Cold-formed Steel Wall Research Articles

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.

Mid-scale and full-scale experiments of cavity-insulated gypsum and calcium-silicate sheathed CFS walls under different fire exposures

Most previous fire experiments of cold-formed steel (CFS) walls were conducted under ISO834 fire exposure, for which the results can not reflect the fire performance in some special scenarios. Meanwhile, full-scale fire experiments of CFS walls are time-consuming and suffer from high equipment requirements and cost. In this paper, two 1.1 m×1.1 m mid-scale non-load-bearing fire experiments and three 3 m×3 m full-scale load-bearing fire experiments of CFS walls were carried out. The specimens used gypsum plaster (GP) board and calcium-silicate (CS) board as the sheathing boards, and rock wool as the cavity insulation. In addition, the experiments involved four different fire exposures. The results show that the time-temperature profiles between the mid-scale and full-scale specimens, which had the identical dimensions and configuration of wall cross-section, tend to be consistent under the same fire condition. Therefore, a simplified experimental method was proposed to determine the fire resistance time for the structural failure of CFS walls with different load ratios through only one non-load-bearing fire experiment of mid-scale specimen, which avoided the current complex implementation that the fire resistance time of CFS walls with different load ratios was determined by carrying out multiple full-scale load-bearing fire experiments. In addition, the horizontal board joints were identified as the weak parts for the fire resistance of CFS walls under different fire exposures, which would cause stud buckling near the horizontal joints during the fire experiments. Moreover, the experiments under different fire exposures shows extended fire resistance time by substituting GP board with CS board as the base-layer sheathing, and the critical temperatures of stud hot flanges, which corresponded to the structural failure of present cavity-insulated GP-CS sheathed CFS walls and the load ratio of 0.27, were close to each other with the average of 693.8 °C. Finally, it was verified that the equal area method can give a rational prediction of the fire resistance time equivalency after correction by reference temperatures.

Recommendations for design of sheathing bracing systems for slender cold-formed steel structural members

The use of sheathing material as a structural component in the Cold-formed steel (CFS) construction holds great potential for stability of the structure and savings in the construction cost. However, there is no robust design method to account the structural contribution of sheathing boards. This paper presents the experimental results of 107 (including unsheathed and sheathed) CFS wall frame studs subjected to out-of-plane loading to study the feasibility of using gypsum board as a structural bracing sheathing material. The test parameters include various shapes and slendernesses of the CFS frame stud, thickness of the sheathing board and spacing between the sheathing bracing connections. The out-of-plane loading is applied as it causes lateral torsional buckling in the CFS structural members thereby creates pull-through failure at the sheathing bracing connections. Moreover, the suitability of the current AISI and Eurocode specification for the design of sheathing braced CFS structural member is studied. The experimental results indicate that the lateral buckling of the symmetric shaped (against the loading axis) CFS wall frame studs can be inhibited by gypsum sheathing. Whereas most of the singly symmetric and point symmetric CFS studs exhibit lateral torsional buckling and biaxial bending, respectively, due to the inadequate bracing effect of gypsum sheathing resulting in pull-through failure at the sheathing bracing connections. Therefore, a set of limitations for the use of gypsum sheathing as a structural bracing is suggested in the form of a generalized design parameter. Finally, the experimental results indicates that the design strength of the CFS wall frame stud can be increased in the range of 39% to 595% based on the shape and slenderness.

Thermal behavior of external-insulated cold-formed steel non-load-bearing walls exposed to different fire conditions

An external-insulated cold-formed steel (CFS) wall is a potential configuration that overcomes the disadvantage of cavity insulation in the fire performance of such walls and can meet the sound and thermal insulation requirements for building structures by increasing the thickness of insulation material. This paper conducted eight mid-scale non-load-bearing fire experiments on external-insulated wall specimens. Four different fire conditions were tested, including ISO 834 fire, external fire, hydrocarbon fire and a typical realistic design fire. A quasi-steady heat transfer state was identified at the final stage of external fire exposure. The effect of substituting the cavity insulation with external insulation on the fire performance is discussed by comparison with the previous fire experiments on cavity-insulated CFS walls. The results show that external insulation is a more reasonable configuration than cavity insulation for improving the fire resistance of CFS walls. In addition, two types of stud buckling, which include the local buckling of the whole stud section and local buckling of stud hot flange and adjacent web, were identified for non-load-bearing walls in fire, and the corresponding cause and conditions were described. In addition, to achieve high efficiency in the thermal performance modeling of CFS walls in fire, a quick and simplified calculation method was developed to get the temperature profile of steel frame based on a one-dimensional finite difference method. Moreover, an unexposed surface temperature of 900 °C was recommended as the criterion to predict the falling-off of the fire-side face-layer gypsum plasterboards of CFS walls in the heat transfer modeling.

Lateral performance of a new hybrid CFS shear wall panel for mid-rise construction

ABSTRACT Hybrid shear walls composed of cold-formed steel (CFS) open sections and square hollow sections (SHS) have recently attracted attention for lightweight midrise buildings, as a result of their relatively strong lateral load-bearing performance. A new hybrid CFS shear wall system with SHS truss skeleton is presented in this study in order to improve the lateral behaviour of lightweight steel frames, in compliance with standard codes. For this purpose, eleven full-scale experimental tests were conducted to assess the shear resistance, stiffness, ductility, and energy absorption of the proposed wall panels. The study also investigates the failure modes of the hybrid walls and suggests solutions for improving the existing structural weaknesses. The results showed that employing the SHS truss configuration for one side of the light steel walls can significantly enhance the energy absorption, compared to the traditional CFS walls. The SHS truss also has a considerable effect on decreasing the chance of chord stud buckling; i.e. load-bearing capacity. Specimens sheathed with gypsum board offer higher strength and ductility ratio with a few minor localized failures, compared to specimens without sheathing board. The results also indicate that the low strength to weight ratio of hybrid walls makes them a practical solution for mid-rise lightweight constructions.

Study on Hear Resistance of Cold-formed Steel Composite Wall with Openings

In order to study the shear resistance of cold-formed steel wall with openings, a numerical model of the specimen for cold-formed steel wall with openings shear test was established using Opensees software, which was used to simulate its shear resistance under cyclic loading. On this basis, the parameters of the factors affecting the shear resistance of cold-formed steel wall with openings were analyzed. The results show that the contribution of the coupling beam to the shear performance of the whole wall is reduced with the increase of the span-depth ratio of coupling beam. When span-depth ratio of the coupling beam is greater than 5, the contribution of the coupling beam to the shear resistance of the wall is ignored. The ratio of opening to wall and the ratio of window to wall have a great influence on the shear resistance of cold-formed steel wall with openings, and the influence of each factor on the shear performance of the cold-formed steel wall with traditional side column is greater than that of the cold-formed steel wall with reinforced end studs. The stiffness of the side column has little effect on the shear resistance of the cold-formed steel wall with openings.

Structural behaviour and design of plywood sheathed cold-formed steel wall systems subjected to out of plane loading

An experimental study was conducted to explore the strength contribution of plywood sheathing boards that are regularly used in the cold-formed steel (CFS) wall panel construction. A series of material tests and 4-point bending full-scale tests were carried out. The testing program includes various key design factors such as sheathing board thicknesses, screw spacings and slenderness of the CFS studs. The test results indicate that the plywood sheathing thickness of 12 mm is sufficient for restraining the lateral torsional buckling (LTB) of the slender CFS studs, which also increased the ultimate moment capacity of the CFS wall panel by a maximum of 150%. However, the improvement in flexural strength varies depending on the local and global slenderness of the CFS wall stud. The spacing between the sheathing-screw connection also significantly influenced the structural contribution of plywood-sheathing. The design calculations were carried out as per the AISI design provisions and latest improvements suggested by the previous research works. The design calculations indicate that the design moment capacity of the CFS wall panel can be increased by a maximum of 48%, and most of the design results are conservative compared to the experimental results. Although, it was found that the modified design provisions of AISI are reliable for the strength predictions, the failure modes predicted greatly varied compared to the experimental results. Therefore, a series of individual sheathing screw connection tests were carried out to discover the key factors that influence the bracing effect of sheathings. On the basis of the results obtained from individual sheathing connection tests, the preliminary modifications that are required for the accurate failure mode predictions are suggested.

Experimental Research on the Shear Performance of the Two-Storey Composite Cold-Formed Thin-Walled Steel Wall

The composite wall made of the cold-formed thin-walled steel has good shear performance. When it is used in buildings, its weak part is located at the joint of floors and becomes the first broken part under the action of the earthquake. The shear test of five Two-storey Composite Cold-formed Thin-walled Steel Walls (TCS) under cyclic loading has been carried out. The influences of axial pressures, types of anti-pulling bolts and panel materials on shear performances are examined. The results show that under the same working condition, the energy dissipation capacity of calcium silicate panel specimens is significantly lager than that of the gypsum panel specimens, and the ultimate bearing capacity is also greater. The axial pressure has a great influence on the ultimate bearing capacity and energy dissipation capacity of the specimens. Compared with the specimens designed according to the Ref. (JGJ227-2011, 2011), the energy dissipation capacity of all specimens is increased by 3.25 times. The extrusion between the self-tapping screw and the wall panel causes the screw to fall off, resulting in a sharp decrease in the rigidity of the specimens at the initial loading stage. After the failure of the wall panel, the bottom and top beam are restricted by double nuts of the anti-pulling bolt at the joint of floors, so the bearing capacity of specimens decreases slowly at the later loading stage. The tilt angle of anti-pulling bolt increases when the TCS wall is loaded to the later stage. The force state of the self-tapping screw on the hold-down is changed from bearing shear force to bearing tension and shear force, resulting in fast failure of the anti-pulling bolt suit. The load borne by the anti-pulling bolt suit is transferred to floor beams and their supporting stiffeners, causing them to collapse rapidly.

Postearthquake fire experiments of cavity-insulated cold-formed steel load-bearing walls lined with plasterboards

Postearthquake fire is one of the most frequent secondary disasters facing mankind. This paper presented a detailed postearthquake fire investigation of cavity-insulated load-bearing cold-formed steel (CFS) walls lined with double-layer gypsum plasterboards on both sides. Five identical full-scale specimens with 3.0 m lengths and 3.0 m widths were constructed. The first two specimens were subjected to axial compression under the condition of ambient temperature or fire, respectively. The other three specimens were first tested under cyclic loading to different drift ratios, and then the fire experiment was carried out. The relationship between the drift ratio and fire resistance time (FRT) is presented, and the following conclusions are drawn. (1) When the drift ratios are less than 2.0%, the reduction of postearthquake FRT is insignificant and should be within 10 min. However, when the drift ratio reaches 3.5%, the residual postearthquake FRT is only 8 min, and the failure mode of wall framing changes to local crushing near the bottom of studs; It is because that local buckling near the bottom of stud occurs from cyclic loading before fire tests, leading to the separation of fire-side sheathing from wall studs. (2) The effect of axial thermal expansion constraints provided by rigid floor slabs to the CFS wall studs is significant under fire conditions. It will accelerate the structural failure of load-bearing CFS walls. (3) For the gypsum-sheathed load-bearing CFS walls, the existence of cavity insulation not only reduces the FRT, but also may change the failure mode of wall studs.

Full-scale experiments of gypsum-sheathed cavity-insulated cold-formed steel walls under different fire conditions

Most previous fire experiments of cold-formed steel (CFS) walls focused on ISO 834 fire. The corresponding results may not represent the actual fire performance of CFS walls in some special circumstances. This paper presents a full-scale experimental investigation of gypsum-sheathed cavity-insulated CFS walls under four different fire conditions. The results show that the axial load has an insignificant effect on the heat transfer of such walls in fire. This realization provides a basis for the indirect coupling method of thermal-mechanical analysis of CFS walls, in which the time-temperature profiles of non-load-bearing CFS walls are adopted in the thermal-mechanical analysis of load-bearing walls. In addition, for CFS walls with the same configuration and load level, different fire conditions do not change the failure mode of steel studs; in particular, the stud hot flanges exhibit almost the same temperature when the structural failure of CFS walls occurs. Hence, a new time equivalency method of CFS walls is proposed, which uses the same temperature of hot flange as the principle of equivalency. Meanwhile, both the equal area method and energy-based method are modified by using reference temperatures, and give a good prediction of the fire resistance time equivalency of CFS walls. Moreover, significant opening of gypsum board joints is observed during the fire exposure; however, this phenomenon is an inherent characteristic of heated gypsum boards and has insignificant correlation with the out-of-plane deflection of CFS walls. Furthermore, staggered board joints are recommended as an important and effective fire resistance configuration of CFS walls.

Pseudo-Dynamic Tests of Cold-Formed Thin-Walled Steel Wall

This paper presents the dynamic response and failure mechanism for the cold-formed thin-walled steel wall. Based on current seismic provisions and previous research, Full-scale pseudo-dynamic tests (PDTs) were conducted on a 3m high cold-formed thin-walled steel wall. The time-history response, hysteretic behaviour, failure mode, stiffness degradation and ductility were investigated to analyse the dynamic response of the cold-formed thin-walled steel wall structure under a series of ground motion records. The results showed that the structural deformation position was concentrated at the intersection of the cross bar and the diagonal bar in the middle of the wall, and other joints had no obvious plastic deformation; The structure was still elastic under the frequently occurred earthquake of 7 degree and 8 degree. Under the rare earthquake, the stiffness degradation was developed rapidly and the bearing capacity was still higher, and also had better ductility. Cold-formed thin-Walled steel structure which exhibits excellent seismic behaviour and ductility, can be used as a reliable and effective assembly structure in seismic regions.

An overview of analysis of Cold-formed steel stud wall subjected to blast loading

This paper is aimed at presenting an overview of research performed worldwide related to analysis of Cold-formed steel (CFS) wall subjected to blast loading. The basics regarding definition of blast, the merits and demerits of using CFS for blast resistant structures, connection details, the methods of improving blast resistance of structures are included in this paper. The overview presented in this paper based on the earlier research works published in journal provide an insight into the topic and the research needs are also highlighted.

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.

Thermal performance of non-load-bearing cold-formed steel walls under different design fire conditions

Most previous fire experiments of cold-formed steel (CFS) walls focused on the ISO 834 or the E119 fire curve. Although the fire performance of CFS walls under ISO 834 or E119 curve can be theoretically converted to that under other fire curves, the corresponding time equivalency methods have not been experimentally examined. This paper presents an experimental investigation of non-load-bearing CFS walls under four different fire conditions. It is proved by the experiments that the maximum temperature of the design fire curve is one of the most important indexes for representing the severity of fire exposure. Especially, the maximum temperature of 680 °C for external fire was not severe to the present non-load-bearing CFS walls. Two specimens were subjected to 285 min of external fire but demonstrated an almost steady-state heat transfer process. Meanwhile, the hydrocarbon fire and realistic design fire demonstrated much more severe damage. It is also proved for the first time that neither the equal area method nor the energy-based method was suitable for the fire-resistance time equivalency of CFS walls. Based on post fire observation, significant local crushing of studs was identified, especially after the fall off of fire-side sheathing. Additionally, it was found that replacing the fire-side base-layer gypsum plasterboard with low-bulk-density calcium-silicate board extends the insulation and structure performance of CFS walls under fire conditions. Moreover, a simplified temperature distribution model and the critical temperature on the fall off of fire-side gypsum plasterboard were recommended for the numerical modeling of CFS walls.

Estimation of Inelastic Interstorey Drift for OSB/Gypsum Sheathed Cold-Formed Steel Structures under Collapse Level Earthquakes

In order to estimate the inelastic interstorey drift of cold-formed steel (CFS) framed structures under collapse level earthquakes, the deflection amplification factor ηp is employed in this paper to compute the maximum interstorey drift ratio (IDRmax) from an elastic analysis. For this purpose, a series of CFS wall specimens were tested under cyclic horizontal loads, and then the hysteresis model of the walls was put forward by test results. In terms of the hysteresis model, a large quantity of elastic-plastic time-history analysis of CFS building structures was conducted based on the storey shear-type model. Furthermore, the deflection amplification factor ηp for estimating IDRmax and the parameters were analyzed. The results indicate that the deflection amplification factor ηp is highly dependent on yielding coefficient of storey shear force ξy, storey number N, period of structure T, and ground acceleration records GA. Eventually, an approximate ξy-N-ηp relationship for estimating the deflection amplification factor ηp is proposed in this paper, which can be used for seismic design in practices.

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.

Numerical study on racking behavior of light steel frames with K-shaped bracing

PurposeThis paper aims to study the lateral behavior of cold-formed steel walls with K-shaped bracing by finite element modeling.Design/methodology/approachThe braces which have the same section as those for studs and tracks are connected to the frame by screw connections. By pushover analysis, lateral performance of two frame categories, with different dimensions and bracing arrangements, is examined, and the force-displacement diagram and the ultimate strength of walls are extracted. Probable failure modes during lateral loading including distortional buckling of studs, buckling in braces and failure of connections are simulated in the numerical model, and some strengthening suggestions would be offered to prevent brittle failures and, therefore, to increase the lateral strength of the walls.FindingsThe strengthened walls are examined, and their seismic behavior is compared with the original walls. Finally, a parametric study is carried out to evaluate the effect of factors such as thickness of frame members, frame height and yield tension of members on lateral behavior of the shear walls.Originality/valueIn the present research, lateral strength and failure modes of nine types of cold-formed steel shear walls with different arrangements of K-shaped bracing are examined by non-linear finite element analysis, and a parametric study is carried out to extract the effect of the wall frame characteristics on the lateral behavior. Shear walls are classified into two series.

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.