Investigations on welded I-beams of normal and high-strength structural steel: Extension of capacity design concepts by implementing welding simulation solutions

Im Stahlbau werden häufig Schweißträger eingesetzt. Als Profilform ist die des I-Trägers am weitesten verbreitet. Die Fertigung dieser Querschnitte erfolgt heute überwiegend vollmechanisiert im Werk durch z.B. Metall-Aktivgas-Schweißen. Dabei bewirkt der Schweißvorgang stets auch Eigenspannungen und Verformungen im Bauteil. Diese sogenannten Schweißimperfektionen zusammen mit weiteren Fertigungstoleranzen überlagern sich im Bauteileinsatz mit Lastspannungen und bewirken dadurch eine Absenkung der Tragfähigkeit. Die Erfassung dieser Einflüsse kann direkt im Rahmen einer vollständig nichtlineareren, sogenannten GMNIA-Berechnung erfolgen. Diesbezüglich sind besonders mit der Annahme der Eigenspannungen in Trägern aktuell noch große Unsicherheiten verbunden. Zur direkten Berücksichtigung von Eigenspannungen kann auf verschiedene vereinfachte Eigenspannungsmodelle aus der Literatur zurückgegriffen werden. Diese basieren größtenteils auf rein geometrischen Festlegungen ohne Berücksichtigung von Fertigungsrandbedingungen oder der Stahlgüte. Nichtsdestotrotz haben sich diese einfachen Modelle, auch mangels des Fehlens aktuellerer Forschungsergebnisse, für numerische Berechnungen im Stahlbau bis zuletzt durchgesetzt. Des Weiteren bestehen heute Möglichkeiten, eine numerische Schweißstruktursimulation zur Ermittlung der Eigenspannungen in Schweißträgern durchzuführen. Auch die vereinfachten Schweißsimulationsmodelle zur Berechnung großer Bauteile haben sich in den letzten Jahren stetig weiterentwickelt. Im Stahlbau erfolgten bisher jedoch kaum Anwendungen dieser Methoden. Ein Schwerpunkt dieser Arbeit liegt deshalb in der Untersuchung von Methoden der Schweißsimulation im Hinblick auf eine Anwendung an Schweißträgern und hier im Speziellen an geschweißten I-Trägern. Im Ergebnis sollte ein numerisch-basierter, einfacher Ansatzes zur direkten Abbildung des Schweißeinflusses in Tragfähigkeitsberechnungen bereitgestellt werden. Mit einem solchen vereinfachten Schweißsimulationsmodell können zudem neben den Schweißeigenspannungen auch die Schweißverformungen berechnet werden. Der Einfluss des Fertigungsprozesses kann dadurch viel genauer in die Bemessung einbezogen werden. Ausgangspunkt der Untersuchungen bildeten Eigenspannungsmessungen an konventionell geschweißten I-Trägern aus normal- und hochfesten Baustählen. Anschließend wurden diese durch numerische Schweißstruktursimulationen ergänzt. Danach erfolgte darauf aufbauend die Ableitung eines vereinfachten, numerischen Berechnungsmodells zur weiteren Berücksichtigung von Eigenspannungen in nichtlinearen Tragfähigkeitsmodellen. Abschließend wurden vergleichende numerische Tragfähigkeitsanalysen durchgeführt und daraus Empfehlungen für eine bessere Erfassung des Schweiß- und Materialeinflusses in der Tragfähigkeitsberechnung abgeleitet.In steel construction, welded beams are often used. As a profile shape, the I-section is most common. Their manufacture is typically done under workshop conditions by means of, e.g., fully mechanized metal active gas welding. The welding process always causes residual stresses and deformations in the component. In use, these so-called weld imperfections superimpose with loading stresses and other manufacturing tolerances, thereby causing a reduction of the ultimate load capacity. The consideration of such influencing parameters can be realized directly in scope of a fully nonlinear, so-called GMNIA-analysis. In this context, however, major uncertainties are still associated with the assumptions on residual stresses in welded beams. For a direct consideration of residual stresses, different simplified residual stress models from the literature are available. For the most part, these models are based on purely geometric specifications without consideration of the manufacturing conditions or the steel grade. Nevertheless, in the absence of recent research, these simple models have maintained for numerical calculations in steel construction until today. Moreover, it is nowadays possible to determine the residual stresses in welded beams numerically by means of a structural welding simulation. In this context, also simplified welding simulation models for the calculation of larger components have been steadily improved in recent years. In steel construction, however, hardly any application of such methods has been made so far. A particular focus of this work is therefore in the investigation of welding simulation methods with regard to their application on welded beams and particularly welded I-beams. The aim was thus to provide a numerically based, simple approach for the direct implementation of welding influences in load calculations. With such a simplified welding simulation model, in addition to the welding residual stresses, the weld deformations can also be calculated. Accordingly, the influence of the manufacturing process can be much more realistically included in the design. Starting point of the investigations were residual stress measurement on conventionally welded I-beams made of normal and high-strength structural steels. Subsequently, numerical structural welding simulations supplemented these. Thereupon, the development of a simplified numerical calculation model for the further consideration of residual stresses in nonlinear load capacity models took place. Finally, comparative numerical load capacity analyses were carried out to provide recommendations for a better determination of welding and material influences in these calculations

Residual Stress Influence on the Flexural Buckling of Welded I-Girders

Abstract. The nonlinear analysis became a common tool to precisely assess the load-bearing behavior of steel beam and column members. The failure level is significantly influenced by different types of imperfections, among geometric also structural imperfections (residual stresses). Here are still gaps in the knowledge. Nowadays, 3-D welding simulation developed to a level where it could provide reliable estimation of weld-induced distortion and residual stresses. Nevertheless, modelling and computational effort are still in a less practicable range. In this study a simplified procedure to implement residual welding stresses in continuous large scale members is proposed and the influence on the ultimate limit state of slender members in compression is evaluated for two common structural steel grades. The results showed significant improvements in the utilization of load bearing capacity compared with simplified design methods. The comparatively general approach in this study offers potential for future optimization. Introduction Welded I-girders are used in different applications in steel construction (e.g. industrial buildings, bridges) due to either dimensions and/or efficiency through customizable plate thicknesses, shapes and/or materials. Many standards, including Eurocode 3 (EC 3) permit the use of non-linear finite element analysis (FEA) for the design of steel structures. The development in this field allows performing "experiments" in computing software instead of the laboratory or expensive in-situ experiments. Still, the implementation of imperfections (including residual stresses due to weld manufacturing) remains a major task in the performance of such analysis. Unlike geometrical imperfections, residual stresses (RS) are not standardized. For that reason, more or less founded simplified distribution functions as proposed by the Swedish design code BSK 99 [1] are used. Limitations on the applicability of this model are not reported except for the plate thicknesses which should not exceed 40 mm. However, the influence of RS seemed somewhat overestimated for many cases comparing conventional structural steel S355 and S690QL. As in the EC 3, direct proportionality of the tensile and compressive RS (the latter are the main interest in this study) and the yield strength is assumed. An opposite effect was recently noticed i

Wild food plants of popular use in Sicily

In the present work the authors report the result of their food ethnobotanical researches, which have been carried out in Sicily during the last thirty years. Data concerning 188 wild species used in the traditional Sicilian cuisine are reported. The authors underline those species that are partially or completely unknown for their culinary use and they illustrate other species that local inhabitants suggested in the prevention or treatment of symptomatologies caused by a refined diet, poor in vegetables. These data want to contribute to avoid the loss of traditional knowledge on uses and recipes concerning wild food botanicals, and to encourage further studies for those species that have not yet been sufficiently researched in their food chemical and nutritional profile. These studies may also suggest new applications for a few botanicals in medico-nutritional fields. The work includes also a short review of the seaweeds and mushrooms traditionally gathered and consumed in Sicily

The role of design in the Lancashire cotton industry, 1900-1939

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