Simple 3D building with asymmetrical loading problem

[piromoplus]

Hi All,

I did model a simple 2-story building in Opensees (3D modelling). Columns/beams are fibre elements and floor is a elastic shell. The plan is rectangular. When I have a symmetrical loading i.e. at top and bottom of plan, the deformation is quite close to SAP2000 result. But If I apply the load at only bottom or top (asymmetrical), the 3D model could not capture the torsion of the structure. What is the problem here? I checked my code with NextFEM designer as well and it seems fine. I really appreciate if you could advise me on this problem.

Best regards,

[piromoplus]

I checked the SAP2000 again. it seems that my code in opensees (or NextFem designer) solve the problem in XY plane only!! How it is possible when I use "model BasicBuilder -ndm 3 -ndf 6". Did I forget anything?

[selimgunay]

Is there a special reason for using shell for the floor. You can use a diapgrahm constraint and that will consider torsion

[piromoplus]

selimgunay wrote:
> Is there a special reason for using shell for the floor. You can use a
> diapgrahm constraint and that will consider torsion


I need to consider both out-of-plane and in-plane impact of floor on the 3D frame. But again, I am not following what is the reason for this problem. The in-plane stiffness of a shell element is conisderably high and should act like a diaphragm... Is there any flexible diaphragm option in OpenSees?

[fmk]

post the model and loads.

[piromoplus]

I sorted it out. -GJ should be defined. Cheers