<p>Vehicles that run on compressed natural gas and hydrogen are currently being developed to reduce greenhouse gas emissions and smog. To meet the need for a safe, reliable fuel storage system, a low-cost, acoustic-ultrasonic system has been developed to detect damage in high-pressure storage cylinders made of Carbon Fiber Reinforced Polymers (CFRP). This structural health monitoring system could lead to lighter, lower cost cylinders, and improved safety in automotive applications that utilize hydrogen and natural gas.</p><p>Several Non-Deconstructive Evaluation (NDE) techniques were investigated in the course of this work, and low-cost piezo-film sensors were selected to monitor the cylinder. These sensors were integrated into the carbon fiber structure, resulting in a sensor network that can be used for real-time structural health monitoring of composite cylinders. The system was operated by exciting the piezo-film sensors with an impulse and then the corresponding structural response (or signature) was measured and analyzed. This was compared to a previously measured response and evaluated for changes which can indicate failures in the tank. The analysis reduces the changes in the structural response to a single damage coefficient, which can then be used for malfunction indication and decision making in an automotive on-board microprocessor control system.</p><p>The technology can be deployed at a reasonable cost, and has been designed to accurately detect damage with little or no maintenance required. Thirty cylinders were used in a test matrix to examine all possible failure mechanisms of the tanks, including: fatigue, cuts and gouges, impact and delaminations, stress rupture, heat damage, and combinations of these damage mechanisms. The damage detection system was capable of detecting damage long before a critical condition arose for all cases. However, further development and testing into larger cylinder designs and testing is still required to develop a final commercial product.

Structural Health Monitoring (SHM) comprises a wide range of techniques for the condition and damage assessment of an existing structure. Vibration-based damage detection (VBDD) techniques, a class of SHM methods, use changes in the dynamic properties (i.e., natural frequencies, mode shapes and damping characteristics) of structures to detect deterioration or damage. The application of VBDD methods to simple structures in a well-controlled laboratory environment has gained some successful results. However, the practical field application of VBDD still faces significant challenges since vibration measurement is subject to the influences of high levels of uncertainty in environmental, structural and loading conditions. In this thesis, the influence of temperature variations on the application of VBDD methods to an in-service complex structure was experimentally and numerically studied. The structure studied was the Attridge Drive overpass in Saskatoon, Saskatchewan.<p> The main objective of this research was to assess the influence of temperature variation on the dynamic properties (natural frequencies and mode shapes) of the overpass, and on the ability of VBDD methods to detect and locate damage. Field dynamic measurements were made on the bridge on numerous occasions under a wide variety of ambient temperatures, using high sensitivity accelerometers and a temperature sensor. Dynamic excitation was provided solely by ambient traffic loading.<p> Finite element models of the overpass were also created and manually calibrated to measured field data. The models were used to simulate the dynamic behaviour of the bridge at a variety of temperatures and under various states of small-scale damage. Numerical analysis was conducted to study the effect of ambient temperature on structures dynamic characteristics and to differentiate the patterns of mode shape changes caused by damage and ambient temperature. It was concluded that the change of ambient temperature mainly affects the elastic modulus of the construction materials and therefore stiffness of the entire bridge. As a result, the eigenfrequencies and mode shapes of the structure are influenced.<p> The dynamic properties extracted from measured experiment data showed an approximately bilinear relationship between the three first natural frequencies and the ambient temperature. The natural frequencies for all three modes increased when the temperature fell.<p> It was also found that, conceptually, it is possible to distinguish the patterns of mode shape changes caused by small-scale damage from those due to thermal effects, but only if a sufficient number of sensors are used to measure the mode shapes; in addition, those sensors must be located close to the damage location.

<p>Vehicles that run on compressed natural gas and hydrogen are currently being developed to reduce greenhouse gas emissions and smog. To meet the need for a safe, reliable fuel storage system, a low-cost, acoustic-ultrasonic system has been developed to detect damage in high-pressure storage cylinders made of Carbon Fiber Reinforced Polymers (CFRP). This structural health monitoring system could lead to lighter, lower cost cylinders, and improved safety in automotive applications that utilize hydrogen and natural gas.</p><p>Several Non-Deconstructive Evaluation (NDE) techniques were investigated in the course of this work, and low-cost piezo-film sensors were selected to monitor the cylinder. These sensors were integrated into the carbon fiber structure, resulting in a sensor network that can be used for real-time structural health monitoring of composite cylinders. The system was operated by exciting the piezo-film sensors with an impulse and then the corresponding structural response (or signature) was measured and analyzed. This was compared to a previously measured response and evaluated for changes which can indicate failures in the tank. The analysis reduces the changes in the structural response to a single damage coefficient, which can then be used for malfunction indication and decision making in an automotive on-board microprocessor control system.</p><p>The technology can be deployed at a reasonable cost, and has been designed to accurately detect damage with little or no maintenance required. Thirty cylinders were used in a test matrix to examine all possible failure mechanisms of the tanks, including: fatigue, cuts and gouges, impact and delaminations, stress rupture, heat damage, and combinations of these damage mechanisms. The damage detection system was capable of detecting damage long before a critical condition arose for all cases. However, further development and testing into larger cylinder designs and testing is still required to develop a final commercial product.

Structural Health Monitoring (SHM) comprises a wide range of techniques for the condition and damage assessment of an existing structure. Vibration-based damage detection (VBDD) techniques, a class of SHM methods, use changes in the dynamic properties (i.e., natural frequencies, mode shapes and damping characteristics) of structures to detect deterioration or damage. The application of VBDD methods to simple structures in a well-controlled laboratory environment has gained some successful results. However, the practical field application of VBDD still faces significant challenges since vibration measurement is subject to the influences of high levels of uncertainty in environmental, structural and loading conditions. In this thesis, the influence of temperature variations on the application of VBDD methods to an in-service complex structure was experimentally and numerically studied. The structure studied was the Attridge Drive overpass in Saskatoon, Saskatchewan.<p> The main objective of this research was to assess the influence of temperature variation on the dynamic properties (natural frequencies and mode shapes) of the overpass, and on the ability of VBDD methods to detect and locate damage. Field dynamic measurements were made on the bridge on numerous occasions under a wide variety of ambient temperatures, using high sensitivity accelerometers and a temperature sensor. Dynamic excitation was provided solely by ambient traffic loading.<p> Finite element models of the overpass were also created and manually calibrated to measured field data. The models were used to simulate the dynamic behaviour of the bridge at a variety of temperatures and under various states of small-scale damage. Numerical analysis was conducted to study the effect of ambient temperature on structures dynamic characteristics and to differentiate the patterns of mode shape changes caused by damage and ambient temperature. It was concluded that the change of ambient temperature mainly affects the elastic modulus of the construction materials and therefore stiffness of the entire bridge. As a result, the eigenfrequencies and mode shapes of the structure are influenced.<p> The dynamic properties extracted from measured experiment data showed an approximately bilinear relationship between the three first natural frequencies and the ambient temperature. The natural frequencies for all three modes increased when the temperature fell.<p> It was also found that, conceptually, it is possible to distinguish the patterns of mode shape changes caused by small-scale damage from those due to thermal effects, but only if a sufficient number of sensors are used to measure the mode shapes; in addition, those sensors must be located close to the damage location.

In any infrastructure project, monitoring and managing the built assets is an important task. Structural Health Monitoring (SHM) is meant for continuous assessment of safety and serviceability of a structure and its elements. SHM has taken a leading role in the field of structural engineering and has become very popular in recent age. Bridge deflection is the basic evaluation index to examine the health status of a bridge structure. The existing bridge monitoring systems have several drawbacks. Hence, a new methodological approach has been proposed to overcome the limitations of traditional contact-based bridge deflection monitoring system and other non-contact based system. This study developed a non-contact linear feature based Deflection Monitoring System (DMS) using Terrestrial Laser Scanning (TLS) and cameras for timber railroad bridges. The process and detailed workflow of building the DMS, its components and sensors involved are discussed here. The efficiency of this DMS is validated against a deflectometer. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2018. / FAU Electronic Theses and Dissertations Collection

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Structural Health Monitoring (SHM) is the process of monitoring the state of a structure to determine the existence, location, and degree of damage that may exist within the entire structure. A structure’s health or level of damage can be monitored by identifying changes in structural or modal parameters. In this research, the structure’s health is monitored by identifying changes in structural stiffness. The Adaptive Least Mean Square (LMS) filtering approach is used to directly identify changes in structural stiffness for the IASC-ASCE Structural Health Monitoring Task Group Benchmark problem for both Phase I and II. The research focuses primarily on Phase II of the benchmark problem. In Phase II, modeling error and noise is introduced to the problem making the problem more realistic. The research found that the LMS filter approach can be used to detect damage and distinguish relative severity of the damage in Phase II of the benchmark problem in real time. Even though the LMS filter approach identified damage, a threshold below which damage is hard to identify exists. If the overall stiffness changes less than 10%, then identifying the presence and location of damage is difficult. But if the time of damage is known, then the presence and location can be determined. The research is of great interest to those in the structural health monitoring community, structural engineers, and inspection practitioners who deal with structural damage identification problems.

Real-time monitoring of fracture critical steel bridges can potentially enhance inspection practices by tracking the behavior of the bridge. Significant advances have occurred in recent years on the development of robust hardware for field monitoring applications. These systems can monitor, process, and store data from a variety of sensors (e.g. strain gages, crack propagation gages etc.) to track the behavior of the bridge. The research outlined in this dissertation is part of a large study focused on the development of a wireless system for use in long-term monitoring of bridges. The wireless monitoring system had a target maintenance-free life of ten years, and independent from the power grid. Thus, the feasibility to harvest energy for the monitoring system is an important step in the development of the system. In addition, the reliability of the sensors in the bridge is very important upon the success of the system. The focus of this dissertation is on two primary aspects of the wireless monitoring system. First, the feasibility to harvest energy from vehicular-induced vibrations is evaluated through analytical models of highway bridges under truck loads. Acceleration results from simple line-element models and detailed finite element models of five steel bridges in Texas and Oregon are compared with actual field data from the same bridges. Second, the dissertation also highlights studies on the identification of strain gages and installation procedures that result in long lives. In addition, the effect of temperature fluctuations and other environmental factors on the sensor drift and noise is also considered. In long-term monitoring applications, slight sensor drift and noise can build up over time to produce misleading results. This dissertation presents the results of transient dynamic analyses of bridges under moving truck loading and laboratory tests on gage durability that were conducted as part of a research project sponsored by the National Institute of Standards and Technology (NIST). / text

As the demands to monitor the health status of structures increase, researchers around the world have proposed several concepts to solve this issue. This research first examines the existing technologies and then works toward a novel structural health monitoring solution. A comprehensive discussion includes major topics from sensor selection and installation to sensing data display. A cyber-physical system combining embedded system, wireless communication, and the Java platform was developed for structural health monitoring. The focus of this system is to continuously monitor structural response and broadcast the information to users worldwide via the Internet. A wireless sensor node is designed to connect up to eight sensor channels. Various sensors have been tested on the sensor node. A data acquisition and repository system was also developed. The use of the Java language makes this system capable of running in virtually any existing computer platform. Distributed design concept expands its functionalities and capabilities. Its graphical user interface offers users a friendly and ease-of-use environment to monitor real-time and historical data in both graphical and numerical ways. Every component of the system has been validated to verify its functionality. Additionally, the whole system has been implemented on a steel pedestrian bridge to observe its performance.

This thesis examines the value of using dispersed conductive fillers as a stress/strain sensing material. The effect of the intrinsic conductivity of the filler on the ability to be effective and the influence of filler concentration on the conductivity are also examined. To meet these objectives, nanocomposites of polyvinylidene fluoride (PVDF) with carbon nanofibers (CNFs) and carbon nanotubes (CNTs) were prepared by melt-blending using a twin screw extruder. Since PVDF has a potential to be piezoresistive based on the type of crystalline phase, the effect of CNFs on PVDF crystallinity, crystalline phase, quasi static and dynamic mechanical property was studied concurrently with piezoresponse. Three time dependencies were examined for PVDF/CNTs nanocomposites: quasi-static, transient and cyclic fatigue. The transient response of the strain with time showed viscoelastic behavior and was modeled by the 4-element Burger model. Under quasi-static loading the resistance showed negative pressure coefficient below yield but changed to a positive pressure coefficient after yield. Under cyclic load, the stress-time and resistance-time were synchronous but the resistance peak value decreased with increasing cycles, which was attributed to charge storage in the nanocomposite. The outcomes of this thesis indicate that a new piezoresponsive system based on filled polymers is a viable technology for structural health monitoring.