Structural elements of the building and the load on them. Loads and effects on steel structures multi-storey buildings

During the construction process and during operation, the building experiences various loads. The structural material itself resists these forces, internal stresses. The behavior of building materials and structures under the influence of external forces and loads is studied by building mechanics.

Some of these forces act on the building continuously and are called constant loads, others - only in separate periods of time and are called temporary loads.

Permanent loads include dead weight of the building, which mainly consists of the weight structural elements that make up its supporting frame. Self-weight acts constantly in time and 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 effect of its own weight is transferred to the foundation, and through it to the foundation soil. Self weight has always been not only constant, but also the main, main load on the building.

Only in recent years, builders and designers have faced a completely new problem: not how to securely support the 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 own weight of structures as a result of the use of new high-strength materials and new design schemes was constantly decreasing, and the dimensions of buildings were growing. The area on which the wind acts, in other words, the windage of the building, increased. And finally, the effect of the wind became more "weighty" than the effect 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 effect of wind increases. So, in the middle part of Russia, the load from the wind (wind speed) at a height of up to 10 m is assumed to be 270 Pa, and at a height of 100 m it is already equal to 570 Pa. In mountainous areas, on the sea coasts, the impact of the wind is much greater. For example, in some areas of the coastline of the Arctic and Primorye, the standard value of the wind pressure at a height of up to 10 m is 1 kPa. A rarefied space appears on the leeward side of the building, which creates a 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 faced big surprises when they began to erect high-rise buildings in cities. It turned out that the street, which never had strong winds, became very windy with the construction of multi-storey buildings on it. From the point of view of a pedestrian, the wind at a speed of 5 m / s is already becoming annoying: it blows clothes, spoils the hair. If the speed is a little higher - the wind is already raising dust, swirling scraps of paper, it becomes unpleasant. A tall building is a solid 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 faster than the wind that would blow in this place if there were no building. With very tall buildings, the force of the wind at the base of the building can be of such magnitude that it knocks down pedestrians.

The amplitude of oscillations of high-rise buildings reaches large sizes, which negatively affects the well-being of people. The creaking and sometimes creaking of the steel frame of one of the world's tallest buildings of the World Trade 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 in high-rise construction. Currently, builders resort to experiments in a wind tunnel. Just like the aircraft builders! 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 should be paid to the effect of snow load on buildings of different heights. On the border between the elevated and lowered parts of the building, a so-called "snow bag" appears, where the wind collects entire snowdrifts. At variable temperatures, when alternate thawing and refreezing of snow occurs, and at the same time suspended particles from the air (dust, soot) also get here, snow, or rather, ice massifs become especially heavy and dangerous. Due to the wind, the snow cover falls unevenly both with flat and pitched roofs, creating an asymmetric load, which causes additional stresses in the structures.

Temporary includes (load from people who will be in the building, process equipment, stored materials, etc.).

Stresses arise in the building from exposure to solar heat and frost. This effect is called temperature and climate. Being heated by the sun's rays, building structures increase their volume and size. Cooling during frosts, they decrease in volume. With such a “breathing” of the building, stresses arise in its structures. If the building has a large extent, these stresses can reach high values exceeding the allowable, and the building will begin to collapse.

Similar stresses in the material of construction also arise when uneven settlement of the building, which can occur not only because of the different bearing capacity of the base, but also because of the large difference in payload or dead weight of individual parts of the building. For example, a building has multi-story and one-story parts. 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 one-story part, which can cause uneven settlement of the building. To remove additional stresses from sedimentary and temperature effects, the building is "cut" into separate compartments with expansion joints.

If the building is protected from temperature deformations, then the seam is called temperature. It separates the structures of one part of the building from another, with the exception of foundations, since foundations, being in the ground, do not experience temperature effects. Thus, the thermal seam localizes additional stresses within one compartment, preventing their transfer to neighboring 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 the other completely, including the foundations, which, thanks to such a seam, have the ability to move one in relation to the other in vertical plane. In the absence of seams, cracks could appear in unexpected places and compromise the strength of the building.

In addition to permanent and temporary, there are also special effects on buildings. These include:

• seismic loads from an earthquake;
• explosive impacts;
• loads arising from accidents or breakdowns of technological equipment;
• impacts from uneven deformations of the base during soaking of subsiding soils, during thawing of permafrost soils, in areas of mine workings and during karst phenomena.

According to the place of application of efforts, the loads are divided into concentrated (for example, the weight of equipment) and evenly distributed (own weight, snow, etc.).

By the nature of the action, loads can be static, that is, constant in magnitude over time, for example, the same own weight of structures, and dynamic (shock), for example, gusts of wind or the impact of moving parts of equipment (hammers, motors, etc.).

Thus, a variety of loads act on the building in terms of magnitude, direction, nature of action and place of application (Fig. 5). You can get a combination of loads in which they 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 own weight; 6 - special effects; 7 - vibration; 8 - moisture; 9 - soil pressure; 10 - noise

It is on such unfavorable combinations of loads that building structures rely. The normative values ​​of all efforts acting on the building are given in SNiP. It should be remembered that impacts on structures begin from the moment of their manufacture, continue during transportation, during the construction of the building and its operation.

Blagoveshchensky F.A., Bukina E.F. Architectural designs. - M., 1985.

It is assumed that all anchor points structures move forward according to the same law X 0 \u003d XJ ()

During an earthquake, the soils of the base of the building begin to move, as shown in Figure 14.

At the same time, an inertial force acts on each unit of the volume of the structure, depending on the inertial parameters concentrated in these volumes - the masses and stiffness characteristics of the structure. These inertial forces are called seismic forces or seismic loads and bring the structure into a stress-strain state.

Let us consider the main approaches that allow determining such important parameters as stiffness, natural frequency and vibration modes of a structure. It is easiest to choose a linear oscillator as a building model, the impact on which is modeled by the horizontal movement of the base according to a given law XQ = X 0 (t), and the system has one degree of freedom, determined by the horizontal displacement of the concentrated mass t(Fig. 15).

Thus, the total displacement X 0 (0 mass t at any moment of time is the sum of the "portable" displacement Xj(t) and the relative displacement caused by the bending of the rod X2(t):

Let us compose the equation of motion using the displacement method, because we are interested in the value of the restoring force (elastic force) equal to

Calculation scheme of a linear oscillator

where is the displacement X t masses in the horizontal

direction caused by the action of a unit force - the rigidity of a linear oscillator.

The mass equilibrium equation will be

Then considering:

where ω 2 is the frequency of natural oscillations of the oscillator, we obtain the equation of motion, in which the parameter that determines the oscillatory system is the frequency of natural oscillations of this system:

Seismic loads can act in any direction, therefore, for real buildings and structures, the equations that determine their movement under seismic load are very cumbersome, but the system is characterized by the same frequency of natural oscillations.

If we generalize the problem of earthquake-resistant construction, then from the point of view of the derived equations, it consists in identifying those structures that are the least strong and rigid, and, accordingly, in increasing their strength (seismic reinforcement) or reducing the load on them (seismic isolation).

Modern regulations set out General requirements to ensure the mechanical safety of buildings and structures. So, in part 6 of Art. 15 of Federal Law No. 384 "Technical Regulations on the Safety of Buildings and Structures" requirements are put forward that "in the process of construction and operation of a building or structure, its building structures and foundation will not reach the limit state in terms of strength and stability ... under variants of simultaneous action of loads and influences."

For the limiting state of building structures and foundations in terms of strength and stability, a state characterized by:

• destruction of any nature;
• loss of shape stability;
• loss of position stability;
• violation of operational suitability and other phenomena associated with the threat of harm to life and health of people, property of individuals or legal entities, state or municipal property, environment, life and health of animals and plants.

In the calculations of building structures and foundations, all types of loads corresponding to the functional purpose and design solution of the building or structure, climatic, and, if necessary, technological impacts, as well as forces caused by deformation of building structures and foundations, must be taken into account.

A building or structure in a territory where hazardous natural processes and phenomena and (or) man-made impacts are possible must be designed and constructed in such a way that during the operation of a building or structure, hazardous natural processes and phenomena and (or) man-made impacts do not cause the consequences referred to in Art. 7 of Federal Law No. 384, and (or) other events that create a threat of harm to life or health of people, property of individuals or legal entities, state or municipal property, the environment, life and health of animals and plants.

For elements of building structures, the characteristics of which, taken into account in the calculations of the strength and stability of a building or structure, may change during operation under the influence of climatic factors or aggressive factors of the external and internal environment, including under the influence of seismic processes that can cause fatigue phenomena in the material building structures, project documentation parameters characterizing the resistance to such impacts, or measures to protect against them, should be additionally indicated.

When assessing the consequences of an earthquake, the classification of buildings given in the seismic scale MMSK - 86 is used. In accordance with this scale, buildings are divided into two groups:

• 1) buildings and standard structures without anti-seismic measures;
• 2) buildings and standard structures with anti-seismic measures.

Buildings and standard structures without anti-seismic measures are divided into types.

A1 - local buildings. Buildings with walls made of local building materials: adobe without frame; adobe or mud brick without foundation; made of rolled or torn stone on clay mortar and without regular (made of brick or regular-shaped stone) masonry in the corners, etc.

A2 - local buildings. Buildings made of adobe or mud brick, with stone, brick or concrete foundations; made of torn stone on lime, cement or complex mortar with regular laying in the corners; made of formation stone on lime, cement or complex mortar; made of "midis" masonry; timber-framed buildings with adobe or clay infill, with heavy earthen or clay roofs; solid massive fences made of adobe or mud brick, etc.

B - local buildings. Timber-framed buildings with adobe or clay aggregates and light slabs:

• 1) B1 - typical buildings. Buildings made of baked bricks, hewn stone or concrete blocks on lime, cement or complex mortar; wooden panel houses;
• 2) B2 - structures made of baked bricks, hewn stone or concrete blocks on lime, cement or complex mortar: solid fences and walls, transformer kiosks, silos and water towers.

AT- local buildings. Wooden houses, chopped into a "paw" or "oblo":

• 1) B1 - typical buildings. Reinforced concrete, frame large-panel and reinforced large-block houses;
• 2) B2 - structures. Reinforced concrete structures: silos and water towers, lighthouses, retaining walls, pools, etc.

Buildings and standard structures with anti-seismic measures are divided into types:

• 1) C 7 - typical buildings and structures of all types (brick, block, panel, concrete, wooden, panel, etc.) with anti-seismic measures for the design seismicity of 7 points;
• 2) C8 - typical buildings and structures of all types with anti-seismic measures for the estimated seismicity of 8 points;
• 3) C9 - typical buildings and structures of all types with anti-seismic measures for the estimated seismicity of 9 points.

When two or three types are combined in one building, the building as a whole should be classified as the weakest of them.

During earthquakes, it is customary to consider five degrees of destruction of buildings. In the international modified seismic scale MMSK-86, the following classification of the degrees of destruction of buildings is proposed:

• 1) d= 1 - weak damage. Weak damage to the material and non-structural elements of the building: thin cracks in the plaster; chipping off small pieces of plaster; thin cracks in the junctions of ceilings with walls and wall filling with frame elements, between panels, in the cutting of furnaces and door frames; thin cracks in partitions, cornices, gables, pipes. There are no visible damage to structural elements. Current repair of buildings is sufficient to eliminate damage;
• 2) d= 2 - moderate damage. Significant damage to the material and non-structural elements of the building, falling layers of plaster, through cracks in partitions, deep cracks in cornices and gables, falling bricks from chimneys, falling individual tiles. Weak damage to load-bearing structures: thin cracks in load-bearing walls; minor deformations and small spalls of concrete or mortar in the frame nodes and panel joints. To eliminate the damage, major repairs of buildings are necessary;
• 3) d= 3 - severe damage. Destruction of non-constructive elements of the building: collapses of parts of partitions, cornices, gables, chimneys; significant damage to load-bearing structures: through cracks in load-bearing walls; significant frame deformations; noticeable panel shifts; chipping of concrete in the frame nodes. Restoration of the building is possible;
• 4) d= 4 - partial destruction of load-bearing structures: breaches and falls in load-bearing walls; collapse of joints and frame nodes; violation of connections between parts of the building; collapse of individual floor panels; collapse of large parts of the building. The building is to be demolished;
• 5) d= 5 - collapses. The collapse of load-bearing walls and ceilings, the complete collapse of the building with the loss of its shape.

Analyzing the consequences of earthquakes, we can distinguish the following main damage that buildings of various design schemes received if the seismic effects exceeded the calculated ones.

In frame buildings, the frame nodes are predominantly destroyed due to the occurrence of significant bending moments and transverse forces in these places. Particularly severe damage is received by the bases of the uprights and the joints of the crossbars with the uprights of the frame (Fig. 16a).

In large-panel and large-block buildings, butt joints of panels and blocks between themselves and with ceilings are most often destroyed. In this case, mutual displacement of the panels, opening of vertical joints, deviation of the panels from their original position, and in some cases collapse of the panels (Fig. 160) are observed.

For buildings with bearing walls from local materials (adobe bricks, adobe blocks, tuff blocks, etc.), the following damage is characteristic: the appearance of cracks in the walls (Fig. 17); collapse of end walls; shift, and sometimes collapse of floors; collapse of free-standing racks and especially stoves and chimneys.

The destruction of buildings is fully characterized by the laws of destruction. Under the laws of destruction of the building

The destruction of a frame building during an earthquake in China (a) and the destruction of panel buildings during an earthquake in Romania (b) The dependence between the probability of its damage and the intensity of the earthquake in points is determined. The laws of destruction of buildings are obtained on the basis of the analysis of statistical materials on the destruction of residential, public and industrial buildings from earthquakes of varying intensity.

Typical damage to brick walls under seismic impact

To construct a curve approximating the probability of occurrence of at least a certain degree of damage to buildings, the normal law of damage distribution is used. This takes into account that for the same building, not one, but five degrees of destruction can be considered, i.e. after destruction, one of five incompatible events occurs. The values ​​of the mathematical expectation M mo of the intensity of an earthquake in points, causing at least a certain degree of destruction of buildings, are given in table 1.

Table 1

Mathematical expectations M mo laws of destruction of buildings

Building classes according to MMSK-86	Degrees of destruction of buildings
	Light d= 1	Moderate d= 2		Partial destruction d = 4
	Mathematical expectations M laws of destruction

Using the data in Table 1 makes it possible to predict the probability of damage to buildings of various classes at a given earthquake intensity.

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, vibrations );

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:

Highly aggressive – acids, alkalis, gases – aggressive gases and liquids in industrial premises;

Medium 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 combustion products 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.

Impact ground water: 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 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; 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, 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 into either 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. Soil freezing 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 bending and stretching, thin-walled, 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

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 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 neglect special conditions 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) floor loads 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;

to) 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;

flow regulation surface water with the help of the vertical planning of the territory, the installation of a surface drainage system, the 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

For selection the best option 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.

Loads and impacts on high-rise buildings are determined on the basis of the design assignment, chapters of SNiP, manuals 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 standard 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 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 are 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 from lightweight concrete on steel profiled flooring 1.5-2 kN/m2; with the addition, if necessary, of a load from a suspended ceiling of 0.3-0.8 kN/m2,
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 the 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 the 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 the 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 trapezoid in individual zones different heights measured 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.
Wind load on elements outer wall, crossbars of tie and frame-tie systems that transmit wind pressure from the outer wall to the diaphragms and stiffeners, are determined by the formula (19.2), using the pressure coefficients c+, c- (positive pressure is directed inside the building) and standard 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 reckon with 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 a 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 pulsations vp, 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 assessment of T1 slightly affects ξ1, it can be recommended for steel frame frames T1=0.1met, for braced and frame-braced frames with reinforced concrete diaphragms and stiffeners T1=0.06mt, where mt 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 vibrations 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. During the construction of 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.