Steel Channel Sections Research Articles

Effect of Partial Closing of the Open Face of Cold-Formed Steel Channel Sections

This document presents the effect of partial closing of the open face of cold formed steel channel. From the past, closed sections are favourably used in CFS for framing applications. Open sections, like channels offer good moment resistance and also offer a clean and flat surface on the outside of the web but when loaded in vertical direction cause twist in the channel section since the loading is not through the shear centre. This twist also causes lateral deflection of the section at the level of the two flanges. In order to restrain and minimize the lateral torsional bucking, an experimental and numerical trial has been performed on the channels which are covered with plate along the length of the beam by 1/3rd, 2/3rd and full cover plate of the beam channel and compared. Specimens with 2/3rd and full length cover plate along the length show improved resistance against lateral deflection and torsion. The performance reduces as length of the beam increases. The specimens of 2/3rd length cover plate show almost equal performance to the specimens of full length cover plate. As a result, 2/3rd cover plate beam can be efficiently used to serve the purpose for better efficiency. Numerical models are developed and compared with the experimental results. Following a series of analyses, it is found that in general, the effect of the covering is more significant on longer specimens. Conclusions derived based on the experimental and numerical results also point to the definite improvement by the partial closing of the channel sections.

Cold-Formed Steel Lipped Channel Section Columns Undergoing Local-Overall Buckling Interaction

This paper presents an experimental and finite element (FE) investigation into the local-overall buckling interaction behaviour of axially loaded cold-formed steel (CFS) channel section columns. Current design guidelines from the American Iron and Steel Institute (AISI) and the Australian and New Zealand Standards (AS/NZS) recommend the use of a non-dimensional strength curve for determining the axial capacity of such CFS channel section columns. This study has reviewed the accuracy of the current AISI (2016), AS/NZS (2018) and Eurocode (EN 1993-1-3) design guidelines for determining the axial capacity of CFS channel sections under local-overall buckling interaction failure. A total of 40 tests were conducted on CFS channel sections covering stub, short, intermediate, and slender columns with varying thicknesses. A nonlinear FE model was then developed and validated against the test results. The validated FE model was used to conduct a parametric study comprising 70 FE models to review the accuracy of the current design guidelines in accordance with AISI (2016), AS/NZS (2018) and Eurocode (EN 1993-1-3). It was found that the AISI (2016) and AS/NZS (2018) are conservative by 10 to 15% on average when determining the axial capacity of pin ended CFS channel section columns undergoing local overall buckling interaction. Eurocode (EN 1993-1-3) design rules were found to lead to considerably more conservative predictions of column axial load capacity for CFS channels.This paper has therefore proposed modifications to the current design rules of AISI (2016) and AS/NZS (2018). The accuracy of proposed design rules was verified using the FE analysis and test results of CFS channel section columns undergoing local-overall buckling interaction.

Effect of web hole spacing on axial capacity of back-to-back cold-formed steel channels with edge-stiffened holes

Recently, a new generation of cold-formed steel (CFS) channel section with edge-stiffened web holes has been developed by industry in New Zealand. However, no research has been reported in the literature to investigate the axial capacity of back-to-back channels with edge-stiffened web holes. This paper presents a total of 73 new results comprising 29 compression tests and 44 finite element analyses (FEA) on axial capacity of such back-to-back CFS channels. The results show that for back-to-back channels with seven edge-stiffened holes, the axial capacity increased by 19.2%, compared to plain channels without web holes. A non-linear finite element (FE) model was developed and validated against the test results. The validated FE model was used to conduct a parametric study involving 44 FE models. Finely, the tests results were compared with the design strengths calculated from the AISI and AS/NZ standards and from the proposed design equations of Moen and Schafer. From the comparison results, it was found that the AISI and AS/NZ design strengths are only 9% conservative to the test results for plain channels without web holes. While Moen and Schafer equations are conservative by 13% and 47% for axial capacity of CFS back-to-back channels with un-stiffened and edge-stiffened web holes, respectively.

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.

On the Lateral-Torsional Elastic Post-Buckling and Strength of Channel Steel Beams

This paper aims at shedding new light on the elastic post-buckling behavior and strength (elastoplastic collapse) of steel channel section beams undergoing lateral-torsional (LT) buckling. This new insight is acquired using a two-node geometrically exact beam finite element developed by the author, which can handle large displacements, including torsion-related warping, Wagner effects, plasticity, residual stresses and arbitrary initial configurations (namely geometrical imperfections). Several cross-sections and loading/support conditions are analyzed. The results obtained show that the LT buckling behavior of channels is asymmetric, meaning that the direction of the geometric imperfection can influence significantly the strength of the beams. Moreover, it is demonstrated that the loading and support conditions play a major role, leading to a significant scatter of results which hinder the definition of a single buckling curve for design purposes. Nevertheless, in all cases considered, the buckling strengths obtained fall significantly above those predicted by the current version of Eurocode 3.

Numerical investigation of cold-formed stainless steel lipped channels with longitudinal stiffeners subjected to shear

The shear response of the cold-formed stainless steel lipped channel sections with longitudinal stiffeners has not been investigated adequately in the past. Therefore, this paper presents the details of numerical investigations conducted to study the shear behaviour of longitudinally stiffened cold-formed stainless steel lipped channel sections. Following a validation study of the finite element models of lipped channel sections, the effect of return lips and web stiffeners on the shear response of lipped channel sections was examined through comprehensive numerical parametric studies. In addition, numerical investigations were conducted to study the elastic shear buckling response of the sections and the shear buckling coefficients were back-calculated. It was found that the longitudinal web stiffeners enhance the shear buckling resistance of lipped channel sections considerably with increased stiffener depth. However, the shear capacity increment is not significant compared to plain lipped channel sections. The presence of the web stiffeners is found to be not preventing the out-of-plane buckling of the sections. The evaluation of Eurocode 3 and the direct strength method shear provisions for stainless steel channel sections with longitudinal stiffeners illustrates inaccurate capacity predictions. Therefore, modifications were proposed and comparisons reveal that the proposed provisions enhance the shear resistance predictions with good accuracy over the codified provisions.

Press-braked stainless steel channel section columns failing by flexural buckling: Testing, numerical simulation and design

The minor-axis flexural buckling behaviour and strengths of pin-ended press-braked stainless steel channel section columns have been investigated in the present paper through laboratory testing and numerical modelling. An experimental programme was firstly conducted, and included initial global and local geometric imperfection measurements and twelve pin-ended column tests about the minor principal axis. The key obtained test results, including the failure loads, the mid-height lateral deflections at the failure loads, the load–mid-height lateral deflection curves and the failure modes, were reported and discussed in detail. The experimental programme was followed by a numerical modelling programme; finite element models were developed to simulate the test responses and then adopted to perform parametric studies to generate further numerical data on press-braked stainless steel channel section columns over a wide range of cross-section dimensions and member effective lengths. The obtained experimental and numerical data were employed to assess the accuracy of the relevant design rules for press-braked stainless steel channel section columns failing by flexural buckling about the minor principal axis, as given in the European code, American specification, Australian/New Zealand standard and SCI design manual. The results of the assessment indicated that (i) the European code yields unsafe flexural buckling strength predictions for those relatively short and intermediate press-braked stainless steel channel section columns with member non-dimensional slendernesses less than around 1.0, (ii) the American specification leads to unsafe predictions of flexural buckling strength for press-braked stainless steel channel section columns over the whole considered range of member non-dimensional slendernesses up to 3.0, and (iii) the Australian/New Zealand standard and the SCI design manual result in lower levels of design accuracy than the European code and American specification, but with significantly reduced number of unsafe flexural buckling strength predictions.

Optimal design of cold roll formed steel channel sections under bending considering both geometry and cold work effects

Optimal design of a structural member is a design process of selecting alternative forms to obtain its maximum strength while maintaining the same weight, leading to the most economical and efficient structure. Amongst steel structures, cold rolled steel ones can effectively gain this requirement as they are thin-walled structures that offer the high ratio of strength over weight. However, the design is very challenging as these members are prone to buckling and failure at low loads. In this paper, the buckling and ultimate strength of cold rolled channel sections was studied using numerical modelling. In order to improve the section strength, the development of various alternative cold rolled formed sections included additional bends such as intermediate stiffeners. The section strength was optimised through a practical approach which altered the stiffener's position and shape and searched for maximum buckling and ultimate strength under bending. In this approach, a nonlinear Finite Element model was first developed for an industrial channel beam subjected to four-point bending tests and this model was validated against experimental test data. The verified model was then used to conduct a parametric study in which the effects of a stiffener's properties on the section strength including its position, shape, size and material properties by the cold work at bends were investigated in detail. Several different cold rolled channel sections having intermediate stiffeners at web and flanges with and without the cold work effect on material properties at the stiffener's bends were considered for this investigation. In addition, a design method, the Direct Strength Method (DSM), was utilised to take into account the effects of a stiffener's properties on the section strength and results were compared with the Finite Element modelling results. It was found that some significant improvements were obtained for the section strength of the optimised sections in comparison to the original sections. An optimal shape for the channel section with maximum ultimate strength in distortional buckling could be obtained with both the stiffeners' position, shape, size and quantity, and the cold work effect. The cold work effect was found most significant in the cases of changing the width of the web stiffeners and the position of the flange stiffeners. It also revealed that, the currently available DSM beam design curve for distortional buckling provided good agreement in predicting buckling load and ultimate strength capacity for most of the considered sections with and without the cold work effect included; however, the DSM provided overestimate results compared to the Finite Element model results in the sections with web intermediate stiffeners, in particular, when the tip of web intermediate stiffener moved away from the web-flange junction in the horizontal direction.

Experimental and numerical studies of laser-welded stainless steel channel sections under combined compression and major axis bending moment

This paper presents an in-depth experimental and numerical investigation into the behaviour of laser-welded stainless steel channel sections under combined compression and bending moment about the major axis. Two laser-welded austenitic stainless steel plain channel sections were considered in the experimental investigation, and for each channel section, four eccentrically loaded stub column tests were conducted under various initial loading eccentricities. The experimental results were then adopted in a numerical investigation for the validation of finite element models, by means of which parametric studies were conducted to generate further structural performance data over a wider range of cross-section sizes and initial loading eccentricities. Both the obtained experimental and numerical results were carefully analysed and then used to evaluate the accuracy of the current codified design rules for welded stainless steel channel sections under combined compression and major axis bending. The evaluation results generally revealed that the codified design rules yield excessively conservative and scattered resistance predictions, owing to the neglect of the favourable material strain hardening of stainless steel and the beneficial stress redistribution within channel sections under combined loading. An improved design approach has been proposed through extension of the deformation-based continuous strength method (CSM) to the case of laser-welded stainless steel channel sections under combined compression and major axis bending. Quantitative evaluation of the new design approach was made through comparing the predicted resistances against the experimental and numerical failure loads, with the results revealing that the new design approach yields a much higher level of design accuracy and consistency than the current codified design rules. Finally, statistical analyses have been conducted to confirm the reliability of the new design approach according to EN 1990.

Effect of staggered bolted connections on CFS channel sections

This research focuses on the effect of staggered bolted connections on the ultimate tensile capacity and failure modes of the cold-formed steel channel sections connected to the gusset plates. The test program includes two series of 113 channel specimens tested under axial tension with one series containing 52 two-bolted specimens and the other with 61 three-bolted specimens. All the specimens were bolted in the web in a staggered fashion, and the main parameters being investigated are different channel dimensions, staggered and gauge distances, and bolt hole diameter. The test results indicate that the tensile resistance of the two-bolt staggered connection is usually bearing controlled and that of the three-bolt staggered connection is net-section rupture. In addition, the original formula s2/(4g + 2dh) proposed by Cochrane is used to calculate the net section area, instead of simplified s2/4g, which could overestimate the net section area upto 10%. Furthermore, the net-section efficiency factor proposed in codes such as EN-1993-1-3, AS/NZS 4600: 2018, and literature to account for in-plane and out-of-plane shear lag, and bending moment due to the eccentricity in loading is evaluated with the test results from three-bolt configurations obtained from this study. It was observed that the current code provisions (EN-1993-1-3:2004, AS/NZS 4600:2018) for staggered bolt configuration yield non-conservative estimates of the ultimate tensile strength. However, the latest equation proposed by Teh and Gilbert [1] (also adopted in AISI 2016), which accounts for all the sources of capacity reduction factors mentioned above, predicted the net section tension capacity accurately. Through the reliability analysis of the equation by Teh and Gilbert [1] based on the present test results, the resistance factor of 0.75 for LRFD and safety factor of 2.05 for ASD design philosophies are suggested.

Web crippling behaviour of cold-formed steel channel sections with edge-stiffened and unstiffened circular holes under interior-two-flange loading condition

Abstract Recently, a new generation of cold-formed steel (CFS) channel sections with edge-stiffened circular holes have been developed by industry in New Zealand. No previous research, however, has considered the web crippling strength of CFS channel sections with edge-stiffened circular web holes under the interior-two-flange (ITF) loading conditions. In this paper, a combination of experimental investigation and non-linear finite element analysis (FEA) are used to investigate the effect of edge-stiffened holes under ITF loading conditions; for comparison, channel sections without holes and with unstiffened holes are also considered. In total, 30 web crippling test results are reported. A non-linear finite element (FE) model is described, and the results were compared against the test results, which showed a good agreement in terms of both the web crippling strength and failure modes. The results indicate that the stiffened web holes can significantly improve the web crippling strength of CFS channel sections. Using the validated FE model, a parametric study was conducted which include 1116 FE analyses, covering the effect of different hole sizes, edge-stiffener lengths and fillet radii, length of the bearing plates and position of the holes in the web. From the results of the parametric study, design recommendations in the form of web crippling strength reduction factors are proposed, that are conservative to both the experimental and FE results.

Flexural capacity of gapped built-up cold-formed steel channel sections including web stiffeners

This paper describes an experimental and numerical investigation to study the flexural capacity of back-to-back gapped built-up cold-formed steel (CFS) channel sections under four-point bending. The gap between the back-to-back channels was formed through intermediate link-channels which were screwed to the webs of the back-to-back channels. A total of 90 results comprising 18 laboratory tests and 72 finite element (FE) analysis results are reported on the flexural capacity of back-to-back gapped built-up CFS channel sections under four-point bending. Three different types of channels were considered to form the built-up channels: plain channels, channels with one web stiffener and channels with two web stiffeners. Two different beam spans as 1000 mm and 2000 mm were tested. Initial geometric imperfections were also measured prior to bending tests for all test specimens. A nonlinear FE model was then developed, the results of which showed good agreement against the laboratory test results. Using the validated FE model, an extensive parametric study was conducted to investigate the effects of web stiffeners and link-channel spacing on the flexural capacity of such gapped built-up beams. It is shown that design in accordance with the American Iron and Steel Institute, AISI (2016) and Australia/New-Zealand standards, AS/NZS (2018) can be conservative by as much as 27%. The flexural capacity of back-to-back gapped built-up sections with two web stiffeners was increased by 10% on average, when compared to the capacity of gapped built-up beams with plain channel sections.

Experimental and numerical studies of pin-ended press-braked S960 ultra-high strength steel channel section columns

Grade S960 ultra-high strength steel is receiving increasing attention owing to its excellent strength-to-weight ratio. However, its application in construction engineering is rather limited due to the lack of adequate design rules, as the current established codes in Europe, North America and Australia/New Zealand only cover the design of steel components with material grades up to S700 (or S690). This prompts investigations into different types of S960 UHSS structural components and development of accurate and efficient design rules for them. The present paper focuses on press-braked S960 UHSS channel section columns prone to flexural buckling about the minor principal axes, with their behaviour and resistances thoroughly examined through experiments and numerical modelling. An experimental programme was firstly performed on two non-slender press-braked channel sections, with five column specimens of varying member lengths employed for each cross-section, and included initial global and local geometric imperfection measurements and pin-ended column tests about the minor principal axes. This was followed by a parallel numerical modelling programme, where finite element (FE) models were developed to simulate the experimental results and afterwards adopted to perform a parametric study to generate additional numerical data over a broader spectrum of cross-section dimensions and member lengths. It is worth noting that there were two orientations associated with minor-axis flexural buckling of press-braked S960 UHSS channel section columns, namely ‘C’ orientation (indicating that columns buckled towards the webs) and ‘reverse C’ orientation (indicating that columns buckled towards the flange tips), and both of the two types of failure modes were carefully examined in the present study. It was found that channel section columns failing by flexural buckling in the ‘reverse C’ orientation generally exhibited superior resistances relative to their counterparts with failure in the ‘C’ orientation. The experimental and numerical data were also used to assess the applicability of the codified provisions for press-braked S700 (or S690) channel section columns failing by flexural buckling about the minor principal axes to the design of their S960 counterparts. The assessment results indicated that (i) the existing European code leads to overall conservative and scattered design flexural buckling resistances, especially for those relatively short and intermediate press-braked S960 UHSS channel section columns with failure in the ‘reverse C’ orientation, and (ii) the North American specification and Australian/New Zealand standard result in a higher degree of design accuracy and consistency than the European code, but with many over-predicted flexural buckling resistances for press-braked S960 UHSS channel section short and intermediate columns failing in the ‘C’ orientation.

Experimental and numerical investigations of cold-formed austenitic stainless steel unlipped channels under bearing loads

While mechanical properties and material stress-strain response of different families of stainless steel (known as austenitic, duplex and ferritic) are different from each other, current cold-formed stainless steel standards do not generally take into account these differences as they provide single equations for any loading scenario to cover all groups of stainless steel. This may lead to inaccurate results, especially for austenitic steel which is a high performance material increasingly used in modern construction, due to its higher ductility and ultimate-to-yield strength ratio. This research aims to investigate the web bearing performance of cold-formed steel channels fabricated with austenitic stainless steels subject to concentrated transverse forces experimentally and numerically. The experimental programme consists of 16 thick unlipped channel specimens with different internal fillet radius and web depth to thickness ratios. For the numerical investigations, 88 detailed nonlinear quasi-static finite element models are used and validated against experimental data. Complementary parametric investigations are then conducted to ascertain the web bearing strengths in terms of various channel sizes, web thicknesses and internal fillet radius. It is found that the equations proposed by current stainless steel standards are unreliable for austenitic steel as they can lead to significantly un-conservative results (up to 43%) under both one- and two-flange loading scenarios. Other equations suggested in the literature for ferritic stainless steel are also shown to provide overestimated results (up to 34%) for austenitic steel channel sections. Based on the experimental and analytical results from this study, new equations are proposed to estimate the web bearing strength of cold-formed austenitic stainless steel channels and their reliability is demonstrated. • Performance of austenitic stainless steel channels subject to bearing loads is investigated. • 16 thick unlipped channels are tested under one- and two-flange loading scenarios. • 88 validated FE models are developed to assess the effects of channel size, web thickness and internal fillet radius. • Current design equations up to 43% overestimate the web bearing strength of austenitic stainless steel channels. • New design equations are proposed and their reliability is demonstrated under IOF, EOF, ITF and ETF loading scenarios.

Numerical study of cold-formed steel channel sections under combined web crippling and bending action

Cold-formed steel sections used in floor systems are vulnerable to web crippling, and with increasing span lengths, they are likely to fail under combined web crippling and bending action. A numerical study was therefore undertaken to investigate the combined web crippling-bending interaction behaviour of unlipped channel sections used as bearers in floor systems with fastened supports. Web crippling finite element models developed and validated by the authors in a recent study were extended to investigate the behaviour of unlipped channels under combined action of web crippling and bending while new finite element models were developed for bending and validated using available experimental results. All three types of finite element models were used in a detailed parametric study to obtain the capacities of 12 unlipped channel sections made of G250 and G450 steels under pure and combined web crippling and bending actions. Comparison of the combined web crippling and bending capacities obtained from finite element analyses with the interaction equations in three cold-formed steel design standards, AISI S100, AS/NZS 4600 and Eurocode 3 Part 1.3, showed that the current design equations are accurate for 50 mm bearing length. However, they can also be used to predict the combined web crippling-bending capacities conservatively for bearing lengths of 100 and 150 mm. A new design equation with a suitable capacity reduction factor was then proposed to improve the accuracy of predicting the mid-span load capacity of channel sections subject to combined web crippling and bending actions. • Investigated the behaviour of unlipped channels with fastened supports under pure and combined web crippling and bending. • Developed and validated finite element models for web crippling and bending actions. • Recommended ABAQUS quasi-static analysis based on explicit conditions instead of general static method. • Current web crippling and bending interaction equations were shown to be conservative. • Proposed new equations to predict the mid-span load capacity under combined web crippling and bending action.

Experimental investigation of post-fire mechanical properties of Q235 cold-formed steel

Abstract Cold-formed steels are commonly used in construction applications. However, there is a lack of understanding on its post-fire mechanical properties. This paper presents an experimental investigation on post-fire mechanical properties of cold-formed steels. The test specimens were cut from flat portion and corners of cold-formed channel sections, which were exposed to temperatures ranging from ambient temperature to 800 °C, and then cooled with water and air. The specimens are of grade Q235, with section thicknesses of 1 mm and 2 mm. The stress-strain curves and mechanical properties of the specimens were obtained from tensile coupon tests. Test results of post-fire mechanical properties are presented. Moreover, evolution of microstructure and fracture morphology of specimens with different cooling methods were examined. Finally, predictive equations are proposed for evaluating the post-fire mechanical properties of Q235 cold-formed steel channel sections.

Cold-formed steel channel sections under end-two-flange loading condition: Design for edge-stiffened holes, unstiffened holes and plain webs

Abstract In cold-formed steel (CFS) channel sections, web holes are becoming increasingly popular. Such holes, however, result in the sections becoming more susceptible to web crippling, especially under concentrated loads applied near the web holes. Traditional web holes are normally punched or bored and are unstiffened. Recently, a new generation of CFS channel sections with edge-stiffened web holes has been developed by the CFS industry and is being widely used. However, no research is available in the literature which investigated the web crippling strength of CFS channel sections with edge-stiffened circular web holes under the end-two-flange (ETF) loading conditions. A combination of experimental tests and non-linear FEA were used to investigate the effect of such stiffened holes on web crippling behaviour under ETF loading conditions. The results of 30 web crippling tests are presented. Non-linear FE models are described, and the results are compared against the laboratory test results; a good agreement was obtained in terms of both the strength and failure modes. The results indicate that the stiffened holes can significantly improve the web crippling strength of CFS channel sections. A parametric study involving 1116 FEA was then performed, covering the effect of different hole sizes, edge-stiffener lengths and fillet radii, length of the bearing plates and position of holes in the web. Finally, design recommendations in the form of web crippling strength reduction factors are proposed, that are conservative to both the experimental and FE results.

Cold Formed Steel Channel Sections with Flange Stiffeners

In recent years the utilization of cold formed steel has been redoubled. This is because high strength to weight ratio of the cold formed steel. The thicknesses cold formed steel members usually range from 0.3 mm to 6.35 mm. The most used cold formed sections are C and Z sections. These sections can be used as secondary beams (purlins) for roof covering, side girts, decks, and panels. Scope of this present study is to investigate the effect on load carrying capacity of cold formed channel sections provided with flange stiffeners. In this project, eighteen numbers of channel sections were analysed by keeping the height to thickness ratio (h/t) as constant and by varying flange width to thickness ratio (b/t) using Ansys 14.0. The h/t ratio and b/t ratio considered are 50 and 25, 35, 45 respectively. The thickness and span of all specimens were kept as 2 mm and 1500 mm respectively. Simply supported boundary condition and two points loading was adopted for both the numerical and experimental analysis. Three numbers of channel sections were fabricated and tested experimentally to check the consistency of results with numerical analysis. The ultimate load and deformed shape of three specimens were obtained from experimental results are compared with the analytical results acquired from Ansys 14.0.

Testing and numerical modelling of S960 ultra-high strength steel angle and channel section stub columns

A comprehensive experimental and numerical study of the cross-sectional compressive behaviour and resistances of press-braked S960 ultra-high strength steel (UHSS) angle and channel section stub columns is reported in this paper. The experimental study was carried out on four equal-leg angle sections and eight plain channel sections, and comprised material testing, initial local geometric imperfection measurements and 18 stub column tests. The experimental setups, procedures and key observations were fully presented. The experimental study was then supplemented by a finite element (FE) simulation programme, in which FE models were firstly developed to replicate the test structural responses and subsequently used to generate further numerical data over a wide variety of cross-section sizes. It is worth noting that the current international standards established in Europe, America and Australia/New Zealand only cover the design of structural members with material grades up to S700, and thus the examined S960 UHSS angle and channel section stub columns are out of the scope of the existing design standards. In this study, the experimentally and numerically acquired data was adopted to assess the applicability of the codified provisions and formulations to the design of S960 UHSS angle and channel section stub columns. The assessment results generally indicated that the current European code leads to overall consistent and accurate predictions of cross-section compression resistances, but with many overestimated predicted resistances for S960 UHSS channel section stub columns, while the American and Australian/New Zealand standards yield unduly scattered design cross-section compression resistances, with unsafe and overly conservative predicted resistances respectively for S960 UHSS channel section stub columns and slender angle section stub columns. Revised codified design rules were also proposed, and shown to yield safe, accurate and consistent design cross-section compression resistances for S960 UHSS angle and channel section stub columns.

Experimental and numerical studies of press-braked S690 high strength steel channel section beams

Abstract The present paper describes an in-depth experimental and numerical investigation into the flexural responses and strengths of press-braked S690 high strength steel channel section beams bent about the minor principal axes in both the ‘u’ and ‘n’ orientations. The experimental study was performed on eight press-braked channel sections, and comprised twenty-four material flat and corner coupon tests, initial local geometric imperfection measurements, and twelve beam tests in the four-point bending configuration. This was followed by a complementary numerical modelling programme, where finite element models were firstly developed and validated against the test results and afterwards adopted for performing parametric studies to obtain an additional numerical data bank over a wide variety of cross-section geometric sizes. The acquired test and numerical data were then employed to evaluate the applicability of the Eurocode slenderness limits for welded and hot-rolled internal webs (in compression) and outstand flanges (in stress gradients) to their press-braked counterparts, revealing that the Eurocode slenderness limits can be safely extended to cover the classifications of plate elements and cross-sections of press-braked S690 high strength steel channel section beams. Evaluation of the accuracy of the cross-section flexural strengths predicted from various design codes established in Europe, North America and Australia/New Zealand was also made, based on the test and numerical data. The results of the quantitative evaluation generally revealed that (i) all the examined design codes lead to overall conservative and scattered predicted cross-section flexural strengths for press-braked S690 high strength steel channel section beams, and (ii) the European code results in more precise design flexural strengths for beams with relatively stocky channel sections, but less accurate strength predictions for beams with relatively slender channel sections, compared to the North American and Australian/New Zealand standards.