Dissertations / Theses on the topic 'Bending reinforced concrete elements'

Il collasso di diverse colonne, caratterizzate da danneggiamenti simili, quali ampie fessure fortemente inclinate ad entrambe le estremità dell’elemento, lo schiacciamento del calcestruzzo e l’instabilità dei ferri longitudinali, ha portato ad interrogarsi riguardo gli effetti dell’interazione tra lo sforzo normale, il taglio ed il momento flettente. Lo studio è iniziato con una ricerca bibliografica che ha evidenziato una sostanziale carenza nella trattazione dell’argomento. Il problema è stato approcciato attraverso una ricerca di formule della scienza delle costruzioni, allo scopo di mettere in relazione lo sforzo assiale, il taglio ed il momento; la ricerca si è principalmente concentrata sulla teoria di Mohr. In un primo momento è stata considerata l’interazione tra solo due componenti di sollecitazione: sforzo assiale e taglio. L’analisi ha condotto alla costruzione di un dominio elastico di taglio e sforzo assiale che, confrontato con il dominio della Modified Compression Field Theory, trovata tramite ricerca bibliografica, ha permesso di concludere che i risultati sono assolutamente paragonabili. L’analisi si è poi orientata verso l’interazione tra sforzo assiale, taglio e momento flettente. Imponendo due criteri di rottura, il raggiungimento della resistenza a trazione ed a compressione del calcestruzzo, inserendo le componenti di sollecitazione tramite le formule di Navier e Jourawsky, sono state definite due formule che mettono in relazione le tre azioni e che, implementate nel software Matlab, hanno permesso la costruzione di un dominio tridimensionale. In questo caso non è stato possibile confrontare i risultati, non avendo la ricerca bibliografica mostrato niente di paragonabile. Lo studio si è poi concentrato sullo sviluppo di una procedura che tenta di analizzare il comportamento di una sezione sottoposta a sforzo normale, taglio e momento: è stato sviluppato un modello a fibre della sezione nel tentativo di condurre un calcolo non lineare, corrispondente ad una sequenza di analisi lineari. La procedura è stata applicata a casi reali di crollo, confermando l’avvenimento dei collassi.

The finite element method (FEM) is commonly used to design the reinforcement in concrete slabs. In order to simplify the analysis and to be able to utilize the superposition principle for evaluating the effect of load combinations, a linear analysis is generally adopted although concrete slabs normally have a pronounced non-linear response. This type of simplification in the modeling procedure will generally lead to unrealistic concentrations of cross-sectional moments and shear forces. Concrete cracks already at service loads, which leads to redistribution of moments and forces. The moment- and force-peaks, obtained through linear finite element analysis, can be redistributed to achieve a distribution more similar to what is seen in reality. The topic of redistribution is however poorly documented and design codes, such as the Eurocode for concrete structures, do not give descriptions of how to perform this in practice. In 2012, guidelines for finite element analysis for the design of reinforced concrete slabs were published in a joint effort between KTH Royal Institute of Technology, Chalmers University of Technology and ELU consulting engineers, which was financially supported by the Swedish Transport Administration. These guidelines aim to include the non-linear response of reinforced concrete into a linear analysis. In this thesis, the guidelines mentioned above are followed to obtain reinforcement plans based on crack control, for a fictitious case study bridge by means of a 3D finite element model. New models were then constructed for non-linear analyses, where the reinforcement plans were implemented into the models by means of both shell elements as well as a mixture of shell and solid elements. The results from the non-linear analyses have been compared to the assumptions given in the guidelines. The results from the non-linear analyses indicate that the recommendations given in the aforementioned guidelines are indeed reasonable when considering crack width control. The shell models yield crack widths equal to approximately half the design value. The solid models, however, yielded cracks widths that were 15 - 20$\%$ lower than the design value. The results show that many factors attribute to the structural behavior during cracking, most noticeably the fracture energy, a parameter not featured in the Eurocode for concrete structures. Some limitations of the models used in this thesis are mentioned as well as areas for further improvement.

Creating sustainability and public infrastructure is a fairly recent subject the engineering community has been debating. Introducing new building materials or introducing new structural designs is a strategy for constructing buildings that have long-term reliability and low maintenance requirements. Fiber-reinforced polymers (FRP) are one of the innovative approaches in the field of civil engineering that offer promising results in this regard. In order to maximize the usage of FRP forms, researchers suggested the development of hybrid structural structures by mixing composite materials with standard materials, such as concrete, to enhance the stability, ductility and buckling resistance of single FRP members. Nevertheless, these composite solutions need more preliminary research to prove its feasibility due to the complexity and large range of hybrid components. However, as there is a current shortage of compulsory codes for the design of composite structures and consequently FRP-concrete members, accurate predictive models need to be created. Thus, the present work aims at testing the structural efficiency of hybrid slabs made of CFRP sheets under a concrete layer in bending and shear configurations by carrying an experimental and analytical analysis. Using Carbon Fiber Reinforced Polymer (CFRP) bonded with resin is usual to strengthen concrete slabs or other elements. This thesis introduces a novel technological definition of thin CFRP-concrete unidirectional hybrid slabs. In bending part, experimental quasi-static three-points bending tests and modal analysis tests were carry out to analyze the influence of the connection systems on the dynamic response. Moreover, the corresponding analytical methodology to calculate their response are presented. Four different connection strategies between CFRP sheet and concrete were tested. These included flexible mesh embedding and particle-based frictional enhancement. The maximum bending moment, the evolution of the neutral axis, the comparison between external moment (calculated from applied load) and internal moment (calculated from strain distribution), the CFRP-concrete interface shear stress, and the evolution of the vertical displacement at the loading point are the main results obtained from the tests. In shear part, this work investigates the shear behavior of hybrid slabs that used different types of particles and/or a flexible high strength fabric to connect both materials: concrete and CFRP sheet. Several pure-shear experiments have been carried out to characterize the interface shear response of these hybrid elements. These increase the experimental database on CFPR-concrete shear connection systems. Experimental results showed that the improvement resulting from fabric embedding is far more significant than other tested connection elements at increasing the shear connection strength between the parts of the composite slabs. Results are divided with technological and scientific contributions. The feasibility of using CFRP sheets in hybrid unidirectional slabs instead of steel sheets is the main technological contribution, which also offers the following advantages: lighter weight and resistance to corrosion. Qualitative and quantitative analysis of the CFRP-concrete connection alternatives point out that combining adherence and frictional based strategies is the most promising method. An analytical method for the modelling of concrete slabs with CFRP was developed. In function of full cross-section interaction some equations for bending ultimate limit states were suggested. The possibility of using simpler formulas for quantifying interlayer slip effects was analyzed in assessing deflections, flexural stiffness, bending efficiency and normal and shear stress distributions. The proposed analytical method was able to capture the structural behavior and performance of the specimens.
La creació d'infraestructura pública i sostenible és un tema de plena actualitat que la comunitat de l¿enginyeria ha estat debatent des de fa anys. Els polímers reforçats amb fibra (FRP) són un dels materials innovadors en el camp de l'enginyeria civil que ofereixen resultats prometedors en aquest sentit. Per maximitzar l'ús de formes de FRP s'estan desenvolupant estructures híbrides barrejant materials compostos amb materials tradicional, com el formigó, per millorar l'estabilitat, ductilitat i resistència al vinclament de membres individuals de FRP. A més, com hi ha una escassetat actual de codis obligatoris per al disseny d'estructures compostes i, en conseqüència, elements de formigó FRP, cal crear models predictius necessaris perquè es puguin estandarditzar. Abordar els problemes esmentats anteriorment és essencial per augmentar la introducció de materials compostos avançats en tipus comuns d'obres i construccions públiques. Així, el present treball té com a objectiu provar l'eficiència estructural de lloses híbrides de làmines de CFRP amb una capa de formigó, en configuracions de flexió i tallant, mitjançant la realització d'un anàlisi experimental i analític. L'ús de polímers reforçats amb fibra de carboni (CFRP) unit amb resina és habitual per reforçar lloses i altres elements de formigó. Aquesta tesi introdueix una definició tecnològica innovadora de lloses híbrides unidireccionals de formigó-CFRP de làmina prima. A la part de flexió es van realitzar assajos experimentals de flexió quasiestàtics, de tres punts, i assajos d'anàlisi modal per analitzar la influència dels sistemes de connexió en la resposta dinàmica. Així mateix, es presenta la metodologia analítica corresponent per calcular la seva resposta. Es van provar quatre estratègies de connexió diferents entre la làmina de CFRP i el formigó. Aquestes van incloure l¿embegut de malla flexible en el formigó i la millora de la fricció basada en partícules. El moment flector màxim, l'evolució de l'eix neutre, la comparació entre el moment extern (calculat a partir de la càrrega aplicada) i el moment intern (calculat a partir de les deformacions), l'esforç tallant de la interfície CFRP-formigó i l'evolució del desplaçament vertical en el punt de càrrega, són els principals resultats obtinguts de les proves. Aquest treball investiga el comportament rasant de lloses híbrides on els materials de CFRP i formigó es van connectar mitjançant diferents tipus d'agregats i tèxtils flexibles d'alta resistència. S'han dut a terme experiments de tall pur per caracteritzar la resposta de la interfície d'aquests elements híbrids. Aquests assajos augmenten la base de dades experimental sobre sistemes de connexió de tall de formigó-CFPR. Els resultats experimentals van mostrar que la tela embeguda produeix una millora en l'augment de la resistència estructural de manera molt més significativa que amb altres sistemes de connexió provats. La viabilitat d'utilitzar xapes de CFRP en lloses unidireccionals híbrides, en lloc de xapes d'acer, és la principal aportació tecnològica que, a més, ofereix els següents avantatges: menor pes i major resistència a la corrosió. Els anàlisis qualitatiu i quantitatiu de les alternatives de connexió CFRP-formigó assenyalen que la combinació d'estratègies basades en adherència i fricció és el mètode més prometedor. Així mateix, es va desenvolupar un mètode analític per a la modelització de lloses de formigó amb CFRP. En funció dels principis de la interfície completa, es suggereixen equacions per calcular els estats límit últims. La possibilitat d'utilitzar fórmules més simples per quantificar els efectes de lliscament entre capes va ser analitzada en l'avaluació de deflexions, rigidesa de flexió, eficiència de flexió i distribucions d'esforços normals i tallants. El mètode analític proposat va ser capaç de capturar el comportament estructural i el rendiment mecànic de les mostres.
La creación de infraestructura pública y sostenible es un tema de plena actualidad que la comunidad de ingenieros ha estado debatiendo desde hace años. La introducción de nuevos materiales de construcción o la introducción de nuevos diseños estructurales es una estrategia eficiente para construir edificios que tengan fiabilidad a largo plazo y requisitos de bajo mantenimiento. Los polímeros reforzados con fibra (FRP) son uno de los materiales innovadores en el campo de la ingeniería civil que ofrecen resultados prometedores en este sentido. Para maximizar el uso de formas de FRP se están desarrollando estructuras híbridas mezclando materiales compuestos con materiales estándar, como el hormigón, para mejorar la estabilidad, ductilidad y resistencia al pandeo de miembros individuales de FRP. Sin embargo, estas soluciones compuestas necesitan más investigación preliminar para demostrar su viabilidad debido a la complejidad y la amplia gama de componentes híbridos. Además, como existe una escasez actual de códigos obligatorios para el diseño de estructuras compuestas y, en consecuencia, elementos de hormigón FRP, es necesario crear modelos predictivos precisos para que puedan estandarizarse. Abordar los problemas mencionados anteriormente es esencial para aumentar la introducción de materiales compuestos avanzados en tipos comunes de obras y construcciones públicas. Así, el presente trabajo tiene como objetivo probar la eficiencia estructural de losas híbridas de láminas de CFRP con una capa de hormigón, en configuraciones de flexión y cortante, mediante la realización de un análisis experimental y analítico. El uso de polímeros reforzados con fibra de carbono (CFRP) unido con resina es habitual para reforzar losas y otros elementos de hormigón. Esta tesis introduce una definición tecnológica novedosa de losas híbridas unidireccionales de hormigón-CFRP de lámina delgada. En la parte de flexión se realizaron ensayos experimentales de flexión cuasi estáticos, de tres puntos, y ensayos de análisis modal para analizar la influencia de los sistemas de conexión en la respuesta dinámica. Asimismo, se presenta la metodología analítica correspondiente para calcular su respuesta. Se probaron cuatro estrategias de conexión diferentes entre la lámina de CFRP y el hormigón. Estos incluyeron el embeber una malla flexible en el hormigón y la mejora de la fricción basada en partículas. El momento flector máximo, la evolución del eje neutro, la comparación entre el momento externo (calculado a partir de la carga aplicada) y el momento interno (calculado a partir de la distribución de deformaciones), el esfuerzo cortante de la interfaz CFRP-hormigón y la evolución del desplazamiento vertical en el punto de carga, son los principales resultados obtenidos de las pruebas. En el estudio del cortante, este trabajo investiga el comportamiento rasante de losas híbridas donde los materiales de CFRP y hormigón se conectaron mediante diferentes tipos de agregados y textiles flexibles de alta resistencia. Se han llevado a cabo experimentos de corte puro para caracterizar la respuesta de la interfaz de estos elementos híbridos. Estos ensayos aumentan la base de datos experimental sobre sistemas de conexión de corte de hormigón-CFPR. Los resultados experimentales mostraron que la tela embebida produce una mejora en el aumento de la resistencia estructural de manera mucho más significativa que con otros sistemas de conexión probados. Los resultados de la tesis se dividen en contribuciones de tipo tecnológico y científico. La viabilidad de utilizar chapas de CFRP en losas unidireccionales híbridas, en lugar de chapas de acero, es el principal aporte tecnológico, que además ofrece las siguientes ventajas: menor peso y mayor resistencia a la corrosión. Los análisis cualitativo y cuantitativo de las alternativas de conexión CFRP-hormigón señalan que la combinación de estrategias basadas en adherencia y fricción es el método más prometedor. Asimismo, se desarrolló un método analítico para el modelado de losas de hormigón con CFRP. En función de los principios de la conexión completa se sugieren ecuaciones conceptuales para calcular los estados límite últimos. La posibilidad de utilizar fórmulas más simples para cuantificar los efectos de deslizamiento entre capas fue analizada en la evaluación de deflexiones, rigidez de flexión, eficiencia de flexión y distribuciones de esfuerzos normales y cortantes. El método analítico propuesto fue capaz de capturar el comportamiento estructural y el rendimiento mecánico de las muestras.
Anàlisi estructural

Numerical Analysis of Passive Force on Skewed BridgeAbutments with Reinforced Concrete WingwallsScott Karl SnowDepartment of Civil and Environmental Engineering, BYU Master of Science Historically bridges with skewed abutments have proven more likely to fail during earthquake loadings (Toro et al, 2013) when compared to non-skewed bridges (Apirakvorapinit et al. 2012; Elnashai et al. 2010). Previous studies including small-scale laboratory tests by Jessee (2012), large-scale field tests by Smith (2014), and numerical modeling by Shamsabadi et al. (2006) have shown that 45° skewed bridge abutments experience a reduction in peak passive force by about 65%. With numerous skewed bridges in the United States, this study has great importance to the nation's infrastructure.The finite element models produced in this study model the large-scale field-testing performed by Smith (2014), which was performed to study the significant reduction in peak passive resistance for abutments with longitudinal reinforced concrete wingwalls. The finite element models largely confirm the findings of Smith (2014). Two models were created and designed to match the large-scale field tests and were used to calibrate the soil parameters for this study. Two additional models were then created by increasing the abutment widths from 11 feet to 38 feet to simulate a two-lane bridge. The 45° skewed 11-foot abutment experienced a 38% reduction in peak passive resistance compared to the non-skewed abutment. In contrast, the 45° skewed 38-foot abutment experienced a 65% reduction in peak passive resistance compared to the non-skewed abutment. When the wingwalls are extended 10 feet into the backfill the reduction decreased to 59% due to the change in effective skew angle.The finite element models generally confirmed the findings of Smith (2014). The results of the 11- and 38-foot abutment finite element models confirmed that the wingwall on the obtuse side of the 45° skewed abutments experienced approximately 4 to 5 times the amount of horizontal soil pressure and 5 times the amount of bending moment compared to the non-skewed abutment. Increases in the pressures and bending moments are likely caused by soil confined between the obtuse side of the abutment and the wingwall.A comparison of the 11- and 38-foot 45° skewed abutment models showed a decrease in the influence of the wingwalls as the abutment widened. The wingwall on the acute side of the 38-foot abutment developed approximately 50% of the horizontal soil pressure compared to the 11-foot abutment. The heave distribution of the 11-foot abutment showed approximately 1- to 2-inches of vertical displacement over a majority of the abutment backwall versus more than half of the 38-foot abutment producing ½ an inch or less.

This thesis describes a non-linear finite element model suitable for the analysis of reinforced concrete, or steel, structures under general three-dimensional states of loading. The 20 noded isoparametric brick element has been used to model the concrete and reinforcing bars are idealised as axial members embedded within the concrete elements. The compressive behaviour of concrete is simulated by an elasto-plastic work hardening model followed by a perfectly plastic plateau which is terminated at the onset the . crushing. In tension, a smeared crack model with fixed orthogonal cracks has been used with the inclusion of models for the retained post-cracking stress and the reduced shear modulus. The non-linear equations of equilibrium have been solved using an incremental-iterative technique operating under load control. The solution algorithms used are the standard and the modified Newton-Raphson methods. Line searches have been implemented to accelerate convergence. The numerical integration has been generally carried out using 15 point Gaussian type rules. Results of a study to investigate the performance of these rules show that the 15 point rules are accurate and computationally efficient compared with the 27(3X3X3) point Gaussian rule. The three- dimensional finite element model has been used to investigate the problem of elasto-plastic torsion of homogeneous members. The accuracy of the finite element solutions obtained for beams of different cross-sections subjected to pure and warping torsion have been assessed by comparing them with the available exact or approximate analytical solutions. Because the present work is devoted towards the analysis of reinforced concrete members which fail in shear or torsional modes, the computer program incorporates three models to account for the degradation in the compressive strength of concrete due to presence of tensile straining of transverse reinforcement. The numerical solutions obtained for reinforced concrete panels under pure shear and beams in torsion and combined torsion and bending reveal that the inclusion of a model for reducing the compressive strength of cracked concrete can significantly improve the correlation of the predicted post-cracking stiffness and the computed ultimate loads with the experimental results. Parametric studies to investigate the effects of some important material and solution parameters have been carried out. It is concluded that in the presence of a compression strength reduction model, the tension-stiffening parameters required for reinforced concrete members under torsion should be similar to those used for members in which bending dominates.

Este trabalho aborda um dos tipos construtivos mais empregados em lajes de edificações no Brasil, que são as lajes com nervuras pré-moldadas com armação treliçada. O objetivo principal do trabalho é contribuir na avaliação da continuidade estrutural relativa aos momentos fletores negativos nos apoios destas lajes. Para a realização deste trabalho, as lajes em concreto pré-moldado formadas por vigota com armação treliçada foram analisadas segundo modelos teóricos e experimentais. Na análise teórica, a consideração da não-linearidade física do concreto é realizada a partir do uso da relação momento x curvatura proposta pelo código modelo CEB-90 em conjunto com a técnica do carregamento incremental. Os resultados do modelo teórico são confrontados com os resultados obtidos em ensaios experimentais de faixas de lajes contínuas dimensionadas com diferentes graus de redistribuição dos momentos fletores negativos. Nas análises realizadas observa-se que: a) o modelo teórico apresenta bons resultados comparados aos resultados experimentais, b) as lajes apresentam boa capacidade de rotação plástica, c) com alta taxa de armadura negativa não ocorre redistribuição de esforços, d) as flechas praticamente independem da taxa de armadura negativa e e) a força última é praticamente independente do grau de redistribuição adotado no dimensionamento.
This work deal with an usual type of slab in Brazil: slabs made by precast joist with lattice reinforcement. The goal of this work is the structural analysis of bending moments in the supports of slabs made by this kind of precast element. Theoretical and experimental models analyze this type of slab. In the theoretical analysis, the non-linear concrete behavior is done by moment x curvature relationship of Model Code CEB-90 add incremental load technique. The theoretical model is compared with experimental results of continuous strip slabs designed with different degrees of bending moment redistribution. In these analysis had been noted: a) the theoretical model presents good results compared with the experimental results, b) the slabs present good plastic rotation capacity, c) with high negative reinforcement ratio in the support does not happen moment redistribution, d) the displacement is practically independent of negative reinforcement ratio and e) the ultimate load is practically independent of redistribution degree idealized in the design.

Tragwerke aus Stahlbeton weisen infolge des Kriechens und Schwindens des Betons ein zeitveränderliches Materialverhalten auf. Die Folge sind Umlagerungen der im Querschnittsinneren wirkende Kräfte und im Zeitverlauf zunehmende Verformungen. Zur Beurteilung dieses Langzeitverhaltens sind geeignete Berechnungsmodelle erforderlich, die im Planungsstadium eine zuverlässige Prognose ermöglichen. Dabei spielen nicht nur reine Stahlbetonkonstruktionen eine Rolle, sondern im Zuge von Ertüchtigungsmaßnahmen werden zur Erhöhung der Tragfähigkeit zunehmend auch textile Bewehrungen aus Carbon- und AR-Glasfasern eingesetzt. Durch die beanspruchungsgerecht aufzubringenden Bewehrungsstrukturen und einen speziellen Feinbeton können sehr geringe Betonschichtdicken realisiert werden. Es entsteht ein Verbundquerschnitt mit unterschiedlichen Betonrezepturen, gleichfalls unterschiedlichem Betonalter und mit mehreren verschiedenen Bewehrungskomponenten. Um Aussagen zum Langzeitverhalten derartiger Konstruktionen treffen zu können, ist eine ganzheitliche Betrachtung über alle diese im Verbund liegenden Komponenten mit ihren jeweiligen Materialeigenschaften erforderlich. Im Rahmen der vorliegenden Arbeit sind in einem ersten Schritt die Stoffgesetze für die beteiligten Materialien Beton, Stahl- und Textilfaserbewehrung zu formulieren. Im Mittelpunkt steht dabei das viskoelastische Verhalten des Betons, für dessen baumechanische Beschreibung ein geeignetes rheologisches Modell in Form einer Feder-Dämpfer-Kombination dargestellt und die zugehörige Spannungs-Dehnungs-Zeit-Beziehung hergeleitet wird. Ferner wird aufgezeigt, wie die erforderlichen Materialparameter mit Hilfe üblicher Berechnungsansätze für Kriechen und Schwinden (z.B. nach EUROCODE 2) kalibriert werden können. Die betrachteten Textilfasern werden zunächst mit linear-elastischem Verhalten in Rechnung gestellt. Auf alternative Ansätze, die auch hier viskoelastische Eigenschaften berücksichtigen, wird hingewiesen, und das Berechnungsmodell ist dahingehend erweiterbar gestaltet. In einem zweiten Schritt werden die Materialmodelle der Einzelkomponenten nach den mechanischen Grundprinzipien von Gleichgewicht und Verträglichkeit und unter der BERNOULLIschen Annahme eines eben bleibenden Querschnittes miteinander in Beziehung gesetzt. Hierfür ist eine inkrementelle Vorgehensweise erforderlich, die mit dem Zeitpunkt der ersten Lastaufbringung beginnt und schrittweise den darauffolgenden Zustand berechnet. Im Ergebnis entsteht ein Algorithmus, der die am Querschnitt stattfindenden Veränderungen im Spannungs- und Dehnungsverhalten unter Einbeziehung der Stahlbewehrung sowie einer ggf. vorhandenen Textilbetonschicht wirklichkeitsnah erfaßt. Für statisch bestimmte Systeme mit bekanntem Schnittkraftverlauf wird gezeigt, wie sich so zu jeder Zeit an jeder Stelle der vorliegende Dehnungszustand und aus diesem über die Krümmung die Durchbiegung berechnen läßt. Der dritte und für viele praktische Anwendungen wichtigste Schritt besteht darin, die am Querschnitt hergeleiteten Beziehungen in ein finites Balkenelement zu überführen und dieses in ein FE-Programm zu implementieren. Auch das gelingt auf inkrementellem Wege, wobei für jedes Zeitinkrement die Spannungs- und Verformungszuwächse aller Elemente mit Hilfe des NEWTON-RAPHSON-Verfahrens über die Iteration des Gleichgewichtszustandes am gesamten System bestimmt werden. Hierzu werden einige Beispiele vorgestellt, und es werden die Auswirkungen des Kriechens und Schwindens mit den sich daraus ergebenden Folgen für das jeweilige Tragwerk erläutert. Ferner wird gezeigt, wie textilbewehrte Verstärkungsmaßnahmen gezielt eingesetzt werden können, um das Trag- und Verformungsverhalten bestehender Bauwerke unter Beachtung des zeitveränderlichen Materialverhaltens kontrolliert und bedarfsgerecht zu beeinflussen
Structures of reinforced concrete show a time-varying material behaviour due to creeping and shrinking of the concrete. This results in the rearrangement of the stresses in the cross-section and time-depending increase of the deformations. Qualified calculation models enabling a reliable prediction during the design process are necessary for the assessment of the long-term behavior. Not only pure reinforced concrete structures play an important role, but within retrofitting actions textile reinforcements of carbon and AR-glass fibres are applied in order to enhance the load-bearing capacity. A small concrete-layer-thickness can be achieved by the load-compatible application of reinforced textile configurations and the usage of a special certain fine-grained concrete. It leads to a composite section of different concrete recipes, different concrete ages and also several components of reinforcement. To give statements for the long-term behaviour of such constructions, a holistic examination considering all this influencing modules with their particular material properties is necessary. Within this dissertation in a first step the material laws of the participated components, as concrete, steel and textile reinforcement, are defined. The focus is layed on the visco-elastic behaviour of the concrete. For its mechanical specification a reliable rheological model in terms of a spring-dashpot-combination is developed and the appropriate stress-strain-time-relation is derived. Furthermore the calibration of the required material parameters considering creep and shrinkage by means of common calculation approaches (e.g. EUROCODE 2) is demonstrated. For the textile fibres a linear-elastic behaviour is assumed within the calculation model. It is also refered to alternative approaches considering a visco-elastic characteristic and the calculation model is configured extendable to that effect. In a second step the material models of the single components are correlated taking into account the mechanical basic principles of equilibrium and compatibility as well as the BERNOULLIan theorem of the plane cross-section. Therefore an incremental calculation procedure is required, which starts at the moment of the first load-application and calculates the subsequent configuration step by step. In the result an algorithm is derived, that realistically captures the occuring changings of stress and strain in the cross-section by considering the steel reinforcement as well as a possibly existing layer of textile concrete. For statically determined systems with known section force status it is demonstrated how to calculate the existing condition of strain and following the deflection via the curvaturve at every time and at each position. The third step - for many practical applications the most important one - is the transformation of the derived relations at the cross-section into a finite beam-element and the implementation of this in a FE-routine. This also takes place in an incremental way, whereat for each time-increment the increase of stress and strain for all elements is identified by using the NEWTON-RAPHSON-method within the iteration process for the equilibrium condition of the whole system. Meaningful numerical examples are presented and the effects of creep and shrinkage are explained by depicting the consequences for the particular bearing structure. Moreover it is shown how the purposeful use of textile reinforcement strengthening methodes can influence and enhance the load-bearing and deflection characteristics of existing building constructions by considering the time-varying material behaviour

The diploma thesis deals with the analysis of internal forces and the design of the reinforcement of a reinforced concrete monolithic slab, a reinforcing wall and a column in the 1st floor of a dairy hall building. The fire resistance of selected structures was taken into account during dimensioning. The calculation of the internal forces was performed by the finite element method in Dlubal RFEM 5.24.

The bending displacement capacity of elongated wall-like gravity-load columns subjected to lateral displacements due to earthquake demands on a high-rise building is of considerable concern. The long cross-sectional dimension makes these members much less flexible compared to square columns. Elongated gravity-load columns are popular because they can be hidden in walls and because they reduce the span of floor slabs, which means the thickness of the floor slabs can be reduced. No previous tests have been done on elongated gravity-load columns subjected to simulated earthquake loading. In the current study, five half-scale specimens including four column specimens and one wall specimen were subjected to constant axial compression and reverse cyclic lateral load to determine the displacement capacity of the members. The cross-sectional width-to-length ratios of the four columns were 1:1 (square), 1:2, 1:4, 1:8 and the wall specimen was 1:8. The load-deformation responses of the specimens were predicted using two nonlinear programs Response2000 and VecTor2, as well as hand calculation procedures. The predictions were used to design the test setup and were compared with the test results in order to better understand the significance of the test results. The predicted load capacities of all specimens were found to be similar to the observed maximum loads; but the displacement capacities of all specimens were significantly higher than predicted. Slip of the vertical reinforcing bars from the column foundations contributed to a large part of the increased displacement capacity of the columns. Only the elongated columns with a cross-sectional width-to-length ratios of 1:4 and 1:8 and the wall specimen suffered complete collapse during the test.

Thesis (M.S.)--West Virginia University, 1999.
Title from document title page. Document formatted into pages; contains xi, 100 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 96-99).

This diploma thesis deals with the analysis of reinforced concrete structure with masonry walls. Scia Engineer was used for finite element analysis. The spatial models include nonlinear behavior of masonry. Furthermore, the ceiling slab above the 1st floor, beams and columns were designed.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
The reinforced concrete structures, when properly designed and performed, have prolonged its life. However, the lack of proper maintenance, acting loads greater than the design ones, pathological manifestations due to aggressive environment and accidents can impair the performance of the structure requiring the need for repair or structural strengthening. The technique of structural strengthening with application of carbon fiber reinforced polymer (CFRP), bonded externally to the reinforced concrete has advantages such as fast execution, which added to the characteristics of the composite as a high modulus of elasticity make wide its use. The aim of this study is to analyze through an experimental program the structural behavior of reinforced concrete beams strengthened in bending with CFRP. The methodology used was the production of three groups of five RC beams each one, with the same dimension of rectangular cross section, for bending test. The first group of beams was called VA. The second and third groups, called VB and VC and had different ratio of reinforcement. In each group of five beams, one beam was not strengthened (reference beam) and the remaining beams were strengthened with two, three, four and five layers of carbon fiber. The experimental results indicate the efficiency of strengthening, noting an increase in stiffness in all strengthened beams. The increase of load capacity was also observed in all groups of beams varying between 9,11% and 16,69%, 55,14% and 86,83%, 89,46% and 126,18%, of the beams of group VA, VB and VC, respectively in relation to the reference beam of each group. Of the carried through study was observed the excellent performance of strengthening in bending with carbon fiber especially in beams with the lowest ratios of reinforcement (group C), besides gathering a lot of information that can be useful for design criteria of the recovered and strengthened structures.
As estruturas de concreto armado, quando convenientemente projetadas e executadas tÃm sua vida Ãtil prolongada, porÃm, a falta de manutenÃÃo adequada, as solicitaÃÃes de cargas superiores Ãs de projeto, as manifestaÃÃes patolÃgicas devido ao meio ambiente agressivo e a ocorrÃncia de acidentes podem comprometer o desempenho da estrutura exigindo a necessidade de uma recuperaÃÃo ou reforÃo estrutural. A tÃcnica de reforÃo estrutural com a aplicaÃÃo de polÃmeros reforÃados com fibra de carbono (PRFC) colados externamente a peÃas de concreto armado apresenta vantagens como a rÃpida execuÃÃo que, somada a caracterÃsticas do compÃsito como alto mÃdulo de elasticidade fazem largo o seu uso. O objetivo desse trabalho à analisar atravÃs de um programa experimental o comportamento estrutural de vigas de concreto armado reforÃadas à flexÃo com PRFC. A metodologia utilizada foi a produÃÃo de trÃs grupos de vigas de concreto armado, com a mesma dimensÃo de seÃÃo transversal retangular para ensaio à flexÃo. O primeiro grupo, denominado grupo VA, foi dimensionado com seÃÃo normalmente armada. O segundo e terceiro grupo de vigas, aqui denominados grupo VB e grupo VC, respectivamente, foram dimensionados com seÃÃo subarmada, com taxas de armaduras distintas. Cada grupo possuÃa cinco vigas, sendo que, uma viga nÃo foi reforÃada (de referÃncia) e as demais vigas foram reforÃadas com duas, trÃs, quatro e cinco camadas de fibra de carbono. Os ensaios experimentais comprovaram a eficiÃncia do reforÃo, constatando-se um aumento de rigidez de todas as vigas reforÃadas. Observou-se tambÃm o aumento da capacidade resistente em todos os grupos de vigas, variando entre 9,11% e 16,69%, 55,14% e 86,83%, 89,46% e 126,18%, das vigas dos grupos VA, VB e VC, respectivamente, em relaÃÃo à viga de referÃncia de cada grupo. O estudo demonstrou o excelente desempenho do reforÃo à flexÃo com fibra de carbono, especialmente nas vigas com menores taxas de armadura (grupo VC), alÃm de reunir uma sÃrie de informaÃÃes que podem ser Ãteis para critÃrios de projeto de estruturas recuperadas e reforÃadas.

The deflection of Glass Fibre Reinforced Polymer Reinforced Concrete (GFRP RC) is often the governing criterion for design. The lack of fundamental research particularly on the tension stiffening behaviour of GFRP RC has hindered both the development of fundamental equations to predict deflection and the use of nonlinear Finite Element (FE) analysis for predicting the structural behaviour of GFRP RC. This thesis investigates the tension stiffening effect of GFRP RC in an effort to improve the predictability of GFRP RC deformation behaviour. The study adopts a holistic approach for tension stiffening which considers the bond as the building block for tension stiffening modelling and tension stiffening as being a macroscopic representation of bond modelling. In this study tension stiffening is experimentally evaluated first against more generic variables like concrete strength, reinforcement ratio and bar diameter. This is followed by a detailed study on bond between concrete and GFRP which results in the development of a strain distribution function to represent bond between cracks. This formed the basis for the development of a comprehensive model to analyse the tension stiffening behaviour of direct tension tests. After evaluating the tension stiffening test results against existing code-based formulations, the CEB-FIP model is recalibrated to represent the tension stiffening behaviour of GFRP RC, thereby providing a simplified means to evaluate tension stiffening behaviour of GFRP RC. The successful implementation of the tension stiffening model is demonstrated through the prediction of deflection of flexural elements using a general nonlinear FE analysis package (ABAQUS) that uses the smeared crack approach to model the reinforced concrete behaviour.

This study developed a reinforced steel rod bending machine for rods with diameters of up to 8 mm and annealed wire cutter for up to 5 kg for replacing manual intervention required to bend rods in reinforced concrete columns. This study aims to reduce the physical effort that could lead to occupational diseases, such as tenosynovitis, bursitis, muscle disorders. Clamp manufacturing possesses great risk for workers, who are exposed to injuries while using different cutting devices, such as grinders and electric saws. They also face potential problems such as muscular fatigue due to the nonergonomic and repetitive work positions. The proposed machine features a mechanical dragging and bending systems and manual shears. Additionally, the proposed machine has been designed theoretically and its effectiveness has been assessed through simulations conducted using the SolidWorks CAD software. A bending machine prototype for producing clamps is developed and its machine productivity is measured. Using this machine, approximately 300 clamps can be bent per hour without possessing any risk to the worker.

Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Zureick Abdul-Hamid; Committee Member: Ellingwood, Bruce R.; Committee Member: Kahn, Lawrence F.; Committee Member: Kardomateas, George A.; Committee Member: Will, Kenneth M. Part of the SMARTech Electronic Thesis and Dissertation Collection.

It has been demonstrated that transverse reinforcement not only provides the strength and stiffness for reinforced concrete (RC) members through direct resistance to external force demands, but also helps confine the inner core concrete. The confinement effect can lead to improved overall structural performance by delaying the onset of concrete fracture and allowing more inelastic energy dissipation through an increase in both strength and deformability of RC members. The objective of this research was to evaluate the effect of confinement due to the transverse reinforcement on enhancing the shear performance of RC members. A new constitutive model of RC members was proposed by extending the Modified Compression Field Theory (MCFT) to incorporate the effect of confinement due to transverse reinforcement by adjusting the peak stress and peak strain of confined concrete in compression. The peak stress of confined concrete was determined from the five-parameter failure surface for concrete developed by Willam and Warnke (1974). The peak strain adjustment was carried out using a relationship proposed by Mander et al. (1988). The proposed analytical model was compared with results from an experimental program on sixteen RC bent caps with varied longitudinal and transverse reinforcement details. Two-dimensional Finite Element Modeling (FEM) using the proposed constitutive model was conducted to numerically simulate the RC bent cap response. Results showed that the proposed analytical model yielded good results on the prediction of the strength but significantly overestimated the post-cracking stiffness of the RC bent cap specimens. The results also indicated that the confinement effect led to enhanced overall performance by increasing both the strength and deformability of the RC bent caps. Two potential causes of the discrepancy in the underestimation of the RC bent cap deformations, namely the effects of concrete shrinkage and interfacial bond-slip between the concrete and main flexural reinforcement in the bent caps, were discussed. Parametric studies showed that the tension-stiffening in the proposed constitutive models to implicitly take into account the bond-slip between the concrete and main flexural reinforcement was the major cause of the overestimation of the post-cracking stiffness of RC bent caps. The explicit use of bond-link elements with modified local bond stress-slip laws to simulate the slip between the concrete and main flexural reinforcement led to good predictions of both strength and deformation.

Six reinforced concrete specimens, modeling the wall of a nuclear reactor containment structure, were tested under cyclic thermal effects and cyclic applied loading. To study the behaviour of the reactor wall, three of the specimens were tested under axial tension, while the other three were tested in flexure. The specimens were subjected to cyclic loads, strains, and a combination of loads and strains, equivalent to 25 and 50 years in the life of the actual structure. The stiffness of the specimen and the cracks on the specimen were monitored.
The test results confirmed that the largest increases in crack widths and the largest drop in stiffness occurred in the cycling that would be equivalent to the first 25 years of the structure's service life. Proposed procedures are given to determine the responses of the tension and bending specimens for monotonic loading, after the equivalent of 25 years, and after the equivalent of 50 years. The influence of cycling was accounted for by determining suitable tension stiffening factors, as a function of the number of cycles of loading and the level of tensile strain.

The main objective of this research is to establish durability design models for flexural concrete elements subjected to a given aggressive environment. Because corrosion of reinforcement due to chloride ingress is the most significant threat to an existing reinforced concrete structure such as a road bridge or a harbor facility which is exposed to chloride-rich environments, corrosion due to chloride ingress is emphasized in this research. The concrete beams can get corroded to different corrosion levels. Mass loss of the reinforcement is an important parameter, and it can help define the corrosion level, and this information can be used to develop a correlation between corrosion, cracking, bond strength at the steel-concrete interface, and the ultimate strength of the reinforced concrete elements. Therefore, the prediction model of reinforcement mass loss under different levels of chloride concentration needs to be established first using the principles of corrosion electrochemistry. Secondly, design development length is determined based on the mass loss prediction and bond strength equation. Thirdly, the model for the prediction of flexural capacity of reinforced concrete beam for a given design service life is established. Some examples of practical durability design are presented. Finally, a step-by-step durability design procedure is recommended for use by practicing engineers. (Abstract shortened by UMI.)

[ES] El principal objetivo de la presente tesis es el desarrollo de una completa metodología para el modelado numérico del UHPFRC desde el material hasta el elemento estructural. Se pretende contribuir al avance del conocimiento del comportamiento mecánico del UHPFRC obteniendo como resultado un procedimiento para la modelización numérica que permita el modelado y diseño estructural que permitiría hacer que este material fuera competitivo para ser utilizado en el mercado de la construcción. En la metodología de modelado propuesta, se considera un comportamiento constitutivo del UHPFRC optimizado por medio de un procedimiento directo y fiable con el que se aprovechan las ventajas del material, resultando en un diseño estructural eficiente desde el punto de vista mecánico y económico. ¿Es necesario producir SH-UHPFRC para conseguir grandes propiedades mecánicas? ¿Es posible generar SS-UHPFRC de manera que queden reducidos los costos iniciales y se mantengan unas propiedades mecánicas y de durabilidad competitivas que comporten un diseño estructural efectivo? El desarrollo de UHPFRC con bajo endurecimiento por deformación y de SS-UHPFRC puede reducir sus propiedades mecánicas, pero si son adecuadamente estudiadas y controladas, éstos podrían ser optimizados. La tesis aborda algunas de estas cuestiones a través del estudio del comportamiento a tracción que va desde SH-UHPFRC hasta SS-UHPFRC. Se pretende llevar a cabo una propuesta de procedimiento fiable para caracterizar el comportamiento constitutivo a tracción y definir un modelo numérico de elementos finitos fiable para modelar con precisión la respuesta de probetas y elementos estructurales armados de UHPFRC. Para definir el procedimiento directo para caracterizar a tracción tanto SH-UHPFRC como SS-UHPFRC, se ha llevado a cabo una campaña experimental y numérica en la que se ha analizado el resultado de ensayar 227 probetas sin armadura fabricadas con UHPFRC con cantidades de fibras cortas y lisas de acero de 120-130kg/m3 y 160kg/m3, ensayadas a flexión a través del ensayo a cuatro puntos (4PBT). El desarrollo y la validación de dicho proceso se respaldan mediante un modelo no lineal de elementos finitos (NLFEM) fiable. La validación numérica llevada a cabo ha sido decisiva para que este procedimiento sea preciso, simple y fiable. Utilizando esta campaña experimental, se ha desarrollado una aplicación predictiva para estimar los parámetros que definen el comportamiento constitutivo a tracción del UHPFRC. Esta aplicación es simple y directa y evita la posible variabilidad producida por malas interpretaciones en la aplicación del proceso. Además, se ha llevado a cabo una segunda campaña experimental constituida por vigas de UHPFRC armadas a flexión con diferentes escalas: 36 vigas cortas con 130 y 160kg/m3 de fibras y dos vigas largas. Esta campaña experimental se ha modelado con el NLFEM aquí desarrollado teniendo en cuenta efectos importantes debidos a la interacción del UHPFRC con las barras de armado. También se han modelado con el NLFEM tirantes de UHPFRC armados de una campaña experimental de otra investigación. El modelo considera efectos debidos a la retracción, al 3D y comportamiento tensión stiffening que generan resultados muy precisos cuando se comparan con los resultados experimentales. Como resultado de la presente tesis doctoral, se ha obtenido un modelo de elementos finitos capaz de modelar con precisión elementos estructurales de UHPFRC armados. Los resultados no sólo demuestran la fiabilidad del NLFEM llevado a cabo sino también la coherencia del procedimiento desarrollado para caracterizar el comportamiento constitutivo a tracción del UHPFRC para los dos casos, tanto SH-UHPFRC como SS-UHPFRC, tanto en elementos estructurales armados a flexión como en elementos estructurales armados a tracción directa. Consecuentemente se ha propuesto una metodología completa y efectiva para el modelado numérico del UHPFRC
[CA] El principal objectiu de la present tesi es el desenvolupament d'una completa metodologia per al modelat numèric de l'UHPFRC des del nivell material fins arribar als elements estructurals. Es pretén contribuir a l'avanç del coneixement del comportament mecànic de l'UHPFRC per mitjà d'un procediment per al modelat numèric útil per al modelat i disseny estructural que permeta fer que aquest material siga competitiu al mercat de la construcció. En la metodologia de modelat proposta, es considera un comportament constitutiu de l'UHPFRC optimitzat per mitjà d'un procediment directe i fiable amb el qual s'aprofiten els avantatges del material, resultant en un disseny estructural eficient des del punt de vista mecànic i econòmic. És necessari produir SH-UHPFRC per a aconseguir grans propietats mecàniques? És possible generar SS-UHPFRC amb el qual queden reduïts els costs inicials mantenint unes propietats mecàniques i de durabilitat competitives que comporten un disseny estructural efectiu? El desenvolupament d'UHPFRC amb baix enduriment per deformació i de SS-UHPFRC pot reduir les seues propietats mecàniques però, si són adequadament estudiades i controlades, aquests podrien ser optimitzats. La tesi aborda algunes d'aquestes qüestions per mitjà de l'estudi del comportament a tracció de l'UHPFRC que va des de SH-UHPFRC fins SS-UHPFRC. Es pretén dur a terme una proposta de procediment fiable per a caracteritzar el comportament constitutiu a tracció i definir un model numèric d'elements finits fiable per a modelar amb precisió la resposta de provetes i elements estructurals armats d'UHPFRC. Per a definir el procediment directe per a caracteritzar a tracció tant SH-UHPFRC com SS-UHPFRC, s'ha dut a terme una campanya experimental i numèrica en la que s'ha analitzat el resultat d'assajar 227 provetes sense armadura fabricades amb UHPFRC amb quantitats de fibres curtes i llises d'acer de 120-130kg/m3 i 160kg/m3, assajades a flexió per mitjà de l'assaig a quatre punts (4PBT). El desenvolupament i la validació de l'esmentat procés són assegurats per mitjà d'un model no lineal d'elements finits (NLFEM) fiable. La validació numèrica duta a terme ha estat decisiva per a que aquest procediment siga precís, simple i fiable. Utilitzant aquesta campanya experimental, s'ha desenvolupat una aplicació predictiva per a estimar els paràmetres que defineixen el comportament constitutiu a tracció de l'UHPFRC. Aquesta aplicació és simple i directa i evita la possible variabilitat produïda per males interpretacions en l'aplicació del procés. A més a més, també s'ha dut a terme una segon campanya experimental constituïda per bigues d'UHPFRC armades a flexió amb diferents escales: 36 bigues curtes amb 130 i 160kg/m3 de fibres i dos bigues llargues de gran escala. Aquesta campanya s'ha modelat amb el NLFEM ací desenvolupat incloent efectes importants deguts a la interacció de l'UHPFRC amb les barres d'armat. Addicionalment, també s'han modelat amb el NLFEM tirants d'UHPFRC armats a tracció provinents d'una campanya experimental d'altra investigació. El model considera efectes deguts a la retracció, al 3D i comportament tensió stiffening que generen resultats molt precisos quan es comparen amb els resultats experimentals. Per tant, com a resultat de la present tesi doctoral, s'ha obtingut un model d'elements finits capaç de modelar amb precisió elements estructurals d'UHPFRC armats. Els resultats del model comparats amb els resultats experimentals no sols demostren la fiabilitat del NLFEM dut a terme sinó que també la coherència del procediment directe desenvolupat per a caracteritzar el comportament constitutiu a tracció de l'UHPFRC als dos casos, tant per a SH-UHPFRC com SS-UHPFRC, tant en elements estructurals armats a flexió com amb elements estructurals armats a tracció directa. Conseqüentment, s'ha proposat una metodologia completa i efectiva per al modelat numèric de l'UHPFRC des del niv
[EN] The main objective of the present PhD thesis is to develop a complete methodology for the numerical modelling of UHPFRC from the material level to structural elements. It intends to contribute to advanced knowledge of mechanical UHPFRC behaviour to lead to a numerically modelling proposal that is useful for structural modelling and design that allows options for this material to be competitive in the construction market. Optimised UHPFRC material constitutive behaviour, characterised by a direct reliable defined procedure, is considered in the proposed modelling methodology to take advantage of these properties, and to lead to an efficient structural design from the mechanical and economical points of view. Is it necessary to produce SH-UHPFRC to obtain excellent properties? Is it possible to develop SS-UHPFRC that leads to lower initial costs and to maintain competitive mechanical and durability properties that result in an effective structural design? The development of low strain-hardening and SS-UHPFRC would lead to reduce its mechanical properties, but they can be optimised if they are studied and controlled. The thesis addresses some of these questions by studying tensile UHPFRC behaviour to cover a wide range of tensile constitutive behaviours from SH-UHPFRC to SS-UHPFRC. It intends to propose a reliable tensile characterisation process and a reliable finite element model capable of accurately simulating the response of UHPFRC specimens and reinforced structural elements. An extensive experimental and numerical campaign with 227 unreinforced four-point bending test (4PBT) specimens with amounts of smooth-straight (13/0.20) steel fibres of 1.53-1.66% (120-130kg/m3) in volume and with 2.00% (160kg/m3), which represents SS-UHPFRC and SH-UHPFRC tensile behaviours, was carried out to set up a direct tensile characterisation procedure involving SS-UHPFRC and SH-UHPFRC. The direct procedure's development and validity are ensured by a reliable non-linear finite element model (NLFEM). Numerical validation was carried out and is decisive for performing the direct procedure to characterise the tensile behaviour of both SS and SH-UHPFRC herein developed accurately, simply and reliably. With the experimental programme herein, a predictive application for estimating tensile UHPFRC parameters was developed. The prediction offers reliable results. The application is simple and direct, and avoids variability in the characterisation procedure due to possible misinterpretations in its application. In addition, a second experimental programme, which includes reinforced concrete flexural beams on different scales, with 36 UHPFRC reinforced short beams with 130 and 160kg/m3 of steel fibres and two full-scale long beams, was carried out and modelled with the NLFEM herein developed including major effects due to the interaction between UHPFRC and reinforcement bars. Additionally, reinforced UHPFRC tensile bars from a recent experimental campaign performed by other researchers were modelled with the NLFEM. The model considers shrinkage effects, tension stiffening behaviour and 3D effects due to the particularities of the test, which provide very accurate results compared to those obtained with the experimental tests. As a result of this PhD thesis, an accurate NLFEM was obtained to model reinforced UHPFRC structural elements. The results of the model compared to the experimental ones demonstrate not only the reliability of the developed NLFEM, but also the coherence of the developed direct procedure to characterise tensile UHPFRC behaviour in both strain-softening and strain-hardening in reinforced flexural and direct tensile structural elements. Consequently, a complete and effective methodology for numerical UHPFRC modelling from the material level to structural elements is proposed.
Mezquida Alcaraz, EJ. (2021). Numerical Modelling of UHPFRC: from the Material to the Structural Element [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167017
TESIS

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Este trabalho apresenta um estudo experimental de vigas curtas de concreto com fibras de aço sujeitas à flexão. Foram ensaiadas no LEM-DEC da PUC-Rio 24 vigas de concreto com fibras de aço com variação do comprimento dos vãos e do consumo de fibras. As vigas foram divididas em dois grupos, sendo o grupo I composto de 12 vigas com consumo de fibras de 40 kg/m3 e o grupo II por 12 vigas com consumo de fibras de 60 kg/m3. Para cada grupo foram executadas quatro vigas com vão de 300 mm, quatro com vão de 500 mm e quatro com vão de 800 mm, com seção transversal de 15 cm x 15 cm para estudo do efeito escala. As vigas foram submetidas à flexão e, através de gráficos, foram avaliados o comportamento da tensão tangencial, momento de flexão, energia de deformação, tenacidade, efeito escala e energia de fratura. Os gráficos obtidos permitem avaliar a influência das fibras para cada parâmetro supracitado. O grupo II apresentou maior resistência, sendo essa diferença pouco significativa. Entretanto, observa-se que, quanto menor o vão maior a influência das fibras, sendo esse acréscimo de 35 porcento para o vão de 300 mm, 30 porcento para o vão de 500 mm e 24 porcento para o vão de 800 mm. O maior consumo de fibras conferiu à matriz maior resistência à flexão e ao cisalhamento, mostrando sempre maior influência para os vãos menores. A energia de deformação e a energia de fratura apresentam diferença considerável para os vãos menores, chegando quase a se igualar nos dois grupos para o vão de 800 mm. Um aumento de desempenho foi observado na análise da tenacidade para o maior vão e houve uma diminuição desse desempenho para o vão de 300 mm. O efeito escala está presente no estudo, mostrando diminuição na resistência à tração com o aumento do vão.
This paper presents an experimental study on short concrete beams reinforced with steel fibers in bending stress. A total of 24 reinforced concrete beams with steel fibers was tested at the LEM-DEC PUC-Rio with variations of length and fiber volume fraction. Two groups were created, group I, consisting of 12 beams with 40 kg/m3 of steel fibers and group II with 12 beams with 60 kg/m3 of steel fibers. In each group four beams with a length of 300 mm, four beams with a length of 500 mm and four beams with a length of 800 mm with cross section of 15 cm x 15 cm were tested with the purpose of investigating the scale effect in this case. The beams were submitted to bending aiming at investigating shear stresses, bending stresses, strain energy, toughness, scale effect and fracture energy. Comparative graphics were made to analyze the influence of the fibers on the reinforced concrete behavior regarding each parameter selected. Group II showed higher resistance, but not significantly. However the smaller the length the larger the influence of the fibers; 35 percent for the length of 300 mm, 30 percent for the length of 500 mm and 24 percent for the length of 800 mm. The largest fiber volume fraction gave the concrete higher resistance when submitted to bending and shear, even more noticeable for the smaller lengths. The strain and fracture energy, however, shows considerable difference for smaller lengths, being almost the same in the two groups for the 800 mm beam. Toughness shows improvement in the longer beam and a decline in the shorter one from group II. The traction resistance shows decline as the length rises, presenting the scale effect in the study.

Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 24, 2008) Includes bibliographical references.

This research explores the use of carbon/epoxy and fiberglass/epoxy fiber-reinforced polymer (FRP) composite rebar manufactured on a three-dimensional braiding machine for use as reinforcement in concrete beams under four-point bending loads. Multiple tows of prepreg composite fibers were pulled to form a unidirectional core. The core was consolidated with spirally wound Kevlar fibers which were designed to also act as ribs to increase pullout strength. The rebar was cured at 121â—¦C (250â—¦F) in an inline oven while keeping tension on the fibers. Five configurations of reinforcing bars were used in this study as reinforcement in concrete beam specimens: carbon/epoxy rebar and fiberglass/epoxy rebar were manufactured on the three-dimensional braiding machine and cured in an inline oven while still under tension immediately after production; carbon/epoxy rebar was manufactured by IsoTruss industries on the three-dimensional braiding machine and was rolled and stored before curing; fiberglass/epoxy rebar was purchased from American Fiberglass; conventional No. 4 steel rebar was also purchased. All bars were embedded in 152 cm (60 in) long, 11 cm (4.5 in) wide, and 15 cm (6.0 in) tall concrete beams. Beams were tested under four-point bending loads after which three 30 cm (12 in) specimens were taken from the ends of each configuration to be tested under axial compression loads in order to investigate the effects of the concrete voids on the concrete strength. Concrete beams reinforced with BYU glass/epoxy rebar manufactured on the three-dimensional braiding machine exhibited 5% greater compression bending stress and 11% greater tension bending stress than concrete beams reinforced with industry manufactured glass/epoxy rebar. Concrete beams reinforced with BYU carbon/epoxy rebar manufactured on the three-dimensional braiding machine exhibited 18% lower compression bending stress and 64% lower tension bending stress than concrete beams reinforced with industry manufactured carbon/epoxy rebar. BYU glass/epoxy rebar has a 3% greater stiffness and 1% greater displacement than industry manufactured glass/epoxy rebar and BYU carbon/epoxy rebar has a 40% greater bending stiffness and 19% lower displacement than industry carbon/epoxy rebar. BYU carbon/epoxy rebar has 49% lower compression bending stress, 1% lower tension bending stress, 28% lower displacement, and a 68% greater bending stiffness than BYU glass/epoxy rebar. BYU glass/epoxy rebar has 38% greater compression bending stress, 30% lower tension bending stress, 26% greater center displacement, and a 105% lower bending stiffness than conventional steel. BYU carbon/epoxy rebar has 8% lower compression bending stress, 31% lower tension bending stress, and 22% lower bending stiffness than steel. The deflections of steel reinforced concrete and BYU carbon/epoxy reinforced concrete are comparable with steel rebar displaying a 1% greater center displacement than BYU carbon/epoxy rebar.

This thesis examines the seismic internal retrofitting of existing deficient reinforced concrete (RC) structures by using structural steel members. Both experimental and numerical studies were performed. The strengthening methods utilized with the scope of this work are chevron braces, internal steel frames (ISFs), X-braces and column with shear plate. For this purpose, thirteen strengthened and two as built reference one bay one story portal frame specimens having 1/3 scales were tested under constant gravity load and increasing cyclic lateral displacement excursions. In addition, two ½
scaled three bay-two story frame specimens strengthened with chevron brace and ISF were tested by employing continuous pseudo dynamic testing methods. The test results indicated that the cyclic performance of the Xbrace and column with shear plate assemblage technique were unsatisfactory. On the other hand, both chevron brace and ISF had acceptable cyclic performance and these two techniques were found to be candidate solutions for seismic retrofitting of deficient RC structures. The numerical simulations by conducting nonlinear static and dynamic analysis were used to estimate performance limits of the RC frame and steel members. Suggested strengthening approaches, chevron brace and ISF, were also employed to an existing five story case study RC building to demonstrate the performance efficiency. Finally, design approaches by using existing strengthening guidelines in Turkish Earthquake Code and ASCE/SEI 41 (2007) documents were suggested.

In this work, several beam finite element formulations are proposed for failure analysis of planar reinforced concrete beams and frames under monotonic static loading. The localized failure of material is modeled by the embedded strong discontinuity concept, which enhances standard interpolation of displacement (or rotation) with a discontinuous function, associated with an additional kinematic parameter representing jump in displacement (or rotation). The new parameters are local and are condensed on the element level. One stress resultant and two multi-layer beam finite elements are derived. The stress resultant Euler-Bernoulli beam element has embedded discontinuity in rotation. Bending response of the bulk of the element is described by elasto-plastic stress resultant material model. The cohesive relation between the moment and the rotational jump at the softening hinge is described by rigid-plastic model. Axial response is elastic. In the multi-layer beam finite elements, each layer is treated as a bar, made of either concrete or steel. Regular axial strain in a layer is computed according to Euler-Bernoulli or Timoshenko beam theory. Additional axial strain is produced by embedded discontinuity in axial displacement, introduced individually in each layer. Behavior of concrete bars is described by elastodamage model, while elasto-plasticity model is used for steel bars. The cohesive relation between the stress at the discontinuity and the axial displacement jump is described by rigid-damage softening model in concrete bars and by rigid-plastic softening model in steel bars. Shear response in the Timoshenko element is elastic. Finally, the multi-layer Timoshenko beam finite element is upgraded by including viscosity in the softening model. Computer code implementation is presented in detail for the derived elements. An operator split computational procedure is presented for each formulation. The expressions, required for the local computation of inelastic internal variables and for the global computation of the degrees of freedom, are provided. Performance of the derived elements is illustrated on a set of numerical examples, which show that the multi-layer Euler-Bernoulli beam finite element is not reliable, while the stress-resultant Euler-Bernoulli beam and the multi-layer Timoshenko beam finite elements deliver satisfying results.

Recent events including deliberate terrorist attacks and accidental explosions have highlighted the need for comprehensive research in the area of structural response to blast loading. Research in this area has recently received significant attention by the civil engineering community. Reinforced Concrete (RC) water reservoir tanks are an integral part of the critical infrastructure network of urban centers and are vulnerable to blast loading. However, there is a lack of research and knowledge on the performance of RC reservoir walls under blast loading. The objective of this research study is to experimentally investigate the performance of reinforced concrete reservoir walls subjected to blast loading and to analyze the structural response. This study provides experimental test data on the performance of reinforced concrete reservoir walls under blast loading and complementary analytical predictions using the Singe-Degree-Of-Freedom (SDOF) analysis method. The reservoir walls in this study were designed according to the water volume capacity using the Portland Cement Association (PCA 1993) methodology. The design was validated using software SAP 2000. The experimental program involved the construction and simulated blast testing of two RC reservoir wall specimens with different support conditions: (1) two opposite lateral edges fixed, bottom edge pinned and top edge free; and (2) two opposite lateral edges fixed, and bottom and top edges free. The first boundary condition was intended to promote two-way bending action, while the second was dominated by one-way bending. The two specimens were each subjected to a total of six consecutive incrementally increasing blast tests. The experimental program was conducted in the shock tube testing facility that is housed in the University of Ottawa. Wall displacements, reinforcement strains, and reflected pressures and impulses were measured during testing. Analytical calculations were conducted using the equivalent SDOF method to simulate the dynamic response of the RC reservoir wall specimens under different blast loadings. Published tables, charts and coefficients contained in Biggs (1964) and UFC 3-340-02 (2008) were adopted in the equivalent SDOF calculations. The analytical results were compared against the ii experimental data. The SDOF method predicted smaller displacements than those recorded during testing. The approximate nature of the parameters and tables used in the equivalent SDOF calculations contributed to the discrepancy between the analytical and experimental results. Furthermore, assumptions regarding the support conditions and neglecting residual damage from previous blast tests contributed to the underestimation of the displacements.

A model is presented to use normalized multi-linear tension and compression material characteristics of strain-hardening textile reinforced concrete and derive closed form expressions for predicting moment-curvature capacity. A set of design equations are derived and simplified for use in spreadsheet based applications. The model is applicable for both strain-softening and strainhardening materials. The predictability of the simplified model is checked by model calibration and development of design charts for moment capacity and stress developed throughout the cross section of a flexural member. Model is calibrated by predicting the results of Alkali Resistant Glass and Polyethylene fabrics. A case for the flexural design of Glass Fiber Reinforced Concrete (GFRC) specimen as a simply supported beam subjected to distributed load is used to demonstrate the design procedure.

The objective of this study was the development of a procedure in GT STRUDL to design reinforced concrete flat plate systems based on the results of finite element analysis. The current state-of-practice of reinforced concrete flat plate design was reviewed, including the ACI direct design and equivalent frame techniques, the yield line method, and the strip design method. The principles of these methods along with a critical evaluation of their applicability and limitations were presented as motivation for a finite element based design procedure. Additionally, the current state-of-the-art of flat plate design based on finite element results was presented, along with various flat plate modeling techniques. Design methodologies studied included the Wood and Armer approach, based on element stress resultants, and the resultant force approach, based on element forces. A flat plate design procedure based on the element force approach was embodied in the DESIGN SLAB command, which was implemented in GT STRUDL. The DESIGN SLAB command provides the user the ability to design a slab section by specifying a cut definition and several optional design parameters. The procedure determines all nodes and elements along the cut, computes the resultant moment design envelope acting on the cross-section, and designs the slab for flexure in accordance with provisions of ACI 318-02. Design examples presented include single-panel flat plate systems with various support conditions as well as multi-panel systems with regular and irregular column spacing. These examples allowed for critical comparison with results from experimental studies and currently applied design methods in order to determine the applicability of the implemented procedure. The DESIGN SLAB command was shown to produce design moments in agreement with experimental data as well as conventional design techniques for regular configurations. The examples additionally showed that when cuts were not oriented orthogonally to the directions of principle bending, resulting designs based on element forces could significantly under-reinforce the cross-section due to significant torsional effects.

For members and flat slabs without shear reinforcement, the shear and punching shear strength are often the determining design criteria. These failure modes are characterized by a fragile behaviour implying possible partial or total collapse of the structure. Despite extensive research in this field, shear and punching shear in reinforced and prestressed concrete structures, remain complex phenomena so much that the current approach is often empirical or simplified. The ability of Steel Fibre Reinforced Concrete (SFRC) to reduce shear reinforcement in reinforced and prestressed concrete members and slabs,or even eliminate it, is supported by several experimental studies. However its practical application remains marginal mainly due to the lack of standard, procedures and rules adapted to its performance. The stationary processes in precast industry offer optimal possibilities for using high performance cementitious materials such as Self Compacting Concrete (SCC) and High Strength Concrete (HSC). For the author, the combination of High Performance Concrete and steel fibres is the following step in the development and the optimization of this industry. The High Performance Fibre Reinforced Concrete (HPFRC) stands between conventional SFRC and Ultra-High Performance Fibre Reinforced Concrete (UHPFRC). The HPFRC exhibiting a good strength/cost ratio is, thus, an alternative of UHPFRC for precast elements. The principal aim of this work was to analyse the shear and punching shear behaviour of HPFRC and UHPFRC structures without transversal reinforcement and to propose recommendations and design models adapted for practitioners. Several experimental studies on structural elements, i.e. beams and slabs, were undertaken for this purpose. Firstly, an original experimental campaign was performed on pre-tensioned members in HPFRC. A total number of six shear-critical beams of a 3.6 m span each, and two full scale beams of a 12 m span each, were tested in order to evaluate the shear and flexural strength. The principal parameter between the specimens was the fibres (...)

Les applications des mesures dynamiques sur les bâtiments existants sont nombreuses : vérification de la vulnérabilité sismique des structures qui ont été construites avant l’apparition des règles parasismiques ; auscultation de la capacité des structures en situation post-sismique ou après des modifications au voisinage (creusement d’un tunnel à côté ou démolition des immeubles voisins par exemple). A l’heure actuelle, ce type de mesure permet le diagnostic d’une structure à l’échelle globale (toute la structure) alors que l’identification et la localisation des endommagements à l’échelle locale (chaque élément de la structure) restent encore à approfondir. Dans le cadre de cette thèse, le diagnostic à l’échelle locale des structures sera étudié. Cette thèse s’insère dans un contexte national de réévaluation des structures existantes du fait du nombre important de bâtiments à réhabiliter. Au sein du LOCIE, nous pensons que le comportement global des bâtiments est certes influencé par l’interaction sol-structure mais au moins autant par la qualité des connexions des éléments de structures entre eux. Il existe un besoin de qualification de ces connexions dont la variabilité du comportement peut provenir aussi bien de défauts de mise en œuvre (positionnement des armatures,…) que du vieillissement des structures. L’objectif principal de cette thèse est de proposer une méthode pouvant caractériser les liaisons entre les éléments de structure afin de pouvoir caler un modèle numérique. Ces caractérisations devaient être possibles à partir de mesures de sollicitations dynamiques. Une première étape de ce travail consistera à caractériser sur une partie de structure une liaison. Cela sera fait sur un portique en béton armé. Par la suite, cette méthode sera adaptée à une caractérisation au sein d’une structure de bâtiment. Pour cela nous ferons appel à la notion de sous-modèle. Un modèle numérique sera associé à cette méthode aussi bien sur la connexion simple que sur l’ensemble du bâtiment. Le travail de thèse s’appuiera sur l’utilisation et le développement de techniques concernant le traitement des données dynamiques ; la réduction de modèles ; l’expérimentation en laboratoire (échelle locale et échelle d’un élément de structure) et la modélisation numérique par éléments finis à plusieurs échelles
There are many of the examples of dynamics measurements applications in the existing building: verification of structural seismic vulnerability, which was constructed before the earthquake building code; auscultation of structural capacity in post-earthquake situation or after modification in surround environment (Excavation of tunnel or demolition the neighbour buildings for example). Currently, this measurement type enables the diagnosis a structure in global scale (a whole structure) while identification and localization of damage in local scale (each elements of the structure) remains to be explored. In this dissertation, diagnosis in locale scale will be studied. This study is significant for its contribution to the national reassessment of existing structures where there is the large number of buildings to be rehabilitated

In general, it is expected that concrete structures using Glass Fibre Reinforced Plastic (GFRP) rebars as reinforcement could have improved durability compared to normal steel reinforcement because of the corrosion resistance of the rebar. However, there are some aspects of the behaviour of the GFRP bars under high temperature that must be explored. The aims of this work are to predict the fire rating of the GFRP rebars when embedded in concrete elements by creating a model and to validate the model by full-scale experiments. The first part of this work evaluates the effects of alkaline environments on the rebar itself, the bond strength at interface between the concrete and the rebar, and the strength of the GFRP rebars at a range of different temperatures (20-120°C). The three types of GFRP rods investigated in this work were subjected to alkaline solutions at 60°C for three different exposure times i. e. 30 days, 120 days and 240 days. Tensile and flexural tests were carried out for the physico-mechanical characterisation on the treated GFRP rebars specimens. As the immersion period and temperature increased, the strength of the rebars decreased. Data obtained from the first part of the work were used to predict long-term performance of the GFRP rebar in fire. The effects of higher temperatures with time on GFRP reinforced concrete members were also studied experimentally in this work. As a result equations were developed. These were validated with the help of the fire tests carried out in second phase of this work on two full-scale GFRP reinforced concrete beams. The first beam was reinforced with GFRP made from thermoset resin and in the second GFRP made from thermoplastic resin was used. Shear reinforcement for the first beam were GFRP stirrups and for the second beam steel stirrups were used. Degradation of flexural and shear capacities due to fire was evaluated using the modified design codes which is based on assessment of the reduction in the initial strengths of concrete and GFRP reinforcement, resulting from the high temperatures developed inside the beam. A comparison of the results for each beam is presented. Fire resistance (load bearing capacity) of GFRP RC beams complied with British Standard BS 478. These results are published for the first time in this work. The predicted failure time using the model compares well with the fire test results. The 3 result also indicated that the basic fire model needed adjustment mainly due to a difference in the assumed and observed failure modes. The importance of data necessary for a more accurate model has been identified as a programme for future work.

Concrete has many advantages as a low cost and sustainable material. However, more than 5% of the planet’s total carbon emissions are associated with the production of cement, which, in fact, is predominantly due to the large volume of concrete used worldwide. It is known that traditionally designed concrete structures typically use more material than structurally required and, therefore, an important question is whether material demand can be reduced through structural optimisation. A major drawback from optimised design, however, is the cost and complexity of producing conventional rigid moulds. Fabric formwork is emerging as a new method for construction, gaining popularity among architects and engineers for the opportunity to build unique forms and to shape concrete elements efficiently. Porous fabrics, acting as controlled permeability formwork, also have proven effect on the durability characteristics of concrete. While fabric formwork has a profound potential to change the appearance of concrete structures, the shapes cast in fabrics are not defined in advance and have been often created unintentionally. The design of load-bearing reinforced concrete structures, however, requires accurate form-prediction and construction methods for securing steel reinforcement inside flexible fabrics, which presents a number of constructability challenges. For example, cover formers cannot be used to ensure adequate thickness of protective cover, inevitably affecting the acceptance of such structures in practice. This research has demonstrated that non-corrodable FRP reinforcement can be incorporated more easily than steel bars in fabric-formed concrete due to its light weight and flexibility, while it is possible to ensure ductility of such structures through confinement of concrete using FRP helices. A novel splayed anchorage system has been developed to provide end anchorage for optimised sections where standard bends or hooks cannot fit. This work also provides an experimentally verified methodology and guidance for the design and optimisation of fabric-formed elements.

Concrete is a widely studied material with a composite nature. It is used both in civil and military buildings and infrastructures. An issue of great importance is the protection of people from terrorist attacks that target critical infrastructure. Explosions, detonations and/or projectile impacts are some of the most severe actions a concrete structure can face. Experimental analysis is necessary in order to understand and predict the response of a structure to such dynamic and strain rate sensitive conditions. However, as the cost of performing experiments is significant and numerical simulations offer improved blast and impact analysis capabilities, there is an effort to limit experiments to validation purposes. In recent years, many researchers have studied the impact loads transferred to reinforced concrete (RC) structures both through direct projectile impacts or blast waves at both near and far field. The aim of the current study is twofold. First, to investigate contact detonations on this type of material (RC), since literature can provide us with limited information. Secondly, to assess the behaviour of the RC structure under combined ballistic impact and contact detonation of a very specific geometry of projectile (HESH) that exists currently on the market and behaves differently from the normal projectiles that consist of one single material. The author analysed and discussed in depth the response of RC members exposed to contact detonations. More precisely, the effect of the mass of explosive (C4) on pressures, impulses and energy balances. Also, she investigated the kinematic response of RC slabs and the structural role of the reinforcing bars. The driving force of this RC structures. Currently, the majority of studies regarding contact blast are focusing either on innovative types of concrete or normal concrete. However, normal concrete is investigated as a control parameter (to prove the effective resistance of the innovative material) rather than a detailed study on the behaviour of the material. Thereafter, the author analysed the response of a RC wall under the combined effect of kinetic energy (terminal ballistics) and contact detonation caused by the impact of a 90 mm HESH (High Explosive Squash Head) projectile fired from a distance of 70 m. The aim was to investigate the response of the structural member under the superposition of those two actions and analyse the combined effects of the impact velocity and detonation on the response of the structure. The numerical modelling is based on a Multi-Material-Arbitrary-Lagrangian-Eulerian approach (MMALE, using LS-DYNA) using the Winfrith concrete constitutive material model to investigate the dynamic response of the RC members under high strain rate conditions. The efficiency of the proposed numerical modelling is validated with experimental results - based on open-arena testing - and provided by the Royal Military Academy of Belgium. Some of the key findings of this research are that the increase of the amount of the explosive affects the damage failure of the RC members from flexural failure to shear failure. In addition, fitting curves that could be used in design, were proposed, that show the relation between the mass of explosive and the resulting pressures and impulses, within the tested range. In the case of the combined blast and impact scenario, the detonation was found to dominate the structural response of the RC slab.

Doutoramento em Engenharia Civil
Sismos recentes comprovam a elevada vulnerabilidade dos edifícios existentes de betão armado. A resposta das estruturas aos sismos é fortemente condicionada pelas características da aderência aço-betão, que exibe degradação das propriedades iniciais quando sujeitas a carregamentos cíclicos e alternados. Este fenómeno é ainda mais gravoso para elementos com armadura lisa, predominantes na maioria das estruturas construídas até à década de 70 nos países do sul da Europa. A prática corrente de conceção, dimensionamento e pormenorização das estruturas antigas leva a que tenham características de comportamento e níveis de segurança associados não compatíveis com as exigências atuais. Os estudos realizados sobre o comportamento cíclico de elementos estruturais de betão armado com armadura lisa são ainda insuficientes para a completa caracterização deste tipo de elementos. Esta tese visou a caraterização da relação tensão de aderência versus escorregamento para elementos estruturais com armadura lisa e o estudo da resposta cíclica de pilares e nós viga-pilar de betão armado com armadura lisa. Foram realizados dez séries de ensaios de arrancamento (nove monotónicos e um cíclico) em provetes com varões lisos. Os resultados destes ensaios permitiram propor novas expressões empíricas para a estimativa dos parâmetros usados num modelo disponível na literatura para representação da relação tensão de aderência versus escorregamento. É ainda proposto um novo modelo monotónico para a relação tensão de aderência versus escorregamento que representa melhor a resposta após a resistência máxima de aderência. Uma campanha de ensaios unidirecionais em pilares e nós viga-pilar foi também realizada com o objetivo principal de caracterizar o comportamento cíclico deste tipo de elementos. No total foram realizados oito ensaios em pilares, sete ensaios em nós viga-pilar interiores e seis ensaios em nós viga-pilar exteriores representativos de estruturas antigas de betão armado com armadura lisa. Os resultados experimentais permitiram avaliar a influência do escorregamento e estudar o mecanismo de corte em nós e a evolução dos danos para elementos com armadura lisa. Com base nos resultados experimentais foi proposta uma adaptação na expressão do Eurocódigo 8-3 para o cálculo da capacidade última de rotação de elementos com armadura lisa. Foi também desenvolvido um estudo paramétrico, com diferentes estratégias de modelação não linear, para a simulação da resposta de pilares considerando o escorregamento da armadura lisa. Por último, foi proposto um novo modelo simplificado trilinear para o aço que contempla o efeito do escorregamento da armadura lisa.
Recent earthquakes have shown the significant vulnerability of existing reinforced concrete buildings. The seismic response of structures is largely conditioned by the bond-slip properties that may experience an accelerated degradation under cyclic loading. The influence of this effect can be even larger for elements with plain reinforcing bars, as typically used in structures built before the 1970s in Southern European countries. The principles, design and practice adopted in the past do not guarantee that the existing reinforced concrete structures meet performance requirements recommended in modern codes. The available studies on the cyclic behaviour of reinforced concrete elements with plain reinforcing bars are still limited. This thesis intended to contribute for the characterization of the bond-slip relationship for plain reinforcing bars and to study of the cyclic response of columns and beam-column joints reinforced with plain bars representative of existing building structures. Ten sets of pull-out tests (nine monotonic and one cyclic) were performed on specimens built with plain bars, which allowed to propose new empirical expressions for some parameters adopted in bond-slip models available in the literature for plain bars. Also, a new monotonic bond-slip model was proposed better representing the post-peak strength bond-slip relationship. An experimental campaign of unidirectional tests on full-scale columns and beam-column joints was carried out to characterize their cyclic response. In total eight columns, seven interior beam-column joints and six exterior beam-column joints were tested, representing old reinforced concrete building structures. The experimental results confirms the influence of the reinforcing bars’ slippage and allowed to better understand the shear mechanism in the joints and damage evolution of elements with plain reinforcing bars. Based on the experimental results, it was proposed a modification to the Eurocode 8-3 expression used to calculate the ultimate rotation capacity of elements with plain reinforcing bars. A comparative study of different strategies for the non-linear numerical modelling of columns taking into account the slippage was also developed. Finally, a new simplified tri-linear steel model was proposed that includes the effect of slippage of plain reinforcing bars.

Cuenca Asensio, E. (2012). ON SHEAR BEHAVIOR OF STRUCTURAL ELEMENTS MADE OF STEEL FIBER REINFORCED CONCRETE [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18326
Palancia

The employment of a novel cutting edge strain monitoring technique named Distributed Optical Fiber Sensors (DOFS) as Structural Health Monitoring (SHM) tools is becoming increasingly common. Its popularity can be attributed to multiple reasons, the most important of which are the possibility of performing completely spatially distributed monitoring with sampling points at distances smaller than 1 mm, the high degrees of deployment configuration complexity thank to DOFS’ size and minimal stiffness, ease of deployment and resistance to Electro-Magnetic Interference, corrosion and extreme temperatures. Due to the inherent nature of SHM, though, up to now, the most common DOFS applications are the monitoring of already built structures and substantiation of their suitability to continue performing as per design. Consequently, most DOFS deployments see their bonding to the external surfaces of RC structures. A novel way of deploying DOFS that has taken hold in the later years consists in adopting DOFS to monitor the evolution of the strains present on the inside of a Reinforced Concrete (RC) structure i.e., bonding DOFS to the surface of embedded reinforcement bars (rebars) or embedding them directly in the concrete mass. Due to its recency, this application is characterized by an almost untapped potential pool. Indeed, SHM-wise, this continuous and highly sensible embedded monitoring system provides access to the ability of starting to detect deformations and damages as early as their appearance inside the structure (versus having to wait for their appearance on their external surface). This superior deformation and damage detection potential can very well help replacing the current time-based inspection model with one based on a performance or risk-based approach. As a consequence, today’s maintenance paradigm could shift from corrective to preventive, resulting in tremendous savings in infrastructure maintenance and a reduction of its associated social impact. Yet, when deploying DOFS inside RC structures several phenomena may jeopardize the extractable results. Among these the non-neglectable possibility of fiber alteration/damage during the pouring of concrete and the possibility of erroneous measurements induced by the friction and/or clamping of the DOFS from the part of concrete aggregates. Whilst the deployment of DOFS with several claddings and coatings could compensate for these issues, the presence of a certain lag in the transmission of strains from the monitored surface to the DOFS’s silica core reduces the accuracy of the measurements and corrections are necessary to account for the strain lag between the fiber core and the substrate. For such applications, the preferable DOFS would be a thin, simply cladded, non-coated DOFS. In this case, though, the DOFS protective function against external SRA-inducing phenomena falls entirely on the adhesive layers with which the fibers are bonded. The present thesis is aimed at improving the viability of coating-less DOFS deployments inside RC structures for Civil and Structural Engineering SHM. This objective is tackled with both a preventive approach and a curing one. The former is achieved by means of experimental investigation aimed at extracting methodologies and techniques that stem factors jeopardizing any DOFS-extracted strain measurement. The latter is achieved creating post-processing algorithms aimed at the cleansing of DOFS-extracted data of any data distortion and anomaly.
Cada vegada és més freqüent l’ús d’una nova tècnica avançada per a la mesura de deformacions anomenada Sensors de fibra òptica distribuïts (DOFS), com a eina de control de la salut estructural (SHM). Els principals motius de la seva popularitat és la possibilitat de realitzar monitoritzacions completament distribuïdes espacialment amb punts de mostreig a distàncies inferiors a 1 mm. Tot i això, a causa de la naturalesa inherent a SHM, fins ara l’aplicació DOFS més comuna ha estat la monitorització superficial d’estructures ja construïdes per tal de demostrar la seva idoneïtat per continuar funcionant segons el disseny. En el cas d´estructures de nova construcció, una forma nova de realitzar els monitoratges DOFS consisteix en estudiar l’evolució de les deformacions presents a l’interior de les estructures de formigó armat (RC). És a dir, unir DOFS a la superfície de les armadures interiors al formigó o bé embegudes directament a la massa de formigó. A causa de la seva novetat, aquesta aplicació es caracteritza per un gran potencial no explorat. En termes de SHM, aquest sistema de monitorització interior al formigó, continu i altament sensible proporciona la capacitat de detectar deformacions i danys tan aviat com apareixen a l’interior de l’estructura (en lloc d’haver d’esperar la seva aparició a la superfície externa). Això pot ajudar a canviar el paradigma de manteniment actual d´estructures de formigó de correctiu a preventiu. Tot i això, quan es desplega DOFS dins d’estructures RC, la fibra és més propensa a patir alteracions / danys durant l’abocament de formigó i a produir mesures errònies induïdes per la subjecció i fricció per part dels àrids del formigó. Tot i que l’ús de DOFS amb diversos revestiments i recobriments exteriors podria compensar aquest problema, la presència dels mateixos provoca una distorsió en la transmissió de les deformacions des de la superfície monitoritzada al nucli de sílice del DOFS, reduïnt la precisió de les mesures obtingudes. Per a aquestes aplicacions, el DOFS preferible seria un que no tingués reocobriment, en contacte directe amb la superfície a monitoritzar. En aquest cas, però, la funció protectora del DOFS contra fenòmens externs que provoquen anomalies de lectura de deformacions (SRA) recau totalment sobre les capes adhesives amb les quals s’adhereixen les fibres. La present tesi té com a objectiu millorar la viabilitat dels desplegaments DOFS sense recobriment dins el formigó per al SHM d’estructures d´enginyeria civil. Aquest objectiu s´aborda amb un enfocament preventiu i un altre de correctiu. El primer s´aconsegueix mitjançant una sèrie de campanyes experimentals dirigides a extreure metodologies i tècniques de col.locació de DOFS que frenin els factors que poden disminuir la precisió de les mesures obtingudes. S´han realitzat proves de laboratori amb prismes de RC sotmesos tant a compressió (induïts per contracció del formigó) com a tensió i amb bigues de RC sotmeses a flexió. Dels resultats, es pot concloure que la tècnica de col.locació que millor impedeix l’aparició de SRA consisteix a situar la fibra dins d’una petita rasa (a la superfície de l´armadura), unir-la amb adhesiu de cianoacrilat i protegir-la amb una capa addicional de silicona. No obstant això, degut a la poca rigidesa de la silicona, encara es produeixen petites diferéncies entre la mesura de la fibra i la deformació real a l´element, però que són menors a les que es tenen amb un un recobriment extern de DOFS. L'enfocament correctiu, en canvi, es va abordar creant algoritmes de post-processament que netegen les dades extretes de DOFS de qualsevol distorsió i anomalia i que ofereixen bons resultats, com es demostra en diverses aplicacions pràctiques.
Enginyeria de la construcció

This study presents a conceptual design process for one-way reinforced concrete slabs cast over Textile Reinforced Concrete (TRC) Stay-in-Place (SiP) formwork elements, aiming at the minimization of the composite slab cost satisfying Ultimate Limit State (ULS) and Serviceability Limit State (SLS) design criteria. The thin-walled TRC element is considered to participate in the structural behaviour of the composite slab. This distinct function of the TRC element (as formwork and as a part of a composite element) distinguishes the design procedure into two States: a Temporary and a Permanent one. Design parameters such as the type of the textile reinforcement (material), the geometry of the TRC cross-section, the flexural strength of the fine-grained concrete in the TRC element and the compressive strength of the cast in-situ concrete are considered as the main optimization variables.