By functional purpose Long-span buildings can be divided into:

1) public buildings (theatres, exhibition pavilions, cinemas, concert and sports halls, indoor stadiums, markets, train stations);

2) special purpose buildings (hangars, garages);

3) industrial buildings (aviation, shipbuilding and machine-building plants, laboratory buildings of various industries).

Load-bearing structures according to the design diagram are divided into:

Block,

Arched,

Structural,

Dome,

Hanging,

Mesh shells.

The choice of one or another scheme of load-bearing structures of a building depends on a number of factors: the span of the building, the architectural and planning solution and the shape of the building, the presence and type of suspended transport, requirements for the rigidity of the coating, type of roof, aeration and lighting, base for foundations, etc. .

Structures with large spans are objects of individual construction; their architectural and structural solutions are very individual, which limits the possibilities of typing and unifying their structures.

The structures of such buildings operate mainly under loads from the structure’s own weight and atmospheric influences.

1.1 Beam structures

Beam long-span roofing structures consist of main load-bearing transverse structures in the form of flat or spatial trusses (truss span from 40 to 100 m) and intermediate structures in the form of ties, purlins and roofing.

According to the outline of the farm there are: with parallel belts, trapezoidal, polygonal, triangular, segmental (see diagrams in Fig. 1).

Truss height hf=1/8 ÷ 1/14L; slope i=1/ 2 ÷ 1/15.

Triangular trusses hf= 1/12 ÷ 1/20L; slope of belts i=1/5 ÷ 1/7.

Fig. 1 - Schemes of construction trusses

Truss cross sections:

When L > 36m, one of the supports of the beam truss is installed movable.

Coverage layout- vertical and horizontal connections along the coating are solved similarly to industrial buildings with roof trusses.

A) normal layout

wall

b) complicated layout - with rafter trusses:

PF

Beam coating schemes are used:

For any types of supporting structures - brick or concrete walls, columns (metal or reinforced concrete);

When supporting structures cannot absorb thrust forces;

When constructing buildings on subsidence or karst soils and undermined areas.

It should be noted that beam roofing schemes are heavier than frame and arched ones, but are easy to manufacture and install.

Truss calculations are performed using methods structural mechanics(similar to the calculation of trusses for industrial buildings).

1.2 Frame structures

Frame structures for building roofs are used for spans

L=40 - 150m, with a span L > 150m they become uneconomical.

Advantages of frame structures Compared to beams, this means less weight, greater rigidity and lower height of the crossbars.

Flaws- large width of columns, sensitivity to uneven settlements of supports and changes in T o.

Frame structures are effective when the linear stiffness of the columns is close to the linear stiffness of the crossbars, which makes it possible to redistribute the forces from vertical loads and significantly lighten the crossbars.

When covering large spans, as a rule, double-hinged and hingeless frames of a wide variety of shapes are used (see Fig. 2).

Rice. 2 - Schemes of through frames

Hingeless frames are more rigid and economical in terms of material consumption, however, they require the construction of powerful foundations and are sensitive to changes in temperature.

For large spans and loads, the frame crossbars are designed as heavy trusses; for relatively small spans (40-50m) they have the same sections and components as light trusses.

The cross sections of the frames are similar to beam trusses.

Frame and cover layout from frame structures is similar to the solution of frames of industrial buildings and beam coverings.

Static calculations of frame structures are performed using structural mechanics methods and specially developed computer programs.

Heavy through frames are designed as lattice systems, taking into account the deformation of all lattice rods.

1.3 Arched structures

Arched roof structures for long-span buildings turn out to be more cost-effective in terms of material consumption than beam and frame systems. However, a significant thrust arises in them, which is transmitted through the foundations to the ground or a tightening is arranged to absorb it (i.e., extinguishing the thrust within the system).

The patterns and outlines of arches are very diverse: double-hinged, three-hinged, hingeless (see Fig. 3).

The most favorable height of the arches: f=1/4 ÷ 1/6 span L.

Arch section height:

Solid wall 1/50 ÷ 1/80 L,

Lattice 1/30 ÷ 1/60 L.

Fig.4- Schemes of supporting hinges of arches and frames (a - tiled,

b - fifth wheel, c - balancer:

1 - plate, 2 - axle, 3 - balancer).

Rice. 5- Key hinges and arches

(a - tile; b - balanced; c - sheet; d - bolted)

After determining M, N, Q, the sections of the arch rods are selected in the same way as the sections of the stubble trusses:

1.4 Spatial structures of coverings of long-span buildings

In beam, frame and arched coating systems consisting of individual load-bearing elements, the load is transmitted only in one direction - along the load-bearing element. In these coating systems, the load-bearing elements are connected to each other by light connections, which are not intended to redistribute loads between the load-bearing elements, but only ensure their spatial stability, i.e. with their help it is ensured HDD coverings.

In spatial systems, connections are strengthened and involved in the distribution of loads and their transfer to supports. The load applied to the spatial structure is transmitted in two directions. This design is usually lighter than a flat one.

Spatial structures can be flat (slabs) and curved (shells).

To ensure the necessary rigidity, flat spatial systems (excluding hanging ones) must be double-belted - forming a mesh system along the surface. Double-belt structures have two parallel mesh surfaces connected to each other by rigid connections.

Single-layer structures with a curved surface system are called single-mesh.

In such designs, the principle of material concentration is replaced by the principle of multiply connected systems. The manufacture and installation of such structures is very labor-intensive and requires special manufacturing and installation techniques, which is one of the reasons for their limited use.

1.5 Spatial grid systems flat coverings

In construction, mesh systems of regular structure, the so-called structural designs or simply structures, which are used in the form of flat coverings of long-span public and industrial buildings.

Flat structures are structures formed from various systems of cross trusses (see Fig. 6):

1) Structures formed from cross trusses running in three directions. Therefore, they are the most rigid, but more difficult to manufacture. These are structures with belt meshes of scalene triangles.

2) Structures formed from trusses running in two directions. These are structures with belt meshes made of square cells.

3) Structures formed from trusses, also running in two directions, but reinforced with diagonals in the corner areas. That's why they are tougher.

Advantages of structures:

Greater spatial rigidity: large spans can be covered with different support contours or column grids; get expressive architectural solutions at the height of the structure.

Hstructures=1/12 - 1/20 L

Repeatability of rods - from standard and same type of rods it is possible to mount coverings of different spans and plan configurations (rectangular, square, triangular and curved).

Allows you to attach suspended transport and change the direction of its movement if necessary.

Structural roofing systems can be either single-span or multi-span, supported by both walls and columns.

The installation of cantilever overhangs behind the line of supports reduces the calculated span bending moment and significantly facilitates the construction of the coating.

Rice. 6- Diagrams of structural covering grids (a - with belt meshes made of equilateral triangular cells; b - with belt meshes made of square cells; c - the same, reinforced with diagonals in conditional zones: 1 - upper chords,

2 - lower chords, 3 - inclined braces, 4 - upper diagonals, 5 - lower diagonals, 6 - support contour).

Disadvantages of structures- increased complexity of manufacturing and installation. Spatial joints of rods (see Fig. 7) are the most complex elements in structures:

Ball insert (a);

On screws (b);

A cylindrical core with slots, tightened with one bolt and washers (c, d);

Welded assembly of flattened ends of rods (e).

Rice. 7 - Interface nodes for structure rods

Structural structures are repeatedly statically indeterminate systems. Their exact calculation is complex and is performed on a computer.

In a simplified approach, structures are calculated using structural mechanics methods - as isotropic slabs or as systems of cross trusses without taking into account torques.

The magnitudes of moments and shear forces are determined using tables for calculating slabs: M slabs; Qplates - then proceed to the calculation of rods.

1.6 Shell coatings

For building coverings, single-mesh, double-mesh cylindrical shells and double-curvature shells are used.

Cylindrical shells (see Fig. 8) are made in the form of arches with support:

a) rectilinear generatrix of the contour

b) on the end diaphragms

c) on end diaphragms with intermediate supports

Fig.8- Schemes for supporting cylindrical shells (1 - shell;

2 - end diaphragm; 3 - connections; 4 - columns).

Single-mesh shells are used for spans B of no more than 30 m.

Double mesh - for large spans B>30m.

On the cylindrical surface there are rods that form meshes of various systems (see Fig. 9):

Diamond mesh (a);

Rhombic mesh with longitudinal ribs (b);

Rhombic mesh with transverse ribs (c);

Rhombic mesh with transverse and longitudinal ribs (d).

The simplest mesh of a rhombic pattern, which is obtained from light standard rods (∟, ○, □) of rolled profiles. However, this scheme does not provide the necessary rigidity in the longitudinal direction when transferring the load to the longitudinal walls.

Rice. 9 - Mesh system of single mesh shells

The rigidity of the structure increases significantly in the presence of longitudinal rods (diagram “b”) - the structure can work as a shell with span L. In this case, the support can be end walls or four columns with end diaphragms.

The most rigid and advantageous are the meshes (pattern “c”), which have both longitudinal and transverse ribs (rods), and the mesh lattice is directed at an angle of 45.

Calculation of shells is performed using methods of elasticity theory and methods of shell theory. Shells without transverse ribs calculated as momentless folds (Ellers method). If there are transverse ribs, ensuring the rigidity of the contour - according to Vlasov’s moment theory (it comes down to solving eight-term equations).

When calculating through mesh shells, through faces of structures are replaced by solid plates of equivalent thickness when working in shear, axial tension and compression.

More accurate calculations of mesh shells are performed on a computer using specially developed programs.

Double mesh shells used when covering spans with a width of more than B>30m.

Their design diagrams are similar to those of double-mesh flat slabs- structures. As in structures, they are formed by systems of cross trusses connected along the upper and lower chords by special connections - a lattice. But at the same time, in shells, the main role in the perception of forces belongs to curved mesh planes; the lattice connecting them is less involved in the transmission of forces, but gives the structure greater rigidity.

Compared to single-mesh shells, double-mesh shells have greater rigidity and load-bearing capacity. They can cover spans of buildings from 30 to 700 m.

They are designed in the form of a cylindrical surface, supported by longitudinal walls or metal columns. At the ends of the shell they rest on rigid diaphragms (walls, trusses, arches with a tie, etc.).

The best distribution of forces in the shell is at B=L.

The distance between the mesh surfaces is h=1/20÷1/100R at f/B=1/6÷1/10.

As in structures, the most complex is the joint of the rods.

Calculation of two-mesh shells is carried out on a computer using specially designed programs.

For an approximate calculation of the shell, it is necessary to reduce the rod system to an equivalent solid shell and establish the shear modulus of the middle layer, which is equivalent in rigidity to the connecting lattice.

1.7 Dome coverings

There are dome designs four types(see Fig. 6): ribbed (a), ribbed-ring (b), mesh (c), radial-beam (d).

Rice. 10- Dome schemes

Ribbed domes

The structures of ribbed domes consist of individual flat or spatial ribs in the form of beams, trusses or semi-arches, located in the radial direction and interconnected by girders.

The upper belts of the ribs form the surface of the dome (usually spherical). The roof is laid along the purlins.

At the apex, to reconnect the ribs, a rigid ring is installed that works for compression. The ribs can be hinged or rigidly attached to the central ring. A pair of dome ribs located in the same diametrical plane and interrupted by a central ring is considered as a single, for example arched, structure (two-hinged, three-hinged or hingeless).

Ribbed domes are spacer systems. The expansion is perceived by walls or a special spacer ring in the shape of a circle or polyhedron with rigid or hinged joints in the corners.

Between the ribs, with a certain pitch, ring purlins are laid, on which the roofing decking. Shoulder straps, in addition to their main purpose, provide general stability of the upper belt of the ribs out of the plane, reducing their design length.

To ensure the overall rigidity of the dome in the plane of the purlins, pitched connections between the ribs are arranged at a certain pitch, as well as vertical connections to decouple the internal belt of the arch - spacers are arranged between the vertical connections.

Design loads- own weight of the structure, weight of equipment and atmospheric influences.

The design elements of the dome cover are: ribs, support and central rings, purlins, pitched and vertical connections.

If the expansion of the dome is perceived by a spacer ring, then when calculating the arch, the ring can be replaced by a conditional tightening located in the plane of each pair of semi-arches (forming a flat arch).

When calculating the support ring - with a frequent arrangement of arches (ribs) of the dome, the action of their thrusts can be replaced by an equivalent uniformly distributed load:

Ribbed-ring domes

In them, shoulder straps with ribs form one rigid spatial system. In this case, the annular girders work not only in bending from the load on the coating, but also from the reactions of the intermediate ribs and perceive tensile or compressive annular forces arising from thrusts at the point of support of the multi-span semi-arches.

The weight of the ribs (arches) in such a dome is reduced due to the inclusion of ring girders as intermediate support rings. The annular ribs in such a dome work in the same way as the support ring in a ribbed dome, and when calculating arches they can be replaced by conditional tightening.

With a symmetrical load, the calculation of the dome can be carried out by dividing it into flat arches with ties at the level of the annular ribs (purlins).

Mesh domes

If you increase the connectivity of the system in a ribbed or ribbed-ring dome, you can get mesh domes with hinged connections of the rods at the nodes.

In mesh domes, between the ribs (arches) and rings (ring purlins) there are braces, thanks to which the forces are distributed over the surface of the dome. In this case, the rods work mainly only on axial forces, which reduces the weight of the ribs (arches) and rings.

The rods of mesh domes are made of closed profiles (round, square or rectangular cross-section). Joints of rods as in structures or mesh shells.

Mesh domes are calculated on a computer using specially developed programs.

They are approximately calculated according to the momentless theory of shells - as a continuous axisymmetric shell using formulas from the corresponding theoretical reference books.

Radial beam domes

They are ribbed domes made up of segmented semi-trusses arranged radially. In the center, segmental semi-trusses are connected to a rigid ring (lattice or solid-wall with stiffening diaphragms).

1.8 Hanging coverings

Hanging coatings are those in which the main load-bearing elements work in tension.

These elements make full use of high-strength steels, since they load bearing capacity determined by strength, not stability.

Load-bearing stretched rods - cables - can be made flexible or rigid.

Hard- made from curved I-beams.

Flexible- made of steel ropes (cables) twisted from high-strength wire with R = 120 kN/cm2 ÷ 240 kN/cm2.

Hanging roof structures are one of the most promising structural forms for the use of high-strength materials. The structural elements of hanging roofs are easy to transport and relatively easy to install. However, the construction of suspended coverings has a number of difficulties, the successful engineering solution of which determines the effectiveness of the covering as a whole:

First drawback- hanging coverings are expansion systems and to absorb the thrust, a supporting structure is required, the cost of which can be a significant part of the cost of the entire covering. Reducing the cost of supporting structures can be achieved by increasing the efficiency of their work - creating coverings of round, oval and other non-rectilinear plan shapes;

second drawback- increased deformability of hanging systems. This is due to the fact that the modulus of elasticity of twisted cables is less than that of rolled steel (Etrosa = 1.5 ÷ 1.8 × 10 5 MPa; E rolled rods = 2.06 × 10 5 MPa), and the area elastic work high-strength steel is significantly greater than that of ordinary steel. Thus, the relative deformation of the cable in the elastic stage of work, ε = G/E, is several times greater than for elements made of ordinary steel.

Most suspended covering systems are instant stiffening systems, i.e. systems that work elastically only under equilibrium loads, and under the action of uneven loads in them, in addition to elastic deformations, kinematic displacements of the system also appear, leading to a change in the integrity of the geometric coating system.

To reduce kinematic movements, suspended coating systems are often equipped with special stabilizing devices and pre-stressed.

Types of Hanging Schemes

1. Single-belt systems with flexible cables

Such coating systems are designed rectangular or curved in plan, for example, round (see Fig. 11).

They are prestressed reinforced concrete shells that work in tension. The stressed reinforcement in them is a system of flexible cables, on which prefabricated cables are laid during installation. reinforced concrete slabs. At this time, an additional weight is placed on the cables, which is removed after laying all the reinforced concrete slabs and sealing the seams. The cables compress the reinforced concrete slabs and the resulting reinforced concrete shell receives a preliminary compressive stress, allowing it to absorb tensile stress from external loads and ensure the overall stability of the structure. The load-bearing capacity of the coating is ensured by the tension of the cables.

In rectangular roofs, the thrust of the cables is absorbed by a supporting structure of guys and anchors fixed in the ground.

Rice. eleven- Single-belt coverings with flexible cables

(a - rectangular in plan; b - round in plan)

In coverings of a round (oval) plan, the thrust is transmitted to the outer compressed ring lying on the columns and the inner (stretched) metal ring.

The sag of the cables of such coverings is usually f=1/10÷1/20 L. Such shells are flat.

The cross-section of the roof cables is determined by installation load. In this case, the cables work as separate threads, and the expansion in them can be determined without taking into account their deformations H=M/f, where M is the beam moment from the design load, f is the sag of the thread.

where V is the beam reaction.

2. Single-belt systems with rigid cables

Rice. 12- 1 - longitudinal flexural-rigid ribs; 2 - transverse ribs;

3 - aluminum membrane, t = 1.5 mm

In such coverings, bent rigid cables attached to the support belt operate under the action of a tensile load with bending. Moreover, under the action of a uniform load, the proportion of bending in stresses is small. Under the action of an uneven load, rigid cables begin to strongly resist local bending, which significantly reduces the deformability of the entire coating.

The sag of the cables of such coverings is usually 1/20 ÷ 1/30 L. However, the use of rigid threads is possible only for small spans, because As the span increases, installation becomes significantly more complicated and their weight increases. Such rigid cables can be used to lay a lightweight roof; there is no need for prestressing (its role is played by the flexural rigidity of the cable).

With a uniform load, the thrust in the cable stay is determined by the formula

H = 8/3 ×[(EA)/(l 2 mо)] × (f+fо) × ∆f +Ho;

where ∆f=f–fо,

f - deflection under load,

fo – initial sag;

m1=1+(16/3)/(fo/l) 2

The bending moment in the middle of the cable is found by the formula

M= q I 2 /8–Hf.

3. Single chord suspended roofs, tensioned using transverse beams or trusses

Rice. 13

Stabilization of such cable-beam systems is achieved either by an increased mass of transverse and flexurally rigid elements, or by prestressing guy wires that connect transverse beams or trusses to foundations or supports. Light roof coverings are tensioned in this way.

Thanks to the bending rigidity of the transverse beams or trusses, the coating acquires spatial rigidity, which is especially evident when the span structure is loaded with local load.

4. Two-belt systems

Rice. 14

Coatings of this type have two cable systems:

- Bearers- having a downward bend;

- Stabilizing- having an upward bend.

This makes such a system instantly rigid - capable of absorbing loads acting in two different directions. The vertical load causes the supporting thread stretching, and for the stabilizing one - compression. The wind suction causes forces of the opposite sign in the cables.

Light roofs can be used in this type of coating.

5. Saddle-shaped strained meshes

Rice. 15

Coatings of this type are used for permanent buildings and temporary structures.

Covering mesh: The supporting (longitudinal) cables are curved downwards, the stabilizing (transverse) cables are curved upwards.

This form of coating allows the mesh to be pre-stressed. The coating surface is light and made from various materials: from steel sheet to film and awning.

The grid spacing is approximately one meter. Accurate calculation of the meshes of such coatings is possible only on a computer.

6. Metal shell membranes

Rice. 16

The shape in plan is an ellipse or a circle, and the shape of the shells is quite diverse: cylindrical, conical, bowl-shaped, saddle-shaped and tent-shaped. Most of them work according to a spatial scheme, making it very profitable and allowing the use of sheets with a thickness of 2 - 5mm.

The calculation of such systems is carried out on a computer.

Main advantage Such coating systems are a combination of load-bearing and enclosing functions.

Insulation and waterproofing are laid on the supporting shell without using roofing slabs.

Shell panels are produced at the manufacturing plant and delivered for installation in the form of rolls, from which the entire shell is assembled at the construction site without the use of scaffolding.

Section 2. Sheet structures

Sheet structures are structures consisting mainly of metal sheets and intended for storing and transporting liquids, gases and bulk materials.

These designs include:

Tanks for storing petroleum products, water and other liquids.

Gas tanks for storage and distribution of gases.

Bunkers and silos for storage and handling of bulk materials.

Large diameter pipelines for transporting liquids, gases and crushed or liquefied solids.

Special designs for metallurgical, chemical and other industries:

Blast furnace casings

Air heaters

Dust collectors - scrubbers, housings for electrostatic precipitators and bag filters

Smoke pipes

Solid wall towers

Cooling towers, etc.

Such sheet structures occupy 30% of all metal structures.

Operating conditions for sheet structures quite varied:

They can be above-ground, above-ground, semi-buried, underground, underwater;

Can perceive static and dynamic loads;

Work under low, medium and high pressure;

Under the influence of low and high temperatures, neutral and aggressive environments.

They are characterized by a two-basic stress state, and in places where they are coupled with the bottom and stiffeners, in places where shells of different curvature are coupled (i.e., at the boundary of changes in the radius of curvature), local high voltage, quickly attenuating as they move away from these areas - this is the so-called edge effect phenomenon.

Sheet structures always combine load-bearing and enclosing functions.

Welded joints of elements of sheet structures are made end-to-end, overlapping and end-to-end. Connections are made using automatic and semi-automatic arc welding.

Most sheet structures are thin-walled rotation shells.

Shells are calculated using the methods of elasticity theory and shell theory.

Sheet structures are designed for strength, stability and endurance.

1.1 Reservoirs

Depending on the position in space and geometric shape they are divided into cylindrical (vertical and horizontal), spherical and teardrop-shaped.

Based on their location relative to the planning level of the earth, they are distinguished: above-ground (on supports), above-ground, semi-buried, underground and underwater.

They can be of constant and variable volumes.

The type of tank is selected depending on the properties of the stored liquid, operating mode, and climatic characteristics of the construction area.

Most widespread received vertical and horizontal cylindrical tanks as the easiest to manufacture and install.

Vertical tanks with fixed roof are low-pressure vessels in which petroleum products are stored with low turnover (10 - 12 times a year). They generate excess pressure in the steam-air zone of up to 2 kPa, and when emptying, a vacuum (up to 0.25 kPa).

Vertical tanks with floating roof and pontoon used for storing petroleum products with high turnover. There is practically no excess pressure and vacuum in them.

High pressure tanks (up to 30 kPa) are used for long-term storage petroleum products with their turnover no more than 10 - 12 times a year.

Spherical tanks- for storing large volumes of liquefied gases.

Drop-shaped tanks- for storing gasoline with high vapor pressure.

Vertical tanks

Rice. 17

Essential elements:

Wall (body);

Roof (coverings).

All structural elements are made of sheet steel. They are easy to manufacture and install, and are quite economical in terms of steel consumption.

The optimal dimensions of a vertical cylindrical tank of constant volume have been established, at which the metal consumption will be the least. Thus, a tank with a wall of constant thickness has a minimum mass if

[(mdn + mpok) / mst] = 2, and the value optimal height reservoir is determined by the formula

where V is the volume of the tank,

∆= t day+t add. cover - the sum of the reduced thickness of the bottom and coating,

tst. - thickness of the housing wall.

In large-volume tanks, the wall thickness varies in height. The mass of such a tank will be minimal if the total mass of the bottom and cover is equal to the mass of the wall, i.e. mday + mcover = mst.

In this case

where ∆= tday. + tpriv. cover,

n - overload factor,

γ f. - specific gravity of the liquid.

Tank bottom

Since the bottom of the tank rests over its entire area on a sandy base, it experiences minor stresses from liquid pressure. Therefore, the thickness of the bottom sheet is not calculated, but is taken structurally, taking into account ease of installation and corrosion resistance.

At V≤1000m and D<15м → tдн = 4мм; при V>1000m and D=18-25m → tdn = 5mm; at D > 25m → tdn = 6mm. Rice. 18

The sheets of the bottom panels are connected to each other along the longitudinal edges with an overlap with an overlap of 30 - 60 mm at tday. = 4 - 5mm, and when tday = 6mm - they are performed end-to-end. The outer sheets - “edges” - are 1-2mm thicker than the sheets in the middle part of the bottom. Everything is supplied from the manufacturer in rolls (Q ≤ 60t).

Wall construction:

Rice. 19

The tank wall consists of a number of belts with a height equal to the width of the sheet. The belts are connected to each other end-to-end or overlapped in a telescopic or stepwise manner. Butt mating is performed mainly at the manufacturer's factory (less often during installation), while lap jointing is performed both at the factory and during installation.

A common method for constructing tanks is by rolling.

Strength calculation- the housing wall is a load-bearing element and is calculated using the limit state method in accordance with the requirements of SNiP 11-23-81

Constructive decisions metal coatings long-span buildings can be beam, arched, spatial, hanging Byte, membrane, etc. Considering that in such structures the main load is its own weight, one should strive to reduce it, which is achieved by using high-strength steels and aluminum alloys.

Beam systems (usually trusses) are included in the transverse frames, which improves the static design of work. For spans of more than 60-80 m, it is advisable to use arched coverings (Fig. 1). For large spans, it is advisable to design such coatings pre-stressed. In the arched covering shown in Fig. 2, the upper chord is provided rigid, and the lower chord and the arch grille are made of cables. After installation of the arch, the support units are forced to shift outward, which causes preliminary tension in the lower chord and braces of the arch.

Picture 1. 1 - arch; 2 - tightening; 3 - fixed hinge support; 4 - movable hinge support

Figure 2.1 - cable; 2 - hard belt

Spatial lattice coating structures can be flat two-layer (double-mesh) and curved single-layer (single-mesh) or two-layer. In double-mesh structures, two parallel mesh surfaces are connected to each other by lattice connections.

Mesh systems with a regular structure are called structural and are used, as a rule, in the form of flat coverings. They represent various systems cross trusses (Fig. 3). Structural flat floors, due to their high spatial rigidity, have a small height (1/16-1/20 of the span); they can cover large spans. By installing cantilever overhangs behind the support line, a reduction in bending moments and the weight of the coating is achieved.

Figure 3. 1,2 - upper and lower waist mesh; 3 - braces; 4 - tetrahedron; 5 - octahedron; 6 - supporting capital

Curvilinear spatial coverings usually have a cylindrical or dome surface.

Cylindrical coatings can be single-mesh or double-mesh (curvilinear structures). In the transverse direction they act as a vault, the thrust of which is perceived by the walls or ties.

Dome coverings can have a ribbed (or ribbed-ring) design (Fig. 4a) or a mesh design (Fig. 4b). In ribbed domes, radially located ribs are connected to each other by ring girders. If the latter form a single rigid spatial system with the ribs, then the annular girders work not only for local bending, but as part of the dome system they also perceive annular compressive or tensile forces. In mesh domes, the structure, in addition to ribs and ring elements, includes braces, which creates conditions under which the rods work only on axial forces.

Figure 4. a - ribbed; b - mesh

Suspended coverings consist of a supporting contour and main load-bearing elements in the form of cables or thin steel sheets working in tension. Since the main elements of the covering work in tension, their load-bearing capacity is determined by strength (rather than stability), which allows the effective use of high-strength ropes or sheet steel. Such coatings are very economical, but increased deformability limits their use for coatings of industrial buildings. In addition, given the large expansion of such systems, it is advisable to take the plan form round, oval or polygonal, which makes it easier to perceive the expansion. In this regard, they are mainly used for covering sports buildings, indoor markets, exhibition halls, warehouses, garages and other large span buildings.

The composition of cable-stayed suspended coverings includes flexible cables (steel ropes or reinforcing bars), located in the radial direction (Fig. 5a), in orthogonal directions (Fig. 5b) or parallel to each other in the same direction (Fig. 6). Curvilinear closed support contours work primarily in compression, and the central ring works in tension. In these cases, only vertical forces are transmitted to the structures supporting the coating (walls, columns, frames). In contrast, with open contours, the thrust is transferred to bearing structures buildings, which requires the installation of anchor foundations that work to pull out, or walls with buttresses, etc. Light reinforced concrete or metal slabs with polymer insulation, three-layer, etc. are laid on the cable system.

Figure 5. a - radial arrangement of the cables; b - orthogonal; 1 - shrouds; 2 - support contour; 3 - central ring

Figure 6. 1,2 - shrouds in the middle and at the end, respectively; 3 - support contour; 4 - reinforced concrete slabs; 5 - anchor foundation

Suspended cable roofing systems are very diverse. A tent cable-stayed system is often used, in which the central ring rests on a column and rises to a higher level than the supporting contour one.

An example of such a system is the covering of a bus depot in Kyiv with a diameter of 161 m. The systems described above are single-belt. In addition to them, two-belt systems are also used (especially under high wind loads), in which the stabilization of the coating is carried out using a reverse curvature contour. In such systems, the supporting cables have a downward bend, and the stabilizing ones - upward. Stabilizing cables with a deck installed on them can be located above the load-bearing ones, which causes compression of the struts (Fig. 7a). When stabilizing cables are located under the load-bearing cables, the connections between them will be stretched (Fig. 7b). A third option is also possible, in which the supporting and stabilizing cables intersect, and the racks are compressed in the middle part of the covering and stretched in the outer parts (Fig. 7b).

Figure 7. 1 - stabilizing shrouds; 2 - racks; 3 - load-bearing cables

Hanging thin-sheet systems - membrane coatings - have also become widespread in foreign and domestic practice.

They are a spatial structure made of a thin metal sheet (steel or aluminum alloys) several millimeters thick, fixed around the perimeter in a supporting contour. Their advantages are the combination of load-bearing and enclosing functions, as well as increased industrial production. In some cases, instead of a continuous membrane, the coating is formed from separate thin steel strips that are not connected to each other. The tapes located in two mutually perpendicular directions can be intertwined, which prevents their delamination.

A continuous membrane covering was successfully used for a universal stadium on Mira Avenue in Moscow, the dimensions of which reach 183x224 m (Fig. 8).

Figure 8. Structural diagram of the covering of the universal stadium on Mira Avenue in Moscow (steel membrane 5 mm thick): a - plan; b - longitudinal section; in - transverse

The sports complex, built in Bishkek, includes a hall for 3 thousand spectators, the covering of which is designed in the form of a prestressed membrane-beam hanging system (Fig. 9). The frame of the building is made of a monolithic reinforced concrete building in the form of braced trusses located along the perimeter with plan dimensions of 42.5 x 65.15 m. The covering consists of a 2 mm thick membrane itself, longitudinal girders and transverse beams - struts. The insulation in the form of mineral wool mats is suspended from the membrane from below, the ceiling is made of stamped aluminum elements.

Membrane coverings are also used in a number of other long-span buildings. So, in St. Petersburg, universal gym with a diameter of 160 m, it is covered with a membrane shell with a thickness of 6 mm. Similar shells also cover a universal sports hall with plan dimensions of 66x72 m for 5 thousand spectators in Izmailovo (Moscow), the Pioneer swimming pool building with plan dimensions of 30x63 m in Kharkov, etc.

Folded roofing vaults are a spatial structure that can be made of metal (steel, aluminum alloys), reinforced concrete, and plastics.

Such coatings made of aluminum alloys are especially effective. The main structural element in the latter can be a diamond-shaped sheet (Fig. 10), bent along a larger diagonal. The diamond-shaped elements can be connected to each other using cylindrical hinges or rigid flange joints. To increase the spatial rigidity of the coating (especially with hinge joints), it is necessary

provide for the installation of longitudinal ties along the protruding nodes of the folded arch.

Figure 9. 1 - building frame; 2 - membrane-beam hanging system

Figure 10.

Long-span coverings are flat, spatial and pneumatic. These coatings are used in public and industrial buildings.

Flat structures are made from beams, trusses, frames, arches, which are made from laminated wood, rolled steel, monolithic and precast reinforced concrete.

Reinforced concrete beams are used to span spans up to 24 m. Beams are used in T- and U-shaped sections.

Trusses and frames (hinged and hinged) made of wood, steel and reinforced concrete cover spans of up to 60 m.

Hingeless frames are rigidly embedded in the foundation. They are very sensitive to uneven precipitation. Therefore, they are used on strong and homogeneous soils. Hinged frames are less sensitive to uneven ground settlements. There are one-, two- and three-hinged frames. Single-hinged - the hinge is in the middle of the span. Double-hinged - hinges in the supports.

Arches are effective structures for covering large spans, because... their outlines can be approximated to the pressure curve and thus the material can be used optimally. Horizontal forces (thrust) arising in arched structures decrease as the radius of the arch outline increases. At the same time, the lifting boom of the arch increases, and, consequently, the construction volume of the building. This leads to an increase in heating costs and levelized costs. Arches are widespread in the coverings of large span sports buildings.

Spatial structures - cross coverings, domes, shells, hanging coverings.

Cross coverings can be folded or mesh.

For covering large spans, folded coatings made of reinforced concrete (up to 50 m) and reinforced cement (up to 60 m) are used. They are formed by flat intersecting elements across the span. Folds are: rectangular and cylindrical; sawtooth; in the form of triangular planes; prismatic type; trapezoidal profile, etc.

Mesh coverings made of reinforced concrete are designed for spans of up to 50 m, and of steel elements - up to 100 m. In these coverings, reinforced concrete and steel triangles intersect. The elements work in two directions, so their height is less than that of beams - this reduces the volume of the building.

Cross structures and systems with flat trusses and frames are made open to the interior. Often they make suspended ceilings, which are strengthened to the bottom of the trusses.

The dome is the most ancient structure. It was used because it is possible to select such shapes that no tensile forces arise in the elements of the arch. In halls where it is desirable to create a large air space (markets, gyms) and where there are no high ongoing heating costs, use various types dome structures made of monolithic or prefabricated reinforced concrete, dome-membranes made of steel sheet 3 mm thick with insulation glued underneath. Temporary exhibition halls are made of glued-plastic structures.

Suspended coverings cover spans of up to 100 m. The main elements of these coverings work in tension and transfer loads from the covering to the anchors. They have curvilinear outlines and are flexible or rigid threads, membranes or hanging trusses. According to their design features, hanging coverings are distinguished: single-belt; two-belt; hyparas (hyperbolic paraboloids) and cable-stayed ones.

In suspended coverings, the load-bearing elements are steel cables. They are pulled through some supporting structure and strengthened with stretch marks. Advantages of hanging structures - saving metal and more efficient use load-bearing elements compared to beam and frame structures, because the cables work in tension. Disadvantages: hanging roofings have low rigidity, so the roofing deck is often deformed; it is difficult to ensure the removal of atmospheric moisture.

Single-belt coverings are used more often than others, because They are technologically advanced to manufacture and easy to install. They can give the structure the most different shapes. Single-belt coverings consist of a system of radial or intersecting braces that transmit horizontal forces to rigid frames, rack frames or closed loop tie beams. Plates are hung on the guy wires, and under this load the guy wires stretch. At this time, the seams between the slabs are cemented and the joints are welded. Due to the elastic deformations of the threads, the plates are compressed, and the structure begins to work as a monolithic shell. In cylindrical coverings, a slight curvature of the covering is created in the direction perpendicular to the axes of the threads. This is done to drain rainwater. From parabolic systems in the shape of an inverted dome, water flows to the center of the coating and is removed internal drain. Risers are installed around the perimeter of the hall, and horizontal distribution pipelines are hidden in the suspended ceiling. The easiest way to drain water is from tent coverings.

In double-belt coverings, two concave belts are used, connected by tensioned threads. The most common are circular ones in terms of design. The threads along the perimeter are attached to the outer ring, and in the center - to the inner one. Depending on the height of the central ring, the system can be made concave or convex. The convex system allows you to raise the central part of the covering and thereby divert water to the outer walls, without resorting to horizontal routing of gutters, and use a folded covering system.

Hyparas (hyperbolic paraboloids) are saddle-shaped hanging coverings. They are formed into lattice membranes by two types of filaments. Some threads are load-bearing, and the second are tensioning. Along the perimeter, the threads are embedded in a closed loop. Plates or disks are laid along the threads. They are monolithic by first loading them with ballast or tensioning the supporting cables with jacks. After this, the tension threads receive the greatest tension and the joints of the plates perpendicular to these threads open. They are sealed with expanding cement mortar. As a result, the structure is converted into a rigid shell. Hyparas cover structures that have a circular plan outline.

Cable-stayed coverings consist of stretched elements - cables; structures working in compression - struts and bending - beams, trusses, slabs and shells. These coatings can have not only a spatial design, but also a flat one. They use straight rods - cables. Therefore, cable-stayed structures are stiffer, and the kinematic movements of their elements are less than those of other suspended coverings.

Shells - single and double curvature. Single curvature - cylindrical or conical surfaces. Double curvature - made in the form of a dome or ellipsoid. According to the structure of the shell, there are: smooth, ribbed, wavy, mesh, monolithic and prefabricated.

Pneumatic ceilings are also used to cover spans up to 30 m. They are used for temporary structures. There are three types: air-supported shells; pneumatic frames; pneumatic lenses. Air-supported shells are cylinders made of rubberized or synthetic fabrics. Excessive air pressure is created inside them. Applicable for sports facilities, exhibitions. Pneumatic frames are elongated cylinders in the form of separate arches with excess air pressure. The arches are connected into a continuous arch with a step of 3-4 m. Pneumatic lenses are large pillows inflated with air, which are suspended from rigid frame structures. Used to set up summer circuses and theaters.

Long span structures play a significant role in world architecture. And this was laid down in ancient times, when this special direction of architectural design actually appeared.

The idea and implementation of long-span projects is inextricably linked with the main desire of not only the builder and architect, but of all humanity as a whole - the desire to conquer space. That is why, starting from 125 AD. e., when the first long-span structure known in history, the Pantheon of Rome (base diameter - 43 m), appeared, and ending with the creations of modern architects, long-span structures are especially popular.

History of long-span structures

As mentioned above, the first was the Pantheon in Rome, built in 125 AD. e. Later, other majestic buildings with large-span domed elements appeared. A striking example is the Church of Hagia Sophia, built in Constantinople in 537 AD. e. The diameter of the dome is 32 meters, and it itself gives the entire structure not only majesty, but also amazing beauty, which is admired by both tourists and architects to this day.

In those and later times it was impossible to build light structures from stone. Therefore, domed structures were characterized by great massiveness and their construction required serious time expenditure - up to a hundred years or more.

Later, wooden structures began to be used to construct the floors of large spans. Here shining example is an achievement of domestic architecture - the former Manege in Moscow was built in 1812 and had wooden spans 30 m long in its design.

The 18th-19th centuries were characterized by the development of ferrous metallurgy, which gave new and more durable materials for construction - steel and cast iron. This marked the advent of long-span aircraft in the second half of the 19th century. steel structures, which have received wide application in Russian and world architecture.

The next building material that significantly expanded the capabilities of architects was reinforced concrete structures. Thanks to the emergence and improvement of reinforced concrete structures, the world architecture of the 20th century was replenished with thin-walled spatial structures. At the same time, in the second half of the twentieth century, suspended coverings, rod and pneumatic systems began to be widely used.

In the second half of the twentieth century, laminated wood also appeared. The development of this technology has made it possible to “bring back to life” wooden long-span structures, to achieve special indicators of lightness and weightlessness, to conquer space, without compromising on strength and reliability.

Long-span structures in the modern world

As history shows, the logic of the development of long-span aircraft structural systems was aimed at improving the quality and reliability of construction, as well as the architectural value of the building. The use of this type of structure made it possible to make the most of the full potential of the load-bearing properties of the material, thereby creating lightweight, reliable and economical floors. All this is especially important for a modern architect, when the modern construction reduction in the mass of structures and structures has been promoted.

But what are long-span structures? Here expert opinions differ. There is no single definition. According to one version, this is any structure with a span length of more than 36 m. According to another, structures with an unsupported covering more than 60 m long, although they are already classified as unique. The latter also include buildings with a span of more than one hundred meters.

But in any case, regardless of the definition, modern architecture It is clear that long-span structures are complex objects. And this means a high level of responsibility for the architect, the need to take additional safety measures at each stage - architectural design, construction, operation.

An important point is the choice of building material - wood, reinforced concrete concrete or steel. In addition to these traditional materials, special fabrics, cables and carbon fiber are also used. The choice of material depends on the tasks facing the architect and the specifics of construction. Let's consider the main materials used in modern long-span construction.

Prospects for long-span construction

Taking into account the history of world architecture and the inevitable desire of man to conquer space and create perfect architectural forms, we can safely predict a steady increase in attention to long-span structures. As for materials, in addition to modern high-tech solutions, increasing attention will be paid to FCC, which is a unique synthesis of traditional material and modern high technology.

As for Russia, given the pace of economic development and the unmet need for facilities for various purposes, including trade and sports infrastructure, the volume of construction of long-span buildings and structures will constantly increase. And here unique design solutions, quality of materials and the use of innovative technologies will play an increasingly important role.

But let's not forget about the economic component. It is this that stands and will stand at the forefront, and it is through it that the effectiveness of a particular material, technology and design solution will be considered. And in this regard, I would again like to remember about laminated wood structures. According to many experts, they hold the future of long-span construction.

Question 59. Design solutions for long-span systems. Loads acting on long-span structures. Layout of frames for long-span coverings

The frames of long-span roofs with beam and frame load-bearing systems have a layout scheme close to the frames of industrial buildings. For large spans and the absence of crane beams, it is advisable to increase the distances between the main load-bearing structures to 12-18 m. The systems of vertical and horizontal connections have the same purposes as in industrial buildings and are arranged in a similar way.

The layout of frame coverings can be transverse when load-bearing frames are placed across the building, and longitudinal, typical for hangars. With a longitudinal layout, the main supporting frame is placed in the direction of the larger dimension of the building plan and the transverse trusses rest on it.

The upper and lower chords of the supporting frames and transverse trusses are untied with cross braces, ensuring their stability.

In arched systems, the pitch of the arches is 12 m or more; The main purlins are laid along the arches, on which the transverse ribs supporting the roof deck rest.

For large spans and heights of the main load-bearing systems (frames, arches), spatially stable block structures are used by pairing adjacent flat frames or arches (Fig. 8), as well as by using triangular sections of arches. The arches are connected in the key by longitudinal connections, the importance of which for the rigidity of the structure is especially great when the lifting boom of the arches is large, when their overall deformability increases.

The transverse braces located between the outer pair of arches are calculated on the wind pressure transmitted from the end wall of the arched covering.

QUESTION 60. Long-span beam structures. Their advantages and disadvantages. Constructive decisions. Loads acting on beam structures. Fundamentals of calculation and design of beam structures.

Beam structures

Long-span beam structures are used in cases where supports cannot withstand thrust forces.

Beam systems for large spans are heavier than frame or arch systems, but are easier to manufacture and install.

Beam systems are used mainly in public buildings - theaters, concert halls, sports facilities.

The main load-bearing elements of beam systems used for spans of 50-70 m or more are trusses; Solid beams with large spans are unprofitable in terms of metal consumption.

Main advantages beam structures are characterized by precise operation, absence of thrust forces and insensitivity to support settlements. Main disadvantage– relatively high consumption of steel and high height, caused by large flying moments and rigidity requirements.

Rice. 1, 2, 3

The cross-sections of the rods of long-span trusses with forces in the rods exceeding 4000-5000 kN are usually taken to be composite of welded I-beams or rolled sections.

The high height of the trusses does not allow them to be transported by rail in the form of assembled shipping elements, so they are supplied for installation in bulk and consolidated on site.

The elements are connected by welding or high-strength bolts. High-precision bolts and rivets should not be used because they are labor intensive.

Long-span trusses are calculated and their sections are selected in the same way as light trusses of industrial buildings.

Due to large support reactions, it becomes necessary to transmit them strictly along the axis of the truss unit, otherwise significant additional stresses may arise.

For spans of 60-90m, the mutual displacement of the supports becomes significant due to the deflection of the truss and its temperature deformations. In this case, one of the supports can be a roller (Fig. 6), allowing free horizontal movements.

If the trusses are installed on high flexible columns, then even with spans of up to 90 m, both supports can be stationary due to compliance upper parts columns

Long-span beam systems can consist of triangular trusses with prestressing, which are convenient to manufacture, transport and install (Fig. 7).

The inclusion of a reinforced concrete slab laid along the upper chords of the truss in joint compression work, the use of tubular rods and prestressing make such trusses economical in terms of metal consumption.

Steel sheets are included in the design sections of the upper and lower chords of the trusses.

In order for a thin sheet to work under compression, a preliminary tensile stress is created in it that is greater than the compressive stress from the load.

QUESTION 61. Frame long-span structures. Their advantages and disadvantages. Constructive decisions. Loads acting on frame structures. Fundamentals of calculation and design of frame structures.

Frame structures

Frames spanning large spans can be double-hinged or hingeless.

Hingeless frames are more rigid, more economical in metal consumption and more convenient to install; however, they require more massive foundations with dense bases for them and are more sensitive to temperature influences and uneven settlements of the supports.

Frame structures, compared to beam structures, are more economical in terms of metal consumption and are more rigid, due to which the height of the frame crossbar is lower than the height of beam trusses.

In long-span coverings, both continuous and through frames are used.

Solid frames are rarely used for small spans (50-60 m), their advantages: less labor intensity, transportability and the ability to reduce the height of the room.

The most commonly used frames are hinged frames. It is recommended to take the height of the frame crossbar equal to: with through trusses 1/12-1/18 of the span, with solid crossbars 1/20 - 1/30 of the span.

Frames are calculated using structural mechanics methods. To simplify the calculations, lightweight through frames can be reduced to their equivalent solid frames.

Heavy through frames (such as heavy trusses) must be designed as lattice systems, taking into account the deformation of all lattice rods.

For large spans (more than 50 m) and low rigid posts, it is necessary to calculate the frames for temperature effects.

Crossbars and racks of solid frames have solid I-sections; their load-bearing capacity is checked using formulas for eccentrically compressed rods.

In order to simplify the calculation of lattice frames, their expansion can be determined as for a solid frame.

Using an approximate calculation, preliminary sections of the frame chords are established;

determine the moments of inertia of cross-sections of crossbars and racks using approximate formulas;

calculate the frame using structural mechanics methods; the design diagram of the frame should be taken along the geometric axes;

Having determined the support reactions, the calculated forces in all the rods are found, according to which their sections are finally selected.

The types of sections, design of nodes and connections of frame trusses are the same as for heavy trusses of beam structures.

Another artificial method of unloading the crossbar is the displacement of the supporting hinges in the double-hinged frame from the axis of the rack inward. In this case, vertical support reactions create additional moments that unload the crossbar.