PSI - Issue 5

V. Epin et al. / Procedia Structural Integrity 5 (2017) 620–626 R. Tsvetkov / Structural Integrity Procedia 00 (2017) 000 – 000

624

5

generation of new cracks. It was assumed that the cracks detected in the load-bearing beams at the instant of installation of first sensors appeared during the previous service life of the building. This made possible the estimation of the deformation level of all the structural elements before the installation of the monitoring system. The numerical analysis reveals the following features of the deformation state of the structure under consideration: - the regions of beam-column junctions are most critical; - the measured beam deflection values correlate with the resultant crack opening near the support columns. Based on the obtained results, the arrangement scheme of sensors was defined, and the developed mathematical model became a part of the analytical unit of the automatic deformation monitoring system. This allowed us to interpret and analyze the measured values of crack width and beam deflections. The described automatic deformation monitoring system was installed in the above mentioned structure in the early 2015. The sensors for measuring crack opening were placed on the longitudinal beams of the air bridge. After the analysis of the deformation processes developing over a period of 2 years, the system was supplemented with sensors for measuring vertical displacements and beam deflections. At present, 54 sensors of different types are placed on 9 beams (see Fig.2). The results given below illustrate the operation of the proposed automatic deformation monitoring system. 5. Monitoring results

5.1. Results of crack opening

Changes in the crack width are shown in Fig.3: (a) recorded by two sensors of the monitoring system during 24 months and (b) during 2 weeks. The sensor CS2 is placed at the junction of one of the column and beam No.2, and the sensor CS7 is placed in a similar way on beam No.3. The corresponding ambient temperature changes are shown in Fig.4. Seasonal ambient temperature changes observed throughout the year were of the order of 50°C (Fig.4a), and diurnal ambient temperature changes – about 10 – 12°C (Fig. 4b).

Fig. 3. Changes in the crack width registered by the sensors CS2and CS7 during two-year monitoring (a) and by the sensor CS7 during two-week monitoring (b).

Fig. 4. Changes in the ambient air temperature after two years (a) and two weeks (b) of monitoring.