The tension component of the beam type spring element is independent of other forces. It is shown in 図 1. The tension at each node is computed by:(1)
F x 1 = f x ( u x ) + C x u ˙ x
F x 2 = F x 1
u x = u x 2 u x 1
Relative displacement of nodes 1 and 2
f x ( u x )
Function defining the force-displacement relationship
It can be linear or nonlinear (Linear Spring to Nonlinear Elasto-plastic Spring: Decoupled Hardening).

図 1. Spring Tension