Shell model (Geometry)
In 
3D Structure module, straight and arc bars (Beams and Columns) can be modeled more accurately for stability, utilization check (against flexural, torsional, lateral torsional and local buckling) and design according to their EC by modeling them with planar shell members.
Definition steps
- Press Analytical model / Shell model option of Beam or Column toolwindow and choose the bar. By default, selecting a bar element generates a complex 3D model built by a group of steel plates derived from the geometry of the selected bar’s profile. All converted plates inherit the original bar element’s steel material.
Figure: Straight bars with constant cross-section
After converting a bar to shell model, the program automatically defines “rigid” Fictitious bar objects at the ends of the shell model to guarantee continuous connection to other objects line 1D members, point supports and point loads. The stiffness of these fictive elements can be modified with the
Properties tool of Fictitious bar command. Alternatively, this function can be turned off by clicking 
after selecting Analytical model in the Beam or Column toolwindow.
Depending on, Beam, Column or Truss member was converted to shell model, the model can be hidden together with the Beam, Column or Truss member object layer.