Ultimate strength and design of lipped channel columns experiencing local/distortional mode interaction - Part I: Experimental investigation

This paper reports the results of an experimental investigation aimed at assessing the post-buckling behaviour and ultimate strength of fixed-ended cold-formed steel lipped channel columns experiencing local/distortional mode interaction. A total of 26 columns were tested and the specimens were carefully selected to ensure various levels of local/distortional interaction effects (more or less close local and distortional critical stresses). The experimental results presented consist of the specimen geometries, material properties, initial imperfections, non-linear equilibrium paths and ultimate strength values. Since the collapse of most columns combines local and distortional deformations, these experimental results may be used to (i) assess the relevance of local/distortional interaction, (ii) calibrate and validate numerical simulations and (iii) provide experimental data aimed at developing a Direct Strength Method (DSM) approach to design cold-formed steel lipped channel columns against local/distortional interaction - such a DSM approach is addressed in Part II of this paper.published_or_final_versionThe 6th International Conference on Advances in Steel Structures in conjunction with IJSSD Symposium on Progress in Structural Stability and Dynamics & IStructE Asia-Pacific Forum (ICASS '09 / IJSSD / IStructE Asia-Pacific Forum), Hong Kong, China, 16-18 December 2009. In Proceedings of the 6th ICASS, 2009, v. 1, p. 460-46

GBT-based semi-analytical solutions for the elastic/plastic stability analysis of stainless steel thin-walled columns exposed to fire

The authors gratefully acknowledge the financial support of FCT (Fundação para a Ciência e a Tecnologia, Portugal), through Project “StaSteFi—Fire design of stainless steel structural elements”.This paper presents and illustrates the application of an efficient Generalized Beam Theory (GBT) semi-analytical solution procedure to determine elastic and plastic bifurcation loads (linear stability analysis) of stainless steel thin-walled members subjected to uniform compression and exposed to fire. Besides global (flexural or flexural-torsional) buckling, the proposed GBT formulation allows for cross-section deformation and therefore makes it possible to capture local and distortional buckling. The temperature effect is taken into account using the material law for stainless steel specified in Eurocode 3 part 1-4 (CEN 2006) and Annex C of part 1-2 (CEN 2009). For plastic buckling, the material tangent moduli are obtained using both J2 small-strain incremental and deformation plasticity theories. For illustrative purposes, the procedure is applied to columns with a lipped channel cross-section.authorsversionpublishe

On the Influence of Local-Distortional Interaction in the Behavior and Design of Cold-Formed Steel Web-Stiffened Lipped Channel Columns

This paper reports the results of a numerical (ABAQUS shell finite element analysis) investigation on the influence of local-distortional (L-D) interaction in the ultimate strength and design of cold-formed steel fixed-ended web-stiffened lipped channel columns -- hereafter termed “WSLC columns”. These results concern columns with various geometries and yield stresses, ensuring a wide variety of combined ratios between (i) the distortional and local critical buckling stresses, and (ii) the yield and the higher of the above buckling stresses. The objectives of this work are two-fold: (i) to acquire in-depth understanding on the mechanics underlying the L-D interaction in the WSLC columns analyzed, all selected to ensure that local buckling is triggered by the flanges, and also (ii) to provide a first contribution towards the efficient Direct Strength Method (DSM) design of these structural elements. The results presented and discussed concern the (i) post-buckling behavior (elastic and elastic-plastic), (ii) ultimate strength and (iii) failure mechanisms of the WSLC columns previously selected to undergo L-D interaction. Special attention is paid to comparing the ultimate strength erosions, due to L-D interaction, exhibited by the WSLC columns investigated here and the “plain cross-section” (i.e., without intermediate stiffeners) columns studied earlier by the authors (Martins et al. 2014a). Finally, the paper closes with some considerations about the impact of the findings reported in this work on the design of cold-formed steel columns undergoing different levels of L-D interaction

Vibration behavior of thin-walled steel members subjected to uniform bending.

This article reports the results of an investigation on the effects of internal moments on the vibration behavior of thin-walled steel members. The analyses are based on the Generalized Beam Theory (GBT), a thin-walled bar theory accounting for crosssection in-plane deformations ? its main distinctive feature is the representation of the member deformed configuration by means of a linear combination of cross-section deformation modes, multiplied by their longitudinal amplitude functions. The study concerns a simply supported T-section (with unequal flanges) members exhibiting a wide range of lengths and subjected to uniform internal moment diagrams ? their magnitudes are specified as percentages of the corresponding critical buckling values. After providing a brief overview of the main concepts and procedures involved in performing a GBT-based structural analysis, the vibration behavior of load-free and loaded T-section members is addressed ? the influence of the applied loadings is assessed in terms of (i) the fundamental frequency difference and (ii) the change in the corresponding vibration mode shape. For validation purposes, some GBT results are compared with values yielded by shell finite element analysis performed in the code ABAQUS (Simulia, 2008)

Double excitation transitions in Mn2+ -doped alkali halides

4 págs.; 4 figs.It is shown in this work that the room-temperature excitation spectra of as-grown crystals of LiF, NaF, NaCl, KCl, and KBr doped with Mn2+ reveal the existence of double excitation peaks. These peaks are related to the formation of precipitated phases containing Mn2+ in the alkali halide lattice. In the case of LiF:Mn2+ the position of the [A14(G), E4(G)] and T14(G) peaks suggests an anomalously small Mn2+- F- distance for the precipitated phase. © 1983 The American Physical Society.Financial support by the Comision Asesora para la Investigacion Cientifica y Tecnica, is gratefully acknowledged.Peer Reviewe

Non-linear behaviour and load-carrying capacity of CFRP-strengthened lipped channel steel columns

This paper reports the results of an experimental and numerical investigation on the non-linear behaviour and load-carrying capacity of CFRP-strengthened cold-formed steel lipped channel columns, devoting special attention to their local-plate and/or distortional buckling behaviours. A preliminary GBT-based study concerning the column elastic buckling behaviour is performed, focusing on determining the (i) sheet location (web, flanges and/or lips) and (ii) carbon fibre orientation (longitudinal, transverse or inclined) that optimize the strengthening procedure (enhanced buckling behaviour vs. cost). Then, an experimental programme comprising a total of 19 short and long fixed-ended lipped channel columns is described. The columns were strengthened with carbon fibre sheets (CFS) bonded at different outer surface locations (web, flanges or lips) and having the fibres oriented either longitudinally or transversally - since the aim of the study is to assess the influence of the CFS on the column structural response, bare steel specimens were also tested. The experimental results, which consist of non-linear equilibrium paths (applied load vs. axial shortening) and ultimate strength values (most of them associated with local-plate and/or distortional failure mechanisms), are subsequently used to calibrate and validate geometrically and physically non-linear numerical analyses based on shell finite element models and carried out in the code Abaqus. Finally, on the basis of both the experimental and numerical results obtained, some relevant conclusions are drawn concerning the most effective CFS location and fibre orientation to strengthen lipped channel steel columns affected by local-plate and/or distortional buckling. © 2008 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex