View Single Post
Old Posted Jul 22, 2007, 5:35 PM
Pandemonious's Avatar
Pandemonious Pandemonious is offline
Chaos Machine
Join Date: Nov 2002
Location: Chicago
Posts: 1,290
Originally Posted by Pandemonious View Post
the tower in that rendering has a height ratio of over FIFTEEN TO ONE... almost DOUBLE what is considered the UPPER END of what is economically feasible for a supertall building (Note: I didn't say it was impossible to build).QUOTE]

Offtopic but could you explain to me something I've never been able to understand? How come there exists such a precise height to width ratio limit for supertall towers? Surely this limit only applies to office use or something where an insane amount of people are in the tower at one time and so the building needs a huge amount of elevators. What would be the limit then for an upper class res tower like the Chicago Spire which definitely doesn't need as many elevators?

I ask because people always talk about this limit when there are tons of supertall towers getting built with a ratio of 10:1 or even more. The Chicago Spire looks really thin, all those crazy tall res towers in Dubai as well, etc
Yes, there are towers that approach larger ratios than the roughly 8:1 (for concrete and/or composite structural systems) that is the higher end I speak of, however.. they are not yet built. CS will have over 9:1... but it is designed more like a mast-like tower (A-la 7SD, the top of the burj is more like just a huge mast like tower also, since the floorplate outside that is so small, but BD has an ENORMOUSLY wide base where the three petals flare out). This concept has ABSOLUTELY NOTHING to do with floor loads, elevator space, or use of building. In fact, an enormously tall building due to height to width ratio, typically will have such a huge base that even a conventional elevatoring system is sometimes possible. This concept of height to width for a supertall buildings is more to do with the building resisting the overturning forces of the wind. It is a simple concept.. a building is so tall, it has so much wind blowing on it, and somehow all of that wind load must be redirected down into the foundation. If a building is too tall and too thin.. that becomes approachingly economically unfeasible given the amount of extra strcture that must go into it... also affecting other aspects of the useability of the structure in the process. It is not some "precise" number as you describe it but can very depending on many factors..
My Diagram:

Last edited by Pandemonious; Jul 22, 2007 at 5:51 PM.
Reply With Quote