Cold-formed Thin-walled Steel Research Articles

Experimental study on monotonic loading of joint of multi-limb assembled cold-formed thin-walled steel concrete composite column and H-shaped steel beam

Experimental study on monotonic loading of joint of multi-limb assembled cold-formed thin-walled steel concrete composite column and H-shaped steel beam

Research Status and Development of Assembled Lightweight Steel Composite Structures

Prefabricated lightweight steel composite structures are characterized by efficient load-bearing, seismic energy-saving, and eco-friendly attributes, primarily used in low-rise and multi-story buildings, adapting to the development of modern architectural industrialization. This review covers the development process, system composition, and current research status of structural seismic performance for typical prefabricated lightweight steel composite structures, including prefabricated cold-formed thin-walled steel structures, prefabricated lightweight steel-lightweight concrete structures, and prefabricated lightweight steel composite frames - lightweight steel composite shear wall structures. The analysis includes the technical features, standard systems, and current environmental applications of the aforementioned structures, raises several issues in the research of prefabricated lightweight steel composite structures, and provides a research outlook for the future development direction of prefabricated lightweight steel composite structures.

Experimental, Numerical and Analytical Evaluation of Load-Bearing Capacity of Cold-Formed S-Beam with Sectional Transverse Strengthening.

The article provides information about strengthening cold-formed thin-walled steel beams made of the sigma profile. An innovative concept for sectional transverse strengthening of thin-walled beams subjected to concentrated forces was investigated. The proposed solution's novelty lies in attaching the sectional transverse strengthening to the beam's cross-section, employing a point crimping technique. This technique requires a specific modification of the cross-section edges, necessitating double-lipped flanges. This strengthening method is innovative, as it has not been previously applied to cold-formed structures. Typically, strengthening is achieved using other cold-formed elements or materials, such as timber, lightweight concrete, or CFRP tapes. The laboratory experimentally validated the proposed method using short- and medium-length beams. The experimental results were then compared with the results of the numerical analyses and the conventional design approach described in EC3. The results demonstrated the feasibility of implementing this type of strengthening, its reliability under load, and the confirmation of an increase in the load-bearing capacity of the experimental samples by 11-24%.

Bond-Slip Behavior Between C-Shaped Steel and Foamed Concrete in CTS Composite Structural Members

The bond-slip behavior between cold-formed thin-walled steel (CTS) and foamed concrete (FC) is a critical issue in the mechanical performance of FC-filled CTS composite wall structures. Thus, this study provides experimental and theoretical research on the bond-slip behavior between CTS and FC. A total of eleven specimens were tested using push-out configurations, considering the number of web holes, foamed concrete (FC) strength, anchorage length, and CTS section splice form. A constitutive model for bond-slip was proposed, and the regression formulas for accurately predicting the characteristic bond strength between CTS and foamed concrete were established. A finite element model was developed to investigate the bond-slip mechanism at the interface between CTS and FC. The bond-slip constitutive model accurately fits the experimental and finite element results. The results indicate that the ultimate bond strength of the specimens increases with the number of web holes; when the number of web holes reaches two, the ultimate bond strength is 155.4% of that of the non-perforated specimens. As the concrete strength increases from 3.43 MPa to 11.26 MPa, the ultimate bond strength of specimens with two web holes improves by 23.1%, while non-perforated specimens have a 54.7% enhancement. When the anchorage length is extended from 200 mm to 400 mm, the ultimate bond strength decreases by 29.3%. Additionally, when steel sections are joined in a double-span I form, the bond strength increases by 91.6% and 95.8% compared to the single-span form and the double-span box form, respectively.

Experimental and numerical investigation on ductile fracture of Q235 cold-formed thin-walled steel

In order to simulate the full-range moment-rotation characteristic of steel storage rack beam-to-upright connections incorporating material fracture, this paper presents experimental and numerical investigations into the fracture behaviour of Q235 cold-formed thin-walled steel (CFTWS) flat and corner materials. A total of 43 specimens derived from Q235 CFTWS plates were tested. Two different thicknesses (1.8 mm and 3.25 mm), three varied bend angles (0°, 70° and 90°), and five types of specimens representing different stress states, were considered. The load-displacement curves and fracture characteristics of each specimen were derived from tests. The refined numerical models were established and validated by the test data. Based on experimental and numerical simulation results, four commonly used ductile fracture models for metal materials were calibrated and compared. The results show that the verified LMVGM fracture model is applicable to Q235 CFTWS flat and corner materials, and then compiled into a USDFLD subroutine in numerical simulation models to predict the flexural behaviour of storage rack beam-to-upright connections. The comparison between test and numerical simulation results illustrates that the established ductile fracture model for Q235 CFTWS materials can accurately simulate the fracture related failure modes of beam-to-upright connections in CFTWS storage racks.

Study on heat transfer behavior of CFS-PSB composite walls

The cold-formed thin-walled steel (CFS)-paper straw board (PSB) composite walls takes as the research object. The thermal performance of the wall was analyzed by the building heat transfer theory and the finite element analysis software ANSYS, explored the influence of relevant parameters on heat transfer coefficient of composite wall and proposed supplementary correction coefficient for applying the type of composite walls. The heat flux density field, temperature distribution field, node temperature, and heat transfer coefficient of the walls were also obtained. The specific parameters analyzed using this model mainly included the insulation material, web height, thickness of the section steel, width of the flange, length of the hole, number of hole rows, and horizontal and longitudinal spacing of the holes. The findings show that an increase in the web height reduces the heat transfer coefficient of the composite wall, which is conducive to improving the thermal insulation performance of the walls. The CFS-PSB composite wall with a web opening can significantly improve the heat transfer performance of the wall, reduce heat loss, and control the local thermal bridging phenomenon. The hole length, specific gravity of the openings, and number of openings were the main parameters affecting the thermal insulation performance of the walls.

Resistance of the Steel Lap Joints Connected by Spot Welding and Brazing

Welding technologies are constantly evolving, and their applicability is expanding, considering also the construction domain. Steel structures benefit from the advances in welding technologies due to the use of thin gauge steel sheets which can now be connected at high quality and automatically. The resistance of the connection between the thin steel sheets is crucial for the durability and safety of a structure made of built-up thin-walled cold-formed steel elements. Generally, self-drilling screws or bolts are used for the connection between thin-walled elements, but the quantity of time and manpower necessary for a large number of connections demands an improved solution. Conventional welding techniques are unsuitable for joining thin sheets, ranging from 0.4 to 1.0 mm to thicker ones measuring 1.0 to 3.5 mm. This article compares the results of an experimental investigation into lap joints connected by spot welding and MIG brazing with the design code provisions. The study examines single-lap joints in steel sheets of 0.8, 1.0, 1.2, 1.5, 2.0 and 2.5 mm thickness, connected using these welding technologies. The results obtained are then compared with analytical relations and processed according to EN 1990. Depending on the thickness of the connected sheets, spot welding can lead to two failure modes: button pull-out fracture and interfacial fracture. MIG brazing, a welding technology that deposits material below the melting point of the base material, is known for its advantages, such as low energy consumption, spatter-free operation, high welding speed, and compatibility with thin sheet metals. However, its application in the structural engineering of cold-formed elements lacks documentation. In the study, the MIG brazed specimens failed in the heat-affected zone of the connection. The results indicate the dependence of the spot weld lap joint resistance on the connected sheets' thickness, while the resistance of the MIG brazed lap joints is influenced by the minimum thickness of the connected steel sheet. The study aims to demonstrate the feasibility of the proposed solutions, evaluate their performance, and establish the limits of their applicability. A statistical interpretation of the results highlights the precision and reliability of joint resistance.

Microstructural Investigation and Mechanical Properties of Resistance Spot Welding Joints of Mild Steel Sheets

Due to its high productivity, low cost, and increased work efficiency, resistance spot welding (RSW) can instantly join two or more steel sheets and it is widely used in the automotive industry and lately in the manufacturing of thin-walled cold-formed steel constructions. However, the RSW of zinc-coated mild steel sheets presents metallurgical challenges, especially when different thickness combinations are used. Therefore, in the present paper a resistance welding machine was used which uses direct current (MFDC) inverter technology combined with SMART AUTOSET technology to weld S250 GD and S350 GD galvanised mild steel sheets with different thicknesses. It is well known that, due to the elevated temperature that occurs during the welding process, followed by rapid cooling, defects such as cracking, porosity, lack of fusion, and an increased amount of brittle phases affect the welding quality. Therefore, the influence of the RSW process parameters established by an automatic sequence on the nugget geometry, microstructure, and mechanical properties was investigated. The phase transformations that took place during the heating-cooling cycle were analysed in detail through metallographic studies. The results showed that the microstructure of the weld nuggets was similar, characterised by columnar grains elongated in the direction of heat evacuation. Nevertheless, there were differences in terms of phase dispersion, defects and mechanical properties that have been linked to the RSW process parameters.

Buckling behavior of thin-walled cold-formed steel latticed column with lacings under axial compression

Extensive research has been undertaken on built-up cold-formed steel (CFS) column with I-shaped or box-shaped section. However, there has been little attention given to lattice CFS columns, particularly regarding their buckling performance and the design methods for determining buckling capacity. This paper proposes a latticed CFS column, formed by combining two G-shaped (complex edge stiffener) channels using lacings (LCCFS). Eighteen LCCFS columns were tested under axial compression, divided into two groups with web widths of 75 mm and 200 mm. The experimental results demonstrated that no distortional buckling failure occurred in the G-shaped channels of all specimens, mainly due to the constraint provided by lacings on the flanges. A general consistency in the ultimate bearing capacities and failure modes was observed among duplicate specimens. Specimens with a small slenderness ratio predominantly experienced local buckling failure, leading to a more abrupt failure. In contrast, specimens characterized by a large slenderness ratio primarily demonstrated failure due to global buckling. The specimens with larger web width-to-thickness ratios exhibited earlier and more pronounced local buckling, resulting in a reduction in axial compressive stiffness. Furthermore, FE models have been developed to analyze the effects of different parameters on the axial compressive buckling performance of LCCFS columns. The existing direct strength method exhibited notable deviations in predicting axial compressive buckling capacity of LCCFS column, which are deemed unsatisfactory. Based on direct strength method, a method was proposed for determining the axial compressive buckling capacity of LCCFS column.

Experimental Study and Design Method of Cold-Formed Thin-Walled Steel Unequal-Leg Angles under Axial Compression

An experimental study of cold-formed thin-walled steel unequal-leg angles (CFTWS-ULAs) under axially oriented pressure is presented in this paper. Firstly, the initial imperfections and material properties of the angle specimens were measured in detail. The angle specimens were tested under fixed-ended conditions. The results of the experiments showed that the angle specimens with small slenderness ratios were susceptible to local buckling, the angle specimens whose legs had high slenderness ratios and low width–thickness ratios were found to easily suffer from the occurrence of flexural buckling, and the angle specimens whose legs had high width–thickness ratios were found to easily suffer from the occurrence of interactive buckling between local buckling and flexural buckling. The finite element analysis of the ULAs was conducted using ABAQUS6.14 finite element software by creating a model. The buckling modes and ultimate bearing capacities of the test specimens were compared, and the finite element analysis verified that the established model built using the finite element is credible and subsequent parametric analysis was performed. The slenderness ratio had the most significant impact on the ultimate bearing capacities of the unequal-leg angles, as indicated by the analysis results. When the width–thickness ratio and the width ratio of the legs fell within a specific range, the ultimate bearing capacities of the unequal-leg angles increased as the width–thickness ratio and the width ratio of the legs increased. Finally, the comparison results showed that the design strengths predicted by the specifications were very conservative, because the local buckling and torsional buckling were calculated at the same time. Therefore, a recommendation was proposed that the calculation of the load-carrying capacity of an unequal-leg angle should ignore torsional buckling.

Verification of Numerical Models of High Thin-Walled Cold-Formed Steel Purlins.

High thin-walled cold-formed steel purlins of the Z cross section are important elements of large-span steel structures in the construction industry. The present numerical study uses the finite element method to analyse the 300 mm and 350 mm high Z cross sections in-depth. The prepared numerical models are verified and validated at several levels with experiments that have been previously published. Significant agreement between the numerical models and the experimental results regarding Mises stress, proportional strain, failure mode, and force-deformation diagram have been obtained. With the verification, the presented procedure and partial findings can be applied to other similar problems. The results can be used to help research and corporate groups optimise the structural design of cold-formed thin-walled steel structures.

Research on post-fire mechanical properties of thin-walled cold-formed steel and its influence on the Σ-shaped columns after fire exposure

This paper conducts a comprehensive investigation into the post-fire mechanical properties of thin-walled cold-formed steel (CFS) and evaluates the design method for the post-fire load-bearing capacity of CFS lipped channel section with web stiffener (Σ-shaped) columns. A total of 144 tensile tests were conducted to determine the mechanical properties of CFS after exposure to heating treatment. The study considered the effects of varied material strengths (Q235 and Q420), plate thicknesses (1.5 mm and 2.5 mm), extraction positions (flat plate, 90° corner, and 45° corner), as well as heating temperatures ranging from 20 °C to 800 °C. The research indicates that the heating temperature does not have a prominent influence on the elastic modulus of CFS, whereas its impact on yield strength is pronounced. After exposure to 800 °C, the yield strength of CFS can be reduced by 40 %, but the strain-hardening effect by cold-working still existed, which enhanced the yield strength by up to 20 %. This paper presents a predictive formula for the reduction factor of the mechanical properties. To assess the influence of post-fire mechanical properties on the load-bearing capacity of CFS columns, a finite element model of Σ-shaped columns was developed and calibrated. The simulation results indicate that the post-fire strain-hardening effect at corners would enhance the load-bearing capacity by less than 6 %. Finally, based on a parametric analysis, it was demonstrated that the Direct Strength Method (DSM) applied for distortional-local interaction buckling columns was still effective once the post-fire mechanical properties were incorporated when slenderness factor λdl > 1.5.

Eccentric compressive performance and design of asymmetric steel columns with complex edges

Box-type houses often use asymmetric cold-formed thin-walled steel columns with complex edges to meet structural requirements. However, there is a need to clarify the mechanical properties of eccentric loading in this section of the steel column. This study conducted eccentric compression tests on 24 asymmetric cold-formed thin-walled steel columns with complex edges, clarifying the specimens' ultimate load-bearing capacity and buckling mode. The results showed that the resistance to pressure provided by the corner was higher than that provided by the two crimped edges. Subsequently, a finite element model was established, and its accuracy was verified by comparing it with experimental results. Finally, based on the formula for calculating the nominal axial strength in AISI, the direct strength method formula for the stable bearing capacity of asymmetric cold-formed thin-walled steel columns with complex edges under in-plane eccentric compression was proposed. This method takes into account the local-global interactive buckling and distortional-global interactive buckling. The comparison between the theoretical calculation results and numerical simulation results demonstrated that the design method proposed in this study is effective and conservative. It can provide a reference for future engineering applications.

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.

Numerical and Experimental Analysis of Buckling and Post-Buckling Behaviour of TWCFS Lipped Channel Section Members Subjected to Eccentric Compression.

The paper presents a static analysis of the buckling and post-buckling state of thin-walled cold-formed steel (TWCFS) lipped channel section beam-columns subjected to eccentric compression. Eccentricity is taken into consideration relative to both major and minor principal axes. An analytical-numerical solution to the buckling and post-buckling problems is described. The solution is based on the theory of thin plates. Equations of equilibrium of section walls are derived from the principle of stationary energy. Then, to solve the problem, the finite difference (FDM) and Newton-Raphson methods are applied. Linear (buckling) and nonlinear (post-buckling) analyses are performed. As a result, pre- and post-buckling equilibrium paths are determined. Comparisons of the obtained numerical results, FE simulation results, and experimental test results are carried out and presented in comparative load-shortening diagrams. Additionally, a comparison of the buckling forces and buckling modes obtained from theoretical analysis and experiments is presented.

Panels of Cold-Formed Steel Profiles: Possibility of Their Use to Repair War-Damaged Large-Panel Buildings

Abstract In the paper, we present the results of an analysis of data samples of 282 damaged buildings; the samples include the age of the building, the type of vertical bearing structures, the type of construction of the external walls, the method of the insulation of the walls, the number of floors, the buildings’ functions, and the extent of the damage. The primary objective of the analysis was to evaluate the possibility of using panels of cold-formed thin-walled steel profiles to repair the damaged structures. The results of a study of typical projects of large panel buildings that were constructed in Ukraine and an analysis of the practical experience of repairing these types of buildings after blast actions can also be found. The research tasks are defined for implementing this technology in the process of repairing large panel buildings.

Bending Properties of Cold-Formed Thin-Walled Steel/Fast-Growing Timber Composite I-Beams

A cold-formed, thin-walled steel/fast-growing timber composite system has recently been presented for low-rise buildings. It aims to increase the use of fast-growing wood as a green building material in structures, thus contributing to the transformation of traditional buildings. This study proposed a composite I-beam combined with fast-growing radiata pine and cold-formed thin-walled U-shaped steel. A four-point bending test was used to measure the bending properties of steel–timber composite I-beams under various connection methods. Based on experimental results, this study examined the specimen’s failure mechanism, mechanical properties, and strain development. In addition, a method for calculating flexural bearing capacity based on the superposition principle and transformed section method was suggested. It is evident from the results that fast-growing timber and cold-formed thin-walled steel can have significant composite effects. Different connecting methods significantly impact beams’ failure mode, stiffness, and bearing capacity. Furthermore, the theoretical method for calculating the flexural bearing capacity of composite beams differs from the test value by less than 10%. This paper’s research encourages the applications of fast-growing wood as light residential components, and it serves as a reference for the development, production, and engineering of steel–timber composite structural systems.

Numerical study on the seismic performance of phosphogypsum-filled cold-formed thin-walled steel composite walls

To conduct in-depth research on the seismic performance of phosphogypsum (PG) filled cold-formed thin-walled square steel tube (PFCFS) composite walls, a series of finite element analyses were conducted using the software ABAQUS. The study examined various factors, including PG strength, oriented strand board (OSB) configuration and thickness, stud strength and thickness, screw spacing, axial force ratio, wall sheathing coverage, and height-width ratio. After summarizing, the main findings are as follows: the lateral behavior of walls is significantly affected by PG strength and wall stud thickness, while wall sheathing configuration has a relatively low impact; increasing PG strength, wall stud thickness and strength, wall sheathing thickness, axial force ratio, and the number of wall sheathings (non vs. single vs. double sheathing), or decreasing self-tapping screw spacing and wall height-width ratio enhance the shear capacity of the wall; increasing PG strength, wall sheathing thickness, or reducing wall height-width ratio improve the lateral stiffness and ductility of the wall; increasing wall stud thickness and adding more wall sheathing can improve the lateral stiffness of the wall. However, this can reduce the wall's ductility; by decreasing self-tapping screw spacing or increasing axial force ratio, the lateral stiffness and ductility of the wall exhibit an increasing-then-decreasing trend; increasing wall stud strength does not significantly affect the lateral stiffness of the wall, but it does decrease the ductility. Finally, the simulated lateral stiffness and shear capacity of the wall were compared with the theoretical values, which showed good agreement.

Fracture behaviour of thin-walled cold-formed steel at elevated temperatures

Cold-formed steel (CFS) is being increasingly used in structural applications due to its high strength-to-weight ratio, ease of construction and versatility. The performance of CFS structures in fire has received signification recent attention, but the fracture behaviour of thin-walled CFS at elevated temperatures, which is fundamental to the fire response of the key components, like connections has yet to be extensively studied; this is therefore the subject of the present paper. First, using experimental data on cold-formed grade S280GD+Z275 steel at elevated temperatures from the literature, damaged true stress-strain curves considering the post-necking behaviour are determined. Then, a fracture prediction approach, implemented in the finite element analysis software Abaqus and considering ductile damage and a damage evolution law is calibrated and validated against the experimental data. Finally, the applicability of the proposed approach to different types of CFS material, including high-strength CFS, is assessed. The results show that the proposed model can accurately predict the fracture behaviour of CFS at elevated temperatures.

Lateral load behavior of shear connections between steel storage racks and the spine bracing with posts

High-rise steel storage racks are cold-formed thin-walled steel frames, which achieve their lateral strength and stiffness by the use of a spine bracing system in the down-aisle direction commonly located at a short horizontal distance away from the main rack frames. The shear connections between the main rack frame and the spine bracing system play a dominant role in the effectiveness of the spine bracing system. This paper experimentally investigates the behavior of the shear connections used in industrial practice between a steel storage rack and the spine bracing system with posts using four groups of three nominally identical connection specimens. By employing a digital image correlation (DIC) system, the tests generate comprehensive data and establish the real-time deformation fields of individual components of such shear connections. Based on the component-based approach, a linear-elastic analytical model is developed for the type of shear connections under consideration. The proposed analytical model explicitly captures the behavior of the individual connection components, including the three-dimensional flexural bending of endplates, as well as the distortions of the open sections of the upright and the bracing post. Based on the proposed model, this paper quantifies the contribution of each component towards the total deformation of the shear connections. The investigation establishes that the cross-sectional distortion of the bracing post and the out-of-plane bending of the upright web are the most flexible components of such shear connections. Recommendations associated with the shear connections under consideration are proposed for the rack designers and manufacturers.