RU2601351C1 - Bearing structure with grid from oval pipes - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: invention relates to construction and can be used for production of frames, lintels, columns, arches, frames and other long bearing grid structures of pipes. Bearing structure with a grid from oval pipes includes belt and rigidly attached to them grid made with flattened ends of bent elements with a zigzag shape. Rod elements of grid have a flat-oval section with ratio of dimensions of 1/2.63, where larger dimension is located in plane of design, smaller - from plane.

EFFECT: technical result consists in reduction of labour intensiveness of manufacturing of bearing structures and reduction of costs thereon.

1 cl, 1 tbl, 7 dwg

Description

The present invention relates to the construction and can be used in the manufacture of trusses, girders, columns, arches, frames and other lengthy supporting lattice structures from pipes. Tubular building structures are distinguished by enhanced technical and economic characteristics, since structural materials (steel, aluminum alloy, metal-plastic, composite, polymer, synthetics, and others) are located in cross sections of elements in a very efficient manner. The further growth of these characteristics due to the use of more rational, especially thin-walled tubular (closed bent-welded) profiles is facilitated by their layouts in the supporting structures with the direct adjoining of the lattice rods to the belts in the form of frameless assemblies.

A well-known technical solution is a metal structure with a lattice of rhombic closed bent-welded profiles. The design includes a belt of tubular rectangular (square) section and a lattice rigidly attached to them, made with flattened ends from curved elements of a V- or W-shaped (zigzag) shape. The rod elements of the lattice have a tubular cross-section of a rhombic shape with a diagonal ratio of 1/2, where the larger diagonal is located in the plane of the structure, and the smaller one is from the plane [Marutyan AS, Ekba S.I. Metal construction with lattice of rhombic closed bent-welded profiles. - Patent No. 2500003, December 10, 2013, bull. No. 34]. A modification of this design is a truss of rhombic pipes (bent-welded profiles) with the same ratio of diagonals of cross sections. For all compressed truss rods, the larger diagonal is located in the plane of the structure, and the smaller diagonal is from the plane, and for all stretched truss rods the larger diagonal is located in the plane of construction, and the smaller is in the plane. The upper and lower zones in the places of the faceless junction of the lattice are flattened [Marutyan AS Farm from rhombic pipes (bent profiles). - Patent No. 2548301, 04/20/2015, bull. No. 11].

These technical solutions are characterized by a disadvantage of known tubular trusses of rectangular, square, pentahedral and pentagonal profiles, which reduces the load-bearing capacity of structures and increases their material consumption due to the angularity of the listed cross-sectional shapes, accompanied by an increased stress concentration.

The closest technical solution (adopted as a prototype) to the proposed load-bearing structures with lattices of flat oval pipes is a supporting structure with a lattice of oval profile. The design includes belts and a lattice rigidly attached to them, made with flattened ends from curved elements of a zigzag shape. The rod elements of the lattice have an oval cross-section with an aspect ratio of 1 / 2.5, where the larger dimension is located in the plane of the structure, and the smaller one is from the plane [Marutyan A.S. The supporting structure is made of oval pipe. - Patent No. 2554643, 06/27/2015, bull. No. 18].

The main disadvantage of the prototype is the complex shape of the oval pipe, the surface of which is characterized by the complete absence of flat sections and the same absence of sections of constant curvature. This difference increases the complexity of both manufacturing the pipe itself and its use in load-bearing structures, which is accompanied by a certain increase in costs.

So, for example, oval pipes are 3.5 ... 4.4% more expensive than flat oval profiles:

- according to the price list dated April 1, 2008 Moscow Tube Works OJSC (6, Barclay St., Moscow) a ton of oval pipe cost 37,090 rubles, and a flat oval pipe - 35,510 rubles (37090/35510 = 1,044);

- according to the price list dated 11/27/2013 KlassiK PKF LLC (21, Marata St., Kiev) a ton of oval pipe cost 8,800 hryvnias, and a flat-oval one - 8500 hryvnias (8800/8500 = 1,035).

The technical result of the proposed solution is to reduce the complexity of manufacturing bearing structures and reduce costs.

The specified technical result is achieved by the fact that in the supporting structures, including belts and lattices rigidly attached to them, made with tapered ends of curved elements of a zigzag shape, the core elements of the lattices have flat oval sections with a ratio of dimensions of 1 / 2.63, where large dimensions are located in planes of structures, and smaller ones from planes.

In the proposed load-bearing structures, the upper and lower zones, as well as the gratings between them, are made of tubular profiles. To directly adjoin the belts with the formation of blockless assemblies, the flat-oval tubes of the gratings are flattened in the places specified by the project and give them zigzag outlines with double bends. The length of the sheet blanks (strips) of flat oval profiles can be selected based on the entire length of the structures or their shipping marks. Flattening and double bending of flat-oval elements of the gratings provide the layout of frameless nodal joints without structural eccentricities, characteristic for truss and sub-truss trusses from rectangular (square) bent-welded closed profiles, which eliminates the appearance of bending moments and positively affects the consumption of structural material. However, at the same time, to increase the degree of unification of the nodes of the upper and lower zones, the use of constructive eccentricities limited to 0.25 of the height of the waist elements is quite justified, which allows them not to be taken into account in the calculations [Guide for the design of steel structures from bent-welded closed profiles. M.: Central Scientific Research Institute of Steel Construction, 1978. - S. 24, p. 4.2.8].

Flattening protects the walls of the waist elements from punching and reduce their thickness. Sheet hinges are formed along the bends of the flat oval profile in the plane of the structures, which correspond to the articulated-rod design schemes (models) and eliminate the need to take into account the stiffness of the nodes, which also helps to reduce the metal consumption. Of the planes of structures, the same bends of flattened sections of plane-oval profiles have the greatest stiffness, close to the stiffnesses of frame fasteners, due to which coupling elements can be reduced in load-bearing structures, as is done, for example, in structures of coatings of the Tagil type [Metal structures. In 3 t. T. 2. Steel structures of buildings and structures. (Designer reference). / Ed. V.V. Kuznetsov (Central Scientific Research Instituteprojectstalconstruction named after N.P. Melnikov). - M.: Publishing house of the DIA, 1998. - S. 235-236]. With articulated fastenings in the planes of structures and rigid (frame) of planes, the calculated lengths of the core elements of the gratings in the planes of structures are twice as long as the calculated lengths from the planes [Metal structures. In 3 t. T. 1. Elements of constructions: Textbook for high schools. / Ed. V.V. Grief. - M.: Higher School, 2004 .-- S. 332, Fig. 6.11]. On this basis, so that the core elements of the gratings in the planes and from the planes of structures have the same flexibility, it is advisable to use such profiles of cross sections in which the radii of inertia along the main central axes also differ by half. Thin-walled tubular sections of a flat oval shape with an aspect ratio of 1 / 2.63, where large dimensions are located in the planes of the structures, and smaller ones from the planes, fully meet this condition. Moreover, the values of the radii of inertia in large dimensions exceed the radii of inertia of similar circular profiles (equal in cross-sectional areas), which in a certain way contributes to a further decrease in the material consumption of the supporting structures. In addition, flat oval profiles in the proposed load-bearing structures with an aspect ratio of 1 / 2.63 differ from flat oval pipes according to GOST R 54157-2010 [GOST R 54157-2010. Steel profile pipes for metal structures. Technical conditions - M .: Standartinform, 2011. - S. 62-65].

The proposed technical solution is illustrated by graphic materials, where in FIG. 1 shows a fragment of a supporting structure with a grating of a flat oval pipe; in FIG. 2 is a cross section of a supporting structure; in FIG. Figure 3 shows a fragment of the supporting structure with a lattice of a flat oval pipe and units unified using structural eccentricities for the upper belt; in FIG. 4 is a cross-sectional view of a supporting structure with standardized units; in FIG. 5 shows a design diagram of a cross section of a flat oval pipe; in FIG. 6 is a design diagram of one of two curvilinear sections of a cross section of a flat oval pipe having the shape of round half rings; in FIG. 7 shows a general view of flat oval profiles.

The proposed technical solution of the supporting structures includes the upper (compressed) belts 1, the lower (extended) belts 2, as well as the lattices 3 connecting them in a zigzag shape from flat oval pipes. The sections of the flat oval pipes are selected with a ratio of 1 / 2.63, where the larger dimension is located in the planes of the structures, and the smaller one is from the planes. In the places provided for by the project for the faceless nodal connections of belts with gratings, flat-oval profiles of lattice elements are flattened to form sites that are necessary and sufficient for convenient placement, centering and reliable fastening of all elements converging in each node (including parts of suspended ceilings, suspended cranes, engineering communications , technological equipment, etc.). Flat-oval profiles of the core elements of the gratings in the places necessary for the project after flattening by double bends give a zigzag shape.

The formation of transitional and flattened sections of the core elements of the tubular section of the gratings is recommended to be made with a slope of the transitional section 1/6 ... 1/4 [1. Trofimov V.I., Kaminsky A.M. Lightweight metal structures of buildings and structures: Textbook. - M.: Publishing house of the DIA, 2002. - S. 152; 2. J.A. Packer, J. Wardenier, X.-L. Zhao, G.J. van der Vegte and Y. Kurobane. Construction with hollow steel sections. Design Guide for rectangular hollow section (RHS) joints under predominantly static loading. CIDECT, 2009. - P. 102]. Sheet hinges are formed along the double bending lines, the distance between which can be selected from the condition of the absolute centering of the frameless units of the supporting structures (trusses) both with triangular lattices and diagonal. Between these hinges, the flattened sections of the flat-oval grating profiles reinforce the flanges of the waist elements, while at the same time observing the necessary and sufficient placement of welds. The latter should be calculated only on the difference in effort in adjacent rods, and they can be welded in the most convenient (lower) position.

To derive the above ratio and quantify the resources of the bearing capacity, it is advisable to calculate the axial moments of inertia I _X and I _Y , as well as the cross-sectional area A of the flat oval tubular profile. The section of this profile can be considered as a figure that includes two rectangles and two half rings. In turn, a sector of a thin-walled ring with an angular parameter α = 90 ° = π / 2 = 1.57 can be taken as a composite half-ring [Reference for resistance of materials. / Ed. G.S. Pisarenko. - Kiev: Naukova Dumka, 1988. - S. 68-69]:

where y _c , I _X , I _Y , A are respectively the ordinate of the center of gravity of the section, the moment of inertia of the section relative to the xx axis, the moment of inertia of the section relative to the y-y axis, the cross-sectional area of the half ring;

R is the radius of the semicircle along its midline, R = 0.5U;

U is the smaller dimension of the cross section of the flat oval pipe in the midline;

V is the larger dimension of the cross section of a flat oval pipe in the midline;

n is the ratio of the smaller to the larger, n = U / V;

t is the wall thickness of the flat oval pipe.

To calculate the axial moments of inertia of a section of a flat oval pipe, you can apply the rule of parallel transfer of axes:

where the value of the larger dimension V is replaced by its ratio with the smaller dimension U, that is, V = U / n.

The cross-sectional area of a thin-walled flat oval pipe can be calculated along the length of the midline:

The obtained calculation formulas must be tested, since the middle line of the cross section of the flat oval pipe was used to derive them. In addition, in the calculation of the moment of inertia of the cross section relative to the yy axis, the second term is excluded, which is very insignificant in its absolute value due to the thickness parameter raised to the third power contained in it. It is advisable to perform the test calculation on the basis of the 12 largest large-caliber and thick-walled flat-oval type A pipes according to GOST R 54157-2010, and its main results are more clearly presented in tabular form. As can be seen, the obtained calculation formulas are correct enough to continue numerical calculations with their application.

In order for the radii of inertia along the main central axes to differ by half (i _X = 2i _Y ), the corresponding moments of inertia must differ by four times, that is, I _X ⁼ 4I _Y.

If we substitute the values of the moments of inertia, then for the ratio of the smaller to the larger (n = U / V), we can obtain the cubic equation

with roots

Of these roots, the second is of practical interest, the value of which can be rounded to n ₂ = 0.38024 = 1 / 2.63, thereby obtaining the above ratio.

If, to continue the computational calculations, we take as the initial data the cross-sectional area A = const with the thickness t = const of the strip (sheet blank), then with respect to flat-oval pipes with the ratio n = 0.38024 = 1 / 2.63, we can write:

It is interesting to compare the results of the new technical solution with its prototype, which is an oval pipe with a ratio of n = 0.4 = 1 / 2.5. Then, taking in this case A = const with t = const, as applied to the prototype, we can similarly write:

A comparison of the results allows us to conclude that all the calculated parameters of the prototype in absolute value exceed the calculated parameters of the proposed solution:

that is, under given conditions, when A = const and t = const, and i _X = 2i _Y (I _X = 4I _Y ), cross-sectional pipes have 10.7 ... 16.5% more cross sections than oval pipes In this case, oval pipes have geometric cross-sectional characteristics 4.5 ... 10.4% more than flat oval pipes.

мм на базе круглой трубы

мм с площадью сечения 9,3965 см², принятой из условия обеспечения прочности на разрыв нисходящего, то есть растянутого, опорного раскоса.The findings can be illustrated by the example from the material of patent No. 2554643 (prototype), where an oval tube was used for a triangular lattice of a zigzag shape

mm based on a round pipe

mm with a cross-sectional area of 9.3965 cm ² , adopted from the condition for ensuring the tensile strength of the downward, that is, stretched, support brace.

мм имеет следующие характеристики:Oval pipe brace

mm has the following characteristics:

- длина раскоса; λ* - приведенная гибкость; R_y - расчетное сопротивление стали по пределу текучести; Е - модуль упругости стали; φ - коэффициент продольного изгиба.where λ is the design flexibility;

- the length of the brace; λ * - reduced flexibility; R _y is the calculated steel yield strength; E is the modulus of elasticity of steel; φ is the coefficient of longitudinal bending.

The characteristics of the same brace from a flat oval pipe will differ slightly:

мм компактнее овальной на 10…17% (121/110=1,1 и 49/42=1,17), то ее несущая способность уменьшилась всего на 1,7% (0,797/0,784=1,017). Такие итоги делают выбор плоскоовальной трубы более обоснованным, поскольку форма ее проще, трудоемкость изготовления и применения в конструкции меньше, а цена ниже.that is, if a flat oval pipe

mm more compact than oval by 10 ... 17% (121/110 = 1.1 and 49/42 = 1.17), then its bearing capacity decreased by only 1.7% (0.797 / 0.784 = 1.017). Such results make the choice of a flat oval pipe more justified, since its shape is simpler, the complexity of manufacturing and use in the structure is less, and the price is lower.

Thus, the proposed technical solution allows, depending on the design solutions, a certain selection of the ratio of the dimensions of the cross section of flat oval pipes, as well as the location of these dimensions in the axial planes of the structures to regulate their stress-strain state. Such regulation provides optimization of the physico-mechanical properties and technical and economic characteristics of the supporting structures of buildings and structures. At the same time, it becomes possible to use round tubes corresponding to their caliber as initial blanks for flat oval profiles, which can lead to an additional positive effect. As factory joints of such blanks, welded joints with longitudinal slots are quite applicable [Marutyan A.S., Kobalia T.L., Pavlenko Yu.I. Welded butt connection of tubular rods. - Patent No. 2429329, 09/20/2011, bull. No. 26], which are easier to place in areas free from flattening.

Claims (1)

The supporting structure with a lattice of flat oval pipes, including belts and a lattice rigidly attached to them, made with tapered ends of curved elements of a zigzag shape, characterized in that the core elements of the lattice have a flat oval cross section with a ratio of dimensions 1 / 2.63, where the larger dimension is located in the plane of the structure, and the smaller one from the plane.

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