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.     

Performance of composite members subjected to axial load and bi-axial bending

This study focuses on the experimental evaluation of steel-concrete composite member seismic performance. Relationships between the members’ seismic performance and structural parameters, such as the sectional steel strength ratios and bi-axial bending magnitudes were defined. Test results show that the strength deterioration rates increased when the members’ steel strength ratios in the weak-axis were increased. The test results also suggested that steel strength ratios in the strong and weak sectional directions be adequately adjusted so that high member performance could be achieved. It is proposed in this study that the ratio between the strong and weak-axes steel strength ratios be set to approximately 2.2 to optimize the member’s seismic performance.     

Simplified design approach for cold-formed stainless steel compression members subjected to flexural buckling

The design criteria of stainless steel compression member are more complicated than those of carbon steels due to the nonlinear stress strain behavior of the material. In general, the tangent modulus theory is used for the design of cold-formed stainless steel columns. The modified Ramberg–Osgood equation given in the ASCE Standard can be used to determine the tangent modulus at specified level of stresses. However, it is often tedious and time-consuming to determine the column buckling stress because several iterations are usually needed in the calculation. This paper presents new formulations to simplify the determination of flexural buckling stress without iterative process. Taylor series expansion theory is utilized in the study for numerical approximations. The proposed design formulas are presented herein and can be alternatively used to calculate the flexural buckling stress for austenitic type of cold-formed stainless steel columns. It is shown that the column strengths determined by using the proposed design formulas have good agreement with those calculated by using the ASCE Standard Specification. A design example is also included in the paper for cold-formed stainless steel column designed by using the ASCE Standard equations and the proposed design formulas.     

Resistance of rectangular concrete-filled tubular (CFT) sections to the axial load and combined axial compression and bending

This paper describes the development of the direct strength method (DSM) for concrete-filled tubular (CFT) sections. The axial and flexural strength of CFT sections with local buckling are proposed based on previous test results. Although Eurocode4 does not allow the use of slender steel skins for CFT sections, the limit of the width-to-thickness ratio for the steel skin has recently been extended to slender sections in AISC specifications. A simple formula for the axial and flexural strength of CFT sections for the DSM is proposed to account for the local buckling of a thin steel skin and for the enhanced compressive strength of concrete from the confining effect of the steel skin. The squash load predicted by the proposed formula is compared with test results and those predicted by AISC specifications and Eurocode4. A formula for strength interactions of CFT members under combined compression and flexure is proposed and is compared with test results. The comparison confirmed that the formula for axial and flexural strength and that for strength interactions can conservatively predict the resistance of CFT columns to the axial load and combined compression and bending.     

钢筋混凝土Z形截面双向压弯柱抗震性能试验研究

为了研究Z形截面钢筋混凝土柱的抗震性能,对缩尺比为1∶2的9根试件进行了拟静力试验,2根试件进行了单调荷载试验。分析了轴压比（n取0.30、0.45）、加载方向（加载角α为0°、45°、90°、135°）、肢高肢厚比（3∶1、4∶1）、纵筋强度等级（HRB400、HRB500）等参数对其抗震性能的影响。研究了Z形截面柱的破坏特征,得到了试件的荷载-位移滞回曲线及骨架曲线、承载力、位移延性系数等力学性能指标。研究结果表明：试件在横向反复荷载作用下的主要破坏形态为弯曲型破坏,破坏主要发生在与加载方向平行的跨中截面,滞回曲线对称、饱满,试件延性好,具有良好的抗震能力。采用数值分析方法编制了Z形截面柱承载力电算程序进行计算,计算结果与试验结果吻合较好。     

建筑信息模型的Web端重建与三维交互方法研究

在BIM技术的背景下,针对现有的BIM服务器多为C/S架构,对电脑软硬件有较高要求、无法跨平台等问题,实现BIM模型在Web端的重建,并实现了对模型的拾取,获取其属性。其方法主要分为两部分,第一部分实现BIM模型从Revit软件中的导出,第二部实现对其导出的模型信息在Web端的三维交互,具有良好的用户体验。     

An equivalent stiffness approach for modelling the behaviour of compression members according to Eurocode 3

The development of design procedures based on inelastic advanced analysis is a key consideration for future steel design codes. In advanced analysis the effect of imperfections has to be modelled in such a way that the incremental analysis fully captures this effect in the process of moment redistribution. In modelling the influence of imperfections on the behaviour of individual members of real structures, different approaches have been used to globally represent this effect in the overall analysis of structural systems. They are referred to as the initial bow imperfection approach or as the equivalent transverse load approach. When using the abovementioned approaches in analysis of multiple member structural systems, the designer is required to arrange the directions of bow imperfections or equivalent transverse loads in such a way that the imperfection arrangement leads to the least constrained solution, i.e. the lowest ultimate load predicted from all possible sets of member initial imperfection arrangements. Since there is still ongoing research on the development of simple application rules ensuring that the designer obtains a unique solution when choosing a certain set of member initial imperfections, there is at the same time interest in the development of alternative approaches to modelling the influence of member imperfections on the behaviour of structural systems. This paper provides the necessary background information as well as describes the formulation and modelling techniques used in the development of a new approach to modelling the influence of imperfections on the stability behaviour of structural components and systems. This new approach, called hereafter an equivalent stiffness approach, has an advantage over the previously described approaches since an imperfect member is treated as a hypothetically straight element, flexural and axial stiffnesses of which at each load level are predicted in a continuous fashion dependent upon the actual force and deformation states. This type of modelling does not require any explicit modelling of equivalent geometric imperfections or equivalent forces and their directions in advanced analysis; therefore also it does not require any buckling mode assessment. Moreover, the effects of strain hardening and section class may conveniently be included in modelling. Finally, European buckling curves are used to estimate the values of parameters of the developed model that can be immediately used in advanced analysis conducted according to Eurocode 3.     

Numerical and experimental investigations of the response of aluminum cylinders with a cutout subject to axial compression

Understanding how a cutout influences the load bearing capacity and buckling behavior of a cylindrical shell is critical in the design of structural components used in automobiles, aircrafts, and marine applications. Numerical simulation and analysis of moderately thick and thin unstiffened aluminum cylindrical shells (D/t=45, 450 and L/D=2, 5, 10), having a square cutout, subjected to axial compression were systematically carried out in this paper. The investigation examined the influence of the cutout size, cutout location, and the shell aspect ratio (L/D) on the prebuckling, buckling, and postbuckling responses of the cylindrical shells.An experimental investigation on the moderately thick-walled shells was also carried out. A good correlation was observed between the results obtained from the finite element simulation and the experiments. Furthermore, empirical equations, in the form of a ‘buckling load reduction factor’ were developed using the least square regression method. These simple equations could be used to predict the buckling capacities of several specific types of cylindrical shells with a cutout.     

The role of frame members and sheathing in partition wall panels subjected to compression

This paper presents an experimental study on the role of frame members and sheathing by means of strain/stress distributions in each of the constituents of a cold-formed steel wall panel. Vertical compression loading was applied, and strain gauges were extensively used during the tests. At a given cross-section of the middle stud, strains/stresses experienced by its flanges are found to be significantly different from those on the web, indicating that the middle stud is not balanced in simple compression mode. However, the averaged stress on the flanges and that on the web follow the same trend as that recorded by the load cell, and can be used to work out the load carried by the stud. Screw connections between the stud and the board not only restrain the lateral displacement of the stud, but also support and re-distribute a portion of the load to the board and then to the bottom track. Upon loading, the axial force experienced by a typical screw is negligibly small initially, increasing slowly with load until substantial stud buckling occurs, resulting in often its pulling-out from the board or the stud/track. The board acts as a shearing member to steady the whole panel, a supporting member to enhance the overall/local buckling performance of the middle stud and sidetracks, as well as a structural member to support part of the vertical load.     

屈服强度550MPa高强冷弯薄壁型钢结构轴压构件承载力计算模式研究

本文收集了目前国内外屈服强度550MPa高强钢材冷弯薄壁型钢结构轴心受压构件的试验数据,参考现行的《冷弯薄壁型钢结构技术规范》(GB 50018—2002),对其承载力的合理计算模式进行了系统研究。结果表明,现行规范考虑板组约束计算截面有效宽厚比的方法对屈服强度550MPa高强钢材冷弯薄壁型钢结构轴心受压构件极限承载力的计算是可靠的。     

A 3D numerical model for reinforced and prestressed concrete elements subjected to combined axial, bending, shear and torsion loading

This paper presents a model for the analysis of reinforced and prestressed concrete frame elements under combined loading conditions, including axial force, biaxial bending, torsion and biaxial shear force. The proposed model is based on the simple kinematic assumptions of the Timoshenko beam theory and holds for curved three dimensional frame elements with arbitrary cross-section geometry. The control sections of the frame element are subdivided into regions with 1D, 2D and 3D material response. The constitutive material model for reinforced and prestressed concrete follows the basic assumptions of the Modified Compression Field Theory with a tangent-stiffness formulation. The validity of the model is established by comparing its results with several well-known tests from the literature. These simulations include a variety of load combinations under bending, shear and torsion. The analytical results show excellent agreement with experimental data regarding the ultimate strength of the specimen and the local strain response from initiation of cracking to ultimate load.     

Finite element analysis of CFT columns subjected to an axial compressive force and bending moment in combination

Proper material constitutive models for concrete-filled tube (CFT) columns subjected to an axial compressive force and bending moment in combination are proposed and verified in this paper by using the nonlinear finite element program ABAQUS compared against experimental data. In the numerical analysis, the cross sections of the CFT columns are categorized into three groups, i.e., ones with circular sections, ones with square sections, and ones with square sections stiffened with reinforcing ties.It is shown that the steel tubes can provide a good confining effect on the concrete core when the axial compressive force is large. The confining effect of a square CFT stiffened by reinforcing ties is stronger than that of the same square CFT without stiffening ties but weaker than that of a circular CFT. Nevertheless, when the spacing of reinforcing ties is small, a CFT with a square section might possibly achieve the same confining effect as one with a circular section.     

轴心受压双钢管混凝土短柱正截面受压承载力理论分析及试验研究

研究了由同心设置的内、外圆钢管构成的轴心受压双钢管混凝土短柱正截面受压承载力,分析了单钢管混凝土柱与双钢管混凝土柱的受力机理,并根据纤维模型法原理,采用适用于钢管混凝土受力特性的钢材与混凝土材料本构关系,给出了轴心受压双钢管混凝土短柱的荷载-位移全过程数值分析和正截面承载力计算公式。进行了5个双钢管混凝土短柱的轴心受压试验,验证理论分析的正确性。理论分析与试验研究表明:轴心受压双钢管混凝土短柱与单钢管混凝土柱的受力全过程都可以分为弹性阶段、弹塑性阶段和破坏阶段。双钢管混凝土短柱的破坏形态为腰鼓形,其外层混凝土的工作性能与单钢管中的混凝土大致相同,但内钢管中的内层混凝土受到的约束效应较大,且不是内、外钢管对它的约束效应的叠加,因此对内层混凝土约束效应的确定是计算承载力的关键。通过与相同含钢率的轴心受压单钢管混凝土短柱受力过程的对比得出:双钢管混凝土柱的承载力明显高于单钢管混凝土柱,且具有非常好的延性和整体     

套管构件中轴压内核本构关系的分析

套管构件是一种新型的承压设计构件。它由内核与套筒组成,且两者之间有间隙,套筒为受压内核提供侧向约束,使得内核可以发生高阶屈曲模态,极大提高了内核的受压承载力。在对比分析已有的内核本构关系模型的基础上,提出了当套筒刚度为有限时内核的轴力-轴向位移简化曲线,该曲线考虑了内核处于与套筒未接触、与套筒一阶模态点接触、与套筒一阶模态线接触这一系列变形过程,并通过算例分析,验证了该简化本构关系的合理性。     

Bearing capacity of reinforced foundation subjected to pull-out loading in 2D and 3D conditions

Steel-framed structures like electricity transmission towers are subjected to great pull-out forces under strong wind conditions. This paper analyses how caisson foundations with reinforcement bars can increase the uplift bearing capacity of those structures. Model tests and numerical analyses in 2D and 3D are used to investigate how the bars' position and direction affect the behavior of the foundation under different load conditions. The test results show that reinforcements stemming diagonally downward from the bottom of the foundation are the most effective against uplift loading because they increase the structure's bearing capacity. However, this gain is less significant when inclined uplift forces are applied to the foundation. The higher the force inclination angle, the less efficient the design becomes. In that case, reinforcements that stem from the foundation's bottom are more effective than those stemming from the foundation's side. The numerical results accurately describe the experimental findings, since the simulations accounted appropriately for both the mechanical behaviors of the soil and the reinforcement as well as the frictional behavior between them. Furthermore, the results from the model tests and analyses carried out in 3D and 2D conditions are compatible.     

钠铁硅系统玻璃形成区和磁化率的研究

研究了钠铁硅系统玻璃的形成区和磁化率。结果证明：（1）在一定实验条件下,钠铁硅系统玻璃形成区的范围是：x(Na2O)=0-52%;x(Fe2O3)=0-20%;x(SiO2)=48%-100%。（2）钠铁硅系统玻璃的磁化率不仅与Fe2O3的含量有关,而且与Fe^3 在玻璃中的结构地位有关,当Fe^3 处于四配位状态时,Fe^3 的3d电子处于弱场高自旋状态,对磁化率的贡献就较大;当Fe^3 处于六配位状态时,Fe^3 的3d电子处于强场低自旋状态,对磁化率的贡献就较小。（3）磁化度的转折点位于x(Fe2O3)＝6％附近。     

3D技术与三维建模在建筑类ECE教学实践中的应用

目前,最新信息技术的3D技术与三维建模已应用在课堂与实践辅助教学中。文章探讨了最新的信息技术与现有教学资源的选择、整合途径与原则,并以建筑英语课程教学与实践(English for Civil Engineer,ECE)为例,探索基于3D技术与三维建模的新教学模式。研究发现,新教学模式在有效教学、知识体系建构、技能与语言迁移、创新思维培养等方面有显著成效。     

砂井地基固结的空间渗流和群井效应的解析分析

本文从Ｔｅｒｚａｇｈｉ－Ｒｅｎｄｕｌｉｃ三维固结方程出发，对砂井地基因结的空间渗流和群井效应作了分析。文中给出的砂井地基因结的解析解可考虑群井共同作用、空间渗流和井阻作用，满足软土的上下边界条件、各砂井中的连续和井阻条件。文末作了数值计算，讨论了空间渗流和群井效应对砂井地基中的孔隙水压力消散及地基因结的影响。     

PFC~(3D)模型中粗粒料孔隙率及摩擦系数的确定方法

在保证粗粒料PFC~(3D)模型和真实土料的相对密实度相同的基础上,提出了一种同时确定模拟孔隙率和摩擦系数的方法。利用颗粒流在不同的摩擦系数下模拟松填法和振动台法分别得到了最大和最小孔隙率,再根据粗粒料实际相对密实度换算出对应的模拟孔隙率,得到了一条关于孔隙率~摩擦系数的曲线。在该曲线上选择一点代入进行模拟三轴试验并将结果与实际试验值对比,经过几次试算即可确定试样模拟孔隙率和摩擦系数。以双江口堆石料的三轴试验值为例,利用本方法确定了相对密实度分别为0.95、0.75和0.65时模拟孔隙率和摩擦系数;同时改变试样的颗粒级配进行验证,结果显示,模拟值与实际试验值相差不大,验证了本方法的合理性。     

Light-absorption ratio variation approach to determination of nickel (II) in ng/ml level with 1, 5-di(2-hydroxy-5-sulfophenyl)-3-cyanoformazan

The light-absorption ratio variation approach (LARVA) has been described and applied to the quantitative detection of ultramicro amounts of Ni by spectrophotometry, which raises notably the detection sensitivity. The complexation between 1, 5-di(2-hydroxy-5-sulfophenyl)-3-cyanoformazan (DSPCF) and Ni(II) at pH 9.11 was investigated and the binary complex was characterized by the spectral correction technique. Results have shown that deltaAr-1 (deltaAr--light-absorption ratio variation) is linear in the range of Ni(II) between 5 and 200 ng/ml. The limit of detection (3sigma) of Ni(II) is only 1.3 ng/ml. The complexation is selective in the presence of fluoride, hexametaphosphate, ethylene diamine tetraacetate and thioglycollic acid. It has been applied to analysis of water quality with satisfactory results.