新型冷弯箱形组合构件力学性能研究

基于箱形截面具有双轴对称、抗弯扭刚度大的特点,提出将冷弯∑形截面两两翼缘相对,并将其卷边焊接形成一种新型冷弯箱形组合截面——DS。应用非线性有限元方法分析新型截面构件在轴压、弯矩及压弯荷载作用时的诸如屈曲模式、承载力、刚度、延性及相关曲线等方面力学性能。同时,还对相同参数的新型截面构件与C形截面构件的单位承载力耗钢量进行比较。分析表明:新型截面构件在承受轴压力时具有高承载力及较高的截面模量,截面加劲充分而使子板件局部屈曲不易出现等力学性能优势。特别适宜承受轴压荷载,同时也适宜承受弯矩和压弯荷载的作用。轴压构件的单位承载力耗钢量一般仅为相同参数C形构件的50%左右,经济效益明显。新型箱形组合构件适于深入试验研究并合理应用于实际工程。     

卷边翼缘工形构件在压弯荷载作用下的稳定承载力设计理论

卷边工形截面构件作为一种高效型材,在弯矩与轴力共同作用下的破坏模型常常是伴随板件局部屈曲的整体失稳。利用板壳有限单元法,研究卷边工形截面构件在板件局部屈曲下的构件整体稳定承载力,建立其稳定承载力设计公式。首先,通过设计大量算例,研究了截面宽高比、腹板高厚比、翼缘宽厚比等截面参数对短柱承载性能的影响,其中考虑了板组之间屈曲的相关作用,获得了考虑板组局部屈曲特性的短柱稳定承载力相关公式。在短柱板件局部失稳承载力研究的基础上,计入构件长细比对长柱面内和面外稳定承载性能的影响,通过数值分析建立了卷边工形构件在压弯荷载作用下的稳定承载力设计公式。     

基于广义梁理论的非线性材料薄壁受压构件屈曲荷载计算方法

提出适用于非线性材料的广义梁理论屈曲荷载计算方法,并对不锈钢薄壁受压构件屈曲荷载进行计算验证。通过定义材料非线性应力应变关系和瞬时弹性模量,对传统线弹性广义梁理论进行修正,建立非线性材料薄壁构件受压屈曲荷载计算方法,推导不锈钢薄板受压局部屈曲、冷弯薄壁不锈钢卷边槽形柱畸变屈曲及箱形不锈钢长柱弯曲屈曲荷载计算公式,并与既有试验数据对比。经验证,线弹性分析方法不适用于不锈钢材料;提出的修正GBT法具有较高精度,且本构关系采用变形法则结果偏于安全,可用于不锈钢等非线性金属材料薄壁构件受压屈曲荷载的确定,为研究和设计提供理论指导。     

Der Einfluss von Imperfektionen in dünnwandigen geschweißten Rechteckquerschnitten unter Druckbeanspruchung

On imperfections in thin‐walled welded rectangular hollow section compressive members. This contribution presents the results of a research project analysing some aspects of stability failure of thin‐walled RHS compression members that are likely to exhibit combined global and local buckling. In particular the influence of various imperfections, namely residual stresses due to weld‐ing and local as well as global geometrical defects, on the load‐carrying capacity is subject to detailed experimental and numerical investigations. The insight into the structural behaviour leads to recommendations for standardized imperfections that should be used in the context of the numerical modelling of class‐4 square and rectangular hollow section members subjected to compression.     

四边形截面圆弧空间钢管桁架拱平面内稳定性及试验研究

通过大挠度弹塑性有限元分析研究桁架拱在集中荷载、水平均布荷载、轴线均布荷载等不同荷载形式下的失稳与破坏机理,考察截面高宽比、矢跨比、腹杆夹角、腹杆尺寸等几何参数对桁架拱稳定承载力的影响,结果表明在不同参数条件下,桁架拱可能发生弦杆局部失稳、腹杆局部失稳、整体失稳以及局部与整体相关失稳等破坏形式;与拱的整体失稳和弦杆局部失稳相比,腹杆失稳会导致承载力的大幅下降,设计中应保证腹杆不先发生破坏。在理论分析的基础上,设计4榀矩形及梯形截面空间桁架拱模型进行了平面内稳定性能试验研究,分析表明两种截面形式的桁架拱在平面内具有基本相同的刚度和承载能力,其承载力设计可以采用相同公式。最后,基于静水压力作用下桁架拱的面内稳定设计曲线,通过大量的算例分析,提出轴力和弯矩共同作用下四边形截面圆弧形空间钢管桁架拱的整体面内稳定承载力设计方法。     

Plastic mechanism analyses of circular tubular members under cyclic loading

This paper presents plastic mechanism analyses of circular tubular members under cyclic loading. In particular, it provides new methods of analyses for circular hollow sections subjected to a constant amplitude cyclic pure bending (CCPB) and a large axial compression–tension cycle (ACTC). The procedure described herein for CCPB considers both prebuckling deformation and local buckling. The prebuckling deformation was simulated using a progressively deforming elliptical cross-section which was observed during the test. The local buckling analysis was performed using a rigid plastic mechanism analysis. Good agreement was found between the predicted and measured hysteresis. However, the present model over-estimates the strength and absorbed energy. For the ACTC, good agreement was found between the predicted and measured collapse curves within the compression half-cycle. More work is needed to model the effect of tension developed during the remaining of the loading cycle. The present models consider the actual local buckling deformation of the cross-section and also avoid the complexity involved in the numerical analyses since they provide the most commonly used closed-form solutions.     

冷弯型钢受压构件的LRFD抗力系数

目前,冷弯型钢抗压构件的LRFD抗力系数取值为0.85,该文旨在研究该系数能否增大。数据库中包含675组同中心荷载柱的试验数据,包含平口卷边C截面、平口卷边Z截面、帽形截面和角形截面以及开孔构件。采用美国钢铁协会标准和直接强度法计算每个试样的强度。直接强度法的计算结果更加精确,其在计算部分有效截面柱的强度时尤为精确。采用一阶二次矩法计算的LRFD抗力系数,与美国钢铁协会标准和直接强度法的规定相符。对于柱的两种破坏情况,达到畸变屈曲极限状态而破坏和由于整体失稳或局部-整体失稳相互作用而破坏,前者的计算结果更为精确。单角钢柱的试验强度与计算强度的比值有很大变化,随着整体长细比的增加,计算结果逐渐变得极为保守。     

Elastic flexural buckling of non-uniform members: Closed-form expression and equivalent load approach

Experienced structural engineers have an intuitive understanding of the buckling behavior of uniform members subjected to compressive loads. The Euler critical load and the concept of buckling length are extensively used in this context. Unfortunately, the extension of this intuitive approach to cases with non-uniform load or non-uniform members is not straightforward. Based on an extensive numerical parametric study, the paper first presents a closed-form expression for the buckling load of constant cross-section members with non-uniform axial loading. Consequently, an equivalent load approach for non-uniform members subjected to non-uniform axial load distribution is proposed and validated. The combination of both procedures has the power of transforming the general complex case of a non-uniform member under non-uniform load into an equivalent simple case of a uniform member subjected to uniform load. The new methodology is simple and direct, and produces more than acceptable approximate results.     

FRP加固局部损伤钢压杆的稳定分析

钢结构中存在大量的轴心受力构件,作为承受永久竖向荷载的主要构件,往往是结构加固的重点.采用能量方法,分析各种杆端约束条件下,纤维增强复合材料（FRP）加固局部损伤的轴心受压钢构件在弹性失稳时的弹性屈曲临界力,并建立普遍适用的近似欧拉公式.利用ANSYS通用有限元分析软件分析FRP的厚度对损伤空心圆管临界力的影响并与该公式解析解进行对比.计算结果表明,该公式计算结果可靠,采用纤维增强复合材料加固修复局部损伤的钢结构可以有效恢复其刚度和稳定性.     

钢构件整体稳定直接分析法研究现状及展望

钢构件整体稳定设计的基础理论不仅是结构设计的依据,也是钢结构直接分析法发展和完善的重要基础。以轴压构件、受弯构件和压弯构件为研究对象,对中国、美国、欧洲现行钢结构设计标准GB 50017—2017、ANSI/AISC 360-16、EN 1993-1-1: 2005中钢构件整体稳定(弯曲失稳、扭转失稳、弯扭失稳)设计的基础理论进行了归纳与总结。基于初弯曲轴压构件弯曲失稳设计的基础理论,揭示了初始几何缺陷对钢构件整体稳定的分析过程和分析结果的影响。从完整的步骤、完备的表达式两方面归纳了钢构件整体稳定的构件直接分析法的应用情况。并就轴压构件、受弯构件以及压弯构件整体稳定的构件直接分析法的研究现状进行了分析,指出了存在的问题,并对后续研究进行了展望。     

冷弯薄壁C型钢绕强轴偏心受压构件的极限承载力

冷弯薄壁型钢结构多采用有效截面法对构件承载力进行计算,该方法计算繁杂且未考虑构件的畸变屈曲性能。直接强度法采用全截面计算各类参数,能够考虑各种单独屈曲模式及其相关屈曲对构件稳定性能的影响,但目前该方法并不能应用于压弯构件。对冷弯薄壁C形钢绕强轴偏压构件的稳定性能进行参数分析,探讨了构件长度、偏心距、腹板高厚比、翼缘宽厚比和卷边高厚比等因素对构件承载力的影响规律。结合有限元分析结果,基于轴压构件和纯弯构件的直接强度法公式,提出了冷弯薄壁型钢绕强轴偏压构件的极限承载力计算方法。     

GBT-based buckling analysis of thin-walled members with non-standard support conditions

This paper reports on the use of a recently developed Generalised Beam Theory (GBT) formulation, and corresponding finite element implementation, to analyse the local and global buckling behaviour of thin-walled members with arbitrary loading and support conditions — this formulation takes into account longitudinal normal stress gradients and the ensuing pre-buckling shear stresses. After presenting an overview of the main concepts and procedures involved in the performance of a GBT-based (beam finite element) member buckling analysis, one addresses in detail the incorporation of non-standard support conditions, such as (i) full or partial localised displacement or rotation restraints, (ii) rigid or elastic intermediate supports or (iii) end supports corresponding to angle connections. In order to illustrate the application and capabilities of the proposed GBT-based approach, one presents and discusses numerical results concerning cold-formed steel (i) lipped channel beams and (ii) lipped I-section beams and columns with various “non-standard” support conditions — while the beams are acted by uniformly distributed or mid-span point loads, applied at the shear centre axis, the columns are subjected to uniform compression. In particular, it is possible to assess the influence of the different support conditions on the beam and column buckling behaviour (critical buckling loads and mode shapes). For validation purposes, most GBT-based results are compared with values yielded by shell finite element analyses carried out in the code Ansys.     

Cyclic performance of steel and composite bracing members

This paper describes an experimental study on the response of hollow and filled steel members to monotonic and cyclic axial loading. Monotonic tests were first performed on short specimens to establish their compressive and tensile axial resistances and to investigate the effect of infill on local buckling and ductility. These were followed by cyclic tests on longer bracing members with three different cross-section sizes. The presence of concrete infill was observed to influence the mode of failure displayed by the specimens, as well as their compression and tension load responses. The ductility capacities of the individual specimens are compared, and the effects of slenderness, steel strength and infill are quantified. The experimental findings are compared with the recommendations of a number of international codes of practice and previous research studies on the seismic response of steel braces. It is found that the infill contributes to the compression resistance of the brace, even after multiple inelastic load reversals, and that it can improve ductility capacity by preventing or limiting local buckling.     

四肢拼合冷弯薄壁型钢截面立柱轴压性能试验研究及数值分析

对不同长细比的8根四肢拼合冷弯薄壁型钢截面立柱的轴压性能进行试验研究,在试验研究的基础上建立考虑材料、几何和接触非线性的有限元模型,并通过对试验试件的数值模拟,验证有限元方法的正确性。采用数值方法分析长细比、连接螺钉间距、截面翼缘宽厚比对四肢拼合冷弯薄壁型钢截面立柱轴压性能的影响。结果表明:试件最终破坏均呈现局部屈曲和畸变屈曲的破坏模式;四肢拼合冷弯薄壁型钢截面立柱的轴压性能具有"1×4≥4"的拼合效应;随着长细比的增大,四肢拼合立柱的最大承载力和刚度逐渐降低;当螺钉间距在150～450mm之间变化时,四肢拼合立柱的最大承载力和刚度变化不大;减小四肢拼合立柱截面的翼缘宽厚比,可以显著提高其最大承载力。     

Q460高强角钢轴心受压构件极限承载力试验研究

为研究Q460高强角钢轴压构件的受力性能,采用静力试验对试件破坏状态和稳定承载力进行分析,两端设置球铰、单刀口铰和双刀口铰支座,分析了不同铰接方式对构件受力性能的影响。结果表明,采用不同支座均能很好地反映杆件的受力性能;短构件的极限承载力由钢材强度控制,长细比变化对其影响很小,长细比等于30和45的试件以局部破坏为主,长细比等于60和80的杆件以整体弯曲失稳为主。比较试验和各规范理论计算结果发现,试验值显著高于中国DL/T5154—2002杆塔技术规定计算值,与美国ASCE 10—97导则计算值吻合较好。     

结合实例研究大直径塔筒局部稳定问题

因建筑造型的需要,大直径塔筒在工程设计中的应用日益广泛。由于塔筒的稳定性与塔筒的几何尺寸、初始缺陷以及加载和约束方式等诸多因素有着密切的关系,如何确保大直径塔筒的局部稳定成为设计中的重点。本文采用数值分析方法系统研究了不开洞和开洞塔筒在一定的轴力与弯矩范围内,内部加劲形式变化对于极限承载能力的影响,明确了不同加劲形式的加劲效率。另外,对影响不开洞和开洞塔筒局部稳定的各几何参数进行了深入的参数化分析,并提出了改善屈曲强度的有效方法。     

Generalised beam theory to analyse the buckling behaviour of circular cylindrical shells and tubes

A formulation of generalised beam theory (GBT) developed to analyse the elastic buckling behaviour of circular hollow section (CHS) members (cylinders and tubes) is presented in this paper. The main concepts involved in the available GBT are adapted to account for the specific aspects related to cross-section geometry. Taking into consideration the kinematic relations used in the theory of thin shells, the variation of the strain energy is evaluated and the terms are physically interpreted, i.e., they are associated with the geometric properties of the CHS. Besides the set of shell-type deformation modes, the formulation also includes axisymmetric and torsion deformation modes. In order to illustrate the application and capabilities of the formulated GBT, the local and global buckling behaviour of CHS members subjected to (i) compression (columns), (ii) bending (beams), (iii) compression and bending (beam-columns) and (iv) torsion (shafts), is analysed. Moreover, the GBT results are compared with estimates obtained by means of shell finite element analyses and are thoroughly discussed.     

钢货架柱畸变屈曲的试验研究

给出受压钢货架柱性能的试验结果。对不同长度的钢货架柱进行试验研究,主要研究那些发生畸变屈曲的试件的性能。畸变屈曲一般发生在中等长度的试件上。即:长于那些发生局部屈曲强度的柱,但是也不能过长,以避免发生整体屈曲。测量了试件的变形量,而且,大部分构件发生的是一种畸变屈曲和整体屈曲组合的破坏模式。此外,已经证实尽管该破坏模式对试件强度的影响不大,但是如果考虑这个因素,目前设计程序的准确性将得到提高。     

铝合金轴心受压构件局部整体相关稳定试验研究

铝合金轴压构件局部与整体相关稳定性能,在国内外尚无系统的研究。为此,该文对12根铝合金6061-T6和6063-T5工形截面轴心受压构件的局部整体相关稳定性能进行试验研究,包括其破坏形式、变形性能以及极限承载力等。将试验结果与中国规范、欧洲规范、美国规范和澳大利亚/新西兰规范计算结果进行对比分析,验证各规范设计方法的可靠性。采用有限元软件ANSYS对试验结果进行模拟计算。研究结果表明：有限元模型能够准确地计算铝合金轴压构件的承载力,可以应用在下一步的参数分析中;各国规范设计方法对弱硬化合金承载力计算的准确程度优于强硬化合金;美规和澳规对弱硬化合金极限承载力的计算较准确,但是对强硬化合金的计算偏于保守;中国规范和欧规分别考虑局部失稳和整体失稳,并将两者的影响进行叠加,计算结果过于保守。因此,需要调整中国规范中的参数,以得到更加合理的设计。     

Recent research advances on ECBL approach.: Part I: Plastic–elastic interactive buckling of cold-formed steel sections

The objective of this two parts paper is to present some recent developments and applications of erosion of critical bifurcation load (ECBL) approach for the interactive buckling. Two different types of problems are analysed: (1) plastic–elastic interactive buckling which implements into the Ayrton–Perry interaction formula the plastic strength of the stub columns evaluated by means of local plastic mechanism analysis, and (2) elastic–elastic interactive buckling for members with perforations.The first part of the paper analyses the occurrence of local plastic mechanisms in cold-formed steel sections in compression, and how they can be implemented in the ultimate limit state analysis of the members. Actually, the failure of thin-walled cold-formed members in compression always occurs with a local plastic mechanism. Starting from this observation, the authors suggest to use in the interactive local-overall buckling analysis the sectional plastic mechanism strength instead of traditional ‘effective section’. The ECBL approach is used to implement the proposed interactive buckling model. Results are compared with those of other two recent methods, namely the direct strength method and plastic effective width approach. Relevant tests are used to evaluate the three methods. Comparisons with European and American design codes are also presented in the paper.