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Extreme team sets to work on design solutions

NEWS: After the shock of the events of 11 September, engineers from Ove Arup are looking at ways of making skyscrapers stay up longer after major impact. Damian Arnold reports from Manhattan.

COULD THE World Trade Center's (WTC) twin towers have been designed to stand up for vital extra hours before its horrific collapse?

This question is being asked by a group of engineers from Ove Arup who convened for the first time in Manhattan this week to develop building design solutions against 'wilful mega destruction'.

Arup's newly formed Extreme Event Mitigation Task Force has given itself three months to analyse the consequences of the devastating terrorist attack on the WTC towers. It will then show clients and the profession a set of solutions for better protected buildings.

'We don't want knee jerk reactions so we are developing a method to take clients through a major analysis of their building, ' says Arup director Tony Fitzpatrick. 'We will show them different disaster scenarios and the design solutions the building would need to deal with them.

'We want to design structures that would stand five or six hours after a plane crashed into it, ' he says. 'The exercise is not about keeping the property but giving the firemen enough time to go in and get everybody to safety without fearing that the building will come down.'

The group will start by calculating exactly how the towers failed and plotted a sequence of events that led to the collapses.

By the end of next week it hopes to have a model showing exactly how the building performed after the impact. The team will then focus on what could have been done to have made the towers last a few vital hours longer.

Fitzpatrick said that by the end of the year Arup will be ready to talk to clients - which include Canary Wharf developer Olympia & York and developers of the tower project at London Bridge - about protecting tall buildings under construction or in design.

Clients have inundated Arup for reviews of buildings it has designed, following the terrorist attack on the WTC. Its analysis will allow the consultant to show them how they could retrofit existing tall buildings to protect against 'wilful mega destruction' forces that were not thought about before 11 September, Fitzpatrick says.

'We already build very tall buildings on earthquake faults in San Francisco and Tokyo, designed against events bigger than they have ever had before.'

And costs need not be prohibitive, he adds. 'Fire protection for example accounts for around a quarter of the total cost of the building. We could be talking about adding 50% on that, which is little more than 10% of the total cost.'

The extreme events team brings together Arup staff from all over the world, including three structural engineers, three fire specialists, a materials expert and a building services expert.

Arup will post results of the task force's work on its website as it progresses, and invite input from outside. It then hopes to feed the final results to the Standing Committee on Structural Safety (SCOSS), the Royal Academy of Engineering and the ICE.

Fitzpatrick says people now need to be, and feel, more protected if they are to be comfortable in such tall structures. But he is keen to stress that this does not take away from his admiration of the WTC towers.

'It's amazing that one of the towers stood up for one and three quarter hours after being hit by a plane with a full tank of aviation fuel. To last that long with blown out fire protection was quite something. There is not one jot of criticism towards that building in what we are doing here.'

Arup's Extreme Events Mitigation Task Force will meet every Friday morning teleconferencing between the US, London and Hong Kong. A weekly update will be posted on the website at www. arup. com

People turning against target high rises

TERRORIST ATTACKS on the World Trade Center (WTC) have brought an end to the construction of 'monumental' skyscrapers in Manhattan, the head of New York's biggest construction industry representative body said this week.

'This will affect design and construction activity in the city for many years to come. Tall buildings in general will be questioned, but monumental tall buildings will be questioned even more, ' New York Building Congress president Dick Anderson told NCE.

'People will still want to build them, but people will not want to work in them, ' he added.

The psychological fallout of the worst ever terrorist attack has seen people refusing to work in high rise buildings.

'One of our members, Raytheon Construction & Engineers, had 190 people working in the World Trade Center, and lost 13. Some of their staff do not want to stay in New York, never mind work in a tall building, ' said Anderson.

And there were also signs, he added, of people expressing concern about working in other landmark tall buildings, such as the Empire State.

The catastrophe would also affect building technology, although how this would develop depends on discussions within the engineering community.

'There are bound to be changes to the way that people design buildings. Engineers say that the risk can be minimised but what are the costs?' he asked.

'Buildings which stand out like beacons can become targets, so there is going to be much less construction activity in this area, ' he said.

Anderson also warned that the turmoil caused by the attacks was likely to overstretch the local construction industry which was already facing a major skill shortage.

With the clear-up effort likely to soak up workers, 'we have a real shortage or people across all stages of the building process', he said.

However, construction activity was returning to normal on sites where workers had left to help in the rescue effort.

Construction employment in the city has reached a 25 year high with around 120,000 working in the industry last year. Construction spending stood at $16.4bn (£11.2bn), a rise of 38% over 1999.

Diarmaid Fleming in Manhattan

Extreme events issues

Evacuation 'We need to consider whether certain events in a building should trigger simultaneous evacuation, ' says a briefing paper by Extreme Event Mitigation Task Force.

'Conventional design has always gone for phased evacuation but when you have an extreme event like this you are looking at total evacuation, ' adds Fitzpatrick. 'We need to ask: how long will the building last if this happens? How many people are in the building?

How are we going to get them out?'

Sprinkler systems

The sprinkler system in the World Trade Center was destroyed on impact. 'Water jacket reliability needs to be looked at now, ' said Fitzpatrick. 'We may have to go for passive means of fire protection.

There's quite a debate to be had.'

Structure

'We need to assess how long buildings need to stay up to get out the number of people that it holds, ' said Fitzpatrick.

This process could lead to designing a level of structure every 10 floors to carry the weight of nine collapsing floors above.

Compartmentalising buildings using a secondary structure as a fall back if the main structure fails should also be considered. 'If the towers had a reinforced concrete core able to continue providing stability after the loss of the floors and perimeter frame, then a shaft providing a safe refuge might have remained, ' says the paper. 'Should we consider dual stability structures, where one stands after the other one has failed?'

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