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### Amplitude of mode shapes

Amplitude of mode shapes

Dear All,

I am a new user of STAAD Pro and interested in the Dynamic Analysis.
From the modal calculation command, we get a frequency, a (mass) participation X-Y-Z % by mode and mode shapes. I have questions as below?

1. Can the STAAD Pro show amplitude of 1st mode, 2nd mode, 3rd mode and other mode in the output?. Or
2. Can we find the amplitude of 1st mode, 2nd mode, 3rd mode and other mode by STAAD Pro?

pvsnak@live.com

### 5 Replies (Most Recent Reply)

•

Answer for 1 and 2 : Yes. Use the command PRINT MODE SHAPES. The values will appear in the ANL file. You can also see them in a table in the Post processing mode's Dynamics page.

Answer for 3 : Mass participation factor is the percentage of the total mass of the structure in a given direction that contributes to the base shear for that mode.

• Dear Saraswathi.I,

Thank for your answers, and I try to do with your advice. I found the way to get mode shapes by mode with the print mode shapes command and the mode shapes is normalized (the number is show in 0 to 0.999 or 1). But I need to know the amplitude (the max. displacement) in unit mm or cm of each mode shapes. Could I ask you that

1. Can we find the amplitude (the max. displacement) in unit mm or cm of each mode shapes by STAAD Pro?.

2. Can I submit my STAAD (.std) file to you? And help to advise.

Sunthorn N. (pvsnak@live.com)

• In reply to Sunthorn Nakkote:

Please send the model STD file to ray.curtis@bentley.com.

The answer to your question is that STAAD does not output the maximum displacement of each mode after consideration has been given to the spectral acceleration of the mode, plus the scale factor and the direction factor. This scaled mode would be the final displacement vector if all other modes were trivial.

We expect that this output will be an option in the next release or next patch for Staad.Pro.

A SET PRINT 17 command will enable this output.

Note that only the modal displacement maximum amplitude is output, not the entire mode. The printed mode shape times the modal displacement would give the entire mode.

• In reply to Raymond Curtis:

Hi Raymond,
How to add a SET PRINT 17? What does the number 17 mean? thanks