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.     

猫头塔结构自振周期研究

以目前输电线路中常用的猫头塔为研究对象,采用有限元软件SAP2000为分析工具,对不同塔高、不同塔头宽度、不同根开的猫头塔进行模态分析,根据分析结果得到输电塔线体系中铁塔沿纵向与横向的第1阶自振周期计算公式。     

Structural behaviour of lattice transmission towers subjected to wind load

Hurricane Wilma hit Yucatan Peninsula in 2005, causing substantial damage to local electrical transmission towers. Based on the failure characteristics observed on such towers, an analytical study is performed to reproduce such failures and assess their vulnerability. Two latticed transmission towers are analysed under the action of 14 different wind velocity patterns corresponding to several national and international wind design codes. Displacement-controlled pushover analyses are performed to reproduce impending failure mechanism for considered wind patterns, and associated gradient wind speed is computed. Results illustrate that consistent cyclonic wind speed patterns lead to better estimates of failure mechanism and gradient wind values than traditional non-cyclonic patterns.     

输电铁塔桩-板复合基础上拔承载力特性试验及理论分析

沿江和沿海地区的地质条件多以软弱地基为主,其地基承载力相对较低,不利于输电线路基础设计、施工和运营安全。设计并制作了单板基础、单桩基础和桩-板复合基础的上拔承载力的试验模型,开展三类基础的上拔承载力试验,研究三类试验基础的上拔承载力特性和失效模式。试验结果表明,与单板基础和单桩基础相比,桩-板复合基础的上拔荷载-位移曲线呈缓慢上升形式,桩-板复合基础具有较高的承载力和抵抗变形能力,其受力特性接近于单桩基础。此外,由复合基础的模拟分析可知,上拔加载后期板和桩的承载比例约各50%,桩和板具有较好的协同受力性能。结合现有复合桩基的相关理论,提出了基于单桩抗拔承载力的桩-板复合基础设计方法,为输电线路的复合基础设计提供参考。     

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.     

输电铁塔结构设计的发展与研究现状

结合当前国内外的研究状况,回顾了输电铁塔结构设计分析理论的基本情况,阐述了目前铁塔结构的分析理论及设计方法的研究现状,分析了铁塔构造设计计算软件的现状和存在的问题,最后提出了今后值得研究的问题。     

多回路输电塔风振系数研究

多回路输电塔由于质量与面积沿杆塔高度存在突变,按照规范公式求解风振系数将偏于危险。基于杆塔的集中质量模型,对输电塔风振系数的频域分析方法进行了探讨,推导了考虑背景响应的等效静力风荷载计算公式。通过比较阐明了多回路输电塔风振系数沿塔高的变化特点,分析了背景响应分量对风振系数的影响,并建议在进行多回路输电塔的抗风设计时,采用杆塔多阶振型的CQC组合计算等效风荷载。     

沿海区段输电线路铁塔及基础防腐分析

结合工程实例，对沿海区段输电线路铁塔及基础的腐蚀原因进行了分析，结合国内现有防腐技术分类提出了铁塔及基础防腐处理的几种办法，以供类似工程参考借鉴。     

输电塔角钢杆件阻力系数及背风面遮挡效应研究

统计分析104个塔身和20个横担节段的几何参数,确定输电铁塔杆件所在平面与铅垂面夹角β的分布范围为0°～15°。基于三维空间风向角下输电铁塔角钢杆件足尺模型风洞试验,获得夹角β=0°～15°(间隔1°)、风向角θ=0°～180°时(间隔5°)的热轧、冷弯单角钢及双拼角钢的风荷载阻力系数,建立输电铁塔角钢风荷载阻力系数数据库及考虑夹角β的修正方法。输电铁塔杆件间距比B/b的分布为7～70,通过风洞试验和CFD仿真分析,确定输电铁塔角钢杆件间距比B/b对背风面杆件风荷载遮挡效应的影响,提出单角钢、双拼角钢背风面风荷载降低系数ηm与间距比B/b的关系曲线。研究结果以期为基于单根杆件阻力系数的输电铁塔及其他高耸桁架结构的风荷载精细化计算提供参考和依据。     

输电塔钢管-插板连接节点板承载力研究

输电工程中输电塔架节点通常采用节点板连接的方式,其受力情况非常复杂。通过对5组输电塔架典型节点的足尺试验和有限元分析,考察节点板的受力性能和破坏模式,并利用多参数有限元分析不同破坏模式下宽厚比、无支长度以及节点板构造等主要参数对节点板承载力的影响,提出有(无)加强环板的节点板承载力计算方法,并与试验和有限元所得的结果进行比较。结果表明:基于插板连接的节点板建议计算方法合理有效,具有较好的适用性。     

Structural assessment of current steel design models for transmission and telecommunication towers

The usual methods of structural analysis involved in the design of steel telecommunication and transmission towers tend to assume a simple truss behaviour where all the steel element connections are considered hinged. Despite this fact, the most commonly used tower geometries possess structural mechanisms that could compromise the assumed structural behaviour. A possible explanation for the structure stability is related to the actual behaviour being close to semi-rigid connections instead of the assumed hinged connections. This paper proposes an alternative structural analysis modelling strategy for the steel tower design considering all the actual structural forces and moments combining three-dimensional beam and truss finite elements. Comparisons of the two above-mentioned design methods with a third method based on the use of spatial beam finite elements to model the main structure and the bracing system on two actually built steel telecommunication towers (40 and 75 m high steel towers) are described. The comparison is based on an extensive parametric study of the tower geometry in order to access the structural tower ultimate and serviceability limit states.     

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。     

有限元模型对输电塔架结构动力特性分析的影响

本文较全面地分析讨论了节点构造和节点刚度等因素对塔架动力性能的影响及在有限元建模中的处理方法。本文选取一个 5 0 0kV输电线路中常见的猫头型塔架 ,建立了 1个空间桁架模型、1个空间刚架模型和 3个由杆单元和梁单元组成的混合有限元模型 ,对输电塔架结构进行了模态分析 ,系统研究讨论了不同有限元模型、连接偏心对模态分析结果的影响 ,指出了各种有限元模型在塔架动力特性分析中的特点和适用范围 ,对输电塔架结构的动力特性研究具有实用意义。     

钢筋混凝土中间层边节点模型化方法研究

钢筋混凝土梁柱节点区非弹性变形包括梁纵筋黏结滑移和节点核心区剪切变形,对钢筋混凝土梁柱组合体的受力性能影响较大,在有限元模型中合理地考虑节点区的这两种非弹性变形是数值计算的难点和关键。利用OpenSees结构分析平台中的梁柱节点单元,根据中间层边节点的受力特点和试验结果,通过对钢筋滑移分量和剪切块分量的计算模型、参数计算方法进行改进,提出了修正梁柱节点单元模型,并以多组试验结果为依据,校核了修正梁柱节点单元模型计算的准确性和适用性。分析结果表明：修正梁柱节点单元模型能有效模拟中间层边节点的整体受力性能和局部非弹性变形特性;改进的梁纵筋滑移模型能更合理地模拟贯穿节点梁纵筋的受力特性;改进的剪切块计算模型能准确模拟节点核心区的剪应力大小,以及两个不同加载方向的节点剪应力差异。     

Failure analysis of a transmission tower subjected to combined wind and rainfall excitations

Many transmission towers have collapsed during severe gales and thunderstorms, and these failures have traditionally been attributed simply to wind loading. This study attempts to reveal the full failure mechanism of tower structures under strong wind excitation considering the rainfall effect. First, the calculation of rain load for a tower‐line system is provided. Then, an uncertainty analytical method for estimating the strength capacity and predicting the failure pattern of transmission towers induced by wind and rain loads is presented. Next, a real collapsed transmission line is considered to establish the finite element model, followed by the determination of the most vulnerable tower, which is then used to perform the uncertainty analysis. The results illustrate that the collapse basic wind speed considering the rainfall effect is smaller than the pure wind condition. In addition, the failure probability of the tower body is the largest, which is consistent with the deterministic method, whereas the most vulnerable tower began to fail from the tower leg in reality, indicating that the initial broken position of the transmission tower may not occur in the location with the largest probability and that the deterministic method is invalid in some cases. Finally, the influence of the wind attack angle and bundle number of transmission conductor is investigated. The most unfavorable wind attack angle is 90°, and the rainfall effect becomes increasingly significant with increases in the bundle number; this relationship should be given particular attention.     

特高压输电钢管塔主材次应力分析

为了研究特高压输电钢管塔的主材次应力问题,对 1 000 kV特高压输电钢管塔SZ2U进行真型试验,实测主材次应力;通过有限元分析, 得出主材次应力的分布规律及影响因素;分别建立考虑有无节点板刚度的有限元梁杆单元模型,并与实测结果进行比较;对塔脚节点建立精细化有限元模型,考察次弯矩作用下节点的受力性能和破坏模式。研究结果表明：对SZ2U塔次应力影响最大的位置在塔脚主材处,实测最大次应力比（弯曲应力占轴力应力的百分比）达到45%;采用考虑节点板刚度的计算模型与实测结果吻合较好;次应力的影响不仅与主材长细比有关,还与主材和斜材的角度有关;塔脚节点在次弯矩作用下的破坏模式为主管受压一侧环形加强板上部管壁屈曲破坏。     

高压输电塔地震作用下的连续性倒塌分析

利用大型有限元分析软件ABAQUS和开发的子程序,分别对某输电塔进行了单向地震作用和三向地震作用下的连续性倒塌分析,研究了输电塔的薄弱部位和连续性倒塌全过程。分析结果表明,采用编制的子程序可以确定输电塔的薄弱部位,可以清晰地得到输电塔在地震作用下的连续性倒塌全过程,输电塔在三向输入作用下更容易发生倒塌。     

钢管塔新型内外法兰节点试验研究与有限元分析

提出了一种适用于钢管塔的新型内外法兰节点连接形式,阐述了该法兰的特点,指出其内外圈螺栓拉力的确定是该法兰节点设计的关键。为考察这种内外法兰节点的受力性能、破坏模式及内外圈螺栓的拉力,以榕江大跨越塔为背景,进行了2个内外塔脚法兰节点的大尺寸缩尺模型静力试验。同时,对试验模型进行了有限元非线性数值分析。试验与有限元分析结果表明:这种法兰节点受力合理,可用于实际工程;榕江大跨越塔新型内外塔脚法兰节点是安全可靠的。最后,结合试验与有限元参数分析结果,建议实际工程中在进行内外法兰节点设计时,当内外圈螺栓规格相同时,其外内圈拉力比值可统一取1.0;当内外圈螺栓规格不同时,建议外内圈螺栓直径相差不宜超过2个级别,其拉力比值可取为1.1。     

Vortex-induced vibration tests of circular cylinders connected with typical joints in transmission towers

Vortex-induced vibration (VIV) tests on full-scale cylinders are undertaken to study the vibration performance of steel tubes connected with typical joints in transmission towers, including [-shaped gusset plate connection, U-shaped gusset plate connection, cross-gusset connection and the flange. Due to the asymmetric flexural stiffness for the cross section of the [-shaped or U-shaped gusset plate, VIV is only generated about the minor axis. The paper presents the relationship between the slenderness ratio and the occurrence wind speed of VIV about the minor axis. Moreover, it has been shown that VIV can occur not only in laminar flows, but also in turbulent flows, and the amplitude decreases as the turbulence intensity rises. The amplitude is affected by the wind attack angle, and drops as the wind attack angle decreases. It is revealed that for the cylinders connected with [-shaped gusset plates with the slenderness ratio of 100∼200, the value of Strouhal number ranges from 0.20 to 0.21and the reduced velocity from 5.0 to 5.5.     

Stability and seismic analyses of leaning towers: the case of the minaret in Jam

The leaning Minaret of Jam, one of the tallest in the world, was declared as the Afghanistan's first World Heritage Site by UNESCO in 2002. The global stability analysis of the tower against soil collapse is first evaluated in the present configuration, in the hypothesis of increasing bending moment at the base section, assuming elastic‐perfect plastic behavior for the soil. Then, a finite element model is set up, which is used for the modal analysis and then for the seismic push‐over analysis, based on both single and multi‐modal approaches. Copyright © 2014 John Wiley & Sons, Ltd.