Quote:
Originally Posted by Don098
The PA is a poor source of information, honestly. Are there any true engineers on here that can address this myth? I have an extremely hard time believing that air pressure inside a building would even approach the PSI needed to bend glass, especially when this building has windows, doors, and other entry ways the reduce any air pressure that could otherwise be built up in a vacuum. Without a seal, I think this myth is completely impossible.
Please provide sources and visual proof. Zen, I don't see any "rather obvious" evidence of a protective film, which to me, would include things like non-reflectivity, an obvious reduction in transparency, and dirt/dust buildup. As much as I'd like to believe you guys, I need proof. Thanks
SPECTACULAR PHOTO UPDATE! If only I could stumble upon these types of posts more often...
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Ok... some engineering rigor is what you ask for, eh?
From Advanced Strength of Materials by J.P. Den Hartog, page 184
Quote:
Case 24. Rectangular plate ab under uniform loading p, clamped along all edges":
Max deflection = u*p*a^4/(E*t^3)
Where u is a constant based on the ratio of length / width of the plate
ratio=1; u=0.138
ratio=1.6; u=0.0251
ratio=2; u=0.0277
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p = Pressure (I found somewhere that 0.00145 psi as an interior to exterior differential in a building, but I will defer to Zen if he has another number)
a = the width of the plate (bottom of the ratio, from above)
E = Young's modulus (i used 9.6e6 psi)
t = thickness (i guesstimated 1 in... Zen?)
So... for my estimate...
length = 120 in (10 ft)
width = 60 in (5 ft)
ratio = 2
max deflection of 0.0000542 in
It's very small... however, I will admit, I'd expect on a a very reflective surface, small deflections can appear larger...
I will be glad to recalculate with more accurate info, if you have it.