# Define Joint Constraints

Form: Define Constraints

Use the Advanced > Define > Joint Constraints command to access the Define Constraint form. Use the drop-down list and buttons on that form to add, modify, or delete constraint definitions. The table below identifies the types of constraints that can be defined using this command.

Note: Do not confuse joint constraints with drawing constraints. Joint constraints are a part of the model and affect its behavior. Drawing constraints are a drafting tool available in the interface to help you draw objects accurately, and they have no effect on the behavior of the model.

1. Select the appropriate type of constraint from the Choose Constraint Type to Add drop-down list.

 Constraint Type Form Define Axis or DOFs Action Rigid Rigid-type constraints are those when all joints in the constraint move together as some type of rigid body. Rotational and translational degrees of freedom may be coupled together. Body Body Constraint DOFs A Body Constraint causes all its constrained joints to move together as a three-dimensional rigid body. Effectively, all constrained joints are connected to each other by rigid links and cannot displace relative to each other. Note: Body Constraints connect a set of two or more joints together. The joints may have any arbitrary position in space. Diaphragm Diaphragm Constraint Axis A Diaphragm Constraint causes all of its constrained joints to move together as a planar diaphragm that is rigid against membrane deformations. All constrained joints are connected to each other by links that are rigid in the plane, but do not affect the out-of-plane deformation. Plate Plate Constraint Axis A Plate Constraint causes all of its constrained joints to move together as a flat plate that is rigid against bending deformations. All constrained joints are connected to each other by links that are rigid for out-of-plane bending, but do not affect the in-plane deformations. Rod Rod Constraint Axis A Rod Constraint causes all of its constrained joints to move together as a straight rod that is rigid against axial deformation. All constrained joints maintain a fixed distance from each other in the direction parallel to the axis of the rod, but the translations normal to the axis and all rotations are unaffected. Beam Beam Constraint Axis A Beam Constraint causes all of its constrained joints to move together as a straight beam that is rigid against bending deformation. All constrained joints are connected to each other by links that are rigid for off-axis bending, but do not affect the translation along or rotation about the axis. Weld Weld Constraint DOFs A Weld can be used to connect the different parts of the structural model that were defined using separate meshes. A Weld is not a single constraint, but rather is a set of joints from which the program will automatically generate multiple Body Constraints to connect coincident joints. Equal Equal-type constraints are those when individual degrees of freedom of different joints are identical. These are usually used for connection and for symmetry conditions. Equal Equal Constraint DOFs An Equal Constraint causes all of its constrained joints to move together with the same or opposite displacements for each selected degree of freedom, taken in the constraint local coordinate system. The other DOFs remain unaffected. Local Local Constraint DOFs A Local Constraint causes all of its constrained joints to move together with the same or opposite displacements for each selected degree of freedom, taken in the separate joint local coordinate system. The other DOFs remain unaffected. Interpolation Interpolation constraints are those when degrees of freedom at one joint are interpolated from the degrees of freedom at some other joints. These are usually used to connect incompatible meshes. Line Line Constraint DOFs A Line Constraint is used to model transitions where two incompatible meshes meet along a line, for example where a finer mesh on one side of the line has elements half as wide as elements in the coarser mesh on the other side. The Line Constraint does not impose rigid behavior on the model. Rather, the deformation along the line is determined by the coarser of the two meshes.

1. Click the Add New Constraint button to access the {Constraint Type} form and define the Constraint Axis or the Constraint DOFs, depending on the type of constraint selected.

2. Click the OK button to return to the Define Constraints form. Click the OK button to complete the definition of the constraint.

• Modify/Show Constraint button.

1. Highlight the name of the a constraint definition to be modified in the Constraints display list.

2. Click the Modify/Show Constraint button to access the {Constraint Type} form and make the necessary changes.

3. Click the OK button to return to the Define Constraints form. Click the OK button to complete the modification of the definition

• Delete Constraint button.

1. Highlight the name of the a constraint definition to be deleted in the Constraints display list.

2. Click the Delete Constraint button to delete the constraint definition