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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. RF-IMP/RSIMP | Features

    • Creation of a pre-deformed FE mesh in RFEM
    • Generation of equivalent imperfections of members as equivalent loads, considering
      • the reduction factors αu and αm (Eurocode)
      • the precamber rises according to buckling stress curves
    • Deformation of the structure due to nodal displacement
    • Generation of imperfections in accordance with:
    • Equivalent imperfections on members and sets of members (for example columns consisting of several members)
    • Visualization of generated imperfection modes
  5. Standards for equivalent imperfections

    RF-IMP/RSIMP | Input

    The add-on module evaluates the pre-deformation of a load case as well as mode shapes of stability or dynamic analysis. Based on this initial deformation, it is possible either to pre-deform the structure or to create a load case with equivalent imperfections of members.

    The pre-deformed initial model is useful especially for structures consisting of surface and solid elements (RFEM) as well as members. It is necessary to specify only the maximum value to which the deformation is to be scaled. All FE or model nodes will be scaled with regard to the initial deformation.

    Equivalent imperfections are particularly useful for beam structures. You can define inclinations and precambers of members and set of members in the additional window. They can be generated automatically according to standards or defined manually. The following standards are available:

    •  EN 1992:2004
    •  EN 1993:2005
    •  DIN 18800:1990-11
    •  DIN 1045-1:2001-07
    •  DIN 1052:2004-08

    Only the imperfection resulting according to the initial deformation on the relevant member is applied. In addition, you can consider the reduction factors. In this way, it is possible to apply the imperfection efficiently.

  6. 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
  7. 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.

  8. 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.

  9. 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.

  10. Imperfection included in load combination

    RF-IMP/RSIMP | Using Equivalent Imperfections

    This generation type creates a normal load case including imperfections. You can modify the load case manually.

    Then, it is possible to combine this load case with "normal" load cases in load combinations.

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