Análise experimental dos efeitos combinados de corrosão e fadiga em vigas de concreto armado

Infrastructure elements, especially reinforced concrete bridges and viaducts, are exposed to a combination of degrading processes throughout their life cycle, such as corrosion and fatigue. The combined effects of both processes are known to be more harmful to the structure than the sum of both deterioration processes considered individually. Due to the limited amount of studies in this field, this research aims to evaluate, by experimental analysis, the combined effects of fatigue and corrosion on reinforced concrete beams. Eight beams measuring 7 x 14 x 130 cm were cast and divided in four groups of 2 beams each: one group for reference beams, one for corroded beams with a loss of mass of 10%, one for beams subjected to 200,000 cycles and the last for corroded fatigued beams. The results show that the combined processes drastically reduce the load capacity of the beams by less than half compared to the reference beams. It was also observed that fatigue life decreased and the failure mode changed to fragile.Elementos de infraestrutura, especialmente as pontes e viadutos de concreto armado, estão expostos a uma combinação de processos de degradação enquanto em serviço, como a corrosão de armaduras e fadiga. Os efeitos combinados de ambos os processos são conhecidos por serem mais prejudicais para a estrutura quando comparados à soma de ambos os processos de deterioração individualmente. Tendo em vista a limitação de estudos nessa área, essa pesquisa busca avaliar, por meio de análises experimentais, a combinação dos efeitos de fadiga e corrosão de armaduras em vigas de concreto armado. Para tanto, foram concretadas oito vigas com dimensões de 7 x 14 x 130 cm, que posteriormente foram divididas em quatro grupos com duas vigas cada: um grupo para vigas de referência (sem degradação), um para vigas corroídas com perda de massa de armadura de 10%, um para vigas submetidas a 200.000 ciclos de carregamento e o último para vigas corroídas e fatigadas. Os resultados mostram que a combinação de processos reduz drasticamente a capacidade de carga das vigas para menos da metade em comparação com as vigas referências. Também foi observado que a vida de fadiga diminuiu e o tipo de ruptura se alterou de dúctil para frágil

Avaliação experimental de vigas de concreto armado corroídas submetidas a ciclos de carregamentos

No Brasil, as obras de arte especiais desempenham um papel fundamental quando o assunto é mobilidade urbana ou transporte de carga e passageiros e influenciam diretamente o desenvolvimento econômico do país. De acordo com o Departamento Nacional de Infraestrutura e Transporte (DNIT), 80% destas obras catalogadas são executadas em concreto armado. O concreto armado é composto por dois materiais que se complementam, o concreto e o aço. O aço contribui com a resistência à tração do concreto e absorve esforços que o concreto não é capaz de resistir. Já o concreto resiste aos esforços de compressão e é responsável pela proteção física e química da armadura, evitando assim manifestações patológicas causadas pelo ataque de agentes agressivos, como a corrosão de armadura. No caso das obras de arte especiais, a entrada dos agentes agressivos na matriz cimentícia pode ser facilitada através da abertura de microfissuras. Estas fissuras são provocadas pelos carregamentos cíclicos causados pela passagem de veículos ao longo do tempo. Por sua vez, a corrosão de armadura diminui a aderência entre o concreto e as barras de aço, favorecendo o desgaste por fadiga. Assim, esta pesquisa tem a finalidade de verificar experimentalmente se existe sinergia entre a corrosão de armadura e a fadiga. O ensaio de corrosão acelerada por imersão modificada (CAIM) foi escolhido para estimular a corrosão. De maneira geral, as vigas foram submetidas a 2 milhões de ciclos de carregamento e depois ensaiadas à flexão até sua ruptura. Foram analisadas a capacidade resistente das vigas, os deslocamentos verticais nos centros dos vãos e a vida de fadiga das mesmas. Os resultados mostraram que para baixos graus de corrosão entre 3-5% de perda de massa, não é possível perceber o efeito sinérgico entre os processos deletérios, devido principalmente, ao ganho de aderência promovido pela expansão da barra sem a fissuração do concreto de cobrimento. Este aumento de aderência torna a viga mais rígida e diminui os deslocamentos verticais das mesmas em comparação às vigas sãs. Para graus de corrosão mais elevados, entre 8-11%, a sinergia dos efeitos deletérios é perceptível na diminuição dos deslocamentos verticais medidos nos centros dos vãos dos elementos ensaiados. Além do mais, o modo de ruptura das vigas com perda de massa mais elevada muda de dúctil para frágil, fato que não permitiria evacuação da estrutura a tempo em uma situação real.In Brazil, reinforced concrete structures such as highway or regular bridges play a key role when it comes to urban mobility or cargo and passenger transportation and directly influence the country's economic development. According to the National Department of Infrastructure and Transportation (DNIT), 80% of these cataloged structures are executed in reinforced concrete. Reinforced concrete consists of two complementary materials, concrete and steel. Steel contributes to the tensile strength of the concrete and absorbs forces that the concrete is not able to withstand. Concrete, however, resists compression efforts and is responsible for the physical and chemical protection of the reinforcement, thus avoiding pathological manifestations caused by attack by aggressive agents such as corrosion. In the case of these RC structures, the entry of aggressive agents into the cementitious matrix can be facilitated by the opening of microcracks. The opening of cracks are caused by the cyclic loading due to the passage of vehicles over time. In turn, the reinforcement corrosion decreases the adhesion between the concrete and the steel bars, favoring fatigue wear. Therefore, this research has the purpose of verifying experimentally if there is synergy between reinforcement corrosion and fatigue. The modified immersion accelerated corrosion test (CAIM) was chosen to stimulate corrosion. In general, the beams were subjected to 2 million loading cycles and then tested under flexural loading until failure. The load-carrying capacity of the beams, the vertical displacements at the centers of the spans and the fatigue life of the beams were analyzed. The results showed that for low degrees of corrosion between 3-5% of mass loss, it is not possible to perceive the synergistic effect between the deleterious processes, mainly due to the gain of adhesion promoted by the expansion of the steel bars without the cracking of the concrete cover. This increase in adhesion makes the beam more rigid and decreases the vertical displacements in comparison to the reference beams. For higher degrees of corrosion, between 8-11%, the synergy of deleterious effects is perceptible in the reduction of the vertical displacements measured in the centers of the spans of the elements tested. Moreover, the mode of failure of the beams with higher mass loss changes from ductile to brittle, a fact that would not allow evacuation of the structure in time in a real situation case

The Role Of Community In Online Learning

This project examined learners’ perceptions of the learning community construct, whether learners’ online and face-to-face interactions led to the development of learning communities and whether the process of building community was different in face-to-face and web-based courses. Courses requiring learners to interact on a personal level early in the course were more likely to develop into learning communities. The degree of distance within the course did not make a difference in whether these learning communities developed. Rather, a sense of trust and of shared hardship as they worked through the course assignments were seen as more important by these learners. In situations where communications were considered inappropriate, developing communities were derailed or development never began. A definition of community emerged from the data that identified characteristics of shared learning goals, exchanging ideas, assisting each other, and an element of trust among the learners within the community

Análisis crítico y propuestas de innovación al método de ensayo de acción de calor y choque térmico a luz de la ABNT NBR 15575 (2013)

The tests of Brazilian Standard NBR 15575: 2013 are part of the knowledge of the civil construction industry, but the heat and thermal shock test is innovative and does not have a consolidated history. The research objective is to analyze the testing critically and present proposalsbased on data meta-analysis. Results showed that the test is very inaccurate in describing the procedure and equipment. This study proposed adjustments and innovations in the test to provide more reliable results, but it does not make propositions regarding visual inspection and the number of cycles. The study concluded that the lack of information on the testing has direct responsibility for the results and that the suggested proposalshave the potential to be incorporated.Os ensaios da ABNT NBR 15575:2013 fazem parte do conhecimento do setor da construção civil, mas o ensaio de ação de calor e choque térmico é inovador e não possui um histórico consolidado. O objetivo da pesquisa é analisar o ensaio criticamente e apresentar proposições.O método de pesquisa é a meta-análise de dados. Os resultados demonstraram que o ensaio é bastante impreciso na descrição do procedimento e do equipamento. Foram propostos ajustes e inovações no ensaio para proporcionar resultados mais fidedignos, porém não foram realizadas proposições quanto à inspeção visual e aos números de ciclos. Conclui-se que a falta de informação do ensaio tem responsabilidade direta nos resultados e que as proposições sugeridas têm potencial para serem incorporadas.Los ensayos de la ABNT NBR 15575:2013 hacen parte del conocimiento del sector de la construcción civil, pero el ensayo de acción de calor y choque térmico es innovador, y no posee un histórico consolidado. El objetivo de la pesquisa es analizar el ensayo críticamente y presentar propuestas. El método de pesquisa es meta-análisis de datos. Los resultados demostraron que el ensayo es bastante impreciso en la descripción del procedimiento y equipos. Fueron propuestos ajustes e innovaciones al ensayo para proporcionar resultados más fidedignos, sin embargo, no fueron realizadas propuestas en cuanto a la inspección visual y a los números de ciclos. Se concluye que la falta de información del ensayo tiene responsabilidad directa en los resultados y que las propuestas sugeridas tienen potencial para ser incorporadas

Concrete structures monitoring using ultrasonic tests

Due to the nature of their use, concrete structures are typically subjected to various aggressive actions derived from the loads and the environmental agents, which make the concrete condition change over time. Constant monitoring of structures isa necessary procedure since the preventive detection of problems allows the use of more straightforward and cost-effective methods for evaluation and repair. In order to carry out continuous monitoring of the state condition of concrete elements, there are many tools available. Nondestructive Testing (NDT) applications are a new strategy to monitor the state of concrete structures continually. Recent advancements in NDT technologies are increasingly turning them into attractive and viable strategies to support this type of monitoring and visual inspection. In particular, besides been viable and attractive, ultrasonic tests are arelatively cheap alternative and represent a range of different methods, each one with its benefits, to analyze concrete structures. The Research Group of LEME-UFRGS has developed research and application of NDT methods in general, and ultrasonic based methods in particular, for the last 15 years. The research done by the group demonstrates that these methods can contribute to monitoring deterioration and the quality of concrete structures. The present study demonstrates particular cases involving ultrasonic pulse testing and ultrasonic tomography. Theaim was to check for these technique improvements for the analysis of concrete elements. The results highlight the potentialities and shortcomings of each technique

Medical conditions and depressive, anxiety, and somatic symptoms in older adults with and without generalized anxiety disorder

OBJECTIVE: The objective of this study was to examine medical illness and anxiety, depressive, and somatic symptoms in older medical patients with generalized anxiety disorder (GAD). METHOD: A case-control study was designed and conducted in the University of California, San Diego (UCSD) Geriatrics Clinics. A total of fifty-four older medical patients with GAD and 54 matched controls participated. MEASUREMENTS: The measurements used for this study include: Brief Symptom Inventory-18, Mini International Neuropsychiatric Interview, and the Anxiety Disorders Interview Schedule. RESULTS: Older medical patients with GAD reported higher levels of somatic symptoms, anxiety, and depression than other older adults, as well as higher rates of diabetes and gastrointestinal conditions. In a multivariate model that included somatic symptoms, medical conditions, and depressive and anxiety symptoms, anxiety symptoms were the only significant predictors of GAD. CONCLUSION: These results suggest first, that older medical patients with GAD do not primarily express distress as somatic symptoms; second, that anxiety symptoms in geriatric patients should not be discounted as a byproduct of medical illness or depression; and third, that older adults with diabetes and gastrointestinal conditions may benefit from screening for anxiety

New investment: an exploratory case study of three mature Edinburgh festivals and their future funding opportunities

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