Verbesserung der Ermüdungsfestigkeit höherfester Baustähle durch Anwendung der UIT‐Nachbehandlung

Enhancement of the fatigue strength of welded high strength steels by application of Ultrasonic Impact Treatment (UIT). According to the present state of the art welded high strength steels have the same fatigue strength as welded standard steels. For an effective application of high strength steels in constructions subjected to fatigue are therefore additional efforts necessary in order to improve the fatigue strength, for example by the application of post‐weld treatment methods. However up to the present it is not possible to apply the positive effects of these methods in the fatigue design of steel structures. Within this paper an experimental test program studying the effectiveness of the post‐weld treatment method “Ultrasonic Impact Treatment” (UIT) on the critical construction detail of the transverse stiffener is presented. The test program comprises small scale fatigue tests on the standard and high strength steel grades as well as full size girder fatigue tests. Based on experimental and numerical investigations recommendations for the fatigue design of welded structures treated by UIT are given.     

Tragverhalten von Kehlnahtverbindungen von höherfesten Feinkornbaustählen

Load Bearing behaviour of fillet weld connections of high‐strength fine grain steel. Latest investigations [1] have proved, that the load bearing capacity of fillet weld connections of thermomechanically rolled fine grain steel S 460 is underestimated in actual design codes [2], [3], [4]. In this article, a possibility of calculating the load bearing behaviour using FE programs is shown. Based on these calculations and the results of large scale tests, the influences of different production processes, different weld materials and the welding parameters on the load bearing capacity of fillet welds are rated.     

Zur Frage der Ermüdungsfestigkeit von Kopfbolzendübeln

Fatigue resistance of headed shear studs. The design concepts in current national and international standards for headed shear studs in composite structures under fatigue loads are based on the assumptions, that the ultimate shear resistance of headed shear studs and the load‐deflection behaviour under service loads are not affected by high cyclic loading up to the theoretical value of their life time. These assumptions do not represent the real behaviour of headed shear studs subjected to fatigue loading. The paper deals with the results of the project C8 within the scope of Collaborative Research Centre 398 funded by the German Research Foundation. Based on a comprehensive program of experimental investigations new damage models to describe the effect of high cyclic loading on the local behaviour of headed shear studs are developed. On this basis the interaction between the local damage at the studs and the global behaviour of composite beams is investigated.     

Einflüsse auf die Betoneigenschaften durch den Einsatz von PP‐Fasern zur Erhöhung der Brandbeständigkeit von WDI‐Innenschalen

Influences on the Characteristics of Concrete through the Application of Polypropylene Fibres to increase the Heat‐Resistance of water‐impermeable Inner Shells By adding 2 kg/m³ polypropylene fibres a spelling of the concrete for inner lining can be avoided reliably in tunnels even under the extreme condition of a fire. The fibres change the characteristics of concrete. The characteristics for an installation of reinforced inner shells especially are negatively influenced. In the article at hand the conclusions of lab experiments are explained. After a practical testing the concrete has been successfully employed at a construction site in Vienna. In addition, details for influencing factors that have to be observed are given.     

Schweißnahtnachbehandlung mit höherfrequenten Hämmerverfahren – Ermüdungsfestigkeit,Qualitätssicherung,Bemessung

Im Rahmen des Forschungsprojekts REFRESH wurden umfangreiche systematische Untersuchungen zur Ermüdungsfestigkeit mit höherfrequenten Hämmerverfahren nachbehandelter Schweißnähte durchgeführt. Die statistisch abgesicherten Ergebnisse belegen die hohe ermüdungsfestigkeitssteigernde Wirksamkeit der Verfahren und ermöglichten die Entwicklung eines experimentell abgesicherten Bemessungskonzeptes. Um die Anwendung überwachen zu können und die Behandlungsqualität sicherzustellen, wurde ein Qualitätssicherungssystem und ein Anforderungskatalog an das Fachpersonal erarbeitet. Die Zertifizierung der Verfahren erfolgt auf Basis eines gemeinsam von der Bundesanstalt für Materialforschung und ‐prüfung und der Versuchsanstalt für Stahl, Holz und Steine der Universität Karlsruhe erarbeiteten Zertifizierungssystems. Postweld treatment by high frequency hammer peening methods – fatigue resistance, quality control, design. In the range of the research project REFRESH comprehensive, systematic investigations regarding the fatigue resistance of welds treated with high frequency peening methods have been conducted. The statistically confirmed results prove the high beneficial effect of the methods and allowed to develop an experimentally verified design concept. In order to control the application quality and to ensure the desired effects a quality assurance system and a catalogue of requirements for specialists has been worked out. The certification of the methods is performed on the base of a common certification system, developed by the German Federal Institute for Material Research and Testing (BAM) and the Research Centre for Steel, Timber and Masonry, University of Karlsruhe.     

Höherfrequente Hämmerverfahren – Ursachen der Steigerung der Ermüdungsfestigkeit und Nachweismodell

Der Einsatz von Schweißnahtnachbehandlungsverfahren zur Optimierung wechselnd beanspruchter Stahlkonstruktionen in Hinblick auf deren Lebensdauerverlängerung oder eine Reduzierung des Konstruktionsgewichts wurde in den letzten Jahren verstärkt untersucht. Dabei erwiesen sich höherfrequente Hämmermethoden als besonders wirkungsvoll zur Steigerung der Ermüdungsfestigkeit. Der vorliegende Artikel zeigt die Potentiale der Verfahren auf und belegt deren Einfluss auf das Rissinitiierungs‐ und Rissfortschrittsverhalten von Schweißnähten. Anhand eines entwickelten Bemessungsmodells wird eine Möglichkeit der rechnerischen Erfassung der positiven Wirksamkeit der Verfahren dargelegt. Reasons and calculation of the improved fatigue life of welds treated with high frequency peening methods. The application of post weld treatment methods in order to optimize fatigue loaded steel structures in view of an extension of their service life or a reduction of the construction weight has been studied intensively in the last years. High frequency peening methods proved to be extreme effectively in order to increase the fatigue strength. The following article shows the potentials of the methods and proves their influence on the crack initiation and crack propagation behaviour of welds. With help of a developed design procedure the possibility of respecting the positive effect on the fatigue strength during the design is provided.     

Beitrag zur Ermüdungsfestigkeit von Schienenschweißnähten bei Kranbahnen

Contribution to characteristic fatigue strength of rail welds at crane runways. The rail welds of today's crane runways usually made of hot rolled sections for light and moderate crane service form one important critical detail of the wheel load application in terms of fatigue. The characteristic fatigue strengths and the definition of damage accumulation under combined loading of the national and European design codes are compared and critically discussed. Moreover, an overview of the few, available test data of large‐scale specimens on the fatigue behaviour under wheel load application is given, and own girder tests are presented.     

Zur Bemessung von Lochleisten als duktile Verbundmittel in Verbundträgern aus höherfesten Materialien

Im Rahmen eines gemeinsamen FuE‐Projekts der HOCHTIEF Construction AG und ArcelorMittal Belval & Differdange S. A. wurden umfangreiche experimentelle und theoretische Untersuchungen an Lochleisten als duktiles Verbundmittel durchgeführt. Ziel der Untersuchung ist die Entwicklung technisch hochwertiger und wirtschaftlicher Verbundbauteile aus höherfesten Werkstoffen (z. B. Beton C50/60 und Stahl S460), [1] bis [4]. Hierbei wurden insbesondere das Tragverhalten, die Traglast, die Duktilität und die Dauerfestigkeit von unterschiedlichen Lochleistenformen sowie das Gesamttragverhalten von Verbundbauteilen mit Lochleisten untersucht. Aufbauend auf den in Versuchen gewonnenen Erkenntnisse wurden Bemessungskonzepte für Lochleisten als Verbundmittel in Verbundträgern aus höherfesten Materialien entwickelt. Design of aperture plates as ductile shear connectors for composite beams with high strength materials. Within a joint research project of HOCHTIEF Construction AG and ArcelorMittal Belval & Differdange S. A. various experimental and theoretical investigations in aperture plates, as ductile shear connector for composite members have been carried out. The aim of the research has been to develop technically advanced and economic composite members with the application of high strength materials (e.g. steel S460 and concrete C50/60). The main focus of the research has been put on the load bearing behaviour, ultimate bearing capacity, ductility and fatigue resistance of different types of aperture plates geometries as well as the related overall bearing performance of the composite members with the application of these plates as shear connectors. Based on the conclusions from the experimental test results, design concepts for aperture plates as shear connectors for composite beams with the application of high strength materials have been developed.     

Untersuchungen zum Ermüdungsverhalten von hochfesten Stählen im Rahmen von LIFTHIGH

Investigations on the fatigue behaviour of high‐strength steels in the scope of LIFTHIGH. In the research project P 512 of FOSTA, different kinds of longitudinal attachments and five variants of butt welded plates made of high strength steel have been already investigated to enlarge the available recommendations. The obtained results provide a basis for further going investigations within the European ECSC‐project LIFTHIGH – “Efficient Lifting Equipment With Extra High Strength Steel”. In this project longitudinal attachments made of fine grain high strength steel with post weld treatment such as TIG‐dressed welds and ground welds have been investigated. For a more precise evaluation of the different variants of butt welded plates made of S 960 QL, these details have been also produced and tested made of S 690 M an S 1100 QL. In addition transverse attachments have been incorporated in the experimental programme.     

Reduktion der Wanddicken bei Tragtürmen von Windenergieanlagen durch den Einsatz höherfester Stähle

Reduction of plate thickness of wind energy converters made by high strength steels. The design of wind energy converters is significantly defined by the fatigue strength of critical notch details, especially welded joints. The usage of high strength steels leads to no economical benefit because the fatigue strength of welded notch details are defined in design rules independently from the yield strength. The application of post weld treatment methods may increase the fatigue strength of these details significantly. Investigations on high frequency peening methods prove that a doubling of the fatigue strength can be achieved for steel grade S 690. An example of a connection detail is presented where it can be shown that by the application of the investigated methods together with a steel S 690 Q the plate thickness can be reduced to 45%.