@misc{LaunertSzczerbaGajewskietal., author = {Launert, Benjamin and Szczerba, Radosław and Gajewski, Marcin and Rhode, Michael and Pasternak, Hartmut and Giżejowski, Marian}, title = {The buckling resistance of welded plate girders taking into account the influence of post-welding imperfections - Part 1: Parameter study}, series = {Materials Testing}, volume = {59}, journal = {Materials Testing}, number = {1}, issn = {0025-5300}, doi = {10.3139/120.110964}, pages = {47 -- 56}, abstract = {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.}, language = {en} } @misc{LoebjinskiRugPasternak, author = {Loebjinski, Maria and Rug, Wolfgang and Pasternak, Hartmut}, title = {Zuverl{\"a}ssigkeitsbewertung von Holzbauteilen im Bestand}, series = {Bauingenieur}, volume = {92}, journal = {Bauingenieur}, number = {2}, issn = {0005-6650}, pages = {65 -- 73}, abstract = {Die aktuellen Bemessungsnormen des Eurocodes beinhalten keine gesonderten Regelungen f{\"u}r bestehende Bauwerke. Dennoch sind diese aus verschiedenen Gr{\"u}nden spezifisch zu bemessen. Dazu geh{\"o}ren sowohl {\"o}ko-nomische Gr{\"u}nde, als auch Anforderungen an die Erhaltung von historischen Konstruktionen. Dieser Beitrag fasst Grundlagen zur Zuverl{\"a}ssigkeitstheorie und zur Ermittlung von Teilsicherheitsbeiwerten zusammen, stellt den aktuellen Stand der Technik zu Normen und Standards der zuverl{\"a}ssigkeitstheoretischen Bemessung und zur Behandlung von Bestandsbauten in der Bemessung dar und zeigt mit vereinfachten Rechnungen das Opti-mierungspotential der Teilsicherheitsbeiwerte f{\"u}r historische Holzkonstruktionen auf.}, language = {de} } @misc{PasternakLaunertKannengiesseretal., author = {Pasternak, Hartmut and Launert, Benjamin and Kannengießer, Thomas and Rhode, Michael}, title = {Advanced Residual Stress Assessment of Plate Girders Through Welding Simulation}, series = {Procedia Engineering}, volume = {172}, journal = {Procedia Engineering}, issn = {1877-7058}, doi = {10.1016/j.proeng.2017.02.013}, pages = {23 -- 30}, abstract = {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.}, language = {en} } @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{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} } @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{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} } @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} } @misc{ShlychkovaPasternak, author = {Shlychkova, Darita and Pasternak, Hartmut}, title = {Numerical analysis and laboratory experiments of lightweight structured sandwich beams made of steel}, series = {Proceedings VII International Scientific Conference VSU 2017, 8-9 Juni 2017, Sofia, Bulgaria}, volume = {Volume 1}, journal = {Proceedings VII International Scientific Conference VSU 2017, 8-9 Juni 2017, Sofia, Bulgaria}, address = {Sofia, Bulgaria}, issn = {1314-071X}, pages = {252 -- 260}, abstract = {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.}, language = {en} }