ETABS 2015: Uplift from Dead Load in shear walls

[pksarguru]

In my model I was getting uplift from dead load in a couple of my shear walls. I thought it might be moment or something being driven into the wall at some floor, but I was able to isolate it to the self weight of the wall. For some reason, when I include the self weight of the wall I'm getting uplift at the bottom.

I'm using 10"CMU walls that are defined as thick shells, meshed at a 4'x4' pattern.

Any thoughts on what might be causing this?

 

[MrHershey]

Really tough to tell without knowing anything about the geometry of the overall structure.

Most odd uplifts I've seen are at short end spans of long continuous members or sometimes you'll see load shed from one element to another nearby element if their stiffnesses are sufficiently different. See the latter quite a bit when we have cracked factors on walls because the way ETABS handles wall crack factors, you'll decrease your axial stiffness as well (not just flexural stiffness). So if they're near or even on top of a column, you'll have a full axial stiffness column leeching load out of a diminished axial stiffness wall.

 

[pksarguru]

Thanks for the reply. I understand it's really difficult to comment on without geometry. I was hoping to hook someone before posting a ton more info. Attached is a plan of the 2nd floor and an elevation of the wall I'm having trouble with. Also, the 3rd-floor geometry is identical. I scoured to see if there might be a node amiss but I haven't seen anything. The axial load diagram also only looks the way it does when the self weight of the wall is taken into account.

 

[MrHershey]

What changes at the fifth floor? Looks normal above the fifth floor but then starts shedding load somewhere else. Perhaps to the nearby column, perhaps to the adjacent walls.

Do you have any stiffness modifiers applied?