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]
-- MaxwellBuchanan, Sep 11 2007

Underground skyscraper Underground_20Skyscraper
Annotations herein suggested this idea. [MaxwellBuchanan, Sep 11 2007]

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.
-- Galbinus_Caeli, Sep 11 2007


//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.

The main purpose of my connections is to provide structural stability by connecting each new skyscraper to its neighbours.

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).

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.

Re the science fiction links, fair enough. Does anyone know if the walkways described were there for structural purposes, or just for access?

I've edited the idea to emphasize more the bracing aspect, and less the access.
-- MaxwellBuchanan, Sep 11 2007


I feel that this idea fails to take into account all matters in relation to plate tectonics.
-- Texticle, Sep 11 2007


//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?
-- MaxwellBuchanan, Sep 11 2007


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.

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.

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.
-- MaxwellBuchanan, Sep 11 2007


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.

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.

Unfortunately, I'm too lazy to find any links on this subject.
-- pertinax, Sep 12 2007


//Skyscrapers have to be flexible in strong winds yet remain rigid enough to prevent large sideways (lateral drift) movement//

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.

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.
-- MaxwellBuchanan, Sep 12 2007


//and make the walkway somewhat flexible and stretchy// Hmmm. I'm not sure about the whole "flex/don't flex" concept.

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.

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.
-- MaxwellBuchanan, Sep 12 2007



random, halfbakery