Eigenvalue analysis

[marie]

Hi,

I would like to ask whether it is possible to get the story mass and mode shape for each story/node in Seismostruct?

Thank you and regards,
Marie

[seismosoft]

Hi Marie,

As described in the Help System of the program, you may obtain modal shapes in the 'Global Response Parameters' output module.

Storey/nodal masses, on the other hand, are not output.

Kind regards,

Seismosoft Support

[marie]

Hi,

Thank you very much for your response. If I'm not mistaken, in eigenvalue analysis, the 'global response parameter' tab is not available and the 'modal quantities' tab doesn't provide the mode shape information, so how could we know the mode shapes for 1st mode, 2nd mode, etc.?

Thank you and regards,
Marie

[seismosoft]

yes, of course, we obviously meant to say 'Step Output' module.

[marie]

Hi,

I'd like to ask how to include nodal load/force (lumped mass) in the eigenvalue analysis as there's no loading option and this can affect frequency of the structure?

Thank you and regards,

[seismosoft]

As explained in the Help System, eigenvalue analysis cannot consider loads.

As far as lumped masses are concerned, these can certainly be defined, again, as described in the Help System

Seismosoft Support

[Leandro]

Actually I am pretty new to the software. Anyway I am running an eigenvalue analysis for a simple structure (4 columns and 4 beams). But I am not getting reliable results in terms of natural frequencies. I cannot understand where is the problem.
Do the software automatically take into account masses of the structural element or do I have to assign them manually?

[huffte]

Leandro, I think if you will try the SeismoStruct Help system search capability and search on the following phrases, you will get some valuable information which will help clear things up. Don't forget to look at the Notes at the end of each section too. They have some valuable information as well.

"Distributed mass - dmass"
"Gravity & Mass"
"Lumped mass - lmass"
"Mass elements - lmass & dmass "

I hope this helps clear things up Leandro. In essence I would recommend section added mass where additional distributed masses are needed and lumped mass elements as often as possible and applicable.

[Leandro]

Dear huffte, thank you for the answer. I am pretty used to carefully read the Help. Basically when I ask questions in the forum it means that I have not been able to find out the information I was looking for in the Help menu.
Actually happened that I could not find proper results in an eigenvalue analysis and a vertical static one confirmed me there was a problem with the total weight of the structure (that is automatically computed by the program, but it is not stated anywhere in the Help). Incredibly the problem disappeared. I think it helped quitting and starting the software again (very first law for computer science).

Anyway, thank you so much for your kind reply.

[seismosoft]

Leandro,

What do you mean with the "total weight of the structure is automatically computed by the program, but it is not stated anywhere in the Help"?

The 'Automatically Transform Masses to Gravity Loads' feature is mentioned in at least the following Help pages: 'Applied loads', 'Element classes -> Mass elements -> Distributed mass', 'Project Settings -> Gravity & Mass'.

Seismosoft Support