A very simple one!
A very simple one!
(OP)
Hi, guys! A friend of mine, who is still in the university has this very simple problem to solve with FEA:
[URL=http://picturepush.com/public/11689282]
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As you see this is a rectangular wall with some uniform edge loads. The problem the girl encountered when analyzing with SAP2000 v.12 was infinitely large displacement of the bottom right node (about 1E+09). I told her that her structure is ill-supported. I also modelled it and I had about the same displacements, so I was sure it is ill-supported. I explained this, but when she went to her assisten professor he told her, that it is absolutely good with boundary conditions - horizontal supports on bottom edge and vertical supports on the left edge). I think I am right, but I want to here some opinions. Thank you!
My Best regards, Stoyan Andreev
[URL=http://picturepush.com/public/11689282]
[/URL]As you see this is a rectangular wall with some uniform edge loads. The problem the girl encountered when analyzing with SAP2000 v.12 was infinitely large displacement of the bottom right node (about 1E+09). I told her that her structure is ill-supported. I also modelled it and I had about the same displacements, so I was sure it is ill-supported. I explained this, but when she went to her assisten professor he told her, that it is absolutely good with boundary conditions - horizontal supports on bottom edge and vertical supports on the left edge). I think I am right, but I want to here some opinions. Thank you!
My Best regards, Stoyan Andreev





RE: A very simple one!
RE: A very simple one!
RE: A very simple one!
my russian is a little rusty ... i suspect you're constraining the edges along the edges, or normal to the edge ?
if you are constaining along the edges then you're right, the body is spinning about the lower LH corner. if we were solving by hand we'd ignore this freedom ('cause we know nothing's happening along there). but FE doesn't; and you havn't constrained this freedom. constrain Mz (out-of-plane) at this node, and the displacement will disappear (and your results should not change either, well, at least there'll be no moment reacted by this constraint).
if you are only constaining the edges along the two edges then to properly constrain the model you'll need to constrain Fz, Mx, My, and Mz at the lower LH corner. actually you can constrain there freedoms anywhere on the model and it should solve, but the displacements will be relative to the point controlled (and the lower LH point will give you a more intuitive answer).
RE: A very simple one!
RE: A very simple one!
constraining along the edges does not constrain in-plane rotation (clearly).
if someone doesn't want to admit they're Wrong, let them live in their own world.
RE: A very simple one!
RE: A very simple one!
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: A very simple one!
looking at the problem again ... both the applied forces are drawn in the y-direction, but i understood that the reactions were along (not normal to) the edges ? if loading is all in the y- direction then i'd expect to see no net load in the x-direction (on edge "p"); in the model world ther would be balancing reactions if you constraints prevent poisson displacements . this is enough to say that the reactions on both edges are generally in-plane ... along and normal to the edges; this way a couple of x-forces will react the Mz moment due to the loading.