Safety assessment method for web-stiffened high-strength steel cold-formed thin-walled C-shaped section perforated component

Abstract

The invention relates to a safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-shaped section perforated component, and belongs to the technical field of structural engineering. According to the safety assessment method for the web-stiffened high-strength steel cold-formed thin-walled C-shaped cross-section component, the influence of web tapping on the axial bearing capacity of the stiffening component under the action of axial pressure is studied for an LQ550 hot-dip aluminum-zinc high-strength steel cold-formed thin-walled C-shaped cross-section component with the wall thickness t not exceeding 1.5 mm, and the safety assessment of the web-stiffened high-strength steel cold-formed thin-walled C-shaped cross-section component is realized. On the basis of a large number of loading tests and nonlinear finite element calculation, the axial pressure bearing capacity ratio of members with different sizes and with or without web holes is obtained, and a calculation formula of the axial pressure bearing capacity reduction coefficient gamma J is obtained through least square fitting. And obtaining a calculation formula of the axial pressure bearing capacity Nu of the steel member with the perforated web plate based on the axial pressure bearing capacity of the steel member with the stiffened web plate and the reduction coefficient gamma J of the axial pressure bearing capacity.

Description

Technical Field

[0001] The invention relates to a safety assessment method for a web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component, belonging to the technical field of structural engineering. Background Art

[0002] In modern architecture and structural engineering, thin-walled steel components are widely used due to their light weight, high strength and good corrosion resistance. In particular, high-strength steel cold-bent thin-walled C-section components have become an important choice in many structural designs due to their excellent mechanical properties and economy, as well as their advantages of light weight, high strength, green environmental protection, reusability and high construction efficiency. In recent years, with the improvement of the performance requirements of building materials, especially in terms of environmental protection and sustainable development, hot-dip aluminum-zinc high-strength steel (such as LQ550) has received more and more attention due to its excellent corrosion resistance and strength.

[0003] Due to the need to arrange water, electricity, heating and ventilation pipelines, holes are often opened in the web of components during the construction process; at the same time, in order to avoid premature local buckling caused by excessive width-to-thickness ratio of the plate, stiffening ribs are often set on the web to improve the bearing capacity.

[0004] At present, there is no quantitative calculation regulation for the axial compressive bearing capacity of cold-bent thin-walled steel members with holes in domestic and foreign specifications, and there are only some structural measures requirements. Therefore, the phenomenon that stiffened cold-bent thin-walled steel members will further aggravate the buckling of the members and reduce the bearing capacity after the holes are opened in the webs often occurs. Although there is a safety assessment method for high-strength steel cold-bent thin-walled C-section members with unstiffened webs and holes in the prior art, such as CN114263310B, the stiffness of the web after stiffening is significantly different from that of the unstiffened straight web, so the impact of opening holes in the stiffened web on the bearing capacity of the member will also be different from the impact of opening holes in the unstiffened web; and the technology invented in CN114263310B does not consider the impact of the member length l on the bearing capacity of the member. Therefore, the prior art, such as CN114263310B, cannot accurately assess the axial compressive bearing capacity of such high-strength steel cold-bent thin-walled C-section members with holes in the webs, and has the defects of being unreliable and inaccurate in its safety assessment.

[0005] It is of great academic significance and engineering value to systematically study the bearing capacity of high-strength cold-bent thin-walled steel components with web stiffening and openings and formulate corresponding safety assessment methods. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a safety assessment method for a high-strength steel cold-bent thin-walled C-section open-hole component with web stiffening, the method comprising the following steps:

[0007] Step 1: Calculate the axial compressive bearing capacity of a high-strength steel cold-formed thin-walled C-section member with a total length of l (mm) and a web stiffener without openings. Set the member to be subjected to a design value of N D The axial pressure (unit of force is uniformly N) is applied, and the web height h (mm), flange width b (mm), curling width a (mm), and wall thickness t (mm) of the section are preliminarily designed based on engineering design experience. According to the Technical Specification for Cold-Formed Steel Structures (GB 50018-2014 Draft for Comments), the direct strength method is used to calculate the distortion and overall related buckling bearing capacity N of the high-strength steel cold-formed thin-walled C-section member with web stiffening and no openings. nd , local buckling critical force N crl ; Introduce height reduction factor β l The influence of member height on the axial compressive bearing capacity of cold-formed thin-walled steel members is considered, and the axial compressive bearing capacity of the modified web-stiffened high-strength steel cold-formed thin-walled C-section member without openings is calculated. nh Considering the design safety and economy, the requirement is: 0.7N nh ≤N D <N nh ;

[0008] Step 2: The web-stiffened high-strength steel cold-bent thin-walled C-shaped cross-section member with web height h, flange width b, and curling width a obtained in step 1 is provided with a square hole, a round hole, or an oblong hole on its web due to the building function, wherein the total area of ​​the opening on the web is A hole , the area of ​​the entire web is A web ; and introduce the total area A of the opening part of the member web hole The area A of the entire web web The ratio β An To measure the influence of the number and size of openings on the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section opening member, the axial compressive bearing capacity reduction factor γ of the web-stiffened high-strength steel cold-formed thin-walled C-section opening member is obtained. J , then the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section open-section member is N u for:

[0009] N u =0.96γ J ×N nh (1)

[0010] For safety considerations, a safety factor of 0.96 is introduced.

[0011] Step 3: Verify the axial compressive bearing capacity N calculated in step 2 u Whether it exceeds the design value of axial pressure N of the high-strength steel cold-formed thin-walled C-section open-hole member with web stiffening D, so as to determine the axial compressive bearing capacity N of the high-strength steel cold-formed thin-walled C-section open-hole member with web stiffening u security.

[0012] Furthermore, in step 3, if 0.7N is calculated u ≤N D ≤N u , it indicates that the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section open-hole member is N u The design safety requirements are met and the cross-section design is economical and reasonable, so the design is completed.

[0013] Furthermore, in step 3, if N D <0.7N u , it is judged that the design section of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component is too large and not economical, so the web-stiffened high-strength steel cold-bent thin-walled C-section component is redesigned to reduce the C-section by reducing the web height h or reducing the flange width b or reducing the wall thickness t, and the calculation is re-performed according to the steps 1 to 3 until the 0.7N is satisfied. u ≤N D ≤N u .

[0014] Furthermore, in step 3, if N D >N u , it is judged that the preliminary design of the section of the high-strength steel cold-bent thin-walled C-section opening member with web stiffening is unsafe, so that its axial compressive bearing capacity N u At this time, the web-stiffened high-strength steel cold-bent thin-walled C-section member is redesigned to increase the C-section by increasing the web height h or the flange width b or the wall thickness t, and the calculation is re-performed according to steps 1 to 3 until 0.7N is satisfied. u ≤N D ≤N u .

[0015] According to the safety assessment method of a web-stiffened high-strength steel cold-formed thin-walled C-section member with openings described in the present invention, in the step 1, based on the loading test and nonlinear finite element calculation of the web-stiffened high-strength steel cold-formed thin-walled C-section member, the distortion and overall related buckling bearing capacity N of the web-stiffened high-strength steel cold-formed thin-walled C-section member without openings are fully considered. nd , local buckling critical force N crl After the influence of lTo measure the influence of component height on the axial compressive bearing capacity of high-strength steel cold-formed thin-walled C-section components with web stiffening and no holes, the corrected axial compressive bearing capacity N of high-strength steel cold-formed thin-walled C-section components with web stiffening and no holes is obtained based on the test and finite element calculation results. nh :

[0016]

[0017] in l is the component height (mm).

[0018] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open-section member, in the step 2, the ratio of the axial compressive bearing capacity of the member with the web opening to the member with the same size without the web opening is obtained based on the loading test and nonlinear finite element calculation of the web-stiffened high-strength steel cold-bent thin-walled C-section open-section member, and the ratio of the axial compressive bearing capacity of the member with the web opening to the member with the same size without the web opening is the true value γ of the axial compressive bearing capacity reduction coefficient of the web-stiffened high-strength steel cold-bent thin-walled C-section open-section member considering the influence of the web opening. p The parameter that affects the ratio of the axial compressive bearing capacity of the member with web openings to the member of the same size without web openings is the total area of ​​openings on the member web A. hole With the entire web area A web The ratio β An , the ratio β An As a variable, the true value of the reduction factor γ obtained from the test and finite element calculation P The numerical fitting based on the least squares method is used to obtain the fitting value of the axial compressive bearing capacity reduction coefficient γ of the high-strength steel cold-formed thin-walled C-section opening member with web stiffening considering the influence of web opening. J The calculation formula is as follows:

[0019]

[0020] Among them, N u Axial compressive bearing capacity of cold-formed thin-walled C-section open-section members with high-strength steel stiffening for webs; N nh The axial compressive bearing capacity of high-strength steel cold-formed thin-walled C-section members with modified web stiffening and no holes.

[0021] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open-section component described in the present invention, the method is applicable to the design and production of cold-bent thin-walled steel sections whose material is LQ550 hot-dip galvanized steel plate and whose wall thickness t does not exceed 1.5 mm.

[0022] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open-section component, when multiple holes need to be opened in the web to meet engineering requirements in actual projects, the hole spacing should be appropriately increased to try to make the hole positions evenly distributed on the component web to reduce the mutual influence of adjacent holes.

[0023] The present invention also provides the application of the safety assessment method of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component in the design and manufacture of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component.

[0024] Beneficial effects of the present invention:

[0025] The safety assessment method of the web-stiffened high-strength steel cold-bent thin-walled C-section open-section member described in the present invention is aimed at LQ550 hot-dip aluminum-zinc high-strength steel cold-bent thin-walled C-section members with a wall thickness t not exceeding 1.5 mm. The influence of the web opening on the axial bearing capacity of the stiffened member under the action of axial pressure is studied. Based on a large number of loading tests and nonlinear finite element calculations, the axial compressive bearing capacity ratio of the members with and without web openings of different sizes and openings is obtained, that is, the axial compressive bearing capacity reduction factor γ caused by the web opening J ; Further, the present invention, based on the combination of experiments and finite element models, found that the web opening parameters that mainly affect the reduction coefficient are: the number of openings and the size of the openings. Based on a large number of experiments and nonlinear finite element calculations, the quantitative relationship between the web opening parameters and the bearing capacity reduction coefficient was obtained, and the axial compressive bearing capacity reduction coefficient γ was obtained by fitting using the least squares method. J The calculation formula is based on the axial compressive bearing capacity of the steel member with web stiffening and no opening and the axial compressive bearing capacity reduction factor γ J The axial compressive bearing capacity of the steel member with web opening is obtained as N u The calculation formula for .

[0026] The axial compressive bearing capacity reduction factor γ of the high-strength steel cold-bent thin-walled C-section member with web stiffening openings according to the present invention J Calculate the γ obtained by formula (3) J The calculated value and the measured value of the loading test do not deviate by more than 4%. Therefore, a safety factor of 0.96 is introduced to make the calculated axial compressive bearing capacity N u The above calculation formula is simple, practical, accurate and reliable, which provides a reliable technical basis for the design and calculation of high-strength steel cold-bent thin-walled C-shaped components with web stiffening openings, which are increasingly used in engineering practice, and helps promote the widespread application of such green and environmentally friendly high-performance materials in prefabricated structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1It is a schematic diagram of the cross-sectional dimensions of the web-stiffened high-strength steel cold-bent thin-walled C-shaped cross-sectional member of the present invention;

[0028] Figure 2 It is a schematic diagram of the web opening dimensions of the web stiffened high-strength steel cold-bent thin-walled C-section member of the present invention;

[0029] Figure 3 It is a schematic diagram of the numbering rules of the web-stiffened high-strength steel cold-bent thin-walled C-shaped cross-section member of the present invention;

[0030] Figure 4 It is a schematic diagram of the finite element model used in the numerical analysis of the present invention.

[0031] Figure 5 It is a schematic diagram of the comparison between the morphology of the test member and the finite element deformation cloud diagram of the high-strength steel cold-bent thin-walled C-section member with web reinforcement and no holes when reaching the ultimate bearing capacity;

[0032] Figure 6 This is a comparison chart of the axial pressure-flange lateral displacement curves obtained by test and finite element simulation for the component numbered J610-N0;

[0033] Figure 7 It is a schematic diagram of the comparison between the test member morphology and the finite element deformation cloud diagram of the high-strength steel cold-bent thin-walled C-section member with web stiffening and openings when reaching the ultimate bearing capacity;

[0034] Figure 8 It is a curve diagram showing the relationship between the axial compressive bearing capacity of components with different numbers and the center position of the opening;

[0035] Fig. 9 It is a curve diagram showing the relationship between the axial compressive bearing capacity and the number of openings of components with different numbers;

[0036] Fig.10 It is a curve diagram of the relationship between the axial compressive bearing capacity of a component with multiple openings and the spacing between the openings;

[0037] FIG11( a ) is a graph showing the relationship between the axial compressive bearing capacity of a stiffening member with a square hole in the web and the side length of the hole;

[0038] FIG11( b ) is a graph showing the relationship between the axial compressive bearing capacity and the hole diameter of a stiffening member with a circular hole in the web;

[0039] FIG11( c ) is a graph showing the relationship between the axial compressive bearing capacity of a stiffening member with an oblong hole in the web and the diameter of the semicircular hole;

[0040] Fig.12 It is a curve diagram showing the relationship between the axial compressive bearing capacity of a stiffening member with multiple oblong holes in the web and the hole diameter of the semicircular part. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In the present invention, the "first" and "second" are only used to distinguish similar components / parts with different positions or different characteristics, and have no other limiting meanings; the "upper" refers to the direction of each component away from the ground, and the "lower" refers to the direction of each component close to the ground.

[0043] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0044] The present invention provides a safety assessment method for a web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component, the method comprising the following steps:

[0045] Step 1: Calculate the axial compressive bearing capacity of a high-strength steel cold-formed thin-walled C-section member with a total length of l (mm) and a web stiffener without openings. Set the member to be subjected to a design value of N D The axial pressure (unit of force is uniformly N) is applied, and the web height h (mm), flange width b (mm), curling width a (mm), and wall thickness t (mm) of the section are preliminarily designed based on engineering design experience. For the preliminarily designed section, the direct strength method is used to calculate the distortion and overall related buckling bearing capacity N of the high-strength steel cold-formed thin-walled C-section member with web stiffening and no openings in accordance with the Technical Specifications for Cold-Formed Steel Structures (GB 50018-2014 Draft for Comments). nd , local buckling critical force N crl ; Introduce height reduction factor β l The influence of member height on the axial compressive bearing capacity of cold-formed thin-walled steel members is considered, and the axial compressive bearing capacity of the modified web-stiffened high-strength steel cold-formed thin-walled C-section member without openings is calculated. nh Considering the design safety and economy, the requirement is: 0.7N nh ≤N D <Nnh ;

[0046] Step 2: The web-stiffened high-strength steel cold-bent thin-walled C-shaped cross-section member with web height h, flange width b, and curling width a obtained in step 1 is provided with a square hole, a round hole, or an oblong hole on its web due to the building function, wherein the total area of ​​the opening on the web is A hole , the area of ​​the entire web is A web ; and introduce the total area A of the opening part of the member web hole The area A of the entire web web The ratio β An To measure the influence of the number and size of openings on the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section opening member, the axial compressive bearing capacity reduction factor γ of the web-stiffened high-strength steel cold-formed thin-walled C-section opening member is obtained. J , then the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-shaped opening member is N u for:

[0047] N u =0.96γ J ×N nh (1)

[0048] For safety considerations, a safety factor of 0.96 is introduced.

[0049] Step 3: Verify the axial compressive bearing capacity N calculated in step 2 u Whether it exceeds the design value of axial pressure N of the high-strength steel cold-formed thin-walled C-section open-hole member with web stiffening D , so as to determine the axial compressive bearing capacity N of the high-strength steel cold-formed thin-walled C-section open-hole member with web stiffening u security.

[0050] Furthermore, in step 3, if 0.7N is calculated u ≤N D ≤N u , it indicates that the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section open-hole member is N u The design safety requirements are met and the cross-section design is economical and reasonable, so the design is completed.

[0051] Furthermore, in step 3, if N D <0.7N u , it is judged that the design section of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component is too large and not economical, so the web-stiffened high-strength steel cold-bent thin-walled C-section component is redesigned to reduce the C-section by reducing the web height h or reducing the flange width b or reducing the wall thickness t, and the calculation is re-performed according to the steps 1 to 3 until the 0.7N is satisfied.u ≤N D ≤N u .

[0052] Furthermore, in step 3, if N D >N u , it is judged that the preliminary design of the section of the high-strength steel cold-bent thin-walled C-section opening member with web stiffening is unsafe, so that its axial compressive bearing capacity N u At this time, the web-stiffened high-strength steel cold-bent thin-walled C-section member is redesigned to increase the C-section by increasing the web height h or the flange width b or the wall thickness t, and the calculation is re-performed according to steps 1 to 3 until 0.7N is satisfied. u ≤N D ≤N u .

[0053] According to the safety assessment method of a web-stiffened high-strength steel cold-formed thin-walled C-section member with openings described in the present invention, in the step 1, based on the loading test and nonlinear finite element calculation of the web-stiffened high-strength steel cold-formed thin-walled C-section member, the distortion and overall related buckling bearing capacity N of the web-stiffened high-strength steel cold-formed thin-walled C-section member without openings are fully considered. nd , local buckling critical force N crl After the influence of l To measure the influence of component height on the axial compressive bearing capacity of high-strength steel cold-formed thin-walled C-section components with web stiffening and no holes, the corrected axial compressive bearing capacity N of high-strength steel cold-formed thin-walled C-section components with web stiffening and no holes is obtained based on the test and finite element calculation results. nh :

[0054]

[0055] in l is the component height (mm).

[0056] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component described in the present invention, in the step 2, based on the loading test and nonlinear finite element calculation of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component, the ratio of the axial compressive bearing capacity of the component with the web opening to the component of the same size without the web opening is obtained, which is the true value γ of the axial compressive bearing capacity reduction coefficient of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component p The parameter that affects the ratio of the axial compressive bearing capacity of the member with web openings to the member of the same size without web openings is the total area of ​​openings on the member web A. hole With the entire web area A web The ratio β An , the ratio βAn As a variable, the true value of the reduction factor γ obtained from the test and finite element calculation P The numerical fitting based on the least squares method is used to obtain the fitting value of the axial compressive bearing capacity reduction coefficient γ of the high-strength steel cold-formed thin-walled C-section opening member with web stiffening considering the influence of web opening. J The calculation formula is as follows:

[0057]

[0058] Among them, N u Axial compressive bearing capacity of cold-formed thin-walled C-section open-section members with high-strength steel stiffening for webs; N nh The axial compressive bearing capacity of high-strength steel cold-formed thin-walled C-section members with modified web stiffening and no holes.

[0059] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open-section component described in the present invention, the method is applicable to the design and production of cold-bent thin-walled steel sections whose material is LQ550 hot-dip galvanized steel plate and whose wall thickness t does not exceed 1.5 mm.

[0060] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open-section component, when multiple holes need to be opened in the web to meet engineering requirements in actual projects, the hole spacing should be appropriately increased to try to make the hole positions evenly distributed on the component web to reduce the mutual influence of adjacent holes.

[0061] The present invention also provides the application of the safety assessment method of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component in the design and manufacture of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component.

[0062] 1. Experimental study on axial compression of cold-formed thin-walled C-section members with web stiffening

[0063] In order to study the stress performance and buckling mode of cold-formed thin-walled C-section high-strength steel members with web stiffening and openings under axial pressure, a cold-formed thin-walled C-section steel member made of hot-dip galvanized LQ550 steel with a nominal wall thickness of 1mm was selected for axial compression loading test. The member length is determined to be 610mm and 1220mm according to the width modulus of the external European pine board in the actual light steel keel house, and the member length is determined to be 610mm and 1220mm according to the width of the European pine board for one span and two spans. At the same time, in order to study the bearing performance of medium-length members, a member with a length of 900mm is added, and the opening design is performed for each member. The opening specimens are laser cut after roll forming. Considering that in actual light steel buildings, the floor height is generally about 3m, and in order to avoid the slenderness ratio of the column being too large in the project, at least one intermediate support will be arranged in the horizontal direction of the frame. Therefore, the height of these columns generally does not exceed half of the floor height, that is, it is determined to be 1500mm. According to the commonly used C-shaped stiffening section size in the project, the following is selected as shown in the attached figure. Figure 1 The J-type cross-section shown in the figure (the web height is large and stiffened, and the nominal size of the cross-section profile is 140×41×11×1mm). Non-perforated components are represented by N, and the types of perforated components include SC (small circular hole), C (circular hole), BC (large circular hole), SG (small oblong hole), G (oblong hole), BG (large oblong hole), and R (square hole). The nominal diameters of the circular holes are 15mm, 35mm, and 55mm respectively; the nominal side length of the square hole is 35mm; the diameter of the semicircular part of the small oblong hole is 15mm, and the length of the straight side is 15mm; the diameter of the semicircular part of the oblong hole is 35mm, and the length of the straight side is 30mm; the diameter of the semicircular part of the large oblong hole is 55mm, and the length of the straight side is 45mm. Schematic diagrams of the shapes and sizes of each hole are shown in the attached Figure 2 For longer components of 1220 mm and 1500 mm, different numbers of openings are designed to analyze the influence of opening spacing and number of openings on the bearing capacity of the component. Figure 3 For example, J610-G1 represents a J-type section with web reinforcement, a member length of 610 mm, and an oblong hole on the web.

[0064] Example 1 to Example 27: The actual measured dimensions of the test components are shown in Table 1 for the web-stiffened cold-bent thin-walled C-section test components.

[0065] Table 1 Geometric dimensions of axial compression test example

[0066]

[0067] The test method is as follows:

[0068] The specimen was installed and aligned before loading. This test used a 500kN hydraulic servo loading actuator for loading. The lower end of the actuator was a bidirectional hinge support connected to the upper end plate of the specimen. A ball joint was also arranged at the bottom of the specimen, connected to the lower end plate of the specimen, to ensure that both ends of the specimen were constrained as hinges to release the bending and torsional deformation of the column end. Before loading, standard tensile specimens were made from laser-cut steel plates from the roll-formed specimens for material property testing. The basic material mechanical properties parameters such as yield strength, tensile strength, elastic modulus, and Poisson's ratio of the LQ550 hot-dip aluminum-zinc steel plate used to make the specimens are shown in Table 2, where the yield strength is taken from the stress value corresponding to the residual deformation of the specimen of 0.2%. There is no obvious strengthening stage of the material after cold bending, and the elongation of the material taken on the cross section is between 7.48% and 9.91%.

[0069] Table 2 Mechanical properties parameters of test materials

[0070]

[0071] Before loading, the initial geometric deformation of the structure was measured, strain gauges were arranged to observe the stress development at key positions, and displacement meters were arranged to observe the deformation development at key positions. Before formal loading, the specimen was preloaded to 10% of the estimated ultimate load (obtained by finite element simulation), and the various acquisition devices were checked to see if they were working properly. During formal loading, the test force-displacement dual-control loading method was adopted. First, the test force control was adopted, and the loading was graded. Before the applied load reached 60% of the estimated ultimate load, or before the specimen had no obvious buckling phenomenon, the force control loading method was adopted, and the loading rate was 1kN / min. The loading amount at each level was about 5% of the estimated ultimate load; then it was switched to displacement control, and the loading was carried out at a constant rate of 0.06mm / min. After each level of loading, the load was held for 1 minute, and the readings of each strain gauge and displacement meter, as well as the deformation of the specimen were observed and recorded, and the buckling of the specimen was recorded in time. After reaching the ultimate load, keep the loading rate unchanged and continue to increase the axial compression displacement. The load decreases at this stage until the actual pressure decreases to 70% of the ultimate load, then unload quickly and stop the test. If the load drops suddenly after the specimen reaches the ultimate load, brittle failure occurs, and the load-displacement curve will not have a gentle descending section, for the sake of test safety, stop the test in time, record the test phenomenon, and save the test data.

[0072] The buckling behavior of the cold-bent thin-walled C-section member with web stiffening and high-strength steel without openings under axial compression load is analyzed in combination with Examples 1 to 4, and the test results are shown in Table 3. The buckling mode L shown in the table represents local buckling, D represents distortional buckling, and O represents overall buckling (including overall bending or overall bending-torsion).

[0073] Table 3 Buckling bearing capacity and buckling mode of specimens without holes

[0074]

[0075]

[0076] Shorter stiffened members (l = 610mm) experience local and global buckling. As the height of the member increases, the slenderness ratio of the member increases, the global torsion and global bending of the member section gradually play a controlling role, and the influence of local buckling and distortional buckling on the bearing capacity gradually weakens. The web stiffening has little effect on the torsional stiffness of the section and the bending stiffness around the weak axis. Therefore, longer stiffened members (l ≥ 900mm) will experience distortional and global buckling. When the cross-sectional size is constant, the ultimate bearing capacity of the member will decrease with the increase of height.

[0077] The buckling behavior of high-strength steel cold-bent thin-walled C-section members with stiffened webs and openings under axial compressive loads is analyzed below in conjunction with Examples 5 to 27.

[0078] Table 4 Buckling capacity and buckling mode of open hole specimens

[0079]

[0080] The test results of the above-mentioned embodiments 5 to 27 are shown in Table 4. Through the experimental study of the stiffened perforated components and the analysis of their buckling behavior, it can be found that most components undergo distortion buckling when they are destroyed, and the deformation is mainly inward. For the 610mm components with a smaller height, overall bending generally does not occur; while for the longer components, in addition to distortion buckling, overall bending is generally accompanied by the occurrence of overall bending when they are destroyed, and a sharp drop in bearing capacity will occur after reaching the load extreme point. Generally speaking, with the increase of the opening size and the number of openings, the ultimate bearing capacity of the component gradually decreases. When the opening size is constant, the bearing capacity of the component with square holes is slightly higher, and the bearing capacity of the components with round holes and oblong holes is not much different.

[0081] 2. Comparison between finite element simulation results and test results

[0082] In combination with Examples 28 to 31, the finite element simulation results of the buckling behavior of cold-bent thin-walled C-section members with high-strength steel stiffening without holes under axial compression load are analyzed and compared with the experimental results.

[0083] The present invention uses finite element software ANSYS for numerical analysis. The LQ550 cold-bent thin-walled C-shaped components used in the test are all simulated using SHELL 181 units. Rigid end plates are built at the upper and lower ends of the established component finite element model to truly reflect the constraint effect of the test loading device on the component. The end plates are made of elastic material with an elastic modulus of E endplate Taken as 2.06×10 5MPa, and the thickness of the end plate is 20mm. During the establishment of the end plate, it is necessary to ensure that the centroids of the upper and lower end plates completely coincide with the centroid of the component to ensure axial compression. Apply translation constraints along the X and Z directions and rotation constraints around the Y axis to the centroid node of the upper end plate; at the same time, apply translation constraints in three directions to the centroid node of the lower end plate. Apply vertical concentrated force to all nodes on the upper end plate along the entire cross-section of the C-shaped component, and transfer the force evenly to the component through the rigid end plate to achieve axial compression. After multiple simulation verifications, the basic size of the mesh division adopted is 5mm×5mm. The finite element model after mesh division is as shown in the attached figure. Figure 4 When carrying out nonlinear numerical calculations, the Von-Mises stress yield criterion is used to determine whether the component material is yielding. When simulating the test component, the material adopts a bilinear isotropic hardening constitutive model, and the basic mechanical performance parameters are shown in Table 2. The arc length method is used to track the response path of the structure to obtain the buckling mode, ultimate bearing capacity and post-buckling performance of the component when it is destroyed.

[0084] According to the measured component dimensions and the initial geometric defect data obtained by three-dimensional morphology scanning, finite element simulations were performed on Examples 1 to 8, and the finite element simulation results were compared with the test results in the following three aspects, including buckling mode, axial compression ultimate bearing capacity, and load-displacement development curves of typical node positions. By comparing with the test results, the reliability of the finite element modeling and nonlinear analysis solution method of cold-bent thin-walled C-section steel components was verified.

[0085] Embodiment 28 to Embodiment 31: correspond to Experimental Embodiments 1 to 4 respectively, and the specific geometric parameters and failure conditions are shown in Table 1 and Table 3 respectively.

[0086] Attached Figure 5 The comparison between the deformation morphology of the test components and the finite element deformation cloud diagram when some components reach the ultimate bearing capacity is given. It can be seen that the test and the finite element simulation are in good agreement in terms of buckling mode and main buckling position. The slight difference is that the finite element is difficult to simulate the sudden bending that occurs during the test. The finite element simulation deformation distribution is relatively gentle, and the deformation change gradient obtained by the test is more drastic (such as Figure 5 (c) and (d) are compared. The ultimate load N obtained from the test listed in Table 3 cr The ultimate load N is obtained by finite element calculation fu The comparison shows that the error of the ultimate bearing capacity of all components is within 2%, which shows that the two are in good agreement. The test and finite element buckling modes of all components are consistent.

[0087] The J610-N0 component was selected and its displacement development was compared with that obtained by finite element simulation. Figure 6As shown. It can be seen that the component test displacement and the finite element displacement development curve are highly consistent, especially before the ultimate load; after crossing the ultimate load, due to the bending of some component sections during the test, the bearing capacity dropped sharply, while the stiffness decay of the finite element calculated component is continuous, and the simulated load drop section stiffness will be greater than the test situation. In actual engineering applications, the focus is mainly on the deformation development of the component before reaching the ultimate load, and the deformation development after destruction is not paid much attention to. Therefore, the finite element simulation of displacement development in the present invention is reliable.

[0088] Through the comparison and verification between the above-mentioned tests and finite element analysis, it is found that the ultimate bearing capacity, buckling mode, and buckling deformation development path obtained from the tests are in good agreement with the situations simulated by the finite element analysis. This shows that the finite element modeling method and nonlinear analysis technology adopted in the present invention are both relatively accurate and reliable. Therefore, the finite element technology can be used to continue to perform relevant parameter analysis in the future.

[0089] In combination with Examples 32 to 35, the finite element simulation results of the buckling behavior of high-strength steel cold-bent thin-walled C-section members with stiffened webs and openings under axial compressive load are analyzed and compared with the experimental results.

[0090] Embodiment 32 to Embodiment 35: correspond to test embodiments 5 to 8 respectively, and the specific geometric parameters and failure conditions are shown in Table 1 and Table 4 respectively.

[0091] According to the method for establishing a finite element model of the present invention, the finite element model of the web-stiffened and perforated member is established by using the initial geometric morphology three-dimensional scanning data of the test member, and one perforated member of each of four lengths is selected. Figure 7 The comparison between the experimental phenomena and the finite element deformation morphology of these components when they reach the ultimate bearing capacity is given in Table 4. It can be seen that the finite element simulation of the web-stiffened and perforated test components is more accurate in terms of the buckling mode and the location of the maximum buckling deformation. The ultimate load N obtained from the test is given in Table 4. cr The ultimate load N obtained by finite element calculation fu The comparison of the load and the buckling mode shows that the maximum relative error between the finite element calculated load and the test load is 3.3%. The buckling mode obtained by finite element simulation is also consistent with the experimental buckling mode. Therefore, it can be considered that the finite element technology method adopted in the present invention to simulate the axial compression performance of cold-bent thin-walled steel members with stiffened webs and openings is accurate and reliable.

[0092] In the subsequent finite element parameter analysis process, all constructed models introduced relatively unfavorable initial defects, which mainly reflected the shrinkage deformation of the mid-span section, and defect modes that reflected the initial geometric defects of local bulging of the web and overall bending of the component around the weak axis, so as to consider the adverse effects of the initial geometric defects; based on the initial morphology scanning results of the actual test components, the defect amplitude was taken as 1.5 mm under the premise of reliable guarantee.

[0093] 3. The revised formula for the axial compressive bearing capacity of cold-formed thin-walled C-shaped members is proposed

[0094] In order to verify whether the calculation formula for the axial compressive bearing capacity of cold-bent thin-walled steel formulated in the specification is applicable to the LQ550 high-strength steel cold-bent thin-walled C-shaped member adopted in the present invention, the experimental ultimate bearing capacity N is compared with the experimental examples 1 to 27 and the finite element calculation model examples 28 to 35 corresponding to the experimental examples 1 to 8. cr 、Finite element calculation of the ultimate bearing capacity result N fu As well as the theoretical ultimate bearing capacity calculated by the direct strength method, the initial defects imposed in the finite element calculation are the defect modes and defect amplitudes proposed in the previous article. The results obtained by the direct strength method are calculated by the relevant formulas listed in the Technical Specifications for Cold-Formed Steel Structures (GB 50018-2014 Draft for Comments) of my country to calculate the strength and stability of the components. The material parameters used in the theoretical calculation are consistent with the measured material parameters in Table 2. The local and overall related buckling bearing capacity N nl According to formula (4), the deformation and overall related buckling bearing capacity N nd Calculate according to formula (5):

[0095]

[0096] In the formula, λ l and λ d is the dimensionless slenderness ratio, γ R is the resistance partial coefficient of cold-formed steel structure, which is 1.165; N crl and N crd are the local buckling critical load and distortional buckling critical load of the component, respectively, which can be calculated according to the local buckling critical stress σ crl and the distortional buckling critical stress σ crd Calculated by multiplying the total cross-sectional area A; N ne For the overall stable bearing capacity of the component, is the overall stability factor of the axially compressed member, which can be obtained by checking the specifications, f y is the yield strength of steel. Buckling critical stress σ crl and σ crd All of them can be calculated using the formulas in the Technical Specifications for Cold-Formed Steel Structures (GB50018-2014 Draft for Comments).

[0097] Through comparison, it is concluded that the test component described in the present invention is mainly damaged by distortional buckling, accompanied by related buckling such as local buckling and overall buckling. Although the relevant buckling effect of components is taken into account in my country's "Technical Specifications for Cold-Formed Steel Structures" (GB 50018-2014 Draft for Comments), there is still a large error in the prediction of the bearing capacity of the test component described in the present invention. When calculating the bearing capacity of components of the same cross-sectional form with different heights, the slenderness ratio is changed mainly due to the change in the height of the component, and the reduction in bearing capacity is mainly reflected in the overall stability coefficient. However, the decrease in the predicted value of the standard calculation formula is small. Specifically, when the cross section is constant, when the height of the component increases from 610mm to 1500mm, its bearing capacity N nl and N nd The decrease range is almost within 1 kN, which is obviously too small and cannot accurately reflect the impact of height change. Therefore, the calculation formula of the bearing capacity of the axial compression member investigated by the present invention in the current specification has certain errors and needs to be corrected.

[0098] According to the buckling phenomenon that occurs when the test member is destroyed in the present invention, the distortion buckling critical load N should be fully considered when revising the existing axial compression bearing capacity calculation formula. crd , local buckling critical load N crl , and the overall stable bearing capacity N ne Therefore, combined with the influence of member height on bearing capacity reduction, based on the test and finite element calculation results, and based on the calculation method in my country's "Technical Code for Cold-Formed Steel Structures" (GB 50018-2014 Draft for Comments), on the basis of formula (4) and formula (5), a revised method for calculating the axial compressive bearing capacity N of LQ550 high-strength steel cold-formed thin-walled C-shaped members (without holes in the web) is proposed. nh The recommended calculation formula is as follows (2):

[0099]

[0100] Where N nd is the deformation and overall related buckling bearing capacity, calculated according to formula (5); β l is the height reduction coefficient, obtained by least squares fitting, l is the component height (mm).

[0101] The axial compressive bearing capacity of the component without openings described in the present invention is calculated using the revised recommended calculation formula. nh , test results N cr And the finite element calculation results N fuBy comparison, it can be found that the theoretical calculation results of the components are close to the prediction of the bearing capacity of the components and the test and finite element ultimate bearing capacity. The average value of the ratio of the calculated value of the revised recommended formula to the test results is 1.064, the standard deviation is 0.044, and the average value of the ratio to the finite element results is 1.001, the standard deviation is 0.057, indicating a good agreement, and it is conservative and safe for the test results. Therefore, this recommended formula can make a relatively accurate and safe prediction of the axial compressive bearing capacity of LQ550 high-strength steel cold-bent thin-walled C-shaped components, and can be used in actual engineering.

[0102] 4. Influence of opening parameters on the axial compressive bearing capacity of cold-formed thin-walled C-section members with web stiffening high-strength steel

[0103] The following nonlinear finite element method is used to construct a finite element model of a component with different opening parameters, calculate the bearing capacity, and analyze the influence of various opening parameters on the axial compression bearing capacity and buckling mode of the component.

[0104] 4.1 Influence of hole type

[0105] In combination with Examples 36 to 47, the influence of the hole pattern of the web opening on the bearing capacity of the cold-bent thin-walled C-section member reinforced with web stiffener high-strength steel under axial compression is analyzed below.

[0106] In order to study the influence of hole type, finite element models of components with four lengths and three hole types (Examples 36 to 47, respectively) were designed and constructed for nonlinear finite element analysis. The hole positions were all located in the middle of the span, and only a single hole was opened to obtain the ultimate bearing capacity of each component and reveal the most unfavorable hole type. The model numbers corresponding to each embodiment are shown in Table 5.

[0107] Table 5 Example of analysis on the influence of opening shape

[0108]

[0109]

[0110] The ultimate bearing capacity of components with different opening shapes calculated in Example 36 to Example 47 is shown in Table 6. It can be found that when the square hole and the circular hole are opened in the mid-span of the web, the difference in ultimate bearing capacity is small, and the ultimate bearing capacity of the oblong hole is the lowest, indicating that the oblong hole is the most unfavorable hole shape. Compared with the components without holes, the ultimate bearing capacity of the J1500 type components is most affected by the web openings. The bearing capacity of the components with square holes is reduced by 4.5%, the bearing capacity of the components with circular holes is reduced by 4.6%, and the bearing capacity of the components with oblong holes is reduced by 4.6%. Among them, the bearing capacities calculated for the three hole shapes of the J1500 type components are very close, and the maximum and minimum values ​​differ by only 0.05 kN.

[0111] Table 6 Bearing capacity of components with different hole shapes

[0112]

[0113] 4.2 Influence of the opening center position

[0114] In combination with Example 38, Example 41, Example 44, and Examples 47 to 63, the influence of the center position of the web opening on the bearing capacity of the web-stiffened high-strength steel cold-bent thin-walled C-section components under axial compression is analyzed below.

[0115] The model numbers corresponding to the embodiments are shown in Table 7, where the opening center height position y / l is the ratio of the distance y (mm) from the opening center to the bottom of the component to the cross-sectional length l (mm).

[0116] Table 7 Example of analysis on the influence of the opening center position

[0117]

[0118] Four components of different lengths were selected, and a single oblong hole was opened on the web. The effect of the change in the center position of the opening on the axial compression bearing capacity was analyzed. The relationship curve is shown in the attached figure. Figure 8 As shown. It can be found that the minimum bearing capacity of the components of the four lengths occurs at the mid-span, indicating that openings at the mid-span are more unfavorable than other positions. Among them, the bearing capacity fluctuation of the J1500-G1 component is more obvious, and the bearing capacity reduction caused by the opening at the mid-span is also the largest, with a reduction of 4.6%. In general, the change in the opening position has little effect on the ultimate bearing capacity of the web stiffening section component, and openings at the maximum defect are more likely to cause a larger bearing capacity reduction. Changes in the opening positions of all components do not bring about obvious changes in the buckling mode and buckling position. The maximum deformation position is affected by the initial defect and is located in the mid-span section, and the deformation amplitude difference is very small.

[0119] 4.3 Effect of the number of openings

[0120] The following is an analysis of the effect of the number of web openings on the bearing capacity of web-stiffened high-strength steel cold-bent thin-walled C-section components under axial compression in combination with Example 38, Example 41, Example 44, Example 47, and Examples 64 to 87.

[0121] The model numbers corresponding to the embodiments are shown in Table 8, wherein the finite element model control group with the same length only changes the number of openings without changing the size of the openings, and the openings are made at equal intervals.

[0122] Table 8 Example of analysis on the influence of the number of openings

[0123]

[0124] The relationship curve between the ultimate bearing capacity of the component and the number of openings obtained by finite element calculation is shown in the attached figure. Fig. 9As shown in the figure, it can be seen that the curve shows a monotonically decreasing trend, indicating that the ultimate bearing capacity of the component gradually decreases with the increase in the number of openings. As the number of openings gradually increases to 7, the bearing capacity of the J610 component is reduced by 4.8% compared with the component without openings, the bearing capacity of the J900 component is reduced by 4.5%, the bearing capacity of the J1220 component is reduced by 6.0%, and the bearing capacity of the J1500 component is reduced by 9.6%. This shows that the same number of openings has a more serious impact on the bearing capacity of components with longer lengths. The buckling mode of the component will not change significantly with the increase in the number of openings, and the maximum deformation amplitude difference is very small.

[0125] 4.4 Effect of opening spacing

[0126] In combination with Examples 88 to 97, the effect of the web opening spacing on the bearing capacity of web-stiffened high-strength steel cold-bent thin-walled C-section components under axial compression is analyzed below.

[0127] The model numbers corresponding to the embodiments are shown in Table 9. The finite element model control group only changes the hole spacing without changing the other hole parameters.

[0128] Table 9 Example of analysis of the influence of hole spacing

[0129]

[0130] In order to study the effect of the hole spacing on the axial compression bearing capacity of the web stiffened section member, the members with three oblong holes of length 1220mm and 1500mm were selected respectively, and the relationship curve between the ultimate bearing capacity of the member and the hole spacing was calculated (one hole was kept at the mid-span, and the spacing between the other two holes was changed). Fig.10 As shown in the figure, the axial compression ultimate bearing capacity of the member increases monotonically with the increase of the opening spacing, but the increase is not large in general. This shows that the larger the opening spacing, the less the opening weakens the bearing capacity. Regardless of the opening spacing, the member always undergoes distortional buckling at the mid-span, and local buckling occurs in the web around the opening.

[0131] 4.5 Effect of hole size

[0132] In combination with Examples 36 to 47 and Examples 98 to 177, the influence of the web opening size on the bearing capacity of the web-stiffened high-strength steel cold-bent thin-walled C-section components under axial compression is analyzed below.

[0133] In order to analyze the influence of different opening sizes on the axial compressive bearing performance of web-stiffened section components, four components with different lengths are designed and three hole types are introduced. All components have only a single hole opened in the mid-span of the web. By changing the side length or diameter of the three hole types, the relationship curve between the axial compressive ultimate bearing capacity of the component and the opening size is obtained.

[0134] Example 36, Example 39, Example 42, Example 45, Example 98 to Example 117: This group of examples all have square holes, and the corresponding model numbers are shown in Table 10.

[0135] Table 10 Example of analysis on the effect of square hole size

[0136]

[0137]

[0138] Example 37, Example 40, Example 43, Example 46, Example 118 to Example 137: This group of examples all have circular holes, and the corresponding model numbers are shown in Table 11.

[0139] Table 11 Example of analysis on the effect of circular hole size

[0140]

[0141] Embodiment 38, Embodiment 41, Embodiment 44, Embodiment 47, Embodiment 138 to Embodiment 165: This group of embodiments all have oblong holes, and the corresponding model numbers are shown in Table 12. Among them, the length of the straight side of the component and the diameter of the upper and lower semicircular parts are changed in equal proportion.

[0142] Table 12 Example of analysis on the effect of the size of the oblong hole

[0143]

[0144]

[0145] The relationship curve between the axial compressive ultimate bearing capacity of the component and the opening size is shown in Figure 11. Figure 11(a) , 11(b) and 11(c) correspond to the three cases of opening square holes, opening circular holes and opening oblong holes respectively. It can be seen from the figure that for any hole type, the axial compression ultimate bearing capacity of the component will decrease with the increase of the hole size. Among them, the bearing capacity of the J610 type component decreases the most. When the side length of the square hole or the diameter of the circular hole increases from 15mm to 70mm, the bearing capacity of the square hole decreases by 5.16%, and the bearing capacity of the circular hole decreases by 4.16%; when the diameter of the semicircular part of the oblong hole increases from 15mm to 75mm, the bearing capacity decreases by 4.41%. Because the final failure of longer components tends to transform into the buckling mode related to the overall buckling, the proportion of its ultimate bearing capacity controlled by the overall buckling bearing capacity increases, so the adverse effect of the mid-span web opening gradually decreases, so the sensitivity to the increase of the hole size decreases.

[0146] Example 166 to Example 177: To study the effect of the size of the opening when there are multiple openings, three oblong holes are opened on the web in this group of examples, and the corresponding model numbers are shown in Table 13. Among them, the straight side length of the component and the diameter of the upper and lower semicircular parts are changed in equal proportion.

[0147] Table 13 Example of analysis of the influence of hole size when opening three oblong holes

[0148]

[0149] For porous components, select components with lengths of 1220 mm and 1500 mm, and open three oblong holes at equal intervals on the webs. The relationship curve between the load-bearing capacity and the hole size is shown in the attached figure. Fig.12 As shown in the figure. The results show that the ultimate bearing capacity of porous components is also significantly affected by the size of the opening. When the diameter of the semicircular part increases from 15mm to 68mm, the bearing capacity of the 1220mm column decreases by 4.83%, and the bearing capacity of the 1500mm column decreases by 5.82%. It is worth mentioning that when the size of the opening increases, the buckling mode of the porous component does not change significantly, and it is still mainly affected by the initial defect.

[0150] 5. Calculation formula for the reduction factor of axial compressive bearing capacity of stiffened cold-bent thin-walled C-section members caused by web openings

[0151] Through the above axial compression tests on cold-bent thin-walled steel with holes in the web stiffening section, as well as a large number of nonlinear finite element parameter analyses of models with different hole types, hole positions, hole numbers, hole spacings and hole sizes on the web under axial compression loads, it is found that although the hole type, position and spacing of the holes have a certain influence on the axial compression bearing capacity of the component, the influence is not significant. When multiple holes need to be opened, the hole spacing can be appropriately increased to try to make the hole positions evenly distributed on the web of the component. The hole type is relatively more unfavorable, so in this section, the two parameters of different hole numbers and hole sizes are still mainly considered to obtain the hole area on the web. On the basis of the recommended formula (2) for the correction of the axial compression bearing capacity of the component without holes, the bearing capacity of the component without holes with web stiffening is reduced, and the bearing capacity reduction coefficient γ is proposed. J , in order to calculate the axial compression bearing capacity of cold-formed thin-walled steel with web openings. Based on the finite element parameter analysis data and test data, the least squares method is used for polynomial fitting, and the calculation formula for the bearing capacity reduction factor of LQ550 steel cold-formed thin-walled C-section opening components with web stiffening under axial compression is obtained as follows:

[0152]

[0153] Among them, N u is the axial compressive bearing capacity of the open component; Nnh is the axial compressive bearing capacity of the web-stiffened member without openings, which can be calculated by the formula (2) proposed in the present invention; β An A is the total area of ​​openings on the web of the member hole With the entire web area A web The ratio of h is the web height. Since the stiffening ribs are small in size, they have little effect on the web surface area. Therefore, for the stiffened section, the distance between the left and right flanges is still taken as the web height, and l is the component height.

[0154] The theoretical calculation results of all web stiffening and opening components by using the above formula (3) are compared with the test results. The average value of the ratio of the theoretical calculation results of all stiffening and opening components by using the above formula (3) to the test results is 0.995, and the standard deviation is 0.022. In addition, except for the test bearing capacity of the component J1220-C3 in Example 7 and the component J1220-G3 in Example 21 which is too low, the test measured γ of other components is J The value is not less than the γ calculated according to formula (3) J The value is 96%, indicating that the calculation results obtained according to formula (3) are in good agreement with the experimental results. Therefore, it can be considered that the fitting formula is basically accurate and reliable.

[0155] In engineering design, the axial compressive bearing capacity of the cold-formed thin-walled C-section member with stiffened high-strength steel and no holes in the web is N nh It can be obtained based on the results of direct strength method, and then the influence of web opening is considered and multiplied by the axial compressive capacity reduction factor γ J The axial compressive bearing capacity of the high-strength steel cold-formed thin-walled C-section member with hinged web stiffening and openings is N u It can be calculated according to the following formula (1):

[0156] N u =0.96γ J ×N nh (1)

[0157] 6. Construction of safety assessment method for high-strength steel cold-formed thin-walled C-section axial compression members with web openings

[0158] Embodiment 178:

[0159] This example provides a safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-shaped (also known as a rolled-edge groove-shaped) cross-section open axial compression member, the method comprising the following steps:

[0160] Step 1: Calculate the axial compressive bearing capacity of a cold-formed thin-walled C-section member with a total length of l (mm) and a web stiffener without a hole. Assume that the member is subjected to a design value of N D The axial pressure (unit of force is uniformly N) is applied. Based on the engineering design experience, the web height h (mm), flange width b (mm), flange width a (mm), and wall thickness t (mm) of the section are preliminarily designed. For the preliminarily designed section, the direct strength method is used to calculate the distortion and overall related buckling bearing capacity N in accordance with the Technical Specifications for Cold-Formed Steel Structures (GB 50018-2014 Draft for Comments). nd , local buckling critical force N crl ; Based on a large amount of research data, the least squares method is used for numerical fitting, and the height reduction coefficient β is introduced l Considering the influence of member height on the axial compressive bearing capacity of cold-formed thin-walled steel members, the corrected axial compressive bearing capacity N nh The calculation formula is shown in formula (2); and the axial compressive bearing capacity N calculated according to formula (2) is nh , compared with the corresponding bearing capacity results obtained by the test loading of all test examples 1 to 8, in all cases, the deviation between the value calculated according to formula (2) and the test value does not exceed 3%. Considering the design safety and economy, the requirement is: 0.7N nh ≤N D <N nh ;

[0161] Step 2: The web-stiffened high-strength steel cold-bent thin-walled C-section member with web height h, flange width b, and curling width a obtained by the step 1 is provided with square holes, round holes, or oblong holes on its web due to the building function, wherein the total area of ​​the holes on the web is A. hole , the entire web area A web , the bearing capacity of the component is reduced by considering the influence of openings; the least square method is used for numerical fitting based on a large amount of research data, in which the influence of the number of openings and the size of the openings is calculated by the total area of ​​the openings on the web of the component A hole With the entire web area A web The ratio β An The bearing capacity reduction factor γ of the cold-formed thin-walled C-section steel member with web openings under axial pressure considering the number of openings and opening size parameters is obtained. JAs shown in formula (3); and the ratio of the bearing capacity of the open hole and the non-hole component calculated according to formula (3) is compared with the corresponding ratio of the bearing capacity of the open hole and the non-hole component obtained by loading all test examples 1 to 27. Except for examples 7 and 21, which have too low bearing capacity due to equipment problems during the test, in all other cases, the deviation between the value calculated according to formula (3) and the test value does not exceed 4%. Therefore, considering safety, a safety factor of 0.96 is introduced. According to formula (1), the axial compressive bearing capacity N of the high-strength steel cold-bent thin-walled C-section open hole component with reduced web stiffening is obtained: u .

[0162] Step 3: Verify the axial compressive bearing capacity N calculated in step 2 u Whether it exceeds the design value N of the axial pressure of the high-strength steel cold-formed thin-walled C-section member with web opening D If 0.7N u ≤N D ≤N u , it indicates that the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section open-hole member is N u The design safety requirements are met and the cross-section design is economical and reasonable, and the design is completed. D <0.7N u , it indicates that the design section of the web-stiffened high-strength steel cold-bent thin-walled C-section open-hole component is too large and not economical. In this case, the web-stiffened high-strength steel cold-bent thin-walled C-section component is redesigned to reduce the C-section by reducing the web height h or the flange width b or the wall thickness t, and the calculation is re-performed according to steps 1 to 3 until the 0.7N u ≤N D ≤N u If N D >N u , indicating that the preliminary design of the section of the web-stiffened high-strength steel cold-formed thin-walled C-section open-hole member is unsafe, making its axial compressive bearing capacity N u If the web height h is too small, the web stiffening high-strength steel cold-bent thin-walled C-section member must be redesigned by increasing the web height h or the flange width b or the wall thickness t to increase the C-section, and recalculate according to steps 1 to 3 until 0.7N is satisfied. u ≤N D ≤N u .

[0163] According to the safety assessment method of a web-stiffened high-strength steel cold-bent thin-walled C-section open axial compression member described in the present invention, the method is applicable to cold-bent thin-walled steel sections whose manufacturing material is LQ550 hot-dip aluminum-zinc steel plate and whose wall thickness t does not exceed 1.5 mm.

[0164] 7. Application of safety assessment method for cold-formed thin-walled C-section members with web openings

[0165] Embodiment 179:

[0166] For the LQ550 high-strength steel cold-formed thin-walled C-section member with a length of 1220mm and web reinforcement derived from actual engineering, an oblong hole needs to be opened due to the crossing of pipelines. The diameter of the semicircular part of the oblong hole is 35mm and the straight side length is 30mm. The design value of the axial pressure of the member is N D =35000(N).

[0167] Step 1: To match the general wall panel thickness, the web height of the designed section is 140 mm. Based on engineering experience, the preliminary design section profile dimensions are: h = 140 mm, b = 41 mm, a = 11 mm, t = 1 mm, and the steel strength design value is f = 500 MPa. According to the current specifications, the direct strength method is used to calculate the relevant buckling bearing capacity N by formula (2): nh =49380(N).

[0168] Step 2: Calculate the bearing capacity reduction factor γ caused by the opening using formula (3) J =0.980, according to formula (1), the axial compressive bearing capacity of the above-mentioned unperforated component N nh The axial compressive bearing capacity N of the cold-formed thin-walled C-section steel member with web stiffening and opening considering the influence of opening is obtained. u =46457(N).

[0169] Step 3: Component design bearing capacity N D =35000(N) <N u =46457 (N), indicating that the section bearing capacity of the preliminary design is safe. The design bearing capacity of the component is compared with the calculated axial compressive bearing capacity of the opening component N u In contrast, 0.7N u =32520(N)≤N D =35000(N)≤N u =46457 (N), indicating that the bearing capacity of the cold-bent thin-walled C-section steel member with web openings meets the design requirements and the section design is economical and reasonable.

[0170] Some steps in the embodiments of the present invention may be implemented using software, and the corresponding software program may be stored in a readable storage medium, such as a CD or a hard disk.

[0171] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component, characterized in that: The method comprises the following steps: Step 1: Calculate the axial compressive bearing capacity of a high-strength steel cold-formed thin-walled C-section member with a total length of l and a web stiffener without openings. Set the design value of the member to be N D The axial pressure is applied, and the web height h, flange width b, curling width a, and wall thickness t of the section are preliminarily set. For the preliminarily designed section, the direct strength method is used to calculate the distortion and overall related buckling bearing capacity N of the high-strength steel cold-formed thin-walled C-section member with web stiffening and no openings. nd , local buckling critical force N crl ; Introduce height reduction factor β l The influence of member height on the axial compressive bearing capacity of cold-formed thin-walled steel members is considered, and the axial compressive bearing capacity of the modified web-stiffened high-strength steel cold-formed thin-walled C-section member without openings is calculated. nh Considering the design safety and economy, the requirement is: 0.7N nh ≤N D <N nh ; Step 2: The web-stiffened high-strength steel cold-bent thin-walled C-section member with web height h, flange width b, and curling width a obtained in step 1 is required to have square holes, round holes, or oblong holes on the web due to building functions, where the total area of ​​the opening on the web is A. hole , the area of ​​the entire web is A web ; and introduce the total area A of the opening part of the member web hole The area A of the entire web web The ratio β An To measure the influence of the number and size of openings on the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section opening member, the axial compressive bearing capacity reduction factor γ of the web-stiffened high-strength steel cold-formed thin-walled C-section opening member is obtained. J , then the axial compressive bearing capacity of the web-stiffened high-strength steel cold-formed thin-walled C-section open-section member is N u for: Among them, 0.96 is the safety factor; Step 3: Verify the axial compressive bearing capacity N calculated in step 2 u Whether it exceeds the design value of axial pressure N of the high-strength steel cold-formed thin-walled C-section open-hole member with web stiffening D , so as to determine the axial compressive bearing capacity N of the high-strength steel cold-formed thin-walled C-section open-hole member with web stiffening u security.

2. The safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 1 is characterized in that: In step 3, if the calculated value is 0.7N u ≤N D ≤N u , then the axial compressive bearing capacity N of the web-stiffened high-strength steel cold-formed thin-walled C-section open-hole member is determined u Meet design safety requirements.

3. The safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 2, characterized in that: In step 3, if N D <0.7N u , it is judged that the design section of the web-stiffened high-strength steel cold-bent thin-walled C-section open member is too large, and the web-stiffened high-strength steel cold-bent thin-walled C-section member is redesigned to reduce the C-section by reducing the web height h or the flange width b or the wall thickness t, and the calculation is re-performed according to the steps 1 to 3 until the 0.7N u ≤N D ≤N u .

4. The safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 3 is characterized in that: In step 3, if N D >N u , it is judged that the preliminary design of the section of the high-strength steel cold-bent thin-walled C-section opening member with web stiffening is unsafe, so that its axial compressive bearing capacity N u At this time, the web-stiffened high-strength steel cold-bent thin-walled C-section member is redesigned to increase the C-section by increasing the web height h or the flange width b or the wall thickness t, and the calculation is re-performed according to steps 1 to 3 until 0.7N is satisfied. u ≤N D ≤N u .

5. The safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 4, characterized in that: In the step 1, according to the loading test and nonlinear finite element calculation of the high-strength steel cold-formed thin-walled C-section member with web reinforcement, the distortion and overall related buckling bearing capacity N of the high-strength steel cold-formed thin-walled C-section member with web reinforcement without opening are fully considered. nd , local buckling critical force N crl After the influence of l To measure the influence of component height on the axial compressive bearing capacity of high-strength steel cold-formed thin-walled C-section components with web stiffening and no holes, the corrected axial compressive bearing capacity N of high-strength steel cold-formed thin-walled C-section components with web stiffening and no holes is obtained based on the test and finite element calculation results. nh : in l is the component height.

6. The safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 5, characterized in that: In the step 2, according to the loading test and nonlinear finite element calculation of the high-strength steel cold-bent thin-walled C-section open-section member with web stiffening, the ratio of the axial compressive bearing capacity of the member with web opening to the member of the same size without web opening is obtained, and the ratio of the axial compressive bearing capacity of the member with web opening to the member of the same size without web opening is the true value γ of the axial compressive bearing capacity reduction coefficient of the high-strength steel cold-bent thin-walled C-section open-section member with web stiffening considering the influence of the web opening p The parameter that affects the ratio of the axial compressive bearing capacity of the member with web openings to the member of the same size without web openings is the total area of ​​openings on the member web A. hole With the entire web area A web The ratio β An , the ratio β An As a variable, the true value of the reduction factor γ obtained from the test and finite element calculation P The numerical fitting based on the least squares method is used to obtain the fitting value of the axial compressive bearing capacity reduction coefficient γ of the high-strength steel cold-formed thin-walled C-section opening member with web stiffening considering the influence of web opening. J The calculation formula is as follows: Among them, N u Axial compressive bearing capacity of cold-formed thin-walled C-section open-section members with high-strength steel stiffening for webs; N nh The axial compressive bearing capacity of high-strength steel cold-formed thin-walled C-section members with modified web stiffening and no holes.

7. The safety assessment method of a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 6, characterized in that: The method is applicable to the design and manufacture of cold-bent thin-walled steel sections whose material is LQ550 hot-dip aluminum-zinc steel sheet and whose wall thickness t does not exceed 1.5 mm.

8. The safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component according to claim 7, characterized in that: When multiple holes need to be opened in the web to meet engineering requirements in actual projects, the hole spacing should be appropriately increased to try to make the hole positions evenly distributed on the web of the component and reduce the mutual influence of adjacent holes.

9. Application of the safety assessment method for a web-stiffened high-strength steel cold-formed thin-walled C-section open-hole component as described in any one of claims 1 to 8 in the design and manufacture of web-stiffened high-strength steel cold-formed thin-walled C-section open-hole components.

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