Springs

Springs are flexible restraints.  Springs applied to nodes are referred to as nodal springs. You may assign a nodal spring to a node with one or more global DOFs (Dx, Dy, Dz, Dox, Doy and Doz) restrained.  To qualify to be a valid flexible restraint, the corresponding spring constant must be specified. A restraint may be designated as linear, compression-only or tension only.  A compression-only restraint is active only when the nodal displacement in the restrained direction is negative.  A tension-only restraint is active only when the nodal displacement in the restrained direction is positive.  If a model contains one or more compression-only or tension-only springs, the whole problem becomes nonlinear and the solution becomes iterative for each load combination.

The forces or moments required to enforce the flexible restraints are called spring reactions.  They are computed by the program.