Page last updated at 07:54 GMT, Saturday, 3 January 2009

Superscraper nears date with destiny

Dubai skyline, with Burj at center
The Burj has been steadily extending its reach above Dubai's skyline since 2006

Lawrence Pollard
BBC News

For over 100 years, where there's been an economic boom and confidence, there have been skyscrapers.

"They're acts of optimism, they're dreams rendered in steel and concrete," says William Baker, the chief structural engineer behind what will soon be unveiled as the tallest building in the world.

Mr Baker's company, Skidmore Owings Merrill, specialises in skyscrapers. He himself has been making sure a superscraper stays up - Burj Dubai.

In the wind tunnel the forces kept going down and the buildings went taller and taller. At a certain height the forces got smaller not bigger
William Baker
Skidmore Owings Merrill
The structure is almost finished and is expected it will be unveiled in a few weeks' time. But no one is saying how tall it will be.

"We're not allowed to say. The client hasn't announced what it is and I don't think they will," says Mr Baker. "It'll turn into urban folklore, you'll have people measuring the shadows on GoogleEarth and trying to figure it out."

All good publicity, and that is after all a large part of what skyscrapers are about - showing off.

The current record holder is Taipei 101, at just over 500 metres high. To qualify as tallest structure, a building must be kitted out and working as hotel, offices, flats - whatever is there.

The Burj (which means Tower in Arabic) will not be fully functioning until later in the year, but the basic structure will be ready soon.

Wind proof

And what a structure. It's based round an idea known as a buttressed central core, with a service shaft made not out of steel but super-concrete, Mr Baker tells me.

If you look down at the plan from above, it's like a propeller in shape, with three arms or wings shooting out from the central core.

Dubai skyline, with Burj at center
Construction began 2004; became world's tallest structure in 2007
Floor count: 160
Estimated current height: 700 metres
This simple geometry means that when the wind gets up, one of the wings will always buttress the tower against it.

"The client's goal was for the world's tallest building, simple. So we went into the wind tunnel with an idea which was only a little taller than Taipei 101.

"Our first results weren't too good, so we changed the building's shape and orientation to reduce the forces - wind is the dominant thing in a tall building and what we did is confuse the wind," Mr Baker says.

You may remember during the Olympics the attention paid to the swimming costumes which used material to mimic the effect of sharkskin.

A slightly rough material creates little pockets of turbulence on its surface which lubricate movement more than a smooth surface.

The same idea helps the Burj slide through the winds when they blow.

"The mullions, the verticals that hold the glass up, stick out and make the surface rough, which is a good thing, like swimmers' costumes.

"In the wind tunnel the forces kept going down and so the buildings went taller and taller. In fact at a certain height the forces got smaller not bigger," Mr Baker says.

High ambitions

Because some breakthroughs were made as the building was going up it was too late to incorporate them all in the Burj.

"We could definitely go taller," says Mr Baker, predicting the possibility of towers 1,000 metres high. If anyone has the money to build them, of course. But what effect has the financial crisis had?

"Every market goes through cycles, the next generation of tall buildings are in a hiatus right now, but there's places with pent up demand. I see China continuing with that, and India will come into it soon."

In the meantime the Burj Dubai will yet again draw attention to the Gulf states and their spending.

Estimates are that the 160 or so floors will have cost several billion dollars to build - it will contain a hotel designed by Giorgio Armani and some office space, but will be mainly apartments, most of which are already sold.

So, for the last time, how high will it be?

"If you put the empire state building on top of the Sears Tower then it's reasonable to say you'll be in the neighbourhood," Mr Baker says.

That's about 400 metres plus 400... a monument to a moment of great confidence - or some might say overconfidence!

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