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.     

Strength and stability criteria for thin-walled stainless steel circular hollow section members under bending

A series of tests consisting of various cross-section geometries were performed on structural stainless steel circular hollow sections (CHS) subjected to bending. The test program comprised a total of eight tests on CHS in two grades of stainless steel, namely 304 and Duplex 2205. For each grade four sections, each with a different slenderness, were tested, in order to cover a range of structural responses. Measurements of overall geometric imperfections and material properties were conducted. The test strengths are compared with the strengths predicted using the American, Australian and European specifications for cold-formed stainless steel structures. In the light of the test results and code recommendations, strength and cross-section classification criteria for stainless steel circular hollow section members in bending are examined.     

Ferritic stainless steel tubular members strengthened with high modulus CFRP plate subjected to web crippling

Web crippling failure of ferritic stainless steel tubular structural members could be found due to localised concentrated loads or reactions. This paper reports experimental and numerical investigation on strengthening of ferritic stainless steel tubular members using externally bonded high modulus carbon fibre-reinforced polymer (CFRP) plate. The CFRP plate strengthening is only applied to a small localise area subjected to concentrated load. A series of tests on CFRP strengthened ferritic stainless steel square and rectangular hollow sections subjected to web crippling was conducted. The web crippling tests were conducted under four loading conditions of end-two-flange (ETF), interior-two-flange (ITF), end-one-flange (EOF) and interior-one-flange (IOF). A total of 37 web crippling tests was conducted in this study. The investigation was mainly focused on the effects of web slenderness of ferritic stainless steel tubular sections on CFRP strengthening against web crippling. The tests were performed on five different sizes of square and rectangular hollow sections. The ferritic stainless steel type EN 1.4003 test specimens were used in this study. Tensile coupon tests were conducted to determine the material properties of the ferritic stainless steel specimens. Most of the strengthened specimens were failed by debonding of CFRP plate from the ferritic stainless steel tubes. Two different failure modes were observed in the tests of the strengthened specimens, namely the adhesion failure as well as the combination of adhesion and cohesion failure. Finite element models have been developed and verified against the test results. The failure loads, failure modes and the load-web deformation behaviour of the ferritic stainless steel sections are also presented.     

不锈钢椭圆中空受压构件的结构响应

冷加工不锈钢椭圆中空截面结合了圆形中空截面和不锈钢的美感以及不同几何形状的横截面相对于两个主轴的结构功效。迄今为止,对这种横截面的构件尚没有结构设计指南,主要是产品相对较新,缺乏基础结构试验数据。对冷加工不锈钢椭圆空心截面受压构件的结构响应进行研究,提出设计建议。为获得结构性能的基础数据,进行一系列试验。首先,通过张拉试验建立基本的材料应力-应变关系。随后,通过短柱试验确定横截面的平均受压响应,通过弯曲试验获得极限承载力以确定不锈钢椭圆中空截面合理的弯曲曲线。对试件进行包括初始缺陷的几何性质测定。对试件的荷载位移响应进行记录并在文中给予介绍。与试验同步,进行了有限元模拟。如果有限元模拟的结果与试验结果不相符,将对个别关键参数进行进一步的研究,包括外形比例、横截面长细比和构件长细比。基于试验与数值分析结果,提出3组不锈钢椭圆中空截面受压限值以及椭圆中空截面柱合理弯曲曲线。     

复式薄壁方钢管混凝土构件受弯性能研究

通过复式薄壁方钢管混凝土构件受弯性能的试验研究,分析了内置圆形截面空钢管和钢管高强混凝土对薄壁方钢管混凝土构件纯弯段受弯性能的影响。试验表明：内置圆形截面空钢管和钢管高强混凝土可有效提高构件的受弯承载力,内置钢管高强混凝土的提高效果更显著;薄壁方钢管混凝土的受弯承载力和抗弯刚度明显较对比空钢管的高;试验过程中未出现钢管角部破坏的情况。对复式薄壁方钢管混凝土纯弯构件受力性能进行有限元分析,分析结果和试验结果吻合较好,外管的约束作用有效提高了夹层混凝土转角处混凝土的抗压强度。有限元参数分析结果表明,构件的受弯承载力和抗弯刚度随着夹层混凝土强度和径宽比的增大而增大,但随着径厚比的增大而减小;同时构件的受弯承载力随着钢管强度的增大而增大。建议了复式实心薄壁方钢管混凝土构件和复式空心薄壁方钢管混凝土构件受弯承载力的简化计算模型,其计算结果精度较高。     

冷成型不锈钢管轴心受压柱试验研究

为研究冷成型不锈钢管轴心受压柱的稳定性能,进行了国产304牌号冷成型不锈钢方管、矩形管和圆管截面,共43根轴心受压柱试验。通过对不锈钢材料、轴压短柱试件和轴压长柱试件的试验研究,得到了试件的材料力学性能和极限荷载。分析了试件的长细比、宽厚比（径厚比）对其破坏模式及变形性能的影响。结果表明：试件的宽厚比（径厚比）对其破坏模式及变形性能有较大的影响。采用GB 50018-2002《冷弯薄壁型钢结构技术规范》、欧洲不锈钢结构设计规范、美国冷成型不锈钢结构设计规范中的计算方法以及Rasmussen提出的设计方法对试验试件进行了计算,并与试验数据对比结果表明,对于圆管试件,采用三本规范计算得到的承载力均高于试验值,偏于不安全,采用Rasmussen 提出方法的计算结果与试验值较为接近;对于方矩管试件,各种方法计算结果相近,除短柱试件试验结果高于计算结果外,其余试件试验值均与计算结果吻合较好;GB 50018-2002《冷弯薄壁型钢结构技术规范》中的计算方法不能直接用于计算不锈钢管轴心受压柱承载力。     

FRP strengthening of lean duplex stainless steel hollow sections subjected to web crippling

This paper presents the experimental and numerical investigations of lean duplex stainless steel hollow sections subjected to web crippling. The test specimens were strengthened with different fibre-reinforced polymer (FRP). The web crippling tests were conducted under end-two-flange, interior-two-flange, end-one-flange and interior-one-flange loading conditions. A series of web crippling tests was conducted. The investigation was focused on the effects of surface treatment, web slenderness, different adhesives and FRPs for the strengthening of lean duplex stainless steel hollow sections against web crippling. The lean duplex stainless steel type EN 1.4162 was used in the investigation. Two different surface treatments, three different adhesives and six different FRPs were investigated in this study. The tests were performed on five different sizes of square and rectangular hollow sections that covered a wide range of web slenderness ratio from 8.1 to 57.3. Three different failure modes were observed in the tests of the strengthened specimens, namely the adhesion, interlaminar failure of FRP plate and combination of adhesion and interlaminar failure of FRP plate. Finite element models have been developed and verified against the test results of the specimens subjected to two-flange loading conditions.     

冷成型双相不锈钢截面材料特性

给出了6个不同截面冷成型双相不锈钢的特性,其中2个为圆形中空截面,4个为矩形中空截面。试样为冷轧双相不锈钢带。确定方形和矩形中空截面高强度冷成型双相不锈钢的材料特性。对每种型材的薄弱和转角处进行拉伸试验,由此测量每种型材的弹性模量、0.2%弹性极限、1.0%弹性极限、抗张强度、断裂延伸率和Ramberg-Osgood参数(n)。通过短柱试验获得冷轧状态全截面的材料特性。测量6种型材的初始局部几何缺陷,绘制每种型材含初始几何缺陷的横截面图。采用断面法测量150×50×2.5截面的残余应力,测量并绘制截面上薄膜屈曲残余应力分布图。此外,给出适用于短柱的有限元模型,并与试验结果进行对比。将不锈钢短柱的试验强度与美国规范、澳大利亚/新西兰规范和欧洲规范的设计强度进行对比。总体看来,三种规范的计算结果都较为保守,其中欧洲规范的计算结果最为保守。     

Residual stress distributions in welded stainless steel sections

Residual stress magnitudes and distributions in structural stainless steel built-up sections have been comprehensively investigated in this study. A total of 18 test specimens were fabricated from hot-rolled stainless steel plates by means of shielded metal arc welding (SMAW). Two grades of stainless steel were considered, namely the austenitic grade EN 1.4301 and the duplex grade EN 1.4462. Using the sectioning method, the test specimens were divided into strips. The residual stresses were then computed by multiplying the strains relieved during sectioning by the measured Young׳s moduli determined from tensile and compressive coupon tests. Residual stress distributions were obtained for 10 I-sections, four square hollow sections (SHS) and four rectangular hollow sections (RHS). Peak tensile residual stresses reached around 80% and 60% of the material 0.2% proof stress for grades EN 1.4301 and EN 1.4462, respectively. Based upon the test data, simplified predictive models for residual stress distributions in stainless steel built-up I-sections and box sections were developed. Following comparisons with other available residual stress test data, the applicability of the proposed models was also extended to other stainless steel alloys. The proposed residual stress patterns are suitable for inclusion in future analytical models and numerical simulations of stainless steel built-up sections.     

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.     

不锈钢轴心受压柱弯曲屈曲承载力分析

为给我国《不锈钢结构技术规范》中轴心受压柱弯曲屈曲稳定部分的编制提供依据,对国外已有的同类构件的设计方法和试验研究数据进行搜集和对比。结果表明：目前的欧洲不锈钢结构设计规范和美国冷成型不锈钢结构设计规范中计算该类构件的公式均存在一定不足。依据搜集到的199个方管、矩形管、圆管、椭圆管、焊接H形钢和冷弯C型钢截面柱的试验数据,根据冷弯效应及残余应力对轴心受压构件稳定性能的影响,将构件依据截面形式分为A、B、C三类,其中方管、矩形管和冷弯C型钢为A类,圆管和椭圆管为B类,焊接H形钢为C类,三类轴心受压稳定曲线均采用Perry公式形式表达。与试验数据对比表明：采用三类曲线能较好地估算构件的稳定承载力且离散性较小。对提出的计算式进行可靠度分析,结果表明其可靠度指标β满足我国GB 50068-2001《建筑结构可靠度设计统一标准》的要求。     

Energy evaluation in reinforced concrete hollow circular sections under bending

Four specimens were tested for monotonically increasing bending. Another four identical specimens, except for possible variations in concrete strength, were tested for reversed cyclic bending. The hollow cylindrical specimens were 128 inches (3.25 m) long and 16 inches (406 mm) in outside diameter with wall thickness of two inches (50.8 mm) and reinforced by both longitudinal and circumferential steel.

Two parameters were varied, the axial load and the longitudinal steel ratio. The effects of the axial load and the longitudinal steel ratio on the specimens stiffness, curvature ductility and energy absorption were quite apparent.

The test results confirmed that the use of ductility factors in evaluating energy absorption or dissipation in reinforced concrete hollow circular sections under bending does not take into account the effect of the stiffness degradation or the pinching effects that are found in the hysteretic behaviour of sections subjected to cyclic bending coupled with high axial forces.     

Strengthening of ferritic stainless steel tubular structural members using FRP subjected to Two-Flange-Loading

Cold-formed stainless steel tubular structural members which may experience web crippling failure due to localise concentrated loads or reactions are investigated. A series of tests on fibre-reinforced polymer (FRP) strengthening of cold-formed stainless steel tubular structural members subjected to End-Two-Flange and Interior-Two-Flange loading conditions is presented. The strengthening only applied to a localise area of the members under concentrated load. A total of 58 web crippling tests were conducted. The investigation mainly focused on the effects of different surface treatment, different adhesive, and FRP for strengthening of stainless steel tubular sections against web crippling. The behaviour of stainless steel members strengthened by different widths of FRP plate against web crippling has been also investigated in this study. The test specimens consisted of ferritic stainless steel EN 1.4003 square and rectangular hollow sections. Two different surface treatments were considered. Furthermore, six different adhesives and six different FRPs were also considered in this study. The properties of adhesive and FRP as well as the bonding between the FRP and stainless steel tube have significant influence on the effectiveness of the strengthening. Most of the strengthened specimens were failed by debonding of FRP plates form the stainless steel tubes. Six different failure modes were observed in the tests, namely the adhesion, cohesion, combination of adhesion and cohesion, interlaminar failure of FRP plate, FRP delaminating failure and web crippling failure. The failure loads, failure modes, and the load-web deformation behaviour of the ferritic stainless steel sections are presented in this study. It was found that the web crippling capacity of ferritic stainless steel tubular sections may increase up to 51% using FRP strengthening.     

Tests of pin-ended cold-formed lean duplex stainless steel columns

This paper describes a test program on cold-formed lean duplex stainless steel columns compressed between pinned ends. Two square hollow sections and four rectangular hollow sections were tested at different column lengths. The material properties of the test specimens were obtained from tensile coupon tests and stub column tests. The test specimens were cold-rolled from flat strips of lean duplex stainless steel (EN1.4162). The column specimens were concentrically loaded between pinned ends. The ultimate loads and the failure modes of each column are presented. The American, Australian/New Zealand and European specifications for stainless steel structures are assessed by comparing the column test strengths and available data in the literatures with the design strengths. It should be noted that these specifications do not cover the material of lean duplex stainless steel. A reliability analysis was carried out to assess the current design rules of stainless steel for lean duplex material. Generally, the specifications are able to predict the strengths of the tested columns. The design approach of using full cross-section area and material properties obtained by stub column tests for all classes of sections including slender sections was recommended. This recommended design approach does not require section classification and calculation of effective area, and provides a more accurate and less scattered prediction than those using the current design rules.     

Experimental investigation on ferritic stainless steel columns in fire

This paper presents the performance of EN 1.4003 ferritic stainless steel hollow section columns when exposed to fire loading. Experimental analysis of the behaviour of ferritic stainless steel structural members in fire represents a novelty. In detail, three column tests were carried out in the framework of the Research Fund of Coal and Steel (RFCS) project named Structural Applications of Ferritic Stainless Steels (SAFSS, RFSR-CT-2010-00026). Tubular thin-walled members were considered in this study because structural applications of ferritic stainless steels generally incorporate such profiles. Three columns were tested: two square hollow sections (SHS) and a rectangular hollow section (RHS) of different length. Fire loading was applied under a constant concentrically compressive load. Identical column tests at room temperature are also reported.     

方中空夹层钢管混凝土纯弯力学性能研究

以空心率为变化参数 ,进行了 5个纯弯构件的试验研究 ,考察了方中空夹层钢管混凝土在纯弯状态下的力学性能。然后在确定钢和混凝土应力 -应变关系模型的基础上 ,采用数值方法对方中空夹层钢管混凝土纯弯构件进行理论分析 ,分析结果和试验结果吻合较好。最后提供了构件抗弯承载力和抗弯刚度的简化计算公式 ,可供有关工程实践参考。     

Tests and behaviour of cold-formed stainless steel tubular X-joints

The paper presents a series of tests on cold-formed stainless steel tubular X-joints. The tubular X-joint specimens were tested without chord preload as well as with three different levels of preload applied to the chord members. The test specimens were fabricated from square and rectangular hollow sections as brace and chord members. A total of 32 tests was performed. High strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens were tested. The test results were compared with the design strengths obtained using the CIDECT Guide and Eurocode for carbon steel structures. It is shown that the design strengths predicted by the current design specifications are very conservative for the test specimens calculated using the 0.1%, 0.2%, 0.5% and 1.0% proof stresses as the yield stresses. The 0.2% proof stress is comparatively more reasonable to predict the design strengths of stainless steel tubular X-joints for both ultimate limit state and serviceability limit state.     

Experimental and numerical investigation of high strength stainless steel structures

The paper summarises research on high strength stainless steel tubular structures conducted at the University of Hong Kong, and the Hong Kong University of Science and Technology. Square and rectangular hollow sections were investigated. The test specimens were cold-rolled from high strength austenitic and duplex stainless steel sheets. The material properties of the test specimens were determined by tensile coupon tests at normal room and elevated temperatures. The initial geometric imperfection and residual stress of the specimens were measured. The experimental and numerical investigation focused on the design and behaviour of cold-formed high strength stainless steel structural members. The results were compared with design strengths calculated using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures.     

钢管混凝土墩柱截面选型

为了获得一种易于操作的钢管混凝土墩柱单肢截面优选方法,对工程中常见的3种截面形式(圆形、矩形与矩形中空夹层截面)进行了截面优选研究。基于统一理论和等效截面思想,提出了表征截面压弯承载力的经济性指标界限偏心率,研究了套箍系数、矩形截面高宽比、矩形中空夹层截面挖空率对界限偏心率以及3种钢管混凝土截面经济性的作用规律。结果表明:套箍系数、矩形截面高宽比、矩形中空夹层截面挖空率越大,矩形和矩形中空夹层截面的经济性越好; 当套箍系数大于0.8,矩形截面高宽比大于2.0,矩形中空夹层截面挖空率大于0.3时,这3个参数对界限偏心率的影响较小; 界限偏心率能够很好地表征钢管混凝土单肢截面的经济性; 在截面内力和材料给定的条件下,通过查界限偏心率表能够快速确定钢管混凝土墩柱最优截面形式,对工程实际具有一定的参考价值。     

Tests on stub stainless steel-concrete-carbon steel double-skin tubular (DST) columns

A new type of composite member, a stainless steel-concrete-carbon steel double-skin tubular (DST) column, is introduced in this paper. This composite member is expected to combine the advantages of all three types of materials, and have additional advantages of esthetics and resistance to corrosion that outer stainless steel offers. A series of tests are performed to investigate the performance of the composite column, and a total of 80 specimens were tested. The main parameters of the tests are the sectional type (circular, square, round-end rectangular and elliptical), the column type (straight, inclined and tapered), and the hollow ratio of the composite section (from 0.5 to 0.75). The results show that all types of columns behaved in a ductile manner, and the mechanical behavior is similar to those columns with double carbon steel tubes. A simplified model for the prediction of the stainless steel-concrete-carbon steel double-skin tubular (DST) columns cross-sectional strengths is suggested as well.