Adam Sandler

Beam mesh - bad results

Discussion created by Adam Sandler on May 28, 2008
Latest reply on May 28, 2008 by Bill McEachern
I'm analyzing a large lattice structure composed mainly of steel angle. Some members are bolted with a single bolt at each end (hinged in one direction), while others are bolted with 2 bolts at each end or welded (rigid end condition).

I've had all kinds of issues getting this model set up correctly in Cosmos Works because there is no way to determine direction 1 and direction 2 for an angle cross section. I've found a very long work-around to determine which is direction 1 and 2, but it turns out not to make any difference in the results - the results can't be correct. Then I tried just using the plain hinged end condition (direction 1 and 2) for members that are bolted with a single bolt at each end, but again the results don't change at all. And when I look at the bending moment diagrams for those beam, they are carrying a moment. Shouldn't a hinged end condition prevent the beam from carrying a moment?

Then I tried making all the members with single bolted ends into truss members (although I don't see what the difference is between a truss and a beam with hinged end condition). The results changed only slightly and surprisingly (suspiciously) resultant displacement decreased. But again when I look at the bending moment diagrams for the truss members, they are carrying a moment.

Am I missing something here? How can a truss (or beam with hinged ends) carry a moment? Shouldn't they be 2 force members (tension or compression only)? Has anyone else come across this?