Field surveys are carried out before the reconstruction of buildings and structures, due to their physical wear and tear or obsolescence. Long-term studies of buildings and structures are carried out in order to study their actual operation and improve calculation and design methods.

During the examination, it is necessary to identify real impacts on structures (force, deformation, temperature, aggressive), as well as the state of structures, actual stresses, deformations and their changes over time for the soils of the base 1, foundations 2, columns in the most critical sections experiencing maximum stresses 3 , walls in the place of the most intense loads and impacts 4, bending elements in places of maximum moments 8 and shear forces 6, nodes 21 (Fig. 3.1).

for foundations - in heavy storage areas

Rice. 3.1. Typical measurement and observation locations for surveys and long-term tests:

a - one-story industrial building; b - multi-storey industrial building; / - stressed zone of the base under the foundation; 2 - foundation; /y _ piz columns; 4 - bottom of the wall; 5 - crane beam; 6 - support zone of the crossbar; 7 - dust bag near the parapet; 8 - middle zone of the crossbar; 9 - dust bag near the lantern; 10 - lantern; 11 - coating; 12 - foundation of the unit with dynamic loads; 13 - brackets for material pipelines; 14 - load on the base, including the impact of high temperature on the structure; 15 - pit; 16 - tank with bubbling; /7 - load in the equipment service area; 18 - places of possible emergency release of aggressive liquids; 19 - places for electric cars to pass; 20 - concentrated loads from equipment; 21 - connection points of prefabricated elements; 22 - places of passage of underground communications

Typically, in buildings and structures there are typical areas of possible additional loads and other impacts, the most likely areas of increased deformability and lower durability of structural elements. Thus, additional impacts and less durability are observed:

• loads 14 (rolled products, ingots, etc.), especially near columns, where stressed zones at the base under the foundation and load are superimposed on one another, resulting in tilting of the foundations; in places where underground utilities 22 pass, from which liquid flows into the base, and changes in the composition of the soil are possible, leading to additional precipitation; when aggressive liquids 18 enter the foundation during emergency releases from process equipment, which leads to swelling of the soil along with the foundation;
• under vibration impacts from equipment 12 or transport, when vibration of the base causes additional settlement of the foundations;
• for foundations - in areas of exposure to aggressive liquids 18, vibrations 12, additional loads from storing any objects 14, location of deep pits, including equipment 15, in the zone of seasonal freezing of the base, during the construction of extensions, when developing closely spaced pits, driving additional piles;
• for columns - in the most stressed areas of the junction with the foundation 3, at the console, at the junction of columns in height; near the floor on ceilings (where there may be exposure to passing traffic or ingress of aggressive liquids); for two-branch columns - in the crane branch; in connecting points with floor crossbars; in places of possible thermal influences, for example, cooling ingots 14;
• for crossbars and floor slabs - in areas of maximum bending moments 8 and transverse forces 6, joints, transmission of concentrated forces 20, passage of light vehicles 19, vibration loads 12, in machine maintenance areas 17, as well as in areas of exposure to aggressive liquids and gases and dust;
• for coatings - in areas of increased moisture on the side of the room, in places of defects 11 and bags with accumulations of process dust 9, 7, caused by the presence of lanterns 10 and parapets, in areas with increased thickness or density of insulation 11 in locations of dynamic equipment, for example, tanks with liquid 16, in which the bubbling process occurs;
• for walls - in areas of increased moisture with freezing and thawing 4, in joints, fastenings to columns, adjoining the floor.

During long-term field surveys of buildings and structures, a program is developed that includes the goals and objectives of the surveys, methods and instruments used, methods for processing and analyzing the results, and safety measures.

The main features of field surveys are: carrying out work in cramped conditions at existing enterprises or operating buildings and structures; real, and not specified by researchers, loads and other influences; the impossibility of eliminating various interferences and long-term adverse effects on devices; the impossibility of using bulky instruments and installations for research that interfere with normal operation; In some cases, there is no possibility of connecting the required voltage to power devices.

All this requires the use of instruments in surveys that are insensitive to interference, small in size, durable, do not reduce their performance over time and under adverse influences, quickly installed and configured, and have autonomous power supply.

Such devices, as experience shows, are: for studying stresses in structures - magnetoelastic sensors (see Chapter 1); to study deformations - comparators (mechanical or optical, see Chapter 1); to determine loads - magnetoelastic or strain gauge transducers; to determine crack opening - grades or comparators; for measuring angular, linear movements, displacements in nodes and parts of structures to assess their spatial work - geodetic instruments; to determine stresses under the base of foundations and in the foundations - string transducers; to study vibration parameters - removable vibration sensors in inventory wells.

All stationary devices must be placed in special protective housings; connecting cables in steel protective sheaths are led to a switch cabinet that is locked with a key.

Rice. 3.2. Photoelastic sensors:

a, b - tape; c, d - round; 1 - photoactive plate; 2 - glue; 3 - reflective layer; 4 - rubber gasket; 5 - object under study;

polaroid film

When taking the next reading, the researcher connects the measuring device to the connecting blocks located in the cabinet, takes measurements, then turns off the device and closes the cabinet. Only in this way can damage to devices, connecting cables and connections in an operating workshop or building in use be avoided. If during inspections instruments are used that must constantly measure and record any parameters over a long period of time (for example, deformations of crane beams in order to determine the actual loads from overhead cranes), then a recorder (BSP, see Chapter 1) is placed inside the switching cabinet ), which can be connected using a limit switch located on the crane runway.

Relatively simple and reliable devices for determining deformations of any structures are photoelastic sensors (Fig. 3.2). These sensors are plates of photoactive material / glued along the edges to structure 5. Measurements are carried out with special overhead polariscopes (see Chapter 4); If a Polaroid film is glued to the surface of the plate, then when the plate is deformed, the observer sees alternating dark and light stripes, which can provide approximate information about the signs and magnitudes of the deformations.

The use of magnetoelastic converters is based on the magnetoelastic effect, which consists in changing the magnetic properties (magnetic permeability, etc.) of a ferromagnet under the influence of mechanical stress.

The most suitable form of the sensing element in order to ensure high sensitivity to changes in magnetic permeability is a toroidal element (Fig. 3.3).

Magnetoelastic transducers can be embedded (placed in concrete during the manufacture of structures) or overhead.

The toroidal sensitive element consists of a ferrite ring core - magnetic core 1 with a toroidal winding 2 and connecting wires 3 for connection to the measuring device. If winding 2 is powered with alternating current with a frequency of up to 20,000 Hz and loaded with a compression force along the normal axis of the ring, then at the output of the sensitive element it is possible to obtain oscillograms 5, indicating a significant change in the peak voltage (several volts) depending on the compressive force or compression stresses.

On the working surfaces where the magnetoelastic transducer is in contact with concrete, titanium or nickel foil 4 is glued to it, and the edge zones are filled with glue. This ensures the safety of the sensor in concrete, eliminates the penetration of liquid into the device, minimizes transverse sensitivity and eliminates edge stress concentration.

For example, a measuring transducer of the BPM type is used as a recording device. Magnetoelastic sensors of various types have operating ranges for compressive stress of 1-10 MPa, 5-50 MPa, diameter 22-78 mm, thickness 5-6.9 mm. A methodology has been created and a measuring system has been developed for conducting long-term studies of stresses in concrete of reinforced concrete structures using magnetoelastic sensors. Sensors (M75, M40, MZO, M20) for direct determination of stresses are installed inside the elements before concreting, then after installation of building elements, the sensors are connected to a recording device - the VRM-4 device, containing a microprocessor complex for measuring, storing, mathematical processing and display of results. After processing, the finished data is displayed on the device display. The number of simultaneously connected magnetoelastic sensors is up to 18 pcs.

Rice. 3.4. Crack observation:

a - magnifying glass MPB-2; b - d - beacons (b, c - plaster; d - inventory); d - crack opening graph; 1 - eyepiece; 2 - scale; 3 - tripod; 4 - magnifying glass; 5 - base; 6, 8 - gypsum beacons; 7 - crack; 9 - inventory steel beacon

During the inspection process, long-term observations of the formation and opening of cracks are organized. In large structures, beacons installed across cracks are used for this purpose, usually located 50-100 cm along the length of the crack.

For long-term observation of the crack opening process during inspections, you can use the MPB-2 magnifying glass, beacons, and comparators (Fig. 3.4).

Magnifying glass MPB-2 is a microscope with 20x magnification, which allows you to determine the width of cracks with an error of 0.05 mm. Beacons can be disposable (usually made of gypsum mortar) or inventory, steel. On the plaster beacon, which has a reduced cross-section at the intersection with the crack, write the installation date and number. When a crack opens, the movement of the two parts of the beacon is measured with an MPB-2 magnifying glass or a comparator. For measurements, risks serve as a comparator (Fig.

The inspection of the technical condition of the aeration tank was carried out in three stages:

1) preparation for the examination;

2) preliminary (visual) examination;

3) detailed (instrumental) examination.

Preparatory work is carried out in order to become familiar with the object of inspection, its space-planning and design solutions, and survey materials; collection and analysis of design and technical documentation.

A preliminary (visual) inspection is carried out for the purpose of a preliminary assessment of the technical condition of building structures based on external signs, and to determine the need for a detailed (instrumental) inspection. At the same time, a complete visual inspection of the building’s structures is carried out, and defects and damage are identified by external signs with the necessary measurements and their recording.

A detailed (instrumental) examination of the technical condition of a building or structure includes:

Measurement of the geometric parameters of buildings or structures, structures, their elements and assemblies necessary to fulfill the inspection purposes;

Engineering-geological surveys (if necessary);

Instrumental determination of defects and damage parameters;

Determination of the actual characteristics of the materials of the main load-bearing structures and their elements;

Analysis of the causes of defects and damage in structures;

Drawing up a final document (conclusion) with conclusions based on the survey results.

The inspection revealed possible damage to structures and their parameters. The measuring work was carried out using a STAYER5x12 tape measure and a LEIKADISTO laser rangefinder.

The technical condition of the structures was assessed in accordance with the recommendations. It is accepted that, depending on the presence and degree of influence of a defect on the load-bearing capacity, a structure can be in one of five states: serviceable, operable, limited operable, unacceptable and emergency.

3.2 Results of full-scale inspection and their analysis

3.2.1 Bottom

The bottom of the structure is monolithic reinforced concrete. In places where the walls and partitions of the tank are installed, grooves are arranged in the bottom. The height of the groove in the places where the walls are installed relative to the bottom, taking into account the concrete filling, is 300 mm. The bottom is covered with a layer of shotcrete plaster 10-20 mm thick.

The bottom inspection was carried out while the aeration tank was temporarily turned off, wastewater was pumped out, and sections of the bottom were cleared of the sediment layer. During the inspection of the structure, no damage indicating uneven settlement and a decrease in the load-bearing capacity of the bottom was noted. There was also no corrosion of concrete and bottom reinforcement. In some areas, local peeling of the shotcrete plaster on the bottom surface was noted. The section for cleaning the groove-ridge of the bottom is shown in Figures 3.1 – 3.2. The technical condition of the monolithic bottom is assessed as operational. There is no aggressive impact on the bottom from wastewater.

clean the surface of the bottom from sediment and old gunite plaster;

Re-gunite the bottom surface with a special waterproofing compound.

Figure 3.1 – Stripping area groove-ridge of the bottom

Figure 3.2 – View of the groove-ridge of the bottom

What is revealed during a field survey

A full-scale survey is carried out directly at the site with the involvement of relevant specialists. During the verification work, the following is revealed:

• what defects appeared during the operation of the building due to deficiencies in the design solution and non-compliance with design standards,
• what defects were made during the construction of the building,
• what defects were made during the installation of prefabricated structures,
• what damage was caused to the object under the influence of an aggressive external environment,
• what mechanical damage appeared during the operation of the building,
• what damage occurred as a result of impacts unforeseen by the design,
• what damage was caused by natural disasters.

When conducting a natural inspection, two types of technical condition monitoring are used: instrumental and technical, the choice of which depends on the duration of operation of the building and the tasks assigned to the inspection.

Instrumental examination

An instrumental inspection of the condition of the building is carried out on the eve of upcoming reconstruction and repair work. The inspection can be carried out partially or completely, and the technical condition of building elements is examined, the characteristics of which have changed somewhat during the operation of the facility. An instrumental examination should identify the presence of faults and the reasons for their occurrence, and assess the general condition of the building. If necessary, long-term monitoring of changes in the condition of supporting structures is organized.

Technical inspection

To set up a facility for planned major repairs, reconstruction or modernization, a full-scale technical inspection is carried out, which makes it possible to find out the actual condition of the entire building or its individual elements, and to obtain an assessment of the actual characteristics of load-bearing structures, and to determine the degree of their wear. This helps to establish what work and in what volume will need to be carried out in order to return the object to its quality characteristics.

It is important that the technical survey is completed as completely as possible, since this helps to develop a higher-quality project and spend less time on its development. It is prohibited to carry out reconstruction or major repairs of a building without a visual technical inspection.

Each technical inspection pursues specific goals; it helps to find out whether an extension or adjustment can be added to the object, how to carry out repairs, after which the load on the building structure will change or not change, etc.

The reason for conducting a visual technical inspection is the customer’s assignment, the building’s technical passport, the previous technical inspection report, the order of the town planning organization regarding the reconstruction or major repairs of the building.

At the moment, a full inspection of any construction site consists of studying technical documentation and a field survey, which, in turn, consists of three stages:

• at the first stage, a preliminary inspection is carried out, which helps determine the volume of work to be done and its cost, the implementation of priority emergency measures is specified,
• at the second stage, a general assessment of the technical condition of engineering systems and building structures is carried out, measures are developed aimed at correcting detected defects,
• the third stage consists of a detailed examination of individual structures with their in-depth study; it is necessarily used in the absence of drawings, when the structures do not correspond to the design documentation data, and in a situation where, after eliminating defects, the structures continue to collapse.

The methods for conducting a visual technical inspection and the scope of work carried out are specified by the organization performing the inspection, based on the customer’s instructions. This takes into account the condition of the building at the time of the inspection, and the results of a laboratory study of building materials. So, if after the second stage of assessment the technical condition of the object becomes clear, then specialists may not carry out the third stage.

In order to determine the technical condition of load-bearing structures when accepting buildings and structures, a thorough field inspection is carried out. During the inspection, all changes that occurred during operation and damage that occurred during this period are recorded. Based on the results obtained, a conclusion is given about the suitability of the building for operation or, conversely, about the need for repair work and the development of an action plan aimed at strengthening the structures. Technical examinations to establish the actual condition of structures are appointed in cases where:

• there is an unplanned increase in loads;


• the building is scheduled for reconstruction, even if an increase in loads is not expected;


• the technical condition of buildings is assessed;


• during operation, defects are identified that can lead to disruption of the structure;


• structures are exposed to impacts that were not foreseen at the design stage.

Based on the results of the examination, if an emergency condition of the facility is identified, its further operation is stopped and the issue of major repairs is resolved.
Depending on what tasks were set, the process of examining structures consists of the following procedures:

• preliminary inspection and familiarization with existing documentation;


• visual inspection of the object and its measurements, when the general dimensions are established and the sections of the structure are checked;


• registration of identified cracks, various types of defects, damage, and establishment of the nature of their occurrence;


• quality control of material, condition of joints and connections;


• checking the condition of foundations and foundation soils;


• performing verification calculations of load-bearing structural elements;


• technical conclusion.

A preliminary inspection is carried out in order to establish compliance of the structural and structural diagrams of load-bearing structures with the requirements specified in the technical documents. At this stage, it is possible to establish the degree of operability of the object, since there is a possibility of its partial or complete loss. This is determined by identifying structural cracks by changing the position in space of structural elements. During inspection, special attention is paid to load-bearing elements that are operated in particularly unfavorable conditions. A visual inspection is carried out to assess the general condition of structures for the presence of wet areas of concrete, corrosion and other defects. Thus, during the preliminary inspection process, information is accumulated that will form the basis for drawing up a program and establishing the scope of survey work.

When an inspection of objects ready for commissioning is carried out, you should carefully read the documentation at all stages of construction and installation work, acts of acceptance of hidden work, conclusions of commissions based on the results of previous inspections, and geological research data. In the case of inspection of objects already in operation, it is necessary to study additional materials, for example, commissioning certificates, as well as materials characterizing the technical condition of the structure, which are annual inspection reports, statements where defects are recorded, documents on measures taken to strengthen and repair work . If technical documents are not available, you should:

• establish the year of construction of the facility and the standards according to which the project was developed;


• draw up design diagrams, taking into account its features;


• identify the organizations carrying out the development and construction of the facility;


• collect information on similar objects for which all technical documentation is available.

When studying documents, first of all, you need to pay attention to plans, calculations, drawings of structures and components, physical and mechanical characteristics of building materials, operating conditions, comments of commissions performing inspections at the stages of construction and acceptance of the facility, measures taken to eliminate deficiencies, information about repair work and strengthening structures.

Often, the causes of damage leading to emergency situations are physical, chemical, biological and other negative impacts not taken into account at the design stage, or deviations from normal operating conditions. In this regard, during the survey it is important to determine the real loads and impacts with the data indicated in the documentation.

During construction or during operation of a building, overloads of load-bearing structures may occur, which is associated with unaccounted force impacts, which, in turn, appear as a result of an increase in payload - additional equipment, additional floor layers during repairs, snow accumulation, etc. P. The main impact on the condition of structures is exerted by environmental factors - temperature, humidity, the degree of aggressiveness of production, etc. Humidity and temperature contribute to the appearance of stress in structural elements and activate corrosion processes, therefore, when inspecting production facilities, it is necessary to take into account data on the temperature of gas and liquid media, solid and bulk substances. Based on the results obtained, an analysis is carried out taking into account data from weather stations at the time of the survey and data obtained during observations preceding the period of survey of the object.

As for the degree of aggressiveness of environments, they are distinguished between non-aggressive, slightly aggressive, and highly aggressive. Observations of weather phenomena, samples to study the composition, properties and concentration in the atmosphere of chemical substances, which can be in a gaseous, liquid or solid state, help to establish the degree of aggressiveness. Samples must be collected within three days. The data obtained as a result of the study allows the degree of aggressiveness of the environment and recalculations of the structure being examined.

A full-scale inspection of the structures of buildings and structures is intended for an objective assessment of their technical condition upon acceptance into operation or taking into account changes that have occurred over time. As a result of the inspection, a conclusion is made about the suitability of the structure for operation or the need for repairs, and measures are developed to strengthen the structures.

Technical examinations are appointed to establish the actual quality condition of structures in the following cases:

• when the perceived load increases to determine the need and measures for strengthening;
• before designating a building for reconstruction, even if this does not imply an increase in loads;
• during periodic assessment of the technical condition of buildings and structures;
• if during operation or construction defects are identified that may disrupt the normal operation of structures;
• if the building structures were exposed to impacts not foreseen during the design (overloads, natural disasters, high temperatures, etc.).

As a result of the examination, the issue of major repairs of the facility, its reconstruction is resolved, or the emergency condition of the structure is recorded when its further operation must be stopped.

Depending on the tasks assigned, the inspection of buildings and structures consists of the following operations:

• preliminary inspection;
• familiarization with the documentation;
• inspection of the object in kind;
• measurements - establishing the general dimensions of structures (spans, heights, etc.) and monitoring the sections of elements;
• identification, establishment of the nature and registration of cracks, defects and damages;
• checking the quality of materials in the structure and monitoring the condition of joints and connections;
• inspection of foundations and foundation soils;
• verification calculations of load-bearing elements;
• drawing up a technical report.

Preliminary inspection aims to establish compliance of the layout and structural diagrams of load-bearing structures with the requirements of technical documentation. During the preliminary inspection, a partial or complete loss of structural performance may be determined, which is determined by a visible change in the position (mutual displacement, settlement) of the structural elements of the structure in space, as well as the presence of structural cracks. During the inspection, the most damaged areas of the structure are identified, as well as load-bearing elements that are in particularly unfavorable operating conditions. The general condition of the structures is visually assessed: the presence of wet areas of concrete, the condition of protective coatings, the presence of corrosion, etc. Thus, during the preliminary inspection, information is collected that makes it possible to clarify the program and scope of the inspection work.

When inspecting structures intended for commissioning, it is necessary to familiarize yourself with the design, construction and installation documentation, where you should pay attention to the acceptance certificates for hidden work, the conclusions of commissions based on the results of previously carried out surveys, and geological survey data.

Inspection of objects in operation must additionally be accompanied by a study of commissioning certificates, construction passports, operation logs, annual inspection reports, defective statements, documents on repairs carried out and other available materials characterizing the technical condition of the building or structure. Particular attention is paid to information on the operating conditions of the facility: the presence of vibration technological loads, aggressive influences, cases of soil freezing at the base of foundations, flooding of basements with atmospheric, ground or technical water, etc.

If there is no technical documentation about the object, it is necessary to establish:

• year of construction of the facility;
• the standards by which the facility was designed;
• characteristic design schemes and their features characteristic of certain periods of development of construction equipment;
• organizations that designed and built the facility;
• information about the object in periodical technical press of the years when it was designed or built, and information on similar objects and structures for which technical documentation is available.

When studying the documentation, it is necessary to pay attention to calculations, plans, longitudinal and transverse sections of structures, working detail drawings of structural elements and assemblies; a design scheme that ensures the spatial rigidity of the structure; physical and mechanical parameters of building materials; deadlines for completing certain types of construction work; operating conditions (loads on load-bearing structural elements; maximum and minimum air temperatures outside and inside the building; harmful emissions associated with the technological process; nature of vibration effects; settlement of foundations and time of settlement stabilization); comments of supervisory commissions during the construction and acceptance of the facility into operation, during previously conducted surveys and measures taken to eliminate deficiencies; data on repairs and enhancements.

In general, the building structures of the structure being examined may be subject to physical, chemical, biological and other types of influences. Often the cause of damage and emergency situations is the underestimation of certain impacts at the design stage of structures or deviations from the normal operating conditions of the structure. In this regard, during the survey it is mandatory to determine the parameters of real loads and impacts and compare the results obtained with the data specified in the documentation.

Overloads of the load-bearing structures of buildings can occur both during the construction of the structure and during its operation. Additional unaccounted force effects appear as a result of an increase in payload when suspending additional equipment from structures, accumulation of snow, ice, and industrial dust. An increase in the permanent load on the floor can occur due to the installation of additional layers when repairing the floor. These deviations are detected during a detailed inspection of the building.

The external environment, characterized by a number of factors, the main ones being temperature, humidity, speed and direction of air flows inside the building, and the degree of aggressiveness of production, has a significant impact on the condition of load-bearing structures.

Exposure to temperature and humidity causes stress in structural elements and also activates corrosion of building materials. When inspecting industrial structures, it is necessary to have information about the temperature of gas and liquid media, granular and solid bodies. The results of temperature and humidity measurements are compared with data from weather stations during the survey period and the results of long-term observations preceding the survey period.

Based on the degree of aggressiveness, non-aggressive, slightly aggressive and highly aggressive environments are distinguished. To establish the degree of aggressiveness of the environment, observations of atmospheric phenomena and instrumental measurements of the composition, properties and concentration of liquid, solid and gaseous chemical substances contained in the air and precipitation that are aggressive to building materials are carried out. Samples to determine the composition and concentration of aggressive substances must be taken within three days above the roof and in the ground layers. The data obtained make it possible to establish the category of environmental aggressiveness and determine the coefficients of operating conditions of building materials necessary for subsequent recalculations of the structure being examined.

When determining the wind load when measuring wind speed and direction, the influence of aerodynamic features of structures and terrain should be excluded. Measurements should be made at a height of 1.5 m from the ground surface and at a height of 2 m above the highest part of the roof.

Inspection of the structure is the most critical part of the examination. It begins with establishing a correspondence between the presented documentation and the actual structure. Identified discrepancies are recorded, assessed and their causes are established. The elimination of deficiencies noted in the acceptance certificates of objects is checked.

Checking basic geometric dimensions is carried out in case of absence or discrepancies between the design documentation and the actual state of the structures. During the survey, the main parameters of the structural design must be checked: spans, heights and sections of columns, other geometric dimensions, on compliance with the specified values ​​of which the stress-strain state of structural elements during their operation depends. In some cases, the horizontality of the floors, compliance with specified slopes, and the verticality of load-bearing elements and fences are also checked.

For relatively small structures, these control measurements are carried out using steel tape measures, plumb lines, levels, etc.

When surveying large objects or their complex configuration, special tools are used to speed up the survey process and ensure its accuracy. Thus, vertical checks are carried out with vertical sighting tools, which make it possible to mark points in height by 100 m or more with an error not exceeding ±2 mm. If it is necessary to check large spans (100 m or more), such as the distance between the centers of supporting platforms of already erected bridge supports, light range finders are used, which speed up the survey process and provide an accuracy of about 1/25000 of the determined length.

Diagnostics of the condition of structures usually produced using several methods: visually, simple mechanical tools, non-destructive testing devices, laboratory and field tests.

Diagnostics of the condition of structures should begin with the most critical elements. The purpose of diagnostics is to identify damage, as well as to identify structural elements, manufacturing, installation, and operation of which are carried out with deviations from design requirements. Load-bearing elements with defects are divided into two groups: elements in which deviations occur that do not cause visible damage, and elements with local damage.

Revealing defects during inspection first groups, special attention should be paid to supporting parts and connections. It is necessary to check the correct support and fastening of the support platforms, the quality of welding, and the loosening of bolted connections. When assessing the condition of welds, first of all you should inspect the seams in the nodes to which rods with large tensile and compressive forces are adjacent. During inspection, it is necessary to fix extra assembly seams, which can change the design design of the structure. It is necessary to inspect compressed elements of metal structures with special care. Bentness of compressed rods is one of the most common defects in metal trusses. Vertical and horizontal connections, as well as nodes connecting connections to foundations, ensuring the spatial rigidity of the structure, are also subject to detailed inspection. One of the grossest violations of operating rules is the removal of vertical cross braces when installing equipment in industrial buildings.

To defects second groups identified upon detailed inspection include weakening of elements caused by local destruction. These can be bolt cuts, cuts, chips, breaks of individual structural elements, etc.

When identifying structural elements weakened by corrosion, it should be borne in mind that metal and reinforced concrete structures are most susceptible to damage in rooms in which, according to the technological regime, the presence of aggressive substances is expected. At the same time, the most significant damage to concrete and steel occurs due to acid and sulfate corrosion, with periodic wetting and poor quality protection. For ordinary buildings and structures, the underground parts of the building are most susceptible to corrosion when exposed to aggressive groundwater and variable temperature and humidity operating conditions, and the load-bearing elements of the coating when roofing materials and insulation materials are destroyed. In this case, the greatest corrosion should be expected in areas with maximum stress, in places where concentrated loads are applied, at the inputs of ventilation systems and in areas with poor ventilation, in areas with accumulation of dust, as well as in places where the protective layer of concrete and anti-corrosion coating is damaged.

Based on the inspection data, corrosion indicators such as the area of ​​distribution and the nature of damage are determined. Based on the nature and area of ​​distribution, corrosion is divided into continuous and local, uniform, uneven and ulcerative.

In load-bearing elements of building structures, the most typical defects are cracks, which are the result of errors in the design, manufacture and operation of structures.

In metal structures, the appearance of cracks in most cases is determined by fatigue phenomena. The appearance and slow development of cracks under load is observed under corrosion conditions. Temperature stresses cause microcracks in welds. The formation of cracks under constant stresses is possible in the presence of structural defects in stress concentration zones. In a metal structural element under static loading, cracks appear at low temperatures or high-speed loading. In these cases, a brittle crack develops quickly and can cause complete failure of the element.

In many cases, for metal structures subject to static loads, a detected crack does not pose an immediate danger. Further development of a crack is often limited by the redistribution of forces and the zone of residual compressive stresses at its tip. The propagation of such a crack is observed only under large overloads.

When inspecting reinforced concrete and stone structures, a detailed analysis of cracks in structures is the most critical stage. Technological cracks appear in concrete before loading, and the formation of new power microcracks occurs under small loads of about 10% of the calculated ones.

Cracks are classified according to their geometric parameters (length, opening width, propagation depth), energy indicators (total surface energy), characteristic stages of the crack formation process with a gradual increase in load, etc. The main criterion for assessing cracks in the structures being examined is the degree of their danger to load-bearing structures. Considering cracks according to their danger indicator, they can be divided into three groups:

• non-hazardous, deteriorating only the quality of the front surface;
• dangerous, causing significant weakening of sections; these also include all unstabilized cracks, the development of which continues;
• intermediate ones, which worsen operational properties, cause physical wear, reduce the durability of the structure, but do not pose an immediate danger.

For structures with cracks of the second and third groups, measures must be taken to restore performance. Depending on the individual characteristics of the structure, different restoration methods are chosen, which may consist in the simplest case - sealing cracks with mortar or strengthening a defective element in the case where its further operation can lead to destruction of the element and the structure as a whole.

In order to correctly calculate the degree of danger of a crack in a reinforced concrete element, it is necessary to find out the reasons for its occurrence. The crack could have formed during the winter period of operation of the structure due to overloading with snow, freezing of the moistened area of ​​concrete, or ice. The appearance of cracks is also possible due to improper operation of building structures, from temporary overloads of load-bearing elements. The formation of cracks is also possible at the stage of installation of structures. The cause may be temporary connections installed incorrectly or in insufficient quantities, poor quality construction and installation work, or violations of the installation sequence. Often, cracks occur due to uneven settlement of the building, which occurred over a short period during installation or operation. Finally, cracks can appear during the manufacture of a building product, as well as during its transportation.

The occurrence of cracks in a reinforced concrete or masonry structure is determined by local overstresses and weakening. The reason for the appearance of high stresses, the formation and development of cracks are:

• overloads caused by static and dynamic force effects; stress concentration on structural inhomogeneities and in zones of changes in the geometric parameters of the load-bearing element, as well as during reinforcement tension; uneven movements of structures due to overloads or differences in the deformation characteristics of building materials; uneven foundation settlements;
• different temperatures of structural elements, or a sharp temperature drop in the cross section of an element, uneven temperature distribution in the volume of concrete of massive structures during an exothermic reaction;
• increased shrinkage of concrete caused by irregularities in manufacturing or unsuccessful selection of the composition of the concrete mixture, uneven shrinkage of the surface layers of concrete in internal areas due to intense loss of moisture on its surface;
• wedging effect of ice in pores, voids, cracks in moistened areas of concrete;
• the wedging effect of reinforcement during its corrosion due to the accumulation of rust.

Local weakening in the concrete of structures, which leads to the appearance of cracks, can also be caused by violations in the manufacturing technology of prefabricated and monolithic reinforced concrete structures and, as a consequence, large heterogeneity of the concrete structure; corrosion of concrete caused by water filtration, high salt content, dissolving ability of filter water; electrochemical and gas corrosion.

All load-bearing and enclosing structures of the building are subject to inspection: roofing, rafters, floors, walls, columns, stairs and foundations. The mating nodes of the elements, support lengths and the quality of welded joints are especially carefully examined.

During the visual inspection, structural elements are identified whose load-bearing capacity is of concern. These include: reinforced concrete structures with significant normal and inclined cracks, traces of reinforcement corrosion; stone structures with cracks and deep damage to the masonry.

When inspecting the walls, defective areas are identified that reduce the thermal protection and strength of the fence. In panel buildings, the joints of wall panels are carefully examined, due to unsatisfactory sealing of which the walls often freeze, and their water permeability and airflow increase.

In brick buildings, the condition of the brickwork is examined, and zones of mechanical and physical and chemical destruction are determined.

Particularly dangerous damage includes cracks that form as a result of uneven settlement of foundations and overloads. Sections of walls with such damage are examined instrumentally using non-destructive testing devices, and if necessary, samples of wall material are taken for testing in laboratory conditions.

When inspecting columns, attention is paid to the condition of the surface, areas of mechanical damage caused by overhead cranes, moving cargo and vehicles are identified, existing cracks are recorded and the reasons for their formation are analyzed. Cracks may indicate corrosion of reinforcement in concrete, loss of local stability of compressed rods, overload of columns, etc.

When inspecting floors, the general condition of their elements is initially assessed, and then the condition of the floors. Those elements where significant deflections, cracks or signs of material corrosion are found are subject to a more thorough examination. At the same time, the length of the platform for supporting the elements on the supporting structure (consoles of columns, walls, crossbars) is specified and the design scheme is adjusted.

When inspecting the coating, the main attention is paid to the condition of the supporting structures: trusses, beams and flooring slabs. In addition, the roof and insulation are examined. Detected traces of roof leaks, areas of waterlogged insulation and rupture of the waterproofing carpet are entered on the roof defect map. The increase in load from water-saturated insulation is taken into account in the verification calculation of the coating strength, and the decrease in the heat-protective properties of the insulation is taken into account in the thermal engineering calculation.

Instrumental inspection is subject to structures with obvious defects and damage detected during visual inspection, or structures determined selectively according to the condition: at least 10% and at least three pieces in a temperature block.

Particular attention is paid to the inspection of buildings that have been exposed to fire. In this case, the examination is conventionally divided into preliminary and detailed.

In progress preliminary surveys collect information about the fire, determine the location of the fire, the time of detection and extinguishing the fire, the maximum temperature, the duration of intense burning and extinguishing agents. Based on available construction documentation and field survey data, floor plans are drawn up, which indicate the location of emergency rooms and structures. The results of the preliminary survey are documented in an act and are subsequently used in developing an action plan for a detailed detailed survey.

To task detailed The survey includes the determination of structural and physical-mechanical damage to structural materials caused by the action of high temperatures and sudden cooling when extinguishing a fire. During a detailed examination, the heating temperature of the surface of structures is determined, and the strength of concrete and reinforcement is assessed.

Based on the results of the visual inspection, a map of defects is drawn up and the degree of physical wear of the structures is assessed.

The data obtained from studying the documentation, instrumental measurements of the geometric and physical parameters of structures are the basis for recalculation and drawing up a conclusion based on the survey results. Based on the recalculation, the issue of the need to conduct full-scale tests of structures is decided or an assessment of the object is given based on the results of only the first stage of the survey.

Full-scale tests of structures make it possible to obtain additional information about the actual boundary conditions, the characteristics of the deformation of the structure, and the stresses in it. When testing with a test load, the structure is not brought to destruction, however, preliminary information about the strength properties of the structure material can be obtained. The destruction of any building material is a long process, which begins for some materials (concrete, brick) at loads 10 times less than the maximum destructive load. The characteristic stages of the destruction process can be detected if modern methods are used during full-scale tests, for example, such as measuring deformations at the mouth of a crack dangerous to the structure, or the acoustic emission method, which records noise that always accompanies the process of microdestruction in a building material.

It should be taken into account that full-scale tests require significant material costs and the allocation of special periods of time - technological windows associated with stopping production. Therefore, if it is possible to give recommendations on restoring the operational properties of an object based on information obtained at the first stage of the survey, then full-scale tests should not be carried out.

In conclusion based on the survey results of a building or structure, a general characteristic of the object is given, a recalculation is carried out, and the actual safety factors for bearing capacity, deformations and the risk of unacceptable cracks are determined. The conclusion should end with conclusions about the suitability of the facility for operation (under the design load, with load limitation, after strengthening) and a forecast of the operability of the structure for a given service life.

The technical report provides an assessment of the causes and degree of danger of the identified defects, and provides a plan for instrumental measurements, the results of which should clarify the cause of local destruction.

A separate group should include surveys for which assessing the condition of structures is not the main task. These surveys are carried out for a group of structures in order to improve the methodology for calculating structures for reliability and durability and solve two problems: studying the statistical parameters of real loads and establishing the degree of aggressiveness of the external environment; determination of physical wear and tear of similar structures and establishment of actual distributions of the probability of failure-free operation of these elements.

Survey data is the basis for drawing up a detailed plan for instrumental measurements and non-destructive tests. The plan for instrumental examinations provides a list of geometric and physical-mechanical parameters that are subject to experimental evaluation, indicates the necessary instruments, and specifies the control method.

Survey program is determined by the objectives of the survey and is individual for each case of technical expertise. For example, a program of periodic inspections carried out during operation to assess the technical condition of buildings includes items that are different from the program of inspections carried out to assess the condition of structures in connection with reconstruction or defective conditions of structures.

Familiarization with design and technical documentation is carried out in order to take into account the design features and operating features of structures; The study of these materials allows us to more accurately draw up an examination program, and often suggest the causes and nature of possible defects.

Familiarization with design and technical documentation, including working drawings and an explanatory note to them, contains data on design loads and impacts, design diagrams, static calculations, recommendations on manufacturing technology, installation and operation; materials from the manufacturer of structures - additional working drawings, certificates of materials, information on quality control, possible replacements, concrete composition, manufacturing mode, operational control (for prestressed structures, information on the method, magnitude and control of reinforcement tension), passports of finished products; construction documents - work production logs, as-built installation diagrams, acts for hidden work, information about damage to structures during transportation and installation, test reports for control cubes of embedment concrete, geodetic survey schemes, object acceptance certificates containing information about defects; materials on the operation of structures, information on repairs or reinforcements performed, data on the aggressiveness of the environment. Often, part of the design and technical documentation is missing, which makes it difficult to carry out the survey, especially when there are no working drawings of the structures being surveyed.

At this stage, it is necessary to establish: the design grade (class) of concrete, the transfer strength of concrete (for prestressed structures), the diameter, class and quantity of working and structural reinforcement, the design of reinforcement products, the geometric dimensions of structures and other data. Subsequently, data on the design class of concrete is used to select a non-destructive method for monitoring its strength.

Data on the transfer strength of concrete and controlled tension of reinforcement may be required to assess the condition of structures.

Reinforcement data is used to select a non-destructive method for determining the position, quantity and diameter of reinforcement, and to assess the presence of areas where placing and compacting concrete has been difficult.

Data on loads, forces and design design are used when choosing the location of sections to control the strength of concrete, placement and amount of reinforcement.

When familiarizing yourself with the technical documentation for the manufacture and conditions of manufacture of structures, you must try to establish the order of concreting and the place of suspension during concreting for monolithic structures, and for prefabricated structures - the conditions of their manufacture (in a closed workshop or on a landfill), the sequence of installation, the time of year of manufacture and construction , composition of the concrete mixture, data on the quality of aggregates and cement, concrete hardening conditions, actual values ​​of transfer, tempering and design strength of concrete, cases of replacement of design diameters and classes of reinforcement. If a statistical method for monitoring the strength of concrete was used in the manufacture of structures, it is advisable to become familiar with the values ​​of the coefficients of variability of concrete strength. If during manufacturing non-destructive methods for monitoring the strength of concrete were used for systematic control, you can use a previously constructed calibration relationship to control the strength of concrete, linking it to the test conditions during the inspection.

When familiarizing yourself with operating conditions, the presence of factors such as alternating freezing and thawing, exposure to high temperatures, the presence of environmental components aggressive to concrete and reinforcement, and repairs and strengthening of structures that have taken place is established.

The presence of loads not taken into account when calculating structures and the possibility of their overloads are revealed, and on the basis of this, the need to determine the actual loads is established.

Inspection of structures subject to reconstruction of buildings and structures is carried out on the basis of a technical specification drawn up by the customer enterprise, which must indicate the basic requirements for structures in connection with the planned reconstruction, in particular, new technological loads, impacts, required room dimensions, etc. d.

As a rule, the terms of reference contain the following sections: justification for performing the work; goals and objectives of the work; state of the issue; composition of the work; summary of reporting materials; responsibilities of the customer.