Double-walled steel pipe concrete column

Abstract

To provide an economical double steel pipe concrete column having excellent resistance against dead weight and a live load and bearing force against repeated load in an earthquake.SOLUTION: A double steel pipe concrete column comprises: an inner steel pipe 5 vertically extendedly arranged, with an upper end connected to an upper structure 4, and a lower end connected to a lower structure 1; an outer steel pipe 6 with the upper end not connected to the upper structure and the lower end not connected to the lower structure, and coaxially arranged outside the inner steel pipe; and first concrete 7 filled in an annular space surrounded by the outside of the inner steel pipe and by the inside of the outer steel pipe. The inner steel pipe is formed of an equilateral square steel pipe, and the outer steel pipe is formed of a circular steel pipe.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a double-walled steel pipe concrete column connected between a superstructure and a substructure. [Background technology]

[0002] In recent years, double-walled concrete columns have been proposed, which have a double-walled structure consisting of an inner and outer steel pipe, with concrete filled inside and in the gaps between them (for example, the column in Patent Document 1, and the concrete-filled steel pipe in Patent Document 2).

[0003] According to the double-walled steel pipe concrete columns described in Patent Documents 1 and 2, the outer steel pipe can not only provide the strength of reinforcing bars but also function as formwork, reducing the amount of work required for reinforcing the columns and removing and installing the formwork, thereby shortening the construction period and reducing labor. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-307702 [Patent Document 2] Japanese Patent Publication No. 2006-265851 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the double-walled steel pipe concrete columns described in Patent Documents 1 and 2 do not clearly define the resistance of the composite column structure of the inner steel pipe, outer steel pipe, and filled concrete to vertical loads, horizontal loads, and bending moments acting on the column. As a result, it is difficult to optimize the shape, dimensions, and plate thickness of the constituent members, making it difficult to provide an economical column that is superior in resistance to its own weight and live loads, as well as in its ability to withstand repeated loads during earthquakes.

[0006] Therefore, the present invention has been made in view of the above circumstances, and provides a double-walled steel pipe concrete column that is economical and has excellent resistance to its own weight and live load, as well as resistance to repeated loads during earthquakes. [Means for solving the problem]

[0007] To achieve the above objective, a double-walled steel pipe concrete column according to one aspect of the present invention comprises an inner steel pipe extending vertically, with its upper end connected to a superstructure and its lower end connected to a substructure; an outer steel pipe not connected to a superstructure at its upper end and not connected to a substructure at its lower end, and coaxially positioned outside the inner steel pipe; and a first concrete filling the annular space enclosed by the outside of the inner steel pipe and the inside of the outer steel pipe, wherein the inner steel pipe is composed of an equilateral rectangular steel pipe and the outer steel pipe is composed of a circular steel pipe. [Effects of the Invention]

[0008] According to the double-walled steel pipe concrete column of the present invention, it is possible to obtain a column that is excellent in resistance to its own weight and live load, as well as in its ability to withstand repeated loads during earthquakes, and is also economical. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a steel pipe concrete column (filled and coated column) according to the first embodiment of the present invention. [Figure 2] This figure shows a view along line II-II in Figure 1 (a cross-section of the filled and covered column of the first embodiment). [Figure 3] This is a diagram showing the column-beam joint of the first embodiment. [Figure 4] This figure shows a cross-section of a steel pipe concrete column (covered column) according to a second embodiment of the present invention. [Figure 5] This diagram shows an overview of the horizontal alternating positive and negative load testing machine used in bending shear experiments on steel pipe concrete columns. [Figure 6] This figure shows the repeated loading patterns applied to a test specimen in the horizontal alternating loading section of a horizontal alternating positive and negative loading test machine. [Figure 7]It is a graph showing the relationship between the horizontal load of the specimen subjected to the bending-shear test and the member angle at the column head. [Figure 8] It is a graph showing the relationship between the vertical load and the bending moment of the specimen subjected to the bending-shear test. [Figure 9] It is a graph showing the axial strain distribution of the inner steel pipe and the circumferential strain distribution of the outer steel pipe of the specimen subjected to the bending-shear test. [Figure 10] It is a diagram showing an overview of the loading test machine used in the short column compression test. [Figure 11] It is a graph for setting the optimal diameter-thickness ratio B / t of the outer steel pipe constituting the filled and coated column of the first embodiment. [Figure 12] It is a graph for setting the optimal width-thickness ratio B1 / t1 of the inner steel pipe constituting the coated column of the second embodiment. [Figure 13] It is a cross-sectional view showing the steel pipe concrete column (filled and coated column, coated column) of the fourth embodiment according to the present invention. [Embodiments for Carrying out the Invention]

[0010] Next, embodiments according to the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thicknesses of the respective layers, etc. are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Also, it is a matter of course that there are portions where the dimensional relationships and ratios are different between the drawings.

[0011] Also, the embodiments shown below are examples of devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention does not specify the material, shape, structure, arrangement, etc. of the constituent parts as the following. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims. [Steel Pipe Concrete Column of the First Embodiment]

[0012] Figure 1 shows the structure of the double steel pipe concrete column 2 according to the first embodiment of the present invention. It rises from the foundation concrete 1 on the first floor, and the steel beam 4 extends horizontally and is joined through the column-beam joint 3 provided at the uppermost part.

[0013] As shown in Figure 2, the double steel pipe concrete column 2 of this embodiment includes an inner steel pipe 5 composed of a square-sectioned rectangular steel pipe vertically rising from the foundation concrete 1, an outer steel pipe 6 composed of a circular steel pipe coaxially arranged outside the inner steel pipe 5, a first concrete 7 filled in the space surrounded by the outside of the inner steel pipe 5 and the inside of the outer steel pipe 6, and a second concrete 8 filled in the internal space of the inner steel pipe 5. The outer steel pipe 6 is a circular steel pipe, but it may also have a structure in which split members divided in the circumferential direction are built in from the side surface of the inner steel pipe 5 and integrated into the circular steel pipe by joining with welding, bolts, etc. Here, the double steel pipe concrete column 2 of the first embodiment is referred to as a filled and covered type column 2.

[0014] The lower end opening of the inner steel pipe 5 of the filled and covered type column 2 is closed by an anchor plate AP, and an anchor bolt 9 rising from the inside of the foundation concrete 1 penetrates and is fixed to the anchor plate AP. Also, a floor slab concrete 10 for forming a floor surface is laid on the foundation concrete 1. Note that this example is based on the form in which the anchor bolt penetrates and is fixed to the anchor plate, but it is not limited to this, and other column base structures such as embedded column bases can also be applied.

[0015] As shown in Figure 3, the column-beam joint 3 is located at the top of the inner steel pipe 5 of the filled-covered column 2 and comprises a connecting steel pipe 11 with two square-frame-shaped diaphragms 12a and 12b welded to its outer circumference at vertical spacing, and four joints 13 made of H-shaped steel with flanges 13a and 13b welded to the diaphragms 12a and 12b and a web 13c welded to the connecting steel pipe 11, extending horizontally in four mutually perpendicular directions. In addition, multiple reinforcing bars 16 are arranged to penetrate the web 13c of the joints 13 and extend in a loop shape around the connecting steel pipe 11, and a third concrete 17 is filled to embed the multiple reinforcing bars 16.

[0016] Returning to Figure 1, a steel beam 4 made of H-shaped steel is bolted to the joint 13 of the column-beam joint 3. Then, a concrete floor slab 10 is laid on the steel beam 4 as the floor of the second floor, and the lower end of the inner steel pipe 5 is welded to the upper end of the connecting steel pipe 11 of the column-beam joint 3. This inner steel pipe 5 is used as a component of the filled-covered column 2 of the second floor, forming a column with the same structure as the filled-covered column 2 of the first floor.

[0017] A predetermined gap (approximately 10-30 mm) is provided between the lower end of the outer steel pipe 6 constituting the first-floor filled-in-coat column 2, indicated by the symbol A1 in Figure 1, and the first-floor concrete slab 10. A predetermined gap is also provided between the upper end of the outer steel pipe 6, indicated by the symbol A2 in Figure 1, and the sheathing member 14 welded to the joint 13 of the column-beam joint 3. Furthermore, a predetermined gap is also provided between the lower end of the outer steel pipe 6 constituting the second-floor filled-in-coat column 2, indicated by the symbol A3 in Figure 1, and the second-floor concrete slab 10. By providing gaps between the lower end of the outer steel pipe 6 and the first and second-floor concrete slabs 10, and between the upper end of the outer steel pipe 6 and the sheathing member 14 of the column-beam joint 3, bending moment and axial force do not act on the outer steel pipe 6.

[0018] Linear column reinforcement bars 15 are positioned embedded in the first concrete 7 between the inner steel pipe 5 and outer steel pipe 6 of the first-floor filled-in-covered column 2 and between the inner steel pipe 5 and outer steel pipe 6 of the second-floor filled-in-covered column 2, and embedded in the third concrete 17 of the column-beam joint 3 (see Figure 2). These column reinforcement bars 15 consist of segmented column bars 15a rising from the foundation concrete 1, segmented column bars 15b welded to the segmented column bars 15a and extending upward, segmented column bars 15c welded to the segmented column bars 15b and extending to the column-beam joint 3, and segmented column bars 15d welded to the segmented column bars 15c and extending between the inner steel pipe 5 and outer steel pipe 6 of the second-floor filled-in-covered column 2. Although an example of a welded joint is shown, it is not limited to this, and mechanical joints and lap joints are also assumed.

[0019] In this embodiment of the filled and covered column 2, both ends of the inner steel pipe 5 are connected to the foundation concrete 1 and steel beam 4, which are structural members of the building, and together they exert resistance to external forces. Furthermore, in order to install the steel beam 4 in a cross shape with the inner steel pipe 5 as the center, connecting steel pipes 11 (column-beam joint 3) of the same shape as the inner steel pipe 5 are connected to the ends of the inner steel pipe 5. By making the inner steel pipe 5 and the connecting steel pipe 11 into square steel pipes, the installation of the cross-shaped steel beam 4 can be easily carried out, resulting in an economical column structure.

[0020] Furthermore, the upper and lower ends of the outer steel pipe 6 that constitute the filled-coated column 2 are not connected to the foundation concrete 1 or the joint 13 of the column-beam joint 3, and there is a gap of about 10 to 30 mm. As a result, stress and deformation that occur in the foundation concrete 1 or the column-beam joint 3 during an earthquake are not transmitted to the outer steel pipe 6, the stress acting vertically on the outer steel pipe 6 is suppressed, and a reduction in load-bearing capacity due to damage such as buckling is prevented. Therefore, there is no need to make the pipe thickness of the outer steel pipe 6 excessively large, and an economical column structure can be made.

[0021] Furthermore, when the first concrete 7 is filled between the outer steel pipe 6 and the inner steel pipe 5, the pressure of the filled concrete acts horizontally outward on the inner surface of the outer steel pipe 6. However, by making the outer steel pipe 6 a circular steel pipe, the tensile force in the outer direction of the outer steel pipe 6 resists the pressure of the filled concrete. Therefore, the thickness of the outer steel pipe 6 required as formwork during concrete filling can be minimized, improving cost-effectiveness. If the pipe thickness of the outer steel pipe 6 is set to 3 mm or more, it can function sufficiently as formwork when filling the first concrete 7, even when used in long members of about 16 m.

[0022] Furthermore, the outer steel pipe 6 can improve the strength of the first concrete 7 by restraining the first concrete 7 from shearing and undergoing minute cracking and volume expansion when the column deforms under load.

[0023] Thus, the way in which the axial force acting from the first concrete 7 causes volume expansion, and how this is restrained by the axial compressive resistance of the outer steel pipe 6, is called the confining effect of the outer steel pipe 6. In this case as well, by making the outer steel pipe 6 a circular steel pipe, the tensile force in the outer circumference of the outer steel pipe 6 resists the expansion, thus minimizing the plate thickness of the outer steel pipe 6 required to exert the confining effect of the outer steel pipe 6 and improving cost-effectiveness. [Steel pipe concrete column of the second embodiment]

[0024] Next, Figure 4 shows the structure of a double-walled steel pipe concrete column 20 according to the second embodiment of the present invention. Similar to the filled and covered column 2 of the first embodiment, it rises from the foundation concrete 1 on the first floor, and a steel beam 4 extends horizontally and is joined via a column-beam joint 3 provided at the top.

[0025] As shown in Figure 4, the double-walled steel pipe concrete column 20 of this embodiment comprises an inner steel pipe 5 made of a square cross-section (equal sides) rectangular steel pipe that rises vertically from the foundation concrete 1, an outer steel pipe 6 made of a circular steel pipe coaxially arranged outside the inner steel pipe 5, and a first concrete 7 filled in the space enclosed by the outside of the inner steel pipe 5 and the inside of the outer steel pipe 6. The structure differs from the filled-cover type column 2 of the first embodiment in that the internal space of the inner steel pipe 5 is not filled with second concrete 8. Here, the double-walled steel pipe concrete column 20 of the second embodiment is referred to as the covered type column 20.

[0026] Similar to the filled-in covered column 2 of the first embodiment, the covered column 20 of this embodiment also uses square-sectioned rectangular steel pipes for the inner steel pipe 5 and the connecting steel pipe 11, which facilitates the installation of cross-shaped steel beams 4 and results in an economical column structure.

[0027] Furthermore, if the upper and lower ends of the outer steel pipe 6 constituting the covered column 20 are not connected to the foundation concrete 1 or the joint 13 of the column-beam joint 3, but instead have a gap of about 10 to 30 mm, then stresses and deformations that occur in the foundation concrete 1 or the column-beam joint 3 during an earthquake are not transmitted to the outer steel pipe 6, the stress acting vertically on the outer steel pipe 6 is suppressed, a reduction in load-bearing capacity due to damage such as buckling is prevented, and there is no need to make the pipe thickness of the outer steel pipe 6 excessively large, resulting in an economical column structure.

[0028] Next, the results of the bending shear tests conducted on the previously described filled-coated column 2 and coated column 20 will be explained based on Figures 5 to 9. This bending shear test was performed using the horizontal alternating positive and negative load testing machine shown in Figure 5. In this machine, a circular steel pipe with a height of 6 m and an outer diameter of 1 m was used as the outer steel pipe 6, with a scale of 1 / 3.3. The cross-section of the specimen was a square-sectioned rectangular steel pipe 120 mm × 120 mm for the inner steel pipe 5, with a pipe thickness of 6 mm, a width-to-thickness ratio of 20, and a yield strength fy = 449 N / mm². 2 So, the outer steel pipe 6 has an outer diameter of 300 mm, a pipe thickness of 1.6 mm, a diameter-thickness ratio of 187.5, and a yield strength fy of 234 N / mm. 2 It is a circular steel pipe. [Table 1]

[0029] As shown in Table 1, bending shear experiments were conducted using five types of specimens SC-1 to SC-5. Specimens SC-1 to SC-4 have the first concrete 7 filled in the space enclosed by the outside of the inner steel pipe 5 and the inside of the outer steel pipe 6, and the second concrete 8 filled in the internal space of the inner steel pipe 5. Specimen SC-5 has the first concrete 7 filled in the space enclosed by the outside of the inner steel pipe 5 and the inside of the outer steel pipe 6, but the internal space of the inner steel pipe 5 is not filled with concrete 8. Furthermore, specimens SC-1 to SC-3 do not have reinforcing bars placed in the first concrete 7, while specimens SC-4 and SC-5 have column reinforcing bars 15 placed in the first concrete 7.

[0030] As shown in Figure 5, a constant vertical load is applied to the top of the specimen in the vertical loading section, and a horizontal load is applied to the top of the specimen in the horizontal alternating loading section in a repeating loading pattern as shown in Figure 6, where the horizontal displacement increases in stages.

[0031] The axial force ratios shown in Table 1 represent the ratio of the introduced vertical load to the calculated value of the yield vertical load when both the concrete (first concrete 7, second concrete 8) and the inner steel pipe 5 yield.

[0032] In actual steel-tube concrete columns, both the upper and lower ends are constrained by the foundation concrete 1 and steel beam 4, so the bending moment is large at both ends and zero in the center. In this experiment, the lower half of the column is modeled, and the bending moment is zero at the top of the specimen and maximum at the bottom.

[0033] Figure 7 shows the horizontal load Q for specimen SC-1 on the vertical axis and the member angle R (rad) at the column head on the horizontal axis. Even after yielding due to increased load, it shows a spindle-shaped hysteresis curve that demonstrates stable energy absorption capacity against repeated loads, indicating that it is a tough column against large earthquakes.

[0034] Figure 8 plots the results for specimens SC-1 to SC-3, with vertical load on the vertical axis and the maximum bending moment Mmax on the horizontal axis. It can be seen that as the axial force ratio increases in the order of specimen SC-2, SC-1, and SC-3, the maximum bending moment Mmax also increases. Here, the solid line in Figure 8 represents the theoretical calculation value for steel-reinforced concrete columns (SRC columns), and the experimental values ​​(specimens SC-1 to SC-3) show load-bearing capacity values ​​that exceed the theoretical calculation value for steel-reinforced concrete columns (SRC columns). Therefore, it can be seen that the filled-and-covered column 2 of the first embodiment, in which the first concrete 7 is filled on the outside of the inner steel pipe 5 and the inside of the outer steel pipe 6, and the second concrete 8 is filled inside the inner steel pipe 5, has superior load-bearing capacity compared to an SRC column.

[0035] Next, Figure 9(a) shows the axial (vertical) strain distribution of the inner steel pipe 5, and Figure 9(b) shows the circumferential (horizontal) strain distribution of the outer steel pipe 6. R is the column inclination angle (%), expressed as the ratio of the horizontal displacement of the column head to the column height. From Figures 9(a) and (b), it can be seen that as the deformation due to repeated horizontal loading increases, the vertical strain in the inner steel pipe 5 increases, indicating that axial stress in the vertical direction is generated in the inner steel pipe 5 due to the bending moment acting on the column. In contrast, in the outer steel pipe 6, the horizontal strain increases, especially at the column base (for example, at a column height of 30 mm). From this, it can be seen that the confined effect is exerted by the first concrete 7 filled inside being constrained by the horizontal tensile resistance force at the column base of the outer steel pipe 6.

[0036] Furthermore, the experimental results of the strain distribution in Figure 9(b) show that the outer steel pipe 6 exhibits a significant confining effect at the base of the column. All of the specimens SC-1 to SC-5 in this experiment are models of the lower half of a column. In an actual steel-pipe concrete column, the bending moment is large at the bottom and top of the column, so the outer steel pipe 6 exhibits a confining effect at two locations: the base and the top of the steel-pipe concrete column.

[0037] The column height of all the specimens SC-1 to SC-5 is 910 mm. Since the horizontal strain at the column base increases in the range below 150 mm in height, it can be said that if the thickness of the outer steel pipe 6 of more than 10% of the column height is increased at the upper and lower ends of the concrete-filled steel tube column, the confinement effect can be effectively exerted. On the other hand, although not shown here, the axial strain of the outer steel pipe 6 is kept low. Since the upper and lower ends of the outer steel pipe 6 are not connected to the structure (foundation concrete 1 or column-beam joint 3), even if the column deforms, there is little axial load transfer to the outer steel pipe 6, and no damage such as buckling occurs, and it can be seen that the increase in bearing capacity due to the confinement effect is being exerted.

[0038] Next, the results of the short column compression experiment on the specimens of the filled and coated column 2 and the coated column 20 described above will be explained. The cross-section of the specimen for the short column compression experiment is such that the inner steel pipe 5 is a square-section rectangular steel pipe of 125 mm × 125 mm, with a wall thickness of 6 mm or 3.2 mm. When the wall thickness is 6 mm, the yield strength f y = 397 N / mm 2 , and when the wall thickness is 3.2 mm, the yield strength f y = 354 N / mm 2 . The outer steel pipe 6 is a circular steel pipe with an outer diameter of 250 mm and a wall thickness of 1.6 mm or 2.3 mm. When the wall thickness is 1.6 mm, the yield strength f y = 230 N / mm 2 , and when the wall thickness is 3.2 mm, the yield strength f y = 215 N / mm 2 . It is a specimen with a scale ratio of 1 / 4. This short column compression experiment employs the loading test machine shown in Fig. 10, and a vertical load is applied to the inner steel pipe 5 and the filled concrete (first concrete 7 or second concrete 8), and no vertical load is applied to the outer steel pipe 6. Also, the outer steel pipe 6 and the bottom plate are separated by a 6-mm slit.

Table 2

[0039] As shown in Table 2, short column compression experiments were conducted using six types of test specimens NO1 to NO6. In all test specimens NO1 to NO6, the space enclosed by the outside of the inner steel pipe 5 and the inside of the outer steel pipe 6 was filled with the first concrete 7. In addition, in test specimens NO1 to NO3, the internal space of the inner steel pipe 5 was filled with the second concrete 8, but in test specimens NO4 to NO6, the internal space of the inner steel pipe 5 was not filled with the second concrete 8. The outer width B1 and pipe thickness t1 of the inner steel pipe 5 and the outer diameter B and pipe thickness t of the outer steel pipe 6 are the dimensions listed in Table 2.

[0040] As is clear from the comparison of specimens NO1 and NO3, and NO4 and NO6, in the experimental results in Table 2, the larger the pipe thickness t1 of the inner steel pipe 5, the greater the maximum load-bearing capacity Nmax, indicating that the cross-sectional area of ​​the inner steel pipe 5 contributes significantly to the load-bearing capacity.

[0041] Furthermore, as is clear from the comparison of specimens NO1 and NO2, and NO4 and NO5, even though no load is applied to the outer steel pipe 6, the greater the pipe thickness t of the outer steel pipe 6, the greater the maximum load-bearing capacity Nmax. From this, it can be seen that the smaller the diameter-to-thickness ratio B / t of the outer steel pipe 6 (the larger the pipe thickness), the greater the restraining effect of the first concrete 7, and the more confining effect it exhibits.

[0042] Furthermore, when comparing the calculated maximum load-bearing capacity Ncal of the outer steel pipe 6 without considering the confinement effect with the experimental maximum load-bearing capacity Nmax, as shown in Table 2, the experimental value Nmax exceeds the calculated value Ncal in all cases, confirming the increase in load-bearing capacity due to the confinement effect.

[0043] Here, in specimen NO3, where the inner steel pipe 5 has a pipe thickness t1 of 3.2 mm and the inside of the inner steel pipe 5 is filled with the second concrete 8, the Nmax / Ncal is 1.29, whereas in specimen NO6, where the inside of the inner steel pipe 5 is not filled with the second concrete 8, it is 1.14. Despite both specimens having a pipe thickness t of 1.6 mm, specimen NO3 shows a greater confining effect of the outer steel pipe 6. This is because, when the inside of the inner steel pipe 5 is not filled with the second concrete 8, the inner steel pipe 5 deforms inward due to the horizontal pressure of the first concrete 7 acting on the outer surface of the inner steel pipe 5, reducing the confining effect.

[0044] Furthermore, when comparing specimen NO1, in which the inner steel pipe 5 has a pipe thickness t1 of 6 mm, with specimen NO4, in which the inner steel pipe 5 is filled with the second concrete 8, the Nmax / Ncal of specimen NO1 is 1.17, while the Nmax / Ncal of specimen NO4 is 1.14. This shows that even when the inner steel pipe 5 is not filled with the second concrete 8, a restraining effect equivalent to that when the second concrete 8 is filled is observed. [Regarding the setting of the diameter-to-thickness ratio B / t and the width-to-thickness ratio B1 / t1]

[0045] Next, the optimal diameter-to-thickness ratio B / t for the outer steel pipe 6 constituting the filled-in, covered column 2 of the first embodiment and the covered column 20 of the second embodiment, and the optimal width-to-thickness ratio B1 / t1 for the inner steel pipe will be described.

[0046] Figure 11 is a graph showing the optimal diameter-to-thickness ratio B / t for the outer steel pipe 6 of the filled-coated column 2. The vertical axis shows the concrete strength increase coefficient K due to the confinement effect of the outer steel pipe 6, and the horizontal axis shows the diameter-to-thickness ratio B / t of the outer steel pipe 6. Here, the concrete strength increase coefficient K1 has the relationship K1 = fc1 / fp1, where fc1 is the concrete strength considering the strength increase due to the confinement effect and fp1 is the unconstrained concrete strength. Furthermore, the curve C1 shown as a solid line in the graph of Figure 11 is a theoretical calculation value based on the calculation formula for laterally constrained high-strength concrete in a circular steel pipe, proposed by Richart et al. and described in their paper (Richart, FE et al: A Study of the Failure of Concrete under Combined Compressive Stresses, University of Illinois, Engineering Experimental Station, Bulletin, No. 185, 1928.11).

[0047] For specimens NO1, NO2, and NO3 of the filled-coated column 2 shown in Table 2, the maximum load-bearing capacity of the concrete alone was calculated by subtracting the maximum load-bearing capacity of the inner steel pipe 5 from the maximum experimental load-bearing capacity, and the value obtained by dividing this by the unrestrained concrete strength is plotted with a circle. As shown in Figure 11, the experimental values ​​indicated with a circle show a concrete strength increase coefficient K1 that exceeds the theoretically calculated value C1. Furthermore, since the second concrete 8 is filled inside the inner steel pipe 5 of the filled-coated column 2, the deformation of the inner steel pipe 5 is restrained by the second concrete 8 even without specifying the width-to-thickness ratio B1 / t1 of the inner steel pipe 5. This theoretical formula is intended for cases without the inner steel pipe 5, but it is used as a reference for setting the applicable boundary based on the trend of the experimental values ​​in this study.

[0048] Therefore, as shown in the graph in Figure 11, the filled and covered column 2 of the first embodiment exhibits a significant confinement effect when the diameter-to-thickness ratio B / t ≤ approximately 200, and can achieve an increase in resistance to repeated loads during earthquakes.

[0049] On the other hand, the optimal diameter-to-thickness ratio B / t for the outer steel pipe 6 of the covered column 20 is the same as in Figure 11. However, since the inner steel pipe 5 of the covered column 20 is not constrained by the deformation of the second concrete 8 inside, it is possible that the inner steel pipe 5 will deform significantly when an external force is applied, reducing the confined effect. Therefore, the optimal width-to-thickness ratio B1 / t1 of the covered column 20 was examined in Figure 12.

[0050] For specimens NO4 and NO6, which are covered column 20 shown in Table 2, the experimental values ​​are indicated by circles in Figure 12, and the approximate curve of the experimental values ​​is shown by a solid line. Figure 12 shows that if the width-to-thickness ratio B1 / t1 ≤ 40, a confinement increase effect of 10% or more is achieved.

[0051] Therefore, in the second embodiment, the covered column 20 can be configured such that the diameter-to-thickness ratio of the outer steel pipe 6 is B / t ≤ 200 as shown in Figure 11, and the width-to-thickness ratio is B1 / t1 ≤ 40 as shown in Figure 12, thereby enhancing the confinement effect and achieving increased resistance to repeated loads during earthquakes. [Third embodiment: Structure in which the outer steel pipe is divided in the axial direction]

[0052] Here, the experimental results of the strain distribution in Figures 9(a) and (b) clearly show that a confining effect is exhibited at two locations, the base and the top of the column. Therefore, the outer steel pipe 6 may be composed of an upper outer steel pipe 6a, an intermediate outer steel pipe 6b, and a lower outer steel pipe 6c, which are divided axially and joined to each other by welding or bolts (see the part indicated by the dashed line in the filled-covered column 2 in Figure 1), and the pipe thickness of the upper outer steel pipe 6a and the lower outer steel pipe 6c may be set to be greater than the pipe thickness of the intermediate outer steel pipe 6b in order to exhibit a confining effect. Note that the upper outer steel pipe 6a, intermediate outer steel pipe 6b, and lower outer steel pipe 6c are not limited to structures joined by welding or bolts, but may also be joined in a way that, for example, overlaps or butts and seals them.

[0053] In other words, by making the upper outer steel pipe 6a and lower outer steel pipe 6c 5.3 mm or thicker (1.6 mm pipe thickness of the test specimen × scale 3.3 = 5.3 mm), and making the pipe thickness of the intermediate outer steel pipe 6b sufficient to serve as formwork for the second concrete 8 to be filled (approximately 3 to 6 mm), a reinforced and economical filled and covered column 2 can be constructed.

[0054] Furthermore, the experimental results of the strain distribution in Figures 9(a) and (b) revealed that the confined effect can be fully realized by increasing the pipe thickness of the outer steel pipe 6 in the portion exceeding 10% of the column height at the upper and lower ends of the column. Therefore, it is desirable to set the height of the upper outer steel pipe 6a and the lower outer steel pipe 6c to 10% or more of the column height.

[0055] Similarly, in the covered column 20 shown in Figure 4, the outer steel pipe 6 may be composed of an upper outer steel pipe 6a, an intermediate outer steel pipe 6b, and a lower outer steel pipe 6c, and the pipe thickness of the upper outer steel pipe 6a and the lower outer steel pipe 6c may be set to be greater than the pipe thickness of the intermediate outer steel pipe 6b to achieve a confined effect. The number of divisions of the outer steel pipe 6 should be three or more. [Fourth embodiment: An insulating material is interposed between the outer steel pipe and the first concrete.]

[0056] Next, Figure 13(a) shows a filled and covered column 2 of the fourth embodiment according to the present invention, and Figure 13(b) shows a covered column 2 of the fourth embodiment according to the present invention.

[0057] In the filled-coated column 2 shown in Figure 13(a), an insulating material 21 made of a resin sheet such as a vinyl sheet or Teflon sheet, or a release agent, is provided over the entire inner surface of the outer steel pipe 6. By filling the space between the outer steel pipe 6 and the inner steel pipe 5 with the first concrete 7, the insulating material 21 is interposed between the inner surface of the outer steel pipe 6 and the outer surface of the first concrete 7.

[0058] When an insulating material 21 is interposed between the outer steel pipe 6 and the first concrete 7, even if an axial force is generated in the first concrete 7, the insulating material 21 interposed between the first concrete 7 and the outer steel pipe 6 prevents the transmission of the axial force to the outer steel pipe 6. Therefore, the confining effect can be enhanced without setting the pipe thickness of the outer steel pipe 6 to be particularly large.

[0059] Here, the dashed curve D1 in the graph of Figure 11 represents the theoretical calculation value for a filled-coated column 2 in which an insulating material 21 is interposed between the outer steel pipe 6 and the first concrete 7, calculated based on the calculation formula for circular steel pipe lateral restraint high-strength concrete proposed by Richart et al., as mentioned above. It can be seen that the confinement effect increases by about 10% compared to the theoretical calculation value C1 for a filled-coated column 2 without the insulating material 21.

[0060] Furthermore, in the covered column 20 shown in Figure 13(b), the first concrete 7 is filled between the outer steel pipe 6 and the inner steel pipe 5, so that an insulating material 21 is interposed between the inner surface of the outer steel pipe 6 and the outer surface of the first concrete 7. In this covered column 20 as well, even if an axial force is generated in the first concrete 7, the insulating material 21 interposed between the first concrete 7 and the outer steel pipe 6 prevents the transmission of the axial force to the outer steel pipe 6, so the confined effect can be enhanced without setting the pipe thickness of the outer steel pipe 6 to be particularly large. [Explanation of symbols]

[0061] 1. Foundation concrete (substructure) 2. Filled and coated type column (steel pipe concrete column) 3 Column beam joint 4. Steel beams (superstructure) 5 Inner steel pipe 6 Outer steel pipe 6a Upper outer steel pipe (split steel pipe body) 6b Intermediate outer steel pipe (split steel pipe body) 6c Lower outer steel pipe (split steel pipe body) 7. First Concrete 8. Second Concrete AP Anchor Plate 9 Anchor bolts 10. Concrete floor slabs 11 Steel pipes for joining 12a, 12b diaphragm 13 Joints 13a, 13b flange 13c Web 14 Mantle member 15 Column reinforcement bars 15a,15b,15d Split column reinforcement 15c split column bar 16 Joint reinforcing bars 17. Third Concrete 20. Covered column (steel pipe concrete column) 21 Insulating material

Claims

1. An inner steel pipe, which extends vertically and is connected at its upper end to the superstructure and at its lower end to the substructure, An outer steel pipe, whose upper end is not connected to the upper structure and whose lower end is not connected to the lower structure, is coaxially positioned outside the inner steel pipe, The system comprises a first concrete filling the annular space surrounded by the outside of the inner steel pipe and the inside of the outer steel pipe, The inner steel pipe is made up of an equilateral rectangular steel pipe, and the outer steel pipe is made up of a circular steel pipe, When the outer diameter of the outer steel pipe is B and the pipe thickness is t, and the outer width of the inner steel pipe is B1 and the pipe thickness is t1, B / t ≤ 200 and B1 / t1 ≤ 40 A steel pipe concrete column.

2. An inner steel pipe, which extends vertically and is connected at its upper end to the superstructure and at its lower end to the substructure, An outer steel pipe, whose upper end is not connected to the upper structure and whose lower end is not connected to the lower structure, is coaxially positioned outside the inner steel pipe, The system comprises a first concrete filling the annular space surrounded by the outside of the inner steel pipe and the inside of the outer steel pipe, The inner steel pipe is made up of an equilateral rectangular steel pipe, and the outer steel pipe is made up of a circular steel pipe, The outer steel pipe is composed of a plurality of divided steel pipe bodies divided in the height direction, and the pipe thickness of a predetermined divided steel pipe body adjacent to the upper structure and the lower structure is set to be greater than the pipe thickness of other divided steel pipe bodies not adjacent to the upper structure and the lower structure.

3. The steel pipe concrete column according to claim 2, wherein the height of a predetermined divided steel pipe body adjacent to the upper structure and the lower structure is 10% or more of the total height of the steel pipe concrete column.

4. An inner steel pipe, which extends vertically and is connected at its upper end to the superstructure and at its lower end to the substructure, An outer steel pipe, whose upper end is not connected to the upper structure and whose lower end is not connected to the lower structure, is coaxially positioned outside the inner steel pipe, The first concrete is filled in the annular space enclosed by the outside of the inner steel pipe and the inside of the outer steel pipe, The system comprises a second concrete filling the internal space of the inner steel pipe, The inner steel pipe is made up of an equilateral rectangular steel pipe, and the outer steel pipe is made up of a circular steel pipe, When the outer diameter of the outer steel pipe is B and the pipe thickness is t, A steel pipe concrete column with a B / t ≤ 200.

5. A steel pipe concrete column according to any one of claims 1 to 4, wherein column reinforcing bars are embedded in the interior of the first concrete, extending in the vertical direction.

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