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Homework Help: Bending Stress in Top of T-Beam

  1. Dec 7, 2014 #1
    1. The problem statement, all variables and given/known data

    T-Beam is Steel with E=200GPa

    Find Max bending stress MC/I (right side where no glue)

    80KG Load at Point "A" shown on the Top view

    Blue stuff is glue, the right side has no Glue, so its just empty space

    2. The attempt at a solution

    I = BH^3/12 , where B = 0.04m H = 0.004
    So I = 2.13 * 10^-10 m^4
    C = 0.029m
    M = 784.8 N * 0.024m = 18.8352 n-m

    Solving that out I get 2.573 GPa which seems too high as steel can only see in MPa of stress.

    So i'm not sure if the number I got is correct or I did something wrong with my calculation.
    Last edited by a moderator: Dec 8, 2014
  2. jcsd
  3. Dec 8, 2014 #2

    The Beam is Supported in the center.

    The Bending is happening not on the axis I assumed, the force is not in the center so

    I = 0.08* 0.004^2 and C = 0.002

    Now I get 88.29 MPa
  4. Dec 8, 2014 #3


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    It's not clear what you are trying to do here. What is this point load and why is it applied to the flange of the beam?

    Your expression for I seems to be incorrect, or at least it is unfamiliar to me. Have you checked to make sure the units make sense?

    Your calculated bending stress values lack meaning if you don't know what stress the beam material is capable of withstanding without permanent deformation.
  5. Dec 8, 2014 #4

    The Beam is rigidly held in place except for the right side, so can assume a simple beam,(Square/rectangle) so I= BH^3/12 is correct.

    I actually am still wrong, there is a moment in the y and x, I need to add them to find total bending stress.
  6. Dec 8, 2014 #5


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    I don't think I'd worry too much about the eccentric 'point' load a few mm off center in the y direction . I'd do it as you had in your original post after correcting the 'c' distance to .002m and checking your steel allowable stress for the material being used, as SteamKing noted .
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