Abstract not available

Thesis (M.S.)--Rutgers University, 2009. / "Graduate Program in Civil and Environmental Engineering." Includes bibliographical references (p. 151-153).

This thesis evaluates the use of High Strength Lightweight Concrete (HSLW) in bridge girders for the I-85 Ramp "B" Bridge crossing SR-34 in Cowetta County, Georgia. This bridge consisted of four spans; all girders were constructed using lightweight expanded slate aggregate. Spans 2 and 3 had a design strength of 10,000 psi, and span 2 was chosen for this research. The BT-54 girders were 107 ft 11½ inches in length. The prestressing strands used in these girders were 0.6 in diameter, grade 270, low relaxation strands. Material properties and member properties were tested. All 5 girders of span 2 were instrumented with vibrating wire strain gages at midspan, as well as with DEMEC inserts for transfer length measurements and with a deflection measurement system. Transfer length measurements found the transfer length of the girders to be 23% less than the values suggested by AASHTO and ACI equations. The deflection measurements showed 4.26 inches of camber at 56-days while the girders were stored at Standard Concrete Products. The camber measurements matched theoretical predictions within 5%. Mechanical property tests found the concrete to be within all design requirements. A stiffness, load test was performed on each of the 5 girders at Standard Concrete Products. The average stiffness value of 8.428 x 106 kip ft2 is recommend for use by GDOT engineers in designing the deck and road profile. This thesis discusses all short term findings from construction to the end of storage. A later report will address long term issues such as creep and shrinkage, as well as the performance of the girders as part of the bridge.

Self-compacting concrete (SCC) was first developed in Japan about two decades ago. Since then, it has been offered as a solution to various challenges inherently associated with traditional concrete construction; i.e. quality and speed of construction, impact of unskilled labour force and noise pollution etc. SCC flows into a uniform level under its own weight and fills in all recesses and corners of the formwork even in highly congested reinforcement areas. In recent years the interest in using SCC in structural members has increased manifold; therefore many researchers have started investigating its characteristics. Nevertheless, before this special concrete is widely accepted and globally used in structures, its structural performance under different conditions should be investigated. This research focuses on investigating the behaviour of high strength self-compacting concrete (HSSCC) in reinforced concrete (RC) structures through a systematic approach in order to bridge part of an existing gap in the available literature. The dissertation is comprised of four main stages; namely, mix design development and mechanical properties of HSSCC, bond performance of deformed bars in HSSCC, experimental investigation on interior RC beam-column joints (BCJs) cast with HSSCC under reversed cyclic excitations, and finally finite element (FE) modelling and analysis of interior BCJs. First, a HSSCC mix proportion yielding compressive strength greater than 100 MPa was developed in the laboratory using locally available materials in New Zealand. Two benchmark concrete mixes of conventionally-vibrated high-strength concrete (CVHSC) and normal-strength conventionally vibrated concrete (CVC) were also designed for comparison purposes. Material characteristics (such as compressive, splitting tensile and flexural strengths as well as modulus of elasticity, shrinkage and microstructural properties) of all mixes were evaluated. It was found that, once the lower quality of material in normal strength concrete is offset by achieving a denser mix in high-strength concrete, mechanical properties of HSSCC are equivalent to or higher than those in CVHSC. Given that the performance of RC structures (and in specific BCJs) is highly dependent on bond between reinforcement and concrete, understanding the bond behaviour in HSSCC was an imperative link between the first and third phases of this research. Therefore, the second phase focused on scrutinizing bond properties of deformed bars in HSSCC using monotonic pull-out and innovative cyclic beam tests. Processing of the pull-out results revealed that a shorter development length may be utilized in HSSCC. In addition, the grade (or ductility) of reinforcing steel was found to substantially influence the post-yield bond performance. Important modifications to the bond model used in the CEB-FIP model code and Maekawa’s bond-slip-strain relationship were suggested from the results of this phase. An innovative cyclic beam specimen and test setup were also designed such that a more realistic bond performance could be observed in the laboratory tests compared to that in real RC structures. Deleterious impact of cyclic loading and buckling of reinforcement on bond performance were investigated using this testing protocol. The third phase of this research focused on the design, fabrication and testing of seven full-size BCJs. BCJs are one of the most critical parts in RC frame structures and their response substantially affects the overall behaviour of the structure. In seismically active regions like New Zealand, the criticality of BCJs is exacerbated with the complexities involved in seismic resistance. The already congested intersection of RC beam and column looks more like a solid steel connection after consideration of earthquake requirements, and placement of concrete becomes problematic in such areas. At the same time, in many of the high-rise structures, normal strength concrete does not meet the capacity requirements; this requires the usage of high-strength concrete. Therefore, once the seismic performance of HSSCC is guaranteed, it can possibly be a solution to both the capacity and compaction problems. Variables such as axial load, concrete type, steel grade, casting direction, and joint shear reinforcement were considered variable in the experimental investigations. It was found that HSSCC has similar seismic performance to that of CVHSC and it can also be incorporated in the joint area of CVC for an enhanced performance. Finally, DIANA (a nonlinear FE program) was used to simulate the experimental results obtained in the third phase of this research. All BCJs were successfully modelled using their relevant attributes (such as the mechanical properties of HSSCC, steel stress-strain response, test setup and loading protocol) and nonlinear FE analyses (FEA) were performed on each model. FE results were compared to those obtained in the laboratory which showed a reasonable agreement between the two. The capabilities of the FEA were scrutinized with respect to the hysteresis loops, energy dissipation, joint shear deformations, stress development in the concrete and steel, and drift components. Integrating the results of all stages of this research provided better understanding of the performance of HSSCC both at the material and structural levels. Not only were none of the seismically important features compromised by using HSSCC in BCJs, but also many other associated benefits were added to their performance. Therefore, HSSCC can be confidently implemented in design of RC structures even in seismically active regions of the world.

The objectives of this thesis comprise of overcoming the challenges in designing lightweight welded structures such as material selection, choice of fatigue design methods, and increased performance by using improvement techniques. Material selection of welded joints is dependent on the filler and base material strengths. Partially and fully penetrated cruciform and butt welded joints were designed in under-matching, matching, and over-matching filler materials. Base material steel grades were S600MC, S700MC, and S960. Current design rules are developed for welds in steel up to yield strength of 700MPa. Therefore, design rules in Eurocode3, AWS d1.1, and BSK 07 were verified and recommendations for developing design rules for designing welded joints in S960 were concluded. Numerical methodology for estimating static strength of welded joints by simulating heat affected zone was also developed. Another objective of the thesis work was to overcome the challenges in selection of fatigue design methods. The available design curves in standards are developed for uniaxial stress states, however, in real life the welds in mechanical structures are subjected to complex multiaxial stress states. Furthermore; weld toe failures are frequently investigated, weld root failures are seldom investigated. Therefore, in this work the multiaxial fatigue strength of welded joints failing at the weld root was assessed using experiments and various nominal and local stress based approaches. Butt welded joints with different weld seam inclinations with respect to applied uniaxial loading were designed to assess the root fatigue strength in higher multiaxial stress ratio regime. The fatigue strength of multi-pass tube-to-plate welded joints subjected to internal pressure only and combined internal pressure and torsion in and 90° out of phase loading was also investigated. Test data generated in this thesis was evaluated together with the test data collected from literature. Last objective of the thesis included investigation of the increased performance in fatigue strength by post weld treatment methods such as HFMI. The behavior of residual stresses induced due to HFMI treatment during fatigue loading is studied. Numerical residual stress estimations and residual stress relaxation models are developed and the effect of various HFMI treatment process parameters and steel grade on the induced residual stress state is investigated. Specimens studied were non load carrying longitudinal attachments and simple plates. Residual stresses in both test specimens were measured using X-ray diffraction technique. / <p>QC 20170206</p>

[pt] Os aços de alta resistência avançados estão sendo desenvolvidos e usados para a indústria automotiva devido à sua excelente combinação de alta resistência e ductilidade, acarretando na minimização de custo e peso e maximização da segurança. A soldagem por fricção e mistura mecânica a ponto (Friction Stir Spot Welding – FSSW) é uma nova variante do processo de fricção e mistura mecânica (Friction Stir Welding – FSW), que é um processo de soldagem no estado sólido, e pode ser aplicada em uma variedade de indústrias que necessitam de soldagem a ponto como a indústria aeroespacial, automotiva, nuclear, óleo e gás, transporte e outras indústrias que necessitam fazer a junção dos metais usando, geralmente, uma configuração de sobreposição. O presente trabalho é um estudo exploratório para melhor compreensão da soldagem por fricção e mistura mecânica a ponto do aço TRIP 800. Diferentes corpos de prova foram produzidos usando velocidades de rotação da ferramenta de 1600, 2000 e 2400 rpm e tempos de espera de 2s e 3s. Além da caracterização metalúrgica e determinação de microdureza, ensaios de cisalhamento e cross-tension foram realizados para avaliar o desempenho mecânico das juntas. / [en] Advanced high strength steels (AHSS) are being developed and are being used for the automotive industry due to their exceptional combination of high strength and ductility, which leads to cost and weight savings and better safety. Friction Stir Spot Welding (FSSW) is a novel variant of Friction Stir Welding (FSW), which is a solid-state joining process without bulk melting and can be applied in a variety of industries that require spot welding such as aerospace, automotive, marine, nuclear, oil and gas, transportation industries and other industries that need to join metals together, generally using an overlap configuration. The present contribution is an exploratory study to a better understanding of a TRIP 800 friction stir spot welding. Different samples were produced using tool rotational speeds of 1600, 2000 and 2400 rpm and dwell time of 2s and 3s. Besides the metallurgical characterization and microhardness determination, lap-shear and cross-tensile tests were carried out to evaluate the mechanical performance of the joints.

O objetivo da pesquisa foi obter subsídios para o projeto de pilares de concreto de alta resistência, submetidos à compressão simples, com concreto de resistência média de 60 MPa. Este projeto faz parte de um plano mais amplo onde já se têm resultados experimentais que traduzem o comportamento de pilares moldados com concreto de resistência média à compressão de 80 MPa. Nestes constatou-se a participação isolada do núcleo de concreto definido pelo eixo da armadura transversal como seção resistente dos pilares. Na etapa experimental foram ensaiados pilares com seções transversais quadradas de 200 mm x 200 mm e retangulares de 150 mm x 300 mm. As alturas dos pilares correspondem a seis vezes a menor dimensão da seção transversal, portanto, 1200 mm e 900 mm, respectivamente. Nos modelos de seção quadrada, o valor médio das relações entre as forças últimas experimentais e as forças últimas teóricas, considerando a seção total de concreto, resultou igual a 0,82, indicando que a seção resistente não é a seção total. Por outro lado, a média das relações entre as forças últimas experimentais e as forças últimas teóricas, considerando apenas a área do núcleo limitada pelo eixo dos estribos, resultou igual a 1,21, o que mostra que a seção resistente pode ser considerada, no Estado Limite Último, como a seção do núcleo. / This research\'s aim is to obtain information for design of high strength concrete columns under concentrically loads with medium cylinder compressive strength of 60 MPa. This project belongs to a more extensive plan which already has experimental results that represent the behavior of columns performed with concrete with medium cylinder compressive strength of 80 MPa. In these models has been verified the independent participation of concrete core defined by the transversal reinforcement axis as resistant section near the ultimate load. In the experimental stage it was tested twelve columns with square (200 mm x 200 mm) and rectangular (150 mm x 300 mm) cross sections. The height of the columns corresponds to six times the smallest dimension of the cross section, 1,200 mm and 900 mm, respectively. The medium value of the ratios between the ultimate experimental force and the ultimate theoretical force, regarding the full concrete section, was 0.82, indicating that the resistant section is not the full section. On the other hand, the medium of ratios between the ultimate experimental force and the ultimate theoretical force, considering only the core area limited by the axis of the lateral reinforcement bars, was 1.21, what shows that the resistant section can be considered as the core section in the Ultimate Limit State.

Atualmente tubos de aço microligados são utilizados na construção de oleodutos e gasodutos para exploração e condução de petróleo e gás natural em águas profundas. Estas aplicações demandam a utilização de ligas metálicas que apresentem elevada resistência mecânica, boa soldabilidade e excelente resistência às falhas associadas ao hidrogênio devido ao trabalho em ambientes sour. O hidrogênio atômico oriundo da corrosão do aço entra na microestrutura do material através da superfície, devido à ação do H2S do meio que inibe a reação de recombinação do hidrogênio (H0+H0=H2) e sua consequente dissipação para o meio em forma de bolhas. O hidrogênio atômico permeia através do material se movendo por difusão através do reticulado cristalino onde interage com defeitos microestruturais denominados traps, tais como inclusões, precipitados, contornos de grão e discordâncias impedindo que este continue a se movimentar. O acúmulo de hidrogênio atômico nestes traps, ao atingir a concentração crítica, leva a ocorrência de falhas seja pela redução localizada da força de coesão dos átomos do reticulado, seja pela formação de tensões internas oriundas da formação de hidrogênio molecular. Diferenças microestruturais influenciam o mecanismo de difusão e aprisionamento do hidrogênio atômico, bem como a concentração crítica de hidrogênio molecular necessária para ocorrência das falhas associadas ao hidrogênio. A deformação plástica, inerente ao processo de conformação de tubos, gera discordâncias que atuam como traps de hidrogênio causando seu aprisionamento e influenciando, portanto, a difusão através do reticulado. O objetivo do presente trabalho é avaliar o efeito da deformação plástica sobre a permeabilidade ao hidrogênio em dois tubos API 5L X65, os quais se diferenciam, principalmente, por apresentarem diferentes teores Mn, levando a diferença microestruturais significativas. Para tanto foram empregados ensaios de permeabilidade de hidrogênio, utilizando metodologia adaptada do trabalho de Devanthan e Stachursky (1962), em amostras não deformadas e deformadas até 1% e 6% de alongamento. Os exames microestruturais mostraram diferenças na fração de perlita e no tamanho médio de grão entre os dois aços. Os resultados para as amostras não deformadas mostram que a permeabilidade e a difusividade aparente do hidrogênio são menores no aço com menor teor de Mn. A deformação plástica reduziu a difusividade aparente de hidrogênio nos dois materiais, sendo esta mais acentuada para o aço com maior teor de Mn. Entretanto, a permeabilidade de hidrogênio após deformação de 1% comportou-se de maneira distinta nos dois aços estudados. Este fato evidencia a influência da composição química e, consequentemente, da microestrutura, na permeabilidade e difusividade aparente de hidrogênio nos materiais submetidos à deformação plástica. / Currently microalloyed steel pipes are used to build pipelines for oil and gas exploration and conduction in deep waters. These applications demand alloys with high mechanical strength, weldability and excellent resistance to hydrogen assisted cracking due to work in sour environment. Atomic hydrogen produced during steel corrosion reaction enters in the microstructure from the metal surface due to the presence of H2S that hinders the hydrogen recombination reaction (H0+H0=H2), hence inhibiting hydrogen dissipation to the environment as bubbles. Atomic hydrogen permeates into the material moving through the lattice by diffusion, wherein it interacts with metallurgical defects such as inclusions, precipitates, grain boundaries and dislocations hindering its transport by diffusion. The accumulation of atomic hydrogen in these traps, upon reaching a critical concentration, leads to the occurrence of failures, either by the localized reduction of the cohesive strength of the atoms in the lattice, or by the build up of internal stresses arising from the formation of molecular hydrogen. Microstructural differences influence the mechanism of atomic hydrogen diffusion and entrapment, as well as the critical molecular hydrogen concentration required for the occurrence of hydrogen assisted cracking. Plastic deformation, which is inherent of pipeline forming process, creates dislocations that act as hydrogen traps, thus affecting hydrogen diffusion through the lattice. This work aims to evaluate the effect of plastic deformation in hydrogen permeation in two API 5L X65 pipeline with differences in chemical compositions especially regarding their Mn contents, which cause significant microstructural changes. Hydrogen permeation tests were performed, using a methodology adapted from the work of Devanathan and Stachursky (1962), in non-deformed and deformed samples up to 1% and 6% elongation. The microstructural characterization shows differences between the pearlite fractions of the two pipelines and in their average grain boundary sizes. The results of the permeation tests in the non-deformed samples showed that hydrogen apparent diffusivity and permeation are lower in the steel with lower Mn content. The plastic deformation reduced the apparent diffusivity of hydrogen in the two materials, however, the diffusivity reduction was more pronounced for the steel with higher Mn content. In addition, the changes in hydrogen permeation in samples deformed up to 1% were different for the two steels. This clearly shows the influence of chemical composition and microstructure in hydrogen permeation and apparent diffusivity in the plastically deformed materials.

Concretos de alta resistência têm sido usados em estruturas, atualmente, em diversas partes do mundo. Entretanto, no Brasil, pouco se conhece sobre seu comportamento. Este trabalho fornece uma visão geral das aplicações, dos materiais empregados na produção, das propriedades mecânicas e do comportamento estrutural dos concretos de alta resistência. Resultados experimentais obtidos por alguns pesquisadores, para pilares com carga axial e para vigas sujeitas a flexão e a cisalhamento, são comparados com valores teóricos, calculados com procedimentos usuais relativos a concretos de resistência usual. Para os pilares, é inquestionável a necessidade do confinamento do núcleo de concreto, utilizando armadura de cintamento. Na flexão das vigas, as taxas mínimas para armadura longitudinal, sugeridas pelas normas para concretos usuais, não são suficientes; é importante ter valores maiores que esses. E para cisalhamento, as recomendações das normas são satisfatórias. / Nowadays, high-strength concrete has been used in structures all over the world. However, in Brazil, not much is known about its behavior. This work provides an overview of the applications, the materials employed in production, the mechanical properties, and the structural behavior of high-strength concrete. Experimental results obtained by several researchers, for columns under axial load and beams under flexure and shear, are confronted with theoretical values, computed by normal procedures relative to normal strength concrete. For columns, it is unquestionable the need of confinement of the concrete core by transverse reinforcement. In beams under flexure, the minimum rates for longitudinal reinforcement, suggested by the codes for usual concrete, are not enough; it is important to have values greater than those. And for shear, the codes requirements are satisfactories.

Orientador: Marcelo dos Santos Pereira / Banca: Marcelino Pereira Nascimento / Banca: Rosinei Batista Ribeiro / Resumo: Este projeto é um estudo do efeito springback em quatro tipos de aços de alta resistência, sendo estes bifásico, baixo carbono, endurecível após pintura e com interstícios livres, aplicados atualmente como matéria-prima na produção de veículos. Neste contexto está inserido o desenvolvimento de novos aços avançados de alta resistência em consonância com o projeto ULSAB-AVC, que visa à produção de veículos seguros e econômicos para o século 21. A caracterização mecânica do efeito springback foi realizada por intermédio de ensaio de conformação mecânica, denominado dobramento de três pontos ao ar, como uma adaptação ao ensaio de flexão cilíndrica livre. Foram avaliadas também as propriedades mecânicas do material definidas pelo ensaio de tração, objetivando a determinação da resistência à tração, do limite de escoamento e do alongamento. Além disso, foi avaliada a caracterização microestrutural dos aços avançados, identificando e quantificando-se as fases presentes em coexistência por meio do processamento digital de imagens. Os resultados mostram que o efeito springback no aço bifásico, devido à sua alta resistência mecânica, apresenta as maiores taxas de springback e causa uma diminuição na "razão de aspecto" dos grãos que sofreram conformação mecânica e tentaram retornar às suas formas originais. Aços de baixo carbono e endurecíveis após a pintura, não sofrem efeito springback suficiente para causar alteração na forma dos grãos, sendo que a variação da "razão de aspecto" depende da combinação do alongamento e resistência mecânica destes aços. Já o aço com interstícios livres, devido a sua menor resistência mecânica, o efeito springback apresenta as menores taxas e a variação da razão de aspecto depende somente da capacidade de alongamento desse aço / Abstract: This is a study of the springback effect on four kinds of high strength steel, wich are dual-phase, low carbon, bake hardening and interstitial free, currently used as feedstock in the production of vehicles. In this context is inserted the development of new advanced high steel resistance in accordance with the project ULSAB-AVC, which aims to produce safe and economical vehicle for the 21st century. The mechanical characterization of the springback effect was performed by means of a test of mechanical conformation, called three-point air bending, done by adapting to unconstrained cylindrical bending test. Were also evaluated the mechanical properties of material defined by the tensile test, in order to determine the tensile strength, yield strength and the elongation. Furthermore, was performed the microstructural characterization of advanced steels by identificating and quantificating of present phases in coexistence by means digital image processing. The results indicates that the springback effect in dual-phase steel, due to its high mechanical strength, has the highest springback rates and causes a decrease in the "aspect ratio" of the grains that suffered mechanical conformation attempting to return to its original forms. Low carbon and bake hardening steels, have not enough springback effect to cause change in the shape of the grains and the change of the "ratio aspect" depends on the combination of both elongation and mechanical strength of these steels. Yet on the interstitial free steel, due to its lower mechanical strength, the springback effect has the lowest rates and the change in "aspect ratio" depends only on elongation capacity of the steel / Mestre