Exposed column base structure and construction method of exposed column base structure

Abstract

To provide an exposed column base structure for suppressing loosening of fastening between a foundation and a base plate, and a construction method of the exposed column base structure.SOLUTION: The exposed column base structure includes anchor bolts 16, a base plate 22 welded to the lower end of a column material 21, a grouting material layer G1, a lower nut 24, a lower washer 25, an upper washer 26, and an upper nut 27. The anchor bolt 16 is fixed to the foundation of the concrete 15 so as to protrude from the upper surface thereof. The base plate 22 has a through-hole 22h into which the anchor bolts 16 are inserted, and the grouting material layer G1 is formed between the base and the base plate 22. The lower nut 24 and the upper nut 27 are screwed to the anchor bolt 16 to fasten the base plate 22 from below and above. The lower washer 25 has a groove side 25g for partitioning a lower path for passing the grouting material from the outside into the through hole side 22h, and the upper washer 26 has a groove side 26g for partitioning an upper path for passing the grouting material from the inside of the through hole side 22h to the outside.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to an exposed column base structure at a joint of a steel column erected on a foundation made of concrete, and a construction method for the exposed column base structure. [Background technology]

[0002] Conventionally, an exposed column base structure has been known in which a concrete foundation and a steel column are joined by inserting an anchor bolt embedded in the concrete foundation into a through-hole in the base plate of the steel column (see, for example, Patent Document 1). In this document, a plate nut for compressive stress resistance is screwed onto a threaded rebar serving as an anchor bolt. Then, a plate nut serving as an anchoring plate is screwed onto the threaded rebar at a position where the anchoring length is 15 times the diameter of the threaded rebar. During construction, the lower end of the threaded rebar is fixed onto the concrete at the base of the foundation, and concrete is poured to a predetermined level to form the foundation concrete, and mortar is used to level it. After the column is installed, non-shrink grout is filled into the gap between the threaded rebar and the through-hole in the base plate. After confirming that the grout has been filled, the base plate is fixed to the foundation concrete by tightening the nut. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-220712 Summary of the Invention [Problem to be solved by the invention]

[0004] In the exposed column base structure described above, when a force acts to topple the steel column, one side of the base plate tends to lift up, causing the anchor bolts arranged on this side to be stretched in the axial direction. Particularly in a structure in which the anchor bolts yield earlier than the steel column or base plate, the axially stretched anchor bolts undergo plastic deformation and remain stretched. Therefore, the stretched anchor bolts expand the gap between the lower nut and the base plate, causing loosening of the fastening. [Means for solving the problem]

[0005] An exposed column base structure that solves the above-mentioned problem comprises an anchor bolt fixed to the foundation made of concrete so as to protrude from the upper surface of the foundation, a base plate welded to the lower end of a steel column and having a through hole through which the anchor bolt is inserted, a grout layer formed by injecting grout material between the upper surface of the foundation and the lower surface of the base plate, a lower nut that screws onto the anchor bolt and tightens the lower surface of the base plate from below with at least its upper part embedded in the grout material layer, and an upper nut that screws onto the anchor bolt and tightens the upper surface of the base plate from above, wherein the fastening structure of the upper nut defines an upper passage for passing the grout material from inside the through hole to the outside of the upper nut, and the fastening structure of the lower nut defines a lower passage for passing the grout material from the outside of the lower nut into the through hole.

[0006] Furthermore, a construction method for an exposed column base structure that solves the above-mentioned problems includes an anchor bolt fixed to a foundation made of concrete, a base plate welded to the lower end of a steel column and having a through hole through which the anchor bolt is inserted, a grout layer injected between the upper surface of the foundation and the lower surface of the base plate, and an upper nut and a lower nut for fastening the base plate from above and below, wherein the fastening structure of the upper nut defines an upper passage through which the grout material passes from inside the through hole to the outside of the upper nut, and the fastening structure of the lower nut defines an upper passage through which the grout material passes from the outside of the lower nut to inside the through hole. A construction method for an exposed column base structure that defines a lower passage through which the grout material passes, comprising: fixing the anchor bolt to the foundation so that it protrudes from the upper surface of the foundation; screwing the lower nut onto the anchor bolt; inserting the anchor bolt into the through hole to form the lower passage; positioning the base plate; screwing the upper nut onto the anchor bolt; supplying the grout material from the lower passage through the through hole and the upper passage to the outside of the upper nut; and forming the grout material layer with at least the upper part of the lower nut buried. [Effects of the Invention]

[0007] According to the present disclosure, loosening of the fastening between the foundation and the base plate of the steel column can be suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a front view showing the entire exposed column base structure according to an embodiment. [Figure 2] FIG. 2 is a partially enlarged view of a main part of the exposed column base structure according to the embodiment. [Figure 3] FIG. 10 is a bottom view of an upper washer used in the exposed column base structure in the embodiment. [Figure 4] 1 is a flow chart illustrating the construction procedure of an exposed column base structure in an embodiment. [Figure 5] This is an oblique view showing the state in which a grout formwork has been placed in the construction procedure of the exposed column base structure in the embodiment. [Figure 6]This is an oblique view showing the state of injecting grout material in the construction procedure of the exposed column base structure in the embodiment. [Figure 7] FIG. 10 is a partially enlarged view of a main part of an exposed column base structure in a modified example. [Figure 8] FIG. 10 is a bottom view showing the bottom surface of the base plate of the exposed column base structure in the modified example. [Figure 9] 9 is a partially enlarged view of a main part of the bottom surface of the base plate in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of an exposed column base structure and a construction method for the exposed column base structure will be described with reference to Figs. FIG. 1 is a front view of the entire exposed column base structure B1 in this embodiment.

[0010] As shown in Fig. 1, the exposed column base structure B1 includes an anchor bolt 16 fixed to a foundation 10 made of reinforced concrete, a base plate 22 fixed (welded) to the lower end of a column material 21, a grout material layer G1, a lower nut 24, and an upper nut 27. Here, the column material 21 is a steel column made of a square steel pipe.

[0011] The foundation 10 is constructed by embedding foundation beam bottom reinforcement 11, foundation beam top reinforcement 12, and stirrups 13 in concrete 15. Furthermore, a plurality of anchor bolts 16 are embedded in the concrete 15 in a state where they are spaced apart and extend vertically so as to protrude upward from the top surface of the concrete 15.

[0012] In this embodiment, only two anchor bolts 16 are shown in FIG. 1, but as shown in FIG. 5, a total of eight anchor bolts 16 are provided around the periphery near and between the corners. As shown in Fig. 1, in this embodiment, threaded rebars are used as anchor bolts 16. Furthermore, a substantially square plate nut 17 is threadedly engaged with each anchor bolt 16. This plate nut 17 is provided at a position lower than the top surface of concrete 15 by the anchorage length.

[0013] Furthermore, a height adjustment member 18 is provided on the upper surface of the foundation 10 in the center surrounded by the anchor bolts 16. FIG. 2 is an enlarged view of the periphery of the anchor bolt 16 protruding upward from the foundation 10 in FIG.

[0014] 2, a lower nut 24 is threaded onto each anchor bolt 16, and a bottom washer 25 is inserted onto the lower nut 24. Furthermore, the anchor bolt 16 is inserted into the through-hole 22h of the base plate 22, and an upper washer 26 is inserted onto the anchor bolt 16. Furthermore, an upper nut 27 and a locking nut 28 are threaded onto the upper washer 26 of the anchor bolt 16.

[0015] The lower nut 24 tightens the lower surface of the base plate 22 from below via a lower washer 25 . Bottom washer 25 has a ring shape and has a groove 25g formed on its upper surface. Groove 25g is provided in a straight line so as to connect the inner and outer peripheral surfaces of bottom washer 25 (ring shape). In this embodiment, groove 25g of bottom washer 25 forms a lower passage for passing grout material through through hole 22h of base plate 22. In this embodiment, bottom nut 24 and bottom washer 25 constitute the fastening structure of the bottom nut.

[0016] The through holes 22h of the base plate 22 are provided corresponding to the positions of the anchor bolts 16 so that the anchor bolts 16 can be inserted therethrough. As shown in Fig. 3, the upper washer 26 is a ring-shaped plate with a hole formed in the center through which the anchor bolt 16 passes. Furthermore, a groove 26g is formed in the lower surface (bottom surface) of the upper washer 26. The groove 26g is provided in a straight line so as to connect the hole and the side surface of the upper washer 26. The groove 26g forms (demarcates) an upper passage on the outside of the upper nut 27 through which the grout material passes.

[0017] The upper nut 27 shown in FIG. 2 tightens the upper surface of the base plate 22 from above via the upper washer 26 . The locking nut 28 prevents loosening of the upper nut 27. In this embodiment, the upper washer 26, the upper nut 27, and the locking nut 28 constitute a fastening structure for the upper nut.

[0018] In this embodiment, a grout layer G1 is provided between the upper surface of the concrete 15 of the foundation 10 and the base plate 22. This grout layer G1 has a height H1 and a generally square shape that is equal to or greater than the width of the base plate 22. Here, the height H1 of the grout layer G1 is, for example, approximately 50 mm. In this embodiment, the above-mentioned lower nut 24 and lower washer 25 are embedded in this grout layer G1. The groove 25g of the lower washer 25, the through hole 22h of the base plate 22, and the groove 26g of the upper washer 26 are filled with grout.

[0019] (Construction method for exposed column base structure B1) Next, a construction method for the above-mentioned exposed column base structure B1 will be described with reference to FIG. First, a foundation with anchor bolts embedded is constructed (step S11). Specifically, the foundation beam bottom reinforcement 11, the foundation beam top reinforcement 12, and the stirrups 13 are placed in a concrete formwork. Furthermore, multiple anchor bolts 16 with plate nuts 17 screwed into them are installed upright in predetermined positions so that their tops protrude from the concrete formwork. Then, concrete is poured into the concrete formwork and cured to form the foundation 10. In this case, the tops of the anchor bolts 16 protrude from the concrete 15 of the foundation 10. Furthermore, a height adjustment member 18 is fixed to the upper surface of the base 10 . Next, a grout form is installed (step S12).

[0020] (Configuration of grout formwork 30) Here, the grout formwork 30 to be installed will be described with reference to FIG.

[0021] The grout formwork 30 has three formwork members 31 and one formwork member 32. The formwork member 32 is a member in which supply holes 32h are formed in the formwork member 31. Each formwork member 31, 32 has a plate-shaped abutting portion 31a extending horizontally, a plate-shaped vertical portion 31b welded to the end of the abutting portion 31a and extending vertically, and an upper surface portion 31c extending horizontally and welded to the upper end of the vertical portion 31b. Furthermore, the formwork member 31 is provided with closing plates 31s and 31t so as to close both ends of the vertical portion 31b and the upper surface portion 31c, respectively.

[0022] Furthermore, plate-shaped position adjustment plates 31p and 31q are welded to both ends of the upper surface 31c of the formwork member 31 in the extension direction so as to protrude upward. The position adjustment plate 31p is provided on the upper surface 31c so as to extend in a direction perpendicular to the extension direction of the upper surface 31c, in the same plane as the closing plate 31s. The position adjustment plate 31q is provided on the upper surface 31c near the closing plate 31t so as to be parallel to the extension direction of the upper surface 31c. Each position adjustment plate 31p is provided in a position so as to be able to abut against the position adjustment plate 31p of the adjacent formwork member 31, 32 when the formwork members 31, 32 are arranged to form a rectangular frame shape.

[0023] (Details of grout formwork installation) 5, the four formwork members 31, 32 are arranged on the upper surface of the foundation 10 to form a rectangular frame shape that surrounds the anchor bolt 16. Then, with the position adjustment plates 31p, 31q of the adjacent formwork members 31, 32 abutting against each other, they are integrated with a vice (not shown) or the like.

[0024] Thereafter, the lower nut, lower washer, base plate, upper washer, upper nut, and locking nut are attached (step S13). Specifically, the lower nut 24 is screwed onto each anchor bolt 16. In this case, the height (level) of the lower nut 24 is adjusted so that the height of the lower end surface of the base plate 22 is a predetermined height. Then, the bottom washer 25 is inserted onto the lower nut 24.

[0025] Next, the pillars 21 are installed by inserting each anchor bolt 16 into the through-holes 22h of the base plate 22. Here, the base plate 22 is positioned so that its peripheral edge rests on the end of the upper surface 31c of the formwork members 31, 32. As a result, a filling space into which grout is filled is formed by the vertical portion 31b and upper surface 31c of the grout formwork 30 and the bottom surface of the base plate 22. Furthermore, the pillar material 21 is erected while adjusting the contact state between the base plate 22 and the height adjustment member 18.

[0026] Next, an upper washer 26 is inserted into each anchor bolt 16, and then an upper nut 27 is screwed onto it. Then, after the upper nut 27 is tightened on each anchor bolt 16, a locking nut 28 is screwed onto each anchor bolt 16. Note that tightening the upper nut 27 also tightens the lower nut 24.

[0027] Next, grout material is filled (step S14). 6, the supply pipe 35a of the grout supply member 35 is inserted into and fitted to the supply hole 32h of the form member 32 of the grout formwork 30 placed on the upper surface of the foundation 10. Then, grout material is supplied to this grout supply member 35.

[0028] The supplied grout material is injected into the formed filling space. The grout material is then supplied from the filling space through the grooves 25g of the bottom washer 25 into the through-holes 22h of the base plate 22, and then further leaks out through the grooves 26g of the top washer 26 to the outside of the top washer 26 (upper nut 27). If it is confirmed that the grout material has leaked out of each groove 26g, it can be determined that the grout material has filled the through-holes 22h, and the supply of grout material is stopped. Thereafter, the grout supply member 35 is removed, and the grout material is allowed to harden. As a result, a grout material layer G1 is formed between the foundation 10 and the base plate 22, and the grout material is filled into the through-holes 22h of the base plate 22. Thereafter, the grout formwork 30 is removed.

[0029] (Operation of the embodiment) Since the grout layer G1 is not interposed between the base plate 22 and the lower nut 24, the distance between the lower nut 24 and the upper nut 27 that fasten the base plate 22 is shortened.

[0030] According to this embodiment, the following effects can be obtained. (1) In the exposed column base structure B1 of this embodiment, an anchor bolt 16 protruding upward from the concrete 15 of the foundation 10 is passed through a lower nut 24, a lower washer 25, a through-hole 22h in a base plate 22 to which a column material 21 is fixed, an upper washer 26, and an upper nut 27. The lower nut 24 and the upper nut 27 are then tightened to the base plate 22. As a result, the grout layer G1 is not interposed between the lower nut 24 and the upper nut 27, and therefore the distance between the lower nut 24 and the upper nut 27 can be shortened. As a result, plastic deformation between the upper nut 27 and the lower nut 24 of the anchor bolt 16 can be suppressed.

[0031] (2) In this embodiment, a bottom washer 25 having a groove 25g on its upper surface is provided on the lower surface of the base plate 22 between the lower nut 24 and the base plate 22. This allows the filling space that becomes the grout material layer G1 to communicate with the through-hole 22h of the base plate 22 via the groove 25g, thereby allowing the grout material to be supplied to the through-hole 22h.

[0032] (3) In this embodiment, a lower nut fastening structure consisting of a lower nut 24 and a lower washer 25 is provided in contact with the underside of the base plate 22. As a result, the lower nut fastening structure contacts the underside of the base plate 22, which is harder than the conventional grout material layer G1, so that tightening by the lower nut 24 fastening structure can be performed more reliably.

[0033] (4) In this embodiment, after the top of the anchor bolt 16 is fixed to the foundation 10 so as to protrude from the foundation 10, the grout formwork 30 is placed around the anchor bolt 16. Then, the peripheral portion of the base plate 22 is placed on the end of the formwork member 31 of the grout formwork 30, and the inclination of the pillar material 21 is adjusted using the height adjustment member 18 placed at the center of the foundation 10. This allows the pillar material 21 to be erected vertically efficiently.

[0034] (5) In this embodiment, the supply pipe 35a of the grout supply member 35 is inserted into and fitted to the supply hole 32h formed in the form member 32 of the grout formwork 30. Then, the grout material is supplied to the grout supply member 35. This allows the grout material to be efficiently supplied to the filling space.

[0035] This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility. In the above embodiment, the lower passage that connects the filling space where the grout layer G1 is formed and the through-hole 22h of the base plate 22 is formed by the groove 25g of the bottom washer 25. This groove 25g does not need to be formed in a straight line shape, and may have any shape as long as it can define a lower passage through which the grout material passes from the outside of the lower nut into the through-hole 22h of the base plate 22.

[0036] Furthermore, the lower passage that connects the filling space and the through-hole 22h of the base plate 22 is not limited to being formed using a bottom washer. For example, the lower passage may be formed around the through-hole of the base plate using a passage-forming member fixed to the bottom surface of the base plate.

[0037] 7, a pair of passage forming plates 42a serving as passage forming members are provided on the bottom surface of a base plate 42. The base plate 42 is welded to the lower end of a column material 41 of a steel column. Here, Fig. 7 is a partially enlarged view of the main part of the exposed column base structure in which a lower passage is formed using a pair of passage-forming plates 42a as passage-forming members. Fig. 8 is a bottom view of the base plate 42 to which the passage-forming plates 42a are fixed, and Fig. 9 is an enlarged view of the main part of Fig. 8.

[0038] 8, the base plate 42 has through holes 42h at positions where the anchor bolts 16 are inserted. Furthermore, a pair (two) of rectangular passage-forming plates 42a are fixed to sandwich each through hole 42h. As shown in FIG. 9, the pair of passage forming plates 42a are spaced apart by a distance D1 that is larger than the diameter d1 of the through hole 42h and smaller than the outer diameter D2 of the bottom washer 45. A pair of passage forming plates 42a are fixed to the lower surface of the base plate 42 at positions spaced apart by a distance greater than the through-hole 42h and sandwiching the through-hole 42h, and correspond to a plurality of plates that form the lower passage.

[0039] 7, after the lower nut 24 is screwed onto the anchor bolt 16, the bottom washer 45 is inserted. The bottom washer 45 is a ring-shaped washer without any grooves. The anchor bolt 16 is then inserted into the through hole 42h of the base plate 42. This allows the pair of passage-forming plates 42a to efficiently form a lower passage above the bottom washer 45, connecting the filling space with the through hole 42h of the base plate 42.

[0040] Furthermore, the pair of spaced-apart passage-forming plates may be fixed integrally to the upper surface of the bottom washer instead of being provided on the bottom surface of the base plate 42. In this case, by inserting and arranging the bottom washer to which the pair of spaced-apart passage-forming plates are fixed onto the anchor bolt 16, a lower passage can be formed below the through-hole 22h of the base plate 22, similar to the passage-forming plate 42a. Furthermore, the pair of passage forming plates 42a are provided two at a time with the through hole 42h in between (one pair). The number and shape of the passage forming plates are not limited to this as long as they are members that can form the space for the lower passage. For example, three or four passage forming plates (plates) may be arranged around the through hole 42h to form a pair, or a U-shaped passage forming plate may be used.

[0041] In the exposed column base structure B1 of the above embodiment, the lower nut 24 is configured to be entirely embedded in the grout material layer G1. The lower nut 24 may have its lower part embedded in the foundation as long as it is configured to be screwed onto the anchor bolt 16, abut against the underside of the base plate 22, and be tightened in response to the tightening of the upper nut 27. In this case, the foundation made of concrete is formed by pouring the foundation after screwing the lower nut onto the anchor bolt. In the above embodiment, a ring-shaped top washer 26 having a groove 26g formed therein is used. However, the shape of the top washer may be any shape as long as it has a groove or the like that defines the upper passage, and may be, for example, a substantially square plate shape.

[0042] In the above embodiment, a total of eight anchor bolts 16 are fixed to the foundation 10 and arranged at the corners of the top surface of the foundation 10 and between the corners. The number and arrangement of the anchor bolts are not limited to the above. For example, a total of eight anchor bolts may be provided, with four at each corner and a pair (two at each corner) arranged diagonally. In the above embodiment, a grout formwork 30 was used that had three formwork members 31 and one formwork member 32 with a supply hole 32h formed therein. The grout formwork for forming the grout layer G1 is not limited to this configuration. For example, a formwork using two L-shaped members each consisting of the two formwork members 31 described above that are previously integrated together may be used, or a formwork using a U-shaped member that can be separated into two parts may be used. In the above embodiment, the column material 21 is a steel column made of a square steel pipe. The column material to which the plate base plate is welded is not limited to a square steel pipe. For example, it may be a steel column made of an H-shaped steel pipe, a circular steel pipe, or the like.

[0043] Next, the technical ideas that can be understood from the above-described embodiment and other examples will be described below. (a) before screwing the lower nut onto the anchor bolt fixed to the foundation, placing a grout form for forming the grout material layer; The construction method for an exposed column base structure according to claim 4, characterized in that the grout material layer is formed by supplying the grout material into the grout formwork after the upper nut is screwed onto the anchor bolt. [Explanation of symbols]

[0044] B1...exposed column base structure, D1...distance, d1...diameter, G1...grout layer, 10...foundation, 11...foundation beam bottom reinforcement, 12...foundation beam top reinforcement, 13...stirrups, 15...concrete, 16...anchor bolts, 17...plate nuts, 18...height adjustment members, 21,41...column material, 22,42...base plates, 22h,42h...through holes, 24...bottom nuts, 25,45...bottom washers, 25g...shaping the lower passage groove forming the upper passage, 26g...groove forming the upper passage, 26...upper washer, 27...upper nut, 28...anti-loosening nut, 30...grout formwork, 31, 32...formwork members, 31a...contact portion, 31b...vertical portion, 31c...upper surface portion, 31p, 31q...position adjustment plates, 31s, 31t...closing plates, 32h...supply hole, 35...grout supply member, 35a...supply pipe, 42a...passage forming plate as a plate forming the lower passage.

Claims

1. an anchor bolt fixed to the foundation so as to protrude from an upper surface of the foundation made of concrete; a base plate welded to the lower end of the steel column and having a through hole through which the anchor bolt is inserted; a grout layer formed by injecting grout between the upper surface of the foundation and the lower surface of the base plate; a lower nut that is screwed onto the anchor bolt and tightens the lower surface of the base plate from below, with at least an upper portion of the anchor bolt being embedded in the grout material layer; an upper nut that is threaded onto the anchor bolt and fastens the upper surface of the base plate from above, The fastening structure of the upper nut defines an upper passage through which the grout material passes from inside the through hole to the outside of the upper nut, An exposed column base structure characterized in that the fastening structure of the lower nut defines a lower passage through which the grout material passes from the outside of the lower nut into the through hole.

2. a washer having a groove formed on an upper surface thereof is disposed between the lower nut and the base plate; The exposed column base structure according to claim 1 , wherein the lower passage is formed by using the groove of the washer.

3. The exposed column base structure described in claim 1, characterized in that the lower passage is formed using a plurality of plates fixed to the underside of the base plate at positions spaced apart by a distance greater than the through hole and sandwiching the through hole.

4. An anchor bolt fixed to a foundation made of concrete; a base plate welded to the lower end of the steel column and having a through hole through which the anchor bolt is inserted; a layer of grout material injected between the upper surface of the foundation and the lower surface of the base plate; an upper nut and a lower nut for fastening the base plate from above and below, The fastening structure of the upper nut defines an upper passage through which grout material passes from inside the through hole to the outside of the upper nut, The fastening structure of the lower nut is a construction method for an exposed column base structure that defines a lower passage through which the grout material passes from the outside of the lower nut into the through hole, The anchor bolt is fixed to the foundation so as to protrude from the upper surface of the foundation; The lower nut is screwed onto the anchor bolt. The base plate is disposed while forming the lower passage by inserting the anchor bolt into the through hole; The upper nut is screwed onto the anchor bolt. A construction method for an exposed column base structure, characterized in that the grout material is supplied from the lower passage through the through hole and the upper passage to the outside of the upper nut, and the grout material layer is formed with at least the upper part of the lower nut buried.

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