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Design failures led to tragedy

Cowboy contractors and corrupt building inspectors have taken the brunt of the blame for the devastation caused by last months' Turkish earthquake. But when Richard Thompson travelled to the disaster zone he discovered that poor design was just as much to

It was around three in the morning in the northern Turkish town of Golcuk and Bulent could not sleep. He went to the kitchen for a drink. Suddenly dogs started barking and from his first floor window he could see them running along the street. About 15 to 20 seconds later the building started to shake, then: BANG! Bulent was thrown to the floor by a massive judder from directly underneath.

The building shook up and down for several seconds before it started to twist. All the power had failed and in the pitch black Bulent could hear objects crashing against walls. The shaking continued to increase as the movement changed to a violent side to side rocking. Then in an instant the block collapsed.

An hour later Bulent was pulled from the rubble. His wife and children were among 22 killed when his block collapsed. The five storey reinforced concrete building is now no more than a pile of broken slabs less than one storey high. Bulent has been living in his car ever since. 'My life is over,' he says.

An estimated 30,000 people died as a result of the 45-second earthquake that hit north west Turkey at 3:02am on 17 August. Most were killed when concrete apartment blocks similar to Bulent's collapsed on their sleeping occupants.

But not every building collapsed. And of those that failed, not all went the same way. Stories such as Bulent's are crucial because they contain vital clues about what happened.

Earlier this week the Institution of Structural Engineers' Earthquake Engineering Field Investigation Team (EEFIT) returned to Britain after spending 10 days in the disaster area. The 12-strong team included structural and geotechnical engineers, as well as seismologists and geophysicists. The team will present its preliminary findings in the next few weeks with a formal report to follow.

The earthquake happened over an area 125km by 50km, just east of Istanbul, when the part of Turkey south of the North Anatolian Fault shifted 2m- 3m west. Its epicentre was near the town of Golcuk on the southern shore of the Sea of Marmara.

Not surprisingly, Golcuk is one of the worst hit towns. Whole districts have been destroyed, with nearly all the devastation resulting from the disintegration of poorly constructed apartment blocks known as beshkats.

Thousands of these five to six storey concrete blocks have been built in the region in the last 10 years to house a massive population boom. Many were thrown up quickly by small local contractors without proper supervision from local authority building inspectors.

Since the earthquake, the Turkish press has been quick to blame cowboy contractors and corrupt building inspectors. But members of EEFIT have found that poor design has been as much to blame as either of these factors.

Bath University earthquake engineering expert Dr Dina D'Ayala, who led the EEFIT team, explained: 'Bad construction is clearly a factor but equally significant has been ground conditions. Many of the buildings have toppled or sunk into soft ground. Others have twisted themselves apart because their design did not provide adequate torsion resistance. All of these are design failures.'

D'Ayala added that most of the beshkats had only been designed for a static vertical load, with insufficient consideration for the dynamic case.

Many buildings collapsed because of 'soft storey' failure due to walls being removed from the ground floor to accommodate shop fronts. This reduces the stiffness of the lower floors and weakens the structures' resistance to torsion, which leads to shear failure at the beam column connection or at the base of the column (see box).

Adapazari, about 40km east of Golcuk, has also been decimated by the earthquake. Here, much of the destruction is a result of ground conditions.

Adapazzari is built on a soft alluvial plane. As the earthquake shook, the soft ground started to shear causing an increase in pour water pressure and ultimately liquefaction.

'The ground turns to porridge,' explained WS Atkins engineer Tim Courtney. 'Buildings simply sink into it'

Whole floors have disappeared into the ground at Adapazari. At one house a car parked in the entrance to a garage was sliced in two by the guillotine of the building.

Turkey's highways survived well, though the large lateral movements damaged many bridge piers and movement joints. The only major bridge collapse was on the main Izmit/ Adapazari highway, when three spans of a post tensioned concrete box girder overbridge fell off their piers in a 2m sideways movement. Subsidence in the abutments of many bridges caused a step between the bridge deck and its approach road.

The most serious damage to the highways occurred over a 10km stretch between Izmit and Adapazari, where the highway crosses the fault line several times. Turkish highways department KGM is carrying out urgent repairs to the road surface where shear forces across the fault have created 100m bands of 0.5m deep undulations.

'Because the two plates are pulling in opposite directions tensile forces between the two sides open up tension cracks,' explained Ove Arup geotechnical engineer Matthew Free. 'Compression forces between them push up the road surface into mounds, creating undulations.'

Water front structures along much of the south coast of the Sea of Marmara performed badly. Large strips of reclaimed land have slumped towards the sea, causing inadequate sea walls to topple.

'What we are seeing generally is that sheet piled structures didn't perform well,' says Babtie engineer Alan Stewart.

Gibb chief geotechnical engineer Dr Robert May added: 'What we have seen perform well are heavy reinforced concrete decks with heavy reinforced piles and properly armoured shoreline protection. I haven't seen any good examples of caisson structure.'

There was virtually no damage to engineered structures. An example of the success of seismically designed buildings can be found at the Toyota car factory at Adapazzari. Massive rupture cracks slice through one corner of the plant and approach roads have been destroyed. However, the Ove Arup designed structure has survived intact.

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