Moment at top of a cantilevered shear wall when modelling in eTabs

[kbneng]

Hi guys,

I'm modelling a simple single storey shear wall with load at the floor level. When I have a model with just a planar wall, the pier moment is zero at the top and maximum at the bottom, which is what I expected. However, when I add perpendicular flange walls and analyse with the same load again, there is now a moment at the top of the wall. This is strange to me because I expected the 3D shear wall to still behave as a cantilever. See attached screenshots.

I've set the floor diaphragm slab to membrane so there shouldn't be any flexural restraint provided by the slab.

I'm curious if this is a real phenomenon or a modelling error?

Thank you!

 

[KootK]

I'm not sure that result is incorrect. The classic moment diagram from your first screen capture is only applicable to the wall core group taken in aggregate I believe. I think that, if you imagine the vertical shears that the core group flanges will oppose on the sides of the web, this pattern starts to make sense. It may well be that you need a more refined FEM discretization as well though.

I think that it's great that you're questioning your output in this way. Truly.

 

[kbneng]

KootK, thank you very much for the suggestions! I tried a finer mesh and the diagram now looks closer to what I expected (see below). Etabs by default only assigns one shell element for one rectangular wall, and that works fine for planar walls, but when we have 3D walls, it looks like a finer mesh is more desirable.

Thanks again for your help!

 

[KootK]

Happy to help KBNeng. I'm glad that it's worked out.