Joint structure

Abstract

Provided is a joining structure that can realize a combination of the thickness of a through diaphragm considering an increase in corner strength and the diameter difference between an upper square steel pipe and a lower square steel pipe. 【Solution means】The joining structure 1 is a joining structure 1 in which an upper square steel pipe 11 and a lower square steel pipe 12 are joined via a through diaphragm 13, the diameter of the upper square steel pipe 11 is smaller than the diameter of the lower square steel pipe 12, and the joint strength calculated using the yield stress of the upper square steel pipe 11 and the yield stress of the through diaphragm 13 j M u1 and the full plastic moment of the upper square steel pipe 11 c M p1 satisfy the following formula (1), and the ratio of the yield stress of the corner 11c of the upper square steel pipe 11 to the yield stress of the flat part 11f of the upper square steel pipe 11 f σ y represented by the corner strength increase rate c σ y is greater than 1. c σ y / f σ y is greater than 1. JPEG2026078958000030.jpg7169

Description

[Technical Field]

[0001] The present invention relates to a joining structure in which an upper rectangular steel pipe and a lower rectangular steel pipe are joined via a through diaphragm. [Background technology]

[0002] In steel-framed buildings, when the diameter of columns changes between floors, a variable-width joint system with a thickened diaphragm is used as one of the joint types. Reducing the column diameter saves material, which has the advantage of reducing costs and GHG (Green House Gas: greenhouse gases such as CO2). As shown in Non-Patent Literature 1 below, the application condition for this variable-width joint system is that the diaphragm does not collapse until the column collapses. The collapse of the diaphragm is the minimum load-bearing capacity of the joint, which can be determined by yield line theory assuming an arbitrary collapse mechanism (hereinafter, j M u ) and the collapse of the column is due to the full plastic moment of the upper column (hereinafter, c M p ) is determined by, j M u ≧ c M p Satisfying this condition is a requirement for applying the differential width joint type. Non-patent documents 2 and 3 below disclose the load-bearing capacity evaluation that forms the basic concept of Non-patent document 1. Patent document 1 below discloses a method for analyzing and modeling the out-of-plane bending strength of a diaphragm that reflects the curvature (shape) of the corners of a square steel pipe. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-162148 [Non-patent literature]

[0004] [Non-Patent Document 1] Architectural Institute of Japan: Steel structure joint design guidelines 4th edition (2021)

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the cold-formed square steel tubular column, which is the main application target of the different-width connection form, when bending the corners, the strength increases due to cold working. The shear strength evaluations disclosed in Non-Patent Documents 2 and 3 are carried out on the premise of not considering the influence (curvature and strength increase) of the corners of the steel tubular column described above for the sake of design simplification. Although there are configurations in which the corner curvature (shape) is reflected in the design as disclosed in Patent Document 1, no shear strength evaluation is carried out considering the strength increase at the corners.

[0006] The strength increase at the corners affects the joint shear strength j M u and the full plastic moment of the column c M p both increase. Therefore, whether considering the strength increase at the corners contributes to the expansion or contraction of the applicable range has not been clarified, and there is a concern that it is impossible to correctly evaluate whether the applicable conditions of the different-width connection form are satisfied. For example, Non-Patent Document 1 sets the applicable range as the case where the upper column is reduced in diameter within a range of 50 mm with respect to the diameter of the lower column, and those with a diameter reduction exceeding 50 mm cannot be used. Patent Document 1 implements the case where the upper column is reduced in diameter within a range of 150 mm with respect to the diameter of the lower column, and those with a diameter reduction exceeding 150 mm have not been implemented. Neither Non-Patent Document 1 nor Patent Document 1 considers the strength increase at the corners, but it has not been clarified in the prior art whether considering it will result in an expansion or a narrowing of the applicable range (feasible range).

[0007] The present invention was made to solve the above-mentioned problems, and one of its objectives is to provide a joint structure that makes it possible to apply combinations of through-diaphragm thickness and diameter differences between the upper and lower square steel pipes, which were not applicable in the conventional art, by taking into consideration the increased strength of the corners. [Means for solving the problem]

[0008] The inventors, through FEA (Finite Element Analysis) studies using the strength of the corners of the square steel pipe as a parameter, discovered that when the ratio of the strength of the corners to the strength of the flat sections (the rate of increase in corner strength) is above a certain level, the diaphragm will not collapse until the column collapses, even with combinations of diaphragm thickness and diameter differences between the upper and lower square steel pipes that were previously inapplicable (due to not meeting the application conditions). Specifically, the joint strength of the conventional technology, which assumes the strength of the corners is the same as that of the flat sections... j M u1 and the full plastic moment of the upper rectangular steel pipe c M p1 The strength of the joint when considering the increased strength of the corners j M u2 and the full plastic moment of the upper rectangular steel pipe c M p2 The difference (increase in load-bearing capacity) is calculated as Δ j M u ( = j M u2 - j M u1 ) and Δ c M p ( = c M p2 - c M p1 ) when Δ c M p Rather than Δ j M u The fact that it is greater (Δ j M u >Δ c M p ) was found. Therefore, conventional technology does not satisfy the application conditions for joining methods ( j Mu < c M p Even if the ratio of the strength of the corner portion to the strength of the flat portion (the rate of increase in corner strength) is above a certain level, in the case of the present invention, the applicable conditions j M u ≧ c M p This satisfies the above. The present invention was made based on these findings. In this invention, the joint strength refers to the collapse resistance of the diaphragm joined between the upper rectangular steel pipe and the lower rectangular steel pipe.

[0009] In one embodiment, the joint structure according to the present invention is a joint structure in which an upper rectangular steel pipe and a lower rectangular steel pipe are joined via a through diaphragm, wherein the diameter of the upper rectangular steel pipe is smaller than the diameter of the lower rectangular steel pipe, and the joint strength is calculated using the yield stress of the upper rectangular steel pipe and the yield stress of the through diaphragm. j M u1 and the full plastic moment of the upper rectangular steel pipe c M p1 The following equation (1) is satisfied, and the yield stress of the flat plate portion of the upper rectangular steel pipe f σ y The yield stress of the corner of the upper square steel pipe relative to the above c σ y Corner strength increase rate expressed as a ratio c σ y / f σ y It is greater than 1.

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[0010] According to one embodiment of the joint structure of the present invention, by considering the increase in strength of the corners, it becomes possible to apply combinations of the thickness of the through diaphragm and the diameter difference between the upper and lower square steel pipes, which were not applicable in the prior art. [Brief explanation of the drawing]

[0011] [Figure 1]This is a plan view showing a joint structure according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view of the joint structure along line II-II in Figure 1. [Figure 3] This is a schematic side view showing a column joint structure with varying widths, including joint structure 1 in Figure 1. [Figure 4] This graph shows the relationship between the ratio of the joint strength jMu1 (jMu1 / cMp1) calculated using the yield stress of the upper rectangular steel pipe and the through diaphragm to the full plastic moment cMp1 of the upper rectangular steel pipe in the joint structure of this embodiment, and the corner strength increase rate (cσy / fσy), which is expressed as the ratio of the yield stress cσy of the corner of the upper rectangular steel pipe to the yield stress fσy of the flat portion of the upper rectangular steel pipe. [Figure 5] This is a perspective view showing the general shape of the analysis model set up in the example. [Figure 6] This is a side view showing the general shape of the analysis model set up in the example. [Figure 7] This graph shows the stress-strain relationship set in the example. [Figure 8] This graph shows the M-θ relationship on the upper surface of the through diaphragm obtained from the analysis of the embodiment. [Figure 9] This is an explanatory diagram showing the collapse mechanism set in the embodiment. [Figure 10] This graph shows the relationship between the maximum analytical moment M in the example and the fully plastic moment cMp2 of the upper square steel pipe considering the increase in corner strength. [Figure 11] This is a contour plot of the equivalent stress of the von Mises stress in the analytical model for angle strength increase rates cσy / fσy of 1.0 and 1.3. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and can be materialized by modifying the components without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in each embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, components from different embodiments may be appropriately combined.

[0013] First, an overview of the joint structure 1 according to an embodiment of the present invention will be described with reference to Figures 1 to 3. Figure 1 is a plan view showing the joint structure 1 according to an embodiment of the present invention, Figure 2 is a cross-sectional view of the joint structure 1 along line II-II in Figure 1, and Figure 3 is a schematic side view showing the differential width column joint structure 2 including the joint structure 1 in Figure 1.

[0014] As shown in Figures 1 and 2, the joint structure 1 according to the embodiment of the present invention is one in which an upper rectangular steel pipe 11 and a lower rectangular steel pipe 12 are joined via a through diaphragm 13. The entire lower end circumference of the upper rectangular steel pipe 11 may be joined to the upper surface of the through diaphragm 13, and the entire upper end circumference of the lower rectangular steel pipe 12 may be joined to the lower surface of the through diaphragm 13. The joining may be performed by welding.

[0015] As shown in Figure 1, the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 have corners 11c, 12c and flat sections 11f, 12f. The corners 11c, 12c are located at the four corners of the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 when viewed in plan or cross-section, and may be in the region of 45 degrees from the center of the corner arc on both sides. The flat sections 11f, 12f may be portions that extend linearly between the corners 11c, 12c when viewed in plan (Figure 1) or cross-section (Figure 2) of the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12.

[0016] In Figures 1 and 2, the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 are arranged coaxially. However, the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 may be eccentric relative to one. For example, one flat plate portion 12f of the lower rectangular steel pipe 12 may overlap one flat plate portion 11f of the upper rectangular steel pipe 11, or one flat plate portion 12f of the lower rectangular steel pipe 12 may overlap one corner portion 11c of the upper rectangular steel pipe 11.

[0017] The diameter of a rectangular steel pipe is generally defined by the distance between its outer surfaces (outer diameter), but in this invention, the diameter of the rectangular steel pipe may be defined by the center of the plate thickness. Diameter D of the upper rectangular steel pipe 11 cu The diameter D of the lower square steel pipe 12 cl Smaller than the diameter D of the upper rectangular steel pipe 11. cu This may be the width between the center of the plate thickness of a pair of opposing flat plate sections 11f. Similarly, the diameter D of the lower square steel pipe 12. cl This may be the width between the center thicknesses of a pair of opposing flat plate sections 12f. As shown in the embodiment in Figure 1, the cross-sectional shapes of the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 may be square. Alternatively, the cross-sectional shapes of the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 may be rectangles having a short side and a long side. If at least one of the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 is rectangular, at least one of the long side and short side of the upper rectangular steel pipe 11 should be smaller than the diameter of the lower rectangular steel pipe 12.

[0018] The upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 are typically formed rectangular steel pipes. Formed rectangular steel pipes are made by bending steel plates to form a rectangle, and then joining the ends on both sides of the steel plates that are butted together. The bending may be done cold. Work hardening may occur at the corners 11c and 12c.

[0019] The joint structure 1 in Figure 1 may be included in the variable-width column joint structure 2 in Figure 3. In the variable-width column joint structure 2, the column 21 on the upper floor and the column 22 on the lower floor are joined via a joint 23. The joint 23 has an upper diaphragm 23a, a rectangular joint panel 23b whose upper surface is joined to the lower surface of the upper diaphragm 23a, and a lower diaphragm 23c whose upper surface is joined to the lower surface of the joint panel 23b. The lower end of the column 21 on the upper floor is joined to the upper surface of the upper diaphragm 23a, and the upper end of the column 22 on the lower floor is joined to the lower surface of the lower diaphragm 23c. The diameter or width of the column 21 on the upper floor is smaller than the diameter or width of the joint panel 23b and the column 22 on the lower floor. The diameter or width of the joint panel 23b is about the same as the diameter or width of the column 22 on the lower floor. In Figure 1, the upper rectangular steel pipe 11 may be a column 21 on the upper floor, the lower rectangular steel pipe 12 may be a connecting panel 23b, and the through diaphragm 13 in Figure 1 may be an upper diaphragm 23a. The connecting portion 23 may also be composed of only one diaphragm. In this case, the upper rectangular steel pipe 11 in Figure 1 may be a column 21 on the upper floor, and the through diaphragm 13 in Figure 1 may be a diaphragm constituting the connecting portion 23.

[0020] A beam 24 may be joined to the joint 23. Figure 3 shows a configuration in which two beams 24 extending left and right in the figure are joined to the joint 23, but the number of beams 24 joined to the joint 23 is arbitrary.

[0021] Next, with further reference to Figure 4, the details of the joint structure 1 according to an embodiment of the present invention will be described. Figure 4 shows the full plastic moment of the upper rectangular steel pipe 11 in the joint structure 1 of this embodiment. c M p1 The joint strength was calculated using the yield stress of the upper rectangular steel pipe 11 and the yield stress of the through diaphragm 13. j M u1 ratio ( j M u1 / c M p1 ) and the yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11 f σ y Yield stress of the corner 11c of the upper square steel pipe 11 relative to c σ yThe graph shows the relationship with the corner strength increase rate expressed as a ratio ( c σ y / f σ y ).

[0022] Incidentally, j M u1 / c M p1 is an index of the joint strength for determining design feasibility in prior art that does not consider the increase in corner strength (e.g., Non-Patent Document 1), and is calculated by the following equations (C) and (E) to (L).

[0023] The joint structure 1 of this embodiment is designed in consideration of the strength increase due to work hardening that occurs at the corner 11c of the upper square steel pipe 11 during forming when deriving the upper limit value given by the yield line theory. By reflecting this strength increase in the design, the joint strength in design and the full plastic moment of the upper square steel pipe 11 are increased. Incidentally, in the calculation of the internal force work used when deriving the yield line theory, the yield stress of the upper square steel pipe 11 is used in the axial yield strain region of the upper square steel pipe 11, and the yield stress of the through diaphragm 13 or the yield stress of the lower square steel pipe 12 is used at the bending yield position.

[0024] That is, the joint structure 1 of this embodiment satisfies the following equation (1) for the joint strength j M u1 calculated using the yield stress of the upper square steel pipe 11 and the yield stress of the through diaphragm 13 and the full plastic moment c M p1 of the upper square steel pipe 11, and the corner strength increase rate c σ y / f σ y is greater than 1. At this time, j M u1 / c M p1 and c σ y / f σ yThe value takes place within region R1 shown in Figure 4. Region R1 is a rectangular region that includes region R2 (a slightly lighter shaded region), region R3 (a slightly darker shaded region), and region R4 (the darkest shaded region). j M u1 / c M p1 is less than 1.0, and c σ y / f σ y This is the region where the value is greater than 1.0.

[0025]

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[0026] Here, c σ y This is the yield stress of the corner 11c of the upper rectangular steel pipe 11. f σ y This is the yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11. The F value, which is the material standard, may be used for the yield stress of the flat plate portion 11f. For example, if it is JIS G3136 SN490 steel or cold press-formed rectangular steel pipe BCP325 made from the same steel (Japan Iron and Steel Federation Product Standard MDCR0003-2017, etc.), then its F value is 325 (N / mm²). 2 ) c σ y The strength is estimated by tensile testing (for example, JIS Z2241:2011 No. 12B full-thickness tensile test specimen (an arc-shaped test specimen is taken from the corner) or No. 4 round bar tensile test specimen (a bar-shaped test specimen is taken with the axis at the position t / 4 of the plate thickness at the corner)) or by the indentation method. Strength estimation by the indentation method follows the method described in "ISO / TR 29381 Metallic materials - Measurement of mechanical properties by an instrumented indentation test - indentation tensile properties".

[0027] Joint strength j M uThe calculation assumes an arbitrary collapse mechanism, and the one with the minimum internal work is determined as the true collapse mechanism. Among the collapse mechanisms, there is one in which the upper rectangular steel pipe 11 (upper floor column 21) axially yields, and in some cases, the true collapse mechanism occurs when axial yield strain occurs in the upper rectangular steel pipe 11. Since the axial yield strain of the upper rectangular steel pipe 11 is formed around the corner 11c, the internal work increases when the strength increase of the corner 11c is taken into consideration in the calculation, and therefore the joint strength j M u It can be said that this will increase.

[0028] Strength increase due to work hardening occurring at the corner 11c of the upper rectangular steel pipe 11 (yield stress of corner 11c) c σ y Considering the rise in the upper rectangular steel pipe 11, c M p It can be said that it also increases. Here, the yield stress of the flat plate portion 11f f σ y Yield stress of corner 11c c σ y The joint strength and the full plastic moment of the upper square steel pipe 11 were calculated considering the large difference (increase in strength of the corner portion 11c compared to the flat portion 11f). j M u2 , c M p2 Let's assume that.

[0029] As mentioned above, considering the increased strength of the corner 11c, the joint strength j M u and full plastic moment c M p Both increase. The results of the analysis shown later show the angle strength increase rate c σ y / f σ y against j M u and c M p It was found that the former showed a greater degree of increase (joint strength due to increased corner strength) j M u Increase amount ( j M u2 - j Mu1 ) to Δ j M u As such, the full plastic moment due to increased corner strength c M p Increase amount ( c M p2 - c M p1 ) to Δ c M p When that happens, Δ j M u >Δ c M p (It was found that this is the case). Therefore, the joint strength was calculated without considering the increase in corner strength. j M u1 and the full plastic moment of the upper rectangular steel pipe 11 c M p1 Even if a joint configuration does not satisfy the current design conditions, it may become a joint configuration that satisfies the current design conditions if the increase in corner strength is taken into consideration. Therefore, by considering the increase in strength of the corner 11c, it becomes possible to apply combinations of thickness of the through diaphragm 13 and the diameter difference between the upper square steel pipe 11 and the lower square steel pipe 12, which were not applicable in conventional technology.

[0030] Furthermore, the joint structure 1 of this embodiment may also satisfy the following equation (2). The inventors confirmed from the results of simulations described later that satisfying equation (2) satisfies equation (A), which is a condition for preventing the through diaphragm 13 from collapsing until the upper rectangular steel pipe 11 collapses.

[0031]

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[0032]

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[0033] Here, α and β are coefficients that define the straight line corresponding to the lower limit of region R2 in Figure 4. α = 1.159 and β = 0.719 may be used. These values ​​of α and β were obtained by the inventor from the results of the simulation described later. Note: Corner strength increase rate c σ y / f σ y The threshold α is determined by the plate thickness of the through diaphragm 13, as well as the diameter, plate thickness, axial force ratio, and material strength of the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12.

[0034] When equation (1) and equation (2) are also satisfied, j M u1 / c M p1 and c σ y / f σ y The value takes place within region R2, as shown in Figure 4. Region R2 is a trapezoidal region that includes regions R3 and R4.

[0035] Furthermore, the joining structure 1 of this embodiment may also satisfy the following equation (3).

[0036]

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[0037] Here, YR is expressed by the following equation (4), f σ u This is the tensile strength of the flat plate portion 11f of the upper rectangular steel pipe 11. When equation (3) is also satisfied in addition to equations (1) and (2), j M u1 / c M p1 and c σ y / f σ y The value takes place within region R3, as shown in Figure 4. Region R3 is a triangular region that includes region R4.

[0038]

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[0039] Equation (3) is used to determine the limit of the strength increase in the corner portion 11c, and it shows that the strength increase due to work hardening does not exceed the tensile strength of the flat portion 11f. f σ u This is estimated by mill sheets, steel material specifications for tensile strength, tensile tests (for example, JIS Z2241:2011 No. 1A full-thickness tensile test specimen or No. 4 round bar tensile test specimen (a rod-shaped test specimen is taken with the axis at the position t / 4 of the plate thickness)), or by the indentation method described above.

[0040] Furthermore, the joint structure 1 of this embodiment may also satisfy the following equation (5). When equations (1), (2), and (3) are also satisfied, j M u1 / c M p1 and c σ y / f σ y The value takes place within the region R4 (trapezoidal region) shown in Figure 4.

[0041]

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[0042] Furthermore, in the joint structure 1 of this embodiment, the diameter and plate thickness of the upper rectangular steel pipe 11 are D cu (mm), t cu (mm) and the plate thickness of the through diaphragm 13 is t d (mm) and the diameter of the lower square steel pipe 12 is D cl When (mm), the following equations (6) and (7) may also be satisfied. Generally, the larger the difference in diameter between the upper square steel pipe 11 and the lower square steel pipe 12, and the smaller the plate thickness of the through diaphragm 13, j M u This is because the value of becomes small (Non-Patent Document 1), and in the range exceeding equations (6) and (7), equation (3) may not be satisfied.

[0043]

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[0044]

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[0045] Although preferred embodiments of the present invention have been described in detail above with reference to the attached drawings, the present invention is not limited to these examples. It is clear to any person with ordinary skill in the art to which the present invention belongs that various modifications or alterations can be conceived within the scope of the technical idea described in the claims, and these are also understood to fall within the technical scope of the present invention.

[0046] For example, in the embodiment, the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 were described as formed rectangular steel pipes with work hardening occurring at the corners 11c and 12c. However, the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12 may be welded rectangular steel pipes formed by arranging four steel plates in a rectangle and joining the four corners by welding, and the weld metal constituting the corners 11c and 12c may be harder than the flat plate portions 11f and 12f. [Examples]

[0047] The present invention will be described more specifically below with reference to examples. The present invention is not limited to these examples.

[0048] The inventors conducted simulation tests of the joint structure 1 using a general-purpose finite element analysis (FEA) program. An analytical model, roughly shown in Figures 5 and 6, was created, and the maximum load-bearing capacity at the joint was determined. Here, the maximum load-bearing capacity refers to the maximum value of the bending moment at the upper surface of the through diaphragm 13. The boundary conditions of the analytical model were a pin roller support at the upper end and a fixed end at the lower end, and a displacement incremental analysis was performed in which a forced displacement (200 mm) in one direction was applied while maintaining an axial compressive force with an axial force ratio of 0.3 at the support point at the upper end. The nominal stress-nominal strain relationship of the material was assumed to be of the perfect elastoplastic type as shown in Figure 7, and this was converted to a true stress-true strain relationship and used in the analysis.

[0049] Table 1 shows the various conditions of the analysis model, and Table 2 shows the calculation results.

[0050] [Table 1]

[0051] [Table 2]

[0052] As shown in Table 1, the plate thickness t of the through diaphragm 13 d In the case where there is no increase in strength of the corner portion 11c of the upper square steel pipe 11, as in No. 1, the joint load capacity j M u ( j M u1 )> Full plastic moment of the upper rectangular steel pipe 11 c M p ( c M p1 The value (60 mm) was standardized to a value that does not satisfy the conditions of Non-Patent Document 1 (Design Guidelines for Steel Structure Joints). The yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11 is 325 (N / mm²). 2 ) and its modulus of elasticity is 205,000 (N / mm²). 2 ) was used. For the sake of simplifying the analysis, the material properties of the weld metal, backing plate, and through diaphragm 13 were the same as those of the flat plate section 11f. As shown in No. 1-5 of Table 1, the yield stress (strength) of the corner section 11c of the upper rectangular steel pipe 11 was changed. The yield stress of the corner section 11c was set to the yield stress of the flat plate section 11f of the upper rectangular steel pipe 11. f σ y Yield stress of the corner 11c of the upper square steel pipe 11 relative to c σ y Corner strength increase rate expressed as a ratio c σ y / f σ y Set the appropriate value and determine the yield stress of the flat plate section 11f. f σ y It was expressed as the product of the strength increase rate at the corners.

[0053] The M-θ relationship obtained from the analysis is shown in Figure 8. M is the bending moment at the top surface of the through diaphragm 13, obtained by multiplying the horizontal load Q at the loading point by the distance L (2000 mm) to the top surface of the through diaphragm 13. θ represents the rotation angle obtained by dividing the displacement δ (up to 200 mm) at the loading point by the distance L (2000 mm) to the top surface of the diaphragm. The analysis maximum M shown in Table 2 is the maximum value taken from the graph in Figure 8, and corresponds to the overall load-bearing capacity of the joint structure 1.

[0054] Table 2 "Calculations" c M p1 " is the total plastic moment of the upper rectangular steel pipe 11 calculated without considering the increase in strength of the corner portion 11c of the upper rectangular steel pipe 11. c M p1 This is the full plastic moment. c M p1 This was calculated based on the following equation (B). In equation (B), t cu D is the plate thickness of the upper rectangular steel pipe 11, cu R is the diameter of the upper rectangular steel pipe 11, cu This is the radius of the corner portion 11c of the upper rectangular steel pipe 11. f σ y This is the yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11.

[0055]

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[0056] Table 2 "Calculations" c M p2 This is the total plastic moment of the upper rectangular steel pipe 11, calculated considering the increase in strength of the corner portion 11c of the upper rectangular steel pipe 11. c M p2 This is the full plastic moment. c M p2 This was calculated based on the following equation (C). In equation (C), t cu D is the plate thickness of the upper rectangular steel pipe 11, cu R is the diameter of the upper rectangular steel pipe 11, cu This is the radius of the corner portion 11c of the upper rectangular steel pipe 11. fσ y This is the yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11. c σ y This is the yield stress of the corner 11c of the upper rectangular steel pipe 11.

[0057]

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[0058] Table 2 "Calculations" j M u1 " is the joint strength calculated using the yield stress of the upper rectangular steel pipe 11 and the yield stress of the through diaphragm 13. j M u1 This is the load-bearing capacity of this joint. j M u1 The calculations were performed based on the following equations (D) to (K), assuming the collapse mechanism shown in Figure 9.

[0059] The various dimensions in Figure 9 are as follows: D cu Diameter of the upper square steel pipe 11 t cu : Plate thickness of the upper square steel pipe 11 D cl Diameter of the lower square steel pipe 12 t cl : Plate thickness of the lower square steel pipe 12 t d : Thickness of the through diaphragm 13 x, y: Variables that determine the collapse mechanism

[0060]

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[0061] In equation (D), j M ua This is the joint strength when the neutral axis is located on the plate of the lower rectangular steel pipe 12. j M ub This is the joint strength when the neutral axis passes through the upper rectangular steel pipe 11. Equation (D) j M ua and j Mub This was calculated based on the following equations (E) and (F). In equations (E) and (F), s m p This is the full plastic moment per unit length at the yield line located at the upper part of the lower rectangular steel pipe 12. D m p D is the total plastic moment per unit length in the through diaphragm 13, cl D is the diameter of the lower square steel pipe 12, cu x is the diameter of the upper rectangular steel pipe 11, l is the misalignment between the upper rectangular steel pipe 11 and the lower rectangular steel pipe 12, and x is a variable that determines the axial yield strain region in the upper rectangular steel pipe 11. cu n y is the axial yield load per unit length in the upper rectangular steel pipe 11, y is the distance between the neutral axis and one side of the upper rectangular steel pipe 11, and N is the axial force.

[0062]

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[0063]

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[0064] Equations (E) and (F) D m p This was calculated based on the following formula (G). In formula (G), d σ y is the yield stress of the through diaphragm 13, and t d This is the thickness of the through diaphragm 13.

[0065]

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[0066] Equations (E) and (F) s m p This was calculated based on the following equation (H). In equation (H), D m pThis is the total plastic moment per unit length in the through diaphragm 13, cl m p This is the full plastic moment per unit length in the lower rectangular steel pipe 12.

[0067]

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[0068] Equation (H) cl m p This was calculated based on the following equation (I). In equation (I), f σ y is the yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11, and t cl This is the plate thickness of the lower rectangular steel pipe 12.

[0069]

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[0070] Equations (E) and (F) cu n y This was calculated based on the following formula (J). In formula (J), f σ y is the yield stress of the flat plate portion 11f of the upper rectangular steel pipe 11, and t cu This is the plate thickness of the upper rectangular steel pipe 11.

[0071]

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[0072] The l in equations (E) and (F) was calculated based on equation (K) below. In equation (K), D cl D is the diameter of the lower square steel pipe 12, cu This is the diameter of the upper rectangular steel pipe 11.

[0073]

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[0074] The evaluation method for joint structure 1 was as follows. First, the maximum load-bearing capacity in the analysis (maximum analysis M) and the calculated full plastic moment of the upper rectangular steel pipe 11 were compared (see Figure 10). At this time, when setting up the analysis and calculating the full plastic moment of the upper rectangular steel pipe 11, the axial force and the increase in corner strength (yield stress of the flat plate section 11f) were used. f σ y Yield stress of corner 11c c σ y (Consider that it is large.)

[0075] Figure 10 shows the maximum analysis M in the embodiment and the full plastic moment of the upper square steel pipe 11 considering the increase in corner strength. c M p2 This graph shows the relationship between the maximum analysis M and the total plastic moment. In the graph of Figure 10, the diagonal line represents the relationship between the maximum analysis M and the total plastic moment. c M p2 This shows that they are equal.

[0076] Analysis of maximum M and full plastic moment c M p2 The region below this line (analysis maximum M < total plastic moment) c M p2 When within ), the maximum load-bearing capacity of the joint structure 1 is the load-bearing capacity of the joint j M u2 It can be determined that this is determined by the joint strength. j M u <Full plastic moment of the upper rectangular steel pipe 11> c M p Therefore, it is considered unsuitable from a design perspective.

[0077] On the other hand, the maximum analysis M and the full plastic moment c M p2 The region above this line (analysis maximum M > total plastic moment) c M p2 When it is within ), it can be determined that the upper rectangular steel pipe 11 is in a fully plastic state (even though the analysis settings adopt a fully elastoplastic stress-strain relationship, the maximum analysis M is the fully plastic moment). c M pThe reason why it exceeds this is thought to be because the plastically deformed upper rectangular steel pipe 11 is restrained by the through diaphragm 13, and the load-bearing capacity increases slightly. Therefore, in this case the joint load j M u >Full plastic moment of the upper rectangular steel pipe 11 c M p The conditions are met and it can be determined that the design is feasible. Table 2 shows the maximum analysis M and the full plastic moment. c M p2 Numbers 4 and 5, which are in the region above the above line, are given by equation (3)( j M u2 > c M p2 This indicates that the condition is met.

[0078] Figure 10 shows that the analysis model without an increase in corner strength (No. 1) does not satisfy the design conditions, but as corner strength increases as shown in No. 2 to No. 5, the maximum analysis M increases, and the corner strength increase rate in No. 3 is shown. c σ y / f σ y (1.15) and the rate of increase in corner strength of No. 4 c σ y / f σ y (1.20) Corner strength increase rate that can be designed between these two values. c σ y / f σ y It was confirmed that a threshold α exists. Linear interpolation gives the corner strength increase rate that can be designed with this analysis model. c σ y / f σ y The threshold α was found to be 1.159.

[0079] Furthermore, the rate of increase in corner strength c σ y / f σ y The threshold α changes depending on the shape of the joint and the strength other than the corner strength. c M p1 against j M u1 ratio j M u1 / c M p1 These are the values ​​representing each joint calculated by equation (D) and equations (D) to (K). The model confirmed in this example j M u1 / c M p1 The value was 0.719.

[0080] Therefore, the threshold α = 1.159 corresponds to the angle strength increase rate. j M u1 / c M p1 If we denote this as β, the value of β was found to be 0.719.

[0081] The results of this analysis indicate that the higher the corner strength, the more likely the column will collapse first, making design feasible. Furthermore, the threshold α changes depending on the shape of the joint and the strength other than the corner strength. Therefore, design is possible in the region above the straight line (Equation 3) connecting the point (β,α) on Figure 4, which was confirmed in this study, and the point (0,0) which represents the limit of design feasibility when the increase in corner strength is not considered.

[0082] j M u1 / c M p1 The larger β=0.719, the more likely it is that the design will result in the through diaphragm 13 not collapsing until the upper rectangular steel pipe 11 collapses, in other words, a safer design. j M u1 / c M p1 It is clear that a larger size makes design feasible.

[0083] Figure 11 is a contour plot of the equivalent stress of the von Mises in the analytical model for corner strength increase rates α of 1.0 and 1.3. In Figure 11, the equivalent stress is 325 (N / mm²). 2) The region above is judged to be plastic. In the model shown as Figure 11(a) with a corner strength increase rate α of 1.0, it was confirmed that most of the upper square steel pipe 11 was not plastic, and the plastic region was concentrated in one place on the through diaphragm 13. In contrast, in the model shown as Figure 11(b) with a corner strength increase rate α of 1.3, it was confirmed that most of the upper square steel pipe 11 was plastic. From these, the analysis maximum M and the total plastic moment c M p2 It was confirmed that it is possible to determine the state of collapse by comparing it with the other elements. [Explanation of Symbols]

[0084] 1:Joint structure 11: Upper rectangular steel pipe 12: Lower square steel pipe 13: Through diaphragm

Claims

1. A joint structure in which an upper rectangular steel pipe and a lower rectangular steel pipe are joined via a through diaphragm, The diameter of the upper rectangular steel pipe is smaller than the diameter of the lower rectangular steel pipe. The joint strength calculated using the yield stress of the upper rectangular steel pipe and the yield stress of the through diaphragm. j M u1 and the full plastic moment of the upper rectangular steel pipe c M p1 and satisfy the following equation (1), Yield stress of the flat plate portion of the upper square steel pipe f σ y Yield stress of the corner portion of the upper square steel pipe with respect to c σ y Corner strength increase rate represented by the ratio of c σ y / f σ y is greater than 1 Joint structure. [Math 1]

2. The joining structure according to claim 1, further satisfying the following formula (2). [Math 2] However, α = 1.159 and β = 0.

719.

3. The joining structure according to claim 2, further satisfying the following formula (3). [Math 3] Here, Y.R. is expressed by the following equation (4): f σ u This is the tensile strength of the flat portion of the upper rectangular steel pipe. [Math 4]

4. The joining structure according to claim 3, further satisfying the following formula (5). [Math 5]

5. The diameter and thickness of the upper rectangular steel pipe are D, respectively. cu (mm), t cu (mm) and the plate thickness of the through diaphragm is t d (mm) and the diameter of the lower square steel pipe is D cl The joining structure according to any one of claims 1 to 4, wherein when (mm), the following formulas (6) and (7) are further satisfied. [Math 6] [Number 7]

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