I/O Options and Subcase Information Entry Defines initial stresses of elements for nonlinear static analysis.


INISTRS = option


Argument Options Description
option <SID>

No default

Set identification of INISTRS or ISTSADD Bulk Data Entry.


  1. INISTRS and ISTSADD Bulk Data Entries will not be used unless selected in the Subcase Information section.
  2. INISTRS and ISTSADD should only be selected by a nonlinear subcase which is not continued from a preceding nonlinear subcase.
  3. When initial stresses are applied, the initial state of the structure is usually not in equilibrium, because the inputs of initial stresses may be procured from output of a preceding analysis with some stress post-processing treatments and/or from results of a preceding analysis with another software. To achieve equilibrium, the initial stresses are resolved, by default, incrementally over the subcase with INISTRS. Alternatively, with PARAM,ISTRSBAL,1 they can be resolved at the first increment of the subcase with INISTRS.
  4. Because of the effect of initial stresses on equilibrium and for a better convergence, it is usually recommended to set the subcase with INISTRS as an initial equilibrating subcase by constraining the structure, as required, however without applying loads. Loads can be applied in a continuation subcase(s) of this initial equilibrating subcase.
  5. Stress output for elements with initial stress accounts for both the balanced initial stress and the contribution from the deformation with loading.