考虑环境影响基于压电阻抗的混凝土结构损伤识别研究

Minor damage in the early age of concrete will cause accumulated damages which may lead to a sudden failure of engineering structures, if it is not found in time. Timely accurate identification of minor and potential damages in the early age of concrete has been always a challenge and is also of great value theoretically and practically in the field of concrete structural engineering. PZT signal-based electromechanical impedance (EMI) technique which has the advantages of high sensitivity and responding swiftly, has been proved to be an effective method in identifying structural minor damage. However, environmental factors such as temperature and moisture, and the characteristics of bonding layer between the PZT sensor and the concrete structure have significant influences on the result of damage identification. This project is aiming at studying the influence rule of environmental variations on electromechanical impedance of PZT sensors, improving the protection measures of PZT sensors to minimize the effect of environmental factors, searching for new signal processing technologies to eliminate the effect of environmental factors on characteristic parameters of concrete damage in EMI technique, to establish a three-dimensional EMI model considering the bonding layer between the PZT sensor and the concrete structure, and to develop EMI technique against the influence of environmental factors, for quantitatively identifying minor concrete damage by using the wavelet spectral finite element method. Moreover, numerical analysis, model test and practical engineering application are applied to verify the accuracy and effectiveness, which can provide accurate and reliable evidences for concrete structural health assessment.

混凝土早期的微小损伤若未及时发现，会引发结构的累计损伤，从而导致结构的突发性失效，及时准确地识别混凝土早期微弱和潜在的损伤，一直是混凝土结构工程领域的难题。基于压电陶瓷(PZT)监测信号的电机耦合阻抗(EMI)具有对结构微小损伤敏感、反应迅速等特点，被证明是一种有效的混凝土微小损伤识别方法，但是环境变化(温度、湿度) 、PZT与混凝土结构粘结层特性对EMI损伤识别结果影响显著。本项目研究环境变化(温度、湿度)对PZT阻抗的影响规律，改进减小环境因素影响的PZT保护措施，探求剔除环境因素对混凝土损伤EMI特征参数影响的信号处理技术，建立考虑PZT与混凝土结构粘结层特性的三维EMI损伤识别模型，通过基于细观损伤的小波谱有限元法开发抗环境影响的混凝土微损伤EMI定量识别技术，进一步通过数值分析、模型实验与实际工程应用验证其精确性、有效性，为混凝土结构健康评估提供准确与可靠的依据。

混凝土结构微小损伤若未及时发现，会引发累计损伤导致结构失效。基于有效机械阻抗理论，建立可以隔绝环境影响的植入式压电传感器(PZT)与结构耦合二维阻抗模型，得到植入式PZT与结构耦合二维模型导纳表达式。将介电常数、压电常数、复合杨氏模量和介电常数等参数的温度函数带入导纳表达式，计算不同温度工况下的导纳理论值。理论解析结果表明随温度升高导纳曲线共振频率和峰值均线性增加。建立三维有限元数值模型分析温度对单个PZT、粘贴式和植入式PZT-混凝土结构阻抗的影响规律，并制作内部植入和表面粘贴PZT的混凝土试块，研究混凝土热传导对裂缝损伤识别结果的影响。利用导纳及其均方根偏差定量评估了温度对混凝土微裂缝损伤识别的影响，结果表明温度变化对混凝土损伤识别结果具有明显放大作用。结合PZT阻抗与谱单元法对混凝土结构微小损伤进行定位和定量识别，构建铁木辛柯梁在完整及裂纹状态下谱单元刚度矩阵，对其控制微分方程进行拉普拉斯变换，通过位移边界条件得到无损和裂纹梁的谱单元刚度矩阵；利用单元集成方法组装获得结构的整体刚度和荷载矩阵，并求解各节点处的振动响应值。将PZT激励电压转化成一般荷载并获取结构响应，选择响应的四阶统计矩作为结构损伤指标，计算统计矩的欧几里得距离，用差分进化算法对目标函数进行优化得到准确的损伤位置和裂纹深度。利用无损梁及附加质量和裂纹损伤数值模型验证了该方法的精确性。最后提出排除环境影响的温度补偿方法。给定温度引起的导纳频率偏移量并修正温度影响下的导纳曲线频率偏移，并对修正前后的导纳曲线作相关性分析，重复计算相关系数找到其最小值对应的频率偏移量进而补偿温度影响。分别对无损和带裂缝混凝土试块在变温条件下的导纳曲线进行补偿，消除了温度对损伤识别结果影响，证明了所提方法的有效性。进一步通过对足尺混凝土隧道管片结构的长期监测补偿研究，结果表明利用该方法有效降低了环境影响，大幅提高了混凝土结构微小损伤识别的精度。