RU2702492C1 - Truss made from roll-welded profiles with regularly variable cross-section belts - Google Patents

Abstract

FIELD: construction.SUBSTANCE: invention relates to construction, namely to grid structure – truss. Truss consists of roll-welded profiles with belts of regular-variable cross-sections and includes a grid and belts assembled by paired channels with untwisted cuts of walls of the same initial roll-welded sections. Sections of channels have regular-variable width, which provides same regular-variable height of composite sections of belts, which values at constant width of sections of belts are determined by relationship 4(z/l-z/l)≤h/h, where z is coordinate of belt extreme support panels middle; l is truss span length; h– belt height in the middle of the same panels; his maximum height of belt in middle of span.EFFECT: reduced level of stress concentration.1 cl, 10 dwg

Description

The proposed technical solution relates to the field of construction and can be used in lattice structures of buildings and structures for various purposes. In particular, these can be planar structures (trusses and sub-trusses, trusses and floor trusses), as well as their spatial modifications: cross-truss systems, trihedral (three-belted) trusses, trellised supports, towers, masts, towers and other supporting structures.

A technical solution is known for trusses from bent-welded profiles of the Molodechno type series with a slope of parallel belts of 1.5% and a triangular lattice system [Steel structures of coatings for industrial buildings with spans of 18, 24 and 30 m with the use of closed bent-welded rectangular sections of the Molodechno type: typical project: series 1.460.3-14 / developer. GPI Lenproektstalkonstruktsiya. - Gosstroy of the USSR. 1980. 135 p .: KM drawings], as well as their later modification with a slope of the upper chords of 10% [Steel structures of coatings for industrial buildings from closed bent-welded rectangular sections with a span of 18, 24 and 30 m with a slope of 10%: a typical design: series 1.460.3-23.98. Issue I / developed. OJSC PI Lenproektstalkonstruktsiya. Gosstroy of the Russian Federation. 2000. 78 p.: Drawings of KM]. A common drawback of the technical solution of the entire model series is that the sections of the belts, selected for the greatest efforts in the middle of the span, are spread over their entire length. This increases the degree of unification of the supporting structures, but increases the consumption of structural material (steel).

It is known to work out standardized trusses from bent-welded profiles with a reduced consumption of structural material by reducing the cross section of the upper belt and unifying it with the lower belt when additional racks are introduced into the triangular lattice [Baranovsky M.Yu., Tarasov V.A. Standardized truss structures with a slope of 10% spans 24, 30, 36 meters. - Construction of unique buildings and structures. 2014. No7 (22). S. 92-106]. However, at the same time, the lower belt turned out to be less loaded in comparison with the upper belt, which, moreover, remained almost with zero margin of bearing capacity in the support sections of the span.

A well-known solution is also the replacement in the triangular lattice of conventional additional racks with additional racks and half-braces (Ψ-shaped racks), which is accompanied by a certain unloading of the upper belt and a corresponding increase in its carrying capacity [Marutyan A.S. Optimization of trusses with racks and half-braces in triangular lattices. - Structural mechanics and calculation of structures. 2016. No4 (267). S. 60-68]. This solution ensures the use of identical sections in the upper and lower zones with approximately equal reserves of their bearing capacity, but increases the complexity due to an increase in the number of rod elements and nodal joints.

A known method of manufacturing a steel support of regular variable section from isosceles corners with shelves of regularly variable width. These corners are dissolved by oblique cuts of the walls of the original square pipe (bent profile) and connected to the supporting (supporting) structure by welding longitudinal and transverse welds [Kuznetsov I.L., Sabitov L.S. A method of manufacturing a steel support of regular variable cross-section. - Patent 2495213, 10/10/2013, bull. No. 28]. Such a technical solution in relation to truss structures needs to be further processed. However, it is close enough to the proposed in order to accept it as an analogue.

It should be noted that the inclusion of additional rod elements in the triangular lattice did not allow avoiding the general drawback of the technical solution of the entire type series. This drawback is eliminated with the help of another well-known technical solution of the truss from bent-welded profiles, including a lattice and belts of step (step-variable) sections [Kozachkova AN Metal farm. - Copyright certificate 1214881, 02/28/1986, bull. No. 8]. Belts are made of channels, interconnected by shelves lying parallel to the plane of the truss. The upper channel, which makes up the belt, has a constant section over the entire length, and the lower one has a variable height of the shelves. At the joints of these channels, the end of the channel with a higher height is made with an inclined wall, the angle of inclination α of which is determined by the dependence:

α = arctan ((N ₁ / (ϕ _e1 R _y ) -N ₂ / ((ϕ _e2 R _y )) / (2 a t)),

where a is the length of the inclined section of the channel wall; t is the channel wall thickness; N ₁ and N ₂ - longitudinal forces in two adjacent panels; ϕ _e1 and ϕ _e2 are the coefficients of longitudinal bending of two adjacent panels; R _y is the design resistance of the material.

Such a technical solution is the closest to the proposed one and can be adopted as its prototype. It provides a reduction in the material consumption of the belt elements, and hence the farm as a whole, however, it negatively affects such technical and economic characteristics of the truss structure as unification and stress concentration. A truss assortment with belts of stepwise variable sections, in addition to bent welded profiles, should also include channel profiles, and this reduces the degree of standardization of standardized trusses. The angular and linear parameters of the core elements of the lattices of such trusses differ significantly, which also negatively affects their unification. Variable section belts are composed of paired channels connected by welding of two longitudinal seams, as well as transverse seams of inclined sections of the channel walls, which coincide with the zones of the welded joints, thereby increasing the level of stress concentration here.

The technical result of the proposed solution is to reduce the consumption of structural material (steel), reduce the level of stress concentration, increase the degree of unification of standardized trusses.

The specified technical result is achieved by the fact that in a farm of closed bent-welded profiles with belts of regularly variable sections, including a lattice and belts arranged in pairs of channels, open oblique cuts of the walls of the same initial bent-welded profiles, the shelves of such channels have a regularly-variable width, which provides the same regularly variable height of the composite sections of the belts, the values of which at a constant width of the shelves (horizontal faces) of the belts are determined by the dependence:

- длина пролета фермы; h_z - высота пояса в середине тех же панелей; h_max - максимальная высота пояса в середине пролета.where z is the coordinate of the middle of the extreme support waist panels;

- span length of the farm; h _z is the height of the belt in the middle of the same panels; h _max - the maximum height of the belt in the middle of the span.

The indicated technical result is also quite achievable in that the described belts of regularly variable sections can be arranged in pairs of channels, one of which has shelves of constant width and the other shelves of regularly variable width.

The proposed truss from bent-welded profiles with belts of regularly variable sections has a fairly universal technical solution, with the implementation of which not only flat, but also spatial modifications of it are possible in the form of trihedral (three-belted) trusses of coatings and floors, systems of cross trusses, trellised supports, towers, masts, towers and other supporting structures. Moreover, the degree of unification of standardized trusses can be increased due to the fact that bent-welded profiles already existing in their assortments may turn out to be quite suitable as initial profiles for manufacturing belts of regularly variable sections. So, in standardized farms, the upper zones of constant sections from rectangular profiles can be replaced with similar belts of regularly variable sections from square profiles of the lower zones of the same farms. In turn, in a similar way, the lower zones of constant sections can also be replaced by similar belts of regularly variable sections from the profiles of the core elements of the gratings (supporting and other braces). In addition, the outlines of the upper and lower zones of regularly variable sections are not very difficult to choose with minimal changes in truss lattices or without changes at all. In particular, for this, in standardized farms with parallel zones of constant sections, it is sufficient to maintain the distance and parallelism of the lower shelves of the upper belts of regularly variable sections and the upper shelves of the lower belts of the same sections.

Comparing the proposed technical solution with its analogue, it is not difficult to notice that one closed bent welded profile of rectangular or square section is much easier to dissolve into two channels than into four corners. It is equally obvious that the assembly of belts of stepwise variable sections according to the prototype is more time-consuming than a similar assembly of belts of regularly variable sections according to the proposed solution. At the same time, the stress concentration in the nodal zones of the truss due to the overlap of the welds according to the prototype is higher, and the length of the seams in the proposed solution is shorter, since there are none at all in the transverse direction. The proposed technical solution allows for two modifications of belts of regularly variable sections from paired channels: in one of them, both elements of variable sections are similar, and in the other (by analogy with the prototype), an element of variable section can be combined with an element of constant section.

The proposed technical solution is illustrated by graphic materials, where in FIG. 1 shows a fragment of a truss from bent-welded profiles with belts of regularly variable sections, arranged in pairs of channels with shelves of regularly variable width; in FIG. 2 - a fragment of a truss from bent-welded profiles with belts of regularly variable sections, arranged in pairs of channels with shelves of constant width and shelves of regularly variable width; in FIG. 3 - a fragment of a trihedral (three-belted) truss from bent-welded profiles with belts of regularly variable sections, arranged in pairs of channels with shelves of regularly variable width (the flooring along the upper belts and part of the braces are not shown conditionally); in FIG. 4 - a fragment of a trihedral (three-belt) truss from bent-welded profiles with belts of regularly variable sections, arranged in pairs of channels with shelves of constant width and shelves of regularly variable width (flooring along the upper belts and part of the braces are not shown conditionally); in FIG. 5 is a snapshot of a slice of various gauge bent welded profiles; in FIG. 6 is a design diagram of sections of bent welded profiles; in FIG. 7 shows the starting mark of a standardized truss from bent sections with a span of 18 m with belts of constant sections; in FIG. 8 - a starting mark of a standardized truss from bent-welded profiles with a span of 18 m with a lower belt of constant cross-section and an upper belt of regularly variable cross-section; in FIG. 9 - a starting mark of a standardized truss from bent welded profiles with a span of 18 m with belts of regularly variable sections; in FIG. Figure 10 shows a pattern of forming belts of regularly variable sections with their calculated parameters for a standardized truss from bent-welded profiles with a span of 18 m.

The proposed technical solution of the truss from bent-welded profiles includes an upper (compressed) belt of regularly variable section from paired channels with regiments of regularly variable width 1, a lower (stretched) belt of regularly variable section from paired channels with regiments of regularly variable width 2, and a lattice connecting them from braces 3. Modified belts of regularly variable sections can have the same pair layout of channels with shelves of regularly variable widths and channels with shelves of constant width. As in the previous case, the modified upper (compressed) belt 4 is connected to the modified lower (extended) belt 5 by a brace of braces 3. The proposed technical solution for the spatial design of bent sections, for example, a trihedral (three-belted) truss, consists of two upper (compressed) belts regularly variable sections from paired channels 1 or 4, one lower (stretched) belt of regularly variable sections from paired channels 2 or 5, as well as two inclined gratings connecting them from braces 3. To the upper belts 1 or 4 a deck is supported, which in most coatings and ceilings forms a hard drive that provides strength, rigidity and stability to the trihedral truss.

To derive the given dependence of the calculated values of the regularly variable heights of the waist elements with their constant width, it is advisable to use the beam equivalent of the truss [Lebedeva N.V. Farms, arches, thin-walled spatial structures. - M .: "Architecture-S"; 2007. - S. 8-9]:

- длина пролета фермы и ее балочного эквивалента; M_max - наибольший (максимальный) расчетный момент в середине пролета.where M _z is the calculated moment in the considered section of the beam equivalent of the farm; z is the coordinate of the section under consideration; q is the intensity of the design load distributed evenly according to the law of the rectangle;

- the length of the span of the farm and its beam equivalent; M _max - the largest (maximum) calculated moment in the middle of the span.

The sections of the belts, selected according to the maximum (greatest) efforts (N _max = ± M _max / H, where N is the distance between the longitudinal axes of the belts), in standardized trusses from bent-welded profiles, as a rule, extend over the entire span. Based on this, to ensure the bearing capacity of a belt of regularly variable section, its height at a constant width should be determined by the same dependence as the moments of the beam equivalent of the truss, which can be written in the form already given:

In order to calculate the bent-welded profile of a regularly variable section, for this section it is advisable to take a composite figure of a pair of vertical rectangles corresponding to the walls (vertical faces), and a pair of horizontal rectangles corresponding to the shelves (horizontal faces). In this case, calculation calculations can be performed along the midline of a thin-walled section without taking into account numerical values containing the thicknesses raised to the second and third degree (t ² , t ³ ), as well as without taking into account angular curves [Marutyan A.S. Optimization of structures from tubular (bent-welded) profiles of square (rectangular) and rhombic sections. - Structural mechanics and calculation of structures, 2016, No. 1. - S. 30-38]:

A = 2tU (1 + 1 / n);

I _x = tU ³ (0.1666666 / n + 0.5) / n ² ;

I _y = tU ³ (0.1666666 + 0.5 / n),

where A is the estimated cross-sectional area of the profile; I _x - calculated axial moment of inertia of the section relative to the x-axis; I _y is the calculated axial moment of inertia of the section relative to the yy axis; t is the thickness of the face;

n is the ratio of the width of the shelf (horizontal edge) U along the midline of the section to the height of the wall (vertical edge) V also along the midline of the section,

n = U / V.

When compressing, the bearing capacity (stability) of the belts of regularly variable sections should be checked using the theoretical and theoretical assumption as a justification, according to which replacing a compressed constant-section rod with a variable-section rod practically does not reduce its stability, while at the same time the overall stability of the truss design and does not increase its deformability [1. Semenov A.A., Poryvaev I.A., Shamilova E.R. Steel truss coating. - Patent 180553, 06/18/2018, bull. 17; 2. Semenov A.A., Poryvaev I.A., Shamilova E.R., Semenov S.A. An algorithm for finding optimal parameters of centrally compressed struts of a tubular section of variable stiffness. - Construction and reconstruction, 2018, No. 2 (76). - S. 51-60]. Proceeding from this, it is permissible to check the stability of a compressed belt of regularly variable stiffness taking into account average cross sections equidistant from the centers of truss nodes.

When tensile, the bearing capacity (strength) of the belts of regularly variable sections must be checked taking into account the calculated net sections, which in the farms coincide with the centers of the nodes, where the belt forces change their values.

In order to show the implementation of the proposed technical solution with greater clarity, it is advisable to use a basic object, for which a standardized truss of bent-welded profiles with a span of 18 m can be allowed [Kuzin N.Ya. Design and calculation of steel trusses for coatings of industrial buildings. - M.: Publishing house of the DIA, 1998. - S. 157-172].

The control ratios of the altitude parameters of the belts of regularly variable sections as applied to the base truss of bent-welded profiles with a span of 18 m with a triangular lattice and 1.5-meter half-panels of parallel belts have the following values:

at z = 1.5 m

h _z / h _max = ^{4 (1.5 / 18-1,5 2/18} 2) = 0.305556 ;

at z = 16.5 m

h _z / h _max = ^{4 (16.5 / 18-16,5 2/18} 2) = 0.305556 .

The next step in the implementation of the proposed technical solution is the replacement of the upper (compressed) belt of the base object from a bent-welded profile □ 160 × 120 × 4 mm with the same belt of regularly variable section □ (60 ... 180) × 120 × 4 mm from the profile □ 120 × 120 × 4 mm, selected for the lower belt of the base object.

The stability of the compressed belt will be ensured provided:

σ / R _y = N / (ϕAR _y ) ≤1,

where σ is the calculated value of the normal stress under compression; R _y is the calculated resistance of the structural material to yield strength; N is the calculated compression force; ϕ is the coefficient of longitudinal bending; A is the calculated cross-sectional area;

ϕ = 1-0.066 (λ _pr ) ^3/2 for 0 <λ _pr ≤2.5;

ϕ = 1.46-0.34λ _pr +0.021 (λ _pr ) ² for 2.5 <λ _pr ≤ 4.5;

λ _pr - conditional flexibility of the compressed element [Guide for the design of steel structures. - M .: TSITP, 1989. - S. 17];

λ _pr = λ (R _y / E) ^1/2 ;

λ is the design flexibility of the compressed element;

- расчетная длина сжатого элемента; i - радиус инерции расчетного сечения; Е - модуль упругости конструкционного материала (для стали E=2100000 кгс/см²).

- the estimated length of the compressed element; i is the radius of inertia of the calculated section; E is the modulus of elasticity of the structural material (for steel E = 2100000 kgf / cm ² ).

At z = 1.5 m and z = 16.5 m, the design cross section □ 80 × 120 × 4 mm of the first and sixth (extreme supporting) panels of the upper belt of regularly variable stiffness has the following parameters:

0.305556≤h _z / h _max = 80/180 = 0.444444;

n = U / V = (8.0-0.4) / (12.0-0.4) = 7.6 / 11.6 = 0.6551724;

A = 2 × 0.4 × 7.6 (1 + 1 / 0.6551724) = 15.36 cm ² ;

I _x = 0.4 × 7.6 ³ (0.1666666 + 0.5 / 0.6551724) = 163.3 cm ⁴ ;

I _y = 0.4 × 7.6 ³ (0.1666666 / 0.6551724 + 0.5) / 0.6551724 ² = 308.6 cm ⁴ ;

i _x = (163.3 / 15.36) ^1/2 = 3.26 cm;

i _y = (308.6 / 15.36) ^1/2 = 4.48 cm;

σ / R _y = 18434 / (0.608 × 15.36 × 2400) = 0.8225,

where λ _x = 300 / 3.26 = 92.0; λ _y = 300 / 4.48 = 66.9; λ _pr = 92.0 (2400/2100000) ^1/2 = 3.1;

ϕ = 1.46-0.34 × 3.1 + 0.021 × 3.1 ² = 0.608.

As you can see, the stability of the extreme support panels of the upper belt of a regularly variable section is provided. Here we can add that the calculated characteristics of the calculated cross-section □ 80 × 120 × 4 mm practically coincided with the characteristics of the bent-welded profile □ 120 × 80 × 4 mm according to TU 67-2287-80 (A = 15.36 cm ² ; I _x = 309, 0 cm ⁴ ; I _y = 164.0 cm ⁴ ).

At z = 4.5 m and z = 13.5 m, the calculated cross-section □ 120 × 120 × 4 mm of the second and fifth (intermediate) panels of the upper belt of regularly variable stiffness has the following parameters:

n = U / V = (12.0-0.4) / (12.0-0.4) = 11.6 / 11.6 = 1.0;

A = 2 × 0.4 × 11.6 (1 + 1 / 1.0) = 18.56 cm ² ;

I _x = 0.4 × 11.6 ³ (0.1666666 / 1.0 + 0.5) / 1.0 ² = 416.2 cm ⁴ ;

I _y = 0.4 × 11.6 ³ (0.1666666 + 0.5 / 1.0) = 416.2 cm ⁴ ;

i _x = i _y = (416.2 / 18.56) ^1/2 = 4.74 cm;

σ / R _y = 33564 / (0.793 × 18.56 × 2400) = 0.9502,

where λ _x = λ _y = 300 / 4.74 = 63.3; λ _pr = 63.3 (2400/2100000) ^1/2 = 2.14;

ϕ = 1-0.066 × 2.14 ^3/2 = 0.793.

As you can see, the stability of the intermediate panels of the upper zone of a regularly variable section is also provided. And here we can add that the calculated characteristics of the design section □ 120 × 120 × 4 mm practically coincided with the characteristics of the bent-welded profile □ 120 × 120 × 4 mm according to TU 67-2287-80 (A = 18.56 cm ² ; I _x = I _y = 416.7 cm ⁴ ).

At z = 7.5 m and z = 10.5 m, the calculated cross-section □ 160 × 120 × 4 mm of the third and fourth (middle) panels of the upper belt of regularly variable stiffness has the following parameters:

n = U / V = (12.0-0.4) / (16.0-0.4) = 11.6 / 15.6 = 0.7435897;

A = 2 × 0.4 × 11.6 (1 + 1 / 0.7435897) = 21.76 cm ² ;

I _x = 0.4 × 11.6 ³ (0.1666666 / 0.7435897 + 0.5) / 0.7435897 ² = 817.7 cm ⁴ ;

I _y = 0.4 × 11.6 ³ (0.1666666 + 0.5 / 0.7435897) = 523.9 cm ⁴ ;

i _x = (817.7 / 21.76) ^1/2 = 6.13 cm;

i _y = (523.9 / 21.76) ^1/2 = 4.91 cm;

σ / R _y = 40867 / (0.8041 × 21.76 × 2400) = 0.9732,

where λ _x = 300 / 6.13 = 48.9; λ _y = 300 / 4.91 = 61.1; λ _pr = 61.1 (2400/2100000) ^1/2 = 2.0655;

ϕ = 1-0.066 × 2.0655 ^3/2 = 0.8041.

As you can see, the stability of the middle panels of the upper zone of a regularly variable section is also provided. Like the extreme and intermediate panels, it can be added here that the calculated characteristics of the design section □ 160 × 120 × 4 mm practically coincided with the characteristics of the bent-welded profile □ 160 × 120 × 4 mm according to TU 67-2287-80 (A = 21.76 cm ² ; I _x = 818.3 cm ⁴ ; I _y = 524.4 cm ⁴ ).

The above computational calculations confirm that the upper (compressed) belt of regularly variable section □ (60 ... 180) × 120 × 4 mm from the profile □ 120 × 120 × 4 mm, selected for the lower (extended) belt of the base object, is quite suitable for use in the farm according to the proposed technical solution, which reduces the consumption of structural material by 5.5% (table).

Thus, it was possible to abandon the rectangular profile of the upper belt, replacing it with the square profile of the lower belt, without introducing additional rod elements into the lattice structure. Moreover, if you keep the distance and parallelism of the lower shelf of the upper belt of a regularly variable section and the upper shelf of the lower belt of a constant section, then the lattice of the base object can be left unchanged for reuse in a new farm.

The final stage of the implementation of the proposed technical solution is the replacement of the lower (stretched) belt of the base object from a bent-welded profile □ 120 × 120 × 4 mm with the same belt of regularly variable section □ (40 ... 120) × 120 × 4 mm from the profile □ 80 × 120 × 4 mm.

The strength of the stretched belt will be provided provided:

σ / (γ _c R _y ) = N / (Aγ _c R _y ) ≤1,

where σ is the calculated value of the normal tensile stress; γ _s is the coefficient of the working conditions of the structure; R _y is the calculated resistance of the structural material to yield strength; N is the calculated tensile force.

If we substitute the value of the coefficient γ _c = 0.95, adopted in the base object, then the formula for checking the strength can be written in the following form:

σ / R _y = N / (AR _y ) ≤0.95.

The limiting flexibility of the rods of the lower (extended) belts, the strength of which is ensured, should not exceed from the plane and in the plane of the truss 400, and when seismic effects are taken into account 350.

At z = 1.5 m and z = 16.5 m, the calculated cross-section □ 40 × 120 × 4 mm of the first and fifth (extreme, but not supporting) panels of the lower belt of regularly variable stiffness has the following parameters:

0.305556≤h _z / h _max = 40/120 = 0.333333;

n = U / V = (4.0-0.4) / (12.0-0.4) = 3.6 / 11.6 = 0.3103448;

A = 2 × 0.4 × 3.6 (1 + 1 / 0.3103448) = 12.16 cm ² ;

I _x = 0.4 × 3.6 ³ (0.1666666 + 0.5 / 0.3103448) = 33.18 cm ⁴ ;

I _y = 0.4 × 3.6 ³ (0.1666666 / 0.3103448 + 0.5) / 0.3103448 ² = 200.9 cm ⁴ ;

i _x = (33.18 / 12.16) ^1/2 = 1.65 cm;

i _y = (200.9 / 12.16) ^1/2 = 4.06 cm;

σ / R _y = 20347 / (12.16 × 2400) = 0.6972;

λ _x = 300 / 1.65 = 181.8;

λ _y = 750 / 4.06 = 184.7.

At z = 4.5 m and z = 13.5 m, the calculated cross-section □ 72 × 120 × 4 mm of the second and fourth (intermediate) panels of the lower belt of regularly variable stiffness has the following parameters:

n = U / V = (7.2-0.4) / (12.0-0.4) = 6.8 / 11.6 = 0.5862068;

A = 2 × 0.4 × 6.8 (1 + 1 / 0.5862068) = 14.72 cm ² ;

I _x = 0.4 × 6.8 ³ (0.1666666 + 0.5 / 0.5862068) = 128.2 cm ⁴ ;

I _y = 0.4 × 6.8 ³ (0.1666666 / 0.5862068 + 0.5) / 0.5862068 ² = 287.1 cm ⁴ ;

i _x = (128.2 / 14.72) ^1/2 = 2.95 cm;

i _y = (287.1 / 14.72) ^1/2 = 4.42 cm;

σ / R _y = 20347 / (14.72 × 2400) = 0.8860;

λ _x = 300 / 2.95 = 101.7;

λ _y = 750 / 4.42 = 169.7.

At z = 7.5 m, the calculated cross-section □ 104 × 120 × 4 mm of the third (middle) panel of the stretched belt of regularly variable stiffness has the following parameters:

n = U / V = (10.4-0.4) / (12.0-0.4) = 10.0 / 11.6 = 0.8620689;

A = 2 × 0.4 × 10.0 (1 + 1 / 0.8620689) = 17.28 cm ² ;

I _x = 0.4 × 10.0 ³ (0.1666666 + 0.5 / 0.8620689) = 298.7 cm ⁴ ;

I _y = 0.4 × 10.0 ³ (0.1666666 / 0.8620689 + 0.5) /0.8620689 ² = 373.8 cm ⁴ ;

i _x = (298.7 / 17.28) ^1/2 = 4.16 cm;

i _y = (373.8 / 17.28) ^1/2 = 4.65 cm;

σ / R _y = 20347 / (17.28 × 2400) = 0.8303;

λ _x = 300 / 4.16 = 72.1;

λ _y = 750 / 4.65 = 161.3.

The above calculated calculations confirm that the lower (stretched) belt of regularly variable section □ (40 ... 120) × 120 × 4 mm from the profile □ 80 × 120 × 4 mm is quite suitable for use in the farm according to the proposed technical solution, which increases the savings construction material up to 10% (table). If you keep the distance and parallelism of the lower shelf of the upper belt of a regularly variable section and the upper shelf of the lower belt of a regularly variable section, the lattice of the base object can be left unchanged, in this case, for re-use in a new farm.

Thus, summing up some results, we can come to the main conclusion that the proposed truss from bent-welded profiles with belts of regularly variable sections is quite effective, rational and promising for use as part of the supporting structures of buildings and structures.

Claims (3)

A truss from bent-welded profiles with belts of regularly variable sections, including a lattice and belts arranged in pairs of channels, open slanting cuts of the walls of the same initial bent-welded profiles, characterized in that the shelves of such channels have a regularly-variable width, which ensures the same regularly -the variable height of the composite sections of the zones, the values of which at a constant width of the sections of the zones are determined by

where z is the coordinate of the middle of the extreme support panels of the belt;

- span length of the farm; h _z is the height of the belt in the middle of the same panels; h _max - the maximum height of the belt in the middle of the span.

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