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In this study, the structural performance of a new type of lightweight composite cold-formed steel and timber (CFST) flooring system has been investigated by conducting four-point bending tests on 13 specimens. A bare cold-formed steel system without timber sheathing was also tested to provide a benchmark response to which the strength and stiffness of the composite system were compared. This paper presents key findings on the flooring system's structural behavior and performance parameters, such as ultimate bending capacity, load-deflection response, load-slip response, and failure modes, by categorizing 13 specimens into four subgroups based on shear connector types and spacings. In the proposed composite CFST flooring system, 45-mm thick structural plywood panels were connected to the 2.4-mm thick cold-formed steel C-section joist using self-drilling screws, coach screws, and nuts and bolts. The performance of different types of shear connectors on the composite action is experimentally investigated and compared with the theoretical plastic section. Furthermore, the load-carrying capacity, effective bending stiffness, and deflection of composite CFST beams were computed theoretically using elastic theory and compared to experimental results, which showed good agreement. [ABSTRACT FROM AUTHOR]

To provide more suggestions for the anti‐fatigue design of cold‐formed steel, a series of high‐cycle fatigue tests are carried out on cold‐rolled steel sheets connected by self‐tapping screws and blind rivets in this paper. Subsequently, fatigue failure mode, fatigue strength, and fatigue damage are analyzed in detail. The test results show that all effective data points are below the S‐N curve of screws in the code. Meanwhile, the fatigue limit values of the fitted curves with 95% survival probability fall within the range of 0.3 to 0.67 times the specified value. Besides, the fatigue damage expansion rate of cold‐rolled steel sheets is less than the standard value. Through further discussion, it is noticed that metal grade has little influence on the fatigue performance, while thickness has a significantly positive influence on the shear resistance and fatigue performance. Moreover, the fatigue performance of the two connection types appears to be similar. Highlights: The base metal has little effect on the fatigue performance of cold‐rolled steel connections.Thickness raises the shear and fatigue performance of cold‐rolled steel connections.The fatigue performance of the two types of cold‐rolled steel connections is similar. [ABSTRACT FROM AUTHOR]

• A new type of CFS wall sheathed with paper straw board is proposed. • The characteristic values of the bearing capacity, lateral stiffness, ductility coefficient and energy dissipation coefficient of CFSSB wall are obtained. • Factors affecting the shear capacity of CFSSSB composite walls are investigated. • A design formula is proposed to predicting shear capacity of CFSSB walls. To explore the application of environmental protection material-paper straw board in cold-formed thin-walled steel (CFS) structures and further develop the sheathing system, an innovative CFS framing wall sheathed by paper straw board (CFSSB) is proposed. Eight CFSSB composite wall specimens and one CFS frame without sheathing were tested under monotonic and reversed cyclic horizontal loads to study the shear performance of the CFSSB composite wall. Also, the shear performance of the wall specimens can be obtained. The key parameters include the value of the vertical load and the form of the CFS frame in this experimental program. By analyzing the specimen's failure forms and failure process, the characteristic values of the bearing capacity, lateral stiffness, ductility coefficient and energy dissipation coefficient are obtained. The results show that the existence of paper straw board and adding diagonal braces to the CFS frame can significantly improve the shear capacity of CFSSB composite walls. The favorable seismic performance of the CFSSB composite wall was demonstrated in the experiment. In addition, a finite element model for CFSSB composite wall is developed using the software package ANSYS. The finite element analysis (FEA) results show a good agreement with the experiment results in terms of failure modes and skeleton curves, which verify the feasibility of the FEA model. Furthermore, extensive parametric analysis was carried out to analyze the factors affecting the shear capacity of the CFSSB composite wall. The FEA results show that the spacing of studs and self-tapping screws greatly influences the shear capacity of walls. Moreover, based on the failure of the screw connections, a formula for calculating the shear capacity of the CFSSB composite wall is proposed. The results of the formula calculation show good agreement with the experiment and FEA results, and it can provide a reference for engineering design. [ABSTRACT FROM AUTHOR]

This paper presents a design approach, the direct stiffness–strength method (DSSM), for the strength prediction of sheathed cold-formed steel (CFS) structural members. The DSSM considers each sheathing–fastener connection as a bracing point and incorporates its stiffness and strength in the CFS wall panel design. The DSSM is formulated and validated based on large experimental test results. The motivation for this work is to address research gaps in the latest American Iron and Steel Institute (AISI) standards for the sheathing braced design of CFS structural members. A total of 41 individual sheathing–fastener connection tests were carried out, including parameters such as four different sheathing board types (to account for the performance of different sheathing) and seven different dimensions of the CFS Z-sections (to account for the slenderness). A new set of expressions was formulated to predict the stiffness and strength of the individual sheathing–fastener connections (bracing points) based on the observations from tests. A design-oriented assessment (comparing the design results with full-scale wall panel test results) indicated that the expressions formulated for DSSM are appropriate for the use of sheathed CFS Z-section member design. Further, this study used a design example to demonstrate the appropriateness of the DSSM approach. Since the introduction of the sheathing braced design concept in conjunction with the direct strength method (DSM) established by the American Iron and Steel Institute in RP13-1, this approach has gained traction among researchers to further enhance it for the various failure modes of the CFS structural members. However, there is an inconsistency in the sheathing bracing design concepts of the AISI design standards. The proposed DSSM is a simple one; it considers each sheathing fastener connection as a bracing point and incorporates its stiffness and strength in the CFS wall panel design. This proposed DSSM can be completed in two steps by checking the bracing ability of the provided sheathing. The DSSM method can be used with any design specification for determining the moment capacity of the CFS member with the contribution of the sheathing board. The design steps involved in DSSM are demonstrated with flowcharts and a design example. The DSSM proved that use of sheathing boards can eliminate the additional steel bracings at the intermediate length and breadth of the CFS wall panels, but steel bracings are required at the building corners for stability. This design method can realize up to a 15% reduction in steel consumption in the CFS building construction. [ABSTRACT FROM AUTHOR]

This paper presents an improved design approach based on the direct strength method (DSM) in American Iron and Steel Institute (AISI) design specification S100 for cold-formed steel (CFS) built-up closed cross-section columns subjected to local, global, and local–global interaction buckling modes. Initially, the failure mode and load data corresponding to various design parameters such as intermediate fastener connection spacing, boundary conditions, material properties, slenderness, and cross sections from various researchers are collected, including the authors' test results. The design predictions using the current DSM design provisions are compared with the collected test results. The results show that the current DSM approach requires improvisation to adequately predict the axial compression load. The data are then analyzed to understand the behavioral features of the built-up closed cross-section column such as limit for interaction buckling, erosion of strength due to arrant interaction buckling, and increase in strength due to flange or web overlapping effect. The interpretation methods used to improve the current design approach are presented. The original DSM design procedure is improved by failure mode classification and modified slenderness to account for increase and erosion in strength. Finally, the safety (accuracy and reliability) of the design predictions from the improved DSM-based approach is assessed using the large amount of data collected. Since the introduction of the direct strength method to the North American Specification for the Design of Cold-Formed Steel Structural Members (AISI S100) in 2001, it has gained traction among design engineers due to its simplicity, advantages over other design methods, and specific design curves for individual buckling modes. To implement the DSM for CFS built-up members, several researchers have proposed different design approaches, and research is still happening. This study is also aimed toward the same objective but is specific to the local–global interaction in built-up members. It is demonstrated why the DSM prediction is unsafe for CFS built-up members with larger intermediate fastener connection spacing and excessively safe for CFS built-up members with closer intermediate fastener connection spacing. An intermediate fastener connection spacing limit that separates the local–global interaction buckling and element overlapping effect is determined. A design proposal for limiting the interaction buckling mode and considering the overlapping effect of elements in the DSM design method is suggested. More specifically, the proposed design method is in line with the current AISI approach so the designer need not confuse how to use this new design approach in practice. Therefore, for further ease of understanding, two design examples for built-up closed cross-section columns—(1) subjected to local–global interaction buckling; and (2) subjected to element overlapping effect—are included in this paper. It is also recommended that future research may focus on further classifying the AISI main specification sections, E2 and F2 (simple classifications based on the global failure modes), based on the interaction buckling modes in built-up cross-section members. [ABSTRACT FROM AUTHOR]

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]

This paper presents the development and background information of the web crippling design provision proposed for cold-formed stainless steel square and rectangular hollow sections (SHS and RHS) incorporated in the recently revised ASCE/SEI 8-22 Specification. The provision was derived based upon reliability requirements as regulated by the ASCE/SEI 8-22 using experimental data from the literature on cold-formed SHS and RHS of austenitic, ferritic, and austenitic-ferritic (duplex and lean-duplex) stainless steel types of various grades including UNS S30400, S30153, S43940, S40977, S32101, and S32202. The accuracy and consistency of the design provisions in the ASCE/SEI 8-22 and SEI/ASCE 8-02 specifications were compared. In addition, the possible extension of validity limits of the new ASCE/SEI 8-22 provision was assessed by utilizing additional finite-element results generated in this study as well as those reported in the literature. It is shown that the validity limits of the new provision could be further extended. Moreover, the direct strength method (DSM) proposed by the authors for web crippling design of cold-formed ferritic stainless steel SHS and RHS was evaluated to check its applicability to other stainless steel types and grades. A modified DSM with updated coefficients is proposed in this study using the format that in line with DSM for members in shear as per ASCE/SEI 8-22. It is shown that the modified DSM can provide well-predicted resistances for cold-formed stainless steel SHS and RHS undergoing web crippling. [ABSTRACT FROM AUTHOR]

The development of simple connection methods is necessary for increasing cold-formed steel (CFS) construction activities. A new splice connection concept for the CFS built-up column-to-column connections is presented in this paper. This simple connection concept will use the same size and shape of the geometry as the CFS built-up column, which will enable a quick erection process. The new splice connection configurations, arrangement, and installation methods for cold-formed steel construction are demonstrated. Twenty-eight experiments, which include four actual columns, two disconnected columns, and 22 columns with splice connections, are carried out. This paper examines the influence of various parameters of splice connections such as length, thickness, and number of fastener rows. The design strength of the actual column is determined using the direct strength method (with modified global and local slenderness approaches) and is compared with the results of the splice connected columns for adequacy. The force transfer mechanism and failure modes of splice connection components are demonstrated in the form of detailed sketches. The smaller length splice connections led to localized failures, while the longer splice connections enabled the uniform force distribution between the built-up column cross-sections. Finally, it is recommended that the splice connection configuration should be a minimum of 300 mm in length, the splice thickness should be equal to the CFS built-up cross-section, and two rows of fasteners for attaining the required design strength of the built-up column members. [ABSTRACT FROM AUTHOR]

Current design specifications for cold-formed steel incorporate the Direct Strength Method (DSM) to design cold-formed steel members under compression. Although the DSM has been used for quite some time, its buckling strength curves have not been experimentally assessed thoroughly. This study attempts to fulfill this objective. First, a thorough literature review was conducted to inspect the buckling strength curves in the DSM, and the issues are summarized in this paper. Second, experimental data associated with compression tests of 453 solid and 228 perforated cold-formed steel columns were collected from the literature. Design parameters (e.g., elastic critical buckling loads) of the columns were then determined and assembled with the experimental results in a database to be used as a source to assess the buckling strength curves in the DSM. Finally, the LRFD resistance factors (ϕc) of the DSM buckling strength curves were determined in accordance with the AISI S100. This paper highlights the level of accuracy of the buckling strength curves in the DSM. [ABSTRACT FROM AUTHOR]

This paper presents a numerical investigation on the residual stresses and co-existent equivalent plastic strains in cold-formed high-strength steel (CFHSS) circular hollow sections (CHS) by using an advanced finite element (FE)-based method. In this method, the entire manufacturing process of the CFHSS CHS was modeled numerically. The accuracy of the numerical predictions of equivalent plastic strains and residual stresses in the CFHSS CHS was verified by comparing the predictions with the existing test results of both the residual stress measurement and load-end shortening response of the stub column. By using the FE-based method, the effects of high-frequency electric resistance welding on the residual stresses and the stub column response were investigated. The through-thickness variations of both the equivalent plastic strains and residual stresses in CFHSS CHS, which are difficult to measure in the laboratory, were explored numerically. Finally, the effect of cold work (which is quantified by the equivalent plastic strains and residual stresses) on the stub column response of CFHSS CHS tubes was evaluated. It can be found that the equivalent plastic strains and longitudinal residual stresses are generally uniform around the cross-section of CFHSS CHS. The transverse and longitudinal residual stresses are generally uniform across each half-thickness, with the inner half-thickness under compression and the outer half-thickness under tension. The results also demonstrate that both the plastic strains and residual stresses may significantly affect the cross-section capacities of CFHSS CHS. [ABSTRACT FROM AUTHOR]

The cold-formed steel shear wall with steel sheathing has gained increasing popularity due to its excellent shear capacity. To extend the applicability of this system to multi-story residences, aside from experimental investigations on the shear walls, it is essential to conduct a comprehensive study on the seismic performance of buildings. In this paper, numerical simulations were conducted on specimens subjected to monotonic and cyclic loading. Subsequently, seismic analysis of mid-rise building models was also carried out to investigate the influence of the proposed shear wall on building seismic performance. The research findings indicate that this study's modeling method can effectively simulate the shear performance of the proposed shear wall under monotonic and cyclic loading. In addition, the proposed shear wall significantly enhances the structural stiffness and improves the seismic performance of the structure under seismic action. [ABSTRACT FROM AUTHOR]

This paper presents a test campaign concerning the structural behavior of cold-formed steel T-joints with semi-oval hollow section (SOHS) chord. Three different sizes of SOHS and nine different sizes of rectangular hollow sections (RHS) or square hollow sections (SHS) were employed as chord and brace members, respectively, to fabricate the T-joint specimens. Robotic gas metal arc welding was adopted to connect the RHS/SHS brace to the flat flange of SOHS chord. The width ratio between brace and chord (β) ranged from 0.29 to 0.96. The brace-to-chord thickness ratio (τ) ranged from 0.46 to 0.72, and the chord width-to-thickness ratio (2γ) ranged from 10.3 to 13.9. A total of 29 T-joint specimens were tested with the chord simply supported and the brace axially compressed. The joint failure strengths, load-deformation histories, and failure characteristics of cold-formed steel T-joints with a SOHS chord are presented and discussed. The behavior of T-joints with a SOHS chord resembled that of RHS/SHS T-joints because the brace was connected to the SOHS chord at the flat flange. The feasibility of the design provisions in current standards initially developed for RHS T-joints was examined. The comparisons demonstrate that the strength predictions by the current standards are quite conservative for T-joints with cold-formed steel SOHS chord. The possible reasons for conservatism in design strength predictions are analyzed and discussed. [ABSTRACT FROM AUTHOR]

Numerical investigation and design of cold-formed high-strength steel (CFHSS) diamond bird-beak (DBB) T- and X-joints are presented in this paper. The 0.2% proof stress of braces and chords was 960 MPa. Tests of CFHSS DBB T- and X-joints undergoing compression loads were carried out by the authors. The test results were used to develop accurate finite element (FE) models in this study. A comprehensive FE parametric study was then performed using the verified FE models. The nominal strengths predicted from the literature and European code were compared to the joint failure strengths and ultimate capacities of 244 DBB T- and X-joints specimens, including 224 FE specimens investigated in this work. The failure of DBB T- and X-joints specimens at chord crown locations was identified as the dominant failure mode. It has been shown that the design provisions given in the literature and European code are unsuitable and uneconomical for the cold-formed S960 steel grade DBB T- and X-joints investigated in this study. Hence, accurate, less dispersed, and reliable design equations are proposed in this work, using two design approaches, to predict the joint failure strengths and ultimate capacities of the investigated DBB T- and X-joints. [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]

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]

In the construction of steel structures, the two most common types of structural members are hot-formed and cold-formed members. This paper mainly describes the analytical and experimental research on the strength and characteristics of CFS bolted built-up sigma sections having different structural arrangements under bending. The cross-sectional dimensions for the parametric study were selected by the sizes available in the market. In this paper, ANSYS workbench software was used to perform FE modeling and observe the local, flexural, and interaction of these buckling. Then, experimental study was performed by varying the arrangement of open section beams between face-to-face and back-to-back, connected using bolts or fasteners different spacings. Further, we conducted bending tests on cold-formed steel built-up members having simple edge stiffeners in the middle. Comparing both analytical and experimental studies, the results indicate that the back-to-back connected built-up beam section provides a flexural capacity higher than the face-to-face built-up section. Moreover, increasing the bolt spacing enhanced the load-carrying capacity of back-to-back sigma section built-up beams. It has also been discovered that the flexural strength of beams is primarily determined by bolt spacing or itsposition. [ABSTRACT FROM AUTHOR]

This paper proposes damage index–based limit-state criteria for seismic design of midrise cold-formed steel (CFS) buildings instead of the drift-based ones, and the Park-Ang damage model was used to calculate the damage indexes. Two 5-story CFS buildings with different wall configurations were tested, and a test-validated numerical model was developed. An incremental dynamic analysis was conducted on a typical midrise CFS building to obtain the degradation parameter β of different CFS walls. The damage indexes computed from numerical analyses were compared with the damage indexes estimated from test observations and the proposed damage index–based limit-state criteria. The results showed that the calculated degradation parameter as well as the proposed damage index–based limit-state criteria are effective for seismic damage assessment and damage level classification of midrise CFS buildings according to the validations by shaking-table tests on two CFS buildings. The Park-Ang damage index used in this paper and the proposed limit-state criteria could be used for performance-based seismic design of midrise CFS buildings. [ABSTRACT FROM AUTHOR]

The possible failure modes of cold-formed steel (CFS) lipped angle (LA) compression members are yielding, local, flexural torsional, or flexural buckling, and any possible interaction among these buckling modes. In general, the strength estimated by current design guidelines are conservative for these members when flexural-torsional buckling (FTB) is the first global buckling mode because the postbuckling strength of this mode is not accounted for in the global buckling strength equations. The initial part of this paper reports the results of an experimental and numerical study of CFS-LA members undergoing independent FTB. Modifications are suggested to global buckling strength equations based on these results. Subsequently, the reduction in the ultimate strength from strength corresponding to independent buckling modes for LA members undergoing interaction between buckling modes such as local-flexural torsional, flexural-flexural torsional, local-flexural, and local-flexural torsional-flexural are studied systematically using finite-element analysis results. A simple and more accurate interaction equation that accounts for these interactions among buckling modes in CFS-LA compression members is proposed. [ABSTRACT FROM AUTHOR]

In this paper, the ultimate shear capacity of the 3-bolt cold-formed steel clip-angle between the cold-formed steel (CFS) beam and column is evaluated through 54 laboratory tests. A series of experiments were conducted by varying (1) thickness, and (2) aspect ratio (L/D) of clip-angles for different depths (D) and widths (A). The experimental program consists of three phases of tests: (1) Phase-I: direct shear load tests on clip-angle attached to a CFS column through 4.6-grade bolts; (2) Phase-II: CFS column replaced with a hot-rolled steel (HRS) column, since the CFS column experienced bearing failure in Phase-I; and (3) Phase-III: 10.9-grade bolts used instead of 4.6, as the 4.6-grade bolts subjected to bolt shear failure in Phase-II. Failure modes observed in the test specimens are (1) shear local buckling of clip-angle; (2) column bearing failure; (3) bolt shear failure; and (4) tear failure in clip-angle. Design shear equations from the literature, for the bolted clip-angle, were found to be inefficient for the high-grade steel (fy=375 MPa to 550 MPa), and conservative for the commonly available low-grade steel (fy=275 MPa). Hence a new shear strength equation is suggested for the clip-angle from the collated data of the present study and past research work. A comparative study between 2-bolt and 3-bolt clip-angle configurations was conducted to evaluate the increase in shear strength. Reliability studies were conducted, and corresponding resistance and safety factors were suggested for the design shear strength calculation corresponding to load and resistance factor design (LRFD), limit state design (LSD), and allowable strength design (ASD) methods. [ABSTRACT FROM AUTHOR]

The construction industry is on the lookout for cost-effective structural members that are also environmentally friendly. Built-up cold-formed steel (CFS) sections with minimal thickness can be used to make beams at a lower cost. Plate buckling in CFS beams with thin webs can be avoided by using thick webs, adding stiffeners, or strengthening the web with diagonal rebars. When CFS beams are designed to carry heavy loads, their depth logically increases, resulting in an increase in building floor height. The experimental and numerical investigation of CFS composite beams reinforced with diagonal web rebars is presented in this paper. A total of twelve built-up CFS beams were used for testing, with the first six designed without web encasement and the remaining six designed with web encasement. The first six were constructed with diagonal rebars in the shear and flexure zones, while the other two with diagonal rebars in the shear zone, and the last two without diagonal rebars. The next set of six beams was constructed in the same manner, but with a concrete encasement of the web, and all the beams were then tested. Fly ash, a pozzolanic waste byproduct of thermal power plants, was used as a 40% replacement for cement in making the test specimens. CFS beam failure characteristics, load–deflection behavior, ductility, load–strain relationship, moment–curvature relationship, and lateral stiffness were all investigated. The results of the experimental tests and the nonlinear finite element analysis performed in ANSYS software were found to be in good agreement. It was discovered that CFS beams with fly ash concrete encased webs have twice the moment resisting capacity of plain CFS beams, resulting in a reduction in building floor height. The results also confirmed that the composite CFS beams have high ductility, making them a reliable choice for earthquake-resistant structures. [ABSTRACT FROM AUTHOR]

A z-section purlin steel sheet is considered in this paper to understand its structural behavioragainst the wind uplift loading. Generally toUDL is considered for a practical & effectivedesign as main aspect of loading. A verylimited research is done on combined bendingand lateral torsional buckling, so it is importantto investigate the impact of combine loading onthe zsection which is partially restrained andapplied with uplift loading. In this to describelateral torsional behavior and bending, ananalytical model is developed for the z-sectionwhich is partially restrained. Thin walledclassical bending theory is used to derive thebending stress formula for the z-section. Thepresent developed analytical model thencompare with the Eurocode EN1993-1-3 modeland with FEA results. [ABSTRACT FROM AUTHOR]

This paper reports the experimental investigation conducted on unwrapped and latex wrapped cold-formed steel column. Various column cross-sections are subjected to repeated lateral loading till failure. All the columns were observed to fail in local buckling. The column cross-section dimension, provision of interior and exterior lip, and the latex wrapping of the columns influenced the lateral load to failure. Increasing the web length of a column section from 100 to 200 mm increased the load-carrying capacity of the column by 70 to 100 %. The local buckling was initiated in the flange portion of the column. The column section with no lip and interior lip exhibited inward buckling of the flange. The column with exterior lip exhibited outward buckling. The provision of lip and latex wrapping did not influence the initial loaddisplacement behavior of the columns. However, it increased the load-carrying capacity of the sections. Energy absorption index and ductility factor were calculated and the effect of latex wrapping of the columns on these parameters was evident. [ABSTRACT FROM AUTHOR]

In this paper, cold-formed steel C-shaped connectors, as one of the most commonly used components in steel wall/framing systems, were investigated under the pull-out failure modes using a detailed numerical study. Finite element models were validated using the data obtained from an experimental program; and the results were compared with the current design equations. Finally, a new pull-out strength equation was proposed based on the critical parameters affecting the behaviour of C-shaped connectors. In addition, initial bending stiffness of C-shaped connectors was studied using a simplified analytical approach; and the results obtained from the proposed new stiffness equation were compared with the initial slope of experimental and numerical force-displacement curves. These comparisons confirm the accuracy of the new strength and stiffness equations in order to apply to the analytical methods such as component-based method in future works. [ABSTRACT FROM AUTHOR]

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 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]

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]

Complementing a companion paper that summarizes the building global response and physical damage of a midrise cold-formed steel (CFS) framed building during an earthquake and postearthquake fire test program, this paper focuses on understanding the seismic behavior of the shear walls utilized in the building system during this test program. In contrast to shear walls tested in an isolated configuration, the shear walls within the full-scale test building were constructed and tested under real-world kinematic constraints and dynamic loading environments. The shear walls located at various planar and vertical locations of the test building were instrumented with a dense array of analog sensors to monitor the shear wall local responses. In this study, the shear wall local responses are correlated with the global responses of the building to advance understanding regarding the behavioral characteristics of individual shear walls and in particular the interactions of the shear walls as part of the lateral-load-resisting system. Important seismic design parameters are inferred from the measured building response using a parameter optimization strategy. Their implications associated with the seismic design of CFS wall-framed structural systems are discussed in relation to code provisions and design guidelines. [ABSTRACT FROM AUTHOR]

To advance understanding of the multihazard performance of midrise cold-formed steel (CFS) construction, a unique multidisciplinary experimental program was conducted on the Large High-Performance Outdoor Shake Table (LHPOST) at the University of California, San Diego (UCSD). The centerpiece of this project involved earthquake and live fire testing of a full-scale 6-story CFS wall braced building. Initially, the building was subjected to seven earthquake tests of increasing motion intensity, sequentially targeting service, design, and maximum credible earthquake (MCE) demands. Subsequently, live fire tests were conducted on the earthquake-damaged building at two select floors. Finally, for the first time, the test building was subjected to two postfire earthquake tests, including a low-amplitude aftershock and an extreme near-fault target MCE-scaled motion. In addition, low-amplitude white noise and ambient vibration data were collected during construction and seismic testing phases to support identification of the dynamic state of the building system. This paper offers an overview of this unique multihazard test program and presents the system-level structural responses and physical damage features of the test building throughout the earthquake-fire-earthquake test phases, whereas the component-level seismic behavior of the shear walls and seismic design implications of CFS-framed building systems are discussed in a companion paper. [ABSTRACT FROM AUTHOR]

The objective of this paper is to to ascertain the reliable mechanical properties of cold-formed Q345 steel at elevated temperatures while considerting the effects of tensile strain rate and specimen width. This paper presents an experimental study on the mechanical properties of cold-formed Q345 steel at temperatures ranging from 20°C to 800°C tested with two specimen widths and three tensile–strain rates, namely 0.06/min , 0.6/min , and 1.2/min. Tensile specimens were fabricated from a steel plate with a nominal thickness of 2.5 mm and tensile tests were carried out to determine the stress–strain relationship, yield strength, tensile strength, and elastic modulus. The test results showed that the tensile–strain rate has a maximum influence of 9% on yield and tensile strength at 600°C and the specimen width has a maximum influence of 14% on yield and tensile strength at 400°C. The maximum influence of the tensile–strain rate and specimen width on the elastic modulus is 18% and 12% respectively at 500°C. The necking phenomenon is less noticeable at temperatures below 300°C but is clearly observed at temperatures above 300°C. The comparison of the test results with predictions obtained from design standards (EC3, AISC, and AS4100) indicates a good agreement on the yield and tensile strength, but the magnitudes of elastic modulus obtained from the test are considerably higher than those obtained from the design standards. Based on averaged values of the test results associated with different tensile–strain rates and specimen widths, predictive equations were proposed to determine the mechanical properties of cold-formed Q345 steel at elevated temperatures. [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]

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 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]

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]

An innovative cold-formed steel center-sheathed shear walls (CFSCSSWs) was proposed in this paper to improve the horizontal load-carrying capacity of conventional cold-formed steel walls. However, the fire behavior of this wall configuration was particularly worthy of attention because it was designed to be used in multi-story buildings, and there is still a lack of in-depth exploration of the fire performance and high-temperature horizontal load-bearing capacity of CFSCSSWs under combined loads. In this study, a compression test was first carried out to obtain the vertical load-carrying capacity of a full-scale CFSCSSW, followed by a fire test on a similar CFSCSSW subjected to combined vertical and horizontal loads to investigate the fire behavior of walls. Then, a finite element model was established and validated by test results to investigate the influence of various critical factors, including vertical and horizontal load ratios, height-width ratio, and sheathing thickness, on the fire behavior of the CFSCSSW. The results showed that the vertical load ratio presented a larger influence on the fire behavior of CFSCSSWs compared to the horizontal load ratio. The increasing aspect ratio can slightly improve the fire resistance of the wall under the same load ratio. The wall with a 0.8 mm thick sheathing exhibits better fire behavior under the same load ratio. A high-temperature horizontal load-carrying capacity calculation method for CFSCSSWs was proposed, and its good accuracy was found. • Load capacity of cold-formed steel center-sheathed shear wall was investigated experimentally and numerically. • Parametric analysis was conducted to investigate the influence of key parameters on the fire behavior of the wall. • A method for predicting high-temperature horizontal load capacity of the wall was proposed. [ABSTRACT FROM AUTHOR]

Cold-Formed Steel Lipped (CFSL) channels are susceptible to a localized failure mechanism known as web crippling, triggered by concentrated loads or reactions applied to the web of the section. These loads induce buckling and distortion in the web, ultimately leading to the member's collapse. It is a challenging task to accurately determine the web crippling capacity of a CFSL channel due to its complexity and various influencing factors. This paper presents hybrid soft computing techniques for accurately predicting the web crippling capacity of CFSL channels subjected to two flange load cases. The developed soft computing techniques combine Artificial Neural Networks (ANN) with either Genetic Algorithms (GA) or Particle Swarm Optimization (PSO) to improve computational efficiency and accuracy. The finite element models of CFSL channels are developed and validated by experimental results and then employed to generate a database, which is used to train machine learning models, including ANN, GA-ANN, and PSO-ANN. Analysis is undertaken on the reliability of existing design formulas for determining the web crippling capacity of CFSL channels. It is shown that the PSO-ANN model outperforms the other models in terms of prediction accuracy. The existing design codes and formulas are not reliable in estimating the web crippling capacity of CFSL channels. However, the proposed model yields good correlation with finite element analysis results. A user- friendly graphical interface tool is developed for the practical design of cold-formed steel lipped channels. • FE model is developed that simulates the web crippling behavior of CFSL channels. • Hybrid ML models are developed for predicting web crippling capacity of CFSL channels. • Reliability of existing formulas for estimating web crippling capacity is investigated. • A user-friendly graphical interface tool is developed for design purpose. [ABSTRACT FROM AUTHOR]

This paper investigates the buckling behaviour and load-carrying capacity of G550 high-strength cold-formed steel multi-limb built-up section columns under axial compression. Each built-up section consists of multiple lipped and unlipped channel sections connected by self-tapping screws. The C3U1 section is formed by three C-sections (i.e. lipped channel section) and one U-section (i.e. unlipped channel section), while the C2U2 section is formed by two C-sections and two U-sections. The experimental programme involved tensile coupon tests, measurements of initial geometrical imperfection, and column tests on ten C3U1 and ten C2U2 multi-limb built-up section columns. The numerical modelling programme was then performed, with the nonlinear finite element models created and validated against the experimental results. The applicability of the codified Effective Width Method and Direct Strength Method for predicting the strengths of G550 high-strength cold-formed steel multi-limb built-up section columns, as specified in the American Specification and Australian Standard, was then evaluated. The evaluation results showed that the codified Effective Width Method led to rather conservative and less accurate failure load predictions for G550 high-strength cold-formed steel multi-limb built-up section columns, while the codified Direct Strength Method provided accurate and consistent failure load predictions and thus applicable to the design of G550 high-strength cold-formed steel multi-limb built-up section columns. Concerning the lack of design guidelines specifically for multi-limb built-up sections, a modified Direct Strength Method was thus proposed as an alternative design method and shown to provide accurate failure load predictions. • The structural performance of G550 high-strength CFS multi-limb built-up section columns was investigated. • 20 axial compression tests on G550 high-strength CFS multi-limb built-up section columns were conducted. • FE models were developed and validated against test results and then used for future analysis. • Codified design methods were evaluated for their applicability to G550 high strength CFS multi-limb built-up section columns. • A modified DSM was proposed as an alternative design method and shown to provide accurate failure load predictions. [ABSTRACT FROM AUTHOR]

This paper aims to explore the enhancement effect of spiral stirrup on concrete-filled cold-formed steel built-up box (CF-CFB) columns. Herein, four specimens were designed and fabricated to explore the impact of the spiral stirrup and riveted form on the axial compression performance of CF-CFB columns. Then, the finite element model of spiral stirrup-reinforced concrete-filled cold-formed steel built-up box (RCF-CFB) stub columns was established, and a systemic parametric investigation was conducted to explore the impact of geometric and material parameters on the compression performance of RCF-CFB stub columns. Afterwards, the analysis included an assessment of contact stress and stress distribution was conducted to uncover the confining effect. The analysis results revealed that the failure mode of the RCF-CFB column was tube buckling and concrete crush, accompanied by the spliced tube separating at the buckling area. The built-in reinforcement could significantly improve the performance of the built-up column, while riveted forms of spliced steel tubes had little effect. Furthermore, the axial bearing capacity of the RCF-CFB column would increase with the enhancement in steel yield strength, concrete strength, tube thickness, and longitudinal bar diameter. Finally, a calculating method to predict the axial bearing capacity of the RCF-CFB column was proposed, and the applicability of the method was demonstrated by comparison with experimental and FE data. • Compression tests were carried out on the performance of the concrete-filled cold-formed steel built-up box columns. • An analysis model of concrete-filled cold-formed steel built-up box stub columns was established and validated. • A practical method for predicting the axial compression load capacity was proposed. [ABSTRACT FROM AUTHOR]

This research paper presents a new flexural design approach for cold-formed steel (CFS) built-up sections failing in local buckling, developed following an extensive numerical investigation involving two novel closed built-up sections. At first, a finite element (FE) model using the widely adopted ABAQUS software was constructed and carefully validated against pertinent experimental data available in the literature. A comprehensive validation process which included comparing flexural strengths, deformed shapes, moment-curvature, and moment-displacement curves was performed. Afterwards, the validated FE model was extended to a numerical parametric investigation comprising of 108 simulations involving both three-point and four-point bending cases. Key parameters, including cross-sectional shapes, slenderness, and screw spacing, were varied primarily to facilitate the formulation of the novel design method. The outcomes of this investigation revealed that the current direct strength method (DSM) available in the North American Specifications (NAS) underestimated the bending strength, particularly for the ultra-thin sections. Considering this observation which is consistent with the findings of past research on similar cross-sections, a Generalised Direct Strength Method (DSM-G) was developed by introducing a new mathematical model, which differs from the traditional slenderness limit equations, instead relying on a conservativeness degree-based approach used for modifying the original DSM equations. The DSM-G method demonstrated a better accuracy in predicting the flexural strengths of different built-up sections (including the ones investigated by other researchers), all failing by local buckling. Moreover, the reliability of DSM-G equations was assessed, satisfying the prescribed threshold index limit suggested in NAS. A comprehensive set of guidelines, along with a design example for implementing the DSM-G method, has been presented to facilitate practical application. • FE investigation on novel CFS closed built-up sections is carried out. • Key parameters like cross-sectional profiles/sizes and screw spacing are varied. • Current DSM predictions of the novel sections are inconsistent. • A new mathematical model is proposed for a new generalized DSM (DSM-G). • DSM-G is reliable and is verified against results from current and previous studies. [ABSTRACT FROM AUTHOR]

Conventional cold-formed steel wall systems suffer from low lateral loading-carrying capacities and stiffnesses, which represent the main barrier to their use in multi-story buildings. To address it, a cold-formed steel center-sheathed shear wall (CFSCSSW) system with higher lateral load-carrying capacity and better lateral structural performance is proposed. This paper presents experimental, numerical, and analytical studies on the behavior of the proposed CFSCSSW subjected to combined vertical and horizontal loads. Firstly, a full-scale test was conducted, with the test setup, loading procedures and measuring instrument reported in detail. The obtained test results, including the load-carrying capacity, failure mode and strains, were fully analyzed. Then, finite element modeling was conducted to simulate the experimental observations, and parametric studies were carried out to investigate the influences of different geometric and loading parameters on the behavior of CFSCSSWs. Finally, a three-strip model with a variable position on end studs (TSM-VPC) was proposed for CFSCSSWs and shown to accurately simulate the direction of the tensile field within the sheathing and also resulted in high accuracy in calculating the load-carrying capacities, followed by a design example. ● An innovative cold-formed steel center-sheathed shear wall (CFSCSSW) system is proposed. ● A full-scale test on CFSCSSW under combined loading is conducted, with test results fully analysed. ● The influences of key geometric and loading parameters are investigated through parametric studies. ● A three-strip model is proposed for calculating the load-carrying capacity of CFSCSSW. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on the performance of cold-formed stainless steel built-up closed section stub columns. The built-up sections were composed by assembling two channel components at the flanges, which were brake-pressed from high-strength austenitic and duplex stainless steel thin sheets. Three types of built-up sectional profiles were formed by connecting two unstiffened channels (i.e., unlipped channels), two edge-stiffened channels (i.e., lipped channels) as well as one unstiffened channel and one edge-stiffened channel, respectively, using self-plugging rivets. Four sectional series were devised to cover nominal overall web height-to-plate thickness ratio values of 50, 60, 67 and 80. In order to obtain the actual material properties considering the cold-work effect, tensile coupon tests were carried out on both flat and corner longitudinal coupon specimens. In addition, a total of 29 fixed-ended stub columns including 19 specimens without holes and 10 specimens with circular web holes were tested under axial compression. The experimental results involving failure modes, ultimate capacities and responses of load versus axial shortening were obtained and fully documented. The effects of sectional profile types, overall web height-to-plate thickness ratio and hole diameter-to-overall web height ratio on the performance of cold-formed stainless steel built-up closed section stub columns were examined. Moreover, the appropriateness of design rules as prescribed in the recently updated American Specification ASCE/SEI 8–22 was evaluated. It was revealed that the codified design provisions generally provided unconservative strength predictions for the high-strength austenitic and duplex stainless steel built-up closed section stub columns both without and with circular web holes. Reliability analyses were performed in this study, and the compressive strength predictions of the built-up closed sections according to the existing design rules were found to be unreliable for the high-strength austenitic stainless steel stub columns without holes as well as the duplex stainless steel stub columns without and with circular web holes. • Compression behaviour of cold-formed stainless steel built-up closed sections was experimentally investigated. • Twenty-nine stub column tests having three built-up sectional profiles were carried out. • Resistances of stainless steel built-up closed section stub columns without and with circular web holes were both examined. • Codified design provisions as per ASCE/SEI 8-22 were assessed. • Reliability analysis was conducted to evaluate the applicability of current design rules. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on cold-formed steel rectangular and square hollow sections (RHSs and SHSs) with subsequent heat-treatment under combined compression and cyclic lateral loads. A total of 25 specimens designed with different parameters, including slenderness ratios (b/t and d/t) and axial load ratio (n) ranging from 0 to 0.5 were tested. Material tests were carried out to confirm the material ductility requirements stated in Eurocode being reached. Failure modes, moment-rotation curves, secant stiffness, energy dissipation and plastic hinge length presented were analysed. In addition, deformation capacity was evaluated in terms of maximum and ultimate rotations. The comparison results between plastic rotation limits proposed by design codes and the test results indicate that AISC 341-16 is more suitable for the design of cold formed hollow sections with moderate heat treatment under this investigation, though the recommended reduction factor of axial load might be conservative. • Cyclic behaviour of cold-formed hollow section with subsequent heat-treatment was investigated. • Twenty-five beam-column specimens were tested under axial load with monotonic and cyclic lateral load. • Secant stiffness and energy dissipation capacity were evaluated. • Comparison among test results and plastic rotation limits from current design codes. [ABSTRACT FROM AUTHOR]

Lightweight EPS materials (LEM)-filled cold-formed steel (CFS) shear wall structure is a new type of green, low-carbon and prefabricated rural residence, which has drawn in expanding consideration due to the promotion of the rural revitalization strategy. However, most of the existing research on this type of residence has focused on its behaviours of components, with little attention was paid to its overall response to resist earthquake disasters. During the past two decades, significant advancements have been made in effectively mitigating building collapses and reducing casualties resulting from earthquakes. Thus, the concept of seismic resilience is proposed, and the seismic performance requirements of structural design have been elevated from "safety" to "resilience". To analyze the seismic resilience of LEM-filled CFS residence, this paper proposed a strut and tie- equivalent spring model to establish the simplified analysis model of a single composite wall, and the precision of the model was confirmed by test results, in which the nonlinear characteristic and the supporting effect of fillers was considered. Subsequently, three LEM-filled CFS residences are designed using the direct displacement-based design method. Then the three-D models are established for nonlinear analysis, and the inter-drift ratio (IDR) and residual inter-drift ratio (RIDR) are adopted to estimate the seismic response of the three archetypes. The seismic resilience of the three archetypes are assessed based on FEMA P58. This paper would provide a guidance for the nonlinear analysis and seismic resilience assessment of this type of residences, and promote the application and popularization of this kind of residence. • A simplified equivalent model is proposed to analysis the seismic performance of LEM-infilled CFS shear wall. • Three LEM-filled CFS residences are designed using the DDBD method based on the calculated equivalent viscous damping. • The seismic resilience of the three archetypes are assessed based on FEMA P58. [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]

In recent years, the use of partially concrete-filled steel tubular (PCFST) columns has been considered due to their cost-effectiveness and reduction of structural weight in bridge piers and building columns. One of the critical discussions about these columns is their impact resistance. In this article, the dynamic response of hollow and PCFST columns with elliptical cross-section under simultaneous loading of static axial compressive load and lateral impact load is presented using finite element modeling in ABAQUS software (FEA). To ensure the accuracy of the numerical modeling, the analysis results are compared with the results of previous works. The effects of different parameters such as impact velocity, the height of the impact location, the impact direction, the impact block mass, the size and shape of the impact block are investigated in this paper. The results of the numerical analysis showed that the partially filled specimens had better performance than the hollow specimens. The changes in impact direction and impact block mass parameters have a significant effect on the failure of the columns, especially when they are under high impact velocity. Changing the impact velocity significantly affects the impact resistance of specimens. However, the size and shape of the impact block did not have a significant effect on the displacement of the column against the impact loading. [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]

Non-structural components contribute significantly to the lateral stiffness of a cold-formed steel (CFS) building structure, but are cumbersome to model explicitly in the structural analysis. They are therefore commonly ignored in a 3D structural analysis, and their benefits are lost to the design. This paper proposes an efficient modelling method that enables practical and accurate 3D elastic analysis of a multi-storey CFS building structure to study its lateral behaviour within the serviceability limit state. Each shear or gravity wall is represented by an equivalent shear modulus four-node orthotropic shell element, which incorporates the lateral stiffness (or flexibility) contributions of all components including sheathing, braces and fasteners as present in the wall. The equivalent shear modulus is determined from the experimental test of a representative wall panel, or from the analysis of a finely detailed finite element model of the panel. The resulting two-storey building model, which has much fewer degrees of freedom compared to conventional models, is verified against full-scale shake table test results with respect to the natural period, the peak storey drift and the peak floor acceleration at two different construction phases. This paper demonstrates that the proposed modelling method not only saves analysis time considerably through the drastic reduction of degrees of freedom, but also compares favourably against a published modelling method in terms of accuracy and modelling efforts. • Proposes a very efficient modelling method for 3D structural analysis of CFS buildings. • Accounts for the lateral stiffness contributions of non-structural components. • Significantly simpler and more accurate than existing methods. • Verified against independent shake table test results. • Leads to more efficient designs of cold-formed steel buildings. [ABSTRACT FROM AUTHOR]

In this paper we present an investigation of the impact of cold-formed steel channel section columns when subjected to an axial impact by a rigid impactor. The work involves both the numerical simulations and experimental tests. The former was done by using nonlinear finite element analysis method and the latter was done by using drop hammer tests. In the present finite element analysis, material nonlinearity, strain rate effect, initial geometric imperfection, and interactions between the impactor and column are considered. It is shown that the impact deformation of the channel-section column under the axial impact of rigid impactor can be characterized initially by its axially compressive deformation, followed by the localized bending deformation in the region where the geometric imperfection is large. The validation of the numerical results using the drop hammer test results demonstrates the appropriateness of the numerical model developed in the paper. • It presents original experimental data of axial impact tests of CFS channel section columns. • FE analysis is provided to simulate axial impact tests of CFS channel section columns under different impact velocities. • Initial geometric imperfection of CFS columns and uses strain rate-dependent elstoplastic stress-strain equation. • The results show that impact velocity significantly affects the final residual deformation of columns. [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]