Unlipped Channels Research Articles

High strength steel unlipped channel sections subjected to ETF loading: Laboratory testing, numerical simulations and web crippling design

This paper presents web crippling and structural design of high strength steel unlipped channel sections under end-two-flange (ETF) loading based on experimental and finite element investigations. The experimental programme was composed of six grade S690 and four grade S960 test specimens, and the corresponding test set-up, procedures and results were reported in detail. The web crippling test results were used in the numerical modelling programme to validate the developed FE models, which were then adopted to perform parametric studies to enlarge parameter ranges of the bearing length, web slenderness and inside bend radius. Given that codified design rules for S690 and S960 high strength steel unlipped channel sections undergoing web crippling are absent, the corresponding normal strength steel design provisions, as stipulated in the European code EN 1993-1-3 and American specification AISI S100, were evaluated for their suitability to high strength steel unlipped channel sections. It is shown that the ultimate strength of high strength steel unlipped channel sections nonlinearly increases with increasing bearing length but with decreasing web slenderness and inside bend radius. The design methods of current EN 1993-1-3 and AISI S100 provide inaccurate and scattered resistance predictions for high strength steel unlipped channel sections. Finally, a modified AISI S100 design method and a slenderness-based design method were proposed, which can outperform the codified design methods.

Tests, simulations and web crippling design of S690 and S960 high strength steel unlipped channel sections under end-one-flange loading

This paper presents experimental and numerical investigations into the web crippling behaviour and structural design of high strength steel unlipped channel sections under end-one-flange loading. An experimental programme including six grade S690 and four grade S960 steel test specimens was firstly carried out, and the corresponding test set-up, procedures and results were reported. The web crippling test results were subsequently used in a finite element programme to validate developed finite element models, which were then adopted to perform parametric studies to cover wider parameter ranges of the bearing length, web slenderness and inside bend radius. It is found that the ultimate web crippling strength of high strength steel unlipped channel sections increases with increasing bearing length but decreasing web slenderness and inside bend radius. Considering that relevant codified design provisions are absent, the design rules of normal strength steel unlipped channel sections, as prescribed in EN 1993-1-3, EN 1993-1-5 and AISI S100, were assessed for their suitability to high strength steel unlipped channel sections. The codified design methods provide inaccurate and scattered resistance predictions for high strength steel unlipped channel sections under end-one-flange loading. Thus, an improved AISI S100 design method and a novel slenderness-based design method were proposed, which can outperform the codified design methods.

An experimental study of cold-formed steel connections with screwed clip angle under tension and shear loads

This paper aims to investigate the performance of typical cold-formed steel (CFS) beam-to-beam connections between floor bearers and floor joists through a series of full-scale experiments. The investigated connections consisted of a lipped channel (floor joist), an unlipped channel (floor bearer), a thin-walled clip angle (connector), and a self-drilling screw (fastener). In this study, customised T-shaped and H-shaped CFS connection specimens were tested to examine the performance under tension and shear loads, respectively. Two sizes of self-drilling screws, 10 G and 14 G, were used with the selected load bearing clip angle. The fabricated connection specimens were subjected to displacement-controlled tension and shear loads. The experiments uncovered the ultimate connection strengths, load-displacement relationships, and failure mechanisms of the designed CFS connections under the applied loads. Moreover, the experimental tensile and shear strengths of the connections were compared with the strengths predicted by the standard design equations. It was found that the screw pullout on the anchored leg of the clip angle was the main mode of failure under the tensile load. On the other hand, two different failure modes—fracturing of 10 G screws or shear buckling of the cantilevered leg of the clip angle with 14 G screws—were observed in the H-shaped specimen under the applied shear load. Among the designed connection specimens, the maximum tensile load capacity was 30.86 kN and the maximum shear load capacity 88.15 kN. The standard design calculations predicted screw pullout failure under tension, while the shear bucking failure mode of the clip angle under shear load was overlooked.

Experimental and numerical investigations of high strength steel unlipped channel sections under interior-two-flange loading

This paper presents laboratory tests, numerical simulations and web crippling design of high strength steel unlipped channel sections under interior-two-flange loading. An experimental programme comprising 10 test specimens (with six for grade S690 high strength steel and four for grade S960 high strength steel) was firstly implemented, and test results including failure modes, full load-deformation curves and ultimate loads were reported. Subsequently, finite element models were constructed and validated against the obtained test results, and then used to conduct supplementary parametric studies to widen the examined parameter ranges of high strength steel unlipped channel sections. Considering that relevant codified design rules are absent, the applicability of the design rules of EN 1993–1-3, EN 1993–1-5 and AISI S100 for normal strength steel unlipped channel sections to their high strength steel counterparts was evaluated against the obtained test and numerical results. It is shown that the resistance predictions from the codified design provisions were generally inaccurate and scattered. Hence, a modified AISI S100 design method and a slenderness-based design method were proposed and demonstrated to be accurate, consistent and reliable for the web crippling design of high strength steel unlipped channel sections under interior-two-flange loading.

Experimental and numerical investigations of high-strength cold-formed steel multi-limb built-up section columns

This paper investigates the buckling behaviour and load-carrying capacity of G550 high-strength cold-formed steel multi-limb built-up section columns under axial compression. Each built-up section consists of multiple lipped and unlipped channel sections connected by self-tapping screws. The C3U1 section is formed by three C-sections (i.e. lipped channel section) and one U-section (i.e. unlipped channel section), while the C2U2 section is formed by two C-sections and two U-sections. The experimental programme involved tensile coupon tests, measurements of initial geometrical imperfection, and column tests on ten C3U1 and ten C2U2 multi-limb built-up section columns. The numerical modelling programme was then performed, with the nonlinear finite element models created and validated against the experimental results. The applicability of the codified Effective Width Method and Direct Strength Method for predicting the strengths of G550 high-strength cold-formed steel multi-limb built-up section columns, as specified in the American Specification and Australian Standard, was then evaluated. The evaluation results showed that the codified Effective Width Method led to rather conservative and less accurate failure load predictions for G550 high-strength cold-formed steel multi-limb built-up section columns, while the codified Direct Strength Method provided accurate and consistent failure load predictions and thus applicable to the design of G550 high-strength cold-formed steel multi-limb built-up section columns. Concerning the lack of design guidelines specifically for multi-limb built-up sections, a modified Direct Strength Method was thus proposed as an alternative design method and shown to provide accurate failure load predictions.

Experimental investigation of cold-formed stainless steel built-up closed section stub columns

This paper presents an experimental investigation on the performance of cold-formed stainless steel built-up closed section stub columns. The built-up sections were composed by assembling two channel components at the flanges, which were brake-pressed from high-strength austenitic and duplex stainless steel thin sheets. Three types of built-up sectional profiles were formed by connecting two unstiffened channels (i.e., unlipped channels), two edge-stiffened channels (i.e., lipped channels) as well as one unstiffened channel and one edge-stiffened channel, respectively, using self-plugging rivets. Four sectional series were devised to cover nominal overall web height-to-plate thickness ratio values of 50, 60, 67 and 80. In order to obtain the actual material properties considering the cold-work effect, tensile coupon tests were carried out on both flat and corner longitudinal coupon specimens. In addition, a total of 29 fixed-ended stub columns including 19 specimens without holes and 10 specimens with circular web holes were tested under axial compression. The experimental results involving failure modes, ultimate capacities and responses of load versus axial shortening were obtained and fully documented. The effects of sectional profile types, overall web height-to-plate thickness ratio and hole diameter-to-overall web height ratio on the performance of cold-formed stainless steel built-up closed section stub columns were examined. Moreover, the appropriateness of design rules as prescribed in the recently updated American Specification ASCE/SEI 8–22 was evaluated. It was revealed that the codified design provisions generally provided unconservative strength predictions for the high-strength austenitic and duplex stainless steel built-up closed section stub columns both without and with circular web holes. Reliability analyses were performed in this study, and the compressive strength predictions of the built-up closed sections according to the existing design rules were found to be unreliable for the high-strength austenitic stainless steel stub columns without holes as well as the duplex stainless steel stub columns without and with circular web holes.

Improvement of CSM for high-strength S690 and S960 unlipped channel columns, beams and beam-columns

Existing design methods that are mainly based on cross-section classification usually predict conservative resistances for high strength steel (HSS) singly symmetric unlipped channel section members. This paper conducted numerical studies on the resistance of cold-formed S690 and S960 HSS channel section members under different loading types. Numerical simulations were firstly carried out to establish suitable finite element (FE) models, and then applied to parametric studies. The obtained numerical results were adopted to assess and modify the continuous strength method (CSM) for the design of cold-formed HSS unlipped channel section members under axial compression or bending loads. An improved beam-column design method of unlipped channel sections was proposed through providing a new linear design curve incorporating the modified CSM formulae, then to evaluate the newly method and the M - N interaction curves specified in existing standards, finally the reliabilities of proposed method were confirmed.

Localised Web Bearing Behaviour of Cold-Formed Austenitic Stainless-Steel Channels: Review of Design Rules and New Insight under Interior Loading

Stainless steels are modern high-performance construction materials exhibiting excellent corrosion resistance, recyclability, ductility, and durability which make them appealing to use in the construction industry. However, when used as structural sections, they are subjected to localised failure in the web. This study aims to examine the structural behaviour of cold-formed low-carbon content standard austenitic 304L and 316L stainless steel channels under localised interior bearing loads. The results of 21 tests on unlipped channels with different cross-section sizes and thicknesses are presented. A nonlinear quasi-static Finite Element (FE) model is then developed. The FE model is validated against experimental test results and demonstrated good agreement in terms of bearing strength and failure modes. In addition, the experimental and FE results are used to compare the results against the results predicted in accordance with the American specification SEI/ASCE 8:2002 and European Standard EN 1993-1-4:2006. It is found that the current design equations are unreliable and too unconservative to use for cold-formed austenitic stainless steel unlipped channels, especially when compared to SEI/ASCE 8:2002, as much as 41%.

Web crippling behaviour of cold‐formed high‐strength steel unlipped channel beams

AbstractConstruction industries have increasingly sought to adopt Cold‐Formed Steel (CFS) sections as primary and secondary load‐carrying members. Also, the evolution of the CFS industry leads to fabrication of high strength CFS sections due to their added benefits such as higher strength‐weight ratio, most appropriate to employ in high‐rise and long‐span applications, and lesser carbon footprint. However, large width‐to‐thickness ratios of these thin‐walled beams make them vulnerable to local buckling failure, a major failure mode being web crippling when subjected to concentrated loads. The design standards predict the web crippling capacity of CFS sections according to the experimental studies conducted in previous years. Innovative concepts like the production of CFS using high‐strength materials should be examined undergoing web crippling. Therefore, the web crippling behaviour of the unlipped channel sections with material strength up to 1000 MPa under all four loading conditions: End‐Two‐Flange (ETF), Interior‐Two‐Flange (ITF), Interior‐One‐Flange (IOF) and End‐One‐Flange (EOF) was investigated in this study. Numerical simulations using Finite Element Analysis (FEA) software (ABAQUS) were conducted on 972 parametric studies following proper validation. New modified equations were proposed to predict the ultimate web crippling capacity of high strength unlipped channel sections and parametric analyses were carried out among various loading conditions.

Web Bearing Test of Cold‐Formed Austenitic Stainless‐Steel Channels Under Interior Loading

AbstractDuctility, durability and high corrosion resistance of stainless steels make them appealing to use in construction industry. When used as structural sections, they are, however, subjected to localised failure in the web. This study aims to examine the structural behaviour of cold‐formed austenitic stainless steel channels under localised interior bearing loads. The results of 21 tests on unlipped channels with different cross section sizes and thicknesses are presented. Nonlinear quasi‐static Finite Element (FE) model is then developed. The FE model is validated against experimental test results and demonstrated good agreement in terms of bearing strength and failure modes. In addition, the experimental and FE results are used to compare the results against the results predicted in accordance with the American specification SEI/ASCE 8:2002 and European Standard EN 1993‐1‐4:2006. It is found that the current design equations are unreliable and too unconservative to use for cold‐formed austenitic stainless steel unlipped channels, especially when compared to SEI/ASCE 8:2002, as much as 41%.

Structural behaviour of Cold‐Formed Steel back‐to‐back welded sections subjected to longitudinal shear

AbstractThe current study focuses on understanding the behaviour of flare v‐groove welds on back‐to‐back connected Cold‐Formed Steel welded sections (G300) subjected to longitudinal shear. A novel welding technique called Cold Metal Transfer (CMT) welding was used for fabrication with copper‐coated steel welding wire as a filler metal (ER70S‐6). This mode of welding has the advantage of controlled material deposition compared to the spray or globular mode of welding. Lap shear tests were carried out on unlipped channels including thickness of the weld, and length of the weld. The weld geometry was observed under an optical microscope after polishing and chemical etching of the weld cross‐section, as American Iron and Steel Institute (AISI) design standard provides no specification on thickness of flare v‐groove welds for CMT welding process. In general, the lap shear specimens failed in plate tearing failure mode and brittle fracture of weld at the weld contours. Additionally, the appropriateness of AISI's shear design strength equations for flare v‐groove welds was verified and preliminary design guidelines are provided addressing the lacunae in AISI design standard.

Web bearing design of cold-formed austenitic stainless steel un-lipped channels under localised interior loading

The high corrosion resistance, recyclability, ductility, and durability of stainless steels make them appealing for use in the construction industry. However, when used as structural channel sections, they are subject to localised failure in the web. This study aims to evaluate the structural behaviour of cold-formed austenitic stainless steel unlipped channels under localised interior loading. The results of conducting a novel testing programme with 21 new tests on such channels with different cross-section sizes and thicknesses are presented. Then a non-linear quasi-static Finite Element (FE) model is developed. The FE model is validated against experimental test results and found to demonstrate a good agreement in terms of bearing capacity and failure modes. It is found that no cold-formed stainless steel standard provides web bearing capacity equations for the localised interior loading (IL) that apply when simulating a floor joist on a solid foundation. The web bearing capacities are compared with capacities determined from the literature (including DSM). It is found that for the case of unlipped channels (unstiffened flanges), the current equations are unreliable and unconservative by up to 36%. The experimental investigation shows that, the American specification (SEI/ASCE 8:2002) is unconservative as much as 41%. Using both experimental and numerical results from this study, a new design equation is proposed for austenitic stainless steel unlipped channels under localised interior loading.

Web crippling resistances of cold-formed stainless steel sections: A proposal for EN 1993-1-4

The current EN 1993-1-4 does not have supplementary web crippling design provision for cold-formed stainless steel sections under local transverse forces. Therefore, designers are generally referring to the guidance in EN 1993-1-3 for cold-formed carbon steel sections. Over the past decades, quite a substantial number of tests have been carried out worldwide to study the behaviour of cold-formed stainless steel sections undergoing web crippling, among which the majority of the data were focused on C-sections as well as square and rectangular hollow sections (SHS and RHS). To this end, tailor-made design provisions for these stainless steel sections can be developed. In this study, up-to-date web crippling test data on cold-formed stainless steel C-sections and SHS/RHS were firstly collected. The applicability of the web crippling design provisions as per the new version of EN 1993-1-3 to stainless steel sections was assessed. New design provisions for cold-formed stainless steel unstiffened C-sections (unlipped channels), stiffened C-sections (lipped channels) as well as SHS and RHS under local transverse forces are proposed in this study. The newly developed web crippling design provisions for C-sections and SHS/RHS were derived based upon reliability requirements as regulated in EN 1990 using available experimental data reported on austenitic, ferritic and duplex stainless steel types of various grades. The proposed design provisions for stainless steel sections have been made in line with the development of the new version of EN 1993-1-3 provisions and therefore are recommended to EN 1993-1-4 for calculating web crippling resistances under local transverse forces.

NUMERICAL STUDY ON BEHAVIOUR OF COLD-FORMED STEEL UNLIPPED CHANNEL SUBJECT TO AXIAL COMPRESSION

Innovation in obtaining construction materials that are efficient and applicable to various conditions is a challenge for researchers. Cold-formed steel is a material breakthrough in construction that has advantages over hot-rolled steel. Many studies have been carried out on Cold-formedsteel subjected to various loadings to examine the behavior and capacities of the sections. This study aims to investigate the behavior and section capacity of cold-formed steel unlipped channels due to axial compression loads. This research begins with conducting a literature study, then carrying out numerical analysis using the finite element method in ABAQUS, numerical test, and calculation of section capacity based on existing research in the literature. The calculation of section capacity is carried out based on SNI 7971-2013 or AS/NZS 4600:2005. The results of the numerical analysis can be seen from the behavior and capacities of the sections of the unlipped channel, the section capacity from the numerical test will be compared with the section capacity obtained from the calculation based on SNI 7971-2013 or AS/NZS 4600.

NUMERICAL MODELLING ON BEHAVIOUR OF COLD-FORMED STEEL UNLIPPED CHANNEL UNDER COMBINED COMPRESSION AND BENDING ACTIONS

Research and development of construction materials continue to be carried out, getting materials, cross-sectional shapes, and manufacturing methods that are more efficient than before. Cold-formed steel is a material breakthrough in construction that has advantages over hot-rolled steel. In this paper, the cross-section of cold-rolled steel unlipped channel will be analyzed which is subjected to a combination of axial and bending loads. Investigating elements will be carried out using the finite element method on ABAQUS, and the results of the analysis produce a visualization of the behavior and capacity of the cold-rolled steel section. The cross-section capacity results obtained from the numerical test results will be compared with the predictions given by SNI 7971-2013 or AS/NZS 4600. Existing research in the literature will be used as a reference in conducting numerical analysis and calculating ultimate capacities.

Local-distortional interaction behaviour and design of cold-formed steel built-up columns

This research highlights the possibility of LD interaction in the built-up columns and provides a detailed design procedure to account for the strength erosion due to LD interaction. For this, a comprehensive numerical study using finite element (FE) method is performed where the FE models are validated using the test results in the literature. In this study, three types of built-up sections, i) back-to-back I section made of two lipped channels, ii) nested section made of two lipped channels, and iii) nested section made of one lipped and one unlipped channel, are selected. The effects of LD interaction, fastener spacing, and end fastener group (EFG) on the ultimate strength of built-up columns are investigated. The study reveals that the LD interaction behaviour of the built-up back-to-back I section in terms of failure mode and normalized ultimate strength result (Pu/Py) is similar to that of a lipped channel. For the built-up nested section, improved strength is observed when the lipped channel fails in distortional buckling. No improvement is observed in the LD strength of built-up sections with reduced fastener spacing or by using EFG. The study shows that the traditional direct strength method (DSM) based design procedure for LD interaction is conservative for built-up sections. Hence, a reliable design procedure is proposed based on the modified DSM equations obtained from the literature. The strength and failure mode predictions of the proposed method match well with those of experimental studies in the literature and the numerical study of this paper.

Effect of web perforations on end-two-flange web crippling behaviour of roll-formed aluminium alloy unlipped channels through experimental test, numerical simulation and deep learning

Aluminium alloy has recently become popular in New Zealand’s construction sector as a sustainable building material. However, in roll-formed aluminium alloy (RFA) channel beams, particularly those having web holes, cripples at points of concentrated or localised loading. In this paper, end-two-flange (ETF) web crippling behaviour of RFA unlipped channels having web holes was investigated using experimental tests, numerical simulations and a deep learning model referred as deep belief network (DBN). A total of 1080 data points was generated to train the DBN, using a finite element (FE) model that was validated using 30 new experimental results reported in this paper. Compared to the test data, the DBN predictions were conservative by around 6%. Using the DBN predictions, a comprehensive parametric study was undertaken which used the validated FE model in order to explore the effects of hole size, hole location, section thickness, and bearing plate on the web crippling strength of RFA channels having web holes. Web crippling strengths obtained from the DBN, tests and finite element analysis (FEA) were utilised to evaluate the performance of current design specifications from the American Iron and Steel Institute (AISI), Australian/New Zealand Standards (AS/NZS 1664; AS/NZS 4600:2018) and Eurocode (CEN 2006, 2007). It is shown that the current design rules are not reliable to predict the web crippling strength of RFA unlipped channels with web holes. As a consequence of the parametric analysis, new web crippling strength and web crippling strength reduction factor formulae for perforated RFA unlipped channels were proposed. A reliability analysis was then conducted, which confirmed that the proposed equations are capable of predicting the ETF web crippling strength of perforated RFA unlipped channels.

Web crippling behaviour of cold-formed high-strength steel unlipped channel beams under End-One-Flange load case

High-strength Cold-Formed Steel (CFS) members are widely adopted as structural members in building structures due to its higher ultimate capacity. The flexural members are often subjected to concentrated transverse loads which may leads to buckling instabilities including web crippling. However, there is no appropriate design rules and studies are available to estimate the web crippling strength of high-strength CFS members. Hence, this paper presents a detailed numerical investigation on high-strength CFS unlipped channel sections subjected to End-One-Flange (EOF) loading condition with nominal yield strengths of 700 MPa, 900 MPa and 1000 MPa. For numerical simulation study, non-linear Finite Element (FE) models were developed and validated with the experimental results followed by an extensive parametric study using ABAQUS. In total, 243 FE models were developed with different geometric and material parameters including section thickness, material strength, web slenderness ratio, inside bent radius to thickness ratio and bearing length to thickness ratio. The ultimate web crippling strength results were compared with the available design guidelines to check their suitability and accuracy in terms of strength prediction. Then, new design rules to predict the web crippling capacity of high-strength CFS unlipped channel section under EOF condition based on unified and Direct Strength Method (DSM) approaches were proposed.

Design of locally buckling cold-formed steel built-up columns formed by unlipped channel sections

This study proposes a design procedure for the local buckling strength prediction of cold-formed steel (CFS) built-up I and box section columns based on the Effective Width Method (EWM) and the Direct Strength Method (DSM). For this, the ultimate strength of the built-up sections made of two plain unlipped channels is obtained using the finite element (FE) analysis. First, some compression tests on built-up sections are performed to validate the FE models. Then, a detailed parametric study using the validated FE models is conducted for sections with a wide range of slenderness (1≤λl≤3) where λl is the square root ratio of yield stress to the local buckling stress of the cross-section. The results show that the local buckling strength of built-up I sections is equal to the sum of its section’ strength, whereas for box sections, the strength can be 20%–25% higher as the nesting of sections will alter the local buckling characteristics. The EWM (with k factor approach) and authors’ DSM based design procedure can predict the strengths of the built-up I sections well but predict conservative strengths for the built-up box sections. This issue is resolved in this paper by proposing a simple cross-sectional model based on the constrained local buckling deformations of the built-up box section. When the buckling stress results of the proposed model were used with the EWM and authors’ DSM design procedures, the predicted local buckling strength results matched well with those of the present numerical study. In addition, the proposed design procedure provided more accurate strength predictions than the existing DSM and those presented in the literature for the built-up section columns.

A novel machine learning method to investigate the web crippling behaviour of perforated roll-formed aluminium alloy unlipped channels under interior-two flange loading

This study presents a novel machine-learning model using the eXtreme Gradient Boosting (XGBoost) tool, for assessing the web crippling behaviour of perforated roll-formed aluminium alloy (RFA) unlipped channels (both fastened and unfastened) under interior-two-flange loading. A total of 1080 data points were generated for training the XGBoost model, utilizing an elastoplastic finite element (FE) model that was validated against 30 experimental results from the literature. A comparison against the numerical failure loads was conducted, and it was found that the prediction accuracy of XGBoost model was 94%. When compared with Ramdom Forest and Linear Regression methods, it was found that the proposed XGBoost model performed better than both the before mentioned methods. The web crippling strengths obtained from the XGBoost model, tests, and finite element analysis (FEA) were utilized to evaluate the performance of current design rules from the American Iron and Steel Institute (AISI), Australian/New Zealand Standards (AS/NZS 1664.1; AS/NZS 4600:2018) and Eurocode (CEN 2007). It is shown that the current design rules are not reliable to predict the web crippling strength of perforated RFA unlipped channels. As a consequence of the parametric analysis, new web crippling strength and web crippling strength reduction factor formulae for perforated RFA unlipped channels were proposed. A reliability analysis was then conducted, which confirmed that the proposed equations are capable of accurately predicting the ITF web crippling strengths of perforated RFA unlipped channels.