Statics Truss Problem Involving Method of Sections

  • Thread starter shizupple
  • Start date
  • #1
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Homework Statement


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


Homework Equations


ƩM=0
ƩFy=0
ƩFx=0

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
 

Answers and Replies

  • #2
741
27
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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