KBC, KEY
Specifies ramped or stepped loading within a load step.
KEYRamping key:
0 | — | Loads are linearly interpolated (ramped) for each substep from the values of the previous load step to the values of this load step. This is the default value. |
1 | — | Loads are step changed (stepped) at the first substep of this load step to the values of this load step (i.e., the same values are used for all substeps). Useful for rate-dependent behavior (e.g., creep, viscoplasticity, etc.) or transient load steps only. |
The loading is ramped for:
The loading is step-applied for transient analysis with transient effects included (ANTYPE,TRANS and TIMINT,ON; TIMINT,ON is the default for transient analysis).
Specifies whether loads applied to intermediate substeps within
the load step are to be stepped or ramped. Used only if DTIME on the DELTIM command is less
than the time span or, conversely, if NSBSTP on the NSUBST command is greater than one. Flags
(FSI, MXWF, MVDI, etc.) are always stepped.
Changing the ramping KEY (i.e., switching
between ramped and stepped boundary conditions) between load steps
is not recommended.
For ramped loading (KBC,0), when a load is applied for the first time, it is interpolated from zero to the value of the current load step, and not from the initial condition or value of the degree of freedom from the previous load step.
Spatially varying tabular loads or boundary conditions do not support direct ramping or stepping options and, instead, apply their full values according to the supplied tabular functions regardless of the KBC setting.
For a static or harmonic cyclic symmetry analysis, any load that varies by sector (CYCOPT,LDSECT) is tabular and is applied as a step change, regardless of the KBC setting; however, any non-tabular loads in the same analysis are ramped or stepped according to the KBC setting.
Irrespective of the KBC setting, loads are usually step-removed. See Stepping or Ramping Loads in the Basic Analysis Guide for more information.
It is sometimes difficult to obtain successful convergence with stepped loading in a nonlinear transient problem. If divergence is encountered, determine if stepped loading was used by default, then determine if it is appropriate for the analysis.
This command is also valid in PREP7.