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Axial force identification is of importance in the field of structural restoration and safety assessment for civil engineering structures composed of axially loaded members, such as roof trusses, truss girders and space trusses. Based on the state of research relating to the identification of the axial forces of iron and steel truss structures and advances in dynamic testing methods in the past decades, a research project has been started with the aim to develop a non-destructive methodology to identify the real axial stress state in existing iron and steel truss structures making use of the modal parameters of the structure’s natural frequencies and mode shapes. The characteristics of the systems of focus are light-weight iron and steel trusses consisting of filigree members that are primarily subjected to axial forces.
Vibration-based Model Updating and Identification of Multiple Axial Forces in Truss Structures
(2016)
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 presented.
Precise identification of the axial forces and corresponding stresses plays a crucial role for the preservation of existing truss structures. The assessment measures require non–destructiveness, minimum intervention and practical applicability. The work aims to develop a non–destructive methodology to identify the axial forces and stress states in iron and steel truss structures based on vibration measurements and the finite element model updating coupled with optimization techniques.
The inverse identification of the stress state in axially loaded slender members of iron and steel truss structures using measured dynamic data is discussed. 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.