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Stuttgart Mühlhausen, Germany

Engineering structures are subjected to continuous and increasing static and dynamic loads from artificial and natural environmental conditions (e.g. wind, traffic loads or wave loading on offshore wind turbine structures). Dynamic Loads can result in fatigue phenomena within the material concrete which are not totally explored even in their beginnings. Especially in the fields of Foundations for wind energy plants on- and offshore fatigue is a big problem. The Fatigue associated load combinations are mostly the decisive ones for design and dimensioning of the structure. The targets of the research are the development of a monitoring system for detecting the initiation or the early stage of a fatigue process in concrete and for the identification of the degree of deterioration in the concrete structure. The full scale model of a new type of gravity base foundation for offshore wind turbines in Cuxhaven projected by the Ed. Züblin AG is an optimal possibility to test the monitoring system within a concrete structure of real dimensions. The objective of this contribution is to provide a short review of concrete fatigue properties, to discuss, demonstrate and portray preliminary analyses results which are decisive for the final fatigue test layout at the Strabag gravity base foundation in Cuxhaven. The conduction of the fatigue tests at the gravity base foundation are planned in the beginning of the year 2013. Copyright © 2012 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

The design of foundations for offshore wind turbines has to be carried out against the backdrop of complex requirements resulting from the dynamic and cyclic loading of the structure and the subsoil caused by wind and waves, an expensive and weather-dependent offshore logistics for transport and installation, the desired minimisation of marine environmental effects and not least the specific features of authorizing procedures for offshore constructions. Moreover the structures have to preserve their functionality under challenging environmental conditions on the high seas for the entire lifetime of 20 or 25 years without the need of extensive inspection and maintenance works. This publication shows, in the view of designing engineers, which variety of aspects have to be taken into account during the design of foundations for offshore wind turbines despite the high demands on the economic efficiency of the foundation. Based on two examples, a gravity base foundation and a jacket foundation, the tasks linked to the foundation, which have to be solved during the several phases of a wind park project will be elucidated. Copyright © 2012 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

Laing D.,German Aerospace Center | Bahl C.,Ed. Zublin AG | Bauer T.,German Aerospace Center | Fiss M.,German Aerospace Center | And 2 more authors.
Proceedings of the IEEE

Solid sensible heat storage is an attractive option for high-temperature storage applications regarding investment and maintenance costs. Using concrete as solid storage material is most suitable, as it is easy to handle, the major aggregates are available all over the world, and there are no environmentally critical components. Long-term stability of concrete has been proven in oven experiments and through strength measurements up to 500 °C. Material parameters and storage performance have been validated in a 20-m 3 test module with more than 23 months of operation between 200 °C and 400 °C and more than 370 thermal cycles. For an up-scaled concrete storage design with 1100-MWh capacity in a modular setup for a 50 MW el parabolic trough power plant of the ANDASOL-type, about 50000 m 3 of concrete is required and the investment costs are approximately 38 million euro. The simulation of the annual electricity generation of a 50 MW el parabolic trough power plant with a 1100-MWh concrete storage illustrates that such plants can operate in southern Europe delivering about 3500 full load hours annually; about 30% of this electricity would be generated by the storage system. This number will increase further, when improved operation strategies are applied. Approaches for further cost reduction using heat transfer structures with high thermal conductivity inside the concrete are analyzed, leading to a 60% reduction in the number of heat exchanger pipes required. For implementation of the structures, the storage is build up of precast concrete blocks. © 2006 IEEE. Source

The paper presents the effect of additional groundwater flow forces that arise as a result of lowering of ground water behind a permeable retaining wall on the overall stability based on the sliding block method. This load situation cannot be solved with current computer programs for the overall stability analysis. The literature also deals with this topic very scarcely. Depending on the permeability of the underground, the groundwater table after drawdown may lie outside the active sliding wedge of a retaining wall, but within the sliding block to be considered for the overall stability of an anchored wall. In such case, the required anchor length is usually calculated in practice assuming a full groundwater table before drawdown. On the basis of practical examples (multi-anchored walls in a multi-layered underground), the article shows that the anchor length determined in such a way may not necessarily lie on the safe side. A concept to account for the groundwater flow forces in the overall stability (sliding block method) has been developed for anchored walls in the geotechnical department of the Zentrale Technik, Ed. Züblin AG. The approach is currently used in practical projects and is presented in detail in the following. Copyright © 2015 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin. Source

Laing D.,German Aerospace Center | Bahl C.,Ed. Zublin AG | Bauer T.,German Aerospace Center | Lehmann D.,German Aerospace Center | Steinmann W.-D.,German Aerospace Center
Solar Energy

Parabolic trough power plants with direct steam generation are a promising option for future cost reduction in comparison to the SEGS type technology. These new solar thermal power plants require innovative storage concepts, where the two-phase heat transfer fluid poses a major challenge. A three-part storage system is proposed where a phase change material (PCM) storage will be deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat, i.e. for preheating of water and superheating of steam. A storage system with a total storage capacity of approx. 1. MW. h is described, combining a PCM module and a concrete module. The storage modules have been constructed for testing in a DSG-test facility specially erected at a conventional power plant of Endesa in Carboneras (Spain). Commissioning of the storage system started in May 2010; testing under real steam conditions around 100. bar will begin in August 2010. © 2010 Elsevier Ltd. Source

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