GAMMA Angle

Open the GAMMA Angle dialog, which is used to change the position of a bar section's local axes, using either method:

Click Geometry menu > Properties > Gamma Angle.
Click .

To define a GAMMA angle:

Select the bars for which you want to change the position of the local coordinate system. Enter the bar numbers in the Bar List field or perform a graphic selection.
Enter the Gamma angle value.
Click Apply.

You can enter a value of the Gamma angle using one of the following methods:

Enter or select the numerical value for the selected bar angle (fields: Value or Special values).
Select the node (the Node option in the Special values field) together with the bar nodes, defines the main bending plane of the bar section.
Select the bar (the Position option in the Special values field and the Number option). The selected bars are turned in such a manner that one of the cross-section principal axes is perpendicular to the longitudinal axis of the highlighted bar. This option is useful when setting roof purlin bars. The consecutive stages for determining a Gamma angle for structure roof bars are shown in the following images.

Initial position of bars

After defining a Gamma angle, the following bars are selected:

In the Bar List field, the numbers of all purlins are entered (See Bar list in the image.)
In the Number field, the number of a bar is entered, which determines the rotation plane (See Bar no. in the image.)

Position of the bars after defining a Gamma angle.

It is assumed that the positive angle is defined according to the right-twist rule.

Note: For 3D frames, the GAMMA angle can be any values in the range between (-360°, 360°).For 2D structures, the GAMMA angle must be a multiple of a 90° angle. Bars in 2D structures can be rotated only by the angles: ±90°, ±180°, or ±270°. For a 2D structure, if a different value is defined for a GAMMA angle, Robot automatically performs an additional rotation, so the GAMMA angle is a multiple of a 90° angle.

The following image of a bar structure shows different methods for defining Gamma angle values.

Note: The rotation of a local system (for all structure types,except for 3D frames, shells, andvolumetric structures) affects only the position of a section and not the loads in a local system. Loads in a local system always correspond to the initial system settings. For 3D frames, shells, and volumetric structures, the rotation of a local coordinate system results in rotating the load as well, if it was defined in the local system.