Quote:
Originally Posted by Toasty Joe
seems like more office buildings built in the last 5 years in Chicago have used reinforced concrete, sometimes a mix of steel & concrete - see some recent posts in the BMO tower thread[/url]
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That's only true for office buildings below a certain height/size. Every large (somewhat arbitrary, but I'll use ~30+ stories, ~600,000+ sf) 'Class A' office tower - with only one exception - built this century in downtown Chicago has been composite structure (concrete core with steel frame). And - the lone exception was not a concrete frame - it was a rarer entirely steel structure (steel core + frame) at 131 S. Dearborn. As I recall, the reason a steel core was selected for that construction was that the project heavily re-used the existing deep foundations from the prior demolished structure on the site, and to accommodate, they selected the significantly reduced load of the all steel structure. The price of steel (again as I recall) was fairly low at the time, and that no doubt factored at least partly into the decision as well.
I believe that a major reason why you increasingly now see a mix of composite structure and all concrete structure for mid-rise and smaller high-rise office here (still somewhat more composite than concrete) is that the concrete frame plays into the 'lofty'/creative space office aesthetic that has marketplace appeal among office tenants (some more than others). It's not necessarily my thing (I don't dislike it though) per se, but I certainly 'get it'. There are also technical construction/engineering/commodity price factors at work without a doubt - but office space market factors are a clear driver in my view.