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Die Ermittlung der Tragfähigkeit und der Lebensdauer von Kopfbolzendübeln in hochzyklisch belasteten Verbundtragwerken erfolgt in den derzeitigen nationalen und europäischen Regelwerken mit getrennten Nachweisen in den Grenzzuständen der Tragfähigkeit, der Ermüdung und der Gebrauchstauglichkeit. Ein möglicher Einfluß aus der Vorschädigung infolge der Ermüdungsbeanspruchung wird beim Nachweis des Grenzzustandes der Tragfähigkeit unter γ‐fachen Einwirkungen nicht berücksichtigt. Es wird über neue Forschungsergebnisse und umfangreiche experimentelle Untersuchungen berichtet, die bei einer hochzyklischen Belastung den Einfluß des Rißwachstums durch den Dübelfuß und die lokale Schädigung des Betons vor dem Dübel auf die Tragfähigkeit berücksichtigen. Im Mittelpunkt stehen neue Berechnungsmodelle zur Vorhersage der Lebensdauer und der statischen Resttragfähigkeit ermüdungsbeanspruchter Kopfbolzendübel sowie die Entwicklung einer verbesserten Schadensakkumulationshypothese. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In recent years, FRCM systems have become a preferred strengthening system in reinforced concrete structures together with masonry structures. The most important factor in the choice of FRCM as a strengthening system is its compatibility with concrete or masonry substrates. In addition, high fire resistance is an important factor in their preference. The components of FRCM composites are known to have high durability separately. However, the durability of composites, composed of a combination of fabric and matrices is still a matter of no detailed reported knowledge. In this experimental study, the durability properties of FRCM composites with lime matrix reinforced with glass and glass-polypropylene hybrid fabrics were investigated. Composite samples were subjected to tensile and bending tests before and after freeze thaw cycles. Load-deformation relations were obtained. As a result of the experimental study, the following results can be drawn: Following freeze thaw cycles, reduction in the bending and tensile performances of the biaxial glass fabric reinforced composite samples as well as matrix samples were obtained. A significant decrease of deformation capability was determined for biaxial glass fabric reinforced matrices and plain matrix.

In current German and international standards for composite structures of steel and concrete, the determination of the ultimate load capacity and the fatigue life of headed shear studs is carried out with separate and independent verifications at the ultimate, serviceability and fatigue limit states. The fatigue resistance is verified in a similar way to steel structures, based on a nominal stresses concept and linear damage accumulation according to Palmgren‐Miner. The effect of pre‐damage due to fatigue loading at both the ultimate and serviceability limit states is not considered. Because cyclic loading of headed shear studs leads to a decrease in the static strength of stud connectors, the assumptions for independent limit states are not given and the reliability index of steel‐concrete composite structures subjected to fatigue loading may fall below the target values in codes. This paper deals with the results of a comprehensive programme of experimental work with more than 90 standard EC4 push‐out test specimens and two full‐scale beam tests which consider the crack propagation through the stud foot and the local damage to the concrete surrounding the studs as relevant consequences of highcycle loading. Based on the results of the push‐out tests, new design methods were developed to predict the fatigue life and the residual strength of headed shear studs after high‐cycle loading. Considering the interaction between the local damage and the behaviour of the global structure, these research results were taken as the basis for simulating the cyclic behaviour of composite beams by means of a damage accumulation method.