JP2019023421A - Pile head structure - Google Patents

Abstract

To provide a pile head structure which can estimate a strength with high accuracy.SOLUTION: A pile head structure 1 includes: a tubular pile 2 extending along an axis C; a lid body 3 which is fixed to a pile head 23 of the pile 2 and shields the pile head 23; a plate 4 which is fixed to the lid body 3 and projects outward of an outer peripheral surface 21 of the pile 2; a sheath pipe 5 surrounding a pile head 23 of the pile 2, the lid body 3 and the plate 4; and concrete 6 which is made to fill the pile head 23 of the pile 2, the lid body 3 and the plate 4, and an inner peripheral surface 57 of the sheath pipe 5. The lid body 3 and the plate 4 are fastened to each other with a bolt 7.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pile head structure.

  The thing of patent document 1 is known as a pile head structure used for the foundation of a structure. In the pile head structure, a cylindrical sheath pipe (unit main body) is welded to the pile head, and a column base is disposed on the inner peripheral side of the sheath pipe. A base plate is fixed to the end of the column base. The column base is fixed to the pile head by filling concrete between the column base and the base plate and the inner peripheral surface of the sheath tube. In such a pile head structure, when an excessive external force is applied to the column base, it is known that a substantially conical fracture surface appears in the concrete, resulting in a “cone-shaped fracture” in which the column base comes off. Yes.

  In patent document 1, while providing a processus | protrusion in the internal peripheral surface of a sheath pipe, designing to satisfy the predetermined conditions regarding the intensity | strength of concrete is proposed. Specifically, it has been proposed to satisfy Pn <Ps, where Pn is the concrete bearing strength due to protrusions and Ps is the cone-like fracture strength of the entire concrete. Thereby, it is supposed that cone-like destruction can be suppressed.

  The pile head structure described in Patent Document 1 is intended to suppress cone-like fracture in the filler around the column base. The present inventors examined application of the structure to another pile head structure (for example, Patent Document 2) in which a sheath pipe and a filler are provided around the pile head. If such an application becomes possible, a cone-shaped fracture can be suppressed even in a pile head structure in which a foundation is formed on the pile head and a beam is supported by the foundation.

JP 2012-136858 A JP 2005-226306 A

  However, even if it is obtained by the same material and manufacturing method, the characteristics of fillers such as concrete and mortar vary. Therefore, the bearing strength Pn and the cone-shaped fracture strength Ps also vary, and it is difficult to accurately predict the strength of the pile head structure.

  This invention is made | formed in view of such a subject, and it aims at providing the pile head structure which can estimate intensity | strength with high precision.

  In order to solve the above-mentioned problem, a pile head structure according to the present invention includes a tubular pile extending along a predetermined axis, a lid fixed to the pile head and shielding the pile head, and a lid A plate that is fixed and extends outward from the outer peripheral surface of the pile, a sheath pipe that surrounds the pile head, lid and plate of the pile, a pile head, lid and plate of the pile, and an inner circumference of the sheath pipe And a filler filled between the surfaces. The lid and pile head plate are fastened with bolts

  According to this configuration, when an external force that pulls out the pile from the sheath tube is applied, the bolt can be broken before the filler is destroyed. The external force that causes the rupture of the bolt can be estimated based on a predetermined theoretical formula based on the material and cross-sectional area of the bolt. The accuracy of this estimation is higher than the estimation of destruction of concrete or the like. Therefore, according to the said structure, it becomes possible to estimate the intensity | strength of a pile head structure correctly.

  According to the present invention, a pile head structure capable of estimating strength with high accuracy can be provided.

It is sectional drawing of the pile head structure which concerns on embodiment. It is a top view of the pile head structure of FIG. It is sectional drawing which shows the III-III cross section of FIG. It is a graph which shows the relationship between extraction force and displacement.

  Hereinafter, embodiments will be described with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same constituent elements in the drawings will be denoted by the same reference numerals as much as possible, and redundant description will be omitted.

  First, the outline of the pile head structure 1 according to the embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a cross-sectional view of the pile head structure 1 and shows a cross section in a plane including an axis C described later. Further, FIG. 1 shows a cross-sectional view of only the sheath pipe 5 and concrete 6 and the ground 9 described later in the configuration of the pile head structure 1. FIG. 2 is a top view of the pile head structure 1, and FIG. 3 is a cross-sectional view showing a III-III cross section of FIG. 2 and 3 omit the sheath tube 5 and the concrete 6.

  The pile head structure 1 is used for the foundation of a structure. The pile head structure 1 includes a pile 2, a lid body 3, a plate 4, a sheath pipe 5, concrete 6, and bolts 7.

  The pile 2 is a steel pipe extending along the axis C, which is a virtual straight line, and the outer peripheral surface 21 thereof is a cylindrical surface. The pile 2 is buried in the ground 9 by hitting the pile head 23 with a hammer or the like. The pile head 23 of the pile 2 is exposed from the ground surface 91 by excavating the ground 9 and forming a recess 93 after the pile 2 is buried. The pile 2 is buried so as to reach a predetermined depth of the ground 9 in order to support the structure against the weight of the structure.

  The lid 3 is a metal member and has a disk shape. The diameter of the lid 3 is substantially the same as the diameter of the outer peripheral surface 21 of the pile 2. The lid 3 is welded to the pile head 23 of the pile 2 and shields the pile head 23. As shown in FIG. 3, the lid 3 has three screw holes 31 formed therein. The screw hole 31 extends along the axis C and penetrates the lid 3. A female screw is formed on the inner surface of the screw hole 31.

  The plate 4 is a metal member and has a disk shape. As shown in FIG. 3, the plate 4 has three through holes 41 formed therein. The screw hole 31 extends along the axis C and penetrates the plate 4 in the thickness direction. The plate 4 is fastened to the lid 3 by a bolt 7 that is inserted through the screw hole 31 and screwed into the screw hole 31 of the lid 3. The bolts 7 are preferably arranged at equal intervals on the same circumference of a circle centered on the axis C. 2 and 3 show an example in which three bolts 7 are provided. However, the number of the bolts 7 is not limited to this, and the bolts 7 are not formed before the cone 2 breaks out. The number of bolts 7 can be set as appropriate so as to break.

  The diameter of the plate 4 is larger than the diameters of the pile 2 and the lid 3. The ratio of the diameter of the plate 4 to the diameter of the pile 2 is preferably about 1.1 to 1.8. For this reason, the plate 4 fastened to the lid 3 is disposed so as to protrude outward from the outer peripheral surface 21 of the pile 2.

  The sheath tube 5 is a metal member and has a cylindrical shape. As shown in FIG. 1, the diameter of the inner peripheral surface 57 of the sheath tube 5 is larger than the diameters of the pile 2, the lid body 3, and the plate 4. The ratio of the diameter of the inner peripheral surface 57 to the diameter of the plate 4 is preferably about 1.2 to 3.0. The shape of the sheath tube 5 is not limited to a cylindrical shape, and any shape may be adopted as long as it can surround the pile 2, the lid body 3, and the plate 4.

  A plurality of injection holes 58 are formed in the sheath tube 5. The injection hole 58 passes through the sheath tube 5 between the outer peripheral surface 55 and the inner peripheral surface 57. The plurality of injection holes 58 are arranged at intervals around the axis C.

  A protrusion 59 is welded to the inner peripheral surface 57 of the sheath tube 5. The protrusion 59 is an annular metal member. The protrusion 59 is welded to a portion of the inner peripheral surface 57 near the lower end 51 of the sheath tube 5. The sheath pipe 5 is arranged so that its central axis substantially coincides with the axis C and surrounds the pile head 23, the lid 3 and the plate 4 of the pile 2.

  Concrete 6 is an example of a filler. The concrete 6 is filled between the pile head 23, the lid 3 and the plate 4 of the pile 2 and the inner peripheral surface 57 of the sheath tube 5. The concrete 6 is poured into the sheath tube 5 from the injection hole 58 in a state having fluidity. During the injection, the lower end 51 and the upper end 53 of the sheath tube 5 are shielded so that the concrete 6 does not leak out. By drying and hardening the poured concrete 6, the sheath tube 5 is fixed to the pile head 23, the lid 3 and the plate 4. In addition to the concrete 6, mortar or the like can also be employed as a filler.

  The pile head structure 1 configured as described above supports the beam 8 from below at the upper end 53 of the sheath pipe 5, as shown in FIG. That is, the pile head structure 1 constitutes a foundation that supports the beam 8. The beam 8 is a member forming a part of the structure, and for example, H-section steel can be used. The beam 8 is arranged so as to extend in a substantially horizontal direction at the lower end of the structure, and the sheath tube 5 abuts on the flange portion of the beam 8 to support the beam 8. The pile head structure 1 resists the load received from the beam 8 by the frictional force generated between the outer peripheral surface 21 of the pile 2 and the ground 9.

  Next, the function of the pile head structure 1 will be described with reference to FIG. FIG. 4 is a graph showing the relationship between the pulling force F and the displacement δ.

  For example, when the structure swings due to an earthquake or the like, a force for separating the sheath tube 5 and the pile 2 from the beam 8 acts. In other words, an external force that pulls out the pile 2 from the sheath pipe 5 acts on the pile head structure 1. FIG. 4 shows the relationship between the pulling force F in the direction along the axis C (see FIG. 1 and the like) and the displacement δ of the sheath tube 5 relative to the pile 2 in the same direction.

  The pulling force F increases with the displacement δ from the initial state of the pile head structure 1. It is considered that when the pile 2 is pulled out from the inside of the sheath tube 5, mainly two forces act to resist the pulling.

  The first is an adhesive force acting between the outer peripheral surface 21 of the pile 2 and the concrete 6. The magnitude of the adhesive force is determined by the area where the outer peripheral surface 21 and the concrete 6 are in contact with each other and the properties of the concrete 6.

  The second is the elastic force of the bolt 7. As described above, the plate 4 is disposed so as to protrude outward from the outer peripheral surface 21 of the pile 2. For this reason, even if it is going to pull out the pile 2 from the inside of the sheath pipe 5, since the overhang | projection part will be caught by the concrete 6, the plate 4 will try to stay in the sheath pipe 5. FIG. As a result, a tensile force acts on the bolt 7 that fastens the plate 4 and the lid 3. The tensile force acting on the bolt 7 and the stress generated inside the bolt 7 increase with the displacement δ.

  The pulling force F reaches F3 at a point S1 where the displacement δ becomes δ1, and thereafter decreases against the increase in the displacement δ. At the point S1, the stress generated inside the bolt 7 exceeds the tensile strength, and the bolt 7 is broken. This tensile strength can be estimated based on a predetermined theoretical formula based on the material, cross-sectional area, and the like of the bolt 7. Therefore, the pulling force F3 at the point S1 can also be estimated relatively easily.

  The pulling force F reaches F1 at the point S2 where the displacement δ becomes δ2, and then starts to increase. Further, the pulling force F reaches F2 at a point S3 where the displacement δ becomes δ3. At point S <b> 3, the adhesion force between the pile 2 and the concrete 6 is cut or the cone 6 of the concrete 6 is broken around the pile 2. Accordingly, the pulling force F starts to decrease after reaching the point S3. In addition, if projections, such as a flat steel, are attached around the pile 2, adhesive force will become larger and F2 can be enlarged.

  According to such a structure of the pile head structure 1, when an external force that pulls out the pile 2 from the sheath tube 5 is applied, the bolt 7 is broken prior to the destruction of the concrete 6. It becomes possible. The external force that causes the bolt 7 to break can be estimated based on a predetermined theoretical formula based on the material, cross-sectional area, and the like of the bolt 7. The accuracy of this estimation is higher than the estimation of the destruction of the concrete 6. Therefore, according to the said structure, it becomes possible to estimate the intensity | strength of the pile head structure 1 correctly.

  Further, the bolt 7 is arranged along the axis C. According to this configuration, the external force at which the bolt 7 breaks can be estimated more accurately.

  Further, the sheath pipe 5 is formed with a projection 59 projecting toward the pile 2 on the inner peripheral surface 57 thereof. According to this configuration, even when an external force that pulls out the pile 2 from the sheath tube 5 is applied, it is possible to suppress the concrete 6 from being discharged from the sheath tube 5.

  Further, the protrusion 59 is formed in a portion near the lower end 51 of the sheath tube 5 in the direction along the axis C. According to this structure, it becomes possible to suppress more reliably that the concrete 6 is discharged | emitted from the inside of the sheath pipe 5. FIG.

  Here, as shown in FIG. 1, an imaginary line L is considered. The imaginary line L extends from the end of the plate 4 toward the inner peripheral surface 57 of the sheath tube 5 and the lower end 51 of the sheath tube 5 and forms 45 ° with respect to the axis C. The imaginary line L intersects the inner peripheral surface 57 of the sheath tube 5 at a portion 571 closer to the upper end 53 of the sheath tube 5 than the protrusion 59. This condition is satisfied even when the sheath tube 5 is not cylindrical.

  It is known that the cone-shaped fracture described above is most likely to occur on a plane that forms 45 ° with respect to the axis C. According to the above configuration, even when the cone-shaped fracture starting from the end of the plate 4 is about to occur, the projection 59 resists the external force acting on the portion inside the imaginary line L, and the concrete 6 is 5 can be restrained. Therefore, according to the said structure, it becomes possible to prevent cone-shaped destruction.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In other words, those specific examples that have been appropriately modified by those skilled in the art are also included in the scope of the present invention as long as they have the characteristics of the present invention. Each element included in each of the specific examples described above and their arrangement, material, condition, shape, size, and the like are not limited to those illustrated, and can be changed as appropriate.

  Pile head structure 1 mentioned above supports beam 8 which constitutes a part of structure from the bottom. However, the present invention is not limited to this embodiment. For example, the present invention can also be applied to a pile head structure that supports a column base of a structure. In this case, if a plate-shaped member is fixed to the upper end of the sheath tube 5 and the lower end of the column base is fixed to the member, the column base can be supported in an upright state.

1: Pile head structure 2: Pile 21: Outer peripheral surface 23: Pile head 3: Lid body 4: Plate 5: Sheath pipe 51: Lower end (one end)
53: Upper end (other end)
57: Inner peripheral surface 59: Protrusion 6: Concrete (filler)
7: Bolt C: Axis L: Virtual line

Claims (5)

A tubular pile extending along a predetermined axis;
A lid that is fixed to the pile head of the pile and shields the pile head;
A plate fixed to the lid and projecting outward from the outer peripheral surface of the pile;
A sheath pipe surrounding the pile head of the pile, the lid and the plate;
A filler filled between the pile head of the pile, the lid and the plate, and the inner peripheral surface of the sheath tube,
A pile head structure in which the lid and the plate are fastened to each other by bolts.   The pile head structure according to claim 1, wherein the bolt is disposed along the axis.   The pile head structure according to claim 1 or 2, wherein the sheath pipe has a protrusion protruding toward the pile on an inner peripheral surface thereof.   The pile head structure according to claim 3, wherein the protrusion is formed at a portion near one end of the sheath pipe in a direction along the axis.   When viewed from a direction orthogonal to the axis, an imaginary line extending from the end of the plate toward the inner peripheral surface of the sheath tube and one end of the sheath tube and forming 45 ° with respect to the shaft is the protrusion. The pile head structure according to claim 4, wherein the pile head structure intersects the inner peripheral surface of the sheath tube at a position closer to the other end of the sheath tube.

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