Effective width equations accounting for element interaction for cold-formed stainless steel square and rectangular hollow sections

Abstract

Rectangular hollow sections featuring high height-to-width (aspect) ratios have shown to offer improved ultimate capacity due to the effects of the interaction between the elements within the cross-section which are particularly significant for slender cross-sections (class 4) undergoing local buckling. The European design rules dealing with stainless steel, EN 1993-1-4 [1], utilises the concept of cross-section classification and the effective width method for the design of slender cross-sections susceptible to local buckling neglecting such interaction effects, hence resulting in conservative predictions. This paper examines the benefits of element interaction effects on cold-formed ferritic stainless steel compressed sections on the basis of carefully validated finite element models. Following parametric studies, the applicability of various alternative design approaches accounting for element interaction to ferritic stainless steel is assessed and effective width curves, as well as a Class 3 limiting slenderness equation, are derived herein as an explicit function of the aspect ratio. Comparisons with the loads achieved in the FE models have shown that the proposed effective width equations allowing for the benefits of element interaction improve capacity predictions making design more cost-effective. Highlights:Numerical modelling of cold-formed ferritic stainless steel stub columns. Study of the influence of some key parameters on the numerical response. Successful validation of the scope of various methods to cover ferritic steel. Incorporation of element interaction effects into the effective width formulation. Reliability analysis and validation of the proposed method against existing tests.

Compressive behaviour of high-strength steel cross-sections

“…Based on the effective width equations applied to constituent plate elements of sections prone to local buckling, a method providing a reduction factor for the gross cross-sectional area has been previously proposed for slender stainless steel sections (Zhou et al, 2013a;Bock et al, 2015). The method, named effective cross-section method herein, expresses the reduction factor as a function of the plate slenderness ̅ and the cross-section aspect ratio / , thus allowing for the influence of the element interaction on the cross-sectional response.…”

“…Maintaining the cross-section outer dimensions and varying the cross-section thickness, cross-sections with a / ratio ranging from 10 to 100 were modelled, where is the compressed flat width, is the plate thickness and = √ 235/ . In line with past studies (Gardner and Nethercot, 2004;Bock and Real, 2015;Wang et al, 2016), the average material properties obtained for each steel grade from the tensile coupon tests (Wang et al, 2016) were incorporated in the FE models. The length of the specimens was set equal to three times the largest cross-section dimension, thus allowing for a sufficient representation of the initial local geometric imperfection pattern but excluding global buckling failure mode (Galambos, 1998).…”

Formulae for Calculating Elastic Local Buckling Stresses of Full Structural Cross-sections

“…The basis to allow for element interaction was laid by considering outstand and internal rectangular plates restrained elastically along the unloaded adjoining edges. Since then, a number of analytical, experimental and numerical studies have been carried out examining the effects of element interaction on the elastic and inelastic local buckling behaviour of various cross-section profiles including I-sections [21][22][23][24][25][26][27][28][29][30][31], rectangular hollow sections [32][33][34][35], cold-formed sections [36][37][38][39] and hot-rolled steel profiles [8]. Recently, Generalized Beam Theory was used to develop semi-analytical expressions for the buckling coefficient k of rectangular hollow sections under combined axial force and bi-axial bending [35].…”

The continuous strength method for the design of hot-rolled steel cross-sections

“…The importance of plate element interaction effects on the ultimate resistance of structural cross-sections has been examined by a number of researchers. Studies have been conducted on square and rectangular hollow sections (SHS/RHS) [9][10][11][12] and I-sections [12][13][14][15][16], while explicit allowance for element interaction through the use of cross-section rather than element elastic buckling stresses in the determination of local and distortional slendernesses is a key feature of the Direct Strength Method (DSM) [17][18][19]. The beneficial influence of strain hardening has also been observed by a number of researchers [6,[20][21][22], and the exploitation of strain hardening is a key feature of the Continuous Strength Method [23,24].…”