How is it possible to consider tension members in RF‑/DYNAM Pro?

Answer

To analyze a structural system with tension members in RF‑/DYNAM Pro, it is recommended to define several natural vibration cases (NVCs) and to use the options of stiffness modification. The natural vibration analysis is a linear analysis of frequencies and mode shapes; the tension members are considered as trusses in RF‑/DYNAM Pro and can cope with tension and compression to the same degree. To estimate how the frequencies change when the tension members fail, you can import this initial state into RF‑/DYNAM Pro by using a load case with the manually deactivated members or a load case with the failed tension members. The defined NVCs can be assigned to dynamic load cases (DLCs) to perform the response spectrum analysis using the export of equivalent loads (the RF‑/DYNAM Pro Equivalent Loads add-on module), for example.

The equivalent loads, that are exported into load cases in the main program RFEM / RSTAB, are evaluated with consideration of all nonlinearities, which can lead to conflicts in some cases. Figure 01 shows an example. In the first case, no stiffness modifications are used in RF‑/DYNAM Pro, and thus all members are considered in the dynamic analysis, but in RFEM/RSTAB, the tension member fail due to the equivalent loads. If you want to perform a completely linear analysis, you have to deactivate the nonlinearities in RFEM/RSTAB. In the second and third case, the initial condition is imported, where the tension members are not available; the equivalent loads are thus based on the same structure as the structure for the calculation of internal forces and deformations.

When using the response spectrum analysis in the RF‑/DYNAM Pro - Forced Vibrations add-on module, the modified stiffnesses of the natural vibration case (NVC) are also used for the subsequent calculation of the results. The entire linear calculation, considering the initial conditions, is performed in the RF‑DYNAM Pro add-on module.

Keywords

Tension member Tension members Nonlinear Dynamic analysis Response spectrum analysis Equivalent Loads

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