Guided Ultrasonic Wave Methodology to Characterize the Performance of FRP Patches in Repaired and Rehabilitated Concrete Components

摘要现有钢筋混凝土（RC）结构的修复、升级和改造是当今结构工程面临的最大挑战之一。在过去十年中，一种被广泛接受的改造方法是将纤维增强塑料（FRP）贴片粘贴到混凝土梁或板的受拉面上，从而增加梁（或板）的抗弯刚度和承载能力。这些玻璃钢贴片在这些应用中的使用量增加，产生了对可靠的无损评估（NDE）技术的需求，这些技术能够表征这些粘合贴片。任何候选的无损检测技术都必须能够（从工程设计的角度）提供有关原位玻璃钢贴片特性的定量和有意义的信息。从质量保证（因此无损检验）的角度来看，最关键的因素是粘合剂粘合层，而不是玻璃钢贴片本身。混凝土修复程序通常使用在受控环境中制造的高质量玻璃钢贴片。这与通常在不利条件下现场组装的粘合层形成对比。对于这些粘接玻璃钢贴片，有两个重要的质量保证/无损检验问题，可以用导波技术解决。首先是关于胶粘剂层材料性能的测量。导波可以用来确定原位粘合剂的粘合性能，如环氧树脂粘合的剪切模量。第二个检查问题是粘合性能的测量，即粘合剂和被粘合剂之间两个界面的粘合质量。这是粘合玻璃钢贴片的关键问题，特别是混凝土-粘合剂界面的粘合性能。提出的研究开发了一种NDE方法，该方法在三个任务中使用引导超声波来表征FRP贴片的原位粘合特性：任务1。了解引导超声波在这些粘合部件中传播的基本机制。本任务检查超声波在粘合到混凝土组件的玻璃钢贴片中的行为，量化某些粘合参数对粘合组件中导波传播的影响。这一前瞻性问题涉及玻璃钢贴片的实验研究和数值模拟，主要集中在直接可测量的声学参数上。任务2。根据相关的工程参数解释任务1中的实验/数值结果，以便在这些声学测量和关键玻璃钢贴片性能指标之间建立定量关系。这项任务将这些直接可测量的导波属性（如提供波速/频率关系的色散曲线）与工程设计中必不可少的材料特性联系起来。本研究量化的具体参数为：原位胶粘剂层的体积特性，包括厚度和刚度；以及该粘合层（特别是混凝土-粘合剂界面）的粘合性能，包括检测任何空隙、间隙或剥离区域。任务3。进行初步研究，以确定用于评估这些导波的反演技术的有效性。该反问题利用神经网络从实验测量的导波中确定原位胶粘剂的体积弹性特性、厚度和粘附特性。这项原理验证研究的结果对于开发一种高效、实时的现场检查方法至关重要。本研究项目的前提是，在为民用基础设施开发创新的NDE方法方面，教育和研究同样重要。除了进行基础研究和应用研究外，学术机构还负有培养学生以满足工作场所要求的主要责任。考虑到这一点，提出了一项教育计划，该计划将教育和培训新一代工程师，以解决与修复和修复的RC部件的NDE相关的问题。

ABSTRACTThe rehabilitation, upgrading and retrofitting of existing reinforced concrete (RC) structures is one of the most difficult challenges facing structural engineering today. One retrofitting method that has gained widespread acceptance over the last decade involves externally bonding fiber reinforced plastic (FRP) patches on to the tension face of a concrete beam or slab, thus increasing the beam's (or slab's) flexural stiffness and loading capacity. The increased usage of these FRP patches in these applications has created the requirement for reliable nondestructive evaluation (NDE) techniques capable of characterizing these bonded patches. Any candidate NDE technique must be capable of providing quantitative and meaningful information (from an engineering design perspective) about the characteristics of an in situ FRP patch. The most critical element from a quality assurance (and thus NDE inspection) point of view is the adhesive bond layer - as opposed to the FRP patch itself. Concrete repair procedures typically use a high quality FRP patch that is manufactured in a controlled environment. This is in contrast to the adhesive bond layer, which is field assembled, often under adverse conditions. There are two important quality assurance/NDE inspection problems for these adhesively bonded FRP patches that can be addressed with guided wave techniques. The first is concerned with the measurement of the material properties of the adhesive layer. Guided waves can be used to determine in situ adhesive bond properties, such as the shear modulus of an epoxy bond. The second inspection problem is the measurement of the adhesion properties, the quality of the bonding at the two interfaces between the adhesive and the adherends. This is a critical issue for bonded FRP patches, especially the adhesion properties of the concrete-to-adhesive interface. The proposed research develops a NDE methodology that uses guided ultrasonic waves to characterize the in situ bond properties of a FRP patch in three tasks: Task 1. Understand the underlying mechanics of the propagation of guided ultrasonic waves in these bonded components. This task examines the behavior of ultrasonic waves in a FRP patch bonded to a concrete component, quantifying the effect of certain bond parameters on the propagation of guided waves in the bonded assembly. This forward problem involves both experimental studies and numerical simulation of FRP patches, concentrating on directly measurable acoustic parameters. Task 2. Interpret the experimental/numerical results from Task 1 in terms of relevant, engineering parameters in order to develop a quantitative relationship between these acoustic measurements and critical FRP patch performance metrics. This task relates these directly measurable, guided wave attributes (such as dispersion curves that provide wave speed/frequency relationships) to material properties that are essential to engineering design. The specific parameters quantified in this research are: the bulk properties of the in situ adhesive layer, including thickness and stiffness; and the adhesion properties of this adhesive layer (particularly the concrete-to-adhesive interface), including detection of any voids, gaps or regions of disbonds. Task 3. Conduct a preliminary study that establishes the effectiveness of an inversion technique for the evaluation of these guided waves. This inverse problem uses neural networks to determine the bulk elastic properties, thickness and adhesion characteristics of an in situ adhesive bond from experimentally measured guided waves. The results of this proof-of-principle study are critical for the development of an efficient, real-time field inspection methodology. This research project operates under the premise that education and research are equally important in developing innovative NDE methodologies for civil infrastructure. In addition to performing basic and applied research, academic institutions have a primary responsibility to train students so that they can meet the requirements of the workplace. With this in mind, an education program is proposed that will educate and train a new generation of engineers to address issues relating to NDE of repaired and rehabilitated RC components.