PSI - Issue 32

G. Gusev et al. / Procedia Structural Integrity 32 (2021) 49–55 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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slopes of the structure in height at 6 points, a block for monitoring deformations in the bearing columns at 20 points, a block for monitoring the ambient temperature at 5 points, a block for monitoring the vibration state in two frequency ranges - from 0.5 to 400 Hz and from 400 Hz to 10 KHz. The system also has a unit for collecting, processing and storing measured data. All current information is sent to the server and displayed on the website in real time. The system serves to analyze the current stress-strain structure and must prevent the development of an emergency. The system can analyze the current state of the facility based on a mathematical model and respond to changes in parameters that determine the safe operation of the building. An important part of the monitoring system is the deformation control unit in the bearing columns. 3.2 Deformation control unit The deformation control unit consists of 20 control points. A strain gauge is located at each control point, which is a unique development. This development has a complex history of creation and use as a high-precision measuring instrument in an aggressive environment. Strain measurements are needed to monitor the change in forces in load bearing columns that can be caused by the evolution of vertical displacements. The evolution of vertical displacement was expected due to the thawing of the ground at the base of the structure. The control of the forces in the bearing columns is able to see the changes in the stress-strain state of the building before the implementation of significant displacements, which are also controlled. Therefore, deformation control is one of the most important tasks in this case. The first attempt was to use standard schemes for measuring deformations on steel elements using strain gauges. A full bridge scheme was used. In the circuit, two strain gauges measured the deformation at the test point. Two more strain gauges performed thermal compensation of deformations on the free plate. The strain gauges were glued to the columns using ethyl cyanoacrylate. The entire scheme was covered with a waterproofing compound - PLASTIK70. This solution didn't work. Although the measurement of deformations during the first three months was carried out in a regular mode, soon there was an uncontrolled increase in readings for all sensors. As it turned out, this was due to the fact that the sensitive elements of the strain gauge lattice were dissolved under the influence of the aggressive environment of the potassium salt. The electrical circuitry of the bridge connection has been broken. Corrosion lasted for several months - this was the reason for an increase in the value of deformations or a change in the electrical signal. The PLASTIK70 formulation failed to protect the electrical circuit from the potash brine, which was formed by the action of rain and pieces of loose ore.

Fig. 2. (a) a strain gauge; (b) a connection diagram of the sensor in the measuring circuit. Figure 2a shows the first version of the strain gauge, where:1 − is a group of active strain gages, 2 − is a temperature compensation group, 3 − is a bridge board, 4 − is a commutation wires. The figure shows a sensor eaten away by corrosion. The electrical circuit in the bridge connection was broken. The components of the strain gage (foil constantan) were found to be sensitive to the potassium salt. Ethyl cyanoacrylate has also been shown to be sensitive to corrosion. The impact of the salt withstood the textolite bridge platinum, which was covered with tin. The tinned twisted-pair copper wires and their insulation also withstood corrosion. Figure 2b shows the connection