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Statics Truss Problem Involving Method of Sections

  1. Oct 10, 2012 #1
    1. The problem statement, all variables and given/known data
    10wpef9.png

    In the traveling bridge crane shown all crossed members are slender tie rods incapable of supporting compression. Determine the forces in members DF and EF and find the horizontal reaction on the truss at A. Show that if CF=0, DE=0 also.

    -Determine force in members DF and EF
    -Find the horizontal reaction on the truss at A
    -Show that if CF=0, DE=0 also
    -Crossed members can't support compression


    2. Relevant equations
    ƩM=0
    ƩFy=0
    ƩFx=0

    3. The attempt at a solution
    I solved for the vertical reactions at A and B.
    ƩMb=0=(1000kN)(24m)+(200kN)(52m)-(Ay)(36m)
    Ay= 956kN

    ƩFy=0=956kN-1000-200+By
    By=244kN

    ƩFx=0=Ax-Bx
    Ax=Bx

    I tried summing moments about E to find the horizontal reactions but they just cancel out.

    I know I have to use method of sections to solve but there is nowhere to make a cut that only cuts 3 members. Everywhere I cut except the very bottoms and far left side has at least 4 members to cut through. There isn't even a way to simultaneously solve for a 4 cut and a 3 cut.

    Any advise on what to do from here would be greatly appreciated.

    Thanks
     
  2. jcsd
  3. Oct 12, 2012 #2
    There is at least one cut through 4 members that is solvable because, by inspection, one of the crossed members would be in compression, and therefore ignorable. Hint: somewhere near E..........
     
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