Experimental response of cold-formed steel lipped channel beam-columns

In this paper, the structural strength and stability of cold-formed steel lipped channel beam-columns under bi-axial moments and axial force are experimentally investigated. The results are employed to evaluate the reliability of the current North American cold-formed steel design standard, AISI-S100-12, for predicting the strength of beam-columns, by both the effective width method (EWM) and the direct strength method (DSM). Fifty-five 600S137-54 (AISI-S200-12 nomenclature) lipped channel beam-column sections with three different lengths: 305 mm (short), 610 mm (intermediate), and 1219 mm (long) are tested under combined bi-axial bending moments and axial force to characterize the failure modes and the member capacity. A loading rig specifically designed to apply eccentric axial load, in order to provide bi-axial bending and compression to the specimens, was developed and detailed herein. The experimental observations reveal that the failure modes are highly dependent on the stress distribution applied on the cross-section by the combined actions. The results show a considerable potential for improvement in current specification approaches which utilize a simple interaction equation, as this typically results in conservative strength predictions. The potential for further improvement of the current specification for predicting the strength of cold-formed steel beam-columns is discussed.     

Column tests of cold-formed steel non-symmetric lipped angle sections

The geometry of angle sections is simple, but the behaviour and design calculations of angle sections can be quite complicated. Furthermore, lipped angle sections with unequal flange widths form a non-symmetric section and the behaviour of the section is even more complicated than a singly-symmetric angle section with equal flange widths. A test program on cold-formed steel non-symmetric lipped angle columns is presented. The non-symmetric angle sections were brake-pressed from high strength structural steel sheets having nominal yield stresses of 450 and 550 MPa with plate thicknesses of 1.0, 1.5 and 1.9 mm. The material properties of the column specimens were obtained by tensile coupon tests. The behaviour and strengths of cold-formed steel non-symmetric lipped angle columns were investigated. The test strengths are compared with the design strengths calculated using the North American Specification for the design of cold-formed steel structural members. In addition, the current design rules in the North American Specification for cold-formed steel non-symmetric lipped angle columns are assessed using reliability analysis. It is shown that the design strengths are generally quite conservative.     

Local/distortional mode interaction in cold-formed steel lipped channel beams

This paper reports a numerical investigation concerning the post-buckling behaviour of cold-formed steel lipped channel beams, subjected to uniform major axis bending, affected by local/distortional mode interaction – the results presented and discussed were obtained through shell finite element analyses performed using the code Abaqus. One analyses simply supported beams (locally/globally pinned and free to warp end sections) (i) with cross-section dimensions ensuring coincident local and distortional critical buckling moments and (ii) having critical-mode initial geometrical imperfections with different shapes and the same overall amplitude – local buckling is triggered either by the compressed flange (most common case) or by the web. The results reported consist of (i) elastic and elastic–plastic post-buckling equilibrium paths, (ii) curves and figures showing how the beam deformed configuration evolves along those paths and, for the elastic–plastic beams, (iii) figures making it possible to visualise (iii₁) the location and growth of plastic strains and (iii₂) the nature of the failure mechanisms detected.     

Coupled instabilities with distortional buckling in cold-formed steel lipped channel columns

The paper addresses the elastic post-buckling behaviours of cold-formed steel lipped channel simply supported columns affected by mode interaction phenomena involving distortional buckling, namely local/distortional, distortional/global (flexural-torsional) and local/distortional/global mode interaction. The results presented were obtained by means of Abaqus shell finite element analyses adopting column discretisations into fine 4-node element meshes. In order to enable a thorough assessment of all possible mode interaction effects, the column lengths and cross-section dimensions were carefully selected to ensure similar local, distortional and/or global buckling loads. One analyses otherwise identical (elastic) columns having initial geometrical imperfections (i) with various configurations (combinations of the competing critical buckling mode shapes) and (ii) sharing the same overall amplitude.     

冷弯薄壁型钢卷边槽形截面构件畸变屈曲控制研究

基于部分加劲板件的畸变屈曲和局部屈曲的稳定系数比较,提出了冷弯薄壁型钢卷边槽形截面构件畸变屈曲发生于局部屈曲之后或畸变屈曲不发生的临界控制条件;给出了通过构件畸变屈曲计算长度控制畸变屈曲的临界条件;提出一种控制畸变屈曲的构造措施,即在卷边间加设缀板,并通过已有试验对其有效性进行验证,同时推导了卷边间缀板的刚度需求。结果表明：通过构件截面尺寸控制畸变屈曲不发生或发生在局部屈曲之后,可以不考虑构件畸变屈曲的影响,简化冷弯薄壁型钢卷边槽形截面构件承载力的计算;计算长度小于畸变屈曲半波长一半的构件不发生畸变屈曲;通过在卷边间加设缀板的构造措施能有效阻止部分加劲板件的转动,构件的畸变屈曲荷载和承载力都有很大的提高,缀板布置间距不同,构件承载力的提高幅度也不同,缀板间距越小,构件承载力提高幅度越大。算例分析表明,满足一定间距和刚度需求的缀板能够提高构件的畸变屈曲承载力或避免畸变屈曲的发生。     

Load-carrying capacities of cold-formed steel cut stub columns with lipped C-section

Cutting roll-formed steel lipped C-sections may produce different extent of cross section distortion along the lengths of the sections and may lead to additional initial geometric imperfections. Ten stub columns cut from two different sections were tested under axial compression. Flanges of the stub columns experienced distortional mode of failure, whereas the webs showed signs of local buckling failures. Ultimate compressive strengths obtained from the test results were 75–77% of the strengths estimated based on BS5950:Part 5. This indicates that geometric imperfections caused by cutting may significantly reduce the ultimate strength of stub columns.     

Flexural-Torsional buckling tests of cold-formed lipped Channel beams under restrained boundary conditions

In this paper, tests on flexural buckling (Lateral-Torsional) of cold-formed steel (CFS) lipped Channel beams under restrained boundary conditions are described. Two point loading for flexural tests have been established for 3.0 m span to obtain uniform bending moment. The section sizes selected for testing are 100×50×10, 100×50×15, and 100×50×20 mm with 1.6 and 2.0 mm thickness for the investigation. Carefully designed loading and support systems were used in the tests to apply gravity load through the web of the section and to ensure that simply supported ends were established. The test results were compared with the moment obtained using BS5950: Part 5 and IS code 801-1975. The influences of warping and torsional restraints on flexural capacity are presented. The influence of buckling length for different boundary conditions proposed by Rhodes is considered to calculate critical flexural-torsional buckling moment.     

加设隔板的冷弯薄壁卷边槽钢受压性能研究

采用有效宽度法和直接强度法分别对冷弯薄壁卷边槽钢轴压柱承载能力进行了分析,在此基础上,对加设隔板这种加固方式的试验效果进行比较分析,结果表明:当采用矩形隔板,在1/2～1/3半波间距布置隔板时,为经济有效的布置方式。     

Behaviour of cold formed lipped angles in transmission line towers

The importance and use of equivalent radius of gyration method is discussed and necessary expressions are derived in this paper. The limiting values of slenderness ratio for the equivalent radius of gyration with the least radius of gyration are discussed to establish the buckling behaviour of lipped angles. Finite Element Analysis on the buckling behaviour of the mathematical models of individual lipped angle members and a full scale X-panel was carried out to compare the values predicted by equivalent radius of gyration. A series of compression tests were carried out on lipped angle sections and their behaviour is studied in the elastic and in the inelastic ranges of loading. These tests were broadly classified under two categories; concentrically loaded members and eccentrically loaded members. Experimental investigations on full scale tower panels with conventional patterns of leg and diagonals were also carried out. The results of the experiments were compared with analytical predictions using torsional flexural buckling equations, Finite Element Analysis and the equivalent radius of gyration approach.     

支吊架用卷边槽钢轴压构件的稳定性研究

采用有限元方法对支吊架用卷边槽钢轴压构件的弹塑性稳定性进行了研究,考虑了构件长细比、截面尺寸、初弯曲、残余应力等因素的影响.研究发现,在轴压作用下构件不会发生局部屈曲和畸变屈曲,只能发生整体失稳;截面高度对整体失稳形式有影响,但对稳定系数的影响较小,壁厚对整体稳定无影响;初弯曲对稳定系数有明显降低作用,且影响程度与构件...     

冷弯薄壁卷边槽钢轴压柱承载力的计算方法

对冷弯薄壁卷边槽钢轴压柱承栽力进行了稳定承载力计算,结果表明：直接强度法可以有效地预测冷弯薄壁卷边槽钢轴压柱的稳定承载力,与GB50018—2002中的有效宽度法计算结果和试验结果吻合良好且偏于安全。     

高强冷弯薄壁型钢卷边槽形截面构件设计可靠度分析

基于已有的承载力试验研究结果,对屈服强度550MPa高强冷弯薄壁型钢中常用的卷边槽形截面轴压构件和偏压构件的计算模式不定性进行了分析,并统计分析了高强冷弯薄壁型钢强度不定性、几何特性不定性。在此基础上,采用改进一次二阶矩方法,按现有规范的抗力分项系数要求,计算了高强冷弯薄壁型钢卷边槽形截面轴压构件和偏压构件不同可能荷载组合下的可靠指标。结果表明：对于宽厚比符合规范要求的屈服强度550MPa高强冷弯薄壁型钢卷边槽形截面轴压构件和偏压构件,按现有规范的抗力分项系数计算得到的可靠指标均能满足目标可靠指标的要求,证明了所采用的承载力计算方法的适用性;但对于宽厚比超出规范要求的轴压和偏压构件,计算得到的可靠指标不能满足目标可靠指标的要求。     

冷弯薄壁卷边槽钢轴心受压构件承载力计算的折减强度法

为了研究冷弯薄壁卷边槽钢轴心受压构件的极限承载力,对15根轴心受压的冷弯薄壁卷边槽钢进行了破坏性试验,并采用有限元分析方法对试件进行模拟分析,有限元计算结果与试验结果吻合良好,验证了有限元方法的有效性,然后对典型截面构件进行大量的有限元参数分析。研究结果表明：冷弯薄壁卷边槽钢轴心受压构件的极限承载力随着构件翼缘宽厚比、腹板高厚比、长细比以及钢材强度的增大而减小。通过参数分析得到了考虑局部屈曲、整体屈曲和畸变屈曲影响的构件屈服强度折减系数,提出了冷弯薄壁卷边槽钢轴心受压构件承载力计算的折减强度法及其相应计算公式,且通过试验验证了本文折减强度法计算卷边槽钢轴心受压构件极限承载力的适用性。     

A design rule for web crippling of cold-formed steel lipped channel beams based on nonlinear FEA

This paper presents the details of a research study conducted with the aim of developing an alternative design rule to predict the web crippling strength of cold-formed steel lipped channel beams. Current empirical web crippling design rules are perceived to be only accurate for the type of sections and the section dimensions that have been tested. A large number of experiments are often necessary to validate these design rules for a wider range of section types and dimensions, and these experiments are often expensive and impractical. Hence, a design rule which is based on a theoretical or numerical model has been attempted through this work.Four series of tests, replicating the four web crippling loading conditions namely: Interior-One-Flange (IOF), Interior-Two-Flange (ITF), End-One-Flange (EOF) and End-Two-Flange (ETF), were performed to predict the ultimate strength of one hundred and eight specimens. The test specimens were manufactured to include three distinct corner radii and two different web heights, and the specimens were tested using three different lengths of load bearing plates. Two additional loading scenarios which could arise due to the loading flange restraint namely—fixed-flange and free-flange were also examined. Finite element models were developed to numerically simulate the tests performed in the experimental investigations. Load-deformation curves were obtained from both the tests and FE models, and the FE models were validated using the test results. The validation showed a close agreement of FE results with the test results which provided the confidence of using the FE model for a parametric study beyond the limits of the experiments. Based on the results of the parametric study, a design rule was developed which is much more flexible to adapt for new types of sections and ranges of dimensions.     

Study on the buckling behaviour of cold-formed angles in transmission towers

Considering the structural characteristics of transmission towers, four sections of cold-formed angles with different slenderness ratios and constrained types were selected for the experimental and numerical study. Experiments and finite element analysis for the ultimate loads of the compression cold-formed angles were carried out. The finite element model well predicts the buckling behaviour of the cold-formed members. For the axial compression members, the load-strain curves as well as the ultimate loads were analyzed, and the experimental ultimate loads were compared with those of calculated by the applicable standards. It shows that the applicable standards aren’t adaptive to the strength design of the compression cold-formed members in transmission towers. Through the analysis of the experimental and FEA results, the fitting curve of the stability coefficients for the cold-formed members in transmission towers was determined. The ultimate loads calculated by the fitting curve are well agreed with the experimental values, especially for the members with relatively low slenderness ratios. Some modification suggestions were proposed for the calculation of the ultimate load for the axial compression cold-formed angle. Experimental analysis on the cold-formed members of the other five constrained types was completed, and the modification formulas of the slenderness ratios for members of different constrained types were obtained.     

高强冷弯薄壁型钢卷边槽形截面轴压构件畸变屈曲性能研究

建立了考虑材料和几何双重非线性的550MPa高强冷弯薄壁型钢卷边槽形截面轴压构件畸变屈曲性能分析的有限元模型,并通过对两种厚度高强冷弯薄壁型钢轴压构件畸变屈曲试验已有结果的分析比较验证了其有效性;采用该模型进一步分析了厚度、长度、初始缺陷模式及幅值等参数对畸变屈曲轴压构件承载力的影响,并对轴压构件畸变屈曲发生机理进行了探讨。结果表明：厚度、长度和初始缺陷模式是影响畸变屈曲轴压构件承载力的主要因素,且卷边面内屈曲是槽形截面轴压构件发生畸变屈曲的主要原因。通过理论计算与试验结果的对比分析,表明可以采用建议方法计算此类复杂截面轴压构件的畸变屈曲承载力。     

Efficiency reduction due to shear lag on bolted cold-formed steel angles

This work presents 66 new experimental tests carried out on cold-formed steel angles fastened with bolts and under tension. In order to calculate tension-members’ ultimate capacity, net-section failure is considered. The shear-lag phenomenon reduces net-section capacity. This reduction is computed through the reduction coefficient which is a function of two parameters: length of the connection and distance of the shear plane to the centroid of the cross-section. This article examines the reduction coefficient performance based upon the new tests and data available in the literature, comprising a total of 108 lab tests. A new expression for the net-section reduction coefficient is suggested.     

Structural behaviour and design of lightweight structural panels using perforated cold-formed thin-walled sections under compression

Cold-formed thin-walled steel sections are widely used as primary loadbearing members in lightweight panels that form walls in residential and other low rise structures. In cold regions, the webs of the steel sections are often perforated to reduce the cold bridging effect in order to increase thermal comfort and reduce energy waste. Perforating the web of a steel section will reduce its loadbearing capacity. This paper presents the results of an experimental and numerical study to investigate the compression behaviour of lightweight structural panels using perforated sections. The primary objective of the tests is to provide experimental data to validate the numerical simulations, which were carried out using the commercial finite element analysis software ABAQUS. The validated FE analysis was used to develop a simple design calculation method to convert a section with perforated web to a section with solid web. In the equivalent solid web, the thickness of the solid web would have the same elastic local buckling strength as the original perforated web with the gross thickness while the thickness of the unperforated flanges remains unchanged. By converting a thin-walled section with perforated web to a solid section with an effective web thickness, the conventional design methods for thin-walled structures can be applied.     

高强冷弯薄壁型钢卷边槽形截面轴压柱畸变屈曲试验研究

本文对550MPa高强冷弯薄壁型钢卷边槽形截面轴压构件畸变屈曲性能进行了试验研究,17根试件的试验结果表明:由于试件局部屈曲一般发生在畸变屈曲之前,促使畸变屈曲提前出现,这种相关作用减弱了构件整体刚度,降低了构件承载力;澳洲规范AS/NZS 4600:1996及北美规范NAS 2004中关于发生畸变屈曲构件承载力的计算方法没有考虑局部屈曲和畸变屈曲相关作用的不利影响。依据试验结果本文提出了一种修正直接强度法的建议计算方法,该法计算结果与试验结果较为接近且偏安全。     

Full-scale fire experiments on load-bearing cold-formed steel walls lined with different panels

Cold-formed steel (CFS) wall systems were increasingly used as primary load-bearing structural components in residential and industrial buildings. Previous studies were mainly to investigate the fire performance of non-load bearing CFS wall systems lined with gypsum plasterboards. In order to improve the fire performance of load-bearing CFS wall systems more efficiently, this paper presented a detailed experimental investigation on five full-scale CFS walls lined with double layers of three different fire resistant panels on both sides, including fire-resistant gypsum plasterboard, bolivian magnesium board and calcium silicate board. The results showed a noticeable disadvantage of the calcium silicate board due to explosive spalling at high temperatures, and this might cause severe safety issues in an actual fire situation. For CFS walls lined with gypsum plasterboard as the face layer and bolivian magnesium board as the base layer on both sides, different load ratios may result in different failure modes, and the fire resistance time would be more than 90 min when the load ratio was less than 0.65. It was also demonstrated that the fire performance of bolivian magnesium board was superior to that of the fire resistant gypsum plasterboard, therefore the former may be recommended to be used in CFS structures to replace gypsum plasterboards as the base layer.