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).
- ICG Iteration Method (Incomplete Conjugate Gradient [RFEM])
- 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.
- Calculation of models consisting of member, shell, and solid elements
- Nonlinear stability analysis
- Optional consideration of axial forces from initial prestress
- Four equation solvers for an efficient calculation of various structural models
- Optional consideration of stiffness modifications in RFEM/RSTAB
- 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
- 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 by means of the equivalent stress check (currently not yet for the design standard ADM 2020).
- 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, and 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)
The parameters of the National Annexes (NA) to Eurocode 3 of the following countries are integrated:
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DIN EN 1993-1-1/NA:2016-04 (Germany)
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ÖNORM EN 1993-1-1/NA:2015-12 (Austria)
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SN EN 1993-1-1/NA:2016-07 (Switzerland)
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BDS EN 1993-1-1/NA:2015-10 (Bulgaria)
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BS EN 1993-1-1/NA:2016-07 (United Kingdom)
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CEN EN 1993-1-1/2015-06 (European Union)
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CYS EN 1993-1-1/NA:2015-07 (Cyprus)
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CSN EN 1993-1-1/NA:2016-06 (Czech Republic)
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DS EN 1993-1-1/NA:2015-07 (Denmark)
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ELOT EN 1993-1-1/NA:2017-01 (Greece)
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EVS EN 1993-1-1/NA:2015-08 (Estonia)
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HRN EN 1993-1-1/NA:2016-03 (Croatia)
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I S. EN 1993-1-1/NA:2016-03 (Ireland)
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ILNAS EN 1993-1-1/NA:2015-06 (Luxembourg)
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IST EN 1993-1-1/NA:2015-11 (Iceland)
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LST EN 1993-1-1/NA:2017-01 (Lithuania)
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LVS EN 1993-1-1/NA:2015-10 (Latvia)
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MS EN 1993-1-1/NA:2010-01 (Malaysia)
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MSZ EN 1993-1-1/NA:2015-11 (Hungary)
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NBN EN 1993-1-1/NA:2015-07 (Belgium)
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NEN EN 1993-1-1/NA:2016-12 (Netherlands)
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NF EN 1993-1-1/NA:2016-02 (France)
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NP EN 1993-1-1/NA:2009-03 (Portugal)
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NS EN 1993-1-1/NA:2015-09 (Norway)
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PN EN 1993-1-1/NA:2015-08 (Poland)
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SFS EN 1993-1-1/NA:2015-08 (Finland)
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SIST EN 1993-1-1/NA:2016-09 (Slovenia)
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SR EN 1993-1-1/NA:2016-04 (Romania)
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SS EN 1993-1-1/NA:2019-05 (Singapore)
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SS EN 1993-1-1/NA:2015-06 (Sweden)
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STN EN 1993-1-1/NA:2015-10 (Slovakia)
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TKP EN 1993-1-1/NA:2015-04 (Belarus)
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UNE EN 1993-1-1/NA:2016-02 (Spain)
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UNI EN 1993-1-1/NA:2015-08 (Italy)
- Automatic generation of FE analysis models: The add-on automatically creates a finite element model (FE) of the steel connection in the background.
- Consideration of all internal forces: The calculation and design checks include all internal forces (N, Vy, Vz, My, Mz, MT) and are not limited to planar loading.
- Automatic load transfer: All load combinations are automatically transferred to the FE analysis model of the connection. The loads are transferred directly from RFEM, so manual data input is not necessary.
- Efficient modeling: The add-on saves you time when modeling complex connection situations. You can also save the created FE analysis model and use it further for your own detailed analyses.
- Extensible library: An extensive and extensible library with predefined steel connection templates is available.
- Wide applicability: The add-on is suitable for connections of any type and shape, compatible with almost all rolled, welded, built-up, and thin-walled cross-sections.
- Selection of nodes in the RFEM model, automatic recognition and assignment of the members connected to the node
- Many predefined components available for easy input of typical connection situations (for example, end plates, cleats, fin plates)
- Universally applicable basic components (plates, welds, auxiliary planes) for entering complex connection situations
- No manual editing of the FE model required by the user, the essential calculation settings can be changed via the configuration settings
- Automatic adaptation of the connection geometry, even if the members are subsequently edited, due to the relative relation of the components to each other
- Parallel to the input, a plausibility check is carried out by the program to quickly detect missing input or collisions, for example
- Graphical display of the connection geometry that is updated in parallel with the input
The program supports you: It determines the bolt forces on the basis of the FE analysis model and evaluates them automatically. The add-on performs the standard-compliant design of bolt resistance for failure cases, such as tension, shear, hole bearing, and punching, and clearly displays all required coefficients.
Do you want to perform weld design? The welds are modeled as elastic-plastic surface elements, and their stresses are read out from the FE analysis model. The plasticity criteria is set in the way that they represent failure according to AISC J2-4, J2-5 (strength of welds), and J2-2 (strength of base metal). The design can be performed with the partial safety factors of the selected National Annex of EN 1993‑1‑8.
The plates in the connection are designed plastically by comparing the existing plastic strain to the allowable plastic strain. The default setting is 5% according to EN 1993‑1‑5, Annex C, but can be adjusted by user-defined specifications, as well as 5% for AISC 360.
You can display all essential results on the FE model. In this case, you can filter the results separately according to the respective components.
Furthemore, RFEM delivers you all design checks in a tabular form, including the display of the formulas used. If you wish, you can transfer the result tables to the RFEM printout report.
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
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)
Do you work with steel connections? The Steel Joints add-on for RFEM supports you when analyzing steel connections by using an FE model. In this case, the modeling runs fully automatically in the background. Nevertheless, you can control this process via the simple and familiar input of components. You can then use the loads determined on the FE model for your design of the components according to EN 1993‑1‑8 (including National Annexes).
For joint components, you can check whether the stability failure is relevant. This requires the Structure Stability add-on for RFEM 6.
In this case, you calculate the critical load factor for all analyzed load combinations and the selected number of mode shapes for the connection model. Compare the smallest critical load factor with the limit value 15 from the standard EN 1993‑1‑1, Clause 5. Furthermore, you can make user-defined adjustment of the limit value. As a result of the stability analysis, the program displays the corresponding mode shapes graphically.
For the stability analysis, RFEM uses the adapted surface model to specifically recognize the local buckling shapes. You can also save and use the model of the stability analysis, including the results, as a separate model file.
To design a Steel connection, you must have the Steel Joints Add-on enabled. The Add-ons in RFEM 6 are activated in the Add-ons tab of the Edit Model - Base Data window. If the Add-on is active, it is displayed in the navigator.
- For a new connection model, you have to select a node in the RFEM model
- After selecting a node, the members connected to the node are automatically recognized and assigned
- In the window for assigning members, select the ones that will be assigned to the connection
- The members marked by us are displayed in the preview window on the right
- Connections can be modeled for multiple nodes in a structure.
- For member settings, select the ones to be supported
- Many predefined components: Allow easy input of typical connection situations, such as end plates, angles, multi-wall sheets, cleats, fin plates
- Universally applicable basic components (plates, welds, bolts, auxiliary planes) for entering complex connection situations
- Graphical display of the connection geometry that is updated in parallel with the input
- The Steel Joints Template included in the add-on allows you to select from several connection types and, and once selected, it will be applied to your model.
- Wide range of cross-section shapes: Includes I-sections, channel sections, angles, T-sections, built-up cross-sections, RHS (rectangular hollow sections), and thin-walled sections
- The Template covers connections from three general categories: Rigid, Pinned, Truss
- Automatic adaptation of the connection geometry, even if the structural components are subsequently edited, based on the relative relation of the components
- The program performs a plausibility check in parallel with the input to quickly detect missing entries or collisions.
- If an error occurs, an error message appears describing the problem.
- The steel connections model and the results can be saved as a separate model file
- The resulting stresses and the results of the stability analysis (joint buckling) can be displayed in a separate model
- In the saved model, you can run a deformation animation on the connection
- Connection components are converted to surfaces and members when they are saved
- The results of the connection design can be entered in the printout report
- When creating a new printout report, select the items added from the Steel Joints Add-on
- Use the tool 'Print Graphics to Printout Report' to insert graphics with the results of the connection, including the control panel, into the report
- Printout report contains the specifications of the connection components, design parameters, results and graphics
- The proposed connection can be applied to all selected nodes in the structure
- The location of the connection can be defined using the 'Main' tab of the Add-on dialog box
- The design is performed for all connections in the structure and after the calculation, the results on all connections can be displayed
- The table shows the results for the individual connections, each connection is designed and can be saved separately
- The design of the connection components is performed according to AISC 360 and Eurocode EN 1993‑1‑8.
- After activating the add-on, it is necessary to activate the design situations for Steel Connections in the "Load Cases and Combinations" dialog box.
- The design of the connection stability (buckling) requires the "Structure Stability" add-on.
- You can run the calculation using the table or the icon in the top bar.
Design of a frame connection with taper and stiffened members. A stress analysis and a buckling stability analysis were carried out for the connection. To display the buckling results, the connection was converted into a separate model.
In addition to other predefined components in the design add-on for steel connections, the universal base component "General Weld" can be used to enter complex connection situations.
- Calculation of deflections and comparison with the normative or manually adjusted limit values
- Consideration of a precamber for the deflection analysis
- Different limit values are possible, depending on the design situation type
- Manual Adjustment of Reference Lengths and Segmentation by Direction
- Calculation of deflections related to the initial structure or to the deformed structure
- Further detailed design checks depending on the selected design standard (for example, vibration design according to EN 1999‑1‑1, 7.2.3)
- Graphical result display integrated in RFEM/RSTAB; for example, the design ratio of a limit value, or the deformation or the sag
- Complete integration of the results into the RFEM/RSTAB printout report
The program does a lot of work for you. For example, the load or result combinations required for the serviceability limit state are generated and calculated in RFEM/RSTAB. You can select these design situations for the deflection analysis in the Aluminum Design add-on. Depending on the specified precamber and reference system, the program determines the deformation values at each location of a member. They are then compared to the limit values.
You can specify the deformation limit value individually for each structural component in Serviceability Configuration. In this case, you define the maximum deformation depending on the reference length as the allowable limit value. By defining design supports, you can segment the components. In this way, you can determine the corresponding reference length automatically for each design direction.
And that's not all. Based on the position of the assigned design supports, the program allows you to automatically determine the distinction between beams and cantilevers. The limit value is thus determined accordingly.
You can find the serviceability limit state design checks in the result tables of the Aluminum Design add-on. They are already fully integrated there. You have the option to display the design results with all the details at each location of the designed members. You can also use graphics with the result diagrams of the design ratios.
You can integrate all result tables and graphics into the global printout report of RFEM/RSTAB as a part of the aluminum design results. RFEM/RSTAB also allows you to display and document the deformations of the entire structure independently of the add-on.
Do you prefer it clear? So do we! That's why all performed design checks for the design standard are displayed for you in a clear way. You determine a design criterion for each design check. You get design details, which include the initial values, intermediate results, and final results, arranged in a structured way for each design check. You can find the calculation process with the applied formulas, standard sources, and results in great detail in an information window in the design details.