MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

FSBEI HPE "BASHKIR STATE UNIVERSITY"

INSTITUTE OF GOVERNANCE AND BUSINESS SECURITY

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 group EUKZO-01-09

Shagimardanova L.M.

Checked by: Fedotov Yu.D.

Introduction

Classification of loads

Combinations of loads

Conclusion

Introduction

When buildings and structures are erected near or close to existing ones, additional deformations of previously built buildings and structures occur.

Experience shows that neglect of the special conditions of such construction can lead to the appearance of cracks in the walls of previously constructed buildings, distortions of openings and staircases, to a shift of floor slabs, destruction of building structures, i.e. to the disruption of the normal operation of buildings, and sometimes even to accidents.

With the planned new construction on the built-up area, the customer and the general designer, with the involvement of interested organizations operating the surrounding buildings, must resolve the issue of examining these buildings in the zone of influence of new construction.

A nearby building is considered to be 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 production of work on the construction of a new building on the deformation of the foundation and structures of an existing one. The zone of influence is determined during the design process.

Classification of loads

Depending on the duration of the 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.

The prestressing forces remaining in the structure or foundation should be taken into account in the calculations as forces from permanent loads.

a) the weight of temporary partitions, gravies and foundations 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 bulk solids in tanks and pipelines, overpressure and rarefaction of air arising during ventilation of mines;

d) loads on floors from stored materials and racking equipment in warehouses, refrigerators, granaries, book depositories, archives and similar premises;

e) temperature technological influences from stationary equipment;

f) weight of the water layer on water-filled flat surfaces;

g) weight of industrial dust deposits, if its accumulation is not excluded by appropriate measures;

h) loads from people, animals, equipment on the floors of residential, public and agricultural buildings with reduced standard values.

i) vertical loads from bridge 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 operating modes of cranes 4K-6K; 0.6 - for the group of the operating mode of the cranes 7K; 0.7 - for the group of operating mode of cranes 8K. Groups of crane operating 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 influences with reduced standard values ​​determined in accordance with the instructions in 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 radical change in the structure of the soil, as well as thawing of permafrost soils;

m) impacts due to changes in moisture, shrinkage and creep of materials.

In areas with an average January temperature of minus 5 ° С and above (according to map 5 of Appendix 5 to SNiP 2.01.07-85 *), snow loads with a reduced calculated 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 equipment maintenance and repair;

c) loads from people, animals, equipment on the 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 lifting and transport equipment (forklifts, electric cars, stacker cranes, telphers, as well as from bridge and overhead cranes with a full standard value);

e) snow loads with full design value;

f) temperature climatic influences with full standard value;

g) wind loads;

h) ice loads.

a) seismic effects;

b) explosive effects;

c) loads caused by abrupt disturbances in the technological process, temporary malfunction or equipment breakdown;

d) impacts caused by deformations of the base, accompanied by a radical change in the structure of the soil (when soaking subsidence soils) or its subsidence in areas of mine workings and in karst.

Combinations of loads

The design of structures and foundations for the limiting states of the first and second groups should be performed taking into account unfavorable combinations of loads or the corresponding forces.

These combinations are established from the analysis of real options for the simultaneous action of various loads for the considered stage of the structure or foundation.

Depending on the composition of the loads taken into account, a distinction should be made 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.

Temporary loads with two standard values ​​should be included in combinations as long-term - taking into account the lower standard value, as short-term - 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 constant and at least two temporary loads, the calculated values ​​of temporary loads or the corresponding forces should be multiplied by the combination coefficients equal to:

in basic combinations for long-term loads y1 = 0.95; for short-term y2 = 0.9:

in special combinations for continuous loads y1 = 0.95; for short-term y2 = 0.8, except for the cases stipulated in the norms for the design of structures for seismic regions and in other norms for the design of structures and foundations. In this case, a special load should be taken without reduction.

In the main combinations, taking into account three or more short-term loads, their calculated values ​​can 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 the combinations of loads for one live load, the following should be taken:

a) a load of a certain kind from one source (pressure or vacuum in a tank, snow, wind, ice loads, temperature climatic influences, load from one forklift, electric car, bridge or overhead crane);

b) load from several sources, if their combined effect is taken into account in the standard 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 bridge or overhead cranes, taking into account the coefficient y ; ice-wind load

Methods for dealing with impacts on buildings and structures

When designing engineering protection against landslide and landslide processes, the advisability of using the following measures and structures aimed at preventing and stabilizing these processes should be considered:

changing the topography of the slope in order to increase its stability;

regulation of surface water runoff with the help of vertical planning of the territory, arrangement of a surface drainage system, prevention of water infiltration into the ground and erosion processes;

artificial lowering of the groundwater level;

agroforestry;

consolidation of soils;

restraining structures;

Retaining structures should be provided to prevent shear, collapse, landslides and falls of soil when it is impossible or economically inexpedient to change the relief of the slope (slope).

Restraining structures are used of the following types:

supporting walls - to strengthen the overhanging rock eaves;

buttresses - separate supports cut into stable soil layers to support individual rock massifs;

shingles - massive structures to support unstable slopes;

facing walls - to protect the soil from weathering and crumbling;

seals (filling of voids formed as a result of falls on the slopes) - to protect rocky soils from weathering and further destruction;

anchoring - as an independent holding structure (with base plates, beams, etc.) in the form of anchoring individual rock blocks to a solid massif on rocky slopes (slopes).

Snow holding structures should be placed in the avalanche initiation zone in continuous or sectional rows up to the lateral 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 the snow cover sliding.

Avalanche-braking structures should be designed to reduce or completely extinguish the avalanche velocity on fan fans 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 initiation and the avalanche has a short acceleration path, it is possible that the avalanche-stopping structures are located 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 when the option is implemented or abandoned.

Variants of technical solutions and measures, their sequence, timing of implementation, as well as maintenance procedures for the created systems and protective complexes are subject to justification and assessment.

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 benefits taken into account. Comparison of options with a difference in the results of their implementation should take into account the costs necessary to bring 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 cost of compensating for the consequences of these impacts. Losses for individual objects are determined by the cost of fixed assets in average annual terms, 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 implementation of engineering protection.

The prevented damage must be summed up 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. Shk. 2010

2.S. B. Ukhov, V.V. Semenov, S.N. Chernyshev Soil mechanics, foundations, foundations. M: Vys. Shk. 2009 r.

.IN AND. Temchenko, A. A. Lapidus, O. N. Terentyev Technology of building processes M: Vys. Shk. 2008 r.

.IN AND. Telichenko, A.A. Lapidus, O.M. Terentyev, V.V. Sokolovsky Technology of erection of buildings and structures M: Vys. Shk. 2010 r.

.SNiP 2.01.15-90 Engineering protection of territories, buildings and structures from hazardous geological cargo.

In order for a building to be technically feasible, it is necessary to know the external influences perceived by the building as a whole and its individual elements (Figure 11.2), which can be divided into two types: power(load) and non-power(environmental impact).

Rice. 11.2.

1 - permanent and temporary vertical force effects; 2 – wind; 3 - special force effects (seismic, etc.); 4 - vibrations; 5 - lateral soil pressure; 6 - ground pressure (rebound); 7 - ground moisture; 8 - noise; 9 – solar radiation; 10 - precipitation; 11 - the state of the atmosphere (variable temperature and humidity, the presence of chemical impurities)

Power effects include various types of loads:

• constants - from the own mass of the building elements, from the soil pressure on its underground elements;
• temporary long-term effects - from the mass of stationary equipment, long-term stored cargo, own weight of partitions that can be moved during reconstruction;
• short-term - from the mass of mobile equipment, people, furniture, snow, from the action of the wind on the building;
• special - from seismic impacts, impacts as a result of equipment failure.

Non-force effects include:

• temperature influences affecting the thermal regime of the premises, as well as leading to temperature deformations, which are already force effects;
• the effects of atmospheric and ground moisture, as well as the effects of moisture vapor in the air of the room, causing changes in the properties of the materials from which the building structures are made;
• air movement, causing its penetration into the structure and premises, changing their humidity and thermal conditions;
• exposure to direct solar radiation, causing a change in the physical and technical properties of the surface layers of the material of structures, as well as the thermal and light conditions of the premises;
• exposure to aggressive chemical impurities 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 deterioration of the internal environment of the premises;
• exposure to sound energy (noise) from sources inside and outside the building, disrupting the normal acoustic mode in the room.

In accordance with the listed loads and influences, the following requirements are imposed on buildings and their structures.

• 1. Strength- the ability to perceive loads without destruction.
• 2. Sustainability- the ability of the structure to maintain balance under external and internal loads.
• 3. Rigidity- the ability of structures to carry the load with minimum, predetermined deformation rates.
• 4. Durability- the ability of the building and its structures to perform their functions and maintain their qualities during the maximum service life for which they are designed. The durability depends on the following factors:
  • creep of materials, i.e. the process of small continuous deformations occurring in materials under conditions of prolonged exposure to loads;
  • frost resistance of materials, i.e. the ability of a wet material to withstand alternating freezing and thawing;
  • moisture resistance of materials, i.e. their ability to resist the destructive action of moisture (softening, swelling, warping, stratification, cracking);
  • corrosion resistance, i.e. the ability of materials to resist destruction caused by chemical and electrochemical processes;
  • biostability, i.e. the ability of organic materials to resist the destructive action of insects and microorganisms.

Durability is determined by the ultimate service life of the building. On this basis, buildings and structures are divided into four degrees:

• 1st - more than 100 years (main structures, foundations, external walls, etc. are made of materials that are highly resistant to the listed types of influences);
• 2nd - from 50 to 100 years old;
• 3rd - from 20 to 50 years (structures do not have sufficient durability, for example, houses with wooden outer walls);
• 4th - up to 20 years (temporary buildings and structures).

The service life also depends on the conditions in which the building and the structure are located, as well as on the quality of their operation.

The most important requirement for buildings and structures is the requirement fire safety... According to the degree of flammability, building materials are divided into three groups:

• non-combustible(do not burn, smolder or charred under the influence of fire or high temperature);
• hardly combustible(under the influence of fire or high temperature, they hardly ignite, smolder or char, but after removing the source of fire or high temperature, combustion and smoldering cease). They are usually protected from the outside with non-combustible materials;
• combustible(under the influence of open fire or high temperature, they burn, smolder or char and, after removing the source of fire or temperature, continue to burn or smolder).

Fire resistance limit of building structures is determined by the duration (in minutes) of resistance to the action of fire until the loss of strength or stability, or until the formation of through cracks, or until the temperature rises on the surface of the structure from the side opposite to the fire, on average, more than 140 ° C.

Buildings or their compartments between fire walls - firewalls (Fig. 11.3), depending on the degree of flammability of their structures, are divided into five degrees of fire resistance. The degree of fire resistance of buildings is determined according to Building Norms and Rules (SNiP) 21-01-97 * "Fire safety of buildings and structures".

Rice. 11.3. Firewalls - firewalls(a) and zones(b):

1 - fire wall; 2 - fireproof ceiling; 3 - fireproof comb

Buildings with load-bearing and enclosing structures made of stone, concrete, brick with the use of slab or sheet non-combustible materials belong to the 1st degree of fire resistance. In buildings of the II degree of fire resistance, materials are also made of non-combustible materials, but they have a lower fire resistance limit. In buildings of III degree of fire resistance, it is allowed to use combustible materials for partitions and ceilings. In buildings of the IV degree of fire resistance for all structures, it is allowed to use combustible materials with a minimum fire resistance limit of 15 minutes, except for the walls of staircases. Temporary buildings are referred to the V degree of fire resistance. The fire resistance limit of their structures is not standardized. In buildings of III, IV and V degrees of fire resistance, it is envisaged to dissect them by firewalls and fire-prevention ceilings into compartments that limit the area of ​​fire propagation.

During construction and operation, the building experiences various loads. External influences can be divided into two types: power and non-power or exposure to the environment.

TO power impacts include various types of loads:

permanent- from the own weight (mass) of the building elements, soil pressure on its underground elements;

temporary (long-term)- from the weight of stationary equipment, long-term stored cargo, own weight of permanent building elements (for example, partitions);

short-term- from the weight (mass) of mobile equipment (for example, cranes in industrial buildings), people, furniture, snow, from the action of the wind;

special- from seismic impacts, impacts as a result of equipment failures, etc.

TO non-force relate:

temperature influences that cause changes in the linear dimensions of materials and structures, which in turn leads to the occurrence of force effects, as well as affecting the thermal regime of the room;

exposure to atmospheric and ground moisture, and vaporous moisture, contained in the atmosphere and in the air of the premises, causing a change in the properties of the materials from which the building structures are made;

air movement causing not only loads (in case of wind), but also its penetration into the structure and premises, changing their humidity and thermal conditions;

exposure to radiant energy the sun (solar radiation) causing, as a result of local heating, a change in the physical and technical properties of the surface layers of material, structures, a change in the light and thermal conditions of the premises;

exposure to aggressive chemical impurities contained in the air, which in the presence of moisture can lead to the destruction of the building structure material (corrosion phenomenon);

biological effects caused by microorganisms or insects, leading to the destruction of structures made of organic building materials;

exposure to sound energy(noise) and vibration from sources inside or outside the building.

At the place of effort load divided into focused(e.g. equipment weight) and evenly distributed(own weight, snow).

By the nature of the action, the load can be static, i.e. constant in value over time and dynamic(drums).

In direction - horizontal (wind pressure) and vertical (dead weight).

That. the building is affected by a variety of loads in terms of magnitude, direction, nature of action and place of application.

Rice. 2.3. Loads and influences on the building.

You can get a combination of loads in which they all act in the same direction, reinforcing each other. It is these unfavorable load combinations that building structures are counting on. The normative values ​​of all efforts acting on the building are given in DBN or SNiP.

It should be remembered that impacts on structures begin from the moment they are manufactured, continue during transportation, during the construction of a building and its operation.

4. Basic requirements for buildings and their elements.

Buildings form a material-spatial environment for people to carry out various social processes of life, work and rest. Therefore, they must answer the series requirements, basic of them:

– functional(or technological) expediency, i.e. the building must be convenient for work, recreation or other process for which it is intended;

– technical expediency, i.e. buildings must be strong, stable, durable, reliably protect people and equipment from harmful atmospheric influences, meet fire safety requirements;

– architectural and artistic expressiveness, i.e. it should be attractive in appearance, have a beneficial effect on the psychological state and consciousness of people;

– economic feasibility, providing for the minimum cost of construction and operation of the building to obtain the maximum usable area.

– environmental.

The main in a building or room is it functional appointment.

The implementation of this or that function is always accompanied by the implementation of some other function that has an auxiliary character. For example, training sessions in the classroom represent the main function of this room, while the movement of people when filling the classroom and after the end of classes is an auxiliary function. Therefore, one can distinguish the main and ancillary functions. The main function for a particular room in another room can be auxiliary, and vice versa.

Premises- the main structural element or part of a building. The correspondence of the premises to one or another function is achieved only when optimal conditions for a person are created in it, i.e. an environment that meets the function it performs in the room.

Environment quality depends on a number of factors. These include:

space necessary for human activities, equipment placement and movement of people;

condition air environment(microclimate) - a supply of breathing air with optimal parameters of temperature, humidity and speed of its movement. The state of the air environment is also characterized by the degree of air purity, i.e. the amount of impurities harmful to humans (gases, dust);

sound mode - the conditions of audibility in the room (speech, music, signals), corresponding to its functional purpose, and protection from interfering sounds (noise) that arise both in the room itself and penetrate from the outside, and have a harmful effect on the human body and psyche;

light mode - the working conditions of the organs of vision, corresponding to the functional purpose of the room, determined by the degree of illumination of the room;

visibility and visual perception- working conditions for people associated with the need to see flat or three-dimensional objects in the room.

The technical feasibility of a building is determined by the decision of its structures, which must be in full compliance with the laws of mechanics, physics, chemistry.

In accordance with the impact of the environment, a complex of technical requirements is imposed on the building and its structures.

Strength- the ability of the building as a whole and its individual structures to perceive external loads and impacts without destruction and significant residual deformations.

Stability (rigidity)- the ability of a building to maintain static and dynamic balance under external influences of the building, depending on the appropriate placement of structures in accordance with the magnitude and direction of the loads and on the strength of their joints.

Durability, meaning the strength, stability and safety of the building and its elements over time. It depends on:

creep materials, i.e. from the process of small continuous deformations occurring in materials under conditions of prolonged exposure to loads.

frost resistance materials, i.e. on the ability of a wet material to withstand repeated alternating freezing and thawing;

moisture resistance materials, i.e. their ability to withstand the destructive action of moisture (softening, swelling, warping, stratification, cracking, etc.);

corrosion resistance, those. on the ability of the material to resist destruction caused by chemical and electrical processes;

biostability, those. on the ability of organic building materials to resist the action of insects and microorganisms.

Durability is determined by the ultimate service life of the building. Practical engineering methods for calculating the durability of buildings have not yet been created, therefore, in building codes and building rules for durability conditionally divided into three degrees:

1st degree - service life over 100 years;

2nd degree - service life from 50 to 100 years;

3rd degree - service life from 20 to 50 years.

What are classes of responsibility or category of complexity of an object?
According to DBN V.1.2-14-2009 "General principles of ensuring the reliability and structural safety of buildings, structures, building structures and foundations" and DBN A.2.2-3: 2012 "Composition and content of design documentation for construction", which applies to:
- construction objects (buildings and structures) for various purposes.
- component parts of objects, their bases and structures made of various materials.

CLASSIFICATION OF CONSTRUCTION OBJECTS
The classes of consequences (responsibility) of buildings and structures are determined by the level of possible material losses and (or) social losses associated with the termination of operation or with the loss of the integrity of the facility.

Possible social losses from abandonment should be weighed against risk factors such as:
- danger to health and life of people;
- a sharp deterioration of the environmental situation in the area adjacent to the object (for example, with the destruction of storage facilities for toxic liquids or gases, failure of sewage treatment facilities, etc.);
- loss of historical and cultural monuments or other spiritual values ​​of society;
- termination of the functioning of systems and networks of communication, power supply, transport or other elements of life support of the population or public safety;
- impossibility to organize the provision of assistance to victims of accidents and natural disasters;
- the threat to the country's defense.

CATEGORY OF DIFFICULTY OF THE CONSTRUCTION OBJECT
The complexity category of the construction object is determined based on the class of consequences (responsibility) in accordance with the table
Possible economic losses should be assessed by the costs associated with both the need to restore the object that failed, and indirect damage (losses from stopping production, lost profits, etc.).

Each building or structure inevitably experiences the impact of certain loads. This circumstance forces us, calculators, to analyze the operation of a structure from the position of the most unfavorable combination of them - so that even in the event of its manifestation, the structure remains strong, stable, and enduring.

For a structure, the load is an external factor that transfers it from a state of rest to a stress-strain state. Collecting loads is not the ultimate goal of an engineer - these procedures refer to the first stage of the structural analysis algorithm (discussed in this article).

Classification of loads

First of all, the loads are classified according to the time of impact on the structure:

• constant loads (acting throughout the entire life cycle of the building)
• temporary loads (act from time to time, periodically or one-time)

Segmentation of loads allows you to simulate the operation of a structure and perform the corresponding calculations more flexibly, taking into account the probability of occurrence of a particular load and the likelihood of their simultaneous occurrence.

Units and mutual conversions of loads

In the construction industry, concentrated power loads are usually measured in kilonewtons (kN), and moment loads are measured in kNm. Let me remind you that according to the International System of Units (SI), force is measured in Newtons (N), length - in meters (m).

The loads distributed over the volume are measured in kN / m3, over the area - in kN / m2, along the length - in kN / m.

Figure 1. Types of loads:
1 - concentrated forces; 2 - concentrated moment; 3 - load per unit volume;
4 - load distributed over the area; 5 - load distributed along the length

Any concentrated load \ (F \) can be obtained by knowing the volume of the element \ (V \) and the volumetric weight of its material \ (g \):

You can get the load distributed over the area of ​​an element through its volumetric weight and thickness \ (t \) (size perpendicular to the plane of the load):

Similarly, the load distributed along the length is obtained by the product of the volumetric weight of the element \ (g \) by the thickness and width of the element (dimensions in directions perpendicular to the load plane):

where \ (A \) is the cross-sectional area of ​​the element, m 2.

Kinematic actions are measured in meters (deflections) or radians (turning angles). Thermal loads are measured in degrees Celsius (° C) or other units of temperature, although they can be specified in units of length (m) or be dimensionless (thermal expansion).

It is assumed that all support points of the structure move translationally according to the same law X 0 = XJ ()

In an earthquake, the soils of the base of the building are set in motion, as shown in Figure 14.

In this case, an inertial force acts on each unit of the structure's volume, which depends on the inertial parameters concentrated in these volumes - the masses and the rigidity 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 us to determine 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 displacement of the base according to a given law X Q = 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 bar X 2 (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 displacement X t masses in horizontal

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

The equilibrium mass equation will be

Then given:

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

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

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).

The modern regulatory documents set out general requirements for ensuring the mechanical safety of buildings and structures. So, in part 6 of Art. 15 of the Federal Law No. 384 "Technical Regulations on the Safety of Buildings and Structures", the requirements were put forward that "during the 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 ... with options for simultaneous action of loads and impacts ”.

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

• destruction of any character;
• loss of form stability;
• loss of position stability;
• violation of serviceability and other phenomena associated with the threat of harm to the life and health of people, property of individuals or legal entities, state or municipal property, the 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 of a building or structure, climatic and, if necessary, technological influences, as well as forces caused by deformation of building structures and foundations must be taken into account.

A building or structure in an area where the manifestation of hazardous natural processes and phenomena and (or) man-made impacts is 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 specified in Art. 7 of Federal Law No. 384, and (or) other events that pose a threat of harm to the 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 strength and stability calculations of a building or structure, can 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 in the material building structures, the design documentation must additionally indicate the parameters characterizing the resistance to such influences, or measures to protect against them.

When assessing the consequences of an earthquake, the classification of buildings given in the seismic scale MMSK - 86 is used. According to 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 from local building materials: adobe without frame; adobe or adobe brick without foundation; made of rolled or torn stone on clay mortar and without regular (brick or stone of the correct shape) masonry in the corners, etc.

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

B - local buildings. Timber-framed buildings with adobe or clay aggregates and lightweight ceilings:

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

V- local buildings. Wooden houses, chopped in "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 typical structures with anti-seismic measures are divided into types:

• 1) С 7 - typical buildings and structures of all types (brick, block, panel, concrete, wood, panel board, etc.) with anti-seismic measures for the design seismicity of 7 points;
• 2) С8 - typical buildings and structures of all types with anti-seismic measures for a design seismicity of 8 points;
• 3) С9 - typical buildings and structures of all types with anti-seismic measures for a design 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.

In 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 - minor 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 floors with walls and wall filling with frame elements, between panels, in cutting ovens and door frames; thin cracks in partitions, cornices, pediments, pipes. No visible damage to structural elements. To eliminate the damage, the current repair of buildings is sufficient;
• 2) d= 2 - moderate damage. Significant damage to the material and non-structural elements of the building, falling plaster layers, through cracks in partitions, deep cracks in cornices and pediments, falling out of bricks from chimneys, falling of individual tiles. Weak damage to the load-bearing structures: thin cracks in the load-bearing walls; slight deformations and small spalling of concrete or mortar in the nodes of the frame and the joints of the panels. Overhaul of buildings is required to eliminate damage;
• 3) d= 3 - heavy damage. Destruction of non-structural 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 deformations of the frame; noticeable panel shifts; spalling of concrete at the nodes of the frame. Reconstruction of the building is possible;
• 4) d= 4 - partial destruction of load-bearing structures: breaks and collapses in load-bearing walls; collapse of joints and nodes of the frame; violation of connections between parts of the building; collapse of individual floor panels; collapse of large parts of the building. The building is subject to demolition;
• 5) d= 5 - landslides. Collapse of load-bearing walls and ceilings, complete collapse of the building with the loss of its shape.

Analyzing the consequences of earthquakes, the following main damages can be distinguished, which were received by buildings of various structural schemes, if the seismic effects exceeded the calculated ones.

In frame buildings, frame nodes are mainly destroyed due to the occurrence of significant bending moments and shear forces in these places. Especially strong damage is received by the bases of the posts and the joints of the crossbars with the posts of the frame (Fig.16a).

In large-panel and large-block buildings, the butt joints of panels and blocks with each other and with ceilings are most often destroyed. At the same time, there is a mutual displacement of the panels, the opening of vertical joints, the deviation of the panels from their initial position, and in some cases the collapse of the panels (Fig. 160).

For buildings with load-bearing walls made of local materials (mud bricks, clay blocks, tuff blocks, etc.), the following damage is typical: 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,

Destruction of a frame building during an earthquake in China (a) and destruction of panel buildings during an earthquake in Romania (b), the relationship between the probability of its damage and the intensity of the earthquake manifestation in points is taken into account. 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 the impact of earthquakes of different intensities.

Typical damage to brick walls during 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. In this case, it is taken into account that for the same building, not one, but five degrees of destruction can be considered, i.e. after destruction occurs one of five incompatible events. The values ​​of the mathematical expectation M mo of the earthquake intensity in points, causing at least certain degrees of destruction of buildings, are given in Table 1.

Table 1

Mathematical expectations of M mo laws of destruction of buildings

Classes of buildings according to MMSK-86	Degree of destruction of buildings
	Easy d = 1	Moderate d = 2		Partial destruction d = 4
	Mathematical expectations M laws of destruction

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