Neue Untersuchungen zum Ermüdungsverhalten von Kopfbolzendübeln

New investigations on the fatigue behaviour of headed shear studs. In current national and international standards the determination of the ultimate load capacity and the fatigue life of headed shear studs subjected to high‐cycle loading take place with separate and independent verifications at the ultimate limit state, serviceability limit state and fatigue limit state, respectively. The effect of predamage due to fatigue loading is not considered. The paper deals with new research based on a comprehensive program of experimental investigations which considers the crack propagation through the stud foot and the local damage of concrete surrounding the stud as relevant consequences of high cycle loading. New design methods to predict the fatigue life and the residual strength after high cycle loading as well as the development of an improved damage accumulation hypothesis are the main subjects of this paper.     

Grout‐Verbindungen von Monopile‐Gründungsstrukturen – Trag‐ und Ermüdungsverhalten

Grouted Joint Connections of Monopile Support Structures – Structural and Fatigue Behaviour. This paper summarises the state of the art for grouted connections of support structures of Offshore Wind Energy Converters (OWECs). Results of numerical and experimental investigations of small and large scale tests of grouted joints which have been carried out within the research project “ForWind – TP V: Fatigue Assessment of Support Structures of Offshore Wind Energy Conversion Systems” at the Institute for Steel Construction, Leibniz Universität Hannover are presented. Furthermore the results of the numerical and experimental investigations are used for an exemplary calculation of a grouted joint connection of an OWEC located in the Baltic Sea. Besides the analysis of grouted joints with plain pipes the effects of an increased mechanical interlock due to shear keys on the fatigue design of grouted connections is demonstrated and fatigue classes for shear keys are presented.     

Neue Untersuchungen zum Ermüdungsverhalten von Verbundträgern aus hochfesten Werkstoffen mit Kopfbolzendübeln und Puzzleleiste

New investigations on the fatigue behavior of composite beams made of high strength materials with two different kinds of shear connection. Scope of the research project [1] was the investigation of the fatigue behaviour of different shear connectors (headed studs ∅︁ 22 mm and puzzle‐strip) together with high strength materials (steel S 460 and concrete C 80/95). For both types of shear connectors cyclic push‐out‐tests as well as large scale experiments with composite beams under cyclic loading have been carried out. The headed studs failed after a mean lifetime of 2,3 million cycles, the residual strength after 1 million cycles was reduced by about 25% compared to the static push‐out strength. In the puzzle‐strip cracks were visible, however, the residual strength was not reduced at all. Further, the push‐out tests with headed studs show a slight improvement of the fatigue behaviour using high strongth concrete (HSC). The cyclic beam tests show that the prediction of the fatigue according to EC 4 – as for specimens with normal strength materials – is not satisfactory. A good prediction of the crack propagation (and fatigue) can rather be achieved by using a crack‐slip‐relationship [6]. Also for shear joints with continuous puzzle‐strips a threshold value can be determined by fracture mechanics to which no further crack propagation (theoretically) occurs. However, this depends on the state of the cutting‐induced heat treatment of the surface material and on the surface roughness.     

Finite‐Elemente‐Berechnungen zum Trag‐ und Verformungsverhalten von Kopfbolzendübeln

Finite Element Calculation of load bearing and deformation behavior of headed studs. In the scope of numerical simulations the composite joint between concrete slab and steel girder is represented by springs or interface elements considering bi‐linear as well as tri‐linear shear‐slip behavior. This method is established to determine the global load bearing behavior for any degree of shear connection. In order to illustrate the concentrated load introduction a three‐dimensional modeling of the shear connector is required. This paper describes a three‐dimensional nonlinear finite element model, which offers the possibility to investigate the local load bearing and deformation behavior of headed studs under shear load. It has been calibrated on shear tests performed by the Institute for Structural Concrete, of University of Technology, Aachen. On the basis of parametrical studies the influence of the concrete strength, the length of the stud as well as the formation of the welded collar have been determined. Furthermore, the limits of the simulation of shear tests are detected.