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Comparing the Stability Analysis of a Column Containing Internal Forces from Load Combinations with an Enveloping Result Combination
This example will show what you should consider when you perform column design for bending and compression with regard to the internal forces from load combinations and result combinations.
Different methods are available for calculating the deformation in the cracked state. RFEM provides an analytical method according to DIN EN 1992-1-1 7.4.3 and a physical-nonlinear analysis. Both methods have different features and can be more or less suitable depending on the circumstances. This article will give an overview of the two calculation methods.
The calculation in RFEM is usually carried out in several calculation steps, the so-called iterations. It is then possible to consider particular characteristics of the model such as objects with nonlinear functions. In addition, by using the iterative calculation, nonlinear effects are taken into account which result from changes in deformation and internal forces in case of the second-order analysis or when considering large deformations (cable theory). In case of complex models, geometric linear calculations are usually not sufficient.
For structural dimensioning according to the valid rules, there are often several options or calculation methods to determine the internal forces. It is up to the engineer to decide which theory is suitable to design the structure.
If you want to design structural components in an RFEM or RSTAB add‑on module, there are several National Annexes available in some add‑on modules. In the case of structures, which are to be analysed mainly according to a specific National Annex, the add‑on modules provide the option to set a default value. Thus, it is not necessary to select the NA again for each new model.
If there are nonlinearities used in a model, for example contact solids, an error message may appear at the end of the calculation due to the locally unfulfilled convergence criteria. The reason for this is that the convergence of the global iteration conditions is governing in the calculation.
To record and display a relation between various calculation results, it is possible to use the calculation diagrams. You can create and display them using the ‘Calculation Parameters’ dialog box available under ‘Calculation’ → ‘Calculation Parameters’.
In RFEM and RSTAB, files can be automatically computed in a sequence of calculation, so the models can be processed overnight, for example.
If you look at the cross‑section properties of the metal category, you can see that there are three types of shear area, whose meaning and calculation are described here.
RSTAB can calculate a critical load factor for each load case LC and each load combination CO in compliance with the second‑order analysis. The critical load factor indicates the number by which the load must be multiplied so that the model under the associated load becomes unstable (buckling).
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