Bewertung der Ermüdungsfestigkeit von Baustrukturen in Offshore‐Windenergie‐Anlagen

Fatigue assessment of support structures for offshore wind energy converters. The structure of wind energy converters secures a reliable energy production. Hence an adequate reliability of the structure and additionally permanent assessment and maintenance is required. Within this paper methods for the assessment of the important damage mechanism fatigue in combination with monitoring of the fatigue reliability utilizing damage indicators are proposed. These methods comprise structural system, material degradation and probabilistic models as well as monitoring data of an offshore wind energy converter prototype. The structural reliability of the structure as designed is calculated based on an overall dynamic analysis using a SN‐approach. Herewith fatigue sensitive components are identified. Damage indicators for monitoring the fatigue reliability based on damage equivalent strains are presented.     

Sanierung eines PCE-Schadens in einem makroskopisch oxischen Grundwasserleiter durch Stimulation anaerober dehalogenierender Bakterien

Grundwasser - Eine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem...     

Inorganic carbon limitations on nitrification: experimental assessment and modelling

Nitrification is a two-step process that involves two different biomass populations: ammonia oxidising biomass (AOB) and nitrite oxidising biomass (NOB). Both populations are autotrophic (i.e. their carbon source is inorganic). Therefore, a deficit of this substrate should result in a decrease of the process rate. Recent technology advances such as the SHARON process have brought new scenarios in biological nitrogen removal where these limitations should be considered. Hence, this work examines the inorganic carbon limitation using respirometric and titrimetric techniques. For this aim, the nitrification rate was measured at different total inorganic carbon (TIC) concentrations. The experimental results obtained show that AOB was limited at TIC concentrations lower than 3mmol CL(-1). At the same time, no carbon source limitation for NOB was observed in spite of the low TIC concentrations attained (lower than 0.1mmol CL(-1)). The AOB limitation could be successfully modelled using Monod, Tessier and sigmoidal kinetics. The best fit was obtained with sigmoidal kinetics. However, unexpected biomass activity (oxygen consumption) was observed despite a very low TIC concentration (lower than 0.1mmol CL(-1)).     

Entwurf und Konstruktion der Egg‐Graben Brücke

Aufgrund der hohen Erhaltungskosten von Brücken gibt es mittlerweile unterschiedliche Ansätze, um die Dauerhaftigkeit zu erhöhen. Vorgespannte Brücken ohne Betonstahl stellen hierfür einen neuen Ansatz dar. Zur Erforschung des Tragverhaltens solcher Strukturen wurde ein Forschungsprojekt gestartet und Großversuche durchgeführt. Die Landesbaudirektion Salzburg war von dieser innovativen Idee überzeugt und hat deshalb die Technologie beim Bau der Egg‐Graben Brücke ausgeschrieben. Die Egg‐Graben Brücke ist eine im Grundriss gekrümmte Bogenbrücke mit einer Länge von 50 m. Nach einer Bauzeit von 18 Monaten erfolgte im November 2009 die Freigabe für den Verkehr. Der vorliegende Aufsatz beschreibt die Technologie, den Entwurf sowie die beim Bau der Brücke gesammelte Erfahrung. Design and Construction of the Egg‐Graben Bridge Due to the high maintenance costs of bridges, there are now various approaches to enhance the durability. Post tensioned bridges without steel reinforcement represent one of these approaches. To investigate the structural behaviour of such constructions, a research project was started and large‐scale tests were carried out. The government of the province of Salzburg could be convinced of this innovative technology and tendered out the method for the construction of the Egg‐Graben Bridge. For the arch bridge, which is curved in plan, the superstructure is prestressed without using further steel reinforcement. After a construction period of 18 months the bridge was opened to traffic in November 2009. The paper describes the technology, the design and the experience gained from the construction of the bridge.     

Risikobasierter Ansatz zur Bewertung der Robustheit von Bauwerken

Ziel des vorliegenden Beitrages ist es, einen Überblick über die aktuellen Entwicklungen im Bereich der Bewertung und der Quantifizierung der Robustheit von Bauwerken zu geben. In diesem Sinne ist eine Zusammenstellung von Ansätzen und Ergebnissen aktueller Veröffentlichungen enthalten. Ein umfassender entscheidungstheoretischer Ansatz für die Berechnung und das Management der Robustheit wird vorgestellt. Dieser beinhaltet die Definition der Robustheit als eine Qualität eines Systems, welches das Bauwerk beinhaltet, d. h. eine Qualität, die auf der Grundlage einer Risikoanalyse bewertet werden kann. Um eine umfassende Risikoanalyse zu ermöglichen, wird ein szenarienbasierter Modellansatz eingeführt, welcher zwei Arten von Konsequenzen im System unterscheidet: direkte Konsequenzen (in Verbindung mit Schäden einzelner Komponenten des Systems) und indirekte Konsequenzen (in Verbindung mit einem Versagen des Systems). Die Definition des Systems spielt deshalb für die Risikoanalyse eine wichtige Rolle, und es wird diskutiert, wie die Robustheit für verschiedene Definitionen zu unterschiedlichen Ergebnissen und Erkenntnissen im Sinne des Managements der Integrität des Bauwerks im gesamten Lebenszyklus unter Berücksichtigung seiner Funktionalität führt. Weiterhin werden wichtige Aspekte der Standardisierung der Robustheitsanalyse, wie auch Anforderungen an die Robustheit, diskutiert und Vorschläge zum Umgang mit diesen Aspekten unterbreitet. Auf der Grundlage der vorgestellten Ansätze zur Berechnung der Robustheit eines Bauwerks wird beschrieben, wie Entscheidungen in Bezug auf den Entwurf, die Zustandsbewertung, auf Inspektionen und Wartung sowie in Bezug auf die Überwachung von Bauwerken, in Hinblick auf das Management der Risiken in allen Phasen des Lebenszyklus, optimiert werden können. Risk based approach for the assessment of the robustness of structures. The present paper serves as an overview of recent developments by the author on the assessment and quantification of robustness of structures; the paper aims in this sense not to present any new results but collects approaches and results from previous publications. A general decision theoretical approach to the assessment and management of structural robustness is outlined. Structural robustness is introduced as a quality of the system comprising the structure; a quality which can be assessed by means of risk assessments. To facilitate an appropriate risk assessment for structural systems a scenario based model approach is outlined which differentiates consequences into two different types: direct (related to damages to individual components) and indirect (related to collapse failures). The definition of the “structural system” thus plays an important role in the risk assessment and it is discussed how the robustness assessed according to different definitions of the structural system will lead to different results and insights of relevance for the lifecycle management of the structural integrity. Furthermore, the important aspects of standardization of robustness assessments as well as requirements to robustness are discussed and suggestions for the treatment of these are proposed. Based on the presented approach to the assessment of structural robustness it is outlined how decisions on design, condition assessment, inspection and maintenance as well as monitoring activities for structures can be optimized for the purpose of managing structural risks over all phases of the life‐cycle of structures.     

Suitability of urban wastes for crop production in Zaria,northern Nigeria: bioavailability and geochemical fractions of potentially toxic elements

A savannah soil amended with two urban wastes and planted with sorghum (Sorghum bicolor) in a pot experiment was evaluated for chemical forms and phytoavailability of Cr, Ni and Pb. The metals were partitioned into seven operationally defined chemical fractions: mobile (F1), easily mobilisable (F2), occluded in Mn oxides (F3), organically bound (F4), occluded in amorphous Fe oxides (FeOx_am, F5), occluded in crystalline Fe oxides (FeOx_c, F6), and residual (F7). Although the application of the urban wastes increased the total concentrations of the metals in the soil, there were no corresponding increases in Cr and Ni uptake by sorghum except for Pb uptake. Waste application increased mobile Ni (F1) but decreased the residual form (F7). The organically bound Pb (F4) was increased at the expense of residual Pb (F7). With respect to Cr, waste application increased Cr form occluded in non-crystalline Fe oxides (F5) in the soil. Bioassay of the test crop indicated that the uptake of Pb by sorghum (Y-Pb) correlated significantly with Pb occluded in non-crystalline and crystalline Fe oxides (F5 and F6). Since a single application of urban wastes to this savannah soil significantly increased Pb uptake by sorghum, the consequences of long-term applications under urban and peri-urban agriculture (UPA) should be of great concern; particularly with respect to children’s exposure to Pb through consumption of food and vegetables.     

INVESTIGATION OF THE TOOL WEAR AND SURFACE FINISH IN LOW-SPEED MILLING OF STAINLESS STEEL UNDER FLOOD AND MIST LUBRICATION

This paper examines the performance of AlN/TiN coated carbide tool during milling of STAVAX® (modified AISI 420 stainless steel) at a low speed of 50 m/min under conventional flood and mist lubrication. Abrasion, chipping, fracture resulting in the formation of crater and catastrophic failure are the wear mechanisms encountered during machining under flood lubrication. The flank wear, and the likeliness of the cutting tool to fracture, chip and fail prematurely increased with an increase in the hardness of the workpiece and a reduction in the helix angle of the tool. Small quantity of mineral oil sprayed in mist form was effective in reducing the flank wear and severity of abrasion wear, and preventing the formation of crater and the occurrence of catastrophic failure. In milling 35 and 55 HRC-STAVAX® using a feed rate of 0.4 mm/tooth and a depth of cut of 0.2 mm under mist lubrication, the cutting edge of the 25° and 40° helix angle tools only suffered small-scale edge chipping and abrasive wear throughout the entire duration of testing. The influence of the ductility of the workpiece on the surface finish and the effectiveness of mist lubricant in improving the surface finish are also discussed.     

Functional cell-surface display of a lipase-specific chaperone

Lipases are important enzymes in biotechnology. Extracellular bacterial lipases from Pseudomonads and related species require the assistance of specific chaperones, designated "Lif" proteins (lipase specific foldases). Lifs, a unique family of steric chaperones, are anchored to the periplasmic side of the inner membrane where they convert lipases into their active conformation. We have previously shown that the autotransporter protein EstA from P. aeruginosa can be used to direct a variety of proteins to the cell surface of Escherichia coli. Here we demonstrate for the first time the functional cell-surface display of the Lif chaperone and FACS (fluorescence-activated cell sorting)-based analysis of bacterial cells that carried foldase-lipase complexes. The model Lif protein, LipH from P. aeruginosa, was displayed at the surface of E. coli cells. Surface exposed LipH was functional and efficiently refolded chemically denatured lipase. The foldase autodisplay system reported here can be used for a variety of applications including the ultrahigh-throughput screening of large libraries of foldase variants generated by directed evolution.     

Evaluation of the corrosion resistance of Ni-Co-B coatings in simulated PEMFC environment

The corrosion resistance behavior of Ni-Co-B coated carbon steel, Al 6061 alloy and 304 stainless steel was evaluated in simulated proton exchange membrane fuel cell (PEMFC) environment. The phase structure of the NiCoB based alloy was determined by Rietveld analysis. The PEMFC environment was constituted of 0.5 M H₂SO₄ at 60 °C and the evaluation techniques employed included potentiodynamic polarization, linear polarization resistance, open circuit potential measurements and electrochemical impedance spectroscopy. The results showed that in all cases the corrosion resistance of the Ni-Co-B coating was higher than that of the uncoated alloys; about two orders of magnitude with respect to carbon steel and an order of magnitude compared to 304 stainless steel. Except for the uncoated 304 type stainless steel, the polarization curves for the coated specimens did not exhibit a passive region but only anodic dissolution. The corrosion potential value, E_corr, was always nobler for the coated samples than for the uncoated specimens. This was true for the stainless steel in the passive region, but in the active state for the carbon steel and Al 6061 alloy. The corrosion of the underlying alloy occurred due to filtering of the solution through coating defects like microcracks, pinholes, etc. During the filtering process the E_corr value of the coating decreased slowly until it reached a steady state value, close to the E_corr value of the underlying alloy.