PSI - Issue 37

Dmitrijs Serdjuks et al. / Procedia Structural Integrity 37 (2022) 555–562 Dmitrijs Serdjuks et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Structural health of the building is determined by the structural health of its separate members and joints. Behavior of structural members and joints should be carried under the control during the whole service life of the building. Distribution of internal forces and deformations in structural members and joints depends on the joint ’s stiffness. The stiffness is the major parameter, which determines structural health of the joints and influences on the behavior of the whole building. The joints are divided into the following groups according to its initial stiffness: pinned joints, semi rigid joints and rigid joints. Pinned joint does not transmit any bending moments and joined members have possibility of free rotation in case if the friction forces are neglected. Semi-rigid joint transfers some bending moments by its sub members and connections and its behavior should be considered in global analysis of the whole buildings structure. Members are rigidly connected to each other and fully transmit bending moments in the rigid joint. The moment - rotation curve (Fig. 1 (a)), which describe s rotation deformation by angle θ as a function of the moment M, applied to the joint, must be used to model the joint’s behavior (Sagiroglu et al. (2015), Chittiprolu et al. (2014), Faridmehr et al. (2019), Baszeń (2017)) . Joints of steel structures can be divided into the following groups depending on the types of joined steel members (Fig.1 (b)): b eams to columns joints (A); beams to beams joints (B ); c olumns to columns joints (C); columns to foundation joints (D). A full-scale experimental test must be performed to obtain the moment-rotation curve, which describes rotation deformation by angle θ as a function of the moment M, applied to the joint. Relation of the joint to the certain group is determined by the existing classification boundaries. The classification boundaries were devised to limit the error to 5% for internal forces and 20% for deformations for steel structures ( Šabatka et al. (2019 ), EN 1993-1-8 (2005)). The changes of internal forces are insignificant in pinned and rigid region even if the stiffness changes 100 times and changing rapidly in the semi-rigid region. The object of the interest for non-destructive testing methods are rigid and semi-rigid joints. Increased internal forces and deformations will develop in the structure if fasteners and details that provide the rigidity of the joint are damaged or destroyed during the service life. Significant second order effects are formed in the steel structures as the result of decreased joints stiffness (Faridmehr et al. (2019)). Therefore, the ability to check the stiffness of the joints and to compare it with the initial stiffness is important. Semi-rigid and pinned beams to beams conditions of a joint are investigated in the current study. Choice of structural health monitoring methods depends on the material of the joined structural members, its loading case, joint structure and stiffness. Vibration analysis methods make it possible to determine possible damages of structures or structural joints due to changes in the frequency response, modal shape and damping. The methods based on vibration analysis are divided into two categories - methods using ready-made mathematical models and methods that do not employ models.

Fig. 1. Groups of structural joints (a) according to its initial stiffness; (b) according to the type of steel members are joined.