【作者】 李刚；

【导师】 张静； 伍贤智；

【作者基本信息】 合肥工业大学 ， 土木工程（专业学位）， 2024， 硕士

【摘要】 风致振动、温度变化和腐蚀等因素的影响下,承力索结构不断退化,失效会导致这些结构灾难性倒塌,从而造成严重破坏。传统人工目检仅限于检测索结构表面缺陷,基于振动的技术通过监测外部载荷、运行条件或结构响应完成,精度有限。超声导波不仅波的传播距离长,且灵敏度高、通用性好,本文针对超声导波的陷频特性与预应力钢绞线的应力变化关系进行了数值模拟和试验研究,提出的新型无损应力监测方法可广泛应用于桥梁拉索、吊杆、体外预应力索的应力监测。主要研究内容包括:(1)对超声导波在杆状波导结构中的传播特性进行理论研究,考虑了边界反射引发的波形转换和模态耦合现象,详细探讨了导波在多模态和有界介质条件下的频散特性。推导了无应力杆状波导中超声导波的传播模式和轴向受力波导的精确声弹性理论,并绘制了其理论频散曲线。(2)基于赫兹理论对七芯钢绞线接触模型进行建模仿真,对实际接触模型的预应力钢绞线进行超声导波缺失频带特性的有限元模拟与相关文献中的实验结果较为一致,从而验证了所提出模型的准确性。结果表明陷波中心频率值的大小在拉伸荷载的作用下逐渐增大,其原因在于钢丝线间接触宽度的增加,而非预应力本身的增加,进而推导了基于纵向模态导波陷频特性的钢绞线应力测量的经验公式。(3)基于Kriging代理模型进行索力识别的同时对影响钢绞线陷波频率的参数进行了分析,包括钢绞线的尺寸,泊松比,螺旋角和弹性模量等。参数分析验证了缺失频带的出现是由于接触区域中心钢丝对外侧钢丝施加的径向位移约束导致钢绞线的截面圆形对称性发生了破坏。(4)对基于钢绞线纵向导波陷频特性的预应力钢绞线应力监测方法进行了试验研究,首先搭建试验平台,包括所需的软硬件系统以及超声导波检测系统的组成和相关技术参数。接着进行了超声导波激励信号的频率选取和钢绞线试件及仪器参数设置,最后进一步讨论了试验结果以及结构参数对陷频的影响分析。更多还原

【Abstract】 Constant degradation and failure of load-bearing cable structures under the influence of wind-induced vibration,temperature changes and corrosion can lead to catastrophic collapse of these structures,resulting in severe damage.Traditional manual visual inspections are limited to detecting surface defects in the cable structure,and vibration-based techniques are accomplished by monitoring external loads,operating conditions,or structural response with limited accuracy.Ultrasonic guided waves not only have a long wave propagation distance,but also have high sensitivity and good generalization.In this paper,numerical simulation and experimental research are carried out to investigate the relationship between the notch frequency characteristics of ultrasonic guided waves and the stress change of prestressing strands,and the proposed new nondestructive stress monitoring method can be widely applied to the stress monitoring of bridge tension cables,suspension rods,and external prestressing tendons.The main research content includes:(1)The propagation characteristics of ultrasonic guided waves in a rod waveguide structure are theoretically investigated,and the dispersion characteristics of the guided waves under multimodal and bounded medium conditions are explored in detail,taking into account the wave transition and mode coupling phenomena induced by boundary reflections.The propagation modes of ultrasonic guided waves in unstressed rod waveguides and the accurate acoustic elasticity theory of axially stressed waveguides are deduced,and their theoretical dispersion curves are plotted.(2)Based on the Hertzian theory for modeling simulation of the contact model of seven-core strand,the finite element simulation of the ultrasonic guided wave missing band characteristics of the prestressed strand of the actual contact model is more consistent with the experimental results in the relevant literature,thus verifying the accuracy of the proposed model.The results show that the magnitude of the notch center frequency value increases gradually under the action of tensile load,which is due to the increase of the contact width between the steel wires rather than the increase of the prestressing force itself,then an empirical formula for the stress measurement of strand based on the longitudinal modal guided wave notch frequency characteristics is deduced.(3)Parameters affecting the strand notch frequency,including strand dimensions,Poisson’s ratio,helix angle,and modulus of elasticity,were analyzed along with the cable force identification based on the Kriging surrogate model.The parametric analysis verified that the missing frequency bands appeared due to the breakdown of the circular symmetry of the strand’s cross-section caused by the radial displacement constraints imposed by the center wire on the peripheral wires in the contact region.(4)An experimental study on the stress monitoring method of prestressed steel strand based on the notch frequency characteristics of strand longitudinal guided wave was carried out,in which the experimental platform was firstly constructed,including the required software and hardware systems,as well as the composition of the ultrasonic guided wave detection system and the relevant technical parameters.Then the frequency selection of the ultrasonic guided wave excitation signal and the parameter settings of the strand specimen and the instrument were carried out,finally the test results and the analysis of the influence of the structural parameters on the notch frequency were further discussed.更多还原