Aluminum alloy tubular columns—Part I: Finite element modeling and test verification

A numerical investigation on fixed-ended aluminum alloy tubular columns of square and rectangular hollow sections is described in this paper. The fixed-ended column tests were conducted that included columns with both ends transversely welded to aluminum end plates using the tungsten inert gas welding method, and columns without welding of end plates. The specimens were extruded from aluminum alloy of 6061-T6 and 6063-T5. The failure modes included local buckling, flexural buckling, interaction of local and flexural buckling, as well as failure in the heat-affected zone (HAZ). An accurate finite element model (FEM) was developed. The initial local and overall geometric imperfections were incorporated in the model. The non-welded and welded material nonlinearities were considered in the analysis. The welded columns were modeled having different HAZ extension at the ends of the column of 25 and 30 mm. The nonlinear FEM was verified against experimental results. It is shown that the calibrated model provides accurate predictions of the experimental loads and failure modes of the tested columns. The load-shortening curves predicted by the finite element analysis are also compared with the test results.     

Ultimate strength of aluminium alloy outstands in compression: experiments and simplified analysis

An experimental investigation was undertaken to study the stability and ultimate strength of aluminium alloy outstands. In the tests, thin-walled cruciform aluminium extrusions were stressed into the post-buckling range in axial compression. The local buckling behaviour of the flanges of a cruciform section is the same as that of an outstand, i.e. a plate element which is free along one unloaded edge and simply supported along the other. Two tempers of alloy AA6082 with significantly different stress–strain curves were tested for five b/t ratios. The experimental ultimate strengths were compared with theoretical predictions, using the classical Stowell theory for plastic buckling in combination with the effective width concept, and with ultimate strength formulae recommended in the literature.     

An experimental study of ultimate compressive strength of transversely stiffened aluminium panels

An experimental investigation was carried out to determine the ultimate strength of welded stiffened aluminium panels in alloy 6082 T6 subjected to in-plane compressive loads normal to the directions of the stiffeners. This load case is not treated in the European standard for aluminium structures, Eurocode 9. A total of 21 panel specimens with various side aspect ratios and both open and closed stiffener sections were tested in a purpose made test rig. Great care was taken to ensure the rig gave very precise boundary conditions. The panels were manufactured by metal inert gas arc welding and friction stir welding. An extensive measurement program was carried out to determine the distribution of material strength and initial geometric imperfections. Small imperfection amplitudes were found. Tensile tests revealed variation in material properties, but the strength values were on average higher than the values stated in Eurocode 9. The panels failed by two different deformation modes; global flexural buckling and local buckling of the plate elements between the stiffeners.     

Experimental investigation of buckling of wind turbine tower cylindrical shells with opening and stiffening under bending

An experimental and numerical study of the buckling behavior of cantilevered shells with opening and stiffening is presented in this paper. Unlike previous experimental studies, the present work focuses on shell slenderness as well as opening and stiffening reflecting the main geometric characteristics of wind turbine towers. The specimens can be classified as medium slenderness shells affected mainly by inelastic effects and secondarily by geometric imperfections. Both load–displacement curves as well as strain measurements are presented and compared with numerical predictions by finite element analyses, accounting for both inelastic effects and geometrical nonlinearity as well as for contact interaction between the various parts of the specimens. A good agreement between numerical and experimental results was found in terms of load–displacement curves and ultimate load. Due to the influence of the shape and size of geometric imperfections, a complete match of the numerically obtained strains to the corresponding experimental ones was not possible. The provided stiffening was found to be able to compensate the strength loss due to the presence of the cut-out.     

The influence of the fabrication process on the buckling of thin-walled steel box sections

Steel box sections are usually fabricated from flat plates which are welded at the corners. The welding process can introduce residual stresses and geometric imperfections into the sections which can influence their strength. For some thin-walled sections, large periodic geometric imperfections have been observed in manufactured sections. Subsequent investigations have indicated that the imperfections are in fact buckling deformations i.e. the box section has buckled due to welding residual stresses prior to any application of external load. The welding procedure and the behaviour of the box sections under load has been modelled using a finite element analysis that accounts for both geometric and material non-linearities. Tests have been carried out on box sections with a range of width to thickness ratios for the plate elements. Modelling has been shown to give good correlation with the test results. The conditions for buckling to take place as a result of the welding process have been established. A design method has been proposed.     

Assessment of the ultimate strength of narrow stiffened panel test specimens

The ultimate strength of five narrow stiffened panels tested with two stiffeners under axial compression until collapse and beyond is determined by finite element analysis, and is compared with experimental results. Models with two half bays plus one full bays in the longitudinal direction are used in the finite element analysis. The material properties used in the finite element analysis have been evaluated by tensile tests. The initial geometrical imperfections also affect significantly the collapse behavior of the stiffened panels. Hence, the initial imperfections of the stiffened plates were measured before the experiment. The results of the FE analysis with measured and with equivalent initial imperfections are compared and conclusions are derived about the possible bias of the results when the initial imperfections are not measured.     

Numerical investigation of channel columns with complex stiffeners—part I: test verification

A numerical investigation on fixed-ended cold-formed steel channel columns with complex stiffeners subjected to axial load is described in this paper. The complex stiffeners of the channel sections consist of simple lips with return lips. The specimens were brake-pressed from high strength zinc-coated structural steel sheets having a nominal yield stress of 450 MPa. A non-linear finite element model is developed and verified against experimental results of fixed-ended channel columns with complex stiffeners. Initial geometric imperfections and material non-linearity are included in the model. The calibrated model is shown to provide accurate predictions of the experimental ultimate loads and failure modes of the tested columns.     

Finite element modeling of bolted connections in thin-walled stainless steel plates under static shear

The recently performed experimental study indicates that the current Japanese steel design standards (AIJ) cannot be used to predict accurately the ultimate behavior of bolted connections loaded in static shear, which are fabricated from thin-walled (cold-formed) SUS304 austenite stainless steel plates and thus, modified formula for calculating the ultimate strength to account for the mechanical properties of stainless steel and thin-walled steel plates were proposed. In this study, based on the existing test data for calibration and parametric study, finite element (FE) model with three-dimensional solid elements using ABAQUS program is established to investigate the structural behavior of bolted shear connections with thin-walled stainless steel plate. Non-linear material and non-geometric analysis is carried out in order to predict the load–displacement curves of bolted connections. Curling, i.e., out of plane deformation of the ends of connection plates which occurred in test specimens was also observed in FE model without geometric imperfection, the effect of curling on the ultimate strength was examined quantitatively and the failure criteria which is suitable to predict failure modes of bolted connections was proposed. In addition, results of the FE analysis are compared with previous experimental results, failure modes and ultimate strengths predicted by recommended procedures of FE showed a good correlation with those of experimental results and numerical approach was found to provide estimates with reasonable accuracy.     

Experimental and Numerical Study on Buckling Behavior of a Rigidly Stiffened Plate with Tee Ribs

In the bridge structures, stiffened plates are usually designed as rigidly stiffened when the orthotropic steel box girder is used as the main load-bearing structure. Therefore, the buckling mode of stiffened plates is plate buckling which occurs in subpanel supported by stiffeners. The orthotropic steel box girder is used as the main girder for Egongyan Rail Special Bridge, which is a self-anchored suspension bridge. Plates of the steel girder are rigidly stiffened with unequal spacing open ribs, and the most slender stiffened plate is the mid web stiffened with Tee ribs. In order to ensure the safety of the bridge, the buckling behavior of the web and orthotropic steel box girder under axial compression, including ultimate strength, post-buckling behavior and failure modes, should be clearly investigated by experimental and numerical methods. The design, loading and testing methods of the 1:4 scale model of the orthotropic steel box girder are introduced in detail firstly. The orthotropic steel box girder and the stiffened web finite element (FE) models are validated by the test results, and the effects of residual stress and the magnitude of geometric imperfections are discussed roughly. Based on the validated web FE model, a detailed parametric study is performed to systematically investigate the effects of residual stress and geometric imperfections on buckling behavior of the web. The effect of shapes of geometric imperfections discussed is highlighted. Through tracing stress states, the failure modes of stiffened plate are in agreement with the experimental phenomenon to some extent. Results show that shapes of geometric imperfections have significantly influenced post-buckling behavior and failure modes of the web, but slightly affected the ultimate strength. It is advised that residual stress and geometric imperfections should be controlled to make full use of excellent performance of steel materials.     

Ultimate strength of stiffened aluminium panels with predominantly torsional failure modes

The aim of this paper is to investigate the ultimate strength of aluminium plates with flatbar stiffeners with a torsional buckling or tripping failure mode. The formulations for torsional buckling of stiffeners in steel plating are still debated. Compared with steel structures, the ultimate strength of aluminium structures is sensitive not only to residual stresses and initial deformations, but also to the deterioration of mechanical strength in heat-affected zones (HAZ). In the present paper, the ultimate strength of stiffened aluminium panels with predominantly torsional failure modes is investigated by experimental and theoretical analysis. Stiffened panels made of the aluminium alloy AA5083-H116 and AA6082-T6 are considered. Various height of flatbar and various thickness of plate and stiffener were studied. The test results are compared with numerical predictions by using the finite element code ABAQUS (ABAQUS Version 5.7 (1997)), considering the influence of initial deflections, welding residual stresses and HAZ. The influence of HAZ and residual stresses on the ultimate strength of stiffened aluminium panels with the actual failure mode is discussed in detail. The numerical predictions are also compared with strength of material formulations used in DNV Rules for Classification of High Speed and Light Craft (Rules for classification of high speed and light craft, Hull structural design (1996)), NORSOK (Design of steel structures (1998)) all for steel, using the relevant values of the modulus elasticity and yield strength of aluminium, as well as EUROCODE 9 (Eurocode 9, Part 1-1: General rules (1998)).     

Experimental investigation for the behaviour of battened beam-columns composed of four equal slender angles

This study presents series of compression tests on battened columns that are composed of four equal slender angles. The angles are formed by bending thin steel sheets, such that the legs outstand width–thickness ratio is slender. Twenty specimens varied in their plate element width–thickness ratio as well as covered short and medium member slenderness were tested. The angles were assembled by batten plates by means of bolts. Measurements of residual stresses and geometrical imperfections were carried out. Moreover the specimens were simulated by a finite element model using shell element that accounts for both geometric and material non-linearities. The measured geometric imperfections and residual stresses were included in the numerical model. Finally, the test results have been compared with those of non-linear finite element model, and also with the predicted ultimate strengths determined by the American and European specifications. Results show that the interaction between slender outstanding width–thickness ratios, overall angle slenderness and overall column slenderness decrease the strength of battened columns. Also, the results of bolted finite element model were in reasonably good agreement with test results that neglect the effect of bolt holes.     

Tests and finite element analysis of pin-ended channel columns with inclined simple edge stiffeners

This paper presents an experimental investigation and a finite element analysis on cold-formed channels with inclined simple edge stiffeners compressed between pinned ends. Compression tests of pin-ended channel columns with inclined simple edge stiffeners have not been performed till now. A total of 36 channel specimens including three different cross sections with different edge stiffener inclined angles and column lengths were tested. Detailed measurements of initial geometric imperfections and material properties of the specimens were also conducted before the above tests. Failure modes include local buckling, distortional buckling, flexural buckling and interaction among these buckling modes were observed in tests. The results indicate that inclined angle and loading position significantly affect the ultimate load-carrying capacity and failure mode of specimens. Moreover, a non-linear finite element model was developed and verified against tests. Geometric and material non-linearities were included in the model. Results from the finite element analysis agree well with experimentally ultimate loads and failure modes. However, it should be improved on prediction for certain displacement.     

剖分T型钢压杆的弯扭屈曲试验研究

《钢结构设计规范》(GB50017—2003)提出对单轴对称截面钢压杆的弯扭屈曲需做单独验算。本文通过27根剖分T型钢压杆的试验,并借助有限元分析软件对剖分T型钢压杆的弯扭屈曲进行了几何非线性及材料非线性的有限元分析,分析时考虑了残余应力、几何缺陷的不利影响,在此基础上对规范(GB50017—2003)计算值、本文试验值、有限元计算值做了分析比较。研究结果表明规范(GB50017—2003)中单轴对称截面压杆的弯扭屈曲计算公式是安全可靠的。     

Numerical modelling and design of LiteSteel Beams subject to lateral buckling

The LiteSteel Beam (LSB) is a new hollow flange channel section developed using a patented dual electric resistance welding and cold-forming process. It has a unique geometry consisting of torsionally rigid rectangular hollow flanges and a slender web, and is commonly used as flexural members. However, the LSB flexural members are subjected to a relatively new lateral distortional buckling mode, which reduces their moment capacities. Unlike lateral torsional buckling, the lateral distortional buckling of LSBs is characterised by simultaneous lateral deflection, twist and cross sectional change due to web distortion. Therefore a detailed investigation into the lateral buckling behaviour of LSB flexural members was undertaken using experiments and finite element analyses. This paper presents the details of suitable finite element models developed to simulate the behaviour and capacity of LSB flexural members subject to lateral buckling. The models included all significant effects that influence the ultimate moment capacities of such members, including material inelasticity, lateral distortional buckling deformations, web distortion, residual stresses, and geometric imperfections. Comparison of elastic buckling and ultimate moment capacity results with predictions from other numerical analyses and available buckling moment equations, and experimental results showed that the developed finite element models accurately predict the behaviour and moment capacities of LSBs. The validated model was then used in a detailed parametric study that produced accurate moment capacity data for all the LSB sections and improved design rules for LSB flexural members subject to lateral distortional buckling.     

Finite element study of steel beams reinforced while under load

The results of a finite element study on the behavior and capacity of W-shape steel beams reinforced with welded plates while under load are presented. The finite element model was verified using test results obtained from a concurrent experimental study involving the testing of six beam specimens reinforced while under load. The verified model was then used to investigate the effect of several influential parameters with the focus on reinforcing patterns, preload magnitudes at the time of welding, and initial imperfections of the unreinforced beam. Numerical results show that an increase in the preload magnitude at the time of reinforcing resulted in a reduction in the ultimate capacity of reinforced beams failing in lateral-torsional buckling. This reduction was more significant for a beam reinforced with a plate welded to its tension flange than that reinforced with a plate welded to each of its flanges. The variation of initial imperfections of unreinforced beams was also shown to affect the ultimate capacity of the reinforced beam. For beams failing by yielding, the effects of preload magnitudes and initial imperfections were marginal.     

Local buckling of steel plates in concrete-filled thin-walled steel tubular beam-columns

The availability of high strength steels and concrete leads to the use of thin steel plates in concrete-filled steel tubular beam-columns. However, the use of thin steel plates in composite beam-columns gives a rise to local buckling that would appreciably reduce the strength and ductility performance of the members. This paper studies the critical local and post-local buckling behavior of steel plates in concrete-filled thin-walled steel tubular beam-columns by using the finite element analysis method. Geometric and material nonlinear analyses are performed to investigate the critical local and post-local buckling strengths of steel plates under compression and in-plane bending. Initial geometric imperfections and residual stresses presented in steel plates, material yielding and strain hardening are taken into account in the nonlinear analysis. Based on the results obtained from the nonlinear finite element analyses, a set of design formulas are proposed for determining the critical local buckling and ultimate strengths of steel plates in concrete-filled steel tubular beam-columns. In addition, effective width formulas are developed for the ultimate strength design of clamped steel plates under non-uniform compression. The accuracy of the proposed design formulas is established by comparisons with available solutions. The proposed design formulas can be used directly in the design of composite beam-columns and adopted in the advanced analysis of concrete-filled thin-walled steel tubular beam-columns to account for local buckling effects.     

关于多高层钢结构柱计算长度(Ⅱ):数例说明

本文先建立四个有初始几何缺陷的框架结构,通过有限元分析分别得到这四个框架的竖向极限荷载Pcr和水平极限荷载Hcr;再对与这四个框架几何及截面相同但没有初始缺陷的框架.用之前计算得到竖向和水平极限荷载分别按一阶弹性分析和二阶弹性分析得到其内力,用我国现行<钢结构设计规范>(GB 50017)中压弯杆件极限承载力验算式计算其名义应力,并与实际结果比较.结果证明.进行钢框架压弯杆件平面内稳定验算时,对框架采用二阶弹性分析.并将柱的计算长度取为实际柱长,所得验算结果较对框架采用一阶弹性分析.并将柱的计算长度取为框架弹性屈曲长度,所得结果合理,且偏于保守.     

Ultimate shear strength of plate elements with pit corrosion wastage

The aim of the present paper is to investigate the ultimate strength characteristics of steel plate elements with pit corrosion wastage and under in-plane shear loads. A series of the ANSYS nonlinear finite element analyses for plate elements under in-plane shear loads are carried out, varying the degree of pit corrosion intensity and the plate geometric properties. Closed-form design formulae for the ultimate strength of pitted plates under edge shear, which are essentially needed for the ultimate limit state based risk or reliability assessment of corroded structures, are derived by the regression analysis of the computed results. The insights developed from the present study will be very useful for damage tolerant design of plated structures with pit corrosion wastage.     

Aluminum alloy tubular columns—Part II: Parametric study and design using direct strength method

A parametric study of aluminum alloy columns of square and rectangular hollow sections was performed using finite element analysis (FEA). The columns were compressed between fixed ends. The parametric study included 120 columns with and without transverse welds at the ends of the columns. An accurate and reliable finite element model was used for the parametric study. Design approaches for aluminum alloy tubular columns with and without transverse welds were proposed. Column strengths predicted by the FEA were compared with the design strengths calculated using the current American, Australian/New Zealand and European specifications for aluminum structures. In addition, the direct strength method (DSM), which was developed for cold-formed carbon steel members, was used in this study for aluminum alloy columns. The design strengths calculated using the DSM were compared with the numerical results. Furthermore, design rules modified from the DSM were proposed. It is shown that the proposed design rules accurately predicted the ultimate strengths of aluminum welded and non-welded columns. The reliability of the current and proposed design rules was evaluated using reliability analysis.     

Q460高强钢焊接工字形截面简支梁整体稳定性能与设计方法研究

为研究Q460高强钢焊接工字形截面简支梁的整体稳定性能,对跨中无侧向支撑的3个双轴对称和6个单轴对称焊接工字形截面简支梁进行了整体弯扭屈曲试验。实测了试件的截面残余应力和初始几何缺陷,并分析其整体弯扭屈曲变形特征和稳定承载力。建立考虑残余应力和初始几何缺陷的有限元模型对简支梁受力进行了模拟,模拟结果与试验结果吻合良好,基于试验验证的有限元模型计算了大量不同截面尺寸和跨度的Q460高强钢焊接工字形截面简支梁的整体稳定承载力。将试验和有限元参数分析结果与GB 50017—2017《钢结构设计标准》、JGJ/T 483—2020《高强钢结构设计标准》、欧洲规范EN 1993-2005和美国规范ANSI/AISC 360-2016的简支梁整体稳定系数公式的计算结果进行比较,结果表明GB 50017—2017和ANSI/AISC 360-2016的计算结果偏于不安全,EN 1993-2005的计算结果过于保守,JGJ/T 483—2020的计算结果偏于安全且最为接近。最后,在JGJ/T 483—2020的简支梁整体稳定系数计算公式基础上引入增大系数,并根据截面高宽比的不同,取用不同的长细比指数对该公式予以修正,修正后的公式更适用于Q460高强钢焊接工字形截面简支梁的设计计算。