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CN-122020748-A - Calculation method for equivalent section modulus of thin-wall steel beam of pure-bending lower belt Kong Lengwan

CN122020748ACN 122020748 ACN122020748 ACN 122020748ACN-122020748-A

Abstract

The invention discloses a calculation method of equivalent section modulus of a straight-bending lower belt Kong Lengwan thin-wall steel beam, which comprises the steps of determining the width b of a web straight section, the width Duan Gaodu h of a flange, the length d of a curled straight section, the thickness t of a plate, the total length e of a long round hole, the occurrence period S of the long round hole, the semicircular radius r at two ends of the long round hole and the yield strength f y of steel, respectively calculating the effective widths of the web, the flange and the curled edge by considering local buckling and the weakening effect of the long round hole based on an effective width method, combining the three to form an equivalent effective section, calculating the effective area A eff and the distance y eff between the effective centroid and the central line of the web, and calculating the effective inertia moment I eff and the equivalent section modulus W eff . The method can realize that the section modulus after reduction can be obtained quickly by substituting the geometric dimension once, is simple and quick, and can provide high-precision zero-iteration front input for the subsequent deformation checking calculation and bending-resistant bearing capacity design.

Inventors

  • LIU FULI
  • YI XIANHUI
  • Peng Zonglai
  • ZHENG HUA
  • LI SONGQIANG
  • ZENG YIPEI

Assignees

  • 中建五局安装工程有限公司

Dates

Publication Date
20260512
Application Date
20260113

Claims (7)

  1. 1. The calculation method of the equivalent section modulus of the thin-wall steel beam of the pure bending lower belt Kong Lengwan is characterized in that the cold bending thin-wall steel beam is of a C-shaped section, and long round holes are continuously formed along a web plate, and the calculation method comprises the following steps: Step 1, determining geometric parameters and material parameters of a cold-formed thin-wall steel beam, wherein the geometric parameters comprise web straight section width b, flange straight Duan Gaodu h, hemming straight section length d, plate thickness t, slotted hole total length e, slotted hole occurrence period S and slotted hole two-end semicircular radius r, and the material parameters comprise steel yield strength f y ; Step 2, based on an effective width method, considering a local buckling effect and a slotted hole weakening effect, respectively calculating an effective width of a web, an effective width of a flange and an effective width of a curled edge; step 3, combining the effective width of the flange, the effective width of the web and the effective width of the curled edge obtained in the step 2 to form an equivalent effective section, and calculating an effective area A eff of the equivalent effective section and a distance y eff from an effective centroid to a central line of the web; ;(1) ;(2) ;(3) In the above formula, ρ w is the flexibility index of the web, ρ f is the flexibility index of the flange, ρ d is the flexibility index of the curl, The effective width coefficient is equivalent to a web, wherein 1.27 is a shape equivalent coefficient; Step 4, calculating an effective moment of inertia I eff around the x axis based on the effective area A eff and the distance y eff from the effective centroid to the web center line; I eff = ;(4) Step 5, calculating an equivalent section modulus W eff according to a formula W eff =I eff /y max , wherein y max is the distance from the outermost fiber of the compressive flange of the equivalent effective section to the centroid, and y max = is calculated as follows ; Finally, the method comprises the following steps: (5)。
  2. 2. The method according to claim 1, wherein the web is a non-stiffened plate, the effective width is calculated by considering both the local buckling effect and the oblong hole weakening effect, and the flexibility index ρ w of the web is obtained by the following calculation formula: ;(6) ;(7) where λ w is the dimensionless aspect ratio of the web and k w is the local buckling coefficient of the web.
  3. 3. The method of claim 1, wherein the flanges are free-standing plates, the effective width of which is calculated taking into account only local buckling effects, and the flexibility index ρ f of the flanges is obtained by the following calculation formula: ;(8) ;(9) Wherein lambda f is the dimensionless width-to-thickness ratio of the flange, and k f is the local buckling coefficient of the flange.
  4. 4. The calculation method according to claim 1, characterized in that the bead is a stiffener, the calculation of the effective width of which considers only the local buckling effect, the flexibility index ρ d of the bead being obtained by the following calculation formula; ;(10) ;(11) Where λ d is the dimensionless aspect ratio of the curl and k d is the local buckling coefficient of the curl.
  5. 5. The computing method according to claim 1, wherein the specific calculation formula of the effective moment of inertia I eff is as follows: ;(12) ;(13) ;(14) ;(15) Wherein I web is the effective moment of inertia of the web, I flange is the effective moment of inertia of the flange, and I lip is the effective moment of inertia of the hem.
  6. 6. The method according to claim 1, wherein the total length e of the oblong holes is 20-60mm, and the occurrence period S of the oblong holes is 50-150mm.
  7. 7. The computing method of any one of claims 1-6, wherein the computing method is applicable to a thin-walled steel beam with Kong Lengwan in an electromechanical shock-resistant hanger system of a building, an assembled utility tunnel hanger, or a shock-resistant support for a high-temperature high-pressure pipeline of an industrial plant.

Description

Calculation method for equivalent section modulus of thin-wall steel beam of pure-bending lower belt Kong Lengwan Technical Field The invention relates to a technology of cold-formed thin-wall steel members, in particular to a calculation method of equivalent section modulus of a thin-wall steel beam of a pure-formed lower belt Kong Lengwan. Background The continuous perforated cold-formed thin-wall steel beam is widely used for anti-seismic support hangers, utility tunnel cross arms and purlines of industrial plants due to light weight, high strength and rapid assembly. In order to meet the functional requirements of pipeline crossing, weight reduction or wind resistance reduction, the web plates are often densely distributed with oblong holes (hole length is 20-60 mm, hole pitch is 50-150 mm) according to the modulus of 200-600 mm, so that a 'periodical rigidity degradation' beam section is formed. However, the current GB 50018-2013 only gives a reduction coefficient of the round holes with the aperture ratio of less than 15%, and no design treatise is made on the dense oblong hole array. If the complete section formula is directly applied, the rigidity is overestimated by 10% -30%, the bearing capacity is overestimated by 25%, and the hidden risk point in the anti-seismic deformation inspection calculation is formed. The prior art routes and drawbacks are as follows: ① Empirical deduction method The 'area moment of inertia folding method' derived from Timoshenko beam theory deducts the open hole section according to the net section and multiplies the open hole section by 0.8-0.9 empirical coefficient, completely ignores the coupling effect of hole type, hole distance and local buckling, and amplifies the error of the slotted hole exponentially with the ratio of hole length to hole distance, wherein the error of the circular hole folding formula provided by AISI 100-2016 is more than 40% under some conditions, and does not cover the hemming stiffening cold-bending section. ② Effective width method simplification The hole area is regarded as zero rigidity, the height of the web plate is reduced in equal proportion, and then the zero rigidity is substituted into a standard effective width formula. The default section strain of the method is constant along the length of the beam, additional shear hysteresis and distortion buckling caused by periodic opening cannot be reflected, the flange-hemming stiffening contribution is overestimated, and the calculation result is generally unsafe. ③ Finite element refinement modeling The SOLID186 or SHELL181 is adopted to establish millimeter-scale grids for single holes/single spans, and high-precision results can be obtained by combining submodels or periodic boundaries, but grid sensitivity is remarkable, when the grid at the hole edge in a certain pipe gallery cross arm case is thinned from 2 mm to 1mm, the equivalent section rigidity fluctuates by 7%, and the method is difficult to popularize in support and hanger batch design. ④ Test regression formula The weighted inertia moment method or the piecewise regression method is only aimed at specific cross sections and specific load combinations, lacks explanation on the mechanism of 'local-distortion-open pore' triple coupling, needs to be re-fitted after the hole pattern or the load mode is replaced, has poor universality and is not dared to be directly adopted by design units. In summary, the prior art has the defects that the coupling between the hole pattern and the buckling is ignored through empirical deduction, the error is always more than 25%, the effective width method enables the hole to be zero-stiffness, periodic shearing hysteresis cannot be reflected, the result is unsafe, the finite element is accurate, but the grid is sensitive, the time is several hours and depends on a senior engineer, the hole pattern or the load is replaced through a test formula, the hole pattern or the load is invalid, and the universality is poor. The defects lead the industry to face three weaknesses of 'the inapplicability of a theoretical formula, the infeasibility of a finite element and the unreliable of an empirical formula' for a long time, and an analytic level calculation method with both precision and efficiency is needed. Disclosure of Invention The invention aims to overcome the defects of the prior art, and provides a calculation method for equivalent section modulus of a straight-bending lower-belt Kong Lengwan thin-wall steel beam, which is based on an effective width method and an explicit parameterization calculation method for hole influence, can realize that the section modulus after reduction can be quickly obtained by substituting the geometric dimension once, avoids traditional trial-and-error effective width iteration and expensive shell unit finite element analysis, and provides high-precision and zero-iteration front input for subsequent deformation checking and bending bearing capacity design. In order