The History Of Skyscrapers.
In the 1800s, industrialisation boosted mass production of steel. As stairs were made redundant and a flexible steel skeleton was invented, the upwards path was cleared for new height records. Steel production gathered speed in 1855, when the converter was invented. Intense heat first removed impurities from the pig iron (чугун), and carbon was added to make steel. The most powerful types of steel include 0.99% carbon.
High structures were heavy, as they required large foundations and ever thicker walls. With a lighter interior skeleton, the load was distributed onto many beams and posts, so buildings could become 10+ floors high.
Lifts were lethal and considered safe only for carrying goods until a safety device was invented, by which a metal rod grabbed teeth on each side of the lift if the cable collapsed. It was then considered safe for people.
While service lifts were already familiar, they were deemed too dangerous to carry passengers: the cable collapse was a danger. That changed in 1853 when mechanic Elisha Graves Otis from Vermont invented an automatic emergency brake.
Otis’ lift was mounted in a metal frame with interior teeth like those of a toothed wheel. On top of the elevator there was a metal rod, and if the cable collapsed this rod was triggered and stuck to the frame. He founded the Otis Elevator Company, which went on to supply lifts for the Eiffel Tower, the Empire State Building, and other great buildings around the world – indeed the Otis name is on the 57 lifts that travel silently up and down Burj Khalifa’s 19 lift wells at a speed of 36km/h.
By the 1960s, skyscrapers based on William Le Baron Jenney’s interior metal skeleton were rising to touch skies around the world. But the steel skeletons, with their interior tubes and beams, took up a lot of internal space, and the higher they went the larger the skeletons, making each square metre of office or living space increasingly expensive, so that it was not considered worthwhile to build structures higher than 300 metres.
A young man from Bangladesh changed that. When engineer Fazlur Rahman Khan arrived in Chicago aged 21 to study building construction, he had never seen a skyscraper before. But Khan completed his education in record time, and soon became famous for his creativity. Khan turned Jenney’s steel construction inside out and invented the tube construction method, by which the massive, interior steel skeleton was replaced by an external structure that supported the building, combined with transverse steel beams which distributed the weight.
The John Hancock Center in Chicago was the first skyscraper built using the new method. When the structure was completed in 1969, it was 344 metres high, with 100 floors. Fazlur Rahman Khan continued developing several variants of his tube design.
The most famous is the bundled tube construction method he used in the 447-metre-high Willis Tower of 1973, also known as the Sears Tower. Inspired by a bundle of bamboo canes, Khan merged several partial structures to distribute wind and weight loads across several constituent parts. Willis Tower consists of nine square posts of different lengths that share the different loads between them.
The world’s highest building, Burj Khalifa, is based on Khan’s ideas, with several tubeshaped parts that are linked. But it also represents a new development.
The engineers behind Burj Khalifa developed a hexagonal core structure supported by the building’s special Y shape. The principle is like the one used in medieval cathedrals, where exterior structures contribute to the support of interior vaults and windows.
Conditions in Dubai also presented a particular challenge during the construction of Burj Khalifa – particularly as it grew higher. It took 40 minutes and a pressure of
206 kg/cm2 to pump concrete to a height of 600 metres, and engineers had to mix the concrete with ice to prevent chemical reactions that would make it brittle in the desert heat of the United Arab Emirates.
Apart from heat, the wind is a challenge for Burj Khalifa. The very first skyscrapers demonstrated how important it was to allow for wind when constructing high buildings. When wind encounters large and straight expanses of building, it speeds up, moving both upwards and downwards along the building. Around sharp corners, powerful whirls of wind can develop, like miniature tornadoes.
This happens both at height and on the ground. In cities with high structures, narrow streets and a square town plan, wind tunnels can form with speeds that knock people over, as has happened in both London and New York. Higher up, wind can make a building sway, and although they can be designed to withstand this without any danger of collapse, people inside the structure can feel sick.
So engineers try to limit such skyscraper motions through wind by breaking up the straight lines in building designs. Burj Khalifa has an asymmetrical shape, using rounded corners and different heights for different elements to break up the wind paths and slow them down. The design means that the building’s maximum sway is 1.5 metres at the tip of the spire; it feels slow and does not cause motion sickness.
Burj Khalifa has held the height record since 2010, but Saudi Arabia is already building the next record holder, the Kingdom Tower, that is to rise close to the landmark level of 1000 metres, a full kilometre high. But then Dubai plans to construct an even higher skyscraper than that, with the 1400-metre high Dubai Creek Tower.
So the 1800s’ race between Chicago and New York City has now moved to the Arabian Peninsula. According to some scientists, it is in principle possible to build as high as Mount Everest, if the foundations are strong enough. So what began by rising from the smouldering ruins of Chicago might one day end up rising 9km into the air.