RU2554643C1 - Load-carrying structure with frame from oval tube - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: load-carrying structure with a frame from an oval tube includes flanges and a frame rigidly attached to them and provided with flattened ends from bent elements of zigzag shape; with that, rod-like elements of the frame have an oval cross-section with the ratio of overall dimensions of 1/2.5, where larger dimension is located in the plane of the structure and the smaller one is located out of the plane.

EFFECT: increasing carrying capacity of the structure with reduction of consumption of its structural material.

4 dwg, 2 tbl

Description

The proposed technical solution relates to construction, namely to long-length building bearing lattice structures of pipes, and can be used in the manufacture of trusses, girders, columns, arches, frames and other frame systems. Tubular building structures are distinguished by enhanced technical and economic characteristics, since the structural material (steel, aluminum alloy, metal-plastic, composite, polymer, synthetics, etc.) is located in a cross section of elements in a very efficient manner. However, the further growth of technical and economic characteristics due to the use of more rational especially thin-walled pipes (closed bent-welded profiles) is restrained due to the complexity of technical solutions of nodal connections of rod elements in lattice structures.

The greatest distribution in tubular farms was given to nodular shaped fittings with direct adjoining of the lattice rods to the belts [1. Metal constructions. In 3 t. T. 1. Elements of construction: Textbook. for universities. / Ed. V.V. Grief. - M.: Higher School, 2001 .-- S. 459, 462, Fig. 7.26, a; 7.28, a; 2. Metal structures: Textbook. for universities. / Ed. Yu.I. Kudishin. - M.: Academy, 2007 .-- S. 292, 295, Fig. 9.24, 9.27]. Here, in order to avoid punching (pulling out), the diameter of the lattice pipe should not be less than 0.3 of the diameter of the belt pipe. In farms of rectangular (square) pipes, this restriction is doubled twice, that is, the width of the lattice rod should be taken at least 0.6 of the transverse size of the belt.

The disadvantage of the described nodes is the noted limitation, the consideration of which leads to an increase in the consumption of material on the rods and increase the metal consumption of the structure.

Another well-known technical solution is a lattice structure with a nodular non-shaped connection of tubular elements of the truss (options), in which the diagonal cross section of a rectangular (square) belt is located in the axial plane of the truss, and the braces at the junction have a through cutout (V-shaped), completely repeating the geometry of this abutment. Due to such a cutout, the connection of each of the elements of the lattice with the belt is carried out along two adjacent walls [1. Zinkova V.A., Sokolov A.A. Nodal non-block connection of tubular elements of the farm. - Patent No. 2229361, 07.20.2008, bull. No. 20; 2. Sokolov A.A., Logachev K.I., Zinkova V.A. Numerical studies of the stress-strain state of nodular sleeveless joints of tubular elements of farms. - Industrial and civil engineering, 2007, No. 8. - S. 40-41; 3. Zinkova V.A., Solodov N.V. The study of the stress-strain state of non-shaped nodes tubular farms. - Modern problems of science and education. - Penza: Publishing House Academy of Natural Sciences, 2013, No. 6. - S. 205-212]. Similarly, in the axial plane of the truss of square pipes, there are diagonals of cross sections of all the rod elements (both the upper belt and the lower belt, and the braces of the lattice between them) [1. Kuznetsov A.F., Kuznetsov V.A. Farm of square pipes. - Patent No. 116877, 06/10/2012, bull. No. 16; 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. 100-101].

A disadvantage of the known technical solution is the difficulty of its application in farms without running coatings, since the edge of the belt can crush sheets of profiled flooring. In running coatings, the very edge of the belt can be wrinkled by the run, therefore, it is necessary to arrange support tables for runs, which negatively affects the material consumption of structures, and also increases the complexity of their manufacture and installation. This drawback can be eliminated with the help of belt elements of a pentagonal section with one horizontal (shelf), two vertical and two inclined walls [Marutyan AS, Kobalia TL, Pavlenko Yu.I., Glukhov SA Nodal non-block connection of tubular elements of the farm. - Patent No. 116526, 05.27.2012, bull. No. 15].

A common drawback of the above technical solutions lies in the increased rigidity of sleeveless nodal connections of tubular trusses [Pokrovsky A.A. About taking into account the stiffness of nodes in the calculations of farms with elements of low flexibility. - Structural mechanics and calculation of structures, 2011, No. 3. - S. 31-32]. In order not to take into account additional bending moments from the stiffness of the nodes, building codes recommend to calculate the tubular trusses according to the hinge scheme, provided that the ratio of the section height to the length of the core elements does not exceed 1/15 ... 1/10 [SNiP P-23.81 *. - M.: OJSC “TsPP”, 2008. - S. 43-44]. Obviously, the diagonal spread of square tubular profiles, transforming them into a rhombic configuration, is accompanied by an increase in the stiffness of frameless nodes, and this happens for two reasons. The first reason is an increase in the height of the cross-section of the core elements. The second reason is the direct conjugation of the walls and ribs between them of the core elements of the lattice with similar walls and ribs between them of the waist elements. In addition, through-cuts of a V-shape at the points of contact of the braces to the belts, which completely repeat the geometry of these joints, require increased accuracy of manufacturing and assembly, which increases the complexity of structures.

The closest technical solution to the proposed supporting structure with an oval tube grill 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 lattice rod elements 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 A.S., Ekba S.I. Metal construction with lattice of rhombic closed bent-welded profiles. - Patent No. 2500003, December 10, 2013, bull. No. 34].

This technical solution is characterized by a disadvantage of known tubular trusses of rectangular, square, pentahedral, pentagonal, rhombic profiles, which reduces the load bearing capacity of the structure and increases its material consumption due to the angularity of the listed cross-sectional shapes, accompanied by an increased stress concentration.

The technical result of the proposed solution is to increase the bearing capacity of the structure with a decrease in the consumption of its structural material.

The specified technical result is achieved by the fact that in the supporting structure, including belts and a lattice rigidly attached to them, made with tapered ends of curved elements of a zigzag shape, the lattice core elements have an oval section with a ratio of dimensions of 1 / 2.5, where the larger dimension is located in plane of construction, and the smaller - from the plane.

In the proposed supporting structure, the upper and lower zones, as well as a triangular or diagonal lattice between them, are made of tubular profiles. For direct adjacency to the belts with the formation of blockless nodes, the oval tube of the grating is flattened in the places specified by the project and double bends give it a zigzag shape. The length of the strip (tape) blank oval profile can be selected based on the entire length of the structure or its shipping mark. Flattening and double bends of an oval profile provide a layout of non-shaped nodal joints without structural eccentricities characteristic of tubular trusses from rectangular (square) bent-welded profiles, which eliminates the appearance of bending moments and positively affects the consumption of structural material. Flattening protects the wall of the waist elements from punching and reduces its thickness. Along the bending lines of the oval profile in the construction plane, sheet hinges are formed that correspond to the hinge-rod design scheme (model) and eliminate the need to take into account the stiffness of the nodes, which also helps to reduce the metal consumption. From the plane of the structure, the same bends of the flattened sections of the oval profile have the greatest stiffness, close to the rigidity of the frame fastening, due to which the connecting elements can be reduced in the supporting structures, as is done, for example, in structures of Tagil coatings [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 plane of the structure and rigid (frame) from the plane, the calculated length of the lattice bar elements in the plane of the structure is twice as long as the calculated length from the plane [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]. Based on this, so that the lattice bar elements in the plane and from the plane of the structure have the same flexibility, a cross-sectional profile in which the radii of inertia along the main central axes also differ by a factor of two is appropriate. This condition is fully met by a thin-walled tubular section of an oval shape 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 out of the plane. Moreover, the value of the radius of inertia over a larger dimension exceeds the value of the radius of inertia of a similar circular profile, which in a certain way contributes to a further decrease in the material consumption of the supporting structures. In addition, oval profiles in the proposed load-bearing structure with an aspect ratio of 1 / 2.5 differ from oval pipes according to GOST R 54157-2010 [GOST R 54157-2010. Steel profile pipes for metal structures. Technical conditions - M .: Standartinform, 2011. - S. 55-61]. They also differ from another well-known technical solution, according to which to increase the load-bearing capacity of a cylindrical pipe to bend it is crimped, deforming into an oval profile with an aspect ratio of 1/3 [1. Nezhdanov K.K., Kuzmishkin A.A., Publishing S.G. New effective profiles. - News of universities. Construction, 2005, No. 10. - S. 117-120; 2. Nezhdanov K.K., Tumanov V.A., Nezhdanov A.K., Publishing S.G. A method of increasing the bending capacity of a cylindrical pipe. - Patent No. 2304479, 08.20.2007, bull. No. 23].

The proposed technical solution is illustrated by graphic materials, where in FIG. 1 shows a fragment of a supporting structure with an oval tube grill; in FIG. 2 is a cross section of a supporting structure; in FIG. 3 shows a design diagram of a cross section of an oval pipe; in FIG. 4 is a general view of oval profiles.

The proposed technical solution for the supporting structure includes an upper (compressed) belt 1, a lower (extended) belt 2, as well as a lattice 3 connecting them in a zigzag shape from an oval pipe. The cross section of the oval pipe is selected with a ratio of dimensions of 1 / 2.5, where the larger dimension is located in the plane of the structure, and the smaller one is out of the plane. In the places provided for by the project for the non-faceted nodal connections of the belts with the grating, the oval profile of the grating elements is flattened to form sites 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.). After flattening in the right places with double bends, they give a zigzag shape to the oval profile of the core elements of the lattice.

The formation of the transition and flattened parts of the core elements of the tubular section of the lattice is recommended to be made with the slope of the transition 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 absolute centering of the frameless units of the supporting structure (truss), both with a triangular lattice and a diagonal one. Between these hinges, the flattened portion of the oval profile of the grill reinforces the flange of the waist element, while providing 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 given ratio and quantify the resources of the bearing capacity, it is advisable to use the calculation formulas of the axial moments of inertia I _0X and I _0Y , as well as the cross-sectional area A _{0 of the} oval tubular profile [Designer Guide for Industrial, Residential and Public Buildings and Structures. Settlement-theoretical. - In 2 kn. Prince 1. / Ed. A.A. Umansky. - M .: Stroyizdat, 1972. - S. 364]:

I _0X = (π / 32) b ² t (3 a + b);

I _0Y = (π / 32) a ² t (3b + a );

A ₀ = (π / 2) t ( a + b),

where a is the smaller dimension of the cross section of the oval pipe;

b - a larger dimension of the cross section of the oval pipe;

t is the wall thickness of the oval pipe.

In order for the radii of inertia along the main central axes to differ by half (i _0X = 2i _0Y ), the corresponding moments of inertia must differ by four times, that is, I _0X = 4I _0Y .

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

4n ³ + 12n ² -3n-1 = 0

with roots

n ₁ = -3.209416; n ₂ = -0.193385; n ₃ = 0.402801.

Of these roots, the latter is of practical interest, the value of which with 100 (0.402801-0.4) / (0.402801 ... 0.4) = 0.695 ... 0.700 percent error can be rounded to n ₃ = 0.4 = 1 / 2.5, thereby obtaining the reduced ratio.

Further calculation calculations are more obvious when using a tubular profile of circular cross section [Reference for resistance of materials. / Ans. ed. Pisarenko G.S. - Kiev: Science. Dumka, 1988. - S. 60-61]:

d = a = b (n = 1);

A _O = πdt = 3.14dt;

I _OX = I _OY = πd ³ t / 8 = 0.3925d ³ t;

i _OX = i _OY = 0.3536d,

where d is the diameter of the round pipe.

The length of the oval L can be calculated by the formula [Korn G., Korn T. Properties of circles, ellipses, hyperbolas and parabolas. / Reference for mathematics. - M .: Nauka, 1978. - S. 70-73]:

L = π (3 ( a + b) - ((3 a + b) ( a + 3b)) ^1/2 ) = 3.14 (3 ( a + b) - ((3 a + b) ( a + 3b)) ^1/2 ).

For n = 0.4 ( a = 0.4b or 2.5 a = b) L = 11.50 a or L = 4.60b, and for n = 1 (d = a = b) L = 2πd = 6 , 28d, then a = 0.5461d and b = 1.356d.

Thus, for an oval pipe with a ratio of the dimensions of its cross section of 0.5461 / 1.365 = 1 / 2.5, you can write:

I _0X = (π / 32) b ² t (3 a + b) = (3,14 / 32) (1,356d) ² t (3 · 0,5461d + 1,365d) = 0,5491d ³ t;

I _0Y = (π / 32) a ² t (3b + a ) = (3.14 / 32) (0.5461d) ² t (3 · 1.365d + 0.5461d) = 0.13582d ³ t;

A ₀ = (π / 2) t ( a + b) = (3.14 / 2) t (0.5461d + 1,365d) = 3,000427dt,

i _0X = 0.4278d;

i _0Y = 0.2128d,

where from

I _0X / I _0Y = 0.5491 / 0.13582 = 4.0249≈4 with an error of 0.619 ... 0.623%;

i _0X / i _0Y = 0.4278 / 0.2128 = 2.0103≈2 with an error of 0.512 ... 0.515%,

where the inaccuracy in calculating the cross-sectional area of the oval and round pipes from the same conditional sheet blank was A ₀ / A _O = 3,000427 / 3,14 = 0,956, and the radius of inertia in the plane of the supporting structure increased in i _0X / i _OX = 0 , 4278 / 0.3536 = 1.21 times.

If we introduce the thin-walled parameters of round pipes t / d = 1/100 ... 1/10, then the obtained ratio of the calculated values of the cross-sectional areas and the growth of the radius of inertia should be changed accordingly to these parameters, that is,

A ₀ / A _O = 0.956 (1 / (1- (1/100 ... 1/10))) = 0.966 ... 1.062;

i _0X / i _OX = 1.21 (1 / (1- (1/100 ... 1/10))) = 1.222 ... 1.344.

Thus, the resource of bearing capacity (stability) of the core elements of the lattice from an oval pipe, ceteris paribus, increases at least 1.2 ... 1.3 times.

The correctness of the design provisions was confirmed by the example using round pipes of rod elements from the range of the MARCHI, Kislovodsk structural system [Rods and nodal elements of the MARCHI / TU 5285-001-47543297-09 system. - M., 2009]. The parameters of 11 gauges of tubular profiles (round and oval derived from them), collected in table 1, clearly illustrate the applicability and practicality of all the above calculations.

To compare the proposed (new) technical solution with the well-known as the base object, three variants of a steel truss for covering an industrial building with a span of 18 m from closed bent-welded profiles were adopted.

1. Rafter truss from bent welded profiles of rectangular (square) section [Kuzin N.Ya. Design and calculation of steel trusses coatings for industrial buildings: a Training manual. - M.: Publishing house of the DIA, 1998. - S. 157-172].

2. Farm with a lattice from a rhombic pipe [Marutyan A.S., Ekba S.I. Metal construction with lattice of rhombic closed bent-welded profiles. - Patent No. 2500003, December 10, 2013; bull. No. 34].

3. Farm with a grid of round pipes.

The material consumption of the compared options is shown in table 2, which shows that in the new solution it has a minimum value.

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 oval pipes, as well as the location of these dimensions in the axial plane of the structure (truss) to regulate the stress-strain state of the structure. 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 pipes corresponding to their caliber as initial blanks for 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 AS, Kobalia TL, 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 an oval tube grill, including belts and a lattice rigidly attached to them, made with tapered ends of curved zigzag elements, characterized in that 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 from the plane.

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