Made available in DSpace on 2014-10-09T12:53:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:29Z (GMT). No. of bitstreams: 1 12220.pdf: 3040591 bytes, checksum: cf07d18c47b6b9bc7f1a361b3a6fe286 (MD5) / Dissertação (Mestrado) / IPEN/D / Universidade Mackenzie. Departamento de Engenharia de Materiais, São Paulo

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Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2016-04-19T15:13:28Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese completa - com FICHA CATALOGRÁFICA - 13-11-15.docx.pdf: 12354706 bytes, checksum: ca0e4da17bca37b3d26461335b9c9552 (MD5) / Made available in DSpace on 2016-04-19T15:13:29Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese completa - com FICHA CATALOGRÁFICA - 13-11-15.docx.pdf: 12354706 bytes, checksum: ca0e4da17bca37b3d26461335b9c9552 (MD5) Previous issue date: 2015-11-15 / Estima-se a existência, desde a década de 1960, de milhares de edifícios de alvenarias de vedação com função estrutural na Região Metropolitana do Recife (RMR). Esses prédios tipo “caixão” foram concebidos, em sua maioria, com blocos cerâmicos com furos na horizontal e possuem até quatro pavimentos. Verifica-se que essas paredes não apresentam requisitos técnicos e desempenho necessários para serem considerados estruturais, de tal forma que o cálculo da resistência à compressão mostra insuficiência na capacidade de suporte, por conseguinte, não atendem a critérios normativos. Portanto, observam-se elevados níveis de patologias e envelhecimento precoce, onde a relação entre o número de acidentes e o número de edificações existentes apresenta probabilidade de falha de aproximadamente 1:500, bem acima do nível aceitável quando envolve a segurança de vidas humanas que é de 1:10.000. Ocorreram 12 desabamentos desses prédios nos últimos 30 anos na RMR, causando 12 mortes. Assim, torna-se importante apresentar um modelo de reforço para estas edificações, especialmente quando se considera que nesses prédios residem cerca de 250.000 pessoas. Este trabalho tem por objetivo avaliar o reforço com argamassa armada e adição de metacaulim na resistência compressiva, ductilidade e durabilidade. Moldaram-se prismas de amostras sem e com reforço sobre substrato sem revestimento e revestido. O reforço foi constituído por capa de argamassa com tela de aço nas duas faces interligadas por conectores de aço e adição de 15% de metacaulim, adicionado por substituição de parte de cimento e adição simples, com traços em volume: 1:1:6:1,5 e 1:0,5:4,5:1,5 (cimento, cal, areia, relação água/cimento). Concluiu-se diante dos ensaios que o reforço proposto contribui substancialmente na resistência à compressão (considerando o fator redutor devido efeito de flambagem) e na forma de ruptura, fornecendo ductilidade (deformação plástica e tenacidade), bem como a metacaulim contribui para a durabilidade, visto em ensaios próprios específicos (resistência mecânica, módulo de elasticidade, velocidade de propagação da onda ultrassônica, absorção por imersão e ensaios acelerados de carbonatação e cloretos). / In Recife Metropolitan Region (RMR), there are thousands of buildings made of non-structural masonry dating from the 1960s, however performing as structural masonry. These four-floor buildings best known as “caixão” were mostly conceived with ceramic bricks horizontally perforated. This kind of masonry does not supply technical requirements and does not perform appropriately to be considered structural. It does not fulfill normative criteria because structural calculus shows that its resistance to compression does not suffice. This consequently leads to high levels of pathologies and premature aging of buildings. The relationship between the quantity of “caixão” buildings in RMR and the number of accidents they are involved in indicates that the probability of failure is about 1:500. This rate is much above the acceptable standard of 1:10.000 concerning human lives safety. Over the past thirty years, 12 “caixão” buildings tumbled down in RMR, causing 12 deaths. It is, thus, relevant to develop a solution for reinforcing these buildings, where approximately 250.000 people live. This study aims to evaluate the use of reinforced mortar and metakaolin addition for reinforcing masonry in order to increase its resistance to compression, ductility and durability. In this research, we shaped sample prisms with and without reinforcement on both mortar and non-mortar substratum. The reinforcement consisted of a layer of mortar with a steel lattice on both faces connected by steel connectors as well as addition of 15% of metakaolin, partly replaced with cement by pure addition, following the volume proportions of 1:1:6:1,5 and 1:0,5:4,5:1,5 (cement, lime, sand, water/cement relation). Conclusively, our proposal substantially increased the masonry resistance to compression, considering the reduction factor due to the buckling effect, providing it with ductility, that is, plastic deformation and tenacity. Additionally, we found that the metakaolin contributes to masonry durability by doing specific experiments of mechanical resistance, elasticity modulus, ultrasound, and absorption by immersion as well as accelerated experiments of carbonation and chlorides.

Strength Reduction Factor (R-Factor), often referred to as Response Modification Factor, is commonly used in the design of lateral force resisting systems under seismic loading. R-Factors allow for a reduction in design base shear demands, leading to more economical designs. The reduction of strength is remedied with ductile behavior in members of proper detailing. Modern seismic codes and provisions recommend R-Factors for many types of lateral force resisting systems. However these factors are independent of the system fundamental frequency and many other important system properties, resulting in factors that may result in an unfavorable seismic response. To evaluate the validity of prescribed R-Factors an extensive analytical parameter study was conducted using a FEM single degree-of-freedom Concentrically Braced Frame (CBF) under incremental dynamic analysis over a suite of ground motions. Parameters of the study include brace slenderness, fundamental frequency, increment resolution, FEM mesh refinement, effects of leaning columns, and effects of low-cycle fatigue. Results suggest that R-Factor can vary drastically for CBF systems with differing properties.

A series of research studies have recently identified an issue called strain localization in welded wire reinforced (WWR) members. This phenomenon reportedly concentrates strains at welded cross wire locations and severely limit ductility. Those that identified the phenomenon used it to imply that WWR is unsafe because it does not warn of failure. This dissertation is investigating details to mitigate the strain localization effect and demonstrate the WWR can be used safely. A moment curvature analysis is developed using Response2000 program and calibrated using experimental data. Parametric study was developed to present a recommendation of details and minimum reinforcement required for WWR slabs. The effect of different types of WWR coating on mechanical properties were investigated. The dissertation next examined the effects of strain rate on the mechanical properties of WWR and traditional rebar. In total, fifty four slabs have been constructed using WWR and rebar with various cross wire spacing, using a realistic design. The strain localization phenomenon was not demonstrated, but WWR slabs are somewhat less ductile than traditionally reinforced members. The WWR members were shown to provide adequate ductility for warning of impending failure visually and with a well-accepted ductility measure. The WWR members were also shown the ability of load redistribution. The effect of coating demonstrates that both galvanizing WWR and coating WWR with epoxy has a positive effect on mechanical properties, along with adding corrosion resistance. The effect of strain rate shows that increase in loading rate tend to increase the yield and ultimate stresses and percent area reduction, however the loading rate increase does not have a significant effect on elastic modulus, elongation and uniform elongation.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19308号 / 工博第4105号 / 新制||工||1633(附属図書館) / 32310 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 白井 泰治, 教授 乾 晴行 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The addition of rare earth (RE) alloying elements is a promising method for improving the strength, ductility and overall formability of magnesium (Mg) alloys. However, the underlying mechanism for this phenomenon remains unclear. An investigation on the effect of the rare earth element, scandium (Sc), on binary Mg-Sc alloys has been pursued. Tension and compression tests were performed on a series of dilute binary Mg-Sc alloys at temperatures of 298 K, 78 K and 4.2 K. As a reference, pure Mg was also investigated for comparative purposes. Differences in tension and compression stress-strain curves highlighted distinct activated mechanisms, where slip dominated in tension and twinning governed compression. The observed increase in ductility and prolonged necking was attributed to a weaker basal texture, enhanced twinning and non-basal slip. A decreased work hardening rate suggests an improvement in dislocation recovery with Sc addition. In compression, Mg-Sc alloys followed Fleischer’s theory of solution hardening, where stress scales with concentration, c, as c^1/2; however, there was a very weak fit with both Fleischer and Labusch models under tension. The strengthening rate displayed by Mg-Sc was relatively weak compared to previously studied Mg-RE systems. However, considering the estimated misfit parameters, the size and modulus misfit was not enough to account for the strengthening rate. The results suggest that hardening of the twinning mode may influence strength. Constitutive modelling, based on a self-consistent plasticity model, was used to characterize the deformation behaviour. The simulations predicted an increased relative activity of non-basal <c+a> slip with Sc addition, supporting experimental results and proposed mechanisms in literature. The results of Mg-Sc alloys have been connected to theories that identify a decrease in stacking fault energy (SFE) as the determining factor for increased strength and ductility of Mg-RE alloys. A comparison of the SFE of previously studied REEs with Sc, demonstrated strong evidence towards the theory’s validity. Sc has been shown to only moderately reduce the SFE of Mg and hence, the present experimental results have shown a moderate increase in strength and ductility. Additional modelling and detailed dislocation analysis are suggested as future steps to further support this theory. / Thesis / Master of Applied Science (MASc)

To address the size limitation of the powder bed fusion system in additive manufacturing, the welding properties of 316L stainless steel manufactured by SLM 125HL are investigated by conducting hot ductility test and nil strength temperature (NST) test with a physical thermal mechanical simulator, Gleeble. In this study, the print orientations (Zdirection and XY-direction) and the laser patterns (stripe and checker board) are studied. In NST test, the orientation showed a statistical significance in NST: Z-direction was 1384°C and XY-direction was 1400°C. In hot ductility test, all of ductility curves show similar behaviors: hardening region, recrystallization region, and liquation region. The additively manufactured 316L shows poor ductility compared to wrought 316L stainless steel. Also, there is a noticeable difference in ductility between laser pattern. Finally, ductility after the thermal cycle shows higher than that before the thermal cycle. For the future recommendation, investigation on the interelayer temperatures and sigma phase determination should be conducted to confirm the hypotheses to explain the phenomena observed in this study.

The alternative seismic design provisions for diaphragms provided in ASCE 7-22 Minimum design loads and associated criteria for buildings and other structures Section 12.10.3 account for both diaphragm ductility and displacement capacity, producing more accurate design forces and decreased detailing when compared to conventional seismic design methods. However, the diaphragm design force reduction factor has not yet been determined for tension-only roof truss diaphragms, a common system used in metal buildings. In this study, experimental tests of two cantilevered diaphragm subassembly specimens with tension-only rod bracing were conducted to determine the load-deformation behavior of the system. The first specimen used 7/8-in. rods, two types of hillside washers, two types of compression members, and two configurations of lateral bracing. The second specimen used 3/4-in. rods, one type of hillside washer, one type of compression member, and one configuration of lateral bracing. Four tests were conducted. One additional test was conducted on each specimen to determine the friction in the test setup. The system developed significant ductility during testing and the yield mechanism was primarily tensile yielding of the rods. The results indicate that a diaphragm design force reduction factor of 2.0 for structures with periods greater than 1.0 second and 1.7 for structures with periods between 0.12 and 0.5 seconds may be appropriate for metal building systems if the lateral bracing of the compression member is prevented from buckling.

The application of carbon reinforced-fiber polymers (CFRP) to structures is a new development that is still under intense research. However, the rehabilitation or retrofit of damage reinforced concrete members by the external bonding of CFRP is becoming increasingly popular in the construction industry. The objective of the tests presented in this thesis is to study different CFRP designs on the reinforced concrete beams and compare their failure modes. The main goal is to determine the CFRP design on the reinforced concrete beams that result in a progressive and gradual failure mode with enough warning before final failure. Different CFRP designs are investigated and compared with theoretical predictions. A retrofitting concept is also employed in this research. The retrofitting concept is the idea of strengthening cracked structures. The strengthening of the beams performed in the lab is carried out under sustained loads and on previously cracking the beams to simulate the realistic case that is usually faced in practice on the field. The RC beams are strengthened in flexure to double their flexural capacity by applying the adequate amounts of CFRP to the tension face of the beams. Due to the CFRP strengthening and increasing the strength capacity of the beams, different CFRP anchorage methods are employed to the beams for additional shear reinforcement to ensure flexural failure. The different CFRP anchorage methods will also be observed for their effectiveness during the debonding and propagation mechanism as well as evaluated for their progressive failure mode.