Just how high can we conceivably build?
WSP | Parsons Brinckerhoff’s Dean McGrail tells James Morgan that, if challenges related to vertical transportation can be overcome, the sky really is the limit for super-tall structures in the Middle East
The Middle East is known the world over for its super-tall buildings. At 828m in height, Dubai’s Burj Khalifa, developed by UAE-headquartered developer, Emaar Properties, holds the current record for the world’s tallest man-made structure. Not content to rest on its laurels, Emaar is now pushing ahead with the development of The Tower at Dubai Creek Harbour. Scheduled to complete in 2020, this project looks set to outgrow its Downtown Dubai counterpart by approximately 100m.
Meanwhile, in Saudi Arabia, Jeddah Economic Company’s (JEC) Jeddah Tower is likely to eclipse all of its competitors upon completion. Although this ambitious project has been beset by delays, it looks set to become the first building in the world to break the 1km height barrier.
More often than not, discussions centred on projects like these lead to one question in particular: how high is it possible to build? In the opinion of Dean McGrail, director of property and buildings in the Middle East for WSP | Parsons Brinckerhoff, the answer to this question depends on funding, space and, perhaps most importantly, vertical transportation technologies.
“Currently, using traditional elevator technology, using steel cables, I’d say that the maximum distance that could be travelled in a single vertical run is about 500m,” he tells Construction Week. “The more slender a building becomes, the fewer elevators it can accommodate. The single biggest limiting factor for high-rise construction at present, therefore, is elevator technology. That’s going to be the next big leap, in my opinion.
“From a purely structural perspective, there would be challenges but – with the right people – they would most likely be overcome. Of course, as you build taller, you might find that your base size becomes less financially viable. However, in terms of engineering expertise and practices, it is possible to go even higher.”
McGrail proceeds by outlining a series of techniques that construction professionals working on super-tall buildings, defined as those standing 300m or above, employ to overcome height-related obstacles.
“From a structural perspective, the biggest challenge [associated with super-tall buildings] is the impact that wind has on the structure,” he explains. “[If left unchecked,] wind will cause a tower to move and oscillate. Chamfered edges represent one design choice that can be employed to [guard against] vortex shedding, a phenomenon wherein air oscillates around a building [causing unwanted movement].
Leaving floors empty represents another technique sometimes employed to mitigate the effects of vortex shedding.
“Put simply, this approach allows air to flow right through the building,” says McGrail. “It is also possible to align these empty floors – which contain no glass or façades – with a tower’s mechanical levels.
“Essentially, a structure must be designed to prevent its occupants from feeling movement caused under wind loading. This phenomenon also has an impact on the tolerances of façades and elevators. For example, the last thing you want is to be travelling in an elevator, only to find that it’s banging into the shaft wall.”
Appropriate building materials and construction techniques also play a significant role in facilitating super-tall construction. These considerations are not limited solely to the materials that are procured; they also extend to the equipment and processes used in their installation.
“The type of concrete required will change depending on the height of a structure,” he says. “The taller you go, the stronger the concrete you’ll need. And when you go tall, everything is impacted. Challenges become greater with every single metre you climb.
“Even the logistics of construction become more complicated. You have to move materials from the base of a building up to the construction site, which could be hundreds of metres in the air. If you’re lifting materials to significant heights, you can actually lose days because of wind effects and turbulence around the structure.
“What’s more, you have to account for factors like concrete-pumping equipment. Anybody who’s ever put their hand in concrete will appreciate that it’s not the most susceptible material to being pumped. Super-tall buildings require special methods for pumping concrete to the work site.”
Nevertheless, given the right people, materials, and equipment, structural challenges can be overcome. As McGrail points out, when it comes to building higher, elevator technology represents the most significant limiting factor at present.
“Once a building’s structure is complete, you then have to deal with challenges connected to people transportation,” he says. “The leading elevator manufacturers are developing a number of promising technologies that could help in this regard. Kone’s UltraRope, for example, enables travel heights of up to 1km.”
McGrail also alludes to technologies like Thyssenkrupp’s Multi, a rope-free concept – still in development – designed to incorporate multiple self-propelled elevator cabins in a single shaft.
“At the moment, the issue with many of these technologies is their state of proveness,” McGrail continues. “Most are not commonplace, and it’s going to take [forward-thinking] developers and building owners to select them for their projects.
“That, for me, will be a major turning point: when we start to see these advanced technologies being used in the market. In turn, I think that the game changer will be the move from cabled elevator systems to elevators with their own internal systems – elevators that move on rails, for example.”
In reality, available funding and potential returns on investment (ROI) tend to determine a building’s ultimate height. McGrail explains: “The single biggest driver for today’s tall buildings is economic viability, and that viability is [typically dependent on] the scale and lease of floor plates. The more efficient the floor plate, the more revenue the developer will achieve from that building.”
With this in mind, McGrail says that WSP | Parsons Brinckerhoff’s primary role and responsibility is to increase the efficiency of its clients’ floor plates.
“The major challenge in this respect is that the taller the building, the larger its core,” he continues. “The higher it goes, the greater the number of elevators that will be needed. For this reason, WSP | Parsons Brinckerhoff has vertical transportation teams that specialise in the optimisation of buildings’ elevator systems: how many, how large, and how fast? That’s the trade-off you’re usually looking at when it comes to super-tall structures. Identifying the best vertical transportation solution represents one of the most important drivers of floor-plate efficiency.”
McGrail also emphasises that the financial equation works both ways. As land prices in the Middle East’s premium areas continue to rise, he predicts that height will become an increasingly important consideration for developers.
“I think that you will see this trend more and more as cities like Dubai continue to develop,” McGrail elaborates. “The cost of land in [more mature markets like] London and New York, for example, is extremely high. In the not-too-distant future, you’re probably going to see similar trends in some parts of the Middle East, wherein developers will be looking to get as much height as possible from their land parcels. The two main challenges that will have to be overcome, therefore, will be the slender ratio, or the ratio between the base of a building and its height, and those related to elevators.”
So, taking into account all of the aforementioned factors, does McGrail think that the Middle East has what it takes to retain its super-tall crown?
“China will be the biggest challenger in this respect,” he responds. “WSP | Parsons Brinckerhoff has worked on projects in excess of 500m in China. In fact, we’ve worked as the building services engineer for 23 of the world’s 100 tallest structures, making us the global number one. We’ve worked as the building structures engineer for eight of the world’s tallest buildings, giving us a global ranking of number four in this field. A large proportion of these projects are located in Asia.
“As it currently stands, the difference between the Middle East and China is the cost of land. It’s economically viable for Chinese developers to build tall because the price of land is high in the country’s urban areas. For the majority of the Middle East, that reason is probably not as strong at present.
“Whether developers in the Middle East lose their appetite to build tall because of this, remains to be seen. I hope they don’t. There’s a large emphasis in this region – a desire – to build the biggest and the best, which is great.”
Encouragingly, McGrail concludes by pointing out that – elevator-technology permitting – money and space are the only factors limiting the height to which we could theoretically build.
“Given unlimited financial resources and a sufficient land parcel, the sky is – quite literally – the limit,” he says. “As WSP | Parsons Brinckerhoff’s structural experts will tell you, if a client has the aspiration [and resources] to build to a particular height, then we can do it.”