Error in eigenvalue analysis

[shiRo]

Dear STKO team
I'm trying to do an eigenvalue analysis on a reinforced concrete bridge pier, but I'm getting an error when I run the analysis, I've attached a picture of the error report and my model file, can you give me some advice on how to solve the problem, thank you very much!
Best wishes

[kesavapraba]

Hi,
the first error

ForceBeamColumn3d::update() could not invert flexibility for element with tag:

typically arises when the Section tangent cannot be inverted due to certain conditions. This error may occur if there are perfectly plastic materials with a zero tangent or if something in the section stiffness matrix is zero, like the torsional stiffness (GJ). You have assigned 0 for GJ! So, it should be an appropriate value for the section.

the second error is related to the number of Eigen value that are requested from -genBandArpack solver. This eigen value solver can provide only N-1 eigen values and vectors, where N is the total inertial/mass DOFs in the model. In your case, you had requested 10 Eigen values and vectors! So, you can request maximum 3 eigen values only - you have to use -fullGenLapack option in such case. Be aware that -fullGenLapack considers the entire mass and stiffness matrices, so it may be costly if the model is large.

I would suggest to read the following article as well:
https://portwooddigital.com/2022/03/06/ ... igen-chew/

[shiRo]

Hi,
the first error

ForceBeamColumn3d::update() could not invert flexibility for element with tag:

typically arises when the Section tangent cannot be inverted due to certain conditions. This error may occur if there are perfectly plastic materials with a zero tangent or if something in the section stiffness matrix is zero, like the torsional stiffness (GJ). You have assigned 0 for GJ! So, it should be an appropriate value for the section.

the second error is related to the number of Eigen value that are requested from -genBandArpack solver. This eigen value solver can provide only N-1 eigen values and vectors, where N is the total inertial/mass DOFs in the model. In your case, you had requested 10 Eigen values and vectors! So, you can request maximum 3 eigen values only - you have to use -fullGenLapack option in such case. Be aware that -fullGenLapack considers the entire mass and stiffness matrices, so it may be costly if the model is large.

I would suggest to read the following article as well:
https://portwooddigital.com/2022/03/06/ ... igen-chew/

Really thanks！It works fine now!

[kesavapraba]

You are welcome