Interpreting Results of Periods of Etabs

[020457]

I have been struggling with the periods on my model specifically along the Y-direction. I have attached the results of the 12 modes of Etabs and I am just wondering whether, for example on my second direction (ConcU01), I have a mass along the y-direction of 23.5% on mode 2 but mode 8 is giving me 33.2% of the mass and therfore giving me a period of 0.10 secs and therfore huge seismic mass against the second mode with a period of 0.57secs. Can anybody tell me if it is safe to use the second mode result rather than the 8th mode...I have attached the data of the periods with corresponding mass participations...thanks for the help

Ramon

 

[dcarr82775]

Have you checked your model to make sure there isn't something amiss that causes the 8th mode to participate that much mass?

Will Etabs do a response spectra analysis?

 

[JoshPlumSE]

The numbers can only be so helpful. In the end, you'll probably understand the structure better by viewing the mode shapes. You can see which portions of the structure are more active for which mode. It's easier to get an intuitive feel for what is happening that way. Maybe you'll find a modeling error, or maybe you'll gain an understanding for why the modes behave that way.