Abstract
This paper investigates the elastic post-buckling behaviour of simply supported thin-walled lipped channel beams undergoing local-distortional (L-D) interaction. The beams are uniformly bent about the major-axis and experience flange-triggered local buckling (most common situation in practice). Three beam geometries are considered, each exhibiting a different type of L-D interaction, namely (i) “true L-D interaction” (close local and distortional critical buckling moments – two critical-mode initial geometrical imperfections are used, akin to the competing critical buckling modes), (ii) “secondary local-bifurcation L-D interaction” or (iii) “secondary distortional-bifurcation L-D interaction” (critical distortional-to-local buckling moment ratio well below or above 1.0, respectively, with “high enough” yield stresses). The results presented and discussed are obtained through elastic geometrically non-linear Generalised Beam Theory (GBT) analyses and provide the evolution, along given equilibrium paths, of the beam deformed configuration (expressed in GBT modal form), relevant displacement profiles and modal participation diagrams, making it possible to acquire in-depth knowledge on the beam L-D interaction mechanics. Particular attention is devoted to interpreting the quantitative and qualitative differences exhibited by the beam post-buckling behaviours associated with the three aforementioned L-D interaction types.
Highlights
The complex thin-walled open cross-section shapes commonly exhibited by cold-formed steel members makes them highly prone to several individual and/or coupled (L-D, L-G, D-G, L-D-G) buckling phenomena
Particular attention was paid to the structural interpretation of the behavioral features stemming from the L-D interaction effects, aimed at shedding fresh light on the mechanics of this coupling phenomenon
The results presented and discussed consisted of equilibrium paths and plots providing the evolution, along those equilibrium paths, of the beam (i) relevant displacements profiles and (ii) deformed configurations
Summary
The complex thin-walled open cross-section shapes commonly exhibited by cold-formed steel members (e.g., with several intermediate and end stiffeners) makes them highly prone to several individual (local, distortional, global L, D, G) and/or coupled (L-D, L-G, D-G, L-D-G) buckling phenomena. By performing GBTbased geometrically non-linear imperfect analyses (GNIA) of prismatic thin-walled members, it becomes possible to unveil and quantify the contributions of the various deformation modes to the member structural response under consideration This feature makes it possible to acquire much deeper insight on that response, providing a much clearer picture of the mechanical aspects involved i.e., GBT GNIA is an ideally suited numerical tool to investigate complex coupled instability problems, like the one addressed in this work. Where Ui and U i (i 1,2,3) are the strain energy terms associated with the total deformation and initial geometric imperfections, respectively, given by
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