TY - CHAP A1 - Loebjinski, Maria A1 - Köhler, Jochen A1 - Rug, Wolfgang A1 - Pasternak, Hartmut ED - Caspeele, Robby ED - Taerwe, Luc ED - Frangopol, Dan M. T1 - Development of an optimization-based and practice orientated assessment scheme for the evaluation of existing timber structures T2 - Life-Cycle Analysis and Assessment in Civil Engineering: Towards an Integrated Vision Y1 - 2019 SN - 978-1-138-62633-1 SN - 978-1-315-22891-4 SP - 353 EP - 360 PB - Taylor & Francis Group CY - London ER - TY - CHAP A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin ED - Seefeldt, Marc T1 - Strength Calculation of Stiffened Structures Taking Into Consideration Realistic Weld Imperfections T2 - European Conference on Residual Stresses 2018, ECRS-10, Leuven, Belgium, 11-14th September, 2018 N2 - 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. Y1 - 2018 SN - 978-1-945291-88-3 SN - 978-1-945291-89-0 U6 - https://doi.org/10.21741/9781945291890-39 SP - 245 EP - 250 PB - Materials Research Forum LLC CY - Millersville, PA ER - TY - GEN A1 - Zebinger, Markus A1 - Gierat, Marek A1 - Pasternak, Hartmut A1 - Krausche, Thomas T1 - Das Seilnetzdach der Schierker Feuerstein Arena im Harz Teil 2: Herstellung, Montage und Schweißsimulation T2 - Bauingenieur N2 - Die Stadt Wernigerode in Sachsen-Anhalt errichtete im Ortsteil Schierke eine Multifunktionsarena. Am Fuße des Brockens, dem höchsten Berg des Harzes und ganz Norddeutschlands gelegen, fügt sich die offene Überdachung 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 überdachte Kunsteisbahn und im Sommer als Fläche für Konzerte, Aufführungen und Sportveranstaltungen genutzt werden kann. Eine ganz besondere Herausforderung war die Herstellung und Montage des circa 190m langen geschweißten Stahlrandträgers. Der Hohlkasten besteht aus vier doppelt gekrümmten Blechen und lagert an lediglich zwei Fußpunkten auf. Der zweite Teil des Beitrags befasst sich mit Schweißeigenspannungen an einem ausgewählten Querschnitt der Überdachung. Y1 - 2018 SN - 0005-6650 VL - 93 IS - 10 SP - 383 EP - 391 ER - TY - GEN A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - Traglastberechnung versteifter Platten und Schalen unter Berücksichtigung realer Schweißimperfektionen T2 - Bauingenieur N2 - 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. Y1 - 2018 SN - 0005-6650 VL - 93 IS - 10 SP - 403 EP - 411 ER - TY - CHAP A1 - Li, Zheng A1 - Pasternak, Hartmut A1 - Partov, Doncho ED - Jendželovský, Norbert ED - Grmanová, Alžbeta T1 - Influence of statistical size effect in steel on structural safety T2 - Proceedings of 16th International Conference on New Trends in Statics and Dynamics of Buildings N2 - 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. KW - Statistical size effect KW - Steel structure KW - Stochastic material model KW - Stochastic FEM KW - Structural safety Y1 - 2018 UR - http://www.newtrends.sk/dokumenty/proceedings_2018.pdf SN - 978-80-227-4845-2 PB - Slovak University of Technology CY - Bratislava ER - TY - CHAP A1 - Ledecky, Lukas A1 - Ciupack, Yvonne A1 - Pasternak, Hartmut A1 - Geßler, Achim A1 - Feldmann, Markus A1 - Kasper, Yann A1 - Albiez, Matthias A1 - Ummenhofer, Thomas T1 - Untersuchungen zur Ermüdungsrisssanierung mit aufgeklebten CFK-Lamellen im Stahlbau T2 - 110 Jahre DASt und 21. DASt-Forschungskolloquium an der Technischen Universität Kaiserslautern Y1 - 2018 SN - 978-3-941687-27-1 SP - 116 EP - 121 PB - Deutscher Ausschuß für Stahlbau DASt CY - Düsseldorf ER - TY - GEN A1 - Moradi, Milad A1 - Pasternak, Hartmut T1 - A Study on the Influence of Various Welding Sequence Schemes on the Gain in Strength of Square Hollow Section Steel T-Joint T2 - Journal of Welding and Joining Y1 - 2017 U6 - https://doi.org/10.5781/JWJ.2017.35.4.7 SN - 2466-2232 SN - 2466-2100 VL - 35 IS - 4 SP - 41 EP - 50 ER - TY - CHAP A1 - Stapelfeld, Christoph A1 - Launert, Benjamin A1 - Pasternak, Hartmut A1 - Doynov, Nikolay A1 - Michailov, Vesselin T1 - The Influence of Geometrical and Welding Imperfections on the Strength of Stiffened Structures T2 - High Performance Steel Structures Research Council (HPSSRC), Delft, Netherlands, 2018 N2 - 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. KW - Welding KW - Stresses KW - Strains KW - Imperfections KW - Stiffened Structures KW - Distortions Y1 - 2018 UR - https://www-docs.b-tu.de/fg-stahlbau/public/Fachgebiet_Stahlbau/publikationen/Workshop_Proceedings_of_HPSSRC-updated_cs.pdf SP - 191 EP - 201 ER - TY - GEN A1 - Ledecky, Lukas A1 - Ciupack, Yvonne A1 - Pasternak, Hartmut A1 - Fischer, Vitali A1 - Stammen, Elisabeth A1 - Dilger, Klaus T1 - Lebensdauer von zyklisch beanspruchten Klebverbindungen im Stahlbau -Teil 1: Einflüsse auf das Tragverhalten T2 - Bauingenieur Y1 - 2019 SN - 0005-6650 VL - 94 IS - 1 SP - 29 EP - 35 ER - TY - GEN A1 - Ciupack, Yvonne A1 - Ledecky, Lukas A1 - Pasternak, Hartmut A1 - Fischer, Vitali A1 - Stammen, Elisabeth A1 - Dilger, Klaus T1 - Lebensdauer von zyklischen beanspruchten Klebverbindungen im Stahlbau - Teil 2: Untersuchungen zur Betriebsfestigkeitsprüfung einer Klebverbindung T2 - Bauingenieur Y1 - 2019 SN - 0005-6650 VL - 94 IS - 2 SP - 56 EP - 62 ER - TY - GEN A1 - Li, Zheng A1 - Pasternak, Hartmut T1 - Statistical size effect of flexural members in steel structures T2 - Journal of Constructional Steel Research N2 - 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. Y1 - 2018 U6 - https://doi.org/10.1016/j.jcsr.2018.01.025 SN - 0143-974X VL - 144 SP - 176 EP - 185 ER - TY - GEN A1 - Li, Zheng A1 - Pasternak, Hartmut T1 - Experimental and numerical investigations of statistical size effect in S235JR steel structural elements T2 - Construction and Building Materials N2 - 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. KW - 3D Random field KW - Stochastic finite element method KW - Mapping interpolation method KW - Statistical size effect KW - Steel structural elements Y1 - 2019 U6 - https://doi.org/10.1016/j.conbuildmat.2019.02.106 SN - 0950-0618 VL - 206 SP - 665 EP - 673 ER - TY - GEN A1 - Ciupack, Yvonne A1 - Pasternak, Hartmut A1 - Geßler, Achim A1 - Feldmann, Markus A1 - Kasper, Yann A1 - Albiez, Matthias A1 - Ummenhofer, Thomas T1 - Repair of Fatigue Cracked CT-specimens Using Adhesively Bonded CFRP Lamellas T2 - 27th Annual International Conference on Composites / Nano Engineering ICCE-27 Y1 - 2019 UR - https://www.b-tu.de/fg-stahlbau/publikationen/veroeffentlichungen ER -