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

559 5

Fig. 2. (a) proposed measuring device with its major components; (b) electrodynamic actuator and it fastening on the steel beam; (c) vibration record .

Vibration records were taken by two 3D accelerometers and the differences of the records were compared for all three directions. Peak values of the cross-correlation function between the responses from the correspondingly orientated pairs of coaxial accelerometers were determined and averaged. The data processing in the following stages: processing of the correlation function between coaxial directions of accelerometers; determination of peak values of correlation functions; averaging of peak values for same stiffness of the joint and directions; and normalization of the values obtained in the previous stage from minimum to maximum in range from 0 to 100 %. SigView software of SigTest (https://sigview.com) was used for processing the vibration signals. Normalized correlation function was calculated as the final measurement outcome. Firstly, the convolution of two signal functions, the responses from accelerometer 1 and accelerometer 2, were calculated. The peak value of the correlation function was determined as the maximum modulo value for the resulting convolution. The peak values in each pair of the coaxial directions were normalized by the maximum value in the experiment. 3.2. Description of investigated steel beams joint A steel beam stand was used to verify the suggested non-model method of vibration analysis for SHM of structural joints, where stiffness of structural joints was a function of vibration parameters of the structure. The steel beam stand, consisting of the main and additional beams, joined together by the semi-rigid joint of a variable stiffness, was the object of the investigation (Fig.3). Both beams have HEA 100 cross sections. Material was S355 strength class steel. The beams were joined by a SRS bolt with the strength class 8.8 and a diameter of 8 mm. The stand was loaded by a system of concentrated vertical forces that varied within a range from 0 to 10 kN. Each step of loading was equal to 1 kN. The vertical loads were applied by adding of the steel pieces to the loading platforms. Three couples of deflectometers and strain measuring devices were used to determine the experimental values of stresses and maximum vertical displacements. Maximum vertical displacements and stresses were determined in positions I, II and III, which are shown in the Fig. 3. Two stages of the steel beams joint were considered in course of the statical experiment. Rigid joint was obtained when the bolt was completely fixed by the maximum force added to the nut by torque wrench. The corresponding torque moment was equal to 150 Nm. Pinned joint was created when the nut was deleted (Topcijs (2021)).