Initial bow imperfections e0 for the verification of Flexural Buckling According to Eurocode 3 Part 1-1 - additional considerations

According to Eurocode 3 Part 1-1, the resistance of compression members may be calculated in two different ways: through the design buckling resistance based on the reduction factor &khgr; or through the cross section resistance based on internal forces according to a second order analysis, also taking into account equivalent initial bow imperfections e0. The second way is especially advantageous in the case of axial forces and bending. Values for equivalent initial bow imperfections e0 are given in codes like Eurocode 3 [4] or DIN 18800 [3]. The presently used values from Table 5.1 of Eurocode 3 will have to be changed in future, as was demonstrated recently by intensive investigations, especially for cases of axial compression and bending moments My or Mz respectively. Additional investigations concerning high-strength steel S700, welded sections and circular hollow sections are presented. The proposed changes included in the newest draft of prEN1993-1-1 are explained through the evaluation of several ultimate load calculations. It is also shown that for the case that the initial bow imperfection e0 is calculated dependent on the non-dimensional slenderness , restrictions regarding interaction and the ratio of Mpl/Mel are also necessary.