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Comment by keiferski | Hacker News Reader

I’d be curious to know the maximum height of a skyscraper that doesn’t have these issues with draining or elevators. Or is the height not actually a problem, only the design of this particular building? Central Park Tower and three others are taller than the one mentioned in the article, although they hint that other towers have similar issues.

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Around thirty stories is the limit for concrete apartment buildings made with unskilled labor (usually Indian or Chinese), so those appear all over Asia and the Middle East where migrant labor is common.

It doesn’t really answer your question, but it’s an interesting reference point.

Thanks, yeah that was sort of my question: what’s the “Model-T” of skyscrapers.

I think the majority of residential towers in Hong Kong are well over 40 floors. Even in the 1990s I remember most buildings that I visited were already over 40.

Are sure it wasn’t 36 or something? Also, not sure how they count floors in HK, but they count them oddly in Beijing, skipping 4, 13, 14, 24, and 34 (if any), which inflates the floor count a bit.

Not completely sure, but AFAICT in post-1990s towns like [1], 45 to 50 floors are fairly common.

[1] https://en.wikipedia.org/wiki/Tin_Shui_Wai

Maybe HK property prices are too expensive so they spend on more skilled labor and not overbuilding the concrete so much? That would allow them to go 40-50 floors with concrete. You can go pretty high with concrete using more advanced building techniques.

> I’d be curious to know the maximum height of a skyscraper that doesn’t have these issues with draining or elevators.

This might be predictable only for elevators (and even then, maybe cable designs/elevator designs can be changed to mitigate the effect of the height).

Everything else can have a design that allows ever larger height (larger vents for drainage, larger pumps for water supply, etc).

It unironically depends on the weather. Specifically the wind. If weight was the only issue we could build towers multiple kilometers high.

Stupid question: If you had sensor good enough, could you build active structures, that anticipate the forces of the wind and angle themselves to "lean" into it, neutralizing the forces at play?

I don't see a problem with anticipation i.e. detect the prevailing forces and apply an equal but opposite force.

I DO see a problem with making the strength on each corner of a building dynamic - if you aren't moving the building back and forth to counter the wind, how would you counter the wind?

One option (almost certainly not practical) would be to have the building shaped like a giant vertical wing, and have it rotate into the wind. It could be tuned to be resistant to wind forces by directing it around, but the apartments may face a different way each day.

Hah, a bit like the roof of an oast house. I like it.

> One option (almost certainly not practical) would be to have the building shaped like a giant vertical wing,

Like a weathercock?

Well, dunno about anyone else, but I'd jump at the chance to live in a (safe) building that always rotated to face the wind.

I originally thought more along some pneumatic nuzzles, basically like direction controll nozzles on a space ship capsule

We are already doing that. Most of these very tall structures have mass dampers, huge weights which are manipulated to compensate the swing induced by wind or ground movements.

That's 1-not active, 2-doesn't compensate, but dampens

Tuned mass dampers don’t but active mass dampers do. Both are in use.

Also damping is achieved by dissipating energy through the counter mouvement of the tuned mass which is literally compensating for the movement put in place by the external force. It doesn’t totally offset it but still.

This is already accomplished passively with tuned mass dampers.

More commonly you'll see things like tuned mass dampers (https://en.m.wikipedia.org/wiki/Tuned_mass_damper) to try to reduce the amplitude of the swaying from wind, earthquakes, elevator vibrations, etc.

So giving this a push, that cancels wind forces out..

No, you don't have to give it a push. You just leave it hanging there and inertia and resonance do the rest.

You would then have to add mechanical devices, which would likely be heavier (requiring even more support structure strength), that would have to move hundreds or thousands of tons of building mass, and with high precision, and then return it to the initial position, while canceling the inertial forces to prevent it from ping-ponging and making it worse. I only have basic engineering knowledge but I can almost hear one of my professors screaming, 34 years later. :)

Many tall buildings have a tuned mass damper near the top that helps to dampen oscillations. It doesn't require any active mechanical devices. Taipei 101 has it out in the open, you can easily find videos of it during earthquakes.

You really, _really_ do not want a skyscraper that collapses if the latest Windows update has a regression.

(I mean, I'm being slightly facetious, but in general things which will kill thousands of people if there's a bug... well, you should be cautious)

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