etabs effective seismic weight

[EYFS]

Hi all,
I was checking the etabs effective seismic weight. I choose the masses only for the self weight of the structure.
etabs calculated the bas shear using part of that mass.any ideas?
picture are attached below.

https://drive.google.com/folderview?id=11iuGGHDzzMhyXDCcV6iOzXA4NLY18NvK

 

[Enrique2015]

Hello,
So ETABS assumes that all elements tributary to the base have grounded mass (i.e not accounted for as seismic mass), so half of the weight of your walls and columns, and if you have any mats or slabs at ground floor, all that mass is neglected. Because of this seismic weight will always be less than your reactions

Enrique

http://www.structuralapps.com

http://www.Tilmanllc.com