Building period when tanks protrude through roof

[EngiNinja]

Hello All! I am working on a building that is about 60 feet tall to the roof. However, supported on this roof level are a large number of 40' tall tanks. The tanks are very closely spaced, so it is almost like there is a solid 40' level above the actual building structure. Does anyone ever let storage or non-building components like this come into play when determining a building's period? If we were to set the "height" of the building to the middle of the tanks, then the reduced Cs formula is applicable. Thanks!

 

[KootK]

What will be in these tanks and how often will they be full? I would expect the tanks to change a great many things about your seismic analysis, mostly for the worse. I also think that it would be wise do do a detailed period calculation rather than employing the code approximation algorithms which assume relatively uniform mass and stiffness distributions up the height of the structure. Sloshing could also have a substantial impact on things.

Often, rooftop equipment is quite rigid and effectively just adds to the mass of the roof diaphragm. Your stuff would seem to be of a drastically different scale however.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[IFRs]

These might be modeled as tanks on a tall platform rather than a platform with tanks on top?