CAREER: Engineered Spatially Periodic Structure Design Integrated with Damage Detection Philosophy

该学院早期职业发展（Career）奖的研究目标是使土木工程师能够设计桥梁和其他关键结构，使结构能够自然地提供有关其结构状态的信号，而只需安装最少的传感器。这将导致更安全，更有弹性的民用基础设施，因为新的建设或改造采用了这些设计。这一点很重要，因为尽管已经用最新的现代技术对这些结构的裂缝进行了检查和监测，但关键结构在没有充分预警的情况下就发生了故障。该研究通过在早期阶段检测损伤，有可能改变结构工程领域。这项研究的教育影响将包括修改现有的钢铁和预应力混凝土设计课程，向本科生介绍损伤检测概念，发展荣誉学院的研究项目，让高中生和本科生参与研究，并在土木工程女学生中发展指导计划。本研究将声学损伤检测方法引入设计阶段，在结构单元中加入空间周期子系统。现有结构表现出一些局部周期性，例如穿孔梁，以及基于应力分布和间距要求的钢连接中的等间距螺栓。可以调整结构的周期性，使设计表现为声学超材料，能够阻挡、重定向和加强由部署的基础设施中新形成的裂缝表面释放的传播弹性波。声学超材料介质中的局部共振影响弹性波谱，使某些频率的波不能传播到介质中，如果频率落在这些停止带内。一旦损伤改变了结构的周期性，弹性波谱就会发生变化，从而很容易将结构损伤检测为正常谐振频率的扰动。高度窄带和敏感的微机械传感器将被调谐到周期子系统的停止带，并战略性地定位，这样一个传感器将足以检测局部损伤。结构设计和周期行为的联合响应将通过分析和数值模型进行测试，并在实验室规模的结构试验中进行验证。

The research objective of this Faculty Early Career Development (CAREER) award is to enable civil engineers to design bridges and other critical structures so that the structure will naturally provide signals about its structural state with only a minimum installation of sensors. This will result in a safer and more resilient civil infrastructure as new construction or retrofitting incorporates these designs. This is significant because critical structures have been failing without sufficient warning despite the fact that the cracks in these structures were already being inspected and monitored with the latest modern techniques. The research has the potential to transform the field of structural engineering by detecting damage at the earliest stage. The educational impact of the research will include modifying existing steel and prestressed concrete design courses to introduce damage detection concepts to undergraduate students, developing Honors College research projects, involving high school and undergraduate students into research, and developing mentoring program within female civil engineering students. In this research, an acoustic based damage detection method will be introduced into the design stage by adding spatially periodic subsystems into structural elements. Existing structures exhibit some localized periodicity such as perforated beams, and equally spaced bolts in steel connections where spacing is based on stress distribution and spacing requirements. The structural periodicity can be tuned to make the design behave as an acoustic metamaterial, which can be able to block, redirect, and strengthen propagating elastic waves released by newly formed crack surfaces in the deployed infrastructure. Local resonance in an acoustic metamaterial medium affects the elastic wave spectrum such that certain wave frequencies cannot propagate to the medium if the frequency falls within these stop bands. Once the periodicity is modified by damage, the elastic wave spectrum will change, and then structural damage can easily be detected as a disturbance of the normal resonant frequencies. Highly narrowband and sensitive micro-mechanical transducers will be tuned to the stop band of the periodic subsystem and positioned strategically such that one sensor will be sufficient to detect the localized damage. The combined response of structural design and periodic behavior will be tested with analytical and numerical models and validated on laboratory scale structural tests.