JP4468102B2 - Pile head support structure - Google Patents

Description

  The present invention relates to a pile head support structure for a pile that supports a structure. More specifically, in the pile head support structure that supports the foundation of the structure with a smaller cross-sectional area than the pile body, the present invention provides a concentric opening in the gap between the pile top and the lower part of the structure. The present invention relates to a pile head support structure that sandwiches a plurality of buffer layers.

FIG. 1 schematically shows the relationship between a structure having piles and the ground. The structure 10 is supported by the pile 30, and the lower end of the pile is supported by the support ground 50. The pile head 20 of the pile 30 is in contact with the lower part of the foundation and supports the structure. The pile 30 normally receives the weight of the structure as an axial force, and receives an earthquake load in the vertical and horizontal directions together with the weight of the structure during an earthquake.
FIG. 2 illustrates the structure of a concrete pile. In the concrete 33, a main bar 31 extends in the axial direction, and a band bar 32 is wound so as to restrain the main bar 31 in the circumferential direction. The concrete pile has a composite structure in which the concrete 33 and the main reinforcement 31 resist resistance to compressive force, tensile force, and bending moment.

  FIG. 3 illustrates a conventional joining method between a pile and a foundation of a structure, that is, a so-called rigid joint. As shown in FIG. 3, in rigid joining, the entire cross section of the pile 30 is brought into contact with the foundation 11 and the axial principal bar 31 of the pile is fixed on the foundation. However, the rigid joint structure generates large stresses on the pile head and foundation during an earthquake. In order to avoid this stress concentration, a rational solution for the method of joining the pile head and the foundation has been required.

To solve this problem, so-called pile head semi-rigid joints have been developed that reduce the bending moment acting on the pile head during an earthquake by reducing the rigidity of the joint between the pile head and the foundation of the structure. ing.
FIG. 4 shows a trial calculation result regarding the influence of the stiffness of the pile head on the bending moment of the pile. When the pile head is rigidly connected (dashed line), the bending moment at the pile head is extremely large, and when the pile head is pin-connected (dotted line), the pile head bending moment is naturally zero, but directly below the pile head It is shown that the bending moment at is very large. When the pile head is semi-rigidly connected (solid line), the value of the maximum moment is smaller than any of the above two, indicating that the structure is the most rational.

  Document 1 (Japanese Patent Laid-Open No. Hei 8-20960) specifically discloses an example of the above-mentioned pile head semi-rigid joint construction method. A cylindrical protrusion is formed on the top of the pile. It is in contact with the bottom surface of the foundation at the top. Since the cross-sectional area of the protruding portion is smaller than the cross-sectional area of the pile body, the rigidity of the joint is reduced as compared with the case where the entire cross-sectional area of the pile body is rigidly connected to the foundation of the structure. According to the embodiment shown in FIG. 1 of the publication, the protruding portion and the pile head in the vicinity thereof are accommodated in a recess formed on the lower surface of the foundation of the structure, and between the pile and the recess. A cushioning material such as styrofoam is sandwiched in the gap, and relative deformation between the foundation and the pile head is allowed.

Document 2 (Japanese Patent Laid-Open No. 2002-242207) discloses a structure obtained by further improving the pile head semi-rigid joint construction method. The point that the area of the joint or the contact portion that supports the structure is smaller than the cross-sectional area of the pile main body is the same as in Reference 1, but the cross-sectional area of the pile head gradually decreases toward the top. According to the embodiment of this document, as shown in FIGS. 5A and 5B, the pile head has a truncated cone shape, and a gap is formed between the inclined surface of the truncated cone and the lower surface of the foundation. The relative displacement of the pile end with respect to the foundation is allowed.
According to this structure, stress concentration occurring near the edge of the joint or contact portion of the pile head during an earthquake is alleviated, and a more rational structural design is possible.

Moreover, the literature 3 (Unexamined-Japanese-Patent No. 2003-27498) makes the cross-sectional area of a foundation | floor bottom gradually reduce toward a junction part or a contact part instead of reducing the cross-sectional area of a pile head gradually in the vicinity of a junction part or a contact part. As a result, the same effect as described above is achieved. According to the embodiment of Document 3 shown in FIGS. 5 (c) and 5 (d), the lower part of the foundation has the shape of an inverted truncated cone whose sectional area gradually decreases toward the joint or contact portion, that is, downward. The shape is exactly the same as the shape of the pile head disclosed in Patent Document 2 upside down.
JP-A-8-20960 JP 2002-242207 A JP 2003-27498 A

  The example of the manufacturing process of the pile head semi-rigid joining construction method currently indicated by literature 2 is explained below.

  After placing the pile by on-site driving, etc., the concrete at the pile head is generally removed to expose the reinforcing bars. Next, a cylindrical side formwork and a perforated disk-like top formwork are installed on the pile head, and the pile head is formed by pouring concrete. As shown in FIG. 6, the top formwork used at that time is a perforated disk shape having an opening in the center, and the thickness in the vertical direction is 0 at the edge of the center opening and on the outer periphery. It is a shape that gradually increases toward the maximum value at the outer peripheral portion.

  The top formwork is made of a foam material such as styrofoam so that relative displacement between the lower part of the structure foundation and the pile head during an earthquake can be allowed.

  The pile top formwork used when forming the pile head is a ring shape having a truncated cone-shaped slope inside as described above (FIG. 6). In order to cut out a shape defined in such a three-dimensional aspect, even when a styrofoam is used as a cushioning material, a special jig is required, so that on-site molding is difficult. Moreover, even if it cut | disconnects using a jig | tool, a dimensional accuracy tends to fall. Furthermore, since the inner edge and the outer edge are acute angles, there is a problem that the edge is particularly easily damaged.

  Also, when forming the pile head, the top surface of the top formwork made of styrofoam etc. is exposed on the poured concrete, but styrofoam has low rigidity, strength and heat resistance, There is an inconvenience that extra care must be taken not to inadvertently place an object on the formwork, walk by an operator, or be damaged by heat generated during welding in the vicinity.

The present invention aims to solve the above-described problems related to the so-called pile head semi-rigid joint construction method. According to the first embodiment, the cross-sectional area of the pile and the structure is smaller than that of the pile body. A plurality of buffer layers having concentric openings with different areas in the space between the pile head and the structure formed around the joint or contact portion. The pile head support structure in which is pinched is provided.
The structure has a shape in which the cross-sectional area of the pile decreases to the upper part and reaches the joint or contact part, and a shape in which the cross-sectional area of the lower part of the foundation decreases to the lower part and reaches the joint part or the contact part. In either case, the same applies.
The plurality of buffer layers may be two or more, and the number of layers is not limited.

In the second embodiment of the present invention, in addition to the above-described features, the rigidity, strength and heat resistance of the uppermost layer of the plurality of buffer layers are higher than the rigidity, strength and heat resistance of the other layers, respectively. It relates to a certain pile head support structure.
Only the uppermost layer of the buffer layer may have higher rigidity, strength and heat resistance than the other layers, and several layers including the uppermost layer have higher rigidity than the layers below it. You may do it. It is desirable that the uppermost layer has rigidity, strength, and heat resistance so as not to be easily damaged due to work such as loading of objects, walking of a person, or welding in the vicinity.

  Specifically, a wood material, a gypsum board, a steel plate, a cement-based molded plate or the like can be used for the uppermost layer.

  In the third embodiment of the present invention, the buffer layer is made of any one of polyethylene, polystyrene, polyurethane or polyvinyl chloride foam, styrofoam, gypsum board, foamed concrete, wood material, cardboard, cloth, and non-woven fabric. It is related with a pile head support structure including a layer.

  The buffer layer functions as a mold when forming the pile head, and at the same time, it must not restrain the relative displacement when a relative displacement occurs between the pile head and the foundation of the structure, such as during an earthquake. It is. Various materials can be used as long as they can satisfy the function, but the above-mentioned materials are particularly effective materials.

According to the first embodiment of the present invention, the buffer layer is composed of a plurality of members having concentric openings with different areas, and each member has a hole having an opening defined by a cylindrical inner surface. It's just a board. Since it is easy to process a plate such as a styrofoam into a perforated disk shape, it can be easily manufactured without a special jig and also at a construction site. In addition, since there are no sharp edges, it is not necessary to give special consideration to damage to the edges.
In addition, a shape substantially equivalent to a smooth truncated cone-like slope can be formed by appropriately setting the number of layers.

  With respect to the second embodiment of the present invention, in the case of a shape in which the cross-sectional area of the pile head decreases toward the top, it is the top layer that forms the joint or contact. If the rigidity and strength of this layer is equal to or higher than the rigidity and strength of other layers, the top layer should be pressed by a support to prevent the top formwork from lifting when placing concrete on the pile head. There is no risk of damaging the formwork. In addition, it is possible to mount an object on the upper part of the mold in a state where it is installed, and since it has heat resistance, there is no problem in welding work in the vicinity. Furthermore, when placing the foundation of the structure on the pile head, the uppermost layer can be used as the lower formwork of the foundation concrete without any trouble.

  On the other hand, even in the case of a shape in which the cross-sectional area of the foundation of the structure decreases downward, if the rigidity, strength and heat resistance of the uppermost layer are higher than those of the other layers, for the same reason as described above, It is possible to prevent damage.

  According to the third embodiment of the present invention, the pile head or the foundation lower part of the structure can be formed appropriately, and at the same time, a relative displacement is generated between the pile head and the foundation lower part of the structure. In such a case, the buffer layer is deformed and does not restrain the relative displacement between the two.

  Each layer constituting the buffer layer may be an independent member, or may be an integrated structure bonded to each other. In particular, when the rigidity of the uppermost layer is higher than the rigidity of the other layers, there is an advantage that the overall strength of the mold is increased and the handling becomes easy by making the whole as a single structure.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 7 illustrates one preferred embodiment of the present invention, and FIG. 8 is an enlarged view particularly near the pile head.
The pile 130 driven into the ground has a main bar 131 extending in the axial direction and a band 132 wound around the outer periphery of the main bar. The band 132 may be a spiral line.

  As shown in more detail in FIG. 8, the cross-sectional area of the pile head is reduced toward the top, that is, upward, and the area of the joint or contact portion 121 is smaller than the cross-sectional area of the pile body. A concentric ring-shaped step surface 122 is formed around the joint portion or contact portion 121. Strictly speaking, the staircase surface 122 has a shape as shown in FIG. 9, but in FIG. 8, the staircase surface is simply indicated by a truncated cone-shaped slope having an inclination angle θ.

  On the other hand, the lower surface of the foundation is joined to the top of the pile at the joint or contact part 121. In the present embodiment, eight core rebars 135 extend in the vertical direction so as to penetrate the pile head and the foundation, and the reinforcing ring 140 surrounds the periphery to maintain the position and shape of the core rebar. Yes.

  In the present invention, it is not always necessary that the core rebar 135 penetrates the pile head and the foundation of the structure, as shown in FIGS. 10 to 11, a structure in which the pile head and the foundation are combined only with concrete, The same applies even if the foundation is a structure or the like that is simply placed on the pile head. Furthermore, the portion where the cross-sectional area gradually decreases toward the joint portion or the contact portion may be a pyramid shape such as a quadrangular pyramid as shown in FIG. 10 (c), and the shoulder as shown in FIG. There may be a portion, and the area gradually decreases thereafter. 7 to 8 and 10 to 11, the portions where the cross-sectional area decreases stepwise are illustrated by slopes.

  A cushioning material is interposed in an annular gap 124 formed in a step shape between the pile head and the lower surface of the foundation. In the event of an earthquake, when the bottom surface of the structure and the pile head are relatively displaced and the gap becomes narrow, the cushioning material can be freely deformed. Can be considered to be joined only at the joint or contact.

Materials that can be used as cushioning materials are acceptable as long as they allow the above deformation, but considering that the pile head and foundation have a reinforced concrete structure, they are much more rigid and stronger than concrete. It is preferable that the material is low. Specifically, polyethylene, polystyrene, polyurethane or polyvinyl chloride foam, styrofoam, gypsum board, foamed concrete, wood material, cardboard, cloth, non-woven fabric and the like can be used.
In addition, since there are many bubbles in the inside, it is particularly preferable to use a foam material whose apparent volume is reduced (bubbles are crushed) when subjected to a certain force or more.

Next, the manufacturing process of the said junction part is demonstrated.
FIG. 12 is a diagram showing a pile head of a reinforced concrete pile 220 placed on site. The area of the top portion 251 of the pile 220 immediately after placing the concrete is substantially the same as the cross-sectional area of the pile body. Next, as already described, for the formation of the pile head, the concrete of the pile head is once removed to expose the main reinforcement 231 and the band reinforcement 232 (FIG. 13).

  FIG. 14 shows a state in which a formwork for forming a pile head is mounted on an upper part of a pile from which concrete has been once removed. The mounted mold has a cylindrical portion 260 and a perforated top plate 261, and an opening 262 is formed at the center of the perforated top plate 261. The perforated top plate 261 may be circular as shown in FIG. 14 (a), or may be square other than circular, for example, as shown in FIG. 14 (b). When the perforated top plate 261 is not circular, the top plate 261 is naturally mounted on the cylindrical portion 260.

FIG. 15 shows an example of a sectional view showing the inside of the state shown in FIG. A mold frame is mounted so as to cover a portion where the main bar 231 and the band bar 232 are exposed, and a cushioning material composed of three buffer layers 262 to 264 on the lower surface of the perforated top plate 261 of the mold frame Is provided. Each of the buffer layers has an opening 270 at the center, but the diameter of the opening is larger as the buffer layer located below. In this embodiment, the perforated top plate 261 is a plywood, and the buffer layers 262 to 264 are all styrofoam.
As shown in FIGS. 14 and 15, the buffer layers 262 to 264 are not limited to being circular but are polygonal or the like, as in the case of the perforated top plate.

FIG. 16 shows an example of a top formwork for forming the shape of the top of the pile head. The formwork may have a perforated ring shape and a cylindrical shape as shown in FIG. 14, or a shape obtained by equally dividing the perforated ring and the cylinder in the circumferential direction as shown in FIG. . In the case of the equally divided formwork, the installation is easy, and the difference is particularly remarkable when the core rebar penetrates the pile head.
FIG. 16B illustrates a rectangular top formwork that can be divided into two.

17 and 18 show pile heads that have been placed using such a formwork. The outer shape of the pile head is cylindrical, but the side surfaces of the top plate 261 and the buffer layers 262 to 264 are exposed on the side surfaces. As is clear from FIG. 15, the joint or contact portion 221 of the concrete is exposed at the top of the pile.
FIGS. 17B and 18B illustrate the case where the outer shape of the mold is a square.

  FIG. 19 illustrates a concrete structure of a pile head obtained by placing concrete on the above-mentioned formwork. As is apparent from the figure, the pile head has a concentric step, and the cross-sectional area gradually decreases as it goes to the top. The flat part which is the top part is a junction part or contact part which the lower surface of a foundation contacts. However, since the cushioning material on the upper surface remains installed even when the formwork on the side surface of the pile head is removed, the concrete structure shown in FIG. 19 is not exposed as described above.

  In the next step, foundation concrete is cast using the top of the pile as the bottom of the formwork. The above-described FIGS. 7 and 8 schematically show a state in which the foundation or the like stands on the joint or contact part 121.

In the above embodiment, the present invention has been described by taking as an example a structure in which the cross-sectional area of the pile head is gradually reduced toward the joint or contact portion. However, the top of the pile is flat, and conversely, the cross-sectional area of the lower end of the foundation. It has already been mentioned that may decrease gradually toward the joint or contact.
The above-described embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above-described embodiments, and all modifications that can be made by those skilled in the art based on the embodiments are described in the claims. And within the scope of equivalents thereof.

Cross section showing the concept of the structure and the ground with piles Conceptual diagram showing the internal structure of reinforced concrete piles Conceptual diagram of conventional structure with rigid connection between pile head and foundation Trial calculation results showing the relationship between joint stiffness of pile and foundation joint and bending moment generated in pile during earthquake Conceptual diagram showing pile / foundation joints by conventional pile head semi-rigid joint construction method Sectional view and perspective view showing a conventional formwork Conceptual diagram of pile head support structure according to the present invention Sectional view showing the structure of the pile and foundation near the pile head support structure according to the present invention Conceptual diagram showing the shape of the pile head and the bottom surface of the foundation of the structure The conceptual diagram which shows the modification of the pile head support structure by this invention The conceptual diagram which shows the modification of the pile head support structure by this invention Perspective view showing pile head after placement The perspective view which shows the state which removed the concrete of the pile head partly The perspective view which shows the state which installed the formwork for shaping | molding in the pile head Sectional drawing of the state shown in FIG. Perspective view of divided top formwork Elevated view of pile head with formwork removed Perspective view of pile head with formwork removed Perspective view showing the shape of concrete members inside the pile head

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Structure 20 Pile | foundation joint part 21 and 121 Joint part or contact part 22 The part in which a cross-sectional area reduces to step shape 30 Pile 31, 131, 231 Main reinforcement 32, 132, 232 Band reinforcement 40 Ground 50 Support ground 124 Space | gap 261 Perforated top plate 262-264 Buffer layer

Claims (2)

In the pile head support structure in which the pile and the structure are joined or in contact with each other with a smaller cross-sectional area than the pile body, the gap between the pile head and the structure formed around the joint or the contact portion, A plurality of buffer layers having concentric openings with different areas are sandwiched ,
The pile head support structure in which the rigidity, strength and heat resistance of the uppermost layer among the plurality of buffer layers are higher than the rigidity, strength and heat resistance of the other layers . In a pile head support structure where the pile and the structure are joined or in contact with each other with a smaller cross-sectional area than the pile body, the pile head places the concrete in the formwork mounted on the top of the pile once the concrete has been removed. Formed,
  The pile head comprising a cushioning material comprising a cylindrical portion, a perforated top plate, and a plurality of buffer layers having concentric openings having different areas under the top plate. Support structure.

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