Section Orientation

Use the subnode to define the orientation of a pipe cross section using a reference point or an orientation vector. There is always one subnode for each cross section, and as many subnodes as needed can be added if the same section appears with different spatial orientations in the structure.

The most common pipe sections are symmetric. In this case, the only effect of the section orientation specification is to simplify the interpretation of section forces. This means that you in many cases can keep the default settings in this node.

	This node is available for 3D components.

Select the (the default) or . For , enter a P.

The coordinate system is defined as follows:

The local x direction is in the edge direction. The positive edge direction can be checked by vector plotting the local edge tangent direction. The coordinates of the reference point define the local xy-plane together with the beam axis. The local coordinate system (exl, eyl, ezl) is formed using the following algorithm:

Here, p is the reference point, and m is the midpoint of the pipe element. The definition of the local coordinate system is illustrated in Figure 12-6.

For the creation of a local coordinate system to be possible, the point cannot coincide with the edge or the edge extension. If this is attempted, an error message is generated.

	The settings for the global coordinates of the point are [1000,1000,1000]. This is useful only for symmetric cross sections.

Often a number of edges in a plane have the same orientation. It is then easy to select all edges and specify a point anywhere in the same plane, not coinciding with an edge or an edge extension.

For enter , V, and optionally the

. The beam orientation is defined similarly to what is described above, with the difference that in this case the direction vector is explicitly defined whereas when an orientation point is used, the direction vector is obtained as the vector from the beam axis to the specified point. The local coordinate system (exl, eyl, ezl) is formed using the following algorithm:

The has the effect of rotating the given vector around the beam axis (using the right-hand rule) before it is used to define the local xy-plane. This simplifies the input for some cross sections, such as L-shaped profiles, where the principal axes have a direction which is skewed relative to a more natural modeling position. This can be written as

Here the directions denoted with a prime are unrotated beam axis orientations obtained by the procedure described above.

Physics tab with node selected in the model tree: