Internal bracings

Use this option to define bracings and lateral supports for all analyzed stability cases (buckling, lateral buckling, and torsion).

Access

• Click in the Lateral buckling length coefficients dialog, or in the Buckling diagrams dialog.

Dialog elements

The dialog box is split into two parts:

• The upper part of the dialog - defined positions of bracings
• The lower part of the dialog - fields for entering successive coordinates of intermediate bracings.

There are two ways to define parameters of bracing elements limiting both the buckling length (in both directions) and the lateral buckling length of a member (separately for the upper and lower flange). Thus, during analysis, you can easily read the sets of bending moments in characteristic points. The options define buckling and/or lateral buckling length coefficients for the member sections between bracings.

Access the parameters for bracings (for buckling analysis) by clicking in the buckling diagrams dialog.

The defined intermediate bracings are displayed in the upper part of the dialog.

The following information is provided:

• Node numbers
• Member numbers
• Clearly-marked member beginning (the origin of the coordinate system).

Moreover, the view includes the following icons:

- click this icon to display information for bracings and lateral supports for buckling in the direction Y

- click this icon to display information for bracings and lateral supports for buckling in the direction Z

- click this icon to display information for bracings and lateral supports for lateral buckling of the upper flange

- click this icon to display information for bracings and lateral supports for lateral buckling of the lower flange.

If you select the Australian code AS4100, the view also includes the icon for bracings for torsional buckling.

Bracings are presented using the following colors:

• Bracings for buckling Y are marked in green
• Bracings for buckling Z are marked in red
• Bracings for torsional buckling are marked in blue (available only for the Australian code AS4100)
• Bracings on the upper flange are marked in violet
• Bracings on the lower flange are marked in violet
• Remaining bracings - in gray.

In the lower part of the dialog there are several tabs:

• Buckling Y
• Buckling Z
• Torsional buckling (this tab is available only for the Australian code AS4100)
• Lateral buckling - upper flange
• Lateral buckling - lower flange.

Each tab contains similar options:

• Define manually coordinates of the existing bracings - defines coordinates of successive points (positions of bracings); these coordinates may be given as relative values (with respect to the member length) or as real ones (in selected length units)
• Add automatically coordinates of bracings:
  • At points with adjoining elements in the buckling plane;

    On the Buckling Y and Z tabs - Use this option to automatically recognize points where the analyzed member is adjoined by other members in a selected buckling plane (such as members adjoining in the XZ plane for buckling Y).

    On the Lateral buckling - upper flange and lower flange tabs - Use this option to automatically recognize points where the analyzed member is adjoined by other members from any direction.

  • At all points where internal nodes are located - Use this option to automatically recognize points where any internal nodes are located, such as points where an analyzed element is adjoined by other members, or points where concentrated forces are applied.
  • At points where bending moments equal zero - Use this option to automatically recognize points where the sign of the bending moment diagram changes (at these points the moment equals zero), as indicated in many national codes, such a point can be assumed as a point at which a member is protected against the loss of stability.
• Buckling coefficients of component segments - Defines values of buckling (lateral buckling) coefficients for the member segments between bracings. After selecting an icon representing the analytical model (bar diagram) of the analyzed member, Robot proposes values of coefficients for extreme segments. For intermediate segments 1.0 is always proposed.
  Use the option to automatically calculate buckling coefficients for the member segments between bracings based on the analysis of rigidity of bracings adjoining the analyzed member in the corresponding buckling plane. Values of calculated buckling coefficients for successive segments are displayed in the field under the bar diagrams.

  Note: The icon is available on the Buckling Y and Z tabs only for steel design codes. To make it active, turn on the Add automatically coordinates of bracings: at points with adjoining elements in the buckling plane option (the remaining manual and automatic options should be cleared).

  Use the Structure: Sway or Non-sway options to specify how the frame is protected against buckling.

• Bracing detection preview
  Note: This option is available, if any of the Add automatically coordinates of bracings options is selected.

  Bracing coordinates proposed for a selected member are displayed in the unavailable field at the bottom of the dialog. Click << to move these coordinates to the field for manual definition of bracing coordinates. Clicking << clears all options for automatic definition of bracing coordinates to avoid duplicating coordinates defined manually and automatically.

  Use the For member no. option to select a structure member for which bracings are previewed. If the Add automatically coordinates of bracings: at points where bending moments equal zero option is selected, you can also choose a load case using the For load case option.

For instance, the image presenting the Internal bracing dialog allows you to define - for a member with fixed supports at both ends - 3 bracings whose relative coordinates (determined with respect to the member beginning) are: 0.25 x L, 0.5 x L, 0.75 x L. Thus defined bracings result in dividing a member into 4 component segments. With the bar diagram defined, Robot proposes 4 buckling length coefficients: 0.7 (fixed and pinned at the ends), 1.0 (pinned at the ends), 1.0 and 0.7.

The image presenting the Internal bracing dialog presents the combined use of manual and automatic options for defining bracings for buckling Y. The bracing 0.5 x L was defined manually, while the bracings 0.25 x L and 0.75 x L were proposed automatically based on the analysis of adjoining members in the XZ buckling plane.