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Homework Help: Popsicle stick bridge,

  1. Mar 10, 2013 #1
    1. The problem statement, all variables and given/known data

    i am building a popsicle stick bridge, and i basically have two trusses, which i am attaching together to make the bridge (each are one side of the bridge), and im having trouble deciding which way to orient the two trusses.

    if you look at the picture below, you can see that there are 2 proposed bridges in the picture, and all four trusses are built identically, so the only question is which design to go with?

    the bridge will be tested by center loaded weight hanging off the bottom middle of the bridge.

    which of these 2 designs would handle that weight better?

    2. Relevant equations

    not much, maybe method of joints analysis but i would prefer to work theoretically based off the image alone.

    3. The attempt at a solution

    bridge on the left:
    it looks like it will mitigate torsion forces awesomely because the bridge itself turns into a maximally rigid gemetric shape. my biggest worry is how this will actually spread the forces compared to the bridge on the right which i understand quite well.

    i googled triangle truss, and there are many images that show this sort of design so i wonder if its legitimate.

    to reiterate, my biggest worry is "how will the downward (negative y direction) force being centrally loaded on the bridge affect this design compared to the bridge on the right? is there a clear winning choice?
    if its a matter of preferance i think i will go with the bridge on the left because it looks radical and innovative.

    bridge on the right:
    standard warren truss with a few mods to aid in mitigating top beam compression forces. would require more popsicle sticks to mitigate torsion/side to side forces during the testing and subsequent crushing of the bridge.

    i would prefer if you guys didnt just hint and steer me in the right direction, but rather explicitly state whether the bridge on the left or right would be superior and why.
    its just a physics 12 level bridge and we arent actually analyzing the force vectors. its just a creative exercise in trusses and whatnot.

    both bridges are going to be 110 popsicle sticks, and if i build the bridge on the right, it should hold around 200 lbs with a span of 50cm.
    i have no idea how the bridge on the left would affect my 200 lb approximation. im hoping it would be similar or better, rather than drastically worse for X,Y,Z reasons.

    heres the image, the trusses are pretty much just laying against eachother in the proposed positions:
  2. jcsd
  3. Mar 10, 2013 #2
    anyone? which bridge looks more legit?
  4. Mar 10, 2013 #3


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    Science Advisor
    Homework Helper
    Gold Member

    Never built one from pop sticks but...

    I would think how the load will be applied to the bottom of the bridge. With the design on the right the lower members are vertical (eg the sticks are upright). With the design on the left the sticks lean over at 45 degrees. I suspect you might see these sticks bend sideways?
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