How to increase the Modal Mass participation ratio

[SilverBeam75]

Hi,

In seismic design, it is required to have a mass participation ratio of 90%+. My model has 75%, what should I do to increase it ? What exactly does it means?

Any help would be appreciated

 

[rscassar]

You need to include more modes in your analysis so that you get over 90%.

 

[slickdeals]

You may have some instabilities in your model (local modes such as cantilever vibrations, extremely flexible beams) that are causing small modal mass participation, but still using up the overall modes in your analysis.

Take a look at the modal mass participating ratios to see if you have a lot of modes with low modal mass.

If not, try to bump up the number of modes as kikflip suggests.