Authors:
Egorov F.A., Ph.D. physics and mathematics sciences; Pospelov V.I., Ph.D. technical sciences; Bykovsky V.A.; Neugodnikov A.P.
In parallel with the rapid growth of construction technologies, the business sector represented by companies specializing in the automation of building management is actively expanding. At the same time, the main goals pursued by building automation systems are resource conservation, safety and comfort. Obviously, of the presented goals, safety has the highest rank of importance. And here a paradox arises in the very approach to ensuring safety, since the primary system — the system for monitoring the structural condition, or more precisely — monitoring the stress-strain state of the building — is usually not represented in the «gentleman's set» of control systems.
Basic monitoring system
The need to create systems for monitoring construction structures today does not require proof or justification. Moreover, in Russia and abroad, there is an active process of developing various systems for technical monitoring of construction structures.
The main question, which can be defined as the most important in this area, is why the existing monitoring systems have not become a tool that reliably and effectively tracks destructive changes in structures? The question is far from simple, and the answer to it should be sought in a complex of reasons.
Let's list the main aspects that influence the development of such systems:
• technical — definition of the physical and technical principles on which the measuring system is based;
• technological — development of methods and techniques for the production of components, installation of the system and operation;
• economic — optimization of the price parameters of the system.
It is obvious that the main reason for the absence of a standard monitoring system is the fact that most of the systems being developed are limited to consideration of one or several monitoring parameters. At the same time, monitoring of specific parameters is based on sensors of various types. Since any measuring system necessarily has two main components: a physical quantity converter and an electronic processing unit, the lack of uniformity in each of these parts greatly increases the diversity of monitoring systems and, as a result, reduces the possibility of creating a standard system.
Information from a large number of different types of measuring systems requires the creation of a complex processing system. On the other hand, system automation specialists develop increasingly complex technologies without asking the question of optimizing physical control procedures. At the same time, specific systems are created for different tasks, designs, and control and measuring conditions. As a result, a mass of independent systems with different operating principles appears, a new system appears for a new task, etc.
Therefore, it is necessary to create a monitoring system in the basic version, which should ensure control of the main parameters responsible for the most common causes of potential accidents. If necessary, the basic version should be expandable, both in the number of control points and in the types of controlled structures, as well as in the list of controlled parameters.
If necessary, the basic monitoring option should be able to be supplemented with control and measuring equipment based on other physical principles.
The stated goal can be achieved by solving the following problems (Table 1).
| Content formulation of the problem. Net Web portal (Starwood information platform and systems) |
Technical statement of the problem |
| Variety of building structures, technologies and projects |
Development of the most unified monitoring system |
| Diversity of existing sensors and control and measuring systems, disparate in terms of automation, signal processing and system diagnostics. |
Definition of a basic (reference) monitoring system based on a single physical principle, supplemented, if necessary, by other types of control and measuring systems |
| Dominance of reinforced concrete elements in the modern construction industry |
Development of a monitoring system with sensors that can be installed inside a reinforced concrete product, while having high stability and accuracy |
| Possibilities of operational modification of the monitoring system for various tasks |
The monitoring system must have maximum flexibility of the measuring unit, combined with the versatility of the electronic unit. This is realized in the case of using sensors of a single physical principle |
Monitoring system based on fiber-optic sensors «Monitoring Center»
Table 2. Technical characteristics of fiber-optic sensors «Monitoring Center».
| Parameter |
Fiber-optic soil pressure sensor |
Fiber-optic deformation sensor |
| Range of measured parameters |
0х10 kgf/cm2 |
Relative deformation — 0ч2•10-2
|
| Measurement error |
2% |
1.5%
|
| Sensitivity threshold |
0.2 kG/cm2 |
10 μ
|
| Power consumption of the signal meter |
No more than 2 W |
No more than 2 W
|
| Temperature exploitation |
-20…+60°C |
-30…+60°C
|
| Corrosion resistance |
yes |
yes
|
| Operating humidity |
0…100% |
0…100%
|
| Service life |
Not less than 10 years |
Not less than 10 years
|
| Overall dimensions of the sensor body |
Diameter – 180 mm, thickness – 20 mm |
60Ч44Ч14 mm |
Presence of power supply in the primary
converter |
absent |
absent |
To achieve the goal of developing an optimal construction monitoring system, defined by the list of tasks, a control and measuring system based on fiber-optic sensors is proposed. Let us formulate the basic principles of this system.
The basic sensor used in the monitoring system is a fiber-optic strain gauge. The sensor has several design options that allow it to be poured into a reinforced concrete structure or attached to the surface of building elements.
Installation of sensors at points of potential destruction (heavy loads, moments) is regulated at the design stage.
Monitoring can be carried out both during installation and during operation of the structure.
The electronic signal processing unit receives constant information about the state of the structure at internal and external control points.
Comparison of this information with design data in continuous mode allows us to draw conclusions about the “health” of the structure.
In this case, the analysis is performed by comparing the results of numerical modeling of the structure's condition with the actually measured data that are included in the calculation. The obtained result allows us to understand how the building as a whole was deformed. It is important to note that information is obtained only on local deformations, and conclusions can be made on the change in the building as a whole.
Additionally, the system includes a fiber-optic temperature sensor, the miniature size of the sensitive element of which allows it to be mounted in the most inaccessible places, including, again, inside reinforced concrete structures.
For important objects or in cases where additional control is required, the number of sensors increases, the system is supplemented with other sensors (both fiber-optic and traditional).
The electronic signal transmission and processing unit used in the system has a unified structure. Signals can be transmitted both via fiber-optic communication channels and via existing electrical networks (which does not require additional work on equipping communication channels), as well as in a wireless format.
The monitoring system based on fiber-optic sensors has an important property of clarity of the physical principle, which is extremely important from the point of view of large-scale implementation. In addition, fiber-optic sensors are an example of the most secure sensors that guarantee explosion safety and fire safety, since they do not have electrical circuits and signals. In addition, fiber-optic sensors are not affected by electromagnetic fields and do not induce them themselves.
Fiber-optic construction monitoring systems, having high accuracy and «unpretentiousness» in terms of stability, durability and operating mode in difficult operating conditions (for example, the possibility of embedding in reinforced concrete structures), in many cases have no competition as a tool for monitoring the level of safety.
Such systems protect houses and buildings from possible emergency events, making no difference between man-made or natural causes of their origin. The operator's console receives a signal about exceeding the specified limits of controlled deformation or temperature, and then experts analyze the received information about the «health» of the building, predict the development of the situation and make recommendations for developing the best solution. A recorded emergency event at the very beginning of its development is real safety, which is created by a fiber-optic construction monitoring system.
Implementation of a fiber-optic monitoring system at a high-rise facility
At the moment, the above-described monitoring system based on fiber-optic sensors is being installed at a multifunctional complex under construction in Moscow. The customer of the monitoring system was the MonArch Concern for a multifunctional business sports and recreational complex, which includes an office building, a hotel and a shopping center. The installation of the monitoring system is carried out by Monitoring-Center. The monitoring system is an in-house development of Monitoring-Center, and the sensors are certified and mass-produced. Scientific guidance is provided by the head of the Department of Soil Mechanics, Foundations and Foundations of Moscow State University of Civil Engineering, Professor Z.G. Ter-Martirosyan.
The most complex block of the multifunctional complex, the office block, with an above-ground part of 33 floors and an underground part of 3 floors, was chosen by the designers as the object of control. As a result of a thorough analysis of the geotechnical parameters of the soil in combination with a complex design solution, it was determined to install 125 sensors on the office block according to the following scheme:
• 24 soil pressure sensors along the foundation sole (sensors of type “M”)
• 21 reinforcement deformation sensors in the foundation (sensors of type “F”)
• 80 strain gauges in vertical elements (type “B” sensors) consisting of:
• 10 pylons with 2 gauges in each at “minus” of the 3rd floor;
• 10 pylons with 2 gauges in each at “minus” of the 1st floor;
• 10 pylons with 2 gauges in each on the 3rd floor;
• 10 pylons with 2 gauges in each on the 18th floor.
The fiber-optic ground pressure gauges are positioned in such a way as to solve 2 monitoring tasks:
• local pressure monitoring at a given point;
• global control of pressure distribution on the foundation slab.
Fiber-optic strain gauges installed in the foundation slab, also, according to the decision of the scientific director of monitoring, must solve 2 problems: local and global. As a local control tool, the strain gauge records the degree of elongation or compression of the reinforcement, which after normalization to the sensor base, using Hooke's law can be converted into stresses and the obtained values can be compared with the calculated ones.
Based on the data obtained as a result of regular recording sessions, the overall assessment of the situation can be given as satisfactory. In general, the reinforcement bars operate in the mode “prescribed” by the calculations, the analysis of individual data for each sensor provides a good correlation with the standards.
The distribution of pressure along the foundation sole provides interesting information on how the slab is loaded.
These data require detailed analysis. But already now some correlation with the data of deformation sensors can be traced. First of all, it is impossible to exclude the influence of the wall in the ground, which certainly presses on the structure of the building being erected, and the resulting, being laid out in the vertical and normal directions, can generate additional forces both in terms of slab deformation and in terms of pressure on the ground.
Today, in the research laboratory «Monitoring-Center» experimental design work is being completed on the creation of a fiber-optic sensor of wind loads on facades. Upon completion of this work, after finalizing the design documentation and carrying out the relevant patent and certification activities, the authors believe that they will be able to offer the construction sector a complete line of fiber-optic measuring systems. Based on such a line of measuring systems, it will be possible to create the most complete and effective system for monitoring the main technical parameters of high-rise and multifunctional buildings.
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