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!"
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.
- 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 identify the cause of instability)
- Visualization of stability mode
- Basis for analysis using imperfect equivalent structures in RF-IMP
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 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 the local buckling of single members on these elements. Therefore, you have the option to divide members automatically.
Several methods are available for the eigenvalue analysis:
- Direct Methods
- The direct methods (Lanczos, roots of characteristic polynomial, subspace iteration method) are suitable for small to medium-sized models. These fast methods for equation solvers benefit from a lot 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 small amount of memory. Eigenvalues are determined one after the other. It can be used to calculate large structural systems with few eigenvalues.
The RF-STABILITY add-on module can also perform the non-linear stability analysis. Also for nonlinear structures, results close to reality are provided. The critical load factor is determined by gradually increasing the loads of the underlying load case until the instability is reached. The load increment takes into account nonlinearities such as failing members, supports and foundations, and material nonlinearities.
- Direct Methods
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 graphic allows for evaluation of the buckling behavior. The graphical display makes it easier to take countermeasures.
Do you have any questions about our products or which are best suited for your design projects? Contact us via phone, email, chat, or forum, or search the FAQ page, available 24/7.
This article demonstrates how to structural design windbreak structures using RFEM and RWIND.
- 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.
Timber Lattice Bridge for Cycling and Pedestrian Use over Reguerón Irrigation Channel in Orihuela, Spain
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