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4.31 Nodal Constraints
A nodal constraint correlates the displacements and rotations between two or more nodes. This makes it possible, for example, to display wall or ceiling slabs in member models without using surfaces.
You have two options for the coupling: In the case of a Diaphragm Constraint, the displacements in the constraint plane as well as the rotations perpendicular to the plane are coupled. Thus, you can model stiffening slabs, for example.
With the constraint type Equal Condition Constraint, it is possible to individually specify the coupled displacements and rotations between the nodes.
For diaphragm constraints, the degrees of freedom are automatically set in the Constraint Condition dialog section or in the table columns E to J. For equal degrees of freedom, you can access all six check boxes to define the constraint conditions.
You can enter the numbers of coupled nodes manually, select them from the list, or use to define them graphically in the work window.
If you want to model a slab with the coupling, you have to enter all corner nodes of the plane.
You have to define the reference axis system for the coupling. You can select the global XYZ Coordinate System or the user-defined UVW coordinate systems from the list or the dialog section. You can also create a New Coordinate System by using the button. The dialog box shown in Figure 11.49 appears.
To adjust the user-defined coordinate systems, use the and buttons.
User-defined coordinate systems make it easier to enter inclined diaphragm constraints for roofs (see Figure 4.218).
This dialog section and the table column D can only be accessed for diaphragm constraints. You have to specify, in which plane a coupling of the displacements or rotations takes place. For the global coordinate system, you can select the planes XY, YZ, and XZ. For a user-defined coordinate system, you can select the planes UV, VW, and UW.
This setting controls, which constraint conditions are automatically activated in the dialog section below and in the table columns E to J.
The check mark at a component of the translational constraints indicates that the displacement is coupled in direction of the corresponding global (or user-defined) axis.
The check boxes are only accessible for the constraint type Equal Condition Constraint. In the case of diaphragm constraints, RFEM automatically defines the constraint conditions through the constraint plane.
You can also define constraint conditions for rotations that control the transfer of moments. The three global (or user-defined) axes are available for selection.