Why are the imperfections taken into account in RFEM and RSTAB when calculating according to the linear static analysis, even though the definition says that no deformations of structural components are considered according to the linear static analysis?


In general, the imperfection describes the incompleteness of a structure or the deviation from an ideal shape caused by the production. There are different ways to simulate the imperfection. In RFEM and RSTAB, the imperfections are modeled as equivalent loads. The definition of the equivalent loads is shown in Figure 01, and is taken from [1]. The same is described in EC 3 [2]. Since these are the equivalent loads that are dependent on the axial force, they are also considered in the calculation according to the linear static analysis. It is recommended to manage loads and imperfections in separate load cases. They can be combined in an appropriate way with each other in load combinations. The load cases with pure imperfections have to be categorized as the "Imperfection" action type in General Data of the load cases (see Figure 02).


Imperfection Linear static analysis Internal forces


[1]   Manual RFEM. (2018). Tiefenbach: Dlubal Software.
[2]   Eurocode 3: Design of steel structures - Part 1‑1: General rules and rules for buildings; EN 1993‑1‑1:2010‑12



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RFEM Main Program
RFEM 5.xx

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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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RSTAB 8.xx

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The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

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