Questions: ?
I wonder if you can assist with a problem to which I am sure the solution is staring me in the face, but which eludes me.? I have attached two data files. The two structures are virtually identical except that the geometric properties of some of the members are a little different.? Also, although the number of members is the same in both files, the number of nodes differs.? I am looking for the lowest eigenvalue, but in spite of the fact that the two structures differ by so little, the eigenvalue for one is three times that for the other.
Reply:??
The fault of your models is that the local axes of the vertical elements in the shorter lattice beams have their axes of bending in the wrong direction, so that the flexural stiffness of the lattice beams are much reduced by the subsequent flexibility.?
Here shows the two convenience method to check the local axis:?
- Open the 3D view of the whole model then check; or
- Click the “Show local axis button” button then to display the local axis to check.