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Re: Structual Design of Glass

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I know this is late, but I really don't trust glass as a structural component. The performance is too tightly tied to fracture mechanics, and is highly dependent on flaws in the product. This may be too paranoid when looking at tempered products (most of my experience is with annealed), but it's a poor choice of product where a single point failure can cost a life.

Glass fails by propagation of cracks, often over many sub-critical cycles. The common theoretical construct is the penny shaped crack (flaw) which grows over time under cyclic loading until the section is no longer viable and a catastrophic failure occurs. Any scratch can initiate a fracture point, and impacts can do the same. Sometimes the fracture cannot be easily detected by visual methods. Unfortunately, architects and owners don't want to hear this. Nor do they want to hear that the proper use of glass should require periodic proof testing; not something that can be easily done. The classic scenario is that a panel is analyzed for the critical flaw size and associated failure stress. Then a test is performed which , by analysis, will induce a stress high enough to essentially guarantee failure, give that a flaw of the critical size exists. By estimating a loading time history for the installed panel, it may be determined how quickly a crack of the critical size above will grow to the point where a code-level load will cause failure. That interval is your testing frequency.

Over time, a glass panel which proof tests fine at installation will see a reduced strength. As I said above, my experience is with annealed glass (mostly for optics in vibration/pressure environments), so this may not be applicable for tempered. Just food for thought.


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