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Homework Help: Bending Moments and Reactions

  1. Nov 24, 2008 #1
    1. The problem statement, all variables and given/known data

    Fixed end beam with

    Length = 1m
    Load 1 = 58.86n @ 0.4m from A
    Load 2 = 39.24n @ 0.85m from A

    Find Ma, Mb, Ra, Rb

    2. Relevant equations

    Not Sure, where help is needed

    3. The attempt at a solution

    Well i think, almost sure from 2 methods that Ra = 40.52511

    I have tried to calculate Rb but keep getting different answers, so far i have got

    Rb = 32.06 and Rb = 57.57

    I think Ma is -9.22, but not 100%. Keep getting different answers for Mb, 9,903 and Mb 2.7 and Mb
  2. jcsd
  3. Nov 29, 2008 #2
    To find the bending moments, you need the support reactions first, then you need to cut the beam into pieces, and then sum the moments independently, from the first whole piece.

    Can you please provide more information for this question, such as, where is A, is A the fixed end, or the open end? Providing a free body diagram of what you done would be helpful too.
  4. Nov 29, 2008 #3
    Since the Moments and reactions of both ends are required, I assume that the beam is fixed at both ends. Could you please confirm?
    At this point, if the sum or Ra and Rb is not 98.1, you are in trouble.

    Before we go further, may I enquire if you have already done some work on indeterminate structures? It will be first year university in engineering or equivalent, or higher. What have you learned so far from the course. Do you have textbooks on structural analysis, such as "Theory of Structures" by Stephen Timoshenko,
    This book is sure to be found in all university libraries. You could use any other ones.

    On second thought, if you have done Strength of Materials, you might have the tools required to solve the problem analytically.

    How did you get your Ma and Mb. Could you post your calculations, even if you think they may be wrong?
    Last edited: Nov 29, 2008
  5. Nov 30, 2008 #4
    If you only need an answer as most practising engineers do, the following link gives the formulae for different loading and boundary conditions:

    As it is a .pdf file, the display of the page will take some time (a couple of minutes).

    If you are doing the problem for a course, I suggest you work on your teacher's notes supplemented by a good textbook.

    Feel free to post questions after you have studied the subject.
    Last edited: Nov 30, 2008
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