the eigenvalue analysis is wrong

[zly123]

I can do gravity analysis on my model, but I get an error when doing modal analysis. What is the reason for this?

[kesavapraba]

Hi, You can post a minimum example model here to find the exact cause for this error. Please check your model for any unconnected nodes/elements and also Eigen analysis settings.

[zly123]

Thanks，it can work now.But the period is smaller than other finite element software.The first period is 0.89s and 2.1s in other software,I want to know what can I adjust could improve the natural period of the structure.

[kesavapraba]

Hi, Mass and stiffness of the structure play role in its natural period. Additionally, boundary conditions (again stiffness!) can also influence the natural period. So, I would suggest you should check the correctness of these details between the two models.

[zly123]

Hi, Mass and stiffness of the structure play role in its natural period. Additionally, boundary conditions (again stiffness!) can also influence the natural period. So, I would suggest you should check the correctness of these details between the two models.

Can you tell me if it's the right thing to do？I want to use these operations to simulate a rigid floor slab.

[kesavapraba]

Hi, You should use rigidDiaphragm instead of rigidLink beam. rigidLink creates single MP constraint between one master and one slave node, however, rigidDiaphragm creates MP constraints accounting all the nodes in the interaction, resulting in rigid plate like behaviour for the floor.

[zly123]

Hi, You should use rigidDiaphragm instead of rigidLink beam. rigidLink creates single MP constraint between one master and one slave node, however, rigidDiaphragm creates MP constraints accounting all the nodes in the interaction, resulting in rigid plate like behaviour for the floor.

Do I still need to constrain the degrees of freedom of the control points?

[zly123]

Hi, You should use rigidDiaphragm instead of rigidLink beam. rigidLink creates single MP constraint between one master and one slave node, however, rigidDiaphragm creates MP constraints accounting all the nodes in the interaction, resulting in rigid plate like behaviour for the floor.

Can you help me check this model, the first natural period I analyzed using other software was 2.07s.Thank you very much!

[STKO Team]

The boundary conditions are fine.
In your model you don't need to fix the Uz,Rx,Ry DOFs of the master-floor nodes because the already belong to other elements.

The reason for your period should be an inconsistency (with respect to the other model you are comparing to) regarding either the stiffness of the mass. Please double check both.
Start with the mass, it's easier. Look at least at the total structural mass in the modal report and see if it makes sense.