Fictitious bar (Geometry)

Fictitious bar property	Description
Icon
Modules where available
Function	Bar elements with given stiffness values
Axis position	Horizontal in
	Arbitrary (horizontal, vertical and skew) in
Geometry	Straight and curved
End connection	Rigid and hinged, or custom defined by Point-point connection
Stiffness	Editable (but, material and cross-section definition is not available)
Load direction	Vertical in
	Arbitrary in
Load type	All point and line load
Available analysis results	Displacement and internal forces
Default Short Command	FICB

Table: Fictitious bar properties

Figure: Fictitious bars connect plate elements

The program automatically generates “rigid” fictitious bars in the end points of “bars” modeled as a shell model (end edges of shell regions; see Shell model).

Definition steps

1. If needed (and available in the current FEM-Design module), set a proper position for the working plane.
2. Start  Fictitious bar command from tabmenu and choose Define.
   
   
3. Set the properties of the new bar at  Default settings:
   
   • Stiffness (General)
     EA, GI_t, EI₁ and EI₂ stiffness values can be assigned to bars. No definition of material and cross-section is needed. The local y’ axis represents the 1^st principal axis, and the local z’ axis defines the 2^nd principal axis.
     The value of rigid stiffness (“infinite” rigidity) can be defined and set as project default at Settings > Calculation> “Rigid” values > Fictitious bar.
   • Connections
     In  , the end connections are fully rigid.
     In 3D modules, the end connections can be set under the Connections tab similarly to Beams. Only the released motion (arrow) and rotation (two-headed arrow) components are displayed in the model view (Display settings).
4. Define the direction of the cross-section 1^st principal axis (local y’ axis; only in 3D modules).
   The y’ axis cannot be modified in the  module, so it is always parallel with the Global X-Y (working).
5. Choose a geometry definition method for the bar reference line (axis).
6. Define the bar in the model view based on the chosen geometry method.

Optional steps:

7. Modify the geometry with the Edit menu commands valid for line elements.
8. Modify the bar properties with the Properties tool of the Fictitious bar tool palette.
9. The fictitious bars are stored on “Modeling tools” Object layers. At layer settings, the default color and pen width can be set for all fictitious bars.