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Proper design of bridge structures requires an appreciation for the possible failure mechanisms that can develop over the lifetime of the bridge, many of which are related to natural hazards. For example, scour is one of the most common causes of bridge failures. Scour occurs due to the erosion of soil and sediment within a channel with flowing water. During a flood event, the extent of scour can be so great that it can destabilize an existing bridge structure. In order to evaluate the scour potential of a bridge, it is necessary to have information regarding the substructure, particularly the bridge foundations. However, as of 2011 there are more than 40,000 bridges across United States with unknown foundations. Generally for these bridges there are no design or as-built plans available to show the type, depth, geometry, or materials incorporated into the foundations. Several non-destructive testing (NDT) methods have been developed to evaluate these unknown foundations. The primary objective of this research is to identify the most current and widely used NDT methods for determining the embedment depth of unknown bridge foundations and to compare these methods to an ultrasonic P-wave reflection imaging system. The ultrasonic P-wave reflection system has tremendous potential to provide more information and address several short-comings of other NDT methods. A laboratory study was initiated to explore various aspects related to the P-wave system performance, in order to characterize the limitations of the system in evaluation of unknown foundations prior to deployment in field studies. Moreover, field testing was performed using the P-wave system and a number of the current NDT methods at two selected bridge foundations to allow comparison between the results. / Civil Engineering

According to the 2019 Canadian infrastructure report card, a concerning amount of municipal infrastructure is in poor or very poor condition. The infrastructure in this condition requires immediate action for rehabilitation or replacement. For concrete infrastructure, an effective repair can extend its service life and ensure that the services it provides continue to meet the community expectations. However, unfavorable environmental factors such as repeated/cyclic loads and freezing and thawing cycles adversely affect the bond between substrate concrete and repair materials, which lowers the structural capacity of repaired structures. So far, researchers have found that bond strength of repair can be affected by surface roughness, surface moisture, chemical adhesion or cohesion, curing regime, properties of substrate and repair materials, use of bond agent, and curing regimes. These findings are mostly based on the studies that focused on cold-jointed cylinders or beams, but in real-life repair situations, repairs of beams or slabs are located at either tension or compression side of the structure. Currently, there is no comprehensive study that investigates the bond of concrete repair under a combination of freezing and thawing and repeated/cyclic loading conditions. In addition, it is challenging to provide a rapid and non-destructive evaluation of the bond deterioration of repair materials. To address these issues systematically, this dissertation breaks the task into four phases. Phase (I) focuses on the development of an engineered “crack-free” repair mix that contains polypropylene (PP) fiber. A novel method is used to surface treat the PP fibers with supplementary cementitious materials. The effectiveness of surface-treating fibers for improved bond strength and reduced cracking is investigated. The compressive, tensile, and flexural strength of this engineered repair mix are determined and compared with two commercially available repair materials. The results from Phase I show that by adding 0.2% (by weight) Metakaolin-treated fibers into concrete mix, the compressive strength improves by up to 15.7% compared to mixes with untreated fibers. This study achieved a strength increase of 13.5% as compared to the reported 3.3% in other studies that use 25 times the amount of metakaolin used in this study. The experimental results confirm that at 0.2% dosage level, the use of novel surface treating technique is a cost-effective way to improve the strength of repair materials. Phase (II) focuses on characterizing the bond strength of various repair systems after freezing-thawing (FT) damage using both non-destructive and destructive methods. Two innovative sounding methods, which overcome the subjectivity of the traditional chain drag method, are used to evaluate FT damage non-destructively. In the experimental study, beams with a U-shaped cut are made to simulate conditions experienced by a concrete structure during a typical repair project. Three types of repair materials are used including cementitious repair concrete, cementitious repair mortar, and polymer-modified cementitious mortar. After up to 300 cycles of freeze-thaw exposure, resonant frequency and bond flexural strength of the prismatic specimens are determined. The empirical equations relating Non-destructive test (NDT) measurements and flexural bond strength of the repaired structures after freeze-thaw (FT) exposure are proposed. The results from Phase II show that the change in dynamic modulus of elasticity determined from NDTs agrees well with the change in other measurements including flexural bond strength, interfacial crack width, and mass loss after freeze-thaw exposure. In this study, linear relationships are established between dynamic modulus of elasticity and flexural bond strength for both cementitious and polymer-modified cementitious repair mortar with a coefficient of determination ranging between 0.87 and 0.95. The proposed empirical models can be used to predict bond flexural strength of repaired structures based on NDT measurement. Also, it was found that the samples repaired with polymer-modified cementitious mortar (Mix P) have superior FT resistance compared to other repaired samples. Phase (III) focuses on investigating the structural capacity and bond performance of repaired beams after cyclic/repeated loading. To accelerate the test process, a novel modified loading regime consisting of cycle groups of increasing cyclic/repeated stress amplitude is proposed. The models proposed by literature and current codes and standards are used to validate the results. Phase (IV) focuses on the development of the damage models for both individual and combined FT and cyclic loading exposure on repaired concrete structures. The results in phase III show the feasibility of using the Palmgren-Miner rule and Goodman linear model to estimate the fatigue life of repaired structures. This was confirmed within the context of this study. This study established the usefulness of using groups of increasing cyclic stress amplitude to accelerate the fatigue test process. The two-million cycle fatigue endurance limit estimated using cycle groups of Mix S (70.8%) was very similar to what was reported in the literature (71%) using the traditional time-consuming cyclic loading method. This study found that the formulas proposed by CSA 23.3 can effectively predict the moment resistance of both intact (control) and repaired RC beams. The ratio of experimental moment resistance values to its predictions ranges from 0.91 to 1.04. Based on the experimental results of previous three phases, an empirical model that predicted the fatigue service life of FT-damaged concrete structures is proposed. Future research requires a more comprehensive study on the FT performance of various polymer-modified cementitious mortars of different mix designs in repairing concrete structures. By increasing the number of tested specimens, a better relationship could be established between destructive and NDT methods. Future research is also required to explore the combined effect of FT and cyclic loading on repaired RC structures experimentally. / Graduate / 2023-03-22

L’évaluation des performances des procédures de Contrôle Non Destructifs (CND) en aéronautique est une étape clé dans l’établissement du dossier de certification de l’avion. Une telle démonstration de performances est faite à travers l’établissement de probabilités de détection (Probability Of Detection – POD), qui intègrent l’ensemble des facteurs influents et sources d’incertitudes inhérents à la mise en œuvre de la procédure. Ces études, basées sur des estimations statistiques faites sur un ensemble représentatif d’échantillons, reposent sur la réalisation d’un grand nombre d’essais expérimentaux (un minimum de 60 échantillons contenant des défauts de différentes tailles, qui doivent être inspectés par au moins 3 opérateurs [1]), afin de recueillir un échantillon suffisant pour une estimation statistique pertinente. Le coût financier associé est élevé, parfois prohibitif, et correspond majoritairement à la mise en œuvre des maquettes servant aux essais. Des travaux récents [2-5] ont fait émerger une approche de détermination de courbes POD utilisant la simulation des CND, notamment avec le logiciel CIVA. L’approche, dite de propagation d’incertitudes, consiste à : - Définir une configuration nominale d’inspection, - Identifier l’ensemble des paramètres influents susceptibles de varier dans l’application de la procédure, - Caractériser les incertitudes liées à ces paramètres par des lois de probabilités, - Réaliser un grand nombre de simulations par tirage aléatoire des valeurs prises par les paramètres variables selon les lois de probabilités définies. Le résultat de cet ensemble de simulations constitue enfin la base de données utilisée pour l’estimation des POD. Cette approche réduit de façon très importante les coûts d’obtention des POD mais est encore aujourd’hui sujette à discussions sur sa robustesse vis-à-vis des données d’entrée (les lois de probabilité des paramètres incertains) et sur la prise en compte des facteurs humains. L’objectif de cette thèse est de valider cette approche sur des cas d’application AIRBUS et d’en améliorer la robustesse afin de la rendre couramment utilisable au niveau industriel, notamment en la faisant accepter par les autorités de vol (FAA et EASA). Pour ce faire le thésard devra mener des campagnes de validations des codes de simulation des CND, mettre en œuvre la méthodologie décrite plus haut sur les cas d’application AIRBUS, puis proposer et mettre en œuvre des stratégies d’amélioration de la robustesse de la méthode vis-à-vis des données d’entrée et des facteurs liés à l’humain. / The performance assessment of non-destructive testing (NDT) procedures in aeronautics is a key step in the preparation of the aircraft's certification document. Such a demonstration of performance is done through the establishment of Probability of Detection (POD) laws integrating all sources of uncertainty inherent in the implementation of the procedure. These uncertainties are due to human and environmental factors in In-Service maintenance tasks. To establish experimentally these POD curves, it is necessary to have data from a wide range of operator skills, defect types and locations, material types, test protocols, etc. Obtaining these data evidences high costs and significant delays for the aircraft manufacturer. The scope of this thesis is to define a robust methodology of building POD from numerical modeling. The POD robustness is ensured by the integration of the uncertainties through statistical distributions issued from experimental data or engineering judgments. Applications are provided on titanium beta using high frequency eddy currents NDT technique. First, an experimental database will be created from three environments: laboratory, A321 aircraft and A400M aicraft. A representative sample of operators, with different certification levels in NDT technique, will be employed. Multiple inspection scenarios will be carried out to analyze these human and environmental factors. In addition, this study will take into account the impact of using different equipments in the HFEC test. This database is used, subsequently, to build statistical distributions. These distributions are the input data of the simulation models of the inspection. These simulations are implemented with the CIVA software. A POD module, based on the Monte Carlo method, is integrated into this software. This module will be applied to address human and ergonomic influences on POD. Additionally this module will help us to understand in a better way the equipment impact in POD curves. Finally, the POD model will be compared and validated with the experimental results developed.