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Which time step should I select for the calculation of the time history analysis in the RF‑/DYNAM Pro add‑on module?

Answer

There are two options available: an automatic time step selection and a manual one. Especially for a structure with nonlinearities, it is always recommended to select the time step manually, because the automatic determination is only carried out on the basis of the defined accelerograms or time diagrams. For this purpose, a time step convergence study should be performed, which compares the calculation time and the accuracy.

The time step to be selected depends on many factors, including the excitation frequency, the frequency and the size of the structure, as well as the degree of nonlinearities. Thus, it is not possible to make a general statement about the size of the time step.

To achieve sufficient accuracy, the governing period T = 1/f should be divided into approximately 20 steps, that is, the time step Δt should be selected as follows:

$\mathrm{Δt}\;<\frac{\mathrm T}{20}\;=\;\frac1{20\mathrm f}\;=\;\frac{\mathrm\pi}{10\mathrm\omega\;}$

For transiently defined suggestions, such as accelerograms or tabulated time diagrams, the shortest time period should be divided into 7 steps:

$\mathrm{Δt}\;=\;\frac{\mathrm{Min}\left\{{\mathrm t}_{\mathrm i+1}\right.-\;{\mathrm t}_{\mathrm i}\}\;}7$

Regardless of the calculation, time steps are specified to save the results.

Keywords

Time step Time history method natural frequency Time Diagrams Accelerogram Dynamic analysis

Reference

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