Multilinear springs - how to define them properly

Hi,

I'm working in STAAD.Pro V8i

I need to define a support with the following:

FX  - multilinear spring

FY - fixed

FZ - multilinear spring

MX - fixed

MY - fixed

MZ - releazed

So far I successfuly used "FIXED BUT" with Linear springs for FX and FY where I defigned KFX and KFZ as 16666kN/m but when I tried to define a multi-linear spring I could not assign it and it was not recorded in the file.

'Help' topic on this subject is not very clear. Could I assign Multilinear Springs in such way that they will substitute previously defined KFX and KFZ or 'FIXED BUT" and "Multilinear Spring' do not work in conjuction at all? Than, what degrees of freedom actually got assigned when I use 'Multilinear' ?

Could you, please, help me with this problem?

Thank  you,

Len Bogdanov