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Homework Help: Maximum bending moment

  1. Jun 25, 2016 #1
    1. The problem statement, all variables and given/known data
    how the author found the maximum moment = 0.29MNm ? is there any formula ? how to find it in this question ?
    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 25, 2016 #2


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    Of course there's a formula. That's what beam tables are for - too look up things like the maximum B.M. without having to work them out from scratch all the time.

    Here is a set of typical beam tables:


    Your beam is Figure 1, page 4.

    BTW, the calculation of the total weight of the wall above has a small error. W = 0.145 MN, rather than 0.145 kN.
  4. Jun 25, 2016 #3
    the shape is rectangular cross section , am i right ? why the moment shouldnt' be a(b^3) / 12 ? but , a(b^2) / 8 ?
  5. Jun 25, 2016 #4
  6. Jun 26, 2016 #5


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    The problem is trying to figure out the dimensions of the cross section of the beam so that max. bending stress is limited to 7.5 MPa.

    Remember, in bending, σ = M ⋅ y / I

    It is postulated that the beam supporting the brick wall is twice as deep as it is wide, or w = b and d = 2 ⋅ b, and I = w ⋅ d3 / 12 and y = d/2
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