Engineers working on the Kingdom Tower, a 3, 280-foot-high construction intended for Jeddah, in Saudi Arabia, are beginning tests on the materials they’ll need to use to construct it. 3, 2800 feet is a little over half a mile, and as a result, advanced materials and techniques will be needed both for the tower itself and for the process of constructing it.
For the final construction, engineers will face challenges like figuring out how to match elevator technology to the new elevation – how to transport people vertically for distances of half a mile or more in an acceptable time without making it feel like the world’s most incongruously upmarket fairground – and how to circulate air, water and other essentials around the building. But that will have to wait until they’ve figured out how to build it at all.
Before the tower even gets off the drawing board, engineers have two major problems to overcome, depth and weight. The Kingdom tower will require foundations around 200 feet deep, which means they’ll penetrate the (salt) water table. Since salt water is notoriously corrosive to steel and concrete, which are certain to be the tower’s two main ingredients, this will present a new set of engineering challenges. After this is solved, at least in theory, weight must be addressed.
The tower will likely contain over 80, 000 tons of steel. That will have to be mixed with new blends of high-strength concrete to cope with the increased stresses of the kilometre-high tower. When the tower simply stands erect, the forces acting on it will mostly be compression – the weight of the floors above will press down on those below, and the walls and skeleton of the building will need to be strong enough to resist. But when the wind blows, the whole building will act like a giant beam, with a mixture of tension, compression and shear forces distributing themselves along its height. That will require even more strength from the building’s structural components.
Having figured out how it’s to be done, though, the engineers will have to figure out how to do it. When Vadim Makhorov and Vitaliy Raskalov climbed the still-unfinished Shanghai Tower, they passed through clouds on the way up. The Kingdom will be significantly taller – a third again higher, in fact – and while, unlike the plucky Russian duo, workers on the project will have safety equipment, they’ll also have a near-impossible job to do when they get to the top.
Concrete in buildings like this is poured, pumped under pressure from a base station through a tube that’s normally no thicker than six inches long a swinging arm to allow it to be laid over the steel rods that hold the building together. That involves some pretty impressive forces on the second floor. Half a mile up, it’s a whole new game.
Something similar has been done before, though. When the Burjj Khalifa went up, an engineering team led by Samsung was able to pour almost six million cubic feet of concrete through a single tube, thanks to innovative pump design from German firm Putzmeister. The Burjj, though, is still not quite Kingdom Tower sized.
It’s always possible that the Kingdom Tower itself might never get off the drawing board. But the methods used to build it will be used, even if that’s for other projects. As Dr. Sang Dae Kim, director of the Council on Tall Buildings, told Construction Weekly, ‘in terms of practicalities, we don’t need to build at two kilometres – but someone with a lot of money might still want to do it.’ The technology will be developed with one eye to the Kingdom Tower, then – and one to the future.