1. Global springs

To be specified if NSPR>0 The input lines below (`Spring location and properties' and optionally `Nonlinear spring stiffness') must be given in one block for each global spring.

Global springs are activated in the static load group with Activate global springs (load type SPRI in standalone) or at the start of dynamic analysis.

Spring location and properties
LINE-ID ISEG INOD ILDOF STIFF/NPAIR DAMP A2

  • LINE-ID: character (8): Line identifier

  • ISEG: integer: Local segment number within line

  • INOD: integer: Local node number within segment

  • ILDOF: integer: Local degree of freedom

    • =1 global X-direction

    • =2 global Y-direction

    • =3 global Z-direction

    • =4 rotation around global X-axis

    • =5 rotation around global Y-axis

    • =6 rotation around global Z-axis

    • = 12 or 21 translation in global XY-plane

    • = 13 or 31 translation in global XZ-plane

    • = 23 or 32 translation in global YZ-plane

  • STIFF/NPAIR

    • STIFF: real >= 0: Constant spring stiffness \([\mathrm {F/L}]\) or \([\mathrm {FL/deg}]\)

    • -NPAIR: integer <= -2: NPAIR is the number of pairs of force-displacement or moment-rotation pairs defining the spring specification

  • DAMP: real, default: 0: Linear damping coefficient \([\mathrm {FT/L}]\) or \([\mathrm {FLT/deg}]\)

  • A2: real, default: 0: Stiffness proportional damping factor

Nonlinear spring stiffness

The following input line is to be given if NPAIR >= 2

PON(1) DISPL(1)...............PON(NPAIR) DISPL(NPAIR)

  • PON(1): real: Spring force \([\mathrm {F}]\) or moment \([\mathrm {FL}]\) corresponding to

  • DISPL(1): real: Spring displacement \([\mathrm {L}]\) or rotation \([\mathrm {deg}]\)

All NPAIR pairs of PON and DISPL values are given on a single input line. The values of PON and DISPL must be monotonically increasing; PON(1) < PON(2) < …​ < PON(NPAIR) and DISPL(1) < DISPL(2) < …​ < DISPL(NPAIR).

Linear extrapolation will be used outside of the range of specified displacement or rotation values. For ILDOF <= 6, values must therefore be given for both negative and positive displacement values to obtain a symmetric spring.

For ILDOF > 6, the first pair of values must both be zero; i.e. \(\mathrm {\:}\) PON(1) = DISPL(1) = 0.0.