PSI - Issue 37

Dmitrijs Serdjuks et al. / Procedia Structural Integrity 37 (2022) 547–554 Dmitrijs Serdjuks et al/ Structural Integrity Procedia 00 (2019) 000 – 000

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© 2022 Dmitrijs Serdjuks et al. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira Keywords: Structural health monitoring, Vibration analysis; Structural joints; Coaxial accelerations © 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira 1. Introduction As the number of people in the world is growing, achieving a faster construction process is actual. In this situation, a popular choice is using structural members, which are manufactured in plants away from the construction site. After that, they are delivered to the construction site to be erected and joined together. One of the essential parts of structural analysis and design is the calculation of joints. Joints play an essential role in the behaviour of the building structures and can be classified according to the several criteria: • Material of the joined structures (timber, steel, precast concrete) • Loading situation (tension, compression, bending, shear, torsion) • Stiffness of joint (rigid, semi-rigid, pinned) • Joint type and/or fastener used (glued connections, carpentry connections, connections with mechanical fasteners, welded joint) The stiffness of the joints particularly influences the total structural firmness of buildings. The stiffness control of the joints during the building lifetime is essential to ensure that the current situation corresponds to the designed one and that the building is safe. The joint stiffness affects the distribution of internal forces in a structure both in members and joints (ultimate limit state) and deformations (serviceability limit state). The joints are classified according to initial stiffness as: • Pinned - does not transmit any bending moments • Semi-rigid - transfers some bending moments, and its behaviour needs to be considered in global analysis • Rigid - members are rigidly connected and fully transmit bending moments The moment-rotation curve, which describes rotation deformation by angle as a function of the moment applied to joint, can be used to model the behaviour of the joints (Sagiroglu et al. (2015), Chittiprolu et al. (2014), Faridmehr et al. (2019), Baszeń (2017)). A full-scale experimental test must be performed to obtain the moment – rotation curve. Usually, the joints are assumed to be pinned or entirely rigid to simplify the analysis and design process. However, there are discrepancies between idealized and actual behaviour. No joint is ideally pinned or completely rigid, but there are some classification boundaries. For example, for the steel structures, the classification boundaries were devised to limit the error to 5% for internal forces and 20% for deformations ( Šabatka et al. (2019), EN 1993-1-8 (2005)). The changes of internal forces are insignificant in the pinned and rigid region. The load capacity of the beam structures depends on the bending moment, so the ideally pinned connection is generally a conservative solution for the beam design. The object of interest for non-destructive testing methods are rigid joints. If, during the structure’s lifetime fasteners that ensure the rigidity of the joint are destroyed, much greater internal forces and deformations will develop in the structure, and it potentially can be dangerous. In addition, as the result of increasing connection flexibility, significant second-order effects are formed in the structures (Faridmehr et al. (2019)). Therefore, checking the joints’ current stiffness and comparing it with the initial stiffness is essential. The structural health of joints is directly related to their stiffness. Structural health monitoring (SHM) methods enable investigation and testing of structural joints behaviour during the whole service life of buildings. Choice of SHM method depends on the material of the joined structural members, its loading case, joints’ structure and stiffness. Since the beginning of the 21st century, many SHM methods have been developed to investigate structural behaviour based on shock and vibration analysis. Vibration analysis methods allow determining possible damages of structural joints based on frequency response, modal shape and damping. Methods of vibration analysis are classified into two categories - methods using ready-made mathematical models and methods that do not employ such the models for