规则钢筋混凝土框架中考虑双向随机偏心距的柱承载力抗震可靠度分析

地震作用下RC框架柱大多处于双偏压受力状态。为考虑双向偏心距随机特性的影响,采用Monte Carlo方法分析了RC框架柱的承载力抗震可靠度。基于已有的试验数据,分析了GB 50010—2010《混凝土结构设计规范》中双偏压构件抗力计算模式的不确定性及其对极限状态方程的影响。以按规范设计的典型RC框架角柱、边柱和中柱为例,结合已有荷载和抗力变量的统计概率参数,通过对荷载效应以及抗力进行抽样,分别按单偏压和双偏压情形计算了RC柱的承载力抗震可靠度。结果表明：对于规则框架结构,双偏压情形下使柱具有较低可靠度的地震作用方向(沿结构主轴)与单偏压情形并不相同;考虑双向随机偏心距后,RC柱的承载力抗震可靠度会较单向随机偏心距下的可靠度有较大程度的降低。     

长期荷载作用下带脱空缺陷钢管混凝土柱的受力性能研究

为研究长期荷载作用对带脱空缺陷钢管混凝土柱受力性能的影响,以脱空类型、脱空率和长期荷载比为主要参数,对长期荷载作用下带脱空缺陷钢管混凝土短柱的变形特性和承载力进行了试验研究。试验结果表明：在长期荷载作用下,与普通无脱空缺陷钢管混凝土柱类似,脱空缺陷钢管混凝土柱徐变系数终值的上限值为0.9;长期荷载比大的脱空缺陷钢管混凝土柱较长期荷载比小的脱空缺陷钢管混凝土柱的承载力略大。采用有限元分析软件ABAQUS,对考虑长期荷载作用影响时脱空构件的受力性能进行分析,有限元计算结果和试验结果吻合良好。利用验证过的有限元模型,系统地分析了长细比、含钢率、钢管屈服强度、混凝土强度、长期荷载比、脱空率和荷载偏心率等参数对长期荷载作用下带脱空缺陷钢管混凝土柱的承载力影响规律。结果表明,混凝土脱空缺陷对考虑长期荷载作用的承载力影响系数的不利影响小于1.5%;现有的考虑长期荷载影响的普通钢管混凝土柱的设计方法可用于预测带脱空缺陷钢管混凝土柱的承载力。     

钢框架高等分析中初始几何缺陷的考虑方法

结构整体和构件的初始几何缺陷是结构产生非线性行为的影响因素之一,在目前的高等分析中常按最不利的缺陷分布来考虑它们的影响。采用蒙特卡罗法可以考虑初始几何缺陷的随机遇合问题,能更加合理地确定初始缺陷的分布规律。通过统计分析得到柱顶侧移和梁跨中挠度的概率密度函数,可由此确定框架可能的最大变形。某一六层单跨框架的计算结果表明:当按缺陷的最不利分布来施加不同的初始几何缺陷时,对框架的极限承载力影响不大,但对框架的侧向变形影响较大:初始几何缺陷越大,框架的最终变形也越大。但按蒙特卡罗法考虑不同的初始缺陷时,与无缺陷框架相比,结构变形增加有限。算例还表明,当框架按高等分析的极限承载力设计时,相应标准荷载作用下的变形不能满足正常使用要求,因此,设计常受正常使用极限状态控制。     

考虑灌浆缺陷的装配式混凝土柱抗震性能数值模拟

使用弹簧单元和考虑缺陷的钢筋灌浆料粘结滑移模型,建立了考虑缺陷影响的装配式混凝土柱的有限元模型。为了证明该数值模型的有效性,将模拟结果与试验结果进行了验证,分析了所用方法的有效性和不足。基于所建模型,针对试件的承载力与延性,分析了循环荷载作用下灌浆缺陷对装配式混凝土柱的性能影响。结果表明:数值模拟方法能较好地模拟灌浆缺陷对装配式混凝土柱的性能影响。单调荷载作用下,在弹性阶段,灌浆缺陷对装配式混凝土柱的承载力、刚度和延性等影响不大;在塑性阶段,灌浆缺陷会导致装配式混凝土柱的承载力下降,延性降低。循环荷载作用下,在弹性阶段,灌浆缺陷对装配式混凝土柱的承载力、刚度和延性影响不大;在塑性阶段,灌浆缺陷导致装配式混凝土柱的承载力下降,刚度退化程度更剧烈,延性降低。     

框架中有摇摆柱时框架柱的稳定系数

本文研究了对摇摆柱提供支持的框架柱的稳定性。结果表明，存在摇摆柱的情况下，框架柱的稳定系数，除了采用放大了的长细比确定外，还要适当降低柱子曲线。通过有限元分析对比，本文建议了一个修正的缺陷因子，在现行压杆稳定系数b曲线的计算公式中应用。本文考察了带摇摆柱框架的总的承载力。结果表明，虽然摇摆柱的侧向稳定承载力是由框架柱提供的，但是在框架柱的长细比小时，总的承载力远远超出框架柱本身的稳定极限承载力。这说明，摇摆柱的承载力是由框架柱的抗侧刚度提供的，柱子长细比小的框架柱的抗侧刚度较大，在满足本身的稳定承载力要求之后，只要稍微增大框架柱的截面，框架柱就能够获得足够的刚度为摇摆柱提供承载力。     

混凝土疏松缺陷对框架柱抗震性能影响研究

针对工程施工中框架柱较常出现的混凝土疏松质量缺陷问题,使用ANSYS软件建立了20种带有不同大小、位置疏松混凝土缺陷的框架柱计算模型,并对其进行了模拟低周反复加载,分析了混凝土疏松缺陷对框架柱滞回曲线、骨架曲线、位移延性系数、塑性滞回耗能以及刚度退化等抗震性能指标的影响。结果表明,混凝土疏松质量缺陷的存在会降低框架柱的滞回耗能能力及延性变形能力,减小框架柱的极限承载力和极限位移,加剧框架柱的刚度退化,改变框架柱在水平地震作用下的破坏形式,给框架柱的抗震带来较为不利的影响。工程施工中要严控施工质量,降低严重施工缺陷出现的概率及影响程度。     

重庆大剧院细长框架柱承载力非线性分析

采用基于柔度法的纤维模型梁柱单元有限元分析程序，考虑材料非线性和几何非线性，以目标柱周边构件组成的局部框架整体作为分析对象进行非线性分析，研究偶然偏心、基础嵌固条件等因素对重庆大剧院钢筋混凝土细长框架柱承载力的影响。结果表明，偶然偏心是影响极限承载力的重要因素，另外，基础嵌固也在一定程度上影响极限承载力，适当加强配筋可以提高柱子的极限承载力，弥补柱底在基础内非完全固定嵌固对极限承载力的削弱。     

新旧建筑抗震设计规范关于“强柱弱梁”的对比和分析

从框架柱弯矩调整系数、抗震构造措施等方面对我国新旧建筑抗震设计规范(GB 50011-2010和GB 50011-2001)关于"强柱弱梁"上规定的差异进行了比较分析,详细地分析了影响"强柱弱梁"实现的主要因素。采用新旧两个抗震设计规范分别对抗震等级为一、二、三级的3个钢筋混凝土现浇楼板框架结构进行了计算分析,分别计算新旧两个规范下,考虑现浇楼板及其钢筋对框架梁抗弯承载力的贡献时节点处柱梁端实际抗弯承载力比,并对其进行了比较分析。     

整体倾斜对钢筋混凝土框架结构受力性能的影响分析

基础不均匀沉降引起的结构整体倾斜会对钢筋混凝土框架结构受力性能产生不利影响。在分析现有钢筋混凝土结构重力二阶效应计算分析方法的基础上,提出了采用等效侧向荷载法分析整体倾斜引起的框架结构内力。采用反弯点法分析了整体倾斜对钢筋混凝土框架柱、梁承载力的影响规律和影响程度,并建立了影响系数的近似计算公式。分析表明,由于受不同因素影响,整体倾斜率相同时的框架梁、柱承载力影响系数变化范围均很大;典型代表性框架梁的承载力比框架柱更容易受到整体倾斜的影响。整体倾斜对钢筋混凝土框架梁、柱承载力的影响不容忽视,应在既有结构可靠性鉴定中予以重视。     

暗柱增强Z形柱框架中节点延性及承载力分析

文章基于Z形异形柱框架节点抗震性能试验,采用Abaqus对Z形节点进行低周往复荷载作用下的分析。通过对节点分析,得到该节点的梁端荷载,梁端位移特征值。之后对Z形柱暗柱增强,并考虑暗柱尺寸对承载力和延性的影响进行分析。结果表明:利用Abaqus对Z形节点的分析结果与试验结果符合良好,暗柱增强后对承载力均有提升作用,而不同尺寸暗柱对延性影响有利有弊。暗柱增强在一定程度上解决异形柱节点承载力,延性较矩形节点低的问题。     

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.     

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 assessment of steel members under compression

The objective of the paper is to analyse the influence of initial imperfections on the behaviour of a steel member under compression. The influence of the variability of initial imperfections on the variability of the load-carrying capacity studied has been calculated by sensitivity analysis. The advantages of Sobol’s sensitivity analysis and the most important properties of Sobol’s sensitivity indices are described. The Sobol’s first order sensitivity indices are evaluated in dependence on the nondimensional slenderness. The Sobol’s sensitivity indices are supplemented with a lucid elaboration based on the Monte Carlo method. Material and geometrical characteristics of a steel member IPE 220 were considered to be random quantities the histograms of which were obtained from experiments. Imperfections that have a dominant influence on the load-carrying capacity are identified.     

柱脚刚接与铰接柱列支撑体系受力性能对比研究

为研究柱脚刚接与柱脚铰接柱列支撑体系的不同受力性能,采用蒙特卡罗方法,考虑柱子和水平撑杆初始几何缺陷的随机遇合,应用有限元程序ANSYS对柱脚刚接和柱脚铰接柱列支撑体系进行大量参数仿真分析。研究结果表明:柱脚刚接柱列支撑体系失稳时柱子呈两个半波的变化趋势,柱脚铰接柱列支撑体系失稳时柱子呈三个半波的变化趋势,因而后者的极限承载力和柱中撑杆内力均大于前者,且后者较高的极限承载力更大幅度地增加了柱中撑杆内力;柱子和水平撑杆初始几何缺陷的随机遇合作用导致柱中水平撑杆受压或拉力的随机性,降低了支撑内力,比GB 50017—2003《钢结构设计规范》中柱列支撑设计公式计算的支撑内力小许多。     

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%。     

Numerical Modelling of Thin-Walled Stainless Steel Structural Elements in Case of Fire

In this paper, the structural response of stainless steel thin-walled elements submitted to fire is analysed numerically by means of the geometrically and materially non-linear Finite Element program SAFIR, including imperfections. In order to make these simulations, two main changes in the program were made: (i) the code was changed in order to deal with the stainless steel 2D material constitutive law to be used with shell elements and (ii) the possibility of the program to take into account residual stresses with shell finite elements was introduced. The stainless steel stress–strain relationship at high temperatures was based on the one presented in part 1.2 of Eurocode 3. To model the strain hardening exhibited by the stainless steels, using the shell element formulation, an approximation to the Eurocode 3 constitutive law was needed. Local and global geometrical imperfections were considered in the simulations. The paper shows the influence of the residual stresses on the ultimate load-carrying capacity of thin-walled stainless steel structural elements in case of fire.     

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.     

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。     

单阶柱上下柱弹塑性阶段的相互作用

单阶柱屈曲时上、下柱存在相互作用,对顶端自由和顶端受转动约束的阶形柱进行了弹塑性有限元极限承载力分析,研究了这种相互作用在弹性阶段和弹塑性阶段的变化。结果表明,在弹塑性阶段,这种相互作用总是朝着增加阶形柱的承载力方向变化,说明目前规范采用依据弹性假定确定的计算长度系数,应用于弹塑性工作的柱子是偏于保守的。通过分析弹塑性阶段上、下柱相对刚度的强弱的变化和柱顶弹性约束相对于柱子刚度的变化,对产生这种结果的原因进行了分析。     

柱顶受轴力的柱列支撑受力分析

采用蒙特卡罗方法,考虑柱子初始缺陷和撑杆初始缺陷的随机遇合问题,应用有限元程序ANSYS对柱顶受轴力的柱列支撑体系进行了大量的仿真分析,得到了柱列纵向支撑体系的两种失稳模式;通过概率统计得到柱中水平撑杆所受内力的双正态概率密度函数,据此确定了可用于实际工程设计的支撑力的大小。结果表明:当柱顶轴力相等时,采用《钢结构设计规范》(GB 50017—2003)中柱列支撑设计公式计算支撑力偏大;当柱顶轴力不等时,采用规范公式计算支撑力将更保守;柱子初始缺陷和撑杆初始缺陷的随机遇合作用导致柱中水平撑杆受压力或拉力的随机性,降低了支撑力。