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Relationship between Beam Section Depth and Bending Moment

  1. Jun 11, 2010 #1
    Ok. There are 2 universal beams. One is 500mm deep and the other one is 400mm deep. For both beams, the top and bottom flanges are 200mm wide x 10mm deep. [SPAN of the beams is not given]

    Questions is..If the maximum bending moment capacity of the 400mm deep universal beam is 200 kn.m. What is the bending moment capacity of the 500mm deep beam?

    What i think is that beam's bending moment has nothing to do with its section depth is it?
    So the answer to the question would be "Cannot be calculated since both the span measurement is not given."

    Or there are other answers to this?

  2. jcsd
  3. Jun 11, 2010 #2
    What on earth are you studying?
  4. Jun 11, 2010 #3
    Bending stress is roughly proportional to the square of the section depth.
  5. Jun 11, 2010 #4


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    Are you confusing 'bending moment' with 'bending moment capacity'? The former is a function of loading, span, end conditions, etc. while the latter is a function of the beam's material properties and cross sectional shape.
  6. Jun 13, 2010 #5
    I'd guess is that the answer they want is something along the lines of

    Sy = M1*y1/I1 = M2*y2/I2

    where you know M1, y1, I1, y2, I2, and can rearrange the above to find M2.
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