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Shear flow in hollow beam

  1. Nov 26, 2016 #1
    1. The problem statement, all variables and given/known data
    for shear flow at D , the Q = Ay , i tried another method , i gt 30000 , instead of 29750, why the ans is different from 29750? why cant i use this method( i break the shaded area into 3 parts ( as shown in figure)

    2. Relevant equations


    3. The attempt at a solution
    Q = Ay = (60x10x35) + (2x30x10x150 = 30000

    http://imgur.com/a/VXDK6
     

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  2. jcsd
  3. Nov 26, 2016 #2

    PhanthomJay

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    The author is wrong the Q is 30 in^3 I don't know why you added those zeroes to get 30000
     
  4. Nov 26, 2016 #3
    http://imgur.com/a/VXDK6
    here' my working , Q = Ay = (60x10x35) + (2x30x10x150) = 30000 , or the author's working 29750 is correct ? which cut is correct ? My cut of section into 3 parts is different from the author's working
    , sorry , i posted the wrong notes...here it is
     

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  5. Nov 26, 2016 #4

    PhanthomJay

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    Ok then you are correct, good work..
     
  6. Nov 26, 2016 #5
    do you mean the author cant cut the beam like this ? why ?
     

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  7. Nov 26, 2016 #6

    PhanthomJay

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    The author cut the beam at the neutral axis to determine Q about the neutral axis, just like you did. But the author messed it up and didn't calculate the areas correctly, what more can I say you are right and they are wrong. Let it be!
     
  8. Nov 28, 2016 #7
    no , i am concern about how should the beam be cut ? i divided the beam into 3 parts like this(red) , whereas the author divided the beam into 3 parts like this (green), i gt 30000 , but the author gt 29750 , there's a difference of 250 , which is correct ?
    i checked thru the author's my working using calculator , i gt 29750 based on his working
     

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  9. Nov 28, 2016 #8

    PhanthomJay

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    come on now I keep telling you the author made a mistake !!!!!

    He/she did not use those green areas...they dimensioned incorrectly. The numbers come out to 27500, but the numbers inputted are wrong. The correct ans is 30,000 mm^3.
     
  10. Nov 28, 2016 #9
    sorry , i messed up QC and QD , question solved
     
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