^^^ Those look like they are thread caps for conduit piping.
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Originally Posted by spyguy
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So this is what I've been hearing about. I believe I mentioned a while back that I heard there would be some crazy structural acrobatics in order to revert the columns that were configured for a triangular tower back to a square floor plate. I heard the word "cantilevered" mentioned, but figured they were talking about just cantilevering the SE corner and building out the rest of those floors like normal, but wow is this a lot to take in.
In my opinion this is an absolutely awesome solution to the problem. They had to canatalever the floors over the SE corner because the columns there were not designed to bear any more weight than what they already do. I heard it was modern as well, but that top is just sick.
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Originally Posted by J_M_Tungsten
I agree. It does look odd with the two combined like that, but the upper part is pretty damn cool looking IMO. I doubt this is a final design, and I doubt the ability of the core to support a 30+ story cantilevered building above it. The original wasn't designed to do anything remotely like that. Reminds me of jenga when you only have one piece near the bottom supporting the top.
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This isn't just a response to you Tungsten, but to address all the comments on the cantilever:
The cantilever here is not a aesthetic decision, I've been hearing for months about this from someone I know who is involved in the project. They had two options here to maximize zoning: either build the tower as designed or find a way to cantilever out over the SE corner of the existing structure which was not designed to support additional floors. Apparently the costs of building it taller were greater than the costs of creating a funky cantilever and they are going with the cantilever.
From what I've heard they are going to be almost nothing in the way of "demolition" on the existing structure and will simply modify the current transfer floor to distribute the load from the core (which is certainly capable of holding the weight) to the large perimeter columns. Then they obviously will build a new transfer floor after the cantilever to rearrange the columns into a usable format. Again, I had assumed they would only cantilever the portion of the building over the SE corner, not the whole way around, but man is this an awesome solution to the problem. Perfect for Chicago, form follows function, we only get a huge cantilever when we need one to solve a problem!