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Cost of tall buildings to go through the roof

Structural design improvements after WTC attack will increase construction costs

ONE OF Britain's top structural engineers has warned that construction costs of tall buildings will escalate as a result of the September 11 terrorist attacks in New York.

Dr John Roberts, chairman of the Institution of Structural Engineers international working group on safety in tall buildings, said the cost of building high rise structures would rise 'a couple of per cent' to cover the design improvements needed following the World Trade Centre collapse.

Structural costs alone could rise as much as 10 per cent, he warned.

The Babtie engineer said cost hikes will pay for more robust structures with heavier connections.

n Structural frames need redundancy and/or robustness so alternative paths are available for transmitting loads when damage occurs.

n Fireproofing needs to adhere under impact and fire conditions that deform steel members, so the coatings provide intended protection.

n Connection performance under impact loads and fire loads needs to be analytically understood and quantified.

His comments followed the publication of the US government's official report into the performance of buildings at the WTC site.

The report by the American Society of Civil Engineers and the Federal Emergency Agency blamed the spread of fires for the collapse and called for research into how structures behave in a blaze.

It also called for closer working between the different disciplines involved in building design.

Dr Roberts said the report echoed many of the comments that will be in his group's report due in early July.

He said: 'There are two key issues. First we need to re-examine the functionality of fire protection methods to ensure they are robust. Until now we only checked how they performed in a fire, not whether they were robust enough for other events.

'Then we have structural robustness, especially the design of the connections. We need more structures whose joints can carry more bending load moments.

'That would improve everything. But full moment connections and ductile full moment connections are expensive. For example the cost of a steelwork package might increase by 10 per cent.

'Structural costs on major office buildings are typically 15 to 20 per cent of the overall cost depending on the type of building. But in a big building they can be as high as 30 per cent. This could increase the overall building cost by a couple of per cent.'

richard. thompson@construct. emap. com