Modal analysis of a tower.

[serrojo]

Dear colleagues,
I have received an ETABS Model created by other specialist, I have to review his model for faults and create e report, it is the first time for me doing this.

So I find that the first 3 mode shapes are torsional, and in my experience the most common case is when the 1st and 2nd modes are x-x and y-y, then the 3rd is torsional.

Is it ok? or it must be something wrong with the model.

As usual all comments are welcome!

Best regards,
Serguei







MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.

 

[Agent666]

Look at the deformed shapes for these modes and review the modal participation ratios. Sometimes there is one element flapping around that needs restraint.

I find it hard to believe the first three modes are torsional, but might be possible (not knowing the configuration of the building)

 

[JasonMcKee71]

It is possible to have torsional modes in tall buildings at first and translational modes appear later.

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
Moment Curvature Analysis
Interaction Diagrams
Reinforcement Design etc.

 

[serrojo]

Dear all,

Thank you for your answers!

After cracking my head, I asked the same question to the engineer, who modeled the structure.

he just told me that he had to open the building's core and that made the periods go crazy.

Now I have received the correct model and it is preforming ok.

Best regards.

MSc. Eng. Serguei Joa
Structural Engineer
Bouygues Batiment International, Cuba.