Technology pushes supertall buildings to greater heights
With the number of supertall buildings - those above 600 meters - set to quadruple within six years, the race for the sky is on.
Twisting up 121 storeys, the new Shanghai Tower puts China on the map as home to the world’s second tallest building.
With the number of supertall buildings – those above 600 meters – set to quadruple within six years, the race for the sky is on. When it opens in 2019, Saudi Arabia’s 1,000 meter tall Jeddah Tower to set to push the boundaries for the world’s tallest building – but experts put no technological limits on how far these skyscrapers could climb into the earth’s 10 kilometer atmosphere in future.
There are real life restraints, however – including vertigo, elevator technology and building restrictions. “Getting large numbers of people out of a building in an emergency is probably the biggest challenge we face,” says Steve Watts, board member of the Council on Tall Buildings & Urban Habitat (CTBUH) and chair of its UK chapter.
But he sees no other insurmountable technical issues: “If a building is wide enough there’s no limit.” In reality, a shortage of land is a major restriction of older cities. The Burj Khalifa’s 120 acre plot would take up about a fifth of the whole of the land included traditionally in the Square Mile of the City of London.
Megatowers are most common in the Middle East and Asia – overtaking the onetime leader, the U.S. One U.S. building – New York’s One World Trade Center – remains in the global top ten. But by 2021, that 541-metre structure will have dropped from 4th to 23rd place if all the proposed developments in China, Malaysia, Dubai and their neighbors come through.
Central London and other European and U.S. locations have tougher building regulations than newer cities in the Middle East and China. It is not just the ‘right to light’ laws that severely restrict developments in the UK capital but numerous other rules such as the Civil Aviation Authority’s curbs on penetrating air space above 300 meters.
European cities predicted to grow higher
London’s 309-meter Shard building is the only European construction in the CTBUH’s current top 100. But Nick Clare, JLL’s UK Head of Project Management, expects to see the skyline changing in Europe, and particularly in the English capital. “Density will mean there will be more tall buildings,” he says. “London will have to get denser – otherwise you’ll be building on the green belt. The city has areas where density can be enhanced and, moreover, where brownfield sites can be used.”
Watts, a partner in costs consultancy Alinea, agrees and believes that the design emphasis will shift from producing striking high rise exteriors to delivering more rational forms and comfortable, flexible and differentiated interiors. The unusual profiles of the Gherkin and other tall buildings were partly a way of using aesthetics and architectural statements to get public and political support. Now, says Watts, “There is more of a focus on how a building will be used. The needs of occupiers are finally rearing their head at concept stage”
This more practical approach is beginning to extend to issues of building maintenance. Traditionally a Cinderella aspect of tall building design, window cleaning and other maintenances matters are being taken more seriously now. The more recent trend of having ventilated facades permits easier access to higher levels. And, adds Watts: “Maintenance is higher up the agenda at the design stage than it used to be.”
Engineers and other specialists are gradually eroding many technical obstacles. For instance, the Jeddah Tower will be a marvel of elevator technology, using carbon fiber rather than steel cables to lighten the load within the lift shaft in order to travel higher and faster than previously possible indoors. Lift technology is a “hugely important” factor, says Clare – citing the Empire State Building as an example. “You had to change cars because the cables couldn’t work around the stretch,” he explains, describing how each elevator could cover just a third of the height of the 381m building back when it was the world’s tallest building.
Giant dampers – pendulums placed within the upper floors – are another area of progress. Counterweights to building sway, these eliminate the nausea that many people experience when a skyscraper moves freely in response to wind or vibration. The 5.5 meter wide damper which sits on the 87th floor of the 508m Taipei 101, the world’s fifth tallest building, was the heaviest damper, at 728 tonnes, until late 2015. Last August the damper moved a full meter, a record in its 11-year history, under the force of Typhoon Soudelor’s 100 mph winds.
Dubai’s 828m Burj Khalifa, today’s tallest building, deals with wind resistance by its tapering shape, rather than by dampers. In contrast, the 632 meter Shanghai Tower, contains a 1,000 tonne damper in harness with an innovative magnets system.
Formula 1 technology drives wind resistance design
Shape also has a huge role to play in skyscraper design. The Shanghai Tower cuts wind pressure by nearly a quarter by twisting round 120 degrees as it spirals up – “the optimal rotation for minimizing wind loads”, according to its architect Gensler. The Jeddah Tower has also been designed in “an aerodynamic shape that helps reduce structural loading due to wind vortex shedding”, according to its architect Smith Gill.
Wind analysis is a central research subject, says Watts. Technology being transferred over from Formula 1 motor racing is “enabling us to understand how different buildings interact with each other from a wind perspective” and to do precision models of how different construction shapes interplay with wind.
Whether really tall buildings are worth the cost is debatable – since dampers, elevator shafts and other parts of the structure consume a disproportionate part of the space at higher levels. But Watts believes that breakthroughs on materials used are overdue.
Graphene, the ultra-thin, ultra-strong form of carbon, is a possibility – and one that could transform cost calculations. “It might be graphene or it might be something else,” he says. “I’m not sure if we’ll get there in the next five years or if it will be twenty-five years, but an advance in technology will at some point drive a step change in the way towers are designed and delivered.”