Study on the Influence of Measured Geometric Shape Deviations on the Deformation Capacity and Post-Buckling Behavior of Hollow Sections Loaded in Compression and Bending

In international design codes on the design of steel structures, the maximum rotational capacity of a section is limited and linked to the definition of cross-sectional classes. For example, in Eurocode 3, class 2 cross-sections are defined as sections that can reach their plastic moment, but fail to reach a rotation capacity of Rcap=3, while Class 1 cross-sections fulfil this demand. Eurocode 8 (seismic design) gives deformation capacity limits for limit states analysis of existing structures and limited by the condition that the normalized axial load is lower than 0,3. The classification of cross-sections necessarily leads to discontinuities in the representation of both strength and deformation capacities. This paper illustrates first steps towards an alternative approach that makes use of a continuous definition of deformation capacities in dependence of cross-sectional slenderness values. In case of the rotation capacity in bending, recently conducted tests on hot rolled and cold finished SHS hollow sections made of mild and high-strength steel grades showed that the choice of different eigenmode-based pre-buckling shapes as initial imperfections for geometrically and materially non-linear (GMNIA) calculations lead to near identical values of the reached maximum moment, yet show significant variation in the post buckling paths. A comparative FEM based evaluation of surface-scan-based real geometry models also showed variability in the post-buckling behaviour as well as different plastic hinge formation spots. This paper presents a detailed look on the effect of different theoretical and measured, scanned imperfection shapes on the post-buckling behaviour of SHS and RHS hollow sections.

View content