Column Loads in Etabs

[fickky]

Hi,

I have a situation where the column loads aren't cumulative (adding up) and the loads aren't right either. These columns are beside the shear walls and I am thinking the load is transferring into walls due to stiffness, is that right? will that happen? Anyone's input will be greatly appreciated, the screenshot is attached.

 

[JoshPlumSE]

Probably not enough info for me to figure it out. Some general thoughts:
1) There is sometimes a difference between what the analysis will show and what force I want to use for design.
2) If the column loads are "bleeding" off into nearby walls, that may be a real effect base on stiffness. If the structure were built all at once and the loads were applied all at once. However, my tendency is to (for gravity loading) to do a manual correction for the design forces in the columns. Meaning that I will manually check the columns for the full gravity loads as if no bleeding occurred.
3) Sometimes I will create a test load case that applies only one large load atop one particular column and just trace that load down through the structure. It really help to simplify the investigation.
4) Similarly, I may break out my DL (or LL) so that there is a different load case for each floor level. That way, I can see that each floor is attributing it's gravity loads properly to the columns or walls.

 

[Agent666]

Are the columns modeled at the wall/shell ends, to model an end region? If so one comment I have on this method is making sure that the axial reduction in stiffness for any columns built integrally with the wall match that applied to the walls for maintaining axial deformation compatibility (to modeel flexural reduction factor, typically f11 or f22 depending on the orientation in your model). Otherwise you'll see weird transfers of load between columns and shell elements. because the axial stiffness is not the same

 

[fickky]

Thanks for the response JoshPlum and Agent666. I have done manual calculations to compare with Etabs output, figured out wrong. I would have to see if the stiffness factors make a difference.

To further add to the information I have provided earlier, its an 11 story tower with 4 story wings. These columns and shear walls are at the end of the tower (stops at four-story level) with steel beam sitting on top of columns which is supporting concrete walls (5th to Roof) and remaining beams the floor slab. I am expecting a reaction from the steel beam on to that column, which should be at least close to manual calculations.