During the design, it is necessary to take into account everything that the building must resist in order not to lose its operational and strength qualities. Loads are considered to be external mechanical forces acting on the building, and influences are internal phenomena. To clarify the issue, we classify all loads and impacts according to the following criteria.
By duration:
- constants - the own mass of the structure, the mass and pressure of the soil in embankments or backfills;
- long-term - the mass of equipment, partitions, furniture, people, snow load, this also includes impacts due to shrinkage and creep of building materials;
- short-term - temperature, wind and ice climatic effects, as well as those associated with changes in humidity, solar radiation;
- special - normalized loads and impacts (for example, seismic, when exposed to fire, etc.).
Among designers, there is also the term payload, the meaning of which is not fixed in regulatory documents, but the term exists in construction practice. The payload is the sum of some temporary loads that are always present in the building: people, furniture, equipment. For example, for a residential building it is 150 ... 200 kg / m 2 (1.5 ... 2 MPa), and for an office building - 300 ... 600 kg / m 2 (3 ... 6 MPa).
By nature of work:
- static - dead weight of the structure, snow cover, equipment;
- dynamic - vibration, gust of wind.
According to the place of application of efforts:
- concentrated - equipment, furniture;
- evenly distributed - the mass of the structure, snow cover.
By the nature of the impact:
- loads of a power nature (mechanical) are loads that cause reactive forces; these loads include all the above examples;
- non-forced impacts:
- changes in outdoor air temperatures, which causes linear temperature deformations of building structures;
- flows of vaporous moisture from the premises - affect the material of external fences;
- atmospheric and ground moisture, chemically aggressive environmental impact;
- solar radiation;
- electromagnetic radiation, noise, etc., affecting human health.
All loads of a power nature are included in engineering calculations. The influence of non-forced impacts is also necessarily taken into account in the design. Let's see, for example, how the effect of temperature affects the structure. The fact is that under the influence of temperature, the structure tends to shrink or expand, i.e. change in size. This is prevented by other constructions with which this construction is associated. Consequently, in those places where structures interact, there are reactive forces that need to be perceived. Also in long buildings it is necessary to provide gaps.
Other influences are also subject to calculations: vapor permeability calculation, thermal engineering calculation, etc.
building requirements
In accordance with the loads and impacts, certain requirements are imposed on buildings and their structures.
Any building must meet the following basic requirements:
1. functional expediency, i.e. the building must fully comply with the process for which it is intended (convenience of living, work, recreation, etc.).
2.technical feasibility, i.e. the building must reliably protect people from external influences (low or high temperatures, precipitation, wind), be durable and stable, i.e. withstand various loads, durable, i.e. maintain normal performance over time.
3. Architectural and artistic expressiveness, i.e. the building should be attractive in its external (exterior) and internal (interior) appearance, favorably affect the psychological state and consciousness of people.
To achieve the necessary architectural and artistic qualities, such means are used as composition, scale, proportions, symmetry, rhythm, etc..
4. Economic feasibility, which provides for the most optimal costs of labor, funds and time for its construction for this type of building. At the same time, along with the one-time construction costs, it is also necessary to take into account the costs associated with the operation of the building.
Building cost reduction can be achieved rational planning buildings and avoidance of frills when establishing the areas and volumes of premises, as well as interior and exterior decoration; selection of the most optimal structures, taking into account the type of buildings and the conditions of its operation; application of modern methods and techniques for the production of construction works, taking into account the achievements of building science and technology.
When developing a technical solution, a feasibility study of the options for the designed structures is carried out, taking into account the cost of erection and operation of the building.
5. environmental requirements.
demands for the reduction of territories allocated for construction. This is achieved by increasing the number of storeys, active development of underground space (garages, warehouses, tunnels, trade enterprises, etc.);
widespread use of operated roofs, effective use of unsuccessful areas of territories (steep terrain, cuts and embankments along railway lines);
saving natural resources and energy. These requirements directly affect the choice of the shape of the building (preference for streamlined compact structures), the choice of structures for external walls and windows, and the choice of orientation of the building in the development.
Environmental requirements affect the decision to improve the built-up area with an increase in landscaping their territory including vertical and replacement of asphalt-concrete pavements with pieces (paving stones, stone and concrete slabs). These activities contribute to the preservation of the water balance and the cleanliness of the air environment of the territory.
Upon completion of construction work, the site should be soil reclamation in order to reduce the damage caused to the natural environment by construction activities.
Of course, the complex of these requirements cannot be considered in isolation from each other. Usually, when designing a building, the decisions made are the result of consistency, taking into account all the requirements that ensure its scientific validity.
chiefof these requirements is functional, or technological, expediency.
room- the main structural element or part of the building. Compliance of the premises with one or another function is achieved only when optimal conditions for a person are created in it, i.e. environment corresponding to the function performed by it in the room.
Inner space buildings are divided into separate rooms. The premises are divided into:
basic; auxiliary; technical.
Rooms located on the same level form a floor. The floors are separated by ceilings.
The internal space of buildings is most often dissected
vertically - on the floors and in plan - on separate rooms.
The premises of the building should most fully correspond to the processes for which this room is designed; therefore, the main thing in the building or its individual premises is its functional purpose.
At the same time, it is necessary distinguish between main and auxiliary functions. So, for example, in the building of educational institutions, the main function is training sessions, so it mainly consists of classrooms (audiences, laboratories, etc.). Along with this, auxiliary functions are also carried out in the building: catering, social events, etc. Special premises are provided for them: canteens and buffets, assembly halls, administrative premises, etc.
All rooms in the building that meet main and auxiliary functions, are interconnected by premises, the main purpose of which is to ensure the movement of people. These spaces are called communication. These include corridors, stairs, lobbies, foyers, lobbies, etc.
Thus, the room must necessarily meet a particular function. At the same time, in it the most optimal conditions for a person should be created, i.e., an environment that corresponds to the function it performs in the room.
Environmental quality depends on a number of factors. These include:
1. space , necessary for human activities, the placement of equipment and the movement of people;
2. air condition (microclimate) - a supply of air for breathing with optimal parameters of temperature, humidity and speed of its movement, corresponding to the normal heat and moisture exchange of the human body for the implementation of this function. The state of the air environment is also characterized by the degree of air purity, i.e., the amount of impurities (gases, dust) harmful to humans;
3. sound mode – conditions of audibility in the room (speech, music, signals) corresponding to its functional purpose, and protection from interfering sounds (noise) arising both in the room itself and penetrating from the outside, and having a harmful effect on the human body and psyche. Related to sound mode acoustics- the science of sound; architectural acoustics- the science of sound propagation in a room; and building acoustics- a science that studies the mechanism of the passage of sound through structures;
4. light mode – working conditions of the organs of vision, natural and artificial lighting, corresponding to the functional purpose of the room, determined by the degree of illumination of the room. Color problems are closely related to the light regime; the color characteristics of the environment affect not only the organs of vision, but also the human nervous system;
5. insolation – conditions of direct influence of sunlight. The sanitary and hygienic significance of direct solar irradiation is extremely high. The sun's rays kill most pathogenic bacteria, have a general health and psychophysical effect on a person. The effectiveness of the influence of solar lighting on buildings and the surrounding area is determined by the duration of their direct exposure, i.e. which in urban areas is regulated by Sanitary Standards (SN).
6. visibility and visual perception – conditions for the work of people associated with the need to see flat or three-dimensional objects in the room, for example, in the audience - notes on the board or a demonstration of the operation of the device; visibility conditions are closely related to the light regime.
7. human traffic which may be comfortable or
forced, in conditions of urgent evacuation of people from buildings.
Therefore, in order to properly design a room, create an optimal environment for a person in it. , it is necessary to take into account all the requirements that determine the quality of the environment.
These requirements for each type of building and its premises are established by the Building Regulations and Rules (SNiP) - the main state document regulating the design and construction of buildings and structures in our country.
Lecture 2
Technical feasibility building is determined by the solution of its structures, which must be in full accordance with the laws of mechanics, physics and chemistry. In order to correctly design the load-bearing and enclosing structures of buildings, it is necessary to know what kind of force and non-force effects they are exposed to.
Loads and impacts on buildings.
Building designs must take into account all external influences , perceived by the building as a whole and its individual elements. These influences are divided for power and non-power(environment impact)
The purpose of structures is the perception of force and non-force effects on the building
External influences on the building.
1 – permanent and temporary vertical force impacts; 2 – wind; 3 - special force effects (seismic or others); 4 – vibrations; 5 – lateral soil pressure; 6 – soil pressure (resistance); 7 - ground moisture; 8 - noise; 9 – solar radiation; 10 - precipitation; 11 – state of the atmosphere (variable temperature and humidity, the presence of chemical impurities)
To force influences There are different types of loads:
- permanent- from the own mass of the building, from the pressure of the foundation soil on its underground elements;
- temporary long-acting- from the mass of stationary technological equipment, long-term stored goods, own mass of partitions that can move during reconstruction;
- short-term- from the mass of mobile equipment, people, furniture, snow, from the action of wind on the building;
-special- from seismic impact, subsidence of the loess or thawed frozen ground base of the building, the impact of deformations of the earth's surface in areas affected by mine workings, explosions, fires, etc.
- impacts arising from emergency situations- Explosions, fires, etc.
Non-forced influences include:
- temperature effects of variable temperatures outside air, causing linear (temperature) deformations - changes in the dimensions of the external structures of the building or temperature forces in them when the manifestation of temperature deformations is constrained due to the rigid fixing of structures;
- exposure to atmospheric and ground moisture, on the material of structures, leading to changes in the physical parameters, and sometimes the structure of materials due to their atmospheric corrosion, as well as the effect of vaporous moisture in indoor air on the material of external fences, during phase transitions of moisture in their thickness;
-air movement, causing its penetration into the structure and premises, changing their humidity and thermal conditions;
- exposure to direct solar radiation, affecting the light and temperature conditions of the premises and causing a change in the physical and technical properties of the surface layers of structures (aging of plastics, melting of bituminous materials, etc.).
-exposure to aggressive chemicals, contained in the air, which, when mixed with rain or ground water, form acids that destroy materials (corrosion);
-biological effects caused by microorganisms or insects, leading to the destruction of structures and to the deterioration of the internal environment of the premises;
-exposure to sound energy (noise) from sources inside and outside the building, disturbing the normal acoustic regime in the room
In accordance with the loads and impacts, they present and technical requirements:
1 Durability- the ability to perceive power loads and impacts without destruction.
2. Sustainability- the ability of the structure to maintain balance under power loads and influences.
3. Rigidity- the ability of the structure to perform its static functions with small predetermined deformation values.
4. Durability- the deadline for maintaining the physical qualities of the building structure during operation. Durability design depends on:
creep- the process of small continuous deformations of the material of construction under long-term loading;
frost resistance- maintaining wet materials of the required strength with repeated alternation of freezing and thawing.
moisture resistance- the ability of materials to withstand the effects of moisture without a significant reduction in the strength of the consequent delamination, excitation, warping and cracking.
corrosion resistance- the ability of materials to resist degradation caused by chemical, physical or electrochemical processes.
biostability- the ability of organic materials to withstand the destructive effects of microargonisms and insects.
MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION
FSBEI HPE "BASHKIR STATE UNIVERSITY"
INSTITUTE OF MANAGEMENT AND SECURITY OF BUSINESS
Department of Economics, Management and Finance
TEST
Subject: Maintenance of buildings and structures
Topic: Types of impact on buildings and structures
Completed by: student of the EUKZO-01-09 group
Shagimardanova L.M.
Checked by: Fedotov Yu.D.
Introduction
Load classification
Load combinations
Conclusion
Introduction
When buildings and structures are erected near or close to existing ones, additional deformations of previously constructed buildings and structures occur.
Experience shows that neglecting the special conditions of such construction can lead to the appearance of cracks in the walls of previously built buildings, distortions of openings and flights of stairs, to shifting of floor slabs, destruction of building structures, i.e. to disruption of the normal operation of buildings, and sometimes even to accidents.
With the planned new construction in the built-up area, the customer and the general designer, with the involvement of interested organizations operating the surrounding buildings, should resolve the issue of surveying these buildings in the zone of influence of the new construction.
A nearby building is an existing building located in the zone of influence of the settlement of the foundations of a new building or in the zone of influence of the construction of a new building on the deformation of the foundation and structures of the existing one. The zone of influence is determined during the design process.
Load classification
Depending on the duration of the action of loads, one should distinguish between permanent and temporary (long-term, short-term, special) loads. Loads arising during the manufacture, storage and transportation of structures, as well as during the construction of structures, should be taken into account in the calculations as short-term loads.
a) the weight of parts of structures, including the weight of load-bearing and enclosing building structures;
b) weight and pressure of soils (embankments, backfills), rock pressure.
Prestressing forces retained in the structure or foundation should be taken into account in the calculations as forces due to permanent loads.
a) the weight of temporary partitions, grouts and footings for equipment;
b) the weight of stationary equipment: machine tools, apparatus, motors, tanks, pipelines with fittings, support parts and insulation, belt conveyors, permanent lifting machines with their ropes and guides, as well as the weight of liquids and solids filling the equipment;
c) pressure of gases, liquids and loose bodies in tanks and pipelines, overpressure and rarefaction of air that occurs during ventilation of mines;
d) loads on floors from stored materials and rack equipment in warehouses, refrigerators, granaries, book storages, archives and similar premises;
e) temperature technological effects from stationary equipment;
f) the weight of the water layer on water-filled flat pavements;
g) the weight of deposits of industrial dust, if its accumulation is not excluded by appropriate measures;
h) loads from people, animals, equipment on floors of residential, public and agricultural buildings with reduced standard values.
i) vertical loads from overhead and overhead cranes with a reduced standard value, determined by multiplying the full standard value of the vertical load from one crane in each span of the building by a factor: 0.5 - for groups of crane operation modes 4K-6K; 0.6 - for group of operation mode of cranes 7K; 0.7 - for the 8K crane operating mode group. Groups of crane operation modes are accepted in accordance with GOST 25546-82;
j) snow loads with a reduced design value, determined by multiplying the full design value by a factor of 0.5.
k) temperature climatic effects with reduced standard values determined in accordance with the instructions of paragraphs. 8.2-8.6 provided q1 = q2 = q3 = q4 = q5 = 0, DI = DVII = 0;
l) impacts caused by deformations of the base, not accompanied by a fundamental change in the structure of the soil, as well as thawing of permafrost soils;
m) effects due to changes in humidity, shrinkage and creep of materials.
In areas with an average January temperature of minus 5 ° C and above (according to map 5 of Appendix 5 to SNiP 2.01.07-85 *), snow loads with a reduced design value are not established.
a) equipment loads arising in start-up, transient and test modes, as well as during its rearrangement or replacement;
b) the weight of people, repair materials in the areas of maintenance and repair of equipment;
c) loads from people, animals, equipment on floors of residential, public and agricultural buildings with full standard values, except for the loads specified in clause 1.7, a, b, d, e;
d) loads from mobile handling equipment (forklifts, electric cars, stacker cranes, hoists, as well as from overhead and overhead cranes with a full standard value);
e) snow loads with full design value;
f) temperature climatic effects with full standard value;
g) wind loads;
h) ice loads.
a) seismic effects;
b) explosive impacts;
c) loads caused by sharp disturbances in the technological process, temporary malfunction or breakdown of equipment;
d) impacts caused by deformations of the base, accompanied by a fundamental change in the structure of the soil (during the soaking of subsiding soils) or its subsidence in areas of mine workings and karst.
Load combinations
The calculation of structures and foundations for the limit states of the first and second groups should be carried out taking into account unfavorable combinations of loads or the corresponding efforts.
These combinations are established from the analysis of real variants of the simultaneous action of various loads for the considered stage of the structure or foundation operation.
Depending on the composition of the loads taken into account, one should distinguish between:
a) the main combinations of loads, consisting of permanent, long-term and short-term,
b) special combinations of loads, consisting of permanent, long-term, short-term and one of the special loads.
Live loads with two standard values should be included in combinations as long-term - when taking into account the reduced standard value, as short-term - when taking into account the full standard value.
In special combinations of loads, including explosive effects or loads caused by the collision of vehicles with parts of structures, it is allowed not to take into account the short-term loads specified in clause 1.8.
When taking into account combinations that include permanent and at least two live loads, the design values of live loads or their corresponding forces should be multiplied by combination factors equal to:
in basic combinations for long-term loads y1 = 0.95; for short-term y2 = 0.9:
in special combinations for long-term loads y1 = 0.95; for short-term y2 = 0.8, except for the cases stipulated in the design standards for structures for seismic regions and in other design standards for structures and foundations. In this case, the special load should be accepted without reduction.
In the main combinations, when taking into account three or more short-term loads, their calculated values \u200b\u200bare allowed to be multiplied by the combination coefficient y2, taken for the first (according to the degree of influence) short-term load - 1.0, for the second - 0.8, for the rest - 0.6.
When taking into account combinations of loads for one live load, the following should be taken:
a) load of a certain kind from one source (pressure or vacuum in the tank, snow, wind, ice loads, temperature climatic effects, load from one loader, electric car, overhead or overhead crane);
b) load from several sources, if their combined action is taken into account in the normative and design values of the load (load from equipment, people and stored materials on one or more floors, taking into account the coefficients yA and yn; load from several overhead or overhead cranes, taking into account the coefficient y ; ice-wind load
Methods of dealing with impacts on buildings and structures
When designing engineering protection against landslide and landslide processes, the feasibility of applying the following measures and structures aimed at preventing and stabilizing these processes should be considered:
changing the slope relief in order to increase its stability;
regulation of surface water runoff with the help of vertical planning of the territory, installation of a surface drainage system, prevention of water infiltration into the soil and erosion processes;
artificial lowering of the groundwater level;
agroforestry;
soil stabilization;
holding structures;
Retaining structures should be provided to prevent shifting, collapse, landslides and fallouts of soils if it is impossible or economically inexpedient to change the slope (slope) topography.
Retaining structures are used of the following types:
supporting walls - to strengthen overhanging rocky cornices;
buttresses - separate supports cut into stable layers of soil to support individual rock masses;
belts - massive structures to maintain unstable slopes;
facing walls - to protect soil from weathering and shedding;
seals (sealing of voids formed as a result of falls on the slopes) - to protect rocky soils from weathering and further destruction;
anchor fastenings - as an independent holding structure (with base plates, beams, etc.) in the form of fastening individual rock blocks to a solid array on rocky slopes (slopes).
Snow-retaining structures should be placed in the zone of avalanche initiation in continuous or sectional rows up to the side boundaries of the avalanche collection. The upper row of structures should be installed at a distance of no more than 15 m down the slope from the highest position of the avalanche separation line (or from the line of snow-blowing fences or kolktafels). Rows of snow-retaining structures should be located perpendicular to the direction of sliding of the snow cover.
Avalanche-retarding structures should be designed to reduce or completely extinguish the speed of avalanches on alluvial cones in the avalanche deposition zone, where the slope is less than 23°. In some cases, when the protected object is in the zone of avalanche origin and the avalanche has a short acceleration path, it is possible to locate avalanche-retarding structures on slopes with a steepness of more than 23 °.
Conclusion
To select the optimal option for engineering protection, technical and technological solutions and measures must be justified and contain estimates of the economic, social and environmental effects in the implementation of the option or its rejection.
Substantiation and evaluation are subject to options for technical solutions and measures, their sequence, timing of implementation, as well as maintenance regulations for the created systems and protective complexes.
The calculations associated with the relevant justifications should be based on source materials of the same accuracy, detail and reliability, on a single regulatory framework, the same degree of elaboration of options, an identical range of costs and results taken into account. Comparison of options with differences in the results of their implementation should take into account the costs necessary to bring the options to a comparable form.
When determining the economic effect of engineering protection, the amount of damage should include losses from the impact of hazardous geological processes and the costs of compensating the consequences of these impacts. Losses for individual facilities are determined by the cost of fixed assets on an average annual basis, and for territories - on the basis of specific losses and the area of the threatened territory, taking into account the duration of the biological recovery period and the period of engineering protection.
The prevented damage should be summarized for all territories and structures, regardless of the boundaries of the administrative-territorial division.
List of used literature
1.V.P. Ananiev, A.D. Potapov Engineering geology. M: Higher. School 2010 2.S.B. Ukhov, V.V. Semenov, S.N. Chernyshev Soil mechanics, bases, foundations. M: High. School 2009 .IN AND. Temchenko, A. A. Lapidus, O.N. Terentiev Technology of building processes M: Vys. School 2008 .IN AND. Telichenko, A.A. Lapidus, O.M. Terentiev, V.V. Sokolovsky Technology of construction of buildings and structures M: Vys. School 2010 .SNiP 2.01.15-90 Engineering protection of territories, buildings and structures from dangerous geological cargoes.
Factors affecting buildings and structures are divided into:
External influences (natural and artificial: radiation, temperature, air currents, precipitation, gases, chemicals, lightning discharges, radio waves, electromagnetic waves, noise, sound vibrations, biological pests, ground pressure, frost heaving, moisture, seismic waves, stray currents , vibration);
Internal (technological and functional: permanent and temporary, long-term and short-term loads from its own weight, equipment and people; technological processes: shocks, vibrations, abrasion, spillage of liquid; 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 the bearing capacity of 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: force effects of loads, aggressive environmental influences.
Aggressive environment - an environment under the influence of which the structure of the properties of materials changes, which leads to a decrease in strength.
The change in structure and destruction is called corrosion. A substance that promotes destruction and corrosion is a stimulant. A substance that hinders destruction and corrosion - passivators and corrosion inhibitors.
The destruction of building materials is of a different nature and depends on the interaction of the chemical, electrochemical, physical, physico-chemical environment.
Aggressive media are divided into gas, liquid, solid.
Gas media: these are compounds such as carbon disulfide, carbon dioxide, sulfur dioxide. The aggressiveness of this environment is characterized by the concentration of gases, solubility in water, humidity and temperature.
Liquid media: these are solutions of acids, alkalis, salts, oil, oil, solvents. Corrosion processes in liquid media proceed more intensively than in others.
Solid media: these are dust, soils. Aggressiveness of this medium is estimated by dispersion, solubility in water, hygroscopicity, humidity of the environment.
Characteristics of the aggressive environment:
Strongly aggressive - acids, alkalis, gases - aggressive gases and liquids in industrial premises;
Moderately aggressive - atmospheric air and water with impurities - air with high humidity (more than 75%);
Slightly aggressive - clean atmospheric air - water not polluted with harmful impurities;
Non-aggressive - clean, dry (humidity up to 50%) and warm air - atmospheric air in dry and warm climatic regions.
Air exposure: the atmosphere contains dust, dirt, destroying buildings and structures. Air pollution combined with moisture leads to premature wear, cracking and structural failure.
However, in a clean and dry atmosphere, concrete and other materials can last for hundreds of years. The most intense air pollutants are the products of combustion of various fuels, therefore, in cities and industrial centers, metal structures corrode 2-4 times faster than in rural areas, where coal and fuel are burned less.
The main combustion products of most fuels are CO 2 , SO 2 .
When CO2 is dissolved in water, carbonic acid is formed. It is the end product of combustion. It has a destructive effect on concrete and other building materials. Sulfuric acid is formed when SO 2 is dissolved in water.
Smoke accumulates more than 100 types of harmful compounds (HNO 3 , H 3 PO 4 , resinous substances, non-combustible fuel particles). In coastal areas, the atmosphere contains chlorides, salts of sulfuric acid, which, in humid air, increases the aggressiveness of the impact on metal structures.
Groundwater impact: groundwater is a solution with varying concentration and chemical composition, which is reflected in the degree of aggressiveness of its impact. The water in the soil constantly interacts with minerals and organic matter. Sustained flooding of the underground parts of the building during the movement of groundwater increases the corrosion of the structure and the leaching of lime in concrete, and reduces the strength of the foundation.
There are general acid, leaching, sulfate, magnesia, carbon dioxide aggressiveness of groundwater.
The following factors have the most significant impact:
· Moisture exposure: As the experience of building operation has shown, moisture has the greatest influence on the wear of structures. Since the foundations and walls of old reconstructed buildings are made mainly of dissimilar stone materials (limestone, red brick, lime and cement mortars) with a porous-capillary structure, when in 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; the 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; the development of microorganisms that cause biological corrosion of materials.
The process of sanitation of buildings and structures cannot be limited to their treatment with a biocidal preparation. A comprehensive program of activities should 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) of the premises, if we are talking about underground structures, for example, basements;
Cut-off horizontal waterproofing device (in the presence of soil moisture suction);
Cleaning, if necessary, of internal surfaces from efflorescence and products of biological corrosion;
Therapeutic treatment with antisalt and biocidal preparations;
Sealing cracks and leaks with special hydro-sealing compounds and subsequent surface treatment with protective waterproofing preparations;
Production of finishing works.
· Impact of precipitation: Atmospheric precipitation, penetrating into the soil, turns either into vaporous or hygroscopic moisture, which is retained in the form of molecules on soil particles by molecular silts, or into a film, over molecular, or into gravitational moisture, freely moving in the soil under the action of gravity. Gravitational moisture can reach groundwater and, merging with it, raise its level. Ground water, in turn, due to capillary rise, moves upward to a considerable height and waters the upper layers of the soil. Under certain conditions, capillary and groundwater can merge and steadily flood the underground parts of structures, as a result of which the corrosion of structures increases and the strength of the foundations decreases.
· Impact of negative temperature: some structures, for example, basement parts, are in the zone of variable humidification and periodic freezing. Negative temperature (if it is lower than the calculated one or 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 the material, its volume increases, which creates internal stresses that increase due to the compression of the mass of the material itself under the influence of cooling. The pressure of ice in closed pores is very high - up to 20 Pa. The destruction of structures as a result of freezing occurs only at full (critical) moisture content, saturation of the material. Water begins to freeze at the surface of structures, and therefore their destruction under the influence of negative temperature begins from the surface, especially from corners and ribs. The maximum volume of ice is obtained at a temperature of - 22 ° C, when all the water turns into ice. The intensity of freezing depends on the pore volume. Stones and concretes with porosity up to 15% withstand 100-300 freezing cycles. Reduction of porosity and, consequently, the amount of moisture increases the frost resistance of structures. From what has been said, it follows that when freezing, those structures that are moistened are destroyed. To protect structures from destruction at low temperatures is, first of all, to protect them from moisture. Freezing of soils in the foundations is dangerous for buildings built on clay and dusty soils, fine and medium-grained sands, in which water rises above the groundwater level through capillaries and pores and is in a bound form. Damage to buildings due to freezing and buckling of the bases can occur after many years of operation if ground cutting around them, dampening of the bases and the action of factors contributing to their freezing are allowed.
· Erection of technological processes: each building and structure is designed and built taking into account the interaction of the processes provided for in it; however, due to the unequal resistance and durability of construction materials and the different influence of the environment on them, their wear is uneven. First of all, the protective coatings of walls and floors, windows, doors, roofs, then walls, frames and foundations are destroyed. Compressed elements of large sections, operating under static loads, wear out more slowly than bent and stretched, thin-walled elements, which operate under dynamic load, in conditions of high humidity and high temperature. Wear of structures under the action of 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 - building area, m 2 - floor area, m 2 | |
| Building height, m | 3,9 |
| Construction volume, m 3 | 588,6 |
| number of storeys | |
| Building characteristics | |
| Foundations | Monolithic reinforced concrete |
| Walls | brick |
| Overlappings | Reinforced concrete |
| Roof | Roofing from roll materials |
| floors | Cement |
| doorways | Wooden |
| Interior decoration | Plaster |
| Attractiveness (appearance) | Satisfactory appearance |
| The actual age of the building | |
| Standard life of the building | |
| Remaining service life | |
| Engineering support systems | |
| Heat supply | Central |
| Hot water supply | Central |
| Sewerage | Central |
| drinking water supply | Central |
| Power supply | Central |
| Telephone | - |
| Radio | - |
| Alarm: - security - fire | availability availability |
| External landscaping | |
| landscaping | Green spaces: lawn, shrubs |
| Driveways | Asphalt road, satisfactory condition |
Loads and impacts on multi-storey buildings are determined on the basis of the design assignment, chapters of SNiP, guidelines and reference books.
Permanent loads
Constant loads practically do not change in time and therefore are taken into account in all loading options for the stage of construction considered in the calculation.
Constant loads include: the weight of load-bearing and enclosing structures, the weight and pressure of soils, and the effects of prestressing structures. Loads from the weight of stationary equipment and utilities can also be considered constant, bearing in mind, however, that under certain conditions (repair, redevelopment) they can change.
The normative values of permanent loads are determined from the data on the weight of finished elements and products or are calculated from the design dimensions of structures and the density of materials (Table 19.2) (density equal to 1 kg / m3 corresponds to a specific gravity equal to 9.81 N / m3 = 0, 01 kN/m3).
Load from the weight of load-bearing steel structures. This load depends on the type and dimensions of the structural system, the strength of the steel used, the applied external loads and other factors.
The normative load (kN / m2 of floor area) from the weight of load-bearing structures made of steel class C38 / 23 is approximately equal to
When calculating crossbars and floor beams, a part of the load g is taken into account, equal to (0.3 + 6 / met)g - for frame systems, (0.2 + 4 / met)g - for tie systems, where mєt is the number of floors of the building, met >20.
For load-bearing structures made of steels of class C38 / 23 with design resistance R and a higher class with design resistance R ", the load from their weight is determined by the ratio The normative value of the weight of 1 m2 of wall, ceiling is approximately: a) for external walls made of lightweight masonry or concrete panels 2.5-5 kN / m2, from effective panels 0.6-1.2 kN / m2; b) for internal walls and partitions 30-50% less than for external ones; c) for a bearing floor slab together with a floor with reinforced concrete panels and floorings 3-5 kN/m2, with monolithic slabs of lightweight concrete over steel profiled flooring 1.5-2 kN/m2; with the addition of a suspended ceiling load of 0.3-0.8 kN/m2, if necessary,
When calculating the design loads from the weight of multilayer structures, they take, if necessary, their own overload factors for different layers.
The load from the weight of walls and permanent partitions is taken into account according to its actual position. If prefabricated wall elements are attached directly to the framing columns, the weight of the walls is not taken into account in the slab calculation.
The load from the weight of the rearranged partitions is applied to the floor elements in the most unfavorable position for them. When calculating columns, this load is usually averaged over the floor area.
Loads from the floor weight are distributed almost evenly and when calculating the floor elements and columns, they are collected from the corresponding cargo areas.
In modern multi-storey buildings with a steel frame, the intensity of the sum of standard loads from the weight of walls and floors, related to 1 m2 of floors, is approximately 4-7 kN/m2. The ratio of all permanent loads of the building (including the own weight of steel structures, flat and spatial stiffening trusses) to its volume varies from 1.5 to 3 kN/m3.
Live loads
Temporary loads on floors. Floor loads due to the weight of people, furniture and similar light equipment are established in SNiP in the form of equivalent loads evenly distributed over the area of \u200b\u200bthe premises. Their normative values for residential and public buildings are: in the main premises 1.5-2 kN/m2; in halls 2-4 kN/m2; in lobbies, corridors, stairs 3-4 kN / m2, and overload factors - 1.3-1.4.
According to paragraphs. 3.8, 3.9 SNiP live loads are accepted taking into account the reduction factors α1, α2 (when calculating beams and crossbars) and η1, η2 (when calculating columns and foundations). Coefficients η1, η2 refer to the sum of temporary loads on several ceilings and are taken into account when determining the longitudinal forces. Nodal bending moments in columns should be taken without taking into account the coefficients η1, η2, since the main influence on the bending moment is exerted by the temporary load on the crossbars of one adjacent to the floor node.
Considering possible layouts of temporary loads on the floors of a building, design practice usually proceeds from the principle of the most unfavorable loading. For example, to assess the largest span moments in the crossbar of the frame system, the schemes of the staggered arrangement of live loads are taken into account; in the calculation of frames, stiffeners and foundations, not only continuous loading of all floors is taken into account, but also possible options for partial, including one-sided, loading. Some of these schemes are very conditional and lead to unjustified margins in structures and foundations. determined according to the instructions of SNiP, is mainly important for roof structures of a multi-storey building and has little effect on the total forces in the lower structures. The operation of the structures of a multi-storey building, their rigidity, strength and stability significantly depend on the correct accounting of the wind load.
According to the calculated value of the static component of the wind load, kN/m2, is determined by the formula
In practical calculations, the normative diagram of the coefficient kz is replaced by a trapezoidal one with the lower and upper ordinates kн≥kв, determined from the conditions of equivalence of diagrams in terms of moment and transverse force in the lower section of the building. With an error of no more than 2%, the ordinate kn can be considered fixed and equal to the normative one (1 - for type A terrain; 0.65 - for type B terrain), and for kv, depending on the height of the building and type of terrain, the following values can be taken:
Ordinate at the level z:kze = kn+(kv-kn) z/H. In a building with a stepped shape (Fig. 19.1), the normative diagram is reduced to a trapezoidal diagram in separate zones of different heights, counted from the bottom of the building. There are also possible ways to bring the building into zones with a different division.
When calculating the building as a whole, the static component of the wind load, kN, in the direction of the x and y axes (Fig. 19.2) per 1 m of height is determined as the result of the aerodynamic forces acting in these directions, and is expressed through the coefficients of the total resistance cx, cy and horizontal dimensions B, L projections of the building on a plane perpendicular to the corresponding axes:
For buildings of a prismatic shape with a rectangular plan with a slip angle β=0, the coefficient su=0, and cx is determined from Table. 19.1, compiled taking into account the data of foreign and domestic studies and standards.
If β=90°, then cx=0, and the value of cy is found according to the same table, by swapping the designations B, L on the building plan.
With wind at an angle of β=45°, the values of cx, cy are given as a fraction in Table. 19.2, while the side of the plan B, perpendicular to the x-axis, is considered longer. Due to the uneven distribution of wind pressure on the walls at β=45° and B/L≥2, one should take into account the possible aerodynamic eccentricity in the application of a load qxc perpendicular to the longer side, equal to 0.15 V, and the corresponding torque with intensity, kN*m per 1 m height
If the building has loggias, balconies, protruding vertical ribs, then friction forces on both walls parallel to the x, y axis should be added to the loads qxc, qyc, equal to:
At an angle β=45°, these forces act only in the plane of the windward walls, and the torques caused by them with the intensity mkr"" = 0.05q(z)LB are balanced. But if one of the windward walls is smooth, the moment mcr"" from friction forces on the other wall must be taken into account. Similar conditions arise when
If the geometric center of the building plan does not coincide with the center of rigidity (or center of torsion) of the carrier system, additional eccentricities of the application of wind loads must be taken into account in the calculation.
The wind load on the elements of the outer wall, the crossbars of the braced and frame-braced systems, which transmit the wind pressure from the outer wall to the diaphragms and stiffeners, is determined by the formula (19.2), using the pressure coefficients c+, c- (positive pressure is directed inside the building) and normative values kz. Pressure coefficients for buildings with a rectangular plan (with some refinement of SNiP data):
In the case of β=0 for both walls parallel to the flow, the values of su equal to:
The same data is used at 0=90° for cx, swapping the designations B, L on the building plan.
To calculate one or another element, one should choose the most unfavorable of the given values of c+ and c- and increase them in absolute value by 0.2 to take into account possible internal pressure in the building. It is necessary to take into account a sharp increase in negative pressures in the corner zones of buildings, where c = -2, especially when calculating lightweight walls, glass, their fastenings; at the same time, the width of the zone, according to the available data, should be increased to 4-5 m, but not more than 1/10 of the wall length.
The influence of the surrounding buildings, the complication of the shape of buildings on the aerodynamic coefficients is established experimentally.
Under the action of the wind flow, the following are possible: 1) lateral swaying of aerodynamically unstable flexible buildings (vortex excitation of the wind resonance of buildings of a cylindrical, prismatic and slightly pyramidal shape; galloping of poorly streamlined buildings associated with a sharp change in the lateral disturbing force with small changes in wind direction and with an unfavorable ratio stiffness of the building in bending and torsion), and guidance; 2) vibrations of the building in the plane of the flow under the pulsation effect of a gusty wind. Oscillations of the first type can be more dangerous, especially in the presence of nearby tall buildings, but the methods for taking them into account have not been sufficiently developed, and testing of large aeroelastic models is required to assess the conditions for their occurrence.
Dynamic the component of the wind load when the building vibrates in the plane of the flow depends on the variability of the velocity fluctuations vп, characterized by the standard σv (Fig. 19.3). Velocity head of the wind at time t with air density p
To take into account the extreme values of ripples, vp = 2.5σv is taken, which corresponds (with a normal distribution function) to the probability of exceeding the accepted ripple at an arbitrary time moment of about 0.006.
The greatest contribution to dynamic forces and displacements is made by pulsations, the frequency of which is close to or equal to the frequency of natural oscillations of the system. The resulting inertial forces determine the dynamic component of the wind load, which is taken into account in accordance with SNiP for buildings with a height of more than 40 m, assuming that the shape of the natural oscillations of the building is described by a straight line,
Since the error in the estimation of Т1 slightly affects ξ1, it can be recommended for steel frame frames T1=0.1mest, for braced and frame-braced frames with reinforced concrete diaphragms and stiffeners T1=0.06met, where met is the number of floors of the building.
Neglecting small deviations of the shape factor ϗ from a straight line, for the total wind load (static and dynamic) in buildings constant width take a trapezoidal diagram, the ordinates of which are:
Depending on the direction of the wind under consideration, the values (calculated, standard) and dimensions (kN/m2, kN/m) adopted for qc, the corresponding total loads are obtained.
The acceleration of horizontal oscillations of the top of the building, necessary for the calculation for the second group of limit states, is determined by dividing the standard value of the dynamic component (excluding the overload factor) by the corresponding mass. If the calculation is carried out for the load qx, kN / m (Fig. 19.2), then
The value of m is estimated by dividing the permanent loads and 50% of the temporary vertical loads related to 1 m2 of floor by the acceleration due to gravity.
Accelerations from standard values of wind load are exceeded on average once every five years. If it is recognized as possible to reduce the return period to a year (or month), then a coefficient of 0.8 (or 0.5) is introduced to the value of the standard velocity pressure q0.
seismic effects. When constructing multi-storey buildings in seismic areas, load-bearing structures must be calculated both for the main combinations, consisting of normally acting loads (including wind load), and for special combinations, taking into account seismic effects (but excluding wind load). When the design seismicity is more than 7 points, the calculation for special combinations of loads is, as a rule, decisive.
The design seismic forces and the rules for their joint accounting with other loads are adopted according to SNiP. With an increase in the natural oscillation period of the building, seismic forces, in contrast to the dynamic component of the wind load, decrease or do not change. For a more accurate assessment of the periods of natural oscillations when taking into account seismic effects, methods can be used.
Temperature effects. A change in ambient temperature and solar radiation cause temperature deformations of structural elements: elongation, shortening, curvature.
At the stage of operation of a multi-storey building, the temperature of the internal structures practically does not change. Seasonal and daily changes in outdoor temperature and solar radiation primarily affect the outer walls. If their attachment to the frame does not prevent thermal deformations of the wall, the frame will not experience additional forces. In cases where the main load-bearing elements (for example, columns) are partially or completely extended beyond the edge of the outer wall, they are directly exposed to temperature and climatic influences, which must be taken into account when designing the frame.
Temperature effects under construction or they are accepted with rough assumptions due to the uncertainty of the temperature of the closure of structures, or they are neglected, taking into account the decrease in time of the forces caused by them due to inelastic deformations in the nodes and elements of the carrier system.
The influence of temperature climatic influences on the operation of the carrier system in multi-storey buildings with a metal frame has not been studied enough.
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