Structural performance of cold-formed high strength stainless steel columns

This paper describes an accurate finite element model for the structural performance of cold-formed high strength stainless steel columns. The finite element analysis was conducted on duplex stainless steel columns having square and rectangular hollow sections. The columns were compressed between fixed ends at different column lengths. The effects of initial local and overall geometric imperfections have been taken into consideration in the finite element model. The material nonlinearity of the flat and corner portions of the high strength stainless steel sections were carefully incorporated in the model. The column strengths and failure modes as well as the load-shortening curves of the columns were obtained using the finite element model. Furthermore, the effect of residual stresses in the columns was studied. The nonlinear finite element model was verified against experimental results. An extensive parametric study was carried out using the verified finite element model to study the effects of cross-section geometries on the strength and behaviour of cold-formed high strength stainless steel columns. The column strengths predicted from the parametric study were compared with the design strengths calculated using the American Specification, Australian/New Zealand Standard and European Code for cold-formed stainless steel structures. The results of the parametric study showed that the design rules specified in the American, Australian/New Zealand and European specifications are generally conservative for cold-formed high strength stainless steel square and rectangular hollow section columns, but unconservative for some of the short columns.     

Nonlinear behavior of concrete-filled stainless steel stiffened slender tube columns

This paper investigates the nonlinear behavior of concrete-filled high strength stainless steel stiffened slender square and rectangular hollow section columns. The stiffened slender tubes had overall depth-to-plate thickness (D/t) ratios ranging 60–160. The concrete strengths covered normal and high-strength concrete. The investigation focused on short axially loaded columns. A nonlinear finite element (FE) model has been developed to study the behavior of the concrete-filled stiffened tube columns. A parametric study was conducted to investigate the effects of cross-section geometry and concrete strength on the behavior and strength of the columns. The results of the concrete-filled stiffened tube columns were compared with the results of the companion concrete-filled unstiffened tube columns. It is shown that the concrete-filled stiffened slender tube columns offer a considerable increase in the column strength and ductility than the concrete-filled unstiffened slender tube columns. The column strengths obtained from the FE analysis were compared with the design strengths calculated using the American specifications and Australian/New Zealand standards. A design equation was proposed for concrete-filled stainless steel stiffened slender tube columns. It is shown that the proposed modified equation provides more accurate design strengths compared to the American and Australian/New Zealand predictions.     

Tests of cold-formed high strength stainless steel compression members

The paper describes a test program on cold-formed high strength stainless steel compression members. The duplex stainless steel having the yield stress and tensile strength up to 750 and 850 MPa, respectively, was investigated. The material properties of the test specimens were obtained from tensile coupon and stub column tests. The test specimens were cold-rolled into square and rectangular hollow sections. The specimens were compressed between fixed ends at different column lengths. The initial overall geometric imperfections of the column specimens were measured. The strength and behaviour of cold-formed high strength stainless steel columns were investigated. The test strengths were compared with the design strengths predicted using the American, Australian/New Zealand and European specifications for cold-formed stainless steel structures. Generally, it is shown that the design strengths predicted by the three specifications are conservative for the cold-formed high strength stainless steel columns. In addition, reliability analysis was performed to evaluate the current 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.     

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。     

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。     

Structural performance of cold-formed lean duplex stainless steel columns

The structural performance of cold-formed lean duplex stainless steel columns was investigated. A wide range of finite element analysis on square and rectangular hollow sections and other available data, with a total number of 259 specimens, were considered. An accurate finite element model has been created to simulate the pin-ended cold-formed lean duplex stainless steel columns. Extensive parametric study was carried out using the validated finite element model. The column strengths predicted from the parametric study together with the available data are compared with the design strengths calculated from various existing design rules for cold-formed stainless steel structures. It is shown that the existing design rules, except for the ASCE Specification as well as the stub column and full area approach, are conservative. Modifications are proposed for the AS/NZS Standard, EC3 Code, and direct strength method. Reliability analysis was performed to assess the existing and modified design rules. It is also shown that the modified design rules are able to provide a more accurate and reliable predictions for lean duplex stainless steel columns. In this study, it is suggested that the modified design rules in the AS/NZS Standard and the modified direct strength method to be used in designing cold-formed lean duplex stainless steel columns.     

Nonlinear analysis of concrete-filled steel SHS and RHS columns

This paper presents an accurate nonlinear finite element model for the behaviour and design of axially loaded concrete-filled square hollow section (SHS) and rectangular hollow section (RHS) steel tube columns. The nonlinear material models for confined concrete and steel tubes were carefully modeled in the finite element analysis. The column strengths and load-axial shortening curves were evaluated. The results obtained from the finite element analysis were verified against experimental results. An extensive parametric study was conducted to investigate the effects of different concrete strengths and cross-section geometries on the strength and behaviour of concrete-filled SHS and RHS steel tube columns. The study was conducted over a wide range of concrete cube strengths ranged from 30 to 110 MPa. The overall depth of the steel tube-to-plate thickness ratio ranged from 10 to 40 covering compact SHS and RHS steel tube sections. The column strengths predicted from the finite element analysis were compared with the design strengths calculated using the American, Australian and European specifications. Based on the results obtained from the parametric study, it is found that the design strengths calculated using the American Specifications and Australian Standards are conservative, while the design strengths calculated using the European Code are accurate, except for the concrete-filled RHS compact steel tube columns having the overall depth of the steel tube-to-plate thickness ratio of 40.     

Experimental and numerical investigations of cold-formed stainless steel tubular sections subjected to concentrated bearing load

Experimental and numerical investigations of cold-formed stainless steel square and rectangular hollow sections subjected to concentrated bearing load are presented in this paper. A total of 124 data are presented that include 64 test results and 60 numerical results. The tests were performed on austenitic stainless steel type 304, high strength austenitic and duplex material. The measured web slenderness value of the tubular sections ranged from comparatively stocky webs of 6.2 to relatively more slender webs of 61.4. The tests were carried out under end and interior loading conditions. A non-linear finite element model is developed and verified against experimental results. Geometric and material non-linearities were included in the finite element model. The material nonlinearity of the flat and corner portions of the specimen sections were carefully incorporated in the model. It was shown that the finite element model closely predicted the web crippling strengths and failure modes of the tested specimens. Hence, the model was used for an extensive parametric study of cross-section geometries, and the web slenderness value ranged from 52.0 to 206.7. The test results and the web crippling strengths predicted from the finite element analysis were compared with the design strengths obtained using the American, Australian/New Zealand and European specifications for stainless steel structures. A unified web crippling equation with new coefficients for cold-formed stainless steel square and rectangular hollow sections subjected to concentrated bearing load is proposed. It is demonstrated that the proposed web crippling equation is safe and reliable using reliability analysis.     

Design of cold-formed stainless steel tubular T- and X-joints

This paper describes the numerical investigation of cold-formed stainless steel tubular T-joints, X-joints and X-joints with chord preload using finite element analysis. The stainless steel joints were fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members. The geometric and material nonlinearities of stainless steel tubular joints were carefully incorporated in the finite element models. The joint strengths, failure modes as well as load-deformation curves of stainless steel tubular joints were obtained from the numerical analysis. The nonlinear finite element models were calibrated against experimental results of cold-formed stainless steel SHS and RHS tubular T- and X-joints. Good agreement between the experimental and finite element analysis results was achieved. Therefore, an extensive parametric study of 172 T- and X-joints was then carried out using the verified finite element models to evaluate the effects of the strength and behaviour of cold-formed stainless steel tubular joints. The joint strengths obtained from the parametric study and tests were compared with the current design strengths calculated using the Australian/New Zealand Standard for stainless steel structures, CIDECT and Eurocode design rules for carbon steel tubular structures. Furthermore, design formulae of cold-formed stainless steel tubular T- and X-joints are proposed. A reliability analysis was performed to assess the reliability of the current and proposed design rules. It is shown that the design strengths calculated using the proposed equations are generally more accurate and reliable than those calculated using the current design rules.     

Experimental investigation on concrete-filled stainless steel stiffened tubular stub columns

This paper presents an experimental investigation on concrete-filled normal-strength stainless steel stiffened tubular stub columns using the austenitic stainless steel grade EN 1.4301 (304). The stiffened stainless steel tubes were fabricated by welding four lipped angles or two lipped channels at the lips. Therefore, the stiffeners were formed at the mid-depth of the sections. In total, five hollow columns and ten concrete-filled columns were tested. The longitudinal stiffener of the column plate was formed to avoid shrinkage of the concrete and to behave as a continuous connector between the concrete core and the stainless steel tube. The behavior of the columns was investigated using two different nominal concrete cubic strengths of 30 and 60 MPa. A series of tests was performed to investigate the effects of cross-section shape and concrete strength on the behavior and strength of concrete-filled stainless steel stiffened tubular stub columns. The measured average overall depth-to-width ratios (aspect ratio) varied from 1.0 to 1.8. The depth-to-plate thickness ratio of the tube sections varied from 60 to 90. Different lengths of columns were selected to fix the length-to-depth ratio to a constant value of 3. The concrete-filled stiffened stainless steel tubular columns were subjected to uniform axial compression over the concrete core and the stainless steel tube to force the entire section to undergo the same deformations by blocking action. The column strengths, load–axial strain relationships and failure modes of the columns are presented. Several comparisons were made to evaluate the test results. The results of the experimental study showed that the design rules, as specified in the European specifications and the ASCE, are highly conservative for square and rectangular cold-formed concrete-filled normal-strength stainless steel stiffened stub columns.     

考虑单侧翼缘受载腹板屈曲的不锈钢钢管设计

本文给出了冷成型不锈钢方钢管和矩形钢管在腹板屈曲时的设计公式。研究了两种单翼缘加载的情况,一种是端部单翼缘加载,另一种是内部单翼缘加载,此外还研究了内部加载的情况。采用屈服线理论预测了不锈钢管截面的腹板屈曲强度。屈服线理论模型是在试验中观察到的破坏模式的基础上发展起来的。在屈服线模型基础上采用不同的假定,给出了计算冷成型不锈钢方钢管和矩形钢管的腹板屈曲强度的三种设计方法。其中两种腹板屈曲设计方法是完全采用屈服线分析理论推导出来的,另外一种设计方法是综合理论分析和经验分析得到的。将试验得到的腹板屈曲强度和这三种设计方法得到的屈曲强度进行了对比。结果表明采用纯理论推导得到的设计方法计算得到的腹板屈曲设计强度偏于保守,而综合了理论分析和经验分析得到的设计方法其计算的腹板屈曲设计强度值比较合理,可以用于单翼缘受载时冷成型不锈钢管的设计。     

国际期刊导读

采用有限元方法,对冷弯不锈钢方管、矩形管支撑和弦杆中的T型、X型及预应力X型节点进行数值分析。考虑几何非线性和材料非线性,获得节点承载力、破坏模式及荷载-位移曲线。利用试验结果,对T型、X型矩形管、方管节点的非线性有限元模型进行修正,直到有限元结果和试验结果足够吻合。采用修正后的有限元模型对172个T型、X型节点进行参数分析,研究冷弯不锈钢管节点强度和性能的影响。将数值分析和试验中获得的节点承载力与按规范计算的设计承载力进行对比。对不锈钢管结构,采用澳大利亚规范、新西兰规范计算;对碳素钢管结构,采用国际管结构发展与研究委员会设计规范和欧洲设计规范计算。通过可靠性分析,分别评价本文提出的设计方法和现有规范的可靠度。结果表明：采用本文方法计算的设计承载力更准确、更可靠。     

Experimental and numerical investigation of cold-formed lean duplex stainless steel flexural members

Experimental and numerical investigation of cold-formed lean duplex stainless steel flexural members is presented in this paper. The test specimens were cold-rolled from flat plates of lean duplex stainless steel with the nominal 0.2% proof stress of 450 MPa. Specimens of square and rectangular hollow sections subjected to both major and minor axes bending were tested. A finite element model has been created and verified against the test results using the material properties obtained from coupon tests. It is shown that the model can accurately predict the behaviour of lean duplex stainless steel flexural members. An extensive parametric study was carried out using the verified finite element model. The test and numerical results as well as the available data on lean duplex beams are compared with design strengths predicted by various existing design rules, such as the American Specification, Australian/New Zealand Standard, European Code and direct strength method for cold-formed stainless steel. Reliability analysis was performed to evaluate the reliability of the design rules. It is shown that these current design rules provide conservative predictions to the design strengths of lean duplex stainless steel flexural members. In this study, modified design rules on the American Specification, Australian/New Zealand Standard, European Code and direct strength method are proposed, which are shown to improve the accuracy of these design rules in a reliable manner.     

椭圆环形截面钢柱的设计

对椭圆环形截面钢柱进行数值模拟和设计。建立准确的有限元模型,模拟两端固接的椭圆环形钢柱。对拉伸试验得出的材料非线性及初始局部(整体)几何缺陷都进行了考虑,通过收敛性研究,以获得最佳的单元网格尺寸。采用此数值模型,对100根柱试件进行参数化研究。对材料屈服、局部屈曲、弯曲屈曲及局部屈曲与弯曲屈曲同时发生的破坏模型进行了分析。将柱的承载力试验值和数值分析结果与基于北美规范、澳大利亚规范、新西兰规范和欧洲规范的计算值进行对比。另外,还采用了不适用于椭圆环形截面钢杆的直接强度法进行分析。对这些设计方法均进行了可靠度分析。     

第五届钢结构进展国际会议（ICASS2007）2007年12月5～7日，新加坡

主办单位：新加坡国立大学 新加坡钢结构协会 钢结构进展国际会议是举办了多年的盛会，第一次到第三次会议在中国香港召开，第四次会议于2005年在中国上海召开。大会旨在为钢结构的科研工作者和工程师们提供一个平台，使他们能够就钢结构、铝结构和组合结构的分析、性能、设计以及施工等方面的最新进展互相交流探讨。     

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 behaviour of stiffened concrete-filled thin-walled hollow steel structural (HSS) stub columns

Test results on concrete-filled steel tubular stub columns with inner or outer welded longitudinal stiffeners under axial compression are presented in this paper. The research was mainly focused on square hollow section (SHS) columns; two rectangular hollow section (RHS) columns were also tested. A longitudinal stiffener was provided on each side of the stiffened SHS column, while only two stiffeners were welded to the longer sides of the stiffened RHS column. The main experimental parameters considered were the height-to-thickness ratio and stiffener rigidity. In addition, empty tubes with or without stiffeners, as well as unstiffened concrete-filled steel tubes were also tested for comparison. Requirements for stiffener rigidity are developed by modifying a formula presented in the literature. Existing theoretical model and design codes were used to predict the load versus axial strain relationships and load-carrying capacities of the adequately stiffened composite sections respectively; reasonable results were achieved.     

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.     

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.