In the calculation parameters of the RFEM 5 and RSTAB 8 programs, under the tab Global Calculation Parameters, there are input fields Number of load steps for load cases/load combinations. These two inputs control the numerical gradual application of the defined load boundary conditions in the respective load cases and load combinations. The reciprocal value of the input describes a fraction of the load.
The solution process then applies the defined load fractions to the model in so-called load steps, gradually, until the full load is reached. In each load step, the equation solver attempts to find equilibrium within the maximum allowed iterations, thereby providing suitable starting values for the next load step.
Visually, one can imagine the solution process collecting the full load of a load case or a load combination in a "watering can" and pouring it portion by portion onto the load-collecting model. The number of load steps correlates with the speed of application. Here, the speed should be understood purely numerically, not as a real time parameter.
Important: The gradual load application has an effect only on nonlinear structural systems. Generally, it delivers higher result quality with an increasing number of load steps. The fundamental goal of this method is to find micro-convergence in the respective load steps to specify new high-quality starting values for the next load step, thus eventually achieving macro-convergence for the entire load case.
