3 Replies Latest reply on Dec 11, 2012 5:03 PM by Justin Strempke

    Table driven load on beam issue

    Justin Strempke
    Justin Strempke Nov 19, 2012 11:22 AM

      I am trying to verify a simple beam bending problem, cantilevered with a triangular, non-uniform load distribution (SW2012 SP5.0).  I have a couple problems/issues when using the Table Driven Load Distribution.  First is when using the Distance option, inputing the Force per unit length.  For normal beam theory calcs, this would be per unit length (width), yet when I put in say 5 lbs/in with a 1 in wide beam 30 in long, I get a shear of 333.5 lbs at the base, instead of the expected 75 lbs (5*1*30/2).  Gravity is turned off as well to isolate the loading.  The moment is also 20* the shear force, when it should be 10 (load applied at 1/3 distance for triangular load).

      NUDL 2.JPG

      The second problem is when using the Percentage option.  Using two points (0,100), it seems to only scale to the first node (not joint), versus the entire length (see image).  Is this a bug or am I not setting something up correctly?  The results agree, with equal shear after the first node so it's not just a graphics issue with the symbol from what I can tell.

      NUDL 1.JPG

      I would think these to be simple, and I was getting errors in a more complicated structure so I wanted to verify with a simple beam, but I think this is where my problems are rooted. 

       

      EDIT:  Tried this on SW2013, same thing.  I also tried swapping origins, fixed ends, etc, same results.

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        • Re: Table driven load on beam issue
          Justin Strempke
          Justin Strempke Nov 21, 2012 9:35 AM (in response to Justin Strempke)

          Has anyone else come across this?

          • Re: Table driven load on beam issue
            Justin Strempke
            Justin Strempke Nov 29, 2012 7:23 PM (in response to Justin Strempke)

            Another update, I have my VAR looking into this too, but I seem to have a similar issue with Force Nonuniform on a solid body as well.  I can put a force to be applied, and the coefficients seem to have zero effect on the magnitude of the loading, only changing the direction relative to the 'active' coefficients.  I can have something changing by +10y/in on a 10' beam, and the far end load is what my applied load is.  Am I just not entering in these coefficients correctly?  The SW Help isn't much use, just says to enter them in.

              • Re: Table driven load on beam issue
                Justin Strempke
                Justin Strempke Dec 11, 2012 5:03 PM (in response to Justin Strempke)

                I guess nobody else uses this or had this problem...  Anyway, found out the beam loading has two main problems.  The origin as represented by the loading and graphic is reversed from the analysis, and the use of IPS units is the culprit for the percent table issue.  For the origin, as example, a high load by the fixed end will produce a much higher stress than if the load is near the end of the beam - contrary to theory.  Flip the origin so the graphic looks opposite what you want, and the stresses work out appropriately.

                 

                For the Percentage, for some reason SW convert 100% in IPS to 2.54% in SI for calcs, hence the ability to only use the first small part of the beam.  A work around, you'd think, would be to enter your known IPS load in as lbs/in, then change the unit drop-down to SI and enter 100%.  Problem is, the force units don't convert correctly.  Instead of going from lbs/in to N/m, they only convert lbs to N, so you're left with N/in for calculations.  Do the leg work and enter your loading in as SI to begin with, in N/m, and the results are fine (provided the origin is correct!).  My VAR said there is a SPR for the units deal, but not sure if it covers this as well so they're looking into that.  For now, I'm just ignoring using beams altogether as they've obviously got some serious bugs!