@misc{KemperLedeckyFeldmannetal., author = {Kemper, Frank and Ledecky, Lukas and Feldmann, Markus and Pasternak, Hartmut and Fischer, Vitali}, title = {Zeitabh{\"a}ngige Windbeanspruchungen von geklebten Fassadenanschl{\"u}ssen}, series = {Bauingenieur}, volume = {92}, journal = {Bauingenieur}, number = {3}, issn = {1436-4867}, pages = {115 -- 122}, abstract = {F{\"u}r die Bemessung lastabtragender Klebverbindungen im Fassadenbereich ist zu beachten, dass die Windbelastungen auf den Bauwerksoberfl{\"a}chen sowohl zeitlich als auch r{\"a}umlich ver{\"a}nderlich sind. W{\"a}hrend f{\"u}r {\"u}bliche Fassadenanschl{\"u}sse eine Bemessung mit charakteristischen Extremwerten ausreichend ist, muss beim Einsatz von sowohl h{\"o}hermoduligen (z.B. Acrylat) als auch niedrigmoduligen (z.B. Polyurethan) Klebstoffen, die beide ein zeit- und temperaturabh{\"a}ngiges Materialverhalten aufweisen, eine vollst{\"a}ndige Beschreibung dieser zeitbezogenen Lasteinwirkungen erfolgen. Nur dadurch wird letztlich die erforderliche betriebsfeste Auslegung eines geklebten Fassadenanschlusses erm{\"o}glicht. Im vorliegenden Beitrag wird die Ermittlung von zeitbezogenen Lasteinwirkungen und die Berechnung der daraus resultierenden Beanspruchungs-Zeit-Funktionen infolge einer nat{\"u}rlichen Windeinwirkungen auf Basis von Windkanalversuchen und Windstatistik thematisiert. Anhand geeigneter Z{\"a}hlverfahren und unter Ber{\"u}cksichtigung von klebstoffspezifischen Materialeigenschaften wird exemplarisch aufgezeigt, inwiefern unterschiedliche Fassadenpositionen und Windeigenschaften f{\"u}r die Auslegung von geklebten Fassadenanschl{\"u}ssen von Bedeutung sind.}, language = {de} } @inproceedings{SimonMoradiHildebrandetal., author = {Simon, Flaviu and Moradi, Milad and Hildebrand, J{\"o}rg and Pasternak, Hartmut}, title = {The influence of the welding sequence on the load bearing capacity and stress distribution of square hollow section steel joints}, series = {Simulationsforum 2016, Schweißen und W{\"a}rmebehandlung, Weimar, Tagungsband 08.-10. November 2016}, booktitle = {Simulationsforum 2016, Schweißen und W{\"a}rmebehandlung, Weimar, Tagungsband 08.-10. November 2016}, editor = {Hildebrand, J{\"o}rg and Loose, Tobias and Reich, Michael}, publisher = {Verein zur F{\"o}rderung der numerischen Analyse der W{\"a}rmebehandlungs- und Schweißprozesse e.V.}, address = {Weimar}, isbn = {978-3-00-054805-5}, pages = {176 -- 187}, abstract = {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.}, language = {en} } @inproceedings{ShlychkovaPasternak, author = {Shlychkova, Darita and Pasternak, Hartmut}, title = {Numerical analysis of lightweight structured sandwich beams made of steel}, series = {16th International Scientific Conference VSU 2016, Sofia, 2016, vol. 1}, booktitle = {16th International Scientific Conference VSU 2016, Sofia, 2016, vol. 1}, publisher = {VSU}, address = {Sofia}, pages = {318 -- 323}, abstract = {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.}, language = {en} } @inproceedings{LedeckyCiupackPasternaketal., author = {Ledecky, Lukas and Ciupack, Yvonne and Pasternak, Hartmut and Fischer, Vitali and Stammen, Elisabeth and Dilger, Klaus}, title = {Untersuchungen zum Tragverhalten und der Lebensdauer von Klebverbindungen im Stahlbau unter zyklischen Belastungen (LebKleb)}, series = {17. Kolloquium Gemeinsame Forschung in der Klebtechnik, Tagungsband, 14. - 15. Februar 2017}, booktitle = {17. Kolloquium Gemeinsame Forschung in der Klebtechnik, Tagungsband, 14. - 15. Februar 2017}, publisher = {DECHEMA}, address = {Frankfurt am Main}, pages = {37 -- 38}, language = {de} } @inproceedings{LedeckyCiupackPasternaketal., author = {Ledecky, Lukas and Ciupack, Yvonne and Pasternak, Hartmut and Mette, Christoph and Stammen, Elisabeth and Dilger, Klaus}, title = {Untersuchungen zum Tragverhalten und der Lebensdauer von Klebverbindungen im Stahlbau unter zyklischen Belastungen (LebKleb)}, series = {16. Kolloquium Gemeinsame Forschung in der Klebtechnik, K{\"o}ln, 2016}, booktitle = {16. Kolloquium Gemeinsame Forschung in der Klebtechnik, K{\"o}ln, 2016}, publisher = {DECHEMA}, address = {Frankfurt am Main}, pages = {39 -- 41}, language = {de} } @misc{CiupackPasternakMetteetal., author = {Ciupack, Yvonne and Pasternak, Hartmut and Mette, Christoph and Stammen, Elisabeth and Dilger, Klaus}, title = {Adhesive bonding in steel construction - Challenge and innovation}, series = {Procedia Engineering}, volume = {172}, journal = {Procedia Engineering}, issn = {1877-7058}, doi = {10.1016/j.proeng.2017.02.048}, pages = {186 -- 193}, language = {en} } @inproceedings{LiPasternak, author = {Li, Zheng and Pasternak, Hartmut}, title = {Development of a stochastic material model at constant stress distribution in steel construction}, series = {16th International Scientific Conference VSU 2016, Sofia, 2016, vol. 1}, booktitle = {16th International Scientific Conference VSU 2016, Sofia, 2016, vol. 1}, publisher = {VSU}, address = {Sofia}, pages = {193 -- 198}, abstract = {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.}, language = {en} } @inproceedings{PasternakKrausche, author = {Pasternak, Hartmut and Krausche, Thomas}, title = {A special Construction Site: the Guyed Mast at Torfhaus in the Harz Mountains, Germany}, series = {Risk and Safety Engineering, 12th International Conference, Kopaonik, 2017}, booktitle = {Risk and Safety Engineering, 12th International Conference, Kopaonik, 2017}, publisher = {The Higher Education Technical School of Professional Studies}, address = {Novi Sad}, isbn = {978-86-6211-107-4}, pages = {540 -- 545}, language = {en} } @misc{LinkeRugPasternak, author = {Linke, Gunter and Rug, Wolfgang and Pasternak, Hartmut}, title = {Festigkeitssortierung von Bauholz in historischen Geb{\"a}uden - Bericht zum Stand der Technik}, series = {Bauingenieur}, volume = {92}, journal = {Bauingenieur}, number = {5}, pages = {229 -- 236}, language = {de} } @misc{StojkovićFolićPasternak, author = {Stojković, Nenad and Folić, Radomir and Pasternak, Hartmut}, title = {Mathematical model for the prediction of strength degradation of composites subjected to constant amplitude fatigue}, series = {International Journal of Fatigue}, volume = {103}, journal = {International Journal of Fatigue}, issn = {0142-1123}, doi = {10.1016/j.ijfatigue.2017.06.032}, pages = {478 -- 487}, language = {en} } @techreport{LaunertPasternakRhodeetal., author = {Launert, Benjamin and Pasternak, Hartmut and Rhode, Michael and Kromm, Arne and Kannengießer, Thomas}, title = {Erh{\"o}hung der Tragf{\"a}higkeit geschweißter I-Tr{\"a}ger aus hochfestem Baustahl durch verbesserte Ans{\"a}tze zur Ber{\"u}cksichtigung von Eigenspannungen}, pages = {4}, language = {de} } @misc{LaunertPasternak, author = {Launert, Benjamin and Pasternak, Hartmut}, title = {Weld residual stresses effects in the design of welded plate girders: Simulation and Implementation}, series = {Ce/papers}, volume = {1}, journal = {Ce/papers}, number = {2-3}, issn = {2509-7075}, doi = {10.1002/cepa.144}, pages = {1039 -- 1047}, abstract = {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 f{\"u}r Materialforschung und -pr{\"u}fung 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.}, language = {en} } @misc{KrauscheLaunertPasternak, author = {Krausche, Thomas and Launert, Benjamin and Pasternak, Hartmut}, title = {A study on the prediction of welding effects in steel box girders}, series = {Ce/papers}, volume = {1}, journal = {Ce/papers}, number = {2-3}, issn = {2509-7075}, doi = {10.1002/cepa.500}, pages = {4410 -- 4416}, abstract = {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.}, language = {en} } @misc{CiupackLedeckyPasternaketal., author = {Ciupack, Yvonne and Ledeck{\´y}, Luk{\´a}š and Pasternak, Hartmut and Fischer, Vitali and Stammen, Elisabeth and Dilger, Klaus}, title = {Bonded steel joints under cyclic loading: Study on structural behaviour and fatigue}, series = {ce/papers}, volume = {1}, journal = {ce/papers}, number = {2/3}, issn = {2509-7075}, doi = {10.1002/cepa.87}, pages = {505 -- 513}, language = {en} } @inproceedings{LiPasternak, author = {Li, Zheng and Pasternak, Hartmut}, title = {Reliability analysis of size effect on flexural members with stochastic finite element method}, series = {12th International Conference on Structural Safety \& Reliability, Vienna, Austria, 6-10 August 2017}, booktitle = {12th International Conference on Structural Safety \& Reliability, Vienna, Austria, 6-10 August 2017}, editor = {Bucher, Christian and Ellingwood, Bruce R. and Frangopol, Dan M.}, publisher = {TU-MV Media Verlag}, address = {Vienna}, isbn = {978-3-903024-28-1}, language = {en} } @inproceedings{LoebjinskiRugPasternak, author = {Loebjinski, Maria and Rug, Wolfgang and Pasternak, Hartmut}, title = {Approaches for an optimisation of partial safety factors for historic timber structures}, series = {Safety, Reliability, Risk, Resilience and Sustainability of Structures and Infrastructure, 12th International Conference on Structural Safety \& Reliability, Vienna, Austria, 6-10 August 2017}, booktitle = {Safety, Reliability, Risk, Resilience and Sustainability of Structures and Infrastructure, 12th International Conference on Structural Safety \& Reliability, Vienna, Austria, 6-10 August 2017}, editor = {Bucher, Christian and Ellingwood, Bruce R. and Frangopol, Dan M.}, publisher = {TU-MV Media Verlag}, address = {Vienna}, isbn = {978-3-903024-28-1}, language = {en} } @inproceedings{PasternakKrausche, author = {Pasternak, Hartmut and Krausche, Thomas}, title = {Design, constructions and assembly of two membrane-cladded double-curved cable net roofs}, series = {6th Structural Engineers World Congress (SEWC 2017), Cancun/Mexico}, booktitle = {6th Structural Engineers World Congress (SEWC 2017), Cancun/Mexico}, publisher = {Universidad Nacional Aut{\´o}noma de M{\´e}xico - UNAM}, pages = {8}, abstract = {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.}, language = {en} } @inproceedings{KrauscheLaunertPasternak, author = {Krausche, Thomas and Launert, Benjamin and Pasternak, Hartmut}, title = {Welding effects in unregularly steel box girders}, series = {6th Structural Engineers World Congress (SEWC 2017), Cancun/Mexico}, booktitle = {6th Structural Engineers World Congress (SEWC 2017), Cancun/Mexico}, publisher = {Universidad Nacional Aut{\´o}noma de M{\´e}xico - UNAM}, pages = {6}, abstract = {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.}, language = {en} } @inproceedings{PasternakJaegerCanas, author = {Pasternak, Hartmut and J{\"a}ger-Ca{\~n}{\´a}s, Andreas}, title = {On the axial buckling of very thin-walled cylindrical shells}, series = {Ce/papers : the online collection for conference papers in civil engineering}, volume = {1}, booktitle = {Ce/papers : the online collection for conference papers in civil engineering}, number = {2-3}, issn = {2509-7075}, doi = {10.1002/cepa.127}, pages = {868 -- 877}, abstract = {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.}, language = {en} } @inproceedings{JaegerCanasPasternak, author = {J{\"a}ger-Ca{\~n}{\´a}s, Andreas and Pasternak, Hartmut}, title = {Influence of closely spaced ring-stiffeners on the axial buckling behavior of cylindrical shells}, series = {Ce/papers : the online collection for conference papers in civil engineering}, volume = {1}, booktitle = {Ce/papers : the online collection for conference papers in civil engineering}, number = {2-3}, issn = {2509-7075}, doi = {10.1002/cepa.133}, pages = {928 -- 937}, abstract = {Material efficiency in modern tank constructions often is achieved by combining thin plates with light and heavy ring stiffeners. While the plates are designed to resist hydrostatic pressure, the stiffeners are designed against wind and external pressure. Axial buckling may occur due to high roof loads and wind since very thin plates are prone to a loss of stability. Test results in the 60s and 70s revealed that closely spaced ring-stiffeners may greatly enhance the axial buckling behavior, allowing for knock-down factors greater unity. However, until today, no design procedure is available allowing for adopting the beneficial effect of ring stiffeners under axial compression into practical design. In this paper a design procedure is proposed that closes this gap in current design codes. One outcome of the conducted literature study revealed that test results of unstiffened shells may be more closely approximated and is shortly presented. The design procedure for ring-stiffened shells was then developed from lower bound curves deduced from categorized buckling tests. The results of a parametrical study, that was conducted over a wide range of r/t-values, is presented. Imperfection depths up to 10t were examined using a stiffener spacing of one buckling half-wave. Especially highly slender stiffened cylinders benefit from ring-stiffening, showing up to 380\% strength gains. Imperfection depths proposed by the current design code were found to be too conservative.}, language = {en} } @inproceedings{PasternakZivaljevicLuxor, author = {Pasternak, Hartmut and Zivaljevic-Luxor, Natasa}, title = {Evolution of an heritage edifice from colossus in Prora to colossus of Prora}, series = {3rd International Conference on Protection of Historical Constructions}, booktitle = {3rd International Conference on Protection of Historical Constructions}, publisher = {IST Press}, address = {Lisbon}, isbn = {978-989-8481-58-0}, pages = {387 -- 388}, language = {en} } @inproceedings{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Numerische Festigkeitsberechnung einer versteiften Struktur unter Ber{\"u}cksichtigung realit{\"a}tsnaher geometrischer und struktureller Imperfektionen}, series = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern, 6./7. M{\"a}rz 2018}, booktitle = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern, 6./7. M{\"a}rz 2018}, publisher = {Deutscher Ausschuß f{\"u}r Stahlbau DASt}, address = {D{\"u}sseldorf}, isbn = {978-3-941687-27-1}, pages = {245 -- 249}, abstract = {Die Festigkeitsberechnung von Strukturen, zum Beispiel Platten oder Schalen, mittels der Finite-Elemente-Methode geh{\"o}rt schon seit l{\"a}ngerem zum Stand der Technik. Ber{\"u}cksichtigt werden bei der Berechnung sowohl geometrische Nichtlinearit{\"a}ten 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 gem{\"a}ß DIN EN 1993-1-5 erh{\"o}ht. In einem Kommentar zur selben Norm findet sich ebenfalls eine Empfehlung zur Ber{\"u}cksichtigung von Schweißimperfektionen in Form von vereinfachten L{\"a}ngseigenspannungsverl{\"a}ufen. Diese werden in Abh{\"a}ngigkeit der Fließgrenzspannung des Werkstoffs bei Raumtemperatur und der Dicken der F{\"u}gepartner angenommen. Sowohl die Annahme rein geometrischer Imperfektionen als auch die Ber{\"u}cksichtigung vereinfachter Eigenspannungszust{\"a}nde, sind mit Sicherheitszuschl{\"a}gen behaftet. Durch eine realit{\"a}tsn{\"a}here Ber{\"u}cksichtigung von strukturellen und geometrischen Imperfektionen, hervorgerufen durch Schweißprozesse, kann die tats{\"a}chliche Tragf{\"a}higkeit 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 Zusammenh{\"a}nge eingegangen. Es folgt die Erl{\"a}uterung des Kopplungsalgorithmus zwischen analytischem Modell und der numerischen Berechnung. Angewendet an der doppelt versteiften Platte, wird ein realit{\"a}tsnaher geometrischer und struktureller Imperfektionszustand berechnet. Eine anschließende Traglastanalyse gibt Aufschluss {\"u}ber 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 L{\"a}ngsrichtung invers, durch den Vergleich der ersten 6 Beulformen sowie der Last-Verformungskurven dreier Imperfektionen, bestimmt. Darauf aufbauen wird die Last-Verformungskurve f{\"u}r einen {\"u}berlagerten Imperfektionszustand berechnet, wobei die geometrischen Imperfektionen aus den Fertigungstoleranzen abgeleitet und die strukturellen idealisiert, gem{\"a}ß DIN EN 1993-1-5, gew{\"a}hlt werden. Abschließend werden alle Last-Verformungskurven einander gegen{\"u}bergestellt. Anhand des Vergleichs kann quantifiziert werden, wie konservativ die einzelnen angenommenen Imperfektionen sind und wie sich der Verformungsverlauf darstellt, berechnet man diesen unter Verwendung realit{\"a}tsnaher geometrischer und struktureller Imperfektionen.}, language = {de} } @inproceedings{JaegerCanasPasternak, author = {J{\"a}ger-Ca{\~n}{\´a}s, Andreas and Pasternak, Hartmut}, title = {Zum Tragverhalten ringversteifter Schalen unter Axialdruck}, series = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern, 6./7. M{\"a}rz 2018}, booktitle = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern, 6./7. M{\"a}rz 2018}, publisher = {Deutscher Ausschuß f{\"u}r Stahlbau DASt}, address = {D{\"u}sseldorf}, isbn = {978-3-941687-27-1}, pages = {227 -- 232}, abstract = {Ringsteifen werden typischerweise bei d{\"u}nnwandigen Tanks am Mantel befestigt, um auch f{\"u}r starken Wind und/oder Unterdruck eine ausreichende Beulsicherheit sicherzustellen. Eine Vielzahl an Ver{\"o}ffentlichungen zum Thema Ringsteifen besch{\"a}ftigt sich ausschließlich mit den vorher genannten Lastf{\"a}llen. Dagegen ist der traglaststeigernde Einfluss der Ringsteifen im Lastfall Axialdruck kaum erforscht. Experimentell wurde vor allem in den 1960er und 1970er Jahren gegen{\"u}ber unversteiften Schalen, f{\"u}r eng-ringversteifte ein erheblich verbessertes Tragverhalten nachgewiesen. Der eingeschr{\"a}nkte Parameterbereich der Untersuchungen verhindert jedoch die Anwendung der Erkenntnisse im Metallbau, wo, aufgrund der Fertigungskosten, eher wenige, daf{\"u}r kr{\"a}ftigere 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 Steifenabst{\"a}nden bis zum Zehnfachen der klassischen Beulhalbwellenl{\"a}nge 1.73√rt. Es wird gezeigt, dass auch mit versteiften Schalen, bei denen der Steifenabstand gr{\"o}ßer als zwei Beulhalbwellenl{\"a}ngen ist, noch Tragf{\"a}higkeitssteigerungen gegen{\"u}ber der unversteiften Schale erreicht werden k{\"o}nnen. Erwartungsgem{\"a}ß sind die Zugewinne an Traglast bei enger versteiften Kreiszylindern am gr{\"o}ßten, wobei vor allem d{\"u}nnwandige Strukturen von der verringerten Imperfektionssensitivit{\"a}t 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 {\"u}berdachten Silos und windbelasteten Flachbodentanks der Fall. Daf{\"u}r ist kein zus{\"a}tzlicher Konstruktionsaufwand notwendig, da lediglich die ohnehin vorhandene Struktur vorteilhafter ausgenutzt wird.}, language = {de} } @inproceedings{LedeckyCiupackPasternaketal., author = {Ledecky, Lukas and Ciupack, Yvonne and Pasternak, Hartmut and Geßler, Achim and Feldmann, Markus}, title = {Reduction of Fatigue Crack Growth Rate in Compact Tension Specimens Using Adhesively Bonded CFRP-Strips}, series = {Proceedings of the METNET Seminar 2017 in Cottbus}, booktitle = {Proceedings of the METNET Seminar 2017 in Cottbus}, editor = {Virdi, Kuldeep and Tenhunen, Lauri}, publisher = {H{\"a}me University of Applied Sciences (HAMK)}, address = {H{\"a}meenlinna}, isbn = {978-951-784-794-0}, pages = {30 -- 42}, language = {en} } @inproceedings{CiupackPasternakYilmazetal., author = {Ciupack, Yvonne and Pasternak, Hartmut and Yilmaz, Emre Mehmet and Sternsdorff, Florian and Vayas, Ioannis}, title = {Hybrid Reinforcement Measures and Innovative Measurement Methods in Steel Construction}, series = {Proceedings of the METNET Seminar 2017 in Cottbus}, booktitle = {Proceedings of the METNET Seminar 2017 in Cottbus}, editor = {Virdi, Kuldeep and Tenhunen, Lauri}, publisher = {H{\"a}me University of Applied Sciences (HAMK)}, address = {H{\"a}meenlinna}, isbn = {978-951-784-794-0}, pages = {43 -- 55}, language = {en} } @inproceedings{PasternakCiupackLedeckyetal., author = {Pasternak, Hartmut and Ciupack, Yvonne and Ledecky, Lukas and Dilger, Klaus and Stammen, Elisabeth and Fischer, Vitali}, title = {Untersuchungen zum Tragverhalten und der Lebensdauer von Klebverbindungen im Stahlbau unter zyklischer Belastung}, series = {18. Kolloquium Gemeinsame Forschung in der Klebtechnik, K{\"o}ln, 27. - 28. Februar 2018}, booktitle = {18. Kolloquium Gemeinsame Forschung in der Klebtechnik, K{\"o}ln, 27. - 28. Februar 2018}, publisher = {DECHEMA}, address = {Frankfurt am Main}, pages = {62 -- 64}, language = {de} } @misc{GarifullinLaunertHeinisuoetal., author = {Garifullin, Marsel and Launert, Benjamin and Heinisuo, Markku and Pasternak, Hartmut and Mela, Kristo and Pajunen, Sami}, title = {Effect of welding residual stresses on local behavior of rectangular hollow section joints. Part 1 - Development of numerical model}, series = {Bauingenieur}, volume = {93}, journal = {Bauingenieur}, number = {4}, issn = {1436-4867}, pages = {152 -- 159}, abstract = {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.}, language = {en} } @misc{PartovPasternakPetkovetal., author = {Partov, Doncho and Pasternak, Hartmut and Petkov, Milen and Nikolov, Radoslav and Dimitrova, Antoaneta}, title = {About the history of orthotropic bridge decks}, series = {Annual of the University of Architecture, Civil Engineering and Geodesy, Sofia}, volume = {51}, journal = {Annual of the University of Architecture, Civil Engineering and Geodesy, Sofia}, number = {4}, issn = {1310-814X}, pages = {295 -- 311}, abstract = {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.}, language = {en} } @misc{GarifullinLaunertHeinisuoetal., author = {Garifullin, Marsel and Launert, Benjamin and Heinisuo, Markku and Pasternak, Hartmut and Mela, Kristo and Pajunen, Sami}, title = {Effect of welding residual stresses on local behavior of rectangular hollow section joints. Part 2 - Parametric studies}, series = {Bauingenieur}, volume = {93}, journal = {Bauingenieur}, number = {5}, issn = {1436-4867}, pages = {207 -- 213}, abstract = {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.}, language = {en} } @misc{LiLaunertPasternak, author = {Li, Zheng and Launert, Benjamin and Pasternak, Hartmut}, title = {Application of the stochastic finite element method in welding simulation}, series = {Welding in the World}, volume = {62}, journal = {Welding in the World}, number = {5}, issn = {0043-2288}, doi = {10.1007/s40194-018-0596-4}, pages = {905 -- 912}, abstract = {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.}, language = {en} } @inproceedings{GarifullinLaunertHeinisuoetal., author = {Garifullin, Marsel and Launert, Benjamin and Heinisuo, Markku and Pasternak, Hartmut and Mela, Kristo and Pajunen, Sami}, title = {Effect of Welding Residual Stresses on Behavior of Tubular T Joints}, series = {17th International Conference on Computing in Civil and Building Engineering}, booktitle = {17th International Conference on Computing in Civil and Building Engineering}, pages = {8}, abstract = {Welded tubular joints are widely used in structural engineering due to their excellent resistance and stiffness, as well as simple connection. However, the welding process induces residual stresses in the welding area that can affect the structural behavior of joints. Currently very few papers investigate welding residual stresses in relation to tubular joints. This paper develops a finite element model of rectangular hollow section T joints considering welding residual stresses. Attention is paid particularly to welding sequences. The developed model is used to evaluate the effect of welding residual stresses on the resistance and initial stiffness of tubular joints. The results show that welding residual stresses increase the plastic resistance of rectangular hollow section joints under in-plane bending and axial brace loading.}, language = {en} } @inproceedings{ZivaljevicLuxorPasternak, author = {Zivaljevic-Luxor, Natasa and Pasternak, Hartmut}, title = {Roofs for archaeological sites integration into public space of metropolitan area}, series = {International Scientific Conference, Nis, Serbia, 31.08-01-09.2018}, booktitle = {International Scientific Conference, Nis, Serbia, 31.08-01-09.2018}, pages = {10}, language = {en} } @inproceedings{JaegerCanasPasternak, author = {J{\"a}ger-Ca{\~n}{\´a}s, Andreas and Pasternak, Hartmut}, title = {On the buckling behavior of ring-stiffened shells under axial compression}, series = {8th International Conference on Thin-Walled Structures, ICTWS 2018, Lisbon, Portugal, July 24-27, 2018}, booktitle = {8th International Conference on Thin-Walled Structures, ICTWS 2018, Lisbon, Portugal, July 24-27, 2018}, pages = {13}, language = {en} } @incollection{LoebjinskiRugPasternak, author = {Loebjinski, Maria and Rug, Wolfgang and Pasternak, Hartmut}, title = {Aktuelle Normen f{\"u}r den Bestandsbau mit Holz und beispielhafte Zuverl{\"a}ssigkeitsuntersuchungen}, series = {Holzbau im Bestand - historische Holztragwerke : Beispiele f{\"u}r substanzschonende Erhaltung}, booktitle = {Holzbau im Bestand - historische Holztragwerke : Beispiele f{\"u}r substanzschonende Erhaltung}, editor = {Rug, Wolfgang}, publisher = {Beuth Verlag}, address = {Berlin}, isbn = {978-3-410-28175-7}, pages = {162 -- 192}, language = {de} } @inproceedings{LoebjinskiRugPasternak, author = {Loebjinski, Maria and Rug, Wolfgang and Pasternak, Hartmut}, title = {Possibilities for a modification of partial safety factors for existing timber structures}, series = {World Conference on Timber Engineering, Seoul, 20 - 23 Aug 2018}, booktitle = {World Conference on Timber Engineering, Seoul, 20 - 23 Aug 2018}, pages = {7}, language = {en} } @inproceedings{PartovPasternakGrekovetal., author = {Partov, Doncho and Pasternak, Hartmut and Grekov, Petar and Nikolov, Radoslav and Dimitrova, Antoaneta}, title = {About the Theory of Orthotropic Steel Plate Established by Wilhelm Cornelius and its Application for Analysis of Two Steel Bridges With Orthotropic Decks in Varna}, series = {X Jubilee International Scientific Conference „Civil Engineering Design and Construction", Sept. 20-22, 2018, Varna, Bulgaria}, booktitle = {X Jubilee International Scientific Conference „Civil Engineering Design and Construction", Sept. 20-22, 2018, Varna, Bulgaria}, pages = {469 -- 481}, language = {en} } @inproceedings{LoebjinskiKoehlerRugetal., author = {Loebjinski, Maria and K{\"o}hler, Jochen and Rug, Wolfgang and Pasternak, Hartmut}, title = {Development of an optimization-based and practice orientated assessment scheme for the evaluation of existing timber structures}, series = {Life-Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision}, booktitle = {Life-Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision}, editor = {Caspeele, Robby and Taerwe, Luc and Frangopol, Dan M.}, publisher = {Taylor \& Francis Group}, address = {London}, isbn = {978-1-138-62633-1}, pages = {353 -- 360}, language = {en} } @inproceedings{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Strength Calculation of Stiffened Structures Taking Into Consideration Realistic Weld Imperfections}, series = {European Conference on Residual Stresses 2018, ECRS-10, Leuven, Belgium, 11-14th September, 2018}, booktitle = {European Conference on Residual Stresses 2018, ECRS-10, Leuven, Belgium, 11-14th September, 2018}, editor = {Seefeldt, Marc}, publisher = {Materials Research Forum LLC}, address = {Millersville, PA}, isbn = {978-1-945291-88-3}, doi = {10.21741/9781945291890-39}, pages = {245 -- 250}, abstract = {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.}, language = {en} } @misc{ZebingerGieratPasternaketal., author = {Zebinger, Markus and Gierat, Marek and Pasternak, Hartmut and Krausche, Thomas}, title = {Das Seilnetzdach der Schierker Feuerstein Arena im Harz Teil 2: Herstellung, Montage und Schweißsimulation}, series = {Bauingenieur}, volume = {93}, journal = {Bauingenieur}, number = {10}, issn = {0005-6650}, pages = {383 -- 391}, abstract = {Die Stadt Wernigerode in Sachsen-Anhalt errichtete im Ortsteil Schierke eine Multifunktionsarena. Am Fuße des Brockens, dem h{\"o}chsten Berg des Harzes und ganz Norddeutschlands gelegen, f{\"u}gt sich die offene {\"U}berdachung in die vorhandene Topologie nahtlos ein. Das unter Denkmalschutz stehende Natureisstadion, mit seinen bestehenden Natursteinterrassen und einem Schiedsrichterturm aus Holz, wurde baulich so konzipiert, dass die Arena in den Wintermonaten als {\"u}berdachte Kunsteisbahn und im Sommer als Fl{\"a}che f{\"u}r Konzerte, Auff{\"u}hrungen und Sportveranstaltungen genutzt werden kann. Eine ganz besondere Herausforderung war die Herstellung und Montage des circa 190m langen geschweißten Stahlrandtr{\"a}gers. Der Hohlkasten besteht aus vier doppelt gekr{\"u}mmten Blechen und lagert an lediglich zwei Fußpunkten auf. Der zweite Teil des Beitrags befasst sich mit Schweißeigenspannungen an einem ausgew{\"a}hlten Querschnitt der {\"U}berdachung.}, language = {de} } @misc{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {Traglastberechnung versteifter Platten und Schalen unter Ber{\"u}cksichtigung realer Schweißimperfektionen}, series = {Bauingenieur}, volume = {93}, journal = {Bauingenieur}, number = {10}, issn = {0005-6650}, pages = {403 -- 411}, abstract = {Imperfektionen, die bei Traglastberechnungen Ber{\"u}cksichtigung finden m{\"u}ssen, haben ihre Ursachen in Herstellungs- und Fertigungstoleranzen oder werden durch das Schweißen und den damit zumeist einhergehenden Nachbehandlungen in den Bauteilen hervorgerufen. Durch die W{\"a}rmewirkung 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 Schweißn{\"a}hte sowie den Schweißparametern bestimmt. F{\"u}r die Ber{\"u}cksichtigung in Traglastberechnungen ist ein physikalisch fundiertes Modell erforderlich, welches die Schweißimperfektionen schnell und pr{\"a}zise berechnet. Das gekoppelte analytisch numerische Hybridmodell erf{\"u}llt 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 Verz{\"u}gen an einer Schiffsektion demonstriert. Darauffolgend wird das Hybridmodell an einer eben und einer gekr{\"u}mmten 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 dar{\"u}ber, welches Potenzial die realit{\"a}tsnahe direkte Ber{\"u}cksichtigung von Schweißimperfektionen birgt.}, language = {de} } @inproceedings{LiPasternakPartov, author = {Li, Zheng and Pasternak, Hartmut and Partov, Doncho}, title = {Influence of statistical size effect in steel on structural safety}, series = {Proceedings of 16th International Conference on New Trends in Statics and Dynamics of Buildings}, booktitle = {Proceedings of 16th International Conference on New Trends in Statics and Dynamics of Buildings}, editor = {Jendželovsk{\´y}, Norbert and Grmanov{\´a}, Alžbeta}, publisher = {Slovak University of Technology}, address = {Bratislava}, isbn = {978-80-227-4845-2}, abstract = {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.}, language = {en} } @inproceedings{LedeckyCiupackPasternaketal., author = {Ledecky, Lukas and Ciupack, Yvonne and Pasternak, Hartmut and Geßler, Achim and Feldmann, Markus and Kasper, Yann and Albiez, Matthias and Ummenhofer, Thomas}, title = {Untersuchungen zur Erm{\"u}dungsrisssanierung mit aufgeklebten CFK-Lamellen im Stahlbau}, series = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern}, booktitle = {110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universit{\"a}t Kaiserslautern}, publisher = {Deutscher Ausschuß f{\"u}r Stahlbau DASt}, address = {D{\"u}sseldorf}, isbn = {978-3-941687-27-1}, pages = {116 -- 121}, language = {de} } @misc{MoradiPasternak, author = {Moradi, Milad and Pasternak, Hartmut}, title = {A Study on the Influence of Various Welding Sequence Schemes on the Gain in Strength of Square Hollow Section Steel T-Joint}, series = {Journal of Welding and Joining}, volume = {35}, journal = {Journal of Welding and Joining}, number = {4}, issn = {2466-2232}, doi = {10.5781/JWJ.2017.35.4.7}, pages = {41 -- 50}, language = {en} } @inproceedings{StapelfeldLaunertPasternaketal., author = {Stapelfeld, Christoph and Launert, Benjamin and Pasternak, Hartmut and Doynov, Nikolay and Michailov, Vesselin}, title = {The Influence of Geometrical and Welding Imperfections on the Strength of Stiffened Structures}, series = {High Performance Steel Structures Research Council (HPSSRC), Delft, Netherlands, 2018}, booktitle = {High Performance Steel Structures Research Council (HPSSRC), Delft, Netherlands, 2018}, pages = {191 -- 201}, abstract = {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.}, language = {en} } @misc{LedeckyCiupackPasternaketal., author = {Ledecky, Lukas and Ciupack, Yvonne and Pasternak, Hartmut and Fischer, Vitali and Stammen, Elisabeth and Dilger, Klaus}, title = {Lebensdauer von zyklisch beanspruchten Klebverbindungen im Stahlbau -Teil 1: Einfl{\"u}sse auf das Tragverhalten}, series = {Bauingenieur}, volume = {94}, journal = {Bauingenieur}, number = {1}, issn = {0005-6650}, pages = {29 -- 35}, language = {de} } @misc{CiupackLedeckyPasternaketal., author = {Ciupack, Yvonne and Ledecky, Lukas and Pasternak, Hartmut and Fischer, Vitali and Stammen, Elisabeth and Dilger, Klaus}, title = {Lebensdauer von zyklischen beanspruchten Klebverbindungen im Stahlbau - Teil 2: Untersuchungen zur Betriebsfestigkeitspr{\"u}fung einer Klebverbindung}, series = {Bauingenieur}, volume = {94}, journal = {Bauingenieur}, number = {2}, issn = {0005-6650}, pages = {56 -- 62}, language = {de} } @misc{LiPasternak, author = {Li, Zheng and Pasternak, Hartmut}, title = {Statistical size effect of flexural members in steel structures}, series = {Journal of Constructional Steel Research}, volume = {144}, journal = {Journal of Constructional Steel Research}, issn = {0143-974X}, doi = {10.1016/j.jcsr.2018.01.025}, pages = {176 -- 185}, abstract = {This paper presents the results of theoretical and experimental investigations on the statistical size effect (SSE) of flexural members in steel. The chain of bundle model is developed, which is based on a stochastic material model by Weibull and lognormal distribution. Furthermore, this model is embedded into the finite element method (FEM) software for the analysis of a complicated structure with a stress gradient. In order to determine the stochastic material model parameters, uniaxial tensile tests were carried out based on specimens using the same steel with different sizes. By comparing the experimental and simulation results, the material parameters could be analyzed based on the relationship between the specimen sizes and strength. Moreover, the 3-point and 4-point bending tests were performed and simulated with the developed model. The experimental and simulation results demonstrate that the SSE also exists in the flexural member, and the equivalent yield stress is closely related to the stress distribution and volume of the structure component.}, language = {en} } @misc{LiPasternak, author = {Li, Zheng and Pasternak, Hartmut}, title = {Experimental and numerical investigations of statistical size effect in S235JR steel structural elements}, series = {Construction and Building Materials}, volume = {206}, journal = {Construction and Building Materials}, issn = {0950-0618}, doi = {10.1016/j.conbuildmat.2019.02.106}, pages = {665 -- 673}, abstract = {This paper presents the analysis of the statistical size effect in steel structural elements using the stochastic finite element (FE) method. The three-dimensional random field theory is applied to simulate the uncertainty of a nonlinear material. The proposed approach, which combines the discrete random field describing the randomness of the material properties via Monte Carlo simulations, is used for computing the bearing capacity variability of the steel structures. In addition, the mapping interpolation method makes it possible to separate the random field mesh and FE model mesh. The three-dimensional random field for the material properties is established according to the yield strength with a lognormal distribution based on reasonable assumptions, and the corresponding random field parameters are studied. Finally, the results of experimental investigation and simulations are compared based on the tensile and bending tests, and they indicate that the statistical size effect cannot be overlooked in S235JR steel structural elements and that the use of stochastic FE in the analysis of the statistical size effect has tremendous potential.}, language = {en} } @misc{CiupackPasternakGessleretal., author = {Ciupack, Yvonne and Pasternak, Hartmut and Geßler, Achim and Feldmann, Markus and Kasper, Yann and Albiez, Matthias and Ummenhofer, Thomas}, title = {Repair of Fatigue Cracked CT-specimens Using Adhesively Bonded CFRP Lamellas}, series = {27th Annual International Conference on Composites / Nano Engineering ICCE-27}, journal = {27th Annual International Conference on Composites / Nano Engineering ICCE-27}, pages = {2}, language = {en} } @misc{CiupackPasternak, author = {Ciupack, Yvonne and Pasternak, Hartmut}, title = {Some Remarks about the New Generation of prEN 1993-1-1}, series = {27th Annual International Conference on Composites / Nano Engineering ICCE-27}, journal = {27th Annual International Conference on Composites / Nano Engineering ICCE-27}, pages = {3}, language = {en} } @misc{TankovaSilvaBalakrishnametal., author = {Tankova, Trayana and Silva, Lu{\´i}s Sim{\~o}es da and Balakrishnam, Marimuthu and Rodrigues, Dulce and Launert, Benjamin and Pasternak, Hartmut and Tun, Tin Yadanar}, title = {Residual stresses in welded I section steel members}, series = {Engineering Structures}, volume = {197}, journal = {Engineering Structures}, issn = {0141-0296}, doi = {10.1016/j.engstruct.2019.109398}, pages = {24}, abstract = {Residual stresses have major influence on the stability of steel members. It is well-known that, due to the differences in manufacturing procedures, the residual stresses for welded and hot - rolled members are rather different. In the same way, despite several studies on residual stresses distribution and magnitude for hot-rolled members were already done, for prismatic and tapered welded I section steel members the investigation is still very scarce. In the current work, an experimental programme on the buckling resistance of tapered members, with different tapering ratios and section heights, was conducted and residual stress measurements were carried out using the sectioning method. Numerical simulations of the heat input during welding were also performed in order to predict the residual stress fields. A statistical analysis of the residual stresses distribution for welded I section members was performed, using the experimental and numerical results, as well as literature data. Systematized information on residual stresses distribution and magnitude was generated and some guidelines for the statistical characterization of residual stresses in welded members were proposed.}, language = {en} } @misc{DoynovStapelfeldMichailovetal., author = {Doynov, Nikolay and Stapelfeld, Christoph and Michailov, Vesselin and Pasternak, Hartmut and Launert, Benjamin}, title = {Distortion analysis of large scaled welded structures}, series = {Mathematical Modelling of Weld Phenomena 12 : selected peer reviewed papers from the 12th International Seminar Numerical Analysis of Weldability : September 23-26, 2018, Graz, Schloss Seggau - Austria}, journal = {Mathematical Modelling of Weld Phenomena 12 : selected peer reviewed papers from the 12th International Seminar Numerical Analysis of Weldability : September 23-26, 2018, Graz, Schloss Seggau - Austria}, editor = {Sommitsch, Christof and Enzinger, Norbert and Mayr, Peter}, publisher = {Verlag der Technischen Universit{\"a}t Graz}, address = {Graz}, isbn = {978-3-85125-615-4}, doi = {10.3217/978-3-85125-615-4}, pages = {254 -- 280}, abstract = {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.}, language = {en} }