The influence of imperfections in the critical temperature of I-section steel members

Abstract

This paper describes the influence of the imperfections in the critical temperature assessment of steel members at elevated temperatures. An extensive numerical investigation using shell FE models is performed in the scope of this work to calculate the critical temperature of steel members for particular combinations of geometric and material imperfections, such as member or plate imperfections and residual stresses, respectively. The behaviour of axial compressed members with I-shape section, both for flexural buckling in the strong- and weak-axis and the lateral-torsional buckling of beams, is analysed considering four different load-levels. The results show that the influence of imperfections increases with the load-level and that the critical temperature of steel members, as expected, decreases with the presence of imperfections. Particularly, the influence of the residual stresses is almost negligible for lower load-levels and could be disregarded in the numerical analyses, however, for a load-level of 65% of the load-bearing capacity, calculated at normal temperature, it is recommended that the residual stresses are included in numerical simulations, since their effects are non-negligible, especially for welded members.