A Body Constraint causes all of its constrained joints to move together as a three-dimensional rigid body. By default, all degrees of freedom at each connected joint participate. A subset of the degrees of freedom can be selected to be constrained.
This constraint can be used to:
Model rigid bodies of any size and type.
Model rigid connections, such as where several beams or columns frame together. This constraint is particularly effective when modeling cases with eccentricities in the connection.
Connect different parts of the structural model that were defined using separate meshes. A separate constraint must be defined for each set of constrained joints. If a large number of these constraints must be created, consider using the weld constraint instead.
The constraint must apply to at least two joints to have any effect on the model. These joints may have any arbitrary location in space.
Use the following areas on the Body Constraints form to make the appropriate entries:
Constraint Name. Use the default or enter a unique name for the constraint being defined.
Coordinate System. Choose the coordinate system in which the constrained degrees of freedom (below) are being defined. If all degrees of freedom are being used, the choice of coordinate system has no effect on the constraint.
Constrained DOFs. Choose the degrees of freedom being constrained. By default, all degrees of freedom are constrained, forming a full -rigid body from the constrained joints.
If only X and Y translation and Z rotation are chosen, this is equivalent to a diaphragm constraint if the joints lie in a plane normal to the Z axis of the chosen coordinate system.
If a translation is chosen but not the two rotations perpendicular to it, there is a risk that the model will be restrained if the joints are not coincident. For example, if translation X is constrained but not rotation Y, and the joints are separated by a non-zero distance in the Z direction, any moments about Y caused by X direction forces will be restrained.
If the Define menu > Joint Constraints command was used to access the Body Constraints form, the defined constraint must be assigned to the joints.
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Access the Body Constraints form as follows:
Click the Define menu > Joint Constraints command to display the Define Constraints form, or select the joints to be constrained and click the Assign menu > Joint > Constraints command to display the Define/Assign Constraints form. Then do one of the following:
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