钢绞线是目前国内外预应力结构中应用最广的一种预应力筋。预应力损失和缺陷产生是直接影响钢绞线使用寿命和结构安全的两大主要因素。但到目前为止，尚无一种检测方法能对这两个因素同时进行评估。本课题提出一种利用超声导波对钢绞线健康状况进行检测的新方法。在理论上，利用波动理论和声弹性理论,建立预应力钢绞线中超声导波动力学模型，得到各模态的频散方程；研究超声导波的传播特性（如频散、多模态和衰减等）；建立应力与超声参量间(如相速度)的关系，为实验研究提供理论依据。在实验上，基于理论分析，优化超声导波检测实验方案，包括选择频散和衰减小，对钢绞线应力和缺陷敏感的模态和频率，专用探头的研制和优化等；建立一套钢绞线超声导波检测实验装置；得到纵向和扭转模态的声弹性系数，通过测得相关超声参量确定应力大小；优化选择适合钢绞线缺陷检测的导波模态，分析各种因素(如温度、周围介质等)对检测效果的影响，以期对预应力钢绞线健康状况进行评价。

At present, seven-wire steel strands are one of most widely used tendons in prestressed structures of domestic and overseas. Prestress loss and defects are two main causes affect directly the service life of steel strands and the safety of whole structures. However up to now, there have no inspection methods which can evaluate these causes simultaneously. In this project, a new method which is ultrasonic guided wave inspection technique is put forward for health monitoring of steel strands. Theoretically, dynamic Models of ultrasonic guided waves in prestressed steel strands are built using theories of wave propagation and acoustoelasticity and consequently dispersion equations are derived. Propagation characteristics of ultrasonic guided waves, such as dispersion, multi-mode, attenuation, are investigated. The relationship between stress and ultrasonic parameters, for example phase velocity, are built. These researches provide a theoretical basis for experimental study. Experimentally, based on the theoretical analysis, experimental scheme of ultrasonic guided wave inspection is optimized, including the choice of modes which attenuation and dispersion are low and be sensitive to stress and defects of steel strands and their excitation frequencies. Special transducers are developed and optimized. Experimental system for inspecting steel strands using ultrasonic guided waves is built. Acoustoelastic coefficients of longitudinal and torsional modes are derived. By measuring related ultrasonic parameters, stress in steel strands is calculated. Guided wave modes used for detecting defects of steel strands are chosen and optimized. The impact of some factor, such as temperature and surrounding medium, on the inspection results is analyzed. From above analysis, health state of prestressed steel strands can be evaluated.

钢绞线是目前国内外预应力结构中应用最广的一种预应力筋。预应力损失和缺陷产生是直接影响钢绞线使用寿命和结构安全的两大主要因素。但到目前为止，尚无一种检测方法能对这两个因素同时进行评估。本课题提出一种利用超声导波对钢绞线健康状况进行检测的新方法。在理论上，利用波动理论和声弹性理论,建立预应力钢绞线中超声导波动力学模型，得到各模态的频散方程；研究超声导波的传播特性（如频散、多模态和衰减等）；建立应力与超声参量间(如相速度)的关系，为实验研究提供理论依据。在实验上，基于理论分析，优化超声导波检测实验方案，包括选择频散和衰减小，对钢绞线应力和缺陷敏感的模态和频率，专用探头的研制和优化等；建立一套钢绞线超声导波检测实验装置；得到纵向和扭转模态的声弹性系数，通过测得相关超声参量确定应力大小；优化选择适合钢绞线缺陷检测的导波模态，分析各种因素(如温度、周围介质等)对检测效果的影响，以期对预应力钢绞线健康状况进行评价。