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.

Due to a lack of knowledge and experience the best approach to deal with wind farm decommissioning has yet to be determined. To fill this void, this paper analyzed the current status in terms of regulations and cost, regarding the decommissioning in Italy and Sweden.   In order to make a comparison between these two countries, the available research papers and reports on the decommissioning cost assessment, removal methods and regulations were thoroughly investigated. Moreover, detailed estimated dismantling cost data was obtained from a wind farm in Italy.   The Italian cost data were compared with data collected in Sweden and along with them, the regulations and legislations related to how these costs have to be assessed as well as what developers are required to do regarding the decommissioning in the permit issuance were included.   The results of this research show that in decommissioning cost assessment both countries does not allow developers to include the possible revenues due to the scraps and to the recycling of components, although totally different methods are pursued.   Some kind of security to ensure that decommissioning occurs is required, normally a bond. The bond amount is a debt investment in which an investor loans money to an entity (corporate or governmental) that borrows the funds for a defined period of time at a fixed interest rate. In Italy the bond requirements are generally high and it has to be paid completely for the permit issuance. In order to develop significant projects, this kind of approach leads to discourage small investors.   On the contrary, in Sweden the current amount of 300.000 SEK per turbine according to the court precedent, the most widespread during the approval of the permit, is definitely low and represent a level playing field for every investor. Swedish regulations are also more flexible and only in the 28% of the cases studied between the years 2009 and 2012, the entire amount of the bond had to be assured before the installation. However, the malleability with regard to wind farms that do not need to provide any security, together with the low bond amount might endanger the decommissioning accomplishment.

This paper examines for the first time the relationship between the net issue values of aggregate bonds, as well as the different bond sectors separately, and economic growth. The other new feature of this study is the usage of quarterly data. Granger causalities are calculated for time series of 15 European countries, the USA, and Japan in order to test if there is a positive relationship between the development of bond markets and economic growth also for shorter time periods. The significant Granger causalities found show the following tendency: Economic growth is causal for net issue values of government bonds, and net issuance of corporate and financial institutions bonds are causal for economic growth. That finding is important for the future architecture of the financial sector, in particular in emerging markets and the new EU member countries. (author's abstract) / Series: EI Working Papers / Europainstitut

We use annual real GDP and the volume of the bond, stock and credit markets to assess the causal relationship between the aggregate bond market development and economic growth in the USA, Japan, Germany, Great Britain, Italy, France and the Netherlands over the 1950 to 2001 period. The literature on the real - financial nexus to date has focused on the credit and stock markets, with few exceptions. Partially due to data availability problems, the impact of bond markets on economic growth has not yet been examined in the same way. To fill this gap we provide empirical evidence for long-run equilibrium and Granger causality in at least one direction in the relationship among real GDP and bond, credit and stock markets in seven economies with large bond markets. The supplyleading hypothesis that development of the financial markets enhances growth is supported in all countries except for Germany. The demand-leading hypothesis that economic development pulls the development of the financial markets is supported only for Germany. A feedback between domestic credits and output is found in Japan. There is evidence for a feedback between the equity markets and real output in Japan and the Netherlands. (author's abstract) / Series: EI Working Papers / Europainstitut

Despite the great abundance of C–H bonds in readily available starting materials, their use in synthesis of functionalized molecules has been hampered by the high bond strengths, rendering them inert to common organic reagents. However, recent progress in the field has addressed this issue, enabling selective C–H bond functionalizations to be performed using catalytic transition metal mediated processes. Herein, the use of sulfonyl chlorides as versatile reagents for C–H bond functionalizations is reported. Using chelation assistance, the regioselective conversion of C–H bonds to either C–S, C–Cl or C–C bonds was achieved. The methodology development, substrate scope determination and mechanistic investigations will be discussed.

Despite the great abundance of C–H bonds in readily available starting materials, their use in synthesis of functionalized molecules has been hampered by the high bond strengths, rendering them inert to common organic reagents. However, recent progress in the field has addressed this issue, enabling selective C–H bond functionalizations to be performed using catalytic transition metal mediated processes. Herein, the use of sulfonyl chlorides as versatile reagents for C–H bond functionalizations is reported. Using chelation assistance, the regioselective conversion of C–H bonds to either C–S, C–Cl or C–C bonds was achieved. The methodology development, substrate scope determination and mechanistic investigations will be discussed.

Over the past decade, extensive research has been conducted on the strengthening of reinforced concrete (RC) structures using externally bonded fibre reinforced polymer (FRP). More recently, near-surface mounted (NSM) FRP reinforcement has attracted an increasing amount of research as well as practical applications. In the NSM method, grooves are first cut into the concrete cover of an RC element and the FRP reinforcement is bonded inside the groove with an appropriate filler (typically epoxy paste or cement grout). The FRP reinforcement is either prestressed or non-prestressed depending on the required level of strengthening. In all cases, the bond between an NSM bar and the substrate material plays a key role in ensuring the effectiveness of NSM strengthening. The present work investigated experimentally the bond behaviour of non-prestressed and prestressed beams reinforced with near surface mounted carbon fibre reinforced polymer (CFRP) bars under monotonic and fatigue loading. Forty concrete beams were cast and tested in seven groups. The test variables considered in this study were: presence of internal steel reinforcement or not, the type of CFRP rod (spirally wound or sand coated) and the prestressing force (non-prestressed or prestressed). Twenty eight beams were strengthened with non-prestressed CFRP rods; fifteen beams without internal steel reinforcement and thirteen beams with internal steel. Ten beams with internal steel were strengthened with prestressed CFRP rods. The beams were tested in four point bending. In each group, one beam was loaded monotonically. The remaining beams were loaded under different fatigue load levels. The minimum load was kept constant for all beams at 10% of their monotonic capacity and the peak load was varied from one beam to another (denoted as a percentage of the peak load level). Twenty eight beams were strengthened with non-prestressed CFRP rods. Bond failures for the beams with and without internal steel, strengthened with CFRP rods and tested under monotonic or fatigue loads was by debonding between the CFRP rod and the epoxy that started at the loading point and as the load was increased or cycled, the debonding spread towards the support until failure occurred. A comparison of the fatigue life curves for the beams with and without steel, strengthened with CFRP rods revealed that the sand coated rod had better bond characteristics than the spirally wound rod (at the same load range the beam strengthened with sand coated rod had a longer life than the beam strengthened with spirally wound rod). Beams with internal steel, strengthened with CFRP rods and tested under fatigue loading failed in bond at high load levels (short fatigue lives) and by rupture of the steel rebar at low load levels (long fatigue lives). Ten beams with internal steel were strengthened with prestressed CFRP rods. The CFRP rods were prestressed to a force of 62 kN which corresponds to 45% and 40% of the monotonic capacity of the spirally wounded and sand coated rods, respectively. Almost all the beams with internal steel that were strengthened with prestressed CFRP rods failed by slipping between the CFRP rod and the epoxy that started at the support and propagated inwards towards the loading point. The exception to this was the beam strengthened with prestressed sand coated rod and tested under monotonic loading that failed by debonding between the CFRP rod and the epoxy that started at the loading point and propagated towards the support. Comparing the load range (kN) versus life curve for the beams with steel, strengthened with prestressed spirally wound and sand coated rods that failed in bond, shows that the beam strengthened with sand coated rod has longer fatigue lives than beam strengthened with spirally wound rod. A model was used to describe the progress of the debonding crack until excessive slipping occurred. The model predicted the number of cycles until excessive slipping between the CFRP rod and the epoxy occurred and the forces in the CFRP rod at all locations in the shear span at the onset of failure with reasonable accuracy.

Sustainable resource management and development have been at the forefront of important issues concerning the construction industry for the past several years. Specifically, the use of sustainable building materials and the reuse and recycling of previously used building materials is gaining acceptance and becoming common place in many areas. As one of the most commonly used building materials in the world, concrete, composed of aggregate, sand, cement and water, can be recycled and reused in a variety of applications. Using crushed concrete as fill and subgrade material under roads, sidewalks and foundations has been the most common of these applications. However, research has been ongoing over the past 50 years in many countries including Germany, Canada, Japan, the United States, China, and Australia investigating the use of crushed concrete from demolished old concrete structures to fully or partially replace the virgin aggregate used to produce new concrete for use in building and pavement applications. Producing concrete using recycled concrete aggregates (RCAs) has several advantages, namely, the burden placed on non-renewable aggregate resources may be significantly decreased, the service life and capacity of landfill and waste management facilities can be extended, and the carbon dioxide emissions and traffic congestion associated with the transport of virgin aggregates from remote sites can be reduced. This research is directed at benchmarking typical RCA sources for usage in structural concrete and investigating the inter-relationships between aggregate properties, concrete properties and the bond properties between reinforcing steel and RCA concrete. The experimental program focused on four main areas: aggregate properties testing, development of concrete mixture proportions, concrete fresh and hardened properties testing, and beam-end bond testing. Four coarse aggregate sources were investigated including one virgin or natural aggregate (NA) source, and three RCA sources. Two RCA sources were derived from the crushing of decommissioned building and pavement structures (RCA-1 and RCA-2) while the third source was derived from the crushing of returned ready-mix concrete (RCA-3). A variety of typical and non-typical aggregate tests were performed to provide a basis for correlation with fresh and hardened concrete properties results. A total of 24 concrete mixtures were developed and divided into three separate categories, 1) control, 2) direct replacement, and 3) strength-based mixtures. The control mixtures were proportioned to achieve compressive strengths of 30, 40, 50 and 60MPa with slump values between 75 and 125 mm and served as a basis for comparison with the RCA concrete mixtures. The direct replacement mixtures were developed to investigate the effect that fully replacing (i.e., 100% replacement by volume) virgin coarse aggregate with RCA has on the fresh and hardened properties of the resulting concrete. The strength-based mixtures were developed to investigate the influence of aggregate properties on reinforcement bond in concrete having the same compressive strength. In addition, two separate experimental phases were carried out which had varying compressive strength ranges, different RCA sources, and different suppliers of the same type GU cement. Concrete properties such as slump, compressive strength, splitting tensile strength, modulus of elasticity, Poisson’s ratio, linear coefficient of thermal expansion (LCTE), modulus of rupture and fracture energy were all measured. In total, 48 beam-end specimens were tested that incorporated three bonded lengths (125, 375, and 450 mm) and four concrete compressive strengths (30, 40, 50 and 60 MPa). Based on the results of the aggregate testing it was found that concrete incorporating pre-soaked (i.e., fully saturated) RCA as a 100% replacement for natural aggregate had slump values between 22% and 75%, compressive strengths between 81% and 137%, splitting tensile strengths between 78% and 109%, modulus of elasticity values between 81% and 98%, LCTE values in the same range, flexural strengths between 85% and 136%, and fracture energies between 68% and 118%, of the equivalent control (natural aggregate) concrete mixture. Overall, reductions in bond strength between natural aggregate and RCA concrete ranged between 3 and 21%. The strength of coarse aggregate as quantified by the aggregate crushing value (ACV) was found to be the most significant aggregate property for influencing bond strength. A regression model (based on the beam-end specimens test results) was developed to extrapolate the experimental development lengths as a function of f’c1/4 and ACV. The model, while not intended for use as a design equation, predicted that the required development lengths for the RCA concrete tested as part of this research study were up to 9% longer as compared to the natural aggregate concrete. A detailed flowchart of the various inter-relationships between aggregate properties, concrete properties and reinforced concrete bond properties was compiled based on the results of this research. A comprehensive guideline for use of RCA in concrete was developed based on the findings of this research. It includes a systematic decision tree approach for assessing whether a particular RCA source can be categorized into one of three performance classes. The range of allowable applications of a concrete which incorporates the RCA source as replacement of natural coarse aggregate will depend on the RCA performance class.

This study adopts Markov-switching ARCH model proposed by Hamilton and Susmel (1994) to explore the behavior of credit spreads for different bond ratings. Specifically, this paper examines the properties of credit spreads and the co-movements of spreads among different durations and credit ratings. The consideration of the population makes the outcome more precise. The contribution of this study is to add to the investors a knowledge as to the credit spread behavior and help them understand the lower rating or longer maturity bonds by the observation of the investment-graded bonds while there are more risks and uncertainties conceal in these high yield bonds or D-rated bonds. The conclusion of this paper may help investors understand credit risk management and thus build appropriate portfolios.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23728号 / 理博第4818号 / 新制||理||1689(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 吉村 一良, 教授 竹腰 清乃理 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM