6 November 2019

FAQ 004193 EN

Gerhard Rehm




Why are imperfections taken into account in RFEM and RSTAB when calculating according to the 1st Order Theory, even though, by definition, no component deformations are considered according to the 1st Order Theory?


In general, an 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 RSTAB and RFEM, imperfections are represented as equivalent loads. The definition of equivalent loads is shown in Figure 01 and is taken from [1] . The same is described in EC3 [2] . Since these are equivalent loads that are dependent on the axial force, they are also taken into account for a calculation according to the 1st Order Theory. 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. Load cases with pure imperfections have to be categorized as action type 'Imperfection' in the general data for load cases (see Figure 02).


Imperfection 1st Order Theory 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

Main Program

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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3,540.00 USD
RSTAB Main Program
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

Price of First License
2,550.00 USD