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I beams and Torsion

  1. Apr 6, 2008 #1
    You have two parallel I-beams. A trolley with 4 wheels runs on top, and carries a total load of say 10kN. How would you evaluate the torsion?

    angle theta = TL/GK
    where (for an I beam) K = [2bt^3 + (d - 2t)(thickness of web)^3] / 3
    and t = thickness of flange
    But, how would you calculate the torque T?
    Say if the beams were 1m apart, if torque was simply 10kN x 0.5m, then the beam would roll over.

    For the equation; tau = T/Q
    how do you calculate Q for an I beam?
  2. jcsd
  3. Apr 6, 2008 #2


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    Science Advisor

    This isn't an easy question to answer. If you are running a trolley on an I-beam, that would mean, most likely, that the beam is set on the ground, effectively constraining the bottom flange from any deflections. That means all of the deflections will be in the web and the upper flange. Combined with multiple point loads, off the top of my I'd say you really need a numeric solution. Then again, I don't have a copy of Roark's in front of me right now to see if this type of problem has a general solution already formulated. You could simplify it to have one point load at the center of the two beams, but you're still in a tough spot.
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