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    Loads and impacts on multi-storey buildings determined on the basis of the design assignment, SNiP chapters, manuals and reference books.

    Constant loads


    Constant loads practically do not change in time and therefore are taken into account in all loading options for the stage of the structure's operation considered in the calculation.
    Permanent loads include: the weight of the bearing and enclosing structures, the weight and pressure of the soil, the effects of prestressing of structures. The loads from the weight of stationary equipment and utilities can be considered constant as well, bearing in mind, however, that in some conditions (repair, redevelopment) they can change.

    The standard values ​​of permanent loads are determined according to the data on the weight of finished elements and products or are calculated according to the design dimensions of structures and the density of materials (Table 19.2) (density equal to 1 kg / m3 corresponds to a specific weight 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 size of the structural system, the strength of the steel used, the applied external loads and other factors.
    The standard load (kN / m2 of floor area) from the weight of load-bearing structures made of steel of 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 in the building, met > 20.
    For load-bearing structures made of steels of class C38 / 23 with design resistance R and higher class with design resistance R "the load from their weight is determined by the ratio The standard value of the weight of 1 m2 of the wall, the ceiling is approximately: a) for external walls made of lightweight masonry or concrete panels 2.5-5 kN / m2, from effective panels 0.6-1.2 kN / m2; b) for internal walls and partitions 30-50% less than for external ones; c) for the load-bearing floor slab together with the floor with reinforced concrete panels and floorings 3-5 kN / m2, with monolithic slabs made of lightweight concrete on steel profiled flooring 1.5-2 kN / m2; with the addition, if necessary, of a load from false ceiling 0.3-0.8 kN / m2,
    When calculating the design loads from the weight of sandwich structures, if necessary, take their own overload factors for different layers.
    The load from the weight of the walls and permanent partitions is taken into account according to its actual position. If you attach precast wall elements directly to the columns of the framing, the weight of the walls is not taken into account when calculating the slabs.
    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.
    The loads from the weight of the floor are distributed almost evenly and are collected from the corresponding cargo areas when calculating floor elements and columns.
    In modern multi-storey buildings with a steel frame, the intensity of the amount regulatory loads from the weight of walls and ceilings, referred to 1 m2 of floors, is approximately equal to 4-7 kN / m2. The ratio of all permanent loads of a building (including the dead weight of steel structures, flat and spatial stiffening trusses) to its volume varies from 1.5 to 3 kN / m3.

    Temporary loads


    Temporary floor loads. Floor loads due to the weight of people, furniture and similar light equipment are set in SNiP in the form of equivalent loads evenly distributed over the area of ​​the premises. Their standard 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 the overload factors are 1.3-1.4.
    According to paragraphs. 3.8, 3.9 SNiP, temporary loads are taken taking into account the reduction factors α1, α2 (when calculating beams and girders) and η1, η2 (When calculating the colony and foundations). The coefficients η1, η2 refer to the sum of temporary loads on several floors and are taken into account when determining longitudinal forces... The nodal bending moments in the columns should be taken without taking into account the coefficients η1, η2, since the main effect on the bending moment is exerted by the live load on the girders of one adjacent to the overlap node.
    Considering the possible schemes for the location of temporary loads on the floors of a building, in design practice, they usually proceed from the principle of the most unfavorable loading. For example, to assess the largest spans in the crossbar of a frame system, the staggered arrangement of temporary loads is taken into account, in the calculation of frames, stiffening trunks and foundations, not only the continuous loading of all floors is taken into account, but also possible options partial, including one-sided, loading. Some of these schemes are very arbitrary and lead to unjustified reserves in structures and foundations. determined according to the instructions of SNiP, is mainly important for the structures of the coating of a multi-storey building and has little effect on the total efforts in the structures located below. 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 lower and upper ordinates kн≥kв, determined from the conditions for the equivalence of the diagrams in terms of moment and transverse force in the lower section of the building. With an error of not more than 2%, the ordinate kн 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:

    The ordinate at the z level: kze = kн + (kв-kн) z / H. In a stepped building (Fig. 19.1), the normative plot is reduced to trapezoidal in separate zones of different heights, measured from the bottom of the building. Methods of bringing the building into zones are also possible.

    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) at 1 m height is determined as the result of aerodynamic forces acting in these directions, and is expressed in terms of the total resistance coefficients cx, cy and horizontal dimensions B, L projections of the building on the plane, perpendicular to the corresponding axes:

    For buildings of a prismatic shape with a rectangular plan at a slip angle β = 0, the coefficient cy = 0, and cx is determined according to table. 19.1, compiled taking into account data from foreign and domestic studies and standards.
    If β = 90 °, then cx = 0, and the value of cy is found according to the same table, interchanging the designations B, L on the building plan.
    With a wind at an angle of β = 45 °, the values ​​of сx, сy are given as a fraction in table. 19.2, while the longer is the side of the plan B, perpendicular to the x-axis. 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, 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 mcr "" = 0.05q (z) LB are balanced. But if one of the windward walls is smooth, the moment mcr "" from the 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 stiffness (or center of torsion) of the supporting system, additional eccentricities of the application of wind loads must be taken into account in the calculation.
    Wind load on elements outer wall, the crossbars of the tie and frame-tie systems, transmitting the wind pressure from the outer wall to the diaphragms and stiffening trunks, are determined by the formula (19.2), using the pressure coefficients c +, c- (positive pressure is directed into the building) and standard values ​​kz. Pressure coefficients for buildings with a rectangular plan (with some clarification of SNiP data):

    In the case β = 0, for both walls parallel to the flow, the values ​​of cy equal to:

    The same data is used at 0 = 90 ° for cx, interchanging the designations B, L on the building plan.
    To calculate this or that element, the most unfavorable of the given values ​​c + and c- should be selected and increased in absolute value by 0.2 to take into account the 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; the width of the zone, according to the available data, should be increased to 4-5 m, but not more than 1/10 of the wall length.

    The influence of the surrounding buildings, the complication of the shape of buildings on the aerodynamic coefficients is established experimentally.
    Under the action of the wind flow, the following are possible: 1) lateral swaying of aerodynamically unstable flexible buildings (vortex excitation of the wind resonance of buildings of cylindrical, prismatic and weakly pyramidal shapes; galloping of poorly streamlined buildings associated with a sharp change in the lateral disturbing force at small changes in wind direction and with an unfavorable ratio bending and torsional stiffness of the building), 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 adjacent tall buildings, but the methods for accounting for them are insufficiently developed and testing of large aeroelastic models is required to assess the conditions for their occurrence.
    Dynamic the component of the wind load during vibrations of the building in the plane of the flow depends on the variability of the pulsations of the velocity vp, characterized by the standard σv (Figure 19.3). Velocity wind pressure at time t at air density p

    To take into account the extreme values ​​of pulsations, it was taken vp = 2.5σv, which corresponds (with a normal distribution function) to the probability of exceeding the accepted pulsation at an arbitrary time instant 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 vibrations of the system. The arising inertial forces determine the dynamic component of the wind load, taken into account according to SNiP for buildings with a height of more than 40 m, on the assumption that the form of natural vibrations of the building is described by a straight line,

    Since the error in estimating T1 insignificantly affects ξ1, it can be recommended for steel frame frames T1 = 0.1met, for braced and frame-braced frames with reinforced concrete diaphragms and stiffening trunks T1 = 0.06 met, where met is the number of floors in 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:

    Depending on the considered wind direction, the values ​​adopted for qс (calculated, normative) and dimensions (kN / m2, kN / m), the corresponding total loads are obtained.
    The acceleration of horizontal vibrations of the top of the building, which is necessary for the calculation according to the second group of limit states, is determined by dividing the standard value of the dynamic component (without taking into account the overload factor) by the corresponding mass. If the calculation is carried out for the load qх, kN / m (Fig. 19.2), then

    The value of m is estimated by dividing the permanent loads and 50% of the temporary vertical loads, referred to 1 m2 of floor, by the acceleration due to gravity.
    The accelerations from the standard values ​​of the 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 head q0.
    Seismic impacts. In the construction of multi-storey buildings in seismic regions, the supporting structures must be calculated as for the main combinations, usually consisting of acting loads(including wind), and for special combinations taking into account seismic effects (but excluding wind load). With a design seismicity of 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 in accordance with SNiP. With an increase in the period of natural vibrations of a 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 vibrations when taking into account seismic effects, you can use the methods.
    Temperature effects. Changes in ambient air temperature and solar radiation cause thermal deformations of structural elements: elongation, shortening, curvature.
    At the stage of operation of a multi-storey building, the temperature of internal structures practically does not change. Seasonal and daily variations in outdoor temperature and solar radiation primarily affect the outer walls. If their attachment to the frame does not prevent thermal deformation 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 removed from the edge of the outer wall, they are directly exposed to temperature climatic influences, which must be taken into account when designing the frame.
    Temperature effects at the stage of 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 reduction in time of the forces caused by them due to inelastic deformations in the nodes and elements of the bearing system.
    The influence of temperature climatic influences on the operation of the supporting system in multi-storey buildings with a metal frame has not been studied enough.

    In the course of 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 different kinds 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 storage of goods, dead weight of permanent elements of the building (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, rest 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 expediency, providing for minimal costs for the 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, 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), arising both in the room itself and penetrating from the outside, and having 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 bases "and DBN A.2.2-3: 2012" Composition and content project 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, when the storage of toxic liquids or gases is destroyed, treatment facilities sewers, 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.).


    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 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 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 to ensure 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 ”.

    Per limit state of building structures and foundations for strength and stability, a condition should be adopted, 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, 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 constructive decision buildings or structures, climatic, and, if necessary, technological influences, as well as efforts caused by deformation of building structures and foundations.

    A building or structure on 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 the "paw" or "bounce":

    • 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, wooden, panel board, etc.) with anti-seismic measures for a 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. Light damage to the material and not structural elements buildings: thin cracks in 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 the cutting of furnaces and door frames; thin cracks in partitions, cornices, pediments, pipes. No visible damage to structural elements. To eliminate damage, it is enough maintenance buildings;
    • 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 frame nodes and panel joints. To eliminate damage, you need overhaul buildings;
    • 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, the nodes of the frame are mainly destroyed due to the occurrence in these places of significant bending moments and shear forces. 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 frame building during an earthquake in China (a) and the 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 distribution law of damage 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 intensity of an earthquake 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

    Building classes 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.

    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, soil pressure, frost heaving, moisture, seismic waves, stray currents , vibration);

    Internal (technological and functional: permanent and temporary loads, long-term and short-term loads from their own weight, equipment and people; technological processes: shock, vibration, abrasion, liquid spillage; fluctuations in temperature; humidity of the environment; 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, they are distinguished: 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 - a stimulant. 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, physicochemical environment.

    Aggressive media are divided into gas, liquid, solid.

    Gaseous 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 are more intense than in others.

    Solid media: dust, soil. The aggressiveness of this medium is assessed by dispersion, solubility in water, hygroscopicity, and humidity of the environment.

    Characteristics of an aggressive environment:

    Highly corrosive - acids, alkalis, gases - corrosive gases and liquids in industrial premises;

    Medium aggressive - atmospheric air and water with impurities - air with high humidity (more than 75%);

    Weakly aggressive - clean atmospheric air - water not contaminated with harmful impurities;

    Non-aggressive - clean, dry (humidity up to 50%) and warm air- atmospheric air in dry and warm climatic regions.

    Exposure to air: 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, dry atmosphere, concrete and other materials can last for hundreds of years. The most intense air pollutants are combustion products of various fuels, therefore, in cities, industrial centers metal constructions corrode 2-4 times faster than in rural areas, where less coal and fuel are burned.

    The main combustion products of most fuels are CO 2, SO 2.

    When CO2 is dissolved in water, carbon dioxide is formed. This is the end product of combustion. It has a destructive effect on concrete and other building materials. Dissolving SO 2 in water produces sulfuric acid.

    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 groundwater: 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 ground constantly interacts with minerals and organic matter. Sustainable watering of the underground parts of the building during the movement of groundwater increases the corrosion of the structure and leaching of lime in concrete, and reduces the strength of the base.

    Allocate general acid, leaching, sulfate, magnesian, carbon dioxide aggressiveness of groundwater.

    The following factors have the most significant impact:

    · Exposure to moisture: as the experience of building operation has shown, moisture has the greatest influence on the wear of structures. Since the foundations and walls of old reconstructed buildings are made mainly of dissimilar stone materials (limestone, red brick, limestone and cement mortars) with a porous-capillary structure, when in contact with water, they are intensively moistened, often change their properties and in extreme cases are destroyed.

    The main source of moisture for walls and foundations is capillary suction, which leads to damage to structures during operation: destruction of materials as a result of freezing; cracking due to swelling and shrinkage; loss of thermal insulation properties; destruction of structures under the influence of aggressive chemical substances 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 thermal and humidity conditions, X-ray and biological analysis of corrosion products);

    Drying (if necessary) of the premises, if it comes 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 biological corrosion products;

    Treatment with anti-salt and biocidal drugs;

    Sealing cracks and leaks with special waterproofing compounds and subsequent surface treatment with protective waterproofing preparations;

    Finishing works.

    · Impact of atmospheric 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, on top of molecular silt, or into gravitational, freely moving in the soil under the action of gravity. Gravitational moisture can reach the groundwater and, merging with it, raise its level. Ground water, in turn, due to capillary rise moves up to a considerable height and watering the upper layers of the soil. In some conditions, capillary and ground water can drain and steadily water the underground parts of structures, as a result of which corrosion of structures increases, and the strength of the foundations decreases.

    · Effects of negative temperatures: some structures, for example, basements, are located in the zone of variable humidification and periodic freezing. A negative temperature (if it is lower than the design one or special measures are not taken to protect structures from moisture), leading to freezing of moisture in the structures and soils of the bases, has a destructive effect on buildings. When water freezes in the pores of the material, its volume increases, which creates internal stresses, which all increase due to the compression of the mass of the material itself under the influence of cooling. The ice pressure in closed pores is very high - up to 20 Pa. 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 temperatures begins from the surface, especially from the corners and edges. 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 concrete with a porosity of up to 15% can withstand 100-300 freezing cycles. A decrease in porosity and, consequently, the amount of moisture increases the frost resistance of structures. It follows from what has been said that during freezing, those structures that are moistened are destroyed. To protect structures from destruction at low temperatures is, first of all, to protect them from moisture. Freezing of soils in the foundations is dangerous for buildings built on clay and silty soils, fine and medium-grained sands, in which water rises through capillaries and pores above the groundwater level and is in a bound form. Damage to buildings due to freezing and bulging of the bases can occur after many years and operation, if the soil around them is cut off, the bases become wet and the factors that contribute to their freezing are allowed.

    · Construction of technological processes: each building and structure is designed and constructed taking into account the interaction of the processes envisaged 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, roofing, then walls, frame and foundations are destroyed. Compressed members of large sections, operating under static loads, wear out more slowly than bending and stretched, thin-walled, which operate under dynamic loads, under conditions high humidity and high temperature... Structural wear due to abrasion - abrasive wear of floors, walls, corners of columns, steps of stairs and other structures can be very intense and therefore strongly 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 flows of people in public buildings.

    Description of the object

    Table 1.1

    general characteristics Pumping station
    Year built
    total area, m 2 - building area, m 2 - area of ​​premises, m 2
    Building height, m 3,9
    Construction volume, m 3 588,6
    Number of storeys
    Construction characteristics
    Foundations Monolithic reinforced concrete
    Walls Brick
    Overlapping Reinforced concrete
    Roof Roll roofing
    Floors Cement
    Doorways Wooden
    Interior decoration Plaster
    Attractiveness ( appearance) Satisfactory appearance
    Actual age of the building
    Standard service 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 improvement
    Landscaping Green spaces: lawn, shrubs
    Driveways Paved road, satisfactory condition

    Each building or structure inevitably experiences the impact of certain loads. This circumstance forces us, calculators, to analyze the operation of the 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 external factor, which 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 structure calculation 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 life cycle building)
    • temporary loads (act from time to time, periodically or one-time)

    Segmentation of loads allows you to simulate the operation of a structure and perform the corresponding calculations more flexibly, taking into account the likelihood 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 \):

    The load distributed over the area of ​​an element can be obtained 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 the directions perpendicular to the plane load):

    where \ (A \) is the area cross section 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).

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