1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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 ?
    ZoRseq4.jpg
    kKIQSpL.jpg
    2. Relevant equations


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

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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:

    http://www.awc.org/pdf/codes-standards/publications/design-aids/AWC-DA6-BeamFormulas-0710.pdf

    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

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted