[pt] O concreto de ultra-alto desempenho (CUAD) é um material cimentício avançado que possui excelente desempenho mecânico, ductilidade e durabilidade devido a uma elevada densidade de empacotamento e ao uso de fibras, promovendo benefícios à vida útil das estruturas. Grande parte das estruturas está sujeita a ações cíclicas, ou seja, variáveis com o tempo, resultando em danos de fadiga, como o surgimento e a propagação de trincas, que podem comprometer sua integridade. Assim, é essencial compreender o comportamento dos materiais sob fadiga para que sejam propostas diretrizes de projeto seguras e adequadas ao bom funcionamento das estruturas. Este trabalho visa, portanto, investigar o comportamento do concreto de ultra-alto desempenho pré-fissurado sob fadiga na flexão, quantificando sua degradação mecânica ao longo do carregamento cíclico a partir dos parâmetros de abertura de fissura (CMOD) e rigidez, contribuindo para o estudo desse tipo especial de concreto. Foram propostas equações para prever a vida à fadiga em relação ao limite superior de carga e estabelecer o limite de fadiga do concreto de ultra-alto desempenho, igual a 75,3 por cento, considerando o limite inferior igual a 30 cento do limite superior. Ainda, avaliou-se o comportamento pós-fadiga de amostras que não sofreram ruptura ao longo de 1.000.000 de ciclos, sendo possível observar que o mecanismo não gerou alterações no desempenho das amostras sob flexão para limites inferiores ao limite de fadiga. / [en] Ultra-high Performance Concrete (UHPC) is an advanced cementitious material that has excellent mechanical performance, ductility and durability due to a high packing density and the use of fibers, contributing to increase the structures lifespan. Most of the structures are subject to cyclic loads, which vary with time, resulting in fatigue damage such as the formation and propagation of cracks that could compromise its integrity. Thus, it is essential to understand the behavior of materials subjected to fatigue so that safe and proper design guidelines can be proposed for the appropriate performance of the structures. Therefore, this work aims to investigate the behavior of pre-cracked ultra-high performance concrete under flexural fatigue, quantifying its mechanical deterioration during cyclic loading through both crack mouth opening displacement (CMOD) and stiffness, which will contribute to the study of this special type of concrete. Equations were proposed to predict fatigue life according to the upper load limit during the cyclic loading and to establish the endurance limit of ultra-high performance concrete in 75,3 percent, considering the lower limit load equal to 30 percent of the upper limit. Also, when evaluating the post-fatigue behavior of samples that did not fail over 1,000,000 cycles it was possible to identify that the cyclic loading did not change the performance of the samples under bending, which was due to the use of upper loads below the endurance limit.

It is important to ensure that vulnerable structures (federal and provincial offices, military structures, embassies, etc) are blast resistant to safeguard life and critical infrastructure. In the wake of recent malicious attacks and accidental explosions, it is becoming increasingly important to ensure that columns in structures are properly detailed to provide the ductility and continuity necessary to prevent progressive collapse. Research has shown that steel fibre reinforced concrete (SFRC) can enhance many of the properties of concrete, including improved post-cracking tensile capacity, enhanced shear resistance, and increased ductility. The enhanced properties of SFRC make it an ideal candidate for use in the blast resistant design of structures. There is limited research on the behaviour of SFRC under high strain rates, including impact and blast loading, and some of this data is conflicting, with some researchers showing that the additional ductility normally evident in SFRC is absent or reduced at high strain loading. On the other hand, other data indicates that SFRC can improve toughness and energy-absorption capacity under extreme loading conditions. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 13 half-scale steel fibre reinforced concrete columns, 8 with normal strength steel fibre reinforced concrete (SFRC) and 5 with an ultra high performance fibre reinforced concrete (UHPFRC), were constructed and tested under simulated blast pressures. The columns were designed according to CSA A23.3 standards for both seismic and non-seismic regions, using various fibre amounts and types. Each column was exposed to similar shock wave loads in order to provide direct comparisons between seismic and non-seismically detailed columns, amount of steel fibres, type of steel fibres, and type of concrete. The dynamic response of the columns tested in the experimental program is predicted by generating dynamic load-deformation resistance functions for SFRC and UHPFRC columns and using single degree of freedom dynamic analysis software, RCBlast. The analytical results are compared to experimental data, and shown to accurately predict the maximum mid-span displacements of the fibre reinforced concrete columns under shock wave loading.

abstract: Being a remarkably versatile and inexpensive building material, concrete has found tremendous use in development of modern infrastructure and is the most widely used material in the world. Extensive research in the field of concrete has led to the development of a wide array of concretes with applications ranging from building of skyscrapers to paving of highways. These varied applications require special cementitious composites which can satisfy the demand for enhanced functionalities such as high strength, high durability and improved thermal characteristics among others. The current study focuses on the fundamental understanding of such functional composites, from their microstructural design to macro-scale application. More specifically, this study investigates three different categories of functional cementitious composites. First, it discusses the differences between cementitious systems containing interground and blended limestone with and without alumina. The interground systems are found to outperform the blended systems due to differential grinding of limestone. A novel approach to deduce the particle size distribution of limestone and cement in the interground systems is proposed. Secondly, the study delves into the realm of ultra-high performance concrete, a novel material which possesses extremely high compressive-, tensile- and flexural-strength and service life as compared to regular concrete. The study presents a novel first principles-based paradigm to design economical ultra-high performance concretes using locally available materials. In the final part, the study addresses the thermal benefits of a novel type of concrete containing phase change materials. A software package was designed to perform numerical simulations to analyze temperature profiles and thermal stresses in concrete structures containing PCMs. The design of these materials is accompanied by material characterization of cementitious binders. This has been accomplished using techniques that involve measurement of heat evolution (isothermal calorimetry), determination and quantification of reaction products (thermo-gravimetric analysis, x-ray diffraction, micro-indentation, scanning electron microscopy, energy-dispersive x-ray spectroscopy) and evaluation of pore-size distribution (mercury intrusion porosimetry). In addition, macro-scale testing has been carried out to determine compression, flexure and durability response. Numerical simulations have been carried out to understand hydration of cementitious composites, determine optimum particle packing and determine the thermal performance of these composites. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2018

It is important to ensure that vulnerable structures (federal and provincial offices, military structures, embassies, etc) are blast resistant to safeguard life and critical infrastructure. In the wake of recent malicious attacks and accidental explosions, it is becoming increasingly important to ensure that columns in structures are properly detailed to provide the ductility and continuity necessary to prevent progressive collapse. Research has shown that steel fibre reinforced concrete (SFRC) can enhance many of the properties of concrete, including improved post-cracking tensile capacity, enhanced shear resistance, and increased ductility. The enhanced properties of SFRC make it an ideal candidate for use in the blast resistant design of structures. There is limited research on the behaviour of SFRC under high strain rates, including impact and blast loading, and some of this data is conflicting, with some researchers showing that the additional ductility normally evident in SFRC is absent or reduced at high strain loading. On the other hand, other data indicates that SFRC can improve toughness and energy-absorption capacity under extreme loading conditions. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 13 half-scale steel fibre reinforced concrete columns, 8 with normal strength steel fibre reinforced concrete (SFRC) and 5 with an ultra high performance fibre reinforced concrete (UHPFRC), were constructed and tested under simulated blast pressures. The columns were designed according to CSA A23.3 standards for both seismic and non-seismic regions, using various fibre amounts and types. Each column was exposed to similar shock wave loads in order to provide direct comparisons between seismic and non-seismically detailed columns, amount of steel fibres, type of steel fibres, and type of concrete. The dynamic response of the columns tested in the experimental program is predicted by generating dynamic load-deformation resistance functions for SFRC and UHPFRC columns and using single degree of freedom dynamic analysis software, RCBlast. The analytical results are compared to experimental data, and shown to accurately predict the maximum mid-span displacements of the fibre reinforced concrete columns under shock wave loading.

The load-carrying and energy-dissipation capacities of ultra-high-performance concrete (UHPC) under dynamic loading are evaluated in relation to microstructure composition at strain rates on the order of 10⁵ s⁻¹ and pressures of up to 10 GPa. Analysis focuses on deformation and failure mechanisms at the mesostructural level. A cohesive finite element framework that allows explicit account of constituent phases, interfaces, and fracture is used. The model resolves essential deformation and failure mechanisms in addition to providing a phenomenological account of the effects of the phase transformation. Four modes of energy dissipation are tracked, including pressure-sensitive inelastic deformation, damage through the development of distributed cracks, interfacial friction, and energy released through phase transformation of the quartz silica constituent. Simulations are carried out over a range of volume fractions of constituent phases to quantify trends that can be used to design materials for more damage-resistant structures. Calculations show that the volume fractions of the constituents have more influence on the energy-dissipation capacity than on the load-carrying capacity, that inelastic deformation is the source of over 70% of the energy dissipation, and that the presence of porosity changes the role of fibers in the dissipation process. The results also show that the phase transformation has a significant effect on the load-carrying and energy-dissipation capacities of UHPC for the conditions studied. Although transformation accounts for less than 2% of the total energy dissipation, the phase transformation leads to a twofold increase in the crack density and yields nearly an 18% increase to the overall energy dissipation. Microstructure-behavior relations are established to facilitate materials design and tailoring for target-specific applications.

Der vorliegende Bericht beschreibt das Verhalten von ultrahochfestem Beton unter zweiaxialer Druckbeanspruchung. Bisher wurden ein Feinkornbeton und zwei Grobkornbetone mit unterschiedlichen Faserzusätzen untersucht. Die Zylinderdruckfestigkeiten nach 28 Tagen betragen rund 150, 160 und 170 N/mm². Besonders bei dem Feinkornbeton wurde eine überwiegend horizontale Ausrichtung der Stahlfasern festgestellt, die zu einer Anisotropie im Materialverhalten führte. Zusammenfassend muss festgestellt werden, dass die zweiaxiale Druckfestigkeit von UHPC nur geringfügig größer ist als die einaxiale. Für die Mischungen mit 2,5 Vol.-% Fasergehalt übersteigt die Festigkeit bei einem Spannungsverhältnis von Spannung 1 zu Spannung 2 gleich Eins die einaxiale Festigkeit um 7 bzw. 10 %. Bei dem Beton mit 0,9 Vol.-% Fasergehalt lag diese zweiaxiale Festigkeit sogar geringfügig unter der einaxialen. Bei der Bemessung von UHPC dürfen somit die vom Normalbeton bekannten Festigkeitssteigerungen unter mehraxialer Druckbelastung, wie sie z.B. bei reinen Druckknoten von Stabwerkmodellen angesetzt werden, nicht verwendet werden! Für die Beschreibung der Bruchkurve kann nach jetzigem Erkenntnisstand das Bruchkriterium nach OTTOSEN als eine gute Näherung empfohlen werden. Die Versuche haben gezeigt, dass sich UHPC in vielen, zum Teil sicherheitsrelevanten Bereichen anders verhält als Normalbeton. Für eine umfassende Beschreibung des Tragverhaltens sind weitere Versuche unter dreiaxiale Druckbelastung und kombinierter Druck-Zug-Belastung notwendig.

At an average age of 42 years, 10% of the nation’s over 607,000 bridges are posted for load restrictions, with an additional 15% considered structurally deficient or functionally obsolete. While there are major concerns with decks in 75% of structurally deficient bridges, often weight and geometry of the deck further limit the load rating and functionality of the bridge. Traditional deck systems and construction methods usually lead to prolonged periods of traffic delays, limiting options for transportation agencies to replace or widen a bridge, especially in urban areas. The purpose of this study was to develop a new generation of ultra-lightweight super shallow solid deck systems to replace open grid steel decks on movable bridges and as well serve as a viable alternative in bridge deck replacements across the country. The study has led to a lightweight low-profile asymmetric waffle deck made with advanced materials. The asymmetry comes from the arrangement of primary and secondary ribs, respectively perpendicular and parallel to the direction of traffic. The waffle deck is made with ultrahigh performance concrete (UHPC) reinforced with either high-strength steel (HSS) or carbon fiber reinforced polymer (CFRP) reinforcement. With this combination, the deck weight was limited to below 21 psf and its overall depth to only 4 inch, while still meeting the strength and ductility demands for 4 ft. typical stringer spacing. It was further envisioned that the ultra-high strength of UHPC is best matched with the high strength of HSS or CFRP reinforcement for an efficient system and the ductile behavior of UHPC can help mask the linear elastic response of CFRP reinforcement and result in an overall ductile system. The issues of consideration from the design and constructability perspectives have included strength and stiffness, bond and development length for the reinforcement, punching shear and panel action. A series of experiments were conducted to help address these issues. Additionally full-size panels were made for testing under heavy vehicle simulator (HVS) at the accelerated pavement testing (APT) facility in Gainesville. Detailed finite element analyses were also carried out to help guide the design of this new generation of bridge decks. The research has confirmed the superior performance of the new deck system and its feasibility.

It is important to ensure that vulnerable structures (federal and provincial offices, military structures, embassies, etc) are blast resistant to safeguard life and critical infrastructure. In the wake of recent malicious attacks and accidental explosions, it is becoming increasingly important to ensure that columns in structures are properly detailed to provide the ductility and continuity necessary to prevent progressive collapse. Research has shown that steel fibre reinforced concrete (SFRC) can enhance many of the properties of concrete, including improved post-cracking tensile capacity, enhanced shear resistance, and increased ductility. The enhanced properties of SFRC make it an ideal candidate for use in the blast resistant design of structures. There is limited research on the behaviour of SFRC under high strain rates, including impact and blast loading, and some of this data is conflicting, with some researchers showing that the additional ductility normally evident in SFRC is absent or reduced at high strain loading. On the other hand, other data indicates that SFRC can improve toughness and energy-absorption capacity under extreme loading conditions. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 13 half-scale steel fibre reinforced concrete columns, 8 with normal strength steel fibre reinforced concrete (SFRC) and 5 with an ultra high performance fibre reinforced concrete (UHPFRC), were constructed and tested under simulated blast pressures. The columns were designed according to CSA A23.3 standards for both seismic and non-seismic regions, using various fibre amounts and types. Each column was exposed to similar shock wave loads in order to provide direct comparisons between seismic and non-seismically detailed columns, amount of steel fibres, type of steel fibres, and type of concrete. The dynamic response of the columns tested in the experimental program is predicted by generating dynamic load-deformation resistance functions for SFRC and UHPFRC columns and using single degree of freedom dynamic analysis software, RCBlast. The analytical results are compared to experimental data, and shown to accurately predict the maximum mid-span displacements of the fibre reinforced concrete columns under shock wave loading.

The application of advanced materials in infrastructure has grown rapidly in recent years mainly because of their potential to ease the construction, extend the service life, and improve the performance of structures. Ultra-high performance concrete (UHPC) is one such material considered as a novel alternative to conventional concrete. The material microstructure in UHPC is optimized to significantly improve its material properties including compressive and tensile strength, modulus of elasticity, durability, and damage tolerance. Fiber-reinforced polymer (FRP) composite is another novel construction material with excellent properties such as high strength-to-weight and stiffness-to-weight ratios and good corrosion resistance. Considering the exceptional properties of UHPC and FRP, many advantages can result from the combined application of these two advanced materials, which is the subject of this research. The confinement behavior of UHPC was studied for the first time in this research. The stress-strain behavior of a series of UHPC-filled fiber-reinforced polymer (FRP) tubes with different fiber types and thicknesses were tested under uniaxial compression. The FRP confinement was shown to significantly enhance both the ultimate strength and strain of UHPC. It was also shown that existing confinement models are incapable of predicting the behavior of FRP-confined UHPC. Therefore, new stress-strain models for FRP-confined UHPC were developed through an analytical study. In the other part of this research, a novel steel-free UHPC-filled FRP tube (UHPCFFT) column system was developed and its cyclic behavior was studied. The proposed steel-free UHPCFFT column showed much higher strength and stiffness, with a reasonable ductility, as compared to its conventional reinforced concrete (RC) counterpart. Using the results of the first phase of column tests, a second series of UHPCFFT columns were made and studied under pseudo-static loading to study the effect of column parameters on the cyclic behavior of UHPCFFT columns. Strong correlations were noted between the initial stiffness and the stiffness index, and between the moment capacity and the reinforcement index. Finally, a thorough analytical study was carried out to investigate the seismic response of the proposed steel-free UHPCFFT columns, which showed their superior earthquake resistance, as compared to their RC counterparts.

The strain capacity of structures depends on the plastic hinge behaviour. There are different proposals in the scientific literature in order to improve this behaviour in reinforced concrete structures such as the following ones: proposals include the use of fiber reinforced concrete, very high performance concrete or replacing in the critical structure zone, the steel reinforcement with shape memory alloy and superelasticity bars (from this point forward SMA), among other solutions. However, the strain capacity of hinges is dependent on the compressed reinforcement buckling, which means a drastic diminishing in the bearing capacity and ductility. This phenomenon happens due to the cover spalling or degradation, or due to an insufficient transverse reinforcement arrangement. The design codes propose requirements related to the diameter of longitudinal bars and to the transverse reinforcement separation to assure the bearing capacity or to assure the hinge rotation without the compressed reinforcements buckle. Nevertheless, the aforementioned requirements are not valid in compressed elements made of new materials (fiber reinforced concrete, very high performance concrete or SMA bars). This doctoral thesis analyzes the compressed steel or NiTi - SMA bars behaviour in elements made of conventional, high strength or very high performance concrete, with or without fibres. Therefore, an experimental research has been carried out to study the local instability of the compressed bars (steel and NITI) in concrete elements. 32 columns subject to a bending-compression load have been analyzed. An analytic model has been proposed to analyze the buckling critical stress and length in the compressed bars in concrete elements. This model has been calibrated based on experimental tests. It has been performed an experimental and numerical research to analyze the behaviour of the NITI bars as isolated bars. It has been proposed an analytic model to calculate the relationship stress-strain of the compressed bars that includes the buckling effect. This model has been verified by both experimental and numerical results. Finally, it has been proposed an expression to calculate the maximum separation of the transverse reinforcement according to the required limited stress, for both steel and SMA bars. In order to define that stress, two criteria have been proposed: one of them is based on stresses and the other one on strains. With respect to the concrete without fibres case, the proposed expression has been compared with the current code. / La capacidad de deformación de las estructuras depende del comportamiento de las rótulas plásticas. Para mejorar dicho comportamiento en estructuras de hormigón armado, en la literatura técnica se propone utilizar hormigón con fibras de acero en su masa, hormigón de muy altas prestaciones o sustituir en la zona crítica de la estructura las armaduras de acero por barras de aleación con memoria de forma y superelasticidad (en adelante SMA) entre otras soluciones. Sin embargo, la capacidad de deformación de las rótulas está condicionada por el pandeo de la armadura comprimida, lo que supone una disminución drástica de la capacidad resistente y de la ductilidad. Este fenómeno se produce porque el recubrimiento del hormigón salta o se degrada, o por una insuficiente disposición de armadura transversal. En las normativas de diseño se proponen requisitos acerca del diámetro y de la separación de la armadura transversal para asegurar la capacidad resistente o la deformación de la rótula sin que las armaduras comprimidas pandeen. Sin embargo, dichas expresiones no son válidas en elementos comprimidos fabricados con nuevos materiales (hormigón con fibras en su masa, hormigones de muy altas prestaciones o barras de SMA). En esta tesis doctoral se analiza el comportamiento de barras comprimidas, de acero o de SMA en base NiTi, en elementos fabricados con hormigones convencionales, de alta resistencia o de muy altas prestaciones, con o sin fibras en su masa. A tal efecto, se ha ejecutado un programa experimental para estudiar la inestabilidad local de las barras comprimidas (acero y NiTi) en elementos de hormigón. Se han analizado un total de 32 soportes sometidos a una solicitación de flexo-compresión. Se ha propuesto un modelo analítico para determinar la tensión y la longitud crítica de pandeo de barras comprimidas en elementos de hormigón. Este modelo ha sido calibrado con los ensayos experimentales. Se ha realizado un estudio experimental y numérico para analizar el comportamiento de las barras de NiTi como barras aisladas. Se ha propuesto un modelo analítico para calcular la relación tensión - deformación de barras comprimidas que incluye el efecto del pandeo. Este modelo ha sido verificado tanto con los resultados experimentales como numéricos. Finalmente, se ha propuesto una expresión para el cálculo de la separación máxima de la armadura transversal en función de la tensión límite requerida, tanto para barras de acero como de SMA. Para la definición de dicha tensión se proponen dos criterios: uno basado en tensiones y otro en deformaciones. En el caso de hormigón sin fibras, la expresión propuesta se ha comparado con la normativa actual. / La capacitat de deformació de les estructures depén del comportament de les ròtules plàstiques. Per a millorar dit comportament en estructures de formigó armat, en la literatura tècnica es proposa utilitzar formigó amb fibres d'acer en la seua massa, formigó de molt altes prestacions o substituir en la zona crítica de l'estructura les armadures d'acer per barres d'aliatge amb memòria de forma i superelasticitat (d'ara endavant SMA) entre d'altres solucions. No obstant això, la capacitat de deformació de les ròtules està condicionada pel vinclament de l'armadura comprimida, la qual cosa suposa una disminució dràstica de la capacitat resistent i de la ductilitat. Este fenomen es produeix perquè el recobriment del formigó salta o es degrada, o per una insuficient disposició de l'armadura transversal. En les normatives de disseny es proposen requisits quant al diàmetre i a la separació de l'armadura transversal per assegurar la capacitat resistent o la deformació de la ròtula sense que les armadures comprimides vinclen. No obstant això, estes expressions no son vàlides en elements comprimits fabricats amb nous materiales (formigó amb fibres en la seua massa, formigons de molt altes prestacions o barres de SMA). En esta tesis doctoral s'analitza el comportament de barres comprimides, d'acer o de SMA compost per NiTi, en elements fabricats amb formigons convencionals, d'alta resistència o de molt altes prestacions, amb o sense fibres en la seua massa. A tal efecte, s'ha executat un programa experimental per estudiar la inestabilitat local de les barres comprimides (acer i NiTi) en elements de formigó. S'han analitzat un total de 32 soports somesos a una solicitació de flexo-compressió. S'ha proposat un model analític per determinar la tensió i longitud crítica de vinclament de barres comprimides en elements de formigó. Este model ha sigut calibrat amb els assajos experimentals. S'ha realitzat un estudi experimental i numéric per analitzar el comportament de les barres de NiTi com barres aïllades. S'ha proposat un model analític per calcular la relació tensió-deformació de barres comprimides que inclou l'efecte del vinclament. Este model ha sigut verificat tant amb els resultats experimentals com numérics. Finalment, s'ha proposat una expressió per al càlcul de la separació màxima de l'armadura transversal en funció de la tensió límit requerida., tant per a barres d'acer com de SMA. Per a la definició de dita tensió es proposen dos criteris: uno basat en tensions i l'altre en deformacions. En el cas del formigó amb fibres, l'expressió proposada s'ha comparat amb la normativa actual. / Pereiro Barceló, J. (2017). INESTABILIDAD DE BARRAS COMPRIMIDAS DE ACERO Y DE SMA EN ELEMENTOS DE HORMIGÓN FABRICADOS CON NUEVOS MATERIALES. RECOMENDACIONES DE DISEÑO [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90650 / TESIS