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Bending of beams

  1. Dec 24, 2014 #1
    Help needed In my course paperwork I cant seem to find the relevant equations needed to complete the following in if someone could help point me in the right direction of equations needed I would be very grateful

    1. The problem statement, all variables and given/known data

    A rectangular hollow beam length of 3m is simply supported at its ends it has width of 10 mm and depth of 200 mm the beam is subjected to a uniformly disturbed load of 2 tonnes/m and a point load of 200N at its centre position
    I) determine the maximum stress due to bending (occurring at the centre point)
    ii) determine the value of the radius of the curvature of the neutral layer
    iii) the factor of safety if the maximum allowable stress of the material is 100MPa

     
  2. jcsd
  3. Dec 24, 2014 #2

    SteamKing

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    If the beam is hollow, what are the dimensions of the interior portion? That's kinda necessary to work this problem.

    Also, I can't believe that you have allowed your notes to become so disorganized that you can't write down anything pertaining to solving this problem. No textbook? Google? Bueller?
     
  4. Dec 24, 2014 #3
    SteamKing thanks for your reply this is the problem all the info on dimensions is as above this is why I am struggling with this I do have text books etc but cannot find anything relevant to solve the above is this possible with the above information?
     
  5. Dec 24, 2014 #4

    SteamKing

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    If the beam is hollow and the internal dimensions are not provided, then you're stuck. A clarification from the instructor of the course is in order.

    It's not clear what text books you have, but searching for 'bending of beams', 'bending stress', or 'radius of curvature' would be a good place to start, if you have a text book on strength of materials. Even if your notes and books have been eaten by zombies, you can Google these terms and come up with something.
     
  6. Dec 24, 2014 #5
    thanks very much I have been told to treat it as a solid so from that do I first calculate the second moment area then (stress/y=M/I)?
     
  7. Dec 24, 2014 #6

    SteamKing

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    Yes, but only after you have determined the bending moment at the center of the beam.
     
  8. Dec 26, 2014 #7
    how do I calculate the bending moment in the centre of the beam?
     
  9. Dec 28, 2014 #8
    Can anyone help I am struggling as the point load in the centre of the beam keeps throwing me can any one help point me in the right direction
     
  10. Dec 28, 2014 #9

    SteamKing

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    Have you calculated the support reactions for the beam? Can you draw the shear force curve for this beam?

    Simply saying 'I don't know.' or 'I lost all of my notes.' is not sufficient to receive help at PF. You must show some effort, either at working your problem directly or at least researching how to solve it.

    You were given some search terms in Post #4. Did you try them?
     
  11. Dec 28, 2014 #10
    hi andrewh21.

    You have so far shown no effort on this problem. SteamKing has been trying to elicit some response from you, but none has been forthcoming, other than "I don't have a clue." This is unacceptable. We are not here to do your homework for you or to teach you the entire subject. I have given you a 1 point warning.

    The least you could have done was to articulate how you would begin to approach a problem like this. Tell us your thinking. What do you think is happening physically?

    At one point, you indicated that you could handle the case of a distributed load, but not the point load case. OK. Tell us what you would do if you had a distributed load.

    What text book are you using?

    I am about to close this thread if I don't see some effort on your part.

    Chet
     
  12. Dec 29, 2014 #11
    As a first step, calculate the reaction forces at the supports. That is just a statics problem, and has nothing to do with beam bending. What do you get for the reaction forces?

    Chet
     
  13. Dec 30, 2014 #12
    Ra=Rb
    Ra*3m=200tonnes/m*3*1.5
    =900Tonnes/m
    from which Ra=900/3=300 tonnes/m =Rb

    anywhere near?
     
  14. Dec 30, 2014 #13

    SteamKing

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    Where do you get 200 tonnes and 300 tonnes from?
     
  15. Dec 30, 2014 #14
    What is the total of the distributed and the point load on the beam?

    Chet
     
  16. Dec 30, 2014 #15
    sorry should have been
    Ra=Rb
    Ra*3m=19613nm/m*3*1.5
    =88258.5nm/m
    from which Ra=88258.5/3=29419.5Nm/m =Rb

    any better?
     
  17. Dec 30, 2014 #16

    SteamKing

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    And what is a N-m/m ?
     
  18. Dec 31, 2014 #17
  19. Dec 31, 2014 #18
    Since when are the units of force Nm?

    Chet
     
  20. Dec 31, 2014 #19
    this is where I am falling down odiously I have UDL of 2 tonnes/m but also this point load I have viewed dozens of worked examples trying to find something similar but nothing I have looked at contains a UDL and a point load it seems to be one or the other any advice on where to look etc would be greatly appreciated

    Andrew
     
  21. Dec 31, 2014 #20
    What if the distributed load wasn't there? Would you then be able to determine the reaction forces at the two ends resulting from the point load? This is a simple freshman physics problem involving static equilibrium.

    Chet
     
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