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Wood rupture - the figures seem strange.

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Adam Frisch

Member
Joined
Jul 22, 2008
Messages
21
Location
London and Los Angeles
Hi.

I'm all new to this, but in my efforts to get my head around certain structures for my design, I need your help. I have access to Birch on my own land, but this could apply to any wood. Here is a list of structural properties for various woods.

http://www.csudh.edu/oliver/chemdata/woods.htm

Now if you look at Birch wood it for the yellow variety gives a Modulus of Rupture of 11.88kg/mm2. This is, as I understand, the breaking or bending force required to break a cross section of 1mm2 of the wood. So one square millimeter would need 11.88kg to break it off.

But here's what I don't get - common sense says there's no way that could be the case. A toothpick is probably about 2-3 square millimeters in cross section and it certainly does not take 22-33kg to break that. Maybe a tenth of that.

What am I not getting?

And is there a good online site that even a dummy like me can get this explained? I have a degree in civil engineering from 15 years ago, but I can't recall a single thing since I never went into that kind of work.

Thanks.
 
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