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Homework Help: Resolving forces in 7 member bridge help

  1. Nov 13, 2012 #1

    I don't answers course just some guidance. I need to find the forces at each joint, and stresses inbetween too. I've calculated the reaction forces by taking moments as 779N at far left and 692.5N at far right.

    Now I'm using trig of course to start from the left and work across finding the stresses but I have forgotten how to find the forces at each joint, and I'm not confident my stresses accurate. Could someone point me in the right direction then I can do the rest.

    Sorry if my drawing is poor, or if any other info is needed just say

    Thanks in advance.
  2. jcsd
  3. Nov 13, 2012 #2


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    You have two options: analysis by sections, or analysis by joints. Analysis by joints may be the simplest and is accomplished by looking at each joint- the forces imparted on each joint by the members must balance to zero for the joint to be static.

    Here's a quick rundown of the two analysis methods: http://emweb.unl.edu/negahban/em223/note12/note12.htm
  4. Nov 13, 2012 #3
    Right can I throw a few answers at you and see if you agree?

    Member of length 19 is undergoing 1164N

    Length 24 along the bottom is 865
  5. Nov 13, 2012 #4
    You could have posted that image directly here and other members viewing would not then be subject to an advertising barrage.

    Why does your truss have no supports?
  6. Nov 13, 2012 #5
    That's all I've been giving,it's been done in excel,and is just the members and a total load, with coordinates for each joint. From there I've found all the lengths and angles and now i'm using that to find stresses
  7. Nov 13, 2012 #6


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    You're going to have to try a little harder on your lengths and angles. For a start, none of your triangles add up to 180 degrees, and because of that I'm guessing your lengths might not match with your angles either.
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