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.
After you have completed the design, the program takes care of clearly arranged results. Thus, the program shows you the resulting maximum stresses and stress ratios sorted by section, member/surface, solid, member set, x-location, and so on. In addition to the tabular result values, the add-on shows you the corresponding cross-section graphic with stress points, stress diagram, and values as well. You can relate the design ratio to any kind of stress type. The current location is highlighted in the RFEM/RSTAB model.
In addition to the tabular evaluation, the program offers you even more. You can also graphically check the stresses and design ratios on the RFEM/RSTAB model. It is possible for you to adjust the colors and values individually.
The display of result diagrams of a member or set of members enables you a targeted evaluation. For each design location, you can open the respective dialog box to check the design-relevant section properties and stress components of any stress point. Finally, you have the option of printing the corresponding graphic, including all design details.
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.
Have you activated the Time-Dependent Analysis (TDA) add-on? Very well, now you can add time data to load cases. After you have defined the start and end of the load, the influence of creep at the end of the load is taken into account. The program allows you to model creep effects for frame and truss structures made of reinforced concrete.
In this case, the calculation is performed nonlinearly according to the rheological model (Kelvin and Maxwell model).
Was the calculation successful? You can now display the determined internal forces in tables and graphics, and consider them in the design.
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 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
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‑/STEEL add-on module (RFEM 5 / RSTAB 8), the following new features have been added to the Stress-Strain Analysis add-on for RFEM 6 / RSTAB 9:
Treatment of members, surfaces, solids, welds (line welded joints between two and three surfaces with subsequent stress design)
Output of stresses, stress ratios, stress ranges, and strains
Limit stress depending on the assigned material or a user-defined input
Individual specification of the results to be calculated through freely assignable setting types
Non-modal result details with prepared formula display and additional result display on the cross-section level of members
For each load case, the deformations can be displayed at the end time.
These results are also documented for you in the printout report of RFEM and RSTAB. You can select the report contents and extent specifically for the individual design checks.
Do you have great respect for the ravages of time? After all, it eventually gnaws at your construction projects. Use the Time-Dependent Analysis (TDA) add-on to consider the time-dependent material behavior of members. Long-term effects, such as creep, shrinkage, and aging, can influence the distribution of internal forces, depending on the structure. Prepare for this optimally with this add-on.
Reinforced concrete usually answers the question "How much can you carry?" simply with "Yes". Nevertheless, you need a three-dimensional moment-moment-axial force interaction diagram for the graphical output of the ultimate limit state of reinforced concrete cross-sections. The Dlubal structural analysis software offers you just that.
With the additional display of the load action, you can easily recognize or visualize whether the limit resistance of a reinforced concrete cross-section is exceeded. Since you can control the diagram properties, you can customize the appearance of the My-Mz-N diagram to suit your needs.
Did you know that you can also display the moment-axial force interaction diagrams (M‑N diagrams) graphically? This allows you to display the cross-section resistance in the case of an interaction of a bending moment and an axial force. In addition to the interaction diagrams related to the cross-section axes (My‑N diagram and Mz‑N diagram), you can also generate an individual moment vector to create an Mres‑N interaction diagram. You can display the section plane of the M‑N diagrams in the 3D interaction diagram. The program displays the corresponding value pairs of the ultimate limit state in a table. The table is dynamically linked to the diagram so that the selected limit point is also displayed in the diagram.
Do you want to determine the biaxial bending resistance of a reinforced concrete cross-section? For this, you have to activate a moment-moment interaction diagram (My-Mz diagram) first. This My-Mz diagram represents a horizontal section through the three-dimensional diagram for the specified axial force N. Due to the coupling to the 3D interaction diagram, you can also visualize the section plane there.
Depending on the axial force N, you can generate a moment curvature line for any moment vector. The program also shows you the value pairs of the displayed diagram in a table. Furthermore, you can activate the secant stiffness and tangent stiffness of the reinforced concrete cross-section, belonging to the moment curvature diagram, as an additional diagram.
The structural analysis program provides you with a clear overview of all performed design checks for the design standard. You have to determine a design criterion for each design check. In addition to the ultimate limit state and the serviceability limit state design, the program checks the design rules of the standard. For each design check, there are the design details including the initial values, intermediate results, and final results, arranged in a structured way. An information window in the design details shows you the calculation process with the applied formulas, standard sources, and results in great detail.
You can display the existing stresses and strains of a concrete cross-section and the reinforcement as a 3D stress image or 2D graphic. Depending on which results do you select in the result tree of the design details, the stresses or strains are displayed to you in the defined longitudinal reinforcement under the load actions or the limit internal forces.