ETABS Warnings " EIGENVALUES WAS FOUND OUT OF SEQUENCE" 1

[ibrahemnasr]

after the analysis completed i notice this warning in the log file
* * * W A R N I N G * * *
EIGENVALUE 20 WAS FOUND OUT OF SEQUENCE

i also notice that the tipe periods are very giant (like 906690 sec) and also the program did not capture any mode shapes
i try using Ritz vector but nothing happend i also try to use negative small frequency shift but No avail

does any one face this problem before

 

[johnbridge231]

can you confirm that the model is not a mechanism? Is the deformed shape under dead loads showing properly?

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[PicoStruc]

Validate your mass and stiffness by hand !

 

[JoshPlumSE]

Not an ETAB's user (I actually work for one of their competitors). But, I agree with JohnBridge. This sounds like an instability in your structure. If you can view that mode shape it should show you what the instability is.

Note: The "Eigenvalue found out of sequence" message is a separate issue. That implies that the program was trying to solve for the first N eigenvalues. After finding the eigenvalues it would go back and run some checks to make sure that these were indeed the N lowest frequencies. If not, then it will throw up this message. There are lots of reasons why this might happen. I used to see it happen when some of the modes occurred at virtually identical frequencies.

 

[inggelu]

You can check the model Analyze>Check....
It is possible to have some errors when the model was defining.
Can be from units of some material or section?
Is not easy to tell about see how the model was made.