The Leaning Tower China

WHETHER YOU love it, hate it, or are just baffled by it – Beijing’s China Central Television (CCTV) headquarters makes you question what you take as certainty.

Buildings aren’t meant to look like they’re falling over.

So in the seismic region of Beijing, two leaning towers joined together by a 70m-long overhang 36 storeys from the ground makes you question not only what you take as certainty, but what China does.

Each of the 200m towers tilts at six degrees in opposite directions, which means that the 13-storey overhang that connects the two is L-shaped.

When the building is complete in 2009, it will allow the state-run broadcaster China Central Television to expand production from 13 channels to 200 worldwide.

This month, the project team finished the race to clad the building before the start of the Olympics. It had been planned to be ready for the opening ceremony, but China Central Television soon realised the deadline to complete such a demanding project was in dreamland.

This is not about spectacle

The building sits in the heart of China’s emerging central business district dwarfing its incumbent buildings, not only in size, but also in sheer arrogance.

Its aura doesn’t spell out the ‘What you see is what you get’ blandness of the surrounding skyscrapers. It is cleverer than that.

On first view, CCTV looks as though it is running at you like a Transformer in mid-morph, but every angle unwraps a new surprise.

Only as you look deeper do you realise the building is joined together by a nine-storey base; and then as you take in its whole character it visually disassembles itself into three modest size buildings – the base and the two towers.

“We put an awful lot of effort into convincing ourselves first and then the Chinese authorities, that we could actually build this structure, and build it economically,” says Arup director Chris Carroll.

Pitched across the road from the site is Arup’s Beijing office where Carroll has been present during key stages of the project.

He forms part of the London team involved on the project, which also includes Arup deputy chairman Cecil Balmond. Carroll was present for all the peer review meetings to convince the state authorities CCTV could be built. With a Master’s degree in seismic engineering, he had to assure the authorities that CCTV was safe.

Despite being involved in nearly ten projects within a 1km of its offices in Beijing, including the Soho Shang Du, a 170,000m sq mixed-use development, and the China World Trade Center development, Carroll explains CCTV has been a huge undertaking for Arup, absorbing 100 of its engineers at peak.

The unique design, crafted by the Office of Metropolitan Architecture (OMA), led by architect Rem Koolhaas, has led gossip merchants to speculate as to what idea fed the design. The most far-reaching of which is surely that the design somehow spells Koolhaas’ name.

In fact the idea is far less “out there”, conceived around the evolution of the television process.

The continuous loop of CCTV ensures that all the departments needed to make television, such as managers, producers, editors, post-production teams and lawyers are put into one building and are in contact with each other in one creative loop.

“The idea is that you get a step change in terms of creativity,” says Carroll. “You get all these forces careering past each other in this loop. If you look at other facilities of this nature, they’re very much horizontal distributions of programme, so there’ll be a production house here, a post-processing house there, and a studio somewhere else and they’re all very disparate.”

When CCTV is complete, it will also allow the 10,000 workers to see much of the building they’re working in.

Breaking the rules

The proposal for CCTV came during the competition to design a new building on the site of 9/11.

Although concerned by the events of 9/11, Carroll says China had a less than emotive stance on a similar attack happening in Beijing. “Their take on it, was that kind of incident couldn’t happen in China,” he says.

Nonetheless to satisfy the peer group, Arup did redundancy checks – removing columns and parts of the façade – to analyse what damage would occur and whether it would lead to a collapse.

The biggest hurdle in obtaining a building permit for CCTV was convincing the Chinese authorities that the tower was structurally safe in the event of an earthquake – more so, as CCTV broke the country’s prescriptive design codes.

“The way the building process works in China is that if your building is completely compliant the Chinese government effectively takes liability of your building,” says Carroll.

It took a year to convince a state employed panel consisting of university professors and eminent structural engineers that CCTV was viable.

Routing gravity

The main stability system is achieved by cloaking the perimeter of the building in a braced steel tube. As such, the building’s skeleton is a diagonal grid of steel supports zigzagging their way across the whole perimeter of the building to resist gravity and any lateral forces. London’s Swiss Re tower, or Gherkin makes use of a similar system.

“By combining the external tube of all of the structure, including the base, the cantilever and the towers, you get a stabilising effect and are spreading the loads further into the foundations,” says Carroll.

The 40m x 60m steel brace that covers the building is the same dimension as the footprint of the tower – making it a structurally efficient building. In a conventional building, if you were using your core to stabilise it, often the central region of a skyscraper, it would be a lot smaller in section, adds Carroll.

Because of the nature of the building pattern CCTV has a large degree of redundancy. “You could fail any one of those braces or you could fail significant proportions of the skin structure and the load redistributes via the bracing around the damaged piece,” says Carroll. “Any bit of yielding, the structure can inherently redistribute the loads around the point of yield.”

The building was constructed in two tower sections that were then joined to complete the continuous loop on 26 December 2007. The main towers stand on piled raft foundations. “Underneath the cantilever we also bring the foundations out further than the base of the tower as a tow to further stabilize that so we distribute the forces better in the piles.”

How we cracked IT

This year marks the 20th anniversary of Koolhaas and Arup’s working relationship. Cecil Balmond and Koolhaas’s first major design together was a competition entry for the Hague City Hall, in 1988.

Koolhaas says that only 21st century computer power permitted CCTV to be both designed and built. Carroll adds that only five years ago it may not have been possible.

Tekla Structures software, also used for London’s Gherkin, aided the connection design and erection phases of CCTV.

Managing director Andrew Bellerby said the advances in software is giving architects more freedom with what they develop.

“I guess nowadays they are trying to out do each other,” he says. “The software is certainly helping push the boundaries – how much further they can take it I don’t know.”

Computer technology was also vital in analysing and convincing the authorities that CCTV was safe. The Arup team went into a laboratory with one of the Chinese universities and tested the large columns and braces to see what yielded first and what damage would occur.

“We made vast numbers of computer simulation models to test the structure in extreme levels of earthquake,” says Carroll. “We also built a 1:20 model of the whole building and put it on a shake table to see where the damaged occurred.”

Arup’s performance-based design approach had three objectives: no structural damage when subjected to a level one earthquake (an event likely to happen in 50 years); repairable structural damage when subjected to a level two earthquake (475 years); and severe structural damage permitted but collapse prevented when subjected to a level three earthquake (2,500 years).

“The building is designed for a 100-year lifespan,” says Carroll, “and even in that extreme event of a level three earthquake the building is designed not to collapse.”

The ambition of CCTV is a reflection of China’s drive to become the elite super power. In that respect the Olympics and its associated developments are a kind of by-product of its ambition.

Pausing for thought, Carroll explains that China’s rise to dominance might have created an environment and opportunity that might be hard to find in the near future.

“A building like [CCTV] can only really be built given a set of circumstances that I think will only have been available in China at this particular time,” he says.

In the next five to ten years, a forest of 200, 250m-plus towers will be built in the business district to cement Beijing’s financial harbour.

For Carroll, CCTV has been a once in a lifetime job. “Anybody who told you designing the central television headquarters with Rem Koolhaas wasn’t the pinnacle of their career, is a braver person than me,” he says. “I’ve no idea what the next years will hold but to be involved in a building like that is probably a once in a lifetime thing.”

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