Quote:
Originally Posted by 10023
Question for you: is this the main determinant of Chicago's prevailing building heights (particularly for office towers) in comparison to NY's?
I had always assumed it was about economics rather than engineering, but I'm curious.
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Engineering and Economics are very intertwined. Buildings cost what they cost largely because of engineering issues, and height above a certain range is definitely one that can increase cost rapidly. It's not that Chicago can't physically build very tall buildings due to some inherent geographic constant. It's just that there is a sweet spot where the engineering challenges do not get too crazy such that structure or mechanicals costs sky rocket. Economically, with the rents in Chicago, it seems like it does not make much sense to blast past that sweet spot.
For example, a very common structural system for office buildings in chicago is to use a centered concrete core wall with gravity only framing surroundings, attaching to the center core. In this system, the centered concrete core is the only element designed to resist wind loads. The gravity columns/beams are only there to hold up gravity loads (not wind). When you get much taller taller than 50 floors, you usually need to engage more of the structure to help resist wind loads. Trump tower, for example, has a central core, but also uses some exterior columns in the lateral system. Those columns need to be tied to the core using outrigger levels, so the core and exterior lateral columns all work together. The analogy always used is a skier with ski-poles. All of that junk makes the structure way more expensive than if they were able to do it with only the center core. This makes developers think twice about breaking some theoretical height value. If, like in NYC, the rent prices are so high that adding 40 more floors and paying for more complicated structure, elevator and mechanical systems, they do it.
http://www.ctbuh.org/LinkClick.aspx?...=krBBJjwsWjo=&