Supports or restraints refer to degrees of freedom at a node that are fixed. This fixity can be in any of the active translational or rotational directions.
There are several ways to define these support conditions:
- Global restraints - in the General specification
- Nodal restraints - in the Nodes table or the Node properties pane
- Generalised restraints - under Constraints
Global restraints apply to all nodes in the model and are most commonly used to constrain the model to act in a plane.
Nodal restraints apply on a node-by-node basis. By default these support conditions are in the global axis system. To apply a skew restraint go to the Explorer pane > Data > Nodes. In the node table that opens, define an axis for the required directions.
The node should then use this as the constraint axis, and the directions defined as restrained will be relative to the constraint axis. Nodal restraints apply in all analysis stages where the node is active.
Change your axes display by selecting the Labels and display methods icon:
Then select from the options in the Axes tab.
Generalised constraints act in the same way as nodal restraints. The main differences are that a single generalised restraint can apply to many nodes and that support conditions can vary from one analysis stage to another.
A restraint provides a fixed support with infinite stiffness. It can be convenient to assign a stiffness to a support (for example to model ground stiffness under a column). This is done by assigning a Spring property to the node. To do this, go to the Explorer pane > Data > Nodes and define the spring property column in the table that opens.
The support stiffness is taken from the spring properties. These then act in the nodal constraint axis directions.
A settlement is where a support has a fixed displacement. This is modelled by applying a restraint to the node and then defining a settlement at the node in a given load case.
To do this, define your restraint condition by going to Explorer pane > Data > Nodes. To apply settlement, go to the Loading tab of the Explorer pane, and select Nodal loading > Settlements.