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  1. Stability Design Including Warping Torsion in RF-/STEEL AISC

    Warping Torsion Analysis in RF-/STEEL AISC

    By using the integrated module extension RF-/STEEL AISC Warping Torsion, the design according to the Steel Design Guide 9 can be performed in RF-/STEEL AISC.
    The calculation is effected with 7 degrees of freedom according to the warping torsion theory and allows the realistic stability design including the consideration of torsion.

  2. Graphical Display of Mode Shape in RF-/STEEL AISC

    Eigenvalue Solver for Member Design in RF-/STEEL AISC

    The determination of the critical buckling moment is carried out in RF-/STEEL AISC by using the eigenvalue solver which allows an exact determination of the critical buckling load.

    The eigenvalue solver is completed by a display window of the eigenvalue graphics which ensures the check of the boundary conditions.

  3. Definition of Lateral Restraints in RF-/STEEL AISC

    Consideration of Lateral Restraints in RF-/STEEL AISC

    In RF-/STEEL AISC, it is possible to consider lateral restraints at any location. It is, for example, possible to stabilize only the upper flange.

    Moreover, user-defined lateral restraints can be assigned, for example single rotational and translational springs at any location at the cross-section.

  4. 2.1 Effective Lengths and Loads

    RSBUCK | Results

    The results of the buckling analysis are displayed in clearly-arranged result tables and graphics. Since RSBUCK is fully integrated in RSTAB, you can adjust all results in detail in the printout report according to your individual requirements.

    Furthermore, you can export all result tables to MS Excel or in a CSV file. A special transfer menu defines all export specifications.

  5. Calculation of buckling shapes

    RSBUCK | Calculation

    RSBUCK determines the most unfavorable buckling modes of a structure. Due to the theory forming the basis of the calculation method, it is generally not possible to exclude lower eigenvalues from the analysis and determine higher eigenvalues at the same time. With RSBUCK, you can determine up to the 10,000 lowest eigenvalues of a structural system.

    By default, RSBUCK uses the average value of the axial forces occurring on the individual members to calculate the eigenvalues/critical load factors. Optionally, the module can also process the most unfavorable axial force of a member. The determination of buckling modes is performed by an eigenvalue analysis for the entire structure. For this, an iterative equation solver is used.

    You only have to specify the following two values:

    • the maximum number of iterations
    • the break off limit

    As you can approximate an exact result as close as possible but never reach it, RSBUCK cancels the calculation process when the defined number of iteration steps has been completed. In the case of a convergence problem, the break off limit determines the moment when an approximate solution can be considered as an exact result. Divergence problems have no solution.

  6. Graphical representation of buckling mode

    RSBUCK | Input

    RSBUCK is distinguished by easy handling, clear data arrangement and great user-friendliness. With only a few mouse clicks, you can define the number of buckling modes to be calculated as well as the load case to be considered.

    Structural data and boundary conditions set in the selected load case are imported automatically from RSTAB. Alternatively, you can edit the imported axial forces or enter new values manually. It is also possible to create further RSBUCK cases in order to perform several analyses each with different boundary conditions.

    For a better result display, it is possible to set the units individually in RSBUCK. If the RSTAB internal forces are not available when starting the RSBUCK module, the program calculates the required internal forces automatically before determining the buckling values.

  7. Table 1.1 General Data

    RSBUCK | Features

    • Automatic import of structural data and boundary conditions from RSTAB
    • Optional consideration of favorable effects due to tension
    • Import of axial forces from RSTAB load cases or user-defined specifications for member
    • Results by member including effective lengths L about weak and strong axis with corresponding effective length factors β
    • Results by member listing standardized buckling modes
    • Results of critical load factors regarding buckling case for entire structure
    • Graphics and animated visualization of buckling modes on the rendered model
    • Identification of members free of compression forces
    • Optional transfer of the effective lengths to other RSTAB design modules for equivalent member designs according to standards
    • Optional export of buckling mode geometry to the RSIMP add-on module in order to create RSTAB imperfections
    • Direct data export to MS Excel
  8. Graphical evaluation of eigenvalues

    RF-STABILITY | Results

    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 graphics allows for the evaluation of the buckling behavior. The graphical display facilitates the provision of countermeasures.

  9. Global Calculation Parameters

    RF-STABILITY | Calculation

    Several methods are available for the Eigenvalue analysis:

    • Direct Methods
      The direct methods (Lanczos, roots of characteristic polynomial, subspace iteration method) are useful for models of small and medium size. These fast methods of equation solvers benefit from lots 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 little memory. Eigenvalues are determined one after the other. It can be used to calculate large structural systems with few stability modes.

    The RF-STABILITY add-on module can also perform the non-linear stability analysis. Also for non-linear structures, the results close to reality are provided. The critical load factor is determined by increasing the loads of the selected load case step by step until the instability is reached. Nonlinearities such as failing members, supports and foundations as well as material nonlinearities are considered when increasing the loads.

  10. Input window

    RF-STABILITY | Input

    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 case of 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. These elements prevent from the determination of the local buckling for an individual member. Therefore, there is the option to divide members automatically.

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