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We explore, in this paper, the demands and behavior on fasteners supplying sheathing-based bracing of gravity loaded cold-formed studs and wall assemblies. The studies are carried out by shell finite element (FE) models, which are compared to analytical solutions and previously completed laboratory tests conducted by the authors. The connection between the sheathing and the stud should be able to develop enough resistance to restrain global buckling of the studs; therefore, special attention has to be given to the demands on these connections for design. Local buckling and stress concentrations may damage some connections and redistribution of forces should be ensured. Classical practice for determining fastener demand - i.e., the 2% rule - may be deficient. An analytical method developed for determining fastener demand is compared to the FE models presented in this paper; the analytical method results in a reasonable prediction of the fastener forces in wall studs. [ABSTRACT FROM AUTHOR]

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

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

In the field of structural engineering the design of cost efficient structures is highly important. This led to the development of cold-formed steel structures (CFS). An advanced CFS structure is introduced in this paper, which uses a special type of polystyrene aggregate concrete (PAC) as bracing material. This material has beneficial insulating and fire protection properties, which makes it a reasonable choice for residential buildings. An experimental programme was performed, to gain information on the flexural and axial behaviour of PAC-encased CFS elements and panels. Both unbraced and braced members were tested to gain information on increment of load-bearing capacity. Several different element sizes were used to be able to investigate the different stability failure modes (i.e. local, distortional and global). Results showed that PAC was able to restrain the global and distortional buckling modes of steel elements, thus providing “full bracing” in most practical cases. These results are introduced in two papers (Part I and II), detailing the failure modes, load increments and the effect of composite action. In this paper – Part II – the background and the results of compression tests are presented, and the bending experiments are detailed in Part I [1] . [ABSTRACT FROM AUTHOR]

In the field of structural engineering the design of cost efficient structures is highly important. This led to the development of cold-formed steel structures (CFS). An advanced CFS structure is introduced in this paper, which uses a special type of polystyrene aggregate concrete (PAC) as bracing material. This material has beneficial insulating and fire protection properties, which makes it a reasonable choice for residential buildings. An experimental program was performed, to gain information on the flexural and axial behaviour of PAC-braced CFS elements and panels. Both unbraced and braced members were tested to gain information on increment of load-bearing capacity. Several different element sizes were used to be able to investigate the different stability failure modes (i.e. local, distortional and global). Results showed that PAC was able to restrain the global and distortional buckling modes of steel elements, thus providing “full bracing” in most practical cases. These results are introduced in two papers (Part I and II), detailing the failure modes, load increments and the effect of composite action. In this paper – Part I – the background and the results of bending tests are presented, and the experiments on the compression elements are detailed in Part II [1] . [ABSTRACT FROM AUTHOR]

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

Drive-in storage racks, made of cold-formed steel, are the main racking system used in industry for storing goods. The storage space utilization of drive-in racks is high at the price of the weak downaisle stability. This paper presents a general analysis of the lateral stiffness of drive-in racks in the downaisle direction. A total of 24 static tests of drive-in rack systems have been conducted under singlepoint horizontal force. The effects of some constructional details, such as bracing configuration, cargo pallets, and the number of bays, are considered. The experimental results indicate that either top plan bracing or back-spine bracing can change the load transfer through rack structures and increase the lateral stiffness of racks. By acting as the horizontal bracings of adjacent columns and reinforcing the rotational stiffness of column bases, the stored pallets are also the beneficial factor for improving the lateral stiffness of racks. According to the special structural characteristic of tested racks, the simplified models and calculation formulas are proposed for the lateral stiffness of tested racks with bracings and without goods. To consider the influence of local deformations in bracing member connectors, sectional area-reduction factors of bracing members are introduced in the simplified calculation method. The lateral stiffness of a complete rack system can be used to determine the lateral horizontal restraint at the top of each rack column, which has large effect on the load-carrying capacity of columns in drive-in racks. In the last part of the paper, three drive-in rack examples with typical section properties and overall dimensions are presented to illustrate the computational procedure of horizontal deflection of drive-in racks. [ABSTRACT FROM AUTHOR]

The aim of this paper is to report an ongoing shell finite element investigation on the distortional post-buckling behaviour, ultimate strength and DSM design of cold-formed steel single-span lipped channel beams under elevated temperatures due to fire conditions. The beam ultimate strengths are computed by means of a steady-state loading strategy that consists of applying an increasing major-axis uniform bending moment to a beam under a uniform and constant (elevated) temperature distribution, until failure is reached. The steel constitutive law at elevated temperatures is simulated by means of the stress–strain–temperature models prescribed in EC3-1.2 for cold-formed steel. The materially and geometrically non-linear response of the cold-formed lipped channel beams is determined through ANSYS shell finite element analyses that incorporate critical-mode (distortional) initial geometrical imperfections. Finally, since there are no specific rules to predict the bending strength of cold-formed steel beams failing in distortional modes at elevated temperatures, the above failure moments and temperatures are used to establish preliminary guidelines for the design of cold-formed steel lipped channel beams under fire conditions. The approach followed is based on the Direct Strength Method (DSM) and has been already employed by other researchers – the currently available design/strength equations/curves, developed for ambient temperature, are modified to account for the appropriate Young’s modulus and yield stress reductions due to the temperature increase. The results presented in the paper provide solid numerical evidence that the currently codified DSM distortional strength curve is not appropriate to predict beam failure moments at elevated temperatures. This is because it either (i) does not account for the material non-linearity due to the elevated temperature (low-to-moderate slenderness range) or (ii) is already inadequate to predict room temperature failure moments (unsafe estimates obtained in the high slenderness range). [ABSTRACT FROM AUTHOR]

The paper reports the results of a numerical investigation on the relevance of web-triggered local–distortional interaction on the ultimate strength of a large number of cold-formed steel fixed-ended (plain) lipped channel, zed, hat and rack-section columns. These results concern columns with various geometries (cross-section dimensions and unrestrained length) and yield stresses, ensuring a wide variety of combined ratios between the (i) distortional and local critical buckling stresses ( R DL ) and (ii) yield and non-critical buckling stresses ( R y ). To avoid interaction with global buckling, all columns have global critical buckling stresses much higher than their local, distortional and yield counterparts. The aim of this study is to identify combinations of these ratios for which L–D interaction is relevant, in the sense that it affects visibly the column elastic and elastic–plastic post-buckling behaviours, ultimate strength and failure mechanism – special attention is devoted to the ultimate strength erosion. The numerical ultimate strength data obtained are then compared with the predictions of (i) the currently codified DSM (Direct Strength Method) strength curves for the design of columns failing in local and distortional modes and (ii) available DSM-based design approaches specifically developed to handle local–distortional interactive failures. Then, experimental results available in the literature concerning lipped channel and rack-section columns failing in local–distortional interactive modes are used to assess the quality of the estimates provided by the DSM-based design approaches. Finally, the paper closes with some considerations on the design of cold-formed steel columns undergoing L–D interaction. [ABSTRACT FROM AUTHOR]

This paper is based on an investigation into the performance of cold-formed C-channels stiffened with cover plates and subjected to pure bending and primarily shear condition tests. Cover plates with three different thicknesses (1.6, 2 and 2.4 mm) were installed at top flanges only as it would be the predicted location for local and distortional buckling. The local and distortional buckling capacities were evaluated via Direct Strength Method, DSM, in accordance with AISI 2007. The accuracy of the interaction equation between the required flexural strength, M , and the required shear strength, V , prescribed by AISI 2007 was also investigated in this paper. A nonlinear finite element model was developed and verified against the test results in terms of maximum strength and buckling failure modes. The results explicitly showed that by attaching the cover plate on top flanges, the non-dimensional slenderness decreased resulted in improved buckling capacities, where the nominal flexural moment of sections, M n , were close to the plastic moment, M P . Besides, it was concluded that the interaction equation between M and V predicted by AISI was conservative for sections with small non-dimensional slenderness values. [ABSTRACT FROM AUTHOR]

This paper presents a non-linear finite element analyses in order to investigate the seismic performances of steel sheathed cold formed shear walls. The numerical models presented here are verified based on experimental tests considering different structural characteristics including: material nonlinearity, geometrical imperfection, residual stresses and perforations. A comparison between the numerical simulations and the test results shows a good agreement proves that the finite element analysis can be used effectively to predict the ultimate capacity of steel sheathed CFS shear panels. A total of 15 models with different structural parameters are investigated. Of particular interests were the specimens' maximum lateral load capacity and deformation behaviour in addition to a rational estimation of the seismic response modification factor. Preliminary conclusions presented in this paper, refer to the seismic characteristics of steel sheathed CFS shear walls and the corresponding dimensions and configuration. [ABSTRACT FROM AUTHOR]

Nowadays, cold-formed constructions are being used more frequently on construction sites because of the good strength-to-cost ratio. However, insufficient studies are published examining the properties of these constructions. This paper investigates the behaviour of bolted gusset-plate joint since it is one of the easiest ways to connect a beam to a column. The paper presents analytical calculations using the component method and experimental test results. The joint was investigated using the mechanical model of three springs. The mechanical model for the calculation of bolt group stiffness was created according to Eurocode 3 Part 1–8 Stiffness formulations (EN 1993-1-8 2005) (originally, it is recommended for elements that are 4 mm and thicker). The technique for the calculation of the stiffness of a gusset plate is presented. The strength of the joint was calculated using the technique introduced in Eurocode 3 (EN 1993-1-8 2005; EN 1993-1-1 2005; EN 1993-1-3 2006; EN 1993-1-5 2006). [ABSTRACT FROM AUTHOR]

Geometric imperfections play an important role in the strength and behavior of thinwalled metal parts such as those commonly used in cold-formed steel construction. The objective of this paper is to detail a newly developed imperfection measurement platform, where the full-three dimensional (3D) imperfect geometry of a cold-formed steel member can be measured and reconstructed with reasonably high throughput and sufficient accuracy to explore all relevant imperfections. The measurement platform is composed of a two-dimensional laser sensor mounted on rotary and linear stages. Specimens are placed within a rotary ring and along a reference beam. The linear stage provides a means to scan the length of the specimen and the rotary stage a means to scan from any angle. Control of the custom linear and rotary stages are detailed in the paper, and corresponding control accuracies are studied. A procedure for registering the individual scans into the complete 3D model reconstruction (point cloud) is provided by specific calibration tests, from which rotation and translation quantities can be found to transform surfaces measured in local coordinates to a universal global coordinate system. A variety of different imperfection quantities, from basic dimensions and out-of-plane deviations to more advanced spectral and modalbased imperfection magnitudes may be rapidly processed from the 3D model. Accurate understanding of geometric imperfections is critical to the long-term success of analysis-based design paradigms for cold-formed steel constructions. The apparatus detailed herein will be used to provide a broad suite of imperfection information to assist in these new efforts. [ABSTRACT FROM AUTHOR]

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

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

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

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

Full-scale shake table investigations are strongly required to understand the actual performance of storage racks and to improve the rack design guidelines. This paper presents the results of full-scale shake table tests on New Zealand standard storage rack frames with two-bay and two-level to determine the dynamic characteristics of a standard rack structure and to measure the damping of the system. The experimental program was conducted in three phases. First, the identification parameters including the natural frequency and damping of the system were determined through a series of preliminary tests. Then, shake table tests were performed to capture the inelastic response of rack frames under low to medium intensities of El-Centro ground motion. Finally, the shake-table tests were repeated with scaling down the time domain and broader ranges of ground motion intensities to consider the performance of taller rack systems. In addition, a comprehensive discussion on the damping of the system is also provided based on the test results. The performance of the rack frame is described through an extensive set of measurements, including rack displacement, pallet sliding, the acceleration of a concrete block and rack frame and the damping of the system in the down-aisle direction. The results indicate that the standard rack frames are able to endure large inelastic deformations without loss of stability. [ABSTRACT FROM AUTHOR]

Globally, cold-formed steel (CFS) construction is gaining popularity as an alternative to traditional methods of construction. However, there is a need for robust design specifications for each structural component and material used in the CFS construction practice. One material that is largely being used in the CFS construction process is the sheathing board for wall panel construction. However, as per the authors' knowledge, there is no consistent criteria or specification for the selection of the sheathing board used in the construction. Besides, there are also no guidelines on parameters to be considered while selecting the sheathing material. Therefore, this paper aims to provide suggestions to select the appropriate sheathing based on the purpose and application of the sheathing. The interdependent parameters that influence the failure of the sheathing board connections such as type of screw, presence of washer, number of sheathing screw connections, edge/end distance, the failure mode of the wall frame studs, and geometry of the frame studs are discussed in the present study. The failure characteristics of four different sheathing boards are examined with the interdependent parameters. In addition, four different screw types are examined for better holding capacity and desired mode of failure. Furthermore, the suitability of existing recommendations for sheathing board requirement and installation methods are investigated. The suggested selection criteria for the sheathing boards are based on the various failure modes observed and the practical issues encountered in the CFS frame construction. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on the shear behaviour of the steel framing system using a perforated section. The perforated steel section has a lower volume of steel, which causes the weight to decrease and lead to lower construction costs. However, perforation in steel will decrease the shear resistance of the steel framing system. The objective of this study was to investigate the shear behaviour of the perforated steel section comparing to the unperforated section in the steel framing system. Critical shear loading from a common steel framing system was obtained using Staad Pro software according to Eurocode Standard. Finite element analysis was performed and the structure capacity results were compared by using eigenvalue. Comparison were made between perforated sections and unperforated section in term of shear capacity and percentage of volume reduction. Perforation steel section with 8 diamond openings was selected with the percentage of shear buckling capacity difference from an unperforated section about 33.02% and 48.18% with circle openings. Shear buckling capacity reduced with the increasing number of web openings. Edge distance also affected the shear behaviour of plain channel section with web openings. [ABSTRACT FROM AUTHOR]

This paper describes an experimental and numerical investigation on the stub column behavior of cold-formed high-strength steel (HSS) circular hollow sections (CHSs). A total of 16 stub column specimens fabricated from Q460, Q690, and Q960 steel plates were tested. Axial load-end shortening responses and failure modes of the stub column tests are presented and discussed. Nonlinear finite-element (FE) models were developed to replicate the stub column tests and subsequently employed to carry out comprehensive parametric studies to further examine the local buckling behavior considering various slenderness values and steel grades. The FE results were used together with experimental results to evaluate the applicability of current codified design methods in Eurocode, North American codes, and Australian standards to cold-formed HSS CHS stub columns. On the basis of the evaluation results, a new form of cross-sectional slenderness limit and a new set of design equations for more efficient designs were proposed and subsequently verified by means of statistical and reliability analyses. [ABSTRACT FROM AUTHOR]

To take full advantages of the bamboo and cold-formed thin-walled steel, a new type of box section beam combined with bamboo and steel channel was proposed in this paper. Five composite beams with different parameters were tested to evaluate the effects of bamboo plywood thickness of composite beams and thickness and sectional dimension of steel channel. The results of experiment showed that the proposed composite beams exhibited excellent flexural bearing capacities and stiffness. The increase of bamboo plywood thickness and sectional dimension of steel channel could improve bearing capacity and flexural stiffness of composite beams, while the increase of steel thickness could enhance the bearing capacity and safety margin of composite beams. Furthermore, a new method to predict the deformation and bearing capacities of composite beams was proposed and matched well with the experimental results. [ABSTRACT FROM AUTHOR]

The behavior and design of hot-rolled and cold-formed steel square and rectangular hollow section (SHS and RHS) columns, made of both normal- and high-strength material, are addressed in this paper. A series of experiments on hot-rolled high-strength steel SHS columns was first conducted—six tests on S690 SHS 100×100×4 columns and six tests on S770 SHS 120×120×6.3 columns were performed. Finite-element (FE) models were developed to replicate the experimental results and to carry out parametric studies to expand the column buckling data pool. The accuracy of the European and North American buckling design rules for normal- and high-strength steel SHS and RHS columns was evaluated through comparisons with the freshly generated test and FE results, as well as with existing test data collected from the literature. Finally, a modified approach was proposed and statistically verified in accordance with existing standards; the new approach features an imperfection factor that is a continuous function of yield strength, reflecting the reducing relative influence of residual stresses and global imperfections with increasing steel grades. Improved consistency in resistance predictions over the existing design provisions is demonstrated across a wide range of steel grades and relative slenderness values. [ABSTRACT FROM AUTHOR]

Summary: Vibration‐based structural identification is an essential technique for assessing structural conditions by inferring information from the dynamic characteristics of structures. However, the robustness of such techniques in monitoring the progressive damage of real structures has been validated with only a handful of research efforts, largely due to the paucity of monitoring data recorded from damaged structures. In a recent experimental program, a mid‐rise cold‐formed steel building was constructed at full scale atop a large shake table and subsequently subjected to a unique multi‐hazard scenario including earthquake, post‐earthquake fire, and finally post‐fire earthquake loading. Complementing the simulated hazard events, low‐amplitude vibration tests, including ambient vibrations and white noise base excitation tests, were conducted throughout the construction and the test phases. Using the vibration data collected during the multi‐hazard test program, this paper focuses on understanding the modal characteristics of the cold‐formed steel building in correlation with the construction and the structural damage progressively induced by the simulated hazard events. The modal parameters of the building (i.e., natural frequencies, damping ratios, and mode shapes) are estimated using two input–output and two output‐only time‐domain system identification techniques. Agreement between the evolution of modal parameters and the observations of the progression of physical damage demonstrates the effectiveness of the vibration‐based system identification techniques for structural condition monitoring and damage assessment. [ABSTRACT FROM AUTHOR]

Purpose: In this work, a numerical algorithm is presented for stability analysis of cold-formed steel (CFS) channel sections. Design/methodology/approach: A nonlinear optimization problem is formulated using energy-based technique of idealized channel section subject shear, compression and biaxial bending. The total potential energy is minimized with respect to skew angle and half wavelength of the buckling mode. The optimization algorithm is updated sequentially using quadratic approximation until minimum buckling coefficient is attained. The developed algorithm is validated using other numerical techniques. Findings: The described algorithm is computationally effective and can be utilized in the industry for analysis of CFS channels under any load combination. Practical implications: The paper offers a new tool for engineers in practice to analyze channels subject to combined loadings. Originality/value: Very limited literature dealt with the stability of channels under combined loading. A new numerical algorithm is provided to practitioners to utilize in the industry for analysis of channel sections under combined loading. Unlike finite element or finite strip methods, the channel is not discretized into subelements. Mathematical programming technique is used to find the buckling load. Parametric studies are then carried out to highlight influences of geometric interaction of the channel components and to provide useful guidance to the design of CFS channels. [ABSTRACT FROM AUTHOR]

This paper investigates the ultimate capacities of domestic cold-formed stainless steel square and rectangular hollow sections (SHS and RHS) undergoing web crippling. The finite element (FE) software Abaqus was employed during the investigation. It verifies the validity of FE models against experimental results available in the literature and performs an extensive parametric study comprised of 224 FE analyses to obtain the web crippling capacities of cold-formed stainless steel SHS and RHS, considering various materials, cross-sectional dimensions, bearing lengths and loading conditions in the parametric study. Based on the obtained FE results, the applicability of existing web crippling design provisions to domestic cold-formed stainless steel SHS and RHS is evaluated. The results indicate that the technical code of cold-formed steel structures (exposure draft) cannot be used for the studied cold-formed stainless steel SHS and RHS. On the other hand, it is shown that the American Specification SEI/ASCE 8-22 and proposed direct strength method (DSM) can lead to safe and accurate design predictions. Therefore, the SEI/ASCE 8-22 and DSM can be used to predict the capacities of domestic cold-formed stainless steel SHS and RHS undergoing web crippling.

Cold-formed steel (CFS) is a popular form of construction in New Zealand and the developed world because it can be cost-effective, durable, sustainable, resilient to extreme environmental and seismic loads and easy to install. When used in domestic and medium-rise buildings, T-Stub connection between CFS channel sections is formed by using self-drilling screws which connect the flanges. In the literature, no prior investigation on the tension capacity of such connection has been reported. Therefore, this paper describes a novel test procedure for determining the tension capacity of such CFS T-Stub connection and the associated mechanism of failure. An experimental test program that comprises thirty experimental tests is reported in this paper. Three channel section thicknesses were examined: 0.55 mm, 0.75 mm, and 0.95 mm. All specimens failed as a result of tilting of the screws and bearing failure. Non-linear elasto-plastic finite element (FE) models were developed, and the predictions were validated against the experimental test results. It was adjudged that there was reasonable agreement in terms of connection strength and failure mode prediction. Finally, the design strengths derived from current design standards were compared with the experimental failure loads. It was found that the American Iron and Steel Institute (AISI 2016) and Australian and New Zealand Standard (AS/NZS 2018) are conservative by 6% and unconservative by 10% for the initial and final failure loads of T-Stub CFS connections, respectively. • A novel cold-formed steel T-stub connection was studied experimentally and numerically. • The results of a total of 30 new experimental tests were reported. • Finite element analysis was conducted and validated against the test results. • The prediction accuracy of current design standards was evaluated. [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 presents a finite strip program CUFSM used to calculate and analyze the elastic distortional buckling of cold-formed thin-walled steel flexural members with stiffeners in the flange, which has different sectional geometric parameters. According to the classical buckling stress formula, the distortional buckling coefficient of the flange can be calculated so as to analyze the influence of changed sectional geometric parameters on it. On this basis, this study provides a simplified formula of distortional buckling stress to calculate 40 members with different sections which are selected from the Technical Code of Cold-Formed Thin-Wall Steel Structures of China but not contained in this paper. Compared with the analysis results of CUFSM, it shows that the two simplified formulas have quite high accuracy and wide applicability for general members provided by the specification. So it is suggested that they can be used for engineering design and standard revision. [ABSTRACT FROM AUTHOR]

This paper presents the seismic performance of two types of cold-formed steel wall systems as characterized during a full-scale five-story building shake table test program: (1) an exterior architectural façade, which spanned the lower three levels of the building, and (2) interior partition wall systems distributed at all levels of the building. The test building was subjected to a suite of earthquake input motions of increasing intensity, first while the building was isolated at its base, and subsequently while it was fixed to the shake table platen. This paper presents the observed physical and measured responses for the two cold-formed steel wall systems and in particular associates physical damage states with measured drift demands in the building. The tests illustrate damage mechanisms for cold-formed steel wall systems when used in architectural façades and highlights areas that should be given particular consideration during seismic design. [ABSTRACT FROM AUTHOR]

Light gauge Steel Frame (LSF) walls are extensively used in the building industry due to the many advantages they provide over other wall systems. Although LSF walls have been used widely, fire design of LSF walls is based on approximate prescriptive methods based on limited fire tests. Also these fire tests were conducted using the standard fire curve (ISO 834-1, 1999 [1] ) and the applicability of available design rules to realistic design fire curves has not been verified. This paper investigates the accuracy of existing fire design rules in the current cold-formed steel standards and the modifications proposed by previous researchers. Of these the recently developed design rules by Gunalan and Mahendran (2013) [2] based on Eurocode 3 Part 1.3 (EN 1993-1-3, 2006 [3] ) and AS/NZS 4600 (Standards Australia (SA), 2005 [4] ) for standard fire exposure (ISO 834-1, 1999 [1] ) were investigated in detail to determine their applicability to predict the axial compression strengths and fire resistance ratings of LSF walls exposed to realistic design fire curves. This paper also presents the fire performance results of LSF walls exposed to a range of realistic fire curves obtained using a finite element analysis based parametric study. The results from the parametric study were used to develop a simplified design method based on the critical hot flange temperature to predict the fire resistance ratings of LSF walls exposed to realistic fire curves. Finally, the stud failure times (fire resistance rating) obtained from the fire design rules and the simplified design method were compared with parametric study results for LSF walls lined with single and double plasterboards, and externally insulated with rock fibres under realistic fire curves. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation on behaviour and design of built-up cold-formed steel section battened columns. The built-up columns were pin-ended and consisted of two cold-formed steel channels placed back-to-back at varied spacing of intersection. The two channels were connected using batten plates, with varying longitudinal spacing. The cold-formed steel channel sections were manufactured by brake-pressing flat strips having a plate thickness of 2 mm. The built-up cold-formed steel section battened columns had different slenderness and geometries but had the same nominal length of 2200 mm. The column strengths, load–axial shortening, load–lateral displacement and load–axial strain relationships were measured in the tests. In addition, the failure modes and deformed shapes at failure were observed in the tests and reported in this paper. Overall, the built-up column tests provided valuable experimental data regarding the column behaviour that compensated the lack of information on this form of construction as well as used to develop nonlinear 3-D finite element models. The column strengths measured experimentally were compared against design strengths calculated using the North American Specification, Australian/New Zealand Standard and European Code for cold-formed steel columns. Generally, it is shown that the specifications were unconservative for the built-up cold-formed steel section battened columns failing mainly by local buckling, while the specifications were conservative for the built-up columns failing mainly by elastic flexural buckling. [ABSTRACT FROM AUTHOR]

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

This paper presents an assessment on the current yield slenderness limits under axial compression for cold-formed and built-up high strength carbon and stainless steel hollow sections. The definition of high strength steel in this paper refers to the materials with nominal yield strength or 0.2% proof stress which is greater than 700 MPa (Eurocode 3: Part 1-12) for carbon steel and greater than 480 MPa (Eurocode 3: Part 1-4) for stainless steel. A total of 147 stub column experimental results was compiled and assessed. Companion 46 finite element simulations were performed in this study and the results concurred with the experimental observations. The structural performance data showed that the current slenderness limits adopted in Eurocode 3, American and Australian Standards for both carbon and stainless steel under axial compression can be safely adopted for the high strength steel counterparts. New slenderness parameters and limits were also proposed to improve the design efficiency. [ABSTRACT FROM AUTHOR]

In this paper attention is focused on the uprights, i.e. vertical elements of the skeleton frames of steel storage rack systems. Their response is quite difficult to predict because of the significant influence of the interaction between local, distortional and overall buckling phenomena, owing to the presence of open mono-symmetric thin-walled cold-formed cross-sections. As a consequence, very high engineering competences are necessarily required to guarantee relevant load carrying capacities with structural systems of extremely limited weight and of very modest costs. Design provisions admit few alternatives, leading to different sizes and weight of the racks and, as consequence, to different degrees of economic competitiveness on the market. In the framework of a more general research project on steel storage rack structures, three options of designing the uprights in Europe have been investigated in the present paper. Several cases from practice have been selected, which comprise of uprights differing for cross-section geometry, slenderness and load conditions. A suitable finite element program for academic use characterized by a refined beam formulation capable of capturing key features of uprights has been used to model the elastic buckling interaction between the axial load and the bending moment. Non-negligible differences have been detected for what concerns the admitted design approaches in terms of beam–column load carrying capacity; furthermore, the direct comparison of the research outcomes offers practical indications for an optimal use of the material in accordance with the required safety standards. [ABSTRACT FROM AUTHOR]

This paper reports the results of an investigation on the structural behaviour and Direct Strength Method (DSM) design of cold-formed steel columns affected by local–distortional coupling interaction, aimed at extending findings unveiled earlier for lipped channels to other cross-section shapes, namely, hat, zed and rack-sections. Following a brief presentation of the most relevant aspects concerning the post-buckling behaviour and strength of columns with those cross-section shapes and identical local and distortional critical buckling stresses, the paper addresses the assembly of a significant column ultimate strength data bank, concerning fixed-ended hat, zed and rack-section columns undergoing strong local–distortional interaction and exhibiting several geometries (cross-section dimensions and lengths) and yield stresses. Then, these ultimate strength data are used to assess the performance of the existing DSM approaches to design columns against local–distortional interactive failures. It is shown that a novel DSM design approach, recently developed and validated in the context of cold-formed steel fixed-ended lipped channel columns affected by local–distortional interaction, can also be successfully applied to hat, zed and rack-section columns under the same circumstances ( i.e. , exhibiting similar interactive failures). [ABSTRACT FROM AUTHOR]

The objective of this paper is to present constrained optimization results for a cold-formed steel (CFS) cross-section shape with maximum axial capacity. In the authors׳ previous work unconstrained shape optimization was performed via stochastic search and gradient-based algorithms. Unconstrained shape optimizations produced a significant capacity increase, more than 140%, above standard CFS cross-sections, but many of the solutions are highly unconventional and have potential limitations both with respect to end use (e.g. attaching boards for walls and floors) and cost of manufacturing. Column capacity is determined using the Direct Strength Method (DSM) which requires inputs for the local, distortional and global critical buckling loads. These critical loads are obtained using the finite strip method, as implemented in the open source software CUFSM, which allows essentially any potential cross-section to be evaluated. To advance the applicability of the optimized results, end-use constraints and manufacturing constraints on the number of rollers employed in forming were both successfully incorporated in the shape optimization presented in this paper, resulting in optimized cross-sections that are more practical and economical with only marginally decreased capacity (usually less than 10%) from the earlier unconstrained optimized solutions. The constraints are implemented within a simulated annealing (SA) algorithm for the optimization. Optimized sections from multiple runs show uniformity, partially indicating the robustness of the final optimized shapes. The implemented constrained shape optimization provides a thorough search with high computational efficiency. The optimized cross-sections from this research provide promising potential shapes for the development of new commercial product families, and the member-level optimization methodology can also be integrated into building optimization in the future. [ABSTRACT FROM AUTHOR]

Current design rules for the member capacities of cold-formed steel columns are based on the same non-dimensional strength curve for both fixed and pinned-ended columns at ambient temperature. This research has investigated the accuracy of using current ambient temperature design rules in Australia/New Zealand (AS/NZS 4600), American (AISI S100) and European (Eurocode 3 Part 1.3) standards in determining the flexural–torsional buckling capacities of cold-formed steel columns at uniform elevated temperatures using appropriately reduced mechanical properties. It was found that these design rules accurately predicted the member capacities of pin ended lipped channel columns undergoing flexural torsional buckling at elevated temperatures. However, for fixed ended columns with warping fixity undergoing flexural–torsional buckling, the current design rules significantly underestimated the column capacities as they disregard the beneficial effect of warping fixity. This paper has therefore recommended the use of improved design rules developed for ambient temperature conditions to predict the axial compression capacities of fixed ended columns subject to flexural–torsional buckling at elevated temperatures within AS/NZS 4600 and AISI S100 design provisions. The accuracy of the proposed fire design rules was verified using finite element analysis and test results of cold-formed lipped channel columns at elevated temperatures except for low strength steel columns with intermediate slenderness whose behaviour was influenced by the increased nonlinearity in the stress–strain curves at elevated temperatures. Further research is required to include these effects within AS/NZS 4600 and AISI S100 design rules. However, Eurocode 3 Part 1.3 design rules can be used for this purpose by using suitable buckling curves as recommended in this paper. [ABSTRACT FROM AUTHOR]

This paper examines the design and load-carrying capacity of fixed-ended web-stiffened lipped channel columns eroded by mode interaction behaviour combined with distortional and local deformations. Initially, the paper presents the results of an experimental investigation of compressive tests on web-stiffened lipped channel columns fabricated from cold-formed mild steel with a thickness of 1.50 mm, which is aimed at determining their failure load-carrying capacity; the experimental investigation also aims to provide experimental evidence of the occurrence of such coupling phenomena concerning distortional and local modes, namely, local-distortional interaction and distortional-local interactive failures. Then, the paper examines the ultimate strength data of experimental columns, both reported in this paper and collected from the literature, and concludes that the current direct strength method (DSM) provides very unsafe predictions concerning such a detrimental interaction nature. Next, two DSM-based design approaches, namely, the nominal strength against local-distortional (NLD) and distortional-local (NDL) procedures, are presented and evaluated on the basis of all available experimental ultimate strength data. Finally, proposals and design considerations based on the DSM-shape for the thin-walled cold-formed steel sections, which fail in mixed modes of distortional and local buckling, are presented. [ABSTRACT FROM AUTHOR]

In this paper, the retrofitting method of thin-walled, cold-formed sigma beams using bonded carbon fibre reinforced polymer (CFRP) tapes is proposed. The effectiveness of the presented strengthening method is investigated by the means of laboratory tests and numerical analysis conducted on simply supported, single-span beams made of 200 × 70 × 2 profile by "Blachy Pruszyński" subjected to a four-point bending scheme. Special attention is paid to the evaluation of possibility to increase the load capacity with simultaneous limitation of beams displacements by appropriate location of CFRP tapes. For this purpose, three beams were reinforced with CFRP tape placed on the inner surface of the upper flange, three with CFRP tape on the inner surface of the web, three beams with reinforcement located on the inner surface of the bottom flange, and two beams were tested as reference beams without reinforcement. CFRP tape with a width of 50 mm and a thickness of 1.2 mm was used as the reinforcement and was bonded to the beams by SikaDur®-30 adhesive. Precise strain measurement was made using electrofusion strain gauges, and displacement measurement was performed using two Aramis coupled devices in combination with the Tritop machine. Numerical models of the considered beams were developed in the Finite Element Method (FEM) program Abaqus®. Experimental and numerical analysis made it possible to obtain a very high agreement of results. Based on the conducted research, it was proved how important is the impact of the applied reinforcement (CFRP tapes) in thin-walled steel structures, with respect to the classic methods of strengthening steel building structures. [ABSTRACT FROM AUTHOR]

This paper describes a finite element analysis (FEA) and design of cold-formed steel built-up closed sections with intermediate stiffeners in the flange and web under axial compression. A finite element model (FEM) was developed and validated using the available experimental results. The validated FEM can be used for further parametric study on strength of built-up closed columns. The results obtained from the parametric study are compared with the current direct strength method (DSM) in the North American specification of cold-formed steel structures for those specimens that failed by only local, distortional, and flexural buckling. It is shown that the current DSM is not quite suitable for the design of cold-formed steel built-up closed columns. Therefore, the improved design equations are proposed by modifying the current design equations used in the DSM for flexural, local, and distortional buckling. The reliability of current DSM and proposed DSM was assessed by reliability analysis. [ABSTRACT FROM AUTHOR]

This paper describes a comprehensive experimental program on cold-formed steel built-up beams with two different cross-sectional geometries. The work aimed to experimentally investigate the interaction between the individual components under increasing loading and to quantify the effect of the connector spacing on the cross-sectional moment capacity and the behavior of the beams. In total, 12 specimens were tested in a four-point bending configuration, with lateral restraints provided at the loading points in order to avoid global instabilities. The built-up specimens were composed of three or four plain channels with nominal thicknesses of 1.2 and 1.5 mm, which were joined together using M6 bolts. Each built-up geometry was tested with three different connector spacings. The specimens were designed to fail by local buckling of their components. Additionally, strut buckling of the channel comprising the top flange in between connector points was observed. The local buckling deformations and the beam deflections were recorded during the tests. The material properties of the test specimens were determined by means of coupon tests and the geometric imperfections were measured prior to testing. The experimental results showed clear evidence of interaction between the local buckling patterns of the components, with the interaction being affected by the connector spacing and the type of geometry. However, the connector spacing showed a less significant effect on the ultimate capacity when failure was governed by local instabilities of the components. [ABSTRACT FROM AUTHOR]

It is highly important to clarify the high-temperature mechanical properties in the design of cold-formed steel (CFS) structures under fire conditions due to the unique deterioration feature in material properties under fire environment and associated reduction to the mechanical performance of members. This paper presents the mechanical properties of widely used steels for cold-formed steel structures at elevated temperatures. The coupons were extracted from original coils of proposed full annealed steels (S350 and S420, with nominal yielding strengths 280 MPa and 350 MPa) and proposed stress relieving annealed steels (G500, with nominal yielding strength 500 MPa) for CFS structures with thickness of 1.0 mm and 1.2 mm, and a total of nearly 50 tensile tests were carried out by steady-state test method for temperatures ranging from 20 to 700°C. Based on the tests, material properties including the yield strengths, ultimate strengths, the elasticity modulus, and the stress-strain curve were obtained. Meanwhile, the ductility of steels for CFS structures was discussed. Then, the temperature-dependent retention factors of yield strengths and elasticity modulus were compared to those provided by design codes and former researchers. Finally, a set of prediction equations of the mechanical properties for steels for CFS structures at elevated temperatures was proposed depending on existing tests data. [ABSTRACT FROM AUTHOR]

The direct strength method (DSM) is a newly developed design method for cold-formed steel members due to its reliability and consistency. It has been well developed and incorporated in the North American Specification and the Australian/New Zealand Standard for the design of cold-formed steel members under compression, bending, and recently, in shear. To date, there are no DSM rules for the design of cold-formed members under localized loading resulting in the web-crippling phenomenon. Recent literature has attempted to propose the DSM design equations for four localized loading cases including the interior one-flange (IOF), end one-flange (EOF), interior two-flange (ITF), and end two-flange (ETF) loading cases specified in the design specifications/standards. However, these proposed DSM equations were calibrated differently depending on the types of loading cases and geometric shapes of the cross-sections by varying coefficients and exponents in the DSM equations. In this paper, consistent and simplified DSM equations previously proposed by the authors are explained and calibrated for use in the design specifications/standards. They include new plastic mechanism models developed for determining the yield load and also cover the design of sections in the inelastic reserve range as observed. Detailed explanations of the yield load (Py) component and references to computing the buckling load (Pcr) component are given. A design example is also included. [ABSTRACT FROM AUTHOR]

Perforated cold-formed steel (CFS) beams subjected to different bending scenarios should be able to deal with different buckling modes. There is almost no simple way to address this significant concern. This paper investigates the bending capacity and flexural behavior of a novel-designed system using bolt and nut reinforcing system through both experimental and numerical approaches. For the experiential program, a total of eighteen specimens of three types were manufactured: a non-reinforced section, and two sections reinforced along the upright length at 200 mm and 300 mm pitches. Then, monotonic loading was applied to both the minor and major axes of the specimens. The finite element models were also generated and proved the accuracy of the test results. Using the proposed reinforcing system the flexural capacity of the upright sections was improved around either the major axis or minor axis. The 200 mm reinforcement type provided the best performance of the three types. The proposed reinforcing pattern enhanced flexural behavior and constrained irregular buckling and deformation. Thus, the proposed reinforcements can be a very useful and cost-effective method for strengthening all open CFS sections under flexural loading, considering the trade-off between flexural performance and the cost of using the method. [ABSTRACT FROM AUTHOR]

This paper presents an analytical investigation on the free vibration, static buckling and dynamic instability of channel-section beams when subjected to periodic loading. The analysis is carried out by using Bolotin's method. By assuming the instability modes, the kinetic energy and strain energy of the beam and the loss of the potential of the applied load are evaluated, from which the mass, stiffness and geometric stiffness matrices of the system are derived. These matrices are then used to carry out the analyses of free vibration, static buckling and dynamic instability of the beams. Theoretical formulae are derived for the free vibration frequency, critical buckling moment, and excitation frequency of the beam. The effects of the lateral restraint applied to the flange, the section size of the beam and the static part of the applied load on the variation of dynamic instability zones are also discussed. [ABSTRACT FROM AUTHOR]

This paper discussed the stiffness and cracking behavior of a new kind of reinforcement-stiffened cold-formed U-shaped steel and concrete composite beam (RCUCB) under negative bending. The static behavior of the RCUCB was discussed based on a negative bending experiment of 10 specimens. The reinforcement system consisting of the inverted U-shaped reinforcement, reinforcement truss, and bottom reinforcement was shown to maintain the integral action of the RCUCB, especially after the yield load. The RCUCB was found to behave well in deformability, ductility, and plastic rotation ability under negative bending: (1) the failure deflection and ductility factor reached L0/33 (where L0 is the effective span) and 17.7 respectively; (2) the ductility factor increased with decreasing steel ratio and decreasing reinforcement ratio; and (3) approximately 84.7%–94.0% of the web height yielded at the peak load, resulting in a plastification coefficient of 1.3–1.9. The damage process was defined with the cracking, yielding, and buckling loads approximately equal to 0.16Pu , 0.61Pu , and 0.90Pu , respectively. During the experiment, the degree of shear connection in the negative bending area showed little effect on the negative bending behavior before yield load. Calculation methods for initial stiffness, second stiffness, and cracking moment were proposed, and the calculation results agreed well with the test results. [ABSTRACT FROM AUTHOR]

Summary: The objective of this paper is to present incremental dynamic analysis (IDA) and seismic performance evaluation results for a two‐story cold‐formed steel (CFS)–framed building. The archetype building was designed to current U.S. standards and then subjected to full‐scale shake table tests under the U.S. National Science Foundation Network for Earthquake Engineering Simulation (NEES) program. Test results showed that the building's stiffness and capacity were considerably higher than expected and the building suffered only nonstructural damage even at excitations in excess of Maximum Considered Earthquake levels for a high seismic zone. For the archetype building, three‐dimensional finite element models at different modeling fidelity levels were created using OpenSees. The models are subjected to IDA using the far‐field ground motion records prescribed in Federal Emergency Management Agency (FEMA) P695. Seismic performance quantification following the FEMA P695 procedure shows that if the modeling fidelity only follows the state‐of‐the‐practice, ie, only includes shear walls, unsafe collapse margin ratios are predicted. State‐of‐the‐art models that account for participation from CFS gravity walls and architectural sheathing have overall performance that are consistent with testing, and IDA results indicate acceptable collapse margin ratios, predicated primarily on large system overstrength. Neglecting the lateral force resistance of the gravity system and nonstructural components, as done in current design, renders a safe design in the studied archetype, but largely divorced from actual system behavior. The modeling protocols established here provide a means to analyze a future suite of CFS‐framed archetype buildings for developing further insight on the seismic response modification coefficients for CFS‐framed buildings. [ABSTRACT FROM AUTHOR]

Summary: This paper presents results of large‐scale experiments with varying levels of fire severity on lateral force‐resisting systems commonly used in cold‐formed steel framed buildings. Gypsum‐sheet steel composite panel sheathed walls, oriented strand board sheathed walls, and steel strap‐braced walls are examined. Postflashover fire conditions of two different intensities as well as 1 hour of fire exposure similar to that in a standard furnace qualification test are studied. Additionally, a full‐scale furnished kitchen fire experiment is conducted for comparison. The results highlight differences in the thermal response and subsequent performance of the walls as well as differing sensitives of the walls to pre‐damage, eg, that might occur during an earthquake. The results are part of a larger effort to provide fragilities for these wall systems in response to realistic fires for performance‐based design. [ABSTRACT FROM AUTHOR]