Analytical modelling of plastic collapse in compressed elliptical hollow sections

Local buckling and ultimate strength of slender elliptical hollow sections in compression

“…For higher yield strengths, the Y mechanism was observed with sequential folding and crushing of the stiff corners occurring at mid-height. This observation is coherent with the findings of [31] since the imperfection shape was symmetrical with a relatively large inward displacement at mid-height. For a/b = 2.0 and a low yield strength, the FD mechanism was found to occur at mid-height, while for a high yield strength a Y mechanism generally occurred, as for sections with a/b = 1.5.…”

“…Additionally, it can be seen upon examination of the spread of results between the three imperfection classes that imperfection sensitivity is considerably lower in the sections with the higher aspect ratios, despite the Class A and Class B imperfections being rather high for some sections. These two observations are commensurate with the findings of [31]. It is also confirmed from examination of the graphs that the CHS curves using the equivalent EHS diameters are overly conservative and wrongly predict significant imperfection sensitivity for sections with high aspect ratios.…”

“…There was good agreement observed between the failure modes determined from the numerical analysis and those observed in the test specimens in [4]. There was also good correlation with the predicted failure modes in [31], where four deformation modes were identified: i) the shell-like "elephant foot" (EF) mechanism which is more prevalent for small imperfection amplitudes, with outward bulges forming a concertina; ii) the shell-like Yoshimura (Y) mechanism, with sequential folding at mid-height, which occurs for imperfection modes with inward displacements at mid-height; iii) the plate-like flip disc (FD) and iv) split flip disc (SFD) mechanisms, which are inward-facing with two parabolic hinge lines folding inwards and outwards, respectively [32]. These latter two mechanisms are most likely to occur in EHS with imperfection amplitudes typically found in practice.…”

Postbuckling strength of slender elliptical hollow sections in compression

“…The four deformation modes identified by Insausti & Gardner (2011) were observed upon examination of the results of the parametric study: i) the shell-like "elephant foot" (EF) mechanism which is more prevalent for small imperfection amplitudes, with outward bulges forming a concertina; ii) the shelllike Yoshimura (Y) mechanism, with sequential folding at mid-height, which occurs for imperfection modes with inward displacements at mid-height; iii) the plate-like flip disc (FD) and iv) split flip disc (SFD) mechanisms, which are inward-facing with two parabolic hinge lines folding inwards and outwards, respectively (Murray 1984). In general, for the lowest aspect ratios (a/b = 1.1 and 1.5), the most prevalent failure mode tended to be the EF mode, with a superposition of FD and EF modes becoming more apparent as slenderness increased.…”

Global instability of elliptical hollow section beam-columns under compression and biaxial bending

“…A number of research projects have focused on the structural response of EHS at the cross-sectional level (Gardner and Chan, 2007;Silvestre, 2008;Chan and Gardner, 2008a, b;Gardner et al, 2008;Zhao and Packer, 2009;Dai and Lam, 2010;Gardner et al, 2011;Insausti and Gardner, 2011;Abela and Gardner, 2012;Sheehan et al, 2012) and a state-of-art review of the behaviour and design of elliptical hollow sections has been made by Chan et al (2010a). In the case of combined compression plus biaxial bending, Chan et al (2010b) and Abela and Gardner (2012) examined the local buckling and cross-sectional resistance of hot-finished elliptical hollow sections and found that the plastic interaction formulae proposed by Nowzartash and Mohareb (2009) provided good predictions of the observed structural performance.…”