RU2664092C1 - Three-sided lattice support with belts of flat oval pipes - Google Patents

Abstract

FIELD: construction.SUBSTANCE: invention relates to the field of construction and can be used as supporting structures for antenna-mast systems, lightning conductors, power transmission lines, radio relay communication, wind power plants, lighting towers, chimneys and other engineering structures. In a three-sided lattice support made of tubular profiles, which includes belts and rods of grids, connected by means of welded sleeves and joints on bolts through flanges, the cross sections of the belts have a flat-oval shape with a ratio of overall dimensions of 1/1.542.EFFECT: reducing the complexity of manufacturing support structures and reducing the cost of them.1 cl, 4 dwg

Description

The invention relates to the field of construction and can be used as supporting structures for antenna mast systems, lightning rods, power lines, microwave links, wind turbines, lighting towers, chimneys and other engineering structures.

A well-known technical solution is a trihedral lattice support with belts of closed triangular, quadrangular or pentagonal profiles made by bending a steel sheet, as well as a symmetrical reverse bending at an angle of 60 ° of both edges of the same sheet in the form of sheet gussets for nodal connections of the bars of the gratings [Sabitov L .S., Kuznetsov I.L., Baterdinov I.R. Trihedral lattice support. - Patent No. 2564337, 05.20.2016, bull. No. 14].

Such a technical solution is 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, which is accompanied by material hardening and an increased stress concentration. In this case, this defect is aggravated by double bends at sharp angles in the opposite directions. Shapes for connecting the rods of the gratings are necessary only in places where they adjoin the belts, and in trihedral tubular supports such joints are completely shapeless, and nodal shapes have limited use in mounting joints [Metal structures. In 3 t. T. 3 / Ed. V.V. Kuznetsova. - M.: Publishing house of the DIA, 1999. - C. 42-43, Fig. 1.29]. Therefore, double gussets along the entire length of the belts can cause an increase in the consumption of structural material and additional costs caused by the processing of the end edges of the grating rods with longitudinal slots to pass these gussets. In addition, such gussets form sinuses that impair the performance of load-bearing structures (especially open ones).

The closest technical solution (adopted as a prototype) to the proposed trihedral lattice support with belts of flat oval pipes is a tubular design in which all the core elements of the belts and lattices (including braces and struts) have round sections, factory connections in the form of welded blockless assemblies and mounting joints on bolts through flanges [Metal constructions. In 3 t. T. 3. / Ed. V.V. Kuznetsova. - M.: Publishing house of the DIA, 1999. - S. 42-43, Fig. 1.28].

The main disadvantage of the prototype is the complex shape (curly) of cutting the end edges of the rods of the gratings (braces and struts) for their direct adjacency in the nodal joints to the belts, the surfaces of which are characterized by the complete absence of flat sections, which requires increased accuracy of manufacturing and assembly and welding operations, increases the complexity and is accompanied by a certain increase in costs. This disadvantage in a certain way limits the scope of application of round pipes, in which they are significantly inferior to rectangular profiles, massively in demand in construction practice.

The technical result of the proposed solution is to reduce the complexity of the manufacture of supporting structures and lower costs.

The specified technical result is achieved in that in a trihedral lattice support of tubular profiles, including belts and lattice rods connected by welded sleeveless assemblies and mounting joints on bolts through flanges, the cross sections of the belts have a flat oval shape with a ratio of overall dimensions of 1 / 1,542.

In the proposed supporting (supporting) structure, all three belts, as well as the gratings between them, are made of tubular profiles. For direct adjacency to the belts with the formation of blockless assemblies, all the core elements of round pipe gratings have a flat groove of the end edges at certain angles of inclination relative to the waist elements. Such cutting is the simplest and most technologically advanced, because it allows processing not individual rods, but batch processing of the same type of elements with flat cutters, milling cutters or band saws. For the convenience of applying weld beads and increasing the degree of unification of frameless nodal joints, the use of structural eccentricities limited by 0.25 of the height of the waist elements from rectangular pipes is justified, which allows them to be ignored in the calculations [Guide for the design of steel structures from bent welded closed profiles / M. : TsNIIproektstalkonstruktsiya, 1978. - S. 24, p. 4.2.8]. This assumption as applied to flat-oval pipe belts needs to be confirmed by appropriate studies and experimental studies. However, it may well serve as a kind of theoretical and theoretical prerequisite in the new technical solution, which provides triangular support for the equal stability of tubular belts of plane oval pipes relative to the axial planes of the gratings. Proceeding from this, so that the core elements of the belts in the planes and from the planes of the gratings have the same flexibility, it is advisable to use the given constructive eccentricity to calculate the optimal parameters of plane oval pipes.

The proposed technical solution is illustrated in FIG. 1-4, where in FIG. 1 shows a perspective view of a fragment of a trihedral lattice support with belts of flat oval tubes; in FIG. 2 is a design diagram of a cross section of a belt with a constructive eccentricity of a frameless assembly; in FIG. Figure 3 shows a cross-section of a support structure with belts of flat oval pipes optimized by the criterion of equidistance; in FIG. 4 is a cross-sectional view of a support structure with belts of flat oval tubes optimized for maximum bending strength.

The proposed technical solution for the supporting structure includes belts 1, as well as lattices connecting them from braces 2 and struts 3. Factory connections are designed in the form of frameless assemblies with one-sided abutments of braces 2 and struts 3 to belts 1, as well as using structural (calculated) eccentricities, in absolute value equal to 1/4 of the smaller overall size of the flat oval section of the waist pipe. Mounting joints 4 are made using coupling bolts through the flanges.

To derive the given ratio of the overall dimensions of the flat oval section of the belts and a quantitative assessment of the resources of their bearing capacity, it is advisable to use the calculation formulas tested when optimizing the parameters of flat oval pipes for truss lattices [Marutyan AS, Abovyan AG Calculation of the optimal parameters of flat oval pipes for trusses. - Structural mechanics and calculation of structures, 2017, No. 4. - S. 17-22]:

I _x = U ³ t (0,0740286 + 0,785 (1 / n-0,363) ² + (1 / n-1) ^3/6);

I _y , = U ³ t (0.5 / n-0.1075);

A = Ut (2 / n + 1.14),

where I _x , I _y , A - respectively, the moment of inertia of the section relative to the xx axis, the moment of inertia of the section relative to the yy axis, sectional area

U is the smaller overall cross-sectional dimension of the flat oval pipe in the midline;

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

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

t is the wall thickness of the flat oval pipe.

When the center of the shapeless nodal connection is combined with the center of gravity of the cross section of the waist pipe, the moments of inertia of the section can be determined taking into account the angle of rotation of the axes:

where α is the angle of rotation of the axes, α = 30 °, cos ² α = 0.75, sin ² α = 0.25.

Obviously, such a section of the waist pipe is rational that is equally stable with respect to the plane of the lattice when the flexibility in the plane of the lattice is equal to the flexibility of this plane, that is, I _xp = I _yp . Then, substituting the values of the moments of inertia, we can obtain the cubic equation

0.0591503n ³ -0.284955n ² + 0.1425n + 0.0833333 = 0 with roots

n ₁ = -0,3389272, n ₂ = 1,0001144, n ₃ = 4.1562863,

of which the second root is of practical interest

n = 1.0001144≈1

with an error of 100 (1.0001144-1) / (1.0001144 ... 1) = 0.01143 ... 0.01144%.

This result shows that in the case of zero eccentricity, a rational technical solution with round pipe belts is adopted as a prototype:

n is 1;

U = V = D;

I _x = U ³ t (0,0740286 + 0,785 (1 / 1-0,363) ² + (1 / 1-1) ^3/6) = 0,3925572U ^{3 3} t t≈0,3925D

with an error of 100 (0.3925572-0.3925) / (0.3925572 ... 0.3925) = 0.01457%;

I _y = U ³ t (0,5 / 1-0,1075) = 0,3925U ³ t = 0,3925D ³ t;

with error

with an error of 100 (0.3925142-0.3925) / (0.3925142 ... 0.3925) = 0.00361%,

where D is the diameter of the equivalent (equal in cross-sectional area) round pipe along the midline of its section;

I _x = I _y = I _xp = I _yp = 0.3925D ³ t = πD ³ t / 8 - axial moments of inertia of the cross section of the same pipe;

A = πDt = 3,14Dt - sectional area of the same pipe.

In the proposed technical solution, when the center of the shapeless nodal connection is shifted relative to the center of gravity of the cross section of the waist pipe by a distance equal to 1/4 of the smaller dimensions of the flat oval section (0.25U), the moments of inertia of the section can be determined taking into account the angle of rotation of the axes and the reduced distance between the axes of the ordinates:

To ensure equilibrium, as in the case of the prototype, taking I _xp = I _yp or I _xp -I _yp = 0, we can obtain the cubic equation

0,0120998n ³ + 0,409955n ² -0,1425n-0,0833333 = 0 the roots

n ₁ = -34.2194198, n ₂ = -0.3103104, n ₃ = 0.6485917,

of which the third root is of practical interest

n = 0.6485917 = 1 / 1.541802≈1 / 1.542 with an error of 100 (1.542-1.541802) / (1.542 ... 1.541802) = 0.01284%.

Thus optimized flat oval section of the waist pipe has the following parameters:

n = 1 / 1.542;

I _x = U ³ t (0,0740286 + 0,785 (l, 542-0,363) ² + (1,542-1) ^3/6) = 1,1917413U ³ t;

I _y = U ³ t (0.5 × 1.542-0.1075) = 0.6635U ³ t;

A = Ut (2 × 1.542 + 1.14) = 4.224Ut;

I _xp = I _x cos ² α + I _y sin ² α = U ³ t (l, 1917413 × 0.75 + 0.6635 × 0.25) = 1,0596854U ³ t;

with an error of 100 (1,0596854-1.0595603) / (1.0596854 ... 1.0595603) = 0.0118%.

To compare the proposed technical solution and its prototype, the obtained values of the calculated parameters should be expressed in terms of the cross-sectional area and the thickness of the sheet blank (strip), taking them as constant values (A = const and t = const):

- round section of a waist pipe

D = A / (3.14t) = 0.3184713A / t;

I _x = I _y = I _xp = I _yp = 0.3925 (0.3184713A / t) ³ = 0.0126779A ³ / t ² ;

- flat oval section of the waist pipe

U = A / (4,224t) = 0,2367424A / t

I _xp = I _yp = 1.0596 (0.2367424A / t ³ ) t = 0.0142376A ³ / t ²

As you can see, the moments of inertia of the section of the waist pipes relative to the planes of the lattices in the proposed technical solution is greater than in its prototype by 100 (0.0142376-0.0126779) / (0.0142376 ... 0.0126779) = 10.95 ... 12.3 %

Of practical interest may be another comparison of the proposed technical solution and its prototype in the case where the flat oval section of the waist pipes has a different overall dimension ratio than that given. Such a ratio can be, for example, 1 / 3,064, obtained as a result of optimization of a flat oval cross-section of a tubular profile from the condition of its greatest bending strength (W _x = W _{x, max} ) [Marutyan AS The method of reprofiling a round pipe. - Patent No. 2623558, 06/27/2017, bull. No. 18]:

n = 1 / 3.064;

A = Ut (2 × 3.064 + 1.14) = 7.268Ut;

U = A / (7.268t) = 0.1375894A / t;

I _x = U ³ t (0,0740286 + 0,785 (3,064-0,363) ² + (3,064-1) ^3/6) = 7,2663913U ³ t;

I _y = U ³ t (0.5 × 3.064-0.1075) = 1.4245U ³ t;

I _xp = I _x cos ² α + I _y sin ² α = U ³ t (7.2663913 × 0.75 + 1.4245 × 0.25) = 5.8059184U ³ t

As you can see, when the center of the shapeless nodal connection is shifted relative to the center of gravity of the cross section of the waist pipe by a distance equal to 1/4 of the smallest of the dimensions of the flat oval section (0.25U), in the case under consideration, the ratios of the moments of inertia of the section were different from unity:

I _{xp /} I _yp = 5.8059184 / 3.3392228 = 1.7396019.

You can bring this ratio to unity by selecting the appropriate eccentricity value:

I _xp / I _yp = 1

I _xp -I _yp = 0

5.8059184-2.8849728-7.268e ² = 0;

e ² = (5.8059184-2.8849728) / 7.268 = 0.4018912;

e = 0.6339488;

I _yp = U ³ t (2.8849728 + 7.268 × 0.4018912) = 5.805918U ³ t.

Then, with an eccentricity of 0.6339488 of the smaller overall size of the flat oval section (0.6339488U or e / U = 1 / 1.5774)

I _xp = I _yp = 5.805918U ³ t = 5.805918 (0.137589A / t) ³ t = 0.0151214A ³ / t ² , which exceeds the moments of inertia of the cross section of the round pipe of the prototype belts by 100 (0.01512-0 , 0126779) / (0.015122 ... 0.0126779) = 16.2 ... 19.3%.

The result obtained is ensured by eccentricity, which cannot be neglected, because because of it the center of the sleeveless assembly shifts beyond the flat oval section of the waist pipe with a ratio of overall dimensions of 1 / 3.064.

Thus, summing up some of the results, we can conclude that the flat-oval section of the waist pipes optimized by the criterion of equidistance with respect to the planes of the gratings with a ratio of overall dimensions of 1 / 1,542 with an eccentricity of 1/4 smaller dimensionless assemblies is quite promising for use in supporting structures. If we add to this that the cutting of the end edges of all the core elements of round pipe gratings is limited to flat cuts, then the positive effect of the proposed technical solution may turn out to be more visual and significant.

Claims (1)

A triangular lattice support made of tubular profiles, including belts and lattice rods connected by welded frameless assemblies and mounting joints on bolts through flanges, characterized in that the cross sections of the belts have a flat oval shape with a ratio of overall dimensions of 1 / 1,542.

Images