| Term Paper Title | Tall Stories |
| # of Words | 2024 |
| # of Pages (250 words per page double spaced) | 8.1 |
Tall Stories
NEWSCIENCE
Picture in your mind the skyline of downtown Toronto. There's the CN
Tower, of course, and the 72-floor First Canadian Place, the city's
tallest skyscraper. Cascading from there are the assorted banks and
hotels and insurance towers.
Now, use your imagination to construct some new buildings, these
ones reaching three, four and five times higher than the others. Top it
all off with a skyscraper one mile high (three times as high as the CN
Tower).
Sound fanciful? It did 30 years ago when Frank Lloyd Wright
proposed the first mile-high building.
But not today. We are now said to be entering the age of the
superskyscraper, with tall buildings poised to take a giant new leap
into the sky. Skyscrapers approaching the mile mark may still be
awhile off, but there are proposals now for megastructures soaring 900
m -- twice as high as the world's tallest building, the 110-story Sears
Tower in Chicago.
Suppose that you were asked to erect such a building. How would
you do it? What are the obstacles you'd face? What materials would you
use? And where would you put it?
Building a superskyscraper, the first thing you would need is a
considerable slice of real estate. Tall buildings require a large base
to support their load and keep them stable. In general, the height of a
building should be six times its base, so, for a skyscraper 900-m tall,
you'd need a base of 150 square m.
That much space is hard to come by in, say, downtown Toronto,
forcing you to look for an undeveloped area, perhaps the Don Valley
ravine, next to the Science Centre. Bear in mind though that the Don
Valley is overlain by loose sand and silt, and tall buildings must
stand on firm ground, or else risk the fate of edifices like the
Empress Hotel in Victoria. This grand dowager, completed in 1908, long
before the science of soil mechanics, has since found herself slowly
sinking into the soft clay.
Soil analysis is especially critical in facing the threat of
earthquakes. The Japanese have learned many times the hard way what
happens when an earth tremor shakes a high-rise constructed on soft,
wet sand. The quake's enormous energy severs the loose connections
between the individual grains, turning the ground into quicksand in
just seconds and swallowing up the building. .
Engineers have actually built machines that condense loose
ground. One machine pounds the earth with huge hammers. Another
plunges a large vibrating probe into the ground, like a blender in a
milk shake, stirring up the sand so that its structure collapses and
the individuals grains fall closer together.
Anchoring a skyscraper in the Don Valley would best be solved by
driving long steel piles down through the sand and silt into the
underlying hard clay till. Or, if the clay till lies too far
underground, inserting more piles into the sand. The friction between
sand and so much steel would then be sufficient to hold the concrete
foundation above in place.
The next obstacle in erecting a superskyscraper, and perhaps the
biggest one, is wind. Tall buildings actually sway in the breeze, in
much the same way that a diving board bends under the weight of a
diver.
Building an edifice that doesn't topple over in the wind is easy
enough. The real challenge is keeping the structure so stiff that it
doesn't swing too far, cracking partitions, shattering windows and
making the upper occupants seasick. As a rule, the top of skyscraper
should never drift more than 1/400 of its height at a wind velocity of
150 km/h.
Older buildings, like the Empire State Building, were built so that
their core withstood all bending stresses. But structural engineers
have since found that by shifting the bracing and support to the
perimeter of a building, it can better resist high winds. The most
advanced buildings are constructed like a hollow tube, with thin, outer
columns spaced tightly together and welded to broad horizontal beams.
Toronto's Fir...Read entire document
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