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Simply Supported Beams Loads and S/BMD's

  1. Nov 9, 2012 #1
    1. The problem statement, all variables and given/known data

    Here is the Simply Supported Beam with a uniform and triangular load.
    http://prntscr.com/jd6b2

    2. Relevant equations



    3. The attempt at a solution

    Newest attempt: http://prntscr.com/jdu7d

    Current Step: Shear Force and Bending Moment Diagrams.
     
    Last edited: Nov 10, 2012
  2. jcsd
  3. Nov 9, 2012 #2

    PhanthomJay

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    How are you arriving at these numbers? And what happened to the 200 kN concentrated point load? The UDL of 50 kN per m acts over 9 feet, not 18 feet, and its resultant lies at its cg. The triangular distribution has a resultant of 225 kN, yes, but you show it acting in the wrong location. It too acts at the cg of the triangle.
     
  4. Nov 10, 2012 #3
    Hmm, I think I have actually interpreted this question wrong.

    Is this image showing one 50kN load being distributed uniformly THEN being triangularly distributed. AND a 200kN point load? (I've been viewing it as two separate loads.

    I got 225 by (50kN * 9m)/2 (Uniformly distributed load)
     
  5. Nov 10, 2012 #4

    PhanthomJay

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    The problem is showing a uniformly distributed load of 50 kN/m acting over the first 9 meters of the beam. It's total load (resultant of the distributted load, which is the 'area' of the rectangle, or (50)9 = 450 kN) acts at its cg 4.5 m from the left end. Thus, when determining reactions, it can be treated as a single concentrated point load of 450 kN acting 4.5 m from the left end. You incorrectly divided that total load by 2, but showed its location correctly.
    Then the problem shows a separate 200 kN concentrated point load acting at the center of the beam 9 m from the left. Don't ignore it.
    Finally, the problem shows a separate triangularly distributed load that varies from 50 kN/m to 0 kN/m acting over the right half of the beam. It's resultant equivalent concentrated load is found by calculating the 'area' of that triangle and placing that load at the cg of the triangle. You correctly located that load as 12 m from the left end, but its value is wrong.
     
  6. Nov 10, 2012 #5
    Alright I've redone it, http://prntscr.com/jdu7d

    The next step is to draw bending moment and shear force diagrams. I'll post when I've got them.
     
  7. Nov 10, 2012 #6
    I've done the shear force diagram, is this right?

    Some reason I can't edit previous posts or the thread.
     
  8. Nov 10, 2012 #7

    PhanthomJay

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    No attachment. You can't edit threads after a certain time has passed..
     
  9. Nov 10, 2012 #8
  10. Nov 11, 2012 #9

    SteamKing

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    Your shear force diagram is incorrect. You have not included the concentrated load of 200 kN.
     
  11. Nov 11, 2012 #10

    PhanthomJay

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    When you try this again, be sure to show the distributed loads in your loading diagram. Do not represent them as concentrated point loads...that only works when you are calculating end reactions. And remember that the slope of the shear diagram at any point is equal to the negative of the load intensity at that point. You have kinks and valleys where there should be none.
     
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