In the construction of pressurized conduits for hydropower plants, segmented bends (mitre bends) are widely used where ducts change direction. In practical applications, different approaches are used to consider the effects for exposed mitre bends in structural steel design. However, formulae for mitre bends embedded in rock or concrete for penstocks in underground installations have not been available so far.
In view of these restrictions on the calculation of underground mitre bends, the authors have developed analytical formulae for mitre bends embedded in rock by introducing terms for the elastic foundation of the rock mass to extend the classical differential equation for cylindrical shells. These formulae allow the whole local stress state in the bend to be calculated, in particular for the stress concentrations at the intersection of the mitre. The formulae were then validated by comparing them with the results of non-linear FE analyses.

After an interruption in the last decades of the 20th century, a number of pressure shafts with steel linings are presently being built or planned. These are frequently connected with the use of high-strength steel and with pumped storage plants. Larger dimensions and higher dynamic loads demand further research beyond the previous state of the art of the 1980s. An advanced concept by the second author, involving the geotechnical interaction of steel lining and rock mass, opens up new potential for the design of linings. This approach postulates ductility requirements for the steel used for liners which may be challenging for the field of modern high-strength steels. This paper provides an overview of the latest investigations dealing with the design of steel liners for internal pressure and the required properties for high-strength steel.

Owing to the increased use of high-strength steel (HSS) grades for steel linings in pressure shafts, the fatigue check becomes more and more critical for the proper design of such components. Eurocode 3, AD 2000 and IIW Recommendations do not consider the specific needs of liners with grouting openings (also called nipples) in combination with the higher steel grades. Therefore, a three-year research project of the Austrian Research Promotion Agency (FFG) was conducted to focus on investigating the fatigue strength of grouting nipples. This project saw a new design concept for steel linings with nipples established which takes into consideration the design concept of the Eurocode. The new findings regarding the fatigue strength of nipples were embedded in this concept.

The design and manufacture of factory-made self-supporting sandwich panels are covered by European standard EN 14509. Two new European Recommendations extend the potential applications for the standard, providing information about the influence of openings on the loadbearing behaviour of the panels and about the possibility of supporting beams, purlins and cladding rails against stability failures. The new European Recommendations were prepared by the European Joint Committee on Sandwich Constructions.

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Offshore wind energy development is lagging far behind the ambitious targets that the German government set at a time when an energy turnaround was propounded. Interest in using monopile foundations in a wider field is therefore growing because this type of foundation has proved to be the most economical solution. Their benefits lie in their simple design, favourable fabrication conditions with a considerable automation potential, and short installation times. Concepts and technologies are being developed to be able to produce and install monopile foundations for water depths down to at least 40 m. The necessary design concepts have to be adapted and extended for these requirements. Approaches are presented in this paper.

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Steels for structural applications for offshore oil and gas as well as offshore wind installations have to fulfil demanding requirements that exceed those for steels used in normal structural steelwork. The applicable steel grades must show an optimum trade-off between sufficient toughness and good strength properties, and at the same time allow easy fabrication, especially concerning weldability. Although sufficient toughness is of importance in order to avoid abrupt failure phenomena such as brittle fracture, good strength properties are necessary to minimize the dead weight of the structure and thus facilitate transport and erection process. The significance of good fabrication properties consist of two facets: good weldability results in easy processing procedures and thus cost-efficiency in fabrication; further, materials with good weldability exhibit a higher resistance to cracking phenomena in the heat affected zone and are therefore more “forgiving” when it comes to non-optimum welding conditions, which may occur during erection in harsh environments.
This steel has to be tailor-made at the steelworks, the aim being to produce it as cleanly as possible with specially adapted alloying concepts. To secure good properties in the half thickness portion of the plates, what is necessary for offshore plates, slabs and ingots have to show an accurate control of the mid thickness segregation. Additionally those plates need higher deformation ratios from slab to plate in order to get a dense structure also in the mid thickness by proper through thickness deformation. These materials are produced with various rolling and heat treatment processes, each chosen depending on the desired grade, thickness and weight of the final plate. The processes in use are normalization of the plates, thermomechanical controlled rolling and the quenching and tempering of the plates.
This article aims to support the designer or fabricator when selecting the steel grade by explaining the different production methods and the resulting properties with respect to the final use.

The effectiveness of high frequency mechanical impact treatment for increasing the fatigue strength of welded structures has been investigated in several research projects over recent years. Based on extensive fatigue test data, design recommendations have been developed by different institutions. Most recommendations provide fatigue strength improvement factors that consider beneficial effects due to the application of post weld treatment methods. Current design recommendations use fatigue test data derived from small-scale specimens, but only very few studies have focused on welded joints with a plate thickness > 15 mm. This paper reviews existing design recommendations and provides a database for welded joints with a plate thickness exceeding those already covered. Butt-welded joints, longitudinal attachments and transverse attachments are covered in particular. Based on the data evaluated, improvement factors are given for a stress ratio of R = 0.1 for axial loading.

Offshore piles have to withstand predominantly cyclic axial loads when they are installed in multi-pile configurations, as in jacket foundations. The dimensions of the pile are governed by both the internal capacity and the fatigue behaviour of the steel cross-section as well as by its external capacity in the pile-soil interaction. Owing to the large numbers of piled foundations required for current and future offshore wind farms, there is an urgent need to optimize the dimensions and related costs of single piles. With regard to the pile capacity, two major topics of research are the determination of possible capacity gains due to pile ageing effects and proper consideration of cyclic degradation. In order to investigate both effects, a large-scale testing facility has been constructed at the BAM TTS site in Horstwalde near Berlin. This open-air facility allows large tubular driven piles to be loaded cyclically in both tension and compression while studying the ageing effects by introducing delays between the testing campaigns. First results already show a moderate increase in pile capacity over time. Concerning the anticipated capacity degradation of cyclically loaded piles, preliminary results show an unexpected behaviour. Additional tests are currently being conducted for further clarification.

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On offshore wind turbine structures, grouted connections are widely used to connect the tower structure to the foundation while accommodating the unavoidable geometrical tolerances effectively. The long-term behaviour of high- and ultra-high-strength grouts primarily depends on the adequate strength and durability of the material plus the process reliability. The performance of the fresh and the hardened grout is influenced by many factors that have to be evaluated and considered individually with respect to the “rough” offshore conditions. Those factors are: mix performance and consistency, the ambient conditions at the place and time of use, the equipment for and stability of the mixing and casting processes, the length of casting time and the thermal and mechanical loads during the early stages. To ensure adequate long-term behaviour, a meaningful quality assurance system should be set up to cover both the materials and the processes. The article emphasises some fundamental experiences gained by the authors with numerous wind turbine parcs in the North Sea and the Baltic Sea.

In many cases, the design checks of grouted connections follow international standards which contain analytical design equations. In order to also obey mechanical consistency especially for structures with significant bending moment and to satisfy basic requirements according to the Eurocodes, different mechanical models have been used in practice in a number of cases. In this regard, non-linear finite element models as well as analysis with strut and tie models have been applied. Findings from these calculations as well as from experimental investigations on both the material and the structural level are analysed and compared. In conclusion, an improved design approach based on a strut model which is easy to handle is presented and exemplified.

Practical examples of modern architecture in the western hemisphere based on structural compositions of steel and glass have been presented several times in recent years. In doing so, their theoretical background has also been discussed. This paper focuses on the relevant architectural manifestations in Japan. Buildings for commercial and public use are the sole interest here - with special emphasis on the ultramodern character of their design. It is planned to consider infrastructure elements such as railway stations and airport structures in a future article.

In the design and making of complex architectural systems, sheet metal is still predominantly used as a cladding material. The objective here is to integrate innovative digital and analogue methodologies to develop a design system for a self-supporting lightweight structure entirely based on the use of sheet metal as a construction material.
A digital working methodology which is informed by fabrication techniques, material behavior and structural performance allows for a highly precise product and a coherent fabrication process.

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