Tall Buildings or On Hyperbole
I recently developed an interest in very tall structures when I found out that the tallest supported structure in the world is not far from me: it’s in North Dakota. This structure is not freestanding, it is a guyed radio tower called the KVLY-TV mast that broadcasts to an area of 22,686 square miles (for comparison, this is more than two states of Massachusetts). For further comparison, the mast is 628.8m high: compare to the current tallest building in the world, Tapei 101, at 508m. That said, since I was overdue for a hair-brained idea, I’ve decided to drive over and see this thing up close this summer (and photograph it). We’ll put somone tall next to it for scale … even though it looks like you have to get literally about a mile away to get the entire mast in your camera viewfinder. Before I leave this topic and move on to the tangential research it inspired, I must note an interesting tidbit about the tower: the top is, apparently, accessible by “service elevator or ladder.” Is it just me, or does it seem like a really bad idea to climb a ladder that is 2,063 (4 tenths of a mile) high? Goodness.
Seeing as this radio/tv tower/mast in North Dakota is the tallest structure in the world, but neither free-standing nor habitable, I turned my investigations to the tallest building in the world. It turns out that the construction of the Sears Tower (527m) was simply the spark that ignited a competitive conflagaration wherein countries vie for the title of tallest building in the world. The criteria vary greatly … technically, the tallest buildling in the world is an oil-rig … but nobody really wants to claim an oil-rig as the torch representative of the fire of their commercial, economic, and cultural dominance. So, I veered away from technicalities and into the world of the skyscraper.
Very tall building experience some weird problems at great heights. First, as a construction material steel is quite flexible, a property which is not inherently bad as it facilitates a building’s ability to ride out earthquakes and to sway in wind, much as a tree does. However, the problem of swaying is generally more a human one than a super-structure-stability one. People get sick when their surroundings are swaying. Furthermore, toilet water sloshing in the bowl at 500m in the air never inspires confidence in the average person. To combat this problem, tall buildings have begun using a surprisingly simple yet extremely effective sway-stopping system called a tuned mass damper. This is exactly what you would expect: a mass (an extremely heavy chunk of … something heavy) that is tuned, with the purpose of combatting oscillation (dampening). I’ll venture deeper into the topic for just a minute. Objects have fundamental frequencies at which they vibrate. Two quick examples. Consider a guitar string … when plucked, the string vibrates at a given frequency which we can hear. The second fundamental of a guitar string is a different case all together and can be better observed using a jump rope. Tie a rope to a chair and move it straight up and down such that a single (half) wave forms (we see this wave, rather than hearing it). This wave is alternatively arching upwards and downwards: you are observing half of the fundamental wavelength. Now, speed up the motion of your hand and shorten the linear distance it moves up and down. Now, you can make more “standing waves” - you are at an order of the fundamental frequency. The swaying/vibrating of a building is therefore combatted when a large mass is elastically coupled to the building (just as guitar strings don’t vibrate well with a bolt attached to them).
Another, rather unsurprising, problem of these huge buildings is weight. Foundations have to be dug deep to get down to stable bedrock - the World Trade Center towers had 6 levels of usable floors beneath ground and likely had a foundation that went much deeper. In fact, a rather interesting side note here, a huge despository of gold and silver was located beneath these buildings: at least 102 million ounces of silver ($430 million worth) and at least 12 tons of gold (over $230 million worth, though many speculate over $160 billion there). Does it strike anyone as odd that there are places where millions of dollars of precious metals are stored, all in one place? I suppose no matter how advanced humans get or how much we mask our reasons with arguments about “the economy,” we’ll always have these tendencies to pack away brightly colored rare things in safe hidden treasure chests. Anyhow … back on track. Getting skyscrapers deep into the ground is not just the issue, Taipei 101 (currently the “tallest habitable floor” building in the world), is suspected to have, due to its tremendous weight, reopened an earthquake fault. Weird.
Yet here we are, overcoming these problems and continuing to build these massive buildings. The tallest building on earth is under construction right now, and it’s a doozy. It’s being put up in Dubai, United Arab Emirates … a city so unlike anything I have ever read about, it deserves it’s own introduction. The UAE is rich with oil wealth, and as such has decided to make its city of Dubai a crown jewel among tourist attractions. Its giant hotel, the Burj al-Arab, is considered the most luxurious in the world. In an architectural stroke of genius, it looks like a giant sail on a boat. Good Lord, just look at that thing; and I haven’t even gotten started. This is the tallest building in the world used all as a hotel; it is called “7 starred” to note that it’s luxury surpasses those “6 star” hotels which, in their own right, are meant to rank above the highest “5 star” max rating that hotels can even be given. Oh, and how about that time they converted the helipad to a tennis court and Andre Agassi and Roger Federer played a game that even a Photoshopping maniac could not have dreamt up? I’m talking about one building in this city. Dubai has a whole crop of tall buildings, ridiculous luxuries, which can be summed up by the largest artifical islands in the world they are assembling. The islands will eventually accomodate a half a million people.
Fittingly, Dubai will be the home to the Burj Dubai (pictured at far right), the tallest building in the world, notably modelled after Frank Lloyd Wright’s mile-high “Illinois” concept (near right), and set to be completed in 2008. Burj Dubai is targeted at an undisclosed height rumored to be around 810m, almost 300m (980 ft.) taller than the venerable Sears Tower.
And that’s about all I have to say about that.
Comments
Mykala
I ALMOST made it through this post. Almost.
John T F Larson
Wow, that was a really long post, but nice comments on the physics behind tall buildings. I particularly like the Forrest Gump quote at the end of the post. Kudos.
Markoe
For ten bucks i'll jump off it.
Dan McKeown
You are on, I have the ten dollars in my pocket right now.
Alexander Micek
That's just silly.
Mykala
I'll give you a hundred. Seriously.
Nils
How tall is the Freedom Tower supposed to be? I thought that it was going to take the gold as the current tallest building in the world upon it's completion.
On another note, this is your longest post you have ever written. And I liked it.
Alexander Micek
I've got the Freedom Tower at 417m at the roof, a bit below the highest floor on Tapei. The Freedom Tower will, however, have a pretty massive spire (in the current iteration of its design) which will make its total height pretty … high.
http://www.skyscraperpage.com/diagrams/?b7788
Oh, and thanks Nils, I've got another longish post in the writing pipeline. :)