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