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Need help on clarifying concepts on materials

  1. Sep 27, 2007 #1
    People tell me that a straight column wood is stronger than applying weight on a slanted angled wood. It seems like common sense that theres more force applied on an angled wood but when I try to prove it I can't seem to prove it with math.. Please help me.
     
  2. jcsd
  3. Sep 28, 2007 #2
    Look at the cellular structure of a piece of wood. Then get an empty paper towel roll and try loading it axially and at a slant. See the similarity?
     
  4. Sep 29, 2007 #3

    PerennialII

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    ....and look up material about classical theory of lamina/laminates/composites for the basic theoretical part of how it goes.
     
  5. Sep 29, 2007 #4

    russ_watters

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    This doesn't have anything to do with wood per se, it has to do with the types of forces being applied. If the column is vertical, the only thing you are doing to it is compressing it. If the column isn't quite vertical, you are adding shear and bending moments to it.
     
  6. Sep 29, 2007 #5
    Russ, what you say is true for isotropic materials. However, most common building materials, such as steel or stone, are anisotropic. Wood is one of the worst of these because of the pronounced cellular structure (grain).
     
  7. Sep 29, 2007 #6

    FredGarvin

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    True and not true. The gist of the question seems to hinge on the type of loading of the member. Even most anisotropic materials are stronger in compression than they are in combined loading.
     
  8. Sep 29, 2007 #7
    I quite agree. If the gist of the question is the type of loading, i.e., compressive, axially compressive, shear, combined, etc, then I have given the wrong answer. If, however, the gist of the question is about wood, then I stand by my answer as about 80% of the story and your point being the final 20%.

    (And, I didn't even mention species).
     
  9. Sep 30, 2007 #8

    FredGarvin

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    No doubt about that. If you ever get a chance to download the wood handbook you get a very good appreciation for the variation in material properties amongst the species of wood available in the US.
     
  10. Sep 30, 2007 #9
    I think it would be taking this guys question a bit out of context to start talking about isotropic anistropic and stuff, the basic idea is that a load placed on a vertical piece of wood is just attempting to compress the wood downwards, with no sideways forces, the second example has, as russ pointed out, bending moments applied to it.
     
  11. Sep 30, 2007 #10
    Yes, but

    I guess we could ask the OP what he had in mind but it's more fun to give answers when you don't know the question. However, going back to Fred Garvin's point about the properties of different species in the US, you can easily come to the point of looking at something like hickory or ash where bending strength is quite comparable to longitudinal strength. Hey OP, what did you mean?
     
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