【作者】 王朋；

【导师】 陈海波；

【作者基本信息】 中国科学技术大学 ， 固体力学， 2014， 博士

【摘要】 输电线路是现代社会一项重要的生命线工程,输电塔是输电线路的基本组成单元之一,因此精确预测输电塔的静动态特性,对输电塔的设计及安全评估起到非常重要的作用。在输电线路中,等边角钢由于其便于连接的优点被广泛应用于格构式输电塔中。其中相当一部分等边角钢通过单面螺栓连接,因此载荷传递时角钢承受偏心载荷。同时在输电塔设计中,为了现场安装方便螺孔直径一般比螺栓直径大1.5mm-2mm,而螺栓连接数量多、螺栓直径小、连接杆件薄(角钢或扁钢)、夹持力低、镀锌金属表面摩擦系数低等因素,使螺栓连接在较低载荷作用下即发生滑移现象。一方面,在相同沉降下,传统的结构分析计算得到的杆件轴力远大于试验测量值,甚至出现计算显示已经破坏的输电塔,现实中仍在正常运行着。另一方面,在相同载荷下,计算得到的结构变形量和结构极限沉降量远远小于试验测量值。经过多年研究已明确,产生这些偏差的主要原因是螺栓滑移和连接偏心,但是现有结构设计分析软件大多未对它们进行有效处理。因此,在输电塔的设计与安全评估时,准确建立输电塔结构中螺栓连接结构的模型就变得非常重要。本文结合研究组承担的“螺栓滑移对承受非均匀沉降输电塔的安全性影响研究”项目,针对输电塔中涉及的螺栓扭矩系数、螺栓滑移机理、输电塔精确分析模型和采动区输电塔安全评估等若干力学问题展开研究,为采动区基础非均匀沉降输电塔的设计与安全评估提供重要参考。论文的主要内容包括：1.输电塔镀锌螺栓扭矩系数的试验研究。通过试验测试了螺栓强度等级、有无垫圈和有无润滑对螺栓连接副扭矩系数的影响,探讨了扭矩系数的控制、调整,以及螺栓连接中要注意的问题,为本研究中螺栓连接的参数控制提供依据,也为设计和施工单位提供参考。2.螺栓连接接头滑移特性的测试与模拟。选取室内小塔和真实输电塔中有代表性的螺栓连接接头,通过螺栓滑移性能试验,获得螺栓连接接头的位移-载荷关系曲线,探讨螺栓连接滑移机理,考察螺栓连接的破坏形态。利用有限元软件ANSYS,建立螺栓搭接角钢结构的有限元模型,模拟螺栓滑移过程,并与试验测量结果进行对比,验证所建模型的有效性。3.建立含螺栓滑移和连接偏心的滑移梁模型,研究输电塔的受力变形特性。基于ANSYS开发了滑移梁分析模型,该模型将试验测量得到的螺栓连接位移载荷关系曲线引入到螺栓连接的分析模型中,并且考虑连接偏心的影响。利用该模型分析了结构在基础非均匀沉降时的受力-变形特性,并与传统分析软件模拟结果和试验测量结果进行对比,验证所提模型的有效性进而模拟了基础沉降工况下,结构的极限承载力。4.发明了可平动顶升装置和位移传感器固定装置。结合本文研究所搭建的室内小塔和ZM11输电塔的基础非均匀沉降测试,设计发明了一种用于在线测量螺栓连接滑移的位移传感器固定装置,同时发明了一种可水平低阻力滑动、并数字显示压力的顶升装置。5.研究螺栓滑移和连接偏心对输电塔动态特性的影响。利用所开发的滑移梁模型对输电塔进行模态分析,首次将试验测量得到的螺栓连接的位移载荷关系曲线引入到基础非均匀沉降输电塔的动态分析中,并且考虑了连接偏心的影响。试验测量了四根塔腿固支和三根塔腿固支,第四根塔腿在不同载荷作用下,输电塔在自然激励下的固有频率与振型,与所开发滑移梁模型和传统分析软件模拟结果进行对比分析,进一步验证了所开发滑移梁模型的有效性。6.通过有限元商业软件ANSYS建立滑移梁模型,模拟了输电塔各种非均匀沉降工况下的极限承载力。当输电塔基础发生非均匀沉降时,通过监测塔腿沉降值作为判断输电塔失稳与否的依据。为今后在煤炭开采区或冻土区的输电塔设计及塔腿沉降时的安全评估提供参考。通过本文研究,建立了格构式结构的精确分析模型,完整地分析了螺栓连接对格构式输电塔结构动静态特性的影响,这将为输电塔更高精度模拟分析起推动作用。更多还原

【Abstract】 Electric transmission towers are the vital components of overhead transmission lines which play an important role in the operation of electric systems. Accurate prediction of the behavior of electric transmission towers is very important for design and accurate reliability assessment of the transmission lines and the power grids. The equal-leg angle steel is widely used in lattice transmission towers because of its light weight with L-shaped section making it easy for storage, transmission and fabrication. The angle steel members in lattice structure are normally bolted through only one of their legs and hence the forces transfering in the members are eccentric. The bolts within the holes are oversized1.5-2mm in lattice structure in order to provide an erection tolerence. For overhead transmission line structures, bolt slippage is likely to occur as relatively the bolt diameters are small, the leg plates are thin, the bearing type joints with lower clamping force are used, and the galvanized faying surfaces have a low coefficient of friction. Conventional analysis softwares for such structures assume the bolted connections as rigid ones and ignore the effect of joint eccentricity. Thus, the calculated deformations are smaller than the experimental ones under the same load. In some instances for structure still functioning well with large non-uniform settlement, failure was predicted by structure analysis softwares. The main reasons for the discrepancy between the experimental results and the analytical solutions are bolt slippage and joint eccentricity after years of ressearch, but most of the existing design softwares have not yet treated them properly. Therefore, it is important to model the joint of the lattice transmission tower properly in the design and safety assessment of the tower.This dissertation is a part of research project Effect of Bolted Joint on the Safty of Transmission Tower with Non-uniform Settlement, which is focused on some mechanics issues of the transmission tower, including the bolt torque coefficient, the slippage mechanism of bolted connection, the accurate modeling of the lattice transmission towers, and the safety assessment of transmission tower in the coal-mining area. The proposed algorithm and simulation results would provide good reference for further engineering applications. The main contents are as follows.1. Research on the torque coefficient of bolts in transmission towers. The torque coefficients of bolts in transmission towers are obtained by experimental measurement. The influence factors on the torque coefficient are analyzed, such as the strength grade of bolt connection and whether washer and lubrication are adopted. Furthermore, how to control the torque coefficient well and some other key issues on the bolt connection are discussed, which would provide the basis for the parameters control of the bolted joints in this study and provide good reference for other engineering applications.2. Test measurement and simulation of bolt slippage. For the representative bolted joints in the lattice structures used in this work, the load-displacement curves, the slippage mechanism and the failure modes of the bolted joints were investigated by tests. Using the finite element software ANSYS, the model of overlap angle steel bolt was established to simulate the bolt sliding process, and compared with the measured results.3. A slipping beam model is established to study the effect of bolted joint on the static characteristics of transmission tower with non-uniform settlement. The slipping beam model was developed based on the ANSYS, to which the deformation-load relationships of representative bolted joints were introduced and the load eccentricity in the structure component was also considered. This model was applied to analyze the deformation characteristics of a designed test tower and the calculated results are compared with those obtained from the traditional rigid-bolt treatment and the experimental measurement, verifying the validity of the proposed model. Observations have also been made for the ultimate load-carrying capacity and deformation properties of the test tower with different non-uniform settlements.4. A horizontal movable lifting device and displacement sensor fixing device are invented served for the test of the designed test tower and the ZM11transmission tower with non-uniform settlements, the displacement sensor fixing device has been invented for the slippage measurement of bolted joint online, and a horizontal movable lifting device has also been invented, which has low horizontal sliding resistance and digital pressure display.5. The effect of bolted joint on the dynamic characteristics of transmission tower was studied for the first time. The modal analysis of the transmission tower was performed by using the slipping beam model, into which the deformation-load relationships of the representative bolted joints were introduced and the load eccentricity in the structure components was also considered. The frequencies and mode shapes of transmission tower under natural excitation with four legs clamped and three legs clamped, the fourth leg under different loads were measured by tests, and compared well with the simulation results.6. The ultimate settlement displacements of the transmission tower with different non-uniform settlements were simulated by the slipping beam model, developed based on the ANSYS. When the transmission tower is subject to non-uniform settlements, we can judged the safety situation of the transmission tower through monitoring tower leg’s subsidence, which would provide good reference for future engineering applications.Through the research in this dissertation, an accurate modeling algorithm for the lattice structure has been established. It has the ability to analyze of the bolted connection effect on the static and dynamic characteristics of the lattice transmission tower. This would promote the higher accuracy of simulation for the transmission towers.更多还原