2 Replies Latest reply on Oct 18, 2010 3:36 PM by Bryce Engle

    Why does an angle bend out of plane?

    Bryce Engle

      If I create a beam in Simulation with the cross section of an angle "L" with the length of the beam along the X axis, pin both ends (immoveable), & apply a load in the Y direction at the center of the beam the resulting deformation is out of plane.  Instead of just up & down in the Y direction it also bows out into the Z direction.  I am using structural angle cross sections.

       

      If I create shear & moment diagrams they match hand calcs--ie shear in the "direction 1" & moment in the "direction 2."  When I look at a bending stress diagram it does not match hand calcs--even if I limit the stress plot to bending in direction 2 only.  As I said--the moment in direction in 2 is correct--so should I not be able to take that moment & divide it by "S" of my structural angle cross section (bending stress = M/S) & get the bending stress?  Doing this does not match the stress plot in direction 2.

       

       

      I can do this with channels, square & rectangle tubes & dividing the given moment by "S" does match the Simulation bending stress in direction 2---Why does this not work if the cross section is an angle shape?

        • Re: Why does an angle bend out of plane?
          Chris Michalski

          the hand calculations are based on the part staying the same shape.  All of your other parts are symmetric so applying the load the center is still symmetric, but with an L-angle the lack of symmetry places the neutral axis away from the center of the face.  The simulation solves for the fact that your L will start to roll because it is stiffer on one side than the other.  If you mirror the L into a U-channel it should be correct because of symmetry places the force coincident to the neutral plane again.

            • Re: Why does an angle bend out of plane?
              Bryce Engle

              Yes I have mirrored a cross section that was angle shaped & bending out of plane into a channel cross section.  I used the same part & simulation study with the same loading & restraints & after mirroring it to a channel it bent as expected--all in plane & matching hand calcs.  I tried this with a channel in both directions--as a "C" and a "U" relative to the load in the Y direction.

               

              I figured this was probably the case but could not find anything in my text books to warn of this in hand calcs.

               

              The simulation results for the angle show more bending stress stress than the hand calcs along direction 2.  The simulation results also have a good amount of bending stress in direction 1, where as hand calcs obviously have zero with the simple Stress = M/S equation.

               

              Thanks