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This paper is an attempt to investigate the structural behavior of concrete-filled cold-formed steel stub columns with semi-oval cross sections via experimental and numerical studies. The test campaign included thirteen stub columns tests on four semi-oval sections infilled with both normal and high strength concrete. The details of test campaign and key observations are described and discussed. Validated against the test data obtained from this study, finite element model was developed to emulate the compressive behavior observed from tests and then used to derive more numerical data via parametric analyses. It is worth noting that the current codified design provisions for concrete-filled steel tubular columns do not explicitly include the semi-oval sections investigated herein. The acquired results from the test campaign and numerical analyses were employed to evaluate the applicability of the American Specifications (ANSI/AISC 360 and ACI318) as well as the European Code (EN1994-1-1). The evaluation results indicate that the aforementioned design rules are generally conservative for compressive strength predictions, among which the predictions by the European Code are the most accurate. Design method considering strength enhancement and confinement effect was proposed with improved accuracy. It is suggested to use the proposed design method for the compressive design of concrete-filled cold-formed steel semi-oval stub columns. [ABSTRACT FROM AUTHOR]

This paper studies the structural performance of cold-formed steel (CFS) face-to-face (FTF) built-up channel sections subjected to axial compression at high temperatures. The material properties of G250 and G450 CFS channel sections at room and high temperatures were acquired from the literature, and the range of temperatures was from 20 to 700 °C. The influences of the section thickness, member length, screw number, and high temperature on the structural performance of such channel sections were examined via a comprehensive parametric analysis involving 576 validated finite element models. As the temperature increased from 20 to 700 °C, the mean axial capacity of the CFS-FTF built-up unlipped and lipped channel sections decreased by 88.9% and 90.2%, respectively. Based on the results of the parametric study, new design equations for the axial capacity of CFS-FTF built-up channel sections at high temperatures were proposed. The mean ratio of the EWM strengths calculated using the American standard (AISI 2016) and Australian/New Zealand standard (AS/NZS 2018) to the FE strengths was 0.77, while the mean ratio of the proposed design strengths to the FE strengths was 1.01. Finally, a reliability analysis was conducted, and it was found that the proposed equations could come close in predicting the axial capacity of CFS-FTF built-up channel sections at high temperatures. [ABSTRACT FROM AUTHOR]

This paper investigates the web crippling strength of cold-formed high-strength steel (CHS) channels with centered web holes subjected to end-one-flange (EOF) loading at elevated temperatures, considering both flanges fastened and unfastened to load plates conditions. The stress-strain curve and material properties for CHS (S690QL steel grade) channels were adopted from the literature, where the temperatures ranged from 20 to 800 °C. The material characteristics were incorporated into finite element (FE) models using ABAQUS. The developed FE model was then validated against the published test results to evaluate the effects of various parameters including web hole diameter, bearing length, cross-section sizes, and flange fastening conditions of such channels at elevated temperatures, and a comprehensive parametric investigation including a total of 1710 validated finite element models was performed. From the parametric study results, it was found that the web crippling strength reduction factor is sensitive to the changes of the hole size and the bearing length, with the parameters of hole size having the largest effect on the web crippling reduction factor; however, the web crippling strength reduction factor remains stable when the temperature is changed from 20 to 800 °C. According to the FEA results, new reliable web crippling strength reduction factor equations for such CHS channels were proposed. In the comparison of proposed design strengths to the numerical failure load, the proposed design equations are suitable to predict the web crippling strength for CHS channels subject to EOF loading at ambient and elevated temperatures. [ABSTRACT FROM AUTHOR]

In order to estimate the inelastic interstorey drift of cold-formed steel (CFS) framed structures under collapse level earthquakes, the deflection amplification factor ηp is employed in this paper to compute the maximum interstorey drift ratio (IDRmax) from an elastic analysis. For this purpose, a series of CFS wall specimens were tested under cyclic horizontal loads, and then the hysteresis model of the walls was put forward by test results. In terms of the hysteresis model, a large quantity of elastic-plastic time-history analysis of CFS building structures was conducted based on the storey shear-type model. Furthermore, the deflection amplification factor ηp for estimating IDRmax and the parameters were analyzed. The results indicate that the deflection amplification factor ηp is highly dependent on yielding coefficient of storey shear force ξy, storey number N, period of structure T, and ground acceleration records GA. Eventually, an approximate ξy-N-ηp relationship for estimating the deflection amplification factor ηp is proposed in this paper, which can be used for seismic design in practices. [ABSTRACT FROM AUTHOR]

The traditional roll position adjustment system on the one-time forming of cold-formed steel unit is not only inefficient, but also has poor stability. Moreover, the error of the roll parameters measured by the manual experience and the caliper measured is very large, which leads to low yield of product and high cost labor. In order to solve the above problems, this paper designs a set of roll position automatic adjustment system that can predict roll parameters. The automatic control technology, sensor technology and industrial communication technology are applied to this system and the high performance PLC controller is used as control core. Three-phase asynchronous motors are controlled by PLC(S7-1500) to drive gear connected with reducer and coupling so as to drive rolls connected with the upper and lower horizontal axis to move. In this paper, the PCA-BP algorithm is used to train the roller parameters prediction model so that the roller parameters of a given model of square-tube are predicted. Then the parameters of the new type of square-tube roll distribution are predicted, and the simulation results are compared with the actual production results while the automatic adjustment was completed. The field application shows that the prediction of square-tube roller parameters based on PCA-BP algorithm is more effective than manual measurement, and the whole system is simple in operation, stable in operation and the time used is less, the maximum measuring error of the roll displacement of the system is only ± 2 mm. The system can predict the corresponding roller parameters according to the specifications of the new model square-tube, and automatically complete the adjustment. The system not only improves the adjustment speed and accuracy, but also avoids the waste of manpower so that business productivity has been greatly improved. [ABSTRACT FROM AUTHOR]

This paper presents a computational methodology to compute the critical buckling stress of built-up cold-formed steel columns joined with discrete fasteners. The fasteners are modeled as three-dimensional beam elements, and their effect is integrated into the spline finite strip framework, evolving the compound strip methodology. Although this technique has been presented in the literature, this paper presents yet another robust framework for the buckling load evaluation of compound cold-formed steel columns with arbitrarily located fasteners. The proposed framework is applied to study the effect of fasteners on the formation of local, distortional, and global buckling modes of built-up section and a comparison is drawn with the buckling behavior of a single section. In this study, the proposed formulations are also used to get insights into the stability behavior of single-span and multi-span compound cold-formed steel columns in the presence of (i) fasteners with varied spacings with respect to span and (ii) the presence of the additional restraining system such as wall panels. For different buckling modes, a significant increment in buckling stress for a built-up section from a single section is observed when the fastener spacing is kept less than the critical buckling half-wavelength of the respective buckling modes. The study on the effect of wall panels shows that in comparison to unsheathed wall studs, the sheathed wall studs that produce additional constraints lead to the elimination of the global buckling deformations. The proposed formulations are simple, yet rigorous and have been validated using finite element-based numerical results. [ABSTRACT FROM AUTHOR]

This data paper presents the experimental investigation of unconfined cold-formed steel double-shear bolted connections where the applied load was stopped at different stages of loading (25% or 65% of the ultimate failure load under monotonic loading) followed by unloading, and finally reloading until failure. A total of 78 bolted connections of cold-formed steel subjected to loading–unloading and reloading conditions with sheet thicknesses ranging from 0.55 to 3.0 mm, bolted with 10, 12, or 16-mm bolts were investigated and compared to the identical specimens subjected to monotonic loading. The failure mode of the specimens tested under both loading conditions was bearing of the inner sheet. The test results show that ultimate capacities obtained from unloading and reloading tests were, on average, lower than those obtained from the monotonic tests. A similar trend was also observed for the displacement corresponding to the ultimate loads. However, the effects of sheet thickness and bolt diameter were found to be less critical. This study establishes a publicly available database of control cases to build the foundation for further study into similar loading regimes. This paper also alludes to several potential use cases for the available data. [ABSTRACT FROM AUTHOR]

This paper investigated the potential applicability of the specification equation for the shear pull-out strength of a power-actuated fastener (PAF) connection to nail connections between steel sheets thinner than 2.9 mm. The tested G300, G450, and G550 specimens had thicknesses ranging from 0.6 to 2.4 mm, connected with 2.5- or 3.6-mm helically knurled nails. The pull-out strength is a function not only of the thickness of the member not in contact with the fastener head, but also of the other member's thickness. The member thicknesses have greater influence than the nail diameter on the pull-out strength, contrary to the design equation. Based on the test results of 93 shear nailed connections failing in pull-out, the paper proposes a design equation that is applicable to connections using helically knurled nails of steel sheets thinner than 2.9 mm. A group effect factor of 0.75 is suggested for serial nail connections based on the test results of 19 multiple nail connections. A resistance factor of 0.55 is recommended for use with the proposed equation for determining the pull-out strength of shear nailed connections in thin steel sheets. An additional finding is that the current design equation for the bearing and tilting strength of a PAF connection is applicable to connections in which the member not in contact with the fastener head is much thinner than the specification minimum of 3.2 mm, and in which the fastener diameter is smaller than the specification minimum of 3.7 mm. [ABSTRACT FROM AUTHOR]

Recently, there has been an increasing number of studies on the distortional buckling analyses of cold-formed steel (CFS) channels with web edge-stiffened holes. However, the literature about the analytical solutions is scarce, and the current design rules, e.g., the American Iron and Steel Institute (AISI 2016) and the Australian/New Zealand standards (AS/NZ 4600: 2018), provide little design advice for CFS channels with edge-stiffened holes. This paper presents an analytical method for estimating the bearing capacity for the distortional buckling of CFS channel beams with edge-stiffened rectangular web holes. To validate the proposed method, comprehensive finite element (FE) analyses were performed. The proposed design equations accurately forecast the distortional buckling moment capacities of the CFS channels with edge-stiffened holes. Specifically, the average error of the critical moment predictions for the distortional buckling of perforated CFS channel beams obtained by the proposed analytical method and the finite element method (FEM) is only 6.59%, where the maximum error reaches 17.76%. Moreover, a parameter study on the effect of the edge-stiffener length on the bearing capacity was carried out as well, and the results show that the edge stiffener indeed significantly enhanced the critical moment when it is below a threshold length, but the enhancement becomes unobvious once surpassing the threshold length. [ABSTRACT FROM AUTHOR]

Perforated cold-formed steel (PCFS) beams are regarded as an economical option for steel construction industry owing to its various advantages. They can provide access for the facilities like electric wires and pipelines to penetrate the web so that extra building space could be saved. However, the web openings might change the web stress distribution as well as reduce the cross-sectional properties, which make the PCFS beams more susceptible to buckling and may have effect on their load-bearing capacity. In this paper, a simplified spring model was proposed based on the use of energy method, to predict the critical moment of lateral-torsional buckling of PCFS channel beams with circular holes in web subject to pure bending. The effect of hole sizes and lateral restraint at the tension flange was examined by using the derived analytical solution. In addition, eigenvalue buckling analysis was conducted by using finite-element package ANSYS to validate the accuracy of the proposed analytical model. The results demonstrated that the proposed analytical solution was reliable and the critical moment predicted can be used for the extension of DSM formulae for the design of PCFS beams when considering the failure caused by lateral-torsional buckling of the beams. [ABSTRACT FROM AUTHOR]

With the background of emission peaks and carbon neutrality, light weight has become an irreversible trend in the development of the automobile industry. It is an inevitable choice to use a large amount of ultra-high-strength steels to realize light weight and safety of automobiles. Ultra-high-strength martensitic steels can be divided into hot-formed steels and cold-formed steels according to the forming process. In recent years, ultra-high-strength martensitic steels have been rapidly developed in automotive battery pack frameworks, door guard beams, bumpers, A-pillars, etc., depending on their good plasticity and advanced forming technology. In this paper, the recent progress of ultra-high-strength martensitic steels for automobiles is systematically reviewed, the mechanisms of alloying, strengthening, and toughening are emphatically expounded, and the hydrogen embrittlement problems in application are summarized. Finally, the prospects of manufacture and application of ultra-high-strength martensitic steels for automobiles in the future are forecasted. [ABSTRACT FROM AUTHOR]

The high yielding strength of advanced high-strength steel (AHSS) provides great opportunities for cold-formed steel (CFS) members with much higher load-carrying capability. However, if manufactured into the traditional cross-section shapes, such as C and Z, the material advantage cannot be fully exploited due to the cross-section instabilities. The purpose of this study was to establish a shape optimization method for cold-formed sections with AHSS and explore the potentially material efficiency that AHSS could provide to these sections in terms of their axial strength. In this study, the insights provided from the elastic buckling analysis and nonlinear finite element (FE) simulations of a set of traditional CFS sections were employed to determine the appropriate section size and length for optimization. Then, the optimization method was established using the particle swarm optimization (PSO) algorithm with the integration of computational analysis through CUFSM and the design approach (i.e., the direct strength method, DSM). The objective function is the maximum axial strength of the CFS sections manufactured with AHSS using the same amount of material (i.e., the same cross-section area). Finally, the optimal sections were simulated and verified by FE analysis, and the characteristics of the optimal cross-sections were analyzed. Overall, the optimization method in this paper achieved good optimization results with greatly improved axial strength capacity from the optimal sections. [ABSTRACT FROM AUTHOR]

Cold-formed steel-stud walls have been utilized as an attractive option for blast-resistant design due to the combination of high strength and ductility that enable them to absorb and dissipate blast energy through large deformation kinematics. However, achieving the available ductility of the steel studs requires special attention to the stud-to-track connection details, which has remained an active area of research and development. While much of the existing literature has described specialized ideal boundaries to ensure that the full tensile membrane response of the studs would be achieved prior to connection failure, the research reported in this paper examines the blast performance of cold-formed steel-stud walls with commercially available connections and bridging. Experimental results from a series of three open-arena blast tests of identical cold-formed steel-stud wall panels are presented. Distortional buckling of the studs around unstiffened punchouts in the web as well as web crippling adjacent to the screwed stud-to-track connection are highlighted in this paper. The results from the research reported in this paper are particularly important since several of these modes of failure have not been investigated in static load tests designed to develop resistance functions for cold-formed steel walls. [ABSTRACT FROM AUTHOR]

The block shear equations specified in the current AISC specification for structural steel buildings and North American cold-formed steel design specifications are based on research results of carbon steel bolted connections. These equations were found to be inapplicable for the welded connections in the literature. This issue is primarily associated with the use of the incorrect assumption on block shear failure mechanism. The present paper examines the accuracy of various block shear equations available in the design specifications and in the literature. The paper also examines the shear hardening capacity and the level of tensile stress over the critical net area with the results of finite element analysis, in which the fracture simulation is considered. It shows that the block shear capacities of lean duplex stainless steel welded connections can be predicted accurately using tensile stress equal to 1.25Fu, as proposed in the literature. [ABSTRACT FROM AUTHOR]

This paper presents the results of a theoretical-numerical study of laterally-restrained thin-walled steel rectangular hollow flange beams subjected to bending, shear and bending and shear interaction. Finite element analyses were carried out by using ANSYS software, and validated by previous experimental tests. Furthermore, the effect of intermediate stiffeners was investigated, where the improvement percentage in bending capacity was 4.4%. Additionally, all the corresponding outcomes were calculated according to EN 1993-1-3. The results showed that current standard rules tend to be somewhat conservative in both bending and bending and shear interaction cases, while they are not quite accurate in shear case. [ABSTRACT FROM AUTHOR]

This paper presents a stress analysis of elements made of a steel cold-formed sigma cross-section, uniformly loaded in a plane parallel to the web and not passing through the shear centre. Such an application of a load very often occurs in engineering practice and corresponds to the application of a load to the upper flange of the crosssection. It usually result in an additional torsional moment. In this paper, special attention is paid to normal stresses from the bi-moment, and shear stresses from restrained and free torsion. The contribution of these stresses to the section utilization was evaluated on the example of a sigma cross-section with different thicknesses of the wall. Furthermore, the paper also included the stresses analysis concerning different load locations at the upper flange. All numerical calculations were made using analytical approach based on Vlasov beam theory. [ABSTRACT FROM AUTHOR]

To overcome the shortcomings of traditional shear walls, structure systems have been proposed and investigated. One such structure system is a steel-reinforced concrete shear wall, which has certain desirable properties such as good load-bearing capacity, stiffness, and seismic performance. This paper proposes an M-section cold-formed thin-walled steel reinforced concrete (MCTSR) shear wall, which uses M-section cold-formed thin-walled steel to function as reinforcements. Six specimens with different permanent formwork types, axial compression ratios, reinforcement diameters, and other parameters were tested under cyclic loading to investigate seismic performance. The results demonstrate that various types of permanent formwork, including cement fibrolite plate, metal lathing, and polystyrene board can meet the requirement of related seismic design codes, construction demand, and assembly requirements, and have no obvious impact on the ultimate load-bearing capacity, lateral stiffness, and stiffness degradation rate. However, it changes the energy dissipation capacity and ductility, which are two important indexes to evaluate seismic performance in engineering practice. The failure mechanism and the influence of axial compression ratio, reinforcement diameter, and space between reinforcements are discussed. The shear-strength equations proposed by various countries' or regions' codes were analyzed, which can be used as a reference for related engineers and designers. Finite-element models for MCTSR shear walls were established for further investigation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, cold-formed portal framing system that comprises tapered box members formed from two cold-formed nested channel sections. The proposed method possesses structural and nonstructural advantages, such as improved seismic performance, enhanced building hygiene through bird and dust resistance, further corrosion resistance, and aesthetic improvement, as a result of fly bracing removal. The novelty of the box member lies in the tapering ability of the section, leading to material and paint savings. To examine the failure mechanisms and structural performance of the tapered box portal frame and to investigate the adequacy of the design method, two full-scale portal frames with an 18.16-m span were built and tested to failure under two common loading scenarios. The first was lateral cyclic loading into the inelastic range in conjunction with a vertically acting permanent load. The possibility of ductile plastic hinge formation in a severe earthquake was investigated using lateral cyclic testing. The second was vertical loading to failure. A novel economic loading setup was used to apply the gravity load on the frame. For the seismic design of this section type, slenderness limits are proposed for seismic applications along with the design ductility. A rotational stiffness value for a nominally pinned portal frame column base was also suggested in this study. [ABSTRACT FROM AUTHOR]

The paper presents a comparison of the effectiveness of strengthening steel thin-walled, cold-formed sigma beams with CFRP tapes and steel tapes. For this purpose, three beams without reinforcement (reference beams) of the "Blachy Pruszyński" type, with a cross-section of ∑200 × 70 × 2 and a span of 280 cm, made of S350GD steel grade, were subjected to laboratory tests in the four-point bending scheme. In the next stage the tests included nine ∑200 × 70 × 2 beams reinforced with Sika CarboDur S512 CFRP tape and six ∑200 × 70 × 2 beams reinforced with steel tape made of S235 steel grade. The length of the reinforcement tapes as well made of steel as well of CFRP was of 175 cm. The location of the tapes within the height of the beams' cross-section was assumed in three variants, namely placing the tape on the upper or bottom flange and on the web. In the case of beams reinforced with CFRP, three beams were tested for each reinforcement location, and in the case of beams reinforced with steel tapes, two beams were tested for each reinforcement location. SikaDur®-30 glue with a thickness of 1.3 mm was used in order to connect steel or CFRP tapes to the beams. The dimensions of the tapes cross-sections in both cases were similar (CFRP tapes: 50 × 1.2 mm, steel tapes: 50 × 1.3 mm). For all types of beams, numerical models were also developed in the Abaqus software. The main aim of this paper was investigation of the influence of mechanical properties of steel or CFRP tapes on the effectiveness of strengthening ∑ beams. For this purpose a comparison of these two solutions with respect to the limitation of displacements and deformations of the beam was performed. The obtained results were considered in the context of the mechanical properties of the materials composing the reinforcement tapes. The tests showed slight differences in the results of strain and displacements obtained for reinforcement made of two different materials. It was also noted that the decisive element was the failure of the joint at the steel-glue interface. Therefore, future studies will pay particular attention to the adhesive layer. [ABSTRACT FROM AUTHOR]

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In this paper, new prefabricated cold-formed light-gauge steel stud wall panels sheathed with fireproof phenolic boards, which are fabricated by connecting the steel studs and the boards by using structural silicone sealant, was proposed. The proposed prefabricated wall has a good fireproof performance and can be manufactured rapidly in a factory. Full-scale tests on the mechanical properties of the prefabricated wall system, consisting of the prefabricated wall and the connection between the wall and the surrounding steel structure under out-of-plane loading, were performed. A total of six specimens were tested considering the effects of the arrangement of the cold-formed light-gauge steel studs, the shape and thickness of the steel connector for jointing the prefabricated wall panel and the surrounding steel structure, and the number of self-tapping screws connecting the surrounding structure. The results show that the out-of-plane stiffness of the prefabricated wall system in the elastic stress state under out-of-plane loading can be increased by increasing the number of self-tapping screws, increasing the thickness of the steel connector, or adopting the symmetrical arrangement of the light-gauge steel studs. The out-of-plane stiffness of the prefabricated wall system and the stiffness contribution of a single special-shaped steel connector can both be increased by increasing the number of special-shaped steel connectors. Furthermore, the special-shaped steel connector is more beneficial to a greater out-of-plane stiffness than the L-shaped steel connector. In addition, the theoretical calculation methods for deflection of the proposed prefabricated wall and flexural stress of the CFS C-channel stud considering the fireproof phenolic board sheathing effect under elastic state were proposed. The predicted results using the proposed method are compared with test results and the predicted results by using other methods. It was found that the predicted results by using the proposed method agreed better with the test results compared with the predicted results using the transformed-section method or the reduced stiffness method, which demonstrates the acceptability and accuracy of the proposed mothed for calculating deflection of the proposed prefabricated wall and flexural stress of the CFS C-channel stud. [ABSTRACT FROM AUTHOR]

Cold-formed steel sections are becoming popular for different steel structures, because they have a high resistance against different straining actions, with a minimal weight compared with hard steel sections. Recently, perforated cold-formed steel (PCFS) sections have been used in many applications, such as perforated upright storage racks. Experimental research into the behavior of steel storage rack uprights subjected to axial compression is presented in this paper. First, tensile tests determined the material qualities of the cold-formed steel uprights. Then, seventeen perforated specimens were examined under axial compression, with five different cross-sections, three different web heights and thicknesses, and varying lengths. The study's goals were to find out how perforations affect the performance and failure mode of steel storage rack uprights, to discuss the interaction of distortional and global buckling, and to verify the accuracy of using the direct strength method (DSM) for predicting the ultimate strength before failure in buckling interactions for perforated uprights. It was found that the failure modes of perforated specimens with stiffeners generally cannot be well predicted using the direct strength method. However, when the modifications proposed by Xianzhong Zhao et al. are used, the accuracy is acceptable. [ABSTRACT FROM AUTHOR]

In recent years, cold-formed steel has been widely used in prefabricated steel structures, and the common cross-section forms are mainly complex lipped angle sections. However, there is a lack of design guidance for such a cross-section due to the complex geometric property. The restraint between adjacent plates cannot be considered proper for the traditional analytical method. Therefore, it is particularly important to study the stability bearing capacity of angle sections with complex edges under axial compression. In this paper, the finite strip software (CUFSM5) was used to analyze the critical stress of 1296 different angle sections under axial compression. The deformation diagram and the critical stress of elastic buckling were obtained. Considering the restraint between adjacent plates, the formula for predicting the critical stress of elastic local buckling of complex lipped angle sections was proposed and verified. Further, the critical stress of elastic distortional buckling of 918 complex lipped angle sections was analyzed by CUFSM. It was found that the cross-sections can be divided into two categories: cross-section without distortional point and cross-section with distortional point. It was found that the critical stress of elastic local buckling of the angle steel section can be significantly improved by the complex edge. Additionally, the critical stress of elastic local buckling of the section is less affected by the edge size for the complex edge section. The accuracy of the Hancock method for calculating the critical stress of elastic distortional buckling of complex lipped angle sections with distortional points was verified. The presented research can provide useful guidelines for designing cold-formed steel angle columns. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the flexural performance of a new steel–concrete composite beam system, which is required to carry higher loads when applied in flooring systems with less self-weight and cost compared with conventional composite beams. This new composite member is prepared by filling a single cold-formed steel C-section with concrete material that has varied lightweight-recycled aggregates. In addition, varied stiffening scenarios are suggested to improve the composite behavior of this member, since these cold-formed C-sections are of a slender cross-section and more likely to buckle and twist under high bending loads than those of hot-rolled C-sections. The influence of using four different lightweight-recycled aggregates that combine together in the infill concrete material was investigated. These recycled aggregates are recycled concrete aggregate (RCA), expanded polystyrene (EPS) beads, crumb rubber aggregates (CRA) and fine glass aggregates (FGA). For this purpose, 14 samples of cold-formed galvanized steel C-purlin were filled with concrete material (containing 0 to 100% recycled aggregates) which are experimentally tested under pure bending load, and 1 additional sample was tested without the filling material. Further numerical models were prepared and analyzed using finite element analysis software to investigate the effects of additional parameters that were not experimentally examined. Generally, the results confirm that filling the C-sections with concrete material that contains varied percentages of recycled aggregates offer significantly improved the flexural stiffness, bending capacity, and ductility performances. For example, using infill concrete materials with 0% and 100% recycled aggregate replacement increased the bending capacity of hollow C-section by about 11.4 and 8.6 times, respectively. Furthermore, stiffening of the concrete-filled C-sections with steel strips or screw connectors eventually improved the composite behavior of the specimens which led to an increase in their bending capacities accordingly, and this improvement enhanced more with an increased number of these strips and connectors. [ABSTRACT FROM AUTHOR]

The paper presents the experimental results and proposed design method for the compression strength of the cantilevered leg of cold-formed steel clip angle connectors. The variations of the test specimens included the plate aspect ratio, material thickness, and material strength. The test results were compared to three existing standard design methods for cold-formed steel members similar to the clip angles, but no good agreement was found. A new design method was therefore developed to calculate the nominal compression strength of the cantilevered leg of clip angles. The new method was based on the elastic buckling solution of thin-walled plate columns. The allowable-strength design safety factors, load and resistance factor design, and limit-state design resistance factors were also produced to support the proposed design method. [ABSTRACT FROM AUTHOR]

This paper examines the accuracy of design equations specified in the North American, European, and Australasian codes for cold-formed steel structures in determining the ultimate tilt-bearing capacity of single-shear bolted connections without washers in flat steel sheets. It points out that all the code equations do not properly distinguish the tilt-bearing failure mode from the conventional bearing failure mode. While the latter takes place downstream of the bolt, the former takes place upstream. Unlike the conventional bearing capacity, the tilt-bearing capacity is affected by the width of the connected sheet and does not vary linearly with either the sheet thickness or the bolt diameter. Furthermore, it is not affected by material ductility. Based on the test results of 156 specimens composed of G2 and G450 sheet steels having various dimensional configurations, this paper proposes a design equation that is dimensionally consistent and that is considerably more accurate than all the code equations. The proposed equation was also verified against single-shear single-row bolted connections tested by independent researchers which failed in the tilt-bearing mode. The verified thicknesses ranged from 0.92 to 3.0 mm, and the bolt diameters ranged from 6.4 to 16 mm. An additional finding is that the tilt-bearing capacity is not significantly affected by the orientation of the bolt head or nut. A resistance factor of 0.75 is recommended for use with the proposed equation for determining the tilt-bearing capacity of single shear single-row bolted connections in cold-reduced steel sheets. [ABSTRACT FROM AUTHOR]

The paper presents experimental and numerical investigation of cold-formed steel (CFS)-framed walls sheathed with corrugated steel sheets. The new wall technology is considered as an alternative shear wall configuration for midrise buildings at strong earthquake and high-wind regions because of its attributes of noncombustibility and higher structural performance than the conventional shear wall types. However, design provisions of such corrugated sheathed CFS-framed shear walls have not been included in the current design standards. To establish comprehensive database information and to observe the performance of the bearing wall for the first time, a test program of full-scale wall assemblies using corrugated steel sheathing was conducted. The test specimens included both shear wall specimens and bearing wall specimens under lateral and vertical/gravity loading. In accordance with the full-scale tests, a numerical model was developed in a computer program, and seismic performance assessment was evaluated through nonlinear time history analysis, i.e., incremental dynamic analysis using a methodology proposed by FEMA. The paper presents the results of the experiments and numerical simulations and produces appropriate seismic performance factors for this new lateral-resisting system. [ABSTRACT FROM AUTHOR]

This paper presents selected issues related to the reinforcement of steel element cold-formed with CFRP tapes. The first section of the paper is a review of source literature and a presentation of the basic information on cold-formed thin-walled steel elements and CFRP composite materials, stressing the advantages and disadvantages of using them to reinforce steel structures. Next, the authors present original research on reinforcing bent thin-walled sigma-type steel beams using adhesive CFRP tapes. Reference beams with a cross-section of Σ200 × 70 × 2 and a length of 3 m, reinforced with CFRP tape, were tested in the four-point bending scheme. Then, the paper discusses a developed numerical model that is consistent with the subject matter of the laboratory tests. The developed numerical model was prepared to represent the failure of the connection between the beam and the composite tape. This was followed by a number of numerical analyses in order to determine the optimum adhesive layer that would allow us to achieve the maximum reduction of the displacements and strains in bent thin-walled sigma-type beams. Three thicknesses of the SikaDur adhesive layer were analyzed in the study. Based on the analyzes, it was found that the increase in the thickness of the adhesive layer slightly reduced the strain and displacement in the beams, but caused a significant decrease in the load value, at which damage appeared in the glued joint. [ABSTRACT FROM AUTHOR]

In the international trend of vigorously developing low-carbon economy and green buildings, environmental protection and conservation have received increased attention in the construction field. Light steel, as an environmental protection material, has gradually become a key direction in the architectural field. The axially compressed columns forming the wall skeleton in the light steel structure usually adopt two cross-sectional forms, namely, cold-formed thin-walled steel built-up cross-section and independent profiled steel cross-section. The cold-formed thin-walled steel cross-section is divided by the splitting method into two types, namely, open type and closed type. This paper analyzes two cold-formed thin-walled steel composite sections and independent section columns. The theoretical calculation, experimental test, and finite element simulation were used, and the multidimensional calculation results were compared to obtain the mechanical properties of axial compression columns. Based on the comparison between the experimental results and the calculation results, it is found that the specification is conservative. The experimental results show that it is more flexible to use composite cross-section columns in the middle of the light steel skeleton; steel columns in the corner of the frame are more conducive to the structure's overall stability. [ABSTRACT FROM AUTHOR]

The current cold-formed steel (CFS) wall is limited to the low-rise cold-formed thin-walled steel structure, which is inappropriate for multi-story constructions due to its low shear resistance and poor corrosion resistance of outer sheathing board. Therefore, a new composite wall of CFS frame sheathing with concrete and plasterboard was proposed, the cast-in situ concrete layer was used for the outer surface in response to the needs of corrosion resistance, and the plasterboard was utilized for the inner surface to reduce weight. This paper presented a quasi-static test on the seismic behavior of one CFS wall and three composite-walls' sheathings with concrete and plasterboard to obtain different failure modes and investigate the influence of different sheathing and opening sizes. Combined with the finite element model, a large parametric study of composite walls was conducted to analyze the impact of load ratio, reinforcement ratio, sheathing board, and concrete and steel strength. Test and finite element analysis (FEA) results demonstrate that the seismic performance of composite walls with concrete and plasterboard is satisfactory considering their shear strength, ductility, and energy dissipation. Load ratio, opening size, and reinforcement ratio significantly affect the seismic performance of the composite wall, while the concrete and steel strength and sheathing board have minimal effects. The seismic design suggestions of composite walls are given based on this study. [ABSTRACT FROM AUTHOR]

In this paper, a total of 254 results comprising 30 shear tests and 224 finite element (FE) analysis results are reported. Simply supported test specimens of cold-formed steel (CFS) channels with aspect ratios of 1.0 and 1.5 were tested. For comparison, specimens with unstiffened web holes and plain webs were also tested. A nonlinear elastoplastic FE model was then developed and validated against the experimental results. Using the validated FE model, a parametric study was conducted to investigate the effect of various influential parameters on the shear capacity of such CFS channels. The test results show that for a channel with edge-stiffened web holes, the shear capacity increased by 14.5% on average when compared with that of a channel with unstiffened web holes. The test and FE results were compared against the design predictions. Upon comparison, it was found that the design rules of CFS channels with unstiffened web holes in accordance with the AISI and AS/NZS can be unconservative by 7% while calculating the shear capacity of CFS channels with edge-stiffened web holes. Therefore, a suitable design formula in the form of a shear capacity reduction factor was proposed for CFS channels with edge-stiffened web holes. [ABSTRACT FROM AUTHOR]

This paper concerns the Eurocode 3 Part 1-3 (EN 1993-1-3) methods for calculating the distortional buckling (bifurcation) load of cold-formed steel-lipped channels subjected to axial force, major and minor axis bending. More specifically, the paper presents the results of a parametric study that assesses the accuracy of the simplified method in EN 1993-1-3, which relies on direct/iterative hand calculations and an approximate mechanical model, through comparison with “exact” numerical results, obtained using semi-analytical linearized buckling analyses based on Generalized Beam Theory, which are also allowed by the code. Isoline error maps are presented for a wide range of geometric and material parameters, covering common commercial profiles and corresponding to a dataset of more than 24,000 cases. These maps make it possible to identify the parameter ranges leading to an acceptable error and, even though they strongly depend on the loading, general remarks concerning the expected error pertaining to the simplified method are drawn.

In this paper, a new type of assembling rivet-fastened rectangular hollow flange beams (ARHFBs) is proposed. The cross-section of the ARHFB consists of two U-shaped and C-shaped components connected by self-locking rivets to form two rectangular hollow flanges. To study the performance and strength of the ARHFB as a flexural member, eight four-point bending tests and more than 40 simulation studies were carried out. The details, results, and comparison of the four-point bending tests, especially the characteristics of the test bench and the lateral support, are presented in this paper. ARHFB sections with varied rivet spacing, web depth, and flange width were experimentally studied. Additionally, a parametric study of ARHFB was conducted using finite element models verified by test results. The influence of span on the loading capacity of ARHFB was discussed. ARHFB can be used in large-span buildings. A more economical ARHFB component selection method was given. The depth of the flange, the strength of the web, and the thickness of the web are important parameters of ARHFB. The loading capacity obtained from the test was compared with the predicted values of the design formulas in the American Iron and Steel Institute (AISI) and the Chinese design standard for cold-rolled steel (GB50018). The calculation and verification of ARHFB flange buckling and lateral torsional buckling were also considered. It is recommended that GB50018 be used to predict the flexural capacity of ARHFBs.

This paper presents the experimental results of an innovative configuration for cold-formed steel (CFS) framed shear walls using corrugated steel sheets as sheathing material. The shear wall configuration comprises corrugated steel sheathings placed inside the steel framing and therefore is known as an in-frame or sheet-in shear wall. The innovative shear wall configuration is noncombustible, is equal in thickness to adjacent walls, and avoids the difficulties inherent in the design and installation of the finish materials used in common corrugated steel sheathed shear walls. The test program in this research comprised cyclic testing of five groups of shear walls in which the stud arrangement, sheathing continuity, framing thickness, and wall aspect ratio varied. The results indicate that shear walls with a lower-profiled field stud and continuous sheathing had satisfactory performance with balanced shear strength and ease of assembly. Based on the test data, shear resistances of in-frame or sheet-in shear walls with corrugated steel sheathing under seismic load are recommended as the basis for design. These innovative shear walls exhibited substantially higher shear capacity than code-certified shear walls, and therefore can be used as a substitute for a lateral force–resisting system in midrise CFS light-framed buildings. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study on the behavior of the cold- formed steel shear wall panel (CFSSWP) with fibrocement panels as sheathing, when it is subjected in-plane shear deformations and flexural deformation under perpendicular monotonically increasing horizontal loads on the longest plane. A full-scale housing section was built with three walls and a ceiling using commonly used construction details in El Salvador. The strength and stiffness of the experimental specimen tested overcame significantly critical demand imposed by the technical design standards in this country. Additionally, a simplified finite element model was defined with the objective to analyze stresses in the components. The results of the numerical model were similar to the experimental model tested. [ABSTRACT FROM AUTHOR]

This study developed a special energy dissipation X-bracing for cold-formed steel (CFS) shear walls to improve the ductility of the corrugated steel sheathing. In previous research, CFS shear walls with corrugated sheathing demonstrated poor ductility under cyclic loading. The paper presents a potential solution by adding a special energy dissipation bracing (EDB) to improve the ductility of the corrugated sheet–sheathed shear walls. The EDB can be tuned according to the CFS shear wall base performance to achieve the highest postpeak deflection capacity, thereby significantly improving the seismic ductility. To prove the concept and analyze the feasibility of the new EDB, a test program of nine full-scale shear walls was conducted. The experimental results showed that with the tuned EDB, the corrugated steel sheet–sheathed shear walls had improved ductility with no considerable reduction in the initial stiffness and shear strength. Installing the proposed EDB can be an efficient approach to enhance the seismic performance of CFS-framed shear walls. Details of the test program and discussion are presented. [ABSTRACT FROM AUTHOR]

This paper presents the experimental investigation on the compressive behavior of cold-formed high-strength steel tubular stub columns. In this paper, the nominal 0.2% proof stress of the high-strength steel was 700, 900, and 1,100 MPa. A total of 25 stub column tests on circular, rectangular, and square hollow structural sections were conducted. Geometric imperfections and load-deformation histories were reported and assessed. The experimental results were compared against the design values calculated from the Australian, European, and North American codes, and the corresponding compactness criteria were assessed. A finite-element model, which incorporated the varying material properties, was described, and the influence of geometric and material imperfections was also evaluated. The finite-element results successfully captured the experimental observations and can be adopted for future parametric studies. [ABSTRACT FROM AUTHOR]

Increasing the lateral strength and stiffness of light-frame structures can lead to reduced damage in the event of an earthquake. Because low-rise wood and cold-formed steel-framed buildings often contain many partition walls, their performance can be improved economically by more effective engagement of gypsum-sheathed walls. This paper describes a series of tests of enhanced screw and adhesive connections between gypsum wallboard and wood and cold-formed steel-framing members. Small wall panels constructed with the improved connections were also tested and compared with wallettes built with conventional drywall screws. Test results indicate that while enhanced screws can increase connection and wall strength modestly relative to conventional screws, a much more significant increase in strength and stiffness can be obtained by using construction adhesives. Test results show that supplementing conventional screws with adhesives increased connection strength and stiffness by a factor of four to five. These adhesive-supplemented connections in light-frame wallettes increased strength by approximately two times and stiffness by approximately three times when compared with wallettes with conventional screw connections alone. This paper describes the response and damage progression of gypsum wallboard connections and framed wallettes using the enhanced screw and adhesive connections. [ABSTRACT FROM AUTHOR]

Cold-formed steel structures have been progressively used in structural buildings in the forms of the typical channel and Zed sections. The channel sections under weak-axis bending can be found in various situations, especially under biaxial bending. The flexural capacities about the weak-axis, therefore, have specific impacts on the flexural capacities of the channels. The unsymmetrical feature of this channel section about the weak-axis results in a variety of behaviors and strengths of cold-formed steel channel beams with the change of moment directions. SupaCee - a new form of the channel section - made by adding stiffeners in the web of the channel section to increase the stability of the sectional web is also considered in the investigation. This paper, therefore, is aimed to investigate the behaviors and sectional capacities of the channel and SupaCee sections under the weak-axis bending. The considered sections are taken as the availably commercial sections in the market. The sectional capacities are determined using an innovative method namely the Direct Strength Method as regulated in the Australian/New Zealand Standard AS/NZS 4600:2018. The bending behaviours of the investigated sections are observed and analysed; the obtained strength results are the basis for the evaluation of sectional capacities of the channel and SupaCee sections under variations of moment directions. It was found that capacities of the channel and SupaCee sections under the weak-axis bending can be governed by local or distortional buckling depending on the moment directions, whereas the capacities of distortional failures are higher than those of local failures. Also, the innovative strengths of SupaCee sections under the weak-axis bending are not demonstrated in comparison with these such strengths of channel sections. [ABSTRACT FROM AUTHOR]

This paper summarizes the background information and methodology used to derive a set of buckling curves proposed for cold-formed stainless steel columns and beams incorporated in the recently revised SEI/ASCE 8-21 Specification. The study is based on experimental and numerical data collected from the literature on cold-formed stainless steel columns and beams featuring ASTM grades 304, 2101, 430, 404, and 443. Because most of the investigated specimens exhibited slender cross-sections, both the effective width method (EWM) and the direct strength method (DSM) are considered to account for the effect of interaction between global and local buckling on member strength. Buckling curves for flexural buckling and lateral-torsional buckling codified in current international standards are assessed based on the SEI/ASCE 8 reliability requirements, and new curves are derived accordingly. The proposed new buckling curves include expressions to account for the postyielding capacity of stainless steel columns and the inelastic buckling resistance of cold-formed stainless steel beams. In addition, a new local buckling strength curve for members in flexure is proposed in the format of the DSM and shown to provide equivalent design resistances to the EWM. [ABSTRACT FROM AUTHOR]

Steel pins are an attractive and efficient alternative technology to screws when connecting cold-formed steel or other materials to cold-formed steel members. However, unlike screws, pins remain an essentially proprietary connection technology based on manufacturer claims of special pin shank design. As such, current cold-formed steel design standards and specifications do not include provisions for their direct use and designers have no simple, rational means for making informed design decisions beyond information provided by manufacturers. This paper reviews the current design model for screws and examines the basic tension pullout/withdrawal limit state of helical knurled steel pin connections for cold-formed steel thicknesses common in residential construction. Included in this paper is a determination of material properties using a nondestructive test method as an alternative to traditional methods for estimation of steel base metal thickness. A simple lower bound friction model is proposed for helical steel pins and the model is calibrated using data from 32 physical pin tests. The calibrated model is shown to provide an acceptable degree of reliability and safety consistent with that of screws in current cold-formed steel design standards and specifications. [ABSTRACT FROM AUTHOR]

Pneumatically driven steel pins have been successfully used for attaching structural sheathing to cold-formed steel framing in both load-bearing and nonload-bearing applications. The design of these types of connections is exclusively based on published manufacturer data. Attempts to analytically quantify/estimate the shear and withdrawal (tensile) strength of pin connections is nearly nonexistent. This paper proposes a mechanics-based equilibrium model for withdrawal strength and presents test data for wood structural panels connected to cold-formed steel with pneumatically driven steel pins. The tests include a range of wood panel and cold-formed steel thicknesses commonly found in light-frame construction. Using the proposed model, empirically modified to reflect observed behavior, equations are presented to estimate the withdrawal strength of connections made with helically knurled pins. The proposed equations are shown to provide reasonably good estimates of strength with a reliability consistent with that of the more commonly used screw fastener. [ABSTRACT FROM AUTHOR]

The use of cold-formed steel (CFS) channels with circular or rectangular web holes is becoming increasingly popular in building structures. However, such holes can result in sections becoming more susceptible to buckle and display lower load-carrying capacities. This paper presents a total of 42 axial compression tests of CFS lipped channel slender columns with and without circular and rectangular web holes, including different hole sizes and cross sections. The test results show that the axial members with a small ratio of width to thickness were governed by global buckling, while the members with a large ratio of width to thickness were controlled by the interaction of local, distortional, and global buckling. The axial strength decreased maximum by 20.48% and 22.98% for the member with circular holes and rectangular holes, compared to a member without a web hole. Then, a nonlinear elastoplastic finite element model (FEM) was developed, and the analysis results showed good agreement with the test results. The validated FE model was used to conduct a parametric study involving 36 FEMs to investigate the effects of column slenderness, dimension of the hole, and the number of holes on the axial strength of such channels. Furthermore, the formulas to predict the global buckling coefficient and the effective area were modified for such sections with holes by using the verified FEM. Finally, the tests and parametric study results were compared against the design strengths calculated in accordance with the developed method. The comparison results show that the proposed design method closely predicts the axial capacity of CFS channels with circular or rectangular web holes. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the buckling behavior and to present the design method of the ultimate strength in the basic effective width method (EWM) for cold-formed steel (CFS) lipped channel stud columns with holes in the web. 28 column tests were conducted under axial compression on the CFS lipped channel stud columns with circular and rectangular holes in different dimensions of cross sections and holes. The tested stud columns included 4 members without holes, 12 members with circular holes, and 12 members with rectangular holes. The test results showed that the stud columns with holes were governed by local buckling or the interaction of local buckling and distortional buckling. Compared with the stud columns without holes, the small hole had a slight influence on the ultimate strength of the tested specimens, and the large hole had a great effect on the ultimate strength of the tested specimens. The load capacities of the specimens decreased with the increase of the dimension of holes. Then, the finite element analysis was carried out to simulate the tested stud columns. The finite element analysis results showed good agreement with the experimental results about buckling modes and ultimate strengths, which indicated that it is feasible to analyze this kind of stud columns with holes by using the finite element method (FEM). Finally, the proposed effective width method was used to predict the ultimate strengths of stud columns with holes based on the proposed buckling coefficient formulas of the plate with holes. The comparison between calculated results and test and finite element results indicated that the proposed EWM is feasible and accurate to predict the ultimate strength of the CFS lipped channel stud columns with holes in the web. [ABSTRACT FROM AUTHOR]

The commentary to the North American cold-formed steel specification recommends physical testing to determine the performance of a bolted connection where the plies are not in contact with each other. This paper presents the laboratory test results of 120 such specimens with sheet thicknesses ranging from 0.55 to 3.0 mm, bolted with 10-, 12-, or 16-mm bolts. Finite-element analyses support the experimental finding that the bearing failure of an unconfined bolted connection is not associated with shear fracture but with crimpling of the critical ply. The bearing capacity varies with the square root of the bolt diameter and nonlinearly with the sheet thickness. Dimensionally consistent and continuous design equations are derived and verified against the results of the laboratory tests and finite-element analyses, the latter supplementing the former with configurations involving 8-mm bolts. The derived relationships between the bearing capacity and the sheet thickness and bolt diameter are also verified against 18 independent test results involving bolted connections through square hollow sections. The presented equation is significantly simpler but more accurate than those proposed in the literature for such connections. A resistance factor of 0.70 is recommended for use with the proposed design equations for determining the bearing capacities of unconfined bolted connections. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on web crippling behaviour of cold-formed stainless steel square and rectangular hollow sections (SHS and RHS) at elevated temperatures. A total of 21 web crippling tests were conducted under the Interior Two-Flange (ITF) loading condition as codified in ASCE/SEI 8–22 Specification at various temperatures up to 800 °C. Tensile flat and corner coupon tests were conducted to obtain the material properties of the cold-formed stainless steel SHS and RHS at various temperatures corresponding to those pre-set in the web crippling tests. Details of the test specimens, setups and procedures are comprehensively documented in this paper. Furthermore, the specimen temperatures together with the test results, including failure modes, web crippling strengths and load-deformation curves are fully reported. The obtained test results were used to evaluate the suitability of codified web crippling design provision as per ASCE/SEI 8–22, where reduced material properties were used in calculating the web crippling strengths at elevated temperatures. In addition, the test results were also compared with the predictions obtained from existing design rules in literatures for cold-formed stainless steel SHS and RHS at elevated temperatures. Moreover, reliability analyses were conducted to assess the reliability levels of these design provisions. It is demonstrated that the available web crippling design provisions can provide generally conservative and reliable strength predictions, and therefore are deemed suitable for predicting the web crippling strengths of cold-formed stainless steel SHS and RHS at elevated temperatures. • This investigation serves as the first test programme to study web crippling behaviour of CFSS sections at elevated temperatures. • Flat and corner coupon tests were conducted to obtain material properties at various temperatures. • A total of 21 web crippling tests were conducted under ITF loading condition with temperatures up to 800°C. • Test results are reported and existing web crippling design provisions are also assessed. [ABSTRACT FROM AUTHOR]

Cold-formed steels (CFS) or light gauge steels (LGS) are steel sections created through processes without heat application, such as roll forming or press-braking. In the past few decades, the utilization of CFS as a structural material has expanded due to its advantages over the other materials used in the construction industry, consequently increasing the number of studies conducted by many researchers. CFS studies have focused on many research areas, including designing, and analyzing members and systems, connections, sustainability, residual stresses, and post-fire data. As a result, several authors have also conducted a literature review involving these areas. However, a literature review for more recent studies involving elevated temperature exposure of CFS has not been conducted. This paper seeks to compile and review the recent publications regarding CFS behavior and performance at high temperatures events. Sixty-nine (69) journal articles published from 2017 to 2023 were retrieved from the Scopus database and systematically reviewed through text mining with the aid of VOS Viewer. Prior studies utilizing finite element analysis and experimental methods to investigate the performance at elevated temperature events of varying CFS sections, systems, and steel grades have been summarized. In addition, this paper also briefly discussed the findings of the recent research works involving member connections of CFS. Key points from the literature review have been emphasized such as the outcome of experimental and numerical validation of existing design rules from different codes such as American Iron and Steel Institute (AISI), Eurocodes, and Australian codes which could vary depending on the CFS section and steel grades. Important points of previous studies regarding the CFS walls, insulations, and screwed connections have also been noted in this paper. Based on the review, research gaps in the prior studies involving elevated temperature exposure of CFS have been identified, such as lack of CFS investigation under fatigue and cyclic loading. These were then recommended as future direction and concentration of CFS at elevated temperatures research works.

Cold-formed steel (CFS) moment connections are often formed by bolting the webs of the connecting elements to a stiffened gusset plate, and local buckling of the web adjacent to the connection typically governs their capacity. This paper aims to study this failure mode in case the connection is subject to combined axial compression, shear, and bending moment. In a first step, the case of pure compressive loading was investigated. Validated geometric and material non-linear analysis with imperfections (GMNIA) finite-lement (FE) models were used to investigate the effects of different design variables, including the cross-sectional geometry and thickness, the bolt group configuration, and the bolt group length. The results were then used to develop design equations for the compressive capacity of CFS bolted connections. In a next step, the FE models were used to assess the capacity of CFS bolted connections subject to combined bending and shear, and combined axial compression, bending, and shear. Suitable interaction equations were proposed and reliability analyses were performed within the framework of both the Eurocode and the American Iron and Steel Institute (AISI) standards. It was concluded that a linear equation accurately captures the interaction between bending moment and axial force, while the effects of a shear force smaller than half of the shear capacity on the bending moment capacity can be neglected. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose relationships for the reduction in mechanical properties of cold-formed steels at elevated temperature. Predicting the degradation of strength and modulus of cold-formed steels with temperature is critical to enable fire design of cold-formed steel members. Here, the properties of elastic modulus, 0.2% proof stress, 2% stress, and ultimate stress are studied for grades up to and including 550 MPa. Data are collected from the literature as well as from recent tests conducted by the authors at Johns Hopkins University. Steady-state and transient test results in the range of 20°C–1,000°C are analyzed. Retention factors are then proposed for the mechanical properties adopting a standardized format developed through committee work with the American Iron and Steel Institute. [ABSTRACT FROM AUTHOR]

The use of cold-formed steel (CFS) elements in residential and industrial buildings is widely gaining popularity due to their ability to provide cost-effective and sustainable solutions. A high degree of flexibility in the manufacturing of various cross-sectional shapes provides a unique opportunity to further improve the load-carrying capacity of these elements through an optimization process, leading to more efficient and economical structural systems. This paper aims to offer a practical methodology for the optimum design of CFS beam-column members with different lengths and thicknesses, subject to various combinations of axial compression and bending moment, but with constant material use. The optimization process is carried out using a genetic algorithm and aims to maximize the resistances of CFS members, determined according to the European design guidelines (Eurocode 3). Six initial prototype cross sections, including both single and built-up channel sections, are selected and their relative dimensions and edge stiffener configurations are allowed to vary during the optimization process. To ensure practically relevant solutions Eurocode 3 slenderness constraints, as well as a range of practical manufacturing and construction limitations, are imposed on the cross sections. Standard commercially available single and back-to-back lipped channel sections are taken as the starting points of the optimization and used to benchmark the efficiency of the optimized sections. Significant gains in capacity (of up to 156% in the present study) can be obtained compared to the initial cross sections, while the optimization results also offer further insights on the material efficiency achievable with various cross-sectional shapes in combined loading scenarios ranging from pure bending to pure compression. [ABSTRACT FROM AUTHOR]