# Springs \[FEA]

Springs are zero-length or short connector elements with custom stiffness properties in each degree of freedom. They are used to model bearings, isolators, soil springs, connections between structural components, and other special boundary conditions.

## Geometry

**Node 1:** The first node connected by the spring element. Can be the same node as Node 2 for a grounded spring.

**Node 2:** The second node connected by the spring element. Together with Node 1, defines the two points between which the spring acts.

## DOF

**Tx:** Translational spring stiffness in the X direction (Force/Length units). A value of 0 means no stiffness in this direction. Right-click any DOF cell for actions: *Set to Free* clears the stiffness; *Set to Fixed* sets a rigid connection; *Edit Stiffness...* opens a stiffness editor for defining nonlinear force-displacement curves.

**Ty:** Translational spring stiffness in the Y direction (Force/Length units). A value of 0 means no stiffness in this direction.

**Tz:** Translational spring stiffness in the Z direction (Force/Length units). A value of 0 means no stiffness in this direction.

**Rx:** Rotational spring stiffness about the X axis (Force\*Length/Radian units). A value of 0 means no rotational stiffness about this axis.

**Ry:** Rotational spring stiffness about the Y axis (Force\*Length/Radian units). A value of 0 means no rotational stiffness about this axis.

**Rz:** Rotational spring stiffness about the Z axis (Force\*Length/Radian units). A value of 0 means no rotational stiffness about this axis.

## 6X6

**6X6 Stiffness Matrix:** A symmetric 6x6 stiffness matrix that defines coupled spring behavior in all 6 degrees of freedom. Use this when the spring DOFs are coupled (e.g., complex bearing or soil-structure interaction models). When provided, this matrix overrides the individual Tx through Rz stiffness values. Enter the upper triangular portion of the symmetric matrix.

## Gap

Gap distances define the clearance before a spring stiffness 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 spring's node to another node (master-slave relationship).

**Tx Link:** Couples the X translation to the specified node.

**Ty Link:** Couples the Y translation to the specified node.

**Tz Link:** Couples the Z translation to the specified node.

**Rx Link:** Couples the X rotation to the specified node.

**Ry Link:** Couples the Y rotation to the specified node.

**Rz Link:** Couples the Z rotation to the specified node.

## Stiffness Option

When a spring has a nonlinear force-displacement curve defined, these options specify what stiffness to use when that spring 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 spring 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

**Multi-Curve Direction:** Specifies the direction for multi-curve nonlinear spring behavior. Used when the spring has different force-displacement curves in different directions.

**Merge Nearest:** Controls whether this spring's nodes are merged with the nearest existing node during mesh compilation.

**Merge w/Same Loc Node:** Controls automatic merging of coincident nodes at the same location.

**Merge w/Spring:** Controls whether this spring's nodes can be merged with nodes connected via other spring elements.

**Use Nonlinear Penalty:** Enables the nonlinear penalty method for enforcing constraints at this spring element.

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

**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.