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Calculating the dead load of a mild structural steel

  1. Sep 20, 2011 #1
    1. The problem statement, all variables and given/known data

    A mild steel beam has a solid square cross section of 100mm and is simply supported by two supports 3m apart. calculate the dead load that can be safely supported when applied to the middle of the beam?

    2. Relevant equations

    3. The attempt at a solution

    given data:

    square cross section of 100m

    Ultimate strength in bending is σb = 450N/mm2

    Ultimate shear in strength = Tut 320 N/mm2

    The maximum bending moment is under the load

    So from the bending formula
    Bending stress (σb) = P / A

    A = Area of cross section

    Dead load P = σbA / 4
    = 450 x 1002 / 4
    = 1125000N (1125KN)

    Can anyone confirm that this is the correct answer.

    Thanks in advance
  2. jcsd
  3. Sep 20, 2011 #2


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    Science Advisor
    Homework Helper

    1884ram: That currently looks incorrect. It looks like you have the wrong formula for bending stress. Find the correct formula for bending stress, and keep trying.

    By the way, N/mm^2 is called MPa. Use the correct unit symbol, MPa. Also, the unit symbol for kilonewton is spelled kN, not KN. Always use the correct capitalization. Also, always leave a space between a numeric value and its following unit symbol. E.g., 3 m, not 3m.
  4. Sep 21, 2011 #3
    Thanks for your reply and advice nvn.

    I have looked into some other equations and i have found the following:

    M / I = σb / y = E / R

    (PL / 2) / a4 / 12 = σb / y

    Are these correct?

    I have tried to use these formulas to calcualte dead load but not sure what the E and R values are:

    M = 480 x 166 666 / 4 = 1 999 992 0 / 1000 = 1 999 9.92 N m

    I = 1 / 12 x 100^4 = 8 333 300 mm^4

    σb = 450 mpa

    y = 1 / 2 x 100 = 50 mm

    E =

    R =

    L = 100
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