Result values for deformations, internal forces, stresses, and so on, can be displayed on the isolines.
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The Structure Stability add-on is a useful tool when analyzing structural components susceptible to buckling. Using the example of a tapered cantilever beam, the determination of the failure mode and the branching load is shown.
In this article, we will explore the various types of stability failures, delving into their key features, causes, and how they manifest in different structural systems.
The modal relevance factor is a result of the linear stability analysis and qualitatively describes the degree of participation of individual members in a specific mode shape.
This article will show you how to use the Torsion Warping (7 DOF) add-on in combination with the Structure Stability add-on to consider cross-section warping as an additional degree of freedom when performing the stability analysis.
The modal relevance factor (MRF) can help you to assess to which extent specific elements participate in a specific mode shape. The calculation is based on the relative elastic deformation energy of each individual member.
The MRF can be used to distinguish between local and global mode shapes. If multiple individual members show significant MRFs (for example, > 20%), the instability of the entire structure or a substructure is very likely. On the other hand, if the sum of all MRFs for an eigenmode is around 100%, a local stability phenomenon (for example, buckling of a single bar) can be expected.
Furthermore, the MRF can be used to determine critical loads and equivalent buckling lengths of certain members (for example, for stability design). Mode shapes for which a specific member has small MRF values (for example, < 20%) can be neglected in this context.
The MRF is displayed by mode shape in the result table under Stability Analysis → Results by Members → Effective Lengths and Critical Loads.
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 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
- Calculation of models consisting of member, shell, and solid elements
- Nonlinear stability analysis
- Optional consideration of axial forces from initial prestress
- Several equation solvers for an efficient calculation of various structural models
- Optional consideration of stiffness modifications via structure modification settings
- Determination of a 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 the stability mode
- Basis for determining imperfection
If there is a load case or load combination in the program, the stability calculation is activated. You can define another load case in order to consider initial prestress, for example.
For this, you need to specify whether to perform a linear or nonlinear analysis. Depending on the application, you can select a suitable calculation method for determining the eigenvalues. Members not integrated in surfaces are usually displayed as member elements with two FE nodes. With such elements, the program cannot determine the local buckling of single members. That's why you have the option to divide members automatically.
Is it possible to consider shear panels and rotational restraints in the global calculation?
In the Steel Design add-on, I have set the boundary conditions in such a way that the I-beam flange is restrained against the horizontal displacement. I then calculated the critical load factors using the Structure Stability add-on, but with no effect on the critical load factor value. What is the reason for this?
Can I incrementally increase the load in RFEM 6 or RSTAB 9?
My model is unstable. What could be the reason?
My model is unstable. What could be the reason?
My model in RFEM 6 / RSTAB 9 is unstable. How can I correct this?
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