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Why does an angle bend out of plane?

Question asked by Bryce Engle on Oct 18, 2010
Latest reply on Oct 18, 2010 by 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?

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