@article{LuongZabelLorenzetal.2017, author = {Luong, Thi Mai Hoa and Zabel, Volkmar and Lorenz, Werner and Rohrmann, Rolf G.}, title = {Non-destructive Assessment of the Axial Stress State in Iron and Steel Truss Structures by Dynamic Measurements}, issn = {1877-7058}, doi = {10.1016/j.proeng.2017.09.447}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-42910}, year = {2017}, abstract = {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.}, subject = {Lightweight truss structures; Stress state; Modal parameters; Finite element model updating; Nature-inspired optimization techniques; Eisenkonstruktion; Stahlkonstruktion; Tragwerk; Dynamische Belastung; Finite-Elemente-Methode}, language = {en} } @phdthesis{Luong2017, author = {Luong, Thi Mai Hoa}, title = {Identification of the state of stress in iron and steel truss structures by vibration-based experimental investigations}, organization = {Bauhaus-Universit{\"a}t Weimar, Fakult{\"a}t Bauingenieurwesen}, issn = {1610-7381}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-44142}, school = {BTU Cottbus - Senftenberg}, year = {2017}, abstract = {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 in the research work 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.}, subject = {State of stress; Truss structures; Vibration measurements; Finite element model updating; Optimization techniques; Finite-Elemente-Modellkalibrierung; Optimierungsmethoden; Fachwerk; Stahl; Tragf{\"a}higkeit; Normalkraft; Finite-Elemente-Methode; Fachwerkbau; Tragwerk; Kalibrieren ; Beanspruchungszustand; Fachwerkartige Stahltragwerke; Schwingungsmessungen}, language = {en} }