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Variation of shear stress at the rectangle cross section

  1. Nov 26, 2016 #1
    1. The problem statement, all variables and given/known data

    In the notes , I dont understand why the shear stress is maximum at the edge ( circle part) .
    2. Relevant equations


    3. The attempt at a solution
    I think it's wrong . Refer to another diagram attached , i found that the shear stress varies parabolically across the vertical length of the beam ... Or they are different case ? Can you explain the case in photo 1 ?
     

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  2. jcsd
  3. Nov 27, 2016 #2

    PhanthomJay

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    fonseh you are getting way too deep on this this is grad school level stuff. Stick to the basics. Vert shear stress distribution is parabolic along the height and horiz shear stress is linear across the flange. You may assume that it is constant across the thickness of the web or flange or rectangle,
     
  4. Nov 27, 2016 #3
    ok , that's the explaination for figure 2 in post # 1 , and I understand it . Can you explain based on figure 1? what is it about ? I dont really understand it
     
  5. Nov 27, 2016 #4
    It's also stated at the bottom of the notes, the shear formula will not give accurate results when used to determine the shear stress at flange -web section, stress concentration here ... why the shear formula is not suitable to caluculate the stress at stress sudden change part ?
     
  6. Nov 27, 2016 #5

    PhanthomJay

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    The shear stress formula is an approximation which is good enough for most applications. If you want to learn grad school topics at this stage, , like stress concentrations at discontinuities or non constant shear stress across a width, then first learn about partial differential equations and then google on Theory of Elasticity and then I wish you luck.
     
  7. Nov 27, 2016 #6
    do you mean the notes in photo 1 is another way we can find the shear stress which is at grad school stage ?
     
  8. Nov 28, 2016 #7

    PhanthomJay

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    Yes, but it is quite complex to get an exact solution and you should not dwell on it. I was ready to quit engineering when I took elasticity theory in grad school land I've long forgotten it except to know that sttess concentrations occur at corners and edges and holes . Forget about it!
     
  9. Jan 3, 2017 #8
    just to be sure , the figure in 7-6 a and 7-6 b is the view of the blue plane, am i right ?
     

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  10. Jan 4, 2017 #9

    PhanthomJay

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    Yes, that is the plane, but the plane is within the beam at a cut cross section. The vertical (and longitudinal) shear stress is maximum at the neutral axis and can be assumed constant across the width of the section, although in actuality is higher at the edges of the neutral axis.
     
  11. Jan 4, 2017 #10
    thanks , i am much clearer on this concept now !
     
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