RU2056489C1 - Thin-walled metal beam of unclosed profile - Google Patents

Abstract

FIELD: civil engineering. SUBSTANCE: planks are attached to metal beam of unclosed profile to enhance anti-torque properties. EFFECT: decreased metal consumption, increased bearing capacity, simplified structure and manufacturing. 2 dwg

Description

 The invention relates to construction and mechanical engineering and can be used in structures experiencing complex resistance, including a combination of torsion deformations with bending deformations and axial compression.

 Known thin-walled metal beam of an open profile, reinforced with anti-torsion bonds in the form of strips, rigidly connected to the edges of opposite shelves.

 In this beam, welding stresses that are harmful to the structure and labor costs during manufacturing are minimized. However, such a beam has insufficient torsional bearing capacity. To increase the bearing capacity, it is necessary to increase the total width of the strips. However, this causes an increase in material consumption, i.e. increasing the metal intensity of the beam.

 Also known are the designs of thin-walled metal beams of an open profile, in which the strips are either located at an oblique angle to the wall in the plane of the cross section of the beam (ed. St. N 706512, class E 04 C 3/06, 1979), or are located at an oblique angle to shelves and form a cross system that does not have intersection points in space (ed. St. N 894126, CL E 04 C 3/06, 1981).

 In these beams, due to some complexity of the design, it is possible to slightly increase the bearing capacity and reduce the metal consumption. However, as before, an increase in the bearing capacity of the beam due to an increase in the total width of the slats causes an increase in the metal consumption of the structure.

 The purpose of the invention is to achieve the optimal ratio between a simultaneous increase in the bearing capacity of the beam during torsion and a decrease in metal consumption.

This is achieved by the fact that in a thin-walled metal beam of an open profile, supported by anti-torsion bonds in the form of strips, the ratio of the total width b of the strips to the length l of the beam with a cross-section height h is selected in the range:
at l≅hb / l (1 / 5-1 / 3);
at 2h≥l> hb / l (1 / 11-1 / 6);
at 3h≥l> 2h b / l (1 / 17-1 / 12);
for l> 3h b / l (1 / 20-1 / 18).

 To determine the design optimum, a special dimensionless design efficiency coefficient was introduced that characterizes the beam with the slats at the same time both in torsional bearing capacity and in metal consumption, an analytical dependence is obtained to determine this coefficient through the physicostructural parameters of the beam and slats, it is shown that when parameters are changed strips their total width is the most influencing on the efficiency coefficient parameter, a study of the efficiency coefficient to an extremum, as a result of which the above relations were obtained between the total width of the slats and the length of the beam for various lengths of the beam and the height of its cross section.

 In FIG. 1 shows a thin-walled metal beam of a channel section, reinforced by trims; figure 2 graphs of the dependences of the efficiency coefficients on the total width of the strips at different lengths of the beam.

A thin-walled metal beam 1 of an open profile with a length l and a cross-sectional height h consists of a wall 2 and shelves 3, to the opposite edges 4 of which there are rigidly connected strips 5, each of thickness δ and width b _i , parallel to wall 2 and distributed uniformly along the length of the beam, this total strip width b Σb _i selected from the above conditions.

 In FIG. 1, an example is a beam of a channel section with straight strips 5 parallel to the wall 2 of the beam, however, these analytical relations are also completely true for designs of a channel section with oblique strips. In the case of a beam of a different section, for example, an I-beam, the ranges of b / l corresponding to the optimum of the efficiency coefficient will shift somewhat, however, the nature of the relations will not change fundamentally.

(1) где С и С_б жесткости на кручение балки с планками и без планок; Р_б и Р_п вес балки без планок и суммарный вес планок.The dimensionless coefficient k of the design efficiency of the beam with slats takes into account simultaneously the load-bearing capacity of the beam during torsion and metal consumption
K

(1) where C and C _{b are the} torsional rigidity of the beam with and without trims; R _b and R _{p the} weight of the beam without strips and the total weight of the strips.

 As follows from (1), the efficiency coefficient k 1 in the absence of strips and the more how many times the strips increase the torsional stiffness of the beam compared to a beam with a fully open profile, but at the same time k the less how many times the presence of the strips increases the beam weight. Thus, the dimensionless coefficient of efficiency k is universal, taking into account both the positive effect of increasing the bearing capacity of the beam during torsion due to the introduction of slats, and the negative effect of increasing the weight of the beam, i.e. metal construction.

(2) где C_Ω- секториальная жесткость планки; I_к момент инерции сечения балки при свободном кручении; I_Ω- секторальный момент инерции; Е и G модули упругости материала при растяжении (сжатии) и при сдвиге.We express the coefficient of efficiency k through the physico-structural parameters of the beam and slats. Hardness C can be written as
C

(2) where C _Ω is the sectorial stiffness of the bar; I _{to the} moment of inertia of the beam section in free torsion; I _Ω is the sectoral moment of inertia; E and G are the elastic moduli of the material under tension (compression) and shear.

•4Ω², (3) где I_п δb³/12 (4);Ω секториальная координата (площадь). Жесткость на кручение балки без планок С_б GI_к/l (5). С учетом выражений (2)-(5) коэффициент эффективности k при подстановке указанных выражений в (1) будет иметь вид:
K

(6)
Из полученной зависимости (6) видно, что изменение параметров планок для получения максимального значения коэффициента эффективности k связано как с изменением суммарной ширины b планок, так и их толщины δ. Аналогическим определением коэффициентов влияния ∂k/∂b и ∂k/∂δ (методика из теории чувствительности), их вычислением и сравнением для балок с различными характеристиками показано, что величина ∂k/∂b превосходит ∂k/∂δ более чем на порядок, то есть ширина планок b является максимально влияющим на коэффициент эффективности k параметром.For the straight bar C _Ω =

• 4Ω ^2, (3) where I _n δb ^3/12 (4); Ω sectorial coordinate (square). The torsional rigidity of the beam without strips C _b GI _k / l (5). Taking into account expressions (2) - (5), the efficiency coefficient k when substituting the indicated expressions in (1) will have the form:
K

(6)
From the obtained dependence (6), it can be seen that a change in the parameters of the bars to obtain the maximum value of the coefficient of efficiency k is associated with both a change in the total width b of the bars and their thickness δ. By analogous determination of the influence coefficients ∂k / ∂b and ∂k / ∂δ (a technique from the theory of sensitivity), their calculation and comparison for beams with different characteristics, it is shown that the value ∂k / ∂b exceeds ∂k / ∂δ by more than an order of magnitude , that is, the width of the slats b is the parameter most influencing the efficiency coefficient k.

 Further, dependence (6) was investigated for extremum by analytical and graphical methods. As a result of such a study, for the beams with different lengths l and height h of the cross section, the necessary ranges of the ratios of the total width b of the slats to the length l of the beam were obtained, at which the efficiency coefficient k is in the areas of maximum values.

 In FIG. Figure 2 shows the results of a graphical study where the dependences of the efficiency coefficient k are plotted on changing the total width b of the slats for beams with a constant cross-section height h 40 cm and various lengths l.

 As a result of the studies, it was proved that the value of the b / l ratios corresponding to the maximum of the efficiency coefficient k is determined not by the absolute values of the beam length l and the height of the cross section h, but by the limiting relations between them. It is rational to set the dependencies for b / l ratios not by a single value corresponding to the peak value of the efficiency coefficient k, but by a range of values under which the values of the coefficient k differ from the maximum by no more than 20%. This is because the beam parameters are usually not strictly nominal, and some “swim” in certain tolerances, and “swimming” k roughly corresponds to these tolerances. If necessary, the ranges of changes in the b / l ratios can be easily sharply compressed, which, however, will somewhat complicate the process of manufacturing a beam with slats.

The main physical and structural parameters of the studied beams when constructing the dependencies in figure 2: h 40 cm; l is variable and indicated on the curves; δ 0.6 cm; Ω = 121.67 cm ² ; I _to 59.74 cm ⁴ ; I _Ω = 148100 cm ⁶ ; P _b = 24.15 kg; E 2.1 · 10 ⁶ kg / cm ² ; G0.8 · 10 ⁶ kg / cm ² . The values of k and b are shown in the graphs in figure 2 (b in cm, k is dimensionless).

Claims (1)

THIN-WALL METAL BEAM OPEN PROFILES, reinforced with anti-torsion bonds in the form of strips, characterized in that the ratio of the total width b of the strips to the length l of the beam with the height h of the cross section is selected in the range
when l ≅ hb / l = 1/5 - 1/3;
for 2h ≥ l> hb / l = 1/11 - 1/6;
at 3h ≥ l> 2h b / l = 1/17 - 1/12;
for l> 3h b / l = 1/20 - 1/18.

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