start.Many lives could be saved this way. This is what we are in the process of doing - writing simple documentation to make buildings safer.'

As part of a growing international community of engineers trying to work with local, national and international governments, Thompson is upbeat about the possibility for making a difference.

'Earthquakes are not natural disasters', he says. 'They are human disasters. We have known how to design for them for a long, long time.

We just need to ensure that knowledge translates into meaningful action.'

Shirley Dent is assistant editor of New Humanist magazine. Contact 020 7430 1371

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