RF-STABILITY Add-on Module for RFEM
Stability Analysis According to Eigenvalue Calculation Method
"The RFEM add-on module RF-STABILITY is a perfect combination with RWIND Simulation. Using RF-STABILITY, I can perform a buckling analysis to get accurate effective lengths. Using RWIND Simulation, I can get accurate wind loads. For unusually shaped structures, it would be a wild guess if calculating wind loads from the standard code... either not conservative or too conservative. My client is happy with the results and impressed!"
Yuri Yurianto, SE, PE, M.Sc.
1 October 2019
The RF-STABILITY add-on module analyzes the stability of structures. The RFEM add-on module determines critical load factors and the corresponding stability modes.
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Features
- Calculation of models consisting of member, shell and solid elements
- Import of axial forces from a load case or combination
- Non-linear stability analysis
- Optional consideration of axial forces from initial prestress
- Four equation solvers for effective calculation of various structural models
- Optional consideration of stiffness modifications in RFEM
- Calculation of buckling modes of unstable models
- Determination of stability mode greater than the user-defined load increment factor (Shift method)
- Optional determination of the mode shapes of unstable models (to recognize the instability cause)
- Visualization of stability mode
- Basis for analysis using imperfect equivalent structures in RF-IMP
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Input
First of all, it is necessary to select a load case or combination whose axial forces are to be used in the stability analysis. It is possible to define another load case in order to consider initial prestress, for example.
Then, you can select the linear or non-linear analysis to be performed. Depending on the case of application, you can select a direct calculation method such as the Method by Lanczos, or the ICG iteration method. Members not integrated in surfaces are usually displayed as member elements with two FE nodes. It is not possible to determine local buckling of single member on these elements. Therefore, there is the option to divide members automatically.
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Calculation
Several methods are available for the Eigenvalue analysis:- Direct Methods
The direct methods (Lanczos, roots of characteristic polynomial, subspace iteration method) are useful for models of small and medium size. These fast methods of equation solvers benefit from lots of the computer memory (RAM). 64-bit systems use more memory so that even bigger structural systems can be calculated quickly. - ICG Iteration Method (Incomplete Conjugate Gradient)
This method requires only a little memory. Eigenvalues are determined one after the other. It can be used to calculate large structural systems with few stability modes.
The RF-STABILITY add-on module can also perform the non-linear stability analysis. Also for non-linear structures, the results close to reality are provided. The critical load factor is determined by increasing the loads of the selected load case step by step until the instability is reached. Nonlinearities such as failing members, supports and foundations as well as material nonlinearities are considered when increasing the loads.
- Direct Methods
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Results
The critical load factors are the first results displayed. They facilitate the evaluation of stability risks. In the case of member models, the module displays the effective lengths and critical buckling loads of the members in the second result window.
In the next result windows, you can check the normalized eigenvalues sorted by node, member, and surface. The eigenvalue graphics allows for the evaluation of the buckling behavior. The graphical display facilitates the provision of countermeasures.
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Price
Eigenvalue Methods in RF-STABILITY
The RF-STABILITY add-on module determines any critical load factors, effective lengths, and eigenvectors of RFEM models. Stability analyses can be carried out by various eigenvalue methods, the advantages of which depend on the structural system as well as computer configurations.
New
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
- How do I perform stability analysis to determine the critical load factor in RFEM 6?
- What is the critical load factor and how is it possible to determine it?
- How does RF‑STABILITY or RSBUCK determine the buckling load? According to the manual calculation, the respective buckling loads should be about 10% higher.
- Why is it not possible to use result combinations in RF‑STABILITY? It is possible in RSBUCK indeed.
- How can I design any SHAPE‑THIN cross-section in detail in RFEM or RSTAB?
- I have calculated a pre-deformed structure according to the second-order analysis with RF-STABILITY and RF-IMP. Why are the deformations of the CO smaller than the applied pre-deformation?
- Is it possible to perform stability analyses on reinforced concrete structures by means of RF‑STABILITY?
- How can I perform a buckling analysis for a surface in RFEM?
- How can I perform a stability/buckling analysis on a plate structure?
- Is it possible to import effective lengths from RF‑STABILITY or RSBUCK in RF‑/TIMBER Pro?
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