Classification of building structures

Building load-bearing structures of industrial and civil buildings and engineering structures are structures whose cross-sectional dimensions 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, industrial, aesthetic, etc.

In the construction of oil and gas pipeline facilities, steel and prefabricated reinforced concrete structures are widely used, including the most progressive ones - prestressed ones. Recently, structures made of aluminum alloys, polymeric materials, ceramics and other effective materials are being developed.

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

1 ) on a geometric basisstructures are usually divided into arrays, beams, slabs, shells (Fig. 1.1) and rod systems:

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

beam- an element in which two dimensions that determine the cross section are many times smaller than the third - its length, i.e. they are in different order:b« I, h« /; a beam 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 invariable systems of rods connected to each other hingedly or rigidly. These include construction trusses (beam or cantilever) (Fig. 1.2).

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

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

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

This division allows us to bring into the system the characteristics of 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 weight (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 cement activity. The amount of cement is taken as a unit, so the ratio between the components of the concrete mixture is 1:2:4. It is permissible to set the composition of the concrete mixture by volume only in small construction, but at the same time, cement should always be dosed by mass.

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

PAGE_BREAK--

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, concrete 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 criteria:

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

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

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

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

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

Depending on the area of ​​application of concrete, there are:

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

hydrotechnical– for dams, sluices, canal linings, etc.;

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

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

Strength characteristics of concrete

Compressive strength of concrete

Compressive strength of concrete AT is the temporary resistance (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 concrete compressive strengthRinncannot be directly used in strength calculations of structural elements.

The main characteristic of the strength of concrete of compressed elements is prismatic strengthRF, - temporary resistance to axial compression of concrete prisms, which, according to experiments on prisms with a base sideaand height hwith respect hla= 4 is approximately 0.75, where R: – cubic strength, or tensile 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 of compressed elements and compressed zones of bent structures is prismatic strength.

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

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

Experiments with concrete prisms the size of a square base aand height hshowed that the prism strength is less than the cubic strength and decreases with increasing ratio hla(Fig. 2.2).

Continuation
--PAGE_BREAK--

Cubic strength of concrete R(for cubes size 150 X150 X150 mm) and prismatic strength Rh(for prisms with height to base ratio hla> 4) can be associated with a certain dependence, which is established experimentally:

The prismatic strength of concrete is used in the calculation of bent 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, they also take Rh. Strength of concrete in axial tension

Concrete strength in axial tensionR/, 10–20 times lower than with compression. 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 cubic 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 divided into classes from B1 to B60.

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

class of concrete in terms of compressive strength, MPa; average strength, which should be ensured in the manufacture of structures, MPa;

coefficient characterizing the security of the concrete class adopted in the design, usually in construction they taket= 0,95;

strength variation coefficient characterizing the homogeneity of concrete;

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

The normative documents use the utass of concrete, however, for some special structures and in a number of current standards, the brand of concrete is also used.

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

For concrete and reinforced concrete structures, the following concrete classes 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 structures working in tension, an additional class of concrete is assigned by 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 resistance- this is the number of cycles of alternate freezing and thawing that water-saturated concrete samples at the age of 28 days withstood without a decrease in compressive strength of more than 15% and a weight loss of not more than 5%. Designated -F . For heavy and fine-grained concrete varies from F 50 to F 500, for lightweight concrete - F 25- F 500, for cellular and porous concrete - F 15- F 100.

Waterproof brandWit is assigned to structures that require limited permeability, for example, reinforced concrete pipes, tanks, etc.

Continuation
--PAGE_BREAK--

Water resistance is the property of concrete to prevent water from passing through it. She's rated filtration coefficient- the mass of water that has passed per unit time under constant pressure through a unit area of ​​the sample at a certain thickness. Grades for heavy, fine-grained and light concretes have been established:W 2, W 4, W 6, W 8, W 10, W 12. The number in the brand means water pressure in kgf / cm 2 , at which its seepage through samples of 180 days of age is not observed.

Self stress brandS p means the value of the prestress in concrete, MPa, created as a result of its expansion. These values ​​vary 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 ) are installed with a gradation step of 100 kg/m 3 : heavy concrete - D = 2300–2500; fine-grained - 88

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

fittings

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.

Reinforcement installed by calculation is called working;installed for constructive and technological reasons - mounting.

Working and mounting fittings are combined into reinforcing 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, rod and wire reinforcement are distinguished. Under the rod in this classification means reinforcement of any diameter withind= 6–40 mm;

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

according to the shape of the surface, the reinforcement is of a periodic profile and smooth. The protrusions in the form of ribs on the surface of the rod reinforcement of a periodic profile, reefs or dents on the surface of the wire reinforcement significantly improve adhesion to concrete;

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

Hot-rolled bar reinforcement, depending on its main mechanical characteristics, is divided into six classes with a symbol:A- I, A-P, A-Sh, A- IV, A- V, BUT- VI.The main mechanical characteristics of the fittings used are given in Table. 2.6.

Continuation
--PAGE_BREAK--

The bar reinforcement of four classes is subjected to thermal hardening; hardening in its designation is marked with an additional index "t": At-Sh, At- IV, At- V, At-VI.The additional letter C indicates the possibility of joining by welding, the letter K indicates increased corrosion resistance. The rod fittings of class A-Sh subjected to drawing in a cold state are marked with an additional index B.

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

The presence of other chemical elements, for example, in grades 20KhG2Ts, 23Kh2G2T, 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.

Reinforcing products used for the manufacture of reinforced concrete structures

Widely used for reinforcing reinforced concrete structures. ordinary reinforcing wire class Vr-I(corrugated) 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 conditional yield strength in tensile wire Vr-I with a diameter of 3–5 mm 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,G)with a diameter of 3–8 mm with a conditional yield strength of wire V-P - 1500-1100 MPa and Vr-P - 1500-1000 MPa.

The reinforcement of reinforced concrete structures is selected taking into account its purpose, the class and type of concrete, the 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 A-Sh and Vr-I . In prestressed structures, mainly high-strength steel of classes V-I, Vr-P, A is used as prestressing 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 ​​the wires, their number in the structure increases significantly, which complicates the reinforcing work, gripping and tensioning the reinforcement. To reduce the complexity of reinforcing work, ropes, bundles of parallel wires and steel cables are used in advance by a mechanized method. Non-twisting steel ropes of class K are produced mainly with 7- and 19-wire (K-7 and K-19).

Strength Conditions for Eccentrically Compressed Tee and I-Profile Members

When calculating elements of a T-section and an I-section, two cases of the location of the neutral axis can occur (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 force 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 a tee or I-section is performed as for a rectangular profile element with a widthbj- and height h.

It should be noted that the calculation of the elements of the tee and I-section for strength is very laborious. The problem of checking the strength of normal sections with known reinforcement is relatively simple to solve, and it is much more difficult to calculate longitudinal reinforcement, especially when several load cases with moments of different signs act.

Continuation
--PAGE_BREAK--

Example 2.5. It is required to check the strength of the section of the column. Column section b= 400 mm; h= 500 mm; a = a"= 40 mm; heavy concrete class B20 (Rb=11.5 MPa, Eb= 24000 MPa); fittings of class A-Sh (Rs= Rsc= 365 MPa); cross-sectional area of ​​reinforcement As= A^= 982 mm (2025); effective length Iq= 4.8 m; longitudinal force n= 800 kN; bending moment m =200 kN m; ambient humidity 65%.

Strength conditions for tension members

Under tension conditions, the lower belts of trusses and lattice elements, arches, walls of round and rectangular tanks, and other structures work.

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

Calculation of central tension elements

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

Calculation of eccentrically tensioned elements with small eccentricities

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

Calculation of eccentrically tensioned elements with large eccentricities

If strength Ngoes beyond the armature As, then a compressed zone of concrete appears in the element. For a rectangular section element, the strength conditions have the form

N-e< R bbx(h– X/2) + RscA&h– a"),

N= RsAs- Rbbs~ RscA^.

Continuation
--PAGE_BREAK--

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

No.< R bambhl + RscA^(h– a"),

N=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-story two-span industrial building using the displacement method and determine the 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, angular or linear displacements of the frame nodes are taken as unknowns.

Fundamentals of calculation of building structures for limit states

For a building, a structure, as well as a foundation or individual structures, the limit states are such 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(in terms of serviceability) provides the required bearing capacity of the structure - strength, stability and endurance.

The limit 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 type of destruction (Fig. 1.4, e);

– destruction under the combined influence of force factors and adverse environmental influences, etc.

Calculation by second group of limit states(according to suitability for normal operation) is made 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 aggressive environments, etc.), then a calculation is made for the formation of cracks. If it is only necessary to limit the width of the crack opening, the calculation is performed on the opening of cracks, and in prestressed structures, in some cases, on their closure.

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

The idea of ​​calculating structures according to first limit statecan be formulated as follows: the maximum possible force impact on the structure from external loads or impacts in the section of the element -Nmust not exceed its minimum design bearing capacity F:

N<Ф { R ; A},

where R is the design resistance of the material; BUT is the geometric factor.

Continuation
--PAGE_BREAK--

Second limit statefor all building structures it is determined by the values ​​of limiting deformations, above which the normal operation of structures becomes impossible:

Drawing up a layout diagram of the building of the pumping shop of the PS

As far as possible, the building is designed from standard elements in compliance with building design standards and a single modular system. The grid of columns can be, for example, 6X9; 6 X12; 6 X18; 12 X12; 12 X18 m

In order to maintain the uniformity of the elements of the coating, the columns of the outermost row are positioned so that the center 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 spacing 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 located with zero reference, aligning the axis of the row with the outer face of the column. The extreme transverse centering axes are shifted 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 made on twin columns with an insert, while at the longitudinal expansion joints the axes of the columns are shifted relative to the longitudinal center axis by 250 mm, and at the transverse expansion joints - by 500 mm relative to the transverse center axis

Foundation structures

There are shallow foundations; pile; deep laying (falling wells, caissons) and foundations for machines with dynamic loads.

Shallow foundations

Reinforced concrete foundations are widely used in engineering oil and gas facilities, industrial and civil buildings. They are of three types (Fig. 4.19): separate- under each column; tape- under rows of columns in one or two directions, as well as under load-bearing walls; solid under the entire structure. Foundations are erected most often 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 of a distribution reinforced concrete slab - a grillage.

Separate foundations are suitable for relatively small loads and a fairly rare placement of columns. Strip foundations under rows of columns are made when the soles of individual foundations come close to each other, which usually happens with weak soils and heavy loads. It is advisable to use strip foundations with heterogeneous soils and external loads of different values, since they level uneven subsidence of the base. If the bearing capacity of 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 subsidence 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 layout 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);

-constructive features of buildings and structures. When setting the depth of the foundation, it is necessary

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

Prefabricated columns close up in special nests (glasses) of foundations. Embedding depth d2 taken equal to (1.0–1.5) - a multiple of the larger size of the cross section of the column. The thickness of the bottom plate of the nest must be at least 200 mm. The gaps between the column and the walls of the glass are taken as follows: at the bottom - at least 50 mm; on top - at least 75 mm. During installation, the column is installed in the socket with the help of linings and wedges or a conductor and straightened, after which the gaps are filled with concrete of class B 17.5 on fine aggregate.

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

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

Typical designs of monolithic foundations, mating with prefabricated columns, are designed for unified dimensions (multiples of 300 mm): sole 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).

In the foundations, the following are accepted: an elongated pedestal reinforced with a spatial frame; foundation slab with a ratio of overhang size to thickness up to 1:2, reinforced with double welded mesh; highly placed reinforced sub-column.

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 limbs. The pressure from the columns is transferred to the foundation, deviating from the vertical within 45 °. This is guided by the assignment of the dimensions of the upper steps of the foundation (see Fig. 4.23, in).

Continuation
--PAGE_BREAK--

Monolithic foundations, like prefabricated foundations, are reinforced with welded meshes only along the sole. With sole side dimensions of 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).

For connection with a monolithic column, reinforcement is produced from the foundation with a cross-sectional area equal to the calculated section of the column reinforcement at the edge of the foundation. Within the foundation, the outlets are connected with clamps into 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 existing requirements. The joints of the outlets are made above the floor level. The reinforcement of the columns can be connected to the outlets with an overlap without welding according to the general rules for the design of such joints. In columns that are centrally compressed or eccentrically compressed at small eccentricities, the reinforcement is connected to outlets in one place; in columns eccentrically compressed at large eccentricities - at least 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 reinforcement of columns with outlets by arc welding. The design of the joint 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 load-bearing walls, strip foundations are performed mainly prefabricated. They consist of pillow 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 a pillow is calculated, the protrusions of which act as cantilevers loaded with reactive ground pressure. R(without taking into account the weight of the weight and soil on it). The cross section of the pillow reinforcement is selected according to the moment

M \u003d 0.5r12 ,

where / is the console departure.

Thickness of solid cushion h set according to the calculation of the transverse force Q= pi, assigning it such that it does not require the installation of transverse reinforcement.

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

The protrusions of the shelf of the brand work as consoles, pinched in the rib. The shelf is assigned such a thickness that, when calculating the transverse force, it does not require reinforcement with transverse rods or limbs. For small departures, the shelf is assumed to be of constant height; at large - a variable with a thickening to the edge.

A separate foundation strip works in the longitudinal direction in bending as a beam, which is under the influence of concentrated loads from 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 according to normal sections for the action of bending moments; transverse rods (clamps) and limbs - by calculation of inclined sections for the action of transverse forces.

solid foundations

Solid foundations are: slab beamless; slab-but-beam and box-shaped (Fig. 4.26). have the highest rigidity box foundations. Solid foundations are made with especially large and unevenly distributed loads. The configuration and dimensions of the solid foundation in 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 (ribbons) of a certain width lying on a deformable foundation. Solid slab foundations of multi-storey buildings are loaded with significant concentrated forces and moments in the places where stiffening diaphragms are described. This must be taken into account when designing them.

Beamless foundation slabs reinforced with welded mesh. Grids are accepted with working reinforcement in one direction; they are stacked on top of each other in no more than four layers, connecting without overlapping - in the non-working direction and overlapping without welding - in the working direction. The upper grids are laid on the frames of the stand.

Basic information about the foundation soils of oil and gas facilities

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

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

Knowledge of the construction 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 relationships. 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.

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

The magmatic ones are granites, diorites, quartz porphyries, gabbro, diabases, pyroxenites, etc.; to metamorphic- gneisses, shales, quartzites, marbles, rhyolites, etc.; to sedimentary– sandstones, conglomerates, breccias, limestones, dolomites. All rocky soils have very high strength, rigid structural bonds and allow the construction of almost any oil and gas facilities on them.

For loose soils called in GOST 25100–95 dispersed, include soils consisting of individual elements formed in the process of weathering of rocky soils. The transfer of individual particles of loose soil by water flows, wind, slumping under the action of its own weight, etc. leads to the formation of large massifs of loose soils. The bonds between individual particles are weak. Loose or dispersed soils do not always have sufficient bearing

capacity, therefore, the placement of structures on such soils must 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 structures.

Continuation
--PAGE_BREAK--

One of the main characteristics of loose soils is the size of individual particles and their association with each other. Depending on the size of individual particles, soils are divided into coarse, sandy and clayey. Coarse clastic soils contain more than 50% by weight of particles larger than 2 mm; sandy loose soils in the dry state contain less than 50% by weight of particles larger 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 divided into more differentiated types: loam, silty loam, sandy loam.

Determination of the dimensions of the base of foundations performed on dispersed soils

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

Its settlement (deformation) depends on the size of the sole of the foundation. Deformation calculation refers to the second group of limit states, and, accordingly, the calculations of the dimensions of the base of the foundation 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 calculated load divided by 1.2 - the average reliability factor for loads:

Nser= Nn or Nser= N/1 ser is assembled to the upper edge of the foundation, therefore, when determining the dimensions 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 Nf as they also put additional pressure on the ground. load Nf can be roughly defined as the product of the volume occupied by the foundation and the soil located on its edges, V =Afd1 , on the average specific gravity of concrete and soil att= 20 kN/m3 (Fig. 4.35); Af is the area of ​​the footing of the foundation.

The pressure under the base 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 for determining the required area of ​​​​the base of the foundation (4.33)

To check the sufficiency of the area of ​​existing or designed foundations, use the formula

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

The calculation of the area of ​​​​the sole 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 design resistance of the soil Rq, we determine the approximate value of the area of ​​​​the base of the foundation according to the formula (4.35)

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

Continuation
--PAGE_BREAK--

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

The bending moment in the section I–I is equal to

MI= 0.125 / p gr(l-lk)2b, (4.36)

and the required cross-sectional area of ​​the reinforcement

BUT= 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 reinforcement is carried out according to the maximum value Asi, where i= 1–3.

The foundations are reinforced along the sole with welded meshes of rods of a periodic profile. The diameter of the rods must be at least 10 mm, and their pitch must not exceed 200 and not 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 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 soil at the edge of the sole from the calculated loads does not exceed l, 2 R. Previously, the 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 favorable foundation loading 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- calculated bending moment, longitudinal and transverse forces in the section of the column at the level of the top of the foundation, respectively; GCT- design load from the weight of the wall and the foundation beam. For foundations of building columns equipped with overhead cranes with a lifting capacity of Q> 750 kN, as well as for the foundations of columns of open crane racks, it is recommended to take a trapezoidal stress diagram under the base of the foundation with a ratio of > 0.25, and for foundations of building columns equipped with cranes with a lifting capacity Q< 750 kN, condition must be met pmin> 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, if possible, be evenly distributed over the sole.

Creases, etc. usually combine enclosing and bearing functions, which corresponds to one of the most important trends in the development of modern Building construction Depending on the design scheme bearing Building construction subdivided 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 consumption of materials; however, their manufacture and installation in many cases are very time-consuming. New types of spatial structures, for example, the so-called. Structural structures made of rolled profiles with bolted connections are both economical and relatively easy to manufacture and install. According to the type of material, the following main types are distinguished Building construction: concrete and reinforced concrete (see. Reinforced concrete structures and products ), steel structures, stone structures, wooden structures.

Concrete and reinforced concrete structures are the most common (both in volume and in 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. Rational areas of application of monolithic reinforced concrete are hydraulic structures, road and airfield pavements, foundations for industrial equipment, tanks, towers, elevators, etc. Special types concrete and reinforced concrete are used in the construction of structures operated at high and low temperatures or in chemically aggressive environments (thermal units, buildings and structures of ferrous and non-ferrous metallurgy, the chemical industry, etc.). Reducing the weight, reducing the cost and consumption of materials in reinforced concrete structures is possible through the use of high-strength concrete and reinforcement, production growth prestressed structures, expansion of 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. At the same time, 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 expediency of their use in areas with high seismicity, hard-to-reach areas of the Far North, desert and high mountain areas, etc. The expansion of the use of high-strength steels and economical rolled profiles, as well as the creation of efficient spatial structures (including those made of thin sheet steel) will significantly reduce the weight of buildings and structures.

The main scope 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 (see article Large panel structures ). Therefore, their share in the total volume of construction is gradually decreasing. However, the use of high-strength bricks, reinforced masonry, 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 factory-made brick and ceramic panels can significantly increase the degree of industrialization of construction and reduce the laboriousness of building buildings from stone materials .

The main direction in the development of modern wooden structures is the transition to structures made of glued wood. The possibility of industrial production and obtaining structural elements of the required dimensions by gluing determines their advantages in comparison with wooden structures of other types. Bearing and enclosing glued structures find wide application in page - x. 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 gravity and the possibility of prefabrication on mechanized production lines. Lightweight three-layer panels (with sheathing made of profiled steel, aluminum, asbestos-cement and with plastic insulation) are beginning to be used as enclosing structures instead of heavy reinforced concrete and expanded clay concrete panels.

Requirements for Building construction FROM terms of operational requirements Building construction must meet their purpose, be fire-resistant and corrosion-resistant, safe, convenient and economical in operation. The scale and pace of mass construction make Building construction industrial requirements for their manufacture (in the factory), efficiency (both in terms of cost and consumption of materials), ease of transportation and speed of installation at a construction site. Of particular importance is the reduction of labor intensity - as in the manufacture Building construction, and in the process of erecting buildings and structures from them. One of the most important tasks of modern construction is weight reduction. Building construction based on the widespread use of lightweight efficient materials and the improvement of design solutions.

Calculation with. to. Building structures must be designed for strength, stability and vibration. This takes into account the force effects that structures are subjected to during operation (external loads, own weight), the effect of temperature, shrinkage, displacement of supports, etc., as well as the forces arising during transportation and installation Building construction In the USSR, the main method of calculation Building construction is the calculation method for limit states, approved by the Gosstroy of the USSR for mandatory use from January 1, 1955. Before that Building construction calculated depending on the materials used for permissible stresses (metal and wood) or for destructive forces (concrete, reinforced concrete, stone and reinforced stone). The main disadvantage of these methods is the use in the calculations of a single (for all acting loads) safety factor, which did not allow correctly assessing the magnitude of the variability of loads of different nature (permanent, temporary, snow, wind, etc.) and the ultimate bearing capacity of structures. In addition, the calculation method for allowable stresses did not take into account the plastic stage of the structure, which led to an unjustified waste of materials.

When designing a building (structure), the optimal types Building construction 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 transportation costs. When designing objects of mass construction, as a rule, standard Building construction and unified dimensional schemes of structures.

Lit.: Baykov V. N., Strongin S. G., Ermolova D. I., Building structures, M., 1970; Building codes and regulations, part 2, section A, ch. 10. Building structures and foundations, M., 1972: Building structures, ed. A. M. Ovechkin and R. L. Mailyan. 2nd ed., M., 1974.

G. Sh. Podolsky

Article about the word Building construction" in the Great Soviet Encyclopedia has been read 27210 times

By function building construction subdivided into bearing and enclosing. There are also structures such as arches, trusses or frames. They are carriers. And such building structures as wall panels, shells, vaults combine both enclosing and load-bearing functions.

Bearing building structures depending on the design scheme, they are divided into flat (beams, trusses, frames, etc.) and spatial (shells, vaults, domes, etc.). Spatial building structures have a more favorable distribution of forces compared to flat structures. This, in turn, requires less material consumption, but the assembly and production of such building structures is extremely labor intensive. To date, new types of spatial structures have appeared - structural structures made of rolled profiles, fixed with bolted joints. This type of building structure is easy to manufacture and install, and economical.

Building structures by type of material are:

• concrete;

These are the most common types of construction structures at the moment.

Modern construction uses reinforced concrete in the form of prefabricated structures. The scope of such structures: the construction of residential, industrial buildings, various structures. The expedient use of monolithic reinforced concrete is various hydraulic structures, pavements of roads, airfields, construction of foundations for industrial equipment, all kinds of tanks, elevators, etc.

When erecting structures that are operated in an aggressive environment or special climatic conditions (for example, elevated temperature, humidity), special types of concrete and reinforced concrete are used. For example, such facilities are thermal units, buildings of the chemical industry and others.

AT reinforced concrete building structures due to the use of especially strong concretes, reinforcement, an increase in the production of stressed structures, it is permissible to reduce the mass of the structure, lower the price and consumption of materials, and increase the scope of light and cellular concretes.

Areas of application of building structures.

Scope of application steel building structures sometimes coincides with the use of reinforced concrete structures. These are, in particular, frames of large-span buildings, workshops with heavy and bulky equipment, large-capacity industrial tanks, bridges, etc. The choice of the type of building structure depends on its cost, construction area, and location of the enterprise. The main advantage of steel building structures over reinforced concrete structures is their low weight. This allows the use of these structures in inaccessible areas: in the Far North, in areas with increased seismic activity, desert, mountainous areas, etc.

The creation of productive three-dimensional structures (from thin-sheet steel), an increase in the use of high-strength steels and economical rolled profiles will make it possible to reduce the weight of buildings and structures.

Main Application stone building structures- construction of walls and partitions. Architectural structures and buildings made of bricks, small blocks and natural stone meet the requirements of industrial construction less than large-panel buildings, so their share in all construction volumes is falling.

Two types of glued wooden structures are also used in construction: load-bearing and enclosing. The load-bearing structures consist of several layers of wood and are glued together. Often they are reinforced by inserting reinforcement.

The production of glued wooden structures is carried out in the factory, all processes are carried out mechanically

The main trend in changing wooden structures is the transition to building structures from glued wood. The admissibility of industrial production and obtaining elements of a certain design of the desired dimensions by gluing them gives advantages in comparison with other types of wooden structures. Glued building structures are widely used in agricultural construction.

In the trends of modern construction, new types of industrial building structures: asbestos-cement, pneumatic, light alloy structures. The advantages of these designs are: low specific gravity, the possibility of prefabrication on mechanical production lines. Lighter three-layer panels are beginning to be used as enclosing structures instead of heavy reinforced concrete and expanded clay concrete panels.

Requirements for building structures.

For reasons of operational requirements, building construction must be fire-resistant, corrosion-resistant, convenient, economical and safe to use. With the increase in the scale and pace of construction, building structures are required to manufacture them in the factory, the structures must be economical in cost and optimal in terms of material consumption, convenient for transportation and distinguished by quick and easy assembly at the construction site.

Much attention is paid to reducing labor intensity, as in the manufacture building structures, and in the process of constructing buildings from them.

An important task of modern construction is to reduce masses of building structures through the use of lightweight productive materials and the development of various design solutions.

Calculation of building structures.

Building construction when designing, they are calculated for strength, stability and vibrations. The calculation takes into account the effects of forces that structures are subjected to during operation: their own weight, external loads, the influence of temperature factors, the displacement of structural supports, and the forces that appear during transportation and installation of building structures.

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

Classification and scope. 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 load-bearing functions, which corresponds to one of the most important trends in the development of modern building structures. Depending on the design scheme, load-bearing 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 consumption of materials; however, their manufacture and installation in many cases are very time-consuming. New types of spatial structures, such as structural structures made of rolled profiles with bolted joints, are both economical and relatively easy to manufacture and install. By 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 volume and in 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 chemically aggressive environments (thermal units, buildings and structures of ferrous and non-ferrous metallurgy, the chemical industry, etc.). Reducing the weight, reducing the cost and consumption of materials in reinforced concrete structures is possible through the use of high-strength concretes and reinforcement, an increase in the production of prestressed structures, and the expansion of applications for 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. 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, S.K. must meet their purpose, be fire-resistant and corrosion-resistant, safe, convenient and economical in operation.

Calculation of S.K. Building structures must be calculated for strength, stability and vibrations. This takes into account the force effects that structures are subjected to during operation (external loads, own weight), the effect of temperature, shrinkage, displacement of supports, etc. as well as the forces 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 perform load-bearing functions to one degree or another (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 separate 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 ensured by the rigid fastening of the rods in the junction or swivel joints and special stiffening elements that give the product or structure a geometrically unchanging shape. The increase in the rigidity of the frame is often achieved by including in the work of the shell, skin or walls of the product or structure.

Ceilings - horizontal load-bearing and enclosing structures. They perceive vertical and horizontal force effects 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 wear resistance, sufficient elasticity and noiselessness, and ease of cleaning. The design of the floor depends on the purpose and nature of the premises where it is arranged.

The roof is the external load-bearing and enclosing structure of the building, which perceives vertical (including snow) and horizontal loads and impacts. (Wind is a load.

Stairs in buildings serve for the 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 decision, the number of storeys, the intensity of the human flow, as well as fire safety requirements.

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

Question number 12. The behavior of buildings and structures in a fire, their fire resistance and fire hazard.

The loads and impacts to which a building is exposed under normal operating conditions are taken into account when calculating the strength of building structures. However, during fires, additional loads and impacts arise, which in many cases lead to the destruction of individual structures and buildings as a whole. Unfavorable 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 (bearing, enclosing) under fire conditions 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.

An indicator of fire resistance is the fire resistance limit, the fire hazard of a structure is characterized by its fire hazard class.

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 standard test conditions, are divided into building structures with the following fire resistance limits.

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

The fire resistance limit of building structures is set according to the time (in minutes) of the onset of one or several successively, normalized for a given structure, signs of limit states: loss of bearing capacity (R); loss of integrity (E); loss of heat-insulating 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 loss of integrity (E.

According to fire hazard, building structures are divided into four classes: KO (non-fire hazardous); K1 (low fire risk); K2 (moderately fire hazardous); KZ (fire hazardous.

Question No. 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 limit is on average 15 minutes. This is due to a fairly rapid decrease in the strength and deformation characteristics of the metal at elevated temperatures during a fire. The heating intensity of the MC (metal structure) depends on a number of factors, which include the nature of the heating of structures and methods for their protection. In the case of a short-term effect of temperature during a real fire, after the ignition of combustible materials, the metal is heated more slowly and less intensively than the heating of the environment. Under the action of the “standard” fire mode, the ambient temperature does not stop rising 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 a beam is exposed to high temperatures during a fire, the section of the structure quickly warms up to the same temperature. This reduces the yield strength and modulus of elasticity. The collapse of rolled beams is observed in the section where the maximum bending moment acts.

The effect of 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 typical for the stretched and compressed elements of the chords and the lattice of the structure.

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

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

Ways to improve fire resistance.

cladding made of non-combustible materials (concreting, cladding made of bricks, heat-insulating boards, gypsum boards, 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 state of a metal structure: =R n * tem.

— 2015-2017 year. (0.008sec.

Fires are easier to prevent than to put out. This rather common phrase is of great importance in the design of buildings and structures, when a fire can be prevented at the very early stage of ignition, or at least its further development.

In this, the so-called passive protection plays an important role - correctly executed structural, space-planning and engineering solutions for buildings and other building structures that ensure that the general requirements of fire protection are met at all stages of their creation and operation.

AT Article 34 of the Technical Regulations it is prescribed that building structures are classified by fire resistance to establish the possibility of their use in buildings, structures, structures and fire compartments of a certain degree of fire resistance or to determine the degree of fire resistance of buildings, structures, structures and fire compartments.

Building structures are classified according to fire hazard to determine the degree of participation of building structures in the development of a fire and their ability to form dangerous fire factors.

According to Article 35 of the Technical Regulations 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:

1) non-standardized;

2) at least 15 minutes;

3) at least 30 minutes;

4) at least 45 minutes;

5) at least 60 minutes;

6) at least 90 minutes;

7) at least 120 minutes;

8) at least 150 minutes;

9) at least 180 minutes;

10) at least 240 minutes;

11) at least 360 minutes.

The fire resistance limits of building structures are determined under standard test conditions. The onset of the fire resistance limits of load-bearing and enclosing building structures under standard test conditions or as a result of calculations is established by the time one or several of the following signs of limit states are reached:

1) loss of bearing capacity (R);

2) loss of integrity (E);

3) loss of thermal insulation due to an increase in temperature on the unheated surface of the structure to the limit values ​​(I) or the achievement of the limit value of the heat flux density at a normalized distance from the unheated surface of the structure (W).

The fire resistance limits of building structures are established in accordance with GOST 30247.0-94 “Building structures. Test methods for fire resistance. General requirements". In this case, the fire resistance limit of windows is set only by the time of loss of integrity (E).

The fire resistance limits of load-bearing and enclosing structures are established by GOST 30247.1-94 “Building structures. Test methods for fire resistance. Bearing and enclosing structures.

In accordance with the requirements of GOST 30247.0-94 and GOST 30247.1-94 in our country, building structures are tested for fire resistance, including metal ones with fire protection. The same regulatory documents set out the main provisions of the method for testing structures for fire resistance.

The essence of the method lies in the fact that a sample of the structure, made as life-size as possible, is heated in a special furnace and at the same time subjected to standard loads. In this case, the time from the start of the test to the appearance of one of the signs characterizing the onset of the fire resistance limit of the structure is determined.

To standardize the fire resistance limits of load-bearing and enclosing structures according to GOST 30247.1-94 the following limit states are used:

For columns, beams, trusses, arches and frames - only the loss of the bearing capacity of structures and nodes R;

For external bearing walls and coatings - loss of bearing capacity R and integrity E, for external non-bearing walls - integrity E;

For non-load-bearing internal walls and partitions - loss of heat-insulating capacity I and integrity E;

For load-bearing internal walls and fire barriers - loss of bearing capacity R, integrity E and heat-insulating capacity I.

The designation of the fire resistance limit consists of symbols standardized for a given design of limit states, as well as a number corresponding to the time to reach one of these states in minutes.

For example:

R 120 - fire resistance limit 120 min - according to the loss of bearing capacity;

RE 60 - fire resistance limit 60 min - for loss of bearing capacity and loss of integrity, regardless of which of the two limit states occurs earlier.

AT Article 36 of the Technical Regulations written:

1. Building structures for fire hazard are divided into the following classes:

1) non-flammable (K0);

2) low fire hazardous (K1);

3) moderately flammable (K2);

4) fire hazardous (K3).

2. The fire hazard class of building structures is determined in accordance with Table 6 of the Appendix to the Technical Regulations.

table 6 of the appendix to the Technical Regulations

The procedure for determining the fire hazard class of building structures

Fire hazard class of structures	Permissible size of damage to structures, centimeters	Availability	Permissible characteristics of the fire hazard of the damaged material +
Group
vertical	horizontal	thermal effect	burning	combustibility	flammability	smoke generating capacity
K0			missing	missing	missing	missing	missing
K1	no more than 40	no more than 25	not regulated	missing	no higher than G2+	not higher than B2+	not higher than D2+
K2	more than 40 but not more than 80	more than 25 but not more than 50	not regulated	missing	no higher than G3+	not higher than B3+	not higher than D2+
K3	not regulated

Note. The "+" sign means that in the absence of a thermal effect, it is not regulated.

3. The numerical values ​​of the criteria for attributing building structures to a certain fire hazard class are determined in accordance with the methods established by fire safety regulations.

Article 37 of the Technical Regulations states:

1. Fire barriers, depending on the method of preventing the spread of dangerous fire factors, are divided into the following types:

1) fire walls;

2) fireproof partitions;

3) fire protection ceilings;

4) fire breaks;

5) fire curtains, curtains and screens;

6) fire water curtains;

7) fire-prevention mineralized strips.

2. Fire walls, partitions and ceilings, filling openings in fire barriers (fire doors, gates, hatches, valves, windows, curtains, curtains) depending on the fire resistance limits of their enclosing part, as well as vestibules provided in the openings of fire barriers Depending on the types of elements of the vestibule locks, they are divided into the following types:

1) walls of the 1st or 2nd type;

2) partitions of the 1st or 2nd type;

3) floors of the 1st, 2nd, 3rd or 4th type;

4) doors, gates, hatches, valves, type 1, 2 or 3;

screens, curtains

5) windows 1, 2 or 3rd type;

6) curtains 1st type;

7) vestibule locks of the 1st or 2nd type.

3. The assignment of fire barriers to one type or another, depending on the fire resistance limits of the elements of fire barriers and the types of filling of openings in them, is carried out in accordance with Article 88 of this Federal Law.

In Article 58 of the Technical Regulations stated:

1. Fire resistance and fire hazard class of building structures must be ensured through their design solutions, the use of appropriate building materials, and the use of fire protection equipment.

2. The required fire resistance limits of building structures, selected depending on the degree of fire resistance of buildings, structures and structures, are given in Table 21 of the Appendix to this Federal Law.

table 21 of the appendix to the Technical Regulations