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Stresses and neutral axis

  1. Mar 14, 2009 #1
    Hey guys,

    A picture of the question is attached, I am not seeking answers just an explanation of some theory.

    Now I understand that

    point A will be under compression due to the weight, tension due to the bending and shear due to torque produced by the wind

    point b will be under compression due to weight, tension due to bending (but different tension to point A because of the different moment) and shear due to torque produced by the wind

    point C will be under compression due to weight and compression due to bending and shear due to torque produced by the wind

    Now when applying the bending stress equation (MY/I) wouldn't either point B and C together or point A on its own lie on the neutral axis? And hence the bending stress would be zero Or would Y (distance from the neutral axis) always be 50mm?

    http://img23.imageshack.us/img23/5238/1233333333.th.jpg [Broken]
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 15, 2009 #2

    nvn

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    VooDoo: If the top edge of the sign is parallel to the y axis, and the x axis is vertical, then points B and C lie on the neutral axis for moment My, and point A lies on the neutral axis for moment Mz.
     
    Last edited: Mar 15, 2009
  4. Mar 15, 2009 #3

    Astronuc

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    If the wind is blowing into the sign (into the page/screen), the A will be under tension. The force would apply a torque about the axis through BC. If the wind blows out of the scree/page, then A would be under compression.

    One has to look at the distance a point is from the axis of rotation, and the torque applied with respect to that axis.

    The post and sign apply a downward load on the base. Torques apply a tension or compression depending on whether they rotate away from or toward a point.

    The base is a cantilever joint.
     
  5. Mar 15, 2009 #4

    PhanthomJay

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    Annd don't forget the longitudinal shear from the wind load, maximum at the transverse neutral axis.
     
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