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Timber beam moment/deflection

  1. Jul 12, 2012 #1
    Hello everyone,

    I have a question regarding the moment and deflection calculation of this handrail beam that I have. I am attaching a picture to give you guys a look at what I am working with.

    The hand railing is 4" x 4" and it is not attached half way, its just resting on that beam, it is however attached with a bolt at the bottom. My question is, when im looking for the resisting moment would I take 89/2 in the section modulus calculations or the full 89mm. Same goes for deflection, when I do the moment of inertia, would I do the full 89 mm or 89/2. If it is 89/2 then how would I incorporate the rest of the beam in the resisting moment/deflection or would it have no effect on it?

    any help would be greatly appreciated, thanks!

  2. jcsd
  3. Jul 12, 2012 #2


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    blackbird2552: In general, it appears you would use (89 - 38) = 51 mm, and 0.5*51, in the section modulus calculation, for the bending stress calculation. You would also use 51 mm in the moment of inertia calculation, for the deflection calculation. The 89 mm portion of the handrail beam would have little or no effect on the deflection.
  4. Jul 13, 2012 #3
    Thank you so much! that is exactly what i needed confirmed and also thanks for clearing up my concept.
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