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Computing Beam Deflection Using Castiglianos' Theorem

  1. May 13, 2010 #1
    I am trying to find the deflection of the beam as described below,

    The beam has an overall length L and a load Q acting downwards at this point, the question is asking for the deflection of the beam at the point three quarters of the way along the beam. The beam has constant flexural rigidity EI.

    I have tried this problem a number of times and keep coming up with two different solutions, depending from which side of the beam I take my moments. The solutions I have are;

    27QL^3/128EI and 11QL^3/384EI

    Could someone please tell me which one is correct? I think it's the first answer but I'm not 100%.
  2. jcsd
  3. May 13, 2010 #2
    It would help to know the support conditions.
  4. May 13, 2010 #3
    The beam is a cantilever beam so is supported just at one end.
  5. May 13, 2010 #4
    Well I make your first go to be correct.

    Can you show some working?
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