Just How Tall Can You Build A Skyscraper?

[Catbird]

The air inside a building wouldn't contribute significantly to it's weight, (think of a pail submurged in a swimming pool.) The air does have mass though. This would need to be accounted for when calculating how the building moves in the wind or during an earthquake.

Depends on the temperature difference of the inside to outside air.

That's a good point. The air inside the building would almost always be warmer than outside. That means that inside air would be less dense and have a slight boyuancy.

[mekender]

Does it matter whether or not the structure is sealed,and the air can move freely?

I believe that it does... Like inside the cabin of a 747 for example. I do not know how significant it is though.

[HTRN]

Erik hit on one of the big limits - elevators. Currently there are two big limits for elevators - the cables, and the meat it transports. The cable issue is due to the taller the elevator, the thicker the cable is, to a point where it will snap under it's own weight because of the length. One of the ways they're trying to get around it, is something that was developed for the Navy - Linear elevators. No cables at all.

The other issue is the passengers. Once you go beyond 8m/sec(roughly 1600ft/min), it starts getting unpleasant, because of the shift in air pressure, notably the "popping ears" deal. I know that it's been an issue on some of the high speed Asian elevators in their skyscrapers.

Frankly, it's cheaper and more efficient to build shorter buildings with larger foot prints.

[Yogimus]

Erik hit on one of the big limits - elevators. Currently there are two big limits for elevators - the cables, and the meat it transports. The cable issue is due to the taller the elevator, the thicker the cable is, to a point where it will snap under it's own weight because of the length. One of the ways they're trying to get around it, is something that was developed for the Navy - Linear elevators. No cables at all.

The other issue is the passengers. Once you go beyond 8m/sec(roughly 1600ft/min), it starts getting unpleasant, because of the shift in air pressure, notably the "popping ears" deal. I know that it's been an issue on some of the high speed Asian elevators in their skyscrapers.

Frankly, it's cheaper and more efficient to build shorter buildings with larger foot prints.

Neither one of those is the reason elevators become an issue.

[HTRN]

Yes it is - Nova did a special on Elevators a coupla months ago. When you have a rep from Otis explaining why elevators can only go so tall and so fast, I tend to take them at their word.

The cable thing means they can't effectively build higher than a certain point. I think the Kalifa towers elevators have six and half miles of cable, weighing nearly 30 tons.

[Yogimus]

Yes it is - Nova did a special on Elevators a coupla months ago. When you have a rep from Otis explaining why elevators can only go so tall and so fast, I tend to take them at their word.

The cable thing means they can't effectively build higher than a certain point. I think the Kalifa towers elevators have six and half miles of cable, weighing nearly 30 tons.

Nope, that's maximum capability. The true limitation will hit WAY before that.

[HTRN]

So you're arguing semantics?

[Termite]

What about using rack gears on the shaft walls, with the elevator attached to a carriage with electrically driven pinion gears?

[Yogimus]

Each elevator has a footprint, as well as a finite number of floors it can service based on occupancy/floor occupancy. REGARDLESS of the speed of the elevators, the time of loading/unloading of a single person is significant enough to require multiple shafts. More shafts = more floorspace of the building being used, until there are literally nothing but elevators in the building. This limit is reached before max-height is reached, assuming every floor is a possible stop.

[Netpackrat]

What about using rack gears on the shaft walls, with the elevator attached to a carriage with electrically driven pinion gears?

Might be an inspection nightmare. Cables you can pretty much inspect visually; gear teeth you might have to UT each tooth individually at some regular time interval.