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Free-standing skyscrapers are
constrained
in their height by (amongst other things)
their need to resist the lateral force of
the
wind.
A similar problem exists in jungles (or
rainforests, as they now are): tall trees
are
at risk of toppling. Jungles solve these
problems to
an extent by a process of cross-linking:
upper branches may intertwine, or be
connected by convenient lianas.
So, convert densely-skyscrapered
downtowns into 3-D networks. Have
sky-
bridges linking the skyscrapers 30 or 50
floors up. With a bit of careful planning
and some complex negotiating, each new
skyscraper could both help to stabilize
its
neighbours and, reciprocally, to be
stabilized by them.
Taller, thinner and more elegant
buildings may be made possible in this
way. As a bonus, the connecting
skybridges would also serve the
conventional purpose of carrying
pedestrian traffic. However, the main
aim here is for structural bracing to
enable taller, narrower buildings.
I know what you're thinking: the shear-
bracing afforded by the skybridges would
be best if they were not at right to the
buildings.
[EDITED to emphasize the structural role
of the connecting bridges - their
"elevated walkway" function is only a
bonus]
Underground skyscraper
Underground_20Skyscraper
Annotations herein suggested this idea. [MaxwellBuchanan, Sep 11 2007]
Taipei 101 (world's tallest completed skyscraper)
http://en.wikipedia.org/wiki/Taipei_101
[21 Quest, Sep 11 2007]
[link]
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I like it. If you had to go from your twentieth floor office to your eighteenth floor dentist two buildings over, then to lunch on the sixteenth floor of yet a third building then back to work would involve only three short down elevator rides and one moderate up ride. Plus a bit of walking from building to building, but you were going to do that anyway. |
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Baked massively in science-fiction. For instance, the planet Coruscant in Star Wars, and the planet Trantor in the Foundation series. In both, it is said that it is possible (although unlikely because of the distance) to walk the entire circumference of the planet without ever touching ground level. |
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//Elevated walkways are
commonplace.// Yes, they are.
However, as far as I'm aware, they are
intended to provide a route between tall
buildings, and are generally not
intended to provide additional bracing
to the buildings. |
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The main purpose of my connections is
to provide structural stability by
connecting each new skyscraper to its
neighbours. |
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I've been to the Petronas towers and
seen the skybridge, but I got the
impression that it wasn't there to brace
the buildings - they look quite capable
of standing by themselves (but maybe
I'm wrong). |
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Looking at the linked image in
[Anathema]'s other link, this looks like a
retrofit walkway, and again doesn't
seem to be designed to stabilize the
joined buildings. |
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Re the science fiction links, fair enough.
Does anyone know if the walkways
described were there for structural
purposes, or just for access? |
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I've edited the idea to emphasize more
the bracing aspect, and less the access. |
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I feel that this idea fails to take into account all matters in relation to plate tectonics. |
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//I feel that this idea fails to take into
account all matters in relation to plate
tectonics.// Damn. I knew there was
something. Weren't the Tectonics big in
the seventies? |
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I'm sorry Max, but I don't think the intent is what matters here. While the skybridge may not have been created for the purpose of bolstering structural integrity for the Patronus Towers, it's mere presence probably adds some support. Is there any STRUCTURAL difference between your elevated walkways and the ones that exist already? Do you know what existing skywalks are made of, and do you have any architectural knowledge that makes you think you can make them better? |
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One thing you need to consider is that many high-rise buildings are designed to sway in high winds because if it's too rigid it'll break ("what does not bend shall break" to quote a quotable person who's name I cannot recall). If you make a skywalk too rigid it may cause problems when the building tries to sway the way it's intended. |
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Whoa. OK, all I'm suggesting here is
that you could design taller, more
slender skyscrapers if they were
designed from the outset to be braced
by eachother. I don't think this is part
of the design of existing skywalks,
which do (as you suggest)
accommodate independent movement
of the buildings rather than trying to
limit it. That's the "STRUCTURAL"
difference. |
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The "what does not bend shall break"
quote is a bit of a red herring. That's
like saying that all structures should be
as non-rigid as possible. In fact, high-
rise buildings are designed to minimize
swaying, but to tolerate the residual
sway which is too expensive (in
structure) to avoid, without suffering
structural damage. |
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It's a design choice: you either link two
floppy buildings with a floppy skywalk,
or link them to become a single, more
rigid structure with a much heftier
bracing structure. |
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A Wiki quote (I'll post the link shortly): |
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//Skyscrapers have to be flexible in strong winds yet remain rigid enough to prevent large sideways (lateral drift) movement.// |
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This might help, as well: |
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//Thornton-Tomasetti Engineers along with Evergreen Consulting Engineering designed a 662[16][17] metric ton steel pendulum that serves as a tuned mass damper. Suspended from the 92nd to the 88th floor, the pendulum sways to offset movements in the building caused by strong gusts.// |
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I believe there's a connection between, on the one hand, more topologically interesting forms of high-density housing and, on the other hand, higher crime rates. |
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Basically, if there there are lots of walkways, making beautiful use of the third dimension then (1) it's harder to see the burglars, vandals and drug-dealers coming and (2) it's very hard to catch them when they leave. |
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Unfortunately, I'm too lazy to find any links on this subject. |
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//Skyscrapers have to be flexible in
strong winds yet remain rigid enough to
prevent large sideways (lateral drift)
movement// |
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Yes, I agree. However, a more relevant
way of expressing the same meaning, in
the present context, would be to say
that "Skyscrapers have to withstand
such flexing as cannot be avoided."
The fact remains that, the less flexing
there is in the first place, the better. |
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But maybe we're getting sidetracked
and sematicized here. Take an extreme
example - a very very tall, very very
narrow skyscraper (much more
extreme than todays most lithe
buildings). There must come a point
where such a structure could be built
only as part of linked web of buildings.
In effect, we are talking about a giant-
sized space-frame here. |
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I could see something like that possibly working, but I think you'd have to make a large group of the buildings (kinda like a grove of trees) and make the walkway somewhat flexible and stretchy (kinda like those city buses that flex in the center when cornering). An example I think fits here very well is steel-frame houses in hurricane areas. Many of them are designed with special joints that allow the frame to have a little play during high winds. It's like those long dog leashes that mount to a stake in the center of your yard. If a large dogs pulls really hard, it might break when it snaps taut, so what they've done is put a spring mechanism at the point where the leash connects to the stake so no matter how hard the dog pulls, the spring gives a little to cushion the snap effect. |
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//and make the walkway somewhat
flexible and stretchy// Hmmm. I'm not
sure about the whole "flex/don't flex"
concept. |
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My general understanding is that, in all
cases, flexibility is built in either
because (a) you can't eliminate it or (b)
the flexing of some parts of the
structure have to be matched to the
flaxings of other parts. |
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What is the advantage of a building
flexing in the wind? I can see that
elasticity is a bonus for a leash or a
ship's hawser, since the stretch
dissipates a sudden shock. However, in
a building impacted by wind, this won't
be the case - rolling with the punches
won't help. As far as I can figure, you
want the building to flex as little as is
economically possible, but to not be
damaged by whatever flexing there is. |
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