Understanding the Hydromechanical Effects of Extreme Events To Improve the Performance of Infrastructure Foundations

Extreme hydroclimatic events like heavy rainfall, flooding, and prolonged drought can potentially cause the failure of infrastructure foundations, leading to socio-economic losses. The objective of this dissertation is to understand the deformation and bearing capacity behavior of drilled shafts subjected to extreme hydroclimatic events, including heavy rainfall, prolonged drought, and earthquake. The Finite Element Method (FEM) results show that during rainfall, the drilled shaft settled caused by a decrease in the porewater pressure in the sand leading to a decrease in the axial bearing capacity. The axial force variation from an experimental investigation showed good agreement with the FEM. The impact of natural hazards on deep foundations can be critical and highly unpredictable when extreme hydrological and seismic events occur simultaneously or in sequence. A multi-hazard analysis was carried out to understand the structural response of deep foundations. When the drilled shaft was subjected to the dynamic load from heavy rainfall followed by dynamic load from the earthquake, the vertical settlement for the drilled shaft was significantly high compared to the case where the drilled shaft was subjected to dynamic load from the earthquake. A case study was adopted to predict the structural response of drilled shaft at the end bent of a proposed bridge subjected to liquefaction-induced lateral spreading caused by extreme earthquake events. The structural response of the bridge foundation before, during, and after liquefaction-induced lateral spreading was predicted using analytical methods and FEM. The comparison results showed that the during-liquefaction scenario was the worst-case

Recent Advancements in Non-Destructive Testing Techniques for Structural Health Monitoring

Structural health monitoring (SHM) is an important aspect of the assessment of various structures and infrastructure, which involves inspection, monitoring, and maintenance to support economics, quality of life and sustainability in civil engineering. Currently, research has been conducted in order to develop non-destructive techniques for SHM to extend the lifespan of monitored structures. This paper will review and summarize the recent advancements in non-destructive testing techniques, namely, sweep frequency approach, ground penetrating radar, infrared technique, fiber optics sensors, camera-based methods, laser scanner techniques, acoustic emission and ultrasonic techniques. Although some of the techniques are widely and successfully utilized in civil engineering, there are still challenges that researchers are addressing. One of the common challenges within the techniques is interpretation, analysis and automation of obtained data, which requires highly skilled and specialized experts. Therefore, researchers are investigating and applying artificial intelligence, namely machine learning algorithms to address the challenges. In addition, researchers have combined multiple techniques in order to improve accuracy and acquire additional parameters to enhance the measurement processes. This study mainly focuses on the scope and recent advancements of the Non-destructive Testing (NDT) application for SHM of concrete, masonry, timber and steel structures

Capteurs à fibre optique pour le monitorage des poutres en béton armé réhabilitées avec des matériaux composites

Plusieurs pays ont un grand besoin de réparer et renforcer leur infrastructure routière. Presque partout. Ie traffic a beaucoup dépassé les charges de design initial. Les pays nordiques connaissent des conditions hivernales extrêmes qui sont combinées avec l'utilisation de sels de déglaçage et qui accélère la détérioration de structures. Au Canada, l'état de détérioration force les gouvernements, dont les gouvernements fédéral et provinciaux, a envisager l'utilisation des polymères renforces de fibres (PRF) pour prolonger la durée de vie des structures existantes. Les matériaux innovateurs PRF utilises pour la réhabilitation des structures déficientes peuvent être facilement instrumentés avec des systèmes de monitorage. Les détecteurs intégrés pourront fournir des informations a propos de l'état des structures, une baisse en performance ou une défaillance majeure, optimisant ainsi leur durée de vie sans en compromettre la sécurité. Les capteurs a fibre optique (CFO) sont des nouveaux candidats pour Ie monitorage a long-terme de structures existantes ou de nouvelles structures pendant leur durée de service. Us sont peu encombrants, nécessitent moins de câblage et sont capables de mesurer des valeurs absolues, un attribut essentiel pour Ie monitorage a long terme. De plus, ils peuvent être associés à des méthodes d'évaluation non-destructive pour mieux connaitre l'état de santé des structures. La recherche actuelle a démontré Ie potentiel des PRF et des CFO dans Ie domaine de génie civil. L'utilisation des PRF comme renforcements externes est devenue une technique très efficace pour augmenter la résistance des structures en béton armé. Toutefois, peu d'études ont porte sur la durabilité à long terme des matériaux composites utilisés pour Ie renforcement externe des poutres en bêton arme. Par conséquent, quelques incertitudes restent quant a leur résistance à la fatigue, combinée avec des conditions extrêmes comme Ie climat nordique. Les CFO ont été intégrés avec succès dans des PRF et testes sous des conditions de charge différentes. Peu d'études portent sur leur résistance a un chargement cyclique, et aucune étude n'a encore été publiée sur leur durabilité à l'exposition environnementale. II est important de comprendre leur comportement dans ces conditions avant de les intégrés à large échelle dans des projets de monitorage.Abstract: In Canada, the extent of deterioration has prompted many authorities, including the federal and provincial governments, to investigate the potential use of fibre-reinforced polymer (FRP) products to extend the life of their existing structures. Fibre optic sensors (FOS) are serious candidates for the long-term monitoring of both existing and new structures throughout their working life. Research up to date demonstrated the potential of both FRP and FOS systems in the civil engineering field. The FRP systems used as an external reinforcement proved to be very efficient in increasing the strength of concrete structures. However, few studies focused on the long-term durability of these materials when used as external reinforcement of RC beams. As a result, there is a concern regarding the fatigue resistance of these materials when they are exposed to harsh environmental conditions. Previous studies showed that the FOS systems were successfully integrated in FRP products and tested in various loading conditions. A few studies touch upon the fatigue resistance of FOS, and no study has been reported on their durability when exposed to aggressive environments. It is important to understand the behaviour of FOS when they are submitted to these conditions before implementing them extensively in long-term health monitoring projects. This extensive experimental project was undertaken in order to assess the durability of FOS systems installed on the FRP used as external reinforcement for reinforced concrete beams. Knowing that the FOS installed on a support structure was submitted to various loading and water exposure conditions, the durability of both the FOS and RC beams strengthened with carbon-fibre-reinforced polymers was assessed. The originality of this study consists in the fact that, to the author's knowledge, it is the only experimental program on the durability of FOS installed on a structural element submitted to various fatigue and post-fatigue loading conditions. In addition, it combines the effects of fatigue loading with water exposure conditions. The maximum strain values as well as the numbers of fatigue cycles to which the FOS were tested are larger than in any other previous study. Moreover, the RC beams strengthened with FRP tested in the same conditions with the FOS, were submitted to environmental fatigue, that is water exposures combined with fatigue loading. Finally, the impact resonance method (IRM), a non-destructive testing technique, was for the first time employed to monitor fatigue damage for this type of specimens."--Résumé abrégé par UMI

Experimental Evaluation of a Distributed Fiber Optic Sensor for Mining Application

Triggered remote seismic events have been widely studied in the earthquake engineering context where various possible explanations have been provided, including directivity of dynamic stresses, a critically stressed environment, the presence of hydrothermal geological environments at remote distances, and so on. Similar events have been observed in underground mining regions; however, they have rarely been studied in terms of the underlying mechanisms such as the presence of faults of marginal stability, increases in the stress gradient between mined out regions as a result of connective fractures, unclamping effect on geological features such as dikes or joint swarms, and so on. This research was triggered in part by the hypothesis that remote seismic events in mines could be triggered when gravity-driven displacements are transferred to distances far from active mining (10’s to 100’s of metres). Accordingly, the thesis focuses on experimental research on a novel deformation sensing sensor for future verification of this assumption. A secondary focus is mathematical modeling to help understand the deformation mechanisms and magnitudes that may take place in a jointed rock mass. Distributed Brillouin sensing systems (DBSs) have found growing applications in engineering and are attracting attention in the field of underground structures including mining. The capability for continuous measurements of strain over large distances makes DBSs a promising monitoring approach for understanding deformation field evolution within a rock mass, particularly when the sensor is installed away from “excavation damaged zones” (EDZ). A purpose-built fiber optic sensing cable, a vital component of DBSs, was assessed in laboratory conditions to establish the capability and limitations of this technology to monitor deformation fields over large distances. A test program was performed to observe DBSs response to various perturbations including axial and shear strain resulting from joint movements. These tests included assessments of the strain-free cable response and the application of extensional and lateral displacement to various sensing cable lengths (strained lengths from 1 m down to 1 cm). Furthermore, tests were done to evaluate the time-dependent behavior of the cable and to observe the effect of strain transfer using a soft host material (i.e., a soft grout) under lateral displacement. The noise level of the DBSs range was ±77 µε, determined through repeated measurements on an unstrained cable. Stretching test results showed a linear correlation between the applied strain and the Brillouin frequency shift change for all strained lengths above half the spatial resolution of the DBSs. However, for strained lengths shorter than half the spatial resolution, no strain response was measurable and this is due to the applied internal signal processing of the DBSs to detect peak Brillouin gain spectrum and noise level. The stability with time of the measurements was excellent for test periods up to 15 hours. Lateral displacement test results showed a less consistent response compared to extension tests for a given applied displacement. The Brillouin frequency shift change is linearly correlated with the applied displacement in tension but it shows a parabolic variation with lateral displacement. Moreover, the registered frequency response (correlated with strain) of the system decreased significantly when the sensing cable was embedded in a sand-filled tube compared with direct cable displacement. A comprehensive laboratory scale testing program was undertaken to study the response of the system to different loading paths in time and space domains. Purely extensional displacement fields were applied to demonstrate that the system could produce repeatable displacement responses for three different configurations of distributed strained patterns. A borehole installation method was developed by testing the sensing cable’s response while embedded in mortar beams. When the cable is directly embedded in the mortar, uncontrolled self-debonding happens that introduces uncertainties in the measurements. This limitation was overcome by anchoring debonded sections of the sensing cable at regular spacing. This arrangement produced consistent strain patterns for each strained interval. It was shown that the performance of the debonded sections changes for longer anchor spacing and for closely spaced joints where more than one joint crosses the debonded interval. The influence of borehole diameter and strength of the filling material were evaluated for their possible effects on the strain transfer process to the sensing cable. With the anchored arrangement of debonded cables, these properties of the grout did not have a measurable effect on the results, and as long as the tensile strength of the grout is low enough to break at the joint locations, the strain transfer performance from the rockmass to the sensing cable was excellent. A study was devoted to understanding such a deformation monitoring system under various shear displacement conditions. These included the difference in response of the system in direct shear compared to tests performed in direct tension. The system response was evaluated for various strained lengths as well as distances over which the bending strains are acting (kink lengths). The latter was found to be an important factor influencing monitoring results. In addition, the system behavior under shear displacement where the sensor is inclined with respect to the joint strike was evaluated to understand the effect of a combined extension and shear displacement. The effect of the existence of two joints over the strained lengths was assessed in both direct and inclined shear. A new relation was established between the registered Brillouin frequency shift change and all contributing components of deformation when the sensor is elongated while under shear displacement. The testing program shows that Distributed Brillouin Sensing (DBS) technology has promise for detecting deformations over long distances. Not only strain localization occurring at pre-existing discontinuities or at developing cracks can be detected by this sensor, but also strain levels well below the typical damage initiation threshold (~0.1%) for hard brittle rocks are above the basic noise level of the system. However, the sensing element is quite fragile when under shear displacement and can easily break at small shear displacements. Therefore, it is better to have an idea of the dominant deformation mechanism in the rock mass before the installation of the sensor. The sensor would be much more durable where the rock mass experiences less shearing. Mathematical simulations of a 2D rock mass were carried out using the distinct element method. Two major parameters including interlocking degree and pre-existing conditions such as mined-out zones at higher levels were studied. Different rock mass models with varying block sizes, joint set orientations, and joint persistency were built to study the effect of interlock on the displacement pattern away from mining. In general, displacement as large as 5 cm could travel distances as far as 500 m away from the active mining zone. The exact displacement pattern is largely controlled by the characteristics of the joints sets. However, the transfer of large displacements was limited to distances of the size of the mining boundary, where rock mass interlocking promote arching. Furthermore, with non-persistent joint sets, a few shear slip events were noticed at higher levels whereas more remote joints did not show slip. All slip events were close to the mining boundary. Remote shear slip events, could not be generated by changing parameters representing the degree of interlock in the rock mass. When a backfilled old mine was added to the middle height of the model, some 500 m away from active mining, results showed that a large number of joints around the old mining zone slipped due to displacements induced by the distant deeper mining. It was found that the pre-existing excavation and the mine extraction strategy is a critical factor for providing conditions under which such slip events at remote distances occur from active mining

On Plume Dispersion after Line Source in Crossflows over Rough Surfaces

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Development of a Long-term, Multimetric Structural Health Monitoring System for a Historic Steel Truss Swing Bridge

The bridge stock across the United States is ageing, with many bridges approaching the end of their design life. The situation is so dire that the American Society of Civil Engineers gave the nation’s bridges a grade of “C+” in the 2013 edition of their Report Card on America’s Infrastructure. In fact, at the end of 2011, nearly a quarter of all bridges in the United States were classified as either structurally deficient or functionally obsolete. Thus, the nation’s bridges are in desperate need of rehabilitation and maintenance. However, limited funds are available for the repair of bridges. Management of the nation’s bridge infrastructure requires an efficient and effective use of available funds to direct the maintenance and repair efforts. Structural health monitoring has the potential to supplement the current routine of scheduled bridge inspections by providing an objective and detailed source of information about the status of the bridge. This research develops a framework for the long-term monitoring of bridges that leverages multimetric data to provide value to the bridge manager. The framework is applied to the Rock Island Arsenal Government Bridge. This bridge is a historic, steel truss, swing bridge that spans the Mississippi River between Rock Island, IL and Davenport, IA. The bridge is owned and operated by the US Army Corps of Engineers (USACE) and is a vital link for vehicular, train, and barge traffic. The USACE had a system of fiber optic strain gages installed on the bridge. As part of this research, this system was supplemented with a wireless sensor network that measured accelerations on the bridge. The multimetric data from the sensor systems was collected using a program developed in the course of this research. The data was then analyzed and metrics were developed that could be used to determine the health of the structure and the sensor networks themselves. Statistical process control methods were established to detect anomalous behavior in the short and long term time scales. Methods to locate and quantify the damage that has occurred in the structure once an anomaly has been detected were demonstrated. One of the methods developed as part of this research was a first order flexibility method. The SHM system this research develops has the desirable characteristics of being continuous temporally, multimetric, scalable, robust, autonomous, and informative. By necessity, some aspects of the developed SHM framework are unique and customized exclusively for the Rock Island Government Bridge. However, the principles developed in the framework are applicable to the development of an SHM system for any other bridge. Application of the SHM framework this research develops to other bridges has the potential to increase objectivity in the evaluation of bridges and focus maintenance efforts and funds on the bridges that are most critical to the public safety.Financial support for this research was provided in part by the Army Corps of Engineers Construction Engineering Research Laboratory (CERL) through a subcontract with Mandaree Enterprise Corporation.Ope

Building of tri-axial strain gauge based on FBG sensors

Since their invention, sensors based on optical fibers are powerful and versatile devices. Nowadays they play a fundamental role in many different fields, e.g., telecommunication, civil engineering, science research and more. Wide applications are related to the possibility of realize the so called Fiber Bragg Grating (FBG). A FBG is a fiber in which a Bragg grating is created: this is a periodic modulation of the refractive index of the fiber core, that acts like a band-rejection filter with respect to the light travelling into the fiber. This particular kind of structure allows to realize several optical devices like Fabry-P ́ erot or Circulator. High reflectivity FBG can be also used as mirrors at the ends of a doped fiber to create fiber laser. The grating period and, consequently, the reflected and transmitted wavelengths, depend on the temperature variation and fiber dilatation or contraction. Observing the wavelength shift it is possible to evaluate the temperature changes or the fiber elongation, this make the FBG a thermometer and a strain gauge. Moreover we can measure external perturbations converting them into fiber strain by a suitable system. So FBGs can be used in devices like flow-meter, magnetic/electric field meter etc. Relevant applications of FBGs can be found in geology and geophysics. Within these fields, in particular, there is a project that is planning to use them as strain sensors: MEDiterranean SUpersite Volcanoes (MED-SUV), an European project under the coordination of European Plate Observing System (EPOS). This project, together with FUTUREVOLC and MARsite, plans to enhance the current knowledge bout geohazards, in order to improve the scientific institutions capacity in preventing the damage on environment and population. MED-SUV is focused on the study of Italian volcanoes: CampiFlogei/Vesuvius and Etna. As a general framework, this thesis is involved in the MED-SUV project, which studies mount Etna. In collaboration with Marwan Technology, a spin-off company of the Department of Physics of Pisa niversity, we have realized a tri-axial strain gauge sensor and the interrogating system that controls it. The sensor is designed to measure the rock movements along the three Cartesian axes. This kind of measurement requires that the sensor is installed in hostile environment, on the slope of mount Etna. For these reasons, the project specifications for the building of sensor and interrogation system are: low cost, low energetic consumption and reduced dimension. In particular, the last parameter is due to the necessity of installing the sensor in the bottom of a 10 meter borehole, dug in the basalt rock. The interrogation system has been realized with the cooperation of the Osservatorio Vesuviano, whose researchers realized the ”GILDA datalogger”, expressly studied to work in hostile environment and that will be use as acquisition system. To interrogate the response of the FBGs, we have assembled an opto-electronic device based on a super luminescent diode, as light source, an Array Waveguide Grating (AWG) as wavelength discriminator, and six photodiodes, to convert light signal into voltage difference. Using energy-saving components, solar panels and battery this interrogation system is designed to work unattended for months. We successfully tested it the in laboratory, verifying that the sensor can measure strain with a sensitivity of the order of 0.5 [με ] and a dynamic range of 120 [με]

Development of optical fibre distributed sensing for the structural health monitoring of bridges and large scale structures

Tesi per compendi de publicacionsPremi extraordinari doctorat UPC curs 2017-2018. Àmbit d’Enginyeria Civil i AmbientalIn this doctoral thesis it is proposed to research and assess the performance of the use of distributed optical fiber sensors (DOFS), more specifically the case of the optical backscattered reflectometry (OBR) based system, to the structural health monitoring (SHM) of bridges and large scale structures. This is a relatively recent technology that has demonstrated great promise for monitoring applications in a wide range of fields but due to its novelty, still presents several uncertainties which prevent its use in a more systematic and efficient way in civil engineering infrastructures. This is even more evident and relevant in the case of the application of this sensing technique to concrete structures. In this way, this thesis pretends to continue and further analyse this topic following the initial applications using the OBR system as a possible alternative/complementary monitoring tool in concrete structures. Therefore, in the present thesis, after an initial and thorough literature review on the use of DOFS in civil engineering applications, a set of experiments and analysis is planned and carried out. Firstly, different laboratory experimental campaigns are devised where multiple aspects of the instrumentation of DOFS technology in civil engineering applications are assessed and scrutinized. Consequently, the study of new implementation methods, comparison and performance analysis of different bonding adhesives and spatial resolution is performed through the conduction of load tests in reinforced concrete beam elements instrumented with OBR DOFS technology. Moreover, the long-term reliability of this sensing typology is also assessed through the conduction of a fatigue load test on two additional reinforced concrete beams. Afterwards, the use of the OBR system technology is assessed for the application in two real world structures in Barcelona, Spain. The first application corresponds to a previous monitoring work conducted in a historical masonry building and UNESCO World Heritage Site, which was subjected to rehabilitation works and where the collected data was analysed and interpreted in this thesis. The second real world structure application is an urban prestressed concrete viaduct that was exposed to major renovation actions, which included the widening of its deck and the introduction of new steel elements on the improved pedestrian sidewalks. This second application was conducted through a relatively extended period of time, which spanned from early summer to deep winter and therefore causing subsequent important thermal variations effects implications on the performance of the instrumented OBR system leading to the necessity of its compensation. Finally, taking into account the previous points, several conclusions are obtained related with the proficiency and limitations on the use of this particular type of optical sensing system in concrete structures. The advantages and disadvantages on the use of different types of bonding adhesives, implementation methodologies and spatial resolutions are described. Additionally, the performance of this technology in real world conditions is studied and characterized.En aquesta tesi doctoral es proposa investigar i avaluar la possibilitat d´aplicació de sensors de fibra òptica distribuïda (DOFS), més concretament un sistema del tipus OBR (Optical Backscattered Reflectometry), a la monitorització de la salut estructural (SHM) de ponts i estructures de grans dimensions. Es tracta d'una tecnologia relativament recent que ha demostrat una gran versatilitat i validesa en diferents aplicacions en un ampli ventall de camps, però que, a causa de la seva novetat, encara presenta diverses incerteses que impedeixen el seu ús d'una manera més sistemàtica i eficient en el cas de les infraestructures d'enginyeria civil. Sent això especialment cert i rellevant en el cas de l'aplicació d'aquesta tipologia de detecció en estructures de formigó. D'aquesta manera, aquesta tesi pretén continuar i analitzar aquest tema seguint les aplicacions inicials utilitzant el sistema OBR com una possible eina i de control alternatiu o complementari en estructures de formigó. Per tant, en aquesta tesi, després d'una revisió inicial i exhaustiva de la literatura sobre l'ús de DOFS en aplicacions d'enginyeria civil, es planifiquen i executen un conjunt d'assaigs experimentals i el seu posterior anàlisi. En primer lloc, es desenvolupen diferents campanyes experimentals de laboratori on s'avaluen i examinen múltiples aspectes de la tecnologia DOFS en aplicacions d'enginyeria civil. Com a conseqüència, s´estudien nous mètodes d'implementació, de comparació i anàlisi de rendiment de diferents adhesius de connexió i de resolució espaial mitjançant la realització de proves experimentals en elements a flexió a de formigó armat equipats amb tecnologia OBR DOFS. A més, la fiabilitat a llarg termini d'aquesta tipologia de sensors també s'avalua mitjançant la realització d'un assaig de fatiga en dos bigues de formigó armat addicionals. Posteriorment, l'ús de la tecnologia del sistema OBR s'avalua de cara a la seva aplicació en dues estructures reals a Barcelona, Espanya. La primera aplicació correspon a un treball de seguiment previ dut a terme en un edifici històric de maçoneria i que és Patrimoni de la Humanitat de la UNESCO (l´hospital de Sant Pau), que es va sotmetre a obres de rehabilitació i on es van analitzar i interpretar les dades recollides durant l´execució de les obres. La segona aplicació és un pont de formigó pretensat urbà que va estar exposat a una important intervenció de renovació, que va incloure l'ampliació de la coberta i la introducció de nous elements d'acer a les voreres de vianants. Aquesta segona aplicació es va dur a terme a través d'un període de temps relativament estès, que va des del començament de l'estiu fins a ben entrat l'hivern i, per tant, va provocar variacions tèrmiques importants tant als materials com als propis sensors, que van tenir conseqüències sobre el rendiment del sistema OBR instrumentat i que va comportar la necessitat de la seva compensació. Finalment, tenint en compte els punts anteriors, s'obtenen diverses conclusions relacionades amb la competència i les limitacions sobre l'ús d'aquest tipus particular de sistema de detecció òptica en estructures de formigó. Es descriuen els avantatges i desavantatges sobre l'ús de diferents tipus d'adhesius de connexió, metodologies d'implementació i resolucions espaials. Addicionalment, s'estudia i caracteritza l'acompliment d'aquesta tecnologia en condicions reals i no de laboratori.Award-winningPostprint (published version