Many thanks for logging this idea. I think it could be really part of a bigger idea, that of providing a clearer description of supports in the Supports dialog rather than just support 1,2 etc. The challenge with multi-linear springs is that they are in fact unusual in that they are a modifier on a previous spring support definition which can be confusing. Perhaps the answer is to develop a new Support multilinear spring definition block which must be defined as the first set of commands after SUPPORT, then a new support type called spring which has the format of:-

(node list) SPRING KX KY KZ MX MY MZ

where

the spring definitions can either be a value (0 free, or -1 fixed) or a reference to one of the multilinear springs something like:-

SUPPORT

DEFINITION MULTILINEAR SPRING

S1 (displacement/stiffness pairs)

S2 (displacement/stiffness pairs)

S3 (displacement/stiffness pairs)

END DEFINITION

* supports in the current format

1 TO 10 FIXED

11 TO 20 PINNED

21 TO 30 FIXED BUT KFY 10000

* now new multilinear supports with spring S1 applied in Y direction, free in X and Z and fixed in MX, MY and MZ

31 TO 100 SPRING 0 S1 -1 -1 -1

In this way a multilnear support is easier to identify and can be a single command in the GUI.