The development of synthetic adhesives based on epoxy resins has opened new possibilities for bonding structural materials together. The present work was concerned with the use of epoxy resins to strengthen reinforced concrete beams by externally bonded steel plates. It was found in the first part that the assessment of the properties of the epoxy adhesive is of paramount importance as they varied considerably with the thickness of the test specimen and the rate of loading. The adhesive proved to offer a bond stronger than concrete in shear and resulted in a composite action between the beams and steel plates. Preloading the beams prior to strengthening them did not have any adverse effect on their behaviour. The added strength from the plates was fully exploited even in beams which were held under a preload of 70% of their ultimate strength while being strengthened. Stopping the plate in the shear span, short of the support, created a critical section where premature bond failure occurred beyond a certain plate thickness. Failure was caused by the combination of high peeling and bond stresses present in the region where the plate was stopped. These stresses were due to the transfer of tensile forces from the plate to the bars in that region and were higher with thicker plates. Bonding steel plates on the tension face of the beams increased their shear capacity by 9 to 15%. This may have been due to dowelling action from the plates which had a greater contact area with concrete than an equivalent amount of internal steel bars. The use of externally bonded steel as shear reinforcement was effective but requires further investigation. The external web strips failed prematurely as compared to equivalent stirrups. The long term deformations in plated beams were highly affected by the conditions of their environment but despite 47 month exposure no visual deterioration of the concrete-epoxy-steel joint was observed.

A substituição do aço pela armadura não metálica objetiva o aumento da durabilidade de estruturas sujeitas à corrosão e a campos eletromagnéticos. Mas, a inserção de um novo material na construção civil demanda especificação de sua composição, comportamento e procedimentos de sua utilização. Este trabalho analisa o comportamento à flexão de vigas de concreto armadas com barras não metálicas. Para esta finalidade foram realizados, uma revisão bibliográfica considerando os trabalhos publicados desde o início das pesquisas até os mais recentes e ensaios dos materiais e de vigas de concreto armado. Os ensaios de determinação das propriedades das barras da armadura não metálica de GFRP (glass fiber polymer – polímero reforçado com fibra de vidro) englobam a determinação do diagrama tensão-deformação e capacidade resistente. As vigas armadas com barras de GFRP foram ensaiadas à flexão em quatro pontos e os resultados comparados com o de uma viga armada com barras de aço CA-50 também ensaiada a flexão. Nos modelos pôde-se perceber a influência das propriedades das barras de GFRP no comportamento geral da estrutura. Por exemplo, as grandes deformações nas barras longitudinais e os deslocamentos dos modelos foram determinados pelo baixo módulo de elasticidade das barras de GFRP. É evidente a necessidade de continuação dos estudos envolvendo barras de GFRP. Estas pesquisas poderão desenvolver meios de se utilizar as propriedades do material em favor do melhor funcionamento da estrutura / Steel reinforcement replacement aims an increase at the durability of structures with corrosion and electrical magnetic problems. But, inserting a new material at the civil construction industry demands specifications of its composition, behavior and procedures for its utilization. This work is a flexural behavior analysis of reinforced concrete beams reinforced with GFRP bars. To make this, a technical literature research was made considering the pioneer until the most recent researches, and components and concrete reinforced beams tests were done. GFRP bars properties tests went from the determination of its strains X stress diagram to its tension resistance. GFRP reinforced beams were submitted to four points flexural tests and the results compared with a CA-50 steel reinforced beam also submitted to the flexural test. The specimens showed the influence of GFRP properties at the behavior of the structure. For example, longitudinal bars large strains and the large displacement of the beam were determined by GFRP bars low longitudinal elastic modulus. Continuing the studies evolving GFRP bars is certainly a need. New researches might be able to design a way to use the composite properties to improve the structure behavior

A substituição do aço pela armadura não metálica objetiva o aumento da durabilidade de estruturas sujeitas à corrosão e a campos eletromagnéticos. Mas, a inserção de um novo material na construção civil demanda especificação de sua composição, comportamento e procedimentos de sua utilização. Este trabalho analisa o comportamento à flexão de vigas de concreto armadas com barras não metálicas. Para esta finalidade foram realizados, uma revisão bibliográfica considerando os trabalhos publicados desde o início das pesquisas até os mais recentes e ensaios dos materiais e de vigas de concreto armado. Os ensaios de determinação das propriedades das barras da armadura não metálica de GFRP (glass fiber polymer – polímero reforçado com fibra de vidro) englobam a determinação do diagrama tensão-deformação e capacidade resistente. As vigas armadas com barras de GFRP foram ensaiadas à flexão em quatro pontos e os resultados comparados com o de uma viga armada com barras de aço CA-50 também ensaiada a flexão. Nos modelos pôde-se perceber a influência das propriedades das barras de GFRP no comportamento geral da estrutura. Por exemplo, as grandes deformações nas barras longitudinais e os deslocamentos dos modelos foram determinados pelo baixo módulo de elasticidade das barras de GFRP. É evidente a necessidade de continuação dos estudos envolvendo barras de GFRP. Estas pesquisas poderão desenvolver meios de se utilizar as propriedades do material em favor do melhor funcionamento da estrutura / Steel reinforcement replacement aims an increase at the durability of structures with corrosion and electrical magnetic problems. But, inserting a new material at the civil construction industry demands specifications of its composition, behavior and procedures for its utilization. This work is a flexural behavior analysis of reinforced concrete beams reinforced with GFRP bars. To make this, a technical literature research was made considering the pioneer until the most recent researches, and components and concrete reinforced beams tests were done. GFRP bars properties tests went from the determination of its strains X stress diagram to its tension resistance. GFRP reinforced beams were submitted to four points flexural tests and the results compared with a CA-50 steel reinforced beam also submitted to the flexural test. The specimens showed the influence of GFRP properties at the behavior of the structure. For example, longitudinal bars large strains and the large displacement of the beam were determined by GFRP bars low longitudinal elastic modulus. Continuing the studies evolving GFRP bars is certainly a need. New researches might be able to design a way to use the composite properties to improve the structure behavior

[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