And about. head of department engineering surveys and inspection of building structures Belskaya Yu.S.
Methods for observing cracks in stone and concrete structures
Cracks in buildings and structures can form due to various reasons. They might just spoil appearance, but may indicate a serious safety threat to people.
Defects that seem insignificant at first glance, if not corrected in a timely manner, can progress and, ultimately, cause complete destruction of structures. Such defects include cracks in stone and concrete structures.
According to the type of development, cracks can be stabilized or unstabilized over time. In order to determine if the development of a crack continues or has stopped, a beacon is installed on it in the place greatest development cracks. When observing the development of a crack along its length, the ends of the crack are fixed with transverse strokes during each inspection. The date of inspection is indicated next to each stroke. The location of the cracks is schematically plotted on the drawing of the walls of the building or structure, noting the numbers and date of installation of the beacons. For each crack, a schedule of its development and opening is drawn up. Based on the results of systematic inspections, a report is drawn up, which indicates the date of inspection, a drawing with the location of cracks and beacons, information about the absence or appearance of new cracks. The rupture of the beacon or the displacement of the plates relative to each other indicates the development of deformations. Beacons are inspected a week after their installation, then at least once a month. In case of intense cracking, daily monitoring is required. The opening width of cracks during observations is measured using crack gauges. The observation log records the number and date of installation of the beacon, the location and layout, the initial width of the crack, and changes in the length and depth of the crack over time. If the beacon is deformed, a new one is installed next to it, which is assigned the same number, but with an index. Lighthouses on which cracks have appeared are not removed until the end of observations. If no change in the size of the cracks is detected within 30 days, their development can be considered complete, the beacons can be removed and the cracks can be repaired.
Gypsum (cement) beacons
Of all the methods, the traditional design of a gypsum or cement beacon for observing cracks has the least cost. Dimensions of beacons: length 250-300 mm, width 70-100 mm, thickness 20-30 mm. Beacons are installed across cracks in places of their greatest development and are securely fixed to the load-bearing part of the walls on both sides of the crack (see Fig. 1).
Beacons are placed in places cleared of plaster, allowing for daily observations. Each beacon is assigned a number and the date of its installation is indicated. It is not allowed to install gypsum beacons in damp places - in this case it is necessary to install beacons made of cement mortar.
Plate beacons
The design of the beacons allows their use in a wide range of weather, temperature and humidity conditions. Readings can be taken both visually and using measuring instruments.
The deformation scale represents 2 plastic plates, one of which is marked with a millimeter grid and a reading scale, and the second with a control crosshair.
The method of using the deformation scale is the most simple solution to monitor cracks that may form as a result of the following phenomena:
Uneven foundation settlement;
- temperature deformations of long walls;
- overloading of individual sections of walls as a result of dismantling the structure without complying with technical requirements.
The deformation scale consists of two plastic plates. They are attached to both sides of the crack so that when the crack opens, the plates slide over one another, and the red crosshair of one plate moves relative to the millimeter scale of the other plate, allowing you to take a report on the scale and enter it in the observation log. The plates must be secured parallel to each other. After attaching the deformation scale to the building, it is assigned a number and the number and date of installation are noted on the scale. By measuring the distance between the scale marks, the size of the crack opening is determined.
Visual monitoring is possible both along the vertical and horizontal axes.
Observation of cracks at 3 – 4 points
In some cases, plate and electronic beacons cannot be used when monitoring cracks. For example, in cases where the risk of damage to beacons is high, or the installation of beacons is undesirable for aesthetic reasons. In these cases, observation of cracks in building structures can be performed using fixed observation points. On each side of the crack, two points are secured using dowels or other devices. The installed devices are usually unnoticeable and at the same time securely fixed. With this method of monitoring cracks, measurements are made using high-precision measuring instruments - digital calipers. The distances between fixed points are measured, and the measurement results are entered into spreadsheets. After processing the data, we obtain the amount of movement of parts of the structure separated by a crack relative to each other along two axes - vertical and horizontal. This method of monitoring the deformations of buildings and structures does not have the capabilities of visual observation, and calculations are required to obtain results.
However, three- or four-point observation is the only reliable and at the same time highly accurate method of observation in places where there is a high probability of losing other types of beacons due to vandals.
We have already written earlier on the website in the article "" how cracks in load-bearing structures and what are the main reasons for their formation. Some idea of monitoring can also be obtained from the article "", published earlier. And today’s publication is devoted to specific monitoring methods and devices used for these purposes - the so-called “beacons”. At the end of the article you can watch a presentation with photographs and diagrams of the lighthouse structures described.
In what cases is it usually necessary to monitor cracks in a building?
- As part of comprehensive monitoring of building deformations
- In the presence of load-bearing structures that have limited operability and emergency conditions
- If the building falls into the zone of influence of new construction or reconstruction
The main task when monitoring cracks is to record changes in their parameters for objective control technical condition designs.
The goals of monitoring may be different, but their essence is the same - timely receipt of information about ongoing changes for decision-making. Based on the monitoring results, decisions can be made on the possibility of further operation, the need and type of repair measures, prompt elimination of factors affecting the development of cracks (for example, dynamic influence from a nearby construction site), prevention emergency situations and so on.
Monitoring objectives, technical condition and design features influence how crack development is monitored. When choosing the method and methods of observation, the following main factors must be taken into account:
- The need to take into account temperature and humidity influence
- The need to quickly obtain information
- Required measurement accuracy
- Cost, reliability and durability of the monitoring system and its components
- The complexity of taking readings and servicing the system
What beacon designs are used for observing (monitoring) cracks and what are the features of their use?
Electronic sensors and monitoring systems
To take into account temperature and humidity influences on structures, it is necessary to make appropriate measurements. Moreover, for an objective assessment of such influences, indicators of temperature/humidity of air and structures both outside and inside the premises may be required. A sufficient amount of such data can only be provided by electronic system continuous monitoring with task-appropriate sensors. It is also possible to obtain the necessary data in fragments using manual measurements with instruments at the time of taking readings from beacons installed on cracks. But this approach should still be considered uninformative, since it does not provide enough data to assess the influence of temperature and humidity on changes in the parameters of cracks in structures.
Electronic devices also have the greatest efficiency in obtaining measurement results. measuring systems with the possibility of remote information transfer. They also generally have the greatest measurement accuracy - they record the width of the crack opening to hundredths of a millimeter. The disadvantages include the impossibility of measuring with one sensor the movement of parts of a structure relative to each other in the vertical and horizontal directions simultaneously.
Accurate electronic measuring monitoring systems allow short-term (2-15 days) observation cycles to be carried out, providing information on current trends in the development of deformations and allowing prompt decisions to be made. Such systems are becoming increasingly widespread, but the main obstacle to their widespread use remains their high cost and low resistance to vandalism. Nevertheless, this is certainly a promising direction in the development of deformation monitoring tools, with the help of which it is already possible to solve a wide range of monitoring tasks.
Gypsum beacons
Of all the methods, the traditional design of a gypsum beacon for observing cracks has the least cost. However, it has a number of disadvantages:
- Ineffective for use in outdoor structures and places where significant temperature fluctuations are possible. In such conditions, the gypsum beacon is “triggered” by temperature deformations, which does not make it possible to unambiguously determine the presence of other factors influencing the crack.
- Low durability and intensive destruction under unfavorable conditions external conditions, high damageability.
- Labor-intensive installation, impossibility of installation at subzero temperatures.
- Dependence of the beacon's performance on the quality of the installation. Failure to comply with the recommended requirements for surface preparation, dimensions and design of the beacon leads to its inoperability.
- Due to the low reliability of the received data, installation is required large quantity lighthouses. Typically at least two per crack and at least one per 3 meter crack.
- The accuracy of crack width measurements is very low due to unevenness at the measurement site. For the same reason, there is no possibility of using high-precision measuring instruments.
- The main thing is that the gypsum beacon is disposable. In most cases, when it is triggered (a crack appears in the body of the beacon), it is necessary to install a new beacon nearby.
Plate beacons
Plate beacons do not have many of the disadvantages of their gypsum counterparts. One of their main advantages is the ease of installation - this is done with quick-curing epoxy glue, or on dowels, or by combining these two methods. Depending on the design, these beacons can be implemented additional features, not available in beacons of other designs:
- The ability to measure the movement of structures along two axes (when using a special design, three) relative to each other - in the vertical and horizontal directions.
- Possibility of using high-precision measuring instruments to measure hundredths of a millimeter change in crack opening width.
- Ease of use, including the ability to add additional information to the beacon.
A signal measuring scale that allows you to visually assess changes in the crack opening width without additional tools.
Currently, this is perhaps the most effective design in terms of the ratio of installation cost, labor intensity of observations and the quality of the results obtained.
Point beacons
Another type of beacons for monitoring cracks are point devices that allow observations to be made at two, three or four points fixed on the structure. The design of such devices can be extremely varied, from simple dowel-nails to special installation devices. Such devices can be made inconspicuously in the color of the wall finish or transparent (made of plexiglass). The advantage of some of them is that there is no need to prepare the surface and clear the finishing layers. The use of special calculation methods makes it possible to track movements in both vertical and horizontal directions. The accuracy of measurements is limited only by the accuracy of the instruments used. The undoubted advantage of most representatives of this type of lighthouse structures is the extremely high resistance to vandalism, achieved by rigid fastening to the structure, with small dimensions of the device.
Sentinel beacons
In addition to those mentioned above, sentry-type beacons (messuras) are common, having a measuring scale and relatively high accuracy measurements without the use of additional tools. These are the most intuitive devices to use, allowing you to easily navigate the changes taking place and take readings. For some reason, it is this type of beacon that most attracts vandals; sometimes even special ones don’t help protective structures. In addition, their cost is significantly higher than plate, point, and even more so gypsum, which significantly reduces the scope of their application. Greater efficiency can be achieved by fixing two points on the structure and using the measurements only as a measuring tool to perform control measurements of the distance between the fixed points.
There are other types of beacon designs, but in conclusion I would like to once again warn against the use of paper and glass beacons, since their designs do not meet the requirements and can be misleading when making observations.
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First, let's quote from regulatory documents, where definitions of beacons and gap gauges are given. The first document is an updated GOST, the requirements of which apply to monitoring deformations of the foundations of buildings and structures.
GOST 24846-2012 Soils. Methods for measuring deformations of the foundations of buildings and structures:
3 Terms and definitions
3.34 beacon, crack gauge: A device for monitoring the development of cracks: gypsum or alabaster tiles attached to both edges of the crack on the wall; two glass or plexiglass plates with marks for measuring the size of the crack opening, etc.
10 Observation of cracks
10.1 Systematic observation of the development of cracks should be carried out when they appear in the load-bearing structures of buildings and structures in order to determine the nature of the deformations and the degree of their danger for the further operation of the facility.
10.2 When observing the development of a crack along its length, its ends should be periodically recorded with transverse strokes applied with paint, next to which the date of inspection should be indicated.
10.3 When observing the opening of cracks along the width, you should use measuring or fixing devices attached to both sides of the crack: beacons, crack gauges, next to which their numbers and installation date are indicated.
10.4 If the crack width is more than 1 mm, its depth must be measured.
Appendix A
(required)
A.1 The program for monitoring deformation of the foundations of buildings and structures should cover:
- for buildings (structures) in use - period of operation, results of inspection of the facility, presence of cracks and places to lay beacons (crack gauges);
The second document is the new STO used at Rosatom facilities.
SRO NP "SOYUZATOMSTROY"
STO SRO-S 60542960 00043-2015 “Geodetic monitoring of buildings and structures during construction and operation”
3 Terms and definitions
…
3.21 lighthouse: A signaling device installed on a crack/seam/joint so that changes in crack parameters (opening, closing, shear, elongation, etc.) can be determined visually - without the use of additional tools and devices.
3.22 crack beacon: A device for observing (monitoring) cracks/seams/joints, combining a signal function for visually identifying the fact of changes in the parameters of cracks/seams/joints with the function of measuring the magnitude of these changes.
…
3.50 gap gauge: A device used to perform, when monitoring the condition of structures, measurements of changes in the parameters of cracks/seams/joints.
Beacon ZI-2.2 according to the classification of STO SRO-S 60542960 00043-2015 is a gap-measuring beacon
An observation beacon or gap gauge is special devices or instruments designed to monitor changes in the state of defects and damage in building structures of buildings and structures. When observing cracks, they are used either to identify the fact of a change in the crack opening width, or to determine the magnitude and direction (crack opening/closing) of a change in the crack opening width. Also, some beacon models may provide the ability to monitor displacement along a crack or from the plane of the observed building structures.
Beacon for measurements on two axes
To monitor cracks, beacons are installed directly at the location of the crack for the period necessary to carry out observations. To monitor structural deformations, readings from installed beacons must be periodically taken and recorded in an observation log. The process of constant observation of structures is called monitoring. Specific dates monitoring are set depending on design features building, observation purposes, location and other parameters of the crack. In the vast majority of cases, the beacon should remain on the crack until the causes of the crack have been completely eliminated and the crack has been completed. repair work to restore/strengthen structures damaged by cracks. Sometimes, beacons can remain on structures after completion of work, to monitor the effectiveness of the repair work carried out. Also, with the help of beacons, changes in the position of building structures of buildings and structures can be observed throughout the entire period of their operation in order to monitor the technical condition.
Types and designs of lighthouses
The simplest beacons are a strip of plaster applied to the structure at the location of the crack. Such a beacon serves to identify the fact of changes in the width of the crack opening and cannot help in determining the quantitative values of these changes. Gypsum and cement beacons have a number of requirements and restrictions on use. what you need to know when installing them. Glass beacons can be made similarly to plaster ones - a strip of glass across the crack, or provide for the possibility of taking measurements in the case where two glass plates are installed on both sides of the crack. Such beacons are the most common due to their low price and ease of installation. However, their use is ineffective due to low accuracy and other problems associated with the design of these beacons. Additional information about glass and other types of lighthouses can be found in the article describing methods for monitoring deformations in building structures. It should be noted that paper and other similar materials cannot be used to observe cracks for a variety of reasons. objective reasons, which can be read about in the corresponding article “The myth about the existence of “paper lighthouses”.
Mechanical beacon
Electronic monitoring device
There are also so-called “mechanical” beacons. These are devices of various designs, the task of which is to measure the magnitude of changes in crack opening. There are a lot of lighthouse designs of this type. Basically, these are some elements installed on both sides of the crack, with a scale and pointer that allow you to see the change in the crack opening value without additional accessories. The most accurate of mechanical devices is a beacon made on the basis of a dial indicator. Expanding the functionality and accuracy of “mechanical” type beacons is possible when using modern high-precision measuring instruments, such as electronic calipers, for measurements. The design of professional observation beacons always includes special reference points, which are used for high-precision measurements.
Monitoring system
The most modern beacons are made using electronic components, such as strain gauges, or using optical technologies. They also have different design and opportunities. In addition to directly measuring the crack opening, they can collect information about temperature and humidity conditions and other parameters. It is possible to equip them with modules for remote information transfer for monitoring the condition of structures in real time. The problems with their use are mainly related to the high price and the difficulty of preventing unauthorized access to them by unauthorized persons. Some
Cracks that appear on the walls of a building not only spoil the aesthetics of the building, but are also a sign serious problems architectural plan.
If such a situation arises, be sure to notify the company responsible for operating the structure.
Specialists must conduct a technical assessment of the structure, establish the degree of safety for further use and approve a list of measures to eliminate the problem.
During the inspection, the age of the damage is taken into account. Beacons are also installed on wall cracks to determine the dynamics of destruction.
Installation of beacons to determine the size of cracks in walls
The degree of danger of a crack that appears is determined by the location of its formation:
- on load-bearing walls– create serious emergency situations;
- on partitions - are local in nature.
The problem area of the structure is monitored using different types lighthouses. Monitoring is also used in buildings identified as emergency or with limited functionality. They monitor the development of the resulting destruction in structures near which active construction works or reconstruction is underway.
Point control method for cracks on walls 
Electronic sensors and monitoring systems 
Gypsum beacons 
Plate beacons
The main purpose of observation is to record in a special log all changes in the parameters of cracks that appear.
The following indicators are needed:
- for a correct assessment of the technical condition of the building;
- decisions on the possibility of further operation;
- the need and complexity of repair work;
- eliminating factors that destroy the building.
When choosing a suitable observation method, they take into account the urgency of obtaining information, the accuracy of the results, the reliability of the method itself and the complexity of the upcoming work.
Types of beacons and features of use
Electronic models
The work uses electronic sensors, capable of transmitting information over a distance. With the help of such beacons on cracks one obtains accurate results damage to walls or partitions.
The procedure is expensive and requires the use of several sensors that measure the displacement of the structure in different directions. But such observations are carried out for no more than 15 days, and the results are recorded with an accuracy of hundredths.
Plaster marks on walls
Are considered the most in an accessible way monitoring the resulting destruction. Before installation, the damaged surface will need to be leveled. If the structure continues to deform, cracks will form in the lighthouse. In this case, control marks are installed nearby.
This takes into account:
- negative reaction of gypsum to the influence low temperatures and natural factors;
- the ability of marks to collapse on their own;
- high error of the obtained results.
The resulting measurement accuracy is also affected by the unevenness of the wall on which the crack has formed. Each tag is assigned a serial number and date. The results are recorded in a journal.
Massuras 
How to prevent cracks from spreading
Measurements using plate fixtures
Such beacons are installed using epoxy glue or screwed using dowels. Models are equipped with a signal scale for taking measurements. The scale contains two axes and additional information, allowing you to fully examine damage in all directions. The measurement results are recorded to the nearest hundredth (in millimeters).
In terms of the ratio of the cost of the device and the effectiveness of the event, this method is considered the most optimal. Also, plate beacons are convenient to use.
Point control method
In the area of displacement of the structure are determined control points and are marked with ordinary dowels or special beacons that are hardly noticeable on the wall. In this case, the surface in the problem area does not need to be pre-cleaned from finishing. This method allows one to observe the development of a split in any direction.
The accuracy of the result depends on the error of the instruments used to perform control measurements. Dowels or other devices are rigidly fixed to the plane and do not fall out during the research period.
Massuras
They are a clock mechanism with a high-precision measuring scale. They are visual devices from which readings can be easily taken, and the result allows you to quickly navigate the changes taking place. Considering high cost devices and the same probability of vandalism, sentry beacons are used when carrying out control measurements.
2.2.8. If found in building structures, cracks, kinks and other external signs of damage, these structures must be monitored using beacons and instrumental measurements. Information about detected defects must be entered into the technical condition log of buildings and structures with a deadline for eliminating the identified defects.
According to their properties and characteristics, cracks in reinforced concrete and concrete structures can be the following: stabilized (over time) and unstabilized, open and through, hairline (up to 0.1 mm), small (up to 0.3 mm), developed (0.3 - 0.5 mm) and large, emergency, deep, surface, vertical and horizontal, single, parallel, intersecting and in the form of a grid.
To monitor the development of cracks in walls, building structures and equipment foundations, beacons are used (Figure 2.2.5), installed in places that allow daily observation of them. If there is a layer of plaster on the structure where cracks appear, it should be removed and checked for cracks in the body of the structure itself. The number of beacons is taken at the rate of 1 beacon per 2 - 3 m of crack length. Each beacon is assigned a number and the date of its installation is indicated. A sketch of the cracks, data on their development and installation of beacons must be given in the technical logbook for the inspection of building structures.
A - plaster; b - metal; c - Belyakov’s designs; 1 - crack; 2 - plaster; 3 - wall of the observed object; 4 - millimeter divisions on the lighthouse plate; 5 - metal pins for fixing the relative position of the plates
Observations of cracks are carried out for 20 - 30 days; if during this time the beacons are intact and the length of the cracks does not increase, then their development should be considered complete. Monitoring of temperature-sedimentation seams of buildings, junction points of fuel supply overpasses to the main building and other buildings and structures should be installed using beacons and gap gauges. If the opening of seams and movements at the interface nodes are not associated with seasonal deformations of structures or do not correspond to them, then the settlements of the foundations of buildings and structures on which these inconsistencies are found must be checked,
The degree of weakening of structural elements due to mechanical (cuts, holes, cuts, etc., not provided for by the design), chemical, electrochemical, biological and other influences should be assessed based on the results of cross-section measurements. The need to determine strength arises in cases where external signs of a violation of the integrity of structures appear (deflections, bulging, cracks, etc.). To determine the strength of concrete using instruments, you should use the methods outlined in.