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

550 4

The calculation of PVCF between two data arrays, i.e., vibration signals in the time domain, from the first and second accelerometers F1 and F2, was performed according to the following algorithm: • Removing the constant component from each signal F1, F2 by subtracting the average value in the entire time window (in our case, 1 sec) • Addition to each of the signals on the left and right an array of zero values, with a duration of 1 sec • Calculation of the convolution of the two received signals • Determination PVCF as the maximum modulo value for the resulting convolution Thus, vibration signals were collected from 3 coaxial pairs of two accelerometers rigidly placed on the joined elements of the stand and NPVCF parameter was finally determined as the measure of the stage of the joint’s stiffness. NPVCF measured at the initial and reliably confirmed the stiff condition of a system or a building is proposed as the reference standard for further monitoring the system or building during its exploitation. 2.2. Timber beam stand A stand of timber beams was arranged as shown in Fig.2 as a simple model in static loading and vibration test to verify the static diagram of the structure and evaluate the proposed method of coaxial correlations correspondingly. The stand consisted of a girder and an orthogonal beam forming T-connection and made of solid timber of C18 strength class with 150x50 mm cross-sections. The beam was freely supported, one with spans of 2.06 m and two spans of 1.5 m each. The girder and the beam were joined rigidly by steel corners and bolts. Static loading was concentrated vertical forces applied to steel pieces on two suspended platforms P1 and P2 shown in Fig.2. Static diagram of the stand depended on the stiffness of the joint varied by tightening screws and bolts in steel corners. A static test used six deflectometers and six strain gauges to verify the static diagram by 7 grades of the joint stiffness e stand. Three static diagrams of the stand were considered for three conditions of the joint (Fig.3): rigid (moment) joint; pinned joint of the girder and beams; no connection between girder and beams when all screws and bolt were deleted. To join beams, steel screws of a diameter 4 mm, steel bolts of a diameter 8 mm, angle profiles Arras Construction Furniture OU 105x105x90x3.0 and perforated steel plates Arras Construction Furniture OU 200x50x3.0 were used. Perforated steel corners provided the joint’s moment load-carrying capacity (rigidity), shown in Fig.3(a).

Fig. 2. Stand of timber beams: (a) layout of static load application; (b) view of the timber beams stand loaded by the set of concentrated vertical forces.