Throng

Continuing on Five this week is the gripping documentary series that explores huge engineering projects from all over the world. This instalment investigates the construction of the Bahrain World Trade Centre, the first skyscraper in the world to be powered by wind turbines incorporated into the building’s design.

The astounding Bahrain World Trade Centre, or BWTC, is the brainchild of South African architect Shaun Killa, who has won fame for skyscrapers throughout the Middle East. A keen sailor with a passion for sustainable design, Killa hit upon the idea for a huge sail-like structure that would draw its energy from integrated wind turbines.

Bahrain’s capital, Al-Manamah, sits on the Persian gulf. Each day, hot air rises, creating an area of low pressure that leads to strong winds. The daily cycle means that Al-Manamah has consistently high on-shore winds around 60 per cent of the time. Killa realised this was the perfect location for a skyscraper powered by wind turbines. “In November 2003, when I first came to Bahrain, there was a tremendous wind blowing,” he says. “My first impression was that I should be sailing.”

Though most turbines stand on vertical poles, Killa’s vision for his audacious construction was to incorporate three huge turbines, each 95 feet in diameter, within the building. These would spin on horizontal bridges, stacked on top of each other between two towers. The sail-like shape of the 50- storey towers would be designed to maximise the movement of the sea breeze through the turbines.

However, Killa needed to find engineers who could construct the turbines. “All the turbine manufacturers we were consulting said it couldn’t be done,” Keeler admits. Eventually two Danish engineers, Lars Tørrild Thorbek and Ole Sangill, responded to Keeler’s pleas and agreed to research whether the wind turbines would produce enough energy to justify the cost of the building.

Thorbek and Sangill set up a scale model of the building in a wind tunnel and used sensors to measure the wind speed between the two towers. The study yielded encouraging results, suggesting that the wind between the towers accelerated by 20 per cent. Thorbek and Sangill also concluded that even winds coming at the building from a 45- degree angle could still turn the blades. They estimated that the turbines could provide 15 per cent of the building’s energy needs.

Killa faced another challenge, however, when it came to building the blades for the turbines. With market forces biased towards higher blade volume and size, the Bahrain tower attracted little interest – the order was too small for many manufacturers to make a profit. However, Killa and the team made a breakthrough when they investigated a pre-existing blade design. They determined an older model would survive the conditions in the Bahrain tower, but they needed to enhance the safety features of the blades.

The engineers also discovered that the marriage of the turbines to the bridges could create a nightmare scenario – resonance. If the vibrations of the bridges and the turbines were ever the same, they could amplify each other and eventually cause the bridges to collapse. To avoid this, the team decided to make the bridges more rigid, so the vibrations would always be faster than those of the turbines.

Finally, two and a half years after construction began, the tower reached its apex. The bridges were lifted into place at the dizzying height of 133 metres. Sangill and Thorbek flew in from Denmark. With a schedule of just seven days to position the turbines and attach them to the generators, any delay could be costly. But raising aerodynamic blades between two towers designed to generate wind provided the construction team with one final challenge...