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The paper develops a stiffness reduction factor to be used in geometric nonlinear beam-element type elastic analysis of cold-formed steel structures. The factor accounts for the reduction in flexural and warping torsion rigidities resulting from local and distortional buckling as well as residual stresses, particular to cold-formed steel structures. The purpose of applying the factor is to accurately account for the geometric second order effects when predicting the internal distributions of moments of cold-formed steel structural frames. The stiffness reduction factor arising from local and distortional buckling is first determined followed by the stiffness reduction factor caused by residual stresses. Subsequently, the two effects are combined in a single expression, which is a format suitable for incorporation in the North American specification for cold-formed steel structures, AISI-S100. [ABSTRACT FROM AUTHOR]

Although cold-formed steel (CFS) framing systems have the potential to support the need for resilient housing, the use of CFS has been restricted due to gaps in understanding its structural behavior and by the limited guidelines provided in design standards. In particular, the contribution from nondesignated lateral systems and portions of the building system not specifically designated by the design engineers has not been substantially investigated through experiments. To address these shortcomings, a two-phased experimental effort was undertaken to assess the impact of gravity walls, finish application, window openings, and their relationship with the designated lateral force–resisting system. The wall-line assemblies tested, which have shear walls placed in-line with gravity walls, adopted chord stud packs with a tie-rod assembly and were either unfinished or finished, and laid out in a symmetrical or unsymmetrical fashion. In addition, both Type I and Type II shear wall and anchorage detailing were investigated. In this paper, the impact of test variables governing the nonstructural detailing of CFS-framed walls has been quantified, and a companion paper presents findings regarding the impact of structural detailing. [ABSTRACT FROM AUTHOR]

The North American construction industry has seen substantial growth in the use of cold-formed steel (CFS) framing for midrise buildings in recent years. In seismic zones, CFS-framed buildings utilize shear walls to provide the primary lateral resistance to earthquake induced loads. Although oriented strand board (OSB) and plywood panels have been traditionally used as the sheathing material for these essential components, more recently, steel sheet sheathing has emerged as a novel strategy due to its strength, ductility, ease of installation, and use of noncombustible material, among other benefits. To address the paucity of data regarding CFS-framed shear wall response within actual wall lines of buildings, a two-phased experimental effort was conducted. Wall-line assemblies were fabricated and tested with shear walls placed in-line with gravity walls. The shear walls chord stud packs include tie-rod assemblies consistent with multi-story detailing. Specimens were either unfinished or finished, and the shear walls were laid out in a symmetrical or unsymmetrical fashion within in the wall line. In addition, both Type I and Type II shear wall and anchorage detailing were investigated. In this paper, the impact of test variables governing the structural detailing of CFS-framed walls are quantified through dynamic and quasi-static tests, and a companion paper presents findings regarding the impact of architectural variations on seismic performance. [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]

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]

Studies on the constructability of cold-formed steel (CFS) members are lacking. In this context, this paper proposes an integrated panel to replace the studs and steel sheet in the steel-sheathed wall system used in light gauge steel frames. The integrated panel was developed, to not only exhibit better structural performance and constructability than the steel-sheathed wall system, but to also reflect the appropriate details for applications to on-site panel construction. Cyclic loading tests were performed to investigate the seismic performances of three integrated panel specimens and a steel-sheathed panel specimen. The integrated panel specimens exhibited greater deformation capacity, ductility and equivalent damping ratio than the steel-sheathed panel. Although the web slenderness of the integrated member was nearly 400, the nominal strength of the integrated panel was predictable on an AISI standard. However, for stud-reinforced integrated panels, the nominal strength was overestimated by 45%–60%, and a draft equation was proposed to predict the yield strength of these panels. The proposed equation accurately predicted the yield strength of the stud-reinforced integrated panel specimens. The study results can aid in the construction of light gauge steel frames that require reinforcing parts with a high web slenderness ratio. [ABSTRACT FROM AUTHOR]

The cold-formed steel (CFS) frame has the advantages of high strength, light weight, high construction efficiency, so it has been widely applied in building structures. However, the research on the seismic performance of multistory frames, especially those with braces, is rarely reported, the design method is also incomplete. In view of this, a pseudo static experiment of a three story double leg C-section CFS frame with brace is carried out. The bearing capacity, ductility, stiffness degradation and energy dissipation performance of the specimens are studied. The finite element analysis (FEA) method is used to simulate the failure process of the CFS frame and the design suggestions are proposed. The experiment result show that the failure process of the cold-formed thin-walled frame without braces has satisfactory ductility and energy dissipation performance; For framed CFS frame, the lateral stiffness and bearing capacity of the CFS frame increases, but the ductility decreases. Replacing double angle steel brace by steel plate strip brace can improving the seismic performance of structures, but there is an optimal width thickness ratio of steel plate strip. In this paper, the optimal width thickness ratio of brace is 5.0. When the design suggestions proposed in this paper are met, the CFS frame can achieve "strong structure, weak brace", so as to improve the seismic performance of the frame. • A double leg C-type cold-formed thin-walled steel frame with backing plate is proposed. • The seismic performance of a new cold-formed thin-walled steel frame is tested and the role of bracing is analyzed. • The simplified analysis model of the new frame is given. • Through finite element simulation, the optimization design method and key parameters of the bracing are given. [ABSTRACT FROM AUTHOR]

Cold-formed hollow structural sections are widely used in structural applications. Indeed, the high strength-to-weight ratio, the high torsional stiffness and the significant biaxial resistance of such sections make them suitable for columns of moment resisting frames. The interest on these sections is confirmed by the increasing number of studies aimed at developing a deep comprehension of the cyclic response of cold-formed hollow sections. Accurate and computationally effective numerical models are, however, still needed to model strength and stiffness deterioration of such members under cyclic loading. In this paper, the cyclic response of members with either square or rectangular hollow cross-section is simulated by means of a rigid beam with concentrated plastic hinges at the ends. The bending moment-chord rotation relation of these plastic hinges is simulated by means of the modified Ibarra-Krawinkler deterioration model. The values of the parameters of the model are calibrated against results of refined finite element numerical models to simulate both the cyclic and the first-cycle envelope responses of cantilever elements. Finally, predictive equations of the values of the parameters of the modified Ibarra-Krawinkler model are proposed as a function of the cross-section geometry, axial load ratio and shear span ratio. • Equations to predict the parameters of the MIK model for HSS members are formulated. • both the cyclic and the first-cycle envelope responses are considered. • residuals of the parameters are modelled so that Monte Carlo analyses may be performed. • laboratory tests available in the literature are used to validate the proposed equations. [ABSTRACT FROM AUTHOR]

Cold-formed built-up box sections (CFBBS) have emerged as a promising solution for applications in light gauge steel framing systems and modular construction. However, they suffer from the inherent local buckling effect. Concrete infill has proven effective in mitigating this issue, yet existing codified provisions lack specific guidelines for the design of concrete-filled CFBBS stub columns. This paper proposed a design methodology that aims to predict the ultimate compressive strength of lightweight concrete-filled CFBBS stub columns. Leveraging finite element (FE) modelling techniques, this study augmented the existing test database and shed light on parametric influences, considering practical considerations, on the structural performances and axial compressive behaviour. The proposed design approach demonstrated superior prediction accuracy and consistency compared to other evaluated design approaches in this study. • Finite element modelling of lightweight aggregate concrete-filled CFBBS stub columns. • Parametric study, incorporating practical considerations, on various aspects of structural performance. • Discussion on mechanical behaviours, encompassing load–end-shortening relationship and interfacial stress analysis. • Proposal of a reliable and accurate design methodology for predicting ultimate compressive resistance. [ABSTRACT FROM AUTHOR]

Cold-formed steel (CFS) framed shear walls with steel sheathing are promising lateral-force-resisting members of mid-rise buildings in seismic regions. Previous studies have demonstrated that steel sheathed CFS framed shear walls have high shear capacity but some shortcomings, such as the low ductility caused by the premature damage of the frame and the shear buckling of the sheathing. This paper presents an experimental study on a novel type of CFS framed shear wall with slitted steel sheathing (CFS-SSWs), which uses longitudinal slits to change the failure mode of the sheathing so that the ductility of the wall can be improved; Meanwhile, stiffeners are utilized to enhance the out-of-plane stability of the slitted sheathing and the integrity of the wall. Six full-scale CFS-SSW specimens were tested under monotonic and cyclic lateral loading. Three types of stiffening approaches (Type I, Type II and Type III) were adopted for the walls. Test results were analysed to investigate lateral performances of walls under different stiffener arrangements, including failure modes, load-displacement hysteresis curves, backbone curves, stiffness and strength degradation, and energy dissipation capacity. The measured strengths of the walls in the tests were assessed using theoretical indexes. It is found that peak loads and energy dissipation capacity of stiffened walls are noticeably higher than those of the unstiffened wall. Type II and Type III are effective stiffening approaches that could mitigate the buckling of the slitted sheathing and enable the links between the slits to reach the full plastic strength. By connecting the stiffeners and studs through stiffener connectors, Type III has the most significant enhancement on the stiffness, strength and ductility of the wall. • A novel type of cold-formed steel framed shear wall, i.e., CFS-SSW, is presented. • Six full-scale CFS-SSW specimens are tested to investigate their lateral behavior. • The stiffened walls show improved performances compared to the unstiffened wall. • Type II and III are effective stiffening methods that can mitigate the buckling. • Type III has the most significant enhancement on the performances of the wall. [ABSTRACT FROM AUTHOR]

This paper aims to perform the experimental test and numerical FE analysis of the cold-formed steel frame structure to provide new proposals to improve the strength, rotation capacity, and seismic energy dissipation in these structures. A 3D full-scale three-story CFS frame structure is experimentally investigated under four sets of input data for 100% and 50% scales of Northridge and Kocaeli earthquake acceleration records using the shaking table test. In each test, the frame acceleration and displacement are observed. A FE model is employed to assert the validity of the experimental test. The results indicated that the maximum story drift ratio of the frame ranges from 1.14% to 3.70%. It is observed that the average similarity ratio of the maximum displacement results between FE analysis and shaking table test is 92%. It is shown that the translational stiffness for the system decrease as the earthquake acceleration records decrease. It is also shown that using the image processing technique in the shaking table test can offer much more acceptable and economical solutions in determining the displacement parameters. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive assessment method of the fragility of low-rise cold-formed steel (CFS) framed wall structures subjected to wind hazards considering the fragility of both the main structure and the cladding system. The effects of wind directions on the fragility of CFS framed wall structures were also studied. For the main structure, the fragility curve is established using the maximum interstory drift ratio (ISDRmax) as the performance index for assessing the wind fragility of the structure. For the cladding system, the probabilistic models of the wind load and the cladding component resistance are established based on Monte Carlo simulation, and then methods for the fragility assessment of single cladding components and the cladding system under wind hazards considering the influence of the number and arrangement of the cladding components are proposed. The results indicated that, under strong wind, the cladding system may be damaged before the required wind resistance capacity of the main structure is exhausted. In particular, the roof sheathing is the most prone to damage, followed by the stud wall. That is, before the main structure is severely damaged or collapses, the cladding systems may be severely damaged, rendering the structure unusable. Therefore, the comprehensive assessment of the fragility of this type of structure subjected to wind hazard considering the fragility of both the main structure and the cladding system is more accurate. This study is of great significance for the improvement of the wind resistance performance of CFS structures and the popularization of this type of structure. [ABSTRACT FROM AUTHOR]

Experiments are generally used to investigate connection behaviour of steel storage racks, but the procedures are expensive and time-consuming. Various connections with complicated geometrical details necessitate simple and reliable design methods. This paper presents a mechanical model based on the component method to predict the initial rotational stiffness of beam-to-upright connections in cold-formed steel storage racks. In the model, five basic deformable components contributing to the initial rotational stiffness of beam-to-upright connections, are involved, i.e. tab in bending, upright wall in bearing, and upright wall in bending, beam-end-connector in bending and shear, upright web in shear. The mechanical model is validated against experiments, and the results show that the initial rotational stiffness values obtained from the mechanical model have a satisfactory agreement with the experimental results. Finally, based on the proposed mechanical model, main components influencing the initial rotational stiffness of connections are analysed in this paper. [ABSTRACT FROM AUTHOR]

Stainless steel, aluminium alloy, and cold-formed steel structures have been increasingly used as the main load-bearing components in civil engineering. However, owing to the rounded stress-strain response of the materials with significant strain hardening, the traditional plastic hinge model based on elastic-perfect plastic material response is not applicable, and the strength reduction of slender cross-sections by local buckling is also not considered. This paper proposed an improved refined plastic hinge method that can apply to different materials and fully consider the strain hardening and local buckling effect. A beam-column element was proposed, in which the second-order effect between axial load and bending moment was incorporated in the stiffness matrix formulation by using the approximate sixth-order polynomial function. The continuous strength method was introduced to the refined plastic hinge model to consider the strain hardening effect of non-slender and the local buckling effect of slender cross-sections by controlling the strength and deformability of the sections. Combining the elastic and plastic limit state criteria, the stiffness degradation function for SHS and RHS was obtained. The accuracy and efficiency of the proposed method were verified by the experimental results for stainless steel, aluminium alloy, and cold-formed steel columns of SHS and RHS under axial and eccentric compression. Finally, the proposed method was used for the design of frames for the materials, the results indicated that it was an effective tool that was ready for design practice. • The 6th-order polynomial function is assumed as the deflection solution of beam-column. • The Continuous Strength Method is introduced to the improved refined plastic hinge model. • The proposed improved refined plastic hinge model can consider the strain hardening and the local buckling effect. • Design method is proposed for stainless steel, aluminium, and cold-formed steel columns and frames with RHS and SHS. [ABSTRACT FROM AUTHOR]

• Shell FE-based modelling protocol for CFS sheathed shear walls has been developed. • UELs were implemented for modelling the sheathing-to-CFS screws shear behaviour. • Thirty-eight sheathed CFS shear walls were simulated under monotonic lateral load. • Effect of construction details on lateral behaviour of CFS walls was investigated. • Results showed conservatism in CFS walls design as per AISI S400-15 and SCI ED002. This paper investigates the effect of modular construction details on laterally-loaded cold-formed steel (CFS) framed shear walls sheathed with wood- and cement-based panels by means of finite-element (FE) analyses. Shell FE-based models have been developed in ABAQUS with the aim of accurately capturing the behaviour, strength and stiffness as well as the corresponding failure modes of CFS framed shear walls subjected to monotonic lateral load (i.e. , wind). User-defined element subroutines were adopted for precise modelling of sheathing-to-CFS screws shear behaviour. The proposed modelling protocol is validated using experimental test results, where an acceptable concordance (4% difference) has been achieved. Subsequently, the effect of modular construction details, which go beyond the scope of the current lateral design provisions (AISI S400), on the lateral behaviour of CFS framed shear walls is assessed. In particular, this paper investigates the impact of: (i) floor and ceiling ledger beams on the interior face of the shear wall, (ii) sheathing boards having different sizes from the overall shear wall and thus the presence of both vertical and horizontal seams, (iii) cement particle boards at the bottom stripe of the shear wall and (iv) different screw spacing in the top and bottom stripes from the middle part of the shear wall. The key parameters, which have most affected the lateral behaviour, were identified, and based on that, rules have been established for optimizing the screws pattern and sheathings layout efficacy in the above-described lateral load resisting system. The obtained results shed light on the capability of the developed modelling protocol to be used as a virtual test bench, particularly in offsite mass production and manufacture (DfMA), for the development of a new CFS framed wall system for lateral stability of lightweight modular houses. [ABSTRACT FROM AUTHOR]

Steel structures can be consistently and efficiently designed using system-based design-by-analysis approaches such as the Direct Design Method. However, since direct design approaches lead to potentially lighter structural configurations, they can also result in larger deformations under service loads. Thus, greater attention may be required to serviceability limit states in structures designed using design-by-analysis approaches than for structures designed elastically at their ultimate limit state following current two-stage approaches, especially for materials showing highly nonlinear stress vs strain responses such as stainless steel alloys. With the aim of investigating the influence of allowing larger deformations in the ultimate limit state design of stainless steel structures, this paper presents an explicit analysis framework for assessing serviceability reliability at system level. Using this framework, the paper investigates the serviceability reliability of cold-formed stainless steel portal frames designed using the Direct Design Method for different load cases, including the gravity load and the combined gravity plus wind load combinations. The study considers six baseline frames covering the most common stainless steel families and international design frameworks (i.e., Eurocode, US and Australian frameworks), for which the reliability of vertical deflection and lateral drift serviceability limit states is investigated using advanced numerical simulations and First-Order Reliability Methods. From the comparison of the calculated average annual reliability indices and the relevant target reliabilities for the different design frameworks, it was found that the reliability of stainless steel frames appears to be adequate for the serviceability limit states investigated for the Eurocode, US and Australian frameworks. [Display omitted] • A general framework for assessing the serviceability limit state reliability at system level is presented. • Vertical deflections under gravity loads and lateral drifts under wind loads are studied. • Six baseline cold-formed frames, including the three main stainless steel families, are investigated. • Reliability results are presented for the Eurocode, US and Australian design frameworks. • Derived reliability indices are compared with suitable target values for each design framework. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic behavior of the cold-formed steel (CFS) frame with bolted moment connections by quasi-static loading tests and numerical analysis. The quasi-static loading test takes the thickness of the gusset plate and the span of the frame as two key parameters. Meanwhile, the effects of the column slenderness ratio, axial compression ratio of the column, height/thickness ratio of the column web, and beam/column linear stiffness ratio are the primary focus of the finite-element method. By using these methods, this paper presents seismic behavior and a simplified hysteretic model for the CFS frame. The results indicate that "failure of the beam end" and "failure of the column base" are the two main failure modes. The CFS frame shows outstanding seismic performance, and the column slenderness ratio, beam/column linear stiffness ratio, axial compression ratio of the column, and height/thickness ratio of the column web mainly affect it. The hysteretic model has been compared with the test results to demonstrate high reliability. The findings presented here provide future reference for the design of such a cross-sectional frame. [ABSTRACT FROM AUTHOR]

Cold-formed steel composite floor systems have been widely used in cold-formed steel framing for mid-rise building construction, primarily owing to its structural and economic efficiency. The composite floors consist of cold-formed steel C-shape joists and subfloor with cold-formed steel form-deck and gypsum-based self-leveling underlayment. This paper presents a theoretical method, an experimental investigation, and a simplified model analysis on the in-plane displacement of cold-formed steel composite floors under horizontal loads. Based on the design method of timber floors, the calculation methodology of the mid-span in-plane displacement of cold-formed steel floor with steel form-deck and gypsum-based self-leveling underlayment is proposed. Subsequently, cyclic shear tests of two full-scale floors with and without gypsum-based self-leveling underlayment were executed to investigate the failure mode, load bearing capacity, and in-plane displacement. The test results indicated that the primary failure mode of the specimens was the shear failure of self-drilling screws that connected the steel form-deck and end joists. Furthermore, the in-plane displacement of the test results agreed well with that of the proposed method. Finally, referring to the deformation results of floors under different loading stages, the composite floor analysis model was simplified to a nonlinear diagonal spring model according to the method of equivalent in-plane stiffness, and it was verified through ABAQUS finite element analysis. This study provides a useful design basis for the design and application of cold-formed steel composite floors. • The calculation method of the mid-span in-plane displacement of composite floors were proposed. • Cyclic shear tests on floors were conducted to investigate the in-plane displacement. • The validity of the proposed methodology was verified against the test results. • The floor analysis model was simplified to a nonlinear diagonal spring model. • The simplified model was verified through ABAQUS finite element analysis. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation on the blast response of cold-formed steel (CFS) structural framing system protected with a functionally graded composite material (FGM) panel. The steel frame consists of four CFS studs, which were protected by 12.5 mm thick gypsum, aluminum composite, and FGM composite materials on both sides. The numerical simulation was performed using ABAQUS on a 1.8 m × 2.4 m, overall wall panel exposed to air blast on one side. A 1.0 kg TNT explosive charge placed at four standoff distances (R) of 1.0 m, 1.5 m, 2.0 m, and 2.5 m from the framing were investigated. The FGM board was modeled using a stepwise material variation using the power-law material function. Deformation and failure modes of the studs, as well as the protective materials, were compared to the same framing system but with different protective materials, including conventional gypsum boards and aluminum composite panels. Based on the observation from the analysis and computational simulation, the proposed protective composite material (FGM) resulted in a smaller deformation at peak overpressure at a given standoff distance (R) and local failure modes on studs. The same frame system with gypsum and aluminum panel exhibited excessive deformation as well as an early collapse of the CFS studs. This observation can lead to an alternative material solution in blast-resistant design. [ABSTRACT FROM AUTHOR]

This study presents an innovative design for a cold-formed steel polyurethane (CFS-PU) composite wall panel, combining a cold-formed steel frame, a polyurethane foam infill, and a gypsum fibreboard sheathing. The foam filling process, in which the foam is injected under pressure, ensures uniform distribution, bonding, and interaction of all panel components. The aim of the study is to evaluate the behaviour of the CFS-PU composite panels and the influence of the PU foam and sheathing on the performance of the CFS frame structure. For this purpose, a comprehensive test programme was conducted with nine full-scale specimens, including four CFS-F specimens without infill and sheathing and five CFS-PU specimens with infill and sheathing on both sides. The study examined various aspects of the specimens, including failure modes, stability, stiffness, load-bearing capacity, and ductility index. By analysing these parameters, valuable insights were gained into the performance characteristics of the composite wall panels. The load-bearing capacity of the CFS-PU test specimens was improved by 2.34 times and the stiffness by 1.47 times compared to the CFS-F test specimens. The positive results highlight the potential of foam and sheathing in improving the axial compression performance of CFS walls. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation followed by numerical modeling for cold-formed steel (CFS) shear wall sheathed by fiber-cement board (FCB) under monotonic lateral load. Afterwards a numerical parametric study was performed taking into consideration various factors affecting the system ductility. The response modification factor was estimated using Equal Energy Elastic-Plastic rule. The results showed that the screw connections between the FCB and the steel framing members are of significant impact on the nonlinear behavior of the system. Also, the X-strap bracing increases the lateral load capacity and the values of response reduction factors (R) of the sheathed CFS shear walls. • The recommended screw spacing is between 100 and 200 mm. • Using noggin members improves the capacity of the shear wall. • The X-strap bracing significantly improves the lateral resistance of the shear wall. • Fiber cement board sheathing enhances the shear stiffness of the shear wall. • Average response reduction factor for this system of shear wall is equal to three. [ABSTRACT FROM AUTHOR]

Highlights • Advanced structural analysis method can design steel structures based on their overall system behaviour. • A system resistance factor is used to control the structural failure risk due to uncertainties in system resistance. • Four typical cold-formed steel portal frames are analysed for their system reliabilities. • A limit-state design criterion is developed which is consistent with a desired level of system reliability. Abstract 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. [ABSTRACT FROM AUTHOR]

The seismic design of light steel frames (LSF) can not only rely on the application of cold-formed steel (CFS). Some mixed systems and integrated solutions such as hybrid systems can offer new possibilities, in particular with regard to applications in mid-rise construction. A hybrid solution is to replace some CFS chord studs with hot-rolled square hollow section SHS, in order to achieve higher capacity. This paper provides the results of experimental studies on the lateral behaviour of a hybrid light-weight steel panel and investigates the implication of any further system improvements for mid-rise construction. Each hybrid wall panel (HWP) consists of a hot-rolled SHS frame, laterally incorporated in a cold-formed panel. The study includes investigating the lateral performance of HWP, while a CFS top chord acting as a load collector, and a hot-rolled steel frame acting as a lateral load resisting system. The behaviour of specimens is investigated under monotonic and cyclic loads, and the step-by-step enhancement is implemented according to the results. The outcomes revealed that although the hysteretic behaviour of the HWP represents pinching effect, mainly due to poor performance of the cold-formed steel collector, by strengthening the top chord design the behaviour is improved. Relying on the cold-formed part to resist the major portion of gravity loads, while the hot-rolled collector transfers the entire lateral load to the hot-rolled frame, results in significantly improved hysteretic behaviour. [ABSTRACT FROM AUTHOR]

The cold-formed steel-framed shear wall sheathed with steel sheet is widely used as a lateral force-resisting system for light-framed construction. However, the boundary conditions of the screw joint are not clear when steel is screwed to the frame. To address this issue, experimental methods have been used to calculate shear strength, but these methods have many limiting factors. In this study, we investigate the structural performance of integrated steel shear walls with varying web width-to-thickness ratios as an alternative to steel-sheathed shear walls used in light-gauge steel frames. The proposed design equation for cold-formed steel integrated shear walls is validated by three specimens and 72 finite element models. This equation allows designers to determine the strength of integrated steel shear walls without conducting full-scale shear-wall tests. [ABSTRACT FROM AUTHOR]

Design-by-analysis methods for steel structures are receiving considerable attention from professional engineers, researchers and standard-writing groups. Designing by analysis, termed as the Direct Design Method (DDM), is premised on the use of geometric nonlinear inelastic finite element analysis to determine the ultimate strength of steel structural frames and subsequently incorporating a system resistance factor ( ϕ s ) to account for the effects of uncertainties in geometric parameters, stiffness and strength. This paper outlines the DDM in the context of cold-formed compact Hollow Steel Sections (HSS), including the reliability analysis framework at system level underpinning the Method. The system resistance factors for a series of representative 3D frames with hollow locally stable cross-sections are derived. [ABSTRACT FROM AUTHOR]

Pallet racks are characterized by boltless beam-column connections and the extensive use of thin-walled cold-formed steel members. Due to the great number of beam-end connector types and member geometries, a reliable evaluation of their structural behavior, especially under seismic loads, requires a thorough modeling of beam-column joints, whose moment-rotation curves can be reliably assessed only through experimental tests. In this paper, the authors present results of monotonic and cyclic tests on four different types of industrial rack joints. Tested joints differ from one another in the type of beam-connector, which is obtained by folding the beam end or is welded to the beam-end section with different welding layouts. Moreover, joints differ in the number of tabs and the relative thickness of the upright and the beam-end connector. Experimental results from cyclic tests allows for moment-rotation curves of joints to be accurately identified, confirming that they are significantly different from traditional steel framed buildings due to pinching in hysteresis loops. Obtained curves can be used for reliable modeling of joints in seismic analyses of steel pallet racks. As producers of steel rack structures are interested in reducing the total welding length of beam-end connectors for time efficiency and cost saving, the influence of the welding layout of beam-end connectors on the structural response and failure mode of joints has also been investigated. Finally, some joints have also been equipped with additional bolts to evaluate their influence on the bearing capacity, initial elastic stiffness and dissipated energy per cycle. [ABSTRACT FROM AUTHOR]

The objective of this paper is to present finite element modeling protocols and validation studies for the seismic response of a two-story cold-formed steel-framed building with oriented strand board sheathed shear walls. Recently, shake table testing of this building was completed by the authors. The building provides an archetype for modern details of cold-formed steel construction, and provides benchmarks for the seismic response of the building system, subsystem, and components. The seismic response of buildings framed from cold-formed steel has seen little study in comparison with efforts on isolated members and shear walls. Validated building-scale models are needed to expand our understanding of the seismic response of these systems. Finite element models corresponding to the archetype building during its various test phases are developed in OpenSees and detailed herein. For cold-formed steel framed buildings accurate seismic models require consideration of components beyond the isolated shear walls, e.g. the stiffness and capacity of the gravity framing is included in the model. Such decisions require model refinement beyond what is typically performed and details for completing this effort accurately and efficiently are described herein. In addition, nonstructural components, including exterior sheathing of the gravity framing, interior gypsum sheathing for the shear walls and gravity framing, and interior partition walls, are included in the building model based on nonlinear surrogate models that utilize experimental characterization of member-fastener-sheathing response. Comparisons between the developed models and testing for natural period, story drift, accelerations, and foundation hold-down forces validate the model. Performance of the tested archetype building is better than predicted by design or typical engineering assumptions. The model developed herein provides insights into how the building achieves its beneficial performance and will be used to further quantify the lateral resistance of each subsystem and the extent of their coupling. In addition, the protocols used to develop the model herein provide a first examination of the necessary modeling characteristics for wider archetype studies of cold-formed steel-framed buildings and the development and substantiation of seismic response modification coefficients. [ABSTRACT FROM AUTHOR]

In order to expand the applications of cold-formed thin-walled steel structures, this study proposes a new type of composite wallboard composed of cold-formed thin-walled C-shaped steel and multi-layer concrete, in which C-shaped steel serves as the skeleton, foam concrete acts as the thermal insulation material, and fine aggregate concrete and cement mortar play the part of envelopes. The composite wallboard can be made in a factory assembly line, meeting the requirements of the building (civil and structural) industry. Two steel-frame composite wallboard shear walls were subjected to reciprocating loading, with the connection mode as the design parameter, to investigate the seismic performance of the structure. The failure mode, hysteresis curve, skeleton curve, strength degradation, stiffness degradation, ductility, and energy dissipation capacity of the specimens were analyzed. On this basis, the finite element (FE) model of the steel-frame composite wallboard was established, and the model's accuracy was verified by comparing the bearing capacity and the skeleton curve. Results show that the structure shows shear failure characteristics, and the cement mortar layer and the fine aggregate concrete layer are separated from the C-shaped steel after being crushed. The infilled foam concrete is also crushed, and the welding seams between the extended C-shaped steel and steel frame of the WP-1 specimen are damaged. The hysteresis curves of the two specimens have a clear pinch, but the area enclosed by the hysteresis loop is large, and the energy dissipation capacity is also present. The yield load and ultimate load of the WP-2 specimen are higher than those of the WP-1 specimen, indicating that the higher the connection strength between the composite wallboard and the steel frame, the greater the ultimate carrying capacity of the specimen. The established FE model can accurately estimate the seismic performance of steel-frame composite wallboard shear walls. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the monotonic and cyclic lateral loading behavior of cold-formed steel (CFS) shear walls sheathed with glued laminated bamboo (glubam ply-bamboo) panels. A total of 16 model shear wall specimens with two types of aspect ratios were tested using ASTM loading protocols. The observed phenomena and the effects of different cyclic loading regimes are discussed. The shear capacity and deformability of ply-bamboo sheathed CFS shear walls are evaluated and compared with wood sheathing panel (WSP) sheathed CFS shear walls through four seismic equivalency parameters recommended by American Iron and Steel Institute (AISI) in 2010 (AISI-RP10-4 2010). The load distribution of the screws along the vertical edges of the panels and the forces in the shear anchors are discussed. The results obtained in this study can further promote the application of bamboo-based material in CFS structures, as potential options for eco-friendly and cost-effective construction. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the behaviour of cold formed steel truss connections. Eighteen full scale cold-formed steel truss connections were tested. Of particular interests are the specimens maximum load capacity and the load-deformation behaviour. The study also looks at the failure modes of the connections. The behaviours exhibited by the connections are discussed and the design capacities calculated from the current CFS design standards are compared to the experimental results of the connections. This study investigates the main factors contributing to the ductile response of the CFS truss connections in order to suggest recommendations for connection designs, and improvements so that the connections respond plastically with a significant drift and without any risk of brittle failure. Also, a number of alternative fasteners are chosen and investigated for comparison with those that are currently specified for trusses' connections. [ABSTRACT FROM AUTHOR]

Target structural reliabilities are implicit in most modern design codes and yet efficiency of design and construction as well as the presence of constraints on the design space mean that structural components in a building system may have as-designed reliabilities that differ from the target reliabilities. This paper presents an investigation of this phenomenon through a detailed examination of the two story cold-formed steel framed building designed and tested as part of the CFS-NEES project and seeks to use this case study to elucidate features of the component and system reliabilities that may prevail in typically designed buildings. Specifically, for the gravity load system of the second floor and the lateral force resisting system the demand to capacity ( D / C ) ratios and reliabilities ( β ) are calculated. The results of these calculations illustrate the excess and highly variable D/C ratios and reliabilities that result from efficient design procedures. Since the ultimate goal of structural design is to ensure performance of the structural system at a target level of reliability the influence of excess and variable component reliability on reliability of the lateral force resisting system is examined by making assumptions about series and parallel-type interaction of the floor diaphragm and shear walls. Finally, discussion is presented about the role of load combinations and their associated coefficients of variation in determining component and system reliability in a cold-formed steel framed building. Future considerations include more robust, high fidelity, modeling of the system effects and evaluation of excess capacity and variability of reliability across suites of other building designs and structural systems such as roof trusses. [ABSTRACT FROM AUTHOR]

Local and distortional buckling reduces the flexural and warping rigidities of steel frames. As a result, the sway buckling load of locally unstable unbraced frames is reduced and sway deflections increase at a faster rate than corresponding locally stable unbraced frames. This leads to greater second order moments and potentially premature collapse, since commonly, unbraced steel frames are designed using elastic analyses (2nd order or 1st order with moment amplification) which assume unreduced values of the flexural and warping rigidities. This paper investigates the effects of second order moments induced by local and/or distortional buckling of the uprights of steel storage rack frames. Using results from the accompanying experimental investigation, calibrated FE models are used to predict the strength of steel storage rack frames with increasingly slender cross-sections. The FE strengths are compared to design strength predictions and conclusions are drawn about the extent to which current specifications are able to accommodate second order moments generated by local and/or distortional buckling. [ABSTRACT FROM AUTHOR]

Built-up back-to-back cold-formed steel channel (BC) members are increasingly used as studs for increasing the compression capacity of light gauge steel framed (LSF) walls, even though the knowledge of their behaviour is limited. In this study, the behaviour and capacities of LSF walls made of slender BC members sheathed with gypsum plasterboards on both sides were investigated using a series of compression tests and detailed finite element studies based on validated models. The numerical and experimental results showed that (1) screw connections of BC members had marginal effects on the compression capacities of the investigated sheathed BC members with non-staggered stud-to-board screw arrangement, and the capacities were mostly equal to twice the capacities of their individual members, (2) the restraints provided by the plasterboards and stud-to-board screw connections effectively prevented sheathed BC members from in-plane flexural buckling and considerably improved their compression capacities, and (3) the Direct Strength Method in the current design standards in combination with the guidelines and recommendations proposed in this study conservatively predicted the compression capacities of these members. Details of this research study, its results and findings are presented in this paper. [Display omitted] • Investigated the behaviour of built-up back-to-back channel (BC) studs sheathed with gypsum plasterboards. • Plasterboards and stud-to-board screws restrained sheathed studs from in-plane flexural buckling and improved the capacity. • The capacity of sheathed BC studs with non-staggered stud-to-board screws was about twice the individual member capacity. • The effect of stud-to-stud screw arrangement was marginal. • Conservative DSM-based design guidelines and recommendations are proposed. [ABSTRACT FROM AUTHOR]

Simplified calculation model of bearing capacity of wall structure. [Display omitted] • The steel frame fabricated with CFS composite wall structure was proposed in this paper. • Cyclic loading tests of five full-scale specimens were conducted. • A simplified superposition method was used to evaluate the bearing capacity of the proposed wall structures. In this study, a novel hybrid wall structure of a hot-rolled steel frame fabricated with a cold-formed steel (CFS) composite wall is proposed. Ceramsite concrete is lightweight concrete that is used in CFS composite walls. The seismic performances, including the failure mode, hysteretic behavior, shear capacity, stiffness, ductility, and energy dissipation performance, of four specimens of steel frame fabricated with CFS composite wall and one specimen of conventional CFS composite wall were evaluated under low-cyclic loading. The experimental results showed that the collaborative working performance of the steel frame and infilled CFS composite wall was optimum, and the proposed fabricated wall structure had a significant effect on the bearing capacity, stiffness, and energy dissipation capacity. The infilled CFS composite walls were damaged earlier than the steel frames. The damage was primarily characterized by the compressive failure at the corners of fillers, loss of diaphragm effect, screw connection failure, and bond-slip failure between the CFS framing and fillers. However, the steel frames exhibited no obvious damage, which effectively restrained the infilled CFS composite walls and prevented them from severe collapse. In addition, enhancing the strength of the fillers and increasing the section area of the studs improved the bearing capacity of the structure; however, they were detrimental to the ductility. Wall opening reduced the bearing capacity and initial stiffness of the structure; however, it improved the ductility. Furthermore, a superposition method was used to calculate the bearing capacity of the proposed structure. The calculated results showed a superior accuracy in comparison with the experimental results. [ABSTRACT FROM AUTHOR]

This study analyzed the flexural buckling behavior of light‐gauge built‐up compression members joined by self‐drilling screws by using the energy method. A nonconventional mechanical model that simulates the flexural buckling behavior of a built‐up member was proposed, and the contradictions of Bleich's model were described. A simple design formula that directly reflects the parameters of built‐up members was derived based on the proposed model. Furthermore, to ensure flexural buckling as a single unit member, the required stiffening stiffness and number of self‐drilling screws were proposed. [ABSTRACT FROM AUTHOR]

This study reviewed some simplified methods of finite element analysis (FEA) for connections in cold-formed steel (CFS) structure, and summarized eight simplified methods divided into three categories. Shear performance tests were performed for six groups of self-piercing riveted (SPR) connection in CFS. A constitutive model of shear behavior for SPR connections was proposed, which was simplified from the load–displacement curve of shear performance test results. The models of SPR connection were established in ABAQUS by the eight simplified methods, and then the FEA results and the test results were compared. The applicable scope of each simplified model was explored, and a simplified method of FEA that was most suitable for the shear behavior of the CFS-SPR connection was proposed. Moreover, the shear performance test of the CFS shear wall with SPR was conducted by considering the rivet spacing, and failure modes and load–deformation curves were obtained. On this basis, numerical models of the CFS-SPR connection shear wall were established. By comparing the test results and the FEA results for the CFS-SPR connection shear wall, the feasibility of a simplified method of FEA applied to the CFS-SPR connection was verified. The main failure modes of the CFS-SPR connection were that the rivet tail pulled out from the bottom sheet and the rivet head pulled over from the top sheet. The SPR connection of the CFS frame could be simplified with a pin or a fastener element, and the SPR connection between the steel frame and the sheathing could be simulated by a Cartesian connector or a Spring2 element. The FEA results were highly similar to the test results for the CFS-SPR shear wall. [ABSTRACT FROM AUTHOR]

The purpose of this research was to study the lateral deformation behavior of cold-formed steel wall panel structures using experimental tests, finite element analysis and analytical methods to study the lateral stiffness of these structures. The wall panel structures were tested by full-scale experiments the experimental results of which were verified by a 3D-finite element model. The verification results showed a good correlation between the experimental tests and a finite element model. The single-column spring model was proposed for an elastic lateral stiffness analysis of the cold-formed steel wall panel structures that were formed by combinations of a guide cantilever beam and springs connection. The spring constants were defined by using the stiffness of the stub-chord connection and the bending stiffness of the chord. The experiments tests and finite element analysis were used to verify this single-column spring model. The comparison results showed good agreement between the analytical prediction, finite element analysis and experimental data in the case of the primary type of cold-formed wall structure. The proposed procedure was an efficient method for elastic lateral deformation analysis of cold-formed wall panel structures which can be used for such configurations. [ABSTRACT FROM AUTHOR]

This paper describes a series of six full-scale laboratory tests conducted on cold-formed steel portal frame buildings in order to investigate the effects of joint flexibility and stressed skin diaphragm action. The frames used for the laboratory tests were of 6 m span, 3 m height, 10° pitch and the frame spacing was 3 m. Vertical loading was applied in two tests, and horizontal loading was applied in another four tests. The laboratory test set-up represented a building having two gable frames and two internal frames. Tests were conducted on frames having two joint types, both with and without roof sheeting. It was shown that as a result of stressed skin action, the internal frame with roof sheeting resisted approximately three times more horizontal load than the bare frame and the deflection of the internal frame was reduced by 90% relative to the bare frame. When the difference in loads between 2D (bare frame model) and 3D (stressed skin model) were considered, it was shown that the joint flexibility of the frame has a significant effect on the load transfer between frames through the roof sheeting. It was found that the ‘true’ loads transferred to the gable frames are between three and seven times higher than the loads deriving from tributary area. By using stressed skin analysis, it is possible to assess the shear force in the roof sheeting so that damage to the fixings is prevented and a more economical design is possible. [ABSTRACT FROM AUTHOR]

The use of cold-formed steel for primary load bearing members in low and medium rise buildings has become an increasingly popular form of construction. The design of connections between these members is crucial to the overall structural integrity of such buildings. However, for beam-to-column joint design, recent codes of practice show ambiguity in the mechanical behaviour. Further research is required to investigate the strength, stiffness and ductility prediction of such connections. This paper addresses these concerns by proposing simplified formulas for the moment-rotation behaviour of light steel frames with bolted top-seat flange cleat joints. A finite element study is presented which is validated against laboratory experimental tests on cold-formed steel arrangements. The validated model is used within a parametrical study to investigate several additional geometrical parameters that are not included in the experimental works. An exponential equation has been proposed for large deformation of top-seat flange cleat joint under monotonic vertical load. The predictions using the equations are compared to the design codes (BS EN1993-1-8) and experimental data. From the comparison, the proposed equation can improve the BS EN1993-1-8 prediction from 168.08% difference, compared to experimental results, to 7.09% difference. The new proposed model gives a safe design for top-seat flange cleat joint in cold-formed steel light frame construction. [ABSTRACT FROM AUTHOR]

Cold-formed thin-walled members are used worldwide to realize semi-continuous steel frames to store goods and products (rack systems). Usually, monosymmetric cross-section members are employed for rack columns but their design is carried out by assuming very simplified approaches, which consider the centroid coincident with the shear center of the cross-section. In routine design, non-uniform (warping) torsion influence is sometimes neglected in structural analysis: internal forces and bending moments are hence incorrect and the coupling between flexure and torsion is never considered also in buckling analysis. As a consequence, an unsafe design could be developed, owing to the use of non-appropriate tools for analysis and verification checks. A numerical study is currently in progress in Italy to define suitable design rules accounting for the monosymmetry of the cross-section members forming rack systems. This paper summarizes the main results related to the warping effects on the resistance checks. A numerical study on typical medium-rise rack frames is presented. In particular, two racks have been selected, differing for interstorey height and total height. Both configurations of unbraced and braced frames have been considered. Four different load conditions have been identified as relevant for rack design and, for each of them, a parametric analysis has been carried out by varying the degree of beam-to-column joint stiffness. Furthermore, warping influence on the distribution on the longitudinal stresses on the cross-section has been investigated, with the scope to quantify the errors when the sole uniform torsion is taken into account in structural analysis, i.e. when the bi-moment is neglected. Design results are then critically analyzed, singling out the importance of the warping on the cross-section resistance checks. Finally, suitable safety factors are proposed to be used when design is developed neglecting warping but an adequate safety level has therefore to be guaranteed. [ABSTRACT FROM AUTHOR]

The objective of this paper is to explore and characterize the impact of practical construction details on the cyclic performance of cold-formed steel framed shear walls sheathed with Oriented Strand Board. The specific construction details explored are motivated from a two-story, ledger-framed, cold-formed steel archetype building that is the focus of a larger effort to advance seismic performance-design for light steel frame construction. This larger effort in cold-formed steel (CFS) research is funded primarily by the National Science Foundation / Network for Earthquake Engineering Simulation (NSF/NEES) effort and is known as the CFS/NEES project. The archetype structure is known as the CFS/NEES building. Shear walls in real construction, such as the CFS/NEES building, have details that differ from shear walls tested and provided for strength prediction in standards such as AISI-S213. Key differences include: (a) ledger (rim track) members attached across the interior face of the studs; (b) OSB panel seams, both horizontal and vertical, may not be aligned with the chord studs or only blocked with strap; (c) interior gypsum board is in place; (d) field studs may have a different thickness or grade from the chord studs; and other differences. In this work, these highlighted differences (a-d) are specifically explored in a series of shear wall tests loaded via cyclic (CUREE) protocols to determine their hysteretic performance. The test results are compared with AISI-S213 and hysteretic material characterizations utilizing an elastic-plastic model and a model capable of exhibiting pinching in the hysteretic loops. [ABSTRACT FROM AUTHOR]

• Investigated the effects of geometric imperfections on the capacities and failure modes of eccentrically loaded studs. • Used simple single stud FE models to investigate the behaviour of sheathed LSF walls under eccentric compression. • Developed an advanced FE model for LSF wall panels by including sheathing, tracks and screw connections. • Validated the advanced model through comparison of failure modes, capacities and load-displacement curves from experiments. • Highlighted the benefits of using advanced numerical modelling over basic single stud modelling for LSF walls. The current numerical studies and design of light-gauge steel framed (LSF) wall and floor systems are largely confined to individual members with idealised boundary conditions. Idealised single stud models of LSF walls that have been extensively used in the past are unable to capture the complex behaviour associated with stud-to-sheathing and stud-to-track connections. The ultimate capacities and failure modes predicted by these models may not always be accurate because of which designers have to resort to expensive and time-consuming full-scale testing. Advanced numerical models that explicitly model all LSF wall components are available in recent literature. However, they are limited to LSF walls under axial compression. In this study, the behaviour of LSF walls made of lipped channel studs under eccentric axial compression was investigated by developing a sheathed stud model simulating the sheathing material, tracks and connections using ABAQUS. This advanced model incorporated material and geometrical non-linearities, contact interactions, non-linear behaviour of stud-to-sheathing connections and explicit modelling of gypsum plasterboard sheathing, and was validated using experimental results. The failure modes, ultimate capacities and load versus axial shortening and lateral deflection curves predicted by the advanced model were compared with those predicted by the simple single stud models and suitable recommendations were proposed for finite element modelling of LSF walls under combined loading actions. This paper presents the details of the development of advanced models of LSF walls subject to compression and bending actions and its findings. [ABSTRACT FROM AUTHOR]

• Investigation of the thermal and structural behavior of the LSF walls at high temperatures by numerical study. • Conducting parametric study to investigate the effect of various parameters on the thermal and structural behavior of LSF wall. • Calculation of temperature distribution and time–temperature profile of the wall component and fire-resistance rating (FRR) of the wall. • Significant influence of sheathing on the fire-resistance rating of walls. Light gauge Steel Frame (LSF) system, are extensively used in residential, commercial and industrial buildings. Its growing popularity in building construction industry is due to several advantages over other construction materials such as light weight, high strength and stiffness, uniform quality, ease of prefabrication and mass production, economy in transportation and handling. Fire safety of cold-formed steel structures has become more important since cold-formed thin-walled steel sections heat up quickly under fire condition (high section factor and high thermal conductivity) and present low fire resistance. LSF wall systems are used as primary load bearing structural members providing strength and stability in multi-story LSF buildings. Therefore a better understanding of the fire performance of LSF wall systems is required. The structural behavior of the LSF walls at high temperatures depends on the temperature distribution at the wall component and the mechanical property of cold-formed steel and other materials used in LSF walls at elevated temperatures. Also, the thermal performance of the LSF wall is influenced by its components, including the stud cross-section, stud size, sheathing, and insulation types and their thicknesses, and thermal properties of them. In this paper, a numerical study was undertaken using the finite element program ABAQUS. The structural finite element analysis were conducted under transient state condition using the time–temperature profiles of wall components obtained from the thermal analysis. The finite element thermal and structural models were first validated by comparing their results with the previous test results and then a parametric study was conducted with considering the effect of various parameters such as type of sheathing and its arrangement, stud web depth, stud flange width, and stud cross-section shape. The temperature distribution and time–temperature profile of the wall component and Fire-Resistance Rating (FRR) of the wall have been calculated. The results showed that sheathing is one of the most critical factors in fire resistance of walls and has a significant influence on the FRR of walls and increasing the stud depth affects the thermal and structural behavior of the LSF wall and leads to an increase in the FRR of the wall against fire. Also, increasing the stud flange width of LSF wall does not affect the thermal behavior and temperature distribution of the wall, but leads to an increase in the FRR of the wall against fire. The stud cross-section shape does not affect the temperature distribution in the cross-section but can affect the wall's behavior under fire conditions. [ABSTRACT FROM AUTHOR]

The primary objective of this work is to provide connection-level force-deformation response appropriate for standard cold-formed steel (CFS) framed steel sheet sheathed shear walls under cyclic loads. Common CFS framing designs increasingly are exploring thicker framing options so that walls can meet gravity demands, overturning demands, and seismic overstrength requirements. For the seismic performance of self-drilling screw-fastened steel sheet sheathed shear walls, the cyclic nonlinear response of the screw-fastened connection is particularly important and should incorporate the impact of shear buckling of the steel sheet on the strength and ductility of the connection. Minimal cyclic connection-level shear test data exist, especially for combinations of screw-fastened thin steel sheet and thick framing steel. A unique lap shear test following current test standards was proposed to elucidate and characterize the cyclic screw-fastened connection behavior. An asymmetric cyclic loading protocol was selected with a small displacement applied in the direction that buckles the thin steel sheet, followed by progressively larger displacements in the opposite direction. A total of 93 tests were conducted, and characterization of the observed cyclic connection response with a multilinear backbone curve appropriate for use in models is provided. Connection strength is sensitive to whether the thin steel sheet ply is buckling away from or toward the fastener head in some test series. Performance of the screw shear strength as per the standard's provisions is evaluated. The work is intended to provide critical missing information for CFS framed steel sheet sheathed shear walls for use in both simulation and design. [ABSTRACT FROM AUTHOR]

The work presented in this paper investigates the strength of moment-resisiting apex brackets of cold-formed steel portal frames. The results of two previously reported full-scale portal frame tests, where the frames failed through buckling of the apex bracket, were used to validate a finite element model that included material nonlinearity, geometric imperfections, and bolt bearing behaviour. From portal frame test results as well as the finite element results, the importance of appropriate detailing for the apex brackets for strength is demonstrated. A simplified finite element model of the apex bracket is then presented, again validated against previously reported experimental tests. The effects of geometrical parameters of the brackets, bolt-group configuration, and yield stress of brackets were investigated through a parametric study comprising 648 models. From the results of this parametric study, design equations are proposed that can be used by practicing engineers to predict the strength of apex brackets used for cold-formed steel portal frames. [Display omitted] • Validate the finite element model of full-scale portal frames. • Present a simplified finite element model of apex brackets. • Propose design equations to predict the strength of moment-resisting apex brackets. [ABSTRACT FROM AUTHOR]

• Extension of the Direct Design Method to stainless steel structures is presented. • Rigorous reliability framework is built for stainless steel structures. • Six stainless steel portal frames are analysed, covering different families. • Reliability indices are presented for different design frameworks under gravity loads. • System γ M , s and ϕ s factors are proposed for different target reliability indices. Current structural codes for steel and stainless steel structures such as AISC 360-16, AISC 370-21, AS/NZS 4100 and Eurocode 3 are based on the traditional two-step member-based design approach, in which internal actions are first obtained from a structural analysis, usually elastic, and the strength of each member and connection is subsequently checked using a structural design standard. However, the most recent versions of these standards already incorporate preliminary versions of the direct, or one-step , system-based design alternative, which is based on the design-by-analysis concept and allows evaluating the strength of structures directly from numerical simulations, although the standards in their current form do not provide reliability requirements for structural systems. Therefore, it is necessary to build a rigorous structural reliability framework to investigate acceptable target reliability indices for structural systems and to provide adequate system safety factors and system resistance factors. While this framework has been developed based on advanced Finite Element analysis for hot-rolled and cold-formed carbon steel structures in recent years in the form of the Direct Design Method (DDM), the framework does not exist for stainless steel structures. This paper presents an extension of the DDM to the analysis of stainless steel structures, in which system reliability calibrations are presented for six stainless steel portal frames under gravity loads covering the three most common stainless steel families and different failure modes using advanced numerical simulations. From the derived reliability calibrations, suitable system safety factors γ M , s and system resistance factors ϕ s are proposed for the direct design of stainless steel frames in the European, US and Australian design frameworks under gravity loads. [ABSTRACT FROM AUTHOR]

Light gauge steel frame (LSF) walls as primary load-bearing components have been increasingly used in the construction of cold-formed steel (CFS) buildings. Their fire safety has thus become an important consideration for designers. Currently, LSF walls made of lipped channel section (LCS) studs are commonly used in low-rise buildings, but with the expansion of CFS applications to mid-rise buildings, cold-formed steel square and rectangular hollow section (SHS/RHS) studs are being used to meet the higher load capacity demands. However, the fire resistance of LSF walls made of SHS/RHS studs has not been investigated yet, so their fire resistance levels (FRLs) are unknown, restricting their use in mid-rise buildings. Four full-scale load-bearing standard fire tests were therefore conducted to investigate the performance of cold-formed steel SHS/RHS stud walls exposed to fire. The test results showed that CFS SHS/RHS stud walls achieved a higher FRL due to the superior elevated temperature mechanical properties of CFS SHS/RHS, while the temperature development exhibited good similarity with uninsulated LCS stud walls of the same wall configuration. However, a different thermal behaviour was observed when SHS/RHS studs were used in cavity insulated walls, as the hollow cavity reduced the temperature difference between the stud hot and cold flanges. This eliminated the fire resistance reduction caused by thermal bowing deformations and provided an improved fire performance than cavity insulated LCS stud walls. This paper presents the details of the fire tests and the results. Unlabelled Image • Conducted full-scale standard fire tests of load-bearing cold-formed steel hollow section stud walls. • Provided detailed fire test results describing the fire performance of SHS/RHS stud walls. • Determine the fire resistance levels of four SHS/RHS wall configurations. • Compared the fire performance of walls made of SHS/RHS and conventional lipped channel studs. • Illustrated the benefits of using hollow section studs in cavity insulated walls. [ABSTRACT FROM AUTHOR]

Light-gauge structures framed with cold-formed steel (CFS) are considered a suitable alternative to the traditional hot-rolled or built-up steel framing as a primary structural system. Recently, CFS has been used as a lateral load resisting system in low- to mid-rise buildings. In this study, the seismic behavior of light-gauge CFS stud walls was evaluated through numerical modeling to investigate the failure modes, load capacities, initial stiffness, ductility ratio, and seismic response modification factor. Studies on different structural components of the light-gauge CFS stud wall were conducted. For framing members, different numbers of mid-field studs were considered. Moreover, the effects of adding blocking and the blocking locations were investigated by increasing their numbers along the wall height. As for the sheathing boards, different types of sheathing materials were investigated, including steel sheets, cement boards, and ferro-cement boards. Furthermore, sheathing openings with different configurations were studied. The numerical model results were verified against the results obtained from an experimental study conducted by the authors and reported in an associated paper. The results revealed that using steel sheathing could significantly increase the loading capacity, as well as the initial stiffness, whereas using cement board and ferro-cement board sheathing had adverse effects on the model behavior. However, models with cement board and ferro-cement board sheathing exhibited lesser instability in their framing members at the ultimate load in comparison with models with steel sheathing. Meanwhile, the presence of an opening in the sheathing resulted in significant reductions in the loading capacity and initial stiffness in comparison with their counterparts without sheathing openings. Unlabelled Image • Summary for existing experimental and numerical researches data regarding light-gauge CFS stud walls are provided. • Numerical models are prepared for full scale CFS stud walls. • Non-linear finite element analysis is performed under monotonic load. • Verification of the proposed FE models against existing experimental results as well as the experiment test results are illustrated. • Loading capacities, ductility ratio, initial stiffness and response modification factors for each model are provided. [ABSTRACT FROM AUTHOR]