Rigid Link

Enables you to define a rigid link between selected nodes in a frame structure.

Access:

Ribbon: Frame Analysis tab Connections panel Rigid Link

Defining a rigid link between nodes is the same as introducing rigid compatibility conditions with respect to all displacements in these nodes. All nodes linked with a parent node constitute a group of nodes comparable to a rigid body. Displacements and rotations defined for a rigid link can be limited to certain selected degrees of freedom.

Rigid links in a structure:

• Act between nodes.
• Can only be used in structures using rotational degrees of freedom. Therefore, you cannot define a rigid in the following types of structures: 2D truss, 3D truss, stress plane, deformation plane, axisymmetric structures, and volumetric structures.
• Are defined in the global coordinate system.

To define a rigid link, define at least two nodes, one parent node and one or more child nodes. Parent node passes its parameters (degrees of freedom) down to child nodes during simulation.

Note:

• If a node is a child node of an existing rigid link, you cannot define it as a node in the rigid link.
• You cannot add a rigid type constraint to the child node. You can only add elastic type of constraint. Use Custom Constraint command to add a constraint with elasticity.
• You cannot define a child node as a node compatible with other nodes. Parent nodes can have compatibility defined with other nodes.
• You cannot use a rotated constraint in the parent node of a rigid link for the selected degrees of freedom.
• You cannot add constraints to child nodes of rigid link.

For example, linear displacements can be blocked, while rotations can be allowed. The first node is the parent node, while the remaining ones are child nodes.

The use of rigid links can be illustrated by defining a floor which is rigid in its plane. But, in the direction perpendicular to the floor plane, it is pliant. A rigid link is defined as a rigid membrane linked with a parent node. Child nodes with a selected set of degrees of freedom are attached. (To achieve full rigidity, all degrees of freedom for the child nodes should be selected.)

	Parent Node	Select the parent node for a rigid link.
	Child Nodes	Select one or more child nodes for a rigid link. Note: You can define a node as a child node only in one rigid link.
	Displacement	Define the displacement degrees of freedom in the node: X axis, Y axis, Z axis.
	Rotation	Define the blocked rotation degrees of freedom in the node: X axis, Y axis, Z axis.
	OK	Create the rigid link and close the dialog box.
	Cancel	Close the dialog box without creating the rigid link.
	Apply	Create the rigid link and keep the dialog box open. Click when you want to create multiple rigid links.

Specify blocked rotation and blocked displacement:

Displacement	Rotation
X - axis: When selected, the displacement in the X direction in child nodes is blocked in the rigid link.	X - axis: When selected, the rotation about the X axis in child nodes is blocked in the rigid link.
Y - axis: When selected, the displacement in the Y direction in child nodes is blocked in the rigid link.	Y - axis: When selected, the rotation about the Y axis in child nodes is blocked in the rigid link.
Z - axis: When selected, the displacement in the Z direction in child nodes is blocked in the rigid link.	Z - axis: When selected, the rotation about the Z axis in child nodes is blocked in the rigid link.