Cold-formed Steel Wall Research Articles

Prediction of In-plane Stiffness for the Cold-formed Steel Frame of the Wall Panel Structure

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

Finite element analysis of lateral response of lightweight foamed concrete-filled cold-formed steel walls

PurposeThe purpose of this study is to improve the lateral capacity of Cold-Formed Steel (CFS) frame walls filled with lightweight foamed concrete (LFC) and supported with straw boards by introducing structural foamed concrete and/or bracing.Design/methodology/approachFinite element models are developed and calibrated based on previous experimental work. Then, these models are extended to conduct a parametric study to quantify the effect of filling CFS walls and structural LFC and the effect of supporting CFS walls with bracing.FindingsResults of the study conclude that the finite element analysis can be used to simulate and analyze the lateral capacity of CFS walls effectively since the maximum deviation between calibrated and experimental results is 10%. The structural LFC usage in CFS walls improves the lateral capacity considerably by (25–75) % depending on the wall properties. Besides, the application of lateral bracing does not always have a positive effect on the lateral performance of these walls.Originality/valueAlthough CFS walls are preferred due to it is light in weight, low in cost, easy to install and recyclable, low seismic performance, buckling vulnerability, poor thermal insulation and sound insulation properties, low lateral stiffness, and low shear strength limit their use. This study proposes the use of structural foamed concrete and a different bracing method than what is available in the literature. This can overcome the drawbacks of the CFS walls alone which can permit the usage of such walls in mid-rise buildings and other applications.

Experiment investigation on lateral performance of CFS composite walls sheathed with magnesium crystal board

Cold-formed steel (CFS) walls with novel sheathing have been of growing interest in hysteretic behavior. This study investigated the effect of diagonal bracings and sheathing magnesium crystal boards (MCBs) on the hysteretic behavior of CFS walls. Furthermore, a novel refined vertical loading system was proposed to solve the key problems caused by conventional distribution beam loading systems. Monotonic or hysteretic loading was conducted on six full-size CFS walls sheathed with MCB and one pure CFS frame wall to obtain the failure modes, yield loads and corresponding displacements, peak loads and corresponding displacements, and lateral stiffness of the specimens. Finally, the failure mode of the MCB located in the vertical seam was observed and discussed, and the influence of the flexible diagonal brace on the lateral bearing capacity and ductility of the CFS wall was further analyzed.

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.

Pull-through failure of crest-fixed steel claddings under combined wind and bushfire conditions

Cold-formed steel (CFS) roof and wall cladding systems are commonly used in Australia and around the world. The use of CFS claddings in bushfire prone areas is becoming more popular due to their non-combustibility and is recommended in the Australian standard AS3959 for construction in bushfire areas. However, severe fire events occur more frequently and in recent bushfire events, strong winds and fire–wind interactions have been observed. Thus, the behaviour of CFS claddings exposed to a combined action of fire and wind needs to be considered for the safe design of buildings in bushfire prone areas. In this study, a small-scale test set-up was developed and used to simulate the wind suction loading on crest-fixed CFS roof and wall claddings while also being exposed to elevated temperatures. Experiments were conducted on three commonly used 0.42 mm high strength (G550) CFS cladding profiles at ambient and elevated temperatures and their critical localised pull-through failures of the crests under the screw heads were investigated at increasing temperatures. The results showed that the failure mode of trapezoidal cladding profiles changed from a transverse splitting type to a localised dimpling type pull-through failure. They also showed different rates of reduction in the pull-through capacity with increasing temperatures and the type of cladding profile. This paper has proposed a suitable equation for the pull-through capacity reduction with increasing temperatures and made suitable recommendations in relation to the use of CFS cladding systems in bushfire prone areas.

Experimental Study on Seismic Performance of Steel Frame Sheathing with Concrete and Plasterboard Composite Wall

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

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.

Mechanical behavior analysis of LEM-infilled cold-formed steel walls

The sustainable development of the engineering structures mainly depends on the environmental- friendly to structural components. This requires the development of sustainable and new materials and structures that would be a worthy alternative for the available. This paper proposed a novel type of cold-formed steel (CFS) shear wall which filling light EPS mortars (LEM) into the space of CFS framing. LEM-infilled CFS walls carry forward the merits of traditional CFS wall, for example lightweight, easy installation, superior earthquake resistance and efficient energy saving. Moreover, employing recycled desulfurization gypsum and EPS in the structural materials reduce environmental pollution. However, the behavior of LEM-infilled CFS wall is not fully explored yet, which results in the low understanding and application of the material around the world. Based on this background, a review of mechanical response tests will contribute to a better awareness. In this paper, three types of mechanical behaviours are discussed including axial compressive behaviour, out-of-plane flexural behaviour, and cyclic behaviour. The previous researches on the mechanical performance of LEM-infilled CFS walls were reviewed. And the typical failure patterns and general results were described and discussed. This work will provide an excellent reference to current practice and future exploration.

Numerical modeling of the post-fire performance of strap-braced cold-formed steel shear walls

Strap-braced, cold-formed steel framed walls are frequently used as the lateral force resisting system in cold-formed steel construction. While the behavior of these walls has been studied under lateral loading and (to a lesser extent) under fire conditions, there is a need to comprehend the influence of multi-hazard interactions, in particular the effect of fire pre-damage on the lateral load resistance of the walls. In this paper, a numerical model of a strap-braced cold-formed steel wall is developed to analyze the thermal and structural response when subjected sequentially to fire followed by shear deformation. The numerical model is validated against full-scale experiments. Coupon tensile tests are conducted to characterize the post-fire properties of the cold-formed steel that are used as inputs to the model. The results show that the numerical model can capture the post-fire response of the cold-formed steel walls including the wall strength, stiffness and ductile failure by yielding of the strap. The lateral behavior of the walls depends primarily on the maximum temperature reached in the cold-formed steel members and the resulting residual properties. Thermal analysis by the finite element method can be used to predict the maximum temperatures across a wall section under a variety of design-relevant fire scenarios, but the results are strongly affected by the quality of the data on thermal properties and by the loss of integrity of the gypsum sheathing. This study validates the numerical modeling strategy and suggests that the post-fire lateral capacity of the walls can be predicted from ambient temperature methods with use of the cold-formed steel residual mechanical properties.

Design of cold-formed steel wall studs subject to non-uniform elevated temperature distributions

The current design rules for cold-formed steel studs used in wall systems subject to non-uniform elevated temperature distributions are complicated with iterations and different elevated temperature section properties. This paper first investigates the accuracy of the current effective width method (EWM) and direct strength method (DSM) based design equations, and then simplifies the calculation process without compromising the accuracy in calculating the load ratios (elevated to ambient temperature capacity ratio). It also improves the accuracy of the current DSM based design equations. It then investigates the possibilities of using uniform temperature based DSM design equations for non-uniform temperature distributions and identifies the possibilities of using hot flange mechanical properties and uniform temperature based DSM design equations. Hence, it proposes a simplified uniform temperature based DSM design method with hot flange mechanical properties and a correction factor based on hot and cold flange temperatures, yield strength, length and depth of studs.

Full-scale fire and postearthquake fire experiments of CFS walls with new configurations

In this paper, autoclaved lightweight concrete (ALC) boards, steel sheets and calcium-silicate (CS) boards were adopted to form a new sheathing configuration of cold-formed steel (CFS) walls. Full-scale fire and postearthquake fire experiments with such walls were carried out. The results showed that the steel sheets improved the mechanical behavior of the screw connectors, and the shear strength of specimen S2 with the new sheathing configuration was 14.7% higher than that of the CFS walls lined with base-layer CS boards and face-layer gypsum plasterboards (GP) on either side. Meanwhile, under the horizontal cyclic load with a drift ratio of 3.0%, obvious residual in-plane deflection and local buckling at the stud bottom of specimen S2 were detected, which caused the residual fire resistance (FR) to drop by 17.7% compared to the FR of specimen S1 without earthquake damage. Moreover, both specimens S1 and S2 with new sheathing configurations showed excellent fire and postearthquake fire performance, and the corresponding FR was at least 120 min longer than the FR of the CFS walls sheathed with double-layer GP or CS boards on either side, which could be attributed to the new sheathing configuration effectively mitigating the damage to the sheathing under earthquake motion, so that the effect exerted by seismic action on the heat transfer of CFS walls was insignificant under postearthquake fire conditions. In addition, both steel sheets and steel strips could protect the joints of the base-layer boards and achieve almost the same insulation performance as sheathing without board joints.

Behavior of screw connections in sheathed cold-formed steel walls

This paper presents a study on the behavior of screw connections in sheathed cold-formed steel (CFS) walls. A finite element (FE) model with solid elements was developed to investigate different failure modes. Suitable solution techniques, element types, mesh sizes, screw modeling, and geometric and material non-linearity were considered in model development. Since the behavior of the sheathing boards is similar to that of other quasi-brittle materials, the Concrete Damage Plasticity (CDP) model was used to model the material behavior using both classical plasticity and continuum damage mechanics. Uniaxial experimental tests were performed on fiber-cement board samples to define material parameters used in the CDP model. The load displacement behavior, ultimate strength, and failure modes obtained from the developed FE model were validated against available experimental results on walls sheathed with cement or gypsum boards. The validated FE model was then used to perform parametric study to investigate the effect of different design parameters on the connection behavior. These parameters are: board type and thickness, CFS profile thickness, screw diameter, screw length, and edge distance. The results of the parametric study were used to develop a design equation for the screw connection strength using nonlinear regression analysis.

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.

Numerical study of cold-formed steel frame walls under compression loading

Bearing walls in cold-formed steel buildings act as a transmitter of vertical loads of the building and as a retainer of the exterior of the building and also absorb the lateral loads of the building such as wind and earthquake loads. In this article, the behaviour of cold-formed steel frame walls under compressive axial load has been investigated numerically. First, the finite element model of the cold-formed steel wall was developed using ABAQUS software, and then, structural analysis was performed, taking into account the effects of geometric and materials nonlinearities. The results of the numerical model were compared with the experimental results to confirm the accuracy of the numerical model. In the following, parametric studies have been carried out considering some parameters affecting the behavior and the ultimate load of cold-formed steel frame walls such as type of sheathing, stud web depth, stud flange width and stud cross-section shape. The results of the structural analysis showed that the type of wall sheathing did not have a significant effect on the ultimate load of the wall, but increasing the web depth of the stud, has led to a decrease in the load-bearing capacity of the steel wall. The wall with hollow flange studs has a higher ultimate load than other sections, and also, the use of web stiffened stud leads to an increase in the final bearing capacity of the wall compared to typical sections.

Fire performance of functionally-graded-material sheathed load bearing thin-walled structural framing

This paper presents the fire rating performance of load-bearing thin-walled system sheathed with Functionally Graded Material (FGM) board under standard ISO834 fire through numerical simulation. FGMs are one of the new classes of advanced composite materials that possess continuous variation of material properties within a given direction. The composition of the FGM sheathing is defined by the volume fractions of the constituents’ materials (metal/ceramic) based on the power-law (P-FGM) material function. The general rule of mixtures is then used to predict the thermo-mechanical properties of the FGM sheathing. Fire rating analyses for the Cold-Formed Steel (CFS) wall system were conducted under steady-state conditions where the elastic buckling load from bifurcation analysis under fire conditions was first obtained. Then using the RIKS ON algorithm, collapse analysis was performed in a time frame until failure deformation occurred. The effect of non-uniform temperature on mechanical and thermal properties of the wall stud was included at each time frame in both elastic and collapse analysis.From the FE analysis using ABAQUS, it was observed that the use of FGM as a sheathing material for fire protection increases the failure time for all load ratios compared with the traditional gypsum board. The increase in failure time has a significant implication for improving the safety of occupants during fire scenarios. The study also shows that the novel composite material (FGM board), if properly designed, can lead to an alternative fire protection material in the thin-walled system.

Study on shear performance of cold-formed thin-walled steel walls sheathed by paper straw board

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

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 fixed-height cold-formed steel wall assemblies bearing on concrete slabs

Cold-formed steel bearing walls are frequently installed on concrete slabs, which do not provide perfectly rigid and uniform conditions. However, existing design guidance assumes bearing condition has no impact on axial capacity, though cold-formed steel compressive members are particularly susceptible to these end conditions. Additionally, studs are typically installed at the edge of the concrete slab, which is prone to spalling and geometric irregularities, and stud walls are occasionally installed inadvertently overhanging from them. In this paper, the impact of non-uniform and partial bearing conditions on the axial strength of cold-formed steel (CFS) wall assemblies is identified and characterized experimentally and numerically. Studs of various cross-sections and bearing conditions were considered. Bearing conditions include: full bearing (edge distance ≥ 20.32 cm (8 inches)), close to the edge, at the edge, and partially overhanging from the slab. In addition to the experiments, high-fidelity finite element modeling of all the systems was conducted to validate the experimental results and elucidate the impact of parameters not captured during the tests. The results provide a means of evaluating existing design guidelines presented in the North American Specification of the American Iron and Steel Institute (AISI S100-16). Twenty-seven tests were conducted on CFS wall assemblies. They reveal that there is a potential need for improvement of current AISI specifications, where all bearing conditions are assumed rigid and uniform. Design recommendations for improving the current specification are discussed.

STUDY ON SHEAR BEARING CAPACITY OF COLD-FORMED STEEL COMPOSITE WALLS WITH LIGHTWEIGHT GYPSUM FILLINGS

In order to calculate the shear bearing capacity of cold-formed steel (CFS) composite walls with lightweight gypsum infillings, the full scale specimens including two unfilled walls and nine infilled walls were tested under reversed cyclic loading. The failure modes of the walls under horizontal loads were studied. The test results show that the failure modes of unfilled CFS walls are characterized by the screw connections between sheathings and CFS frames, thus causing the loss of stressed skin provided by sheathings. There are two possible failure modes of CFS walls with fillings. One is the compressive failure at the corner of gypsum fillings, and the other is the flexural failure of CFS studs. According to above-mentioned failure modes and limit equilibrium theory, a shear bearing capacity calculation model based on superposition method is proposed considering the contributions of sheathings and infill materials. Then the calculation equations of shear bearing capacity are also derived. The model can reflect the impact of screw connections strength, infill material strength and CFS frames strength on shear bearing capacity of the walls. The ratios of the theoretical calculation values to the test values are between 0.947 and 1.112, which demonstrates that the theoretical calculation values have a good agreement with tests values.

Sheathing-fastener connection strength based design method for sheathed CFS point-symmetric wall frame studs

Cold-formed steel (CFS) in construction delivers cost effectiveness and design flexibility. The instability failures of CFS Structural members significantly influences the failures of sheathing boards attached as an external cover. Therefore, present study experimentally examines the structural behavior of sheathing fastener connection in cold-formed steel wall frame. As a first attempt, strength and stiffness of the sheathing fastener connection is determined against the failure modes of point symmetric CFS wall frame studs. A new test setup has been developed to investigate the individual sheathing fastener failure modes. Parameters investigated include sheathing board types (varying thickness) and different dimensions of point-symmetric CFS studs. A total of forty-one individual fastener connection tests were carried out. The experimental investigation revealed that the fastener connection strength varies depending on the geometric dimensions of CFS stud and material composition of sheathing board. The result indicated that the bracing effect provided by plain gypsum board (fiber less) is insignificant and should not be considered for design. For sheathing boards with fiber composition, a generic parameter [ratio to design moment (Mx or My) to CFS stud depth (h)] is introduced to consider the structural bracing effect in CFS wall panel design. The limitations to consider the bracing effect of sheathing in the design of CFS wall frame studs are suggested for minor axis buckling and major axis buckling.