Sigle degree of freedom oscillator

[lish hit]

I want do a SDOF nolinear analysis,so I build a model――Sigle degree of freedom oscillator（the systerm is composed of a Mass,a Spring and a damping pot, a very classical model can be found out in almost textbook ）,I do it like this:
Define Spring with bilinear material(here I use Stell02),define Damping Pot with Viscous materail,then parallel them, fixed end and mass connect with a Zero-Length Element(use Parallel materail which motioned above)

but I have some problem can’t sovle:

1.I want get the Spring force-deformation relationship(not Spring+Damping Pot),but I don’t kown how can realize it,I use
recorder Element -file matStrain.out -time -ele 1 material 1 strain
recorder Element -file matSteess.out -time -ele 1 material 1 stress
here 1 reprsent Spring material Tag
but failed,(I think the command don’t work with the material which had been paralleled???)

2．Can’t done Eigen analysis,if a sysyterm only have Zero Lengh elemet and mass,Does OS can’t sovle Eigen problem???

3. Anyone else already done the SDOF oscillator program? if somebody had done it,could you sent it to me for reference,Thank you!