Factors affecting buildings and structures are divided into:
External influences(natural and artificial: radiation, temperature, air currents, precipitation, gases, chemical substances, lightning discharges, radio waves, electromagnetic waves, noise, sound vibrations, biological pests, soil pressure, frost heaving, moisture, seismic waves, stray currents, vibrations);
Internal (technological and functional: constant and temporary, long-term and short-term loads from their own weight, equipment and people; technological processes: shocks, vibrations, abrasions, liquid spills; temperature fluctuations; environmental humidity; biological pests).
All these factors lead to accelerated mechanical, physical and chemical destruction, including corrosion, which leads to a decrease in bearing capacity individual structures and the entire building as a whole.
Below is a diagram of the influence of external and internal factors on buildings and structures.
During the operation of structures there are distinguished: force effects of loads, aggressive environmental influences.
An aggressive environment is an environment under the influence of which the structure and properties of materials change, which leads to a decrease in strength.
Changes in structure and destruction are called corrosion. A substance that promotes destruction and corrosion is a stimulant. Substances that impede destruction and corrosion - passivators and corrosion inhibitors.
Destruction building materials is of a different nature and depends on the interaction of the chemical, electrochemical, physical, physicochemical environment.
Aggressive media are divided into gas, liquid, and solid.
Gas media: these are compounds such as carbon disulfide, carbon dioxide, sulfur dioxide. The aggressiveness of this environment is characterized by gas concentration, solubility in water, humidity and temperature.
Liquid media: these are solutions of acids, alkalis, salts, oil, petroleum, solvents. Corrosion processes in liquid media occur more intensely than in others.
Solid media: dust, soil. The aggressiveness of a given environment is assessed by dispersion, solubility in water, hygroscopicity, and environmental humidity.
Characteristics of aggressive environment:
Strongly aggressive – acids, alkalis, gases – aggressive gases and liquids in production premises;
Moderately aggressive – atmospheric air and water with impurities – air with high humidity(more than 75%);
Weakly aggressive - clean atmospheric air - water uncontaminated with harmful impurities;
Non-aggressive – clean, dry (humidity up to 50%) and warm air– atmospheric air in dry and warm climates.
Air exposure: The atmosphere contains dust, dirt that destroys buildings and structures. Air pollution combined with moisture leads to premature wear, cracking and destruction of the building structure.
However, in a clean and dry atmosphere, concrete and other materials can survive for hundreds of years. The largest intensive air pollutants are combustion products various fuels, therefore, in cities, industrial centers metal constructions corrode 2-4 times faster than in rural areas, where less coal and fuel are burned.
The main combustion products of most types of fuel include CO 2 and SO 2 .
When CO 2 dissolves in water, carbon dioxide is formed. This is the end product of combustion. It has a destructive effect on concrete and other building materials. When SO 2 dissolves in water, sulfuric acid is formed.
More than 100 types of harmful compounds accumulate in smoke (HNO 3, H 3 PO 4, tarry substances, unburned fuel particles). In coastal areas, the atmosphere contains chlorides and sulfuric acid salts, which humid air increases the aggressiveness of the impact on metal structures.
Impact groundwater: groundwater is a solution with varying concentration and chemical composition, which is reflected in the degree of aggressiveness of its impact. Water in the soil constantly interacts with minerals and organic matter. Sustainable watering underground parts buildings, when moving groundwater, increases corrosion of the structure and leaching of lime in concrete, reduces the strength of the foundation.
There are general acid, leaching, sulfate, magnesium, and carbon dioxide aggressiveness of groundwater.
The following factors have the most significant impact:
· Exposure to moisture: As experience in the operation of buildings has shown, moisture has the greatest impact on the wear and tear of structures. Since the foundations and walls of old reconstructed buildings are made mainly of heterogeneous stone materials (limestone, red brick, limestone and cement mortars) with a porous-capillary structure, upon contact with water they are intensively moistened, often change their properties and, in extreme cases, are destroyed.
The main source of moisture in walls and foundations is capillary suction, which leads to damage to structures during operation: destruction of materials as a result of freezing; formation of cracks due to swelling and shrinkage; loss of thermal insulation properties; destruction of structures under the influence of aggressive chemicals dissolved in water; development of microorganisms causing biological corrosion of materials.
The process of sanitation of buildings and structures cannot be limited to treating them with a biocide preparation. A comprehensive program of activities must be implemented, consisting of several stages, namely:
Diagnostics (analysis of heat and moisture conditions, X-ray and biological analysis of corrosion products);
Drying (if necessary) premises, if we're talking about about underground structures, for example, basements;
Shut-off device horizontal waterproofing(in the presence of soil moisture suction);
Cleaning, if necessary, internal surfaces from efflorescence and biological corrosion products;
Treatment with anti-salt and biocidal preparations;
Sealing cracks and leaks with special water-sealing compounds and subsequent treatment of surfaces with protective waterproofing preparations;
Production of finishing works.
· Exposure to precipitation: precipitation, penetrating into the soil, they turn into either vaporous or hygroscopic moisture, retained in the form of molecules on soil particles by molecular silts, or into film moisture, on top of molecular moisture, or into gravitational moisture, freely moving in the soil under the influence of gravity. Gravitational moisture can reach groundwater and, merging with it, increase its level. Groundwater, in turn, due to capillary rise, moves upward to a considerable height and floods the upper layers of the soil. Under some conditions, capillary and groundwater can merge and steadily flood the underground parts of structures, resulting in increased corrosion of structures and a decrease in the strength of foundations.
· Impact of negative temperature: Some structures, for example, basement parts, are located in an area of variable moisture and periodic freezing. Negative temperature (if it is below the design temperature or if special measures are not taken to protect structures from moisture), leading to freezing of moisture in structures and foundation soils, has a destructive effect on buildings. When water freezes in the pores of a material, its volume increases, which creates internal stresses, which increasingly increase due to compression of the mass of the material itself under the influence of cooling. The ice pressure in closed pores is very high - up to 20 Pa. Destruction of structures as a result of freezing occurs only with complete (critical) moisture content and saturation of the material. Water begins to freeze at the surface of structures, and therefore their destruction under the influence of negative temperatures begins from the surface, especially from the corners and edges. The maximum volume of ice is obtained at a temperature of -22C, when all the water turns into ice. The intensity of freezing depends on the pore volume. Stones and concrete with porosity up to 15% can withstand 100-300 freezing cycles. Reducing porosity, and therefore the amount of moisture, increases the frost resistance of structures. From the above it follows that when freezing, those structures that are moistened are destroyed. Protect structures from destruction during negative temperatures- This is first of all to protect them from moisture. Freezing of soils in the foundations is dangerous for buildings built on clay and silty soils, fine- and medium-grained sand, in which water rises through capillaries and pores above the groundwater level and is in a bound form. Damage to buildings due to freezing and heaving of the foundations can occur after many years of operation if the soil around them is cut off, the foundations are moistened, and factors contribute to their freezing.
· Construction of technological processes: each building and structure is designed and constructed taking into account the interaction of the processes provided for in it; however, due to the unequal resistance and durability of structural materials and the different influence of the environment on them, their wear is uneven. First of all, they are destroyed protective coatings walls and floors, windows, doors, roofing, then walls, frame and foundations. Compressed elements large sections, operating under static loads, wear out more slowly than bending and stretched, thin-walled, which operate under dynamic loads, in conditions high humidity And high temperature. Wear of structures due to abrasion - abrasive wear of floors, walls, corners of columns, steps of stairs and other structures can be very intense and therefore greatly affect their durability. It occurs under the influence of both natural forces (winds, sandstorms) and as a result of technological and functional processes, for example due to the intensive movement of large human flows in public buildings.
Description of the object
Table 1.1
| general characteristics | Pumping station |
| Year of construction | |
| Total area, m 2 - built-up area, m 2 - area of premises, m 2 | |
| Building height, m | 3,9 |
| Construction volume, m 3 | 588,6 |
| Number of storeys | |
| Construction characteristics | |
| Foundations | Monolithic reinforced concrete |
| Walls | Brick |
| Floors | Reinforced concrete |
| Roof | Roofing made from roll materials |
| Floors | Cement |
| Doorways | Wooden |
| Interior decoration | Plaster |
| Attractiveness ( appearance) | Satisfactory appearance |
| Actual age of the building | |
| Standard service life of a building | |
| Remaining service life | |
| Systems engineering support | |
| Heat supply | Central |
| Hot water supply | Central |
| Sewerage | Central |
| Drinking water supply | Central |
| Electricity supply | Central |
| Telephone | - |
| Radio | - |
| Alarm system: - security - fire | availability availability |
| External landscaping | |
| landscaping | Green spaces: lawn, shrubs |
| Driveways | Asphalt road, satisfactory condition |
During construction and operation, the building experiences various loads. External influences can be divided into two types: power And non-force or environmental influences.
TO forceful impacts include various types of loads:
permanent– from the own weight (mass) of the building elements, soil pressure on its underground elements;
temporary (long-term)– from the weight of stationary equipment, long-term stored cargo, the dead weight of permanent building elements (for example, partitions);
short-term– from the weight (mass) of moving equipment (for example, cranes in industrial buildings), people, furniture, snow, from the action of wind;
special– from seismic impacts, impacts resulting from equipment failures, etc.
TO non-forceful relate:
temperature impact, causing changes in the linear dimensions of materials and structures, which in turn leads to the occurrence of force effects, as well as affecting the thermal conditions of the room;
exposure to atmospheric and ground moisture, and vaporous moisture, contained in the atmosphere and indoor air, causing a change in the properties of the materials from which the building’s structures are made;
air movement causing not only loads (with wind), but also its penetration into the structure and premises, changing their humidity and thermal conditions;
exposure to radiant energy sun ( solar radiation) causing, as a result of local heating, a change in the physical and technical properties of the surface layers of the material, structures, a change in the light and thermal conditions of the premises;
exposure to aggressive chemical impurities contained in the air, which in the presence of moisture can lead to the destruction of the material of building structures (the phenomenon of corrosion);
biological effects caused by microorganisms or insects, leading to the destruction of structures made of organic building materials;
exposure to sound energy(noise) and vibration from sources inside or outside the building.
Where the effort is applied loads are divided into concentrated(e.g. weight of equipment) and equalsmeasuredlydistributed(own weight, snow).
Depending on the nature of the load, they can be static, i.e. constant in magnitude over time and dynamic(drums).
In direction - horizontal (wind pressure) and vertical (own weight).
That. a building is subject to a variety of loads in terms of magnitude, direction, nature of action and location of application.
Rice. 2.3. Loads and impacts on the building.
There may be a combination of loads in which they will all act in the same direction, reinforcing each other. It is these unfavorable combinations of loads that building structures are designed to withstand. The standard values of all forces acting on the building are given in DBN or SNiP.
It should be remembered that impacts on structures begin from the moment of their manufacture and continue during transportation, during the construction of the building and its operation.
Every building or structure inevitably experiences the effects of certain loads. This circumstance forces us, the designers, to analyze the operation of the structure from the perspective of their most unfavorable combination - so that even if it occurs, the structure remains strong, stable, and durable.
For a structure, the load is an external factor that transfers it from a state of rest to a stress-strain state. Load collection is not ultimate goal engineer - these procedures relate to the first stage of the structural calculation algorithm (discussed in this article).
Load classification
First of all, loads are classified according to the time of impact on the structure:
- constant loads (act throughout the entire life cycle building)
- temporary loads (act from time to time, periodically or one-time)
Segmentation of loads allows you to simulate the operation of a structure and perform the corresponding calculations more flexibly, taking into account the probability of the occurrence of one or another load and the probability of their simultaneous occurrence.
Units of measurement and mutual conversions of loads
In the construction industry, concentrated force loads are typically measured in kilonewtons (kN) and moment loads in kNm. Let me remind you that according to International system units (SI) force is measured in Newtons (N), length - in meters (m).
Loads distributed over volume are measured in kN/m3, over area - in kN/m2, over length - in kN/m.
Figure 1. Types of loads:
1 - concentrated forces; 2 - concentrated moment; 3 - load per unit volume;
4 - load distributed over the area; 5 - load distributed along the length
Any concentrated load \(F\) can be obtained by knowing the volume of the element \(V\) and the volumetric weight of its material \(g\):
The load distributed over the area of the element can be obtained through its volumetric weight and thickness \(t\) (size perpendicular to the load plane):
Similarly, the load distributed along the length is obtained by multiplying the volumetric weight of the element \(g\) by the thickness and width of the element (dimensions in directions perpendicular to the load plane):
where \(A\) is the area cross section element, m 2.
Kinematic influences are measured in meters (deflections) or radians (angles of rotation). Thermal loads are measured in degrees Celsius (°C) or other temperature units, although they can also be specified in units of length (m) or be dimensionless (temperature expansions).
→ Building structures
Loads and impacts on buildings
Buildings as a whole and their individual parts experience various influences from loads (mechanical forces) and influences, for example, from changes in the temperature of external and internal air.
Under the influence of these loads and impacts, internal forces arise in the materials of building structures, the magnitude of which per unit area (intensity internal forces), is called voltage. Voltage is most often measured in kg/cm2.
As a result of stresses in materials and structures, deformations can occur, i.e. tension, compression, shear, bending, torsion or more complex deformations.
Deformations can be elastic, i.e., disappearing after the impact that caused the deformation is eliminated, and plastic, i.e., remaining after the impact is eliminated.
The load can be concentrated when its pressure area is small compared to the size of the body to which it is applied, and can be taken as a point, for example, the load from a person on the floor.
If the pressure area is relatively large, then the load is called distributed. If the load is evenly distributed over the area, then it is called uniformly distributed, for example, the weight of a layer of water on water-filled flat coverings. The nature of the application of loads may be different, for example, on the basement wall of a building from the outside, the soil pressure increases as it goes deeper and is expressed in the form of a triangle with the base at the level of the basement floor.
Tensile strength, or ultimate strength of a material, is the stress in the material at various types deformation (tension, compression, torsion, bending) corresponding to the maximum (before failure of the sample) value of the load, and is measured by the ratio of the maximum load to the area of the initial cross-section of the sample (i.e., the cross-section of the undeformed sample) usually in kg/cm2.
The main characteristics of the resistance of materials to force influences are standard resistance (R”), established on the basis of tests.
Rice. 1. Load distribution diagram in the building
a - plan; b - section
Standard resistances can be mainly the strength limits under various deformations or the yield limits of materials, which are stresses under various types of deformation, which are characterized by the fact that the residual (plastic) deformation is distributed throughout the entire working volume of the sample at a constant acting load. Regulatory resistance various materials and structures are given in SNiP II-A. 10-62.
Possible change in the resistance of materials, products and structures in an unfavorable direction compared to standard values, caused by variability mechanical properties(heterogeneity of materials), is taken into account by the uniformity coefficients (k), which are given in SNiP II-A 10-62.
Features of the materials, structural elements and their connections, foundations, as well as structures and buildings in general, which are not directly reflected in the calculations, are taken into account by the operating conditions coefficients (t) given in SNiP II-A. 10-62.
The resistances of materials taken into account by calculation are called design resistances ® and are defined as the product of standard resistances (R1’) by uniformity coefficients (/g), and in necessary cases and on the coefficients of working conditions (t).
The values of design resistances for determining the calculation conditions, taking into account the corresponding coefficients of operating conditions, are established by the design standards for building structures and foundations of buildings and structures for various purposes.
The greatest loads and impacts that do not constrain or violate normal operating conditions and in possible cases controlled during operation and production are called normative.
Possible deviation loads in an unfavorable (more or less) direction from their standard values due to variability of loads or deviations from normal operating conditions are taken into account by overload factors (p), established taking into account the purpose of buildings and structures and their operating conditions.
Various standard loads on floors, loads from technological equipment, overhead cranes, snow and wind loads, as well as overload factors are given in chapter SNiP II-A. 11-62.
The loads taken into account by the calculation, defined as the product of the standard loads and the corresponding overload factors, are called design loads.
All loads and influences that cause forces (stresses) in structures and foundations of structures, taken into account during design, are divided into permanent and temporary. Constant loads and impacts include such loads and impacts that may occur during the construction or operation of structures constantly, for example: the weight of permanent parts of buildings, the weight and pressure of soils, prestressing forces, the weight of wires on the supports of power lines and antenna devices of communication structures, etc.
Temporary loads or impacts are those that may not be present during certain periods of construction and operation of the structure.
Depending on the duration of action, temporary loads and impacts are divided into:
a) temporary long-acting ones, which can be observed during the construction and operation of a structure for a long time, for example: loads in the premises of book depositories and libraries, loads on floors storage facilities, weight of stationary equipment, pressure of liquids and gases in tanks and pipelines, etc.;
b) short-term acting, which can be observed during the construction and operation of the structure only for a short time, for example: loads from mobile handling equipment, snow and wind loads, wave and ice pressure, temperature climatic influences, etc.; »
c) special ones, the occurrence of which is possible in exceptional cases, for example: seismic impacts in areas subject to earthquakes, water pressure during catastrophic floods, loads arising from the destruction of part of a building, etc.
When calculating building structures, not all loads and impacts affecting them are taken into account, but only certain combinations of loads and impacts (main, additional, special combinations), which are given in SNiP II-A. 10-62 and II-A. 11-62.
According to the nature of the action, loads are divided into static (gradually changing) and dynamic (shock, rapidly and periodically changing).
Dynamic loads and impacts on building construction accounted for as specified regulatory documents for design and calculation load-bearing structures subject to dynamic loads and impacts. In the absence of the necessary data for this, the dynamic influence on structures can be taken into account by multiplying the design loads by the dynamic coefficients.
During construction and during operation, the building experiences various loads. The material of the structure itself resists these forces and internal stresses arise in it. Behavior of building materials and structures under the influence external forces and loads is studied by structural mechanics.
Some of these forces act on the building continuously and are called permanent loads, others act only at certain periods of time and are called temporary loads.
Constant loads include dead weight of the building, which mainly consists of the weight of the structural elements that make up its supporting frame. Self-weight acts constantly in time and in the direction from top to bottom. Naturally, the stresses in the material of the supporting structures in the lower part of the building will always be greater than in the upper part. Ultimately, the entire impact of its own weight is transferred to the foundation, and through it to the foundation soil. Its own weight has always been not only constant, but also the main, main load on the building.
Only in last years builders and designers faced completely new problem: not how to securely support a building on the ground, but how to “tie” it, anchor it to the ground so that it is not torn off the ground by other influences, mainly wind forces. This happened because the dead weight of the structures as a result of the use of new high-strength materials and new design diagrams was constantly decreasing, and the dimensions of the buildings were growing. The area affected by the wind, in other words, the windage of the building, increased. And finally, the impact of the wind became more “weighty” than the impact of the weight of the building, and the building began to tend to lift off the ground.
is one of the main temporary loads. As altitude increases, the impact of wind increases. Thus, in the central part of Russia, the wind load (wind speed) at a height of up to 10 m is taken to be equal to 270 Pa, and at a height of 100 m it is already equal to 570 Pa. In mountainous areas and on sea coasts, the impact of wind increases significantly. For example, in some areas of the Arctic and Primorye coastlines, the standard value of wind pressure at a height of up to 10 m is 1 kPa. On the leeward side of the building, a rarefied space occurs, which creates negative pressure - suction, which increases the overall effect of the wind. The wind changes both direction and speed. Strong gusts of wind also create a shock, dynamic effect on the building, which further complicates the conditions for the operation of the structure.Urban planners encountered big surprises when they began to erect high-rise buildings in cities. It turned out that the street, on which strong winds had never blown, with the construction on it multi-storey buildings It became very windy. From a pedestrian’s point of view, wind at a speed of 5 m/s is already becoming annoying: it flutters clothes and ruins hair. If the speed is a little higher, the wind is already raising dust, swirling pieces of paper, and becoming unpleasant. A tall building is a significant barrier to air movement. Hitting this barrier, the wind breaks into several streams. Some of them go around the building, others rush down, and then near the ground they also go to the corners of the building, where the strongest air currents are observed, 2-3 times higher in speed than the wind that would blow in this place if there were no building. At very tall buildings The force of the wind at the base of the building can reach such proportions that it knocks pedestrians off their feet.
Oscillation amplitude high-rise buildings reaches large sizes, which negatively affects people’s well-being. Creaking and sometimes grinding steel frame one of the world's tallest International Buildings shopping center in New York (its height is 400 m) causes anxiety among people in the building. It is very difficult to foresee and calculate in advance the effect of wind during high-rise construction. Currently, builders are resorting to wind tunnel experiments. Just like aircraft manufacturers! they blow models of future buildings in it and, to some extent, get a real picture of air currents and their strength.
also applies to live loads. Particular attention must be paid to the influence of snow load on buildings of different heights. At the border between the higher and lower parts of the building, a so-called “snow bag” appears, where the wind collects entire snowdrifts. At variable temperatures, when the snow alternately thaws and refreezes and at the same time suspended particles from the air (dust, soot) also get here, snow, or more precisely, ice masses become especially heavy and dangerous. Due to the wind, the snow cover lies unevenly both on flat and pitched roofs, creating an asymmetric load that causes additional stress in structures.Temporary includes (load from people who will be in the building, technological equipment, stored materials, etc.).
Stresses also arise in the building from exposure to solar heat and frost. This effect is called temperature-climatic. Warming up sun rays, building structures increase their volume and size. Cooling during frosts, they decrease in volume. With such “breathing” of a building, stresses arise in its structures. If the building is large, these stresses can reach high values exceeding permissible values, and the building will begin to collapse.
Similar stresses in the structural material arise when uneven settlement of the building, which can occur not only due to different load-bearing capacities of the foundation, but also due to large differences in the payload or dead weight of individual parts of the building. For example, a building has a multi-story and a single-story part. In the multi-storey part, heavy equipment is located on the floors. The pressure on the ground from the foundations of a multi-story part will be much greater than from the foundations of a single-story part, which can cause uneven settlement of the building. To relieve additional stress from sedimentary and temperature effects, the building is “cut” into separate compartments using expansion joints.
If a building is protected from temperature deformations, then the joint is called a temperature joint. It separates the structures of one part of the building from another, with the exception of the foundations, since the foundations, being in the ground, do not experience temperature effects. Thus, expansion joint localizes additional stresses within one compartment, preventing their transfer to adjacent compartments, thereby preventing their addition and increase.
If the building is protected from sedimentary deformations, then the seam is called sedimentary. It separates one part of the building from another completely, including the foundations, which, thanks to such a seam, are able to move one in relation to another in vertical plane. Without seams, cracks could appear in unexpected places and compromise the strength of the building.
In addition to permanent and temporary, there are also special impacts on buildings. These include:
- seismic loads from an earthquake;
- explosive effects;
- loads arising from accidents or breakdowns of technological equipment;
- impacts from uneven deformations of the base during soaking of subsidence soils, during thawing of permafrost soils, in mining areas and during karst phenomena.
According to the place where forces are applied, loads are divided into concentrated (for example, the weight of equipment) and uniformly distributed (its own weight, snow, etc.).
By the nature of the action, loads can be static, that is, constant in value over time, for example, the same dead weight of structures, and dynamic (shock), for example, gusts of wind or the impact of moving parts of equipment (hammers, motors, etc.).
Thus, the building is subject to the most various loads by size, direction, nature of action and place of application (Fig. 5). A combination of loads may result in which they will all act in the same direction, reinforcing each other.
Rice. 5. Loads and impacts on the building: 1 - wind; 2 - solar radiation; 3 - precipitation (rain, snow); 4 - atmospheric influences (temperature, humidity, chemicals); 5 - payload and dead weight; 6 - special impacts; 7 - vibration; 8 - moisture; 9 - soil pressure; 10 - noise
It is these unfavorable combinations of loads that building structures are designed to withstand. The standard values of all forces acting on the building are given in SNiP. It should be remembered that impacts on structures begin from the moment of their manufacture and continue during transportation, during the construction of the building and its operation.
Blagoveshchensky F.A., Bukina E.F. Architectural structures. - M., 1985.
