8. Definition of buckling and lateral-torsional buckling constraints

To define the XY, XZ and LTB buckling, the user must select the proper tab pages in the lower right area. The Buckling XY page displays the list of constraints for the XY plane, with data for each constraint, such as the constrained node, the length, the constraint type and the n coefficient, if that particular option has been selected.


Note: It is not allowed to remove all constraints. At least one must remain and that is set automatically to Rotation constraint type.

At the same time, at every 3D display window, the constraints on every node are being displayed using special symbols, whose color codes are described in the following table:

instant-wiki-md80 Translation constraint Buckling ΧΥ, instant-wiki-md81 Rotation constraint Buckling ΧΥ

instant-wiki-md82 Translation constraint Buckling XZ, instant-wiki-md83 Rotation constraint Buckling XZ

instant-wiki-md84 Lateral-Torsional Buckling K : Translation constraint, Kw : Rotation constraint

In general, the translation constraints are displayed using golden coloured cones, and the rotation constraints are coloured mauve. Specifically for LTB, where K and Kw factors are supplied, a cone is displayed for each factor, with the inner one showing the K constraint and the outer one the Kw constraint.

Note : The constraint types have been renamed from the previous versions of Member Design. The type Translation Constraint was known as Pinned and the type Rotation Constraint was know as Fixed. The Sway, Non-Sway constraint type is covered by a specific option that applies to the whole member.

Press the Add button to add a new constraint. This will append a new line in the list of constraints. In the Length column, select one of the available lengths along the member where the constraint can be attached. In the next column, select the type of constraint between Translation, Rotation and n value. If the constraint type n value is selected, then the value can be entered in the next column.

A separate table at the bottom of the page displays a list of the buckling lengths and related buckling factors (K). Both the lengths and the factors can be edited and a change in the value of each will be reflected on the other. If a constraint is a added or removed, or the constraint type is changed, the buckling lengths and factors are recomputed.

The Sway member option is available only for members that have both ends constrained in the selected direction and at least one of them is a rotation constraint. If any other constraints are defined inside the member or one of the end constraints is removed, the Sway option is cleared and disabled.

In the same way, the constraints in the XZ and Lateral-Torsion can be defined in their respective pages.