Im Turmbau von Windenergieanlagen haben sich insbesondere bei großen Turmhöhen Beton‐ oder Hybridtürme etabliert, welche durch ihre bessere Transportfähigkeit die traditionellen Stahltürme abgelöst haben. Speziell die Fertigteilbauweise bringt jedoch aufgrund der erforderlichen Fugen Fragestellungen mit sich, welche durch die derzeitigen Modelle und Berechnungsansätze nicht zufriedenstellend gelöst werden. Bei der Ausbildung sogenannter Trockenfugen (Horizontalfugen) zwischen den Segmenten erfolgt die Kraftübertragung der Querkräfte und Torsionsmomente ausschließlich über die Reibung in der Fuge, wobei der Reibwiderstand durch die externe Vorspannung und den Reibbeiwert erzeugt wird. Die Querkrafttragfähigkeit in der Fuge ermittelt sich über einen linearen Ansatz, wonach die zulässige Querkraft der Vorspannkraft, multipliziert mit dem Reibbeiwert, entspricht. Für die Übertragung der Torsionsmomente erfolgt die Berechnung nach den bekannten Torsionstheorien nach Bredt und Saint‐Venant, wonach die Fuge, solange diese überdrückt ist, ein sehr großes Torsionsmoment übertragen kann. Kommt es jedoch im Grenzzustand der Tragfähigkeit zum Aufklaffen der Fuge, fällt das zulässige Moment um ein Vielfaches ab und wird somit zu einem Grenzkriterium in der Bemessung des Turms. Nach aktuellen Untersuchungen beschreiben diese Ansätze das Trag‐ und Verformungsverhalten einer solchen Fuge unzutreffend, woraus sich in der Bemessung sowohl ein Unsicherheitsbereich, aber auch ein sehr großes ungenutztes Potenzial ergibt.

No abstract

The technology of prestressing concrete structures has been a well‐established field in structural engineering since the last century. Nowadays, new materials developed for reinforcing concrete structures, such as fibre‐reinforced polymers (FRPs), open further possibilities for engineers. FRP tendons are more and more often investigated as an efficient and suitable material for prestressing, and there are already some field applications of this technology. This paper aims to describe the current state of knowledge in the field of prestressing with FRP tendons, with regard to available materials, developed anchorages and undertaken investigations. Researches conducted in areas such as bond strength, ductility, durability, long‐term behavior, and high‐temperature resistance are described and summarized. Our goal was to provide a summary of what has been achieved so far in the research field of prestressing concrete structures with FRP tendons; however, field applications and standardization issues are not part of this review.

The quality of strain measurements using distributed fiber optic sensors (DFOS) depends largely on the bond between the host material and the optical fiber. Experimental investigations were carried out to test the suitability of five different DFOS types for crack monitoring. The DFOS were subsequently bonded to two 4 m long reinforced concrete (RC) beams, so that the influence of the application technique could be evaluated. DFOS measurements were verified by digital image correlation (DIC) and electrical strain gauges (SGs). For the different DFOS types, clear differences in the measured strain curves and determined crack widths were observed. The focus was on two robust DFOS, which can be deployed on construction sites. Compared to the layered sensing cable, a monolithic DFOS showed a clear strain distribution with pronounced strain peaks even for closely spaced cracks. The crack widths obtained by integrating the strain curves showed high agreement with DIC measurements.

For nearly a decade since the mapping of the multiple endocrine neoplasia type 1 (MEN1) locus to 11q13 and the suggestion that it is a tumour suppressor gene, efforts have been made to identify the gene responsible for this familial cancer syndrome. Recently, we have identified the MEN1 gene by the positional cloning approach. This effort involved construction of a 2.8-Mb physical map (D11S480-D11S913) based primarily on a bacterial clone contig. Using these resources, 20 new polymorphic markers were isolated which helped to reduce the interval for candidate genes by haplotype analysis in families and by loss of heterozygosity (LOH) studies in approximately 200 tumours, utilizing laser-assisted microdissection to obtain tumour cells with minimal or no admixture by normal cells. The interval was narrowed by LOH to only 300 kb, and nearly 20 new transcripts that map to this region of 11q13 were isolated and characterized. One of the transcripts was found by dideoxyfingerprinting and cycle sequencing to harbour deleterious germline mutations in affected individuals from MEN-1 kindreds and therefore identified as the MEN1 gene. The type of germline mutations and the identification of mutations in sporadic tumours support the Knudson's two-hit model of tumorigenesis for MEN-1. Efforts are being made to identify the function of the MEN1 gene-encoded protein, menin, and to study its role in tumorigenesis.