Tension vs compression

Discussion in 'Crane Use' started by Phil, Jan 10, 2011.

  1. Phil

    Phil Member

    I took this from another post so as not to derail it.

    [ QUOTE ]
    Engineers use it (wood being 5x stronger in tension) as design guide when designing wood structures. Its 5 times stronger when you are pulling on it than if you are pushing on it or trying to put pressure in the middle.

    On construction sites contractors have had us try to lift a single 2"x4" out of concrete and we lifted 3000# on it and it didn't budge.

    [/ QUOTE ]

    if you bend a straight branch (or 2x4) in to a "U" shape you create tension wood on the outside of the bend and compression wood on the inside of the bend. When the branch finally brakes, it brakes the tension wood first. So does this mean compression wood is even stronger than tension wood?

    Is there anyone that can take a 2x4x6" and pull it apart and take the same size piece and try to crush it? I'm just curious.
  2. SingleJack

    SingleJack Member

    The following PDF link to the USDA, Forest Service, Forest Product Lab may be helpful:

    Wood: Strength and Stiffness

    The data in Table 2 appears to conflict with the "5 times stronger" statement. And, as with everything else in tree work, compression vs. tensile strength is very species dependent.
  3. Jamin_Mayer

    Jamin_Mayer Active Member

    Nice link.

    We should get C.E.U.'s for reading all of that. [​IMG]
  4. classictruckman

    classictruckman Well-Known Member

    According to that table wood is generally 2x stronger in tension than compression and almost 10x stronger than shear force. And bending is almost as strong as tension force.
  5. SingleJack

    SingleJack Member

    FWIW - A note of caution about tensile loading of wood

    <u>Just in case</u> there is some intent by the OP (or anyone) to use wood as a structural element under tension, it should be noted that joint design and attachment method are critical. A poorly designed wooden attachment will fail in compression or shear long before maximum tensile strength is realized. It is 'old-world' technology so there are many excellent reference sources available.
  6. classictruckman

    classictruckman Well-Known Member

    That is very true, structural flaws will cause failure long before you reach the tensile strength of the wood.

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