Answer:
Members with the "Spring" or "Dashpot" member type only have axial stiffness; that is, in the direction of the local x‑direction. The bending stiffness and the stiffness perpendicular to the longitudinal member axis are negligibly small and are not considered in RFEM and RSTAB.
If a spring should be used in the structure, it only acts in one direction; in the other two directions (local y- and z-directions), this member type must have an additional support, otherwise the system becomes unstable.
