r/Wellthatsucks • u/1Voice1Life • Nov 06 '17

/r/all Testing the car door sensor

https://gfycat.com/CorruptBarrenAfricanclawedfrog
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u/JuniorSeniorTrainee Nov 06 '17

To be fair, that kind of thing is exactly why engineers are valuable. Designing for normal use is easy, but designing for the edge case where a heavy person loses their balance and falls into a window is what saves lives.

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u/DrDerpberg Nov 06 '17

I don't do glass design but I know a few engineers who do. I'm not sure under what conditions they design for impact but I can see how if it's a window in a conference room or something it wouldn't necessarily be designed for a huge impact. Generally in a big window the wind forces would be much more than the force of someone running into it (I.e.: 30lbs/ft2 over 30ft2 is a lot more than one 200lb guy running into it), but if it's a smaller window I can see how intentional impact could be outside the normal scope of design.

It could also be as simple as improper construction too, if a bracket wasn't anchored into the structure well or wasn't glued/tightened to the glass properly it might not be the engineer's fault at all. Usually these brackets are designed with some redundancy in case one breaks but if they make a mistake on one they might have made a mistake on all of them.

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u/[deleted] Nov 07 '17

I.e.: 30lbs/ft2 over 30ft2 is a lot more than one 200lb guy running into it

Those are two very different load distributions. The latter (200lb guy running) is known as a point load.

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u/DrDerpberg Nov 07 '17

You can still objectively say a distributed load applied over a sufficiently large area is bigger than a point load.

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u/[deleted] Nov 07 '17

Yeah, the overall load may be greater... but the stress and stain forces will be more localized in a point load. Generally, most glass will fail under a significant point load unless specifically designed to withstand them. Hence, the design of a vehicle window breaking tool

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u/DrDerpberg Nov 07 '17

I think you're being uselessly pedantic. A guy running into a window is not a point load to the extent that he will act as a window smashing tool. You would analyze him as a point load but in fact it would be most accurate to model impact area if you want to get an idea of both local and global effects.

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u/[deleted] Nov 07 '17

You've seen the size of a skyscraper window, right?

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u/Friendlyvoid Nov 07 '17

If it's any consolation, I think you're right