When you specify more than one substep in a load step, you may choose to ramp apply or step apply the loads:
If you ramp apply the loads, their values are incrementally applied at each substep in a linearly interpolated fashion, reaching the full values at the end of the load step.
If you step apply the loads, their values are fully applied at the first substep and remain constant for the remainder of the load step.
Use the KEY argument on the KBC command to specify
whether loads are ramped (KBC,0) or stepped (KBC,1) for the load step. The default
setting of KEY depends on the discipline and type of analysis.
If you are applying rotational velocity loads (OMEGA, CMOMEGA, and
CMROTATE) in a ramped (KBC,0) fashion, there is a third option: you can choose
quadratic interpolation instead of linear interpolation by setting the OMGSQRDKEY argument on
the KBC command to 1.
Various load step options control load application, such as time, number of substeps, the time step, and load ramping or stepping. Other types of load step options include convergence tolerances (used in nonlinear analyses), damping specifications in a structural analysis, and output controls.