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Springs and arches suspending a fabric

  1. Dec 2, 2014 #1
    1. The problem statement, all variables and given/known data

    The distance from the spring attachment to the arch in 9 feet.
    The distance from the arch to the arch is 20 feet.
    There are three arches. So, End plate-spring to arch to arch to arch to spring-end plate.

    The tarp weights 750 lbs and is 60 ft by 20 ft.
    There are 20 springs attached to the end plates (north and south) and 60 springs on the base (east and west).
    Snow can accumulate at a value of 25 lb/ft^2.

    What are all the forces and the parameters needed to define the springs (K, X1, and X2).

    2. Relevant equations

    F=mg
    F=K(X1-X2)

    3. The attempt at a solution

    F=32.2(750)=24150
    Modeling just from the arch to the spring as a single string/rope->
    24150/60=402.5 lb/ft
    Spring is Ra and arch is Rb, F is mg of tarp
    Ra+Rb=F
    402.5*9/2=1811.25 = Ra=Rb

    So, 1811.25=K(X1-X2)

    This just seems bad wrong

    I really want to find out what my K value should be and I want the spring to be about 8 inches.
     

    Attached Files:

  2. jcsd
  3. Dec 2, 2014 #2
    Can anyone figure out the relationship between the problem statement and the figure? If not, I'm going to delete this thread.

    Chet
     
  4. Dec 3, 2014 #3
    The image is my attempt to model the problem as a beam (which I now think is a bad idea). The image shows the uniform force, Ra, and Rb.
     
  5. Dec 3, 2014 #4
    I still don't understand the problem statement. Maybe it's just me.

    Chet
     
  6. Dec 3, 2014 #5
    Ok, well basically...
    I'm trying to determine what spring to use to ensure the tarp remains tight, even during snow fall.

    There are three arches supporting the tarp and all four ends are attached to springs. The north/south ends (20' length side) are attached in an arch shape and the east/west ends (60' length sides) are attached vertically to the base and the tarp.

    Does that help?

    I can draw the design I have right now- if that would help.
     
  7. Dec 3, 2014 #6
    A good diagram would be very helpful. I'm still unable to picture it.

    Chet
     
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