problem about eigen value analysis

foadEng · Post by **foadEng** » Sun Feb 21, 2010 6:15 am

Hi
I am modeling a 3d building with opensees and during eigen value analysis, I am facing this error:

"BandArpackSolver : : Error in dgbtrf
Warning FrequencyAlgo : :solveCurrentStep<> - the EigenSOE failed in solve<>.
EigenAnalysis : : analyze <> - algorith, failed"

I should say that in my model, I want to release the moment at the end of some beams, before doing this (I mean releasing the moment at the end of some elements, it worked but after that it failed).
Please help me to solve this problem!
thanks!

Post by **fmk** » Mon Feb 22, 2010 10:40 am

you probably have a rigid body mode somewhere .. i presume you are adding another dimmy node and using equalDOF on the translational dof

foadEng · Post by **foadEng** » Mon Feb 22, 2010 10:31 pm

Yes, I am adding another node and using equalDOF for translational DOFs. and also I am using a rigid diaphragm in every story, Is this related?
thanks for your advice!

Post by **fmk** » Tue Feb 23, 2010 11:20 am

my guess is your model is incorrect, try starting at the unreleased model and adding a few moment releases at a time until you figure out what is going on.

also, be careful when using rigid diaphragms with the nonlinear beam columns as the constraint that the element has no axial deformation while undergoing bending can result in crazy elemental forces.

foadEng · Post by **foadEng** » Thu Feb 25, 2010 9:56 am

Thank you for your help,
my problem almost has been solved, but while doing the analysis I faced another problem! results are not normal, for example the periods are around 0.0012 which can't be true. I have used rigid diaphragm and also fixZ command to tie the nodes in the same planes together.
thanks!