Classification of building structures and requirements for them. Main building structures of buildings and structures, their types and functional purposes

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

Classification and scope. The separation of building structures on functional purpose on carriers and enhanced significantly conditionally. If designs such as arches, farms or frames are only carriers, then panels of walls and coatings, shells, vaults, folds, etc. Usually combine enclosing and bearing functions, which is responsible for one of the most important trends in the development of modern building structures. In a dependence on the calculated scheme, the carrying construction structures are divided into flat (for example, beams, farms, frames) and spatial (shells, vaults, dome, etc. .). Spatial structures are characterized by more advantageous (compared to flat) distribution of effort and, accordingly, less consumption of materials; However, their manufacture and installation in many cases turn out to be very laborious. New types of spatial structures, such as structural structures from rolling profiles on bolted compounds, differ in both the efficiency and comparative simplicity of manufacture and installation. According to the type of material, the following main types of building structures distinguish: concrete and reinforced concrete.

Concrete and reinforced concrete structures are the most common (both by volume and by applications). Special types of concrete and reinforced concrete are used in the construction of structures operated at high and low temperatures or under conditions of chemically aggressive media (thermal units, buildings and structures of black and non-ferrous metallurgy, chemical industries, etc.). Reducing the mass, reduction in cost and consumption of materials in reinforced concrete structures is possible on the basis of the use of high-strength concrete and fittings, growth in the production of pre-stressed structures, expanding the use of light and cellular concrete applications.

Requirements for building structures. From the point of view of the operational requirements of S. K. must meet its purpose, being fire-resistant and corrosive, safe, convenient and cost-effective in operation.

Calculation S. K. Building structures should be calculated for strength, stability and oscillations. At the same time, the power impacts are taken into account, which are exposed to operation (external loads, own weight), the effect of temperature, shrinkage, displacement of the supports, etc. As well as efforts arising from 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 basis. The building wall is the main building design. Along with the enclosing features of the wall simultaneously, supporting functions are performed simultaneously (serve support for the perception of vertical and horizontal loads.

Frame (Franz. Carcasse, from Ital. Carcassa) in the technique of the cable (skeleton) of any product, a structural element, a whole building or structure consisting of separate bonded rods. The frame is performed from wood, metal, reinforced concrete, etc. Materials. It determines the strength, stability, durability, product form or structure. Strength and stability are provided with rigid bonding rods in the interface nodes or a hinge compound and special elements of rigidity, which give the product or structure a geometrically unchangeable form. An increase in the rigging frame is often achieved by inclusion in the work of the shell, trim or walls of the product or structure.

Overlap - horizontal bearing and enclosing structures. They perceive vertical and horizontal strengths and transmit them to bearing walls or frame. Cleansing provide heat and sound insulation of the premises.

Floors in residential and public buildings should meet the requirements of strength and resistance to wear, sufficient elasticity and silentness, convenience of cleaning. The floor design depends on the purpose and nature of the premises where it is arranged.

The roof is an outdoor carrier and a fencing construction of a building that perceives vertical (including snow) and horizontal loads and exposure. (Wind - load.

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

The windows are arranged for the lighting and ventilation (ventilation) of the rooms and consist of window openings, frames or boxes and the filling of openings called window bindings.

Question number 12. The behavior of buildings and structures in the conditions of fire, their fire resistance and fire danger.

Loads and exposure to which is subject to the building under normal operating conditions, take into account when calculating the strength of building structures. However, there are additional loads and impacts during fires, which in many cases lead to the destruction of individual structures and buildings as a whole. Adverse factors include: high temperature, gas pressure and combustion products, dynamic loads from falling fragments of collapsed elements of the building and spilled water, sharp temperature fluctuations. The ability of the design to maintain its functions (carriers, enclosing) in the fire conditions resist the effect of fire is called fire resistance of the construction structure.

Building structures are characterized by fire resistance and fire danger.

The fire resistance limit is the limit of fire resistance, the fire danger design characterizes the class of its fire danger.

Building structures of buildings, structures and structures depending on their ability to resist the effects of fire and the spread of its dangerous factors under conditions of standard tests is divided into building structures with the following fire resistance limits.

- non-normalized; - at least 15 minutes; - at least 30 minutes; - not less than 45 minutes; - at least 60 minutes; - not less than 90 minutes; - not less than 120 minutes; - not less than 180 minutes; - at least 360 min .

The limit of fire resistance of building structures is set in time (in minutes) of the occurrence of one or sequentially several normed for this design, signs of limit states: loss of bearing capacity (R); Integrity loss (E); The loss of heat-insulating capacity (I.

The limits of fire resistance of building structures and their conditional notation are set according to GOST 30247. At the same time, the limit of fire resistance of windows is established only by the time of integrity loss (E.

For fire hazard, building structures are divided into four classes: Co. (inexpensive); K1 (low-dryed); K2 (moderate-sucking); KZ (fire hazardous.

Question # 13. Metal structures and their behavior in conditions of fire, ways to increase fire resistance structures.

Although metal structures are made of non-aggravated material, the actual limit of their fire resistance on average is 15 minutes. This is explained by a fairly rapid decrease in the strength and deformative characteristics of the metal at elevated temperatures during a fire. The intensity of heating MK (metal structure) depends on a number of factors to which the nature of the heating of structures and their protection methods are. In the case of a short-term temperature in a real fire, after igniting combustible materials, the metal is heated more slowly and less intensively than the heating of the environment. Under the action of the "standard" fire regime, the ambient temperature does not cease to increase and the thermal inertia of the metal, which causes some heating delay, is observed only during the first minutes of the fire. Then, the temperature of the metal is approaching the temperature of the heating medium. Protection of the metal element and the effectiveness of this protection also affect metal heating.

Under action on the beam of high temperatures, during the fire, the cross section of the design is quickly heated to the same temperature. This reduces the yield strength and the elastic module. The collapse of rolling beams is observed in a cross section where the maximum bending moment is valid.

The effect of a fire temperature on a farm leads to exhaustion of the bearing capacity of its elements and 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 belt elements and the design grille.

The exhaustion of the carrying capacity of steel columns in a fire may occur as a result of the loss: the strength of the rod structure; the strength or stability of the elements of the connecting lattice, as well as the assemblies of the fastening of these elements to the branches of the column; stability by individual branches in areas between the connecting grid nodes; overall stability of the column.

Behavior in conditions of fire Arches and frames depends on the static design of the structure, as well as the design of the cross section of these elements.

Ways to increase fire resistance.

· Facing from non-combustible materials (wedding, lining from brick, thermal insulation plates, plasterboard sheets, plaster.

· Fire retardant coatings (short-scale and intumery coatings.

· Suspension ceilings (between the design and ceiling, an air gap is created, which increases its limit of fire resistance.

The limit state of the metal structure: \u003d R n * TEM.

- 2015-2017 year. (0.008 sec.

The construction supporting structures of industrial and civil buildings and engineering structures are called designs, the dimensions of the sections of which are determined by the calculation. This is the main difference from the architectural structures or parts of buildings, the sizes of the sections of which are prescribed according to architectural, heat engineering or other special requirements.

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

In the construction of gas-conductor objects, steel and precast concrete structures are widely used, including the most progressive - pre-tense, recently the development of structures from aluminum alloys, polymeric materials, ceramics and other efficient materials are obtained.

Building structures are very diverse in its intended purpose and use. Nevertheless, they can be combined according to some signs of the generality of certain properties and more expedient to classify everything according to the following basic signs:

1) The geometric sign of the structure is made to divide on arrays, bars, stoves, shells (Fig. 1.1) and rod systems:

An array is a design in which all sizes of one order;

bar is an element in which two sizes that determine the cross section are many times less than the third - its length, i.e. They are different about: B "I, H" /; The bar with a broken axis is made called the simplest frame, and with a curvilinear axis - arch.

the stove is an element in which one size is many times less than two others: H "A, H" I. The stove is a special case of a more general concept - a shell, which, unlike the stove, has a curvilinear outline;

the rod systems are geometrically immutable system of rods interconnected by articulated or rigidly. These include building farms (beam or console) (Fig. 1.2).

according to the nature of the design scheme, the design is divided into statically definable and statically indefinable. First include systems (designs), efforts or voltages in which can be determined only from equations of the statics (equations of equilibrium), to the second - such for which some of the equations of statics are not enough and to solve the introduction of additional conditions - deformation compatibility equations.

according to the design materials used, they are divided into steel, wooden, reinforced concrete, concrete, stone (brick);

4) by the nature of the stress-strain state (VAT), i.e. Calculated in the designs of internal efforts, stresses and deformations under the action of external load, it can be conditionally divided into their sodium groups: the simplest, simple and complex (Table 1.1).

Such a separation allows you to bring the characteristics of the types of stress-deformed states of structures that are widespread in construction practice. In the presented tablemetno, reflect all the subtleties and features of these states, but it makes it possible to compare and evaluate them in general.

Folds, etc. usually combine enclosing and supporting functions, which corresponds to one of the most important trends in the development of modern Building construction Depending on the settlement scheme carriers Building construction divided into flat (for example, beams, farms, frames) and spatial (shells, vaults, dome etc.). Spatial structures are characterized by more advantageous (compared to flat) distribution of effort and, accordingly, less consumption of materials; However, their manufacture and installation in many cases turn out to be very laborious. New types of spatial structures, for example, t. N. Structural structures from rolling profiles on bolted compounds are distinguished by both the cost-effectiveness and comparative simplicity of manufacturing and editing. According to the type of material distinguish the following main types Building construction: concrete and reinforced concrete (see Reinforced concrete structures and products ), steel structures, stone structures, wooden designs.

Concrete and reinforced concrete structures are the most common (both by volume and by applications). For modern construction, it is especially characteristic of reinforced concrete In the form of prefabricated structures of industrial production used in the construction of residential, public and industrial buildings and many engineering structures. Rational applications of monolithic reinforced concrete - hydraulic structures, road and airfield coatings, foundations for industrial equipment, tanks, towers, elevators, etc. Special species concrete and reinforced concrete is used in the construction of structures operated at high and low temperatures or under conditions of chemically aggressive media (thermal units, buildings and structures of black and non-ferrous metallurgy, chemical industries, etc.). Reducing the mass, reduction in cost and consumption of materials in reinforced concrete structures is possible on the basis of using high-strength concrete and reinforcement, production growth pre-stressed structures, expansion of areas of use of lungs and cellular concrete.

Steel structures are mainly applied mainly for frameworks of large-scale buildings and structures, for workshops with heavy crane equipment, domain, high-capacity tanks, bridges, tower facilities, etc. Areas of applying steel and reinforced concrete structures in some cases coincide. At the same time, the choice of design type is made taking into account the ratio of their values, as well as depending on the construction area and location of the construction industry enterprises. The essential advantage of steel structures (compared to reinforced concrete) is their smaller mass. This determines the expediency of their application in areas with high seismicity, hard-to-reach areas of the Far North, deserted and high-mountainous regions, etc. Expanding the volume of the use of steels of high strength and cost-effective rental profiles, as well as the creation of effective spatial structures (including thin steel) will significantly reduce the weight of buildings and structures.

The main area of \u200b\u200bapplying stone structures - walls and partitions. Buildings from brick, natural stone, small blocks, etc. to a lesser extent satisfy the requirements of industrial construction than large-pointed buildings (see Article Large-pointed structures ). Therefore, their share in the total construction volume is gradually decreasing. However, the use of high-strength bricks, arm-change and so-called. Integrated structures (stone structures reinforced with steel reinforcement or reinforced concrete elements) allows you to significantly increase the carrying capacity of buildings with stone walls, and the transition from manual masonry to the use of brick and ceramic panels of factory manufacturer is to significantly increase the degree of industrialization of construction and reduce the consideration of building buildings from stone materials. .

The main direction in the development of modern wooden structures is the transition to structures from glue wood. The possibility of industrial manufacturing and obtaining structural elements of the required size by gluing determines their advantages compared to wooden structures of other types. Bearing and enclosing teen designs find a wide application in S.-H. construction.

In modern construction, new types of industrial designs receive significant distribution - asbestos-cement products and designs, pneumatic building structures, Constructions from light alloys and using plastic masses. Their main advantages are low specific gravity and the possibility of factory manufacture on mechanized flow lines. Light three-layer panels (with profiled steel, aluminum, asbestos cement and plastic insulation) begin to be used as enclosing structures instead of heavy reinforced concrete and ceramzite-concrete panels.

Requirements for Building construction FROM point of view of operational requirements Building construction Must meet your destination, there are fire-resistant and corrosive, safe, convenient and cost-effective in operation. The scale and pace of mass construction are presented to Building construction Requirements of the industrialism of their manufacturing (in factory conditions), efficiency (both at the cost and consumption of materials), convenience of transportation and speed of installation on a construction site. Of particular importance is the decrease in time consumption - as in the manufacture Building constructionand in the process of building buildings and structures. One of the most important tasks of modern construction is a loss of mass Building construction Based on the wide use of easy effective materials and improving constructive solutions.

Calculation with. to. Building structures should be designed for strength, stability and oscillations. At the same time, the power impacts are taken into account, which are subjected to operations (external loads, own weight), the effect of temperature, shrinkage, props of supports, etc., as well as efforts arising during transportation and installation Building construction In the USSR, the main method of calculation Building construction is the method of calculating limit states, Approved by the USSR State Building for Mandatory Application from January 1, 1955. Before that Building construction Calculated depending on the materials used on allowed voltages (metal and wooden) or by destroying efforts (concrete, reinforced concrete, stone and arm-change). The main disadvantage of these methods is the use of a single (for all current loads) of the strength of the strength that did not allow correctly evaluating the amount of variability in various parts of the loads (permanent, temporary, snow, wind, etc.) and the limit carrying ability of structures. In addition, the method of calculating the allowed stresses did not take into account the plastic stage of the design, which led to an unjustified processing of materials.

When designing a building (facilities) optimal types Building construction And materials for them are chosen in accordance with the specific conditions for the construction and operation of the building, taking into account the need to use local materials and reducing transportation costs. When designing mass construction objects, typical Building construction and unified overall schemes of structures.

LIT: Baikov V.N., Strong S. G., Yermolova D. I., Construction structures, M., 1970; Construction standards and rules, part 2, section A, ch. 10. Building construction and foundations, M., 1972: Building structures, ed. A. M. Ovechkin and R. L. Mail. 2 ed., M., 1974.

G. Sh. Podolsky

Article about the word " Building construction"In the Big Soviet Encyclopedia was read 27210 times

Classification of building structures

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

1 ) on geometric signdesigns are made to divide on arrays, bars, stoves, shells (Fig. 1.1) and rod systems:

– array- construction in which all sizes of one order;

bar.- an element in which two sizes that determine the cross section are many times less than the third - its length, i.e. They are different about:b.« I., h.« /; The bar with a broken axis is made called the simplest frame, and with a curvilinear axis - arch.

plate- an element in which one size is many times less than two others: h.« a., h."I.The stove is a special case of a more general concept - a shell, which, unlike the stove, has a curvilinear outline;

rod Systemsthey are geometrically immutable rods interconnected or rigidly interconnected. These include building farms (beam or console) (Fig. 1.2).

by the nature of the calculation schemedesigns divide on statically definedand statically indefinable.First include systems (designs), efforts or voltages in which can be determined only from equations of the statics (equations of equilibrium), to the second - such for which some of the equations of statics are not enough and to solve the introduction of additional conditions - deformation compatibility equations.

according to the materials useddesigns divide on steel, wooden, reinforced concrete, concrete, stone (brick);

4) by the nature of the stress-strain state(VAT),those. arising in the structures of internal efforts, stresses and deformations under the action of external load, it can be conventionallyshare their sodium groups: simplest, simpleand sophisticated(Table 1.1).

Such a separation allows you to bring the characteristics of the species stress-deformed states of structures that are widespread in construction practice. In the table below
It is difficult to reflect all the subtleties and features of these states, but it makes it possible to compare and evaluate them in general.

Concrete

Concrete is called artificial stone material obtained in the process of solidification of a mixture of binding, water, small and large aggregates and special additives.

The composition of the concrete mix is \u200b\u200bexpressed in two ways.

In the form of mass ratios (less often in volume, which is less accurate) between the amounts of cement, sand and rubble (or gravel) with the obligatory indication of the water-cement ratio and the activity of cement. The amount of cement is taken per unit, so the ratio between the components of the concrete mixture is 1: 2: 4. Set the composition of the concrete mix in volume is permissible only on a small construction, but at the same time cement should always be dosed by weight.

On large objects and central concrete plants, all components are dosed by mass, while the composition is designated in the form of a consumption of materials on 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 mass of materials 2400 kg / m 3

To ensure reliable operation of carrier elements under specified operating conditions, concrete for reinforced concrete and concrete structures must have certain, predetermined physicomechanical properties and, first of all, sufficient strength.

Concretes are classified for a number of features:

by destinationdistinguish structural, special (chemically persistent, thermal insulation, etc.);

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

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

by structure- dense, passioned, cellular, coolers.

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

Depending on the application of concrete, distinguishes:

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

hydrotechnical- for dam, gateways, channel cladding, etc.;

concrete for enclosing structures(lightweight concrete for walls of buildings); for floors, sidewalks, road and airfield coatings;

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

The strength characteristics of concrete

Concrete strength for compression

Concrete strength for compression IN the temporary resistance (in MPa) of the concrete cube with a rebier of 150 mm, made, 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 in shape differ from the cubes, so concrete strength for compressionR.inn.it cannot be directly used in the calculations of the strength of structural elements.

The main characteristic of the strength of concrete compressed elements is prismatic strengthRf, - temporary resistance to the axial compression of concrete prisms, which, by experiments on the prism in the base sidebutand height h.in relation hLA= 4 is approximately 0.75, where R.: – cube strength, or temporary resistance to concrete compression,found when testing the sample in the form of a cube with an edge of 150 mm.

The main characteristic of the strength of the concrete of compressed elements and compressed zones of bending structures is prize strength.

To determine the prism strength, the sample - the prism is loaded in the press of a stepped compressive load before destruction and measure deformations at each level of loading.

The dependence of compressive stresses is built. butfrom relative deformations E, which is non-linear, as in concrete, along with elastic, there are also inelastic plastic deformations.

Experiments with concrete prisms of square base butand height h.showed that the prism strength is less cubic and decreases with increasing relationship hLA(Fig. 2.2).

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Cube strength concrete R.(for cubes of 150 h.150 h.150 mm) and prisment strength R.h.(for prisms with a height rate to the base hLA> 4) can be associated with a certain dependence, which is established experimentally:

The prisoner of concrete strength is used in calculating bending and compressed concrete and reinforced concrete structures (for example, beams, columns, compressed farms, arches, and the like.)

As a characteristic of concrete strength, a compressed zone of bending elements also take R.h.. Concrete strength with axial stretching

Concrete strength with axial stretchingR./, 10-20 times lower than when compressed. Moreover, with an increase in the cube strength of the concrete, the relative strength of concrete under tension is reduced. The strength of concrete concrete when tensile can be associated with cubic strength empirical formula

Classes and brands of concrete

Concrete quality control characteristics are called classesand stamps.The main characteristic of concrete is the class of concrete for compressive strength in or M. M. Class of concrete determines the value of the guaranteed compressive strength in MPa with a US provision of 0.95. Concretes are divided into classes from B1 to B60.

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

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

the coefficient characterizing the concrete class adopted when designing is usually taken in construction.t.= 0,95;

coefficient of variation of strength characterizing the homogeneity of concrete;

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

In regulatory documents, Yutass concrete is used, but the concrete brand is also used for some special designs and in a number of existing standards.

In production it is necessary to ensure the average strength of concrete. Exceeding of a given strength is allowed not by more than 15%, as it leads to the consumption of cement.

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

For designs running for stretching, the concrete class is additionally assigned. strength on axial stretching- Only for heavy, lungs and fine-grained concrete - from the WP ? 3,2.

An important characteristic of concrete is brand by frost resistance- This is the number of cycles of alternate freezing and thawing, which was withstanding the water-saturated samples of concrete at the age of 28 days without a decrease in compressive strength of more than 15% and weight loss no more than 5%. Denotes -F. . For heavy and fine-grained concrete varies from F. 50 T. F. 500, for light concrete - F. 25- F. 500, for cellular and invoked concrete - F. 15- F. 100.

Stamp on waterproofW.assigns for structures to which permeability limiting requirements are presented, for example, to reinforced concrete pipes, to reservoirs, etc.

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Water resistant This property of concrete is not to pass through yourself. It is estimated filtering coefficient- Weight of water that passed per unit of time under constant pressure through the unit of the sample area with its thickness determined. Installed grades for heavy, fine-grained and lightweight concrete:W. 2, W. 4, W. 6, W. 8, W. 10, W. 12. Figure in the brand means water pressure in kgf / cm 2 in which it does not observe its seeping through the samples of the 180-day age.

Mark on self-printingS. p. means the value of the pre-voltage in concrete, MPa, created as a result of its expansion. These values \u200b\u200bvary fromS. p. 0.6 before S. p. 4.

When determining its own weight of the structures and for thermal calculations, the density of concrete is of great importance.Main density concrete brandsD. (kg / m 3 ) Installed in graduation increments of 100 kg / m 3 : Heavy concrete - D. \u003d 2300-2500; fine-grained - 88.

D. \u003d 1800-2400; Light - D. \u003d 800-2100; cellular - D. \u003d 500-1200; Personal - D. = 800–1200.

Armature

The reinforced concrete armature consists of separate working rods, grids or frameworks that are set to perceive the current efforts. The required number of reinforcement is determined by the calculation of elements of structures on load and exposure.

Armature installed by calculation is called working;installed on constructive and technological reasons - mounting.

Working and assembly reinforcement are united in reinforcement products -welded and knitted grids and frames that are placed in reinforced concrete elements in accordance with the nature of their work under load.

The valve is classified in four signs:

depending on the manufacturing technology, the rod and wire fittings differ. Under the rod in this classification implies the reinforcement of any diameter withind.\u003d 6-40 mm;

depending on the method of subsequent hardening, hot-rolled fittings can be thermally hardened, i.e. subjected to heat treatment, or hardened in cold condition - exhaust, drawing;

on the form of the surface, the reinforcement is a periodic profile and smooth. Protrusions in the form of ribs on the surface of the rod fittings of the periodic profile, reefs or dents on the surface of the wire fittings significantly improve the adhesion with concrete;

– according to the method of use in reinforcing reinforced concrete elements, the strained fittings differ, i.e. subjected to preliminary tension, and unwired

The rod hot-rolled reinforcement, depending on its main mechanical characteristics, are divided into six classes with a symbol:A.- I., A-P, Ah, A.- IV., A.- V., BUT- Vi.The main mechanical characteristics of the applied fittings are given in Table. 2.6.

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Thermal hardification is subjected to core reinforcement of four classes; Hardening in its designation is noted by an additional index "T": at-sh, at- IV., A.t.- V., A.t.-Vi.An additional letter C indicates the possibility of joining the welding, the letter K - on the increased corrosion resistance. Cold Cold Stand-free Class A-W Class Fittings is observed by an additional index V.

Each class of reinforcement corresponds to certain marks of reinforcement status with the same mechanical characteristics, but various chemical composition. The design of the steel grade reflects the content of carbon and alloying additives. For example, in the brand 25G2C, the first figure denotes the carbon content in the hundredths of the percent (0.25%), the letter G is that the steel is doped with manganese, the number 2 - that itsthe content can reach 2%, the letter C - the presence in silicon steel (silicia).

The presence of other chemical elements, for example, in brands 20HG2C, 23X2G2T, is indicated by letters: X - chrome, T - titanium, C - zirconium.

The rod fittings of all classes has a periodic profile except for round (smooth) class fittingsA.- I..

Reinforcement products used for the manufacture of w / w designs

For reinforcement of reinforced concrete structures, widely used ordinary reinforcement wire classI.(corrugated) with a diameter of 3-5 mm, obtained by cold drawing of low carbon steel through the system of calibrated holes (filters). The smallest value of the conditional yield strength during the stretching of the wire vI. with a diameter of 3-5 mm is 410 MPa.

The method of cold drawing also produced high-strength reinforcing wire of classes in P and BP-and - smooth and periodic profile (Fig. 2.8,d)with a diameter of 3-8 mm with a conditional limit of the fluidity of the wire in-P - 1500-1100 MPa and BP-P - 1500-1000 MPa.

The reinforced concrete armature is chosen according to its purpose, class and type of concrete, the conditions for the manufacture of reinforcement products and the environmental environment (risk of corrosion), etc. As the main working reinforcement of conventional reinforced concrete structures, it is advantageously necessary to apply Steel Classes A-W and VRI. . In pre-hard structures, high-strength steel classes in-and, BP-P classes are used as strained reinforcement- VI, AT. - VI, A.- V., A.t.- V.andA.t.-VII.

The reinforcement of pre-hard structures of solid high-strength wire is very effective, however, due to the small area of \u200b\u200bthe cross section, the number of them in the design increases significantly, which complicates the reinforcement, the capture and tension of the reinforcement. To reduce the labor-intensity of reinforcement work, the ropes, bundles of parallel wires and steel cables are used in advance. Unbreakable steel ropes of class K are mainly 7- and 19-wire (K-7 and K-19).

The strength of the secccentral compressed elements of the taving and foreign profile

When calculating the elements of the tag and a foreign profile, two cases of the neutral axis are found (Fig. 2.40): the neutral axis is located in the shelf and the neutral axis crosses the edge. With a known reinforcement, the position of the neutral axis is determined when comparing strengthN.with an effort, perceived by the shelf.

If condition is satisfied: N.< R.b.b." fh." f. , that neutral axis is located in the shelf. In this case, the calculation of the brand or foreign section is performed as for the element of the rectangular profile widthbJ.- and height h..

It should be noted that the calculation of the elements of the brand and foreign profile for strength is very laborious. A relatively simply solves the task of testing the strength of normal sections with a known reinforcement and is much more complicated - the calculation of the longitudinal reinforcement, especially with the action of several loadments with the moments of different signs.

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Example 2.5. It is required to check the strength of the cross section of the column. Column cross section b.= 400 mm; h.\u003d 500 mm; a \u003d A "\u003d 40 mm; Concrete Heavy Class B20 (R.b.\u003d 11.5 MPa, E.b= 24000 MPa); Class A-W Armature (R.s.= R.sC\u003d 365 MPa); The area of \u200b\u200bthe cross section of the armature A.s.\u003d A ^\u003d 982 mm (2025); Calculated length IQ.= 4.8 m; Longitudinal force n.\u003d 800 kN; bending moment m \u003d.200 kN m; Environmental humidity 65%.

Strength conditions of stretched elements

In the conditions of stretching, the lower belts of farms and the elements of the lattice, tightening the arches, the walls of round and rectangular tanks and other structures are operating.

For stretched elements, the use of high-strength pre-hard fittings is effective. When designing stretched elements, special attention should be paid to end plots, which should ensure reliable transmission of effort, as well as on the docking of the reinforcement. The joints of the reinforcement are executed, as a rule, welded.

Calculation of centrally stretched elements

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

Calculation of extracently stretched elements with small eccentricitis

If strength N.does not go beyond the boundaries outlined by reinforcement A.s.and A." s., with the advent of the crack concrete completely turns off from the work and the longitudinal force is perceived by the reinforcement A.s.and L.

Calculation of extracently stretched elements with large eccentricitis

If strength N.go beyond fittings A.s., the element appears a compressed zone of concrete. For the element of rectangular cross section, the strength conditions are

N -e.< R b.bX (H.– h./2) + R.sCA & H.– but"),

N.= R.s.A.s.- R.b.bS.~ R.sCA.^.

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When using relative values £, = xLH^ andbutt.= 2; (1 - 1/2) strength conditions are converted to mind

N-E.< R b.a.m.bHL + R.sCA ^ (H– but"),

N \u003d R.S.A.S.-R £ Bh.-R.sC4.

Static calculation of the transverse frame of a single-storey industrial building

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

Constructive elements of the building and the initial data for the calculation to take according to the previous practical session.

When calculating the methods of displacements for unknown, angular or linear movements of the frame nodes are accepted.

Basics of calculating building structures for limit states

For the building, facilities, as well as bases or separate designs, the limits are called such states under which they cease to meet the specified operational requirements, as well as the requirements specified in their erection.

Building structures are calculated in two groups of limit states.

Calculation of PO first group of limit states(according to the suitability of operation) provides the required carrying ability of the structure - strength, stability and endurance.

The limit states of the first group include:

overall loss of stability of the form (Fig. 1.4, a, 6);

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

fragile, viscous or other nature of destruction (Fig. 1.4, e);

– destruction under the joint impact of power factors and adverse effects of the external environment, etc.

Calculation of PO second group of limit states(according to suitability for normal operation) is made for structures, the magnitude of deformations (displacements) of which can limit the possibility of their operation. In addition, if, according to the conditions of operation, the formation of cracks is unacceptable (for example, in reinforced concrete tanks, pressure pipelines, during the operation of structures in aggressive environments, etc.), then calculate the formation of cracks. If it is only necessary to limit the width of the cracking of the cracks, perform calculation of cracks, and in preframed structures in some cases - and by closing them.

The method of calculating building structures on the limit states aims to prevent any of the limit states that may arise in the design (building)if they are operating during the entire service life, as well as when they are erected.

The idea of \u200b\u200bcalculating designs for first limit stateit can be formulated as follows: The maximum possible power impact on the design from external loads or influences in the section of the element -N.should not exceed its minimum calculation capacity F:

N.<Ф { R. ; A.},

where R. - calculated material resistance; BUT - geometric factor.

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The second limitfor all building structures, the values \u200b\u200bof limit deformations are determined, with exceeding the normal operation of structures becomes impossible:

Compilation of the Layout Scheme of the NPS Pump Workshop

As far as possible, the building is designed from typical elements with compliance with the norms of construction design and a single modular system. The grid columns can be, for example, 6h.9; 6 h.12; 6 h.18; 12 h.12; 12 h.18 m.

In order to preserve the same type of elements of the coating of the column of the extreme row, so that the split axis of the row of columns takes place at a distance of 250 mm from the outer edge of the columns (Fig. 1.16) at a column step equal to 6 m or more.

The columns of the extreme row in step 6 m and the cranes with a carrying capacity of up to 500 kN are located with zero binding, combining the axis of the row with the outer face of the column. The extreme transverse drive axles are shifted from the axis of the end columns of the building by 500 m. With a high length in the transverse and longitudinal directions, the building shall be separated by temperature seams into separate blocks. Longitudinal and transverse temperature seams are performed on paired columns with an insert, while at the longitudinal temperature seams of the axis of the columns is shifted relative to the longitudinal center axis by 250 mm, and in transverse temperature seams - by 500 mm relative to the transverse center axis.

Designs of foundations

Distinguish the foundations of shallow downlock; pile; Deep downstream (lowered wells, caissons) and foundations for machines with dynamic loads.

Foundations of shallow downlock

Reinforced concrete foundations are widely used in engineering oil and gas structures, industrial and civil buildings. They are three types (Fig. 4.19): individual- under each column; tape- under the rows of columns in one or two directions, as well as under the bearing walls; solid- Under all the construction. The foundations are erected most often on natural grounds (they are predominantly reviewed here), but in some cases they are performed on piles. In the latter case, the foundation is a group of piles, combined on top of the distribution reinforced concrete slab - woodwork.

Separate foundations are suitable at relatively low loads and a fairly rare placement of columns. Ribbon foundations under the rows of columns are done when the soles of individual foundations close to each other, which usually happens with weak soils and large loads. It is advisable to apply ribbon foundations for inhomogeneous soils and external loads, different by value, as they level uneven base precipitations. If the carrying capacity of tape foundations is insufficient or deformation of the base under them more permissible, then solid foundations are arranged. They even more equalize the rainfall. These foundations are used for weak and inhomogeneous soils, as well as with significant and unevenly distributed loads.

Depth of the Boundage of Foundation d.\ (The distance from the layout of the layout to the basement sole) is usually assigned to:

geological and hydrogeological conditions of construction platform;

climatic features of the construction area (plot depth);

-Constructive features of buildings and structures. When prescribing the depth of the foundation is necessary

also take into account the features of the application and the magnitude of the loads, the technology of manufacturing work in the construction of foundations, the materials of foundations and other factors.

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

Separate foundations of columns

According to the method of manufacturing, foundations are prefabricated and monolithic. Depending on the size of the collection foundations of the columns are performed by one-piece and composite. Dimensions one piece foundations(Fig. 4.20) is relatively small. They are performed from heavy concrete classes B15-B25, installed on sandy-gravel compacted preparation with a thickness of 100 mm. The foundations involve the reinforcement, located on the sole as welded grids. The minimum thickness of the protective layer of reinforcement is taken 35 mm. If under the foundation there is no preparation, then the protective layer makes at least 70 mm.

Column columnsclose up in special sockets (glasses) foundations. Depth of sealing d.2 they are taken equal to (1.0-1.5) - multiple the larger size of the cross section of the column. The thickness of the bottom plate of the socket must be at least 200 mm. The gaps between the column and the walls of the glass are taken as follows: lower - at least 50 mm; on top - at least 75 mm. When mounting, the column is installed in the socket using linings and wedges or conductor and rhyutte, after which the gaps are filled with a class concrete at 17.5 on the fine filler.

Prefabricated foundations of large sizes, as a rule, are performed by composite from several mounting blocks (Fig. 4.21). More materials are consumed on them than for solid. At high moments and horizontal spaces, blocks of compound foundations are combined with a welding release, anchors, mortgage parts, and the like.

Monolithic individual foundations are arranged under the teams and monolithic frames of buildings and structures.

Typical constructions of monolithic foundations mounted with team columns are developed under the unified dimensions (multiple 300 mm): the area of \u200b\u200bthe sole - (1.5 x 1,5) - (6.0 x 5,4) m, the foundation height - 1.5 ; 1.8; 2.4; 3.0; 3.6 and 4.2 m (Fig. 4.22).

The foundations adopted: an elongated subds, reinforced with spatial frame; The foundation plate with the ratio of the departure size to the thickness of up to 1: 2, reinforced by a double welded grid; Highly placed reinforced postpone.

The monolithic foundations mounted with monolithic columns are in the form of steps and pyramidal (stepped on the formwork device easier). The total height of the foundation is assumed that it is not necessary to reinforce it with clamps and revenge. The pressure from the columns is transmitted to the foundation, deviating from the vertical within 45 °. These are guided by appointing the size of the upper stages of the foundation (see Fig. 4.23, in).

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Monolithic foundations, like prefabs, rein with welded grids only by sole. With the sole sole size of more than 3 meters, non-standard welded grids are used in order to save, in which half of the rods are not adjusted to the end per 1/10 length (see Fig. 4.23, e).

To communicate with the monolithic column of the foundation, it produces fittings with an area of \u200b\u200bcross section equal to the calculated cross section of the assembly of the column at the edge of the foundation. Within the foundation, the issues are connected by clamps into a frame that is installed on concrete or brick pads. The length of the releases from the foundations should be sufficient for the junction of the reinforcement according to the existing requirements. The stakes of the releases are made above the floor level. The reinforcement of columns can be combined with the releases of the venge-standing without welding according to the overall rules for the design of such joints. In columns, centrally compressed or extra-tridentically compressed with small eccentricitis, the reinforcement is connected to the releases in one place; In columns, hiddenly compressed for large eccentricity, - not less than two levels on each side of the column. If there are three rods on one side of the cross section of the column, then the first connect the average.

Armature of columns with releases is better to connect arc welding. The design of the joint must be convenient for mounting and welding.

If all the cross section is rejected only by four rods, then the joints are performed only by welded.

Ribbon foundations

Under the bearing walls, tape foundations are mainly national teams.They consist of pillow blocks and foundation blocks (Fig. 4.24). Pillow blocks can be a constant and variable thickness, solid, ribbed, empty. Put them closely or with gaps. Calculate only the pillow, the protrusions of which work as consoles loaded by reactive pressure of the soil r(excluding weight weight and soil on it). Pillow reinforcement section pick up at the time

M \u003d 0.5p12 ,

where / - departure console.

Thickness of solid pillow h.install by calculation on the transverse force Q.= pI, assigning it to such that the transverse reinforcement is not required.

Ribbon foundations under the rows of columns are asked as separate tapes of the longitudinal or transverse (relative to the rows of columns) of direction and in the form of crossbars (Fig. 4.25). Ribbon foundations can be national teamsand monolithic.They have a brand cross section with a pionera. With high connectedness soils, a tavary profile with a shelf is sometimes used. At the same time, the volume of earthworks and formwork decreases, but the mechanized ground removal is complicated.

The protrusions of the brand shelves work as consoles pinched in the edge. The shelf is prescribed such thickness so that when calculating the transverse force in it, it did not require reinforcement of transverse rods or revenues. With small departures, the shelf takes a constant height; With a large variable with thickening to the edge.

A separate foundation belt operates in the longitudinal bending direction as a beam under the influence of focused loads from the columns on top and the distributed jet pressure of the soil from the bottom. Ribs are reinforced like multiplet beams. The longitudinal workforce is prescribed by the calculation of normal sections on the action of bending moments; Transverse rods (clamps) and bending - the calculation of inclined cross sections on the action of transverse forces.

Solid foundations

Solid foundations happen: slaughterhouses; Plate-but-beet and boxed (Fig. 4.26). The greatest rigidity is possessed boxed foundations.Complete foundations are made at particularly large and unevenly distributed loads. The configuration and dimensions of the continuous foundation in the plan are installed so that the equal main load from the structure takes place in the center of the sole

In buildings and structures of high length, continuous foundations (except for the ending sections of small length) can be considered approximately as independent bands (ribbons) of a certain width lying on a deformable base. Solid slab foundations of multi-storey buildings are loaded with significant focused forces and moments in the field descriptions of stiffness diaphragms. This should be taken into account when they are design.

Watchless foundation platesreinforced welded grids. Grids are taken with working reinforcement in one direction; They are placed on each other by no more than four layers, connecting without a flush - in the non-working direction and the twentieutlessness without welding - in the working direction. The upper grids are placed on the coasters framework.

Basic information about the grounds of oil and gas structures

The soils are any rocks such as loose and monolithic, which occur within the weathelation zone (including soils) and are the object of engineering and construction activities of a person.

Most often as grounds are used non-cemented, bulk and clay soils, less often, as less often go to the surface, - rock soils. The classification of soils in construction is accepted in accordance with GOST 25100-95 "Soils. Classification.

Knowledge of the construction classification of soil is required to assess their properties as grounds for the foundations of buildings and structures. Soils are divided into classes according to the total nature of structural connections. There are a class of natural rocky soils, a class of natural dispersed soils, a class of natural frozen soils, a class of technogenic soils.

Rock soils consist of igneous, metamorphic and sedimentary rocks with structural clutch, high strength and density.

To magmatic relatedgranites, diorites, quartz porphyres, gabbro, diabases, pyroxenites, etc.; to metamorphic- Gneus, shale, quartzites, marbles, rhyolitis, etc.; to sediment- Sandstones, conglomerates, breccia, limestone, dolomites. All rock soils have very high strength, structural rigid connections and allow you to erect almost any oil and gas objects to them.

To loose soils called in GOST 25100-95 dispersedthe soils consisting of individual elements formed during the weathering of rock soils are believed. Transferring individual particles of loose soil with aqueous streams, wind, fastening under the action of its own weight, and the like. leads to the formation of large arrays of loose soils. Communication between individual particles is weak. Loose or dispersed soils do not always have a sufficient carrier

ability, therefore, placing on such soils structures must be justified. A thorough study of the properties of the soil in a natural state is required, as well as their change under the influence of loads from structures.

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One of the main characteristics of loose soils is the size of individual particles and their connectedness with each other. Depending on the size of individual particles, the soil is divided into large-chip, sandy and clay. Large-grained soils contain more than 50% by weight of particles of more than 2 mm; sand bulk soils in a dry state, it contains less than 50% by weight of particles of more than 2 mm; clay soils possess the ability to significantly change properties depending on the saturation of water.

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

Determination of the size of the soles of foundations performed on dispersed soils

As noted, for foundations on dispersed soils normal is considered when the grade of the foundation does not exceed the limit value,in this case, the pressure on the ground under the basement sole usually does not exceed the calculated resistance of the soil R.(See § 4.1.4.2).

It depends on the size of the soles of the foundation (deformation). The deformation calculation refers to the second group of limit states,and, accordingly, the calculations of the size of the basement soles should be carried out by loads adopted for the calculation of the second group of limit states - IVSER (service load). The service load is received equal to the normative load or is determined approximately through the calculated load divided by 1.2 - the average factor of reliability in loads:

N.ser.\u003d N.n.or N.ser.\u003d N./1 ser.it is assembled to the upper cutting of the foundation, so when determining the size of the soles of the foundation, it is necessary to take into account the load on its own weight and weight of the soil, located on the basis of the foundation Nf.since they also have additional pressure on the ground. Load Nf.you can roughly define as a product of a volume occupied by the foundation and soil located on its cuts, V \u003d.A.f.d.1 , on the average share of concrete and soil w.t.= 20 kN / m3 (Fig. 4.35); AF- The area of \u200b\u200bthe foundation soles.

Pressure under the basement base is determined by the formula

P.= N.+ N./ A.= (4.32)

Having equated pressure under the basement of the foundation with the calculated soil resistance p.= R., it can be derived to the formula for determining the required area of \u200b\u200bthe soles of the foundation (4.33)

To verify the adequacy of the area of \u200b\u200bexisting or projected foundations, the formula is used

With the horizontal location of the soil formation (homogeneous, evenly compressed soil) for buildings and foundations of a conventional design, it can be considered that the size of the basement soles (according to formula (4.33)) (or a proven existing foundation (4.34) is selected in this way (or a proven existing foundation (4.34)) Satisfy the requirements for calculating deformations (4.34) and the calculation of the limit of the foundation can not be done. (See 2.02.01-83 *) in more detail.

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

By installing the tables on the tables (see Table 4.6, 4.7) the value of the computational resistance of the soil R.q., determine the approximate value of the area of \u200b\u200bthe foundation of the foundation by formula (4.35)

then prescribe the size of the basement soles and, by determining the mechanical characteristics of the soils (the specific grip of the GP, the angle of internal friction of the FP (see Table 4.4, 4.5), determine the refined value of the calculated soil resistance R.according to formula (4.14), according to which, in turn, we specify the required size of the foundation of the foundation by formula (4.33), and finally accept the foundation sole.

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Prior to calculation, it is necessary to make sure that the size of the foundation does not intersect with the edges of the pyramid of the pyramid. To determine the cross section of the reinforcement mesh, the bending moments in each stage are calculated (Fig. 4.36).

Bending moment in section I-I - Inane

Mi \u003d 0.125 / p.gR (L-LK) 2B, (4.36)

and the required cross-sectional area of \u200b\u200breinforcement

BUT\u003d MI / 0.9RSH. (4.37)

For cross section II-II, respectively

M.II.= 0.125rg.(1- l.1 ) 2 b.; (4.38)

A.sii.= M.II./0,9 R.s.(h.- h.I.). (4.39)

The selection of reinforcement is carried out at the maximum value. A.sI, where i.= 1–3.

Foundations are reinforced by the sole of welded grids from the rods of the periodic profile. The diameter of the rods must be at least 10 mm, and their step is not more than 200 and at least 100 mm.

Calculation of foundations for extreme columns

With the joint action of vertical and horizontal forces and moments, i.e. With off-centrular loading, the foundations are design of rectangles in terms, stretched in the plane of the moment actions.

The size of the foundation in the plan must be appointed so that the greatest pressure on the ground at the edge of the sole from the calculated loads does not exceed l., 2 R.. Pre-dimensions can be determined by formula (4.35), as for the central loaded foundation.

The maximum and minimum pressure under the edge of the foundation is calculated by the formulas of high-center compression for the least advantageous loading of the foundation under the action of the main combination of the calculated loads.

For load scheme shown in Fig. 4.34, 4.35:

N.= N.+ G.Ct.+ y.m.d.I.A.f., (4.41)

where M., N., Q.- the estimated bending moment, longitudinal and transverse force in the cross section of the column at the level of the foundation, respectively; G.Ct.- Calculated load on the weight of the wall and the foundation beam. For foundations columns of buildings equipped with bridge cranes with a lifting capacity Q.> 750 kN, as well as for foundations of the columns of an open crane hoist, it is recommended to take a trapezoidal voltage sole under the basement base with ratio\u003e 0.25, and for foundations columns of the building equipped with cranes with carrying capacity Q.< 750 kN, you need to perform a condition p.mIN.\u003e 0; In the buildings without cranes in exceptional cases, the Epur is allowed (Fig. 4.37). In this case e.> 1/6.

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

Introduction

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

Classification of building structures

Concrete and reinforced concrete structures are the most common (both by volume and by applications). For modern construction, the use of reinforced concrete in the form of prefabricated structures of industrial manufacture, used in the construction of residential, public and industrial buildings and many engineering structures. Rational applications of monolithic reinforced concrete - hydraulic structures, road and airfield coatings, 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 under conditions of chemically aggressive media (thermal units, buildings and structures of black and non-ferrous metallurgy, chemical industries, etc.). Reducing the mass, reduction in cost and consumption of materials in reinforced concrete structures is possible on the basis of the use of high-strength concrete and fittings, growth in the production of pre-stressed structures, expanding the use of light and cellular concrete applications.

The main area of \u200b\u200bapplying stone structures - walls and partitions. Buildings from brick, natural stone, small blocks, etc. To a lesser extent satisfy the requirements of industrial construction than large-poinners. Therefore, their share in the total construction volume is gradually decreasing. However, the use of high-strength bricks, arm-change and so-called. complex structures (stone structures reinforced with steel reinforcement or reinforced concrete elements) allows you to significantly increase the carrying capacity of buildings with stone walls, and the transition from manual masonry to the use of brick and ceramic panels of factory manufacturing is to significantly increase the degree of industrialization of construction and reduce the labor intensity of building buildings from stone Materials.

The main direction in the development of modern wooden structures is the transition to structures from glue wood. The possibility of industrial manufacturing and obtaining structural elements of the required size by gluing determines their advantages compared to wooden structures of other types. Bearing and enclosing gear structures are widely used in S.-H. construction.

In modern construction, a significant distribution is obtained by new types of industrial designs - asbestos-cement products and structures, pneumatic building structures, structures of light alloys and with the use of plastic masses. Their main advantages are low specific gravity and the possibility of factory manufacture on mechanized flow lines. Light three-layer panels (with profiled steel, aluminum, asbestos cement and plastic insulation) begin to be used as enclosing structures instead of heavy reinforced concrete and ceramzite-concrete panels.