Quote:
Originally Posted by 10023
What does climate control have to do with it? Are you saying that’s just a visual illusion created by condensation, etc?
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It's got all sorts of effects on how a thin, flexible, material like glass looks. First of all, if the floors not entirely sealed off, just the wind itself can be pushing hard on the glass flexing it out of it's resting state. Then there is the fact that the glass isn't designed to just be at ambient outdoor temperature, it's designed to hold the line between the inside and outside temperatures. It's going to look entirely different when one side is heated the the other isn't than when it's all 30 degrees. I mean think about it, if the glass panels are cut and fitted to the frames in a climate controlled factory where it's 70 degrees and designed to wall off 72 degree temps from whatever is going on outside, of course the glass is going to look funny when the entire panel is chilled to 30 degrees. All of those materials expand at different rates with temperature and it's going to go from a perfectly fitting pane of glass in a metal frame to all kinds of warped as a result.
Also once the enclosure is complete, you have to deal with air pressure gradients in a building of this size. The entire enclosure is designed to work together or you get crazy stuff happening like the doors at the bottom of the Sears Tower blowing out because of the stack effect (they are an ultra strong airlock to prevent this). Also most large HVAC systems like the ones found in a building of this size create a slight positive air pressure which essentially "inflates" the entire glass structure again flexing the glass from its resting state. The point being that glass highrises are designed to balance these forces as much as possible and a piece of glass that's just hanging out there in the air isn't being subjected to those loads.
Climate control is actually one of the more interesting aspects of construction IMO. There's a lot going on there that isn't readily apparent. We even deal with it on small buildings where you must get the building warmed up and keep it warmed up throughout construction if you want to have a perfect result. I just wrote a check to People's gas for $1500 for all the gas I used keeping what was basically a framed shell warm all winter. You have to keep the framing warm or it will move later once you have all the insulation in and drywall done. I've seen 2x4's warp or "walk" (i.e. 2x4's were 16" apart and then ripped loose from their nails and slid along the plate to only be 15" apart as they expanded and contracted) as far as an inch when warmed from below freezing to room temperature. I can't imagine what they deal with when they warm up these concrete supertall buildings after having them essentially open to the elements all winter.
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