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 case of application, you can select a direct calculation method, such as the Lanczos method or the ICG iteration method. 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.
You can select several methods that are available for the eigenvalue analysis:
Direct Methods
The direct methods (Lanczos [RFEM], roots of characteristic polynomial [RFEM], subspace iteration method [RFEM/RSTAB], and shifted inverse iteration [RSTAB]) are suitable for small to medium-sized models. You should only use these fast solver methods if your computer has a larger amount of memory (RAM).
In contrast, this method only requires a small amount of memory. Eigenvalues are determined one after the other. It can be used to calculate large structural systems with few eigenvalues.
Use the Structure Stability add-on to perform a nonlinear stability analysis using the incremental method. This analysis delivers close-to-reality results also for nonlinear structures. 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. After increasing the load, you can optionally perform a linear stability analysis on the last stable state in order to determine the stability mode.
As the first results, the program presents you with the critical load factors. You can then perform an evaluation of stability risks. For member models, the resulting effective lengths and critical loads of the members are displayed to you in tables.
Use the next result window to check the normalized eigenvalues sorted by node, member, and surface. The eigenvalue graphic allows you to evaluate the buckling behavior. This makes it easier for you to take countermeasures.
Consideration of 7 local deformation directions (ux, uy, uz, φx, φy, φz, ω) or 8 internal forces (N, Vu, Vv, Mt,pri, Mt,sec, Mu, Mv, Mω) when calculating member elements
Usable in combination with a structural analysis according to linear static, second-order, and large deformation analysis (imperfections can also be taken into account)
In combination with the Stability Analysis add-on, allows you to determine critical load factors and mode shapes of stability problems such as torsional buckling and lateral-torsional buckling
Consideration of end plates and transverse stiffeners as warping springs when calculating I-sections with automatic determination and graphical display of the warping spring stiffness
Graphical display of the cross-section warping of members in the deformation
You can perform the calculation of the warping torsion on the entire system. Thus, you consider the additional 7th degree of freedom in the member calculation. The stiffnesses of the connected structural elements are automatically taken into account. It means, you don't need to define equivalent spring stiffnesses or support conditions for a detached system.
You can then use the internal forces from the calculation with warping torsion in the add-ons for the design. Consider the warping bimoment and the secondary torsional moment, depending on the material and the selected standard. A typical application is the stability analysis according to the second-order theory with imperfections in steel structures.
Did you know that The application is not limited to thin-walled steel cross-sections. Thus, it is possible for you, for example, to perform the calculation of the ideal overturning moment of beams with solid timber cross-sections.
A wide range of available sections, such as rolled I-sections; channel sections; T-sections; angles; rectangular and circular hollow sections; round bars; symmetrical and asymmetrical, parametric I-, T-, and angle sections; built-up cross-sections (suitability for design depends on the selected standard)
Design of general RSECTION cross-sections (depending on the design formats available in the respective standard); for example, equivalent stress design
Design of tapered members (design method depending on the standard)
Adjustment of the essential design factors and standard parameters is possible
Flexibility due to detailed setting options for basis and extent of calculations
Fast and clear results output for an immediate overview of the result distribution after the design
Detailed output of the design results and essential formulas (comprehensible and verifiable result path)
Numerical results clearly arranged in tables and graphical display of the results in the model
Integration of the output into the RFEM/RSTAB printout report
Design of tension, compression, bending, shear, torsion, and combined internal forces
Tension design with consideration of a reduced section area (for example, hole weakening)
Automatic classification of cross-sections to check local buckling
Internal forces from the calculation with Torsional Warping (7 DOF) are taken into account using the equivalent stress check (currently not yet available for the ADM 2020 design standard).
Design of cross-sections of Class 4 with effective cross-section properties according to EN 1993‑1‑5 (licenses for RSECTION and Effective Sections are required for the RSECTION cross-sections)
Shear buckling check with consideration of transverse stiffeners
Stability analyses for flexural buckling, torsional buckling, and flexural-torsional buckling under compression
Lateral-torsional buckling analysis of the structural components subjected to moment loading
Import of the effective lengths from the calculation using the Structure Stability add-on
Graphical input and check of the defined nodal supports and effective lengths for stability analysis
Depending on the standard, a choice between user-defined input of Mcr, analytical method from the standard, or use of internal eigenvalue solver
Consideration of a shear panel and a rotational restraint when using the eigenvalue solver
Graphical display of a mode shape if the eigenvalue solver was used
Stability analysis of structural components with the combined compression and bending stress, depending on the design standard
Comprehensible calculation of all necessary coefficients, such as interaction factors
Alternative consideration of all effects for the stability analysis when determining internal forces in RFEM/RSTAB (second-order analysis, imperfections, stiffness reduction, possibly in combination with the Torsional Warping (7 DOF) add-on)
Entering soil layers for soil samples is performed in a clearly arranged dialog box. A corresponding graphical representation supports clarity and makes checking the input user-friendly.
An extensible database facilitates the selection of soil material properties. The Mohr-Coulomb model as well as a nonlinear model with stress and strain dependent stiffness are available for a realistic modeling of the soil material behavior.
You can define any number of soil samples and layers. The soil is generated from all entered samples using 3D solids. Assignment to the structure is carried out using coordinates.
The soil body is calculated according to the nonlinear iterative method. The calculated stresses and settlements are displayed graphically and in tables.
Simple definition of construction stages in the RFEM structure including visualization
Adding, removing, modifying, and reactivating member, surface, and solid elements and their properties (for example, member and line hinges, degrees of freedom for supports, and so on)
Automatic and manual combinatorics with load combinations in the individual construction stages (for example, to consider mounting loads, mounting cranes, and other loads)
Consideration of nonlinear effects such as tension member failure or nonlinear supports
Have you created the entire structure in RFEM? Very well, now you can assign the individual structural components and load cases to the corresponding construction stages. In each construction stage, you can modify release definitions of members and supports, for example.
You can thus model structural modifications, such as those that occur when bridge girders are successively grouted or when columns are settled. Then, assign the load cases created in RFEM to the construction stages as permanent or non-permanent loads.
Did you know that The combinatorics allows you to superimpose the permanent and non-permanent loads in load combinations. In this way, it is possible for you to determine the maximum internal forces of different crane positions or to consider temporary mounting loads available in one construction stage only.
If there are geometry differences arising between the ideal and the deformed structural system from the previous construction stage, they are compared in the program. The next construction stage is built on top of the stressed system from the previous construction stage. This calculation is nonlinear.
Was the calculation successful? Now you can view the results of the individual construction stages graphically and in tables in RFEM. Moreover, RFEM allows you to consider the construction stages in the combinatorics and include it in further design.
You have two options for a building model. You can create it when you start modeling the structure, or activate it afterwards. In the building model, you can then directly define the stories and manipulate them.
When manipulating the stories, you can choose whether to modify or retain the included structural elements using various options.
RFEM does some of the work for you. For example, it automatically generates result sections, so you don't need to perform a lot of calculations.
You can display the results as usual via the Results navigator. Furthermore, the dialog box of the add-on shows you the information about the individual floors. Thus, you always have a good overview.
The Dlubal structural analysis software does a lot of work for you. The input parameters, which are relevant for the selected standards, are suggested by the program in accordance with the rules. Furthermore, you can enter response spectra manually.
Load cases of the type Response Spectrum Analysis define the direction in which response spectra act and which eigenvalues of the structure are relevant for the analysis. In the spectral analysis settings, you can define details for the combination rules, damping (if applicable), and zero-period acceleration (ZPA).
Did you know that Equivalent static loads are generated separately for each relevant eigenvalue and excitation direction. These loads are saved in a load case of the Response Spectrum Analysis type and RFEM/RSTAB performs a linear static analysis.
The load cases of the type Response Spectrum Analysis contain the generated equivalent loads. First, the modal contributions have to be superimposed with the SRSS or CQC rule. In this case, you can use the signed results based on the dominant mode shape.
Afterwards, the directional components of earthquake actions are combined with the SRSS or the 100% / 30% rule.
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
Compared to the RF-/STAGES add-on module (RFEM 5), the following new features have been added to the Construction Stages Analysis (CSA) add-on for RFEM 6:
Consideration of construction stages at RFEM level
Integration of the construction stage analysis into the combinatorics in RFEM
Additional structural elements, such as line hinges, are supported
Analysis of alternative construction processes in a model
Compared to the RF-/STEEL Warping Torsion add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Torsional Warping (7 DOF) add-on for RFEM 6 / RSTAB 9:
Complete integration into the environment of RFEM 6 and RSTAB 9
7th degree of freedom is directly taken into account in the calculation of members in RFEM/RSTAB on the entire system
No more need to define support conditions or spring stiffnesses for calculation on the simplified equivalent system
Combination with other add-ons is possible, for example for the calculation of critical loads for torsional buckling and lateral-torsional buckling with stability analysis
No restriction to thin-walled steel sections (it is also possible to calculate ideal overturning moments for beams with massive timber sections, for example)
Compared to the RF-/DYNAM Pro - Equivalent Loads add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Response Spectrum Analysis add-on for RFEM 6 / RSTAB 9:
Response spectra of numerous standards (EN 1998, DIN 4149, IBC 2018, and so on)
User-defined response spectra or those generated from accelerograms
Direction-relative response spectrum approach
Results are stored centrally in a load case with underlying levels to ensure clarity
Accidental torsional actions can be taken into account automatically
Automatic combinations of seismic loads with the other load cases for use in an accidental design situation
Compared to the RF‑/ALUMINUM add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Aluminum Design add-on for RFEM 6 / RSTAB 9:
In addition to Eurocode 9, the US standard ADM 2020 is integrated.
Consideration of the stabilizing effect of purlins and sheets by rotational restraints and shear panels
Graphical display of the results in the gross section
Output of the used design check formulas (including a reference to the used equation from the standard)
Are you afraid that your project will end in the digital tower of Babel? The Building Model add-on for RFEM supports you in your work on a construction project with several stories. It allows you to define a building by means of stories at specified elevations. You can adjust the stories in many ways afterwards and also select the story slab stiffness. Information about the stories and the entire model (center of gravity, center of rigidity) is displayed for you in tables and graphics.