Mechanical APDL Basic Analysis Guide

(that is, it can increase, decrease, or even become negative), and it is reset to zero at the beginning of
each load step. As a result,time is not considered a "counter" in arc-length solutions.

The arc-length method is an advanced solution technique. For more information about using it, see
Nonlinear Structural Analysis in the Structural Analysis Guide.

A load step is a set of loads applied over a given time span. Substeps are time points within a load step
at which intermediate solutions are calculated. The difference in time between two successive substeps
can be called a time step or time increment. Equilibrium iterations are iterative solutions calculated at a
given time point purely for convergence purposes.

2.4. Stepped Versus Ramped Loads

2.4. Stepped Versus Ramped Loads

When you specify more than one substep in a load step, the question of whether the loads should be
stepped or ramped arises.

• If a load is stepped, then its full value is applied at the first substep and stays constant for the rest of
  the load step.


• If a load is ramped, then its value increases gradually at each substep, with the full value occurring
  at the end of the load step.

Figure 2.4: Stepped Versus Ramped Loads

1

2

Time

Load

Fullvalueapplied

atfirstsubstep

(a)Steppedloads

1

Time

Load

Loadstep

Final

load

value

Substep

2

(b)Rampedloads

The KBC command (,Main Menu> Solution> Load Step Opts> Time/Frequenc> Freq & Substeps:
Transient Tab / Main Menu> Solution> Load Step Opts> Time/Frequenc> Time and Substps / Main
Menu> Solution> Load Step Opts > Time/Frequenc> Time & Time Step, or Main Menu> Solution>
Load Step Opts> Time/Frequenc> Freq & Substeps / Main Menu> Solution> Load Step Opts>
Time/Frequenc> Time and Substps / Main Menu> Solution> Load Step Opts> Time/Frequenc>
Time & Time Step) is used to indicat e whether loads are ramped or stepped.KBC,0 indicat es ramped
loads, and KBC,1 indicat es stepped loads. The default depends on the discipline and type of analysis.

Load step options is a collective name given to options that control load application, such as time,
number of substeps, the time step, and stepping or ramping of loads. Other types of load step options
include convergence tolerances (used in nonlinear analyses),damping specifications in a structural
analysis, and output controls.

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Stepped Versus Ramped Loads