TY - GEN A1 - Luong, Thi Mai Hoa A1 - Zabel, Volkmar A1 - Lorenz, Werner A1 - Rohrmann, Rolf G. T1 - Vibration-based Model Updating and Identification of Multiple Axial Forces in Truss Structures T2 - Procedia Engineering N2 - Safety assessment of existing iron and steel truss structures requires the determination of the axial forces and corresponding stresses in truss structural members. The results of the axial force determination can be integrated as part of a structural health monitoring scheme for existing trusses. In this work, a methodology is proposed to identify multiple axial forces in members of a truss structure based on the modal parameters. Vibration test allows the identification of the natural frequencies and mode shapes, globally of the truss structure as well as locally of the individual bars. The method calibrates the numerical model of the truss structure using a genetic algorithm and strategic validation criteria. The validation criteria are based on the identified natural frequencies and global mode shapes of the truss structure as well as information of the axial forces in the individual bars of the truss, which are estimated from the natural frequencies and five amplitudes of the corresponding local mode shapes of the single bars based on an analytical-based algorithm. The calibration allows the identification of the axial forces in all bars of the truss structure. For mode pairing strategy, a technique makes use of the enhanced modal assurance criteria with the calculation of the modal strain energies. Moreover, the modal strain energies are also used to select the relevant local mode shape of the individual bars. The feasibility and accuracy of the proposed methodology is verified by laboratory experiments on several truss structures. In situ tests on existing trusses are intended. The results from one of the laboratory tested structures, i.e. a two-bar system, are included in this paper. KW - Truss structures KW - axial force KW - dynamic test KW - model updating KW - optimization technique Y1 - 2017 U6 - https://doi.org/10.1016/j.proeng.2017.04.499 SN - 1877-7058 VL - 188 SP - 385 EP - 392 ER - TY - GEN A1 - Luong, Thi Mai Hoa A1 - Zabel, Volkmar A1 - Lorenz, Werner A1 - Rohrmann, Rolf G. T1 - Non-destructive Assessment of the Axial Stress State in Iron and Steel Truss Structures by Dynamic Measurements T2 - Procedia Engineering N2 - This paper is concerned with the inverse identification of the stress state in axially loaded slender members of iron and steel truss structures using measured dynamic data. A methodology is proposed based on the finite element model updating coupled with nature-inspired optimization techniques, in particular the particle swarm optimization. The numerical model of truss structures is calibrated using natural frequencies and mode shapes from vibration tests, as well as additional information of the axial forces in selected truss members based on the experimentally identified modal parameters. The results of the identification are the axial forces or corresponding stresses in truss structures and the joint rigidity in relation to pinned and rigid conditions. Attention is given to several examined aspects, including the effects of the axial tensile and compressive forces on the dynamic responses of trusses, mode pairing criteria, as well as modeling assumptions of joints and the use of a joint rigidity parameter. Considering the pairing of modes, it is performed by adapting an enhanced modal assurance criterion that allows the selection of desired clusters of degrees-of-freedom. Thus, information extracted from the measurements related to specific modes is utilized in a more beneficial way. For modeling of joints, the numerical model of a truss structure includes rotational springs of variable stiffness to represent semi-rigid connections. Moreover, a fixity factor is introduced for practical estimation of the joint flexibility. The effectiveness of the proposed methodology is demonstrated by case studies involving simulated and laboratory experimental data. KW - Lightweight truss structures KW - stress state KW - modal parameters KW - finite element model updating KW - nature-inspired optimization technique Y1 - 2017 U6 - https://doi.org/10.1016/j.proeng.2017.09.447 SN - 1877-7058 VL - 199 SP - 3380 EP - 3385 ER - TY - CHAP A1 - Luong, Thi Mai Hoa A1 - Lorenz, Werner A1 - Rohrmann, Rolf G. A1 - Zabel, Volkmar A1 - Said, Samir T1 - Finite Element Model Calibration of a Historic Wiegmann–Polonceau Truss Based on Experimental Modal Parameters T2 - Experimental Vibration Analysis for Civil Structures: Testing, Sensing, Monitoring, and Control N2 - This paper describes the experimental calibration of an existing Wiegmann–Polonceau roof truss based on modal parameters. Dynamic tests allowed the determination of the natural frequencies and mode shapes of the global truss and of individual truss members. The global and local modal configurations as well as coupled vibration of truss members are discussed. In addition, as truss members are axially loaded, the effect of stress stiffening on the modal parameters is considered. Moreover, several finite element models with different modelling assumptions for the details of the connections and member geometrical characteristics such as gusset plates and turnbuckles were developed. A suitable numerical model was chosen to represent the truss structural behavior. This paper focuses on the local measurement and analysis strategies applied to single truss members. The possibility of using a local analysis method, namely methods that consider individual members as part of a structure, is demonstrated to assess the behavior of the global truss structure. The comparison of the results after calibration reveals a very good correlation between the experimentally identified and numerically estimated modal parameters of the historic truss. KW - Historic truss structures KW - Coupled vibration KW - Stress stiffening KW - Modal analysis KW - Finite element model calibration Y1 - 2017 SN - 978-3-319-67443-8 U6 - https://doi.org/10.1007/978-3-319-67443-8_18 SP - 212 EP - 224 PB - Springer International Publishing CY - Cham ER - TY - CHAP A1 - Luong, Thi Mai Hoa A1 - Ramos, Luís F. A1 - Aguilar, Rafael ED - Proulx, Tom T1 - Identification of the Tensile Force in Tie-rods of Historical Constructions T2 - Civil Engineering Topics, Volume 4, Proceedings of the 29th IMAC, A Conference on Structural Dynamics, 2011 N2 - This paper addresses the problem of the bending curvature due to self-weight of tie-rods when using dynamical approach to identify the tensile force in tie-rods of historical constructions. Although several dynamic testing methods have been proposed in the literature, the effect of bending curvature due to self-weight of the rods on their frequency values has not been studied. In this work, the bending curvature due to self-weight of tie-rods with small cross-section-to-length ratios is proven to have significant effect on their frequency values of the first vibration mode at low tensile stresses. As a result, the accuracy of the identified tensile force in tie-rods will be affected if the effect is not accurately considered. Four tie-rod specimens of different characteristics were tested in laboratory by dynamic tests. A numerical model was developed for axially loaded tie-rod using a FE program, assuming Euler beam with uniform cross-section and rotational springs at both supports. By calibrating the experimental and numerical results, the most suitable dynamical analysis for tie-rod models to take into account the effect of bending curvature due to their self-weights is concluded. In particular, the analysis should be performed in two steps: (i) first, the static geometric non-linear analysis to obtain the deflected shape of the tie-rod due to its self-weight and an applied tensile force; (ii) then, the modal analysis is run on the deflected tie-rod to achieve the frequencies and mode shapes via free vibration at that applied tensile force. When the effect of bending curvature due to self-weight of tie-rods is neglected, the frequency of the first mode should be excluded. Based on these conclusions, two techniques to identify in-situ the tensile stress in tie-rods are discussed. They are frequency-based identification techniques that minimize the measurement errors. In addition, a methodology to estimate a range of tensile stress using a formula or two selfconstructed standard charts is proposed. KW - Axial force KW - Tie-rod KW - Historical constructions KW - Finite element model updating Y1 - 2011 SN - 978-1-4419-9316-8 SN - 978-1-4419-9315-1 U6 - https://doi.org/10.1007/978-1-4419-9316-8_6 SP - 71 EP - 81 PB - Springer CY - New York, NY ER - TY - CHAP A1 - Luong, Thi Mai Hoa T1 - Experimentelle und numerische Untersuchung der Normalkraft in historischen Stahl-Zugankern mit Hilfe von dynamischen Methoden T2 - 23. Hanseatische Sanierungstage vom 1. bis 3. November 2012 im Ostseebad Heringsdorf/Usedom N2 - In der Masterarbeit wurde eine zerstörungsfreie Untersuchungsmethode zur Berechnung der Zugkraft in Zugankern unter Berücksichtigung der Verformung infolge des Eigengewichtes entwickelt. Die Arbeit beschäftigt sich speziell mit der Untersuchung von Zugankern in historischen Mauerwerksgewölben. Für das Verfahren werden dynamische Ansätze verwendet, um zunächst die Eigenfrequenzen des Zugankers zu bestimmen. Aus den ermittelten Eigenfrequenzen kann dann die vorhandene Normalkraft in den Zugankern abgeschätzt werden. Die Untersuchungen wurden sowohl experimentell im Labor, als auch analytisch mit Hilfe der Finiten-Elemente-Methode durchgeführt. Die verschiedenen Einflüsse, wie zum Beispiel die Auflagerungsbedingungen, Länge und Querschnitt des Zugankers sowie die vorhandene Normalspannung wurden bei den Untersuchungen berücksichtigt. Y1 - 2012 SN - 978-3-410-22995-7 SN - 978-3-8167-8794-5 SP - 113 EP - 130 PB - Beuth [u.a.] CY - Berlin [u.a.] ER - TY - THES A1 - Luong, Thi Mai Hoa T1 - Identification of the State of Stress in Iron and Steel Truss Structures by Vibration–based Experimental Investigations N2 - Safety evaluation of truss structures depends upon the determination of the axial forces and corresponding stresses in axially loaded members. Due to presence of damages, change in intended use, increase in service loads or accidental actions, structural assessment of existing truss structures is necessary. Precise identification of the stresses plays a crucial role for the preservation of historic truss structures. The assessment measures require non-destructiveness, minimum intervention and practical applicability. Motivated by the preservation of existing truss−type constructions composed of axially loaded slender members, the present work aims to develop a non-destructive methodology to identify the axial forces or corresponding stress states in iron and steel truss structures. The approach is based on vibration measurements and the finite element method combined with optimization techniques. After a state of the art review, numerical and experimental studies were carried out on different partial systems of truss-type structures. The examined aspects included the effects of structural loading on the dynamic performance of truss structures, modelling of joint connections, mode pairing criteria, selection of updating parameters and definition of an objective function, as well as the use of different optimization techniques. A methodology consisted of a two-stage model updating procedure using optimization techniques was proposed for the determination of multiple member axial forces and estimation of the joint flexibility of truss-type constructions. In the first stage optimization, the validation criterion is based on the experimentally identified global natural frequencies and mode shapes of the truss. Additionally, the axial forces in selected individual members of the truss are used. They are estimated from the natural frequencies and five amplitudes of the corresponding local mode shapes of the members using an analytically−based algorithm. Based on the results of the identified axial forces in the first stage, a second optimization procedure for the joint stiffness is performed. In this stage, the modal parameters of the global natural frequencies and mode shapes are used as validation criterion. From the results of the investigated systems, the identified axial forces by the proposed methodology agree well with the experimentally measured axial forces. Furthermore, recommendations are given in the work for a guideline of measuring concepts and assessment strategies applied to existing iron and steel truss-type structures. KW - Finite element model updating KW - Optimization techniques KW - State of stress KW - Truss structures KW - Vibration measurements Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:co1-opus4-44142 ER - TY - RPRT A1 - Luong, Thi Mai Hoa T1 - 8th International Conference on Structural Analysis of Historical Constructions (SAHC 2012) N2 - The eighth SAHC conference took place from 15th to 17th October 2012 in Wroclaw, Poland, and is one of the most prestigious events in the field of preservation of historic constructions. In line with the theme of the conference, the meeting place was the UNESCO World Heritage listed Centennial Hall Complex, one of the best-known cultural heritage buildings in Wroclaw. Over 500 people from more than 50 countries gathered in Wroclaw over the three days to discuss a wide range of topics including ongoing research, latest trends and methods, and their applications in monument conservation. Academics and professionals from a broad spectrum of backgrounds were represented, including scientists, engineers, architects, designers, conservationists, archaeologists and students. KW - SAHC 2012 Y1 - 2012 UR - http://www.em-a.eu/en/home/newsdetail-ema-members-report/8th-international-conference-on-structural-analysis-of-historical-constructions-sahc-2012-1017.html ER -