eigenvalue analysis error

[mrathore]

I have modelled a three storyed structure (3D) with Y as vertical direction. I have applied masses in X and Z direction at each floor to CM where CM is connected to other nodes of floor by rigid diaphragm. Theoretically it should give six modes of vibrations, but it is giving only upto four, as soon as we type "eigen 5" following message comes:

Code: Select all

BandArpackSolver::Error with _saupd info = -9999
Could not build an Arnoldi factorization.IPARAM(5) returns the size of the curre
nt Arnoldi
factorization. The user is advised to check thatenough workspace and array stora
ge has been allocated.
Warning FrequencyAlgo::solveCurrentStep() - the EigenSOE failed in solve().
EigenAnalysis::analyze() - algorithm failed
OpenSees >

What should I do? I need at least six modes for the analysis.

Thanks in advance

[arbarbosa]

Try to assign a very small mass in (e.g. 1e-9) the Z direction and it should let you get the other modes.

[Prayag Sayani]

Try undocumented command

eigen -fullGenLapack numEigenvalues?

you should use

eigen -fullGenLapack 6 in your case.

I hope it will work,

[mrathore]

Thanks a lot Prayag.

This option should be included in manual.

Thanks again