====== STIFF ======
Concentrated stiffness \\
===== Description =====

This element defines a stiffness for a given degree of freedom. \\ It can be used for instance for a foundation for which the stiffness originates only from a solid-solid contact element. It can also be used as a linear spring between the initial position and the actual position of the node. \\
This element can only be used with law [[laws:lstiff|LSTIFF]]
\\
Type: 17 \\
Implemented by: AM Habraken, 1992
==== Files ====
Prepro: STIFFA.F \\
Lagamine: STIFFB.F
===== Input file =====

^ Line 1 (A5)^^
|TITLE|"STIFF" in the first five columns|
^Line 2 (I5)^^
|NELEM|Number of elements|
^Definition of the elements (2I5/5I5) repeated NELEM times^^
|LMATE|Material law|
|LSPRING| = 1 if use as a spring; an associated force is calculated  (stiffness of law [[laws:lstiff|LSTIFF]] multiplied by the node displacement along the relevant DoF between the initial and actualized position) \\ = 0 if use as stiffness only (no associated force)|
|NODES|Node number|
|IDDL|Number of the degree of freedom|

===== Results =====
Sigma: Effort in the spring if LSPRING = 1 ; else nothing