I was getting ready to go to my morning ethics class. 9/11/2001 evokes the same question for our generation that the shooting of JFK did for the previous one: where were you? We remember how the Twin Towers went down. I never had the privilege of knowing them intimately when they stood, but as I did research on skyscrapers, I found out that for a while, before I was born, they were the tallest buildings in the world.
For two years, One World Trade Center was the tallest building in the world. With 110 floors, it reached 417 meters into the sky. The year Roberta Flack took pole position on the U.S. Billboard Top 100 with “The First Time Ever I Saw Your Face” (1972), One World Trade Center took the throne from the long-reigning Empire State Building to become the tallest building in the world. Two World Trade Center, its slightly shorter twin (but only by less than two meters) sat solidly beside it.
Two years later, when Barbara Streisand sat at the top of the charts with “The Way We Were” (1974), Chicago’s Sears Tower unseated the New York twin. Almost three decades afterwards, when Lifehouse held the top spot on Billboard’s Top 100 with “Hanging by a Moment” (2001), two planes piloted by terrorists tore the Manhattan Skyline in half, killing thousands.
One and Two World Trade Center were iconic skyscrapers to which an entire nation seemed to give a soundtrack. It’s in the spirit of remembering the Twin Towers that I post the first of two entries today – on skyscrapers.
The Tallest Thing in the Place
There once was a great scholar named Joseph Campbell whose ideas greatly influenced George Lucas in the conception of Star Wars. Among the many brilliant ideas he brought to the world about comparative mythology and religion, this was one:
You can tell what’s informing society by… what the building is that’s the tallest building in the place. When you approach a medieval town, the cathedral’s the tallest thing in the place. When you approach at 17th century city, it’s the political palace that’s the tallest thing in the place. And when you approach a modern city, it’s office buildings and dwellings that are the tallest things in the place. – Joseph Campbell interview with Bill Moyers on PBS, “The Power of Myth”
It’s not just applicable to Western civilizations. Templo Mayor (~60 meters, completed in 1497) was the tallest man-made structure in the ancient Aztec city of Tenochtitlan, now located in modern-day Mexico City. It’s also been true over time: the Great Pyramid in Giza (~138 meters, 2600 BC) was the tallest thing in ancient Egypt.
In many places,* the tallest thing is the skyscraper. The tallest man-made structures in the world have gone from being cathedrals and monuments to communication towers and functional buildings. Today, the tallest man-made thing in the world is a skyscraper – where people work and play. Society, it seems now, informs itself.
This Tall is Different
Skyscrapers are reaching higher into the sky at an astounding pace. The world’s tallest building has gone from being 7 floors in 1874 (40 meters, Equitable Life Insurance Building, New York City) to 102 floors in 1944 (381 meters, Empire State Building), to 163 floors today (828 meters, Burj Khalifa, Dubai). We even distinguish between supertall (300m+) and megatall (600m+) buildings now (the Council for Tall Buildings and Urban Housing). The graphic below shows how the Burj Khalifa measures up to somewhat shorter free-standing structures. The World Trade Center Twin Towers are colored gray (in CTBUH classifications, their status is “demolished”).
It is challenging enough to build skyscrapers, but supertall and larger buildings are different beasts altogether. Earlier this year, Allianz assessed construction risks for supertall buildings in the 21st century. Some of the risks are true for all skyscrapers, but there are a few risks that constitute differences in kind for supertall buildings.
Supertall buildings are more vulnerable to sway from strong winds at their heights. Less vertically daunting skyscrapers are traditionally cube-shaped and have similarly quadrilateral bases. Architects and designers can deviate from this structure to taste. Taller buildings, however, can’t be cubes. Otherwise, the entire structure can go the way of Chez Three Little Pigs after the Big Bad Wolf has gotten to it. So the Burj Khalifa’s foundation is a three-petal triangle for stability, and the structure itself is tapered to reduce wind loads.
(Photo source. When they started building, it was Burj Dubai. When they finished, it was Burj Khalifa. Whoever has the money, you know…)
Even after designs are set, you need to build the thing. Using material that is durable in the face of strong winds and then getting that material to higher highs pose problems. For instance, pumping concrete past a certain altitude requires immense pressure. And concrete typically sets two hours after it’s mixed. Read about these challenges with respect to the Kingdom Tower project, set to start construction later this year in Jeddah, Saudi Arabia.
However, according to high-rise building experts, the single biggest obstacle to constructing buildings taller than the Burj Khalifa is elevator technology. Today, Allianz reports, lifts can only travel up to around 600 meters high in supertall and megatall buildings. The Burj Khalifa holds the record for tallest elevator in the world at 504 meters long. Getting people to go higher is the biggest thing that is holding us back.
Loving an Elevator
Safety is a big challenge for elevators in taller buildings. An elevator falling for long distances down megatall building shafts could reach temperatures of Fahrenheit 572 degrees (300 degrees Celsius). You would be cooked. But there are convincing safeties, thanks to Elisha Otis who started it all with his device that prevents elevators from falling if cables break. I would hope that they hold for supertall buildings as well as smaller skyscrapers. (Tom Harris explains the multitude of modern safety mechanisms very well.)
Moving people up and down the building efficiently becomes more difficult with many more floors. Taipei 101 in Taipei, Taiwan, currently boasts the fastest elevators in the world. Built by Toshiba, each unit goes 60.6 kph (37.7 mph) at full velocity. Taipei 101 is about half a kilometer tall. A kilometer- or mile-high building is a bit more of a challenge, but you don’t want to shuttle more people by shovelling them into faster elevators.
Elevators to the viewing deck at the Burj Khalifa (a little over halfway up the building at 452 meters high) travel a touch slower at 36 km per hour, but use two decks per elevator car to double capacity per trip. That’s right – double-decker elevators (and these are the fastest in the world).
The Kingdom Tower will use double-decker elevators as well, but take capacity a step further by using a different elevator call system. Instead of buttons, you type in the floor to which you wish to go. Then they group passengers. VIPs can also call lifts from their mobiles (e.g. from their cars) so that the cabin gets to the ground floor just as they arrive.
It also helps to have many lifts. The Burj Khalifa has 58 elevators (supplied by Otis). Taipei 101 has 66 (supplied by Toshiba). Kingdom Tower will have 57 (to be supplied by Kone). Each building has different types of elevators (long distance, short distance, VIP, service) serving different floors and entries in an optimized network of “vertical transportation devices” (yes, an official name).
But the biggest bottleneck to making elevators go higher is material in nature. There are two basic types of elevator: hydraulic elevators and roped elevators. It would be absurd to use hydraulic lifts (which push cabins up using pistons) for anything more than a few floors high for that matter. (You would have to dig nearly as deep as the building is tall to fit the pistons underground.) Roped elevators, which use cables to pull cabs up the structure, are the best bet for supertall buildings. But more cables are required to take cabins to higher floors, and cables are heavy.
One lift in the Kingdom Tower project, for example, would require 20 tons of cable using typical steel rope material. The elevator supplier, Kone, developed a new material: carbon fiber rope. One elevator now needs only three tons of cable, and because the material is lighter, uses less energy than steel ropes. Armed with this technology, they are fixing to give Kingdom Tower the world’s highest elevator rise at 660 meters. This breakthrough in materials may help us break the 1-kilometer-tall ceiling in the future.
So let’s say we get there. Higher highs. The kilometer-high. The mile-high. What if something untoward were to happen to them?
Back to 2001. Robin Gershon et. al. studied the World Trade Center evacuation in a 2011 paper. On average, people in One World Trade Center (WTC1) and Two World Trade Center (WTC2) were first aware of the situation at 8:46 and 8:47, respectively. It took people an average of six minutes in both towers to decide to evacuate after they learned about the emergency. It took 40 minutes for evacuees to fully descend WTC1 (they spent, on average, a minute per floor) and half of that for WTC2 (on average, 22 minutes to descend and 30 seconds per floor). In WTC1, it took at least one person 102 minutes to get to the bottom. Some people delayed – to take some last calls, shut down computers, pack up – and this turned out to be costly. Nevertheless, the structure of the buildings, disaster preparedness and emergency response personnel worked wonders:
87% of all occupants in the World Trade Center successfully evacuated.
The kind of thinking that goes into evacuation preparedness in high- (and not-so-high) buildings is complex. And after 9/11, experts and practitioners put even more effort into learning something from the disaster. What’s the best way to evacuate skyscrapers?
Yoni Shimshoni presented some very cool external evacuation methods at the CTBUH. Kone, an elevator company, did a study on combined elevator and staircase evacuations, which could, under appropriate circumstances, be more efficient and safer than stairs alone. And Wieslawa Sikora et. al. from AGH University of Science and Technology in Krakow, Poland used computer modeling to figure out the best way to evacuate skyscrapers. Their research suggests that staggered evacuation (evacuating floors in chunks, not all at once) may take a bit more time, but could avoid stampedes and jamming in stairwells.
How does this work in practice? I looked for evacuation procedures for the tallest buildings in Manila – glassy, purple-topped and pulsating residential twin towers. I couldn’t find anything very helpful. I hope the residents, especially near the top, know what to do in case of emergency.
I wonder if skyscraper administrators would ever consider distributing wingsuits.
Onward and Upward
Today on Manhattan, the new One World Trade Center shines proudly at 541 meters (546 meters to the tip of the antenna) with 104 floors. It is the tallest building in the United States and in the Western hemisphere – a sign of resilience and perhaps a taste of things to come.
In 2001, the terrorists went for the tallest things in the place. Today and on this day in years to come, not only should we remember how they went down – we should also remember how they stood and what they stood for… and
look forward to what will stand tomorrow.
(continued in Part 2…)
* Not in all places. Technically, where there were cathedrals, they were the tallest structures in the place and remained so until the advent of the skyscraper. There are also some exceptions. For a while, the Eiffel Tower was the tallest man-made structure in the world; the monument is still the tallest thing in the place in Paris. The tallest thing in the place in Washington, DC is the Washington Monument. What informs these societies? This is a different discussion.