JP7728097B2 - Square steel pipe column reinforcement structure - Google Patents

Description

The present invention relates to a square steel pipe column reinforcement structure.

The seismic performance of a building is evaluated based on the strength and deformation capacity of its constituent members. When a square steel pipe column has a large width-to-thickness ratio (outer diameter/plate thickness), local buckling occurs at the end of the column when subjected to external force, resulting in a premature loss of strength and poor deformation capacity, which becomes a problem. In response to this, architectural design involves verifying safety by increasing the design external force in accordance with the width-to-thickness ratio of the square steel pipe column. Meanwhile, in order to improve the seismic performance of square steel pipe columns, construction methods have been proposed to improve the strength or deformation capacity of the columns, and the majority of these methods are aimed at improving strength.

In order to improve the strength or deformation capacity of square steel pipe columns, reinforcement structures such as placing reinforcing materials at the column ends are sometimes adopted. For example, rib plate reinforcement and cover plate reinforcement methods are sometimes used to improve the strength of square steel pipe columns. For example, the latter method is summarized as a design method for seismic retrofitting of existing buildings in the "STKR Column Reinforcement Design and Construction Manual, Supplement to the 2018 Cold-Formed Square Steel Pipe Design and Construction Manual by the Building Center of Japan (General Incorporated Foundation)."

Patent Document 1 describes a reinforcement method intended to improve the deformation capacity of square steel pipe columns. This document describes a structure that aims to improve the deformation capacity of square steel pipe columns by placing reinforcing material through a gap on at least one side of the outer or inner surface of the end of the square steel pipe column, so that when the square steel pipe column experiences local buckling deformation, the reinforcing material abuts against the column, thereby restricting local buckling deformation. Alternatively, the Japan Building Disaster Prevention Association's "Damage Classification Criteria and Restoration Technical Guidelines for Earthquake-Affected Buildings, etc. (2015)" describes a repair method intended to restore the strength of damaged square steel pipe columns. This method involves welding cover plates from the outside to the areas of earthquake-damaged square steel pipe columns where local buckling deformation has occurred, restoring the strength to the same level as the original steel pipe.

JP 2012-136929 A

However, square steel pipe columns with a large width-thickness ratio lose their strength quickly when subjected to external forces, resulting in poor deformability. Furthermore, many conventional reinforcement methods for square steel pipe columns are primarily aimed at improving strength, and excessive strength improvements can have a negative impact on the design of surrounding components. When reinforcing columns, the fit between the reinforcing material and the wall material can be problematic. Construction methods with complex structures can also result in a significant increase in labor hours.

The present invention was made to solve these problems, and aims to provide a square steel pipe column reinforcement structure that is simple in structure, has a reduced weight, and can improve the performance of square steel pipe columns.

The square steel pipe column reinforcement structure of the present invention comprises a square steel pipe column and a plate-shaped reinforcing member provided on at least one of the outer surface and inner surface of the side wall portion of the square steel pipe column at a position away from the longitudinal end face of the square steel pipe column, and when the diameter of the square steel pipe column is D, the plate thickness of the square steel pipe column is t, the reinforcement length from the end face to the end of the reinforcing member is _hr , and the plate thickness of the reinforcing member is _t , the relationship of ( _hr /D ≧ 0.6) and the relationship of formula (1) hold.

In this square steel pipe column structure, by selecting an appropriate reinforcement size according to the square steel pipe column to be reinforced, local buckling of the square steel pipe column is permitted while the buckling deformation is moderately restrained, thereby mitigating the decrease in strength after local buckling and improving deformability. Furthermore, by limiting reinforcement to the end of the square steel pipe column where local buckling may occur, a significant increase in labor costs can be avoided. Furthermore, by attaching the reinforcement at a certain distance from the longitudinal end face of the square steel pipe column, excessive increases in strength of the square steel pipe column that would affect the design of surrounding components can be prevented. Because the reinforcement has a plate-like structure, its protrusion from the surface of the square steel pipe column is small, thereby reducing the impact on the interface with wall materials. Furthermore, by satisfying the relationship ( _hr /D ≧ 0.6), sufficient reinforcement length can be ensured, thereby ensuring the performance required of the square steel pipe column. Furthermore, since the relationship of Equation (1) holds, excessive weight increases can be suppressed. As a result, the performance of square steel pipe columns can be improved with a simple structure and a reduced weight.

In a steel box column reinforced structure, the relationship ( _hr /D≧0.8) may be satisfied, which further ensures the performance required of a steel box column.

In a steel box column reinforced structure, the relationship (t _r /t ≧ 0.26) may be satisfied, which further ensures the performance required of a steel box column.

In a steel box column reinforced structure, the relationship of formula (2) may be satisfied. In this case, excessive weight increase can be further suppressed.

The square steel pipe column reinforcement structure comprises a square steel pipe column and a plate-shaped reinforcing member provided on at least one of the outer and inner surfaces of the side wall portion of the square steel pipe column at a position away from the longitudinal end face of the square steel pipe column, and when the diameter of the square steel pipe column is D and the reinforcement length from the end face to the end of the reinforcing member is _hr , the relationships ( _hr /D ≧ 0.6) and (weight increase rate = (reinforcement weight)/(square steel pipe column weight) ≦ 0.08) hold.

In this square steel pipe column, by selecting an appropriate reinforcement size according to the square steel pipe column to be reinforced, local buckling of the square steel pipe column is permitted while the buckling deformation is moderately restrained, thereby mitigating the decrease in strength after local buckling and improving deformability. Furthermore, by limiting reinforcement to the end of the square steel pipe column where local buckling may occur, a significant increase in labor costs can be avoided. Furthermore, by attaching the reinforcement at a certain distance from the longitudinal end face of the square steel pipe column, excessive increases in strength of the square steel pipe column that would affect the design of surrounding components can be prevented. Because the reinforcement has a plate-like structure, the amount of protrusion of the reinforcement from the surface of the square steel pipe column is small, thereby reducing the impact on the interface with wall materials. Furthermore, by satisfying the relationship ( _hr /D ≧ 0.6), sufficient reinforcement length can be ensured, thereby ensuring the performance required of the square steel pipe column. Furthermore, since the relationship (weight increase rate = (reinforcement weight) / (square steel pipe column weight) ≦ 0.08) holds, excessive weight increase can be suppressed. As a result, the performance of the square steel pipe column can be improved with a simple structure and a weight-suppressed structure.

This invention improves the performance of square steel pipe columns with a simple and lightweight structure.

1 is a perspective view showing a column-beam joint structure 50 in which a square steel pipe column reinforcing structure 100 according to an embodiment of the present invention is adopted. FIG. 1 is a diagram showing the entire square steel pipe column 1. FIG. 1 is a diagram showing a square steel pipe column reinforcement structure. FIG. 1 is a table showing a list of test specifications and test results. 10 is a graph showing test results. FIG. 1 is a diagram illustrating an outline of an analytical model. 10 is a graph showing the analysis results. FIG. 10 is a diagram showing a modified form of the analysis result. 10 is a graph showing the analysis results. FIG. 10 is a diagram showing the effective range of reinforcement specifications for a square steel pipe column reinforced structure. FIG. 10 is a diagram showing a reinforcing member of a square steel pipe column reinforcing structure according to a modified example.

A preferred embodiment of the present invention will be described below with reference to the drawings.

Figure 1 is a perspective view showing a column-beam connection structure 50 that employs a square steel pipe column reinforcement structure 100 according to an embodiment of the present invention. Figure 2 is a diagram showing the entire square steel pipe column 1. As shown in Figures 1 and 2, the column-beam connection structure 50 comprises a square steel pipe column 1, a beam 2 connected to the square steel pipe column 1, and a connection core 3. Note that Figures 1 and 2 merely show one example of an application of the square steel pipe column reinforcement structure, and the application can be changed as appropriate.

The square steel pipe column 1 is composed of a steel pipe with a rectangular cross section. The upper square steel pipe column 1 and the lower square steel pipe column 1 are connected to each other in the vertical direction via a connecting core 3. The square steel pipe column 1 has four side walls 10. The square steel pipe column 1 has a lower end face 1a and an upper end face 1b in the longitudinal direction (vertical direction).

The beams 2 on all four sides are connected to the square steel pipe columns 1 via connecting cores 3. The beams 2 have an H-shaped cross section and include upper and lower flanges 2a, 2b, and a web portion 2c that connects the flanges 2a, 2b together.

The connecting core 3 comprises a steel pipe section 3a with a rectangular cross section and diaphragms 3b, 3c formed on the upper and lower end faces of the steel pipe section 3a. The lower end face 1a of the upper square steel pipe column 1 is connected to the diaphragm 3b of the connecting core 3. The upper end face 1b of the lower square steel pipe column 1 is connected to the diaphragm 3c of the connecting core 3. The upper and lower flanges 2a, 2b of the beam 2 are also connected at the positions of the upper and lower diaphragms 3b, 3c.

The square steel pipe column reinforcement structure 100 comprises the square steel pipe column 1 described above and multiple reinforcing members 20. The reinforcing members 20 are rectangular plate-shaped members provided on at least one of the outer and inner surfaces of the side wall portions 10 of the square steel pipe column 1, at positions spaced apart from the end faces 1a and 1b of the square steel pipe column 1. In this embodiment, the reinforcing members 20 are rectangular and fixed to the outer surfaces of the side wall portions 10. The reinforcing members 20 are provided near the lower end face 1a of the square steel pipe column 1 on all four side wall portions 10. The reinforcing members 20 are provided near the upper end face 1b of the square steel pipe column 1 on all four side wall portions 10. Therefore, a total of eight reinforcing members 20 are provided for one square steel pipe column 1.

Next, the dimensional relationship of the square steel pipe column reinforcement structure 100 will be described with reference to Figure 3. While Figure 3 shows the configuration of the lower side of the square steel pipe column 1, the upper side has a similar configuration. As shown in Figure 3(a), the diameter of the square steel pipe column 1 is defined as D. The plate thickness of the square steel pipe column 1 is defined as t. As shown in Figure 3(b), the reinforcement length from the lower end face 1a of the square steel pipe column 1 to the end 20a of the reinforcement 20 away from the end face 1a is defined as _hr . The gap from the lower end face 1a of the square steel pipe column 1 to the end 20b of the reinforcement 20 closer to the end face 1a is defined as _Sr. The ends 20a, 20b are parallel to the end face 1a of the square steel pipe column 1. The width of the reinforcement 20 is defined as _br . The reinforcement 20 is positioned at the center of the side wall portion 10 in the width direction. The widthwise ends 20c, 20d of the reinforcing member 20 are parallel to the widthwise ends 10a, 10b of the side wall portion 10, spaced apart from the widthwise inward ends 10a, 10b. The plate thickness of the reinforcing member 20 is defined as _tr . The length of the square steel pipe column 1 is defined as L. Specifically, the "diameter D of the square steel pipe column x plate thickness t" may be in the range of "□200 x 6 to □550 x 19" for cold-roll-formed square steel pipes, and "□350 x 12 to □1000 x 32" for cold-press-formed square steel pipes. The plate thickness of the reinforcing member may be in the range of "0.26≦t _r /t ≦1.0." The reinforcing length may be in the range of "0.6≦hr / _D ≦2.0." The width of the reinforcing member may be in the range of "0< _br /D ≦0.8." The gap may be set to "0≦S _r /D≦0.27".

Next, we will explain how to set the preferred dimensional relationships between each part of the square steel pipe column reinforced structure 100. First, with reference to Figures 4 to 6, we will explain tests on the bearing capacity of the square steel pipe column reinforced structure 100. Specifically, to confirm the reinforcing effect of the square steel pipe column reinforced structure 100, a full-scale three-point bending test (monotonic/cyclic loading) was conducted with the plate thickness t _r and reinforcement length _hr of the reinforcement 20 as variables. The test specimen shown in Figure 4(a) was prepared. Figure 4(b) shows an enlarged view of the portion indicated by "A" in the figure. Two test specimens were prepared, each with reinforcement 20 attached to all four sides of a square steel pipe column 1. The end of each square steel pipe column 1 on the side where the reinforcement 20 was attached was supported by a support member 32. The opposite end of each square steel pipe column 1 was supported by a support member 31. A load was applied to the central support member 32, measurements were performed, and the local buckling characteristics were observed. In addition, a test specimen for "non-reinforcement" in which no reinforcing material 20 was provided was also prepared.

Tests were conducted under two conditions: monotonic loading (where loads are applied monotonically) and cyclic loading (where loads are applied repeatedly). Figure 5 shows the test specifications and results. Figure 6(a) shows the load-deformation relationship under monotonic loading. Figure 6(b) shows the load-deformation relationship under cyclic loading. The maximum strength of the reinforced specimens was equivalent to that of the unreinforced specimens, confirming that the strength was equivalent to that of the original square steel pipe column. Furthermore, the "2.3 x 360" reinforcement had the highest reinforcement effect, with deformation capacity 1.36 times that of the unreinforced specimen under monotonic loading and 1.60 times that of the unreinforced specimen under cyclic loading. In this case, the two specimens with the longest reinforcement length (360 mm) were encircled, while the specimen with the shortest reinforcement length (240 mm) was unencircled. It was confirmed that the encircled type was more effective in improving deformation capacity. The "encircling" type refers to a deformation mode in which deformation progresses while the reinforcement restrains the local buckling deformation of the square steel pipe column (see, for example, Figure 9(a)). The "non-encircling" type refers to a deformation mode in which local buckling occurs from an unreinforced portion that exceeds the reinforcement length _hr from the end face of the square steel pipe column connected to the diaphragm to the end of the reinforcement, and deformation progresses (see, for example, Figure 9(b)). The "gap" type, which will be described later, refers to a deformation mode in which local buckling occurs from a gap Sr from the end face of the square steel pipe column connected to the diaphragm to the end face of the reinforcement closer to the end face, and deformation progresses (see, for example, Figure 9(c)).

Next, we will explain the analytical tests with reference to Figures 7 to 10. Here, to confirm the effect of the construction method on the required performance of the square steel pipe column 1, we constructed a model that can precisely reproduce the full-scale test results (Figures 7 and 8(b) and (c)), and then conducted a parametric study on the plate thickness and reinforcing length of the reinforcing material 20 using FEM analysis. Figure 7 is a diagram showing an overview of the analytical model. Figures 8(b) and (c) are graphs showing the results of a comparison between the full-scale test and the analytical results under the condition of "reinforcement 2.3 x 360." Figure 8(b) shows the results of monotonic loading, and Figure 8(c) shows the results of cyclic loading.

The analytical conditions were as follows. The conditions for the square steel pipe column were "width-thickness ratio D/t = 33.3,""steel pipe used: BCR295," and "shear span ratio L/2D = 5." Rectangular SS400 steel was used as the reinforcement. The parameters for "non-dimensional plate thickness t _r /t" were set to 0.13, 0.26, 0.36, 0.50, and 0.67 (e.g., when 300×9/t _r /t = 0.5, t _r = 4.5 mm). The parameters for "non-dimensional reinforcement length _hr /D" were set to 0.4, 0.6, 0.8, 1.0, and 1.2 (e.g., when 300×9/hr / _D = 0.6, _hr = 240 mm). The width b _r = 0.5D and the gap S _r = 0.2D were fixed. The material data was set based on the results of a full-scale material test. The repeated loading history consisted of one loop of ±1δp, followed by two loops of ±2δp and ±4δp (see FIG. 8(a)).

Figure 9 shows the deformation behavior of the analysis results for local buckling behavior (the values in parentheses are roughly divided into the thickness and length of the reinforcement). Figure 10(a) is a graph showing the results of comparing the load-deformation relationship between an unreinforced model and a reinforced model. Figure 10(b) is a graph showing the relationship between the reinforcement plate thickness and reinforcement length and the deformation capacity (cumulative plastic deformation factor _E η _A (D/t = 33.3)). Note that in Figure 10(b), "*1" indicates the "Structural Rank I" required for columns as described in the "Kouzai Club: Square Steel Pipe Design Research Group Report 1993." For "*2," an analytical model with a width-thickness ratio that is the boundary between each member rank was created, and reference values derived through FEM analysis are shown.

As shown in Figure 9, the following three types of local buckling behavior were observed depending on the combination of non-dimensional plate thickness and reinforcement length. Furthermore, when the reinforcement length was short, the non-entrapment type behavior was observed, as shown in Figure 9(b). Furthermore, as shown in Figure 10(b), when the reinforcement length was relatively long, the entrapment type behavior was observed, as shown in Figure 9(a), or the gap type behavior was observed, as shown in Figure 9(c). For the same reinforcement thickness, the reinforcement effect (cumulative plastic deformation ratio _E η _A ) satisfies the following relationship: (a) entrapment type or (c) gap type > (b) non-entrapment type. It was confirmed that even if the reinforcement length is increased beyond the reinforcement length at which the transition from the (b) non-entrapment type to the (a) entrapment type or (c) gap type first occurs, the reinforcement effect almost reaches a plateau.

From the above-described tests and analyses, a map showing the relationship between the "non-dimensional reinforcement length h _r /D" and the "non-dimensional plate thickness t _r /t" was obtained, as shown in FIG. 11(a). In FIG. 11(b), the mapping was performed using representative values: "width-thickness ratio D/t = 33.3,""shear span ratio L/2D = 5,""reinforcement width b _r /D = 0.5," and "gap S _r /D = 0.2." This map was created based on the performance evaluation and weight gain evaluation based on the analysis results shown in FIG. 10(b). The weight gain is defined as "weight gain = (reinforcement weight) / (square steel pipe column weight)." When multiple reinforcements are used, the weight gain is the total weight of the reinforcements. Specifically, the darkest grayscale region E2 corresponds to a region classified as having a performance evaluation of "Structural Rank I (local buckling) or higher" and a weight gain of 6% or less. The next dark grayscale region E3 is a region classified as having a performance evaluation of "Structural Rank I (local buckling) or higher" and a weight increase rate of 8% or less. The next dark grayscale region E4 is a region classified as having a performance evaluation of "FA⇔FB boundary (reference) or higher" and a weight increase rate of 8% or less. Regions without a grayscale region are regions that do not satisfy any of these conditions. It is preferable to set the parameters of the square steel pipe column reinforced structure 100 to the conditions within region E1, which includes regions E2, E3, and E4.

Based on the above-described mapping, the effective range of the reinforcement specifications for the steel box column-reinforced structure 100 was determined. From the results of the mapping, to fall within region E1, the "dimensionless reinforcement length h _r /D" must be 0.6 or greater. Therefore, the effective range is (h _r /D ≧ 0.6). To fall within region E1, the weight gain must be 8% or less. Therefore, the relationship "weight gain = (reinforcement weight) / (steel box column weight)...(*)" can be expressed using each parameter as shown in Equation (3). By rearranging Equation (3) using the "width-thickness ratio D/t = 33.3,""shear span ratio L/2D = 5,""reinforcement width b _r /D = 0.5," and "gap S _r /D = 0.2," and by defining the "weight gain of 8% or less" as the effective range, the relationship shown in Equation (4) can be obtained. Although the cross-sectional area A of the square steel pipe varies depending on the size, the shapes are nearly similar even when the sizes are different. Therefore, after substituting the specific values of D, t, and A, the same formula, namely, formula (4), is obtained. Further rearrangement of this formula yields formula (1). Therefore, it is preferable that formula (1) holds true as the reinforcement specification for the square steel pipe column reinforced structure 100.

11(a), as the reinforcement specifications for the square steel pipe column reinforced structure 100, region E2 is most preferable, region E3 is next preferable, and region E4 is next preferable. Therefore, it is preferable that the relationship ( _hr /D ≧ 0.8) holds so as to fall within the range of region E2 or region E3. It is also preferable that the relationship ( _tr /t ≧ 0.26) holds so as to fall within the range of region E2 or region E3. It is also preferable that the weight gain rate in formula (4) be 6% or less so as to fall within the range of region E2, so that the following formula (2) holds.

The following describes the functions and effects of the square steel pipe column reinforcement structure 100 according to this embodiment.

The square steel pipe column reinforcement structure 100 comprises a square steel pipe column 1 and a plate-shaped reinforcing member 20 provided on at least one of the outer surface and inner surface of the side wall portion 10 of the square steel pipe column 1 at a position spaced apart from the longitudinal end faces 1 a, 1 b of the square steel pipe column 1, and when the diameter of the square steel pipe column 1 is D, the plate thickness of the square steel pipe column 1 is t, the reinforcing length from the end face to the end 20 a of the reinforcing member 20 is _hr , and the plate thickness of the reinforcing member 20 is _t , the relationship ( _hr /D ≧ 0.6) and the relationship of formula (1) hold.

In this square steel pipe column reinforcement structure 100, by selecting an appropriate reinforcement size according to the square steel pipe column 1 to be reinforced, local buckling of the square steel pipe column 1 is permitted while the buckling deformation is moderately restrained, thereby mitigating the decrease in strength after local buckling and improving deformability. Furthermore, by limiting reinforcement to the end of the square steel pipe column 1 where local buckling may occur, a significant increase in labor costs can be avoided. Furthermore, by attaching the reinforcement 20 at a certain distance from the longitudinal end face of the square steel pipe column 1, an excessive increase in strength of the square steel pipe column 1 that would affect the design of surrounding components can be prevented. Because the reinforcement 20 has a plate-like structure, the amount of protrusion of the reinforcement 20 from the surface of the square steel pipe column 1 is small, thereby reducing the impact on the interface with the wall material. Furthermore, by satisfying the relationship ( _hr /D ≧ 0.6), the reinforcement length can be sufficiently secured, thereby ensuring the performance required of the square steel pipe column 1. Furthermore, since the relationship of formula (1) holds, an excessive increase in weight can be suppressed. As described above, the performance of the square steel pipe column 1 can be improved with a simple structure and a structure in which the weight is suppressed.

In the square steel pipe column reinforced structure 100, the relationship ( _hr /D≧0.8) may be established. In this case, the performance required of the square steel pipe column 1 can be further ensured.

In the square steel pipe column reinforced structure 100, the relationship (t _r /t ≧ 0.26) may be established. In this case, the performance required of the square steel pipe column 1 can be further ensured.

In the steel pipe column reinforced structure 100, the relationship of formula (2) may be established. In this case, excessive weight increase can be further suppressed.

The square steel pipe column reinforcement structure 100 comprises a square steel pipe column 1 and a plate-shaped reinforcing member 20 provided on at least one of the outer surface and inner surface of the side wall portion 10 of the square steel pipe column 1 at a position spaced apart from the longitudinal end face of the square steel pipe column 1. When the diameter of the square steel pipe column 1 is D and the reinforcement length from the end face to the end 20a of the reinforcing member 20 is _hr , the relationships ( _hr /D ≧ 0.6) and (weight increase rate = (reinforcement weight)/(square steel pipe column weight) ≦ 0.08) hold.

By satisfying the relationship ( _hr /D ≧ 0.6), the reinforcement length is ensured sufficiently, thereby ensuring the performance required of the square steel pipe column 1. Furthermore, since the relationship (weight increase rate = (reinforcement weight) / (square steel pipe column weight) ≦ 0.08) holds, excessive weight increase can be suppressed. As described above, the performance of the square steel pipe column can be improved with a simple structure that suppresses weight.

The present invention is not limited to the above-described embodiments. The dimensions described in the above embodiments are merely examples and may be modified as appropriate without departing from the spirit of the present invention.

For example, the shape of the reinforcing member 20 is not limited to the above-described embodiment. For example, the shape shown in Figure 12 may be adopted. In Figure 12, the reinforcing member 20 provided on one side wall portion 10 is divided into two. Note that the number of divisions and the division method are not particularly limited.

1...square steel pipe column, 10...side wall portion, 20...reinforcement material, 100...square steel pipe column reinforcement structure

Claims (4)

Square steel pipe column,
a plate-shaped reinforcing member provided on at least the outer surface of the outer surface and the inner surface of the side wall portion of the square steel pipe column at a position spaced from the end face in the longitudinal direction of the square steel pipe column,
The diameter of the square steel pipe column is D,
The plate thickness of the square steel pipe column is t,
The reinforcement length from the end face to the end of the reinforcing material is defined as _hr ,
When the plate thickness of the reinforcing material is t _r , the relationship of (h _r /D ≧ 0.6) and the relationship of formula (1) are established,
The square steel pipe has a yield point or a lower limit of the proof stress of 295 N/ ^mm2 , a width-thickness ratio D/t of 33.3, and a shear span ratio L/2D of 5,
The reinforcing material is a rectangular SS400 steel material, has a width b _r of 0.5D, and a gap S _r from the end face of the square steel pipe column to the reinforcing material is 0.2D,
A square steel pipe column reinforcement structure in which the reinforcing material is fixed at the center position in the width direction on each of the four outer surfaces of the square steel pipe.

The square steel pipe column reinforced structure according to claim 1, wherein the relationship ( _hr /D≧0.8) is satisfied. The square steel pipe column reinforced structure according to claim 1 or 2, wherein the relationship (t _r /t ≧ 0.26) is satisfied. The square steel pipe column reinforced structure according to any one of claims 1 to 3, wherein the relationship of formula (2) holds.