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Homework Help: Bnding Moment diagram with one/two support/s?

  1. Jul 19, 2010 #1
    I have drawn a beam that I have made up that has two supports on it but only one is in contact with the beam. how would I go about drawing a BM diagram for this beam? The BM diagram has to show the values at (from left to right) the first support, the first dotted line, the second support and the second dotted line.

    Any help apreciated



    Attached Files:

  2. jcsd
  3. Jul 19, 2010 #2
    Your beam is called a see-saw.

    Try forgetting the disconnected support and inverting the beam, so the loads and supports are interchanged.

    Does this help?
  4. Jul 20, 2010 #3
    yea thanx. Ill use this to give it a go. Ill let u know if I crack it and mabe post what I get as my answer up. Hopefuly tho ill of done it correct :D

    At least I know what it is now, never done anythin like this one befor. Thnx for the help.
  5. Jul 20, 2010 #4
    The bending moment diagram is a graph showing the variation of bending moment along the beam. To draw it, you could calculate the bending moment at different sections of the beam, and then plotting their values, using the beam itself as a base line. One definition of the bm at a section is: the algebraic sum of the moments on one side of that section. As there are two sides to every section, you will have an automatic check on the bending moment at that section. We can call these ML and MR. They should be exactly the same if everything is in order and sign conventions applied correctly. In your case, you will go round and round, unable to get ML to be the same as MR. Why is that? Because, until you connect the beam with its second support, you have a mechanism, for which the BM diagram is a bit pointless.
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