Ermittlung der Vorkrümmungen e0 für die Berechnung von Aluminiumtragwerken nach DIN EN 1999-1-1 nach Theorie II. Ordnung

Determination of initial bow imperfections e0 for second-order analysis of aluminum structures according to EN 1999-1-1.

The initial bow imperfection e0 is required if structures are designed with the internal forces and moments from second-order analysis. The National Annex DIN EN 1999-1-1/NA/A1 as a NDP to 5.3.2(3) of DIN EN 1999-1-1 describes how e0 may be calculated. Based on this, formulae are derived for calculating the relative initial bow imperfections e0/L for six very different types of cross sections which cover a very wide range. Linear as well as nonlinear M-N-interaction relations are used depending on the type of cross section. These formulae describe e0/L as product of functions of which the first depends on the cross section, the second on the proof strength fo and the third on relative slenderness, buckling class and interaction relation. The numerical evaluation of these formulae gives conservative limit values for e0/L. However, due to the wide range of the parameters these values will in general be that far on the safe side that the application of the formula with the relevant parameters is recommended. For members where fo due to the HAZ is variable over the cross section a linear and alternatively a nonlinear interaction relation may be used as safe approximation. This is demonstrated with a thin-walled circular tube.