The world’s top cities are instantly recognisable by their skylines – the finest examples of tall building architecture and engineering have helped create iconic metropolises for decades.
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And the innate human desire for exploration has enhanced the appetite across the globe for building ever taller.
It is not endeavour that is spurring the need to reach for the sky. Increasing urban density is testing landspace and its ability to accommodate the influx of people who live and work in cities. As with New Civil Engineer’s Going Underground theme of a couple of months ago, clients are trying to find space below and above ground in new ways to allow cities to adapt to this urbanisation.
The challenge – often spearheaded by engineers – is how to create super tall buildings that are also super smart.
Two fifty one landscape
“Engineering is the enabler for height,” points out Council on Tall Buildings and Urban Habitat executive director Antony Wood.
He explains that from the iron frame heralding the birth of skyscrapers, along with the advent of steel and the first safety elevators, technical advancements have been key. “So there have been technologies to make skyscrapers more efficient but I’m not sure there’s been a technology to allow us to make a massive head-jump,” he argues.
But it is not just a case of tweaking around the edges of tall buildings, engineers are in an age of pushing boundaries to find efficiencies and improvements to the way buildings are designed, built and inhabited.
Definitely we’ve got the tools and toolkit to build smarter and faster but we’re only going to do it from a commercial pressure perspective
Raj Kotecha, Laing O’Rourke
“Definitely we’ve got the tools and toolkit to build smarter and faster but we’re only going to do it from a commercial pressure perspective, and I think it takes better client relationships in order to actually do that,” enthuses Laing O’Rourke engineering project leader Raj Kotecha. “We can push them to the absolute limits.
“We have the capability to build taller and smarter; whether or not our end users or clients want us to is a different story.”
The economics and client desire are paramount. But these factors are also at the root of the controversy that so often surrounds tall buildings. Because these iconic headline grabbers can create great PR for the cities that host them, they are hard to ignore.
Can we go too high?
The collapse of the World Trade Center Towers 15 years ago triggered a fear that perhaps the end of building tall was nigh. Perhaps people would no longer wish to pay for a lofty ambition of living and working at height.
Fortunately for tall building enthusiasts, places like Dubai were to soon find themselves in the midst of an economic boom so any fear that there would be little appetite to build offices and living space in the sky evaporated. There was enough money to build confidence that it was worth the risk of finding out. And 2010 saw the anointing of the Burj Khalifa as the world’s tallest building, which at 824m tall, surpassed its predecessor for the title, Tapei 101, by 320m.
As is always the way, when one world record is set, there are those eyeing up ways to beat it. And so well before the opening of the Burj Khalifa, the Mile High tower in Jeddah was in development.
Jeddah Tower challenge
The name changed to the Jeddah Tower as the mile high height became economically challenging – contractors advised it was impractical. The challenge of geology and transporting materials at height in 2008 led to the decision to shave around 500m off the tower.
“We could go double or triple the height we’re at now with the Jeddah tower, technically speaking, we can,” explains Wood. “I don’t think the industry has been sitting there thinking: ‘I wish we could go to 1,000m, but we’ve got to wait until such a technology comes in’.”
“The main barrier to even greater heights is not technical, but economic – why would we build a mile-high tower, is it really necessary? So engineering has been the great enabler, not the driving force.”
What has followed, is an acceptance that, for now, mega-tall construction is determined by the practicalities. On that building, the structural engineering is based on conservatism with regard to materials and design – it is a rather traditional concrete-heavy structure to ensure stability against wind loading and overturning moments – leaving innovation to be found within the detail, notably in logistics.
The main barrier to even greater heights is not technical, but economic – why would we build a mile-high tower, is it really necessary? So engineering has been the great enabler, not the driving force
Antony Wood, Council on Tall Buildings and Urban Habitat
Of the things that have the potential for engineers to influence with innovation today, Wood suggests: “It’s perhaps mundane things, like the pumping of concrete at great heights, efficiencies in structural engineering like outrigger systems, the development of composite columns, the natural benefits of steel and concrete, steel in tension and concrete in compression, and putting them together rather than one or the other.
“I think we will go higher. I think, maybe not forever, but for an appreciable time yet, there will be a quest to have the world’s tallest building.”
Taller buildings are increasingly being engineered as complete systems, linking air conditioning, heating and ventilation, security, fire protection, lighting, energy management, water and lift systems with software and hardware that manage them.
Add to that the way they are built is getting smarter – notably with offsite building techniques.
Contractor Laing O’Rourke is leading the way on this, with its Design for Manufacture and Assembly concept. It is the right approach, argues Kotecha, because waiting for the economic case to be made for efficiencies from above is futile.
“At the end of the day, a lot of the clients I come across, for them cost and programme are key,” he elaborates. “How the structure, or asset, comes together they are not too fussed about. When it comes down to two stage tenders, it’s very difficult to convince the client that an innovative approach to how to build is the way to go, because no one wants to be the first one, no one wants to be the guinea pig.”
Limitless offsite potential
“At the same time, it just makes it more and more difficult for them to benchmark you against another builder. So that throws up a challenge. “But the potential for offsite construction is limitless, according to Kotecha.
“I don’t think there is a limit. We’ve looked at projects within Laing O’Rourke that ran up to 50, or 60-storeys and we’ve come up with schemes we think would work. I remember a couple of evenings playing around with a mile high tower and we came up with a concept for it we thought would work.”
“I think within 10, 15 years you’ll see buildings a lot taller than this [the 41 storey Two Fifty One building, see previous page] go up [built predominantly offsite]. And the mega tall, probably shortly after that, maybe 15 years.”
The challenge is getting buy in: an easier sell with, say structural engineers, according to Kotecha, but still more challenging is breaking down the stigma of offsite with architects.
Ultimately engineers are faced with persuading clients and supply chain partners, in the process reducing risk, that innovative ideas need to be cultivated to get the best out of the tallest, most iconic structures.
The London view
A report earlier this year revealed the total pipeline of tall buildings – 20 storeys or more – in London has now reached the heady heights of 436, an increase of 119 in a year. Under construction the number rose in the same period from 70 to 89.
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Although a large number are arranged in clusters as part of wider masterplans, the news is not welcomed by all.
Two years ago when the number was lower, lobbying body the Skyline Campaign issued a missive. While it maintained that it was not fundamentally opposed to building high, it said the skyline of London was “out of control” and said that while many tall buildings reflected the trend to build taller for residential needs they were “neither essential to meeting housing needs, nor the best way to achieve greater densities”.
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“Their purpose is more to create investments than homes or cohesive communities,” it argued. “They have the potential to cause permanent damage to the city’s urban fabric and to its global image and reputation.”
The statement pre-empted the views of the people. In August, an Ipsos Mori poll of more than 500 Londoners found that of those in inner London almost half said they were worried about the rise of tall buildings and that there are too many.
Only 8% said purpose built high-rise blocks of 20 storeys or more were what is needed. Some 59% supported controlling the number of 50-storey plus buildings and limiting the height of new developments. Only 16% believed outright that there should be no height limit imposed.
Offsite case study – Two Fifty One
Part of the regeneration plan for Elephant & Castle in South London, Two Fifty One is a 41 storey residential and mixed use tower. Laing O’Rourke is deploying its Design for Manufacture and Assembly (DfMA) ethos in a design and build contract. Arup is design partner, Waterman structural and MEP consultant and the architect is Allies & Morrison.
The idea of DfMA is to build twice – once virtually – and exploit offsite manufacturing methodology as far as possible. Over 72% of the structure and cladding on the tower is being manufactured offsite.
The upshot is only 15% is built wet on site thanks to the development of Laing’s patented E6 floor system. Less wet concrete pouring means less temporary back propping. And that means less people on site – creating control and efficiencies in programme, and perhaps more importantly, safer construction.
It changes the number and type of skills needed, explains Kotecha. Only 24 people are on site actually building the structure.
More multi-talented people are identified as relevant by the contractor, which is now developing a training programme for DfMA technicians to skill them in the new ways of constructing offsite.