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FAQ 003429 | There are two different add-on modules for a response spectrum analysis in RF‑/DYNAM Pro. What can be the reasons for the different results of both add-on modules?
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There are two different add-on modules for a response spectrum analysis in RF‑/DYNAM Pro. What can be the reasons for the different results of both add-on modules?Answer
The differences between the two modules are explained in this FAQ.
In the case of the same settings, there should also be the same results calculated in both add-on modules. However, this does not apply to the existing nonlinearities. The reason is that there are no nonlinearities considered in the RF‑/DYNAM Pro add-on module. If displaying the results in the Forced Vibrations add-on module, all nonlinearities are thus ignored. In contrast, the equivalent loads are calculated on a linear structural system, but the exported load cases are then calculated on a real structure in RFEM and RSTAB, that is, with all nonlinearities. This may lead to inconsistent results.
If you deactivate the nonlinearities for the exported load cases, you should obtain the same results.
The way of considering nonlinearities in the response spectrum analysis is described on the basis of tension members in this FAQ.
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Dlubal FAQ Response spectrum Dynamic analysis Difference Result Nonlinearity Equivalent load Frequently Asked Question FAQ about Dlubal Question and Answer about Dlubal
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Using Modified Stiffnesses for Dynamic Calculations
In RFEM, it is possible to modify stiffnesses for materials, cross -sections, members, load cases, and load combinations in many places.
![Window '1.1 General Data' for Serviceability Limit State with Settings for Nonlinear Calculation According to [2]](/-/media/Images/website/img/000001-010000/009301-009400/009376.png?la=en&mlid=149164433F8D4E0D89705EF3B002E4A8&hash=3AB14C4B44380D5CD55A73A5E3D45D8D86BFB424)
Considering the Stiffness of Gas Solids in Nonlinear Time History Analysis
The stiffness of gas given by the ideal gas law pV = nRT can be considered in the nonlinear dynamic analysis.
The calculation of gas is available for accelerograms and time diagrams for both the explicit analysis and the nonlinear implicit Newmark analysis. To determine the gas behaviour correctly, at least two FE layers for gas solids should be defined.
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