带初始缺陷的平面钢框架的敏感性分析

给出一个门式刚架承载力的敏感性和统计性分析。阐述了包括2个单层受压柱系统的典型稳定性问题,这个系统的要素相互影响,并且结合随机的不完善性,将影响承载力。采用Sobol敏感性分析法研究相互影响的因素。Sobol敏感性分析法应用于区别主要输入的随机缺陷和它们的高阶互动效应对承载力的影响。根据试验结果,考虑了大部分缺陷。采用拉丁超立方抽样方法,实现了对初始缺陷的模拟。几何非线性解决方案提供了数值解。采用梁单元对框架实现网格划分。平面钢框架的柱分别考虑采用2种边界条件。分析了承载力设计值与柱长度系数之间的关系。     

Sensitivity analysis of stability problems of steel plane frames

The objective of the paper is to analyse the influence of initial imperfections on the load-carrying capacity of a single storey steel plane frame comprised of two columns loaded in compression. The influence of the variance of initial imperfections on the variance of the load-carrying capacity was calculated by means of Sobol’ sensitivity analysis. Monte Carlo based procedures were used for computing full sets of first order and second order sensitivity indices of the model. The geometrical nonlinear finite element solution, which provides numerical results per run, was employed. The mutual dependence of sensitivity indices and column non-dimensional slenderness is analysed. The derivation of the statistical characteristics of system imperfections of the initial inclination of columns is described in the introduction of the present work. Material and geometrical characteristics of hot-rolled IPE members were considered to be random quantities with histograms obtained from experiments. The Sobol sensitivity analysis is used to identify the crucial input random imperfections and their higher order interaction effects.     

Sensitivity analysis of steel plane frames with initial imperfections

The article presents the sensitivity and statistical analyses of the load-carrying capacity of a steel portal frame. It elaborates a typical stability problem of a system comprising two single-storey columns loaded in compression. The elements of this system mutually influence each other, and this fact, in conjunction with the random imperfections, influences the load-carrying capacity variance. This mutual interaction is analysed using the Sobol’ sensitivity analysis. The Sobol’ sensitivity analysis is applied to identify the dominant input random imperfections and their higher order interaction effects on the load-carrying capacity. Majority of imperfections were considered according to the results of experimental research. Realizations of initial imperfections were simulated applying the Latin Hypercube Sampling method. The geometrical nonlinear solution providing numerical result per run was employed. The frame was meshed using beam elements. The columns of the plane frame are considered with two variants of boundary conditions. The dependence between mean and design load-carrying capacities and column non-dimensional slenderness is analysed.     

Stability problems of steel structures in the presence of stochastic and fuzzy uncertainty

General ideas and problems of probability approach and its utilization in the verification of structural design procedures of EUROCODES are mentioned. The paper is aimed at the probability study of the ultimate limit state of a steel compressed member designed economically according to EUROCODE 3. The theoretical failure probability (reliability index) vs. ratio of permanent to variable load action is calculated by means of the Monte Carlo simulation method. The misalignment of the failure probability according to EN1990 is analysed. Initial imperfections are generally considered as random variables and random fields. The non-linear beam FEM is used. The influence of initial curvature shape and size variability of the member axis on the variability of load-carrying capacity is investigated. The probabilistic analysis is supplemented with the fuzzy analysis of the influence of uncertainties on the failure probability.     

随机节点位置安装偏差与杆件偏心对单层球面网壳承载力的影响研究

单层球面网壳属于缺陷敏感性结构,其稳定承载能力受各种缺陷影响。为量化节点位置安装偏差缺陷、杆件对节点的偏心缺陷及其二者耦合作用对网壳稳定承载力的影响程度,对1000个随机产生的K6型单层球面网壳展开深入研究。首先提出了能够考虑随机节点安装偏差、随机杆件偏心的力学模型,然后阐述了两种随机缺陷在数值计算中的实现方法,最后获得了不同大小的节点安装偏差、杆件偏心距对单层网壳稳定承载力的影响程度与规律。计算结果表明：节点安装偏差对网壳极限荷载的影响更为显著,杆件偏心对极限荷载的影响相对较小;当节点安装偏差较小时,杆件偏心对网壳极限荷载的影响更为显著;节点安装偏差相同时,杆件偏心越大,网壳极限荷载越小。当最大节点安装偏差R1=2cm、最大杆件偏心R2=10mm时,缺陷网壳的极限荷载较理想网壳平均下降了10.94%;当R1=4cm、R2=10mm时,极限荷载平均下降了16.43%。     

Imperfection sensitivity of elastic and elastic-plastic torispherical pressure vessel heads

The paper deals with the results of a systematic numerical investigation of the nonlinear elastic and elastic plastic load-carrying behaviour and imperfection sensitivity of torispherical pressure vessel heads under uniform external pressure. In particular, the presentation focuses on the qualitative and quantitative influence of the radius-to-thickness ratio R/t, the yield stress σ₀ and the magnitude of initial geometric imperfections (in the shape of the elastic bifurcation mode) on the elastic-plastic load-carrying behaviour. It is found that thinner shells are more sensitive to the value of the yield stress and the magnitude of initial geometric imperfections, but their load-carrying capacity, relative to the elastic bifurcation pressure, may also be significantly higher than that of thicker shells.     

钢管格构柱稳定极限承载力研究

用弹塑性大挠度有限元对不同类型、不同腹杆布置形式的钢管格构柱进行了稳定极限承载力研究,并与规范结果进行了比较,分析了腹杆布置形式及腹杆长细比对极限承载力的影响,为合理设计钢管格构柱提供参考。     

杆件初弯曲对半刚接单层柱面网壳稳定承载力的影响研究

为了系统地研究杆件初弯曲对半刚接单层柱面网壳稳定承载力的影响,对5种矢跨比的半刚接网壳进行了双重非线性全过程分析。首先阐述了焊接球节点刚度及随机杆件初弯曲的确定方法,然后深入研究了杆件初弯曲对5种矢跨比的半刚接网壳稳定承载力的影响程度,最后探讨了具有杆件弯曲的半刚接网壳的破坏过程。研究结果表明,杆件初弯曲对半刚接网壳稳定承载力的影响程度与网壳矢跨比和初弯曲分布形式有关。如杆件初弯曲对矢跨比为1/3、1/4半刚接网壳的影响甚微,对矢跨比为1/5半刚接网壳的影响较为明显。矢跨比为1/6半刚接网壳的承载能力对个别杆件的弯曲形式较为敏感,而对某些杆件的初弯曲形式不敏感;随着矢跨比的减小,具有杆件初弯曲的半刚接网壳的极限荷载的离散性先增大后减小;网壳达到极限状态之后,失稳区域的竖向位移、杆件的弯曲应力和节点的转角迅速增大,网壳的受力状态转变为弯曲应力状态,当失稳区域的位移较大时,会引起该区域部分杆件丧失稳定,最终导致网壳发生整体失稳。     

竖向荷载和水平荷载共同作用下钢管拱平面内稳定承载力设计研究

采用二阶弹塑性有限单元法对竖向荷载和水平荷载共同作用下的圆形截面两铰抛物线钢管拱的平面内稳定承载力进行研究。考虑材料非线性、残余应力、初始几何缺陷、矢跨比和长细比等因素对钢管拱平面内力稳定承载力的影响。结果表明：残余应力对其竖向承载力影响很小;初始几何缺陷会显著降低中等长细比钢管拱的承载力;矢跨比和长细比是影响钢管拱承载力的重要因素,但拱的竖向承载力并不随矢跨比和长细比的均匀变化而变化。研究竖向荷载和水平荷载共同作用下两铰抛物线钢管拱达到平面内极限状态时的N-M相关关系,并拟合两铰压弯抛物线钢拱承载力N-M相关关系统一表达式。提出了竖向荷载为全跨均布和半跨均布荷载,同时考虑水平方向荷载作用的两铰抛物线钢拱平面内整体稳定承载力设计建议,可供相关设计问题参考应用。     

直接分析设计法中的受压构件等效初始缺陷研究

在GB 50017—2017《钢结构设计标准》中，仅对考虑材料弹性阶段的直接分析设计法中的构件初始缺陷取值作出了规定，对考虑材料弹塑性发展的直接分析设计法中未给出构件初始缺陷取值的具体数值。为此，基于钢结构塑性稳定理论，利用轴心受压构件稳定系数反向推导其等效初始缺陷，包括初始几何缺陷和残余应力。根据不同的截面类型和钢材牌号，给出受压构件不同的等效初始缺陷，使直接分析设计方法能够真正地应用于实际工程中。利用直接分析设计软件NIDA，建立带有初始缺陷的弯曲单元，模拟受压构件的等效初始缺陷，得到构件的稳定承载力系数，并与轴压构件稳定系数φ进行对比分析，验证了构件等效初始缺陷取值的正确性。     

考虑弯矩作用梭形钢格构柱稳定承载力非线性有限元分析

以2010年上海世博会世博轴工程中采用的梭形钢格构柱为研究对象,应用大挠度弹塑性有限元法研究考虑弯矩作用时梭形格构柱的稳定承载力。分析了初始几何缺陷作用方向、分布形式对梭形格构柱稳定承载力的影响,并与试验结果进行了比较。分析结果表明：梭形格构柱在轴力和弯矩共同作用下的一阶弹性屈曲模态表现为“S”形和“C”形两种形式;考虑弯矩作用后,初始缺陷作用方向对梭形格构柱的稳定承载力有较大影响;对一阶屈曲模态为“S”形的梭形格构柱,计算稳定承载力时只需考虑“S”形缺陷的影响,而对一阶模态为“C”形的梭形格构柱有必要综合考虑“C”形和“S”形缺陷的影响。与试验结果比较表明,建议方法计算梭形格构柱的稳定承载力安全、合理。图12表1参11     

Probability analysis of double layer barrel vaults considering the effect of initial curvature and length imperfections simultaneously

Load carrying capacity of reticulated space structures majorly depend on the structures’ imperfections. Imperfections in initial curvature, length, and residual stress of members are all innately random and can affect the load-bearing capacity of the members and consequently that of the structure. The present study investigated the effect of the probability distribution of initial curvature imperfection and lack of fit of members on the load-bearing capacity of double-layer barrel vault space structures with different types of support. A random number was first assigned to each member using gamma and normal distributions for initial curvature and member length imperfections, respectively. Afterwards, the ultimate bearing capacity and the collapse behavior of the structure was determined using nonlinear finite-element analysis in OpenSees software and finally structures reliability was acquired. The results demonstrate that the collapse behavior of doable-layer barrel vault space structures is sensitive to the random distribution of initial imperfections.     

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.     

内钢板中空方形钢管混凝土叠合柱轴压力学性能研究

为研究中内钢板中空方形钢管混凝土（CFST）叠合柱的轴压力学性能,以内钢板与钢管的强度和壁厚为参数对8个叠合短柱进行轴压试验,以截面尺寸、钢管内外混凝土强度、钢材强度、纵筋与钢管用钢量分配为参数对81个叠合短柱进行有限元分析,对典型构件受力全过程、各部分接触作用以及承载力进行研究。在美国结构设计规范ANSI/AISC 360-16、欧洲钢结构设计规范BS EN 1994-1-1、GB 50936—2014《钢管混凝土结构技术规范》和T/CECS 663—2020《钢管混凝土加劲混合结构技术规程》的组合柱承载力计算公式中增加内钢板承载力项,得到内钢板中空方形CFST叠合构件的轴压承载力计算式。结果表明：轴压荷载作用下,内钢板中空方形CFST叠合柱钢管外混凝土、内钢板、钢管、纵筋以及核心混凝土能协同工作;内钢板强度与壁厚对构件承载力、延性和刚度影响均较小;截面尺寸和混凝土强度对构件承载力贡献最大,但构件延性随着混凝土强度的增大而降低。在T/CECS 663—2020和ANSI/AISC 360-16的组合柱承载力计算公式中增加内钢板贡献项计算得到的承载力值与试验和有限元结果最为接近。     

高强冷弯薄壁型钢卷边槽形截面轴压构件畸变屈曲性能研究

建立了考虑材料和几何双重非线性的550MPa高强冷弯薄壁型钢卷边槽形截面轴压构件畸变屈曲性能分析的有限元模型,并通过对两种厚度高强冷弯薄壁型钢轴压构件畸变屈曲试验已有结果的分析比较验证了其有效性;采用该模型进一步分析了厚度、长度、初始缺陷模式及幅值等参数对畸变屈曲轴压构件承载力的影响,并对轴压构件畸变屈曲发生机理进行了探讨。结果表明：厚度、长度和初始缺陷模式是影响畸变屈曲轴压构件承载力的主要因素,且卷边面内屈曲是槽形截面轴压构件发生畸变屈曲的主要原因。通过理论计算与试验结果的对比分析,表明可以采用建议方法计算此类复杂截面轴压构件的畸变屈曲承载力。     

Buckling and postbuckling of imperfect cylindrical shells under external pressure

A comprehensive nonlinear finite element elastic stability analysis was performed with the aim of explaining the effect of a deep single longitudinal initial dent on the load-carrying behaviour of an externally-pressurized cylindrical shell. The numerical results are compared with available test results and agree well, at least qualitatively. Imperfection sensitivity studies were carried out comparing the effect of the single dent with the effect of evenly distributed periodic initial imperfections. Imperfection sensitivity tends to vanish for increasing amplitudes of the idealized case of a single dent.     

Coupling Effect of Nodal Deviation and Member Imperfection on Load-Carrying Capacity of Single-Layer Reticulated Shell

Single-layer reticulated shell is sensitive to imperfections. To clarify the effect of member imperfection, nodal deviation and their couplings on load-carrying capacity of reticulated shell, the equivalent load method (ELM) is developed in the present study to establish single-layer reticulated shell with random member imperfection, and its realization procedures in FEM package are well-elaborated. The main conclusions are summarized as follows: the proposed ELM is of high efficiency to form member imperfection in space structures. For reticulated shell only with member imperfection, the limit load is more or less influenced by member imperfection. With the increase of amplitude of member bow imperfection, limit load gradually decreases. Load-carrying capacity of reticulated shell with larger amplitude of bowed member is more sensitive to bending direction of bowed member than the one with smaller amplitude. Load-carrying capacity of the reticulated shell considered is extremely sensitive to nodal deviation. For reticulated shell with nodal deviation and member imperfection, the effect of member imperfection on load-carrying capacity is closely related to the magnitude of nodal deviation. Load-carrying capacity of shell with smaller nodal deviation is obviously affected by member imperfection, while not sensitive to member imperfection for reticulated shell with larger one. Member imperfection can be neglected when nodal deviation is large enough. Load-carrying capacity of reticulated shell is also influenced by bending angle of bowed member. On the whole, load-carrying capacity of reticulated shell with larger amplitude of member imperfection is more sensitive to bending direction than the reticulated shell with smaller one.

     

厚壁冷弯方矩管和热轧H型钢轴压极限承载力的对比研究

运用ANSYS有限元软件,在综合考虑初始几何缺陷、残余应力、冷弯效应等因素的基础上,分析了厚壁冷弯方、矩钢管和热轧H型钢轴心压杆的极限承载力,并将它们的极限承载力计算结果进行对比,得出相关结论,为轻钢结构框架柱构件截面选型提供了参考.     

三肢钢管格构柱稳定极限承载力研究

用弹塑性大挠度有限元对不同腹杆布置形式的三肢钢管格构柱进行了稳定极限承载力研究,并与规范结果进行了比较,分析了腹杆布置形式及腹杆长细比对极限承载力的影响,为合理设计三肢钢管格构柱提供参考。     

Variance‐based global sensitivity analysis for fuzzy random structural systems

There have been increasing advances in the sophisticated approaches like fuzzy randomness to handle different uncertainties in civil engineering; however, less attention has been paid to the formulation of a sensitivity analysis for fuzzy random structural systems. In this study, the main objective is to present the formulation of fuzzy Sobol sensitivity indices to quantify the influence of fuzzy random structural parameters. Meanwhile, uncertainty in derivation of limit states and acceptance criteria in collapse analysis is addressed briefly and treated using fuzzy model parameters. To show the application of the established sensitivity test, the collapse behavior of a steel moment frame subjected to sudden column removal is evaluated thoroughly. The proposed fuzzy sensitivity indices are determined for the problem and the overall influence of fuzzy acceptance criteria on the collapse assessment is shown using fragility analysis. The results show that the presented fuzzy sensitivity analysis can give detailed insight into the characteristics of fuzzy random systems, and the epistemic uncertainty in derivation of limit states can have significant effects on the reliability‐based collapse analysis. It is worth mentioning that to alleviate high computational demands in fuzzy probabilistic collapse analysis, a neural network metamodel is applied in conjunction with the genetic algorithm which is also of practical value to engineers and researchers.