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I-Beam mass

  1. Sep 14, 2013 #1
    1. The problem statement, all variables and given/known data

    A structural I-beam is made of steel. L = 12.1 cm, H = 32.0 cm and the width of the beam is W = 1.11 cm. What is the mass of a section 1.75 m long? The density of steel is 7.56E+3 kg/m3.

    2. Relevant equations
    d=m/v


    3. The attempt at a solution

    I can't copy the image of the i-beam here.. but, as you might expect, it resembles an i. I found the volume of the total beam, and subtracted from it the volume of the missing section. Then I converted cubic cm to cubic metres and multiplied by the density of steel. Then I found the ratio of length 1.75m to 12.1 cm and multiplied that by my newfound mass.. something is wrong, though.

    mass= (7.56e3kg/m^3)((12.1*1.11*32.0-10.99*1.11*29.78)cm^3)(10^-2m/cm)^3/(0.121m)=7.275 kg. Thanks in advance.
     
  2. jcsd
  3. Sep 14, 2013 #2

    SteamKing

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    If you can't copy the image, try to describe the section.

    1. What is the depth of the beam, from top of the top flange to the bottom of the bottom flange?
    2. What is the width of the flange?
    3. What is the thickness of the flange?
    4. What is the thickness of the web (the bit connecting the two flanges)?

    OTOH, if you calculate the cross sectional area of the beam, then the volume will be L*Area, and from this you can find the mass of the beam.
     
  4. Sep 14, 2013 #3
    The flange and web are unknown to me. How do I calculate the cross sectional area of the beam?
     
  5. Sep 14, 2013 #4

    SteamKing

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    If the flange and web are unknown, how do you expect to calculate the mass of the beam? The dimensions given in the OP must refer to some of the features of the beam.
     
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