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In the companion paper, test results were presented to explore the flexural performance of cold-formed ferritic stainless steel (FSS) closed built-up beams. Each specimen was fabricated by joining two lipped channels in a face-to-face configuration and securing them with spot welds at intermediate points along the beam span. Sectional aspect ratio, compression flange's sectional slenderness and moment gradient were the key parameters varied to explore their influence on the flexural response of such members through tests. The current paper establishes a simplified finite element (FE) model of cold-formed FSS closed built-up beams and verifies it against the test results. Further, an extensive parametric study is carried out using the validated FE model to generate a large pool of data points. A wider database comprising of test results, numerical results obtained from this study and numerical results available in the companion paper were used to critically examine the adequacy of the current Australian Specifications (AS/NZ), American Standard (SEI/ASCE-8), European Code (EN 1993-1-4), Modified Eurocode approach suggested by Gardner and Theofanous, and Direct Strength Method (DSM) in North American Specification (AISI-S100: 2016), Modified DSM approach proposed by the authors in the literature and Continuous Strength Method (CSM) for cold-formed steel (CFS) flexural members. This makes the current study the first to extensively assess the accuracy of the various design guidelines available in the codes and other relevant literature, which explicitly highlighted their grave limitations. Accordingly, through suitable modifications and recommendations, new design rules are proposed to reliably and safely predict the flexural capacity of cold-formed FSS closed built-up beams. [ABSTRACT FROM AUTHOR]

Built-up back-to-back cold-formed steel (CFS) channel members (BBC members) are utilized as CFS compression members with enhanced load-bearing capacity in building structures. In this study, finite-element (FE) models of BBC compression members with pinned warping-fixed and pinned warping-free ends were established and verified using test results available in the literature. Using the developed FE models, detailed parametric studies were conducted to assess the behavior and capacity of slender BBC compression members with pinned warping-free ends, varying cross sections, and screw arrangements. The results were first compared with those of their individual (channel) members and BBC members with pinned warping-fixed ends. They were then used to evaluate the direct strength method (DSM) design rules in the CFS design standards used in North America and Australia/New Zealand. Finally, new reliable design rules based on the DSM equations and some analytical equations in the literature were proposed for the BBC compression members with pinned warping-free ends, together with suitable recommendations. This paper includes the main details of this study with a summary of its important findings and proposals. [ABSTRACT FROM AUTHOR]

• A series of compression tests to investigate member buckling behaviour and ultimate strengths of cold-rolled aluminium alloy channel columns are performed. • The aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural channel columns. • The observed failure modes are flexural, flexural-torsional and local-global interaction buckling failure modes. • The experimental results are compared with predictions by current Australian/New Zealand, North American and European design specifications. Cold-rolled aluminium alloy sections have been recently introduced in Australia as newly developed thin-walled products. To fabricate these sections, the roll-forming process used in cold-formed steel production has been employed, which has proven to be more cost-effective than the conventional extrusion process. This paper describes a series of compression tests to investigate member buckling behaviour and ultimate strengths of cold-rolled aluminium alloy 5052-36 channel columns. Twenty-eight specimens of three commercially available sections (C10030, C25025 and C40030) were tested at the University of Sydney. Two configurations of end boundary conditions were specially designed to capture flexural, flexural-torsional and local-global interaction buckling failure modes. Prior to testing, initial geometric imperfections were measured using a laser scanning method, and flat/corner coupons were tested to determine compressive and tensile strengths of the aluminium alloy material. The experimental results are compared with ultimate column strength predictions by current Australian/New Zealand, North American and European design specifications for aluminium structures. Additionally, the test results provide data for calibration of finite element models of cold-rolled aluminium structural members for use in parametric and similar studies. A companion paper describes such parametric study and the derivation of new design guidelines for member buckling of cold-rolled aluminium channel columns based on the numerical parametric data and the experimental data presented herein. [ABSTRACT FROM AUTHOR]

• Experiments on the member buckling and ultimate strengths of cold-rolled aluminium alloy channel columns are performed. • The aluminium alloy 5052-H36 materials are used to fabricate the cold-rolled aluminium structural channel columns. • Non-linear FE models are developed using ABAQUS to simulate laboratory experiments and calibrated against the test results. • A parametric study based on FE models is performed to extend the data by varying cross-section dimensions and member lengths. • Experimental and numerical results are ued to calibrate the new design equations for cold-rolled aluminium alloy columns. The paper first presents the development of detailed finite element (FE) models for investigating the member capacity of cold-rolled aluminium alloy 5052-36 channel columns. The numerical non-linear FE models are developed using the commercial FE software package ABAQUS to simulate laboratory experiments and calibrated against the test results. The experimental program was performed by the authors at the University of Sydney and the detailed test results are fully described in a companion paper. The calibrated numerical FE models with actual mechanical properties and measured geometric imperfections in analyses accurately predict the experimental results and behaviours, including flexural and flexural-torsional buckling as well as local-global interaction buckling failure modes. A parametric study is subsequently performed to extend the data range by varying cross-section dimensions and member lengths. The effects of loading eccentricity positions and initial geometric imperfections are also considered in the parametric study. The experimental and numerical results are compared with design strength predictions from current Australian/New Zealand, American and European specifications for aluminium structures in the companion paper. In this paper, the Direct Strength Method (DSM) for the design of compression members as per the Australian/New Zealand standard AS/NZS 4600 for cold-formed steel structures is adopted for comparison. The DSM design rules for cold-formed steel compression members are found to provide more accurate predictions than those of current specifications for aluminium structures and therefore used to propose improved design equations for cold-rolled aluminium alloy columns. Finally, a reliability analysis is performed to evaluate the safety level of current design specifications and the proposed design rules. [ABSTRACT FROM AUTHOR]

• The web crippling behaviour of cold-formed steel channels with elongated un-stiffened and edge-stiffened web holes under end-two-flange loading condition was studied numerically. • The results of a total of 1536 new finite element analysis were reported. • Design formulae in the form of the web crippling reduction factors were proposed. • The direct strength method (DSM) equations were also presented to evaluate web crippling strengths. Over the last decade, cold-formed steel (CFS) channels with circular edge-stiffened web holes have been widely used in New Zealand. In the case of web crippling, previous studies have revealed that the use of an edge-stiffened hole almost results in the same strength as an equivalent channel-section having a plain web. Such circular edge-stiffened web holes could be extended to elongated holes. In terms of web crippling, however, no experimental or numerical works on such elongated holes were reported in the literature. In this paper, a numerical investigation was carried out to investigate the web crippling behaviour of CFS channels with elongated un-stiffened and edge-stiffened web holes under the end-two-flange (ETF) loading condition. The finite element (FE) models were validated against the test results of CFS channels with circular edge-stiffened web holes; good agreement in terms of the load-displacement relationships and failure modes was shown. A parametric study was then conducted, comprising 1,536 FE models. Compared to CFS channels with a plain web, for the case of channels with an elongated un-stiffened web hole, the average web crippling strength reduction for sections with an aspect ratio of two and three was 21 % and 36 %, respectively. However, for an elongated edge-stiffened hole, the reduction in the web crippling strength was only 5 % and 8 %, respectively. Finally, design equations in the form of the web crippling reduction factor (R p) and the equations based on the direct strength method (DSM) for CFS channels with elongated web holes under ETF loading conditions were recommended. [ABSTRACT FROM AUTHOR]