RFEM – Online Manual

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RFEM – Online Manual

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4.2 Lines

General description

The geometry of the model is defined by lines. They are essential for creating members, surfaces, and solids. Every line is defined by a start and end node. To define complex types of lines, additional intermediate nodes are required.

Figure 4.24 New Line dialog box
Figure 4.25 Table 1.2 Lines

The line number is automatically assigned in the New Line dialog box and can be changed in it. The order of the line numbers is not important.

To adjust the order of line numbers retroactively, select Tools → Renumber in the menu (see Chapter 11.4.18).

Line Type

In RFEM, the following line types are available for selection in the menu and in the table list:

    • Single line
    • Polyline
    • Arc
    • Circle
    • Ellipse
    • Elliptical arc
    • Parabola
    • Hyperbola
    • Spline
    • NURBS
    • Trajectory
    • Line on surface

The different types of lines are described on the following pages.

Nodes No.

Every line is geometrically defined by a start and end node. They define the line orientation that also affects the position of the line coordinate system. The nodes can be entered manually, selected graphically, or redefined (see Chapter 4.1). If a line requires control points or intermediate nodes, they are also included in the nodes list.

The display of line orientations can be activated in the Display navigator.

Figure 4.26 Activating Line Orientations in the Display navigator

The line orientation can be changed quickly in the graphic: Right-click the line and select Reverse Line Orientation in the shortcut menu. The numbers of the start and end nodes will be switched.

The coordinate systems of lines can be activated in the Display navigator: Go to Model → Lines and select Line Axis Systems x, y, z including Indexes (see Figure 4.102).

Line Length

This table column shows the total length of the line.


Table column D provides information about the global axis the line is parallel to, or in which plane spanned by global axes the line lies. If there is no entry, the line is in an arbitrary spatial position.


This field allows you to enter user-defined notes. Use the [Apply Comment] button to import saved comments (see Chapter 11.1.4). A Generated comment appears for lines created by RFEM (e.g. a pipe).

Line / Polyline
Figure 4.27 Graphical input dialog box New Line

Selecting the line entry in the pull-down menu opens the New Line dialog box shown in Figure 4.24. The figure above shows the general dialog box for entering lines graphically. Use the list button in the toolbar to open it.

A "real" line is defined by only one start node and one end node. Such a line represents a direct connection between both nodes.

A polyline is a polygonal chain consisting of several straight line sections. The intermediate nodes are therefore listed in addition to the numbers of the start and end nodes in the dialog box (see Figure 4.24). To simplify line management, "real" lines are handled as polylines.

When entering polylines graphically, existing nodes, grid points, or snap objects can be selected as definition nodes. It is also possible to set nodes freely into the work plane.

For example, if line loads or line supports are only effective for sections of a polyline, you can retroactively split a polyline into "real" lines: Right-click the polyline and select Explode Polyline in the shortcut menu. You can also access this function via Edit → Model Data → Lines → Explode Polyline.

Figure 4.28 New Line dialog box, Rotation tab

In the second tab of the dialog box, you can define a Rotation of the line. Specify either an Angle β or a Help node that the line axis y or z is to be aligned with. The help node can be selected in the list, defined graphically, or newly created.

A rotation of the line may facilitate the input of line loads acting in local line direction. Line rotation does not affect surfaces or members because they have their own coordinate system.

The local line axis systems are shown in Figure 4.102.

Figure 4.29 New Line dialog box, Arc tab

An arc can be defined by the following parameters:

    • Three nodes
    • Center node, edge node, and opening angle
    • Edge nodes and radius, opening angle, or rise
    • Tangents and radius

In the Nodes at Arc dialog section, you can define the start, intermediate, and end nodes directly, select them graphically, or newly create them. The node order is shown in the small dialog graphic.

Based on these three nodes, RFEM determines the Arc Parameters specified in the dialog section below. It is possible to change the radius r, the rise h, and the opening angle α. The node coordinates are adjusted accordingly.

The coordinates of the arc center that result from the arc nodes or parameters are displayed in the Center of Arc dialog section. When you change data manually or select nodes graphically with the button, the coordinates of nodes are adjusted as well.

In the Subsequent adjustment by displacing node at list, you can specify the node you want to change the coordinates of.

When you define the arc graphically using a toolbar button, the via Three Nodes option allows you to select or create the nodes directly in the graphic.

If you select one of the other input options, you have to select two nodes first, as shown on the left in Figure 4.30 and Figure 4.31. Then, another dialog box (shown on the right) appears where you define the arc parameters.

Figure 4.30 New Arc dialog box - definition type Arc via Center Node, Edge Node and Angle

In the Options dialog section (in Figure 4.30 and Figure 4.31 on the right), you can select the arc's plane from the list. The Included Angle can be defined directly in the graphic or entered manually and applied with [Apply].

To adjust an already defined arc, double-click its arc line. The Edit Line dialog box opens where you can modify the data in the Arc - Three Nodes dialog tab (see Figure 4.29).

Figure 4.31 New Arc dialog box - definition type Arc via Edge Nodes and Radius, Angle or Rise

In the Definition Type dialog section (right box), select the appropriate arc parameter from the list. Then, set the arc directly in the graphic or enter it manually and click the [Apply] button.

In the Step text box, you can enter the spacings after which the pointer snaps when dragging the arc radius, angle, or rise.

The orientation of the circular arc can be adjusted by selecting the Reverse orientation check box, which determines whether the arc is placed to the "right" or the "left" of both nodes.


A circle can be defined by the following parameters:

    • Three nodes
    • Center point and radius
Figure 4.32 New Line dialog box, Circle - Normal tab

You can enter the Circle Radius and the coordinates for the Center of Circle manually or graphically by using the button. The Point of Normal to Circle Plane determines the plane in which the circle is generated. Use the three buttons in the dialog section to select one of the global axes.

Figure 4.33 New Circle dialog box - definition type Center and Radius

When you define the circle graphically by using one of the toolbar buttons, you can select or create the three nodes or the center and radius directly in the graphic.


To define an ellipse, three nodes are required.

Figure 4.34 New Line dialog box, Ellipse tab

The ellipse is generated by the Nodes on Ellipse: The largest distance between the three entered nodes is assumed to be the principal axis of the ellipse.

When you use the toolbar button to define the ellipse graphically, you can set it directly by selecting three nodes in the work plane.

Elliptical arc / Parabola / Hyperbola

The following curves of conic sections can be defined:

    • Elliptical arc
    • Parabola
    • Hyperbola