Basic architectural and building structures for residential, industrial, agricultural and public buildings. Fundamentals of structural solutions for buildings classification of building structures by shallow foundations

Building structures, supporting and enclosing structures of buildings and structures.

Classification and fields of application. The division of building structures according to their functional purpose into bearing and enclosing structures is largely arbitrary. If structures such as arches, trusses or frames are only load-bearing, then wall and roof panels, shells, vaults, folds, etc. usually combine enclosing and supporting functions, which meets one of the most important trends in the development of modern building structures.Depending on the design scheme, supporting building structures are divided into flat (for example, beams, trusses, frames) and spatial (shells, arches, domes, etc. .). Spatial structures are characterized by a more favorable (in comparison with flat) distribution of forces and, accordingly, less material consumption; however, their manufacture and installation in many cases turns out to be very time consuming. New types of spatial structures, for example structural structures made of rolled sections on bolted joints, are distinguished by both cost-effectiveness and relative ease of manufacture and installation. By the type of material, the following main types of building structures are distinguished: concrete and reinforced concrete.

Concrete and reinforced concrete structures are the most common (both in terms of volume and areas of application). Special types of concrete and reinforced concrete are used in the construction of structures operating at high and low temperatures or in conditions of chemically aggressive media (heating units, buildings and structures of ferrous and nonferrous metallurgy, chemical industry, etc.). Reducing the weight, reducing the cost and consumption of materials in reinforced concrete structures are possible on the basis of the use of high-strength concretes and reinforcement, an increase in the production of prestressed structures, and the expansion of the areas of application of lightweight and cellular concrete.

Steel structures are used mainly for frames of large-span buildings and structures, for workshops with heavy crane equipment, blast furnaces, large-capacity tanks, bridges, tower-type structures, etc. The areas of application of steel and reinforced concrete structures in some cases coincide. A significant advantage of steel structures (compared to reinforced concrete) is their lower weight.

Requirements for building structures. From the point of view of operational requirements, SK must meet its purpose, be fire-resistant and corrosion-resistant, safe, convenient and economical to operate.

Calculation of SK Building structures must be designed for strength, stability and vibration. This takes into account the force effects to which the structures are subjected during operation (external loads, dead weight), the effect of temperature, shrinkage, displacement of supports, etc. as well as the efforts arising from the transportation and installation of building structures.

Foundations of buildings and structures - parts of buildings and structures (mainly underground), which serve to transfer loads from buildings (structures) to a natural or artificial foundation. The building wall is the main building envelope. Along with the enclosing functions, the walls simultaneously, to one degree or another, perform bearing functions (they serve as supports for the perception of vertical and horizontal loads.

Frame (French carcasse, from Italian carcassa) in technology - the skeleton (skeleton) of any product, structural element, whole building or structure, consisting of individual rods fastened together. The frame is made of wood, metal, reinforced concrete and other materials. It determines the strength, stability, durability, shape of a product or structure. Strength and stability are provided by the rigid fastening of the rods at the mating or hinge joints and special stiffeners that give the product or structure a geometrically unchangeable shape. An increase in the rigidity of the frame is often achieved by including the shell, sheathing or walls of a product or structure into operation.

Overlapping - horizontal bearing and enclosing structures. They perceive vertical and horizontal forces and transmit them to the load-bearing walls or frame. Ceilings provide heat and sound insulation of the premises.

Floors in residential and public buildings must meet the requirements of strength and resistance to wear, sufficient elasticity and noiselessness, ease of cleaning. The design of the floor depends on the purpose and nature of the premises where it is installed.

Roof is an external load-bearing and enclosing structure of a building, which perceives vertical (including snow) and horizontal loads and influences. (Wind is a load.

Stairs in buildings serve for vertical connection of rooms located at different levels. The location, the number of stairs in the building and their dimensions depend on the adopted architectural and planning solution, number of storeys, the intensity of the human flow, as well as fire safety requirements.

Windows are arranged for lighting and ventilation (ventilation) of premises and consist of window openings, frames or boxes and filling the openings called window frames.

Question number 12. Behavior of buildings and structures under fire conditions, their fire resistance and fire hazard.

The loads and impacts that a building is exposed to under normal operating conditions are taken into account when calculating the strength of building structures. However, in case of fires, additional loads and effects arise, which in many cases lead to the destruction of individual structures and buildings as a whole. Adverse factors include: high temperature, pressure of gases and combustion products, dynamic loads from falling debris of collapsed building elements and spilled water, sharp temperature fluctuations. The ability of a structure to maintain its functions (load-bearing, enclosing) in a fire to resist the effects of fire is called the fire resistance of a building structure.

Building structures are characterized by fire resistance and fire hazard.

The indicator of fire resistance is the fire resistance limit, the fire hazard of a structure characterizes the class of its fire hazard.

Building structures of buildings, structures and structures, depending on their ability to resist the effects of fire and the spread of its hazardous factors under standard test conditions, are subdivided into building structures with the following fire resistance limits.

- non-standardized; - not less than 15 minutes; - not less than 30 minutes; - not less than 45 minutes; - not less than 60 minutes; - not less than 90 minutes; - not less than 120 minutes; - not less than 180 minutes; - not less than 360 minutes ...

The fire resistance limit of building structures is established by the time (in minutes) of the onset of one or sequentially several, normalized for a given structure, signs of limiting states: loss of bearing capacity (R); loss of integrity (E); loss of thermal insulation capacity (I.

The fire resistance limits of building structures and their symbols are set in accordance with GOST 30247. In this case, the fire resistance limit of windows is set only by the time of the onset of the loss of integrity (E.

By fire hazard, building structures are subdivided into four classes: KO (nonflammable); K1 (low fire hazard); K2 (moderately fire hazardous); KZ (fire hazardous.

Question number 13. Metal structures and their behavior in a fire, ways to increase the fire resistance of structures.

Although metal structures are made of non-combustible material, their actual fire resistance is 15 minutes on average. This is due to a rather rapid decrease in the strength and deformation characteristics of the metal at elevated temperatures during a fire. The intensity of heating of the MC (metal structure) depends on a number of factors, which include the nature of heating the structures and how they are protected. In the case of a short-term effect of temperature in a real fire, after the ignition of combustible materials, the metal is heated more slowly and less intensively than heating the environment. Under the action of the "standard" fire mode, the ambient temperature does not cease to rise and the thermal inertia of the metal, which causes a certain delay in heating, is observed only during the first minutes of the fire. Then the temperature of the metal approaches the temperature of the heating medium. The protection of the metal element and the effectiveness of this protection also affect the heating of the metal.

When high temperatures are applied to the beam in a fire, the section of the structure quickly warms up to the same temperature. At the same time, the yield point and elastic modulus decrease. The collapse of rolled beams is observed in the section where the maximum bending moment acts.

The impact of the fire temperature on the truss leads to the exhaustion of the bearing capacity of its elements and the nodal connections of these elements. The loss of bearing capacity as a result of a decrease in the strength of the metal is characteristic of stretched and compressed elements of chords and lattice of the structure.

Exhaustion of the bearing capacity of steel columns under fire conditions can occur as a result of loss of: strength by the structure bar; strength or stability by elements of the connecting lattice, as well as the attachment points of these elements to the branches of the column; stability by separate branches in the areas between the nodes of the connecting grid; the overall stability of the column.

The behavior of arches and frames under fire conditions depends on the static scheme of the structure, as well as the structure of the section of these elements.

Methods for increasing fire resistance.

· Cladding made of non-combustible materials (coating, cladding made of bricks, thermal insulation boards, plasterboard sheets, plaster.

· Fire retardant coatings (non-intumescent and intumescent coatings.

Suspended ceilings (an air gap is created between the structure and the ceiling, which increases its fire resistance limit.

Limiting state of a metal structure: \u003d R n * tem.

- 2015-2017 year. (0.008 sec.

Classification of building structures

Structures are called structural load-bearing structures of industrial and civil buildings and engineering structures, the dimensions of the sections of which are determined by calculation. This is their main difference from architectural structures or parts of buildings, the cross-sectional dimensions of which are assigned according to architectural, heat engineering or other special requirements.

Modern building structures must meet the following requirements: operational, environmental, technical, economic, production, aesthetic, etc.

In the construction of gas and oil pipelines, steel and prefabricated reinforced concrete structures are widely used, including the most progressive ones - prestressed. Recently, structures made of aluminum alloys, polymer materials, ceramics and other effective materials have been developing.

Building structures are very diverse in their purpose and application. Nevertheless, they can be combined according to some signs of commonness of certain properties and it is most expedient to classify them according to the following main features:

1 ) on a geometric basisit is customary to divide structures into massifs, beams, slabs, shells (Fig.1.1) and rod systems:

– array- a construction in which all dimensions are of the same order;

bar- an element in which two dimensions defining the cross section are many times smaller than the third - its length, i.e. they are of different order:b« I, h« /; a bar with a broken axis is usually called the simplest frame, and with a curved axis - an arch.

plate- an element in which one size is many times smaller than the other two: h« a, h“I.A slab is a special case of a more general concept - a shell, which, unlike a slab, has a curvilinear outline;

rod systemsare geometrically unchangeable systems of rods, hinged or rigidly connected to each other. These include building trusses (girders or cantilevers) (Fig. 1.2).

by the nature of the design schemestructures are divided into statically definableand statically undefined.The former include systems (structures), the forces or stresses in which can be determined only from the equations of statics (equations of equilibrium), the latter are those for which the equations of statics alone are not enough and for the solution requires the introduction of additional conditions - equations of compatibility of deformations.

by materials usedstructures are divided into steel, wood, reinforced concrete, concrete, stone (brick);

4) by the nature of the stress-strain state(VAT),those. arising in structures of internal forces, stresses and deformations under the action of an external load, it is conditionally possibledivide them into three groups: protozoa, simpleand complex(Table 1.1).

This division allows you to bring into the system the characteristics of the species stress-strain states of structures, which are widespread in construction practice. In the presented table
it is difficult to reflect all the subtleties and features of these states, but it makes it possible to compare and evaluate them as a whole.

Concrete

Concrete is an artificial stone material obtained in the process of hardening a mixture of binder, water, fine and coarse aggregates and special additives.

The composition of the concrete mixture is expressed in two ways.

In the form of ratios by mass (less often by volume, which is less accurate) between the amounts of cement, sand and crushed stone (or gravel) with the obligatory indication of the water-cement ratio and the activity of cement. The amount of cement is taken as a unit, so the ratio between the constituent parts of the concrete mixture is 1: 2: 4. It is permissible to establish the composition of the concrete mixture by volume only in small construction, but the cement should always be dosed by weight.

At large facilities and central concrete plants, all components are dosed by weight, while the composition is indicated as the consumption of materials per 1 m3 laid and compacted concrete mix, for example:

Cement 316 kg / m 3

Sand 632 kg / m 3

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Crushed stone ……………………………………… .1263 kg / m 3

Water 189 kg / m 3

Total weight of materials 2400 kg / m 3

To ensure reliable operation of load-bearing elements under given operating conditions, concretes for reinforced concrete and concrete structures must have certain predetermined physical and mechanical properties and, first of all, sufficient strength.

Concrete is classified according to a number of characteristics:

by appointmentthere are structural, special (chemically resistant, heat-insulating, etc.);

by the type of binder- based on cement, slag, polymer, special binders;

by type of placeholder- on dense, porous, special aggregates;

by structure- dense, porous, cellular, large-porous.

Concrete is used for various types of building structures manufactured in precast concrete factories or erected directly at the site of their future operation (monolithic concrete).

Depending on the area of \u200b\u200bapplication of concrete, there are:

usual- for reinforced concrete structures (foundations, columns, beams, floors, bridge and other types of structures);

hydraulic engineering- for dams, sluices, lining of canals, etc .;

concrete for building envelopes(lightweight concrete for building walls); for floors, sidewalks, road and airfield surfaces;

special purpose(heat-resistant, acid-resistant, for radiation protection, etc.).

Strength characteristics of concrete

Compressive strength of concrete

Compressive strength of concrete IN is the ultimate strength (in MPa) of a concrete cube with an edge of 150 mm, manufactured, stored and tested under standard conditions at the age of 28 days, at a temperature of 15–20 ° C and a relative humidity of 90–100%.

Reinforced concrete structures differ in shape from cubes, therefore compressive strength of concreteRinncannot be directly used in strength calculations for structural elements.

The main characteristic of the strength of concrete in compressed elements is prismatic strengthRf, - temporary resistance to axial compression of concrete prisms, which, according to experiments on prisms with the base sideaand height hwith regard hla= 4 is approximately 0.75, where R: – cube strength, or ultimate compressive strength of concrete,found when testing a sample in the form of a cube with an edge of 150 mm.

The main characteristic of the strength of concrete in compressed elements and compressed zones of bent structures is prismatic strength.

To determine the prismatic strength, the sample - the prism is loaded in a press with a stepped compressive load until fracture and the deformations are measured at each loading step.

The dependence of the compressive stresses is plotted afrom relative deformations e, which is non-linear, since in concrete, along with elastic, inelastic plastic deformations also occur.

Experiments with square-base concrete prisms aand height hshowed that the prismatic strength is less than the cubic strength and decreases with an increase in the ratio hla(fig. 2.2).

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Cubic strength of concrete R(for cubes 150 x150 x150 mm) and prismatic strength Rh(for prisms with a height to base ratio hla> 4) can be associated with a certain dependence, which is established experimentally:

The prismatic strength of concrete is used when calculating bending and compressed concrete and reinforced concrete structures (for example, beams, columns, compressed elements of trusses, arches, etc.)

As a characteristic of the strength of concrete in the compressed zone of bending elements, it is also taken Rh. Axial tensile strength of concrete

Concrete strength under axial tensionR/, 10–20 times lower than when compressed. Moreover, with an increase in the cubic strength of concrete, the relative tensile strength of concrete decreases. The tensile strength of concrete can be related to the cube strength by the empirical formula

Classes and grades of concrete

The control characteristics of the quality of concrete are called classesand stamps.The main characteristic of concrete is the class of concrete in terms of compressive strength B or grade M. The class of concrete is determined by the value of the guaranteed compressive strength in MPa with a security of 0.95. Concrete is subdivided into classes from B1 to B60.

The class of concrete and its grade depend on the average strength:

compressive strength class of concrete, MPa; average strength that should be ensured during the production of structures, MPa;

the coefficient characterizing the security of the concrete class adopted in the design is usually taken in constructiont= 0,95;

coefficient of variation of strength, characterizing the homogeneity of concrete;

concrete grade by compressive strength, kgf / cm 2 ... To determine the average strength (MPa) for the class of concrete (with a standard coefficient of variation of 13.5% and t\u003d 0.95) or according to its brand, the formulas should be used:

In regulatory documents, concrete is used, however, for some special structures and in a number of current standards, the concrete grade is also used.

In production, it is necessary to ensure the average strength of the concrete. Exceeding the specified strength is allowed by no more than 15%, as this leads to an overconsumption of cement.

For concrete and reinforced concrete structures, the following are used classes of concrete for compressive strength:heavy concrete from B3.5 to B60; fine-grained - from B3.5 to B60; lungs - from B2.5 to B35; cellular - from B1 to B15; porous from B2.5 to B7.5.

For tensile structures, a concrete class is additionally assigned axial tensile strength- only for heavy, light and fine-grained concrete - from VDZ to V ? 3,2.

An important characteristic of concrete is the grade frost resistanceIs the number of cycles of alternating freezing and thawing that water-saturated concrete samples withstood at the age of 28 days without a decrease in compressive strength of more than 15% and a weight loss of no more than 5%. Denoted -F ... For heavy and fine concrete ranges from F 50 to F 500, for lightweight concrete - F 25- F 500, for aerated and porous concrete - F 15- F 100.

Waterproof gradeWit is assigned for structures that have requirements for limiting permeability, for example, reinforced concrete pipes, tanks, etc.

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Waterproofness is the property of concrete to prevent water from passing through itself. She is estimated filtration coefficient- the mass of water that has passed per unit time under constant pressure through a unit area of \u200b\u200bthe sample at a certain thickness. Grades for heavy, fine-grained and lightweight concrete are established:W 2, W 4, W 6, W 8, W 10, W 12. The number in the stamp means the water pressure in kgf / cm 2 at which its seepage through samples of 180 days of age is not observed.

Self-stress markS p means the value of prestress in concrete, MPa, created as a result of its expansion. These values \u200b\u200brange fromS p 0.6 to S p 4.

When determining the own weight of structures and for heat engineering calculations, the density of concrete is of great importance.Concrete grades by average densityD (kg / m 3 ) installed with a graduation step of 100 kg / m 3 : heavy concrete - D \u003d 2300-2500; fine-grained - 88

D \u003d 1800-2400; lungs - D \u003d 800-2100; cellular - D \u003d 500-1200; porous - D = 800–1200.

Armature

The reinforcement of reinforced concrete structures consists of individual working rods, meshes or frames, which are installed to absorb the acting forces. The required amount of reinforcement is determined by calculating structural elements for loads and impacts.

The fittings installed by calculation are called working;installed for design and technological reasons - assembly room.

Work and assembly fittings are combined into reinforcement products -welded and knitted meshes and frames, which are placed in reinforced concrete elements in accordance with the nature of their work under load.

Reinforcement is classified according to four criteria:

depending on the manufacturing technology, a distinction is made between rod and wire reinforcement. In this classification, rod is meant reinforcement of any diameter withind\u003d 6–40 mm;

depending on the method of subsequent hardening, hot-rolled reinforcement can be thermally hardened, i.e. heat treated, or hardened in a cold state - drawing, drawing;

according to the shape of the surface, the reinforcement is of periodic profile and smooth. Ribbed protrusions on the surface of periodic bar reinforcement, reefs or dents on the surface of wire reinforcement significantly improve adhesion to concrete;

– according to the method of application in the reinforcement of reinforced concrete elements, prestressing reinforcement is distinguished, i.e. pre-tensioned and non-tensioned

Hot-rolled rod fittings, depending on their main mechanical characteristics, are divided into six classes with a symbol:A- I, A-P, A-Sh, A- IV, A- V, A- Vi.The main mechanical characteristics of the used fittings are given in table. 2.6.

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Bar reinforcement of four classes is subjected to thermal hardening; hardening in its designation is marked with an additional index "t": Am-Sh, Am- IV, At- V, At-VI.The additional letter C indicates the possibility of joining by welding, and the letter K indicates increased corrosion resistance. Cold drawn bar reinforcement of class A-Sh is marked with an additional index B.

Each class of fittings corresponds to certain grades of fittings with the same mechanical characteristics, but different chemical composition. The steel grade designation reflects the content of carbon and alloying additives. For example, in the 25G2S brand, the first digit indicates the carbon content in hundredths of a percent (0.25%), the letter G - that the steel is alloyed with manganese, the number 2 - that itthe content can reach 2%, letter C - the presence of silicon (silicon) in steel.

The presence of other chemical elements, for example, in brands 20ХГ2Ц, 23Х2Г2Т, is indicated by the letters: X - chromium, T - titanium, C - zirconium.

Bar reinforcement of all classes has a periodic profile with the exception of round (smooth) reinforcement of the classA- I.

Reinforcement products used for the manufacture of reinforced concrete structures

For the reinforcement of reinforced concrete structures, they are widely used ordinary reinforcing wire of class Вр-I(grooved) with a diameter of 3-5 mm, obtained by cold drawing low-carbon steel through a system of calibrated holes (dies). The smallest value of the conventional tensile yield strength of the wire Vr-I with a diameter of 3–5 mm it is 410 MPa.

The method of cold drawing also produces high-strength reinforcing wire of classes V-P and VR-I - smooth and periodic profile (Fig. 2.8,d)with a diameter of 3–8 mm with the nominal yield strength of wire VP - 1500–1100 MPa and VR-P - 1500–1000 MPa.

The reinforcement of reinforced concrete structures is selected taking into account its purpose, class and type of concrete, conditions for the manufacture of reinforcing products and the operating environment (risk of corrosion), etc. As the main working reinforcement of conventional reinforced concrete structures, steel of classes А-Ш and Вр-I ... In prestressed structures, predominantly high-strength steel of classes V-I, VR-P, A is used as prestressed reinforcement- VI, At - VI, A- V, At- VandAt-VII.

Reinforcement of prestressed structures with solid high-strength wire is very effective, however, due to the small cross-sectional area of \u200b\u200bwires, their number in the structure increases significantly, which complicates reinforcement work, gripping and tension of reinforcement. To reduce the complexity of reinforcement work, ropes pre-twisted in a mechanized way, bundles of parallel wires and steel cables are used. Non-twisting steel ropes of class K are manufactured mainly with 7- and 19-wire (K-7 and K-19).

Strength conditions of eccentrically compressed T-and I-profile elements

When calculating the elements of the T-profile and I-profile, two cases of the location of the neutral axis can be encountered (Fig. 2.40): the neutral axis is located in the shelf and the neutral axis intersects the rib. With a known reinforcement, the position of the neutral axis is determined by comparing the forceNwith the effort perceived by the shelf.

If the condition is met: N< Rbb" fh" f , then the neutral axis is located in the shelf. In this case, the calculation of the T-section or I-section is performed as for an element of a rectangular profile with a widthbj- and height h.

It should be noted that the strength calculation of T-and I-profile elements is very laborious. The problem of checking the strength of normal sections with a known reinforcement is relatively simple to solve, and the calculation of longitudinal reinforcement is much more difficult, especially when several loadings are applied with moments of different signs.

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Example 2.5. It is required to check the strength of the column section. Column section b= 400 mm; h\u003d 500 mm; a \u003d a "\u003d 40 mm; heavy concrete, class B20 (Rb\u003d 11.5 MPa, Eb= 24000 MPa); fittings of class A-Sh (Rs= Rsc\u003d 365 MPa); sectional area of \u200b\u200breinforcement As\u003d A ^\u003d 982 mm (2025); calculated length Iq= 4.8 m; longitudinal force n\u003d 800 kN; bending moment m \u003d200 kN m; ambient humidity 65%.

Strength conditions for tensile members

Under stretching conditions, the lower chords of trusses and lattice elements, tightening of arches, walls of round and rectangular tanks and other structures work.

For tensile members, it is effective to use high-strength prestressed reinforcement. When designing stretched elements, special attention should be paid to the end sections, where reliable transmission of forces must be ensured, as well as to reinforcement joining. Rebar joints are usually welded.

Calculation of centrally stretched members

When calculating the strength of centrally tensioned reinforced concrete elements, it is taken into account that cracks that are normal to the longitudinal axis appear in the concrete, and the entire force is absorbed by the longitudinal reinforcement.

Calculation of eccentrically stretched members at low eccentricities

If strength Ndoes not go beyond the boundaries outlined by fittings Asand A" s, with the appearance of a crack, the concrete is completely turned off from work and the longitudinal force is absorbed by the reinforcement Asand L.

Calculation of eccentrically stretched members at large eccentricities

If strength Ngoes beyond the reinforcement As, then a compressed concrete zone appears in the element. For a rectangular element, the strength conditions are

N -e< R bbx (h– x/2) + RscA & h– a"),

N= RsAs- Rbbs~ RscA^.

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When using relative values £, = xlh^ andat= 2; (1 - 1/2) strength conditions are converted to the form

N-e< R bambhl + RscA ^ (h– a"),

N \u003d RSAS-R £ bh-Rsc4.

Static calculation of the transverse frame of a one-story industrial building

It is required to perform a static calculation of the transverse frame of a one-storey two-span industrial building by the displacement method and determine bending moments, longitudinal and transverse forces in the characteristic sections of the columns according to the initial data.

The structural elements of the building and the initial data for the calculation should be taken from the previous practical lesson.

When calculating by the displacement method, the angular or linear displacements of the frame nodes are taken as unknowns.

Fundamentals of calculation of building structures for limit states

For a building, structure, as well as foundations or individual structures, limiting states are those states in which they cease to meet the specified operational requirements, as well as the requirements specified during their construction.

Building structures are calculated according to two groups of limit states.

Calculation by the first group of limit states(for serviceability) provides the required bearing capacity of the structure - strength, stability and endurance.

The limiting states of the first group include:

general loss of shape stability (Fig. 1.4, a, 6);

loss of position stability (Fig. 1.4, c, d);

brittle, ductile or other nature of destruction (Fig. 1.4, e);

– destruction under the joint influence of force factors and unfavorable influences of the external environment, etc.

Calculation by the second group of limit states(according to suitability for normal operation) is produced for structures, the magnitude of deformations (displacements) of which may limit the possibility of their operation. In addition, if, according to the operating conditions of the structure, the formation of cracks is unacceptable (for example, in reinforced concrete tanks, pressure pipelines, during the operation of structures in corrosive environments, etc.), then the calculation is based on the formation of cracks. If it is only necessary to limit the width of crack opening, the calculation is performed for crack opening, and in prestressed structures, in some cases, for their closure.

The method of calculating building structures by limiting states is intended to prevent the occurrence of any of the limiting states that may arise in a structure (building)during their operation during the entire service life, as well as during their construction.

The idea of \u200b\u200bcalculating structures by first limiting statecan be formulated as follows: the maximum possible force effect on the structure from external loads or actions in the section of the element -Nshould not exceed its minimum design bearing capacity F:

N<Ф { R ; A},

where R - design resistance of the material; A - geometric factor.

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Second limiting statefor all building structures is determined by the values \u200b\u200bof ultimate deformations, above which normal operation of structures becomes impossible:

Drawing up the layout diagram of the pumping shop building

As far as possible, the building is designed from standard elements in compliance with building design standards and a single modular system. The column grid can be, for example, 6x9; 6 x12; 6 x18; 12 x12; 12 x18 m.

In order to preserve the uniformity of the coating elements, the columns of the extreme row are positioned so that the alignment axis of the row of columns passes at a distance of 250 mm from the outer edge of the columns (Fig.1.16) with a column pitch of 6 m or more.

The columns of the extreme row with a step of 6 m and cranes with a lifting capacity of up to 500 kN are positioned with a zero reference, aligning the axis of the row with the outer edge of the column. The extreme transverse alignment axes are displaced from the axis of the end columns of the building by 500 m. With a large length in the transverse and longitudinal directions, the building is divided by expansion joints into separate blocks. Longitudinal and transverse expansion joints are performed on paired columns with an insert, while at longitudinal expansion joints the axes of the columns are shifted relative to the longitudinal centerline axis by 250 mm, and at transverse expansion joints - by 500 mm relative to the transverse centerline axis

Foundation structures

Distinguish between shallow foundations; pile; deep-laid (drop wells, caissons) and foundations for machines with dynamic loads.

Shallow foundations

Reinforced concrete foundations are widely used in engineering oil and gas structures, industrial and civil buildings. They are of three types (fig. 4.19): separate- under each column; tape- under the rows of columns in one or two directions, as well as under load-bearing walls; solid- under the entire structure. Foundations are most often erected on natural foundations (they are mainly considered here), but in some cases they are also performed on piles. In the latter case, the foundation is a group of piles, united on top by a distribution reinforced concrete slab - a grillage.

Separate foundations are arranged with relatively low loads and a rather rare arrangement of columns. Strip foundations under rows of columns are made when the soles of individual foundations are close to each other, which is usually the case with weak soils and high loads. It is advisable to use strip foundations in case of heterogeneous soils and external loads that are different in value, since they level out uneven foundation settlements. If the bearing capacity of the strip foundations is insufficient or the deformation of the base under them is more than permissible, then solid foundations are arranged. They even out the sediments of the base even more. These foundations are used for weak and heterogeneous soils, as well as for significant and unevenly distributed loads.

Foundation depth d\ (distance from the leveling mark to the base of the foundation) is usually assigned taking into account:

geological and hydrogeological conditions of the construction site;

climatic features of the construction area (freezing depth);

–Design features of buildings and structures. When assigning the depth of the foundation, it is necessary

also take into account the peculiarities of the application and the magnitude of the loads, the technology of work during the construction of foundations, foundation materials and other factors.

The minimum depth of foundations during construction on dispersed soils is taken at least 0.5 m from the planning surface.When building on rocky soils, it is enough to remove only the upper, heavily destroyed layer - and the foundation can be made. The cost of foundations is 4-6% of the total cost of the building.

Separate column foundations

According to the manufacturing method, foundations are prefabricated and monolithic. Depending on the size, the prefabricated foundations of the columns are made integral and composite. Dimensions solid foundations(Figure 4.20) are relatively small. They are made of heavy concrete of classes B15-B25, installed on sand and gravel compacted preparation with a thickness of 100 mm. In the foundations, reinforcement is provided, located along the sole in the form of welded nets. The minimum thickness of the protective layer of the reinforcement is assumed to be 35 mm. If there is no preparation under the foundation, then the protective layer is made at least 70 mm.

Prefabricated columnsare embedded in special sockets (glasses) of foundations. Embedment depth d2 take equal to (1.0-1.5) - multiple of the larger cross-sectional dimension of the column. The bottom plate of the nest must be at least 200 mm thick. The gaps between the column and the walls of the glass are taken as follows: at the bottom - not less than 50 mm; top - not less than 75 mm. During installation, the column is installed in the nest using spacers and wedges or a conductor and straightened, after which the gaps are filled with concrete of class B 17.5 on a fine aggregate.

Prefabricated foundations of large sizes, as a rule, are made up of several mounting blocks (Fig. 4.21). They consume more materials than solid ones. At significant moments and horizontal spacers, the blocks of composite foundations are interconnected by welding of outlets, anchors, embedded parts, etc.

Monolithic separate foundations are arranged for prefabricated and monolithic frames of buildings and structures.

Typical structures of monolithic foundations mated with prefabricated columns are designed for unified dimensions (multiples of 300 mm): foot area - (1.5 x 1.5) - (6.0 x 5.4) m, foundation height - 1.5 ; 1.8; 2.4; 3.0; 3.6 and 4.2 m (Fig.4.22).

The foundations include: an elongated sub-column, reinforced with a space frame; foundation slab with an overhang to thickness ratio of up to 1: 2, reinforced with a double welded mesh; highly placed reinforced podkolnok.

Monolithic foundations, mated with monolithic columns, are stepped and pyramidal in shape (stepped formwork is simpler). The total height of the foundation is taken such that it is not required to reinforce it with clamps and bends. The pressure from the columns is transmitted to the foundation, deviating from the vertical within 45 °. This is guided by when assigning the dimensions of the upper steps of the foundation (see Fig. 4.23, in).

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Monolithic foundations, like prefabricated ones, are reinforced with welded meshes only along the sole. When the side of the sole is more than 3 m, in order to save steel, non-standard welded meshes are used, in which half of the rods are not brought to the end by 1/10 of the length (see Fig.4.23, e).

To connect with a monolithic column, reinforcement is produced from the foundation with a cross-sectional area equal to the design cross-section of the column reinforcement at the foundation edge. Within the foundation, the outlets are connected with clamps to a frame, which is installed on concrete or brick pads. The length of the outlets from the foundations must be sufficient for the arrangement of the reinforcement joint in accordance with the existing requirements. Release joints are made above the floor level. Column reinforcement can be connected with overlap outlets without welding according to the general rules for the design of such joints. In columns, centrally compressed or off-center compressed at small eccentricities, the reinforcement is connected to the outlets in one place; in columns, eccentrically compressed at large eccentricities - at least at two levels on each side of the column. If at the same time there are three rods on one side of the column section, then the middle one is connected first.

It is better to connect the armature of columns with outlets by arc welding. The joint design should be convenient for installation and welding

If the entire section is reinforced with only four rods, then the joints are only welded.

Strip foundations

Under the load-bearing walls, strip foundations are performed mainly national teams.They consist of cushion blocks and foundation blocks (Fig. 4.24). Pillow blocks can be of constant and variable thickness, solid, ribbed, hollow. Lay them close or with gaps. Only the pad is calculated, the protrusions of which act as cantilevers loaded with reactive soil pressure r(excluding the mass of weight and soil on it). The section of the cushion reinforcement is selected by the moment

M \u003d 0.5p12 ,

where / is the console departure.

Thickness of solid cushion hset for lateral force Q= pi, appointing it in such a way that no transverse reinforcement is required.

Strip foundations under the rows of columns are erected in the form of separate ribbons of the longitudinal or transverse (relative to the rows of columns) direction and in the form of cross ribbons (Fig. 4.25). Strip foundations can be prefabricatedand monolithic.They have a T-shaped cross-section with a shelf at the bottom. For soils of high cohesion, a T-profile with a shelf on top is sometimes used. At the same time, the volume of excavation and formwork is reduced, but mechanized excavation is more complicated.

Brand shelf protrusions work like consoles, pinched in a fin. The shelf is assigned such a thickness that, when calculating the shear force, it does not require reinforcement with transverse bars or bends. For small overhangs, the shelf is assumed to be of constant height; at large - variable with thickening to the edge.

A separate foundation strip works in the longitudinal direction for bending like a beam, which is under the influence of concentrated loads from the columns from above and distributed reactive soil pressure from below. The ribs are reinforced like multi-span beams. Longitudinal working reinforcement is assigned by calculation for normal sections for the action of bending moments; transverse bars (clamps) and bends - by calculation of inclined sections for the action of shear forces.

Solid foundations

Solid foundations are: slab-free; slab-and-beam and box-shaped (Fig. 4.26). The greatest rigidity is possessed by box foundations.Solid foundations are made with especially large and unevenly distributed loads. The configuration and dimensions of the solid foundation in the plan are set so that the resultant of the main loads from the structure passes in the center of the sole

In buildings and structures of great length, solid foundations (except for end sections of small length) can be approximately considered as independent strips (tapes) of a certain width, lying on a deformable base. Solid slab foundations of multi-storey buildings are loaded with significant concentrated forces and moments in the places where stiffness diaphragms are described. This should be taken into account when designing them.

Beamless foundation slabsreinforced with welded meshes. The grids are accepted with working fittings in one direction; they are stacked on top of each other in no more than four layers, connecting without overlap - in the non-working direction and with an overlap without welding - in the working direction. The upper nets are laid on the support frames.

Basic information about the soils of the foundations of oil and gas structures

Soils are any rocks, both loose and monolithic, lying within the weathering zone (including soils) and being the object of human engineering and construction activities.

Most often, unconsolidated, loose and clayey soils are used as bases, less often, since they rarely come to the surface, rocky soils. The classification of soils in construction is adopted in accordance with GOST 25100–95 “Soils. Classification ".

Knowledge of the building classification of soils is required to assess their properties as foundations for the foundations of buildings and structures. Soils are divided into classes according to the general nature of structural bonds. Distinguish: the class of natural rocky soils, the class of natural dispersed soils, the class of natural frozen soils, the class of technogenic soils.

Rocky soils are composed of igneous, metamorphic and sedimentary rocks with structural cohesion, high strength and density.

The magmatic ones includegranites, diorites, quartz porphyries, gabbros, diabases, pyroxenites, etc .; to metamorphic- gneisses, schists, quartzites, marbles, rhyolites, etc .; to sedimentary- sandstones, conglomerates, breccias, limestones, dolomites. All rocky soils have a very high strength, structurally rigid bonds and make it possible to erect almost any oil and gas facilities on them.

To loose soils, called in GOST 25100-95 dispersed,includes soils consisting of individual elements formed in the process of weathering of rocky soils. Transfer of individual particles of loose soil by water currents, wind, sliding under its own weight, etc. leads to the formation of large masses of loose soils. The bonds between individual particles are weak. Loose or dispersed soils do not always have sufficient bearing

ability, therefore, the placement of structures on such soils should be justified. A thorough study of the properties of the soil in its natural state is required, as well as their change under the influence of the load from the structures.

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One of the main characteristics of loose soils is the size of individual particles and their cohesion with each other. Depending on the size of individual particles, the soils are subdivided into coarse, sandy and clayey. Coarse soils contain more than 50% by mass of particles with a particle size of more than 2 mm; sandy bulk soils dry contain less than 50% by weight of particles with a particle size of more than 2 mm; clay soils have the ability to significantly change properties depending on saturation with water.

According to the size of individual particles, clay and sandy soils are subdivided into more differentiated types: loam, silty loam, sandy loam.

Determination of the size of the soles of foundations carried out on dispersed soils

As already noted, for foundations on dispersed soils it is considered normal when the foundation settlement does not exceed the limiting value,in this case, the pressure on the ground under the base of the foundation usually does not exceed the calculated soil resistance R(see § 4.1.4.2).

Its settlement (deformation) depends on the size of the basement base. Deformation analysis refers to the second group of limiting states,and, accordingly, the calculations of the dimensions of the basement base should be carried out according to the loads adopted for the calculation of the second group of limit states - iVser (service load). The service load is assumed to be equal to the standard load or is determined approximately through the design load divided by 1.2 - the average safety factor for loads:

Nser\u003d Nnor Nser\u003d N/1 serassembled up to the top edge of the foundation, therefore, when determining the size of the base of the foundation, it is necessary to take into account the load from its own weight and the weight of the soil located on the ledges of the foundation Nfas they also put additional pressure on the ground. Load Nfcan be roughly defined as the product of the volume occupied by the foundation and the soil on its edges, V \u003dAfd1 , on the average specific gravity of concrete and soil att= 20 kN / m3 (Fig.4.35); Af- the area of \u200b\u200bthe foot of the foundation.

The pressure under the sole of the foundation is determined by the formula

P= N+ N/ A= (4.32)

Equating the pressure under the base of the foundation to the calculated soil resistance p= R, you can derive a formula to determine the required area of \u200b\u200bthe foundation foot (4.33)

To check the sufficiency of the area of \u200b\u200bexisting or designed foundations, use the formula

With a horizontal bedding of soil layers (homogeneous, evenly and not strongly compressible soil) for buildings and foundations of a conventional structure, it can be assumed that the dimensions of the foundation soles selected in this way (according to formula (4.33)) (or a verified existing foundation (according to formula (4.34)) satisfy the requirements of the calculation for deformations (4.34) and the calculation of the foundation settlement can be omitted (for more details, see paragraph 2.56 of SNiP 2.02.01–83 *).

The calculation of the area of \u200b\u200bthe base of the foundation is usually performed in the following sequence.

Having established according to the tables (see tables 4.6, 4.7) the value of the calculated soil resistance Rq, we determine the approximate value of the area of \u200b\u200bthe base of the foundation according to the formula (4.35)

then we assign the dimensions of the foundation sole and, having determined the mechanical characteristics of the soils (specific adhesion spi, the angle of internal friction fp (see Tables 4.4, 4.5), we determine the updated value of the design soil resistance Raccording to the formula (4.14), according to which, in turn, we specify the required dimensions of the base of the foundation according to the formula (4.33), and finally accept the base of the foundation.

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Before calculating the reinforcement, make sure that the dimensions of the foundation do not intersect with the faces of the punching shear pyramid. To determine the cross-section of the mesh reinforcement of the lower step, bending moments are calculated in each step (Figure 4.36).

Bending moment in section I – I is equal to

MI \u003d 0.125 / pgr (l-lk) 2b, (4.36)

and the required cross-sectional area of \u200b\u200bthe reinforcement

A\u003d MI / 0.9Rsh. (4.37)

For section II – II, respectively

MII= 0.125 RUBgr(1- l1 ) 2 b; (4.38)

AsII= MII/0,9 Rs(h- hI). (4.39)

The choice of fittings is carried out according to the maximum value Asi, where i= 1–3.

The foundations are reinforced along the bottom with welded meshes made of rods of a periodic profile. The diameter of the rods must be at least 10 mm, and their pitch must be no more than 200 and no less than 100 mm.

Calculation of foundations for extreme columns

With the combined action of vertical and horizontal forces and moments, i.e. under eccentric loading, the foundations are designed as rectangles in the plan, elongated in the plane of the moment.

The dimensions of the foundation in the plan should be assigned so that the greatest pressure on the ground at the edge of the sole from the design loads does not exceed l, 2 R. Preliminary dimensions can be determined by the formula (4.35), as for a centrally loaded foundation.

The maximum and minimum pressure under the edge of the foundation is calculated using the eccentric compression formulas for the least advantageous loading of the foundation under the action of the main combination of design loads.

For the load diagram shown in Fig. 4.34, 4.35:

N= N+ GCT+ ymdIAf, (4.41)

where M, N, Q- design bending moment, longitudinal and transverse forces in the column section at the level of the top of the foundation, respectively; GCT- design load from the weight of the wall and foundation beam. For foundations of building columns equipped with overhead traveling cranes with a lifting capacity Q> 750 kN, as well as for foundations of columns of open crane trestles, it is recommended to take a trapezoidal stress diagram under the base of the foundation with a ratio\u003e 0.25, and for foundations of columns of a building equipped with cranes with a lifting capacity Q< 750 kN, the condition must be met pmin\u003e 0; in buildings without cranes, in exceptional cases, a diagram is allowed (Fig. 4.37). In this case e> 1/6.

It is desirable that from constant, long-term and short-term loads, the pressure is, if possible, evenly distributed over the sole.

Introduction

Structures are called structural bearing structures of industrial and civil buildings and engineering structures, the dimensions of the sections of which are determined by calculation. This is their main difference from architectural structures or parts of buildings, the cross-sectional dimensions of which are assigned according to architectural, thermal engineering or other special requirements.

Modern building structures must meet the following requirements: operational, environmental, technical, economic, production, aesthetic, etc.

Classification of building structures

Concrete and reinforced concrete structures are the most common (both in terms of volume and areas of application). For modern construction, the use of reinforced concrete in the form of prefabricated industrial structures used in the construction of residential, public and industrial buildings and many engineering structures is especially characteristic. Rational areas of application of monolithic reinforced concrete - hydraulic structures, road and airfield pavements, foundations for industrial equipment, tanks, towers, elevators, etc. Special types of concrete and reinforced concrete are used in the construction of structures operated at high and low temperatures or in conditions of chemically aggressive environments (heating units, buildings and structures of ferrous and nonferrous metallurgy, chemical industry, etc.). Reducing the weight, reducing the cost and consumption of materials in reinforced concrete structures are possible on the basis of the use of high-strength concretes and reinforcement, an increase in the production of prestressed structures, and the expansion of the areas of application of lightweight and cellular concrete.

Steel structures are mainly used for frames of large-span buildings and structures, for workshops with heavy crane equipment, blast furnaces, large-capacity tanks, bridges, tower-type structures, etc. The areas of application of steel and reinforced concrete structures in some cases coincide. In this case, the choice of the type of structures is made taking into account the ratio of their costs, as well as depending on the construction area and the location of the construction industry enterprises. A significant advantage of steel structures (compared to reinforced concrete) is their lower weight. This determines the feasibility of their use in areas with high seismicity, hard-to-reach areas of the Far North, desert and high-mountain areas, etc. Expansion of the scope of application of high-strength steels and economical rolled profiles, as well as the creation of efficient spatial structures (including from thin sheet steel) will significantly reduce the weight of buildings and structures.

The main area of \u200b\u200bapplication of stone structures is walls and partitions. Buildings made of bricks, natural stone, small blocks, etc. to a lesser extent meet the requirements of industrial construction than large-panel ones. Therefore, their share in the total volume of construction is gradually decreasing. However, the use of high-strength bricks, reinforced stone, etc. complex structures (stone structures reinforced with steel reinforcement or reinforced concrete elements) can significantly increase the bearing capacity of buildings with stone walls, and the transition from manual masonry to the use of prefabricated brick and ceramic panels - significantly increase the degree of industrialization of construction and reduce the labor intensity of erecting buildings from stone materials.

The main direction in the development of modern wooden structures is the transition to glued timber structures. The possibility of industrial production and obtaining structural elements of the required dimensions by means of gluing determines their advantages over other types of wooden structures. Load-bearing and enclosing glued structures are widely used in agriculture. construction.

In modern construction, new types of industrial structures are becoming widespread - asbestos-cement products and structures, pneumatic building structures, structures made of light alloys and using plastics. Their main advantages are low specific weight and the possibility of factory production on mechanized production lines. Lightweight three-layer panels (with cladding made of profiled steel, aluminum, asbestos cement and with plastic insulation) are starting to be used as enclosing structures instead of heavy reinforced concrete and expanded clay concrete panels.

The division of building structures according to their functional purpose into bearing and enclosing structures is largely arbitrary. If structures such as arches, trusses or frames are only load-bearing, then wall and roof panels, shells, vaults, folds, etc. usually combine fencing and load-bearing functions, which corresponds to one of the most important trends in the development of modern building structures. Depending on the design scheme, supporting building structures are divided into flat (for example, beams, trusses, frames) and spatial (shells, vaults, domes, etc.). Spatial structures are characterized by a more favorable (compared to flat) distribution of forces and, accordingly, lower material consumption. However, their manufacture and installation in many cases are very laborious. New types of spatial structures, for example structural structures made of rolled sections on bolted joints, are distinguished by both cost-effectiveness and relative ease of manufacture and installation. By the type of material, the following main types of building structures are distinguished: concrete and reinforced concrete, steel, stone, wood.

Concrete and reinforced concrete structures are the most common in terms of both volume and application. For modern construction, the use of reinforced concrete in the form of prefabricated industrial structures used in the construction of residential, public and industrial buildings and many engineering structures is especially characteristic. Rational areas of application of monolithic reinforced concrete: hydraulic structures, road and airfield pavements, foundations for industrial equipment, tanks, towers, elevators, etc. Special types of concrete and reinforced concrete are used in the construction of structures operating at high and low temperatures or in conditions of chemically aggressive environments (heating units, buildings and structures of ferrous and nonferrous metallurgy, chemical industry, etc.). The use of high-strength concretes and reinforcement, an increase in the production of prestressed structures, the expansion of the use of lightweight and aerated concretes contribute to a decrease in mass, a decrease in the cost and consumption of materials in reinforced concrete structures.

Steel structures are mainly used for frames of large-span buildings and structures, for workshops with heavy crane equipment, blast furnaces, large-capacity tanks, bridges, tower-type structures, etc. The areas of use of steel and reinforced concrete structures in some cases coincide. In this case, the choice of the type of structures is made taking into account the ratio of their costs, as well as depending on the construction area and the location of the construction industry enterprises. A significant advantage of steel structures over reinforced concrete is their lower weight. This determines the feasibility of their use in areas with high seismicity, inaccessible areas of the Far North, desert and high mountain areas. Expansion of the use of high-strength steels and economical rolled profiles, as well as the creation of effective spatial structures, including those of thin sheet steel, will significantly reduce the weight of buildings and structures.

The main area of \u200b\u200bapplication of Stone structures is walls and partitions. Buildings made of bricks, natural stone, small blocks, etc., meet the requirements of industrial construction to a lesser extent than large-panel buildings. Therefore, their share in the total construction volume is gradually decreasing. However, the use of high-strength bricks, reinforced masonry and complex structures (stone structures reinforced with steel reinforcement or reinforced concrete elements) can significantly increase the load-bearing capacity of buildings with stone walls, and the transition from manual masonry to the use of prefabricated brick and ceramic panels - significantly increase the degree of industrialization of construction and reduce the labor intensity of the construction of buildings from stone materials.

The main direction in the development of modern wooden structures is the transition to glued timber structures. The possibility of industrial production and obtaining structural elements of the required dimensions by means of gluing determines their advantages over other types of wooden structures. Bearing and enclosing glued structures are widely used in rural construction.

In modern construction, new types of industrial structures are becoming widespread - asbestos-cement products and structures, pneumatic building structures, structures made of light alloys and using plastics. Their main advantages are low specific weight and the possibility of factory production on mechanized production lines. Lightweight three-layer panels (with sheathing made of profiled steel, aluminum, asbestos cement and with plastic insulation) are used as enclosing structures instead of heavy reinforced concrete and expanded clay concrete panels.

From the point of view of operational requirements, building structures must meet their purpose, be fire and corrosion resistant, safe, convenient and economical to operate. The scale and pace of mass construction impose industrial requirements on building structures for their manufacture (in a factory), cost-effectiveness, ease of transportation and speed of installation at a construction site. Reducing labor intensity both in the manufacture of building structures and in the process of erecting buildings and structures is of particular importance. One of the most important tasks of modern construction is to reduce the mass of building structures based on the widespread use of lightweight effective materials and improving design solutions.

When designing a building (structure), the optimal types of building structures and materials for them are selected in accordance with the specific conditions of construction and operation of the building, taking into account the need to use local materials and reduce transport costs. When designing objects of mass construction, as a rule, standard building structures and unified dimensional schemes of structures are used.

Building construction,bearing and enclosing structures of buildings and structures.

Classification and fields of application.Division of building structures by functional purpose into load-bearing and fencing largely conditional. If structures such as arches, trusses, or frames are only load-bearing, then wall and roof panels, shells, vaults, folds, etc. usually combine enclosing and supporting functions, which meets one of the most important trends in the development of modern building structures.Depending on the design scheme, supporting building structures are divided into flat (for example, beams, trusses, frames) and spatial (shells, arches, domes, etc. .). Spatial structures are characterized by a more favorable (in comparison with flat) distribution of forces and, accordingly, less material consumption; however, their manufacture and installation in many cases turns out to be very time consuming. New types of spatial structures, such as structural structures made of rolled sections on bolted joints, are distinguished by both cost-effectiveness and comparative ease of manufacture and installation. By the type of material, the following main types of building structures are distinguished: concrete and reinforced concrete.

Concrete and reinforced concrete structures - the most common (both in terms of volume and areas of application). Special types of concrete and reinforced concrete are used in the construction of structures operated at high and low temperatures or in conditions of chemically aggressive environments (heating units, buildings and structures of ferrous and nonferrous metallurgy, chemical industry, etc.). Reducing the weight, reducing the cost and consumption of materials in reinforced concrete structures are possible on the basis of the use of high-strength concretes and reinforcement, an increase in the production of prestressed structures, and the expansion of the areas of application of lightweight and cellular concrete.

Steel structures They are mainly used for frames of large-span buildings and structures, for workshops with heavy crane equipment, blast furnaces, large-capacity tanks, bridges, tower-type structures, etc. The areas of application of steel and reinforced concrete structures in some cases coincide. A significant advantage of steel structures (compared to reinforced concrete) is their lower weight.

Requirements for building structures.From the point of view of operational requirements, SK must meet its purpose, be fire-resistant and corrosion-resistant, safe, convenient and economical to operate.

Calculation of S.K. Building structures must be designed for strength, stability and vibration. This takes into account the force effects to which the structures are subjected during operation (external loads, dead weight), the effect of temperature, shrinkage, displacement of supports, etc., as well as the forces arising during the transportation and installation of building structures.

Foundations of buildings and structures - parts of buildings and structures (mainly underground), which serve to transfer loads from buildings (structures) to a natural or artificial foundation.
The building wall is the main building envelope. Along with the enclosing functions, the walls simultaneously, to one degree or another, perform bearing functions (serve as supports for the perception of vertical and horizontal loads).

A frame (French carcasse, from Italian carcassa) in technology is the skeleton (skeleton) of any product, structural element, whole building or structure, consisting of individual rods fastened together. The frame is made of wood, metal, reinforced concrete and other materials. It determines the strength, stability, durability, shape of a product or structure. Strength and stability are provided by the rigid fastening of the rods at the mating or hinge joints and special stiffeners that give the product or structure a geometrically unchangeable shape. An increase in the rigidity of the frame is often achieved by including the shell, sheathing or walls of a product or structure into operation.

Roof - external load-bearing and enclosing structure of a building, which perceives vertical (including snow) and horizontal loads and influences. (Wind - load)

Windows are arranged for lighting and ventilation (ventilation) of premises and consist of window openings, frames or boxes and filling the openings called window frames.

Question number 12. Behavior of buildings and structures under fire conditions, their fire resistance and fire hazard

Building structures are characterized by fire resistance and fire hazard.

The indicator of fire resistance is the fire resistance limit, the fire hazard of a structure characterizes the class of its fire hazard.

Building structures of buildings, structures and structures, depending on their ability to resist the effects of fire and the spread of its hazardous factors under standard test conditions, are divided into building structures with the following fire resistance limits:

Non-standardized; - not less than 15 minutes; - not less than 30 minutes; - not less than 45 minutes; - not less than 60 minutes; - not less than 90 minutes; - not less than 120 minutes; - not less than 180 minutes; - not less than 360 minutes.

Fire resistance limit of building structures is established by the time (in minutes) of the onset of one or sequentially several, normalized for a given structure, signs of limiting states: loss of bearing capacity (R); loss of integrity (E); loss of thermal insulation capacity (I).

The limits of fire resistance of building structures and their symbols are set according to GOST 30247. In this case, the limit of fire resistance of windows is set only by the time of the onset of loss of integrity (E).

By fire hazard building structures are subdivided into four classes: KO (nonflammable); K1 (low fire hazard); K2 (moderately fire hazardous); KZ (fire hazardous).

Question number 13. Metal structures and their behavior in a fire, ways to increase the fire resistance of structures.

The behavior of arches and frames under fire conditions depends on the static scheme of the structure, as well as the structure of the section of these elements.

Ways to increase fire resistance:

· Cladding made of non-combustible materials (coating, cladding made of bricks, thermal insulation boards, gypsum plasterboards, plaster);

· Fire retardant coatings (non-intumescent and intumescent coatings);

· Suspended ceilings (an air gap is created between the structure and the ceiling, which increases its fire resistance limit).

Limiting state of a metal structure: σ \u003d R n * γ tem

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