This sensational image has been released of Santiago Calatrava's proposed addition to Chicago's skyline.
Backed by US-based developer the Fordham Company, the tower would become the tallest building in the US at a cool 600 metres.
The skyscraper, known as the Fordham Spire, will rise 115 storeys and will dwarf its neighbour, the 440m-tall Sears Tower, which is currently the tallest building in the country.
The scheme boasts 90,000m 2
of space on a prime 0.9ha site and includes plans for a five-star hotel with 250 luxury condominium residences.
In an era of prolonged terrorist threat, the developer is keen to promote the building's heavily reinforced concrete core, including two emergency exit systems. The twisting form, which causes the building to resemble a drill bit, will help reduce the effects of wind turbulence.
Calatrava's design is a tall, slender form with a rippled glass facade. This is achieved by structural innovation - each floor of the tower is built out from the central core like a separate 'box', with gently curving concrete sides. As these 'boxes' are stacked up, each is rotated by a little more than two degrees from the one below. The result is that the floors turn 270 degrees around the core as they rise.
The Spanish architect said: 'It is a real challenge to design a building for this city, following in the paths of so many great architects. But when I saw this site, it was obvious that this is a place where a great building can be made - virtually in the middle of the skyline when you see it from the lake.
'Like many of my designs, the tower was inspired by a sculpture I had made. It is a real challenge to design a building for Chicago, following in the paths of great architects from Louis Sullivan and Frank Lloyd Wright to Ludwig Mies van der Rohe.'by Rob Sharp