Exposed column base foundation structure

Abstract

To provide an exposed column base foundation structure capable of suppressing a compressive cleavage crack caused by a compressive force out of a tensile force and the compressive force acting on a column type foundation body of the exposed column base foundation structure via an anchor bolt and a base plate.SOLUTION: In an exposed column base foundation structure 100, a base plate 41 is directly or indirectly placed on a top end 11 of a column type foundation body 10 made of reinforced concrete and having a rectangular parallelepiped shape, a steel column 30 is fixed to an upper surface of the base plate 41, a plurality of anchor bolts 50 fixed to the base plate 41 are embedded in the column type foundation body 10, and a foundation beam 20 made of reinforced concrete is fixed to at least one of four side surfaces 13 of the column type foundation body 10. Anchor bolts 50B in the vicinity of the side surfaces to which the footing beams are not fixed are fitted into notches 65 of the steel plates 60 having the notches 65, and upper surfaces 61 of the steel plates 60 are embedded in the column type foundation body 10 so as to be flush with the top end 11.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an exposed column base foundation structure. [Background technology]

[0002] The foundation structures of steel-framed column bases include exposed-type column base foundations, in which a base plate fixed by anchor bolts embedded in a reinforced concrete foundation (column-type foundation body) is exposed at the top of the column-type foundation body, wrapped-in-concrete column base foundations, in which a base plate is embedded in a foundation (wrapped-in-concrete foundation), and embedded-type column base foundations, in which a base plate is embedded in a reinforced concrete foundation. Of these, exposed-type column base foundation structures are generally designed as semi-fixed column bases, and have the advantage that the rigidity can be changed from a pinned column base to a fixed column base during design and that construction is easier than other column base foundation structures.

[0003] A foundation beam extending to one or more sides is often fixed to the side of the column-type foundation body that forms the above-mentioned exposed-type column base foundation structure, and the main reinforcement bars (upper end main reinforcement bars and lower end main reinforcement bars) that form the foundation beam are fixed to the column-type foundation body, so that the foundation beam is rigidly connected to at least one of the four side surfaces of the rectangular parallelepiped-shaped column-type foundation body, for example.

[0004] When horizontal forces during an earthquake act on a building frame including columns, and columns are repeatedly loaded with pushing and pulling forces, the column foundation is subject to repeated compressive and tensile forces acting on it via anchor bolts and base plates, which can cause cracks in the column foundation. Of these, cracks caused by tensile forces acting on anchor bolts are, for example, bond splitting cracks between anchor bolts made of deformed reinforcing bars and the column foundation. Various measures against bond splitting cracks have been proposed, and as one example, Patent Document 1 describes an exposed fixed column base for steel pipe columns in which spiral reinforcement is arranged concentrically around the anchor bolt and embedded in foundation concrete. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 59-31336 Summary of the Invention [Problem to be solved by the invention]

[0006] As a countermeasure against cracks in exposed-type column base foundation structures, such as the exposed-type fixed column base of a steel pipe column described in Patent Document 1, various technologies have been published regarding countermeasures against bond splitting cracks caused by tensile forces acting on anchor bolts. However, no technology has been disclosed regarding countermeasures against compression splitting cracks caused by compressive forces acting on the column-type foundation body via the base plate.

[0007] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an exposed-type column base foundation structure that can suppress overall cracking due to adhesion cracking and compression cracking by suppressing compression cracking caused by compressive forces among the tensile forces and compressive forces acting on the column-type foundation body of an exposed-type column base foundation structure via anchor bolts and base plates. [Means for solving the problem]

[0008] In order to achieve the above object, one aspect of the exposed column base foundation structure according to the present invention is as follows: An exposed-type column base foundation structure, in which a base plate is placed directly or indirectly on the top end of a rectangular parallelepiped column foundation made of reinforced concrete, a steel column is fixed to the upper surface of the base plate, a plurality of anchor bolts fixed to the base plate are embedded in the column foundation, and a foundation beam made of reinforced concrete is fixed to at least one of the four side surfaces of the column foundation, The anchor bolt, located near the side to which the foundation beam is not fixed, is fitted into the notch of a steel plate having a notch, and the steel plate is embedded in the column-shaped foundation so that the upper surface of the steel plate is flush with the top end.

[0009] According to this aspect, the anchor bolt near the side to which the foundation beam is not fixed is fitted into the notch of the steel plate having a notch, and the steel plate is embedded in the column-type foundation so that the upper surface of the steel plate is flush with the top end, so that the compressive force acting through the base plate can be dispersed over as wide a range as possible of the column-type foundation via the steel plate, and compression splitting cracks that can occur when the compressive force is concentrated in the vicinity of the anchor bolt in the base plate can be suppressed. This makes it possible to suppress overall cracking due to compression splitting cracks and adhesion splitting cracks.

[0010] In this embodiment, steel plates are fitted into the anchor bolts in the vicinity of the side of the column-type foundation to which the reinforced concrete foundation beam is not fixed, and steel plates are not fitted into the anchor bolts in the vicinity of the side to which the foundation beam is fixed. This is based on the finding by the inventors that part of the compressive stress acting on the column-type foundation through the base plate is borne by the nearby foundation beam, reducing the compressive stress acting on the column-type foundation, making it difficult for compression splitting cracks to occur in the column-type foundation.

[0011] Another aspect of the exposed column base foundation structure according to the present invention is as follows: An exposed-type column base foundation structure, in which a base plate is placed directly or indirectly on the top end of a rectangular parallelepiped column foundation made of reinforced concrete, a steel column is fixed to the upper surface of the base plate, a plurality of anchor bolts fixed to the base plate are embedded in the column foundation, and a foundation beam made of reinforced concrete is fixed to at least one of the four side surfaces of the column foundation, The anchor bolt located near the side to which the foundation beam is not fixed is inserted into the bolt hole of a steel plate having a bolt hole, and the steel plate is embedded in the column-shaped foundation so that the upper surface of the steel plate is flush with the top end.

[0012] According to this aspect, the steel plate is embedded in the column-type foundation with anchor bolts near the side to which the foundation beam is not fixed being inserted into the bolt holes of the steel plate instead of notches. This also makes it possible to distribute the compressive force acting through the base plate over as wide an area as possible of the column-type foundation via the steel plate, and suppresses compression splitting cracks that can occur when the compressive force is concentrated in the vicinity of the anchor bolts in the base plate, for example.

[0013] Another aspect of the exposed column base foundation structure according to the present invention is as follows: The present invention is characterized in that, in a plan view, the notch faces toward the center of the column-shaped foundation body.

[0014] According to this embodiment, the steel plate is arranged with the notch facing the center of the column-type foundation body when viewed in a plane, so that the area of ​​the steel plate other than the notch can be aligned, for example, to the outer periphery (side surface) of the top end of the column-type foundation body, effectively suppressing compression splitting cracks that may propagate outward from the anchor bolt.

[0015] Another aspect of the exposed column base foundation structure according to the present invention is as follows: The base plate has a rectangular shape in a plan view, The steel plate is characterized in that it has a rectangular or approximately rectangular shape in plan view, with plan dimensions that are ¼ or more of those of the base plate.

[0016] According to this embodiment, the steel plate has a rectangular or approximately rectangular shape in plan view with plan dimensions that are ¼ or more of the rectangular base plate in plan view. This makes it possible for the steel plate to cover an area of ​​the base plate that is greater than or equal to the area borne by the anchor bolts to which the steel plate is attached, out of the four anchor bolts located near the four corners of the rectangular base plate in plan view, and therefore makes it possible to distribute the compressive force over as wide an area as possible.

[0017] Another aspect of the exposed column base foundation structure according to the present invention is as follows: When the top end of the foundation beam is lower than the top end of the column-type foundation body, the side to which the foundation beam is fixed is regarded as the side to which the foundation beam is not fixed, and the steel plate is installed on the anchor bolt in the vicinity of that side.

[0018] According to this aspect, when the top end of the foundation beam is lower than the top end of the column-type foundation body, the side to which the foundation beam is fixed is regarded as the side to which the foundation beam is not fixed, and a steel plate is installed on the anchor bolt near the side, taking into consideration that the compressive force bearing capacity of the foundation beam is reduced due to the top end of the foundation beam being lower than the column-type foundation body, and therefore the compressive force can be distributed over as wide a range as possible by the steel plate installed on the anchor bolt near the side to which the foundation beam is fixed. For example, when the top end of the foundation beam is about 200 mm or more lower than the top end of the column-type foundation body, the compressive force bearing capacity of the foundation beam is considered to be reduced, and a steel plate is installed on the anchor bolt near the top end. Effect of the Invention

[0019] As can be understood from the above explanation, according to the exposed-type column base foundation structure of the present invention, among the tensile and compressive forces acting on the column foundation body of the exposed-type column base foundation structure via the anchor bolts and base plate, compression splitting cracks caused by compressive forces can be suppressed, and overall cracks due to adhesion splitting cracks and compression splitting cracks can be suppressed. [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a vertical cross-sectional view of an example of an exposed-type column base foundation structure according to an embodiment. [Diagram 2] FIG. 2 is a view taken along the line II-II of FIG. [Diagram 3] FIG. 2 is a perspective view of an example of a steel plate. [Figure 4A] FIG. 11 is a plan view of another example of an exposed-type column base foundation structure according to an embodiment. [Figure 4B] FIG. 11 is a plan view of yet another example of an exposed-type column base foundation structure according to an embodiment. [Figure 4C] FIG. 11 is a plan view of yet another example of an exposed-type column base foundation structure according to an embodiment. [Figure 4D] FIG. 1 is a plan view of an example of an exposed-type column base foundation structure according to a reference example. [Figure 4E] FIG. 11 is a plan view of another example of an exposed-type column base foundation structure according to a reference example. [Figure 4F] FIG. 11 is a plan view of yet another example of an exposed-type column base foundation structure according to a reference example. [Figure 4G] FIG. 11 is a plan view of yet another example of an exposed-type column base foundation structure according to a reference example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an example of an exposed-type column base foundation structure according to an embodiment will be described with reference to the accompanying drawings. In this specification and the drawings, substantially identical components may be designated by the same reference numerals to avoid redundant description.

[0022] [Exposed column base foundation structure according to the embodiment] An example of an exposed-type column base foundation structure according to an embodiment will be described with reference to Fig. 1 to Fig. 4. Here, Fig. 1 is a vertical cross-sectional view of an example of an exposed-type column base foundation structure according to an embodiment, Fig. 2 is a view taken along the line II-II in Fig. 1, and Fig. 3 is a perspective view of an example of a steel plate. Also, Figs. 4A to 4C are plan views of another example of an exposed-type column base foundation structure according to an embodiment.

[0023] As shown in Figure 1, the exposed-type column base foundation structure 100 is formed by fixing an end face 23 of a foundation beam 20, also made of reinforced concrete, to one side 13 (the right side 13 in the illustrated example) of a rectangular column-type foundation body 10 made of reinforced concrete, placing a base plate 41 welded to the lower end 31 of a steel column 30 via a grout layer 45 on the top end 11 of the column-type foundation body 10, and fixing the base plate 41 to the column-type foundation body 10 with multiple anchor bolts 50 (four in the illustrated example).

[0024] In this way, since the base plate 41 is placed on the top end 11 of the column-type foundation body 10 via the grout layer 45, the base plate 41 is indirectly placed on the top end 11.

[0025] In the exposed-type column base foundation structure 100, the top end 11 of the column-type foundation body 10 and the top end 21 of the foundation beam 20 are flush with each other.

[0026] The steel column 30 is formed of an H-shaped steel. Here, the steel column may also be formed of a square steel pipe or the like.

[0027] Of the four anchor bolts 50, the two on the foundation beam 20 side are anchor bolts 50A near the side to which the foundation beam is fixed, and the two on the opposite side to the foundation beam 20 are anchor bolts 50B near the side to which the foundation beam is not fixed. Each anchor bolt 50 has a second fixing plate 51 at its lower end, and a nut 52 is fastened to the upper part protruding from the base plate 41.

[0028] Four anchor bolts 50 are arranged near each of the four corners of the rectangular parallelepiped column foundation body 10, and a plurality of rising bars 55 are arranged between each anchor bolt 50. A plurality of tie bars 56 surrounding each anchor bolt 50 and the rising bars 55 are arranged at intervals in the vertical direction.

[0029] The foundation beam 20 has two tiers, upper and lower, each with four upper end main reinforcements 25A and four lower end main reinforcements 25B, and a plurality of stirrups 27 surrounding each main reinforcement 25 are arranged at intervals in the longitudinal direction of the main reinforcement 25.

[0030] In addition, each main reinforcement 25 is provided with a first anchor plate 26 at its end, and the first anchor plate 26 is aligned in the vicinity of the anchor bolt 50B and fixed inside the column-type foundation 10.

[0031] As shown in Figures 1 and 2, an anchor bolt 50B located near the side to which the foundation beam is not fixed is fitted into a notch 65 of a steel plate 60, and the steel plate 60 is embedded in the column-type foundation body 10 so that an upper surface 61 of the steel plate 60 is flush with the top edge 11.

[0032] As shown in Fig. 2, in the exposed-type column base foundation structure 100, a unique steel plate 60 is installed for each of the two anchor bolts 50B located near the side to which the foundation beam is not fixed. More specifically, in the plan view shown in Fig. 2, the steel plate 60 is embedded above the column-type foundation body 10 with the notch 65 facing toward the center of the column-type foundation body 10.

[0033] 3, the thickness t of the steel plate 60 is 2.3 mm, 3.2 mm, 4.5 mm, 6 mm, 9 mm, 25 mm, etc., which are the thicknesses of commercially available steel plates, and among these, it is preferable to apply a thin steel plate with a thickness t of 3.2 mm or 4.5 mm. For example, it has been determined by analysis by the present inventors that the effect (dispersion of compressive force) cannot be fully expected from a steel plate with a minimum thickness of 2.3 mm, and that the load at the time of crack occurrence is smaller in a steel plate with a thickness of 6 mm or more than that in a steel plate with a thickness of 3.2 mm or 4.5 mm.

[0034] Specifically, a column-type foundation model (square in plan view with plan dimensions of 400mm x 400mm) was created on a computer, and steel plate models of various thicknesses were placed on the top surface of the column-type foundation model.The load (compressive force) at the time when cracks occur 50mm below the top of the column-type foundation model (when the maximum principal strain is 100μ) was then calculated using FEM (Finite Element Method) analysis.

[0035] The analysis results showed that thicknesses of 3.2 mm and 4.5 mm had the same level of compressive force, while thicknesses of 6 mm, 9 mm, and 25 mm had decreasing compressive force.

[0036] From the results of this analysis, the thickness t of the steel plate 60 is preferably set to 3.2 mm or 4.5 mm.

[0037] As shown in Fig. 1, when a horizontal force H during an earthquake acts on a steel column 30 (including a building frame), a pushing force and a pulling force act alternately as axial forces on the steel column 30. In the example shown in Fig. 1, a pushing force N acts on the steel column 30, and part of the pushing force N acts as a compressive force N1 on the top end 11 of the column-type foundation 10 via the base plate 41 (and the grout layer 45 below it).

[0038] At the top end 11 of the column-type foundation body 10, the steel plate 60 is embedded in the anchor bolt 50B near the side where the foundation beam is not fixed, so that the compressive force N1 can be dispersed over as wide a range as possible of the column-type foundation body 10 via the steel plate 60. This makes it possible to effectively suppress compression splitting cracks that may occur in the column-type foundation body 10 when the compressive force N1 acts intensively on the base plate 41 near the anchor bolt 50, etc. This also makes it possible to suppress overall cracks due to adhesion splitting cracks and compression splitting cracks.

[0039] The reason why the steel plate 60 is not installed on the anchor bolt 50A located near the side where the foundation beam is fixed is that the compressive stress due to the compressive force N1 acting on the column-type foundation body 10 through the base plate 41 is borne by the nearby foundation beam 20, and the compressive stress acting on the column-type foundation body 10 is reduced, making it less likely for compression splitting cracks to occur in the column-type foundation body 10.

[0040] Furthermore, by embedding the steel plate 60 above the column-type foundation body 10 with the notch 65 facing the center of the column-type foundation body 10, the area of ​​the steel plate 60 other than the notch 65 can be aligned with the outer periphery (side surface 13) of the top end 11 of the column-type foundation body 10, which leads to effective suppression of compression splitting cracks that may propagate outward from the anchor bolt 50.

[0041] As shown in FIG. 2, the outline BL of the base plate 41 is indicated by a dashed line inside the outline of the column-type foundation 10, and its area is indicated as A1.

[0042] In contrast, when the area A2 of the steel plate 60 is shown as a roughly rectangular shape in plan view having plan dimensions that are at least 1 / 4 of the area A1 of the base plate 41, this is preferable because the steel plate 60 can cover an area of ​​the base plate 41 that is at least the area (A1 / 4) borne by the anchor bolt 50B, to which the steel plate 60 is attached, of the four anchor bolts 50 located near the four corners of the rectangular base plate 41 in plan view.

[0043] Although not shown here, instead of notch 65, a steel plate having a bolt hole may be embedded in a column-type foundation with an anchor bolt near the side to which the foundation beam is not fixed being inserted into the bolt hole of the steel plate.

[0044] Next, another example of the exposed-type column base foundation structure according to the embodiment will be described with reference to Figs. 4A to 4C.

[0045] The exposed-type column base foundation structure 100A shown in FIG. 4A has two foundation beams 20 fixed to each of two adjacent side surfaces 13 (the upper and right side surfaces 13 in the illustrated example) of a column-type foundation body 10.

[0046] In this embodiment, only the lower left anchor bolt, which is located away from the two foundation beams 20, is the anchor bolt 50B near the side to which the foundation beam is not fixed, and therefore a steel plate 60 is installed only on this anchor bolt 50B.

[0047] On the other hand, the exposed-type column base foundation structure 100B shown in Fig. 4B has two foundation beams like the exposed-type column base foundation structure 100A, but one of them (the right side in the illustrated example) is a foundation beam 20A whose top end is lower than the top end 11 of the column-type foundation body 10. For example, the top end of the foundation beam 20A is set to be about 200 mm or more lower than the column-type foundation body 10. In addition, in each figure including Fig. 4B, the foundation beam 20A with a low top end is marked with diagonal lines to distinguish it from the foundation beam 20.

[0048] As such, since it is difficult to expect the effect of reducing the compressive stress acting on the column-type foundation body 10 as described above from the foundation beam 20A, which has a relatively low top end, the side 13 to which the foundation beam 20A is fixed is regarded as the side to which the foundation beam is not fixed, and a steel plate 60 is installed on the anchor bolt 50B near that side 13.

[0049] Therefore, in the exposed-type column base foundation structure 100B, unlike the exposed-type column base foundation structure 100A, a steel plate 60 is installed for each of the two lower anchor bolts 50B.

[0050] On the other hand, the exposed-type column base foundation structure 100C shown in Figure 4C has a configuration in which a foundation beam 20A with a relatively low top end is fixed to each of two adjacent side surfaces 13 (the upper and right side surfaces 13 in the illustrated example) of the column-type foundation body 10.

[0051] In this embodiment, the side 13 to which the foundation beam 20A is fixed is regarded as the side to which the foundation beam is not fixed, so that the steel plate 60 is installed for all four anchor bolts 50B.

[0052] In contrast, Figures 4D to 4G all show configurations (reference examples) in which steel plates 60 are not installed on any of the anchor bolts 50A, since all of the anchor bolts are anchor bolts 50A near the side to which the foundation beams are fixed.

[0053] Specifically, the exposed-type column base foundation structure 100D shown in Fig. 4D has three foundation beams 20 fixed to three side surfaces 13 of the column-type foundation body 10, and the exposed-type column base foundation structure 100E shown in Fig. 4E has four foundation beams 20 fixed to four side surfaces 13 of the column-type foundation body 10. The exposed-type column base foundation structure 100F shown in Fig. 4F has two foundation beams 20 and one foundation beam 20A with a low top end fixed to three side surfaces 13 of the column-type foundation body 10, and the exposed-type column base foundation structure 100G shown in Fig. 4G has two foundation beams 20 fixed to two side surfaces 13 of the column-type foundation body 10, and two foundation beams 20A with a low top end fixed to the other two side surfaces 13.

[0054] In each of the exposed-type column base foundation structures 100D to 100G according to these reference examples, the compressive stress acting on the column-type foundation body 10 is reduced by the multiple foundation beams 20 even without installing steel plates 60, thereby suppressing compression splitting cracks that may occur in the column-type foundation body 10.

[0055] In addition, the present invention is not limited to the configuration shown here, and may be implemented in other embodiments in which other components are combined with the configurations and the like of the above-mentioned embodiment. In this regard, the present invention may be modified within the scope of the gist of the present invention, and may be appropriately determined according to the application form. [Explanation of symbols]

[0056] 10: Column type foundation body 11: Top 12: Bottom 13: Side 20: Foundation beam 20A: Foundation beam with low top 21: Top 22: Bottom 23: End face 25: Main reinforcement 25A: Top main bar (main bar) 25B: Bottom main bar (main bar) 26: First fixing plate 27: Rib muscles 30: Steel column 31: Bottom edge 41: Base plate 45: Grout layer 50: Anchor bolt 50A: Anchor bolt (anchor bolt near the side where the foundation beam is fixed) 50B: Anchor bolt (anchor bolt near the side where the foundation beam is not fixed) 51: Second fixing plate 52: Nut 55: Standing muscle 56: Stitching 60: Steel plate 61:Top surface 65:Notch 100,100A,100B,100C: Exposed column base foundation structure 100D, 100E, 100F, 100G: Exposed column base foundation structure N: Pushing force N1: Compressive force

Claims

1. An exposed-type column base foundation structure, in which a base plate is placed directly or indirectly on the top end of a rectangular parallelepiped column foundation made of reinforced concrete, a steel column is fixed to the upper surface of the base plate, a plurality of anchor bolts fixed to the base plate are embedded in the column foundation, and a foundation beam made of reinforced concrete is fixed to at least one of the four side surfaces of the column foundation, An exposed-type column base foundation structure, characterized in that the anchor bolt located near the side to which the foundation beam is not fixed is fitted into the notch of a steel plate having a notch, and the steel plate is embedded in the column-type foundation body so that the upper surface of the steel plate is flush with the top end.

2. An exposed-type column base foundation structure, in which a base plate is placed directly or indirectly on the top end of a rectangular parallelepiped column foundation made of reinforced concrete, a steel column is fixed to the upper surface of the base plate, a plurality of anchor bolts fixed to the base plate are embedded in the column foundation, and a foundation beam made of reinforced concrete is fixed to at least one of the four side surfaces of the column foundation, An exposed-type column base foundation structure, characterized in that the anchor bolt located near the side to which the foundation beam is not fixed is inserted into the bolt hole of a steel plate having a bolt hole, and the steel plate is embedded in the column-type foundation body so that the upper surface of the steel plate is flush with the top end.

3. The exposed-type column base foundation structure according to claim 1 , characterized in that, in a plan view, the notch is directed toward the center of the column-type foundation body.

4. The base plate has a rectangular shape in a plan view, 3. The exposed-type column base foundation structure according to claim 1, wherein the steel plate has a rectangular or approximately rectangular shape in plan view, the rectangular or approximately rectangular shape having plan dimensions equal to or greater than 1 / 4 of the base plate.

5. 3. An exposed-type column base foundation structure as described in claim 1 or 2, characterized in that when the top end of the foundation beam is lower than the top end of the column-type foundation body, the side to which the foundation beam is fixed is regarded as the side to which the foundation beam is not fixed, and the steel plate is installed on the anchor bolt in the vicinity of that side.

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