Critical Load Factor
RFEM and RSTAB can calculate the critical load factor for each load case (LC) and each load combination (CO) in the case of a geometrically nonlinear calculation (second-order analysis and following).
The critical load factor indicates the number by which the load must be multiplied until the model under the associated load becomes unstable (buckling).
The critical load factor is determined internally by a load increment. The obtained load factor becomes the critical load factor when the program can no longer find the equilibrium in the deformed system for the given loading condition (= becomes unstable).
In contrast to the solution of a buckling eigenvalue problem (such as in RS-BUCK and RF-STABILITY), this procedure also helps you consider other structural nonlinearities (for example, support failures, member failures, etc.) in an optimal way.
You can activate the calculation of the critical load factor for each load case and load combination in the "Calculation Parameters" tab. For the iterative process itself, an initial load factor k0 and a load factor increment Δk must be specified. In addition, you can define the process more precisely by specifying a refinement, an additional stopping condition, and an initial load.
If the program can no longer find the equilibrium for load factor 1.0, and the initial load factor is < 1.0 (unstable), no result is given due to the lack of internal forces and deformations in load step 1.0.
Since the calculation of the critical load factor can significantly increase the computation time due to the iterative approach, you should set this function only for the desired load situations (LC, CO).
Dipl.-Ing. (BA) Andreas Niemeier, M.Eng.
Mr. Niemeier is responsible for the development of RFEM, RSTAB, and the add-on modules for tensile membrane structures. Also, he is responsible for quality assurance and customer support.
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Very small torsional moments in the members to be designed often prevent certain design formats.
Result of eigenvalue analysis for single-span beam with lateral and torsional restraint with rigid intermediate supports
Result of eigenvalue analysis for single-span beam with lateral and torsional restraint without intermediate supports
Compared to the RF-/STABILITY (RFEM 5) and RSBUCK (RSTAB 8) add-on modules, the following new features have been added to the Structure Stability add-on for RFEM 6 / RSTAB 9:
- Activation as a property of a load case or a load combination
- Automated activation of the stability calculation via combination wizards for several load situations in one step
- Incremental load increase with user-defined termination criteria
- Modification of the mode shape normalization without recalculation
- Result tables with filter option
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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids, and contact elements
Structural engineering software for designing frame, beam, and truss structures, as well as performing linear and nonlinear calculations of internal forces, deformations, and support reactions