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This document includes the pre-normative recommendations developed in the NewGeneSS research project for the design of stainless steel frames using advanced analysis, {"references":["https://doi.org/10.1016/j.jcsr.2020.106378","https://doi.org/10.1016/j.engstruct.2020.111775","https://doi.org/10.1016/j.strusafe.2022.102211","https://doi.org/10.1016/j.jcsr.2022.107425"]}

Decarburization of steels during heat treatment is a major problem for wear applications and for thin structural components as it often results in poorer surface hardness, strength, and fatigue performance. Additionally, corrosion is a major problem in many engineering applications. To address these issues, this study introduces a novel low-cost surface treatment that utilizes raw materials obtained from automotive waste. This technique was applied on a high-carbon low-alloy martensitic steel that is commonly used in industrial applications for its hardness, strength, and low production cost. The reduction in decarburization led to improved abrasion performance, while the steel’s corrosion resistance was significantly improved through the formation of a thin ceramic layer across the steel’s surface. This treatment, therefore, not only offers a cost-effective solution to decarburization and corrosion, but it also promotes a more sustainable future.

The paper presents an overview of a research project at the University of Sydney aimed at developing a general framework for the analysis and design of functional components of buildings and structures, where such components achieve large shape changes (morphing) via buckling. The shape changes are optimised, e.g. to reduce energy consumption by minimising solar radiation loads or maximising natural air ventilation. The underlying driver for the project is to develop innovative building technology solutions to reduce the energy consumption of the next generation of low-, medium- and high-rise buildings. The paper first summarises recent work on plate elements supported along three edges, in which temporary intermediate restraints are used to load the plate into the post-buckling range and subsequently released to generate an abrupt shape change in response to an external signal triggered by shading or ventilation demand. This investigation is backed by an analysis of the placement of intermediate restraints to optimise the plate deflection by maximising the pre-buckling compression of the plate. Next, a study is presented on optimising the topology of plates to maximise their shading or ventilation capacities under applied compression or bending. Considering both buckling and nonlinear post-buckling, the analytical framework optimises the spatial distribution of plate thickness. Experiments on optimised plates are reported as well, in which shape memory alloy (SMA) and piezoelectric (PZT) actuators are used to induce compression and buckling. Subsequently, morphing induced by flexural–torsional buckling is investigated where simple 3-member frame geometries are devised to achieve large lateral buckling displacements and twist rotations under low-power external excitation. Lastly, an application of functionalised buckling for shading of buildings is illustrated which employs a bi-stable mechanism powered by shape memory alloy actuation.

This study presents an experimental investigation into active nonlinear buckling control of optimally designed laminated plates via a new control method using shape memory alloy (SMA) and piezoelectric (PZT) actuators. In this control method, the SMA actuators are used to control the magnitude of plate buckling deformation whereas the PZT actuators are mainly used to control the direction of plate buckling deformation by inducing initial bending in a desired direction. New problem formulation and solution algorithm are presented for the concurrent design optimization of PZT actuators and their host structure for maximizing targeted plate buckling deformation. Specimens are prepared using the 3D printing technique based on one selected optimum design of the PZT laminated plate. An active buckling control experiment is conducted to demonstrate the proposed control of both the direction and magnitude of plate buckling deformation via PZT and SMA actuators. A comparison between the present experimental and numerical results indicates a reasonable correlation in the buckling deformations at the selected observation points.

This paper concerns the underpinning system reliability calibrations that will enable the implementation of the next generation of system-based design-by-analysis method of steel rack frames, i.e., a design approach where analysis and capacity checks are carried out in a single step by using fully nonlinear analysis. The paper details the design framework of the new approach, referred to as the Direct Design Method (DDM), and derives system strength statistics for five typical configurations of rack frames using Monte-Carlo simulations, taking into account the randomness of geometric and material properties. The nominal models of rack frames are developed in accordance with the Australian Standard AS4084. The mean-to-nominal ratios (bias) and coefficient of variation of the system strengths are obtained, and will be used in the companion paper to derive the system resistance factors consistent with a given structural reliability.

This is the second of two papers introducing the underpinning structural analyses and reliability studies that implement the system-based design-by-analysis method of steel rack frames, referred to as the Direct Design Method (DDM). The present paper presents the reliability analyses and derivation of system reliability index (β) versus system resistance factors (ϕs) curves. Results are presented for nominal system strengths as per Australian Standard AS4084 for several nominal models, including models that exclude sectional imperfections, and models without member and sectional imperfections. The effect of model uncertainty is also assessed. A detailed example of the DDM applied to the design of a rack frame is presented and the benefits of the DDM are demonstrated when compared to the traditional design approach which is based on elastic analysis.

This paper presents a comprehensive investigation of the numerical modelling of cold-formed steel single C-section portal frames using shell elements. The model accounts for the semi-rigid behaviour of connections using mesh-independent point-based fasteners at the location of physical bolts. The behaviour of deformable fasteners is ascribed though the use of connector sections. Nonlinear analysis is carried out to obtain the load-displacement response leading to the prediction of frame strength. The predicted strengths of frames are compared with experimental results. The main cause of the observed flexural-torsional buckling behaviour of frames is highlighted and the importance of using an accurate fastener model is emphasized.

Cold-formed steel (CFS) built-up members are formed by connecting several single members by fasteners. This paper presents experimental, numerical and analytical studies on the effect of fastener configurations on the flexural rigidity of built-up sections. In this research, two zinc-coated steel C-sections are connected back-to-back to form a double-web built-up I-section, which is subject to weak-axis bending. A closed-formed expression for the flexural rigidity of built-up sections as a function of fastener stiffness, number and position of fasteners, and section geometry is then derived. This is validated against the tests and finite element modelling, and can be adapted more generally to determine the stiffness and global strength of CFS built-up members in bending.

This paper presents a method to identify the critical member in a single-layer latticed dome, which in the context of progressive collapse is defined as the member whose removal causes the most severe damage. The distribution of critical members in four typical types of single-layer latticed domes, including the Kiewit dome, the Ribbed dome, the Schwedler dome and the Lamella dome, is investigated through a comprehensive Alternate Path analysis scheme composed of hundreds of individual dynamic nonlinear analyses. The Alternate Path analyses also confirm the progressive collapse mechanism of single-layer latticed domes, i.e., the nodal snap-through buckling at either end of the initially removed member. On this basis, a critical member identification method is established, using an index that implicitly estimates the relative vulnerability to node buckling following the removal of a member to determine the criticality of this member. This method along with two other methods, using either static axial force or free vibration response, are evaluated via comparison against the nonlinear dynamic Alternate Path analysis results, and this proposed method shows a beyond-compare accuracy. Furthermore, based on the established understanding of the progressive collapse mechanism and the factors influencing the node buckling resistance, three methods for increasing the progressive collapse resistance of single-layer latticed domes are presented.

This paper presents the generalisation of an energy-based method for the modal decomposition of buckled shapes of thin-walled members. This comprehensive method is derived and validated for fully decomposing the elastic buckling solution of a thin-walled member into the pure buckling mode classes of global, distortional, local, shear and transverse extension. The first three modes are de-facto prerequisites for buckling capacity predictions found in current design standards for thin-walled structures. In the literature, two main methods, namely the generalised beam theory (GBT) and the constrained finite strip method (cFSM), are widely employed for modal decomposition. Recently, an alternative energy-based approach has been presented for the decomposition of buckling modes into the classical local, distortional and global modes. This method is generalised in the present study to achieve a complete decomposition that also accounts for shear and transverse extensional modes in addition to global, distortional and local modes. In this method, each of the buckling classes is separated by imposing constraints that are defined by enforcing specific criteria on the total strain energy of the member. The adopted criteria are based on the fundamental mechanical assumptions of the GBT which were also implemented in the conventional cFSM and later were further detailed for modal classification in the generalised cFSM. This paper is accompanied by a paper in which derivation of a modified global torsion mode for sections with closed loops is presented and the applicability of the proposed method is demonstrated using a series of numerical examples.

This paper is a companion to (Khezri and Rasmussen, 2019) [1], where the generalised strain energy-based method for the modal decomposition of buckled shapes of thin-walled members is introduced. The paper presents the application of the proposed method for full modal decomposition to various thin-walled members. A series of numerical examples are presented in order to verify the robustness and capabilities of the proposed modal finite strip method (mFSM). In addition, the problem of global torsional modes in sections with closed cell(s) is revisited in this paper. In sections with closed loops, the classical global torsion modes does not exist due to presence of in-plane shear strains. In the context of the proposed energy-based method, a modified global torsion buckling mode is derived that allows for the occurance of shear in closed cell. The pure global buckling curves obtained incoporating the modified global torsion base vectors are compared with the generalised constrained FSM (cFSM) and generalised beam theory (GBT) results. It is shown that the proposed modal decomposition method is capable to accurately capture the modal behaviour of thin-walled sections.

Cold-formed steel haunched portal frames are popular structures in industrial and housing applications. They are mostly used as sheds, garages, and shelters, and are common in rural areas. Cold-formed steel portal frames with spans of up to 30 m (100 ft) are now being constructed in Australia. As these large structures are fairly new to the market, there is limited data on their behavior and design recommendations. An experimental program was carried out on a series of portal frame systems composed of back-to-back lipped channels for the columns, rafters, and knee braces. The system consisted of three frames connected in parallel with purlins to simulate a free standing structure, with a span of 14 m (46 ft), column height of 5.3 m (17 ft), and apex height of 7 m (23 ft). Several configurations were tested including variations in the knee connection, sleeve stiffeners in the columns and rafters, and loading of either gravity only or combined horizontal and gravity loads. Deflections were recorded at various locations to measure global and local movements of the structural members. A total of eight frames with unbraced columns were tested and one frame with braced columns. Experimental results are presented herein including frame strengths and failure modes for the various frame configurations and loading conditions, as well as quantified moment-rotation relations for the column base connection. The contributions and effects of the different knee connections and sleeve stiffeners are presented. The overall frame behavior of these structures and suggested design considerations are discussed.

Cold-formed steel haunched portal frames are popular structures in industrial and residential sectors. They are commonly used in rural areas for sheds, garages, and shelters, and are now being constructed with spans of up to 30 m in Australia. As these large structures are relatively new to the market, there is limited data on their behavior and design recommendations, including connection stiffness and design. Numerical and experimental parametric studies were conducted on a haunched portal frame composed of back-to-back lipped channel sections bolted through the webs for the main frame members, and back-to-back L-brackets bolted though the webs at the connections. An advanced shell finite element model was created and validated with experimental results to confirm the suitability of the modeling technique. The validated finite element model was then used for parametric studies to determine the effects of various components of the frame, including column base connection stiffness and modifications to the knee brace-to-column connection design, on the frame capacity and behavior. An experimental program was conducted to quantify column base connection stiffness where the connection was comprised of L-brackets bolted through the column flanges at the base. Stiffness was quantified for bending about the column major and minor axes for various thickness L-brackets and for a U-bracket. Apex in-plane connection stiffness was quantified experimentally for several rafter channel thicknesses and depths. Discussions of the results of the parametric studies are presented in addition to the resulting design recommendations for constructing effective long-span cold-formed steel portal frames.

The steel industry is developing a design-by-advanced analysis specification for cold-formed steel construction. This effort provides an opportunity to utilize the latest nonlinear structural analysis (advanced analysis) to design steel structures based on their overall system behaviour. This paper concerns the system reliability calibrations of this design-by-analysis method, with a particular focus on cold-formed steel portal frames. Four typical portal frames are considered. The system reliability assessment takes into account all important random variables. A limit-state design criterion is developed which is consistent with a desired level of system safety.

The recent requirements in construction for lower energy consumption have accelerated the trend towards the use of high performance buildings. In these Nearly Zero Energy Buildings (NZEB), simple measures such as natural light control are practiced for maximising the light intake and minimising the heat gain, as required. These modern building envelopes interact with the external environment and are designed to respond to occupant demand, achieving the target energy efficiency and comfort needs. In these kinetic facades, shape morphing triggered by buckling is targeted for energy-saving structural applications. Among the structural forms that are suitable for such applications are thin plates, which are prone to buckling under small in-plane strains. This study presents a novel concept with application in shading control modules. In the proposed models, buckling of slender plates are configured to create a bistable mechanism with closed and open states. The proposed mechanism is simulated using finite element software to validate the feasibility of the core concept and to evaluate buckling as a reliable mechanism in kinetic facade control modules.

As the requirements in construction industry for lower energy consumption are becoming more stringent, shape morphing triggered by buckling is targeted for energy-saving structural applications. Among the structural forms that are suitable for such applications are thin plates, which are prone to buckling under small in-plane strains. Deployable point-supports can be utilised to enhance and guide the buckling behaviour of thin plates based structural systems and subsequently to achieve desired morphogenesis. In adapting such framework, this study presents novel concepts with application in ventilation control modules. In the proposed models, temporary point-restraints are initially deployed to load the plate into the post-buckling range of the primary plate element. The ventilation system is activated when the temporary point-supports are released, causing the primary plate to buckle into the desired opening form. The proposed models are simulated using finite element software to determine the feasibility of the proposed idea and determine the effectiveness of buckling as a reliable mechanism in kinetic facade control modules. The proposed prototype can be operated using electric and mechanical external motors or alternatively smart materials can be used for sensing and actuation as required.

This paper presents recent research carried out at the University of Sydney on the full-range behavior of top-and-seat angle connections. A total of 18 tests were conducted, covering two co...

Traditional member-based two-step design approaches included in current structural codes for steel structures, as well as more recent system-based direct-design alternatives, require building rigorous structural reliability frameworks for the calibration of partial coefficients (resistance factors) to achieve specified target reliability requirements. Key design parameters affecting the strength of structures and their random variations are generally modelled by nominal or characteristic values in design standards, which are combined with partial coefficients that need to be calibrated from measurements on real samples. While the statistical characterization of material and geometric properties of structural steels has been consolidated over the last decades, information about the characterization of structural stainless steels is virtually non-existent due to the limited pool of available data. Thus, this paper presents the basic ingredient for developing reliability frameworks for stainless steel structures and components by statistically characterizing the main random parameters affecting their strength through a comprehensive database collected from the literature. Based on the collected data, appropriate probabilistic models are proposed for geometric properties, material properties, imperfections and residual stresses of different stainless steel alloys and cross-section or product types. The data is equally applicable to member-based reliability analyses as described in existing codes and system-based analyses targeted at the direct-design of stainless steel structures by advanced analysis. This research project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant Agreement No. 842395. The time dedicated by numerous authors of referenced papers to provide additional data and information is also much appreciated.

This paper presents a series of full-scale tests on long-span cold-formed steel single C-section portal frames subjected to gravity load and combined gravity and lateral load. The tests wer...

This work studies an optimal design problem to maximize the airflow opening of a thin-walled structure for efficient ventilation. The airflow opening is defined in terms of nodal displacements as the area swept by a deformed free edge, or the volume formed between the deformed and undeformed configurations or their combination. In this study, a novel formulation for the airflow opening in a plate or shell with large deflections is derived by using the principle of virtual work and the constructed generalized virtual force. In this formulation, the airflow opening can be evaluated via only two finite element analyses for one real and one virtual load cases. By using the present formulation, the maximum airflow problem is formulated as a topology optimization problem for a laminated thin-walled structure, and is subsequently solved by using a moving iso-surface threshold method. Numerical examples are presented for the optimum laminated flat plates of three edges simply supported and one edge free with designable and non-designable layers and under in-plane compression along the two opposite simply-supported edges. The numerical results show that the airflow opening can be maximized when the optimized laminated plate deforms in a shape similar to its critical buckling mode and the opening is much larger than that of the flat plate with the same amount of material and constant thickness.

Steel storage pallet racks are slender structures sensitive to the second-order effects. Therefore, the stability and seismic response of unbraced pallet racks are greatly influenced by the behaviour of the connections between pallet beams and uprights. In recent applications, a bolt has been installed in the otherwise boltless connections broadly used in pallet racks, in order to improve the behaviour of the connections and the stability of the overall structure. In this paper, an experimental study is presented to evaluate the cyclic performance of bolted connections in cold-formed steel storage pallet racks. Seven groups of bolted connections were tested under cyclic loads in a single pallet beam cantilever test setup. Upright thickness and beam height, the number of tabs and the number of bolts in the beam-end-connector were varied to assess their impact on the performance of a bolted pallet beam-to-upright connection. The moment-rotation hysteretic and backbone curves of all tested connections were obtained, as were the behavioural factors corresponding to their stiffness degradation, ductility and energy dissipation capacity. The focus of the paper is to investigate the cyclic behaviour of steel storage rack beam-to-upright bolted connections, and to identify the most significant influencing geometric parameters. Comparisons of the cyclic response and failure modes between connections with and without bolts are also provided. Finally, based on the experimental results, the so-called Pinching4 model is used to characterise the hysteretic performance of bolted pallet beam-to-upright connections for further use in the design by advanced analysis of rack structures under seismic loads.

Cold-formed steel haunched portal frames are popular structures in industrial and housing applications. They are mostly used as sheds, garages, and shelters, and are common in rural areas. Cold-formed steel portal frames with spans of up to 30 m are now being constructed in Australia. As they are relatively new to the market, current design recommendations are fairly limited. In the specific frame system analyzed herein, the column is partially restrained against twist rotation at an intermediate point where the knee brace joining the column and rafter is connected. An experimental program was carried out on a series of portal frame systems composed of back-to-back channels for the columns and rafters. It was found that changing the knee brace and knee brace-to-column connection bracket significantly affected the buckling capacity of the column, however this was not captured in design calculations. In order to correctly predict frame behavior and ultimate loads for design purposes, the column buckling capacity must be accurately calculated. This paper presents an energy method approach to calculate the buckling load of a column with an intermediate elastic torsional restraint. Various end conditions of the column are considered including column base semi-rigidity, as well as multiple loading conditions. Displacement functions are determined based on measured experimental data. The Southwell and Meck plot methods to determine column buckling loads are discussed. The column buckling loads determined from the plot methods and calculated by the energy analysis are compared to the experimental column buckling loads. It is shown that the energy method outlined herein predicts the buckling load within 6% for columns with an intermediate elastic torsional restraint.

The buckling behaviour of thin-walled tubes with regular convex polygonal sections (hereafter the “convex” will be implied) has been analysed a number of times over the last half a century, yet literature on such members in torsion has traditionally been lacking. Despite recent advances, there is still significant scope to further expand understanding of the behaviour of these members in torsion. Using the generalised constrained finite strip method (cFSM) and a semi-analytical finite strip method (FSM) that utilises an augmented longitudinal displacement field of sines and cosines, the elastic buckling behaviour of long regular polygonal tubes in uniform torsion is assessed. The analysed polygons all have the same centreline perimeter and uniform thickness of constituent plate elements. It is found that the signature curves of critical stress vs. buckling half-wavelength converge as the number of sides in the tube is increased and that notable differences between the signature curves of tubes with consecutive numbers of sides occur at shorter and shorter half-wavelengths as the number of sides is increased, due to the decreasing width of the individual flats and also the occurrence of an increasing number of distortional modes. At very long half-wavelengths flexural buckling occurs in a helical-like manner, similar to the twisting of a hosepipe. The mechanics of this buckling mode are briefly investigated and it is noted that it is necessary to include all of the non-linear components of the in-plane shear strain, as opposed to only the flexural components, in order to obtain accurate solutions for this mode. Results for pure local and pure distortional buckling are also compared to those obtained via Generalised Beam Theory (GBT).

This paper reports on experiments addressing the buckling and collapse behavior of common built-up cold-formed steel (CFS) columns. The built-up column consists of two individual CFS lipped channels placed back-to-back and connected at the web using two self-drilling screw fasteners at specified spacing along the column length. The experiments aim to quantify ultimate strength, composite action, member end fixity, and buckling interactions and collapse behavior for common built-up CFS members. The testing also explicitly explores the effect of sheathing, as typically employed in cold-formed steel framing, on the response. The experiments provide benchmarks for design that include specific considerations for both thin-walled buckling and fastener behavior. A total of 17 monotonic, concentric compression tests with a column length of 1.83 m (6 ft) are completed with an array of position transducers monitoring displacements at key locations. Tests are conducted with the built-up member seated in CFS tracks. Results indicate a large range of deformation behavior, with local-global interaction and flexural-torsional modes common in many of the unsheathed specimens. Columns sheathed with oriented strand board on both flanges behave as braced against global buckling in the plane of the wall, and local buckling induced failures prevail. The end condition for the tested built-up members seated in track is determined to be semi-rigid, but generally closer to fixed than pinned.

This paper reports on experiments addressing the buckling and collapse behavior of back-to-back lipped channel built-up cold-formed steel (CFS) columns assembled using 16 different CFS lipped channel sizes. The lipped channel sections are connected at the web using a pair of self-drilling screw fasteners at a specified spacing along the column length of 1.83 m (6 ft). These experiments aim to quantify the effect of two web fastener layouts on composite action for each section size, study member end fixity, observe buckling and collapse behavior, and provide benchmarks for design that includes specific considerations for thin-walled member buckling. A total of 32 monotonic, displacement-controlled, concentric compression tests are completed with up to 17 position transducers monitoring displacements at key locations. All tests are conducted with the built-up member seated in CFS tracks, as would be found in practice. Local–global interaction is shown to be a prevalent failure mode, and the stud-to-track end condition is determined to be semi-rigid, but generally closer to a fixed condition. End rigidities are estimated using a Southwell approach. Rational design approaches extending the application of the Direct Strength Method (DSM) and employing current state-of-the-art numerical modeling techniques are proposed and validated with test data. In addition, the development of definitive design recommendations that help reduce the complexity of fastener designs and incorporates the DSM framework when predicting built-up member strength is underway.

The conventional numerical approximation of Mindlin plate equations can lead to erroneous solutions for thin plates. The so-called shear-locking problem has been well studied in the context of the finite element method (FEM) whereas the development of numerical formulations for its successful elimination in meshfree methods is still a subject of intensive research. This paper studies the effectiveness of some of the most commonly adopted techniques for the reduction of shear-locking and presents the application of a shear-locking-free formulation based on first-order Mindlin plate theory. In this modified formulation, the shear strains are incorporated as degrees of freedom (DOFs) in lieu of the rotational DOFs in the conventional Mindlin theory formulation. A straightforward transformation technique is presented for the enforcement of boundary conditions and comparisons are made with available analytical and numerical solutions. The generalised reproducing kernel particle method (RKPM) is adopted as the numerical tool and a series of numerical examples are presented to demonstrate the accuracy and performance of the presented method.

Steel storage pallet racks are usually unbraced in the down-aisle direction in order to make palletised goods always accessible. The down-aisle stability of unbraced rack structures mainly depends on the performance of beam-to-upright connections and column bases. Beam-to-upright boltless connections are commonly employed for their convenience in assembly and adjustment. Since storage racks are being designed to considerable heights for the purpose of improving warehouse efficiency, steel storage rack beam-to-upright bolted connections are gradually being introduced to improve the structural stability. The paper presents an experimental investigation into the flexural behaviour of beam-to-upright bolted connections of steel storage pallet racks. A total of twenty-one specimens were tested under monotonic loading in a single cantilever test setup, including three different size pallet beams, three different upright thicknesses, and beam-end-connectors with two or three tabs. This study examines deformation patterns and failure modes of the connections, their rotational stiffness, moment resistance and corresponding connection rotations. The results show that steel storage rack beam-to-upright bolted connections, classified as “semi-rigid” and “partial-strength” connections, generally experience ductile failure modes. The effects of critical geometric parameters, i.e. upright thickness, beam height and the number of tabs, on the flexural behaviour of bolted connections are also investigated. In addition, comparisons of performance and failure modes between bolted and boltless connections are made. Moreover, in order to promote the design by advanced analysis of rack structures, a preliminary theoretical model based on the Component Method is proposed to predict the initial rotational stiffness of beam-to-upright bolted connections in steel storage pallet racks. A good agreement is obtained between the initial rotational stiffness derived from the theoretical model and the experimental tests.

In this paper, the compound strip method is applied to the stability analysis of cold-formed steel built-up sections. A beam element with adjustable stiffness properties is adopted to represent the utilised fastener and the associated stiffnesses of the connection elements are incorporated in the global stiffness matrix of the built-up sections. The presented method allows for modelling arbitrarily-located discrete fasteners in the context of the semi-analytical finite strip method. The proposed numerical technique is verified against finite element solutions through various numerical examples and shown to be both accurate and versatile. Some typical and also complex built-up sections with various fastener configuration and end boundary conditions are analysed to evaluate the influence of fastener spacing. The extent of composite behaviour in built-up sections is determined by investigating the enhancement of buckling capacity and changes in the corresponding buckling modes. The simplicity of the proposed technique expedites extensive parametric studies of cold-formed built-up sections and facilitates the search for optimal placement of fasteners and choice of section geometry.

The design-by-analysis approach lays the foundation for the next generation of structural design standards in which the strength and structural safety check are performed in a single step at system level, without recourse to a structural standard for individual member checks. However, to date, no attempt has been made towards considering the failure of joints in the structural analysis, without which the complete set of limit states cannot be accurately predicted. This paper presents a new analysis approach that incorporates macro-element joint models based on the Generalised Component Method in the FE analysis of steel frame buildings. The new analysis approach is termed Generalised Component Method-based finite-element (GCM-FE) analysis. The fundamental aspects and principles of the GCM-FE analysis approach are established in this paper, including the framework of GCM-FE analysis, the constitutive models for the connection components and the implementation of GCM-FE analysis in commercial numerical software including an automatic modelling technique. The GCM-FE joint modelling method is first validated against the experimental results of three steel beam-to-column connection types, including the bolted moment end-plate connection, top-and-seat angle connection and web angle connection. GCM-FE analysis is subsequently performed on a two-storey four-bay irregular steel frame, showing apparent advantages over the traditional analysis methods which adopt simplified joint models. The GCM-FE analysis not only provides the ultimate resistance and failure mode of the frame, but also accurately predicts the load-redistribution process inside the connections and the resultant effect on the structural framework.

Thin-wall structural sections and members are susceptible to three fundamental instabilities: local, distortional and lateral-torsional buckling. For cold-formed purlins or girts commonly used in roof and wall systems, distortional buckling may govern the predominant failure mode when the compression flange is not attached to sheathing or panels. The paper presents an experimental and numerical investigation on the behaviour and strength of cold-rolled aluminium beams subjected to distortional buckling. A total of eighteen specimens were tested in a four-point bending configuration with six various types of cross-sections and two different thicknesses. In the pure bending region between the two loading points, the upper compression flanges were kept free to allow distortional buckling to form. Subsequently, detailed finite element (FE) models of cold-rolled aluminium beams using the software ABAQUS were developed with the incorporation of measured material inelasticity and initial geometric imperfections. Good agreement between the experimental results and the FE models was achieved. The reliable and verified FE models along with the test data in this paper will be used in a separate publication to undertake a detailed parametric study and calibration of new proposed design rules for cold-rolled aluminium beams subjected to distortional buckling.

Built-up sections are increasingly used as structural elements in the cold-formed steel (CFS) industry. They are composed of two or more component sections connected by discrete fasteners, typically spaced evenly along the length and potentially with fastener groups at the ends. Conventionally, two singly symmetric C-sections are connected to form a doubly symmetric cross-section, and current design guidelines are limited to this particular application. As a means towards broadening the application of built-up CFS sections, the cross-sections in this study were composed of three or four lipped channel sections. The paper presents an experimental investigation of the strength and behaviour of built-up section columns of various lengths and cross-sectional shapes. As observed in the tests, singly-symmetric columns composed of three channel sections (3C) experienced either local, distortional and/or flexural-torsional buckling failure modes, while doubly-symmetric columns formed by four sections (4C) failed in local, distortional and/or flexural buckling modes. The current AISI Specification specifies the use of a modified slenderness ratio only for built-up sections composed of two sections connected back-to-back, whereas the design proposal in this paper recommends the use of an effective rigidity approach coupled with the Direct Strength Method for predicting the strengths of the test 3C and 4C built-up sections. This proposal also suggests a design procedure for the built-up sections experiencing flexural-torsional buckling, which is neither explicitly stipulated in current design standards nor in previous studies.

Cold-formed Hollow Steel Sections (HSS) are widely used in the construction industry. The distribution of residual stress in non-stress-relieved cold-formed HSS is complex due to the highly non-uniform variation around the cross-section and through the plate thickness. Modeling residual stress in frame analysis is therefore a difficult task. This paper presents a practical method for approximating the effects of different components of residual stress on the behavior of cold-formed HSS by modifying the steel stress-strain curve. The method proposes a convenient means of including residual stress in beam element-based nonlinear frame analysis. A probabilistic study is then carried out to study the effect of the uncertainty in residual stress on frame strength.

In this paper, the compound strip method is utilised and extended for the stability analysis of cold-formed steel built-up sections. The discrete fasteners are incorporated in the analysis such that they can be placed anywhere within the length of the member. A beam element with geometrical and material properties of the fastener is adopted to model the connection between the individual sections. The stiffness matrix terms for the connection element are derived and added directly to the global stiffness matrix of the considered built-up sections. The proposed numerical technique is verified through various examples and the results are compared with the finite element solutions. The results obtained demonstrate that the developed technique can accurately and efficiently model the behaviour of cold-formed steel built-up sections. Furthermore, the influence of the fasteners properties, their longitudinal spacing and also the boundary conditions on the overall buckling behaviour of built-up sections is examined through numerical examples. The simplicity of the proposed technique facilitates an extensive parametric study of cold-formed built-up sections including the search for optimal placement of fasteners and combinations of component sections in built-up profiles.