SSTIF

SSTIF, Key
Activates stress stiffness effects in a nonlinear analysis.

SOLUTION: Nonlinear Options

Key

Stress stiffening key:

OFF	—	No stress stiffening is included (default unless NLGEOM,ON).
ON	—	Stress stiffening is included (default if NLGEOM,ON).

Command Default

SSTIF will be turned on if NLGEOM,ON; otherwise it will be turned off.

Notes

Activates stress stiffness effects in a nonlinear analysis (ANTYPE,STATIC or TRANS). (The PSTRES command also controls the generation of the stress stiffness matrix and therefore should not be used in conjunction with SSTIF.) If used within the solution processor, this command is valid only within the first load step.

When NLGEOM is ON, SSTIF defaults to ON. This normally forms all of the consistent tangent matrix. However, for some special nonlinear cases, this can lead to divergence caused by some elements which do not provide a complete consistent tangent (notably, elements outside the 18x family). In such a case, Ansys, Inc. recommends issuing an SSTIF,OFF command to achieve convergence. For current-technology elements, setting SSTIF,OFF when NLGEOM is ON has no effect (because stress stiffness effects are always included).

This command is also valid in PREP7.