PSI - Issue 5

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

625

R. Tsvetkov/ StructuralIntegrity Procedia 00 (2017) 000 – 000

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The value of crack width recorded by a number of sensors correlates with seasonal and diurnal air ambient temperatures. The influence of diurnal temperature changes on the crack width is less pronounced because the beam is affected per day by comparable factors (e.g. loads caused by the number of pedestrians). With account of these temperature changes some sensors (CS2, CS7, CS11) showed the tendency of the crack to increase with time. This fact motivated the installation of additional sensors for measuring beam deflections.

5.2. Results of beam vertical displacements

Fig. 5 presents the plots illustrating the changes in beam vertical displacements recorded by the hydrostatic level../../../../../../Documents and Settings/trans1/Local Settings/Temp/-970360710 sensors HS3 and HS4 placed on beam No.3 in the region near the support column and at the beam center relative to the sensor HS5 placed at the junction of beam No.3 and the wall of the main building. Fig.5a presents data obtained during two month monitoring, Fig.5b – during two-week monitoring. The hydrostatic level../../../../../../Documents and Settings/trans1/Local Settings/Temp/-970360710 sensors provide accurate measurements of seasonal and diurnal changes in the vertical displacements of the beams relative to the wall of the main building.

Fig. 5. Changes in the vertical displacements registered by the sensors HS3 an HS4 during two months of monitoring (a) and by the sensor HS4 during two weeks of monitoring (b).

The taut string sensors SS8 and SS9 (see Fig.2) placed on beam No. 3 at the beam center and near the support column reflect seasonal and diurnal changes in vertical displacements.

Fig. 6. Changes in the vertical displacements registered by the string sensors SS8, SS9 after two months of observations (a) and by the sensor SS9 after two weeks of recording (b).

The taut string and hydrostatic level sensors, independently of each other, execute control over the deformation process taking place in reinforced concrete beams. The results obtained by both types of sensors are in good qualitative and quantitative agreement. A slight quantitative discrepancy can be attributed to the fact that the external factors have different impacts on measurement subsystems. In the case of taut string sensors, the higher level of noise is associated with their higher sensitivity to dynamic factors. Both measurement subsystems are able to measure the vertical displacement of the beams with the accuracy quite sufficient for reliable registration of the deformation process in these beams at pre-critical and critical fracture stages.