杏吧原创

WHEN , the world looked up in wonder at the tallest building on the planet. Like a colossal inverted icicle rising out of the desert in Dubai, the Burj stands at 828 metres tall, 320 metres higher than the former 鈥渨orld鈥檚 tallest鈥�, Taiwan鈥檚 .

Yet its reign may be short-lived. The 838-metre-high Sky City in Changsha in China鈥檚 Hunan province, is scheduled for completion in April 2014, depending on legal approvals. By 2019, the record is likely to pass to Kingdom Tower in Jeddah, Saudi Arabia, which is aiming to break the 1-kilometre mark.

The global race to build higher is hotting up. Governments and private investors are constantly raising the bar 鈥� but it is teams of engineers that make new records achievable.

鈥淔ifty years ago, no one would have believed that we could build an 800-metre tower in Dubai,鈥� says , a structural engineer at , a global engineering and design consultancy. 鈥淣ow, I believe there is no limit on how high we can build.鈥�

鈥淔ifty years ago, no one would have believed we could build an 800-metre tower in Dubai鈥�

Agrawal should know. She recently helped design and build the tallest building in the European Union, in London. 鈥淲e had hundreds of engineers working on it,鈥� she says. Geotechnical engineers studied how construction might affect the movement of trains rumbling through London鈥檚 underground rail network. Acoustic engineers made sure sound wouldn鈥檛 travel between floors, or up and down lift shafts or laundry chutes. Mechanical engineers developed heating, cooling and ventilation systems. And public-health engineers worked on the building鈥檚 water supply and drainage. As a structural engineer, Agrawal helped design the skeleton of the building.

One key technological development that is enabling engineers to design supertall buildings is the use of 3D computer models. These models take information about a building鈥檚 size, shape, weight, and the forces it will exert and have exerted on it, and give engineers details about the minimum amounts of materials they should use to ensure a strong, safe structure. 鈥淲hen you can only do hand calculations, you make conservative assumptions to calculate the amount of load beams and columns can take, and as a result, their size,鈥� says Agrawal. 鈥淐omputer models allow us to assess loads more accurately, and therefore reduce the amount of materials in our structures.鈥� Buildings constructed from fewer materials weigh less and so can be built taller.

Going higher creates other challenges for engineers. Supertall buildings should be able to withstand earthquakes and strong winds, for example. In the case of a fire, it is impossible to evacuate all of the occupants quickly. Instead, engineers endeavour to keep them safe where they are. That is where fire-safety engineers come in. 鈥淢y whole life is spent trying to make sure that buildings or bits of buildings don鈥檛 collapse in the heat of a fire,鈥� says , a structural fire safety engineer at the University of Edinburgh, UK.

Most modern skyscrapers are constructed with either steel or reinforced concrete. In a fire, heat can sap these materials of their strength, but it does so in different ways. To find out more, Bisby and his research group are recreating infernos in the lab. 鈥淲e are testing scale models of buildings subjected to artificial fires,鈥� says Bisby. The team uses propane burners to heat the structures up to 800 掳C. 鈥淚t鈥檚 a safe and easy way for us to simulate the kind of temperatures you would get in a building fire,鈥� he says. Most labs take a more traditional approach, and use huge furnaces to heat life-size chunks of building structures, such as a pieces of concrete walls.

鈥淭he fire should be able to completely burn out on its own 鈥� with no intervention from the fire brigade 鈥� without the building collapsing,鈥� Bisby says. Only the people on the burning floor and the floors immediately above and below need to be evacuated. The rest are 鈥渄efended in place鈥�. So engineers put a lot of work into ensuring that fire is not able to spread between floors. For example, windows are designed to break to release heat and prevent a fire damaging other floors.

Whether people will ever feel truly safe staying put in a burning building is another matter. 鈥淚f I was in a supertall building and the floor below me was on fire, and somebody told me 鈥榚verything鈥檚 fine 鈥� stay where you are鈥�, I would probably say 鈥榮od that, I鈥檓 out of here鈥� and take the stairs,鈥� says Bisby.

For those wanting a swifter exit, Zhou Miaorong, a retired machinist in Shanghai, China, recently designed an evacuation slide that runs alongside a staircase inside a high-rise building. . A more mainstream trend is to fireproof a skyscraper鈥檚 lifts. 鈥淚n the last decade or so there鈥檚 been a real move towards recognising that if you have an appropriate fire-rated lift in a fireproof shaft, you can really speed up the evacuation,鈥� says Bisby.

At the moment, a single journey in a lift can only take you part way up or down a supertall building. The sheer weight of the steel cable that raises the carriage limits the height of the shaft. But this is set to change: in June, engineers at in Espoo, Finland, revealed a new type of lift cable made of carbon fibre. Length-for-length, UltraRope is one-seventh the weight of steel rope, and could raise lifts 1 kilometre in a single run.

If being part of something big 鈥� really big 鈥� appeals to you, a degree in engineering is a good place to start. Academic research suits those who like the freedom to choose their projects. 鈥淚 don鈥檛 have a boss,鈥� says Bisby. 鈥淎s long as I鈥檓 productive, no one asks any questions. It鈥檚 a brilliant career.鈥�

Agrawal prefers consultancy work. 鈥淚t鈥檚 a very creative job,鈥� she says. 鈥淧eople have this perception of engineers sitting at a desk doing difficult mathematics all day, but actually I work with people, I鈥檓 out and about on-site and I do a lot of sketching and drawing and brainstorming ideas. It鈥檚 extremely rewarding.鈥�

This article appeared in print under the headline 鈥淰iew from the top鈥�