We will reveal the incredible stories behind these structures, and the inventions which helped them to go higher.
Construction Challenge #1: Mobility – Introduction to High-End Elevators
The first and foremost obstacle to skyscrapers were – stairs.
The first breakthrough happened in 1870 with the Equitable Life Building in New York which was only 40m tall. Builders realized that they could go taller, however, they need to find an alternative to make people climb higher. There was an obvious solution for the problem – the elevator.
Prof. Andrew Scott Dolkart, Historic Preservation at Columbia, GSAPP, and Director of the school’s Historic Preservation Program says that “people were reluctant to walk stairs in old buildings as they were dark, and climbing stairs get them incredibly winded. Before elevators were introduced, if you have a business on the fifth floor, you are undoubtedly going to lose clients.”
But early elevators had one deadly fault, nothing stopped them from falling if the hoist cable failed. That’s when Elijah Grave Otis, demonstrated free-fall safety. A safety device that prevents elevators from falling even if the hoist cable broke. Equitable Life Building included the first fully automated safety elevator and was the first office building to feature passenger elevators.
Equitable Life Building had only seven stories, however, Burj Khalifa has 163 floors. The height that stretches elevator technology to its absolute limit. The Burj Khalifa took the idea of elevators to its extreme, as it accommodates over 35,000 people, and getting these people in and out is a herculean task.
To cope up with the numbers, Burj Khalifa has 57 (55 single deck and 2 double deck) elevators made by Otis Elevator Company. Some reach a maximum speed of 36km/h and move 120 floors within 50s. Another issue with the elevators was stopping 50 tons of moving mass. To stop these juggernauts speeding, emergency brakes spring into action. Metal brakes bite down on the guide rails and produce enough braking power to stop these elevators.
Construction Challenge #2: Materials – Reinventing New Materials
Safety elevators guided skyscrapers to break through the barriers, but when they approached 93m for the Flatiron Building in New York, traditional building materials weren’t suitable for the task. New materials needed to be used because the Monadnock Building in Chicago (60m) began to sink into the soft Chicago soil due to its extremely heavy structure. Thus, stones weren’t suitable as skyscraper material.
When the architect of the Monadnock Building, Daniel Burnham, was planning the Flatiron Building he faced a problem. The extremely narrow plot prescribed a triangular 22 story skyscraper. He knew that there was no room for stone walls, as it would waste valuable space. This took stone out of the equation, so he designed the building out of steel columns and beams, locked together into a steel skeleton. Steel was much stronger than stone, and so the skeleton can be light and thin, yet it can support the entire weight of the whole structure. To keep the weather out Burnham simply hung thin masonry walls off the steel frame, like curtainwalls.
Flatiron Building was one of the tallest buildings in New York on its completion, which was only possible with its steel skeleton. Steel construction truly moved the skyscraper a step further and was considered to be the new breed of building.
The skeleton of the Burj Khalifa integrates the best of steel and stone. Over 30 thousand tons of steel is used. The steel is embedded in artificial stone – concrete. The reinforced concrete backbone is covered with a high-tech curtain wall of glass and steel. The curtain wall of the Burj Khalifa cost around hundred million dollars, and various prototypes were tested before the final cladding was selected.
Glass materials for curtain walls were also reinvented, which we will discuss in our next construction challenge.
Construction Challenge #3: Heat – Turning the Building into a Giant Oven
The next construction challenge for the engineers at Burj Khalifa was to stop the baking Desert Sun from turning the building into a giant oven.
As steel catapulted skyscrapers to unseen heights, and walls no longer had to bear the entire weight of the building, it gave architects the complete freedom to use new materials. In 1947 when the Headquarters of the United Nations (155m) was designed in New York they wanted a building with glass so that the interior would be light and bright. However, they faced an issue – heat. They didn’t want a 39-story greenhouse.
Willis Carrier, an American Engineer cracked the problem by inventing modern air conditioning. His machine could cool and dry hot moist air by simply making it wet with a fine mist of cold water. The invention from Carrier was an ideal solution to the heating problem faced by the Headquarters of the United Nations. Thus, air conditioning allowed the skyscrapers to rise, even in the hottest climates.
When it comes to Burj Khalifa, air conditioning matters more than any place. In Dubai, temperatures easily reach 40°C in the shade, and the average humidity is 90%, which makes an extreme environment for a skyscraper. The key element to withstand the brutal desert sun is built into the glass skin.
The glass has two coatings on it. The outside coating is titanium, which captures the UV rays and reflects it just like sunscreen. However, it is useless against IR rays that radiate from the hot desert sand. The inner coating is silver that reflects the IR rays back out of the building. When UV and IR rays are reflected, it drastically reduces the amount of heat penetrating into the building. John Zerafa, the Façade Project Director, conducted a test with normal glass and found that when the outside temperature reaches 46 °C the inside temperature is 98 °C. The internal temperature was just below boiling point.
The new glass panels solved the heat problem, keeping the heat out, with a total of 24,348 specially coated panels for Burj Khalifa.
The next construction challenge was to complete the Burj Khalifa within the allotted time.
The same issue was faced with the twin towers, the World Trade Center. To reach the dizzying 417m developers had to find a solution for this mammoth problem since every day the building isn’t finished costs money. The idea was to reduce the construction time to the minimum and the solution was to use prefabricated sections for the towers which were then assembled on site. They built the sections offsite and shipped the prefabricated sections to the site precisely when they were needed. The next problem was to quickly lift and place these 50-ton prefabricated sections. The developers found a revolutionary crane in Australia known as the Kangaroo Crane. It could lift 50 tons and 4 of them could reach every corner of the twin tower. Once the crane assembles the 3rd floor, the bottom of the crane jumps to the 3rd floor and locks into position – thus moving up with the completion of each 3 floors.
With the help of prefabricated sections and jumping kangaroo cranes, the builders of the Twin Towers could finish 2 floors every week.
The jumping kangaroo crane was the first choice at Burj Khalifa, however, builders took the prefabrication to the next level – Jump forming. The team built molds at the base, inserted steel reinforcement bars and poured concrete in. Once the concrete set, the team lifted the molds to the next level and repeated the process. Kangaroo cranes hoist the steel cages up. This way, builders could go at a pace of one new floor every week.
When Burj Khalifa reached higher, builders faced another challenge, they needed to pump concrete higher. Putzmeister created a new super high-pressure trailer concrete pump to pump concrete higher than anyone has ever done. Due to this amazing pumping system challenge, it owns a record for a building for the highest vertical concrete pumping (606m). It was the combined effort of raw machine power and subtle chemistry.
Construction Challenge #5: Wind – Deceiving it to go Higher
With Burj Khalifa soaring higher into the clouds it became exposed to a new enemy. The one that exploited every weakness – wind.
At high speed, wind can be extremely dangerous for skyscrapers. Air rushes around the building and creates mini tornadoes called vortices which create areas of low pressure that suck the building sideways. The taller the skyscraper gets, the more dangerous the vortices.
To build Sears Tower (442m) in Chicago, a reputedly windy city, architects had to turn the skyscraper inside out. As the Sears Tower would be 100+ floors tall, a height which exposed it to enormous wind forces. Building a skyscraper using a traditional steel skeleton would create massive problems. The taller a steel skeleton gets, the more it's prone to bending in high winds. Gusts off Lake Michigan could buffet the skyscraper at 80 km/h plus, this would cause the upper floors to sway, affecting the people inside. Sears Tower’s architects invented a technology that could beat the wind. The steel frames were shifted from the inside to the outside of the building. This exoskeleton helped the building resist bending from the wind. Sears Tower consists of 9 such tubes which lock together to make it rock-solid. It is said, that even when the wind speeds are over 90km/h the top floors move only 15 cm. An insignificant value for a skyscraper.
For Burj Khalifa, rather than fighting the wind, Bill Baker, the Structural Engineer at SOM went with a design to deceive it. Burj Khalifa was given an unpredictable shape, which breaks the winds hold on the building. Bill said, “when we were designing the building, we were actually designing the wind. In a way, the wind behaves around the building and it makes a tremendous difference. We would never be able to go this tall if we had not done that.”
Construction Challenge #6: Earthquake
After conquering mobility, materials, gravity, heat, and wind, skyscrapers faced their next big challenge – earthquakes.
In Asia, where booming economies wanted to showcase their wealth, super-tall skyscrapers became the objects of desire. However, Asia is the nemesis for skyscrapers because of earthquakes. To make Taipei 101 possible, skyscrapers had to take another leap forward. As earthquakes hit the city about twice a year, it was not a question of if, but when an earthquake would strike Taipei 101. To survive the violent quakes, Taipei 101 needed a dash of elasticity. Designers made the building rigid where it had to be, and flexible where it could afford to be. The 36 rigid steel shoes filled with concrete gave the building strength. This forms the columns, and they stand firm during earthquakes while the rest of the structure is elastic. In fact, halfway through the construction process, Mother Nature tested this design to its limit. On 31st March 2002 an earthquake shook Taipei 101. It shattered the smaller buildings nearby, however, Taipei 101 stood still.
Engineers of the Taipei 101 claim that during an earthquake Taipei 101 is the safest place in the city.
Burj Khalifa has a massive reinforced concrete skeleton which can withstand earthquakes of up to 6 on the Richter scale. However, the engineers faced another problem. To make this skyscraper stand on the desert sand, it required extraordinary measures. The ground below Burj Khalifa consists of a 3 to 4 meter layer of sand. Below this are weak sandstones and limestones which aren’t suitable to support the structure. The future of the Burj Khalifa and its colossal weight rests on one scientific principle – friction. Engineers went with skin friction piles, where the weight of the skyscraper is carried on the friction of the pile, the side of the pile. The foundation totally relies on the super strong grip created between the ground and the sides of the each pile. Beneath the tower, engineers drove 192 pile to a depth of 50m, to support a 3.7m thick raft of solid concrete. Bill Baker, the Structural Engineer at SOM says that “The building so far has gone down around 30 millimeters, which is just slightly more than an inch, about the thickness of my thumb. It is very small number for a building of this size”.
In just 130 years skyscrapers conquered all the forces of nature with the power of human ingenuity.
Construction Challenge #7: Evacuation – During an Emergency
As skyscrapers soared higher and higher into the sky, they became more vulnerable. One of the fears which threaten their existence is terrorism. Now the final technological leap of the world’s biggest skyscraper is to keep its occupants safe.
After the attack of 9/11 many believed that no super tall building would ever be built again. Mike Hurley, former fire director at the World Trade Center says “I don’t think anyone could foresee those events of September 11th, where planes would be used basically as missiles to fly into a building. But once that occurred it became a fire safety issue, and then we began our typical plan to evacuate the occupants.”
Evacuating occupants from a skyscraper is not an easy challenge. The taller the building gets the further people must walk to get to safety. Mike Hurley says that “Making the occupants walk down the stairs is a real challenge for the rescuing team. You may think that walking down the stairs would be a lot easier than walking up the stairs. But it is not, it’s almost as difficult as walking up. Everybody has a different pace of walking, few may be physically fit, a few could be injured, some may have lost their shoes and it's sure isn’t going to be easy for anybody.”
Burj Khalifa has built-in fire protection as its concrete backbone is naturally fire resistant. But the skyscraper is nearly twice the height of the Twin towers, so how do people get out during an emergency. The answer is – they don’t.
Burj Khalifa contains nine very special rooms – refuge rooms. These refuge rooms are built from layers of reinforced concrete and fireproof sheeting. The walls can withstand the heat of the fire for 2 hours. A special supply of air is pumped into the refuge rooms through fire resistant pipes, and the sealed fireproof doors ensure that no smokes leaks into the room. Occupants in the refuge room can seek shelter from a fire until the emergency services bring the fire under control. Refuge rooms are available at every 30 floors, which make them easily accessible without much effort.
Refuge rooms are a fundamental concept, however, the safest place is of no use if the access route is blocked by smoke. Dale Mills, Fire Fighter says that “in a fire, it’s not normally the fire that kills you, but the smoke inhalation. 98% of people die in a fire because of smoke.”
Architects and engineers have thought of this situation and have come up with a technology to take the smoke out of the equation. The Burj Khalifa comes with an early warning system which guards it 24/7. If the fire is initiated, the smoke detectors and heat sensors detect it, and a network of high-powered fans kick in. These fans force clean cool air into the building through the fire resistant ducts. The fresh air forces the smoke out of the stairwell, thus keeping the evacuation routes clear.
Thus Burj Khalifa comes with fire safety kit for the 21st-century skyscraper.
With its inauguration on 4th January 2010, Burj Khalifa became the tallest structure that mankind has ever built on this planet. Standing on the shoulders of historic engineering marvels, the Burj Khalifa is really an ultimate skyscraper, until someone builds an even bigger one.
Hobbes S Sujith is a Senior Writer and Digital Marketing Lead at Advenser. He has 12+ years’ experience in the industry. During his free time, he spend his time with family, martial art and motivating people around him.
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