Nodes [FEA]

Nodes are points in space that define the structural geometry. Each node has 6 degrees of freedom (3 translations + 3 rotations) and can serve as connection points for elements or as support locations with boundary conditions.

Geometry

X: Global X coordinate of the node. Defines the position along the longitudinal axis of the structure.

Y: Global Y coordinate of the node. Defines the position along the transverse axis of the structure.

Z: Global Z coordinate of the node. Defines the vertical position (elevation) of the node.

Coordinate System: Reference coordinate system for this node. When assigned, the node's X, Y, Z coordinates are interpreted relative to the selected coordinate system rather than the global system. Useful for defining nodes in rotated or translated local frames.

Alignment: Associates the node with a roadway alignment. When selected, the node can use alignment-based (local) coordinates where XLocal represents the station along the alignment, YLocal the transverse offset, and ZLocal the vertical offset from the alignment profile.

Group: The FE group to which this node belongs. Groups are used to organize nodes for load application, result extraction, staged construction, and filtering purposes.

DOF

Degree of freedom (DOF) constraints define the boundary conditions at the node. A value of 0 or -1 means the DOF is free (unconstrained). A value of 1 means the DOF is fully fixed (restrained). A positive value other than 1 represents a spring stiffness in the corresponding direction.

Tx: Translation constraint in the X direction. Enter 0 for free, 1 for fixed, or a positive spring stiffness value (Force/Length units). Right-click any DOF cell for the action 6x6 Stiffness Matrix... which opens a dialog to edit the full coupled 6x6 stiffness matrix.

Ty: Translation constraint in the Y direction. Enter 0 for free, 1 for fixed, or a positive spring stiffness value (Force/Length units).

Tz: Translation constraint in the Z direction. Enter 0 for free, 1 for fixed, or a positive spring stiffness value (Force/Length units).

Rx: Rotation constraint about the X axis. Enter 0 for free, 1 for fixed, or a positive rotational spring stiffness value (Force*Length/Radian units).

Ry: Rotation constraint about the Y axis. Enter 0 for free, 1 for fixed, or a positive rotational spring stiffness value (Force*Length/Radian units).

Rz: Rotation constraint about the Z axis. Enter 0 for free, 1 for fixed, or a positive rotational spring stiffness value (Force*Length/Radian units).

6X6

6X6 Stiffness Matrix: A symmetric 6x6 stiffness matrix that defines coupled spring support behavior in all 6 degrees of freedom. This is used for complex foundation springs where the translational and rotational DOFs are coupled (e.g., soil-structure interaction). When provided, this matrix overrides the individual Tx through Rz spring values. Enter the upper triangular portion of the symmetric matrix.

Gap

Gap distances define the clearance before a spring constraint engages. The spring has zero stiffness until the gap is closed, then the specified stiffness activates. Used for modeling contact behavior such as expansion joint closures or bearing lift-off.

Tx Gap: Gap distance in the X direction before the Tx spring engages.

Ty Gap: Gap distance in the Y direction before the Ty spring engages.

Tz Gap: Gap distance in the Z direction before the Tz spring engages.

Rx Gap: Rotational gap about the X axis before the Rx spring engages.

Ry Gap: Rotational gap about the Y axis before the Ry spring engages.

Rz Gap: Rotational gap about the Z axis before the Rz spring engages.

Links

Links couple a DOF of this node to the same DOF of another node (master-slave relationship). When linked, both nodes share the same displacement or rotation in the linked direction.

Tx Link: Couples the X translation of this node to the specified node. Both nodes will have the same X displacement.

Ty Link: Couples the Y translation of this node to the specified node.

Tz Link: Couples the Z translation of this node to the specified node.

Rx Link: Couples the X rotation of this node to the specified node.

Ry Link: Couples the Y rotation of this node to the specified node.

Rz Link: Couples the Z rotation of this node to the specified node.

Stiffness Option

When a node constraint has a nonlinear force-displacement curve defined, these options specify what stiffness to use when that constraint participates in a linear analysis. Since linear analysis requires a single constant stiffness, the Linear Mode and Effective Stiffness fields determine how the nonlinear curve is linearized.

Tx Linear Mode: Determines how the nonlinear stiffness curve in the X translation direction is linearized for linear analysis.

Tx Eff. Stiffness: The effective linear stiffness in the X translation direction to use in linear analysis when the constraint has a nonlinear curve defined.

Ty Linear Mode: Determines how the nonlinear stiffness curve in the Y translation direction is linearized for linear analysis.

Ty Eff. Stiffness: The effective linear stiffness in the Y translation direction.

Tz Linear Mode: Determines how the nonlinear stiffness curve in the Z translation direction is linearized for linear analysis.

Tz Eff. Stiffness: The effective linear stiffness in the Z translation direction.

Rx Linear Mode: Determines how the nonlinear rotational stiffness curve about the X axis is linearized for linear analysis.

Rx Eff. Stiffness: The effective linear rotational stiffness about the X axis.

Ry Linear Mode: Determines how the nonlinear rotational stiffness curve about the Y axis is linearized for linear analysis.

Ry Eff. Stiffness: The effective linear rotational stiffness about the Y axis.

Rz Linear Mode: Determines how the nonlinear rotational stiffness curve about the Z axis is linearized for linear analysis.

Rz Eff. Stiffness: The effective linear rotational stiffness about the Z axis.

Settings

Merge Nearest: Controls whether this node is merged with the nearest existing node during mesh compilation. Set to Yes for secondary nodes (load application points, boundary condition nodes) that should snap to a nearby primary structural node.

Merge w/Same Loc Node: Controls automatic merging of coincident nodes at the same location. Set to No when you need separate nodes at identical coordinates (e.g., to insert a spring or hinge between two elements).

Merge w/Spring: Controls whether this node can be merged with another node that is connected via a spring element.

Use Nonlinear Penalty: Enables the nonlinear penalty method for enforcing constraints at this node. Used for advanced nonlinear contact analysis.

Disp Based Force Scaling NL: Enables displacement-based force scaling for nonlinear analysis at this node.

Force Scaling Node Group: The FE group of nodes used as reference for the displacement-based force scaling calculation.

Force Scaling Factors: The scale factors applied to the force scaling calculation.