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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 möglich. / Reinforced 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.

Very limited research studies have been conducted to examine bond of glass fibre reinforced polymer (GFRP) bars with high concrete strength. The current research project aims to compare between bond measured from a pull-out test and a hinged beam test for GFRP bars embedded in high strength concrete. Different parameters influencing bond such as GFRP bar diameter, embedment length and surface configuration were investigated in both test methods, while the bar position, i.e. top or bottom, was only studied in hinged beams. Seventy-two pull-out cubes, eight pull-out prisms and twenty-four hinged beams reinforced with GFRP bars were constructed and tested to failure. Twelve pull-out cubes and four hinged beams reinforced with steel bars were also tested for comparison purposes. The results showed that bond stress – slip curves obtained from various testing methods were similar, consisting of high initial stiffness, followed by nonlinear ascending and softening branches. In addition, it was found that the experimental bond strength obtained from hinged beams was higher than both bond strengths measured by the pull-out cube and pull-out prism. However, when a finite element analysis was conducted for hinged beams, it was shown that the tensile force in the reinforcing bar estimated by equilibrium conditions is overestimated as the large deformation of hinged beams at failure was not considered. Therefore, if the tensile force obtained from the finite element analysis is used to calculate the bond strength, it would be similar to that obtained from pull-out cube and prism. Moreover, it was found that the distribution of tensile and bond stresses was nonlinear along the GFRP embedment length and bond stress at the vicinity of the free end increased with increasing the load due to redistribution of bond stresses along the embedment length. Bond strengths were compared against the prediction methods provided in ACI-440.1R, CSA-S806, CSA-S6 and JSCE 1997. In general, all design codes showed conservative results for all specimens tested and ACI predictions gave a good agreement with experimental data compared to other codes. Artificial neural network models were developed to predict bond strength of GFRP bars in concrete. These models used bar diameter, embedment length, concrete compressive strength and concrete cover as input variables. The developed ANN models showed to be able to predict bond strength of GFRP bars in concrete and, therefore, were used to conduct a parametric study. / Higher Education Institute, Government of Libya

[pt] Este trabalho tem como objetivo inicial apresentar o project bond como um instrumento de financiamento para um project finance. O project bond está baseado no lançamento de bonds (títulos de dívida) especificamente para o financiamento de um projeto, sendo o fluxo de caixa gerado pelo projeto a principal fonte pagadora do empréstimo. Como a estruturação de um project finance envolve a criação de uma SPE (Sociedade de Propósito Específico), é através desta empresa que os bonds são emitidos para financiar um projeto. O project bond pode representar apenas uma parcela da dívida utilizada no project finance, não sendo necessariamente responsável pela totalidade do financiamento do projeto. Uma vez contextualizado este instrumento financeiro, e comparado com outras formas de financiamento, busca-se efetuar uma comparação entre duas emissões de bonds da Petróleo Brasileiro S.A (Petrobras) no mercado internacional: um bond corporativo lançado pela empresa e um project bond emitido por uma SPE para financiamento do Projeto Marlim. O presente trabalho busca ainda verificar se fez diferença para a Petrobras, em termos de custo de dívida, financiar-se no mercado de capitais internacional via bond corporativo ou via project bond e analisar se o mercado internacional avalia de forma diferente o risco de um bond corporativo da Petrobras e o risco de um project bond de um projeto da empresa. / [en] This work has as initial objective to present the project bond as a financing instrument for a project finance. The project bond is based on the bonds issue (debt titles) specifically for the financing of a project, being the cash flow generated by the project the main source payer of the loan. As the structuring of a project finance involves the creation of a SPC (Specific Propose Company), it is through this company, that the bonds is issued to finance a project. The project bond can represent a portion of the debt just used in the project finance, not being necessarily responsible for the totality of the financing of the project. After comparing this product with other financing products, it is make a comparison among two emissions of bonds from Petróleo Brasileiro S.A (Petrobras) in the international market: a corporate bond issued by the company and a project bond issued by a SPC to finance the Marlim Project. The present study still try to verify if it made difference for Petrobras, in terms of debt cost, to be financed at the international capital market through corporate bond or through project bond and to analyze if the international market evaluates in a different way the risk of a corporate bond of Petrobras and the risk of a project bond of a Petrobras project.

Within the last few years, a significant contribution to the discovery of sp2C−H activation processes and useful applications for cross-coupling C−C bond formation has been achieved by the use of ruthenium(II) arene catalysts. The aim of this thesis is to describe a modular approach for the synthesis of several ruthenium(II) arene complexes with the potential for C−H activation. Another cutting-edge field, catalytic enantioselective functionalization of C−H bonds by transitional metal catalysts, has also been realized within the last few years. It represents a highly atom- and step-economic approach toward the generation of structural complexity. However, the majority of current methodologies rely on the usage of late third- row transition metals such as pallidum, iridium and rhodium. There is a need that motivates the search for cheaper, relative earth abundant metals that could have similar catalytic ability. Herein is also represented a preliminary study of a ruthenium(II)-catalyzed enantioselective access to chromane moiety enabled by chiral transient directing group.

<p> In a study of the structures of some polyatomic cations of Group VI and VII, the compound Se4(HS2O7)2 has been prepared and its structure determined by single crystal X-ray diffraction. The bonding in the square planar cation has been discussed in terms of molecular orbital and valence bond theory. The anion geometry has been discussed and simple rules proposed to predict the changes which occur in bond length and bond angle when one or more oxygen in an SO4 tetrahedron is bonded to another atom or group.</p> <p> A θ/θ vertical diffractometer has been constructed, and computer programmes written, so that cation structures could be determined in solution. The structures of the Se4 2+ and Te4 2+ cations have been determined in fluorosulphuric acid, and are shown to be square planar.</p> <p> Liquid diffraction studies of 3:1, I2/S2O6F2 solutions have shown the presence of a cation containing a linear chain of three iodine atoms.</p> / Thesis / Doctor of Philosophy (PhD)

Consideration of the reinforced concrete beam as a composite beam with incomplete interaction, the effect of principal strains in the shear span is studied. The influence of bond slip on the formation of cracks is studied both analytically and experimentally. / Thesis / Master of Engineering (ME)

<p> This thesis describes an investigation into the effects of Lewis acid complexation on the photochemistry of α,β unsaturated carbonyl compounds.</p> <p> Initial studies involved the use of Nuclear Magnetic Resonance (NMR) and Ultraviolet (UV) spectroscopy in examining Lewis acid modification of the photostationary state for E/Z isomerization of various acyclic enones. The results obtained provide a good understanding of the origin of the perturbation of the photostationary state of these systems. In the course of these investigations, the question also arose as to the possible effects of complexation upon the photochemistry of cyclic enone systems where E/Z isomerization cannot occur, particularly whether this would catalyze [2+2] cycloadditions to the enone carbon/carbon double bond. Lewis acid complexed enones are widely used as activated dienophiles in Diels Alder reactions, and have been recently reported to serve as activated 'enophiles' in a photochemical dimerization of coumarin.</p> </p> The examination here is focused upon endo-tricyclo [5.2.1.02,6] deca-4,8-dien-3-one. (See Diagram in thesis). </p> <p> Reported here is a detailed investigation of the photochemistry of the AlEtCl2 complex of this compound, and the results are interpreted mechanistically. The reaction gives rise to a single product which reaches a photostationary state with the reactant complex. The isomerization is formally a [1,3] sigmatropic shift involving the isolated double bond. It seems likely however, to proceed by the formation of an allyl cation intermediate.</p> / Thesis / Master of Science (MSc)

<p> Trimethylsilylstyrenes undergo protiodesilylation (Scheme 1, path A), via the β-silyl carbonium ion under acidic conditions. In contrast, the corresponding trichlorosilyl substituted compound was found to undergo an oligomerization reaction (Scheme 1, path B) with triflic acid as the catalyst. (See Diagram in Thesis)</p> <p> The β-effect [(σ-p)π overlap] may play a significant role in the weakening of the silicon-carbon bond and thus promote the cleavage process, as is observed in scheme 1, path A. Introduction of electronegative chloro groups on silicon weakens the β-effect and hence the silyl leaving group ability, resulting in oligomerization of the styrene (Scheme 1, path B).</p> <p> In this oligomerization reaction, chain termination by an internal Friedel-Crafts reaction competes with the chain propagation. As a result, indane terminated low moldecular weight oligomers are formed. The case is similar to β-methyldichlorosilylstyrene, with the only difference that here ca. 20% desilylation has occured, again reflecting the fact that subtle changes in the β-effect acan influence the course of electrophilic reactions.</p> / Thesis / Master of Science (MSc)

<p> The solution stability of chelates formed between several metal-ions and 5-substituted-8-hydroxyquinolines has been determined. The dependence of solution stability on (a) the solvent composition, and (b) the basicity of the ligand donor sites has been examined.</p> <p> It was found that the effect of solvent composition on metal chelate stability is essentially independent of the metal-ion. A mathematical description of the relationship between metal-chelate stability and ligand basicity has been derived and gives excellent agreement with the experimental data. The relative contributions of the N-M and the O-M bond to chelate stability are evaluated and shown to vary slightly with the metal-ion. Also, the character of the bonding in the metal chelates is implied.</p> / Thesis / Doctor of Philosophy (PhD)