Mass participation not satisfactory/composite structure

[MADIEN.SALMOUN]

Hi Guys,

I tried to analyze a composite structure with concrete beams on the 4th and 5th story ,  When i run modal analysis i keep getting 56%  mass participation in X direction and 73% in Y. I tried every thing i know can any one help me .

[MADIEN.SALMOUN]

HI,

I HAVE PROBLEM WITH MY MODEL 

I TRIAD ALL SOLUTION NOMATTER I DID , THE REAL MASS VALUE WOULD NOT BE OVER 36% 

CAN ANY ONE HELP ME PLEASE , 

[Simau]

@MADIEN.SALMOUN 

Share your model

Zip it before attaching

[Simau]

@MADIEN.SALMOUN 

Please don't open a new thread as this one below has the same topic

https://forums.autodesk.com/t5/robot-structural-analysis-forum/mass-participation-not-satisfactory-c...

[MADIEN.SALMOUN]

Here is my model , and Sorry about the repetition

[Simau · Accepted solution]

@MADIEN.SALMOUN 

In modal case #9 you have to set number of mode to 600 or more.

The basement if very stiff so its mass will be mobilized at very high frequencies

[MADIEN.SALMOUN]

Thank you for your time, it worked!

I have another question, when I change the panel calculation model for floor the mass value change and real mass participate, why? is there preferred panel calculation model to get it done correctly? 

[okapawal]

@MADIEN.SALMOUN 

This is an issue in modal analysis, when you use panel calculation model with load distribution but without finite elements nor diaphragm, the mass of panels is neglected.

As a workaround, you can set load to mass conversion for the self-weight load case.  Don't forget to check "Disregard density" for modal analysis in this solution.

Alternatively you can use any other panel calculation model.  I would recommend using diaphragm in case of seismic analysis.

[okapawal]

This issue has been corrected in Robot Structural Analysis 2024 release. Release notes 

Corrected calculation for panels with curtain wall calculation model which mass was not taken into account in modal analysis.