5 Replies Latest reply on Nov 4, 2010 12:07 PM by Wyatt Goettle

    Cable as Spring Connector

    Wyatt Goettle

      I am running a static analysis on a trussed structure that lifts objects from the ground.  The structure has 4 guy-wires that anchor the top of the structure to the ground.  Using a "link" connector will cause the links to bear load when lifting, so I need to use a "spring" connector in extension only.  Does anyone know where to set the K-value for different sizes of cables being used?

       

      I've attached a screen shot of my setup.

       

      Regards,


      Wyatt

        • Re: Cable as Spring Connector
          Ryan Werner

          Not sure about k values but if you can find some data from a cable maker specifying the stretch given a load you could use Hooke's Law (F=-kx) to get some approximate k values.  I honestly dont know if that kind of information will be easy to find though or if you have already thought of that.

           

          Ryan W.

          • Re: Cable as Spring Connector
            Bill McEachern

            K is just the spring rate in lbf/in. A rod is AE/L. With cables thought they usually give you a stiffness - I think bridge strand is something like 1/3 of the rod value - though don't quote me do some homework and get a number. SS aircraft cable is well published as well.

            • Re: Cable as Spring Connector
              Wyatt Goettle

              I figured this out.  First off one needs a formula for Elastic Stretch of the cable and this is [Change in Load * Length of Cable]\[Metallica area of Cable * Modulus of Elasticity of the cable].  Once this is known, one can find Axial Stiffness of the cable by  [Change in Load \ Elastic Stretch].

               

              This value can be input into the Axial Stiffness field of the Spring Extension Connector.

               

              A couple things to be aware of here:

              1. The metallic area of the cable is not only dependant on diameter, but also wire size, core type, strands, and lay arrangement.
              2. The modulus will increase as the load on the cable increases. Generally speaking, a range of load on the cable can be assigned a certain Modulus.  For example with a 5/8" 6x36 EIP IWRC rope; 0-20% loading to break gives 12e6 psi while 21-65% gives 14e6 psi.

              This was an interesting day where I learned a lot about wire rope!

               

              Later,

              Wyatt