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4.22 Intersections

General description

If surfaces intersect and internal forces are transferred on the common line, you have to create an intersection. Otherwise, you would have two independent subsystems without any connection. The following example demonstrates the effect.

Figure 4.185 Deformations due to self-weight without intersection (left) and with intersection (right)

Each time the model is changed, RFEM must recalculate the intersections. When complex models are designed, recalculating data is very time-consuming for the graphical representation. The input is slowed down accordingly.

Figure 4.186 New Intersection dialog box
Figure 4.187 Table 1.22 Intersections
Intersection through two surfaces

In the text boxes or table columns, enter the numbers of the two intersecting surfaces. In the New Intersection dialog box, you can select the surfaces from the list. You can also use to select them graphically.

Intersections (of more than two surfaces, if need be) can be created quickly in the graphic: Select the surfaces by drawing a window. You can also use the multiple selection by holding down the [Ctrl] key. Then, right-click one of the selected surfaces. The shortcut menu opens where you select Surface → Create Intersection. RFEM creates the intersection automatically.

Figure 4.188 Shortcut menu Surface → Create Intersection
Line Numbers Generated by Intersection

When creating an intersection, RFEM generates a line that is shared by both surfaces ("intersection line"). The number of the new line is shown in the dialog field and table column.

Intersection lines are labeled as the line type Intersection in Table 1.2 Lines. The comment identifies them as Generated lines. The Edit Line dialog box can also be used for intersection lines so you can assign member or support properties.

Active surface components

An intersection line divides a surface into components that can be individually set active or inactive. Inactive surface components are not displayed in the work window. Neither are finite elements created nor is loading applied for this. Only active surface components exist for the equation solver.

Components of intersections can be activated and deactivated as follows:

    • Edit Surface dialog box
    • Double-click the original surface in the Data navigator. When you double-click the surface in the work window, use the [Go to] button available in the Component dialog tab (see Figure 4.71) to open the edit dialog box of the original surface.
    • The Active Surface Components section of the Integrated / Components dialog tab lists all surface components created during the intersection's generation.
Figure 4.189 Edit Surface dialog box, Integrated tab
    • The surface component marked in the list is highlighted in color in the work window. To deactivate a component, clear the corresponding check box. The inactive surface component is subsequently displayed without filling color.
    • Shortcut menu of surface component in the Data navigator / shortcut menu
    • Directly right-click the Surfaces navigator entry or the component in the work window. Then, use the shortcut menu to activate or deactivate the surface component.
Figure 4.190 Shortcut menu of a surface component in the navigator and work window
    • The shortcut menu provides further useful features for editing the component or original surface.

The geometric information of the original surface is kept internally by the program as it is needed for recalculating the intersection after modifications. Therefore, inactive surface components cannot be deleted, only hidden.