Cold-formed Steel Wall Research Articles

Heat transfer mechanism of superabsorbent polymers phase change energy storage cold-formed steel wall under fire

The superabsorbent polymer phase change materials (SAP materials) exhibit exceptional water absorption and retention properties, offering substantial potential for fire protection in steel structures, thereby reducing the need for sheathing boards and fire-retardant coatings, while minimizing energy consumption. Understanding the heat-mass exchange theory of SAP materials is crucial for enhancing their application in the building industry. This study develops a comprehensive theoretical model for heat-mass exchange in cold-formed steel (CFS) walls incorporating SAP materials. An equilibrium phase change model and a simplified thermal radiation model were developed to capture the water loss and dynamic heat exchange processes in SAP materials. These models were integrated into a transient fluid-solid-thermal coupling model using Ansys Fluent and User Defined Functions. In the case study, the newly developed numerical models can accurately predict temperature field changes in CFS walls with SAP materials, demonstrating the heat transfer mechanisms of hot and cold flanges at different temperature rise stages. The developed numerical model was used to investigate the effects of factors such as the moisture content of the SAP material, web depth, and flange width on the fire resistance of the CFS wall. Results indicated that increasing the wall stud height improves fire resistance, while increasing flange width has little effect on hot flange temperature. These findings provide a theoretical foundation and practical guidelines for the application of SAP phase change insulation materials in the building industry, promoting energy reduction and supporting sustainable construction practices.

Fire performance of superabsorbent polymers protected full-scale cold-formed steel wall lined with plasterboards

Superabsorbent polymers (SAPs) have shown promise in enhancing the fire resistance of steel structures because of their exceptional absorbency and water retention capabilities. This study innovatively applies SAP insulation to cold-formed steel (CFS) walls with gypsum (GP) boards to improve fire performance. One full-scale CFS wall underwent axial compression testing at ambient temperature, and four full-scale fire experiments were conducted on CFS walls with load ratios of 0.27 and 0.85. All specimens were sheathed with double layers of GP boards, and rock wool served as the cavity insulation, with SAP insulation material applied to the cavity of wall studs. Additionally, a novel finite element model was developed to simulate the fluid-heat interaction within a furnace-CFS wall. The simulation results showed that SAP insulation material significantly changes the fire-induced failure mode in wall studs at a 0.27 load ratio, transitioning from hot flange (HF) local buckling to local buckling of the whole stud section. The inclusion of SAP insulation material absorbs heat, effectively delaying the rise in wall stud temperature. This property significantly enhances the structural performance of CFS walls during fire exposure. With SAP insulation material, the fire resistance time of the CFS walls increased by over 66 min compared to non-SAP insulation material counterparts. Moreover, increasing the stud web depth and reducing the HF width-to-thickness ratio can enhance the fire performance of CFS walls. The HF critical failure temperature of specimen S2 with an HF width-to-thickness ratio of 80 was 783 °C, 150 °C higher than that of specimen P2 with an HF width-to-thickness ratio of 67. Additionally, the adverse effect of screws on the fire performance of the CFS wall was localized. After 120 min of fire exposure, the temperature on the ambient side, which was severely influenced by the screws, was 360 to 370 °C.

Effect of solid blocking on lateral bracing requirements for cold-formed steel wall studs

The effectiveness of horizontal bracing in increasing the strength of cold-formed steel (CFS) load-bearing walls has been widely acknowledged. However, while significant research has been conducted regarding the bracing requirements for CFS bearing walls, the effect of solid blocking, which prevents columns (studs) within the wall from rotating, has not been fully explored. In this study, we propose an analytical method to quantitatively assess the effect of solid blocking on bracing requirements for CFS load-bearing walls. This method is comprehensive as it can be applied to systems with different bracing patterns, load patterns, or non-identical columns (studs), and it accounts for the columns’ initial curvature and semi-rigid end connections. It has been verified that considering the solid blocking always decrease the bracing requirements because the existence of solid blocking increases the system’s stiffness and subsequently decreases the additional displacement as well as the brace force, as expected. An example consisting of 23 CFS studs is presented to illustrate how the effect of solid blocking on bracing requirements is influenced by the location and interval of solid blocking, the stiffness of column end connections, and the characteristics of tie bracing. The results indicate that the effect of solid blocking on bracing requirements increases when the location of solid blocking is closer to the anchor and the solid blocking interval is smaller. Moreover, a modification to the equation in AISI S100 is proposed to account for the effect of solid blocking on the strength requirement of tie bracing. Overall, this research contributes to a better understanding of the role of solid blocking in CFS load-bearing walls and provides insights for optimizing bracing design in practice.

Fire resistance time prediction and optimization of cold-formed steel walls based on machine learning

Many full-scale experiments and numerical studies have been conducted to determine the fire performance of cold-formed steel (CFS) walls, but these studies are expensive and time consuming. This study proposes a machine learning (ML) based framework aiming at accurately predicting the fire resistance time (FRT) and optimizing the design of CFS walls under ISO 834 fire condition. To overcome the limitation of 32 experimental data points in the literature, a validated numerical method was used to generate 592 data points to expand the dataset of CFS walls, considering different wall configurations, various sheathing board types and thicknesses. The XGBoost (eXtreme Gradient Boosting) model was trained with numerical data and tested with experimental data. The hyperparameter tuning of the XGBoost model was implemented with Bayesian optimization, and it was found that the XGBoost model accurately predicted the FRT of CFS walls, with R2 and MAPE values being 0.933 and 8.46 %, respectively. The prediction process of the XGBoost model was interpreted by the SHAP (SHapley Additive exPlanations) method to determine the relative importance of input variables. The NSGA-II algorithm was adopted to optimize the FRT-cost dual-objective of CFS walls and the Pareto front including optimal solutions was emerging. The cost for each solution of Pareto front sets was lower than that in the real dataset at same FRT level. This phenomenon implied that the ML-based optimization framework successfully identified the cost-efficient design process. The proposed ML-based optimization framework offers a promising alternative for engineers to design CFS walls effectively with both mechanical and economic objectives.

Restoring force model of phosphogypsum-filled cold-formed thin-walled square steel tube composite wall

The phosphogypsum (PG)-filled cold-formed thin-walled square steel tube (PFCFS) composite wall is a new type of cold-formed steel (CFS) wall. The restoring force model (including the skeleton curve and hysteresis rules) is an important performance of this type of walls. Based on the characteristics of load–displacement curves of the walls, a Pinching4 model for the skeleton curve of the walls is developed. The lateral stiffness and shear capacity of the walls are calculated by theoretical formulas, while other parameters are determined through data fitting. Moreover, the hysteresis rules of the walls adopt the Pivot model, and the Pivot parameters (α and β) of the walls are determined based on the principle of equal energy. Finally, based on the above restoring force model, the energy dissipation analysis for the walls with different parameters was conducted. The results show that improving the PG strength, stud thickness, or reducing the height-width ratio of the walls significantly enhances the energy dissipation capacity of the wall; increasing the OSB thickness, axial force ratio, or reducing the screw spacing gradually improves the energy dissipation capacity of the wall; the OSB configuration and the stud strength have a smaller impact on the energy dissipation of the wall; the energy dissipation capacity of the wall when the hold-down fails is lower.

Seismic performance of various types of cold-formed steel composite shear walls with CFRP-toughened screw connections

The cracking of screw connections at the corners of wallboards is a typical failure mode for cold-formed steel (CFS) shear walls, resulting in premature performance degradation of CFS structures. A toughening method with carbon fiber reinforced polymer (CFRP) sheets at screw connection locations is proposed for strengthening the CFS shear walls. Totally 6 full-scale CFS shear walls with or without CFRP-toughened connections were tested, and the parameters of the lamination scheme, wallboard type and screw distance were investigated. A numerical model is developed for simulating the seismic behaviour of the tested specimens, and a theoretical model for predicting their shear strength is proposed. Results showed that the shear strength and lateral stiffness of the CFS walls with CFRP-toughened screw connections increased by more than 30 %, and the continuous lamination scheme provided greater strength. The fastener-based numerical model could effectively be used for predicting the hysteretic performance of toughened CFS shear walls well; both the pinch behaviour and ultimate strength are predicted well, and it can be used as an effective tool for the seismic design of toughened CFS shear walls with a theoretical model.

Fire performance enhancement of cold-formed steel walls: experimental and numerical study

Cavity-insulated cold-formed steel (CFS) walls, with gypsum plasterboard (GP) on both sides, are widely used in the construction industry. However, their fire performance is compromised by the faster rise in the temperature of the hot flange (HF), which is influenced by cavity insulation and board joints. This study aims to optimize cavity insulation configuration to enhance fire performance. Two mid-scale, non-load-bearing fire experiments on CFS walls were conducted, employing double-layered GP boards and rock wool insulation, under ISO834 time-temperature fire conditions. Meanwhile, a finite element model of physical space fluid-heat coupling of furnace-CFS walls considering joints with time was developed to reveal joint mechanisms and configurations. The results showed that non-insulated stud CFS walls had slower HF temperature rise and similar insulation compared to insulated counterparts, delaying HF temperature reach to 537 °C by 14 min. The base-layer joints had the least adverse impact on the HF temperature rise than overlapped joints and face-layer joints. The HF temperatures for various joint configurations reached 537 °C at different times: 57 min for the face layer, 62 min for the base layer, and 49 min for overlapped joints. Considering the construction cost-effectiveness, it was found that adding steel strips (the same width as the flange) at the joint position could significantly decelerate the HF temperature rise. In 60 min, the HF temperature in the model with additional steel strips dropped by 94 °C lower than in the 10 mm overlapped joint model. Finally, based on finite element results, design equations were proposed for predicting HF temperature variation over time across joint types.

Numerical studies of pull-through failures in cold-formed steel battens at sub-zero temperatures

Cold-formed steel (CFS) roof and wall cladding systems comprising thin, high strength steel battens and claddings are popularly used in the building industry worldwide. These cladding systems have been observed to encounter failures under combined snow and strong wind actions during blizzards. Significant damage is caused by the disengagement of the entire roof/wall cladding when localised pull-through failures occur in thin-walled steel battens at the batten to truss/rafter screw connections due to a splitting mechanism around the screw head. This study uses detailed finite element analyses of the pull-through failures of a range of batten configurations under combined wind and sub-zero temperature conditions. Suitable finite element models capable of simulating the pull-through failures of battens were developed and validated using experimental results, followed by detailed numerical parametric studies. The main outcomes of this study are accurate design equations and capacity reduction factors essential for predicting the pull-through capacities of CFS battens at sub-zero temperatures.

A novel modular CFS composite frame-wall structure: Experimental investigation and numerical analysis

Due to the advantages with short-time installation and waste reduction, modular structures are promising. In the process of applying cold-formed steel (CFS) structures in multi-rise buildings, the combination of steel frames and CFS walls can improve the lateral performance of the structures. A novel modular CFS composite frame-wall structure was proposed, which was comprised by modular steel frames and modular CFS shear walls. Five full-scale modular CFS frame-wall components derived from the composite structures were tested under cyclic loads. The layout of sheathings, configuration of CFS diagonal bracings and door openings were varied to study their effects on lateral performance of the modular CFS composite structures. The results indicate the modular steel frames and CFS shear walls can do well in working cooperatively. The bearing capacity of the specimens with sheathings is more than twice that of the specimens without sheathings. In contrast, the effect of the diagonal bracings is not so significant due to the failure of the screw in the ends. Besides, the simplified models based on equivalent line elements was put forward and verified by experiments. A 6-story CFS composite frame-wall archetype structure was designed and its 3D numerical model was built on basis of the mentioned above simplified approaches. The nonlinear time-history analyses were carried out to evaluate the seismic response of the structures. Results show that the inter-story drifts of the designed structures under the earthquake waves of collapse levels are less than the drift limits 1/50. The designed structures have good seismic performance.

Fire behavior of full-scale cold-formed steel center-sheathed shear walls under combined loads

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

Experimental, numerical and analytical studies on full-scale cold-formed steel center-sheathed shear walls subjected to combined loading

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

Seismic performance and risk mitigation of CFS shear walls with CFRP-reinforced screw connections and special-shape L-section end studs

Cracking damage of screw connections and buckling of end studs always resulted in performance degradation of cold-formed steel (CFS) shear walls. To improve the seismic performance and to avoid the brittle failure of CFS shear walls, two methods for strengthening CFS walls are proposed in this paper: carbon fiber reinforced plastic (CFRP) toughened screw connections (CFRP-SC) and special-shape built-up end studs with L-shaped sections (SBC-L). A total of 5 full-scale strengthened CFS walls with CFRP-SC or SBC-L were tested to examine the performance, and simplified numerical models of strengthened CFS walls and 5-story CFS buildings were developed and validated. Nonlinear dynamic analyses are performed to investigate the effects of those two methods on seismic responses and risks of CFS buildings, and the risk mitigation of CFS buildings is then discussed. The results show that the CFS shear walls with CFRP-SC can mitigate the damage to screw connections and wallboards nearby those connections, especially for the connections at the corners of the walls. The connections could continually dissipate the earthquake energy due to large loading and deformation capacities. The SBC-L can effectively delay the buckling failure of end studs, thus enhancing the shear resistance of CFS walls. Due to the two methods, the collapse probability of the CFS building with CFRP-SC in service life is reduced by almost 40.8%, and that of the building with CFRP-SC and SBC-L is reduced by almost 59.7%.

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.

Study on the shear resistance of CFS walls with built-up side columns

This study experimentally and numerically investigated the shear resistance of cold-formed steel (CFS) walls with built-up side columns. Horizontal monotonic and reversed cyclic loading tests were performed on four full-scale CFS walls. The influence of aspect ratio on the shear resistance of the walls was investigated in terms of load-displacement curves, skeleton curves, energy dissipation, stiffness degradation, and cyclic bearing capacity degradation. The shear capacity, stiffness, and energy dissipation capacity of CFS walls with built-up side columns (CFSWs) were effectively improved with decreasing aspect ratio. In addition, finite element models of the wall specimens were established using ABAQUS and validated against the test results. A parametric study with twelve finite element models was also conducted to examine further the effect of essential parameters, including the aspect ratio, stiffeners, and thickness, on the lateral behavior of CFSWs.

Experimental investigation on seismic performance of cold-formed steel strap-braced stud walls under lateral cyclic and vertical loading

Cold-formed steel (CFS) construction offers several benefits over traditional construction, including being lightweight, sustainable, recyclable, quick to build, insect and rot-resistant, and suitable for computer-aided design and manufacture. Despite extensive research on CFS elements, there are still gaps in our understanding of the behaviour of CFS structural systems, particularly their response to severe earthquake events. This experimental program aims to provide a better understanding on the seismic behaviour of strap-braced stud-walls as a lateral force resisting system for residential medium-rise buildings. An innovative test rig is developed that is capable of applying a constant vertical load during lateral cyclic testing, replicating the loading conditions expected during an earthquake event in such cases. For the first time, seven full-scale tests are conducted on CFS walls under vertical and horizontal loading using standard sections in New Zealand. The vertical capacity, lateral stiffness, ultimate strength, ductility, and failure mechanisms of the specimens are investigated. Subsequently, a modified detailing is suggested, which allows CFS walls to exhibit considerably better seismic behaviour compared to the systems with conventional detailing. It is shown that by adopting the modified detailing, CFS walls exhibit an ideal elastic-plastic curve with negligible degradation in successive cycles and a high ductility factor exceeding 5. The results of this study should prove useful for more efficient design of CFS strap-braced stud walls for mid-rise buildings.

Pull-out failure capacities of cold-formed steel batten screw connections at sub-zero temperatures

Cold-formed steel (CFS) roof and wall cladding systems are used worldwide, and are constructed using high-strength, thin steel battens and claddings. In North American countries, which are frequently subjected to blizzards (winter storms), these cladding systems are particularly vulnerable to pull-out failures during combined windstorm and snowy conditions. Despite extensive research studies investigating the pull-out failure mechanism and the critical parameters of screw connections between cladding and battens at ambient temperature, the behaviour of these connections under blizzard conditions has not been experimentally investigated. To fill this knowledge gap, an experimental study was undertaken that included 144 laboratory tests of screw connections in battens of varying grades and thicknesses, and three distinct types of screws. The pull-out failure capacities of screw connections in battens were evaluated under wind suction loading at four different temperatures, including ambient and sub-zero temperatures. The results of the study provided insights into the pull-out failure mechanisms of screw connections in battens and enabled the development of suitable design rules for combined wind action and sub-zero temperature conditions. The findings of this study are expected to be of significant value to engineers and building designers who are involved in the construction of lightweight cold-formed steel buildings.

Structural displacement estimation by a hybrid computer vision approach

Structural displacement is an important indicator of structural safety in structural health monitoring (SHM). As one of the vision-based methods, optical flow can provide displacement measurement of pixels in images. However, estimating structural displacement by predicting the optical flow between the current frame and the initial frame may be subject to limited accuracy due to environmental variations. Alternatively, calculating structural velocity by predicting the optical flow of adjacent frames and integrating to obtain displacement may introduce displacement drift attributable to cumulative errors. This study proposes a hybrid structural displacement estimation method to eliminate the effects of environmental variations and cumulative errors. In comparison to the existing methods, the novelty of the proposed method is to effectively integrate deep learning-based dense optical flow and correlation template matching (CM), for achieving both high accuracy and improved robustness. Deep learning-based dense optical flow was used for optical flow prediction between adjacent frames through correlation calculations and iterative updating to obtain the structural velocity. Pyramid-accelerated CM was employed to locate the regions of interest (ROI) of the structure in each frame, and the structural displacement was then estimated by counting temporal changes in these locations. By fusing estimated structural velocity and displacement using the Kalman filter, optimized structural displacement results were obtained, and temporal cumulative errors using dense optical flow could be eliminated. The proposed method was validated in an indoor shaking table test of a three-story reinforced concrete structure, and an outdoor shaking table test of a cold-formed steel wall system. The results indicated that the proposed method reduced the root mean square error of estimated displacement by over 89% compared with dense optical flow and by over 36% compared with CM. Furthermore, the proposed method was able to process 1080p high-definition images at a rate of 5.43 frames per second, indicating its high efficiency for applications.

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

Fire performance of gypsum-sheathed cold-formed steel walls with rectangular section studs

This study conducted axial compression experiment of one full-scale CFS wall at ambient temperature and four full-scale fire experiments of CFS walls with two initial load ratios of 0.27 and 0.85. Specimens were sheathed with double layers of gypsum plasterboard, rock wool was the cavity insulation and the wall studs had rectangular cross sections. A finite element model was used to optimize the arrangement of rock wool cavity insulation for the CFS walls. The results showed that the failure mode changed from local buckling of the hot flange under a load ratio of 0.27 to local buckling of the whole stud section under a load ratio of 0.85. The fire resistance time of the specimen without rock wool insulation in the stud cavity was 7 min longer than that of the specimen with rock wool insulation. This was attributed to the thermal radiation effect of the stud cavities, which delayed the increase in hot flange temperature and improved the fire resistance time of the CFS walls. Thus, for CFS walls with rock wool-insulated cavities, the stud cavity configuration was more reasonable without than with rock wool insulation. When the axial thermal expansion load was considered, the load on the wall studs increased by a maximum of 43.3 kN per stud. In addition, for CFS walls with low load ratios of 0.27, the wall studs near the face-layer board joints tended to buckle first.