When it comes to building high-profile high-rise towers in London, architects are constantly raising the bar. The Swiss Re tower brought new ideas into play, but Ken Shuttleworth's Vortex may soon be the talk of the town, writes Chris Mugan.
The Vortex is the name given to a huge and highly innovative project designed by Ken Shuttleworth's MAKE Places Ltd. Shuttleworth, who parted from Foster & Partners after providing the creative drive for major projects such as the Swiss Re building, Wembley Stadium and Hong Kong Airport, has chosen a £200m landmark project as his first endeavour.
Having brought many staff with him from Foster & Partners, he has a proven team capable of radical new thinking, and they have done him proud, delivering an elegant design for an innovative but relatively simple structure that could come to dominate the London skyline.
The name Vortex is derived from the building's shape, which is hyperboloid – a slightly tapering column twisted to create a narrow waist at the centre of the tower. In shape, it is the polar opposite of the Swiss Re Tower, affectionately known as 'the Gherkin'. This underlines that MAKE Places is not simply rehashing the ideas that have been successful in the past. Also, at 984ft, it would be twice the height of the Swiss Re tower.
GHERKIN WITH A TWIST
'Swiss Re raised the stakes for high-rise design,' says Sean Affleck, a partner at MAKE Places. 'It is an incredible building, and has helped a lot in pushing the boundaries. The top and bottom are the most valuable spaces in a high-rise tower, and this was a key driver. We wanted to tune the form of the building to its function. We had the concept of the shape right from the start.'
Like many buildings, Swiss Re has a central core that takes the force and holds an external skin. Over time, these central cores, which typically hold the lifting mechanisms, have been getting smaller.
The Vortex is based on a different concept, with rotation enabling the use of leaning columns as straight structural elements.
'Swiss Re is great, but its top is tiny,' says Affleck. 'We wanted a bigger top, and we created that with a structural rigour that delivered a simple geometry and an efficient structure.'
SUPPORTED BY SIMPLICITY
The radical departure from the shapes typically seen in high-rise structures has given rise to many potential benefits. One of these is structural integrity. Modelling shows that the Vortex would be able to remain standing even if an element were to catastrophically fail or the building was damaged from the outside.
'If a frame is built very efficiently, as in Swiss Re, and all the structural elements are straight, then you can have a curved skin,' says David Glover, partner at Arup, who as a structural engineer had a strong influence on the design. 'We wanted a very rigid external frame that was also highly redundant. Our structure is very forgiving and looks after itself if an element fails. A diagonal load-carrying structure gives good redundancy.'
The curved structure of the Vortex has a very simple mathematical algorithm at its heart. This offers further advantages in the construction phase. 'We can place an element in space using mathematics, not just drawings,' says Affleck. 'With drawings, sometimes errors can creep in as data is transferred between different programs. In a tall building, errors at the base can be a big problem at the top. Using the mathematics of a simple shape, we define every point.'
THE UPWARD SPIRAL
Though the Vortex project has not yet found a site, and is not gearing up for construction, there is already proof of how this approach plays out in the construction phase. 'It has been proven in practice,' says Glover. 'The degree of checking that you can do is far greater.'
The shape has also proven advantageous in wind tunnel testing.
Studies have shown that Vortex performs well compared with more traditional high-rise towers, which tend to create a downdraft and gusts of wind at street level.
With the Vortex, this downdraft is virtually eliminated, as the wind is taken away from the street by the inclined surface at the building's base.
The ability to use flat plane glazing is another efficiency derived from the use of straight structural elements in a leaning configuration. This allows different variations of glazing to be used for different purposes, such as commercial and residential. Planes are easier to manage, and cheaper to install and source, than the curved glass panels that characterise Swiss Re.
The tapering of the lower floors to the tower's waist is further expected to soften the building's profile on the skyline. With no sharp edges, and shadows forming around its curved sides, a very tall structure will perhaps seem less imposing than some of the existing buildings on the skyline.
SCALING THE HEIGHTS
'Why has this come about now?' asks Glover. 'Really because the lift technology has only just arrived. There has a been a big rise in lifting capability in the last five years.'
Indeed, the use of innovative lifting technology has been a key element in the success, and the form, of the design. 'As in any high-rise building, lifts are important in terms of space,' says Julian Olley, the partner at Arup responsible for the lifts in Vortex.
'Lift cores eat up space. We looked at the conventional arrangement – what I call 1960s US design – and compared that to the use of a sky lobby half way up. The Vortex has a very narrow waist, so by putting the sky lobby there it minimises the use of space. It fits the building very well.'
Conventional lift design, seen in buildings such as the Canary Wharf tower, generally uses banks of lifts from the base for each set of 20 floors. The Vortex, in contrast, would be theoretically divided into thirds, with the sky lobby right at the centre. The lower third would be served by lifts from the base, with an express lift to the sky lobby.
From here, passengers could travel either up or down in a set of lifts serving the middle third of the building, with a further set servicing the upper third and the roof. This design is new, but not a first, with three other buildings around the world employing a similar system. However, the design is not the only innovative part of the lift plan.
'Tyssen has developed twin lifts, which have two independent cars in a single shaft,' says Olley. 'Passengers have a destination select control, not an up or down arrow. They key in the floor they need and the system tells them which lift to get in. There are no buttons in the lifts at all. You don't stop at each floor. Passengers are grouped according to the floors they are going to. This ensures that there are no collisions and that lifts in the same shaft are always at least two floors apart.'
The aim is to provide the same service a passenger would get in a conventional lift, but using less space inside the building. This maximises the potential floor plate at each level, which is helped by locating the sky lobby in the narrowest part of the tower.
Furthermore, this technology is not much more expensive than a conventional set-up, as the extra expense is only for the software to manage the lifts in the shaft. 'This has never been done before in this configuration or on this scale,' notes Olley. 'You must be sure the lifting works.'
A RADICAL APPROACH
As well as new lifting technology, the project has also benefited from cutting-edge design technology. Parametric modelling has given designers the ability to adjust the plan and provide a range of different solutions to cater for different blends of residential, commercial and public space.
'We can tune the building to its final use,' says Affleck. 'Computer modelling allows us to change parameters and instantly see how that would affect all the other elements of the building. It is an interactive process of design, and the project is still evolving. The end use of the building and the client brief also determine the height of the building.'
At 300m, the Vortex would dwarf the buildings around it. Its radical shape has allowed designers to go way beyond what is perceived as a difficult threshold – around 200m – where different problems start to arise.
'Lift cores have been getting smaller,' says Glover, 'and they tend to hold the building up. This makes 200m tricky to build beyond, as efficiencies in the structure often tend not to work. We don't need a core for the sake of a core, as it does not deliver a good net-to-gross ratio.'
The Vortex has also been conceived with the latest in environmental design firmly in mind. Underground cooling systems and wind turbines – more effective at higher levels – are important features. Mixed use, including the provision of landmark public spaces, is also vital for both client and designers.
Shuttleworth's team have succeeded in bringing these concerns together with commercial and structural goals in a simple and elegant solution. In so doing, they may well have begun a new chapter in high-rise tower design. Already it has inspired more external frame structures in regions like the Middle East. Once the building has found a site, the age of the Vortex could soon be upon us.