How to build the foundation structure

Abstract

To provide a construction method of a foundation structure constituted of a steel-framed superstructure and piles which are connected by simple work capable of suppressing the increase of the number of members and reducing the weight.SOLUTION: A construction method of a foundation structure 100 includes the steps of: arranging the lower parts 41 of a footing main reinforcement around a pile head 11 exposed from a drilled hole B formed in a ground A of a pile 10 buried in the ground A, and setting up a formwork 50 so as to enclose the pile head 11 and the lower part 41 of the footing main reinforcement; placing concrete in the formwork 50 to construct a footing foundation lower part 31 made of reinforced concrete; arranging a steel column-to-beam joint 20 via a support member 71 installed on an upper surface of the footing foundation lower part 31; placing a covering plate 61 on a gusset plate 62 so as to enclose at least a portion of the beam-to-column joint 20 that includes at least the lower column 23; installing an upper part 51 of the footing main bar; and placing concrete in an area surrounded by the closing plate 61 and the gusset plate 62 to construct a footing foundation upper part 32.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for constructing a foundation structure, and more particularly to a method for constructing a foundation structure in which a steel-framed superstructure and piles are connected. [Background technology]

[0002] Traditionally, in steel-framed buildings, the superstructure, such as columns and beams, is generally made of steel (S) construction using steel pipes and steel sections, while the foundation beams are generally made of reinforced concrete (RC). Construction of the RC portion requires time and effort, including the arrangement of reinforcement bars, installation of formwork, pouring of concrete, and subsequent removal of the formwork, and construction takes time due to each step and curing of the concrete. For this reason, in order to shorten construction time, improve workability, and reduce the number of people required, the use of steel-framed foundation beams is beginning to be implemented.

[0003] By using steel for the foundation beams, it is possible to reduce the weight of the structure, thereby reducing the cost of piles, and shorten the construction period by eliminating the need for reinforcing the footing foundation, installing formwork, and pouring concrete.

[0004] For example, Patent Document 1 describes a foundation structure that joins steel-framed columns and beams to piles. In this foundation structure, a column-foundation beam joint member made of a cylindrical steel pipe with a column bracket and a beam bracket joined together is installed to surround the pile head, and concrete is poured into this steel pipe to integrate the column beam and pile. No reinforcement is placed in the concrete poured into the steel pipe. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-008543 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the technology described in Patent Document 1, the beam bracket is joined to the side peripheral surface of the cylindrical steel pipe, and the side surface of the beam bracket of a steel frame structure needs to be cut into a curved surface that matches the outer peripheral surface of the steel pipe. However, cutting into such a curved surface is difficult.

[0007] Furthermore, because the footing, which is the joint with the pile head, is made of steel pipe as a single unit, the column-foundation beam joint components become larger and heavier.The steel pipe is unreinforced, and the stress from the pile head during an earthquake is transmitted to the superstructure through the steel pipe, so the steel pipe needs to be thick enough to withstand this stress, which also increases the weight.

[0008] Because column-beam joint members also serve as footings, in order to ensure edge clearance, in the case of precast piles, a width of 2 to 2.5 times the pile diameter is required, depending on the construction method, while in the case of cast-in-place concrete piles, a width of 200 to 300 mm or more is required in addition to the pile diameter. In recent years, in order to reduce construction time and costs, the pile diameter has been increased and the number of piles reduced, but in such cases, the column-beam joint members become even larger. As a result, not only do column-beam joint members become very heavy, but their width can also become so large that they become difficult to transport.

[0009] In view of the above, the present invention aims to provide a method for constructing a foundation structure in which a steel-framed superstructure and piles are connected by simple work, thereby preventing the components from becoming larger and reducing their weight. [Means for solving the problem]

[0010] The method for constructing a foundation structure of the present invention is characterized by comprising the steps of: arranging the lower parts of main reinforcement around the pile heads of piles buried in the ground and exposed through excavation holes formed in the ground, and installing a formwork so as to enclose the pile heads and the lower parts of the main reinforcement; pouring concrete into the formwork to construct a lower part of the foundation made of reinforced concrete; arranging a steel column-beam joint via support members installed on the upper surface of the lower part of the foundation; installing steel plates that surround the column-beam joints so as to enclose at least a part including the lower parts of the columns; installing the upper parts of the main reinforcement; and pouring concrete into the part surrounded by the steel plates to construct an upper part of the foundation.

[0011] According to the method for constructing a foundation structure of the present invention, the lower part of the foundation made of reinforced concrete and the upper part of the foundation made of concrete containing the lower part of the column-beam joint are constructed separately, thereby making it possible to simplify the construction work of the foundation structure.

[0012] In addition, the lower part of the foundation is made of reinforced concrete, and the steel beam-column joint only constitutes a part of the upper part of the foundation. Therefore, compared to the column-foundation beam joint member described in Patent Document 1, it is possible to reduce the size and weight of the steel beam-column joint.

[0013] In the method for constructing a foundation structure of the present invention, it is preferable to arrange shear reinforcement bars, including a plurality of peripheral reinforcements surrounding the outer periphery of the lower part of the main reinforcement and arranged at intervals in the vertical direction, and core reinforcement bars connecting the peripheral reinforcement bars within the area surrounded by the plurality of peripheral reinforcement bars, and then pour concrete into the formwork.

[0014] In this case, it is possible to use shear reinforcement in addition to the main reinforcement to bear the stress transmitted from the pile head during an earthquake.

[0015] In addition, in the method for constructing a foundation structure of the present invention, after pouring concrete into the formwork, it is preferable to connect the upper end of the lower part of the main reinforcement and the lower end of the upper part of the main reinforcement with a mechanical joint.

[0016] In this case, after the process of constructing the lower part of the foundation is completed, it is possible to connect the upper part of the main reinforcement to the lower part of the main reinforcement. Therefore, when constructing the lower part of the foundation, work can be done without the upper part of the main reinforcement being present, which makes it possible to simplify the work of constructing the lower part of the foundation.

[0017] Furthermore, in the method for constructing a foundation structure of the present invention, it is preferable that the steel plates comprise first steel plates fixed to each of the plurality of beams that constitute the column-beam joint, and a plurality of second steel plates that connect the first steel plates together.

[0018] In this case, it is possible to connect the upper part of the main reinforcement to the lower part of the main reinforcement before connecting the first steel plate and the second steel plate, which may make it possible to easily perform this connecting work.

[0019] Furthermore, in the method for constructing a foundation structure of the present invention, a U-shaped bar is restrained below the lowest peripheral reinforcement so that the opening is at the top, and it is preferable that the bar is arranged in multiple places around the pile head so that it spans the shear reinforcement bars and forms a diamond shape when viewed from above.

[0020] In this case, it is possible to prevent cracks in the unreinforced portion near the concrete surface of the lower part of the foundation. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic front view showing a foundation structure according to an embodiment of the present invention. [Figure 2] FIG. [Figure 3] FIG. 10 is a schematic longitudinal cross-sectional view showing the state in which reinforcing bars are arranged around the pile head when constructing the foundation structure. [Figure 4] Schematic cross-sectional view of line IV-IV in Figure 2. [Figure 5] Schematic cross-sectional view of line VV in Figure 3. [Figure 6] Schematic cross-sectional view of line VI-VI in Figure 3. DETAILED DESCRIPTION OF THE INVENTION

[0022] A base structure 100 according to an embodiment of the present invention and a method for constructing the same will be described with reference to Figures 1 to 6. Note that Figures 1 to 6 are diagrams for schematically explaining this embodiment, and the dimensions are exaggerated.

[0023] Referring to Figure 2, this foundation structure 100 is a structure consisting of a footing foundation 30 that connects steel piles 10 (steel pipe piles) buried in the ground A with a steel-framed column-beam joint 20 formed by rigidly joining foundation beams 22 to the lower parts of columns 21. The footing foundation 30 has a two-tiered structure in which a lower footing foundation section 31 and an upper footing foundation section 32 are separately prepared.

[0024] Referring to Figure 3, a pile 10 is buried in ground A formed by placing crushed stone in a borehole B formed in the ground GL and pouring concrete on top of the crushed stone. A pile head 11 of the pile 10 is exposed from the ground A, and the upper end of the pile head 11 is located above the ground GL. The pile 10 is not limited to a specific construction method or type, and may be a precast pile or a cast-in-place pile.

[0025] 3 to 5, a step of arranging reinforcing bars 41 to 45 to construct the footing foundation lower part 31 around the pile head 11 is then carried out. At this time, at least the lower parts 41 of the footing main reinforcement and shear reinforcement 42 are arranged. In addition, bar reinforcement 43, base reinforcement 44, pile head reinforcement 45, and the like are also arranged as necessary. Here, the footing main reinforcement 41, 51 is formed by connecting the lower part 41 for the footing foundation lower part 31 and the upper part 51 for the footing foundation upper part 32.

[0026] The lower part 41 of the footing main reinforcement for the footing foundation lower part 31 is provided with a mechanical anchor 41a at the lower end and a mechanical joint (relay joint) 41b at the upper end.

[0027] The lower part 41 of the footing main reinforcement surrounds the pile head 11, and multiple reinforcements are arranged to extend vertically along the outer periphery of the lower part 31 of the foundation footing to be formed, surrounding the entire outer periphery.

[0028] In order to be able to bear the stress transmitted from the pile head 11 to the footing foundation lower part 31 during an earthquake, shear reinforcement 42 is arranged in addition to the lower part 41 of the footing main reinforcement. The shear reinforcement 42 surrounds the periphery of the lower part 41 of the footing main reinforcement in a substantially rectangular frame shape and consists of multiple periphery reinforcements 42a arranged at intervals above and below, and substantially rectangular core reinforcements 42b that connect the periphery reinforcements 42a within the area surrounded by the multiple periphery reinforcements 42a. Although not shown, assembly reinforcement may be arranged to support the core reinforcements 42b.

[0029] The perimeter reinforcement 42a and core reinforcement 42b can be hooked onto other reinforcing bars by bending their ends and secured with binding wires. However, the bottommost perimeter reinforcement 42a is larger than the other perimeter reinforcement 42a due to the expansion caused by the mechanical anchors 41a provided at the lower ends of the lower parts 41 of the footing main reinforcement. If the bottommost perimeter reinforcement 42a is welded closed, there will be no joints, which is preferable because the strength loss will be minimal even if large deformation occurs during an earthquake.

[0030] It is preferable that the shear reinforcement 42 be arranged so that the amount of reinforcement at the bottom is large so that it can bear the shear stress that occurs when the moment of the pile head 11 is transmitted to the lower part 31 of the footing foundation by lever action and then transmitted to the column-beam joint 20 of the upper part 32 of the footing foundation via the lower part 31 of the footing foundation.

[0031] Furthermore, it is preferable to arrange the U-shaped bar reinforcing bars 43 so that their openings face upward. Four bar reinforcing bars 43 are arranged around the pile head 11 so that they cross the periphery reinforcement bars 42a diagonally and form a diamond shape (lozenge shape) when viewed from above. Both ends of the base 43a of each bar reinforcing bar 43 are fixed to the underside of the center of each side of the lowest periphery reinforcement bars 42a, and foot portions 43b extending upward from both ends of the base 43a of each bar reinforcing bar 43 extend upward parallel to the lower portions 41 of the footing main reinforcement.

[0032] By arranging the bar reinforcement 43 in this way, it is possible to prevent cracks in the unreinforced portion near the concrete surface of the footing foundation lower part 31. Furthermore, base reinforcement 44 may be arranged directly above the pile head 11 to bear the stress of the foundation slab.

[0033] In addition, pile head reinforcement bars 45 are arranged as necessary, extending upward from the top of the pile head 11 to above the upper end of the pile head 11. The pile head reinforcement bars 45 may be omitted if sufficient stress transmission is possible with the footing main reinforcements 41, 51, but it is preferable to arrange them when tensile axial force is applied or the ground is soft.

[0034] Then, a step of installing formwork 50 is performed along the periphery of the portion that will become the footing foundation lower portion 31. Formwork 50 may be a disposable formwork that does not need to be removed after pouring concrete. The width of footing foundation 30 is preferably at least 2.5 times the pile diameter for precast piles, and at least 0.4 m plus the pile diameter for cast-in-place concrete piles, and the embedding depth of pile head 11 into footing foundation lower portion 31 is preferably 0.5 to 1.0 times the pile diameter. Note that after the step of installing formwork 50, a step of arranging reinforcing bars 41 to 45 around pile head 11 may be performed.

[0035] Thereafter, concrete is poured into the formwork 50. As a result, the concrete filled in the formwork 50 hardens, forming the footing foundation lower section 31. Then, after a predetermined period of time has passed, the formwork 50 is demolded. The demolded area is backfilled with earth and sand to a predetermined height. The footing foundation lower section 31 is made of reinforced concrete, and more than half of it is buried underground. Note that if the formwork 50 is a disposable formwork, it can be left buried and there is no need to demold it.

[0036] In this way, a leverage mechanism created by embedding the pile 10 in the footing foundation lower part 31 is utilized to realize a stress transmission mechanism between the pile 10 and the footing foundation 30.

[0037] Next, as shown in FIG. 2, a step of placing the beam-column joint assembly 20 at a predetermined position above the footing foundation lower portion 31 with a gap therebetween is carried out.

[0038] The beam-column connection structure 20 is a structure in which a steel foundation beam 22 is rigidly joined to the lower part of a steel column 21 by welding or the like. Here, the beam-column connection structure 20 is made up of a lower column 23, an upper column 24, a lower plate 25, an upper plate 26, and four cross beams 27. The lower column 23 and the upper column 24 are each made of a square steel pipe, the lower plate 25 and the upper plate 26 are each made of a substantially rectangular steel plate, and the four cross beams 27 are each made of shaped steel such as an I-beam or an H-beam.

[0039] The lower column 23 and the upper column 24 constitute the column 21, and the lower column 23 corresponds to the lower part of the column 21. The lower column 23 and the upper column 24 may be made of cylindrical steel pipes or may be made of steel beams such as I-beams or H-beams.

[0040] The lower plate 25 is joined by welding or the like to the lower end surface of the lower column 23 so as to close the lower opening of the erected lower column 23. The upper plate 26 is joined by welding or the like to the upper end surface of the lower column 23 so as to close the upper opening of the erected lower column 23. The upper plate 26 is then fixed by welding or the like to the lower end surface of the erected upper column 24 so as to close the lower opening of the upper column 24.

[0041] The side end faces of the web portions of the four cross beams 27 are fixed to the side surfaces of the lower column 23 by welding or the like, and the side end faces of the upper and lower flange portions are fixed to the side surfaces of the lower plate 25 and the upper plate 26 by welding or the like. As a result, the four cross beams 27 extend horizontally in a cross shape as a whole, centered on the lower column 23. The lower plate 25 and the upper plate 26 each function as a diaphragm.

[0042] Here, gusset plates (splicing plates) 62 for fixing the cover plates 61 are fixed in advance to the beam-column joint 20. The gusset plates 62 are two steel plates having side surfaces conforming to the side surfaces of the web and upper and lower flanges of the shaped steel that forms the cross beam 27, and one steel plate fixed to the underside of the lower flange of the cross beam 27, and are provided with through holes (not shown) through which bolts 63 are inserted. The gusset plates 62 are fixed to both side surfaces of each cross beam 27 of the beam-column joint 20 by welding or the like, thereby preventing gaps from forming between them. In this embodiment, the gusset plates 62 are made up of three steel plates installed on the left, right, and lower sides of the cross beam 27, but these steel plates may be joined together to form a single steel plate.

[0043] The column-beam connection 20 with the gusset plate 62 fixed thereto is then lowered from above so that the central axes of the pile 10 and the column 21 are aligned, and placed at a predetermined height from the ground using a hoist or similar device. The column-beam connection 20 is preferably fabricated in a factory, transported to the construction site, and then directly placed on the footing foundation lower section 31 from a transport vehicle. The column-beam connection 20 can then be placed by installing a support member 71 on the upper surface of the footing foundation lower section 31 and placing the column-beam connection 20 on top of this support member 71. The cross beams 27 of adjacent column-beam connection 20 are then joined to each other using steel beams (not shown) with bolts and nuts to form a stable foundation beam 22.

[0044] A cover plate 61 is fixed to the gusset plate 62. The cover plate 61 is made of two rectangular steel plates with a plurality of through holes (not shown) formed at the side edges at intervals in the vertical direction, and the side edges are fixed together by welding or the like so that they form an L shape when viewed from above. Bolts 63 are inserted through the through holes of the cover plate 61 and the gusset plate 62, and are fastened by screwing nuts 64. This connects the two cross beams 27 via the cover plate 61 and the gusset plate 62.

[0045] 6, the gusset plate 62 is smaller than the cover plate 61, but this is not limiting, and the gusset plate 62 may be the same size as or larger than the cover plate 61. The gusset plate 62 and the cover plate 61 may be joined by on-site welding. In this case, there is no need to form through holes in them.

[0046] Here, the cover plate 61 extends downward from the lower end surface of the cross beam 27. The thickness of the cover plate 61 is set so that it can bear the stress generated in the footing foundation upper part 32 during an earthquake. However, there is a vertical gap between the lower end of the cover plate 61 and the footing foundation lower part 31, and a horizontal gap between the outer periphery of the footing foundation lower part 31 and the inner periphery of the cover plate 61, so the cover plate is not supported by the footing foundation lower part 31.

[0047] Next, the lower end of the upper part 51 of the footing main reinforcement is connected to the mechanical joint 41b provided at the upper end of the lower part 41 of the footing main reinforcement. The upper part 51 of the footing main reinforcement becomes an obstacle when joining the gusset plate 62 and the cover plate 61, so it is desirable to perform the connecting work after the joining work is completed. The upper part 51 of the footing main reinforcement has a mechanical anchor 51a provided at its tip. The tip may also be bent into a U-shape to form a 180° hook.

[0048] It is preferable to arrange the barbed reinforcing bars 72 at a height approximately the same as the upper ends of the upper parts 51 of the footing main reinforcement. These barbed reinforcing bars 72 may be arranged in a diamond shape when viewed from above, similar to the barbed reinforcing bars 43 described above, or may be arranged in a well shape to avoid the columns 21. Note that the cover plate 61 may be fixed to the gusset plate 62 after the upper parts 51 of the footing main reinforcement and the barbed reinforcing bars 72 have been arranged.

[0049] Then, concrete is poured into the space surrounded by the cover plate 61. At this time, the cover plate 61 functions as a formwork, so there is no need to set or remove the formwork. The upper part 32 of the foundation footing is formed by solidifying the concrete filled inside, with the outer periphery covered by the cover plate 61.

[0050] In the upper part 32 of the footing foundation formed in this way, a concrete joint surface between the lower part 31 of the foundation footing and the upper part 32 of the foundation footing is formed as a stress transmission mechanism to the pile 10, and the upper part 51 of the footing main reinforcement of a predetermined length is embedded. And, because the cover plate 61 bears the shear stress, there is no need to arrange shear reinforcement in the upper part 32 of the foundation footing.

[0051] In Fig. 1, the upper ends of the upper parts 51 of the footing main reinforcement are fixed in the slab 73 located above the upper end surface of the cross beam 27. However, this is not limited to this, and the upper ends of the upper parts 41 of the footing main reinforcement may be located below the upper end surface of the cross beam 27 as long as the fixing length required for stress transmission is secured.

[0052] As explained above, in the foundation structure 100 of this embodiment, the footing foundation 30 has a two-tiered structure in which the footing foundation lower part 31 and the footing foundation upper part 32 are separately constructed. The footing foundation lower part 31 is made of reinforced concrete containing reinforcing bars 41 to 45 arranged around the pile head 11, and the footing foundation upper part 32 is made of concrete containing the lower column 23 and formed by solidifying concrete in the area surrounded by the cover plate 61, and these are connected by the connected footing main reinforcements 41, 51 so that stress can be transmitted.

[0053] When the footing foundation 30 is formed as an integral unit, the difference in elevation between the bottom and upper end of the footing foundation 30 is large, and the work space is narrow, making the work difficult. Furthermore, after the reinforcing bars 41 to 45 are arranged around the pile head 10, the formwork 50 is placed around the footing foundation lower part 31 while the column-beam joint 20 is supported, and the gap with the cover plate 61 of the footing foundation upper part 32 is adjusted before concrete is poured into the formwork 50 and the cover plate 61. This means that concrete is poured from above the cover plate 61, making the work difficult.

[0054] It is conceivable to form the cover plate 61 and formwork 50 integrally with steel pipes, as in Patent Document 1, but this would increase the weight of the column-foundation beam joint member, making it difficult to move and install. Also, because the footing foundation lower section 31 is buried underground, a vibrator cannot be applied from the outside of the formwork 50, but must be inserted from above.

[0055] In this embodiment, after the footing foundation lower portion 31 is formed, concrete is poured into the cover plate 61 while the column-beam connection structure 20 is supported, so the amount of concrete poured between the footing foundation lower portion 31 and the footing foundation upper portion 32 is small, and the difference in elevation between the pouring areas is small, making it possible to simplify the work. In addition, since the support member 71 is installed in the center of the top surface of the footing foundation lower portion 31 in a plan view and supports the column-beam connection structure 20 with this, support is simpler than when temporary support members are erected from the surrounding ground surface to support each cross beam 27, and joining to the cross beam 27 of adjacent column-beam connection structures 20 is also easier.

[0056] Furthermore, the footing foundation lower part 31 is made of reinforced concrete, and the column-beam joint 20 only constitutes a part of the footing foundation upper part 32. Therefore, compared to the column-foundation beam joint member described in Patent Document 1, it is possible to make the column-beam joint 20 smaller and lighter.

[0057] The present invention is not limited to the above-described embodiment and can be modified as appropriate. For example, in forming the footing foundation upper portion 32, the column-beam connection body 20 is installed in a predetermined position, and then the cover plate 61 is connected to the gusset plate 62 fixed to the column-beam connection body 20 using bolts or the like. However, the present invention is not limited to this.

[0058] For example, the column-beam connection structure 20 with the cover plate 61 connected to the gusset plate 62 may be moved to the installation position. However, in this case, it is necessary to connect the cover plate 61 on-site and then move the column-beam connection structure 20, which is time-consuming. Alternatively, the column-beam connection structure 20 may be integrated by fixing the cover plate 61 to the gusset plate 62 by welding or the like in a factory, and then moved to the installation position. However, this is not preferable because it increases the size of the column-beam connection structure 20. Note that the cover plate 61 does not have to be made of two rectangular steel plates whose side ends are fixed together by welding or the like so that they form an L-shape when viewed from above, but may be made by bending a single rectangular steel plate into an L-shape.

[0059] In these cases, there is no need to connect the cover plate 61 and the gusset plate 62 with bolts or the like at the installation position of the beam-column connection assembly 20. Therefore, after the upper part 41 of the footing main reinforcement and the bar-like reinforcement 72 are arranged, the beam-column connection assembly 20 may be lowered and moved to the installation position while avoiding these. Furthermore, in this case, the footing main reinforcement may not be divided into upper and lower parts, and this undivided, integrated footing main reinforcement may be arranged around the pile cap 11. Furthermore, concrete may be poured into the pile cap 11, the lower columns 3, and the upper columns 24 up to a predetermined height. [Explanation of symbols]

[0060] 10...Pile, 11...Pile head, 20...Column beam connection, 21...Column, 22...Foundation beam, 23...Lower column (lower part of column), 24...Upper column, 25...Lower plate, 26...Upper plate, 27...Horizontal beam, 30...Footing foundation, 31...Lower part of footing foundation (lower part of foundation), 32...Upper part of footing foundation (upper part of foundation), 41...Lower part of footing main reinforcement (lower part of main reinforcement), reinforcing bar, 41a...Mechanical anchor, 41b...Mechanical joint, 42...Shear reinforcement, reinforcing bar, 42a...Peripheral reinforcement, 42b...Core reinforcement, 43...Hairpin reinforcement, reinforcing bar, 43a...Base, 43b...Foot, 44...Base reinforcement, reinforcing bar, 45...Pile head reinforcement, reinforcing bar, 50...formwork, 51...upper part of footing main reinforcement (upper part of main reinforcement), 51a...mechanical anchor, 61...covering plate (steel plate, second steel plate), 62...gusset plate (steel plate, first steel plate), 63...bolt, 64...nut, 71...support member, 72...bar, 73...slab, 100...foundation structure, A...ground, B...borehole, GL...ground surface.

Claims

1. A process of arranging main reinforcement bars divided into upper and lower parts or lower parts of undivided integrated main reinforcement bars around the pile head exposed from a borehole formed in the ground of a pile buried in the ground, and installing a formwork so as to enclose the pile head and the lower parts of the main reinforcement bars; A step of pouring concrete into the formwork to construct a lower foundation portion made of reinforced concrete; a step of placing a steel beam-column joint via a support member installed on the upper surface of the foundation lower portion; a step of installing a steel plate surrounding the column-beam joint so as to enclose at least a portion including a lower portion of the column; Installing the upper portion of the main reinforcement; A method for constructing a foundation structure, comprising a step of pouring concrete into the area surrounded by the steel plates to construct an upper part of the foundation.

2. 2. The method for constructing a foundation structure according to claim 1, further comprising the steps of: arranging shear reinforcement bars, including a plurality of outer periphery reinforcements surrounding the outer periphery of the lower part of the main reinforcement and spaced apart in the vertical direction; and core reinforcement bars connecting the outer periphery reinforcement bars within the area surrounded by the plurality of outer periphery reinforcement bars; and then pouring concrete into the formwork.

3. 3. The method for constructing a foundation structure according to claim 1, wherein after concrete is poured into the formwork, the upper end of the lower part of the main reinforcement and the lower end of the upper part of the main reinforcement are connected by a mechanical joint.

4. A method for constructing a foundation structure described in any one of claims 1 to 3, characterized in that the steel plates consist of first steel plates fixed to each of the multiple beams that constitute the column-beam connection, and multiple second steel plates that connect the first steel plates to each other.

5. A method for constructing a foundation structure as described in claim 2, characterized in that a U-shaped bar is restrained below the lowest outer peripheral reinforcement with its opening facing upward, and the bar is arranged in multiple places around the pile head so that it spans the shear reinforcement bars and forms a diamond shape when viewed from above.

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