Does anyone know why etabs asign masses to "Base" (I assume is the nodes in the foundation

[GJoeRMK]

Hello everyone:
I am having issues at understand why Etabs is assining masses in reaction nodes, it doesnt make any sense, I lumped masses at story levels, but Etabs doing at base level (reactions) is just wonkers. Any way to undo that behavior?

 

[JoshPlumSE]

Is it related to self weight of the elements that are connected to those joints / locations?

FWIW, I believe this is one of the main reasons why people sometimes opt to NOT include self weight in their definition of mass.

I know I've had this issue before with other programs (RISA). I believe in that case (which was quite awhile ago now), I assigned a material with no weight to the columns or walls at the lowest level (or half the lowest level) so that I could get to 90% mass participation.

That being said, using static correction vectors (in an eigen solution) or Ritz vectors (instead of an Eigen solution) is probably an easier solution than what I did back then.

 

[GJoeRMK]

Hello Josh,
Yes, I activated self weight on section definition and that goes to my load dead case which has the self weight multiplier set to 1, my model has frames and shell elements (walls), so I guess part of that goes to the joints in the foundation. Thanks for your recommendation