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1
Gagné, Olivier C. "Bond lengths and bond valences of ions bonded to oxygen: their variability in inorganic crystals". Acta Crystallographica B, 2015. http://hdl.handle.net/1993/31697.
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A large amount of information concerning interatomic distances in the solid state is available, but little has been done in recent times to comprehensively filter, summarize and analyze this information. Here, I examine the distribution of bond lengths for 135 ions bonded to oxygen, using 180,331 bond lengths extracted from 9367 refined crystal structures collected from the Inorganic Crystal Structure Database (ICSD).
The data are used to evaluate the parameterization of the bond-length—bond-valence relation of the bond-valence model. Published bond-valence parameters for 135 cations bonded to oxygen, and the various methods used in their derivation, are evaluated. New equations to model the relation are tested and the common form of the equation is found to be satisfactory. A new method (the Generalized Reduced Gradient Method, GRG method) is used to derive new bond-valence parameters for 135 cations bonded to oxygen, leading to significant improvements in fit for many of the ions.
The improved parameterization is used to gain crystal-chemical insight into the milarite structure. A literature review of 350+ published compositions is done to review the end-members of the milarite group and to identify compositions that should have been described as distinct minerals species. The a priori bond-valences are calculated for minerals of this structure, and are used to examine the controls of bond topology on site occupancy, notably by localizing the major source of strain of the structure (the B site). Examination of the compositions of all known milarite-group minerals shows that compositions with a fully occupied B site are less common than those with a vacant B site, in accord with the idea that the B site is a local region of high strain in the structure.
The bond-length distributions for the ions of the alkali and alkaline-earth metal families are examined. Variations in mean bond-lengths are only partly explained by the distortion theorem of the bond-valence model. I have found that bond length also correlates with the amount of vibrational displacement of the constituent ions. The validity of some uncommon coordination numbers, e.g., [3]-coordinated Li+, [3]-coordinated Be2+, is confirmed.October 2016
2
Buterakos, Lewis A. "Bond length and bonded radii variations in nitride molecules and crystals". Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040653/.
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Perkins, Jake. "Concrete fluidity effects on bond of prestressed tendons for lightweight bridge girders". Thesis, Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/1080.
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Loflin, Bryan. "Bond and Material Properties of Grade 270 and Grade 300 Prestressing Strands". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/33838.
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The first objective of this thesis was to determine the material properties of grade 270 and grade 300 prestressing strand of various sizes. Tension tests were performed on each type of strand. The data from these tests was used to determine modulus of elasticity, yield stress, ultimate stress, and ultimate elongation for each strand. The yield stresses and ultimate stresses for many of the strands did not meet the requirements found in ASTM A416. The ultimate elongation results far exceeded the requirements and the measured elastic moduli were near the modulus recommended by AASHTO LRFD. A secondary objective from the tension tests was to evaluate a gripping method which used aluminum tubing to cushion the strands against notching. The grips performed very well. Most of the strand breaks did not occur in the grips and when a strand did break in the grips, the failure occurred after significant post-yield elongation.
The second objective was to evaluate the bond properties of grade 270 and grade 300 prestressing strands. The North American Strand Producers (NASP) Bond Test and Large Block Pullout Test (LBPT) were performed on six different strand grade and strand size combinations. Both of the tests are simple pullout tests on untensioned strand. The results for each strand type were compared to one another as well as to measured transfer and development lengths from beams using the strand from the same reel. All of the strands showed sufficient bond in the beams, but one strand type did fail both the NASP Test and the LBPT. Both pullout tests were acceptable methods to evaluate strand surface condition and the benchmarks set for 0.5 in. diameter regular strand were conservative for the strands used in this thesis. Little difference was evident in the bond performance of grade 270 and grade 300 prestressing strand.Master of Science
5
Melo, Neto Carlos Alberto Moreira de. "Uso da técnica de análise de componentes principais na redefinição do parâmetro BLA". reponame:Repositório Institucional da UnB, 2016. http://dx.doi.org/10.26512/2016.02.D.20462.
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Dissertação (mestrado)—Universidade de Brasília, Instituto de Física, Programa de Pós-Graduação em Física, 2016.A alternância dos comprimentos de ligação (Bond Length Alternation, BLA) em cadeias moleculares conjugadas longas tem sido tópico de discussões por muitas décadas, tanto experimental quanto teoricamente. O BLA é um parâmetro estrutural que vem da diferença entre o comprimento de ligações duplas e simples ao longo da cadeia conjugada. Neste trabalho nós utilizamos um método estatístico muito utilizado em várias áreas do conhecimento, a Análise dos Componentes Principais (do inglês Principal Components Analysis - PCA), criado por Karl Pearson em 1901, para redefinir o parâmetro BLA. Com esta técnica calculamos um parâmetro estrutural, comparável ao BLA, de um grupo de 17 moléculas derivadas de tertiofeno e, a partir disto, fizemos comparações com a forma mais comum de calcular o BLA, o que nos forneceu uma forma alternativa de calcular este parâmetro. Com a PCA podemos ir mais além ao cálculo do parâmetro estrutural e, por exemplo, podemos identificar quais ligações têm maior relevância para o valor do BLA. Outro ponto desta análise que merece destaque, foi mostrar a evolução dos coeficientes gerados por esta técnica, chamados de PC1, assim como, a evolução dos valores do BLA com o aumento do número de moléculas presentes no grupo inicial para o cálculo e a diferença em relação a aromaticidade de tais moléculas, mostrando qual o número mínimo para que esta técnica possa ser aplicada.
The Bond Length Alternation (BLA) in long conjugated molecular chains have been the topic of discussion for many decades, both experimentally and theoretically. The BLA is a structural parameter that comes from the difference between the length of double and single bonds along the conjugated chain. In this work we have used a statistical method widely used in many fields of knowledge, the Principal Component Analysis, created by Karl Pearson in 1901, to redefine the parameter BLA. With this technique we calculated the BLA of a group of 17 molecules derived from terthiophene and made comparisons with the most common way to calculate the BLA, which provided us with an alternative way to calculate the parameter. With the PCA we can go further the BLA and we can also identify which bonds are more relevant to its value. Another point that is worth mentioning, was showing the evolution of the coefficients generated by this technique, as well as the evolution of BLA values, along with the increasing number of molecules present in the initial group for the calculation and the differences between the aromaticity of such molecules, resulting in the minimum number to apply this technique.
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Nicoll, Jeffrey Scott. "Systematics of bond length and radii variations in flouride and silicate molecules and crystals". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-08042009-040412/.
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Bartelmehs, Kurt Lane. "Bond length and bonded radii variations in sulfide molecules and crystals containing main group elements". Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/91160.
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Molecular orbital calculations on 18 hydrosulfide molecules containing selected main group X-cations yield minimum energy bond lengths, Rt(XS), that reproduce those observed in chemically similar sulfide crystals. A least-squares analysis shows that Rt(XS) can be estimated by the equation R = l.83(s/r)-0.21, where s is the Pauling bond strength and r is the row number of the X-cation in the periodic table, with 98% of the variation of Rt(XS) being explained in terms of a linear dependence on R. In addition, R serves to rank observed XS bond lengths in sulfide crystals for main group X-cations for rows 1 through 5 of the periodic table to within 0.12Å on average, with R accounting for 96% of the variation in the observed bond lengths.
Bonded radii obtained from electron density maps calculated for the molecules show that the radii of both the X-cations and S atom increase with Rt(XS). A similar trend has been found to hold for the bonded radii and the Rt(XO) bond lengths calculated for hydroxyacid molecules (Finger and Gibbs 1985). The radius of S is smaller (1.16Å) when bonded to highly electronegative atoms like 4-coordinate As and larger (1.67Å) when bonded to a considerably less electronegative atoms like 4-coordinate Li but is smaller than Shannon's (1.70Å) crystal radius and Pauling's ionic crystal radius (1.84Å).M.S.
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Larson, Kyle Hatch. "Evaluating the time-dependent deformations and bond characteristics of a self-consolidating concrete mix and the implication for pretensioned[sic] bridge applications". Diss., Manhattan, Kan. : Kansas State University, 2006. http://hdl.handle.net/2097/219.
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Tassinari, Aurelio. "Bond behaviour and kb factor in GFRP rebars casted in concrete". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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A proper bond between reinforcement and concrete is key for an appropriate composite action of both materials in reinforced concrete structures. However, to-date limited studies exist on bond of fiber reinforced polymer (FRP) bars in concrete members under flexure. In this paper, the bond strength developed by FRP and steel rebars is evaluated and compared, by testing reinforced concrete beams under three point bending load. The investigation included several beams that were 183 cm long × 15 cm wide × 36 cm deep: many of them were reinforced with sand coated GFRP rebars, while steel was used to reinforce the remaining ones. For each of the reinforcing systems, various different embedded lengths were tested. The beams were tested under a 3-point-bending setup and they were monitored using several measuring devices: LVDTS, potentiometers and strain gauges. Preliminary results show that the GFRP rebars have lower bond capacity than the ones made of steel. Moreover, it was inferred that the embedded lengths suggested by actual code provisions for GFRP rebars are too conservative.
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Costello, Kelly. "A Theoretical and Practical Analysis of the Effect of Drilling Fluid on Rebar Bond Strength". Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7489.
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Drilled shafts are large cylindrical cast-in-place concrete structural elements that can be favored due to cost-effectiveness. These elements however, require strict quality control during construction to ensure a stable excavation. Drilling fluid is often used in construction to attain this stability. Drilling fluid, or slurry, can be ground water or salt water, but is typically made from a mixture of water and mineral or polymer powder to form a viscous fluid slightly more dense than ground water. During concreting, the drilling fluid is displaced by the heavier concrete, which is tremie placed at the base of the excavation from the center of the reinforcement cage. While concrete used for drilled shafts should be highly fluid, it does not follow an ideal, uniform flow. The concrete rather builds up inside the reinforcement cage to a sufficient height before then pressing out radially into the annular cover region. This concrete flow pattern associated with drilled shafts has been shown to trap slurry around/near the steel reinforcement and affect reinforcement bond strength.
Presently there are no specifications relating to slurry effects on reinforcing bar bond strength from the American Concrete Institute (ACI) or the American Association of State and Highway Transportation Officials (AASHTO). This dissertation analyzes longitudinal reinforcing bar concrete bond strength data recorded from 268 specimens constructed with tremie-placed concreting conditions in varying drilling fluids. Reinforcement used for testing were No. 8 deformed rebar. Based on the results found from this analysis, this dissertation recommends the use of a slurry modification factor to current bond strength and development length specifications.
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Carroll, James Christopher. "Grade 300 Prestressing Strand and the Effect of Vertical Casting Position". Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28806.
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The purpose of this study was to investigate the influence an increase in strand strength and the effect the as-cast vertical location had on transfer length, development length, and flexural strength and to resolve the discrepancies regarding the definition of the top-bar/strand effect. Two types of test specimens were fabricated and tested investigating each respective item. The increase in strand strength was found to influence transfer length, development length, and flexural strength, while the as-cast vertical location was only found to influence transfer length, and in turn development length. Contrary to the historical definition, the top-bar/strand effect was found to be more dependent on the amount of concrete cast above the strand than the amount below it, with transfer lengths showing a steady increase with a decrease in the amount of concrete cast above the strand. As a result of the findings of this study, a new transfer length equation was proposed and a previously proposed flexural bond length equation was recommended for use in lieu of the current code provisions. The current equations for flexural strength were found to give adequate estimates for flexural strength, although a decrease in ductility was noted.Ph. D.
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Stanford, Kirk Alan. "STRENGTHENING OF STEEL STRUCTURES WITH HIGH MODULUS CARBON FIBER REINFORCED POLYMERS (CFRP) MATERIALS: BOND AND DEVELOPMENT LENGTH STUDY". NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-12202008-112409/.
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Cost-effective solutions for the rehabilitation and strengthening of steel structures, such as steel bridges and steel monopole towers used for cellular phone antennas, are greatly needed by government transportation departments and industry. Rehabilitation is often required due to loss of cross-section from corrosion and/or changes of the demand or use of a structure. Current techniques for strengthening steel structures have several drawbacks including requiring heavy equipment for installation, their fatigue performance, in addition to the need for ongoing maintenance due to continued corrosion attack. The current research program proposed the use of a new high modulus carbon fiber reinforced polymer (CFRP) for strengthening of steel structures. This program includes extensive research to select the resin for wet lay-up of carbon fiber sheets and the adhesives for bonding of pre-cured laminate strips. The bond behavior of FRP materials to steel structures is quite different from that of concrete structures. Preliminary test results showed the occurrence of very high bond stresses for most strengthening applications due to the amount of strengthening required for developing the material for steel structures and bridges.
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Basso, Trujillo Pasquale. "Bond strength of reinforcing bars with different encasement qualities : guidelines for the development length of reinforcing bars in shotcrete". Doctoral thesis, Université Laval, 2021. http://hdl.handle.net/20.500.11794/69807.
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Depuis plusieurs années, le béton projeté a été utilisé pour la stabilisation des talus et le renforcement des structures dégradées. À ce jour, il est également utilisé pour construire des éléments complets tels que des murs de refend, colonnes, coquilles minces, revêtements de tunnels et poutres. Cependant, depuis quelques années, les ingénieurs en structures ont soulevé une préoccupation particulière concernant la qualité d'enrobage des barres d'armature. En effet, des imperfections peuvent être créées spécifiquement derrière les barres d'armature si le béton n'est pas projeté correctement ce qui pourrait provoquer la rupture prématurée des éléments structuraux. Essentiellement, peu de recherche a été faite à ce sujet et les recommandations courantes reposent sur des fondements entièrement empiriques servant uniquement à évaluer la qualité de l'enrobage de barres d'armature des carottes des panneaux de caractérisation. Cette étude a pour but d'augmenter les connaissances scientifiques concernant la réduction de l'adhérence entre les barres d'armature et le béton causé par ces imperfections afin d'inclure ce phénomène dans les guides destinés à l'inspection et à la conception des structures en béton projeté. Pour contrebalancer la perte d'adhérence, le cas échéant, des facteurs de modification pour l'équation de la longueur de développement des barres d'armature en traction est proposée. À cette fin, l'étude présente une phase expérimentale, une phase de modélisation et finalement une phase analytique. La phase expérimentale inclut des éprouvettes de type « pull-out » faites en béton projeté et en béton coulé ayant des vides artificiels (pour recréer les imperfections parfois observées en béton projeté). Des éprouvettes de type « beam-end » coulées avec des vides artificiels ont également été testées. La phase de modélisation inclut seulement des éprouvettes de type « beam-end » et les principaux résultats étudiés comportent la charge maximale et le type de rupture des éprouvettes, lesquels se sont montrés influencés principalement par la longueur transversale des vides (périmètre non-adhéré) et le recouvrement du béton. Les résultats ont permis d'établir des périmètres non-adhérés limites pour lesquels une rupture par déchaussement pourrait survenir. Cependant, puisqu'une certaine perte d'adhérence a été observée même avant les limites établis, la phase analytique a permis de proposer des facteurs de modification pouvant être utilisés avec l'équation de la longueur de développement. Ainsi, des recommandations ont été développées pour permettre aux ingénieurs de prendre des décisions concernant l'intégrité des structures pendant les inspections ou d'inclure le béton projeté lors de la conception de ces structures si des vides sont relevées ou susceptibles d'être créés derrière les barres d'armature.For many years, shotcrete (sprayed concrete) has been used for slope stabilization and the reinforcement of degraded structures. Nowadays, it's also used to build full-depth structural reinforced concrete elements such as shear walls, columns, thin shells, tunnel linings and girders. However, concerns regarding the encapsulation quality of the reinforcing bars have been raised by structural engineers. Indeed, imperfections could be created specifically behind the reinforcing bars if concrete is inappropriately sprayed which could cause the premature failure of structural elements. Essentially, very little research has been completed on the subject and the current guidelines rely completely on empirical evidence which serves only to evaluate the encasement quality of reinforcing bars from cores taken from pre-construction panels. This study aims to increase the scientific understanding regarding the bond stress reduction between reinforcing bars and concrete caused by the presence of such imperfections in order to include this phenomenon in the current inspection and design guidelines for shotcrete structures. To counteract the bond stress loss, if any, modification factors to be used in conjunction with the development length equation of reinforcing bars in tension is proposed. To do so, the study includes an experimental, a modeling and lastly an analytical phase. The experimental phase includes sprayed as well as cast in-place with artificial voids (to recreate the imperfections observed when shotcrete is incorrectly applied) “pull-out” specimens. Cast in-place “beam-end” specimens with artificial voids were also studied. The modeling phase only includes “beam-end” specimens and the main studied results were the ultimate load and the mode of failure of the specimens which were found to be mainly influenced by the transversal length of the voids (or un-bonded perimeters) and the concrete cover. The results allowed to establish un-bonded perimeters limits beyond which a possible reinforcing bar pull-out failure could occur. However, since a certain bar stress loss was still observed even below the limits established, the analytical phase served to propose modification factors to be used in conjunction with the development length equation. Thus, important guidelines have been created for structural engineers allowing them make decisions regarding the integrity of shotcrete structures during the inspection phase or to take into account shotcrete during the design phase of structures if imperfections are observed or are susceptible to be created behind the reinforcing bars.
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Arnold, Matthew Lukas. "Un-tensioned pullout tests to predict the bond quality of different prestressing reinforcements used in concrete railroad ties". Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/15625.
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Master of ScienceDepartment of Civil Engineering
Robert J. Peterman
An experimental testing program was conducted at Kansas State University (KSU) to test the bond characteristics of various 5.32-mm-diameter steel wires and smaller diameter (less than 0.5 in.) strands used in prestressed concrete railroad ties. A total of 13 wires and six strands produced by seven different steel manufacturers were used during this testing. Since no wire bond pullout test currently exists, one was developed and its validity tested. This un-tensioned pullout test could serve as a quality control test similar to the standard test for strand bond (ASTM A1081) that has been developed for pretensioned strands. This strand test is currently not verified for strands less than 0.5-in. in diameter, so the procedure was also scrutinized using strands common in the concrete railroad tie industry. Some of the wires and strands contained surface indentations. It is generally accepted that indentations in the reinforcements improve the bond between the steel and concrete. To further complicate the issue, reinforcements with different surface conditions (rust, oils, lubricants) are allowed to be used in the concrete ties which further affects the bond quality of the reinforcements. However, no standardized indentation patterns (shape, size, depth of indent, etc.) or surface conditions (degree of rusting, amount of surface lubricants, etc.) are utilized by all wire and strand manufacturers. Thus, the corresponding bond behavior of these different reinforcements when placed in various concrete mixtures, in terms of average transfer lengths and typical variations, is essentially unknown. The purpose of this testing program was to develop (in the case of wires) or verify/develop (in the case of strands) a pullout testing procedure predictive of the reinforcement’s bond performance in a prestressed application. The test should be relatively inexpensive, demonstrably repeatable, and easily reproducible. Results from the un-tensioned pullout tests were compared to transfer length measurements from accompanying pretensioned concrete prisms in the lab. Additionally, pullout tests and transfer length measurements were obtained at an actual concrete railroad tie manufacturing plant. The obtained data was compared to the lab data and analyzed to further understand the relationship between un-tensioned pullout tests and pretensioned concrete members.
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Bakhshandeh, Mohammad. "Macro Synthetic Fiber Reinforced Concrete: Effect Of Fiber Embedded Length On Interface Properties". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Summary of the Thesis
This thesis concerns the study of the Macro-Synthetic Fiber, with the main objective of analyzing the effect of fiber embedded length on interface bond properties regard to different concrete mix design parameters. In particular the effect of different fiber embedded length, Water-Cement ratio (W/C), Cement-Sand ratio (C/S) and Cement strength on interfacial bond properties will be studied.
The research is carried on by means of experimental direct pull-out tests on crimped macro-synthetic fibers embedded for two different lengths in a cementitious matrix characterized by different mix design. The experimental program employed is a part of a bigger experimental campaign on macro fiber reinforced concrete behavior which is under investigation at the University of Bologna.
This experimental campaign was done to contribute the overall understanding of the fiber reinforced concrete, with the main goal of the calibration of a constitutive debonding law through numerical model and codification of fiber reinforced concrete in future, which is discussed in details in 5 Chapters in this study.
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Ritter, Laura. "Der Einfluss von Querzug auf den Verbund zwischen Beton und Betonstahl". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-132733.
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Der Verbundwerkstoff Stahlbeton zeichnet sich durch das effektive Zusammenwirken seiner beiden Einzelkomponenten Stahl und Beton aus. Dieses wiederum kann nur durch ausreichend gute Verbundbedingungen zwischen beiden Baustoffen gewährleistet werden. Die Verbundeigenschaften werden von zahlreichen Faktoren beeinflusst, zu denen u.a. die Oberflächenprofilierung des Stahls, die Betonfestigkeit und die Umschnürungswirkung durch den umgebenden Beton oder eine Querbewehrung zählen. Auch eine quer zum Stab angreifende Belastung kann einen erheblichen Einfluss auf den Verbundmechanismus und die Verbundversagensart haben. Bei Stahlbetonbauteilen unter einer zweiaxialen Zugbelastung, wie sie z.B. in Behälterwänden oder zweiachsig gespannten Platten auftritt, unterliegt die Bewehrung sowohl einer Längszug- als auch einer Querzugbeanspruchung. Im Rahmen der vorliegenden Arbeit wurde der Einfluss einer Querzugbelastung auf das Verbundverhalten zwischen Rippenstählen und Normalbeton mit Hilfe von würfelförmigen Ausziehkörpern mit einer kurzen Verbundlänge untersucht. Dabei lag das Querzugniveau stets unterhalb der Risslast des Betons, so dass keine Risse entlang des einbetonierten Stabes auftraten. Neben der Höhe der Querzugbelastung wurden im Versuchsprogramm die Betonfestigkeit, der Stabdurchmesser und die Betondeckung variiert. Anhand der Versuchsergebnisse konnte gezeigt werden, dass sich auch unter einer Querzugbelastung der Verlauf der Verbundspannungs-Schlupf-Beziehung nicht ändert. Die Art des Verbundversagens wird jedoch maßgeblich durch den Querzug beeinflusst, welcher ein Spaltbruchversagen in jedem Fall begünstigt. Mit steigendem Querzug tritt auch bei großen Betondeckungen statt eines Ausziehversagens ein Spaltbruchversagen ein. Mittels des vorgeschlagenen Berechnungsmodells können in Abhängigkeit des Querzugniveaus und der Größe der Betondeckung Grenzlinien für den Wechsel im Verbundversagensmodus bestimmt werden. Hierbei wurde ebenfalls der Einfluss der Probekörpergeometrie auf die Versuchsergebnisse in die Berechnung einbezogen, so dass die angegebenen Grenzlinien auch für reale Einbettungslängen der Bewehrung gelten. Weiterhin wurde anhand der Versuchsdaten sowie eines Datensatzes aus der Literatur ein Verbundmodell für kurze Verbundlängen entwickelt, das den Einfluss der bezogenen Rippenfläche der Bewehrung und der Betonfestigkeit sowohl auf die Verbundspannungen als auch auf die zugehörigen Schlupfwerte berücksichtigt. Über einen zusätzlichen Datensatz zum Einfluss der Verbundlänge im Ausziehversuch konnte ebenfalls die Abhängigkeit zwischen den mittleren Verbundspannungen, den zugehörigen Schlupfwerten und der Verbundlänge spezifiziert werden. Somit ist eine Übertragbarkeit der Ergebnisse von Ausziehversuchen mit kurzen Verbundlängen auf eine reale Einbettungslänge im Bauteil möglich. Für die Bemessung von Stahlbetonkonstruktionen in den Grenzzuständen der Tragfähigkeit und der Gebrauchstauglichkeit erfolgt die Ableitung geeigneter Verformungskriterien für die Relativverschiebung zwischen Betonstahl und Beton und deren Verifizierung an Versuchsdaten aus der Literatur. Die aufgestellten Verformungskriterien in Abhängigkeit der Stahlspannung erlauben eine direkte Ermittlung bemessungsrelevanter Verbundspannungen anhand experimenteller Ausziehversuche. Die Berücksichtigung einer Querzugbelastung ist dabei in allen vorgestellten Berechnungsansätzen ebenfalls möglichReinforced concrete as composite material is characterised by an effective interaction of its individual components reinforcing steel and concrete. This only can be assured by adequate bond conditions between these two materials. The bond quality is influenced by a wide range of parameters, amongst others including the rib geometry of the bar, the concrete strength and the confining action by the surrounding concrete or transverse reinforcement. Moreover loads, which act transverse to the reinforcing bar, can influence the bond mechanism and the bond failure mode significantly. Reinforced concrete structures, such as containment walls or two-way slabs, are often exposed to multiaxial loading conditions. In case of biaxial tensile stresses, reinforcement and surrounding concrete are loaded in tension in longitudinal as well as in transverse direction. An extensive experimental program was carried out in order to investigate the bond behaviour between reinforcing steel and normal strength concrete due to transverse tension. Cubic-shaped pullout specimens with a short bond length were used. The transverse tension level remained always below the cracking stress of concrete, meaning that no crack occurred along the pullout bar. The test program contained the variation of the transverse tension level, the concrete strength, the bar diameter and the concrete cover. From the test results no systematic influence of the transverse tension level on the shape of the bond stress-slip-relationship can be detected. The bond failure mode is significantly influenced by transverse tension, which promotes splitting failure. The higher the transverse tension level, even for high concrete covers, splitting failure occurs instead of pulling out the bar. From the test results, a failure criterion depending on the concrete cover and the transverse tension level could be determined, which indicates the failure mode and corresponding bond stress. For this purpose, the influence of the specimen geometry on the test results was considered, which results in a failure criterion that is also valid for real embedment lengths of the reinforcement. Furthermore, a bond model for short bond lengths has been developed, based on the test results and a dataset from literature. The model considers the influence of the related rib area of the reinforcing bar and the concrete strength on the bond stresses as well as on the corresponding slip values. By an additional dataset concerning the influence of bond length in pullout tests, the bond stresses and corresponding slip values could be specified as a function of the bond length. Therefore, the test results of pullout test with short bond lengths are transferable to real embedment lengths in structural elements. For the structural design of reinforced concrete elements in the ultimate and serviceability limit states, appli\\-cable deformation criterions concerning the relative displacement between reinforcing steel and concrete has been derived and verified by test data from literature. By means of the developed deformations criterions dependent on the steel stress, design bond stresses can be determined directly from experimental pullout tests. The consideration of transverse tensile loads is also possible for all presented design formulas
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Azzam, Aussama, e Mike Richter. "Investigation of Stress Transfer Behavior in Textile Reinforced Concrete with Application to Reinforcement Overlapping and Development Lengths". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-77838.
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Die kontinuumsmechanische Untersuchung der Lastübertragungsmechanismen zwischen den Rovings im textilbewehrten Feinbeton trägt wesentlich zum Gesamtverständnis des mechanischen Verhaltens des Verbundmaterials bei. Neben der Erfassung der gegenseitigen Beeinflussung sich kreuzender Rovings erfordert insbesondere die mechanische Modellierung und numerische Simulation von Bewehrungsstößen und Endverankerungen die Kenntnis dieser Übertragungsmechanismen. Die numerischen Simulationen sollen u. a. zeigen, welche Endverankerungslängen und welche Übergreifungslängen an Bewehrungsstößen erforderlich sind und wie die Querbewehrung die Rissbildung beeinflusstThis paper concerns with the investigation of stress transfer mechanisms between yarns and concrete matrix and their influence on the overall behavior of textile reinforced concrete (TRC). This investigation considers textile reinforcement splices and textile reinforcement development lengths and carried out by means of Finite-Element simulations and fracture mechanic approaches. A first modeling procedure is made towards analyzing and investigating the damage mechanisms in TRC specimen under tension loading which are mainly characterized by matrix cracking and yarn pullout. This modeling approach allows for considering the yarn crack bridging which is a main characteristic behavior of TRC. In the same manner, 3D Finite-Element models are conducted for calculating the required reinforcement development lengths and the reinforcement overlapping lengths. The conducted approach takes into account different damage mechanisms observed in the corresponding experimental investigations which are also used for calibrating the modeling procedures. Moreover, the presented approach covers a wide range of required textile reinforcement overlapping lengths and development lengths and provides the corresponding ultimate loads
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Lorenz, Enrico. "Endverankerung und Übergreifung textiler Bewehrungen in Betonmatrices". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-170583.
Texto completo da fonteResumo:
Die sichere Einleitung und Übertragung der wirkenden Kräfte ist Bedingung für die Funktionsfähigkeit und die vollständige Ausnutzung der Tragfähigkeit von Textilbetonbauteilen und -verstärkungsschichten. So kann es bei ungünstiger Konfiguration und Anordnung der Einzelkomponenten des Verbundbaustoffes zur Ausbildung einer Vielzahl verschiedener Verbundversagensformen kommen. Diese umfassen neben der Bildung von verbundschädigenden Delaminations- und Spaltrissen lokale Abplatzungen der Betondeckung oder einen vorzeitigen Auszug der Garne aus dem Beton. Besonders beansprucht sind in diesem Zusammenhang die bei einer Anwendung von Textilbeton erforderlichen Endverankerungs- und Stoßbereiche der textilen Bewehrungen. Zur sicheren Ausbildung und Bemessung dieser wichtigen Detailpunkte liegen jedoch momentan noch keine umfassenden und zusammenhängenden Untersuchungen vor. Hauptziel der vorliegenden Dissertation war daher eine systematische Erforschung und Beschreibung des Tragverhaltens von Textilbeton in Endverankerungs- und Übergreifungsbereichen. Eine funktionierende und schädigungsfreie Verbundkraftübertragung bildet die Grundlage für die sichere Lasteinleitung und -übertragung. Daher wurden im ersten Teil der Arbeit ausführliche Untersuchungen zur Charakterisierung der zwischen Bewehrungstextil und Feinbetonmatrix wirkenden Kräfte und -mechanismen durchgeführt. Nach der Entwicklung eines geeigneten Versuchsaufbaus erfolgten umfangreiche Parametervariationen zur experimentellen Überprüfung des textilspezifischen Verbundverhaltens. Den Schwerpunkt der Untersuchungen bildete die Identifikation und Bewertung der aus verschiedenen Verarbeitungsparametern der textilen Bewehrungen resultierenden Verbundeinflüsse. Die Versuchsergebnisse ermöglichen die Bestimmung der zugehörigen Verbundspannungs-Schlupf-Beziehungen (VSB) mithilfe eines erarbeiteten Modellierungsverfahrens. Die so ermittelten Verbundkennwerte bilden die Grundlage für die weiteren rechnerischen Untersuchungen. Im zweiten Teil der Arbeit erfolgten Forschungen zum Tragverhalten von Endverankerungsbereichen. Hierbei stand der im Regelfall bemessungsrelevante Grenzzustand eines vorzeitigen Auszuges der Textilien aus der Betonmatrix im Mittelpunkt. Die Arbeiten umfassten experimentelle und theoretische Untersuchungen zur Beschreibung der Kraftübertragung. Aufbauend auf die ermittelten Verbundkennwerte wird ein unabhängiger analytischer Auswertealgorithmus zur Beschreibung des Verbundtragverhaltens in Endverankerungsbereichen dargestellt. Dieser ermöglicht eine detaillierte rechnerische Bestimmung der erforderlichen Endverankerungslängen von Textilbeton in Abhängigkeit konkreter bzw. untersuchter Bewehrungstextilien. Den dritten Forschungsschwerpunkt bildeten Untersuchungen zum Tragverhalten von Übergreifungsstößen in Textilbetonbauteilen. Mithilfe von umfassenden experimentellen und theoretischen Analysen an unterschiedlich konfigurierten und bewehrten Textilbetonen konnten die maßgebenden Versagensmechanismen untersucht und grundlegende Vorgaben für die Bemessung und Ausführung der Übergreifungsbereiche abgeleitet werden. Die gewonnenen Erkenntnisse wurden anhand von großformatigen Bauteilversuchen mit entsprechend konstruierten Übergreifungsstößen bestätigt. Zum Abschluss wird ein vereinfachtes Ingenieurmodell vorgestellt. Dieses erlaubt eine allgemeingültige und hinreichend genaue Bemessung der untersuchten Detailpunkte unter Beachtung der maßgebenden GrenzzuständeThe safe introduction and transmission of forces is a requirement for the workability as well as the possibility to make full use of the load bearing capacities of components and strengthening layers made of textile reinforced concrete. Accordingly, an unfavourable configuration and arrangement of the composite material’s individual components can lead to various modes of bond failure. These can result from the formation of bond damaging delamination cracks and longitudinal matrix splitting, local spalling of the concrete layer in the outer reinforcement layers or early yarn pull-out from the concrete. In this context, the areas of end anchorage and lap joints of the textile reinforcement, which cannot be avoided when using textile reinforced concrete, are particularly prone to failure. However, no comprehensive and coherent investigations regarding the safe configuration and dimensioning of these essential details are available yet. Consequently, systematic research into textile reinforced concrete’s load-bearing behaviour in the areas of end anchorage and lap joints and the subsequent description was the main goal of this dissertation. A working and damage-free transmission of bond force is the basis for a faultless load transmission and introduction. As a result, extensive tests concerning the characterization of the mechanisms and forces acting between reinforcing textile and fine grained concrete matrix were carried out as the first part of the investigations. After an appropriate test setup had been developed, a great variety of parameters was applied to experimentally examine the bond behaviour specific to the textile. The determination of the influencing factors resulting from various parameters in the textile reinforcement’s processing was a focus in the research. Based on a specifically developed modelling technique, the test results could be used to calculate the corresponding bond stress-slip-relation. The bond parameters, which were determined like this, served as the basis for the following calculations. The second part of the investigations was concerned with the load-bearing behaviour in end anchorage areas. In this case, the limit state of a yarn pull-out from the concrete matrix, which is usually essential for the dimensioning, was at the centre of attention. The investigations encompassed experimental and theoretical tests regarding the description of the force transmission. Based on the determined compound parameters, an independent analytic evaluation algorithm, which served to describe the load carrying behaviour of the bond in the end anchorage area, was presented. Through this algorithm, the detailed calculation of the required end anchorage lengths of textile reinforced concrete depending on the specific reinforcement textile was possible. The third research focus was on tests regarding the load-bearing behaviour of lap joints in textile reinforced concrete components. With the help of comprehensive experimental and theoretical analyses of variously configured and reinforced textile reinforced concretes, the decisive failure mechanisms were examined. Furthermore, fundamental demands for the dimensioning and execution of the lap joint areas could be derived. The findings were confirmed through tests on large-sized building components with corresponding lap joints. At the end of the investigations, a simplified engineering model is presented. This model makes a universally valid and exact dimensioning of the examined details possible while also paying attention to the decisive limit states
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Tasligedik, Ali Sahin. "Lap Splice Behavior And Strength Of Cfrp Rolls". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609694/index.pdf.
Texto completo da fonteResumo:
Behavior of lap splices formed by CFRP rolls has been studied. CFRP rolls have been prepared by using CFRP sheets of a certain width. Strengthening methods that use CFRP rolls as reinforcement may require an epoxy anchored lap splice due to the conditions at the strengthening regions. It may not always be possible to strengthen the region by using only one roll fan anchored at both ends, but using two rolls from opposite faces of the member and lap splicing them at the middle so that they act as a single roll. Lap splice behavior can be studied best by using flexural beam bond specimens if the reinforcing material is steel. Therefore, it has initially been suggested that flexural beam specimens reinforced for flexure with CFRP rolls as tension reinforcement can be used in studying the lap splice behavior. However, due to the difficulties encountered in the beam tests, another type of test specimen was introduced, which was a direct pull-out specimen. In this type of test specimen, lap spliced CFRP rolls have been tested under direct tension, in which the tension has been applied by making use of concrete end blocks that transfer the tension to the rolls. Eleven tests have been made in total. Full material capacity of the rolls could not be achieved due to premature failures. However, important conclusions and recommendations have been made for future studies.
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Mitchell, Chad S. "A review of initial end slip as criteria of acceptable strand bond quality and the relationship between strand diameter and transfer length for prestressed concrete members". Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1594486111&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
Texto completo da fonte
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Harding, Alexander. "The prediction of mutagenicity and pKa for pharmaceutically relevant compounds using 'quantum chemical topology' descriptors". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/the-prediction-of-mutagenicity-and-pka-for-pharmaceutically-relevant-compounds-using-quantum-chemical-topology-descriptors(40e87ff2-e161-4f4c-9e90-3a4e9087dc9e).html.
Texto completo da fonteResumo:
Quantum Chemical Topology (QCT) descriptors, calculated from ab initio wave functions, have been utilised to model pKa and mutagenicity for data sets of pharmaceutically relevant compounds. The pKa of a compound is a pivotal property in both life science and chemistry since the propensity of a compound to donate or accept a proton is fundamental to understanding chemical and biological processes. The prediction of mutagenicity, specifically as determined by the Ames test, is important to aid medicinal chemists select compounds avoiding this potential pitfall in drug design. Carbocyclic and heterocyclic aromatic amines were chosen because this compounds class is synthetically very useful but also prone to positive outcomes in the battery of genotoxicity assays.The importance of pKa and genotoxic characteristics cannot be overestimated in drug design, where the multivariate optimisations of properties that influence the Absorption-Distribution-Metabolism-Excretion-Toxicity (ADMET) profiles now features very early on in the drug discovery process.Models were constructed using carboxylic acids in conjunction with the Quantum Topological Molecular Similarity (QTMS) method. The models produced Root Mean Square Error of Prediction (RMSEP) values of less than 0.5 pKa units and compared favourably to other pKa prediction methods. The ortho-substituted benzoic acids had the largest RMSEP which was significantly improved by splitting the compounds into high-correlation subsets. For these subsets, single-term equations containing one ab initio bond length were able to accurately predict pKa. The pKa prediction equations were extended to phenols and anilines.Quantitative Structure Activity Relationship (QSAR) models of acceptable quality were built based on literature data to predict the mutagenic potency (LogMP) of carbo- and heterocyclic aromatic amines using QTMS. However, these models failed to predict Ames test values for compounds screened at GSK. Contradictory internal and external data for several compounds motivated us to determine the fidelity of the Ames test for this compound class. The systematic investigation involved recrystallisation to purify compounds, analytical methods to measure the purity and finally comparative Ames testing. Unexpectedly, the Ames test results were very reproducible when 14 representative repurified molecules were tested as the freebase and the hydrochloride salt in two different solvents (water and DMSO). This work formed the basis for the analysis of Ames data at GSK and a systematic Ames testing programme for aromatic amines. So far, an unprecedentedly large list of 400 compounds has been made available to guide medicinal chemists. We constructed a model for the subset of 100 meta-/para-substituted anilines that could predict 70% of the Ames classifications. The experimental values of several of the model outliers appeared questionable after closer inspection and three of these have been retested so far. The retests lead to the reclassification of two of them and thereby to improved model accuracy of 78%. This demonstrates the power of the iterative process of model building, critical analysis of experimental data, retesting outliers and rebuilding the model.
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Lorenz, Enrico, e Regine Ortlepp. "Berechnungsalgorithmus zur Bestimmung der Verankerungslänge der textilen Bewehrung in der Feinbetonmatrix". Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1244049857647-62309.
Texto completo da fonteResumo:
Dieser Beitrag befasst sich mit der experimentellen und analytischen Bestimmung der Verankerungslängen textiler Bewehrungsstrukturen einer Textilbetonverstärkungsschicht. Die experimentelle Untersuchung des Verbundverhaltens erfolgte anhand von Pull-Out-Versuchen. Die analytische Betrachtung des Verbundproblems geschieht aufbauend auf multilinearen Lösungen der Verbunddifferentialgleichung anhand der experimentell ermittelten Kraft- Rissöffnungs-Beziehungen. Mit Hilfe eines separaten Modells wird aus der so ermittelten Verbundspannungs-Schlupf-Beziehung (VSB) die zur Verankerung einer entsprechenden Kraft F erforderliche Verankerungslänge lE bestimmt. Die Überprüfung der Berechnung erfolgt anhand von unabhängig in experimentellen Versuchen zur Bestimmung der Verankerungslänge ermittelten Werten. Es konnte eine gute Übereinstimmung der berechneten mit den versuchstechnisch bestimmten Verankerungslängen festgestellt werden.
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Eckfeldt, Lars. "Möglichkeiten und Grenzen der Berechnung von Rissbreiten in veränderlichen Verbundsituationen". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2005. http://nbn-resolving.de/urn:nbn:de:swb:14-1138179912681-09751.
Texto completo da fonteResumo:
Die vorliegende Arbeit reflektiert die aktuelle Diskussion von Modellen zur Vorhersage von Rissbreiten und versucht, objektive Vergleichskriterien aufzustellen sowie Folgerungen für mögliche Lösungswege zu ziehen. Am Beginn steht eine ausführliche Auseinandersetzung mit dem Verbundmechanismus zwischen Betonstahl und Beton und den Möglichkeiten der Verbundanalyse. Ausgehend von eigenen Versuchen an kurzen Verbundlängen zur Untersuchung des Verbundverhaltens von Bewehrung in hochfesten Betonen wird in der Arbeit nach Möglichkeiten zur Vorhersage von Gleit- und Sprengbrüchen gesucht. Für Sprengbrüche, also Längsrissbildung, ist ein verbesserter Versuchsaufbau entwickelt worden, der Rückschlüsse auf die Verformungsentwicklung in der potentiellen Sprengbruchfläche und den Aufbau eines Verbundwiderstands unter Belastung ermöglicht. Es stellte sich trotz der Fortschritte in der Versagensanalyse dieser Versuche heraus, dass es wenig sinnvoll ist, die gewonnenen Verbundgesetze direkt auf lange Verbundlängen zur Ermittlung von Rissbreiten anzuwenden. Zur Simulation der mit Bauteilsituationen vergleichbaren langen Verbundlängen wird dagegen eine Hypothese über den Widerstand einer potentiellen Längsbruchfläche verwendet. Dabei wird die mögliche Reaktion von gekoppelten und voneinander abhängigen Betonzugringen um einen Betonstahl, vom Lasteintrag beginnend, sukzessive fortschreitend aufgebaut. Die Aufteilung der Zugringe folgt dabei einer Annahme über die Entwicklung von lokalen Verbundrissen nach Goto. Damit ist die Zugringtheorie von Tepfers auf lange Verbundlängen übertragbar und Simulationen von Zugstäben nahe an Tepfers theoretischen Ansätzen werden so ermöglicht. Die Rechnersimulationen an langen Verbundlängen im Vergleich zur Prognose nach MC 90 wurden für Einzelrissbildung und abgeschlossene Rissbildung an zylindrischen Dehnkörpergeometrien durchgeführt. Zur Verifizierung der zeitabhängigen Einflüsse wie Zwängungen aus Schwinden und Zugkriechen sind einfache Ansätze entwickelt worden. Am Ende dieser Analysen steht eine Neubewertung normativer Ansätze (MC 90/DIN 1045-1 sowie EN 1992-1-1) zur Berechnung einer charakteristischen Rissbreite. Eine Schlüsselstellung nimmt die richtige Prognose des wirksamen Rissabstands in allen Berechnungsmodellen ein. Anhand eines neu zusammengestellten Datensatzes und vorhandener Vergleichsdatensätze wurde die Performance der Modelle untersucht. Anwendungsbereiche, die problematisch erscheinen, konnten eingegrenzt werden. Es war zu folgern, dass die Ansätze für den effektiven Bewehrungsgrad und die Verbundspannung zu verbessern sind. Die daraufhin mit einem additiven Sicherheitselement und einem variablen Mindestwert entwickelte Modellalternative gegenüber den normativen Vorschlägen ist nun zielgerichteter und kann dabei eine effektivere und zuverlässigere Prognose der Rissbreite und damit der konstruktiven Bewehrungslösung liefern. Die Anforderungen an die Performance eines Rechenwertes der Rissbreite wk sind um ein Effektivitätskriterium für den Rissabstand srk ergänzt worden, dessen Vorhersagequalität entscheidend für effiziente und zuverlässige Vorhersagen der Rissbreite ist. Die Zuverlässigkeit des DIN-Ansatzes für Mindestbewehrung im Grenzzustand der Gebrauchstauglichkeit ist ebenfalls geprüft worden. Umfangreiche Zusammenstellungen, Beispiele und Parameterstudien sind im Anhang der Arbeit hinzugefügt, um die theoretischen Ergebnisse zu stützen und Lesern Vergleichsmöglichkeiten zu bieten. Dazu gehören auch zwei Ablaufpläne und Hilfsmittel für einfache Absicherungen, die die zu erwartenden Schwierigkeiten bei der Verwendung des normativen DIN 1045-1 Ansatzes zur Beschränkung auf kleine Rissbreiten ausgleichen könnenThe doctoral thesis reflects the recent discussion on the finding of suitable verification models for crack width control. It tries to assemble criteria for the comparison in order to draw conclusions from the outcome. In the very beginning stands a widespread analysis of the bond mechanisms between the reinforcing steel and the concrete. Starting from own testing on short embedment lengths in HPC, opportunities are researched for the prediction of a sliding or splitting failure of the surrounding concrete during bar pull-out. An improved test setup is developed by the Author to verify the splitting failure mechanism that finally leads to longitudinal cover cracking. It enables to obtain better indications for the inner strain development in the later failure plane, showing the development of the bond resistance during loading. Although progress were made in the quality of analysis, it turned out that, a direct implementation of obtained bond laws is less successful to take care of the apparent problem of long embedment lengths. The description of that problem is essential within the crack width verification. Differently, a method is suggested to simulate a probable longitudinal splitting plane and its potential to resist an applied longitudinal load. In that method, the possible reaction of interlinked concrete tension rings around a steel bar is thought to form a growing global resistance with every added resistance ring in a sequential chain that are decreasingly loaded if the distance to the load application increases. The segmentation follows an approximation of the possibly development of local bond cracks acc. to Goto. In this, the application of the tension ring theory from Tepfers were successfully overtaken to the problem of long embedment lengths. It enables for simulations close to the original theory of tensile rings formed by concrete around the reinforcing steel. Comparing the results with MC 90, the simulation of long embedment lengths were performed using imaginary cylindrical test-specimen, enabling the verification of single and stabilized cracking. Simplified methods were developed in order to implement time-dependent influences like restraint from creep and shrinkage.An extensive evaluation of the normative methods (MC 90/ DIN 1045-1 and EN 1992-1-1) for verifications of a characteristic crack width stands at the end of the studies. A key position within the models is held by the realistic prognosis of the accountable crack distance. Using a newly compiled dataset and already existing data for comparison, the performances of current models were verified for predicting crack widths or distances. Complicated fields of its application could be marked and isolated. It was concluded that, the approaches for the determination of the effective reinforcement ratio and the bond stress should be improved. The developed alternative for calculation is assembled with an added safety feature and a variable minimum for the crack distance. It can lead to a more reliable prognosis for crack distances and the depending crack widths in order to design a more efficient reinforcement detailing. The requirements on the performance of a determined characteristic crack width wk are extended by the application of a criteria of effectiveness for the calculated crack distance srk. The reliability of the MC 90 -approach and the DIN-approach for minimum reinforcement has also been checked. Extensive compilations of data, examples and parameter studies are added to the appendix in order to backup the theoretical results and to invite others to compare. Two calculation flow charts and helptools are integrated to ensure the quality of crack width calculations also in cases where smaller crack widths must be verified, using informative and normative methods in MC 90/ DIN 1045-1
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李玉嫻 e Yuk-han Li. "Telomere length variation and lineage chimerism in bone marrow transplantation". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31227594.
Texto completo da fonte
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Eckfeldt, Lars. "Möglichkeiten und Grenzen der Berechnung von Rissbreiten in veränderlichen Verbundsituationen". Doctoral thesis, Technische Universität Dresden, 2004. https://tud.qucosa.de/id/qucosa%3A24631.
Texto completo da fonteResumo:
Die vorliegende Arbeit reflektiert die aktuelle Diskussion von Modellen zur Vorhersage von Rissbreiten und versucht, objektive Vergleichskriterien aufzustellen sowie Folgerungen für mögliche Lösungswege zu ziehen. Am Beginn steht eine ausführliche Auseinandersetzung mit dem Verbundmechanismus zwischen Betonstahl und Beton und den Möglichkeiten der Verbundanalyse. Ausgehend von eigenen Versuchen an kurzen Verbundlängen zur Untersuchung des Verbundverhaltens von Bewehrung in hochfesten Betonen wird in der Arbeit nach Möglichkeiten zur Vorhersage von Gleit- und Sprengbrüchen gesucht. Für Sprengbrüche, also Längsrissbildung, ist ein verbesserter Versuchsaufbau entwickelt worden, der Rückschlüsse auf die Verformungsentwicklung in der potentiellen Sprengbruchfläche und den Aufbau eines Verbundwiderstands unter Belastung ermöglicht. Es stellte sich trotz der Fortschritte in der Versagensanalyse dieser Versuche heraus, dass es wenig sinnvoll ist, die gewonnenen Verbundgesetze direkt auf lange Verbundlängen zur Ermittlung von Rissbreiten anzuwenden. Zur Simulation der mit Bauteilsituationen vergleichbaren langen Verbundlängen wird dagegen eine Hypothese über den Widerstand einer potentiellen Längsbruchfläche verwendet. Dabei wird die mögliche Reaktion von gekoppelten und voneinander abhängigen Betonzugringen um einen Betonstahl, vom Lasteintrag beginnend, sukzessive fortschreitend aufgebaut. Die Aufteilung der Zugringe folgt dabei einer Annahme über die Entwicklung von lokalen Verbundrissen nach Goto. Damit ist die Zugringtheorie von Tepfers auf lange Verbundlängen übertragbar und Simulationen von Zugstäben nahe an Tepfers theoretischen Ansätzen werden so ermöglicht. Die Rechnersimulationen an langen Verbundlängen im Vergleich zur Prognose nach MC 90 wurden für Einzelrissbildung und abgeschlossene Rissbildung an zylindrischen Dehnkörpergeometrien durchgeführt. Zur Verifizierung der zeitabhängigen Einflüsse wie Zwängungen aus Schwinden und Zugkriechen sind einfache Ansätze entwickelt worden. Am Ende dieser Analysen steht eine Neubewertung normativer Ansätze (MC 90/DIN 1045-1 sowie EN 1992-1-1) zur Berechnung einer charakteristischen Rissbreite. Eine Schlüsselstellung nimmt die richtige Prognose des wirksamen Rissabstands in allen Berechnungsmodellen ein. Anhand eines neu zusammengestellten Datensatzes und vorhandener Vergleichsdatensätze wurde die Performance der Modelle untersucht. Anwendungsbereiche, die problematisch erscheinen, konnten eingegrenzt werden. Es war zu folgern, dass die Ansätze für den effektiven Bewehrungsgrad und die Verbundspannung zu verbessern sind. Die daraufhin mit einem additiven Sicherheitselement und einem variablen Mindestwert entwickelte Modellalternative gegenüber den normativen Vorschlägen ist nun zielgerichteter und kann dabei eine effektivere und zuverlässigere Prognose der Rissbreite und damit der konstruktiven Bewehrungslösung liefern. Die Anforderungen an die Performance eines Rechenwertes der Rissbreite wk sind um ein Effektivitätskriterium für den Rissabstand srk ergänzt worden, dessen Vorhersagequalität entscheidend für effiziente und zuverlässige Vorhersagen der Rissbreite ist. Die Zuverlässigkeit des DIN-Ansatzes für Mindestbewehrung im Grenzzustand der Gebrauchstauglichkeit ist ebenfalls geprüft worden. Umfangreiche Zusammenstellungen, Beispiele und Parameterstudien sind im Anhang der Arbeit hinzugefügt, um die theoretischen Ergebnisse zu stützen und Lesern Vergleichsmöglichkeiten zu bieten. Dazu gehören auch zwei Ablaufpläne und Hilfsmittel für einfache Absicherungen, die die zu erwartenden Schwierigkeiten bei der Verwendung des normativen DIN 1045-1 Ansatzes zur Beschränkung auf kleine Rissbreiten ausgleichen können.The doctoral thesis reflects the recent discussion on the finding of suitable verification models for crack width control. It tries to assemble criteria for the comparison in order to draw conclusions from the outcome. In the very beginning stands a widespread analysis of the bond mechanisms between the reinforcing steel and the concrete. Starting from own testing on short embedment lengths in HPC, opportunities are researched for the prediction of a sliding or splitting failure of the surrounding concrete during bar pull-out. An improved test setup is developed by the Author to verify the splitting failure mechanism that finally leads to longitudinal cover cracking. It enables to obtain better indications for the inner strain development in the later failure plane, showing the development of the bond resistance during loading. Although progress were made in the quality of analysis, it turned out that, a direct implementation of obtained bond laws is less successful to take care of the apparent problem of long embedment lengths. The description of that problem is essential within the crack width verification. Differently, a method is suggested to simulate a probable longitudinal splitting plane and its potential to resist an applied longitudinal load. In that method, the possible reaction of interlinked concrete tension rings around a steel bar is thought to form a growing global resistance with every added resistance ring in a sequential chain that are decreasingly loaded if the distance to the load application increases. The segmentation follows an approximation of the possibly development of local bond cracks acc. to Goto. In this, the application of the tension ring theory from Tepfers were successfully overtaken to the problem of long embedment lengths. It enables for simulations close to the original theory of tensile rings formed by concrete around the reinforcing steel. Comparing the results with MC 90, the simulation of long embedment lengths were performed using imaginary cylindrical test-specimen, enabling the verification of single and stabilized cracking. Simplified methods were developed in order to implement time-dependent influences like restraint from creep and shrinkage.An extensive evaluation of the normative methods (MC 90/ DIN 1045-1 and EN 1992-1-1) for verifications of a characteristic crack width stands at the end of the studies. A key position within the models is held by the realistic prognosis of the accountable crack distance. Using a newly compiled dataset and already existing data for comparison, the performances of current models were verified for predicting crack widths or distances. Complicated fields of its application could be marked and isolated. It was concluded that, the approaches for the determination of the effective reinforcement ratio and the bond stress should be improved. The developed alternative for calculation is assembled with an added safety feature and a variable minimum for the crack distance. It can lead to a more reliable prognosis for crack distances and the depending crack widths in order to design a more efficient reinforcement detailing. The requirements on the performance of a determined characteristic crack width wk are extended by the application of a criteria of effectiveness for the calculated crack distance srk. The reliability of the MC 90 -approach and the DIN-approach for minimum reinforcement has also been checked. Extensive compilations of data, examples and parameter studies are added to the appendix in order to backup the theoretical results and to invite others to compare. Two calculation flow charts and helptools are integrated to ensure the quality of crack width calculations also in cases where smaller crack widths must be verified, using informative and normative methods in MC 90/ DIN 1045-1.
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Andreou, Eftychia. "Performance evaluation of RC flexural elements strengthened by advanced composites". Thesis, University of South Wales, 2002. https://pure.southwales.ac.uk/en/studentthesis/performance-evaluation-of-rc-flexural-elements-strengthened-by-advanced-composites(f441fa99-6428-46c2-8053-8e362546044c).html.
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The flexural performance of composite systems made of reinforced concrete, Fibre Reinforced Polymers (FRPs) and adhesives was studied during the current research. The experimental investigation was principally concentrated on the potential use of Kevlar® 49 (aramid fibre) for RC beam strengthening. The main aims of research have been; (a) to investigate the relative merits of using Aramids in comparison to other FRPs, (b) strength optimisation of systems to prevent excessive losses of ductility, (c) to examine the failure mode and crack patterns, together with salient strength factors at ultimate limit state and (d) to carry out analytical modelling using a commercial FE package. The experimental investigation comprised of testing 55 simply supported RC beams of either 1.5m or 2.6m length. In addition to the parametric studies included in points (a)-(d) above (to assess the section characteristics), further experimentation was conducted to investigate the beam performance by varying the factors of; (e) beam shear span, (f) FRP anchorage length, (g) concrete surface preparation, (h) FRP end-anchoring, (i) beam precracking, (j) introduction of air-voids within the bond line of FRP/concrete, (k) influence of cyclic loading and, (1) exposure to aggressive environment. The results from current tests confirm elements of reports from other researchers (by thorough review of literature) that all FRPs have great potential for flexural strengthening of RC members. This is valid even in cases where additional environmental degradation and/or cracking (due to serviceability loads), had taken place. Aramid fibres were found to result in favourable outcomes concerning both strength and ductility enhancements. It was determined, both from experiments and non-linear modelling, that the amount of FRP fibre content is an important factor in every strengthening application. Experimentation showed that depending on the existing condition of the structure (concrete strength, internal reinforcement ratio, section dimensions, degradation level and load configuration), there seems to be a unique level of optimum fibre content. The FRP levels in excess of the optimum were seen to lead to premature brittle tearing-off failure modes. It was also found that to prevent premature beam failure (due to incompatibility of stress at concrete and FRP interface), a maximum possible anchorage length should be considered in order to deliver an optimum section performance. The results from the analytical modelling indicated a most satisfactory agreement with the experimental data after the initial mechanical properties were calibrated. It was found that actual representation of material properties (e.g. steel constitutive law) are of great significance, for an accurate modelling of RC element loaded behaviour. The bond developed between the FRP and concrete is one of the key parameters for achieving good performance of the systems. It was determined that concrete surface preparation and priming is beneficial, while the introduction of air-voids due to poor workmanship can reduce the section load bearing capabilities. Cyclic loading on FRP strengthened sections was found to curtail the full rotational capacity utilisation of the beam. However, even the above mentioned curtailed behaviour was more advantageous than cyclically loaded beam performance without FRP strengthening.
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Anderson, Eric James. "BRIDGING THE GAP IN UNDERSTANDING BONE AT MULTIPLE LENGTH SCALES USING FLUID DYNAMICS". Case Western Reserve University School of Graduate Studies / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=case1164998210.
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Sosale, Guruprasad. "Measurement and analysis of surface topography over multiple length scales: application to titanium bone implants". Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18433.
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The performance of bone (osseous) implants is critically dependent on the interactions of the implant surface with the surrounding osseous tissue. Correlating surface topography with bioperformance is essential for the optimized design of osseous implants. The goal of this thesis is to develop a robust methodology for the measurement and analysis of aperiodic surface topographies, such as those encountered on bone implants, over multiple length scales. Two widely used measurement techniques, namely, Atomic Force Microscopy (AFM) and White-Light Interferometry (WLI), are compared and contrasted. A custom-designed MATLAB-based program is developed to analyze the images from both tools, and to extract fourteen different statistical topography parameters. The errors associated with measurement and image analysis are identified, and guidelines are suggested to minimize their effect. This methodology is then applied to measure the topographies of two commonly-used titanium implant surfaces. Previous studies have shown that both surfaces have similar average (root-mean-square) roughness but elicit significantly different bioresponses. Here, it is demonstrated that the two surfaces differ in several other topography parameters, most significantly in surface slope, peak curvature, and developed interfacial area, and crucially, that these differences are strongly scale dependent. These findings form the basis for devising robust quantitative topography-performance correlations for titanium bone implants.La performance des implants osseux dépend de façon critique de l'interaction entre la surface de l'implant et le tissu osseux environment. Le but de cette thèse est de développer une méthodologie fiable pour mesurer et analyser la topographie de surfaces non périodiques à différentes échelles. Ainsi, deux techniques de mesure extrêmement utilisées, la microscopie à force atomique et l'interférométrie à lumière blanche ont été comparées et confrontées. Un programme développé sur le logiciel MATLAB a été conçu pour analyser les images obtenues par ses deux instruments et en extraire quatorze différents paramètres topographiques statistiques. Les erreurs associées à la mesure et à l'analyse d'image ont été ensuite identifiées et des recommandations ont été suggérées pour minimiser leurs effets. Cette méthodologie a été ensuite appliquée pour mesurer les topographies de deux implants en titane communément utilisés. Il apparaît que ces deux surfaces ont une moyenne quadratique similaire pour la rugosité, mais présentent néanmoins des réponses biologiques différentes. Dans cette recherche, il a été démontré que les deux surfaces présentent, en plus, plusieurs différences pour d'autres paramètres topographiques, notamment de façon significative, pour l'inclinaison des surfaces, la courbure des pics et l'aire interraciale développée. Ces différences dépendent fortement d'un facteur d'échelle, et forment la base pour d'autres études afin de développer des relations quantitatives entre la topologie de la surface et les réponses biologiques associées.
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Rattray, Kevin R. "Site-directed mutagenesis of the poly-glutamic acid domains of full-length recombinant bone sialoprotein". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0005/MQ42093.pdf.
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Souiri, Moncef. "Correlation entre les parametres de resonance paramagnetiques et de la liaison chimique : ions des metaux de transition et muonium". Strasbourg 1, 1986. http://www.theses.fr/1987STR13213.
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Recherche de relations entre parametres de l'hamiltonien de spin en rpe de defauts ponctuels (decomposition par le champ cristallin, constante de couplage hyperfin) et les parametres de la liaison chimique du reseau hote (ionicite, electronegativites de l'anion et du cation, longueur de liaison). Bonne correlation dans le cas de l'ionicite et de l'electronegativite de l'anion; absence de correlation avec la longueur de liaison, explicable par une relaxation locale, et mise en evidence dans les matrices ternaires. Application de l'analyse au muonium: la constante de couplage hyperfin est correlee a l'electronegativite du cation dans le cas du muonium normal, qui serait localise seulement dans les cristaux covalents; cette constante est tres faible pour le muonium anormal qui serait engage dans une liaison covalente avec le voisin le plus proche
31
Griffiths, Mark. "Towards ligand design : Quantum Chemical Topology descriptors of heterocyclic compounds and pKa prediction from ab initio bond lengths". Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/towards-ligand-design-quantum-chemical-topology-descriptors-of-heterocyclic-compounds-and-pka-prediction-from-ab-initio-bond-lengths(cea30196-c1ce-4801-b6d9-c81c330ae7e4).html.
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Bioisosterism is a field that is widely applied to biological molecules, including drugs and agrochemicals. Bioisosterism is the replacement of an active fragment in a molecule with another fragment similar in activity. The replacement is designed to alter the behavior of the molecule in its target environment. In previous work a bioisostere database called the Quantum Isostere Database (QID) was built out of descriptors derived from the theory of Quantum Chemical Topology (QCT). The current work aims to expand the existing QID to include ring fragments. A series of rings were characterised by QCT properties taken from the ring. It was found that four features of a ring each independently have a systematic effect on the ring’s properties. In other words, each of the characteristics of a ring can be changed and have the same effect on the ring’s properties irrespective of the other ring features. The rings were also characterised using the three QCT properties taken from a point within the ring. The three properties established a space where rings were positioned based on their respective three properties. The positions of the rings showed that the space was able to discern between ring types, and that the features of a ring could be predicted if only its three properties were known. To improve the QID the alignment method and scoring were tested. The alignment procedure is unable to correctly align collinear fragments. Therefore, a principal axis alignment procedure was successfully employed to align collinear fragments. For terminal fragments an alternative alignment procedure was proposed to account for the increased rotational freedom. A global axis system meant that the direction dependent properties for all fragments were expressed in this new axis system. This idea was extended further and it was found that the geometry of a molecule was imprinted in the electrostatics when they were expressed in the global axis system. Finally, a pKa prediction method which correlates a single ab initio bond length was tested against two data sets (enols and guanidines). The method relies on subsets to form, where molecules within a subset share a chemical or structural commonality. These subsets were able to distinguish between the five tautomeric forms for the guanidines and different conformations for the enols. All predictions were within 1.0 pKa units of experimental values.
32
Fazzini, Serena. "One dimensional extended Hubbard model: two-particle bound states and resonances". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7614/.
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In questo lavoro di tesi è stato svolto uno studio analitico sul modello di Hubbard esteso unidimensionale al fine di osservare la presenza di eventuali risonanze che possano dare origine alla formazione di stati legati di due particelle. L'esistenza di uno stato legato stabile ha suscitato grande interesse negli ultimi anni, sia in ambito teorico che sperimentale, poichè è alla base di molti fenomeni che vengono osservati nei sistemi a molti corpi a basse temperature, come il BCS-BEC crossover. Pertanto si è ritenuto utile studiare il problema a due corpi nel modello di Hubbard esteso, che in generale non è integrabile. Il modello considerato contiene interazioni a primi e secondi vicini, in aggiunta all'interazione di contatto presente nel modello di Hubbard.
Il problema è stato indagato analiticamente attraverso il Bethe ansatz, che consente di trovare tutti gli autovalori e le autofunzioni dell'Hamiltoniana. L'ansatz di Bethe sulla funzione d'onda è stato generalizzato per poter tener conto dei termini di interazione a più lungo raggio rispetto all'interazione di contatto.
Si trova che, in questo modello, nel limite termodinamico, possono avvenire delle risonanze (o quasi-risonanze) in cui la lunghezza di scattering diverge, contrariamente a quanto avviene nel modello di Hubbard. Tale fenomeno si verifica quando il livello energetico discreto degli stati legati “tocca” la banda di scattering. Inoltre, con l'aggiunta di nuovi termini di interazione emergono nuovi stati legati. Nel caso in esame, si osservano due famiglie di stati legati, se lo spin totale delle due particelle è 1, e tre famiglie di stati legati, se lo spin totale è 0.
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Goda, Ibrahim. "Micromechanical models of network materials presenting internal length scales : applications to trabecular bone under stable and evolutive conditions". Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0055/document.
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Des méthodes micromécaniques spécifiques ont été développées pour la détermination du comportement effectif de matériaux cellulaires dotés d’une architecture discrète à l’échelle microscopique. La méthode d’homogénéisation discrète a été appliquée à des structures tissées monocouches ainsi qu’à l’os trabéculaire. La topologie discrète initiale de ces milieux est remplacée à l’échelle mésoscopique par un milieu effectif anisotrope micropolaire, qui rend compte des effets d’échelles observés. Ces méthodes d’homogénéisation permettent d’accéder à des propriétés classiques et non classiques dont la mesure expérimentale est souvent difficile. Des modèles 3D ont été développé afin de décrire la rupture fragile et ductile de l’os trabéculaire, incorporant des effets de taille des surfaces d’écoulement plastique. Nous avons construit par des analyses éléments finis de la microstructure de l’os trabéculaire un milieu de substitution 3D homogène, orthotrope de type couple de contraintes, sur la base d’une équivalence en énergie. Les tissus osseux ont la capacité d’adapter leur densité locale et leur taille et forme aux stimuli mécaniques. Nous avons développé des modèles de remodelage interne et externe dans le cadre de la thermodynamique des processus irréversibles, aux échelles cellulaire et macroscopique. Finalement, le remodelage interne anisotrope a été couplé à l’endommagement de fatigue, dans le cadre de la théorie continue de l’endommagementA methodology based on micromechanics has been developed to determine the effective behavior of network materials endowed with a discrete architecture at the microscopic level. It relies on the discrete homogenization method, which has been applied to textile monolayers and trabecular bones. The initially discrete topology of the considered network materials results after homogenization at the mesoscopic level in anisotropic micropolar effective continuum, which proves able to capture the observed internal scale effects. Such micromechanical methods are useful to remedy the difficulty to measure the effective mechanical properties at the intermediate mesoscopic level scale. The bending and torsion responses of vertebral trabecular bone beam specimens are formulated in both static and dynamic situations, based on the Cosserat theory. 3D models have been developed for describing the multiaxial yield and brittle fracture behavior of trabecular bone, including the analysis of size-dependent non-classical plastic yield. We have constructed by FE analyses a homogeneous, orthotropic couple-stress continuum model as a substitute of the 3D periodic heterogeneous cellular solid model of vertebral trabecular bone, based on the equivalent strain energy approach. Bone tissues are able to adapt their local density and load bearing capacities as well as their size and shape to mechanical stimuli. We have developed models for combined internal and external bone remodeling in the framework of the thermodynamics of irreversible processes, at both the cellular and macroscopic levels. We lastly combined anisotropic internal remodeling with fatigue continuum damage
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Stone, Cora Emma. "Neutron studies of amorphous solids". Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396244.
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Alba, Jeff. "THE EFFECTS OF ALPHA-ACTININ-3 KNOCKOUT ON BONE LENGTH AND DENSITY IN THE CRANIAL BASE AND CALVARIAL BONES". Master's thesis, Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/509374.
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Oral BiologyM.S.
The R577X ACTN3 stop codon polymorphism associates with skeletal Class II and open bite malocclusions. In mice Actn3 KO condylar growth is altered, producing an increase in trabecular number, but decrease in trabecular thickness and separation. This study expands these findings by comparing bone length and quality in the cranial base and calvarial bones of Actn3-/- and Actn3+/+ genotype mice. The heads of 20, 3-month old female mice (10 WT and 10 KO) were scanned using the Skyscan 1172 microCT scanner at a resolution of 9.4µm using a 0.5mm Aluminum filter. The raw microCT data was reconstructed. The macro-anatomy (linear measurements) were obtained using the line measurement tool in CTAn software. Micro-anatomy (Bone volume and trabeculation) were also assessed using the CTAn software. The presphenoido-basisphenoidal and basisphenoido-basioccipital synchondroses were evaluated in entirety and five sutures (frontal, parietal, fronto-parietal, bregma and pari) were segmented as a 1mm wide X 1mm deep X height of suture region of interest. No statistically significant difference between Actn3 KO and WT mice was found in linear measurements of the cranial base and calvarial bones. The ratio of bone volume to total volume (BV/TV) and trabecular separation (Tb. Sp.) of Actn3 KO and WT suture sites were found to have no statistically significant difference (p range 0.9957-0.0953) The Tb. Sp. of the presphenoido-basisphenoidal synchondrosis was the only location to show statistical significance (p = 0.0331). Tb.Sp of the basisphenoido-basioccipital synchondrosis was found to be nearly statistically significant (p= 0.1818), with power analysis predicting significance at n=51. As seen in previous studies, Actn3 KO mice are shown to have an altered bone quality in cartilaginous growth areas, including the mandibular condyle and cranial base synchondroses.
Temple University--Theses
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Pogosian, Anna. "Finite Element Analysis of Osseointegrated Transfemoral Implant : Identification of how the Length of Implant Affects the Stress Distribution in Cortical Bone and Implant". Thesis, KTH, Medicinteknik och hälsosystem, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-238445.
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An alternative method of conventional prosthesis is osseointegrated transfemoral implant, in where the prosthesis is fixated directly to the bone. The benefits with this system is increased range of motion, sensory feedback and reduced soft tissue problem. One of the drawbacks of this method is the effect of stress shielding, which could in long term lead to bone loss and bone resorption. The aim of this study is to investigate how the length of the fixture (60, 80 and 100 mm) of OPRA system (Osseointegrated Prosthesis for the Rehabilitation of Amputees) affects the stress distribution in femoral bone and implant during short walk by using Finite Element Methods. The finite element model used in this study was constructed of three major parts: THUMS model (Total Human Model of Safety) of left thigh, implant and bone graft. The analysis was performed through the software LS-DYNA, with an implicit solver. The loading of the total gait cycle was applied in the distal end of the implant, whereas the proximal end of the thigh was fixed. The FE simulation revealed lower stress distribution in the distal end of femoral bone, and higher in the proximal end. Implant 60 had lowest effect of stress shielding. The highest stress distribution in OPRA implant was shown in the abutment shaft, in the interface with bone graft. The length of the fixture did not have any impact on the stress distribution in the implant.
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Foulet-Fonseca, Gloria. "Etude par spectroscopie vibrationnelle des complexes méthylcarbyniques et méthylcarbéniques de chrome". Paris 13, 1987. http://www.theses.fr/1987PA132028.
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Etude en particulier de complexes, du type br(co)::(4)crcch::(3), br(co)::(4)crcchd::(2) et d'une série de mélanges isotopiques. Mise en évidence de la non-équivalence des liaisons c-h du groupe methyle. Etablissement d'un champ de forces pour les complexes méthylcarbyniques
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Berg, Xaver [Verfasser], e Karl Oliver [Akademischer Betreuer] Kagan. "Untersuchung der pränataldiagnostischen Marker prenasal thickness, nasal bone length, prefrontal space ratio und prenasal thickness-nasal bone ratio bei Feten mit einer Trisomie 18, Trisomie 13, Monosomie X und Triploidie / Xaver Berg ; Betreuer: Karl Oliver Kagan". Tübingen : Universitätsbibliothek Tübingen, 2018. http://d-nb.info/1199115215/34.
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Safsaf, Abdelaziz. "Etude structurale par diffraction des rayons x d'un phosphonate et de quelques hydroxydiphosphonates". Paris 13, 1989. http://www.theses.fr/1989PA132001.
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Pour les acides phosphoniques, diphosphoniques et diphosphonates organiques acides, la corrélation entre la longueur p-oh et la distance oh. . . O est linéaire. Les molécules d'éthanédiphosphonate-1,1 (hydroxy-1 "0,0,0',o'"-tetramethyl) et les molécules dérivées, possedent une relative flexibilité (corrélation linéaire entre l'angle p-c-p et le décalage des deux groupes acides phosphoniques)
40
Yu, Jiayi. "Synthesis and Characterization of Amino Acid-based Poly(ester urea)". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1366901855.
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Borodulina, Svetlana. "Micromechanics of Fiber Networks". Doctoral thesis, KTH, Hållfasthetslära (Inst.), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-188481.
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The current trends in papermaking involve, but are not limited to, maintaining the dry strength of paper material at a reduced cost. Since any small changes in the process affect several factors at once, it is difficult to relate the exact impact of these changes promptly. Hence, the detailed models of the network level of a dry sheet have to be studied extensively in order to attain the infinitesimal changes in the final product. In Paper A, we have investigated a relation between micromechanical processes and the stress–strain curve of a dry fiber network during tensile loading. The impact of “non-traditional” bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds, is discussed. In Paper B, we studied the impact of the chemical composition of the fiber cell wall, as well as its geometrical properties, on the fiber mechanical properties using the three-dimensional model of a fiber with helical orientation of microfibrils at a range of different microfibril angles (MFA). In order to accurately characterize the fiber and bond properties inside the network, via statistical distributions, microtomography studies on the handsheets have been carried out. This work is divided into two parts: Paper C, which describes the methods of data acquisition and Paper D, where we discuss the extracted data. Here, all measurements were performed at a fiber level, providing data on the fiber width distribution, width-to-height ratio of isotropically oriented fibers and contact density. In the last paper, we utilize data thus obtained in conjunction with fiber morphology data from Papers C and D to update the network generation algorithm in order to produce more realistic fiber networks. We also successfully verified the models with the help of experimental results from dry sheets tested under uniaxial tensile tests. We carry out numerical simulations on these networks to ascertain the influence of fiber and bond parameters on the network strength properties.QC 20160613
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Barros, Silvana de. "Efeito da respiração lenta na pressão arterial e na função autonômica em hipertensos". Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/5/5148/tde-22092017-134829/.
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INTRODUÇÃO: A respiração lenta é indicada como tratamento não medicamentoso da hipertensão arterial. Porém, os mecanismos fisiológicos envolvidos na redução da pressão arterial (PA) ainda são desconhecidos. A redução na atividade nervosa simpática (ANS) pode ser um dos mecanismos envolvidos na redução da PA. OBJETIVOS: Avaliar o efeito crônico da respiração lenta na PA e na ANS em hipertensos. MÉTODOS: Foram randomizados hipertensos, com e sem uso de anti-hipertensivos, em grupo controle (GC), orientados a ouvir músicas serenas com uso de aparelho de MP3, ou grupo respiração lenta (GRL), treinados a reduzir a frequência respiratória com auxílio de um dispositivo eletrônico, tendo como alvo terapêutico uma frequência respiratória menor que 10 respirações por minuto, por um período de 15 minutos diários, durante 8 semanas. Antes e após o período de intervenção, foi realizada monitorização ambulatorial da pressão arterial (MAPA), dosagem de catecolaminas plasmáticas e medida da atividade nervosa simpática periférica (ANSP) pela técnica da microneurografia. RESULTADOS: Completaram o estudo 17 voluntários no GRL e 15 no GC. Não houve mudança na PA de consultório antes e após a intervenção nos dois grupos. Observou-se redução na pressão arterial sistólica (PAS) e diastólica (PAD) na vigília entre os períodos pré e pós-intervenção apenas no GC (131±10 / 92±9 vs 128±10 / 88±8 mmHg, p < 0,05). Não foi observada diferença na concentração de catecolaminas plasmáticas (pg/ml) em ambos os grupos entre os períodos pré e pós-intervenção: GRL 302 (220-256) vs 234 (156-318), p=0,35; e GC 201 (144-230) vs 221 (179-274), p=0,97. Nos voluntários que realizaram microneurografia, GRL (n=10) e GC (n=10), observou-se redução significativa da PAD de sono entre os períodos pré e pós- intervenção apenas no GC (83±6 vs 79±4 mmHg, p < 0,05) A ANSP (impulsos/minuto) medida pela microneurografia apresentou elevação no período pós-intervenção em comparação ao período pré-intervenção nos dois grupos: GRL (16±6 vs 22±8, p < 0,05) e GC (20±5 vs 23±5, p < 0,05). CONCLUSÕES: A respiração lenta, realizada por 15 minutos diários durante 8 semanas, não reduziu a pressão arterial, os níveis de catecolaminas plasmáticas e a atividade nervosa simpática periférica de hipertensosINTRODUCTION: Slow breathing is indicated as nonpharmacological treatment of hypertension. However, the physiological mechanisms involved in blood pressure (BP) reduction are still unknown. The decrease in sympathetic nerve activity (SNA) may be one of the mechanisms involved in BP reduction. OBJECTIVES: To evaluate the chronic effect of slow breathing on BP and SNS in hypertensive patients. METHODS: Hypertensive patients, with or without use of antihypertensive drugs, were randomized to listen serene songs using an MP3 player (Control Group - CG) or device-guided slow breathing group (DGB), who were trained to reduce respiratory rate with assistance of an electronic device, targeting a respiratory rate of less than 10 breaths per minute, for a period of 15 minutes per day for 8 weeks. Before and after the intervention period, ambulatory blood pressure monitoring (ABPM), plasma catecholamines concentration and muscle sympathetic nerve activity (MSNA) using the microneurography technique were performed. RESULTS: 17 volunteers in the DGB and 15 in the CG completed the study. There was no change in office BP before and after intervention in both groups. There was a reduction in daytime systolic (SBP) and diastolic (DBP) before and after intervention only in the CG (131±10 / 92±9 vs 128±10 / 88±8 mmHg, p < 0,05). No difference in plasma catecholamines concentration (pg/ml) was observed in both groups before and after intervention: DGB 302 (220-256) vs 234 (156-318), p = 0.35; CG 201 (144-230) vs 221 (179-274), p=0.97. In the volunteers who underwent microneurography, DGB (n=10) and CG (n=10), there was a significant reduction in sleep DBP only in the CG: 83±6 vs 79±4 mmHg, p < 0,05. The MSNA (bursts/minute) measured by the microneurography showed a rise after the intervention in both groups: DGB (16±6 vs 22±8, p < 0.05) and CG (20±5 vs 23±5, p < 0.05). CONCLUSIONS: Slow breathing, performed for 15 minutes daily for 8 weeks, did not reduce blood pressure, plasma catecholamine concentration and muscle sympathetic nerve activity in hypertensive patients
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Forthomme, Damien. "High Resolution Laser Spectroscopy Of Selected Molecules In The Gas Phase". Thesis, Fredericton: University of New Brunswick, 2011. http://hdl.handle.net/1882/35387.
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Alengry, Jonathan. "Etude expérimentale et modélisation de la longueur de bon mélange. Application à la représentativité des points de prélèvement en conduit". Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4308/document.
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La surveillance des rejets gazeux des installations nucléaires dans l'environnement et de contrôle des dispositifs d'épuration reposent sur des mesures régulières de concentrations des contaminants en sortie de cheminées et dans les réseaux de ventilation. La répartition de la concentration peut être hétérogène au niveau du point de mesure si la distance d'établissement du mélange est insuffisante. La question se pose sur l'évaluation du positionnement des points de piquage et sur l'erreur commise par rapport à la concentration homogène en cas de non-respect de cette distance. Cette étude définit cette longueur dite de « bon mélange » à partir d'expériences menées en laboratoire. Le banc dimensionné pour ces essais a permis de reproduire des écoulements dans des conduits longs circulaire et rectangulaire, comprenant chacun un coude. Une technique de mesure optique a été développée, calibrée puis utilisée pour mesurer la distribution de la concentration d'un traceur injecté dans l'écoulement. Les résultats expérimentaux en conduit cylindrique ont validé un modèle analytique basé sur l'équation de convection-diffusion d'un traceur, et ont permis de proposer des modèles de longueur de bon mélange et de représentativité de points de prélèvement. Dans le conduit à section rectangulaire, les mesures acquises constituent une première base de données sur l'évolution de l'homogénéisation d'un traceur, dans la perspective de simulations numériques explorant des conditions plus réalistes des mesures in situMonitoring of gaseous releases from nuclear installations in the environment and air cleaning efficiency measurement are based on regular measurements of concentrations of contaminants in outlet chimneys and ventilation systems. The concentration distribution may be heterogeneous at the measuring point if the distance setting of the mixing is not sufficient. The question is about the set up of the measuring point in duct and the error compared to the homogeneous concentration in case of non-compliance with this distance. This study defines the so-called "well mixing length" from laboratory experiments. The bench designed for these tests allowed to reproduce flows in long circular and rectangular ducts, each including a bend. An optical measurement technique has been developed, calibrated and used to measure the concentration distribution of a tracer injected in the flow. The experimental results in cylindrical duct have validated an analytical model based on the convection-diffusion equation of a tracer, and allowed to propose models of good mixing length and representativeness of sampling points. In rectangular duct, the acquired measures constitute a first database on the evolution of the homogenization of a tracer, in the perspective of numerical simulations exploring more realistic conditions for measurements in situ
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Nordström, Jakob. "Short Proofs May Be Spacious : Understanding Space in Resolution". Doctoral thesis, KTH, Teoretisk datalogi, TCS, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4704.
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Om man ser på de bästa nu kända algoritmerna för att avgöra satisfierbarhet hos logiska formler så är de allra flesta baserade på den så kallade DPLL-metoden utökad med klausulinlärning. De två viktigaste gränssättande faktorerna för sådana algoritmer är hur mycket tid och minne de använder, och att förstå sig på detta är därför en fråga som har stor praktisk betydelse. Inom området beviskomplexitet svarar tids- och minnesåtgång mot längd och minne hos resolutionsbevis för formler i konjunktiv normalform (CNF-formler). En lång rad arbeten har studerat dessa mått och även jämfört dem med bredden av bevis, ett annat mått som visat sig höra nära samman med både längd och minne. Mer formellt är längden hos ett bevis antalet rader, dvs. klausuler, bredden är storleken av den största klausulen, och minnet är maximala antalet klausuler som man behöver komma ihåg samtidigt om man under bevisets gång bara får dra nya slutsatser från klausuler som finns sparade. För längd och bredd har man lyckats visa en rad starka resultat men förståelsen av måttet minne har lämnat mycket i övrigt att önska. Till exempel så är det känt att minnet som behövs för att bevisa en formel är minst lika stort som den nödvändiga bredden, men det har varit en öppen fråga om minne och bredd kan separeras eller om de två måtten mäter "samma sak" i den meningen att de alltid är asymptotiskt lika stora för en formel. Det har också varit okänt om det faktum att det finns ett kort bevis för en formel medför att formeln också kan bevisas i litet minne (motsvarande påstående är sant för längd jämfört med bredd) eller om det tvärtom kan vara så att längd och minne är "helt orelaterade" på så sätt att även korta bevis kan kräva maximal mängd minne. I denna avhandling presenterar vi först ett förenklat bevis av trade-off-resultatet för längd jämfört med minne i (Hertel och Pitassi 2007) och visar hur samma idéer kan användas för att visa ett par andra exponentiella avvägningar i relationerna mellan olika beviskomplexitetsmått för resolution. Sedan visar vi att det finns formler som kan bevisas i linjär längd och konstant bredd men som kräver en mängd minne som växer logaritmiskt i formelstorleken, vilket vi senare förbättrar till kvadratroten av formelstorleken. Dessa resultat separerar således minne och bredd. Genom att använda andra men besläktade idéer besvarar vi därefter frågan om hur minne och längd förhåller sig till varandra genom att separera dem på starkast möjliga sätt. Mer precist visar vi att det finns CNF-formler av storlek O(n) som har resolutionbevis i längd O(n) och bredd O(1) men som kräver minne minst Omega(n/log n). Det gemensamma temat för dessa resultat är att vi studerar formler som beskriver stenläggningsspel, eller pebblingspel, på riktade acykliska grafer. Vi bevisar undre gränser för det minne som behövs för den så kallade pebblingformeln över en graf uttryckt i det svart-vita pebblingpriset för grafen i fråga. Slutligen observerar vi att vår optimala separation av minne och längd i själva verket är ett specialfall av en mer generell sats. Låt F vara en CNF-formel och f:{0,1}^d->{0,1} en boolesk funktion. Ersätt varje variabel x i F med f(x_1, ..., x_d) och skriv om denna nya formel på naturligt sätt som en CNF-formel F[f]. Då gäller, givet att F och f har rätt egenskaper, att F[f] kan bevisas i resolution i väsentligen samma längd och bredd som F, men att den minimala mängd minne som behövs för F[f] är åtminstone lika stor som det minimala antalet variabler som måste förekomma samtidigt i ett bevis för F.Most state-of-the-art satisfiability algorithms today are variants of the DPLL procedure augmented with clause learning. The two main bottlenecks for such algorithms are the amounts of time and memory used. Thus, understanding time and memory requirements for clause learning algorithms, and how these requirements are related to one another, is a question of considerable practical importance. In the field of proof complexity, these resources correspond to the length and space of resolution proofs for formulas in conjunctive normal form (CNF). There has been a long line of research investigating these proof complexity measures and relating them to the width of proofs, another measure which has turned out to be intimately connected with both length and space. Formally, the length of a resolution proof is the number of lines, i.e., clauses, the width of a proof is the maximal size of any clause in it, and the space is the maximal number of clauses kept in memory simultaneously if the proof is only allowed to infer new clauses from clauses currently in memory. While strong results have been established for length and width, our understanding of space has been quite poor. For instance, the space required to prove a formula is known to be at least as large as the needed width, but it has remained open whether space can be separated from width or whether the two measures coincide asymptotically. It has also been unknown whether the fact that a formula is provable in short length implies that it is also provable in small space (which is the case for length versus width), or whether on the contrary these measures are "completely unrelated" in the sense that short proofs can be maximally complex with respect to space. In this thesis, as an easy first observation we present a simplified proof of the recent length-space trade-off result for resolution in (Hertel and Pitassi 2007) and show how our ideas can be used to prove a couple of other exponential trade-offs in resolution. Next, we prove that there are families of CNF formulas that can be proven in linear length and constant width but require space growing logarithmically in the formula size, later improving this exponentially to the square root of the size. These results thus separate space and width. Using a related but different approach, we then resolve the question about the relation between space and length by proving an optimal separation between them. More precisely, we show that there are families of CNF formulas of size O(n) that have resolution proofs of length O(n) and width O(1) but for which any proof requires space Omega(n/log n). All of these results are achieved by studying so-called pebbling formulas defined in terms of pebble games over directed acyclic graphs (DAGs) and proving lower bounds on the space requirements for such formulas in terms of the black-white pebbling price of the underlying DAGs. Finally, we observe that our optimal separation of space and length is in fact a special case of a more general phenomenon. Namely, for any CNF formula F and any Boolean function f:{0,1}^d->{0,1}, replace every variable x in F by f(x_1, ..., x_d) and rewrite this new formula in CNF in the natural way, denoting the resulting formula F[f]. Then if F and f have the right properties, F[f] can be proven in resolution in essentially the same length and width as F but the minimal space needed for F[f] is lower-bounded by the number of variables that have to be mentioned simultaneously in any proof for F.
QC 20100831
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Nicolau, José Eduardo. ""O transplante de medula óssea alogênico de curto período de internação"". Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/5/5136/tde-08082005-114337/.
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Foram analisados os resultados retrospectivos do transplante de medula óssea alogênico em 100 pacientes portadores de leucemia mielóide crônica, divididos em dois grupos: Grupo I, de 49 pacientes que recebeu alta hospitalar após a pega medular, e grupo II, de 51 pacientes, que recebeu alta precocemente, antes da pega medular, para acompanhamento ambulatorial. Foram comparados os dias de ocupação de leitos hospitalares, a morbidade e a mortalidade entre os grupos de alta até o dia 100 pós transplante. Verificou-se que, no grupo de alta precoce, houve, significativamente, menos dias de ocupação de leitos hospitalares, sem aumento da morbidade e da mortalidadeWe analyzed the results of a retrospective study of 100 patients with chronic myelogenous leukemia submitted to allogeneic stem cell transplantation in one of two settings: Group I, with 49 patients, transplanted in the traditional inpatient and group II, with 51 patients, in partial outpatient. We compared the median number of days spent in hospital, morbidity and mortality within 100 after bone marrow transplantation. We concluded that there was a significant reduction in the median of hospital length of stay in the partial outpatient group, without increasing morbidity and mortality
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Roothaer, Xavier. "Approche multi-échelle du comportement mécanique des os porteurs et non-porteurs : vers une personnalisation des modèles numériques EF de l'être humain". Thesis, Valenciennes, Université Polytechnique Hauts-de-France, 2019. http://www.theses.fr/2019UPHF0020.
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Le squelette humain a pour fonction de protéger les organes internes tout en participant au système de locomotion. Afin d’en assurer la rigidité mécanique, l’os cortical est présent dans toutes les parties du squelette. Le remodelage osseux, processus dynamique, est actif tout au long de la vie. Il permet à l’os cortical d’adapter sa géométrie et son architecture interne en fonction des contraintes qui lui sont appliquées. Étant un processus complexe, le remodelage osseux est amené à dysfonctionner chez les personnes âgées et fragiliser leurs os. Ainsi, cette thèse étudie les os porteurs et non porteurs humains en se concentrant sur le fémur et l’humérus. La revue de la littérature, effectuée dans le chapitre 1, met en évidence plusieurs verrous scientifiques à résoudre. En effet, pour diverses raisons pratiques, le fémur est très largement étudié, délaissant l’étude des autres os. Cela a pour effet d’en impacter les données matériaux utilisées par les modèles numériques du corps humain, souvent extraites d’études très anciennes et obsolètes dont les sujets humains diffèrent. De plus, les études architecturales sont, pour la plupart, limitées à des analyses en 2D et ne sont pas adaptées par rapport à l’architecture osseuse complexe. Par conséquent, le second chapitre décrit une méthode innovante capable d’analyser et de quantifier l’architecture en 3D à partir de scans tomographiques. Les canaux, connectivités et BMUs, berceaux du remodelage osseux, sont automatiquement détectés. 77 échantillons, prélevés sur humérus et fémurs gauche et droit, sont scannés et quantifiés à partir de cette méthode. Étant donné que de nombreuses caractéristiques, jamais mesurées auparavant, sont obtenues, des essais de traction et d’indentation sont effectués afin de comprendre et de mettre en évidence l’impact de l’architecture sur le comportement mécanique. Par conséquent, l’intégralité des échantillons, précédemment scannée, est testée. Dans l’objectif d’extraire des tendances générales, les humérus et fémurs sont comparés suivant différents tests statistiques. De même, l’impact de la latéralité est aussi étudié. Pour terminer, une étude de corrélation, suivie d’une étude de régressions, est effectuée afin de fournir des fonctions polynomiales destinées à prédire le comportement mécanique à partir d’une simple étude architecturaleThe human skeleton aims at participating to the locomotor system, protecting and serving as brackets for the internal organs. To ensure the mechanical stiffness of the entire body, the cortical bone can be found in every part of the skeleton. A dynamic process occurs throughout the life and is named bone remodelling. This process adapts the cortical bone architecture and the shape of bones according to their functions. Due to its complexity, bone remodelling can defect in the elderly and weakens bones. This thesis studies the bearing and non-bearing long human bones by focusing on the humerus and femur. A survey of the state of the art, detailed in the first chapter, reveals several lacks. First, the femur is widely investigated compared to the other bones and this unbalance creates a lack of data for the other bones. Therefore, inputs for numerical human models come from deprecated and contradictory studies where the extra-individual differences impact the trends. Second, architectural studies are mainly limited to in-plane assessment whereas the vascular network is complex and needs more robust analyses. Thus, the second chapter describes an innovative method to 3D assess the cortical vascular network from tomographic data. This Python script automatically detects canals, connectivity and Bone Multicellular Units (BMUs), cradle of the bone remodelling activity. Then, 77 samples from left and right femurs and humeri of ten human cadavers are scanned and analysed using this method. As this method provides numerous novel features of the cortical architecture, tensile and indentation tests are also carried out in order to understand and exhibit the impact of the architecture on the mechanical behaviour. Hence, all the scanned samples are tested and available for statistical analysis. So as to identify global trends, humerus and femur are compared using different statistical tests. Likewise, the bias impact is also investigated. Finally, a correlation study followed by a regression study is described so as to provide polynomial functions in order to be used to predict the mechanical behaviour from an architectural study
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Reznickova, Anna. "Computational study of the C-CI bond length". 2010. http://hdl.handle.net/10090/16191.
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Yan, Jiaqiang Goodenough John B. "A study of bond-length fluctuations in transition metal oxides /". 2004. http://repositories.lib.utexas.edu/bitstream/handle/2152/2094/yanj042.pdf.
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Yan, Jiaqiang. "A study of bond-length fluctuations in transition metal oxides". Thesis, 2004. http://hdl.handle.net/2152/2094.
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