PSI - Issue 37

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

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3.3. Discussion Shear stiffness of the considered joint for grades 1-7 were analyzed according to the standard EN 1995-1-1 and shown in Fig.7 (a) by the blue line. Shear stiffness of the joint is obtained on the base of the slip modulus, calculated for the screws and the bolt according to EN 1995-1-1 (2004) and EN 26891 (2013). The shear stiffness of the screw with a diameter of 4 mm and the bolt with a diameter of 8 mm were 1.61 and 2.58 N/m. Shear stiffnesses of the joint were 61.8 and 10.3 N/m for the rigid and pinned conditions of the joint, correspondingly. It was shown that shear stiffness for 1-7 grades of the joint stiffness decreased consequently with the grade. NPVCF values reduced to shear stiffness and shown in the identical Fig.7(a) by red line had the same declining trend, but a different character with a sharper decrease between grades 2 and 3. Changes of the experimentally determined rotation stiffness and the respectively reduced NPVCF values by seven grades of the joint stiffness are shown in Fig. 7 (b). The patterns of the changes of the reduced NPVCF and rotation stiffness coincided to a large extent.

Fig. 7. (a) shear stiffness and corresponding normalized peak values of the correlation function for grades of stiffness 1-7 of the considered joint; (b) rotation stiffness and corresponding normalized peak values of the correlation function for grades of stiffness 1-7 of the considered joint.

The study showed that the differences between NPVSF parameters calculated based on 3D coaxial accelerometers correlation for the rigid, semi-rigid and pinned conditions of the joints enabled quantification and specification of the joint’s shear and rotation stiffness. The proposed vibration analysis method of coaxial accelerometers correlation for quality assessment of structural joints was successfully demonstrated for timber beam joints. Analysis of vibration in 3D space enables assessment of the stiffness of joints of planar structures in general cases. For quality assessment of structural joints of spatial structures, the analysis of vibration in 6D space is preferable. It enables the evaluation of shear and rotation stiffness in 6 degrees of freedom . 4. Conclusions A vibration analysis method of 3D coaxial accelerometers correlation for quality assessment of structural joints in three spatial directions was proposed. The method is based on the mathematical analysis of natural vibrations of structural joints in 3D spatial directions using 3D accelerometers located at different parts of a joint and oriented coaxially. The method enables the evaluation of the changes of the structural joint’s shear and rotation stiffness caused by the damaging or degradation of the joint during exploitation. The proposed method was experimentally tested on the timber T-joint in the rigid, semi-rigid and pinned conditions. It was shown that the difference between the peak values of the normalized correlation functions obtained for the rigid, semi-rigid and pinned joints enabled specification of the joints’ shear and rotation stiffness.