火灾下不锈钢梁—柱节点数值分析

评估了EC3中不锈钢梁-柱节点发生或不发生侧向扭转屈曲的设计准则的准确性和安全性。对焊接方式相同的H型钢梁-柱节点进行了大量数值参数研究,以此为基础进行评估。研究中考虑了残余应力、截面高厚比、弯矩图形状和不锈钢等级的影响。提出了火灾下不锈钢梁-柱节点的新设计方程,计算结果与数值分析结果进行对比,结果表明,新设计方程比EC3中设计方程更为安全。此外,对火灾时不锈钢梁在梁端弯矩与横向荷载共同作用下的侧向扭转屈曲进行了研究。     

Testing and numerical modelling of lean duplex stainless steel hollow section columns

Stainless steels are employed in a wide range of structural applications. The austenitic grades, particularly EN 1.4301 and EN 1.4401, and their low-carbon variants EN 1.4307 and EN 1.4404, are the most commonly used within construction, and these typically contain around 8%–11% nickel. The nickel represents a large portion of the total material cost and thus high nickel prices and price volatility have a strong bearing on both the cost and price stability of stainless steel. While austenitic stainless steel remains the most favourable material choice in many applications, greater emphasis is now being placed on the development of alternative grades with lower nickel content. In this study, the material behaviour and compressive structural response of a lean duplex stainless steel (EN 1.4162), which contains approximately 1.5% nickel, are examined. A total of eight stub column tests and twelve long column tests on lean duplex stainless steel square (SHS) and rectangular hollow sections (RHS) are reported. Precise measurements of material and geometric properties of the test specimens were also made, including the assessment of local and global geometric imperfections. The experimental studies were supplemented by finite element analysis, and parametric studies were performed to generate results over a wider range of cross-sectional and member slenderness. Both the experimental and numerical results were used to assess the applicability of the Eurocode 3: Part 1-4 provisions regarding the Class 3 slenderness limit and effective width formula for internal elements in compression and the column buckling curve for hollow sections to lean duplex structural components. Comparisons between the structural performance of lean duplex stainless steel and that of other more commonly used stainless steel grades are also presented, showing lean duplex stainless steel to be an attractive choice for structural applications.     

Interaction of bending and axial compression of stainless steel members

The paper deals with the buckling behaviour of stainless steel members with the main focus on developing design formulae for use in the latest version of the European Standard EN 1993-1-4: Eurocode 3-Design of steel structures-Part 1-4: General rules — Supplementary rules for stainless steel. Brussels; 2005.It is based on numerical simulations of single span members of various section type, which are subjected to axial compression and bending. Both flexural buckling and lateral-torsional buckling are dealt with so that the buckling behaviour of both I-sections and hollow sections can be covered.On the basis of these numerical results interaction factors have been derived in context with the design model for member design in Eurocode 3-1-1. For statistical evaluation the test results available from other authors have been used.The outcome of this investigation has been incorporated in the present EN 1993-1-4 as a recommendation in restricted form.     

不锈钢受弯构件的试验研究

采用国产的304牌号不锈钢,针对冷成型SHS、RHS和焊接工字钢截面,11种不同截面规格,共39根受弯构件,进行受弯构件试验研究。考察两端简支不锈钢梁在不同的加载方式和腹板约束条件下的极限承载力和破坏形式。通过试验发现:两端简支不锈钢冷成型SHS、RHS梁在集中荷载作用下根据加载方式和腹板约束条件的不同,主要有3种破坏形式,即整体弯曲破坏、腹板压屈破坏、两者耦合破坏。两端简支不锈钢焊接工字形梁在集中荷载作用下以发生弯扭失稳为主。在对两端简支不锈钢梁截面的抗弯强度、非线性挠度以及平面外稳定等受力性能分析的基础上,将试验结果与欧洲不锈钢设计规范(EN1993-1-4)和美国不锈钢设计规范(SEI/ASCE 8-02)进行对比分析。对比结果表明:试验得到的构件抗弯强度和平面外稳定承载能力均高于上述规范计算值,规范偏于保守;按上述规范计算得到的挠度小于试验值,规范偏于不安全。     

Proposed residual stress model for roller bent steel wide flange sections

The manufacturing process of structural wide flange steel sections introduces residual stresses in the material. These stresses due to hot-rolling or welding influence the inelastic buckling response of structural steel members and need to be taken into account in the design. Based on experimental data standardized residual stress models have been proposed for inclusion in inelastic buckling analyses. By incorporating these residual stress models their effect on the resistance of beams and columns can be obtained. Residual stress models for roller bent steel sections are currently not available. Roller bent wide flange sections are manufactured by curving straight members at ambient temperature. This manufacturing technique, which is also known as roller bending, stresses the material beyond its yield stress, thereby overriding the initial residual stresses prior to bending and generating an entirely new pattern. This paper proposes a residual stress model for roller bent wide flange sections, based on earlier conducted numerical investigations which were validated by experimental research performed at Eindhoven University of Technology. The proposed residual stress model can serve as an initial state of a roller bent steel section in fully non-linear finite element analyses to accurately predict its influence on the inelastic buckling response.     

Cold-formed high strength stainless steel cross-sections in compression considering interaction effects of constituent plate elements

This paper presents a numerical investigation of cold-formed high strength stainless steel square and rectangular hollow sections in compression. A non-linear finite element model which includes geometric and material non-linearities was developed and verified against experimental results. The model was then used for an extensive parametric study to investigate the interaction effects of constituent plate elements on Class 3 slenderness limit and section capacities of cold-formed high strength stainless steel square and rectangular hollow sections in compression.The numerical investigation shows that the interaction effects of constituent plate elements on cross-section response are quite obvious particularly for slender sections. The design provisions on Class 3 slenderness limit and effective width equations specified in the EC3 Code and proposed by Gardner and Theofanous are suitable for square hollow sections, but not for rectangular hollow sections since they do not take into consideration of interaction effects of constituent plate element. Hence, the new Class 3 slenderness limit and the section capacity design equations based on the whole cross-section response are proposed in this study, which carefully consider the interaction effects of constituent plate elements.     

焊接不锈钢工字形截面梁整体稳定性试验研究

不锈钢材料在建筑结构中已得到广泛应用。为研究焊接不锈钢梁的整体稳定性能,进行了纯弯状态下的静力试验研究。试验包括10个试件,材料类型为奥氏体型316。截面类型采用了双轴对称和单轴对称工字形截面,试件的端部约束采用夹支,试验过程持续加载,直至达到试件的承载力峰值。基于试验结果,研究了焊接不锈钢梁的失稳破坏形态和极限承载力;对比了试验极限弯矩与理论弹性弯矩、塑性弯矩的差异,并将试验结果与有限元分析结果进行了对比。结果表明：试件的承载能力随着跨度的增大而减小,有限元分析能够准确预测试件的承载力,与试验结果吻合良好。     

Design of cold-formed steel channels with stiffened webs subjected to bending

The objectives of this study are to investigate the structural behaviour and evaluate the appropriateness of the current direct strength method on the design of cold-formed steel stiffened cross-sections subjected to bending. The stiffeners were employed to the web of plain channel and lipped channel sections to improve the flexural strength of cold-formed steel sections that are prone to local buckling and distortional buckling. An experimental investigation of simply supported beams with different stiffened channel sections has been conducted. The moment capacities and observed failure modes at ultimate loads were reported. A nonlinear finite element model was developed and verified against the test results in terms of strengths, failure modes and moment–curvature curves. The calibrated model was then adopted for an extensive parametric study to investigate the moment capacities and buckling modes of cold-formed steel beams with various geometries of stiffened sections. The strengths and failure modes of specimens obtained from experimental and numerical results were compared with design strengths predicted using the direct strength method specified in the North American Specification for cold-formed steel structures. The comparison shows that the design strengths predicted by the current direct strength method (DSM) are conservative for both local buckling and distortional buckling in this study. Hence, the DSM is modified to cover the new stiffened channel sections investigated in this study. A reliability analysis was also performed to assess the current and modified DSM.     

Lateral-torsional buckling of stainless steel I-beams in case of fire

This work presents a numerical study of the behaviour of stainless steel I-beams subjected to lateral-torsional buckling in case of fire and compares the obtained results with the beam design curves of Eurocode 3.New formulae for lateral-torsional buckling, that approximate better the real behaviour of stainless steel structural elements in case of fire are proposed. These new formulae were based on numerical simulations using the program SAFIR, which was modified to take into account the material properties of the stainless steel.     

残余应力分布对焊接不锈钢工字形截面梁整体稳定性能的影响

焊接残余应力导致不锈钢梁截面纤维过早达到屈服,并严重降低不锈钢梁的抗弯刚度。为了研究残余应力对焊接工字形不锈钢梁侧扭屈曲的影响,根据目前被广泛采纳的不锈钢工字形截面残余应力分布模型,采用有限元方法,对残余应力分布模型的主要因素进行参数化分析,研究这些因素对不锈钢梁侧扭屈曲的影响,使对焊接工字形不锈钢梁的整体稳定性能的研究更加完善。结果表明:翼缘残余压应力峰值对不锈钢梁侧扭屈曲的影响最为显著。     

Structural response of stainless steel oval hollow section compression members

Cold-formed stainless steel oval hollow sections (OHS) offer the combined aesthetic appeal of circular hollow sections and stainless steel, together with the structural efficiency associated with cross-sections of differing geometric properties about their two principal axes. To date, no structural design guidance exists for these cross-sections, principally due to their relatively recent introduction and a lack of fundamental structural test data. This paper examines the structural response of stainless steel OHS compression members and presents design recommendations. A series of laboratory tests was carried out to generate fundamental structural performance data. Tensile coupon tests were initially performed to establish the basic material stress–strain characteristics of the sections. These were followed by stub column tests to determine the average compressive response of the cross-sections and flexural buckling tests to obtain ultimate load carrying capacity data for use in the determination of a suitable buckling curve for stainless steel OHS. Measurements of the geometric properties of the test specimens including initial imperfections were carried out. The full load–displacement responses of the specimens were recorded and have been presented herein. A finite element (FE) modelling programme was performed in parallel with the experimental study. Once the FE models had been validated against the test results, parametric studies were carried out to further investigate the influence of individual key parameters, including the aspect ratio and local slenderness of the cross-sections as well as the member slenderness. Based on the obtained experimental and numerical results, a class 3 limit for stainless steel OHS in compression and a suitable buckling curve for OHS columns have been proposed.     

侧向扭转屈曲时冷成型钢梁的特性及设计

建筑物中越来越多地使用冷成型钢梁作为楼板的辅助及受力构件,其在没有足够侧向约束时的性能和瞬时承载力将受到侧向扭转屈曲的影响。以往对侧向扭转屈曲的研究主要针对热成型卷边钢梁,因此需要对简单支撑下相同弯曲度冷成型卷边槽钢梁的特性进行数值模拟。采用业内广泛认可的有限元分析软件ABAQUS进行建模,对不同条件下冷成型钢梁微单元的侧向扭转屈曲性能和承载力进行分析和模拟。将瞬时承载力结果与冷成型钢结构规范中当前设计准则的预测结果进行比较并对其进行适当的修正。欧洲的设计规范较为保守,而澳大利亚、新西兰和北美的设计规范则较为宽泛。基于有限元分析结果,对规范中的瞬时承载力设计公式进行修正。阐述了参数分析的细节问题,修正了当前设计规范,提出了侧向扭转屈曲时冷成型卷边槽钢梁的新设计准则。     

Interaction of buckling modes in castellated steel beams

This paper investigates the behaviour of normal and high strength castellated steel beams under combined lateral torsional and distortional buckling modes. An efficient nonlinear 3D finite element model has been developed for the analysis of the beams. The initial geometric imperfection and material nonlinearities were carefully considered in the analysis. The nonlinear finite element model was verified against tests on castellated beams having different lengths and different cross-sections. Failure loads and interaction of buckling modes as well as load-lateral deflection curves of castellated steel beams were investigated in this study. An extensive parametric study was carried out using the finite element model to study the effects of the change in cross-section geometries, beam length and steel strength on the strength and buckling behaviour of castellated steel beams. The parametric study has shown that the presence of web distortional buckling causes a considerable decrease in the failure load of slender castellated steel beams. It is also shown that the use of high strength steel offers a considerable increase in the failure loads of less slender castellated steel beams. The failure loads predicted from the finite element model were compared with that predicted from Australian Standards for steel beams under lateral torsional buckling. It is shown that the Specification predictions are generally conservative for normal strength castellated steel beams failing by lateral torsional buckling, unconservative for castellated steel beams failing by web distortional buckling and quite conservative for high strength castellated steel beams failing by lateral torsional buckling.     

Experimental study of lateral-torsional buckling behavior of stainless steel welded I-section beams

Investigations on lateral-torsional buckling behavior of stainless steel welded I-section beams were carried out through fourpoint bending tests. The Chinese austenitic stainless steel adopted in this study contains approximately 17% of Cr, which could be graded as EN 1.4401. The non-linear stress-strain relationship of the material, the residual stress distribution of the section and the ultimate moment capacity of the welded I-section beams were obtained from the experiments, and they were compared with those results predicted by analytical models recommended by several researchers. Besides, a new model is proposed to predict the residual stress distribution of the stainless steel welded I-section beams.     

Fire testing and design of stainless steel structures

Despite significant progress in recent years in the development of room temperature design guidance for stainless steel structures, fire resistant design has received relatively little attention. This paper reports on studies carried out to investigate the performance of unprotected stainless steel beams and columns in fire. Material tests were carried out on five grades of stainless steel to determine strength and stiffness retention factors at elevated temperatures; both strength and stiffness retention were shown to be superior to that of carbon steel beyond 600 ^°C. The temperature development characteristics of a range of stainless steel sections were investigated, and compared to those of carbon steel sections. Full scale fire tests were conducted on six stainless steel columns, and four stainless steel beams. Finite element modelling of the tests was carried out, and parametric studies were performed to supplement the test data. All tests were carried out as part of the European project ‘Development of the use of stainless steel in construction’. Design recommendations for stainless steel columns and stainless steel beams supporting a concrete slab, based on the ECCS model code for fire engineering, were validated against the test and finite element results. These recommendations have been incorporated into the Euro Inox/SCI Design Manual for Structural Stainless Steel, and implemented in Eurocode 3: Part 1.2, with minor adjustments for consistency with carbon steel.     

多孔钢梁在组合屈曲模态下的非线性分析

讨论了一般强度和高强度多孔钢梁在组合屈曲模态下的非线性分析。建立一个考虑腹板和翼缘初始几何缺陷、残余应力和材料非线性等情况的多孔钢梁的三维有限元模型。用具有不同长度,不同截面,不同荷载条件和不同失效模态的多孔梁的试验结果验证了此有限元模型。该模型能计算多孔梁的失效荷载,跨中荷载-挠度关系和失效模态。用120根多孔梁的有限元计算数据进行了参数分析,研究截面几何尺寸,梁长和钢材料强度对多孔梁强度和屈曲性能的影响。参数研究结果显示:由于组合腹板的扭转和腹板后屈曲引起的多孔梁失效对承载力有很大的影响。对于长细比较小的多孔梁,应用高强度钢材料将能显著提高失效荷载值。将有限元计算得到的失效荷载与利用澳洲规范计算的多孔梁平面外屈曲计算结果进行了对比,发现规范的计算结果对于平面外屈曲的一般强度多孔梁是不保守的,而对于组合腹板扭转和腹板后屈曲的高强度多孔梁的失效则非常保守。     

Lateral buckling strengths of cold-formed rectangular hollow sections

Code rules for designing steel beams against lateral buckling which are based on data for hot-rolled I-sections are unnecessarily conservative when used for cold formed rectangular hollow section beams.Cold-formed rectangular hollow section beams have different stress-strain curves, residual stresses, and crookedness and twist. The effects of residual stress on the inelastic buckling of I-section beams are not nearly as pronounced for hollow sections with two webs, while the strengthening effects of pre-buckling deflections are greater for hollow sections. Simplistic code rules for top flange loading are very conservative when applied to hollow sections.This paper reviews elastic lateral buckling behaviour and the strength rules used to design steel beams. It develops realistic models for cold-formed rectangular hollow beams which are analysed to predict the effects of moment distribution, load height and yield stress on their strengths. The results of the analyses are used to develop improved design rules which remove much of the conservatism of present design rules.     

Experimental investigation of concrete-filled cold-formed high strength stainless steel tube columns

This paper presents an experimental investigation of concrete-filled cold-formed high strength stainless steel tube columns. The high strength stainless steel tubes had a yield stress and tensile strength up to 536 and 961 MPa, respectively. The behaviour of the columns was investigated using different concrete cylinder strengths varied from 40 to 80 MPa. A series of tests was performed to investigate the effects of the shape of the stainless steel tube, plate thickness and concrete strength on the behaviour and strength of concrete-filled high strength stainless steel tube columns. The high strength stainless steel tubes were cold-rolled into square and rectangular hollow sections. The depth-to-plate thickness ratio of the tube sections varied from 25.7 for compact sections to 55.8 for relatively slender sections. The columns had different lengths so the length-to-depth ratio generally remained at a constant value of 3. The concrete-filled high strength stainless steel tube specimens were subjected to uniform axial compression. The column strengths, load-axial strain relationships and failure modes of the columns were presented. The test strengths were compared with the design strengths calculated using the American specifications and Australian/New Zealand standards that consider the effect of local buckling using an effective width concept in the calculation of the stainless steel tube column strengths. Based on the test results, design recommendations were proposed for concrete-filled high strength stainless steel tube columns.     

钢－混凝土连续组合梁负弯矩区的局部失稳

本文提出截面曲率延性Ｋ１、Ｋ２和Ｋ３的概念，来描述二类截面局部失稳对连续组合梁内力重分布的影响，采用非线性增量迭代法，分析了３６组二跨连续组合梁承受均布荷载时弯矩重分布的情况。研究表明：二类截面连续组合梁的局部失稳，可采用对中间支承处弯矩调幅３０％来等效。本文提出的设计方法，可避免复杂的弹塑性稳定计算。     

Experimental and numerical studies of lean duplex stainless steel beams

Stainless steel is well suited to a range of engineering applications owing to its durability and favourable mechanical properties. The most widely used grades of stainless steel are from the austenitic family and typically contain around 18% chromium and 8%-11% nickel — these grades have a relatively high initial material cost, due, in part, to their high nickel content, and a nominal yield strength (in the annealed condition) of around 220 N/mm². A new, low nickel grade of stainless steel (UNS 32101/EN 1.4162), commonly referred to as ‘lean duplex’, has been developed, that offers over two times the strength of the familiar austenitic grades and at approximately half the initial cost — this lean duplex stainless steel appears well suited to load-bearing applications in construction. This paper reports material and 3-point bending tests on lean duplex stainless steel hollow sections. The 3-point bending tests were replicated by finite element (FE) analysis and, upon validation of the numerical models, parametric studies were conducted to assess the effect of key parameters such as cross-section aspect ratio, cross-section slenderness and moment gradient on the strength and deformation capacity of lean duplex stainless steel beams. Based on both the experimental and numerical results, appropriate slenderness limits and design rules, suitable for incorporation into structural stainless steel design standards, have been proposed.