Cold-formed Steel Wall Panels Research Articles

Experimental axial-compressive behaviour of bare cold-formed-steel studs with semirigid-track and ideal-hinged boundary-conditions

Studs are the primary load-bearing components in cold-formed steel (CFS) wall panels, connected to tracks at both ends with self-tapping screws, forming a semirigid boundary condition (BCT). Most existing tests on the axial compressive behaviour of bare CFS studs are based on either theoretically-hinged (BCH) or fully-fixed boundary conditions. Previous researchers have employed BCT only on sheathed stud-wall panels. However, practicing engineers and current design codes, e.g., Eurocode 3, follow an all-steel design. Therefore, this research experimentally investigated bare-CFS-studs' axial compressive behaviour with BCT, considering, for the first time, the combined effect of the tracks' warping rigidity, stud-to-track gap, non-linear connection stiffness, and bare studs' various cross-sectional slenderness. Forty-two industry-standard lipped channel sections (studs) of five thicknesses (1.2-3 mm), three depths (75–125 mm), and two heights (1.2 & 1.5 m) were tested under static-concentric axial compressive loading with BCT. Another fourteen studs were tested with BCH, a comparator to BCT. Results demonstrated that the studs' global failure mechanisms were flexural-torsional in BCT instead of flexural in BCH. Studs' axial stiffness was two-phased in BCT due to the stud-to-track gap, compared to single-phased stiffness in BCH. >1.8 mm stud-to-track gap caused stud-to-track connections' failure and studs' sudden capacity reduction during gap closure. Studs achieved 1.22 times higher axial-compressive strength, 2.3 times more axial-shortening, 0.7 times lower axial stiffness, and 58% lower axial-compressive strain at the web-midheight under BCT-PhaseII than BCH. Tested strengths were compared with EC3 design strength, and an effective-length-factor of 0.65 was suggested for efficient design of studs with BCT.

Axial performance of cold-formed steel single-stud wall panels with dissimilar fibre-cement and calcium silicate boards sheathing configuration

In practical applications, it is typical for different types of sheathings (referred to as dissimilar) to be connected at both flanges of the stud (lipped channel-section) in cold-formed steel (CFS) panelised construction (e.g. one-side has interior sheathing and the other exterior sheathing). However, limited studies are available on the axial behaviour of CFS studs with different combinations of sheathings present at both-flanges of a stud. This novel experimental study investigates the structural behaviour of fourteen (14) CFS panels with sheathing on one-side only and different sheathing on both flanges of the wall panel using combinations of seven (7) different sheathing boards [fibre-cement boards (FCB) (8 mm/10 mm/12 mm thick); calcium silicate boards (CSB) (12 mm thick); and heavy duty FCB (6 mm/9 mm/12 mm thick)]. The ultimate axial strength, load-deformation behaviour and failure patterns are the parameters compared. Analytical/semi-analytical design methodologies namely; Rayleigh-Ritz (R-R) method, finite-strip method based on direct strength method (DSM) and differential equation of equilibrium method (DEEM) are validated based on the experiments. Limited studies are available to verify the efficacy of these methods to estimate the axial strength of CFS wall panels with dissimilar sheathing on both flanges. Results establish that DSM may be used efficiently rather than the R-R method and DEEM.

Experimental Investigation and Design Methodology of Built-Up I-Section Cold-Formed Steel Wall Panels with Sheathing under Axial Loading

Experimental Investigation and Design Methodology of Built-Up I-Section Cold-Formed Steel Wall Panels with Sheathing under Axial Loading

Axial compressive behaviour of cold-formed steel single-stud wall panels with one-sided sheathing and two-sided dissimilar sheathing board configurations: Experimental and analytical study

For practical reasons, it is typical for different types of sheathings (referred to as dissimilar) to be connected at both flanges of the stud (lipped channel-section) in cold-formed steel (CFS) panelized construction (e.g. one side has interior sheathing and the other exterior sheathing). However, limited studies are available on the axial behaviour of CFS studs with different combinations of sheathings present at both-flanges of a stud. This novel experimental study investigates the structural behaviour of nineteen (19) CFS panels with sheathing on one side only and different sheathing on both flanges of the wall panel using combinations of eight (8) different sheathing board types [fibre-cement boards (FCB) (8 mm/10 mm/12 mm thick); calcium silicate boards (12 mm thick); orient strand board (12.5 mm thick); and heavy duty FCB (6 mm/9 mm/12 mm thick)]. Also, first time an attempt is made to study the effect of dissimilar configuration using eight (8) different sheathing board types on axial strength of CFS panels in India. Experimentally tested single stud wall panel specimens consist of; one bare single-stud; eight (8) specimens sheathed with different types of sheathing boards on one flange only; and ten (10) specimens with combinations of different sheathing boards on both-flanges. Average test results are obtained by performing two (02) tests for each specimen. The strength enhancement of a bare single-stud from the sheathing boards has been investigated by testing specimens with a single layer of sheathing at one-flange and combinations of different sheathing boards on both-flanges. The ultimate axial compressive strength, load–deformation behaviour and failure patterns are the parameters compared. A new analytical and semi-analytical design methodologies namely; Rayleigh–Ritz (R-R) method and finite-strip method based on direct strength method (DSM) are adopted for evaluating the axial compressive strength of the CFS wall panels with dissimilar sheathing. Limited studies are available to verify the efficacy of R-R method and DSM to estimate the axial compressive strength of CFS wall panels with dissimilar sheathing on both flanges. Results establish that DSM may be used efficiently rather than the R-R method for axial compressive strength prediction of dissimilar sheathed CFS wall panels. The predicted values show good agreement with the experimental test results, and therefore, demonstrate that the semi-analytical method may be applied efficiently in design.

Application of Direct Stiffness-Strength Method for Design of Gypsum and Plywood sheathed CFS wall panels Subjected to Bending

The cold-formed steel (CFS) wall frames need to be stiff-strong to inhibit the instability failures. The current design specifications do not have a robust design method for sheathed CFS wall panels. A safe wall frame design is possible by providing adequate bracing to resist the instability failures, which the sheathing boards can do. A new design method based on the demand and supply approach called “Direct Stiffness-Strength Method” (DSSM) is developed to fulfill sheathing-bracing design needs. Nevertheless, it is necessary to validate the suitability of the DSSM for the design of CFS wall frames with various sheathing materials. In this study, a total of 58 CFS sheathed panels were tested under out-of-plane loading with varying design parameters such as global (λe), local (λl), and distortional slenderness (λd), two sheathing board types (Gypsum and Plywood), sheathing board thicknesses (tb), and sheathing fastener connection spacing (df). The full-scale test results indicate that the resistance of the sheathing fastener connection is sensitive to the thickness of the fibrous sheathing board plywood. The full-scale test results were compared with the design strength of CFS wall panels using DSSM. The sheathed CFS wall panel design indicates that the current DSSM method is unconservative for gypsum sheathing (both 12.5 mm 15 mm thicknesses) and overly safe for 12 mm thick plywood sheathing. This can be attributed to the omission of sheathing thickness in the DSSM approach to determine the stiffness and strength of the sheathing fastener connection. Further, the reasons for the inaccurate prediction of the current DSSM method are discussed in detail. A set of new resistance factor values are proposed for the accurate design prediction of sheathed CFS wall panels. Finally, the paper presents and discusses the application of the proposed design approach and provides evidence for the benefits of DSSM.

Comparative study of analytical/semi-analytical methods for prediction of axial strength of cold-formed steel wall panels with sheathing

ABSTRACT Load-bearing cold-formed steel (CFS) wall panels comprise of a stud (C-section), track (U-section) and sheathing. Sheathing is fastened to the CFS frame with self-drilling screws, which has an effect on the axial load-carrying capacity of panels. Experiments are complex and often expensive as they require use of different resources (raw material, manpower etc.). Therefore, conducting experiments is not always possible and an efficient design tool is necessary. Few studies are present in literature on comparing the effectiveness of available design methodologies. For the first time, an attempt is made to compare all the three (03) presented mathematical models together to predict the axial strength of CFS wall panels with sheathing. The present study examines the effectiveness of such analytical/semi-analytical tools, namely, Rayleigh-Ritz (R-R) method, Differential equation of equilibrium (DEEq) method and Constrained and Unconstrained Finite Strip Method – Direct Strength Method (CUFSM-DSM) for estimation of axial load-carrying capacity of sheathed CFS panels. The results show that CUFSM-DSM can be utilized meritoriously for evaluation of sheathed CFS wall panels.

Evaluation of Axial Strength of Sheathed Cold-Formed Steel Wall Panels Using Rayleigh-Ritz Method and Direct-Strength Method: Comparative Study

Sheathed cold-formed steel (CFS) wall panels comprise studs, tracks, and sheathings on one side or both sides. It has been observed in the literature that sheathing contributes significantly to the axial load carrying capacity of CFS wall panels. Limited studies are available on comparing the efficacies of available design methodologies to evaluate the axial strength of CFS wall panels with sheathing. The present study investigates the efficacy of analytical/semianalytical methods, namely, the Rayleigh–Ritz (R–R) method and direct strength method (DSM), for evaluating the axial load carrying capacity of sheathed CFS panels. In DSM, three elastic buckling loads are evaluated, namely, local, distortional, and global, using an open-source finite strip method based software CUFSM version 4.05. The bracing provided by sheathing to the section is presumed as springs. For the first time, a problem is undertaken to verify the efficacy of both the mathematical models together to evaluate the axial load carrying capacity of sheathed CFS wall panels. The evaluated results by both the models are compared with experimental strengths of sheathed CFS wall studs from the experimental database including the tests conducted by the authors. Results demonstrate that DSM may be used effectively for predicting axial strength of sheathed CFS wall panels, as a substantially lower coefficient of variation (CoV) is obtained for DSM, which is 0.1274, than the R–R method (CoV=0.1897). DSM is suggested over the R–R method for evaluating the axial load carrying capacity of sheathed CFS wall studs as it better takes into account the local buckling and inelastic effects.

Effect of axial loading on cold-formed steel wall panels with fibre-cement and calcium silicate boards sheathing: Experimental and analytical studies

Sheathed Cold-formed Steel (CFS) wall framed buildings provide various advantages such as speed of construction, environmentally green, high strength-to-weight ratio etc. over construction with conventional materials. In this type of construction, walls are the main load-bearing elements. It has been observed in literature that sheathing significantly influences the load-carrying capacity of CFS wall frame. However, limited studies are available on axial behaviour of calcium silicate board (CSB) sheathed CFS wall panels. Fibre cement board (FCB) sheathed wall panels are proposed in the present study and the same are investigated for their performance under axial loading. A detailed series of experiments on full-scale sheathed perforated CFS single-studed wall panels are carried out and load factors which may be adopted by designers or researchers for evaluating axial strength of sheathed CFS panels, are proposed. Sheathings using FCB and CSB boards are applied on the specimens. Effect of variation of parameters such as type of sheathing, sheathing thickness, layer configuration of sheathing (number of layer on either side) on the load factors are also investigated in the present study. ‘Differential equation of equilibrium’ based analytical method is validated with the experimental results in the present study. In the adopted analytical method, the stud is assumed as channel section restrained by sheathing based springs. The value of spring stiffnesses is obtained analytically as specified in the literature, using modulus of elasticity, obtained through experiments. Suitable modification factor is recommended for panels with sheath on one side, while predicting axial strength of CFS panels with sheath, analytically. The proposed factor may be used with confidence as the experimental results agree well with the analytical results.

Investigations on cold-formed steel wall panels with different sheathing boards under axial loading: Experimental and analytical/semi-analytical studies

Sheathed cold-formed steel (CFS) wall panels consists of studs, tracks and sheathings. Sheathing is attached to the CFS frame using self-drilling screws which influences the strength of wall panels under axial loading. As observed in literature, sheathing affects the strength and failure mechanisms of CFS wall panels. Most of the previous studies are conducted using gypsum and orient strand boards (OSB). Limited studies are available on behaviour of CFS stud with fibre cement board (FCB), heavy duty fibre cement board (HDFCB), calcium silicate board (CSB) and magnesium oxide (MGO) board sheathings. For the first time, a comparative experimental study is presented on axial performance of CFS wall panels using FCB, HDFCB, CSB, OSB and MGO boards. Axial strength, load-deformation response and failure modes are studied and estimated. Load factors (Wn/WSingle-Stud) are also evaluated for all specimens, which may be adopted by designers and researchers in absence of experimental data. Different analytical and semi-analytical design methodologies are adopted for evaluating the strengths of CFS wall panels namely; Differential Equation of Equilibrium based method, Rayleigh-Ritz method and Direct strength method (DSM) as per AISI S100. Limited studies are available on comparing the efficacies of available design methodologies. The present study also investigates the efficacy of such analytical/semi-analytical tools for evaluation of axial strength of CFS panels with sheathing. For the first time, a problem is undertaken to compare all the three (03) mathematical models. Results demonstrate that DSM may be used effectively for axial strength prediction of sheathed CFS wall panels. Further, DSM is used for predicting the axial strength of the tested specimens. The predicted results agree well with the experimental results.

Experimental and numerical investigation of cold-form steel wall frame panels with plasterboards under flexural loading

The structural behaviour of the cold-formed steel (CFS) wall panels under flexural loading is normally characterised by buckling modes, deflection, flexural stiffness. This research mainly investigates these fundamental behaviours of CFS wall panels at elastic limits where four-point bending loading has been incorporated into the panels. The paper presents the results of the experimental and numerical studies of the composite CFS wall panels. Three specimens are tested, and then the finite element (FE) model has been developed and validated by comparing its results with test data. A parametric study has been conducted to investigate the composite behaviour of CFS wall panels with different combinations of CFS studs and gypsum plasterboards. The test and FE model results demonstrate that back-to-back CFS studs can be used to overcome the buckling problem for light load-bearing wall panels due to their higher rigidity. It is found that stud types and gypsum plasterboard have a significant influence on the elastic behaviour and failure modes of the CFS wall panels.

Direct stiffness-strength method design for sheathed cold-formed steel structural members - Recommendations for the AISI S100

This paper presents a new design procedure for considering the bracing effect of sheathing boards that are attached to the cold-formed steel (CFS) structural members. The previous investigations show that the current AISI design specification for sheathing bracing design of CFS wall panels is unconservative (i.e. design standard predict a larger failure load than the experimental test results) due to exaggerated sheathing stiffnesses calculated from ideal loading conditions rather than worst-case loading conditions. Therefore, a new design procedure is suggested based on the performance (strength and stiffness) of the individual sheathing fastener connections. A new and simplified test setup is also introduced to simulate the realistic failure modes of the sheathing fastener connections using a conventional universal testing machine. A total of 67 individual sheathing fastener connection tests were carried out, including parameters such as ten different dimensions of the CFS stud (to account for the slenderness) and seven various sheathing board types (to account for the performance of each sheathing type). Based on the individual sheathing fastener connection test results, new expressions are formulated to predict the stiffness and strength of the individual sheathing-fastener connections. A statistical and application-oriented merit-based assessment indicated that the proposed expressions are appropriate for the use of sheathing braced design. In particular, the individual sheathing fastener-connection strength and stiffness arrived by the proposed expressions are conservative in predicting the failure mode and design strength of the sheathed CFS panel. Finally, this paper demonstrates the effectiveness of the proposed simplified design method by illustrating with the help of a design example, which quantifies the benefit of adopting this method in AISI design guidelines.

Criteria for Selection of Sheathing Boards in Cold-Formed Steel Wall Panels Subjected to Bending: Construction Applications and Performance-Based Evaluation

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.

Numerical modelling and design of hybrid cold-formed steel wall panels

Hybrid cold-formed steel (CFS) wall panel, composed of square hollow sections (SHS) and CFS open sections, can offer some great advantages with respect to the lateral performance of light steel frames, in particular for applications in mid-rise construction. This paper presents non-linear finite element modelling of hybrid wall panels, calibrated through experimental tests, and their applications to different designs. The study involves the lateral behaviour of the proposed hybrid walls in terms of load-displacement curve, failure mode, stiffness, ductility ratio, energy absorption, and strength to weight ratio. First, a numerical model, verified and calibrated based on the experimental tests on the hybrid wall panels, is presented. Thereafter, using the validated numerical model, twenty new hybrid wall panel designs are proposed in order to investigate the effect of different SHS brace configurations on the hybrid panels’ performance. The comparison of the experimental and numerical results indicates that superior seismic performance can be achieved from the proposed hybrid CFS wall designs.

Comparative Study on Cold-Formed Steel Single-Stud and Multiple-Studs Wall Panels with Magnesium Oxide Sheathing under Axial Loading: Experimental and Analytical

AbstractA comprehensive study has been carried out experimentally and analytically on the axial performance of sixteen (16 nos.) cold-formed steel (CFS) wall panels including one bare CFS wall fram...

Influence of Sheathing-Fastener Connection Stiffness on the Design Strength of Cold-Formed Steel Wall Panels

AbstractThis paper investigates the bracing effect of sheathing fastener connection on point-symmetric shaped cold formed steel (CFS) studs through full-scale laboratory tests. The test parameters ...

Seismic characteristics of hybrid cold-formed steel wall panels

The current standards for seismic design of cold-formed steel (CFS) structures are only limited to the lateral force-resisting systems which are not appropriate for mid-rise constructions due to their low shear resistance. Therefore, innovative hybrid CFS systems have recently been proposed and developed in response to the needs of CFS provisions as well as lightweight steel industry in mid-rise construction. This paper presents an experimental program on lateral cyclic behaviour of six full-scale hybrid wall panels with truss structural design and aims to investigate and characterize the seismic performance of this new CFS solution. The performance of the wall panels is compared in terms of seismic characteristics and response modification factor (R factor). A comprehensive comparison between lateral strength to weight ratio of the hybrid panels of this study and 87 previously tested CFS walls is also carried out to investigate the capability of using hybrid walls in modular lightweight steel buildings. The cyclic results demonstrate that the seismic performance of specimens with appropriate truss frame is satisfactory considering their shear strength, ductility and R factor values. The high strength to weight ratio of the hybrid walls of this study compared to the previously tested CFS panels also indicates the hybrid panels are well appropriate for modular lightweight buildings in seismic regions.

Flexural Behaviour and Design of Cold-Formed Steel Wall Panels Sheathed with Particle Cement Board

The bracing effect of Particle Cement Board (PCB) sheathing for the Cold-formed steel (CFS) wall stud is explored in this study. Owing to the higher slenderness, the CFS wall stud requires additional bracing to inhibit the instability failures such as flexural and lateral torsional buckling. Twenty sheathed CFS wall studs were tested to investigate the structural effect of PCB sheathing under out-of-plane loading. The key design factors such as sheathing arrangements (screw spacing and sheathing thickness) and slenderness of the CFS studs were examined. The experimental results indicated that the CFS studs with vulnerability to fail in both local buckling (fcrl <<fy) and LTB (fcre <<fy) can be effectively braced by particle cement board sheathing. The experimental results, together with the failure modes of the sheathed CFS studs were compared with the predicted strengths using the latest sheathing braced design rules. The critical elastic buckling stresses corresponding to different failure modes for the direct strength method (DSM) of CFS structural member design were determined using the latest modified rule. The latest sheathing braced design rules accurately predicted the failure modes of the PCB sheathed CFS stud. However, the design moment capacities predicted by the latest sheathing braced design rules are overly conservative compared to the experimental moment capacities. The reasons pertaining to the over conservative design predictions are discussed. A set of preliminary suggestions to effectively codify the design rules for the CFS wall panels are given.

Sheathing braced design of cold-formed steel structural members subjected to torsional buckling

The objective of this work is to examine the bracing effect of sheathing boards in inhibiting the instability failure modes of cold-formed steel (CFS) studs in the wall panel construction. A development of accurate and robust sheathing braced design concepts for CFS wall panels will eliminate the need for additional lateral steel bracing, thereby leading to efficient use of construction materials. The current design method by the American Iron and Steel Institute lacks in accurately predicting the design strength of the sheathed CFS stud. Therefore, the current investigation endeavors to fill the gap by carrying out experiments that simulate the behavior of the CFS studs subjected to out-of-plane loading. A total of sixty-seven experiments were carried out with seven different sheathing board types and ten different CFS studs to accomplish the objective. The experiments were carried out using a newly devised test set-up that simulates the worst case failure mode of the sheathing board. The experimental results indicate that the strength, stiffness and failure modes of the sheathing boards vary depending on the following; (i) fiber composition and material properties of the sheathing board; (ii) dimensions of the CFS stud. In addition, the test results also indicated that the stiffness of the sheathing board against the pull-through failure was not influenced by the thickness of the sheathing boards. Based on the inferences (trend of sheathing stiffness and failure modes) from the test results, a new expression is formulated to determine the stiffness of the sheathing board on a function of the tensile modulus of the sheathing board (Es) and dimensions of the CFS stud (d/2). The validation study indicates that the new expression is accurate in terms of both statistical and design application.

Investigation on sheathing-fastener connection failures in cold-formed steel wall panels

Torsional buckling is a common mode of failure in highly slender Cold-formed Steel (CFS) stud wall frames. The torsional buckling mode will induce pull-through in sheathings attached on either side of wall panel leading to failure. This paper presents an experimental investigation to understand the performance of various sheathing boards against torsional buckling of CFS structural members. A total of forty-two specimens were tested including various parameters such as seven types of sheathing boards and six different types of CFS studs. In addition, the influence of different fasteners types that are used in the installation of sheathing boards on the CFS wall frames is also examined. The test results indicate that it is necessary to use the fastener with rubber washer (hex-washer head fasteners) to avoid pull-through failures in the sheathing. The load magnitudes at which the pull-through failure or the sheathing breakage occurs is reported for the different sheathing and CFS studs. In general, the sheathing board with the fiber composition performed well compared to the sheathing materials made of particle composition. In addition, the study also indicates that the performance of the sheathing board depends on the geometric dimensions of the CFS studs. The influence of CFS stud geometry in the sheathing-fastener connections is pictorially presented in the form of a plot. The force developed at each sheathing-fastener connection to achieve the target design moment in the CFS wall panels is calculated using a simple theoretical expression and compared against the experimental results obtained from this study. An appropriate sheathing board that offers resistance against torsional buckling of CFS stud is suggested based on the observed experimental failure modes.

Bracing effect of sheathing in point-symmetric cold-formed steel flexural members

This paper presents an experimental investigation on sheathed cold-formed steel wall panels subjected to out-of-plane loading. The objective is to determine the two-sided gypsum sheathing effect on the design and behavior of the point-symmetric CFS studs. The design parameters such as global slenderness of the CFS stud, sheathing thickness and distance between the fasteners are varied, totaling twenty full-scale experiments that were tested under four-point bending. In general, the experimental results indicate that the gypsum sheathing board with a thickness of 15 mm and a fastener spacing of 150 mm hindered the occurrence of the biaxial bending of the point-symmetric CFS stud and led the CFS stud to reach its yield moment. To quantify the bracing effect of sheathing, the design predictions were carried out as per the current AISI report. The design results indicated that the design strength of a majority of the point-symmetric CFS studs can be drastically increased by the sheathing's bracing effect. However, few design results are unconservative compared to the experimental results which was confirmed by the reliability analysis as per AISI. Further investigation reveals that the current AISI design procedure requires significant modification with respect to the loading conditions and geometry of the CFS stud. In addition, the present study also discovered certain procedures to make the current sheathing braced design methods conservative and robust.