...
- Constraint
...
- is
...
- a
...
- set
...
- of
...
- two
...
- or
...
- more
...
...
- that
...
- are
...
- constrained
...
- such
...
- that
...
- their
...
- displacements
...
- relate.
...
- Constraints
...
- may
...
- be
...
- used
...
- to
...
- model
...
- 1).
...
- rigid-body
...
- behavior,
...
- in
...
- which
...
- joints
...
- translate
...
- and
...
- rotate
...
- together
...
- in
...
- a
...
- rigid
...
- connection;
...
- 2).
...
- equal-displacement
...
- behavior,
...
- in
...
- which
...
- displacement
...
- along
...
- certain
...
- degrees
...
- of
...
- freedom
...
- (DOF)
...
- is
...
- equal;
...
- and
...
- 3).
...
- symmetry
...
- /
...
- anti-symmetry
...
- conditions.
...
- Constraints
...
- enhance
...
- computational
...
- efficiency
...
- by
...
- reducing
...
- the
...
- number
...
- of
...
- equations
...
- necessary
...
- for
...
- solution.
...
- Multiple
...
- constraints
...
- should
...
- not
...
- be
...
- assigned
...
- to
...
- a
...
- single
...
- joint.
...
- Body
...
- constraint
...
- is
...
- applied
...
- to
...
- a
...
- set
...
- of
...
- joints
...
- that
...
- translate
...
- and
...
- rotate
...
- together
...
- as
...
- a
...
- rigid
...
- body.
...
...
...
- is
...
- automatically
...
- applied
...
- to
...
- all
...
- DOF
...
- within
...
- the
...
- constraint,
...
- though
...
- only
...
- certain
...
- DOF
...
- may
...
- be
...
- specified.
...
- Body
...
- constraints
...
- 1).
...
- simulate
...
- rigid
...
- connections;
...
- 2).
...
- connect
...
- portions
...
- of
...
- a
...
- model
...
- that
...
- are
...
- defined
...
- by
...
- separate
...
- meshes;
...
- and
...
- 3).
...
- connect
...
...
- to
...
...
- .
- Welds are applied to a region of the model, generating multiple sets of body constraints among joints that are coincident, meaning located within a specified tolerance. Only joints within the weld are checked for coincidence. Welds are useful for connecting parts of a model that are defined by different meshes. Additional information on these constraint types, and others, is available in the Analysis Reference Manual (Constraints and Welds, page 49).
- Restraints concern only the behavior of individual joints. Restraints differ from constraints in that constraints are associated with relationships among sets of joints. Restraints should not be applied to joints that are part of a constraint. Instead, restraints may be replaced with either stiff springs or large stiffness properties along those DOF. Restraints must be applied when joint displacement is known at specific DOF. Displacement may be zero, as with support points, or nonzero, as with support settlement. The reaction, generated during analysis, is the force necessary to produce a specified restraint displacement. Restraints should also be applied when stiffness is zero along specific DOF, as with the out-of-plane translation and in-plane rotation of a planar frame. Additional information is available in the Analysis Reference Manual (Restraint Supports, page 34)