Prepreg is a fibre reinforced polymer composite material often used by the aeronautical industry. The material supplier has pre-impregnated the fibre often with an epoxy resin and cured it to a semi-viscous B-stage where the material is tacky (adhesive). Manual layup of prepreg components is still common because there are only a few automated layup techniques which has limited geometric capability and high investment cost. Swerea SICOMP is a research institute which have in collaboration with partners developed a manufacturing demonstrator for automated layup of carbon fibre prepreg components based on robotic handling. The manufacturing demonstrator is able to; feed out prepreg from a spool onto a cutting table, cut the prepreg into plies, pick the plies from the cutting table and place them on a layup table, consolidate the prepreg plies on the layup table and remove the backing paper that covers one side of the prepreg. Three robustness problems has been identified and these forms the bulk of this master’s thesis. The first problem is that the robot is unable to place the plies on the cutting table with sufficient accuracy due to fluctuating position of the prepreg on the cutting table. The second problem is that the end effector used for the pick and place operation sometimes fails to pick the adhesive plies from the cutting table. The problem originates in limited holding force by the end effectors suction cups and limited capability to perform a peeling motion when picking due to the design of the end effector. The third problem is that process variables like temperature is believed to effect the robustness of the demonstrator but has not been further studied. The first problem was solved by implementing a probing routine which measures the position of the prepreg on the cutting table with an array sensor mounted to the robot. The measurement values are used to reprogram subsequent operations. The second problem seems to be solved by designing and implementing a new pick and place end effector. The new end effector has higher holding force and better capability to perform a peeling motion while picking and placing the tacky prepreg plies. Tests with the new end effector has been promising, the pick and placeoperation performs robustly, but all ply geometries was not tested and some minor adjustment is needed to further improve the placing accuracy. The third problem has not been solved but studied. A literature study reviled that temperature, relative humidity and prepreg out of freezer age is likely to effect the prepreg adhesive properties which in turn is known to effect the robustness. A test procedure has been devised to test how these variables effect the robustnessof the demonstrator. The tests should be conducted when all process steps in the demonstrator is up and running.

A técnica caracterizada pela colagem de polímeros reforçados com fibras de carbono (PRFC) em elementos estruturais de concreto vem sendo aplicada com sucesso no reforço de estruturas em todo o mundo. Resistência à corrosão, elevada resistência à tração, baixo peso, facilidade e rapidez de aplicação, são algumas das características interessantes que têm contribuído para a sua disseminação. Nesta pesquisa propõe-se uma inovação construtiva fundamentada no desenvolvimento de um compósito de alto desempenho à base de cimento Portland e fibras de aço (macro + microfibras), destinado a constituir o que está sendo preliminarmente chamado de substrato de transição. A finalidade desse substrato é a de controlar melhor a fissuração do concreto da viga e retardar ou até evitar o desprendimento prematuro do reforço polimérico. Devido à carência de pesquisas semelhantes a aqui proposta, foi realizado um estudo preliminar em vigotas moldadas com fibras de aço e reforçadas externamente com manta de PRFC, onde se verificou que a concepção do substrato de transição é válida. Partiu-se então para a realização de ensaios visando à obtenção de um compósito cimentício com características apropriadas para constituir o substrato de transição. Os resultados e as análises efetuadas mostram que foi possível desenvolver um material de elevado desempenho, traduzido por um comportamento de pseudo-encruamento, com elevados ganhos de resistência e tenacidade ao fraturamento. A aplicação do reforço com manta sobre a superfície do substrato de transição, formado a partir da reconstituição do banzo tracionado da viga com o compósito cimentício, mostrou melhorar significativamente os níveis de desempenho da peça reforçada. Do estudo realizado foi possível comprovar a eficiência da técnica de reforço proposta, além de reunir uma série de informações que podem ser exploradas para se tornarem úteis como critérios de projeto de estruturas recuperadas e reforçadas. / The technique characterized by bond of the carbon fibers reinforced polymer (CFRP) in structural elements of concrete comes being applied successfully in the strengthening of structures in the whole world. Resistance to the corrosion, high tensile strength, low weight, easiness and rapidity of application, is some of interesting characteristics that have contributed for its dissemination. The objective of this research is to develop an innovate strengthening method for RC beams, based on a high performance cement-based composite of steel fibers (macro + microfibers) to be applied in a transition layer. The purpose of this transition layer is to better control the cracking of concrete and to be late or until avoid the premature detachment of strengthening. Due to lack of similar research here the proposal, was carried through a preliminary study in short beams molded with steel fibers and strengthened with CFRP sheet, where if it verified that the conception of the transition layer is valid. Tests were developed to get a cement-based composite with characteristics to constitute the layer transition. The results shown that were possible to develop a material of high performance with a pseudo strain-hardening behavior, high strength and fracture toughness. The application of the strengthened about the layer transition surface showed significantly to improve the levels of performance of the strengthening beam. Of the carried through study it was possible to prove the efficiency of the new strengthened technique and describe various information that can be explored to become useful as criteria of project of repaired and strengthened structures.

Este trabalho apresenta o desenvolvimento de uma técnica de incremento da resistência e da rigidez à flexão de ligações de elementos de concreto pré-moldado, com aplicação de laminados de polímero reforçado com fibra de carbono (PRFC). O procedimento adotado consiste na colagem dos laminados de PRFC em entalhes no concreto de cobrimento, de acordo com a técnica conhecida como \"near-surface mounted\" (NSM), de modo a incorporar à ligação novos elementos resistentes à tração. Para solidarizar a ligação e possibilitar a transferência de esforços de compressão entre os elementos de concreto existentes, preenchem-se os espaços vazios (grauteamento) com argamassa fluida à base de cimento Portland. Foram desenvolvidos modelos em escala reduzida, com o intuito de representar os mecanismos resistentes de uma ligação viga-pilar composta por encaixe de dente Gerber e consolo, com uso de chumbador, almofada de apoio e graute. Esse tipo de ligação é muito utilizado na construção de galpões e tem, na sua concepção original, comportamento essencialmente de articulação. Em uma etapa preliminar, realizaram-se ensaios para a caracterização da aderência segundo a configuração de reforço proposta. Os resultados dessa análise subsidiaram a fixação do comprimento de laminado a ancorar e a escolha do tipo de resina a empregar para colagem do reforço. Os modelos representativos da técnica de reforço proposta foram preparados, cada um deles, pela montagem de um elemento de pilar-consolo com elementos de viga nos respectivos chumbadores e almofadas. Foram também preparados modelos de referência para o estudo da influência da almofada de apoio e do grauteamento no comportamento resistente e da deformabilidade da ligação. Nesses modelos, as juntas eram perfeitamente conjugadas, isto é, os trechos de viga foram concretados com um elemento pré-moldado de pilar-consolo posicionado dentro da fôrma, sem disposição de almofadas. Todos os modelos de ligação foram reforçados e submetidos a ensaios estáticos. Esses ensaios consistiram na aplicação de carregamento cíclico alternado de curta duração, solicitando-se os modelos a momento fletor positivo ou negativo. Este trabalho também apresenta procedimento executivo de ensaios dinâmicos para avaliação da rigidez dos modelos de ligação em três condições: modelo íntegro reforçado, modelo reforçado fissurado (após aplicação de carregamento de aproximadamente 30% do carregamento de ruptura da ligação, em ensaio estático) e modelo reforçado rompido. Com o reforço, a ligação apresentou comportamento semi-rígido e adquiriu resistência à flexão compatível à de estrutura monolítica armada com barras de PRF. / This work presents the development of a technique for flexural strengthening and stiffness increasing of precast beam-to-column connections by the embedding of FRP strips into grooves made on the concrete cover. According to this technique, the tension in the connection is transferred by the Near-Surface Mounted (NSM) FRP strips. To allow the transference of compression efforts among the concrete elements, the empty spaces are filled out with grout. Small-scale specimens were developed to represent the resistant mechanisms of pined beam-to-column connection composed by elastomeric cushion and dowels. Preliminary experimental tests on bond behavior of NSM strips were carried out. The results analysis conducted the decision about the adhesive type and bond length to be employed in the beam-to-column connection specimens. Each specimen was made of the assembly of a column section connected to beam sections through their respective dowels and cushions. The connection specimens were reinforced by embedding CFRP strips in the lateral concrete cover and filling out the spaces between beams and column. In addition, control specimens were prepared to study the influence of the cushion and grout in the connection performance. In those models, the joints were conjugated perfectly, which means that the beam sections were laid inside the wooden forms and cast together with a precast column section with no cushions between them. Experimental static and dynamic tests were done. The tests results show that strengthened connection exhibits semi-rigid behavior and acquires flexural strength compatible to monolithic structure reinforced with FRP bars.

O objetivo deste trabalho é apresentar um modelo para análise probabilística de vigas de concreto armado recuperadas à flexão, através da utilização conjunta do método de simulação de Monte Carlo e do método dos Elementos Finitos. Para uma análise da confiabilidade, foram projetadas vigas de concreto armado seguindo as recomendações da NRR 6118:2003. Após, foi considerado que as armaduras tracionadas de flexão sofreram reduções de 10%, 20% e 30% na sua área da seção transversal, sendo, então, feita uma análise da segurança estrutural remanescente. Para o projeto de recuperação das vigas danificadas, estão apresentados os procedimentos do Bulletin 14 da fédération internationale du béton (fib) para o dimensionamento de sistemas de reforço com material compósito colado externamente às estruturas. Assim, a confiabilidade destas vigas recuperadas pôde ser estimada e comparada à confiabilidade das vigas originais. Dentro do processo de simulação, a resposta em termos da carga de ruptura das vigas de concreto armado recuperadas foi obtida através de uma análise numérica não-linear utilizando um modelo de elementos finitos. Devido à importância do deslizamento entre o substrato de concreto e o sistema de reforço estrutural, foram implementados dentro do modelo de elementos finitos, elementos unidimensionais de interface, quadráticos com seis pontos nodais para a captura deste comportamento. As análises probabilísticas através do método de simulação de Monte Carlo usando um modelo de elementos finitos mostraram que se atinge bom nível de segurança no projeto de vigas de concreto armado seguindo as recomendações da NBR 6118:2003. Entretanto, danos nas armaduras tracionadas de flexão podem fazer com que a confiabilidade caía para níveis inaceitáveis. Como solução, o projeto de recuperação estrutural de acordo com o Bulletin 14 da fib fez com que a confiabilidade das vigas recuperadas fosse no mínimo igual à confiabilidade das vigas originais. Assim, a probabilidade de falha das vigas recuperadas foi menor quando comparado à probabilidade de falha das vigas originais. / The objective of this work is to present a model for probabilistic analysis of RC beams rehabilitated for flexure, through the simultaneous utilization of the Monte Carlo method and the finite element method. Initially, three RC beams were designed following the NBR 6118:2003 recommendations. In the next step, it was considered that a reduction of the steel reinforcement area of 10%, 20% and 30% had occurred. Then the procedures for strengthening systems design with externally bonded carbon fiber reinforced polymers (fib, Bulletin 14) were employed for the rehabilitation of the damaged RC beams. Finally, the reliability of the RC beams rehabilitated for flexure could be evaluated and compared to that of the damaged and undamaged RC beams. In the Monte Carlo method, the RC beams failure load was obtained numerically through a nonlinear finite element model. Due to the importance of the slip between the concrete substrate and the external reinforcement, it was introduced in the finite element model a special one-dimensional interface element, with six nodal points and quadratic shape functions. The probabilistic analysis through the Monte Carlo method using a finite element model showed the high reliability attained in the RC beams design following the NBR 6118:2003 recommendations. However, the damage in the internal steel reinforcement can lead to an unacceptable reliability level. As a solution, the design of structural recovery according to the Bulletin 14 produced a reliability level for the RC beams rehabilitated for flexure at least equal to the reliability level of the undamaged RC beams. Consequently, the failure probability of the RC beams rehabilitated for flexure was lower then the failure probability of the undamaged RC beams.

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

In the light of extreme events of natural disasters (earthquakes or hurricanes) and accidents (fire or explosion), repairing and strengthening of existing concrete structures has become more common during the last decade due to the increasing knowledge and confidence in the use of composite advanced repairing materials. The past experience from real fires shows that it is exceptional for a concrete building to collapse as a result of fire and most fire-damaged concrete structures can be repaired economically rather than completely replacing or demolishing them. In this connection an experimental study was conducted to investigate the effectiveness of fibre reinforced polymer jackets for axial compressive and seismic shear performance of post-heated columns. This study also investigates the effectiveness of ferrocement laminate for the repairing of post-heated reinforced concrete columns.A total of thirty-five reinforced concrete columns were constructed and then tested after categorising them into three main groups: un-heated, post-heated and post-heated repaired. The post-heated columns were initially damaged by heating (to a uniform temperature of 500°C). The concrete cubes were also heated to various temperatures to develop the relation between compressive strength and ultrasonic pulse velocity. The residual compressive strength of the concrete cubes and reinforced concrete columns were determined by ultrasonic testing. The post-heated columns were subsequently repaired with unidirectional glass or carbon fibre reinforced polymer and ferrocement jackets. The experimental programme was divided into two parts. The columns of experimental part-1 were tested under axial compressive loading. The columns of experimental part-2 with a shear span to depth ratio of 2.5 were tested under constant axial and reversed lateral cyclic loading. The results indicated that the trend of reduction in ultrasonic pulse velocity values and in residual compressive strength of concrete was similar with increasing temperature. The reduction in residual stiffness of both post-heated square and circular columns was greater than the reduction in ultimate load. The circular sections benefited more compared to the square cross-sections with fibre reinforced polymers for improving the performance of post-heated columns in terms of compressive strength and ductility tested under axial compression. GFRP and CFRP jackets performed in an excellent way for increasing the shear capacity, lateral strength, ductility, energy dissipation and slowed the rate of strength and stiffness degradation of fire damaged reinforced concrete square and circular columns tested under combined constant axial and reversed lateral cycle loading. However, the effect of a single layer of glass or carbon fibre reinforced polymer on the axial stiffness of post-heated square and circular columns was negligible. The use of a ferrocement jacket for the repairing of post-heated square and circular columns enhanced the axial stiffness and ultimate load carrying capacity of columns significantly.

Die vorliegende Arbeit beschäftigt sich mit der Umschnürung von gedrungenen Stahlbetonstützen mittels Kohlefasergelegen. Die durch Epoxidharz mit dem Altbeton verbundenen Kohlefasern (CFK-Umschnürung) bewirken hierbei eine starke Behinderung der Querdehnung des Betons, wodurch dieser in einen dreidimensionalen Spannungszustand versetzt wird. Die Betondruckfestigkeit kann dadurch nachträglich deutlich gesteigert und das Verformungsverhalten positiv beeinflusst werden. Forschungsaufgabe war es, Wissenslücken und aufgeworfene Fragen, die sich aus einer intensiven Literaturrecherche zur Thematik ergaben, zu schließen und einen eigenen Bemessungsansatz zu entwickeln. Hierzu wurden Beton- und Stahlbetondruckglieder mit verschiedenen Abmessungen und Durchmessern sowie unterschiedlichen Längs- und Querbewehrungsgehalten hergestellt. Danach erfolgte die Umschnürung dieser Prüfkörper mit verschiedenen CFK-Materialien in variierenden Dicken und anschließende Bauteiltests in Form von weggesteuerten Druckversuchen. Neben dem Materialverhalten konnten mittels elektrischen Messsystemen, wie z. B. induktiven Wegaufnehmern sowie auf den Prüfkörpern aufgebrachten Dehnungsmessstreifen, auch die Versagenszustände zuverlässig bestimmt werden. Die Auswertung und Interpretation der gewonnenen Daten mündete in empirischen Gleichungen zur Beschreibung der maximalen Druckfestigkeit und Dehnung von CFK-umschnürten Bauteilen aus unbewehrtem oder bewehrtem Beton. Darüber hinaus konnten Aussagen zur tatsächlichen Bruchdehnung der eingesetzten Kohlefasern getroffen und entsprechende Abminderungsfaktoren abgeleitet werden. Unter Berücksichtigung der Datenreihen anderer Forschergruppen wurde die eigene Datenbasis vergrößert und die gewonnenen Erkenntnisse bestätigt. Als Ergebnis steht ein empirischer Bemessungsansatz zur Verfügung, der Bemessungsgleichungen zur Querschnittstragfähigkeit und zugehörigen Dehnung von CFK-umschnürten unbewehrten und bewehrten kreisrunden Stützenquerschnitten bietet. Darüber hinaus können Spannungs-Dehnungs-Beziehungen hergeleitet werden. Durch die Entwicklung von charakteristischen Bemessungsgleichungen gelingt eine einfache Implementierung in bestehende Sicherheitskonzepte. Das entwickelte Modell oder Teile davon eignen sich zur Verwendung in den zur Entstehungszeit der Dissertation vorhandenen Bemessungsvorschriften oder können zu deren Verbesserung herangezogen werden. / This thesis deals with the confinement of short reinforced concrete (RC) columns by carbon-fibre-sheets (CF sheet). In doing so, the connection of concrete surface and CF sheet is enabled by an epoxy resin (CFRP confinement). Thereby, concrete’s lateral expansion is efficiently restricted in cases of imposed axial compressive deformation; therefore, the elastic CFRP resisting response generates an ever increasing lateral compressive stress state on concrete, leading to structural upgrade of the member core to provide a remarkable higher concrete strength and sufficient deformability. Research assignment was to solve open-ended questions and knowledge gaps, which unfolded during an intense literature review, and to present an own proposal of a material model. For this, plain and reinforced concrete columns with different geometrical shape, variable diameter, and different longitudinal and transverse reinforcement elements were produced, and were confined with different CF sheets in variable thickness. Executed deformation controlled compression tests provided investigations concerning the structural behaviour of the test specimens, and electrical measurement techniques such as LVTD and strain gauges enabled a sufficient monitoring of failure modes. The evaluation and interpretation of the received data resulted in empirical equations to predict the ultimate strength and accompanying ultimate axial strain of CFRP confined columns with and without reinforcement. Furthermore, the tests allowed conclusions concerning the rupture strain of the deployed CFRP confinements, and leaded to FRP efficiency factors, capable to predict the actual ultimate strain of the reinforcing fibres. Further data bases, which are available in literature, confirmed the own proposals. As a result, this thesis provides an empirical material model, which deals with proper design equations to predict the load bearing capacity and the deformability of CFRP confined plain and reinforced circular concrete columns. Moreover, it is possible to generate entire stress-strain curves in axial direction. Developed characteristic equations and values allow an easy implementation in existing limit state concepts. The developed model or parts of it are sufficient to be implemented in design guidelines, or they may help to enhance them.

Die Mischbauweise stellt eine Möglichkeit dar, insbesondere im Automobilbau, aber auch in anderen Industriezweigen Leichtbau zu betreiben. Dazu werden verschiedenartige Werkstoffe miteinander kombiniert. Vorzugsweise handelt es sich um Kombinationen aus faserverstärkten Kunststoffen und Leichtmetallen. Nach dem Motto “Der richtige Werkstoff am richtigen Ort” können so belastbare und gleichzeitig leichte Konstruktionen realisiert werden. Eine große Herausforderung besteht dabei jedoch im Fügen solch unterschiedlicher Werkstoffe. Aufgrund großer Unterschiede in Bindungsart und Schmelztemperatur sind klassische Fügeverfahren nicht anwendbar. Zum Verbinden von Metallen mit Faser- Verbund-Werkstoffen (FKV) wurden deswegen vorhandene Technologien adaptiert oder neue entwickelt. Im Rahmen dieser Dissertation wurde mit dem modifizierten Blindnieten ein neuer Lösungsansatz entwickelt, der sowohl mechanische als auch thermische Fügeverfahren miteinander kombiniert. Dazu wird ein rotierender Blindniet in sich überlappende Bleche getrieben und das darunter liegende Material unter Ausbildung einer Hülse aus dem Oberblech verdrängt. Anschließend wird der Niet ausgeformt und der Prozess ist abgeschlossen. Durch die Reibwärme wird die thermoplastische Matrix des FKV geschmolzen und die Fasern werden beweglich und können verdrängt werden. Dadurch kommt es zu einer geringeren Faserschädigungen und es können Delaminationen komplett vermieden werden. Untersuchungen wurden vorzugsweise an Materialkombinationen in Mischbauweise durchgeführt. Es wurden Aluminium- und Magnesiumbleche mit verschiedenen FKV mit Glas- oder Kohlefaserverstärkung gefügt. Für eine große Anwendungsbreite wurden ebenso Verbindungen von mehreren Metallblechen untersucht. Alle Kombinationen konnten so gefügt werden, dass in relativ kurzer Prozesszeit eine qualitativ hochwertige Verbindung entsteht. Mit einer geeigneten Parameterwahl sind Fügezeiten unter drei Sekunden möglich. Die mechanisch technologischen Gütewerten zeigen, dass mittels modifiziertem Blindnieten hergestellte Verbindungen mindestens die gleiche Lasten aufnehmen können, wie konventionelle Verfahren. Unter Scherbelastung kann die Belastbarkeit um bis zu 68 % gesteigert werden. Es hat sich gezeigt, dass mit dem neuen Verfahren eine wirtschaftliche Lösung für den Mischbau zur Verfügung steht. / Composite constructions provide an opportunity to introduce lightweight design in automotive and other industries. Therefore different kind of materials are combined. Preferably, these are combinations of fibre reinforced plastics and lightweight metal alloys. With the slogan 'the right material at the right place' tough and lightweight constructions can be realized. A big challenge the joining of these different materials. Because of big differences in the chemical bindings and in the melting temperature, conventional joining methods cannot be used. To join fibre reinforced plastics (FRP) existing processes were adapted or newly developed. In the course of this work with the modified blind riveting a new approach was developed, which combines mechanical and thermal joining processes. Therefore a rotating blind rivet is penetrated through two overlapping sheets by deforming the sheet material. After that the rivet is set and the process finished. Because of the friction heat the thermoplastic matrix of the FRP is slightly melted and the fibres can be moved without breaking them. Investigations were done mainly with lightweight material combinations. Sheets made out of aluminum and magnesium were joined with glass or carbon fibre reinforced plastic sheets. For a wider application field also combinations of two metal sheets were investigated. All combinations could be joined in a relatively short cycle time and high quality. So it is possible to reach a joining time of under 3 seconds. Under shear load the strength of joints made by modified blind riveting can be up to 68 % higher than conventional riveted joints. It has been shown that the new process can be exploited economically.

In this paper, we look at the shear-out failure of carbon fiber reinforced plastics connections in the automotive industry. Contrary to the aircraft industry, the boundary conditions of automotive applications favor this failure mode strongly. Moreover, the use of other joining technologies than that used in the aircraft industry, such as joining by forming, leads to new challenges. The different influences, typical for joining by forming, on ultimate shear-out strength were first investigated separately and then transferred and validated on connections related to praxis by an analytical model. Special attention was given to effects that resulted from oversized pre-holes, acting clamping forces, and the reduced quality of the laminates in the immediate vicinity of the joint due to the joining process.

No description available.