Cold-formed Steel Channel Sections Research Articles

Axial capacity of cold-formed steel channel sections with slits

Cold-formed steel (CFS) studs often include slits in their webs to improve thermal performance. However, the inclusion of such slits reduces their axial capacity. The literature contains limited experimental studies on the axial capacity of these studs with slits, and no non-linear elasto-plastic finite element studies have been reported. This research aims to address this gap. Non-linear elasto-plastic finite element models were developed and validated against experimental test results. A parametric study consisting of 960 finite element analysis (FEA) models was then conducted, covering the effects of different channel dimensions, slit sizes, section thicknesses, and stud lengths. Ultimate axial capacities obtained from these analyses were compared to the current codified direct strength method (DSM) predictions as per the Australian/New Zealand Standard AS/NZS 4600. Finally, design recommendations in the form of strength reduction factors are proposed. Based on these recommendations, modified DSM design equations with a reliability index above 2.5 are presented.

Experimental and numerical investigations on cold-formed titanium-clad bimetallic steel angle and channel section stub columns

Titanium-clad bimetallic steel (TCBS) exhibits outstanding corrosion resistance, and can be advantageously applied in corrosive environments. This study investigated an innovative application of TCBS in cold-formed stub columns. During the cold-forming process, TCBS demonstrated no discernible separation at the bonding interface of the Q235 substrate layer and TA1 cladding layer, indicating the maintenance of synergistic deformation between the cladding and substrate layers. The compressive behavior and ultimate resistance of cold-formed TCBS angle and channel section stub columns were investigated using both experimental and numerical methods. These tests included material tensile flat and corner coupon tests, initial local geometric imperfection measurements, and stub column tests. The stub column test comprised four cold-formed TCBS angle section stub columns and three cold-formed TCBS channel section stub columns covering the non-slender and slender cross-sections. The experimental results were utilized to validate the finite-element (FE) model, which was then used in a parametric study to obtain further numerical data at different cross-sections. A comparative analysis of the ultimate resistance from the tests and numerical analyses with the predicted results from design approaches in EN 1993-1-1, AISI S100, and the direct strength method (DSM) was revealed. The evaluation findings generally showed that the EN 1993-1-1 design method forecasts for cold-formed TCBS channel section stub columns were dangerous. The non-slender cross-section classification coefficient, which was inapplicable to cold-formed TCBS channel steel stub columns, was the primary cause of the above unsafe prediction. As for the design approaches in AISI S100 and DSM for cold-formed TCBS angle and channel section stub columns, as well as those in EN 1993-1-1 for cold-formed TCBS angle section stub columns, they were judged safe but conservative. The above prediction error was mainly caused by ignoring the enhancement in strength properties of the TCBS after the cold-forming process. The considerations mentioned above led to the proposal and demonstration of modifying recommendations that offered safe, accurate, and consistent design approaches to ultimate resistance for the cold-formed TCBS angle and channel section stub columns.

Numerical Investigation of the Axial Load Capacity of Cold-Formed Steel Channel Sections: Effects of Eccentricity, Section Thickness, and Column Length

Cold-formed steel channel (CFSC) sections have gained widespread adoption in building construction due to their advantageous properties, including superior energy efficiency, expedited construction timelines, environmental sustainability, material efficiency, and ease of transportation. This study presents a numerical investigation into the axial compressive behavior of CFSC section columns. A rigorously developed finite element model for CFSC sections was validated against existing experimental data from the literature. Upon validation, the model was employed for an extensive parametric analysis encompassing a dataset of 208 CFSC members. Furthermore, the efficacy of the design methodologies outlined in the AISI Specification and AS/NZS Standard were evaluated by comparing the axial load capacities obtained from the numerically generated data with the results of four previously conducted experimental tests. The findings reveal that the codified design equations, based on nominal compressive resistances determined using the current direct strength method, exhibit a conservative bias. On average, these equations underestimate the actual load capacities of CFSC section columns by approximately 11.5%. Additionally, this investigation explores the influence of eccentricity, cross-sectional dimensions, and the point-of-load application on the axial load capacity of CFSC columns. The results demonstrate that a decrease in section thickness, an increase in column length, and a higher degree of eccentricity significantly reduce the axial capacity of CFSC columns.

Assessment of residual resistant capacity of cold-formed Q1100 ultra-high strength steel channel section stub column with corrosion

Experiment and numerical analysis were conducted in this study to reveal the residual resistant capacity of the cold-formed Q1100 ultra-high strength steel (UHSS) channel section stub column with grooving corrosion. Based on the results of tensile coupon test, the strength properties of the Q1100 UHSS were barely changed by the cold-forming process. A clear reduction in the ductile properties was observed, after the cold-forming process. The load-end shortening curve of the cold-formed Q1100 UHSS channel section stub columns with different grooving corrosions were obtained through the axial compressive experiment. The initial resistant stiffness was reduced by the grooving corrosion significantly, because of the reduction in the cross-section area. Decrease in the corrosion angle and increment in the corrosion length enhanced the adverse effects of grooving corrosion on the resistant capacity. Local buckling was observed in the flange and web. The flanges near the corrosion weakening area were more prone to local buckling, because of the stress transfer from web to flange. A numerical modelling method was proposed to simulate the resistant performance of the cold-formed Q1100 UHSS channel section stub columns with different grooving corrosions, which was validated by the comparison in load-end shortening curve, ultimate resistance and failure mode. Effects of corrosion angle, corrosion length, and corrosion location on the resistant capacity and failure mode were investigated through the parametric study. Compared with corrosion location, the corrosion angle and corrosion length exhibited more significant effects on the resistant capacity of the cold-formed Q1100 UHSS channel section stub columns.

Nonlinear web crippling analysis and design of cold-formed high strength steel channel sections having different stiffened flanges

Web crippling analysis and design of cold-formed high strength steel channel sections having different stiffened flanges are presented in this paper. 3D finite element models were developed for the analysis of sections with unstiffened flanges, stiffened flanges with simple lips, stiffened flanges with inward return lips and outward return lips loaded under End-Two-Flange (ETF) and Interior-Two-Flange (ITF) loading conditions. The models were verified against tests recently reported by the authors on cold-formed high strength channel sections having different stiffened flanges. The web crippling strengths, load-displacement relationships and failure modes were predicted numerically and compared well against that measured experimentally. Extensive parametric studies were performed using the validated models on 280 channel sections having different web slenderness, ratios of bearing length to web thickness, cross-section geometries and shapes of flange lips. The web crippling numerical strengths were compared with the web crippling design strengths specified in North American Specification, Australian/New Zealand Standards and Eurocode as well as with other proposed design equations in the literature. In addition, a reliability analysis was performed to assess the reliability of the design rules. It is found that the design strengths were either unconservative or conservative, and generally unreliable for the cold-formed channels with unstiffened and stiffened flanges investigated. Therefore, a modification for the North American Specification design equation was proposed. The modified proposed design equation provided more accurate and reliable web crippling strengths compared with specified and available in the literature web crippling design strength predictions.

Behaviour of Cold Formed Steel Column with Complex Edge Stiffened Web Openings

Cold-Formed Steel (CFS) sections have gained in popularity due to numerous favourable properties, and with continued research into the various restrictions of such members, their utility in the construction industry has increased dramatically. CFS sections were widely utilised in structural and non-structural applications as they offer lightweight constructions, high strength-to-weight ratios, greater stiffness due to improved sectional profiles, simplicity of installation and assembly, and so on. Optimising these CFS aspects will enable the building of structures at extremely cheap costs. Buckling occurs when the column strength exceeds the cross-section yield. Owing to CFS material characteristics, edge or double stiffeners are used as a best strategy for strengthening the CFS. The primary objective of this research is to examine the strengthening method for CFS G-section columns with edge stiffened hole sections using CATIA software. The results suggest that adding edge reinforced holes to the column enhances its rigidity. The test findings revealed that CFS channel sections with edge-stiffened web apertures had a greater compression resistance than plain channel sections. The G section column with three edge reinforced holes has a low stiffness and utilised as a support element in seismically active structures.

Numerical investigation of cold-formed steel channels with edge-stiffened and unstiffened elongated web holes under shear

Over the past decade, cold-formed steel (CFS) channel sections having edge-stiffened circular web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened web holes, while still allowing full building service integration. In the case of shear, previous research has found that the use of edge-stiffened web holes significantly improves the shear strength of such channel sections. However, no studies are available in the literature investigating the shear strength of CFS channel sections with edge-stiffened elongated web holes. The issue is addressed herein. Non-linear finite element (FE) analyses are used to investigate the shear strength of CFS channel sections with a shear span aspect ratio of 2.0. The FE models were validated against the experimental test results of sections having unstiffened elongated web holes and edge-stiffened circular web holes; good agreement in terms of the load-displacement curves and failure behaviour was shown. Using the validated FE models, a parametric study was conducted, comprising 2124 finite element analyses (FEA) results. The parametric results were then compared to the design predictions of the American Iron and Steel Institute (AISI 2016), and Australia/New Zealand Standards (AS/NZS 2018) and Wanniarchchi et al. (2017) for unstiffened elongated web holes, showing that the design predictions are unconservative in comparison results. Moreover, the direct strength method (DSM) approach of Pham et al. (2020a and 2023) provides conservative results for channels with unstiffened elongated web holes. It was also found that the design equations proposed by Chen et al. (2022) for edge-stiffened circular web holes were unconservative in predicting the shear strength of channels having edge-stiffened elongated web holes. Therefore, design equations in the form of a shear reduction factor and a modified DSM approach for CFS channel sections having unstiffened and edge-stiffened elongated web holes were proposed. Finally, a reliability analysis was carried out to ensure that the proposed equations are reliable to predict the shear strength of CFS channel sections with edge-stiffened and unstiffened web holes.

Experimental and numerical investigation of corroded cold-formed steel channel section columns subjected to in-plane compression and bending

This paper investigates the effect of corrosion on bearing capacity of corroded cold-formed steel (CFS) channel section columns subjected to in-plane compression and bending. Herein, 14 CFS columns with different column lengths and corrosion degrees were investigated. The mass loss rate, surface morphology, and initial geometric imperfections of corroded CFS columns were measured. The eccentric compression test of corroded CFS columns that were accelerated corrosion by the outdoor periodic spray test were carried out. The relationships among the failure mode, load–strain curves and load–axial displacement curves, and mass loss rate were analyzed, and then the deterioration laws of bearing performance of corroded CFS channel section columns were discussed. The non-linear finite element model for corroded CFS columns considering surface morphology was then developed by using Geomagic Studio and ABAQUS. The results indicated that the local and overall initial geometric imperfections of corroded specimens were greater than those of non-corroded specimens. With increasing mass loss rate, the distortional buckling deformation of corroded CFS columns occurred in advance and the failure locations were diversified. Corrosion exhibited a greater impact on the buckling critical load than on the ultimate load and post-buckling strength. The failure positions of corroded CFS channel section columns subjected to in-plane compression and bending were found to be mainly related to the areas with severe corrosion of the flange.

Design recommendation of cold-formed steel built-up sections under concentric and eccentric compression

A parametric investigation and design proposal for the back-to-back built-up cold-formed steel (CFS) channel sections with V-stiffeners and Σ-stiffeners under concentric and eccentric loading are presented in this paper. A nonlinear finite element model considering the initial geometric imperfection was developed and validated against experimental results. A total of 594 simulations were conducted involving a variety of slenderness ratios, eccentric axis directions, eccentricity, screw spacing and number of longitudinal holes. Simulation results including the load-carrying capacity, failure modes, ultimate bearing capacity versus eccentricity relationships, and load versus lateral displacement relationships were discussed. The influence of several member parameters on the load-carrying capacity and buckling modes was analyzed. Additionally, the applicability of the design strengths calculated from Chinese standard GB50018–2002 and North American specifications AISI S100–16 was evaluated based on the preliminary experimental results and simulation results. It was shown that both methods are conservative. Finally, a proposed DSM-based interaction equation considering the relationship between P/Pnd and M/Mnd was proposed and evaluated.

Web crippling behaviour of cold-formed steel channel sections having elongated edge-stiffened web holes under interior-two-flange loading condition

In the past decade, cold-formed steel (CFS) channel sections having circular edge-stiffened web holes have been developed in New Zealand. Such edge-stiffened holes increase the strength of the CFS channel sections, compared to an equivalent section having unstiffened holes, while still allowing full service integration. In the case of web crippling, previous research has found that use of edge-stiffened holes almost results in the same strength of an equivalent channel-section having a plain web. Such circular edge-stiffened web holes can now be extended to elongated edge-stiffened web holes. However, for such elongated holes, no experimental tests have been reported in the literature. In this paper, a numerical investigation was carried out, and non-linear finite element (FE) analyses were used to investigate the web crippling behaviour of CFS channel sections having edge-stiffened web holes under the interior-two-flange (ITF) loading condition. The cases of both flange fastened and flange unfastened were considered. The FE models were validated against test results of sections having circular edge-stiffened web holes; good agreement in terms of the load–displacement curves and deformed shapes was shown. Using the validated FE models, a parametric study was carried out on CFS channel sections having elongated un-stiffened and edge-stiffened web holes, comprising 1,227 finite element analyses (FEA) results. Compared to sections having a plain web, for the case of an elongated opening, without any edge-stiffener, having an aspect ratio of two and three, the average reduction in web crippling strength was 39% and 49%, respectively. However, for an edge-stiffened hole, the reduction in the web crippling strength was reduced to only 2% and 16%, respectively. Finally, the design equations in the form of the web crippling reduction factor (Rp) and the equations based on the direct strength method (DSM) for CFS sections with elongated web holes were proposed.

Web crippling tests on cold-formed high strength steel channel sections having different stiffened flanges and stiffened web

This paper reports 59 tests on cold-formed high strength steel channel sections with different stiffened flanges and stiffened web. The test specimens were brake-pressed from high strength zinc-coated grades G450, G500 and G550 structural steel sheets. The test program consisted of 6 series of channel sections having different stiffened flanges, web slenderness, material strengths and loading conditions. The loading conditions were End-Two-Flange (ETF), and Interior-Two-Flange (ITF) loadings as specified in the North American Specification for cold-formed steel structures. The web crippling test strengths and load–displacement relationships of the channel section specimens were obtained from the tests. The channel sections having stiffened flanges as well as the channel sections having stiffened web enhanced the web crippling strengths of the specimens, especially for those specimens loaded under ETF loading condition. The web crippling test strengths were also compared with the design strengths calculated using the current North American Specification and European Code for cold-formed steel structures. In addition, reliability analysis was performed to assess the reliability of the design rules. Generally, it is found that the predictions obtained from the North American Specification are unconservative and unreliable for the cold-formed high strength steel channel section specimens, except for the specimens with unstiffened flanges under ITF loading condition, while the European Code was unreliable but conservative in predicting the web crippling strengths, except for the specimens with unstiffened flanges under ETF loading condition.

Flexural Behavior of Built-Up Cold-formed Steel Channel Section Strengthened with Oriented Strand Board

The objective of the study is to determine the flexural behavior of the built-up cold-formed steel (CFS) channel section strengthened with an oriented strand board (OSB) in the three-point bending experiment. CFS with a variety of shapes and grades is classified as a steel-based material and exposed to buckling failure when subjected to compression or flexural load. Thus, the CFS channel section with 100 mm of the web, 50 mm of the flange, 12 mm of the lip, and 1.55 mm of thickness has been selected. Then, the built-up CFS channel section is designed by filling with an OSB between the gap of each section. Channel, face-to-face built-up, and back-to-back built-up CFS sections are three types of tested specimens. From the result and discussion, the specimen with back-to-back built-up CFS section is recognized to sustain the ultimate load with the highest value when compared with other specimens.

Shear strength design of cold-formed steel channel sections with web openings

Cold-formed steel (CFS) members are increasingly used as the main loading-bearing elements in modern construction practice, due to the advantages such as high strength-to-weight ratio, and ease of transportation and assembly. Often, web openings are cut out of CFS elements to allow for services, plumbing, heating and electrical systems, which may result in considerable reductions in their shear strength. This study aims to investigate the behaviour and design of CFS channel members with web openings under shear loads. To this end, detailed Finite Element (FE) models of CFS back-to-back channel members were developed featuring material non-linearity and geometric imperfections, and validated against the results of experimental tests. The validated FE models were then employed to carry out a comprehensive parametric study to investigate the effects of opening size and shape (square and circular web openings), as well as cross-sectional web slenderness on the strength, stiffness, failure mechanism, and ductility of CFS elements under shear forces. The results demonstrated that the shear strength of the CFS members can be significantly affected, up to 88 % and 30 %, by the size of openings and web slenderness, respectively. It was also found that while the ductility ratio of the CFS elements can be improved by increasing the opening size, elements with lower web slenderness showed less ductile behaviour. Based on the results of the parametric study, a practical design equation was developed for the shear strength of CFS members with web openings, and the predictions were compared with those determined by the AISI and other existing methods. Finally, a reliability analysis was performed within the framework of the European design standard.

Incremental stiffening approach for CFS built-up-beams with large imperfections: Tests and flexural-behaviour

Cold-formed steel (CFS) members generally have slender cross-sections making them more prone to geometric imperfections. The presence of different geometric imperfections with varying magnitudes can significantly influence the structural behaviour of CFS members, which is well-reported in the literature. However, limited data is available on the strengthening of CFS beams with large imperfections. This paper reports the findings of the first experimental investigation that focuses on adopting incremental stiffening approach to strengthen CFS built-up beams with large geometric imperfections induced due to poor fabrication and subsequent testing. CFS channel sections were used to construct both open and closed built-up beams, which were evaluated under four-point loading with simply supported boundary conditions. The incremental adoption of simple, yet effective stiffening approaches helped in attaining considerable improvement in both capacity and stiffness characteristics. The peak load, flexural stiffness, and failure mode exhibited by each tested specimen were used as key performance indicators. The results, in general, confirmed the feasibility of adopting incremental stiffening for improving both the capacity and the stiffness in distressed CFS built-up beams by up to 145% and 125%, respectively. Also, it is shown that a yield capacity of up to 100% and a plastic capacity of up to 80% can be achieved through the proposed stiffening approach. The presented test results will supplement the current inadequate database on distressed CFS beams, and should prove useful for more efficient design of such systems.

Full-scale tests of load-bearing LSF walls made of built-up CFS channel sections under fire conditions

Built-up cold-formed steel (CFS) studs, such as back-to-back channels (BC) and nested channels (NC) are used in light gauge steel framed (LSF) wall systems instead of the conventional channel studs for improving their load-bearing capacity. However, the knowledge and understanding of their behaviour under fire conditions is limited. In this study, the behaviour of load-bearing LSF walls made of BC and NC studs under fire conditions was investigated using four full-scale standard fire tests. The obtained fire test results were evaluated in terms of both thermal and structural behavioural characteristics and fire resistance level (FRL), and were used in the comparison with those for conventional LSF walls made of single channel studs. The test results showed that (1) without cavity insulation, the thermal and structural behavioural characteristics of the LSF walls made of BC and NC studs are very similar to those of LSF walls made of channel studs, and their FRLs can be taken as the same for the same load ratio (2) LSF walls made of BC and NC studs with two layers of 16 mm thick gypsum plasterboards on each side and without cavity insulation have an FRL of 120 min for a load ratio of 0.4, and (3) the use of cavity insulation reduces the FRL of LSF walls made of NC studs. This paper presents the details of this research study and its outcomes.

Prediction of axial load capacity of cold formed lipped channel section using machine learning

Cold Formed steel channel sections are widely used as both structural and non-structural members. The axial load carrying capacity of Cold Formed steel sections depends on buckling modes such as local, distortional, global buckling, their interactions and geometrical imperfections. Although existing standards are adequate for determining axial load-carrying capacity, the present study proposes an alternative method based on recent machine learning algorithms. Experimental data pertaining to axial load tests conducted on Cold Formed steel lipped channel sections are collected and modelled using the finite element method. Validated finite element models are used further to generate the input–output data set by sampling the input geometric and strength parameters of the section required for training machine learning models. Latest machine learning models, namely Linear Regression, Lasso Regression, K-Nearest Neighbours, Decision Tree, Random Forest, Adaptive Boost, Extreme Gradient Boosting, Light Gradient Boosting Machine, Categorical Boosting, Gradient Boosting Regression, Support Vector Machine and Artificial Neural Network, are used in this study to predict the axial load capacity. The Random Forest model is the best-performing algorithm for axial capacity prediction, with an accuracy of 99.10% for the test data set. Further, SHapely Additive exPlanations analysis is carried out to estimate the order of significance of the input variables and to justify the prediction of the best-performing machine learning model.

A Novel Approach to Improve the Distortional Buckling Strength of a Stiffened Cold-Formed Steel Channel Section under Axial Compression

This study investigates the distortional buckling strength of a partially closed cold-formed steel (CFS) channel section with intermediate web stiffeners and outward lips under axial compression. Generally, a closed CFS cross section has higher torsional resistance when compared to an open cross section. However, an open cross section is more popular in the construction industry. Despite the popularity of CFS open sections, distortional buckling can reduce the load-carrying capacity of such open cross sections. To improve the distortional buckling strength of the proposed selected section, a simple spacer plate is added externally to the channel section in the transverse direction. Initially, a numerical model is developed using the finite element software ANSYS, which is then validated against the experimental results available in the literature. A detailed parametric study was also conducted to investigate the influence of thickness, depth, and spacing of spacer plates on the distortional buckling strength of stiffened CFS channel sections. From the results of the parametric study, it was found that the presence of spacer plates can increase the axial capacity of stiffened CFS channel sections by as much as 32%. Finite element results were compared with the design strengths calculated in accordance with the direct strength method (DSM).

Effect of corrosion on the buckling behaviour of cold-formed steel channel section columns under axial compression

Effect of corrosion on the buckling behaviour of cold-formed steel channel section columns under axial compression

Structural Performance of Cold-Formed Steel Face-to-Face Built-Up Channel Sections under Axial Compression at High Temperatures through Finite Element Modelling

This paper studies the structural performance of cold-formed steel (CFS) face-to-face (FTF) built-up channel sections subjected to axial compression at high temperatures. The material properties of G250 and G450 CFS channel sections at room and high temperatures were acquired from the literature, and the range of temperatures was from 20 to 700 °C. The influences of the section thickness, member length, screw number, and high temperature on the structural performance of such channel sections were examined via a comprehensive parametric analysis involving 576 validated finite element models. As the temperature increased from 20 to 700 °C, the mean axial capacity of the CFS-FTF built-up unlipped and lipped channel sections decreased by 88.9% and 90.2%, respectively. Based on the results of the parametric study, new design equations for the axial capacity of CFS-FTF built-up channel sections at high temperatures were proposed. The mean ratio of the EWM strengths calculated using the American standard (AISI 2016) and Australian/New Zealand standard (AS/NZS 2018) to the FE strengths was 0.77, while the mean ratio of the proposed design strengths to the FE strengths was 1.01. Finally, a reliability analysis was conducted, and it was found that the proposed equations could come close in predicting the axial capacity of CFS-FTF built-up channel sections at high temperatures.

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.