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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3.2. Results of vibration experiment The vibration test examined the ability of the proposed method of coaxial accelerations correlation to determine the stiffness of the joint in the timber beam stand. The decrease of the rigid joint stiffness was modelled by the gradual removal of screws and bolts in the connecting steel corners. Seven grades of stiffness were considered: Grade 1 (initial): Rigid joint, all screws and bolts tightened (Fig.3(a)) Grades 2-5: rigid joint with the decreased stiffness with gradually loosened screws and bolts (Fig.5(b)) Grade 6: pinned joint, with only one bolt (Fig.3(b)) Grade 7: absence of the joint between the girder and the beam (Fig.3(c)) The beam was subjected to a vibration load provided by electrodynamics actuators, fixed on the edge of the beam, as shown in Fig. 5 (a). Vibration response signals in both parts of the joint, the girder and the beam, were recorded in 3 spatial directions by two 3D accelerometers fixed respectfully on the girder and the beam (Fig.5) and transferred to the computer. A vibration test was done at all seven grades of the joint. Differences in the vibration signals were noted in three directions: 0-1, 2-3 and 4-5. The highest values of PVCF were obtained in the direction 4-5. NPVCF values, 5 repeated measurements and average, in 7 grades of joint stiffness are shown in Fig.6. The vibration experiment confirmed that the differences in vibration signals occur due to loss of the joint stiffness and the decrease of NPVCF values calculated from coaxial correlations reflect the grade of stiffness loss in the joint of the timber beams stand.

Fig. 5. (a) scheme of the timber beams dynamic loading; (b) accelerometers placement near considered joint with an indication of directions for vibration records fixations.

Fig. 6. Normalized peak values of correlation functions, obtained for the five measurements for the seven grades of the joint stiffness and its average values curve.