Stability Analysis: Buckling Shapes and Imperfections with RF-STABILITY & RF-IMP


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Generation of Pre-Deformed Initial Structures and Equivalent Imperfections for Nonlinear Calculation

The RF-IMP/RSIMP add‑on module performs automatic generation of imperfections for the geometrically nonlinear calculations.

Thus, it is possible to perform the ultimate limit state design including stability in the course of the second‑order or the large deformation analysis for beam structures as well as models consisting of shell and solid elements.

  1. 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
  2. Standards for equivalent imperfections


    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.

  3. Pre-deformed FE-mesh


    When generating a pre-deformed FE mesh in RFEM, the displacement data of each individual node is saved in the background. This can be used for the calculation of load combinations in RFEM. In order to check the generated data, the pre-deformation is displayed in tables and graphically.

    In the case of displacing structural nodes, the node coordinates are modified directly after generation. When generating equivalent imperfections, the module creates a normal load case including member imperfections. To facilitate the data check, generated imperfections are displayed in result tables as well as graphically.

  4. Data import from RF-IMP

    Using Pre-Deformed FE Mesh in RFEM

    It is possible to use the previously created pre-deformed FE mesh in load combinations. For this, select the corresponding RF-IMP case in the calculation parameters of the load combination. Then, the calculation of internal forces is performed for the imperfect structure.

  5. Imperfection included in load combination

    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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