Sky High

Once a city known for just two iconic skyscrapers, Riyadh’s skyline will soon be a sea of them.

AECOM, Gensler, Goettsch, SOM and Foster and Partners are all among the firms that have tall towers under construction at the King Abdullah Financial District (KAFD) while a few miles away, the Burj Rafal is racing ahead, set to eclipse both the Kingdom and Al Faisaliah Towers on King Fahd Road.

The CTBUH recently announced that 2010 was the best year on record for tall towers, with 66 buildings of 200m or higher completed in 2010. China had 21 tall buildings completed in 2010, and the UAE 11, including the Burj Khalifa, which was one of eight supertalls (buildings over 300m in height) completed that year.
All this suggests that the trend for building tall in emerging markets like China, Saudi Arabia and the UAE is still going strong despite the financial crisis. At the same time, as Riyadh’s spate of tall towers shows, it is getting a lot easier to hit 200m or 300m when building new skyscrapers.

“The knowledge base in the profession has definitely changed. I think the idea of doing a tall building isn’t seen as being a particular challenge,” explains Duncan Swinhoe, Gensler principal and lead architect on the 300m World Trade Centre at KAFD. “There’s a lot of competent architects and engineers that have the knowhow to do these things.”

“I think we’re now into the next bracket up, which is into the super tall buildings, those that are 300m plus, that are still a technical challenge.”

Gensler’s WTC tower is one of two that the firm is developing at the KAFD, both commercial and both utilising a range of new technologies in order for them not just to be tall, but to be aesthetically interesting.

In the past, where the emphasis may have been on building tall for the sake of building tall, technology is allowing new towers to be both big and beautiful.

“The material we are using on the facade is glass reinforced plastic (GRP). It’s not a new thing but it’s very lightweight, very durable and very strong,” Swinhoe explains.

“As a structural element it is self supporting, so that has allowed us to create these very distinctive facade profiles. They’re made out of moulds so it gives you much more flexibility to create apertures that are much more architecturally interesting. It allowed us to mould to the facade to respond to the environment.”

Another key element to GRP, Swinhoe says, is that it allows an architect to use large windows without compromising on sustainable targets. At the KAFD, where green benchmarks are extremely strict, Gensler was able to protect the glass from excessive heat gain without overtly reducing the windows in the south and west facing facades.

“There are very few ways of accommodating a regular arrangement of windows that allows offices to be put into a commercial floor plate and create a usable workplace around the whole perimeter of the building, especially one that allows the interiors to work and allows you to have a relatively opaque wall,” he says.

“Using GRP allowed us to hit those numbers in terms of opacity and transparency but in a way that makes the building look much more fluid and dynamic and contemporary.”

Niall Mc Loughlin, senior vice president at Damac Properties, agrees that materials have come a long way in the last decade, but points out that cost and an aversion to the risk of using new products is keeping some architects away.

“Some innovations, such as photovoltaic glass, are likely to be increasingly important in the future, but right now are very expensive for the early adopters,” Mc Loughlin says.
He adds that while Damac uses new materials in its designs where there is a strong case for them, they are not reckless.

“We are not experimental with new technology, because the risks are too high if we make the wrong decision,” he says.

Materials isn’t the only area where technology has allowed architects to build taller, more aesthetically pleasing towers in recent years. Modelling too, both in terms of BIM and wind tunnel testing, has come on in leaps and bounds.

“Wind modelling has improved and, more importantly, there seems to be a greater acceptance amongst clients that they now recognise the worth of it. Before it was seen as a bit of an unnecessary expense,” says Mark Lavery, an associate director of tall buildings at Buro Happold.

He cites both the Burj Khalifa and the as-yet-unbuilt Nakheel Tower as examples of where wind modelling not only tested the strength of the buildings, but also had an effect on the design. The facades and other design elements were actively effected by how the models performed.

“The facade was integral to the structural design,” Lavery says. “The slots and the shapes and the angles and so on all had a huge impact and were studied at very early stages to try and define and overall external geometry that was optimised for wind.

“There is a real move towards that now,” he adds. “We can get earlier testing and earlier results. The earlier you get these results the more options we’ve got in the geometric design and addressing the geometric properties of the building and the facade and shape issues.”

And it’s not just in terms of design where modelling can have a major impact, Swinhoe adds, it’s cost too. At Gensler’s Shanghai Tower, due to be the tallest building in Asia when it is completed next year, wind modelling was able to save a great deal of money.

“The modelling that we carried out took 25% out of lateral structural stability system. It was aerodynamically tuned through the CFD modelling, and then eventually in the actual wind tunnel testing verified that we were able to fine tune the structural form and the architectural form to make the building cheaper,” he says.

It’s also aiding the construction process, according to Lavery.

“There is a more integrated platform that allows engineers and architects to fine tune the forms and structures to make them more efficient. This is allowing us to build tall with less risks involved,” he says.

But Lavery also feels that there still needs to be more testing of buildings, especially those that have already been built, to study how they are effected by factors such as seismic movements and wind.

A performance-based design approach should be considered during wind design, looking at how existing buildings behave under different levels of load.

“It’s going to come down to an analysis of what we have done before and how those buildings have behaved. That’s traditionally how engineering and architecture evolved until code came along, it was how the last number of jobs had worked,” he says.

“There’s been a little bit of that subsequently, you’re always learning off the last job you did, but we need to start pushing the boundaries of the technology and our understanding of how buildings do behave and working on new ways to design them.”

One of the biggest considerations for building tall is lifting, and elevator technology – and how it fits in with use – is key to dictating how large a tower can be. In mixed use developments, such as the Burj Khalifa, multiple elevators are needed to ferry people to each of the floors.

“Destination control is an absolute must in making efficient high rise buildings, as well as a multi-stacking of zones within the building. So, like the tube station, you have the main express mainline which take you to the main destinations very quickly, where passengers get their local lifts – ten floors or so – in a much more contained group,” explains Swinhoe.

This was integral to the firm’s WTC project, where a high volume of businessmen and women would be arriving at all hours of the day. Swinhoe says that the solution was to make the platform levels, where people get out to change lifts, like sky gardens, with food and beverage outlets and shops.

“They have to feel like it is a point on the journey rather than the transfer being just jumping from one lift to another. The lift is just one of those modes of transport you take to get there,” he says.

Lavery points out that lifting is one of the biggest challenges when building super tall towers, particularly buildings, that may one day need exceed 1km.

“It just comes down to logistics, if you have a 500 metre lift shaft you’ve got a cable that needs to extend 500 metres long, the weight of that cable becomes a limiting factor. That’s why you end up having shuttle lifts and express lifts and sky lobbies, you service it from those kind of areas,” he says.

“If you get anything above that you’re hitting problems. The Nakheel tall tower was a case in point. The strategy there was to lift between sky lobbies at speed and then you would locally service between lobbies.”

In terms of the actual technology, suppliers too are trying to make life easier for architects building taller and taller.

Otis, which supplied the elevators for the Burj Khalifa, has unveiled a raft of new technology over the last few years, particularly in areas pertaining to operating procedures and sustainability.

Its compass technology, for example, improves the flow of traffic in a building so that the elevators on the fastest, most direct route to pick up passengers from every floors.

“The system constantly evaluates real-time passenger traffic and dynamically adjusts floor sectoring to deliver the service customers need, when they need it,” says Sebi Joseph, general manager for the Middle East at Otis.

Technology aside, the question remains whether anything is currently preventing architects from building even taller. Whether, at some point, a contractor or structural engineer would have to say, enough is enough, you simply can’t go that high.

In terms of construction, Damac’s Mc Loughlin says no.

“When it comes to building tall structures, the physical construction of the building is not particularly difficult. We could keep building floor after floor until we reached the moon,” he says.

“What is challenging about super-tall structures is evaluating and accommodating the impact of elements such as wind, and the force and direction of the winds at the higher levels of the structure, and whether that will be likely to cause the building to sway.”

But even if wind technology was able to continue to enable architects to build taller and taller, Gensler’s Swinhoe says the question is should they, rather than could they.

“I think whilst technology may enable you to build tall, the fundamental questions for us is should we build tall,” says Swinhoe. “I think in very dense urban areas, with higher land values and issues of transport the case for building tall is quite clear, from both a sustainable and an economic standpoint.

“But at the same time I think the limits are economic rather than technical. A lot of people quite rightly question whether value is truly being driven out of some of these property adventures. That’s the real limit.”