# What is the practical limit on tall buildings? **URL:** \ **Category:** Factual Questions\ **Created:** [April 19, 2014, 2:12pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485 "2014-04-19T14:12:13Z")\ **Posts on this page:** 17\ **Page:** 4
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [April 30, 2014, 3:42pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/61 "2014-04-30T15:42:03Z")
> [@Quercus](#): > > Can someone explain the ‘Keira’ joke? That’s the name of the little girl who asked the question at the top of the page. ---
**Author:** ![Folacin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/folacin/32/3195_2.png) [@Folacin](https://boards.straightdope.com/u/Folacin)\ **Post date:** [April 30, 2014, 3:43pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/62 "2014-04-30T15:43:03Z")
> [@Quercus](#): > > Can someone explain the ‘Keira’ joke? From the XKCD forum, the assumption is that Keira is the name of the little girl who wants to build the billion story tower. Ninja’ed ---
**Author:** ![SpyOne](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@SpyOne](https://boards.straightdope.com/u/SpyOne)\ **Post date:** [April 30, 2014, 3:46pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/63 "2014-04-30T15:46:19Z")
> [@Quercus](#): > > Can someone explain the ‘Keira’ joke? Keira was the name of the little girl who wanted to build a billion-story building in the question he was answering. ---
**Author:** ![SpyOne](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@SpyOne](https://boards.straightdope.com/u/SpyOne)\ **Post date:** [April 30, 2014, 3:53pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/64 "2014-04-30T15:53:42Z")
> [@Siam\_Sam](#): > > I’ve heard that the sway in skyscrapers helps them during earthquakes, that because of it the building stands a better chance of riding out an earthquake than does a low-rise building that ends up a pile of matchsticks. True or no? The way I heard it, the biggest danger to a building in an earthquake is when the oscillation of the building matches the osculation of the earthquake. This is why the quake in Kobe in the late 90s damaged a lot of buildings engineers thought it shouldn’t have damaged. Taller buildings osculate slower, due to being an upside down pendulum. I have heard this is useful in an earthquake, but lack the technical expertise to know mow helpful that is. ---
**Author:** ![SpyOne](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@SpyOne](https://boards.straightdope.com/u/SpyOne)\ **Post date:** [April 30, 2014, 4:18pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/65 "2014-04-30T16:18:56Z")
> [@Exapno\_Mapcase](#): > > I don’t know what you mean by this Okay, I’ll try to be clearer. I’m not talking about anything like that Levilator, where the cars can pass each other. I mean two separate elevators, serving different sets of floors, whose shafts are stacked one on top of the other. So that there is an elevator that serves floors 1-10, but if you take note of the exact longitude and lattitude of the door to that elevator on the ground floor, then go to that longitude and lattitude on floor 11, you’ll find a door to _another_ elevator, one that serves floors 11-19. The advantage is this: instead of building 6 elevators that serve all the floors in the building, I build 2 that serve 1-10, and two that go express to 11, where two more elevators serve 11-19. I only gave up space in the footprint for 4 elevators in the bottom 10 floors, not 6. This example is riddled with flaws, but I hope it gets across what I’m describing. flaws include that not all 6 elevators need to go all the way to the top, that in such a short building 2 express elevators is probably a waste, and that the system I’ve described probably can’t handle as many people as quickly as 6 elevators could. > [@](#): > > This introduces long wait times into almost every elevator ride instead of just some. Wait times are already a limiting factor. Wait times are certainly an issue, and this system certainly would require multiple waits for most journeys, but those waits needn’t be long. It is a difficult balance between number of elevators (non-revenue space) and wait times. I think I used to know the accepted standard for how long a wait for an elevator was considered too long, but I can’t recall it. My point is simply that, while getting the wait times down to acceptable levels may be challenging, the method for tackling that challenge is well established. > [@](#): > > The Willis Tower elevators - they have 104, BTW, top out at 8.1 m/s. The Taipei 101 building has elevators that top out at 16.8 m/s. But I was talking about acceleration, not speed. One can always (theoretically, and within limits) design a faster elevator, that won’t help you if it accelerates fast enough to make folks barf. > [@](#): > > The emergency needs for a tall building are different from those of a city of separate smaller builders with varying degrees of construction safety built in. But are they really so different that they become economically unfeasible? Why should a tall building require so much more in emergency services than the same population (residences, retailers, and industry) spread over 6 square miles? > [@](#): > > The Petronas Towers in Kuala Lumpur are connected by a skybridge that is designed partly to increase support during sway. And that bridge was the focus of a lot of the stuff about how impressive the engineering was when it was built. I didn’t mean to imply that I thought high-level skybridges were _impossible_, just that they aren’t particularly easy, and that I doubt we’ll see multiple bridges connecting multiple towers, especially towers (and therefore bridges) that were not all built at the same time, any time soon. I was going to say “in our lifetimes”, but I plan on sticking around for a while, and the world changes pretty fast these days, so maybe. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [April 30, 2014, 4:40pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/66 "2014-04-30T16:40:14Z")
> [@Exapno\_Mapcase](#): > > I don’t know what you mean by this. The Willis (nee Sears) Tower has 16 double-deck (i.e. multiple floor) elevators, but I don’t think it has multiple elevators in a single shaft. In fact. I don’t think any tall building does. The WTC towers had this system, otherwise known as [sky lobbies](http://en.wikipedia.org/wiki/Sky_lobby). Express elevators served floors 1, 44, and 78. Local elevators served the sky lobbies and the floors above. So you had three short colinear elevator shafts instead of one long one. I think **SpyOne** was thinking of the John Hancock center, which has sky lobbies. The Sears[sup]1[/sup] Tower doesn’t. ETA: Actually, according to that Wikipedia page the Sears tower _does_ have one sky lobby, which conflicts with my memory of the place. I will assume that Wikipedia is mistaken and that I remain infallible. [sub]1. Whatchoo talkin’ 'bout, Willis?[/sub] ---
**Author:** ![SpyOne](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@SpyOne](https://boards.straightdope.com/u/SpyOne)\ **Post date:** [April 30, 2014, 7:58pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/67 "2014-04-30T19:58:10Z")
Indeed, that would be what I was trying to describe. I wasn’t thinking of the John Hancock Center specifically, although it appears to be the first built of the 29 buildings wikipedia mentions as using it. As their illustration of how it worked in the World Trade Center shows, the local elevators that served floors 44 through 77 are directly above the local elevators that served floors 1 through 43, and the local elevators that served 78 through the top were above the local elevators for floors 44-77. (Although it is worth noting that in at least several examples, not all of the local elevators at a given lobby reach all of the floors in that section. The John Hancock offers the simplest: express to 44, where elevators then serve either 45-65 or 65-92. Locals going from the lower half to the upper half of the condos may either go down to 44 or up to 65 to change elevators.) I had mistakenly described this as “multiple elevators in one shaft” because, … I hadn’t realized that many of the local elevators actually stopped well before reaching the next lobby up, so they don’t have a continuous shaft through the building. But on those elevators that do reach all the way, that is effectively what they are: one shaft through the building, but three elevators in that shaft. No need to go around one another because none serves a floor that the others would pass. The top one never goes below 78 (for the WTC), and the one below it never goes above 77, so there’s no conflict. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [April 30, 2014, 8:14pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/68 "2014-04-30T20:14:08Z")
One problem with the sky lobby system is intra-building travel. For example, say you have a 200-storey tower with sky lobbies on 50, 100, and 150. If you work on the 152nd floor, you have to take the express elevator to 150, then the local to 152. No big deal. But suppose you want to visit your colleague on 148, just four floors away. You’d have to go down to the 150 sky lobby, then take the express all the way down to 100, then the local up to 148. (Remember, your local elevator only serves 150-200.) That’s a journey of nearly 100 floors just to go 40 feet. My proposed solution to this problem is to have large, three-story atriums at each sky lobby. (If you’re building a 200-floor tower, you can afford the space.) The sky lobbies would be large mall-like meeting places with restaurants and stores and such, rather than just a transfer point. So our hypothetical sky lobby would occupy floors 149-151. The express elevator would stop at 150, then you could take escalators to the local elevators on 149 (down to 100) or 151 (up to 200.) That gives you a one-floor buffer zone between colinear elevators but makes them easily accessible going in either direction. This makes intra-building trips much more efficient. Now you can take the local elevator from 152 down to 151, grab a snack on 150, then take another local elevator to 148. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [April 30, 2014, 8:42pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/69 "2014-04-30T20:42:44Z")
> [@friedo](#): > > This makes intra-building trips much more efficient. Now you can take the local elevator from 152 down to 151, grab a snack on 150, then take another local elevator to 148. Or, walk down four flights of stairs. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [April 30, 2014, 8:55pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/70 "2014-04-30T20:55:39Z")
> [@Telemark](#): > > Or, walk down four flights of stairs. Good luck transiting any large office building via the stairs. A lot of them have doors that only open from the occupied areas, to be used for emergency egress only. ---
**Author:** ![SpyOne](https://avatars.discourse-cdn.com/v4/letter/s/82dd89/32.png) [@SpyOne](https://boards.straightdope.com/u/SpyOne)\ **Post date:** [May 1, 2014, 12:45am UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/71 "2014-05-01T00:45:43Z")
> [@friedo](#): > > just four floors away. You’d have to go down to the 150 sky lobby, then take the express all the way down to 100, then the local up to 148. (Remember, your local elevator only serves 150-200.) That’s a journey of nearly 100 floors just to go 40 feet. Actually, there is probably no elevator that stops at both 150 and 100, so you’ll have to go all the way down to the ground, get on the express to 100, and then take the local to 148. 300 floors to travel 40 feet. > [@](#): > > Good luck transiting any large office building via the stairs. A lot of them have doors that only open from the occupied areas, to be used for emergency egress only. Yeah, there’s a trend that has to stop. Seriously. As we all get more fitness conscious and such, it ought to be possible for folks to walk a couple of flights of stairs if they so choose. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [May 1, 2014, 1:51am UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/72 "2014-05-01T01:51:35Z")
I always love these internet discussions among young, healthy people proclaiming that everybody can use stairs. It’s no big deal. News flash: you’re wrong. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [May 1, 2014, 2:14am UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/73 "2014-05-01T02:14:30Z")
> [@Exapno\_Mapcase](#): > > I always love these internet discussions among young, healthy people proclaiming that everybody can use stairs. It’s no big deal. > > News flash: you’re wrong. Hey, I’m on the far side of 50 and I understand that taking the stairs isn’t a solution for everyone. But it is an option for a lot of people and some use of the stairs may alleviate the need for 3 story atrium every 50 floors to avoid some walking. Obviously there will still need to be solutions for the mobility impaired, but there are other solutions. ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [May 1, 2014, 2:25am UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/74 "2014-05-01T02:25:36Z")
I’m leaning toward Joe Hamilton myself now. The nose looks right. [Check out these images](https://www.google.co.th/search?q=%22joe+hamilton%22+burnett&tbm=isch&tbo=u&source=univ&sa=X&ei=G69hU5PCA6-TiQeq8oGwBg&ved=0CDkQsAQ&biw=1024&bih=629). ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [February 22, 2016, 2:21pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/75 "2016-02-22T14:21:40Z")
Bumped. PBS’s _Nova_ had an episode awhile back on supertall and megatall skyscrapers. The consensus among the engineers, architects and scientists interviewed seemed to be that if you have the money for it, there’s no practical upper limit to skyscraper construction. There’s now a proposal for a mile-high tower in Tokyo: [Dizzying Heights: A mile-high skyscraper - CNN Style](http://www.cnn.com/2016/02/10/architecture/tokyo-mile-high-skyscraper/index.html) ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [February 22, 2016, 2:36pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/76 "2016-02-22T14:36:27Z")
> [@Siam\_Sam](#): > > I’m leaning toward Joe Hamilton myself now. The nose looks right. [Check out these images](https://www.google.co.th/search?q=%22joe+hamilton%22+burnett&tbm=isch&tbo=u&source=univ&sa=X&ei=G69hU5PCA6-TiQeq8oGwBg&ved=0CDkQsAQ&biw=1024&bih=629). Huh. I seem to have posted the above in this thread by mistake a couple of years ago. Think it was supposed to go in that one where they were trying to identify the mystery man on Johnny Carson. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [February 22, 2016, 5:48pm UTC](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485/77 "2016-02-22T17:48:39Z")
I was wondering. He didn’t look _that_ tall to me. [Previous page](https://boards.straightdope.com/t/what-is-the-practical-limit-on-tall-buildings/686485.md?page=3)