Abstract
Most cold-formed steel columns display open and rather thin-walled cross-sections which mean that their structural behaviour is strongly affected by local and global buckling. Th e local mode, that occurs for shorter profi les, is characterized by (i) the local plate mode (LPM) characterized by the simultaneous flexural buckling of the web and fl anges and (ii) by the distortional mode (DM) characterized by the displacements of flange-stiff ener edges (that remain plane). The global mode occurring for long profi les is characterized by (i) the fl exural mode (FM) characterized by the translation of the whole section in the direction of the major principal axis and (ii) by the fl exural-torsional mode (FTM) characterized by the simultaneous translation and rotation of the whole section. Th e possibility of using the results of linear stability analysis in the national codes of thin-walled cold-formed steel structural elements (for instance, European and Brazilian Codes) arises, i.e. local and global buckling instability modes and corresponding bifurcation stresses determining the ultimate strength of members. Two powerful numerical methods are chosen to perform a linear stability analysis of a cold-formed steel structural member: (i) the Finite Strip Method, (i1) the Semi-Analytical Finite Strip Method (trigonometric functions are used in the approximation of displacement) used for simply supported boundary conditions, (i2) the Spline Finite Strip Method (‘spline’ functions are used in the approximation of displacement) used other boundary conditions and (ii) the Finite Element Method. The linear local and global stability results of for Z, C and rack cold-formed columns are used to obtain ultimate strength through the procedures adopted in the Eurocode 3, Part 1.3 and in the Brazilian Code (NBR 14.762/2001). The obtained numerical estimates by specifi cations are compared with experimental results available in literature.
Highlights
Most cold-formed steel profiles display open and rather thin walled cross-sections which mean that their structural behavior is strongly affected by local and global buckling
The global mode can be characterized by (i) the flexural mode (FM) that involves the translation of the whole section in the direction of the major principal axis and (ii) the flexural-torsional mode (FTM) that occurs in the translation and rotation of the whole section
Linear Stability Analysis is carried out by computational programs developed by the authors of this paper: (i) the Finite Strip Method where the results were obtained by two computer programs developed by Prola (2001): (i1) the Semi-Analytical Finite Strip Method used for supported boundary conditions, (i2) the Spline Finite Strip Method (‘spline’ functions are used in the approximation of displacement) used for other boundary conditions and (ii) the Finite Element Method where the results are obtained by a computer program developed by Pierin (2005)
Summary
Most cold-formed steel profiles display open and rather thin walled cross-sections which mean that their structural behavior is strongly affected by local and global buckling. The local mode, which occurs for shorter bars, involves plate deformations (remain your axis in original configuration). Local modes can be characterized by (i) the local plate mode (LPM) that involves only the flexural deformations of the web and flange and (ii) the distortional mode (DM) that includes the displacements of flange-stiffener edges remaining plane. The global mode occurring for long profiles is characterized by axis deformations. The aim of this article is (i) to present the numerical procedures based on Finite Strip and Finite Element in order to perform the stability analysis of thin-walled profiles and (ii) to study the ultimate strength of Z, C and rack cold-formed columns
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