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

既有钢筋混凝土(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。一种在过去十年中得到广泛接受的加固方法是在混凝土梁或板的拉伸面上粘贴纤维增强塑料(FRP)补丁，从而增加梁(板)的抗弯刚度和承载能力。随着这些FRP贴片在这些应用中的使用增加，对能够表征这些粘合贴片的可靠无损评估(NDE)技术产生了需求。任何候选的无损检测技术都必须能够提供有关原位FRP补丁特性的定量和有意义的信息(从工程设计的角度)。从质量保证(以及无损检测)的角度来看，最关键的元素是粘合层，而不是玻璃钢补丁本身。混凝土修补程序通常使用在受控环境中制造的高质量FRP补丁。这与粘结层形成对比，粘结层通常是在恶劣条件下现场组装的。对于这些粘合的玻璃钢贴片，有两个重要的质量保证/无损检测问题可以用导波技术解决。第一个涉及粘结层材料性能的测量。导波可以用来确定原位粘接性能，如环氧粘接的剪切模数。第二个检查问题是粘接性能的测量，即胶粘剂和被粘结物之间两个界面处的粘接质量的测量。这对于粘结的玻璃钢补片来说是一个关键问题，特别是混凝土与粘结剂界面的粘合性能。建议的研究开发了一种无损检测方法，该方法使用导波来表征FRP贴片的原位粘结特性，分三个任务：任务1.了解导波在这些粘结组件中传播的基本机理。本课题研究粘接在混凝土组件上的FRP贴片中的超声波行为，量化某些粘结参数对粘接组件中导波传播的影响。这一前沿问题涉及玻璃钢贴片的实验研究和数值模拟，主要集中在可直接测量的声学参数上。任务2.根据相关的工程参数解释任务1的实验/数值结果，以便在这些声学测量和关键的FRP补丁性能指标之间建立定量关系。此任务将这些可直接测量的导波属性(如提供波速/频率关系的频散曲线)与工程设计所必需的材料属性相关联。本研究中量化的具体参数包括：原位粘结层的整体性能，包括厚度和硬度；以及该粘结层的粘接性能(特别是混凝土与粘结剂的界面)，包括检测任何空洞、间隙或脱粘区域。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。这个反问题使用神经网络来根据实验测量的导波来确定原位粘结剂的整体弹性性质、厚度和粘合特性。这项原则证明研究的结果对于开发高效、实时的实地检查方法至关重要。这一研究项目的运作前提是，在为民用基础设施制定创新的无损检测方法方面，教育和研究同等重要。除了进行基础和应用研究外，学术机构的首要责任是培养学生，使他们能够满足工作场所的要求。考虑到这一点，提出了一个教育计划，将教育和培训新一代工程师，以解决与修复和修复的RC部件的无损检测相关的问题。

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.