Use Of Cold-formed Steel Research Articles

Buckling resistance of axially loaded cold-formed steel built-up stiffened box sections through experimental testing and finite element analysis

The use of cold-formed steel (CFS) built-up sections in engineering practice is widely gaining popularity due to their ability to provide sustainable solutions and optimised section design opportunities. This paper presents an experimental and numerical investigation conducted on CFS built-up stiffened box section columns under axial compression. A total of 13 new experimental tests were conducted with specimens having an overall web depth up to 550 mm. Detailed nonlinear elasto-plastic finite element (FE) models were then developed and verified against the test results. Upon verification, a parametric study involving 144 FE models was carried out to investigate the effects of section thickness, column length, and screw spacing on the buckling resistance of CFS built-up stiffened box sections. The test and finite element analysis (FEA) results were compared with the buckling resistances determined by the American Iron and Steel Institute (AISI S100) and Australian and New Zealand Standards (AS/NZS 4600). It was found that the buckling resistances determined by the AISI S100 and AS/NZS 4600 for CFS built-up stiffened box sections were conservative by 9.3% on average, compared to experimental and FEA results. Modified Direct Strength Method (DSM) design equations for predicting the buckling resistances of CFS built-up stiffened box sections were then proposed, and a reliability analysis was conducted to assess the feasibility of the proposed equations.

Axial strength of slotted perforated cold-formed steel channels under pinned-pinned boundary conditions

The use of cold-formed steel (CFS) channel sections is becoming popular as the load-carrying members in building structures, and such channel sections are often perforated for the ease of installation of services. However, limited experimental investigation has been reported in the literature for such channel sections under pinned-pinned boundary conditions. In this paper, a total of 16 CFS channel sections with and without slotted web holes were tested under pinned-pinned boundary conditions, and it was shown that all specimens with short lips failed by distortional-local buckling interaction controlled by distortional buckling and all specimens with long lips failed by local buckling. Moreover, the slotted web holes caused the axial capacities to decrease slightly by 2.4% on average for specimens failed mainly by distortional buckling and 6.4% on average for specimens failed by local buckling. A nonlinear elasto-plastic finite element (FE) model was also validated against the test results, a parametric study was conducted using the validated FE model. In addition, the results obtained from the tests and parametric study were compared against the results predicted by the current direct strength method (DSM) in AISI S100–16 for CFS channel sections with web holes. It indicates that the results predicted by the DSM are un-conservative for most CFS channel sections with web holes under pinned-pinned boundary conditions, especially un-conservative by 27.0% on average for CFS channel sections failed by local buckling. Therefore, new design formulas were developed based on the current DSM formulas for CFS channel sections with web holes.

DSM design of LSF walls subject to distortional buckling

With the new advancements in constructions technologies, the use of cold-formed steel (CFS) construction is becoming popular due to its inherent advantages over conventional construction materials. These high performing CFS sections, such as the web stiffened lipped channel studs, are more likely to be subjected to distortional buckling under compression load. Although many numerical and experimental studies have been undertaken on unsheathed CFS columns subjected to distortional buckling, there is limited research on light gauge steel framed (LSF) walls subject to distortional buckling. The behaviour of sheathed wall studs is significantly different to that of columns due to the complicated boundary conditions provided by the stud-to-sheathing contact interactions and screw connections. Although CFS design standards recognize the sheathing boards as a means of providing lateral and rotational restraints, they do not provide any information on their effects on studs subject to distortional buckling. In this study, the suitability of currently available numerical modelling techniques on predicting the distortional buckling behaviour of LSF walls was investigated. It was identified that the distortional buckling capacity is highly sensitive to the in-plane restraints provided by screw connections. The effects of stud geometry, stiffness of screw connections and stud length on the distortional buckling capacity were investigated in a detailed numerical parametric study involving more than 3500 finite element analyses. Finally, the accuracy of the current direct strength method was investigated and suitable modifications are proposed. Moreover, alternative simplified design methods and their accuracy are also discussed.

The Influence of Web Holes on the Behaviour of Cold-Formed Steel Members: A Review

The use of cold-formed steel (CFS) members in structural engineering has been on the increase recently due to a wide range of benefits. The placement of electrical and/or plumbing installations within the floor or wall thickness requires that members are being manufactured with holes along the web, inevitably affecting their resistance. This article aims at providing a useful and comprehensive overview of the existing literature regarding CFS members with web holes. Experimental and numerical research on CFS members with web holes subjected to pure compression, bending, web crippling and shear is outlined and discussed. Although research on these types of members date back to the early 1970s, the greatest progress in the research field of CFS members with web holes was achieved during the past 15 years; hence, mostly the research conducted during this period was addressed. Additionally, design proposals are summarised for each of the aforementioned stress states. A brief description of the main concepts of design presented in four principal design codes, as well as numerical solution methods for predicting global, local, and distortional buckling modes, is also presented, aiming to collect the accessible up-to-date knowledge of CFS members with holes and identify areas that were modestly covered by previous research.

A Critical Review on Optimization of Cold-Formed Steel Members for Better Structural and Thermal Performances

The construction and building sectors are currently responsible globally for a significant share of the total energy consumption and energy-related carbon dioxide emissions. The use of Modern Methods of Construction can help reduce this, one example being the use of cold-formed steel (CFS) construction. CFS channel sections have inherent advantages, such as their high strength-to-weight ratio and excellent potential for recycling and reusing. CFS members can be rolled into different cross-sectional shapes and optimizing these shapes can further improve their load-bearing capacities, resulting in a more economical and efficient building solution. Conversely, the high thermal conductivity of steel can lead to thermal bridges, which can significantly reduce the building’s thermal performance and energy efficiency. Hence, it is also essential to consider the thermal energy performance of the CFS structures. This paper reviews the existing studies on the structural optimization of CFS sections and the thermal performance of such CFS structures. In total, over 160 articles were critically reviewed. The methodologies used in the existing literature for optimizing CFS members for both structural and thermal performances have been summarized and presented systematically. Research gaps from the existing body of knowledge have been identified, providing guidelines for future research.

Numerical study on the rotation capacity of SIP-strengthened cold-formed steel beams

The use of cold-formed steel (CFS) beams in moment-resisting frames (MRFs) has recently become a topic of interest to many researchers. In this research, a numerical study has been performed to investigate an innovative seismic protection system and new energy dissipation technique called steel interconnected part (SIP), to allow CFS to be used in regions with high seismic activity. Through this technique, a steel part has been connected to 2C-channel back-to-back CFS beams to improve both strength and structural behavior. The steel part does not require much space because of its shape, which can be easily connected to the CFS beams. Finite element procedure in ABAQUS has been used to model the 2C-channel back-to-back connected with a through plate by bolts. In this paper, a total of 240 models have been studied under monotonic loading and 27 models under cyclic loading. The rotation capacity of CFS beams strengthened with SIP has been reported with different through plate dimensions. Different beam profile slenderness ratios with different geometric configurations for SIP have been studied. In the CFS beams without SIP, early loss of strength has been observed with premature flange and web buckling. The results revealed that the beams are strengthened using SIP can delay local failures and improve strength, initial stiffness, ductility and energy dissipation behavior, which cannot be attained by conventional CFS elements and connections. The proposed SIP system revealed promising results, that could achieve all the desired performance objectives and satisfy the requirements of common seismic codes.

Behavior of CSC-Type Shear Connectors under Pry-Out Shear Test: Analytical Study

The use of cold-formed steel (CFS) shapes in steel-concrete composite sections has increased over the past 20 years in the construction industry worldwide. This system has constructive advantages such as high load-bearing capacity, high stiffness and ductility, ease of transportation and assembly, and full usage of the capacity of the materials. Additionally, CFS sections are considered a sustainable alternative in construction.The capacity of the system depends on the effectiveness of shear connectors during the transfer of stress between materials. Currently, the push-out experimental test follows a standardized procedure to evaluate the capacity of shear connectors in composite sections, but CFS shapes have demonstrated premature failures by local buckling, thus questioning the applicability of the experimental test for such configurations.In this research, the capacity of the proposed confined shear connectors (CSC) is evaluated in composite systems, through the alternative pry-out test methodology. From numerical models, the effects of the steel shape thickness, the thickness of concrete slabs, the compressive strength of concrete and the separation between connectors in composite systems are studied. The analysis concluded that, under this test methodology, the separation between connectors does not represent statistically significant changes in the final capacity of the composite system.

Experimental Investigation and Load Capacity of Slender Cold-Formed Lipped Channel Sections with Holes in Compression

The use of cold-formed steel (CFS) channels with circular or rectangular web holes is becoming increasingly popular in building structures. However, such holes can result in sections becoming more susceptible to buckle and display lower load-carrying capacities. This paper presents a total of 42 axial compression tests of CFS lipped channel slender columns with and without circular and rectangular web holes, including different hole sizes and cross sections. The test results show that the axial members with a small ratio of width to thickness were governed by global buckling, while the members with a large ratio of width to thickness were controlled by the interaction of local, distortional, and global buckling. The axial strength decreased maximum by 20.48% and 22.98% for the member with circular holes and rectangular holes, compared to a member without a web hole. Then, a nonlinear elastoplastic finite element model (FEM) was developed, and the analysis results showed good agreement with the test results. The validated FE model was used to conduct a parametric study involving 36 FEMs to investigate the effects of column slenderness, dimension of the hole, and the number of holes on the axial strength of such channels. Furthermore, the formulas to predict the global buckling coefficient and the effective area were modified for such sections with holes by using the verified FEM. Finally, the tests and parametric study results were compared against the design strengths calculated in accordance with the developed method. The comparison results show that the proposed design method closely predicts the axial capacity of CFS channels with circular or rectangular web holes.

Performance-based assessment of CFS strap-braced stud walls under seismic loading

The use of cold-formed steel (CFS) systems has significantly increased in the past few decades, especially in the construction of low to mid-rise buildings. Compared to hot-rolled sections, CFS members are often more economical and efficient due to their low weight, ease and speed of construction and greater flexibility in manufacture. In most conventional CFS buildings, diagonally strap-braced stud walls provide the primary lateral force-resisting system. This study aimed to develop a better understanding of the structural behaviour of CFS strap-braced stud wall systems under seismic loading. To achieve this, a detailed numerical model was developed, accounting for material nonlinearity, initial geometric imperfections, nonlinear behaviour of the connections and secondary moments due to P-Δ effects. This model was validated against previous experimental results on full-scale wall systems. A comprehensive parametric study was then conducted using the validated model to investigate the effect of key design parameters, namely the number of studs, the presence and intensity of vertical loading, the thickness of the structural elements and the steel grade of the straps, on the seismic performance of the system. The lateral load-resisting capacity, deformation capacity, ductility and energy dissipation under lateral loading were investigated and are here discussed. An efficiency index was proposed for each of these variables, allowing design solutions to be rated in terms of their ability to improve the material efficiency of the system, and design recommendations were derived for performance-based design.

Moment capacity of back-to-back cold-formed steel channels with edge-stiffened holes, un-stiffened holes, and plain webs

The use of cold-formed steel (CFS) back-to-back channels as floor joists is increasing steadily, and such beams often include un-stiffened holes for installation of services, which reduces their flexural strength due to the reduced web area. A new generation of CFS channels with edge-stiffened holes has been widely used. However, no research has been undertaken to understand the effects of composite actions on moment capacity of such built-up beams. In this paper, fourteen new experiments are reported on back-to-back channels with various hole spacing, which were tested under four-point loading. Finite-element models were also established and validated with the experiments. Upon validation, a parametric study involving 63 FEMs was conducted to investigate the effects of beam length, diameter of hole, stiffener length and fillet radius. The test results show that for back-to-back channels with five edge-stiffened holes, the moment capacity increased by 15.4%, compared to that of a plain channel. For comparison, the same section with un-stiffened holes had a 15.1% reduction in moment capacity. Test results also show that distortional buckling was the predominant failure mode for all cases. The test and FE results were compared against the design moment capacities predicted by the American Iron and Steel Institute (AISI) and Australian and New Zealand Standards (AS/NZS) for plain channels. For channels with holes, design procedure was proposed by Moen and Schafer. It is revealed that these equations are conservative by around 23% and 49% for CFS channels with un-stiffened and edge-stiffened holes, respectively.

BEHAVIOR OF PARTIAL STRENGTH OF BEAM-TO-COLUMN CONNECTION WITH GUSSET PLATE FOR COLD-FORMED STEEL SECTIONS

The use of cold-formed steel (CFS) as part of a major construction has been rapidly increasing recently, as it is considered viable as an alternative to the conventional hot-rolled steel section. However, information about CFS as part of a non-composite system is still limited as the connection is designed as a pinned connection, only good for roof trusses and wall paneling. The aim of this research is to propose a connection for CFS sections that could enhance the strength of typical CFS connections, from pinned to partial strength connections. This paper presents the behavior of the partial strength of a non-composite beam-to-column connection for a cold-formed steel section where a gusset plate was used as a stiffener. This type of proposed connection for CFS is not limited only to the construction of roof trusses and wall cladding, but is also able to provide better flexural strength in semi-continuous construction. The proposed connections consisted of 6 specimens divided into two types, the first of which were stiffened by the gusset plate and the second of which were enhanced further with the top, seat and web angles. From the results of the experimental tests it was concluded that all the proposed connections can be categorized as partial strength connections, where the strength was more than 25% of the connected beam and suitable for use in semi-continuous construction. A relatively good agreement was recorded for the comparison between the experimental results and the predicted results from the EC3 component method super-imposed with a haunched gusset plate and top, seat and web angle components, which differed in the range of 1.31 to 1.5 times for the moment resistance and 1.07 to 1.37 times for the stiffness of the proposed connections.

Structural Size Optimization of Single and Built-Up Cold-Formed Steel Beam-Column Members

AbstractThe use of cold-formed steel (CFS) elements in residential and industrial buildings is widely gaining popularity due to their ability to provide cost-effective and sustainable solutions. A ...

Distortional buckling behavior and design method of cold-formed steel lipped channel with rectangular holes under axial compression.

The use of cold-formed steel (CFS) channel sections with rectangular holes in the web is becoming gradually popular in building structures. However, such holes can result in sections becoming more susceptible to be distortional buckling and display lower load-carrying capacities. This paper presents a total of 44 axially-compressed tests of CFS lipped channel columns with and without rectangular web holes including different hole sizes and cross-sections. The test results show that the specimens were controlled by distortional buckling or interaction of local buckling and distortional buckling. The load-carrying capacities of specimens with rectangular holes were lower than that of specimens without hole. The load-carrying capacities of specimens were gradually decreased with the increasing of dimensions of holes. Then a nonlinear elasto-plastic finite element model (FEM) was developed and the analysis results showed good agreement with the test results. The validated FE model was used to conduct a parametric study involving 16 FEM to investigate the effects of the section, the dimension of the hole, and the number of holes on the ultimate strength of such channels. Furthermore, the formulas to predict the distortional buckling coefficient were developed for the section with holes by using the verified FEM. Finally, the tests and parametric study results were compared against the distortional buckling design strengths calculated in accordance with the developed method. The comparison results show that the proposed design method closely predict the load carrying capacity of CFS channel sections with rectangular web holes.

Parametric study and simplified design equations for cold-formed steel channels with edge-stiffened holes under axial compression

The use of cold-formed steel (CFS) channels with web holes are becoming increasingly popular. Such holes, however, result in sections becoming more susceptible to lower axial compressive resistance. Traditional holes are normally punched at the web and un-stiffened. Recently, a new generation of CFS channels with edge-stiffened holes has been developed by the CFS industry but no information is available in the literature to accurately predict the axial capacity of such sections. The current design guidelines in accordance with the American Iron and Steel Institute (AISI 2016) and Australia New Zealand standards (AS/NZ 4600:2018) do not provide any design rules for CFS channels with edge-stiffened holes. In this paper, a numerical model that accurately simulated results from the experimental testing of CFS channels with edge-stiffened holes under axial compression as published in a previous paper by the authors was employed to carry out a parametric study which involved 348 finite element (FE) models. Variables which were examined included column slenderness, stiffener length, fillet radius, hole size, hole location and hole spacing. A comparison of the numerical results with current design rules for CFS channels with un-stiffened holes revealed that the design equations were not accurate for such sections; design equations are therefore proposed in which an enhancement factor is applied to the original equations. The enhancement factor was obtained using bivariate linear regression analysis. The proposed design equations closely predict the enhanced axial capacity of CFS channels with edge-stiffened holes.

Behaviour of rectangular gusset plate with angle cleat connections for cold-formed steel section

Cold-formed steel (CFS) members designed with proper stiffener can significantly increase the loading capacity of the connected member even though they are thin and slender. Design recommendations of connections especially for CFS sections are mostly related to the load-carrying capacities of individual fasteners such as bolts, screws, and rivets. The proposed bolted top-seat flange cleat joint in this paper should be able to categorize as semi-rigid that can further enhance the use of CFS in structural steel. This paper aims to investigate the behaviour of cold-formed steel section with gusset plate integrated with angle cleats. The full-scale isolated joint test was conducted on three specimens where the size of column size is C30024, and the size of beams is C20024, C25024, and C30024. All sections are 2.4mm thick. The connections were stiffened with a rectangular gusset plate of 10mm thick and angle cleat of 6 mm thick, respectively. The result of the test showed that the moment resistance (Mj) of the connection for beam sections C20024, C25024 and C30024 were 45.3 kNm, 48,8 kNm, and 52.5 kNm respectively. The initial stiffness (Sj,ini) of the connections for beam section C20024, C25024 and C30024 were 510 kNm/rad, 650 kNm/rad and 610 kNm/rad respectively. The experimental results showed that the ratio of the moment resistance ranged from 1.00 to 1.16, and the ratio of initial stiffness ranged 1.00 to 1.35 as compared to the numerical analysis adopted from EC3 code.

Experimental Analysis of Cold-Formed Steel C-Sections with the Notch Subjected to Axial Compression

Studies on the use of cold-formed steel (CFS) C-section, which is a civil engineering material, in building and civil engineering work are still on-going. The advantages of the CFS C-section are becoming so interesting that it is often being used as a roof truss system, storage rack, and wall framing. In order to have a roof truss system with a strong, safe, and stable condition, a study on truss member was carried out using the cut-curving process. Before the CFS C-section was curved, the process started by cutting the section in a proper way. A parametric study was conducted to determine the suitability of the cut pattern which recognised as a notch in the section and find out whether or not the notch depth would affect the ultimate load of the CFS C-section column. The study of CFS C-section was separated into two parts; firstly, to investigate the mechanical behaviour of the column in different notch depths and secondly, to investigate the behaviour in different column height with fixed notch depth. The notch width of 3 mm and notch spacing of 100 mm for both parts were fixed. Total specimen for both parts were 15 specimens. The results of the study showed that the reduction of the ultimate load was about 56–65% of the variation of notch depth section when compared with the normal section. Therefore, the ultimate load of the section with the notch decreased when the notch depth increased. In addition, the study illustrated that the reduction of the ultimate load was 64–82% of the variation of column height between 100 mm to 500 mm. Finally, the average percentage of the column height was 72% which can use in the modification of CFS C-section without notch to CFS C-section with notch calculation.

Experimental and analytical study on composite connection with cold-formed steel of double channel sections

The opportunity of Cold-Formed Steel (CFS) as an alternative construction material is still worth to be considered. The amounts of research concerning using this material is the evidence that the use of CFS is getting more acceptable. However, the studies of CFS as part of composite joint is yet to be established. This paper presents the use of 10mm thick hot-rolled gusset plate slipped between double lipped C-channel arranged back-to-back to form the proposed composite connection. Two specimens with and without seat angle were tested until failure. The weakness of thin plate behavior at the joint area was reduced by means of angle stiffener placed at the column web. The calculation procedure was developed due to limited design rule in Eurocode for this connection type, and compare with the experimental results to obtain the relationship between these two methods. It can be concluded that the use of seated angle has contributed to an increase in connection capacity.

Effects of edge-stiffened web openings on the behaviour of cold-formed steel channel sections under compression

The use of cold-formed steel (CFS) channel sections are becoming popular as the load-carrying members in building structures, and such channel sections often include web openings for the ease of installation of services. Traditional web openings are normally punched, and are unstiffened which can restrict the size and spacing of web openings. Recently, a new generation of CFS channel sections with edge-stiffened web openings has been developed, and is widely used in New Zealand. However, no experimental investigation has been reported in the literature for such channel sections under compression. In this paper, a total of 75 results comprising 26 axial compression tests and 49 finite element analysis results are reported on the compression resistance of CFS channel sections with both edge-stiffened and unstiffened web openings. For comparison, channel sections without web openings were also tested. For all specimens, initial imperfections were measured using a laser scanner. A nonlinear elasto-plastic finite element model was also developed, and the results showed good agreement with the test results. A parametric study was conducted using the validated finite element model to investigate the effect of opening spacing and column length on compression resistance of channel sections. It is shown that for the case of a channel section having seven edge-stiffened web openings, the compression resistance increased by as much as 22%, compared to a plain channel section. For comparison, the same section having unstiffened web openings had a 20% reduction in compression resistance, compared to a plain channel section.

Effect of screw distance on combined profiles cold-formed steel in increasing the compression member capacity

The use of cold-formed steel (CFS) as a frame in a single-story structure building system has been widely applied. However, the use of cold-formed steel for multi-story buildings is still constrained in the structure system, especially column. In the conventional structure, columns used in large dimension, height, h> 150 mm and thickness, t> 1.2 mm which makes the construction cost expensive. An innovation of cold-formed steel combine profile into one compression member unit is very interesting to study, furthermore, previous research provides information on a variety of cold-formed steel behaviors with small dimensions of height, h <150 mm and thickness, t <1mm, which can be developed into columns with greater strength. There have been a lot of research on behavior on cold-formed steel, but the study on screw optimization especially on combined profile to become compression member still need to develop. From the compression test on double profile back to back and flange to flange length, l = 300 mm and screw distance variation, 25 to 150 mm with 50 mm intervals, indicating a response similarity at screw spacing 25 mm, 50 mm and 75 mm, while the screw distance 100 mm, 125 mm and 150 mm experienced backline capacity.

Sustainability of Cold-formed Steel Portal Frames in Developing Countries in the Context of Life Cycle Assessment and Life Cycle Costs

There is often a demand in developing countries for single-storey buildings, for industrial and agricultural use. Whilst conventional hot-rolled steel sections are still commonly used for the primary column and rafter members, for frames of modest span (up to 30m), a viable alternative can be the use cold-formed steel sections. Advantages include pre-galvanised sections that do not require painting to prevent rusting; reduced transportation and acquisition costs as the cold-formed steel used for the secondary members can come from the same supplier; bolted joints that are easy to assemble on site. This paper compares both types of portal steel buildings in terms of a life-cycle assessment (LCA) and a life-cycle cost (LCC). Three sizes of buildings are considered: 18m, 24m and 30m. It is shown that in terms of the primary framing, use of cold-formed steel for the 18m and 24m span buildings can result in up to 30% less embodied carbon than hot-rolled steel. However, when secondary members and cladding are taken into account in the LCA, the differences in embodied carbon of cold-formed and hot-rolled steel are found to be negligible. LCC is concerned not only with the cost of the steel, but also with the labour costs and the cost of having a crane on site. It is shown that the 18m and 30m span cold-formed steel frames are cheaper than the hot-rolled steel frames by 33% and 15%, respectively, primarily owing to the fact that the erection of cold-formed steel portal frames have less demand for having a crane onsite. The use of LCA and LCC has therefore helped quantify associated embodied carbon and costs, with differences between section types for the primary framing shown to be relatively negligible when considered in context of the entire building, and the real differences between the two types of steel due to the ease of erection on site.