# Cubic Stiffness Block

Cubic Stiffness blocks store a set of coefficients that determine two cubic
polynomials defining a force verses deflection curve. If the Direction block selects
the cubic stiffness formulation for TY direction, then the property file, for
example, must contain a `[CUBIC_STIFFNESS_TY]`

block.

The following table describes the parameters stored in a Cubic Stiffness block.
Abbreviations are: [F] = force, [L] = length.

Parameter | Type | Dimension FX, FY, FZ | Dimension TX, TY, TZ |
---|---|---|---|

EN | real | [L] | Angle |

ENS | real | [F][L^{-1}] |
[F][L]/Angle |

RN | real | [L] | Angle |

RNF | real | [F] | [F][L] |

OS | real | [F][L^{-1}] |
[F][L]/Angle |

OF | real | [F] | [F][L] |

O | real | [L] | Angle |

RP | real | [L] | Angle |

RPF | real | [F] | [F][L] |

EP | real | [L] | Angle |

EPS | real | [F][L^{-1}] |
[F][L]/Angle |

In a property file, a cubic stiffness block has this
form:

```
[CUBIC_STIFFNESS_TY]
EN = -0.20
ENS = 200000.0
RN = -0.10
RNF = -30000.0
O = 0.0
OF = 0.0
OS = 20000.0
RP = 0.10
RPF = 30000.0
EP = 0.20
EPS = 200000.0
```