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- Welded Joints, Welding Simulation, Engineering Models, Load Capacity Calculation (1)
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- Welded plate girders; Welding simulation; Residual welding stress; Load capacity (1)
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- Welding imperfections (1)
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- parameter study (1)
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Institute
Experimental research and integrated modelling with shell finite elements for sheet roof covering
(2010)
Thermovision - Entwicklung eines neuen Verfahrens zur Dehnungsanalyse beanspruchter Stahlbauteile
(2002)
Untersuchung des thermoplastischen Verhaltens verschiedener Baustoffe mit Hilfe der Thermovision
(2003)
Diskret gelagerte, axialbelastete und über den Auflagern längsversteifte Kreiszylinderschalen
(2004)
Kleben von Stahl
(2005)
This article presents experimental and numerical results of the fabrication of welded plate girders under workshop conditions. Main concerns are the prediction of imperfections with the aid of simulation tools and/or simplified engineering models. Their impact on the component design is evaluated in a case study. Special focus is put on the effect of residual welding stress. For this, different simplified distributions are compared with results from welding simulation. The findings confirm the thesis that present recommendations on the implementation of weld-induced imperfections must be rated conservative. This suggests that it is necessary to establish new models. Guidance on future problems in this context will be given.
Beim Aufbau großer Stahlstrukturen im Brücken- oder Stahlhochbau wird heute vermehrt auf modulare Fabrikfertigung gesetzt. Ein Fügen dieser Module auf der Baustelle zu einer Gesamtstruktur ist aber weiterhin notwendig. Als Fügeverfahren wird hier häufig das MAG-Mehrlagenschweißen eingesetzt. Gerade an dicken Blechen stellen Baustellenschweißungen nicht nur besondere Anforderungen an den ausführenden Betrieb, die Bauleitung und Bauüberwachung, sondern auch an den Konstrukteur. Wichtig für den Konstrukteur ist die Kenntnis der sich durch Schweißungen einstellenden Schrumpfung der Bauteile, der auftretenden Verzüge und Eigenspannungen. Gerade bei Baustellenschweißungen müssen diese Aspekte in der Konstruktionsphase der Einzelkomponenten mit berücksichtigt werden, um die erforderlichen Toleranzen bei der Montage einzuhalten. Eine genaue Kenntnis der durch Schweißungen verursachten Phänomene ist in den Konstruktions- und Montagebetrieben oft nur aus mehrjährigen Erfahrungen vorhanden. Ein grundlegendes, vollständiges Bild der Abläufe beim Schweißen auf der Baustelle, das es ermöglicht, dieses Wissen auf neue Konstruktionen zu übertragen, fehlt bisher. Insbesondere für die immer öfter im Brücken- und Stahlhochbau eingesetzten höherfesten Feinkornbaustähle (z.B. S460) ist die Kenntnis des Verhaltens bei Baustellenschweißungen notwendig.
Hier setzt der Forschungsantrag an. Mit Hilfe der Schweißsimulation können die Auswirkungen von Schweißnähten, wie die Entstehung von Verzügen und Eigenspannungen am Bauteil, global dargestellt werden. Eine anschließende Struktursimulationen (Festigkeits- und Steifigkeitsberechnungen) mit aus der Schweißsimulation integrierten Ergebnissen bildet die Basis für ergänzende Untersuchungen.
Montagestöße sind außerdem durch Verschmutzung und Witterung negativ beeinflusst. Die Montage kann beispielsweise bei niedrigen Temperaturen unterhalb des Gefrierpunkts durchgeführt werden müssen. Diese Situation wurde in einer Klimakammer simuliert und die Auswirkungen der Umgebungstemperatur bei der Montage auf das Tragverhalten der Verbindung untersucht. Für die im Rahmen des Vorhabens untersuchten Fälle ist kein Einfluss variierender Umgebungstemperaturen bis -10 °C auf die resultierenden Schweißeigenspannungen festzustellen. Der Vergleich von Verzug und Eigenspannung gegenüber normativ vorgegeben Toleranzwerten sowie vereinfachten Ingenieurmodellen für die Approximation des Eigenspannungsverlaufs zeigt große Defizite. Bei realitätsnaher Implementierung der Eigenspannungen in die Traglastberechnung können z.T. große Reserven im Rahmen der nichtlinearen Traglastberechnung ausgenutzt werden.
Implementation of longitudinal welding stresses into structural calculation of steel structures
(2016)
Conversion factors of the temperature effect on the shear strength of adhesively bonded steel joints
(2016)
This article presents the latest results of an ongoing national research project on improved models for the prediction of welding residual stresses of thick-plated welded I-girders. The experimental program is presented and the importance of different influencing factors on the residual stresses is discussed in detail. All results are compared for mild (S355J2+N) and high strength (S690QL) steel. Finally, conclusions for further works are drawn.
Grundlegende Studien zum Beulverhalten von engringversteiften Kreiszylinderschalen unter Axialdruck
(2016)
Measurement and numerical modeling of residual stresses in welded HSLA component-like I-girders
(2016)
The present contribution shows the residual stress results obtained from experiments with the sectioning method in comparison to global (structural) welding simulation models on component-like (i.e., large scale) I-girders made of structural steel grades S355 and S690QL. Plates were welded by conventional gas metal arc welding using two different heat inputs. In addition, the base material was assumed to be approximately stress-free. Based on these results, conclusions and recommendations for the design of welded I-girders are drawn.
Welding is the most important joining technique and offers the advantage of customizable plate thicknesses. On the other hand, welding causes residual stresses and deformations influencing the load carrying capacity. Their consideration in the design requires simple and fast models. Though welding simulation has contributed to accurately access to these values nowadays, their application to large components remains still in a less practicable range. Nevertheless, many studies emphasized the need to make corrections in recently available simplified models. Especially the influence of residual stresses seems somewhat overestimated in many cases if comparing conventional structural steel S355 and high-strength steel S690. In times of computer-aided design, an improved procedure to implement weld-inducted imperfections appears overdue. This will be presented in two parts. The first part illustrates the potential influence of post-welding imperfections exemplified for weak axis buckling in comparison with the general method in accordance with Eurocode 3. Residual stresses and initial crookedness were varied systematically in order to produce a scatter band of capacities. An approach to characterize the borders of these imperfections was undertaken before that. The excessive scattering of reduction factors for the load bearing capacity demonstrates the importance of these variables. Results were finally evaluated against advanced simulation models which will be further detailed in part two of this contribution.
This article provides an impression on potentials in applying nowadays welding simulation tools in construction design. This is carried out exemplary on plate girders from two structural steel grades. The calculated residual stresses are compared with measurements by sectioning method. It has been repeatedly stated that present Eurocode models fail to approximate the residual stresses. Especially for high strength steel (HSS) only limited information is available on realistic occurring residual stresses in typical I-girders. The investigations are aimed to give further guidance on these values. A few proposals on advanced models are discussed.
For stadium roofs light weight constructions, that are tensioned between a cantilevering steel compression ring, are commonly build around the globe, mostly for social events like sport games and concerts. They allow having no columns in the viewing area and also spanning the whole arena. With the additional use of membranes as the roof shell, the inside of the building will get naturally lighted. With the knowledge of the occurring loads, an economic structure can be found to optimize the edge structure. Frequently the form finding process will use the death loads as decisive action because for only one load case a moment free form can be determined. Other load cases will cause bending in the girder. The process also allows having only supports at the low points and a cantilever arises. These types of roofs will be compared with two exemplary canopies in Germany. The main focus will be on the assembly of the edge girder, which will evoke challenges for planning as well as the actual manufacturing process. The steel edge girder is double curved and has a spatially shape. The welded box exists of 4 to 5 curving plates that have thicknesses from 15mm to 55mm and will vary in their height. Due to welding residual stresses occur during the assembly in the factory as well as on the construction side. For the design of the girders, the residual stresses need to be determined. The identified results of the residual stresses will vary through the plate thickness and will differ for residual longitudinal and residual transverse stresses. The longitudinal residual stresses, as the relevant residual stresses for axial forces, will be farther scrutinized. Due to its complex geometry the challenges of the simulation will be presented for the manufacturing process and the construction site assembly. For the farther investigation the calculated stresses will be taken for a load capacity calculation of a section of the edge girder. Due to the forming geometry and the welding process, both effects need to be considered. This calculation will also show that the edge girder needs to be stiffened in the inside with bulkhead plate’s und longitudinal stiffeners. Both authors are involved in the verification of the objects (Customer Centre in the Autostadt Wolfsburg-CC, Schierke-Arena ‐FA in the Harz Mountains) mentioned below.
Several approaches on geometrical and structural imperfections are given in the literature for I sections and rectangular box girders. Those approximations of the residuals stress state can be implemented into the structural analysis using multi-purpose FEM program packages. The knowledge of the stress state of free forming cross sections has still to be determined. To fulfil a safe design, the assumptions mostly will be very conservative due to the lack of the assumed stress state. This will result directly to increased thicknesses or additional stiffening of the plates. Not only the material cost will rise, but also the fabrication costs like welding will be affected. This paper aims to provide an overview on the possibilities in the numerical prediction of weld residual stresses and weld induced deformations for cross sections with unique shapes. With the obtained values the tendencies of the residual stress state and deformations will be used to optimize the design. A representative example on a section used in a steel compression ring of a realized roof is described and analyzed using a simplification of a numerical welding simulation. The reduced simulation of the originally transient weld procedure was held to a practically reasonable level and can be reproduced for similar problems. The calculations used the Abaqus Welding Interface (AWI) to automate working steps in conjunction with the definition of weld passes and their sequencing. The field of the method that is discussed also a need of further investigations to prove its applicability. Some experimental back up is requires to verify the result quality. Nonetheless, this method could already help to show up tendencies or to identify potential critical spots in the design.
Major advances in the buckling analysis of cylindrical shells have been achieved in the last two decades. Eurocode nowadays provides rules for tanks up to r/t = 5000. However, since only few literature has become available in the past, dealing specifically with very thin walled shells in the range between r/t = 1500 and r/t = 10000, code provisions either are quite conservative or, in case of r/t > 5000, do barely exist. Employing modern construction methods, close-to perfect, very thin-walled shells can be built that are out of the scope of the design codes. Therefore, to achieve more economical designs and a better sustainability, sophisticated design tools have to be used.
In this paper, modifications and extensions of the current design procedure are proposed to overcome current limitations and drawbacks. A review of experiments with a special focus on cylinders with high r/t-ratios was conducted and modified lower bound approximation curves for the knock-down factor α deduced. They were checked against representative experiments from literature. Test results recalculated using an axisymmetric imperfection to explore their equivalent imperfection depth, proved that even small imperfections drastically reduce the buckling strength. Using a parametric study, the result range of α was extended up to r/t = 10000. The design proposal could be approved and an equation for the determination of an equivalent imperfection depth that relates the dependence of α to the imperfection depth and the r/t-ratio is proposed.
Welded tubular joints are widely used in structural engineering due to their excellent resistance and stiffness in contrast to open sections, as well as simpler end preparation. Welding residual stresses that occur in these joints after the welding process can affect their structural behavior. Some recent experimental studies have shown that this effect can be considerable. This study numerically evaluates the influence of welding residual stresses on the behavior of rectangular hollow section T joints. The paper consists of two parts. Part I develops and validates a finite element model for the joints directly taking into account welding residual stresses by means of an upstream thermomechanical simulation of the welding process. It is proven that particular attention needs to be paid to the discretization of the model, the material properties and the adequate description of the weld heat input. The validation with experimental results shows that the developed numerical model properly captures the local structural behavior of tubular joints and can be efficiently used for further investigations. Part II employs the constructed model to investigate the effect of welding residual stresses on the resistance and initial stiffness of the considered joints.
Development of a stochastic material model at constant stress
distribution in steel construction
(2016)
This paper briefly presents the results of theoretical and experimental investigations on the size effect in metal. The Chain of Bundle Model, which is based on a stochastic material model by Weibull and log-normal distribution, will be developed and the possibility to approximately determine the parameter ξ of the model is given. The tests were performed on specimens from the same steel with different sizes. According to the experiments, the relationship between the sizes of the specimens and the strength can be analyzed through probability- and reliability theory. The theoretical and experimental results show that if the volume increases hundredfold, the strength will be reduced to 90% ~ 95%. Therefore, the size effect plays an unnegligible role in steel construction.
The aim of this contribution is to investigate the influence of welding sequencing patterns on the load bearing capacity of a S355 steel square hollow section (SHS) T-Joint. The failure and the joint behavior under loading condition are analyzed. The FE-software SYSWELD v2014 is used for the thermo-mechanical simulation of the welding process. The type of welding process used is metal active gas (MAG) welding. A fillet weld with a throat thickness of 5 mm is performed. After the welding simulation, the results in terms of stresses and distortion are validated with the experimental data. Due to the geometrical characteristics of this type of joint, a compressive test is performed. A load is applied on the upper surface the vertical member (brace). The force-displacement behavior is plotted and discussed. The differences and influencing parameters are identified. The model is prepared for the subsequent sensitivity study which will be done in the software OptiSLang, which is developed by Dynardo GmbH.
Using a special technology it is possible to produce thin "honeycomb" structured plates. Such plates have been used e.g. for the roof of the sport complex "Olimp" in Odessa. That roof gives an extraordinary impression.
That is why the question: how do structured plates behave as beams with C-section under concentrated force in the middle of the upper flange? In an ongoing project, two of those structured plates were assembled in different ways trough point welding. "Sandwich" beams were modelled and calculated using the nonlinear finite elements. Using Abaqus software load deformation curves for each beam and local stability were analyzed. Those sandwich beams may be used in exhibition stand construction.
Weld residual stresses effects in the design of welded plate girders: Simulation and Implementation
(2017)
Eurocode 3 offers different possibilities on a numerically-aided design of welded plate girders. In this, a geometrically and materially nonlinear analysis of the imperfect structure (GMNIA) provides the theoretically highest possible degree of realism. A correct implementation of “imperfections” is of critical importance in the practical application of this method. The current design rules are based on long term experience in terms of traditional (“old”) welding procedures and regular (“low strength”) steel grades. Thus, they provide very approximate (but safe) rules for these structures. With the introduction of modern shop welding operations and materials, many of these assumptions seem to be over-conservative. A revision of these rules is being processed in different national and international research projects. This particular study focusses on the weld residual stresses and their effects in conventional steel S355 and high strength steel S690. Metal active gas (MAG) welding under shop welding conditions was used. The measurement of weld residual stresses on component-like samples (carried out by the BAM Bundesanstalt für Materialforschung und -prüfung in Berlin) has been widely published. The hereupon based (simplified) welding simulation as part of a subsequent structural analysis is shown here. A novel numerical approach how to directly incorporate the results into large structural components models is presented. The capacity analysis is performed on a simple example for weak-axis buckling. The results indicate significant improvements in the utilization of load-bearing capacity and underline the superior buckling assignment for the S690 compared to conventional S355. The experimental validation of the findings is currently being prepared.
For standard sections including I-girders and rectangular box girders, several approaches on geometrical and structural imperfections are given in the literature, which can be implemented in a numerical analysis. For complex sections, as found in many of today's lightweight roof structures, these assumptions are conservative due to the sections typically unique shape, which leads to increased thicknesses or additional stiffening of the plates. This, on the other hand, can significantly affect fabrication costs. This paper aims to provide an overview on the possibilities in the numerical prediction of weld residual stresses and weld-induced deformations for these sections. The obtained values can be used in a subsequent numerical analysis to understand the structural behavior and optimize the design. A representative example on a section used in a steel compression ring is described and analyzed using the numerical welding simulation. A simplification of the originally transient weld procedure is used in order to reduce computation times to a practically reasonable level. In this context, the Abaqus Welding Interface (AWI) helps to automate working steps in conjunction with the definition of weld passes and their sequencing, which shall be shown in here. The applicability of this method is discussed showing also a need of further investigations in this field. This is especially with regard to result quality, which requires some experimental back-up. Nonetheless, this method could already help to show up tendencies or to identify potential critical spots in the design.
Reliability analysis of size effect on flexural members with stochastic finite element method
(2017)
Die Festigkeitsberechnung von Strukturen, zum Beispiel Platten oder Schalen, mittels der Finite-Elemente-Methode gehört schon seit längerem zum Stand der Technik. Berücksichtigt werden bei der Berechnung sowohl geometrische Nichtlinearitäten als auch das nichtlineare Verhalten des Werkstoffs. Die geometrischen und strukturellen Imperfektionen werden bei der Ermittlung der Festigkeit zumeist in ausschließlich geometrischen Imperfektionen, wie bspw. Kombinationen aus Fertigungstoleranzen und den Ergebnissen von Beulanalysen zusammengefasst. Zur Rechtfertigung dieser Vorgehensweise werden die geometrischen Imperfektionen gemäß DIN EN 1993-1-5 erhöht. In einem Kommentar zur selben Norm findet
sich ebenfalls eine Empfehlung zur Berücksichtigung von Schweißimperfektionen in Form von vereinfachten Längseigenspannungsverläufen. Diese werden in Abhängigkeit der
Fließgrenzspannung des Werkstoffs bei Raumtemperatur und der Dicken der Fügepartner angenommen. Sowohl die Annahme rein geometrischer Imperfektionen als auch die Berücksichtigung vereinfachter Eigenspannungszustände, sind mit Sicherheitszuschlägen
behaftet. Durch eine realitätsnähere Berücksichtigung von strukturellen und geometrischen Imperfektionen, hervorgerufen durch Schweißprozesse, kann die tatsächliche Tragfähigkeit einer Struktur wesentlich exakter bestimmt werden. Inhalt dieses Artikels ist die Anwendung eines analytisch-numerischen Hybridmodells zur
Schweißimperfektionsberechnung an einer doppelt versteiften Platte und einer anschließenden Festigkeitsanalyse. Eingangs wird das analytische Modell vorgestellt und auf die grundlegenden
physikalischen Zusammenhänge eingegangen. Es folgt die Erläuterung des Kopplungsalgorithmus zwischen analytischem Modell und der numerischen Berechnung. Angewendet an der doppelt versteiften Platte, wird ein realitätsnaher geometrischer und
struktureller Imperfektionszustand berechnet. Eine anschließende Traglastanalyse gibt Aufschluss über das Verformungsverhalten unter achsialer Krafteinwirkung. Zur Bewertung der Ergebnisse wird ein Modell gleicher geometrischer Abmessungen und Werkstoffkennwerte aus
der Literatur herangezogen. Berechnet wurden die ersten 6 Eigenformen mittels analytischer und numerischer Modelle sowie die Last-Verformungskurven unter der Annahme unterschiedlicher geometrischer Imperfektionen. Um die Vergleichbarkeit der Ergebnisse zu sichern, wird eingangs die Lagerung des Modells sowie der Kraftangriffspunkt in Längsrichtung invers, durch den Vergleich der ersten 6 Beulformen sowie der Last-Verformungskurven dreier
Imperfektionen, bestimmt. Darauf aufbauen wird die Last-Verformungskurve für einen überlagerten Imperfektionszustand berechnet, wobei die geometrischen Imperfektionen aus den
Fertigungstoleranzen abgeleitet und die strukturellen idealisiert, gemäß DIN EN 1993-1-5, gewählt werden. Abschließend werden alle Last-Verformungskurven einander gegenübergestellt.
Anhand des Vergleichs kann quantifiziert werden, wie konservativ die einzelnen angenommenen Imperfektionen sind und wie sich der Verformungsverlauf darstellt, berechnet man diesen unter
Verwendung realitätsnaher geometrischer und struktureller Imperfektionen.
Ringsteifen werden typischerweise bei dünnwandigen Tanks am Mantel befestigt, um auch für starken Wind und/oder Unterdruck eine ausreichende Beulsicherheit sicherzustellen. Eine Vielzahl an Veröffentlichungen zum Thema Ringsteifen beschäftigt sich ausschließlich mit den vorher genannten Lastfällen. Dagegen ist der traglaststeigernde Einfluss der Ringsteifen im Lastfall Axialdruck kaum erforscht. Experimentell wurde vor allem in den 1960er und 1970er Jahren gegenüber unversteiften Schalen, für eng-ringversteifte ein erheblich verbessertes Tragverhalten nachgewiesen. Der eingeschränkte Parameterbereich der Untersuchungen verhindert jedoch die Anwendung der Erkenntnisse im Metallbau, wo, aufgrund der Fertigungskosten, eher wenige, dafür kräftigere
Ringsteifen eingesetzt werden. Der Beitrag baut auf den experimentellen Studien als Grundlage auf und erweitert die
Erkenntnisse mittels numerischer Parameterstudien von eng-ringversteiften Schalen auf Kreiszylinder mit Steifenabständen bis zum Zehnfachen der klassischen Beulhalbwellenlänge 1.73√rt. Es wird gezeigt, dass auch mit versteiften Schalen, bei denen der Steifenabstand größer als zwei Beulhalbwellenlängen ist, noch
Tragfähigkeitssteigerungen gegenüber der unversteiften Schale erreicht werden können. Erwartungsgemäß sind die Zugewinne an Traglast bei enger versteiften Kreiszylindern am größten, wobei vor allem dünnwandige Strukturen von der verringerten
Imperfektionssensitivität profitieren. Die Ergebnisse, angewandt auf die Baupraxis, erlauben eine wirtschaftlichere Bemessung
von Tanks und Silos mit Ringsteifen, sofern Axialdruck eine bemessungsrelevante Lastsituation darstellt. Dies ist in der Regel bei überdachten Silos und windbelasteten Flachbodentanks der Fall. Dafür ist kein zusätzlicher Konstruktionsaufwand notwendig, da
lediglich die ohnehin vorhandene Struktur vorteilhafter ausgenutzt wird.
Тhe development of steel bridges after the WWII is characterized by new constructive forms like: steel roadway closed sections, new static systems considering the roadway as a plate rather than a beam grid, new computational methods covering rod statics and statics of continuum, and determining the internal forces of the roadway as internal forces of an orthotropic plate. Moreover, the main girders, the roadway and the horizontal links connect statically and constructively in a whole monolithic structure. Thus, the construction follows better the real distribution of internal forces in steel structure. Loading possibility of high-quality steel material is well used, by which the economic effect of the construction increases significantly compared to the riveted old bridges. The application of this theory in Bulgaria in the period 1976 – 1992 allowed the Bulgarian bridge construction to build several unique by their size steel road bridges of steel orthotropic decks.
Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of rectangular hollow section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.
Due to the uncertain microscopic structure of the material, the strength of the material exhibits strong randomness. This randomness results in uncertain response of the structure in the sequentially coupled thermal-mechanical analysis by welding simulation. Because of the limitations of deterministic welding simulation, the stochastic finite element method with random field will be introduced into the welding simulation, so that the welded structure can be more accurately calculated in the stability and reliability structural analysis. Particularly, it is necessary to propose reasonable distributions of residual stress from welding simulations based on statistical and reliability theories. This paper is intended to implement the stochastic finite element method in the welding simulation using a general-purpose simulation program and to demonstrate the potential of the proposed approach. Furthermore, the statistical distribution function of the welding simulation response is obtained by maximum entropy fitting method. Then, a numerical example is presented by the proposed method.
Imperfektionen, die bei Traglastberechnungen Berücksichtigung finden müssen, haben ihre Ursachen in Herstellungs- und Fertigungstoleranzen oder werden durch das Schweißen und den damit zumeist einhergehenden Nachbehandlungen in den Bauteilen hervorgerufen. Durch die Wärmewirkung des Schweißens entstehen sowohl sehr große Verformungen als auch signifikante Zug und Druckspannungen. Der strukturelle und geometrische Imperfektionsgrad wird somit maßgeblich von der Anzahl und der Lage der Schweißnähte sowie den Schweißparametern bestimmt. Für die Berücksichtigung in Traglastberechnungen ist ein physikalisch fundiertes Modell erforderlich, welches die Schweißimperfektionen schnell und präzise berechnet. Das gekoppelte analytisch numerische Hybridmodell erfüllt diese Kriterien. Die mathematischen Grundlagen des analytischen Modells sowie die Kopplung mit der numerischen Finite-Elemente-Berechnung werden eingangs vorgestellt und die Anwendung zur Berechnung von Verzügen an einer Schiffsektion demonstriert. Darauffolgend wird das Hybridmodell an einer eben und einer gekrümmten versteiften Platte zur Berechnung der Schweißimperfektionen angewendet. Anschließende Traglastberechnungen sowie der Vergleich mit den Ergebnissen unter der Annahme einer geometrischen Ersatzimperfektion in Form des kritischsten Eigenwerts gibt Auskunft darüber, welches Potenzial die realitätsnahe direkte Berücksichtigung von Schweißimperfektionen birgt.
The work presents an innovative approach for simulation of welding induced distortions, which allows taking into consideration the local effects of the welding process as well as the global interactions in the structure. The approach bases on an integration of analytical and numerical calculation’s procedures in a hybrid model, realized with the aid of the inherent strain concept. The analytical procedure calculates the shrinkage strain components and area of the plastic deformed zone, caused by welding. The calculated strains are then transferred to the global finite element model in order to predict the distortions and stresses in the structure after every welding stage, as well as their final state. The consideration of welding scenarios, weld sequence, clamping conditions and the assembling stages is done by taking into account the intermediate variation of the strain state during the manufacturing steps.
The article gives the theoretical basis of the analytical model. The consideration of the essential physical relations is put into discussion. The application of the model is illustrated on complex structures. Its reliability and practicability are demonstrated by means of a validation study.
Understanding and predicting sandwich structure behavior in fire has been of particular interest to researchers for a long time. Sandwich panel joints are playing an important role since they not only connect sandwiches to a bearing structure, but also play a key role in stabilization of the whole building. This paper presents an investigation of a sandwich panel behavior. The sandwich panel consist of two steel layers and PIR core between them and is connected to a HEA 160 flange with the help of a screw. Using ABAQUS software, this connection is modelled and deformation fields with temperature distribution area are analyzed. The modelling process includes many stages associated with each other: static, heat transfer and sequential analysis that includes both previous analyses.
Numerical analysis and laboratory experiments of lightweight structured sandwich beams made of steel
(2017)
Using special technology it is possible to produce thin steel plates with a 3-D structure - hexagonal staggered pattern. Such sheets find a range of application in automotive and aerospace industry. The question is: Can we use those sheets also for building applications? Therefore their behaviour under external loads has to be studied.
As an example beams with C-section made of structured sheets under concentrated force in the middle of the upper flange are investigated. This article provides information about load capacity of beams, assembled from structured plates with different thickness. Using Abaqus software beams were modelled and deformation fields for each of them were analyzed. To compare computer calculations with actual results, real sized beams made of structured sheets were constructed in laboratory and bending tests were conducted.
The influence of an improved strength grading in situ on modelling timber strength properties
(2019)
Against the background of the earthquake-proof design of steel structures, it makes sense to use structures with sufficient ductility and energy dissipation capacity. The joints are often a weak point in such systems. Methods for reinforcing beam-to-column connections with the aid of adhesively bonded CFRP products are the subject of the work. Advantages of such reinforcement methods are the avoidance of residual stresses (compared to welded steel lamellas), avoidance of cross-sectional weakening (in comparison to bolted solutions) and, above all, the possibility of retrofitting existing steel structures.
The Influence of Geometrical and Welding Imperfections on the Strength of Stiffened Structures
(2018)
The strength calculation of stiffened plates and shells via finite element simulation has been part of the state of the art for a long time. Geometrical nonlinearities as well as the nonlinear material behavior are considered within the calculation. To simplify, both types of imperfections, geometrical and structural ones, are mostly combined in these strength calculations being considered as equivalent geometrical imperfections. Values for standard cases are included in EN 1993-1-5 in case of plated structures or 1-6 in case of shells. A second possibility is the separate definition of fabrication tolerances and residual stresses, as far as they are known. With increasing complexity of the structure, less information are however available on geometrical and particularly structural imperfections. Nevertheless, by means of a more realistic consideration of these values, the actual ultimate load can be determined significantly more exactly and the performance of high performance steel structures is increased.
In the investigated cases, deformations and stresses arise mainly due to welding. Therefore, the topic of this article is the application of an analytical numerical hybrid model for predicting imperfections induced by welds. This is presented on an example of a stiffened steel structure and a subsequent ultimate load calculation. At the beginning the analytical model, its physical basis as well as the physical interrelationships are introduced and explained. This is followed by the explanation of the coupling procedure between the analytical model and the numerical calculation for the calculation of weld-induced deformations and residual stresses. The significance of the hybrid model is proven by means of a few sample applications. For a realistic determination of the weld imperfections in the investigated stiffened structure, the coupled hybrid model is used afterwards. An ultimate load analysis gives information about the load carrying behavior under axial loading. The results are compared with the results of an ultimate load analysis from a literature example assuming different eigenvalues with different scaling. The results underline the potential additional utilization of load bearing capacity by this new approach.
This paper present the investigation of the statistical size effect in steel structure and the corresponding reliability. This study described the randomness of material properties through two different ways. These two proposed simulation methods, which are an extension and supplement to traditional simulation methods, can effectively simulate the statistical size effect for the tensile and flexural components in steel structures. The test results show that the variations of the yield and tensile strength increase with the decreasing specimen volume. Besides, the structural component strength is not only related to the specimen volume, but also the stress distribution. It is found by studying the influence of statistical size effect on structural reliability that the strength, which is obtained by small specimens through statistical analysis in the laboratory, is no more accurately applicable to large construction. The core idea is that the stochastic material proper-ties are directly embedded in mechanical calculations to develop a more accurate and economical design method for steel structure.
Strength Calculation of Stiffened Structures Taking Into Consideration Realistic Weld Imperfections
(2018)
The topic of this article is the application of an analytical numerical hybrid model for a realistic prediction of imperfections induced by welds. At the beginning, the analytical model, its physical basis as well as the physical interrelationships are explained. This is followed by the explanation of the coupling procedure between the analytical model and the numerical calculation. Afterwards, the coupled hybrid model is applied on the investigated stiffened curved structure for the determination of the weld imperfections. An ultimate load analysis gives information about the load carrying behavior under axial loading. The results are compared against the traditional approach using eigenmode-based imperfections. The comparison underlines the potential additional utilization of load bearing capacity by this new approach.
Die Ergebnisse aus drei Traglastversuchen und einer umfangreichen numerischen Parameterstudie (FE-Berechnungen) zum Tragverhalten von Wellstegträgern mit quadratischen Stegöffnungen werden vorgestellt. Es werden versteifte Stegöffnungen mit einem umlaufenden Versteifungskranz betrachtet. In der Parameterstudie werden die Einflüsse der Stegöffnungsgeometrie, der Trägergeometrie und der Position der Stegöffnung auf die Querkrafttragfähigkeit der Wellstegträger untersucht.