基于多波屈曲单元的输电铁塔结构抗风极限荷载分析

为了有效预测输电铁塔结构抗风极限荷载,提出了一种多波屈曲单元来模拟辅助构件支撑的受力构件,按截面边缘屈服准则确定了多波屈曲单元的受压极限应力;对某110 kV鼓型直线输电铁塔结构抗风极限荷载进行了数值研究。研究结果表明:所提出的多波屈曲单元可有效考虑辅助构件的支撑作用和受力构件的初弯曲影响,结构建模时可不考虑辅助单元;该方法简单易行,可有效预测大型输电铁塔结构抗风极限荷载。     

风力涡轮钢结构塔楼的优化设计

为了使用于安装风力涡轮机的钢结构塔楼设计成本最小化,该塔楼结构形式为一个微锥形的焊接环肋壳体钢结构。用3个柱形壳单元组件来模拟45m高的钢壳,每个单元都有15m高,并且都有恒定的平均直径和厚度。根据欧洲规范1第2～第4章(Eurocode1,Part2～4)计算风荷载。设计中考虑壳体屈曲和环肋的局部屈曲。环肋非常必要,它可以阻止塔楼变成椭圆形。为计算生产成本,要考虑将这些钢壳加工为接近圆柱形状的加工成本和组装焊接部件的成本。成本最小化包括材料和生产成本最小化。最适宜的壳厚度、环肋的个数和直径采用Rosenbrock法直接计算。结果表明,采用环肋的数量越少,成本就越低。这个方法可以被用来预测微锥形塔楼的最小设计成本,满足细长型结构的需要,这种结构以动力荷载导致的弯曲为结构的主要荷载。     

基于完全气弹模型风洞试验输电塔风荷载识别

按照基本缩尺律,设计、制作了输电塔完全气弹模型,并通过大气边界层风洞试验,测试了多种风速、风向条件下输电塔的位移与加速度响应。通过加速度响应功率谱识别出结构的固有频率,并采用Hilbert-Huang变换结合随机减量法识别出包含结构阻尼和气动阻尼的结构总阻尼。利用虚拟激励法建立了由测点位移响应来识别结构顺风向、横风向风荷载的方法。由识别出的风荷载谱曲线,利用非线性最小二乘法拟合得到输电塔顺风向、横风向风荷载经验公式。研究结果表明：风洞试验设计、制作的输电塔气弹模型,测试得到的模型第1阶自振频率与有限元计算结果吻合较好;横风向荷载谱形态与顺风向的相比有较大的区别,其能量分布在一个更宽的频带上,其峰值频率是顺风向的3～4倍。     

输电塔塔身斜材埃菲尔效应研究

本文结合某500kV双回路直线塔,分别利用英国BS8100规范、我国高耸结构设计规范和电力行业杆塔结构设计规范的方法对其塔身斜材埃菲尔效应进行计算和对比分析。同时,以三个实际工程为算例,建立了塔线耦联体系有限元模型,计算得到了塔架各杆件在模拟风场中的内力时程,得出了塔身斜材埃菲尔效应的分布规律和特点。,以及对于塔架的塔身斜材,采用折减系数法设计计算是偏于安全的结论。同时,为简化铁塔计算,建议在工程设计中塔身斜材内力一般可取主材内力的3%。     

±800kV特高压T型长横担输电塔风振特性研究

±800kV特高压直流塔是T型长横担输电塔型,属于风敏感结构,风与结构的相互作用十分复杂,风荷载常常是设计的主要控制荷载。本文以某一±800kV直流塔为工程背景,建立了详细的有限元计算模型,获得了结构的自振动力特性。在考虑节点风荷载空间相关性的基础上,利用Kaimal谱对结构的风荷载进行了准确的数值模拟。结合动力时程积分法,计算得到了结构的风致振动响应时程。研究了结构位移平均值、位移均方根值和加速度均方根值的分布特点,同时分析了结构各层的风振系数分布特点,并与我国规范进行了对比。通过研究,揭示了直流塔的风致振动特性,结果可作为直流塔结构抗风设计的参考。     

输电塔线体系的风(雨)致振动响应与稳定性研究

根据输电塔线体系在风(雨)激励下破坏的实际状况,建立了"三塔两跨"有限元分析模型,其中,输电塔采用三自由度梁单元,导(地)线采用索单元;提出雨荷载的计算方法以及与风湍流共同作用于输电塔线体系的荷载组合原则;分析输电塔、导(地)线和结构体系的结构动力特性及其相互关系;采用数值模拟方法,建立设计与灾害荷载的不同工况组合,分别在时域和频域内对输电塔的动力响应规律进行分析;采用结构主要组件(如主立柱杆件和输电线)强度分析的方法,分析结构强度的变化和灾害发生的可能性原因。研究表明:输电塔线体系的运动耦合性对结构动力特性有不容忽视的影响;降雨对输电塔线体系的响应具有明显影响,且有与风湍流同时作用的激励特征;结构体系发生连续倒塔破坏的原因是风雨共同作用,结构局部动态受压失稳造成的。     

Wind-loaded reinforced-concrete cooling towers: buckling or ultimate load?

Wind loadings govern the design of most cooling towers. Until now, proof of suffiecient safety against buckling under wind load has been a major concern for the designers of such shells.In this paper it is demonstrated that a typical cooling tower made of reinforced concrete would not buckle—at least not in the classical sense of the word. Failure would rather be initiated by rapid propagation of cracks in tensile zones followed by temporary stiffening and, finally, by yielding of the reinforcement.The theoretical part of this paper is restricted to a presentation of the constitutive model, discussion of the equation for incremental-iterative ultimate-load analysis and of the condition for instability. The numerical part contains a detailed study of a built hyperbolic cooling tower.It is shown that: (a), buckling loads resulting from linear and geometrically nonlinear prebuckling analyses are considerably larger than the ultimate load; and (b), results based on a certain form of ‘equivalent axisymmetric pressure’ are on the unsafe side of corresponding results from the ‘actual’ wind load. It is also demonstrated that the ‘crack load’, representing a lower bound to the ultimate load, can be estimated by means of a linear-elastic nonaxisymmetric analysis of the cooling tower.     

风荷载作用下某钢管火炬塔架的有限元分析

对一个高168.3m的火炬塔架进行了设计计算分析.该火炬塔架采用横截面为正三角形的钢管结构方案,构件连接考虑为刚接.建立了该钢管火炬塔架的三维有限元模型,采用通用结构分析程序SAP84对结构的自振特性进行分析,并计算了塔架在台风荷载作用下和地震荷载作用下的结构变形和构件内力.计算结果表明,塔架及排气筒不会出现涡激共振;结构设计中水平顺风向风荷载起主要的控制作用;该火炬塔架的变形、构件内力及稳定性均满足规范要求.     

某羊角型输电塔的风振响应分析

本文首先简述了应用线性滤波法中的自回归模型(AR模型)模拟出给定风速功率谱的风速时程序列,并验证其与目标谱的一致性,再通过规范公式推导脉动风载与风速之间的关系,从而得到作用在各节点的脉动风荷载时程样本。本文以某羊角形输电塔为原型进行了模拟计算分析,用有限元分析软件ANSYS建立了有限元模型,并用MATLAB生成塔架迎风面各节点上的风荷载时程信号作为动力输入。利用ANSYS对结构进行了模态分析,结果显示结构的基本模态为平面振动,但是同时具有扭转模态和局部振动模态;对此输电塔结构进行了平均风作用下的静力分析,同时,基于ANSYS时程分析方法计算了结构在一般风荷载作用下的风振响应。结果表明,在考虑一般风荷载作用的情况下,输电塔在顶部出现最大的位移和加速度响应,而在底部出现最大的轴力响应,但由于本文输电塔结构杆件的变截面设计,最大的应力出现在约1/3高处的杆件上。相对于平均风的作用,结构响应在一般风荷载下呈现出明显的动力放大效应。     

相关屈曲对平面钢桁架柱屈曲性能的影响

利用ANSYS 14.0软件建立平面钢桁架柱模型,采用特征值屈曲分析和非线性分析方法模拟结构的整体屈曲、局部屈曲和相关屈曲（两种屈曲模式相互作用）.发现弦杆长细比对整体屈曲临界力PE和局部屈曲临界力P1的大小起控制作用,当PE＞P1时,屈曲模式的相互作用降低了结构的极限承载力;当PE＜P1时,屈曲模式的相互作用不仅降低了结构的极限承载力,还改变了结构的初始后屈曲性能.     

高层建筑局部构件的风荷载效应

在高层建筑对局部构件进行强度验算时,不应采用整体结构的风荷载计算公式.局部构件自身及其与主体结构连接处的风荷载内力效应,应为主体结构由于风荷载引起的振动,对于局部构件的支座动力输入,另加局部构件的直接风荷载.本文给出与规范相衔接的近似计算方法.     

Simulation of static and kinetic buckling of unstiffened and stiffened cooling tower shells

Natural draught cooling tower shells are loaded mainly by their dead weight and by the wind, which may both cause buckling failure. The present paper compares various numerical procedures to investigate the stability behaviour of cooling tower shells. These are a complete nonlinear analysis, a linear eigenvalue analysis for a stationary non-axisymmetric wind load, and a linear eigenvalue analysis for a wind load, approximated to be axisymmetric. The aim is to evaluate whether a geometrically nonlinear analysis can be replaced by a time-saving classical buckling analysis, probably even for an axisymmetric state of stress. The third procedure, as the most conservative, but a very effective one, will be applied to investigate the mechanical influence of ring stiffners on the buckling behaviour of cooling tower shells. Kinetic instability phenomena will also be examined. The structural improvement resulting from ring stiffeners will be quantified and summarized in design recommendations.     

基于风洞试验的苏通大跨越输电塔风振系数研究

苏通大跨越输电塔的结构形式有别于普通的钢结构杆塔,其塔身下部结构采用钢管混凝土、上部结构采用钢管,质量突变大,主要受风荷载控制,并且塔高超出GB 50009—2012《建筑结构荷载规范》的梯度风高度限制。为此,采用气动弹性模型和刚性模型的边界层风洞试验确定苏通大跨越输电塔的风致响应和气动力,基于试验数据计算不同风向角下的惯性力风振系数、位移风振系数和有效荷载风振系数,并进行对比。并通过有限元分析梯度风高度对惯性力风振系数的影响,同时将有限元分析得到的风振系数分布和加权值与DL/T 5154的风振系数规定作比较。结果表明：上述3种风振系数分布规律并不相同,由其分别确定的等效位移接近于试验值;考虑梯度风高度后,风振系数变小,分布形状影响小;苏通大跨越输电塔的惯性力风振系数加权值小于1.6,且风振系数由下到上不是单调增大。     

考虑脉动风影响的风电塔风致动力响应数值分析与现场监测比较

本文基于"风轮-机舱-塔体"三维仿真模型,进行风电塔在暴风荷载作用下的风致动力响应分析,并基于规范中的风荷载计算方法与动力分析方法对风电塔的应力、位移和内力进行计算分析,同时研究风电塔风轮受不利风向影响时的力学特性变化规律,并对风电塔在常规风荷载作用下的应力和位移进行现场监测比较研究。结果表明,基于规范计算的风电塔的应力、位移及内力要比动力分析的计算值偏小;脉动风时程激励下,风电塔的最大应力值低于结构的最小许用应力值,但结构顶部的水平位移超过结构的位移限值,在风电塔设计中应予以注意。风电塔受不利方向的暴风影响会产生很大的内力,塔底最大剪力和弯矩增大了91%和106%,在风电塔设计过程中应该重点考虑;基于常规风荷载作用下的应力和位移的数值仿真结果与监测结果吻合较好。     

Buckling analysis of a cooling tower shell with measured and theoretically-modelled imperfections

Geometrical imperfections were measured using photogrammetric techniques on an existing reinforced concrete cooling tower shell. The imperfections, related to the radii of such a real shell, were used as input data to create a real shape of the cooling tower. Numerical analysis was carried out for three models: (P) perfect shell of revolution, (M) shell with measured imperfections, (T) shell with a theoretical imperfection corresponding to the primary buckling mode under dead load. The buckling analysis was related to the linearized eigenvalue problem of elastic shells. The shell midsurface was approximated by eight-node quadrilateral isoparametric finite elements. Computations were carried out using the ANKA computer code. Critical values of the load parameter enable confirmation of a partial correlation between existing imperfections and buckling modes under dead load. The most disadvantageous direction of the wind load application on the real shell was found, in order to evaluate the decrease in the load-carrying capacity of the cooling tower shell against buckling. Theoretically modelled imperfections give rather unrealistic values of buckling loads of the real shell.     

风荷载作用下输电塔极限承载力和失效模式计算模型

针对现有输电塔极限承载力和失效模式研究未考虑计算模型影响的问题,剖析了空间桁架、空间刚架和空间梁桁组合3种常用计算模型的力学基础和模拟方法;以110 kV鼓形直线输电铁塔为例,对比研究了0°,45°,60°,90°四种风向工况下3种计算模型的弹性响应,同时对比分析了最不利工况下各计算模型极限承载力和失效模式的计算结果,揭示了不同计算模型对结构极限承载力和失效模式的影响规律。结果表明:空间刚架和空间梁桁组合模型较桁架模型能给出偏安全的弹性响应结果;该类输电塔最不利风荷载工况下的极限活荷载乘子约为2.00,空间梁桁组合模型能反映铁塔结构的延性破坏性质,给出偏安全的极限承载力计算结果;该类输电塔高承载构件主要集中在塔腿主材,空间刚架和空间梁桁组合模型都能较准确识别出高承载构件;建议采用空间梁桁组合模型进行输电塔极限承载力和失效模式的分析。     

Numerical analysis and full‐scale experiment on K‐joint deformations in the crank arms of lattice transmission towers

After completion of the construction process including wire stringing of 1,000 kV ultrahigh voltage (UHV) cat‐head electric transmission towers, the outward horizontal K‐joint deformation of one side crank arm may usually exceed 70 mm. Joint slip effects were ignored in the initial structural design of transmission towers, which induced that the calculated K‐joint displacements are much lower and the real deformation cannot meet with the requirement of the acceptant code. First, the shortcomings of the traditional unit load method used to calculate the displacements of transmission towers connected by bolt joints were analyzed. Second, a coefficient for describing the axial force state of bolted joints was proposed. The connection numbers for different types of members in the crank arms of a UHV cat‐head transmission tower were determined. The traditional unit load method was enhanced by importing the force state coefficient and specifying the detailed connection numbers. The K‐joint displacements calculated by the enhanced formula were compared with the experimental results by full‐scale tower experiment. It shows that the enhanced unit load method is suitable for calculating K‐joint deformations in the crank arms of UHV cat‐head transmission towers. Lastly, contribution weight coefficients of different members for K‐joint displacements of the UHV cat‐head transmission tower were calculated by the enhanced unit load method. For bolt joints connected with the tower members with high contribution weight coefficients, the manufacturing accuracy of bolt holes should be improved, and the bolt clearance should be decreased, which can significantly reduce the K‐joint deformation of UHV cat‐head transmission towers.     

Experimental and computational simulation for wind effects on the Zhoushan transmission towers

Long-span transmission tower and conductor line systems become important infrastructures in modern societies. The analysis of wind-induced dynamic responses of transmission towers is an essential task in the design of spatial lattice tower structures. Wind effects on the world's tallest transmission tower are presented in this paper. The tower with a total height of 370 metres, part of the Zhoushan long-span transmission project, enables high voltage conductor lines to span as long as 2750 metres over the typhoon-prone sea strait. A multi-DOF aeroelastic model test with and without conductor lines was carried out to investigate the dynamic performances of Zhoushan tower during typhoon events. Using the response measurement results in the wind tunnel, the inertial force based gust loading factors (GLFs) are applied to represent dynamic wind load effects on the tower for structural design purposes. Time domain computational simulation approach is also employed to predict dynamic responses of the transmission tower and the displacement based gust response factors (GRFs). The fair comparison of GLFs or GRFs are made between the results of the experimental approach and the computational simulation approach, which is an effective alternative way for quickly assessing dynamic wind load effects on high-rise and complex tower structures.     

输电塔塔头平均风荷载的CFD模拟

为了得到典型输电塔塔头的风荷载系数,为抗风分析提供依据,采用CFD方法对其不同风向角时的平均风荷栽进行模拟,并进行对比分析.结果表明:风向角为0°时,输电塔塔头、横担等的顺风向风荷载系数CY与方形格构塔身的顺风向风荷栽系数CY基本相等;风向角为90°时,上游部分风荷载Cx明显比下游部分大,有显著的遮挡效应;当风向与线路...     

考虑土壤-结构共同作用影响的双曲冷却塔可靠度

本文建立了对风荷载、自重和温度荷载组合作用下的双曲冷却塔结构进行可靠度分析的半随机过程模型,研究了考虑土壤-结构共同作用、塔底用连续弹性支承和离散支柱所造成的可靠度评估差异.运用等效静态的方法,考虑湍流动态风荷载响应.将动态随机过程模型转化为静态随机变量模型.TR荷载组合规则被用来考虑各荷载效应之间的关系.以广东茂名90米双曲冷却塔作为算例,数值结果表明不考虑共同作用的设计是保守的.