JP6345741B2 - Design method and manufacturing method of pile head joint - Google Patents

Description

  The present disclosure relates to a method for designing and manufacturing a pile head joint.

  The pile foundation that supports the superstructure generally has a plurality of piles and a foundation concrete portion such as a pile cap or a footing that is provided so as to surround the upper end portion (pile head) of the pile. In order to strengthen the connection between the pile head portion and the foundation concrete portion, for example, as disclosed in Patent Document 1, a joining member and a reinforcing bar are used. A pile head, a joining member, a reinforcing bar, and a foundation concrete part constitute a pile head joined part.

More specifically, in the pile head joint portion disclosed in Patent Document 1, a plurality of joint members are attached to the outer peripheral surface of the pile head at intervals in the circumferential direction. The joining member has a lower plate portion and an upper plate portion that are separated from each other in the axial direction of the pile head portion, and a screw portion of a reinforcing bar is coupled to the lower plate portion of the joining member. The shaft portion of the reinforcing bar extends through the insertion portion of the upper plate portion of the joining member and protrudes upward from the end surface of the pile head.
In the pile head joint portion disclosed in Patent Document 1, the foundation concrete portion pushes the upper plate portion upward with a force, and even if the screw portion is formed on the reinforcing bar by screw machining, the pile head portion and the foundation The joint of the concrete part can be effectively reinforced.

JP 2015-34458 A

When the present inventors examined, in the pile head joint part which patent document 1 discloses, according to the presence or absence of the crack of a foundation concrete part, and the presence or absence of the yield of the upper board part of a joining member, the pile head joint part of It was found that it was necessary to calculate the allowable bending moment for each case. There is no description in Patent Document 1 regarding the necessity of such case classification.
The pile heads, joint members, reinforcement bars and foundation concrete can be used to ensure that the bending moments generated at the pile heads can be reliably endured if the allowable bending moments at the pile head joints are accurately grasped. It is possible to determine the specifications of the part and to suppress the specification from becoming excessive. As a result, it is possible to ensure a sufficient allowable bending moment at low cost by calculating the allowable bending moment of the pile head joint according to the case.

  In view of the above circumstances, the object of at least one embodiment of the present invention is to attach a joining member having a lower protrusion and an upper protrusion spaced apart from each other in the axial direction of the pile head to the outer peripheral surface of the pile head. In the pile head joint where the foundation concrete part is attached to the shaft part of the reinforcing bar with the screw part connected to the lower protrusion, a sufficiently large allowable bending moment can be realized at low cost. It is providing the design method and manufacturing method of a pile head junction which make it possible.

(1) A method for designing a pile head joint according to at least one embodiment of the present invention includes:
A pile head,
A plurality of joining members fixed to the outer peripheral surface of the pile head;
A plurality of reinforcing bars respectively attached to the pile head via the joining member;
A foundation concrete portion constituted by concrete surrounding the pile head, the plurality of joining members, and the plurality of reinforcing bars,
The reinforcing bars are
A shaft portion having irregularities on the surface;
A screw portion connected to one end side of the shaft portion and having a smaller cross-sectional area than the shaft portion, and
The joining member is
A lower protrusion fixed to the outer peripheral surface of the pile head;
An upper protrusion fixed to the outer peripheral surface of the pile head, and an upper protrusion disposed above the lower protrusion in the axial direction of the pile head;
A screw portion of the reinforcing bar is coupled to the lower protrusion,
The shaft portion of the reinforcing bar extends between the lower protrusion portion and the upper protrusion portion in the axial direction of the pile head portion, and protrudes upward from the end surface of the pile head portion. ,
In the design method of the pile head joint,
A specification selection step of selecting specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part;
Based on the specification selected in the specification selection step, an allowable bending moment calculation step for calculating an allowable bending moment of the pile head joint,
A specification suitability determination step for determining suitability of the specification selected in the specification selection step based on the allowable bending moment, and
In the allowable bending moment calculation step,
A portion of a foundation concrete portion surrounding a portion of a shaft portion of the reinforcing bar protruding upward from an end surface of the pile head, and a shaft portion of the reinforcing bar extending between the lower protrusion portion and the upper protrusion portion. Assuming that cracks occur between the part of the foundation concrete part surrounding the part,
While considering the tensile yield strength of the shaft portion of the reinforcing bar, the allowable bending moment is calculated ignoring the resistance acting on the foundation concrete portion from the joint member.

  According to the above configuration (1), when it is assumed that cracks occur in the foundation concrete part, while considering the tensile yield strength of the shaft part of the reinforcing bar, the resistance acting on the foundation concrete part from the joining member is ignored. By calculating the allowable bending moment, the allowable bending moment can be accurately calculated. As a result, according to the configuration (1), it is possible to realize a pile head joint having a sufficiently large allowable bending moment with low-cost specifications.

(2) A method for designing a pile head joint according to at least one embodiment of the present invention,
A pile head,
A plurality of joining members fixed to the outer peripheral surface of the pile head;
A plurality of reinforcing bars respectively attached to the pile head via the joining member;
A foundation concrete portion constituted by concrete surrounding the pile head, the plurality of joining members, and the plurality of reinforcing bars,
The reinforcing bar is
A shaft portion having irregularities on the surface;
A screw portion connected to one end side of the shaft portion and having a smaller cross-sectional area than the shaft portion, and
The joining member is
A lower protrusion fixed to the outer peripheral surface of the pile head;
An upper protrusion fixed to the outer peripheral surface of the pile head, and an upper protrusion disposed above the lower protrusion in the axial direction of the pile head;
A screw portion of the reinforcing bar is coupled to the lower protrusion,
The reinforcing bar extends between the lower protrusion and the upper protrusion in the axial direction of the pile head, and extends upward from an end surface of the pile head.
In the design method of the pile head joint,
A specification selection step of selecting specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part;
Based on the specification selected in the specification selection step, an allowable bending moment calculation step for calculating an allowable bending moment of the pile head joint,
A specification suitability determination step for determining suitability of the specification selected in the specification selection step based on the allowable bending moment, and
In the allowable bending moment calculation step,
A portion of a foundation concrete portion surrounding a portion of a shaft portion of the reinforcing bar protruding upward from an end surface of the pile head, and a shaft portion of the reinforcing bar extending between the lower protrusion portion and the upper protrusion portion. Assuming that no cracks occur between the foundation concrete part surrounding the part,
The allowable bending moment is calculated in consideration of the tensile yield strength of the screw portion of the reinforcing bar and the resistance acting on the foundation concrete portion from the joining member.

  According to the above configuration (2), when it is assumed that no cracks are generated in the foundation concrete part, the tensile yield strength of the screw part of the reinforcing bar is taken into consideration, and the resistance acting on the foundation concrete part from the joining member is taken into consideration. By calculating the allowable bending moment, the allowable bending moment can be accurately calculated. As a result, according to the configuration (2), a pile head joint having a sufficiently large allowable bending moment can be realized with low-cost specifications.

(3) A method for designing a pile head joint according to at least one embodiment of the present invention,
A pile head,
A plurality of joining members fixed to the outer peripheral surface of the pile head;
A plurality of reinforcing bars respectively attached to the pile head via the joining member;
A foundation concrete portion constituted by concrete surrounding the pile head, the plurality of joining members, and the plurality of reinforcing bars,
The reinforcing bar is
A shaft portion having irregularities on the surface;
A screw portion connected to the lower end side of the shaft portion and having a smaller cross-sectional area than the shaft portion, and
The joining member is
A lower protrusion fixed to the outer peripheral surface of the pile head;
An upper protrusion fixed to the outer peripheral surface of the pile head, and an upper protrusion disposed above the lower protrusion in the axial direction of the pile head;
A screw portion of the reinforcing bar is coupled to the lower protrusion,
The reinforcing bar extends between the lower protrusion and the upper protrusion in the axial direction of the pile head, and extends upward from an end surface of the pile head.
In the design method of the pile head joint,
A specification selection step of selecting specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part;
Based on the specification selected in the specification selection step, an allowable bending moment calculation step for calculating an allowable bending moment of the pile head joint,
A specification suitability determination step for determining suitability of the specification selected in the specification selection step based on the allowable bending moment, and
The allowable bending moment calculation step includes:
Considering the tensile yield strength of the screw portion of the reinforcing bar and calculating the first allowable bending moment as the allowable bending moment in consideration of the resistance acting on the foundation concrete portion from the joint member Bending moment calculation process;
While considering the tensile yield strength of the shaft portion of the reinforcing bar, the second permissible bending moment is calculated as the permissible bending moment ignoring the resistance acting on the foundation concrete portion from the joining member Bending moment calculation process;
An allowable bending moment selection step of comparing the first allowable bending moment and the second allowable bending moment and selecting a smaller one of the first allowable bending moment and the second allowable bending moment as the allowable bending moment; Including.

  According to the configuration (3), by selecting the smaller one of the first allowable bending moment and the second allowable bending moment as the allowable bending moment, safety can be ensured regardless of whether or not cracks have occurred in the foundation concrete portion. It is possible to realize a pile head joint having a sufficiently large allowable bending moment with low cost specifications.

(4) In some embodiments, in the configuration (3),
In the allowable bending moment selection step, when the yield strength of the upper protrusion is smaller than the difference between the tensile yield strength of the shaft portion and the tensile yield strength of the screw portion, the first allowable bending moment is the allowable bending moment. Selected as a moment.

  According to the configuration (4), when the yield strength of the upper protrusion is smaller than the difference between the tensile yield strength of the shaft portion of the reinforcing bar and the tensile yield strength of the screw portion, the first allowable bending moment is the allowable bending moment. Selected as. That is, when the yield strength of the upper protrusion is smaller than the difference between the tensile yield strength of the shaft portion of the reinforcing bar and the tensile yield strength of the screw portion, the upper protrusion yields, and the first allowable bending moment Therefore, the first allowable bending moment is selected as the allowable bending moment. As a result, according to the above configuration (4), it is possible to accurately calculate the allowable bending moment in anticipation of safety, and to realize a pile head joint having a sufficiently large allowable bending moment with low-cost specifications. Is possible.

(5) In some embodiments, in any one of the configurations (1) to (4),
The specification suitability determination step includes
Based on the rotation angle of the pile head corresponding to the allowable bending moment and the allowable bending moment, an elastic rotation stiffness calculation step of calculating the elastic rotation stiffness of the pile head joint,
The pile head when an assumed horizontal force is applied to the pile head in consideration of the elastic rotational rigidity of the pile head joint, under the condition that no axial compression force is applied to the pile head. The generated bending moment calculation process for calculating the generated bending moment generated in the part,
A bending moment comparison and determination step for determining whether or not the generated bending moment calculated in the generated bending moment calculation step is smaller than the allowable bending moment,
One of the conditions for determining that the specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part are appropriate is that the generated bending moment is the allowable bending moment in the bending moment comparison determining step. It is determined that it is smaller than.

Conventionally, in the case of a pile head joint in which the foundation concrete portion is attached to the reinforcing bar, the generated bending moment generated at the pile head joint has been calculated as having a fixing degree of 1. Here, the degree of fixation is the ratio M of the pile head bending moment M ₀ that occurs when semi-fixed to the pile head bending moment M _0f that occurs when the pile head is completely fixed, according to the “Building Foundation Structure Design Guidelines” of the Architectural Institute of Japan. Defined as ₀ / M _0f . In the case of a pile head pin, M ₀ = 0, so the fixing degree is 0, and in the case of pile head fixing (rigid connection), M ₀ = M _0f , so the fixing degree is 1. In the pile head semi-rigid joint, if the fixing degree is α, 0.0 <α <1.0.
In view of this point, the present inventors have examined that even when the foundation concrete portion is attached to the reinforcing bar, the generated bending moment may be calculated without setting the fixing degree to 1, that is, the elasticity. It was found that there is a case where the generated bending moment may be calculated in consideration of the rotational rigidity. Specifically, it was found that when the axial compressive force is not acting on the pile head, the fixing degree may be calculated without being set to 1.
Therefore, in the above configuration (5), an assumed horizontal force acts on the pile head in consideration of the elastic rotational rigidity of the pile head joint, under the condition that no axial compressive force acts on the pile head. The generated bending moment generated at the pile head is calculated. Thus, by considering the elastic rotational rigidity of the pile head joint, the degree of fixation can be made smaller than 1, and the generated bending moment of the pile head can be reduced. Accordingly, the generated bending moment can be reduced under the condition that the axial compressive force is not applied to the pile head, and the generated bending moment can be made smaller than the allowable bending moment. As a result, according to the configuration (5), it is possible to realize a pile head joint having an allowable bending moment that is sufficiently large with respect to the pile head generated bending moment with low-cost specifications.

(6) In some embodiments, in the configuration (3) or (4),
The specification suitability determination step includes
Elastic rotation for calculating the elastic rotational rigidity of the pile head joint based on the larger of the first allowable bending moment and the second allowable bending moment and the rotation angle of the pile head corresponding to the allowable bending moment Stiffness calculation process;
The pile head when an assumed horizontal force is applied to the pile head in consideration of the elastic rotational rigidity of the pile head joint, under the condition that no axial compression force is applied to the pile head. The generated bending moment calculation process for calculating the generated bending moment generated in the part,
A bending moment comparison determination step of determining whether or not the generated bending moment of the pile head calculated in the generated bending moment calculation step is smaller than the allowable bending moment,
One of the conditions for determining that the specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part are appropriate is that the generated bending moment is the allowable bending moment in the bending moment comparison determining step. It is determined that it is smaller than.

According to the above configuration (6), as in the case of the above configuration (5), the generated bending moment can be reduced under the condition that the axial compressive force is not applied to the pile head, and the allowable bending moment. The generated bending moment can be made smaller.
On the other hand, when the elastic rotational rigidity is evaluated as being underestimated, that is, when the degree of fixing is evaluated as being underestimated, the calculated bending moment of the pile head is too small. When such a generated bending moment and an allowable bending moment are compared, there is a possibility that a problem may arise in the validity of the comparison result.
In this respect, according to the configuration (6), the elastic rotational rigidity of the pile head joint is determined based on the rotation angle of the pile head corresponding to the larger one of the first allowable bending moment and the second allowable bending moment. Since it calculates, it is prevented that the magnitude | size of elastic rotational rigidity is evaluated too small. As a result, according to the above configuration (6), the validity of the result when the generated bending moment and the allowable bending moment are compared is ensured, and the pile head joint having a sufficiently large allowable bending moment is reduced. It can be reliably realized with low cost specifications.

(7) In some embodiments, in the configuration (5) or (6),
The elastic rotational rigidity calculation step includes a step of calculating an extension amount of the reinforcing reinforcement on the tension side among the reinforcing bars in consideration of adhesion of the foundation concrete portion to the shaft portion of the reinforcing bars.

When the amount of elongation is calculated excessively, the rotation angle of the pile head is overestimated, and the elastic rotational rigidity of the pile head joint is underestimated. When the elastic rotational rigidity is evaluated as being underestimated, that is, when the fixing degree is evaluated as being underestimated, the calculated bending moment is too small. When such a generated bending moment and an allowable bending moment are compared, there is a possibility that a problem may arise in the validity of the comparison result.
In this respect, according to the above configuration (7), the amount of extension of the reinforcing bar is calculated in consideration of the adhesion of the foundation concrete portion to the shaft portion of the reinforcing bar, thereby preventing the extension amount from being excessively calculated. . As a result, according to the configuration (7), the validity of the result when the generated bending moment and the allowable bending moment are compared is ensured, and the pile head joint having a sufficiently large allowable bending moment is reduced. It can be reliably realized with low cost specifications.

(8) In some embodiments, in any one of the configurations (5) to (7),
The bending bending moment generated at the pile head when the assumed horizontal force is applied to the pile head, calculated by ignoring the elastic rotational rigidity of the pile head joint, is the allowable bending moment. Further comprising a rigid joint occurrence bending moment comparison and determination step of determining whether or not greater than
One of the conditions for determining that the specifications of the pile head, the joint member, the reinforcing bar, and the foundation concrete part are appropriate is that the rigid joint generated bending moment is determined in the rigid joint generated bending moment comparison determination step. It is determined that the allowable bending moment is greater than the allowable bending moment.

  According to the above configuration (8), when the bending moment generated by ignoring the rotation angle of the pile head is larger than the allowable bending moment, the pile head, the joining member, the reinforcing bar, and the foundation concrete portion Since it is determined that the specification is appropriate, it is possible to prevent the specification of the pile head, the joining member, the reinforcing bar, and the foundation concrete portion from becoming excessive. As a result, according to the configuration (8), a pile head joint having a sufficiently large allowable bending moment can be reliably realized with low-cost specifications.

(9) In some embodiments, in any one of the configurations (1) to (8),
In the allowable bending moment calculation step,
It is assumed that the resistance bending moment of the reinforcing concrete projecting upward from the end of the pile head and the foundation concrete portion surrounding the reinforcement is the bending moment borne by the virtual RC section including the end face of the pile head,
The diameter of the pile head is Dp,
The diameter of the virtual RC cross section is D,
When the length of the foundation concrete portion attached to the shaft portion of the reinforcing bar between the lower protrusion portion and the upper end of the upper protrusion portion in the axial direction of the pile head is defined as Le:
Dp + Le ≦ D ≦ Dp + 2Le
The diameter D of the virtual RC cross section is set so as to satisfy the relationship represented by

According to the said structure (9), the resistance bending moment of the foundation concrete part surrounding the said reinforcement and the reinforcement reinforcement which protrudes upwards from the edge part of the said pile head is the virtual RC cross section containing the end surface of a pile head. Assuming the bending moment to bear, the following formula:
Dp + Le ≦ D ≦ Dp + 2Le
Since the diameter D of the virtual RC cross section is set so as to satisfy the relationship expressed by:, the size of the virtual RC cross section diameter can be set larger than in the past. The larger the virtual RC cross-sectional diameter, the smaller the stress acting on the foundation concrete part and the pile head, and the greater the allowable bending moment can be calculated. As a result, according to the configuration (9), a pile head joint having a sufficiently large allowable bending moment can be realized with low-cost specifications.

(10) In some embodiments, in any one of the configurations (1) to (9),
The specification selection step, the allowable bending moment calculation step, and the specification suitability determination step are repeated so that the allowable bending moment approaches the generated bending moment.

  According to the configuration (10), a pile head joint having a larger allowable bending moment can be realized at a low cost by repeating the specification selection process, the allowable bending moment calculation process, and the specification suitability determination process. is there.

(11) A method for manufacturing a pile head joint according to at least one embodiment of the present invention,
Of the pile head, the joint member, the reinforcing bar, and the foundation concrete part determined to be appropriate by the method for designing a pile head joint according to any one of the above configurations (1) to (10) A pile head joint construction step for constructing the pile head joint is provided based on the specifications.

  According to the said structure (11), the specification of a pile head, a joining member, a reinforcing bar, and a foundation concrete part is selected by the design method of any one pile head joint part of the said structure (1) thru | or (10). Therefore, a pile head joint having a sufficiently large allowable bending moment can be realized with low-cost specifications.

  According to at least one embodiment of the present invention, a joining member having a lower projection and an upper projection spaced apart from each other in the axial direction of the pile head is attached to the outer peripheral surface of the pile head, and the lower projection Pile head joint that can realize a sufficiently large allowable bending moment with low-cost specifications in the pile head joint where the foundation concrete part is attached to the shaft of the deformed reinforcing bar with the threaded part A design method and a manufacturing method are provided.

It is a figure which shows schematic structure of a structure. It is a figure for demonstrating a pile head junction part. It is a figure which shows schematically the pile head in FIG. 2, a joining member, a reinforcing bar, and a fixing body, A left half is a side view, A right half is sectional drawing. It is a figure which shows a joining member schematically, (a) is a front view, (b) is a side view, (c) is a top view, (d) is a bottom view. It is a side view which shows a reinforcing bar roughly. It is sectional drawing which shows a pile head, a joining member, and a part of reinforcing bar roughly. It is a top view which shows a part of pile head part, and a joining member schematically. It is a flowchart which shows roughly the procedure of the design method of the pile head junction part which concerns on 1st Embodiment. It is a figure for demonstrating the resistance mechanism model for calculating an allowable bending moment, (a) is the mechanism I, (b) is the mechanism II, (c) is a figure for demonstrating the mechanism III. It is a figure for demonstrating the reason which can consider the tensile yield strength of the axial part of a reinforcing bar in the state B in which the crack has generate | occur | produced. It is a figure for demonstrating the proof stress increase of the foundation concrete part by the bearing effect in a pile head junction part. It is a figure for demonstrating the proof stress increase of the foundation concrete part by the bearing effect in the eccentric compression state in a pile head junction part. It is a figure which shows roughly the horizontal force test apparatus of a pile head junction part. It is a graph which shows the application pattern of the horizontal force made to act on a pile head junction part by the horizontal force test apparatus of FIG. It is the photograph which picked up the foundation concrete part of a pile head joint part after a horizontal force test using a horizontal force test device, and photographed the internal condition of a foundation concrete part. It is the photograph which picked up the foundation concrete part of a pile head joint part after a horizontal force test using a horizontal force test device, and photographed the internal condition of a foundation concrete part. It is the photograph which picked up the foundation concrete part of a pile head joint part after a horizontal force test using a horizontal force test device, and photographed the internal condition of a foundation concrete part. It is the photograph which picked up the foundation concrete part of a pile head joint part after a horizontal force test using a horizontal force test device, and photographed the internal condition of a foundation concrete part. It is a figure for demonstrating that virtual RC section diameter D was set up from the occurrence situation of a crack in a foundation concrete part. It is a figure for demonstrating the symbol in [Formula 1]-[Formula 3]. It is a figure for demonstrating the symbol in [Formula 4]. It is a figure for demonstrating that the determination position of a reinforcing bar cross-sectional strength differs in the case of the state A in which the crack has generate | occur | produced from the case of the state B in which the crack has generate | occur | produced. It is a flowchart which shows the schematic procedure of the allowable bending moment calculation process in the design method of the pile head junction part which concerns on 3rd Embodiment. It is a flowchart which shows the schematic procedure of the allowable bending moment selection process in the case of Cc ≧ Tby−Tsy. It is a flowchart which shows the schematic procedure of the specification suitability determination process in the design method of the pile head junction part which concerns on 4th Embodiment. It is a figure for demonstrating the symbol in [Equation 5] and [Equation 6]. It is a graph which shows the distribution in the axial direction of the pile head of the force which acts on a reinforcing bar in the case of the state B in which the crack has generate | occur | produced. It is a graph which shows the distribution in the axial direction of the pile head of the force which acts on a reinforcing bar in the case of the state A where the crack has not generate | occur | produced. It is a flowchart which shows the schematic procedure of the design method of the pile head junction part which concerns on 5th Embodiment. It is a flowchart which shows the schematic procedure of the design method of the pile head junction part which concerns on 6th Embodiment. It is a flowchart which shows the schematic procedure of the manufacturing method of the pile head junction which concerns on the design method of the pile head junction which concerns on 7th Embodiment, and 8th Embodiment. It is a figure for demonstrating the pile arrangement | positioning used for the pile stress integrated analysis. It is a graph which shows the analysis result of pile stress integrated analysis, and is a graph which shows the NM curve of pile P1 when N value = 3.0. It is a graph which shows the analysis result of pile stress integrated analysis, and is a graph which shows the NM curve of pile P1 when N value = 1.0. It is a graph which shows the analysis result of pile stress integrated analysis, and is a graph which shows the NM curve of the pile P2 when N value = 1.0. It is sectional drawing which shows roughly the pile head of the other pile head joint part which can be designed with the design method of the pile head joint part which concerns on 1st Embodiment, a joining member, a reinforcing bar, and a part of partition member. It is a figure which shows a partition member schematically, (a) is a front view, (b) is a side view, (c) is a top view. It is a top view which shows a pile head, a joining member, and a partition member roughly. It is a figure which expands and shows a part of FIG. It is a figure for demonstrating the effect of a partition member. It is a figure which shows roughly the pile head of the other pile head joint part which can be designed with the design method of the pile head joint part which concerns on 1st Embodiment, a joining member, a reinforcing bar, and a part of partition member, The left half Is a side view, and the right half is a cross-sectional view. It is a top view which shows a pile head, a joining member, and a partition member roughly. It is a figure which shows schematic structure of a partition member, Comprising: (a) is a top view, (b) is a longitudinal cross-sectional view.

Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Absent.
For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of the other constituent elements.

  Hereinafter, although the design method and manufacturing method of the pile head junction part which concern on embodiment of this invention are demonstrated, an example of the pile head junction part of a design object is demonstrated first as the premise.

[Configuration of pile head joint]
FIG. 1 is a diagram illustrating a schematic configuration of the structure 1. The structure 1 includes a plurality of piles 2, a pile cap 4a joined to each of the pile heads of the plurality of piles 2, a beam 5 connecting the pile caps 4a, and the pile 2 via the pile cap 4a. With a supported superstructure 6. The pile 2, the pile cap 4 a and the beam 5 constitute a pile foundation 8 for supporting the upper structure 6.
The pile foundation 8 may have a footing instead of the pile cap 4a. Hereinafter, the pile cap 4a and the footing are also referred to as a foundation concrete portion 4.

  FIG. 2 is a diagram for explaining the pile head joint 10. FIG. 3 is a diagram schematically showing a pile head, a joining member, a reinforcing bar (fixing bar), and a fixing body in FIG. 2, in which the left half is a side view and the right half is a cross-sectional view. 4A and 4B are diagrams schematically showing the joining member, in which FIG. 4A is a front view, FIG. 4B is a side view, FIG. 4C is a top view, and FIG. 4D is a bottom view. FIG. 5 is a side view schematically showing a reinforcing bar. FIG. 6 is a cross-sectional view schematically showing a part of a pile head, a joining member, and a reinforcing bar. FIG. 7 is a top view schematically showing a part of a pile head and a joining member.

As shown in FIGS. 1 to 7, the pile head joint portion 10 includes an upper end portion (pile head portion) 12 of the pile 2, a plurality of joining members 14, a plurality of reinforcing bars 16, and a foundation concrete portion 4. It has.
The pile 2 may be a cast-in-place pile or a ready-made pile. However, the joining member 14 is fixed to the outer peripheral surface of the cylindrical pile head 12 by welding. For this reason, in the case of a cast-in-place pile, the pile 2 is a steel pipe concrete pile. In the case of a ready-made pile, the pile 2 is a steel pipe pile (SPP pile) or a concrete pile with an outer shell steel pipe (SC pile), or a concrete having a steel reinforcing band attached to the upper end. Pile, for example, reinforced concrete pile (RC pile), prestressed concrete pile (PC pile, PRC pile), or high strength prestressed concrete pile (PHC pile).
In this embodiment, the pile 2 is an SC pile and covers a cylindrical concrete portion 17 made of concrete, a metal end plate 18 covering both ends of the concrete portion 17, and an outer peripheral surface of the concrete portion 17. And an outer shell steel pipe 19. The end plate 18 has an annular shape and is welded to the outer shell steel pipe 19.

The plurality of joining members (joint couplers) 14 are made of metal, and are fixed to the outer peripheral surface of the pile head 12 by welding at intervals in the circumferential direction of the pile head 12.
The plurality of reinforcing bars 16 are made of metal and are respectively attached to the pile heads 12 via the joining members 14.
The foundation concrete portion 4 is made of concrete and surrounds the pile head 12, the plurality of joining members 14, and the plurality of reinforcing bars 16.
In addition, although not shown in figure, in the foundation concrete part 4, the split reinforcement, the main reinforcement of the beam 5, etc. may be arrange | positioned.

Here, the reinforcing bar 16 includes a shaft portion 20 having an uneven surface, and a screw portion 21 that is connected to one end side of the shaft portion 20 and has a smaller cross-sectional area than the shaft portion 20. The reinforcing bar 16 may have screw parts 21 on both sides of the shaft part 20. In this case, a nut as the fixing body 22 may be screwed to the screw portion 21 on the upper end side of the reinforcing bar 16.
For example, a deformed bar as shown in FIG. 5 can be used as the reinforcing bar 16.

  The bonding member 14 includes a lower protrusion 23 and an upper protrusion 24. The lower protrusion 23 and the upper protrusion 24 are fixed to the outer peripheral surface of the pile head 12 by welding, and protrude laterally from the outer peripheral surface of the pile head 12. The upper protrusion 24 is disposed above the lower protrusion 23 in the axial direction of the pile head 12. For example, the joining member 14 is welded to the outer peripheral surface of the pile head 12 so that the position of the upper surface of the upper protrusion 24 matches the position of the upper end surface of the pile head 12 in the axial direction of the pile head 12. Is done.

  The screw portion 21 of the reinforcing bar 16 is coupled to the lower protrusion 23. For example, as shown in FIG. 4, a screw hole 26 is formed in the lower protrusion 23, and the screw part 21 is screwed into the screw hole 26. Or although not shown in figure, a through-hole is formed in the lower side projection part 23, and a nut is welded on the lower side of the lower side projection part 23 coaxially with a through-hole. In this case, the nut can be regarded as a part of the lower protrusion 23, and the screw 21 can be regarded as being screwed into the lower protrusion 23 by screwing the screw 21 into the nut. it can.

The shaft portion 20 of the reinforcing bar 16 extends between the lower projection portion 23 and the upper projection portion 24 in the axial direction of the pile head portion 12 and projects upward from the end surfaces of the upper projection portion 24 and the pile head portion 12. It is extended.
Therefore, the upper protrusion 24 has a shape that allows the reinforcing bars 16 to pass therethrough. On the other hand, the upper protruding portion 24 includes the portion of the foundation concrete portion 4 attached to the portion of the shaft portion 20 of the reinforcing bar 16 extending between the lower protruding portion 23 and the upper protruding portion 24, and the axis of the pile head portion 12. It is configured to engage in a direction.
For example, as shown in FIG. 4, the upper protruding portion 24 has a fork portion 29 in which a notch 28 that allows passage of the reinforcing bars 16 is formed. The fork portion 29 is concrete attached to the shaft portion 20. It is comprised so that a part of part 4 and the pile head part 12 may be engaged in the axial direction.

Preferably, the joining member 14 further includes a connecting portion 30 formed integrally with the lower protrusion 23 and the upper protrusion 24, two reinforcing beam portions 32, and two reinforcing rib portions 34.
The connecting portion 30 has a plate shape extending in the axial direction and the circumferential direction of the pile head portion 12, and connects the lower protruding portion 23 and the upper protruding portion 24 to each other. The connection part 30 has the curved surface 35 which can be arrange | positioned along the outer peripheral surface of the pile head 12 on the pile head 12 side.
The reinforcing beam portion 32 extends in the axial direction of the pile head portion 12 and has a prismatic shape. The reinforcing beam portion 32 is integrally formed on both sides of the connecting portion 30 in the circumferential direction of the pile head portion 12. The reinforcing beam portion 32 extends between the lower protrusion 23 and the upper protrusion 24.
The reinforcing rib portion 34 is integrally formed at a corner formed between the reinforcing beam portion 32 and the lower protrusion 23.

Preferably, as shown in FIG. 7, both sides of the connecting portion 30 are welded to the outer peripheral surface of the pile head 12 in the circumferential direction of the pile head 12. Therefore, a groove surface 36 inclined with respect to the outer peripheral surface of the pile head 12 is provided on both sides of the connecting portion 30 in the circumferential direction of the pile head 12, and the outer periphery of the groove surface 36 and the pile head 12 is provided. A weld bead 38 is formed between the surfaces. Preferably, the groove surface 36 and the weld bead 38 extend from the lower protrusion 23 to the upper protrusion 24 in the axial direction of the pile head 12.
In addition, the shape of the joining member 14 is not limited to what was mentioned above, For example, the joining member described in Unexamined-Japanese-Patent No. 2015-34458 can be used.

[Method of designing a pile head joint according to the first embodiment]
FIG. 8 is a flowchart schematically showing a procedure of a method for designing a pile head joint according to the first embodiment. FIG. 9 is a diagram for explaining a resistance mechanism model for calculating an allowable bending moment.
As shown in FIG. 8, the design method of the pile head joint includes a specification selection step S1, an allowable bending moment calculation step S2, and a specification suitability determination step S3.

  In the specification selection step S1, the specifications of the pile head 12, the joining member 14, the reinforcing bar 16, and the foundation concrete portion 4 are selected. The specification of the pile head 12 is the specification of the pile 2 and includes a pile diameter, a pile type, a material, and the like. The specifications of the joining member 14 are the shape, size, material, and the like of the joining member 14. The specifications of the reinforcing bar 16 are the shape, size, material, and the like of the reinforcing bar 16. The specifications of the foundation concrete portion 4 are the shape, dimensions, material, and the like of the foundation concrete portion 4.

In the allowable bending moment calculating step S2, the allowable bending moment (short-term allowable bending moment) sMa of the pile head joint 10 is calculated based on the specification selected in the specification selecting step S1.
In the specification suitability determination step S3, the suitability of the specification selected in the specification selection step S1 is determined based on the allowable bending moment sMa. For example, in specifications properness determining step S3, by comparing the generated bending moment M ₀ of the allowable bending moment SMA and pile head, is smaller than generating the bending allowable moment M ₀ bending moment SMA, it is appropriate selected specifications It is determined.

  Here, in the allowable bending moment calculation step S2, the allowable bending moment sMa is calculated based on the resistance mechanism model shown in FIG. When a shearing force Q acts on the pile head joint 10 and a bending moment M is generated, it is considered that the following mechanisms I, II, and III are appropriately combined to resist the bending moment M.

As shown in FIG. 9A, the mechanism I is a resistance as a virtual RC cross section in which the reinforcing bar 16 is regarded as the main bar, and the compression force C acting on the reinforcing bar 16 and the pile head 12 and the reinforcing bar. 16 is a resistance against a pulling force T acting on 16. Hereinafter, the component of the allowable bending moment sMa by the mechanism I is also referred to as a first allowable bending moment component sMa1.
The mechanism II is a resistance against the compressive force C acting on the outer peripheral surface of the pile head 12 from the foundation concrete portion 4 as shown in FIG. Hereinafter, the component of the allowable bending moment sMa by the mechanism II is also referred to as a second allowable bending moment component sMa2.
The mechanism III is resistance to the compressive force C acting on the unevenness of the joining member 14 from the basic concrete portion 4 as shown in FIG. Hereinafter, the component of the allowable bending moment sMa by the mechanism III is also referred to as a third allowable bending moment component sMa3.

And in the allowable bending moment calculation step S2 of the present embodiment, the upper portion 40 of the foundation concrete portion 4 surrounding the portion of the shaft portion 20 of the reinforcing bar 16 protruding upward from the end face of the pile head portion 12, and the lower protrusion portion It is assumed that a crack 44 has occurred between the lower portion 42 of the foundation concrete portion 4 surrounding the portion of the reinforcing bar shaft portion 20 extending between the upper projection portion 24 and the upper projection portion 24 (FIG. 9A). reference). The crack 44 typically extends downward from the upper protrusion 24 obliquely by 45 degrees. For this reason, the crack 44 is also referred to as an oblique crack 44.
In the following description, a state where no crack 44 is generated is also referred to as “state A”, and a state where the crack 44 is generated is also referred to as “state B”. In the present embodiment, it is assumed that the state is B.

In the state B, due to the presence of the crack 44, the mechanism III in the resistance mechanism model cannot be expected, and the resistance based on the mechanism III needs to be ignored.
On the other hand, it is necessary to consider the tensile yield strength of the reinforcing bar 16 as the mechanism I regardless of the presence or absence of the crack 44, but when the crack 44 exists, the tensile yield strength of the reinforcing bar 16 is The tensile yield strength of the shaft portion 20 of the reinforcing bar 16 can be considered. The cross-sectional area of the shaft portion 20 is larger than the cross-sectional area of the screw portion 21, and the tensile yield strength of the shaft portion 20 is larger than the tensile yield strength of the screw portion 21. For this reason, the fact that the tensile yield strength of the shaft portion 20 of the reinforcing bar 16 can be taken into account works advantageously in calculating the allowable bending moment sMa.

  FIG. 10 is a diagram for explaining the reason why the tensile yield strength Tby of the shaft portion 20 of the reinforcing bar 16 can be considered in the state B. When the crack 44 is generated, since the lower portion 42 of the foundation concrete portion 4 is attached to the reinforcing bar 16 below the crack 44, the generation of the resistance force Fsb due to the attachment can be expected. In general, the sum (Fsb + Tsy) of the resistance force Fsb and the tensile yield strength Tsy of the screw portion 21 is designed to be equal to or greater than the tensile yield strength Tby of the shaft portion 20, so that the tensile yield strength of the shaft portion 20 is increased. Reinforcing bars 16 can withstand up to Tby.

For this reason, in the allowable bending moment calculation step S <b> 2 of the present embodiment, when calculating the reinforcing bar 16 protruding upward from the end of the pile head 12 and the resistance of the foundation concrete portion 4 surrounding the reinforcing bar 16, While considering the tensile yield strength Tby of the shaft portion 20 of the bar 16, the allowable bending moment sMa is calculated ignoring the resistance acting on the foundation concrete portion 4 from the joining member 14. That is, the first allowable bending moment component sMa1 is calculated as the allowable bending moment sMa.
The calculation of the allowable bending moment sMa in consideration of the tensile yield strength Tby is, specifically, the calculation of the allowable bending moment sMa using a function that directly or indirectly includes the tensile yield strength Tby as a variable. Means that.

  According to the design method for the pile head joint described above, when it is assumed that the crack 44 is generated in the foundation concrete portion 4, that is, in the state B, the tensile yield strength Tby of the shaft portion 20 of the reinforcing bar 16 is considered. On the other hand, the allowable bending moment sMa can be accurately calculated by calculating the allowable bending moment sMa while ignoring the resistance acting on the foundation concrete portion 4 from the joining member 14. As a result, according to the above-described pile head joint design method, the pile head joint 10 having a sufficiently large allowable bending moment sMa can be realized with low-cost specifications.

  In addition, in the design method of a pile head junction part mentioned above, it is not necessary to consider the resistance based on the mechanism II. When considering the resistance based on the mechanism II, the sum (sMa1 + sMa2) of the first allowable bending moment component sMa1 and the second allowable bending moment component sMa2 may be calculated as the allowable bending moment sMa. Thus, if the resistance based on the mechanism II is taken into consideration, the allowable bending moment sMa is increased, and the specifications of the pile head 12, the joining member 14, the reinforcing bar 16, and the foundation concrete portion 4 can be suppressed. On the other hand, if the resistance based on the mechanism II is not taken into consideration, the allowable bending moment sMa becomes small, and a safety factor can be expected.

Hereinafter, the mechanisms I to III shown in FIGS. 9A to 9C will be described in detail.
[Mechanism I]
The resistance based on the mechanism I is a resistance due to the compressive force C generated in the pile head 12 and the tensile force T of the reinforcing bar 16. Here, as shown in FIG. 11, the pile head joint part 10 compresses the concrete of the foundation concrete part 4 (pile cap 4a) larger than the pile cross-sectional area Ac. For this reason, the compressive proof stress fc of the concrete which the pile head junction part 10 contact | connects rises by the local bearing effect. Pile cap cross-sectional area (support area) A ₀ and Kuidan area (Bearing area) Ac ratio is 5 times or more, Bearing effect of more than twice the expected pure compression. Note that due to the bearing effect, the compressive yield strength fc of the concrete is (A ₀ / Ac) ^0.5 times.

And as shown in FIG. 12, when the eccentric compression state by bending is considered, bearing pressure area Ac 'becomes smaller than pile cross-sectional area Ac, and also a bearing effect becomes large.
In calculating the resistance based on the mechanism I, that is, the first allowable bending moment component sMa1, an increase in yield strength due to the bearing effect is taken into account in the present embodiment by enlarging the virtual RC sectional diameter D.
As in this embodiment, when calculating the short-term allowable bending moment sMa of the pile head joint 10, the reinforcing bar 16 resists the tensile force T, and a cylindrical body having a virtual RC cross section is generated in the foundation concrete part 4. It is common to assume that the compressive force C is borne.

  In the case of the pile head joint method using the main reinforcement method as in this embodiment, it is described in the Architectural Institute of Japan “Guideline for Structural Design of Architectural Buildings (1988)” or Road Association “Pile Foundation Design Handbook 2006 Revised Edition”. A method of performing cross-sectional inspection of a pile head joint as a virtual RC cross section having a diameter D obtained by adding 200 mm to the pile diameter is common. Recently, in the Road Association “Road Bridge Specification / Explanation IV Substructure” revised in March 2012, the diameter D of the virtual RC cross section is set to 0.25Dp + 100mm to the pile diameter Dp. A method of checking as a diameter with 400 mm) added is shown. The Japan Road Association is reviewing and revising the diameter D of the virtual RC cross section. Therefore, also when calculating the allowable bending moment sMa in the present embodiment, it is possible to employ a cross-sectional verification method for the pile head joint 10 assuming a virtual RC cross-section.

  Here, FIG. 13 schematically shows a horizontal force test apparatus 50 for the pile head joint 10, and FIG. 14 shows a horizontal force application pattern. The horizontal force test apparatus 50 can apply a horizontal force by the actuator 51 and can measure the horizontal displacement d1. The member angle on the vertical axis of the graph shown in FIG. 14 is a value (d1 / 1600) obtained by dividing the horizontal displacement d1 by 1600, which is the distance from the pile head to the applied point. Further, the horizontal force test apparatus 50 can measure the vertical displacements d2 and d3.

15 to 18 are photographs in which the foundation concrete portion 4 of the pile head joint portion 10 is beaten after the horizontal force test using the horizontal force test apparatus 50 and the internal state of the foundation concrete portion 4 is photographed. And FIG. 19 is a figure for demonstrating that the virtual RC cross-sectional diameter D was set from the generation | occurrence | production state of the crack in the foundation concrete part 4. FIG.
In addition, in FIGS. 13-19, the up-down direction of the pile head junction part 10 is reversed from the relationship of the structure of the horizontal force test apparatus 50. FIG.

  As shown in FIGS. 15 to 18, after the horizontal force test, a crack 52 extending obliquely downward from the lower protrusion 23 at an angle of about 45 degrees is generated inside the foundation concrete portion 4. Therefore, a length (hereinafter also referred to as an effective adhesion length) in which the foundation concrete portion 4 adheres to the shaft portion 20 of the reinforcing bar 16 between the lower projection 23 and the upper end of the upper projection 24 is denoted by Le. In this case, a value obtained by adding 2Le to the pile diameter Dp is set as the maximum value of the diameter D of the virtual RC cross section. That is, the reinforcing bars 16 resist the tensile force, and the compressive force generated in the foundation concrete portion 4 is assumed to be borne by the cylindrical body having the virtual RC cross-sectional diameter D (where D = Dp + 2Le).

Preferably, between the diameter D of the virtual RC cross section and the pile diameter Dp, the following formula:
Dp + Le ≦ D ≦ Dp + 2Le
The diameter D is selected so that the relationship indicated by
More preferably, between the diameter D of the virtual RC cross section and the pile diameter Dp, the following formula:
Dp + 1.5Le ≦ D ≦ Dp + 2Le
The diameter D is selected so that the relationship indicated by
For example, the effective adhesion length Le is 140 mm or more and 200 mm or less.

  By selecting the diameter D of the virtual RC cross section in this way, the size of the virtual RC cross section diameter D can be set larger than the conventional one. As the virtual RC sectional diameter D is larger, the stress acting on the foundation concrete portion 4 and the pile head portion 12 can be reduced, and the allowable bending moment sMa can be calculated larger. As a result, according to the above configuration, a pile head joint having a sufficiently large allowable bending moment sMa can be realized with low-cost specifications.

Then, the first short-term allowable bending moment component sMa1 by mechanism I can be calculated as follows with reference to the Architectural Institute of Japan “Reinforced Concrete Structure Calculation Standards / Description (2010)”.
The first allowable bending moment component sMa1 of the pile head joint 10 with respect to the allowable axial force Na can be obtained by the following equation [Formula 1]. And the allowable axial force Na of a virtual RC cross section depends on the smaller one of N _{1 to} N ₃ .

  In addition, the cross-section primary moment Scn and the cross-section secondary moment Icn of the concrete portion in the virtual RC cross section are based on the following equation (2).

  The cross-sectional primary moment Sn and the cross-sectional secondary moment In regarding the neutral axis are expressed by the following equation (3).

In addition, the symbol in a formula represents the following, respectively, and FIG. 20 has shown the detail of these symbols. In the state B where the crack 44 is generated, the nominal cross-sectional area of the shaft portion 20 of the reinforcing bar 16 is used as the nominal cross-sectional area a _b of one reinforcing bar in the equation shown in [Equation 3].
a _b : nominal cross-sectional area of one reinforcing bar (mm ² )
D: Diameter of virtual RC cross section (mm)
D _b : Reinforcing bar arrangement diameter (mm)
d _c : Distance from the compression edge to the center of gravity of the compression side reinforcing bar (mm)
d _t : distance from the tension edge to the center of gravity of the tension side reinforcing bar (mm)
f _c : Allowable compressive stress level of foundation concrete part (N / mm ² )
f _b : allowable compressive stress level or allowable tensile stress level (N / mm ² ) of the reinforcing bar
I _cn : secondary moment of inertia (mm ⁴ ) with respect to neutral axis _created by compressed concrete surface
I _n : Sectional moment of inertia relative to the neutral axis (mm ⁴ )
_s M _a1 : First short-term allowable bending moment component (N · mm)
n _e : Young's modulus ratio R: Radius of virtual RC cross section (mm)
R _b : Reinforcing bar arrangement radius (mm)
S _cn : Cross section primary moment with respect to neutral axis _created by compressed concrete surface S _n : Cross section primary moment with respect to neutral axis (mm ³ )
X ₀ : Distance from the centroid of the virtual RC section to the neutral axis (mm)
θ: angle (rad) defining the neutral axis position in a circular cross section
θ _i : Reinforcing bar position arrangement angle (rad)

[Mechanism II]
The second short-term allowable bending moment component sMa2 by the mechanism II is due to the bearing resistance of the foundation concrete portion 4, and can be calculated by the following equation [Formula 4]. As the bearing pressure strength σ _c of the mechanism II, 2/3 · F _c which is an allowable compressive stress degree of the RC structure can be used.
However, with respect to bearing capacity sigma _c, it may be taken into consideration an increase in compressive strength due to restraint effect of the pile cap 4a which pile 2 is embedded.
In addition, in the allowable bending moment calculation step S2, the second short-term allowable bending moment component sMa2 may or may not be considered.
FIG. 21 shows details of symbols in the formula.

[Mechanism III]
Third short-term permissible bending moment component sMa3 by mechanism III, in Formula shown in equation (1), replacing the allowable tensile strength of reinforcement 16 in the compressive strength C _c due to unevenness of the bonding member 14 AIJ "reinforced concrete structure It can be calculated with reference to “Calculation Criteria / Comment (2010)” (RC allows local plasticization of concrete when it is allowed for a short time). It is considered that the strength of the compressive reaction force of the unevenness of the joining member 14 is determined by the bearing failure of the concrete (in this case, the oblique crack 44 from the joining member 14 does not occur. The yield strain of the reinforcing bar 16 is the compressive yield of the concrete. Greater than strain).
However, the third short-term allowable bending moment component sMa3 is ignored in the allowable bending moment calculation step S2 when it is assumed that the oblique crack 44 is generated in the pile head joint 10.
Also, if the expected resistance by mechanisms III, the joining member 14 is designed so as not to yield the compression force C _c.

[Method of designing a pile head joint according to the second embodiment]
Hereinafter, a method for designing a pile head joint according to the second embodiment will be described. In the following description of the embodiments, differences from the above-described embodiment will be mainly described, and description of the same or similar configurations will be omitted or simplified.

In the design method of the pile head joint according to the second embodiment, in the allowable bending moment calculation step S2,
A reinforcing bar extending between the upper part 40 of the foundation concrete part 4 surrounding the part of the shaft part 20 of the reinforcing bar 16 protruding upward from the end face of the pile head part 12, and the lower protruding part 23 and the upper protruding part 24. Assuming that no crack 44 occurs between the lower portion 42 of the foundation concrete portion 4 surrounding the portion of the sixteen shaft portions 20,
-When calculating the resistance of the reinforcing bar 16 protruding upward from the end of the pile head 12 and the resistance of the foundation concrete part 4 surrounding the reinforcing bar 16, the tensile yield strength Tsy of the screw part 21 of the reinforcing bar 16 is taken into consideration. In addition, the allowable bending moment sMa is calculated in consideration of the resistance acting on the foundation concrete portion 4 from the joining member 14, which is different from the method for designing the pile head joint according to the first embodiment.

That is, in the second embodiment, it is assumed that the crack 44 does not occur, and the first 'allowable bending moment component sMa1' by the mechanism I and the third allowable bending moment component sMa3 by the mechanism III are considered. . That is, as the allowable bending moment sMa, the sum (sMa1 ′ + sMa3) of the first allowable bending moment component sMa1 ′ and the third allowable bending moment component sMa3 is calculated.
The calculation method of the first 'allowable bending moment component sMa1' is as follows. In the equation shown in [Equation 3], the nominal sectional area of the screw portion 21 of the reinforcing bar 16 is defined as the nominal sectional area _ab of one reinforcing bar. Is different from the calculation method of the first allowable bending moment component sMa1 only in that is used.
On the other hand, the second allowable bending moment component sMa2 by the mechanism II may or may not be considered as in the case of the first embodiment.

Here, FIG. 22 is a diagram for explaining that the determination position of the reinforcing bar cross-sectional strength is different from that in the first embodiment (see FIG. 10). In the state A where the crack 44 is not generated, the resistance force Fsb from the foundation concrete part 4 cannot be expected as in the case of the state B. For this reason, it is necessary to consider the tensile yield strength Tsy of the screw portion 21 as the tensile yield strength of the reinforcing bar 16, and therefore, in the equation shown in [Equation 3], the nominal cross-sectional area a _{b of} one reinforcing bar As the nominal cross-sectional area of the screw portion 21 of the reinforcing bar 16 is used.

According to the design method of the pile head joint portion according to the second embodiment described above, when it is assumed that no crack 44 is generated in the foundation concrete portion 4, that is, in the case of the state A, the screw portion 21 of the reinforcing bar 16. The allowable bending moment sMa can be accurately calculated by considering the tensile yield strength Tsy and calculating the allowable bending moment sMa in consideration of the resistance acting on the foundation concrete portion 4 from the joining member 14. As a result, according to the pile head joint design method according to the second embodiment, the pile head joint 10 having a sufficiently large allowable bending moment sMa can be realized with low-cost specifications.
Note that calculating the allowable bending moment sMa in consideration of the tensile yield strength Tsy and the resistance acting on the foundation concrete portion 4 from the joint member 14 is specifically, directly or indirectly using the tensile yield strength Tsy as a variable. It is meant that the allowable bending moment sMa is calculated using the function included in the above and the function including the resistance acting on the foundation concrete portion 4 from the joining member 14 directly or indirectly as a variable.

[Pile head joint design method according to the third embodiment]
Hereinafter, a method for designing a pile head joint according to the third embodiment will be described.
The design method of the pile head joint according to the third embodiment is different from the design method of the pile head joint according to the first embodiment and the second embodiment in the allowable bending moment calculation step S2. FIG. 23 is a flowchart showing a schematic procedure of an allowable bending moment calculation step S2 in the method for designing a pile head joint according to the third embodiment.

As shown in FIG. 23, the allowable bending moment calculating step S2 in the pile head joint design method according to the third embodiment includes the first allowable bending moment calculating step S4, the second allowable bending moment calculating step S5, and the allowable bending moment. It has a moment selection step S6.
In the first allowable bending moment calculating step S4, the tensile yield strength Tsy of the screw portion 21 of the reinforcing bar 16 is considered, and the resistance acting on the foundation concrete portion 4 from the joint member 14 is taken into consideration as the allowable bending moment sMa. A first allowable bending moment sMaA is calculated. 1st permissible bending moment sMaA is permissible bending moment sMa calculated by the design method of the pile head joint part of a 2nd embodiment mentioned above.

  In the second allowable bending moment calculating step S5, the tensile yield strength Tby of the shaft portion 20 of the reinforcing bar 16 is considered, while the resistance acting on the foundation concrete portion 4 from the joining member 14 is ignored and the allowable bending moment sMa is determined. A second allowable bending moment sMaB is calculated. The second allowable bending moment sMaB is the allowable bending moment sMa calculated by the above-described pile head joint design method according to the first embodiment.

  In the allowable bending moment selection step S6, the first allowable bending moment sMaA and the second allowable bending moment sMaB are compared, and the smaller of the first allowable bending moment sMaA and the second allowable bending moment sMaB is set as the allowable bending moment sMa. select.

  According to the method for designing a pile head joint according to the third embodiment described above, by selecting the smaller one of the first allowable bending moment sMaA and the second allowable bending moment sMaB as the allowable bending moment sMa, Regardless of the occurrence or non-occurrence, it is possible to realize the pile head joint 10 having a sufficiently large allowable bending moment with a low cost specification in anticipation of safety.

Preferably, the compressive strength Cc acting on the joining member 14 from the foundation concrete portion 4 by the mechanism III is larger than the difference between the yield strength Tby of the shaft portion 20 of the reinforcing bar 16 and the yield strength Tsy of the shaft portion 20. (Cc ≧ Tby−Tsy). FIG. 24 shows a schematic procedure of the allowable bending moment selection step S6 in such a case (Cc ≧ Tby−Tsy).
The allowable bending moment selection step S6 includes a yield determination step S7, a first allowable bending moment selection step S8, and a second allowable bending moment selection step S9.
In the yield determination step S <b> 7, it is determined whether or not the upper protruding portion 24 yields by the compressive force Cc acting on the upper protruding portion 24 from the foundation concrete portion 4.

As a result of the determination in the yield determination step S7, when it is determined that the upper projection 24 yields, a first allowable bending moment selection step S8 is executed. In the first allowable bending moment selection step S8, the first allowable bending moment sMaA is selected as the allowable bending moment sMa.
On the other hand, as a result of the determination in the yield determination step S7, when it is determined that the upper protrusion 24 does not yield, the second allowable bending moment selection step S9 is executed. In the second allowable bending moment selection step S9, the second allowable bending moment sMaB is selected as the allowable bending moment sMa.

  According to the above configuration, when the yield strength of the upper protrusion 24 is smaller than the difference between the tensile yield strength Tby of the shaft portion 20 of the reinforcing bar 16 and the tensile yield strength Tsy of the screw portion 21, the first allowable bending is performed. Moment sMaA is selected as the allowable bending moment sMa. That is, when the yield strength of the upper projection 24 is smaller than the difference between the tensile yield strength Tby of the shaft portion 20 of the reinforcing bar 16 and the tensile yield strength Tsy of the screw portion 21, the upper projection 24 yields. Therefore, it is determined that the first allowable bending moment sMaA is smaller, and the first allowable bending moment sMaA is selected as the allowable bending moment sMa. Thereby, according to the above configuration, it is possible to accurately calculate the allowable bending moment sMa in anticipation of safety, and to realize the pile head joint portion 10 having a sufficiently large allowable bending moment with low-cost specifications. It is.

[Pile head joint design method according to the fourth embodiment]
Hereinafter, a method for designing a pile head joint according to the fourth embodiment will be described. Design method of pile joint according to the fourth embodiment, the specification in appropriateness determination step S3, in that for calculating the occurrence bending moment M _theta in consideration of the elastic rotation stiffness K _0, the first embodiment to the third embodiment It is different from the design method of the pile head joint of the form.
FIG. 25 shows a schematic procedure of the specification suitability determination step S3 in the pile head joint design method according to the fourth embodiment. The specification suitability determination step S3 includes an elastic rotational rigidity calculation step S10, a generated bending moment calculation step S11, and a bending moment comparison determination step S12.

In the elastic rotational stiffness calculation step S10, the elastic rotational stiffness K ₀ of the pile head joint 10 is determined based on the allowable bending moment sMa and the rotational angle (pile head rotational angle) θ ₀ of the pile head 12 corresponding to the allowable bending moment sMa. Is calculated. At this time, the elastic rotational rigidity K ₀ is calculated for each range of the axial force acting on the pile head joint 10 as follows.
When 0 <Axial force, elastic rotational rigidity K ₀ is not considered (fixed degree α ₀ = 1).
When Axial Force ≦ 0 The elastic rotational rigidity K ₀ is calculated by the following equation [Formula 5].

In the state B, the pile head rotation angle θ ₀ can be obtained by the following equation (6) according to the position of the reinforcing bar 16 where the cross-sectional strength is determined (see FIG. 10). FIG. 26 shows details of symbols in the formula. In [Expression 6], 0.5 sfa · ψb · lb ₁ and 0.5 sfa · ψb · lb ₂ represent resistances acting on the shaft portion 20 due to adhesion of the foundation concrete portion 4, respectively. The resistance increases in proportion to the distance from the position at which the cross-sectional strength is determined, and the tensile force acting on the shaft portion 20 is reduced or canceled according to the distance from the position at which the cross-sectional strength is determined. As a result, the distribution of force in the axial direction of the pile head 12 is as shown in FIG. 27, and the area of the hatched area in FIG. 27 is divided by ( _ab · Eb). The elongation amount δb can be obtained.

  In addition, about Ty in said [Formula 6], the tensile yield strength Tby of the axial part 20 of the reinforcing bar 16 can be used. Moreover, you may use what multiplied the coefficient of 0-1 to the tensile yield strength Tby of the axial part 20 as Ty.

On the other hand, in the state A, the pile head rotation angle θ ₀ can be obtained by the following equation (7) according to the position where the cross-sectional strength of the reinforcing bar 16 is determined (see FIG. 22). In [Expression 7], 0.5 sfa · ψb · (lb ₁ + lb ₂ ) represents the resistance acting on the shaft portion 20 due to the adhesion of the foundation concrete portion 4. The resistance increases in proportion to the distance from the position at which the cross-sectional strength is determined, and the tensile force acting on the shaft portion 20 is reduced or canceled according to the distance from the position at which the cross-sectional strength is determined. As a result, the force distribution in the axial direction of the pile head 12 is as shown in FIG. 28, and the area of the hatched area in FIG. 28 is divided by ( _ab · Eb). The elongation amount δb can be obtained.

  As for Ty in [Expression 7], the tensile yield strength Tsy of the screw portion 21 of the reinforcing bar 16 can be used. Further, as Ty, a value obtained by multiplying the tensile yield strength Tsy of the screw portion 21 by a coefficient of 0 to 1 may be used.

In the generated bending moment calculation step S11, under the condition that the axial compression force is not acting on the pile head 12 (axial force ≦ 0), the pile is considered in consideration of the elastic rotational rigidity K ₀ of the pile head joint 10. When an assumed horizontal force H is applied to the head 12, a generated bending moment M _θ generated in the pile head 12 is calculated. For this purpose, the elastic degree of elasticity α ₀ is obtained using the elastic rotational rigidity K ₀ as shown in the following [Equation 8]. Then, the generated bending moment M _θ is obtained by multiplying the bending moment (rigid joint generated bending moment) M ₀ generated when the horizontal force H is applied by the fixed degree α ₀ .

In bending moment comparison judgment step S12, it generates bending moment calculation step S11 generated bending moment M _theta computed at determines whether less than the allowable bending moment SMA. Result of the determination, is smaller than generating the bending moment M _theta allowable bending moment sMa (sMa> M _θ), selected in the specification selection step S1, pile head 12, the bonding member 14, reinforcement 16 and foundation concrete specifications of part 4 is determined to be appropriate, determines if the generated bending moment M _theta allowable bending moment SMA or (sMa ≦ M _θ), specification to be inappropriate. In other words, pile head 12, the bonding member 14, one of the conditions specification of reinforcement 16 and the foundation concrete portion 4 is determined to be appropriate, generates bending moment M _theta is less than the allowable bending moment SMA (SMA > M _θ ).

Note that L ₀ is the distance (rotation radius) from the outermost reinforcing bar to the rotation center O, but as shown in FIG. 26, it is simply from the end of the pile head 12 on the compression side to the tension side. It may be set to the same value as the distance to the center of the reinforcing bar 16, or may be set to the same value as the pile diameter Dp. The turning radius L ₀ is usually smaller than the distance from the end of the pile head 12 on the compression side to the center of the reinforcing bar 16 on the tension side or the pile diameter Dp, and if the turning radius L ₀ is set larger, it is safe. Can be expected. Of course, the turning radius L ₀ may be obtained more accurately by simulation or experiment.

Conventionally, in the case of the pile head joint portion 10 in which the foundation concrete portion 4 is adhered to the reinforcing bar 16, the generated bending moment M _θ generated at the pile head portion 12 is calculated on the assumption that the fixing degree α ₀ is 1. (M _θ = M ₀ ).
In this regard, the present inventors etc. studied, even when the reinforcement 16 is foundation concrete portion 4 are attached, even when calculating the bending moment M _theta generate fixed degree alpha ₀ without 1 If good, that is, it was found that if the elastic rotational stiffness K ₀ may be calculated occurrence bending moment M _theta in consideration exists. Specifically, it has been found that when the axial compressive force is not acting on the pile head 12, the fixing degree α ₀ may be calculated without being set to 1.

Therefore, in the method for designing a pile head joint according to the fourth embodiment, the elastic rotational rigidity K ₀ of the pile head joint 10 is taken into account under the condition that no axial compressive force acts on the pile head 12. Te, and it calculates the occurrence bending moment M _theta occurring pile head 12 when assuming the horizontal force H to pile head 12 is applied. Thus, by considering the elastic rotational rigidity K ₀ of the pile head joint 10, the fixing degree α ₀ can be made smaller than 1, and the generated bending moment M _θ can be made smaller. Thus, under the condition that the axial compressive force on the pile head 12 is not acting, it is possible to reduce the occurrence bending moment M _theta, is possible to reduce the bending moment M _theta generation than the allowable bending moment sMa it can. As a result, according to the method for designing a pile head joint according to the fourth embodiment, the pile head joint 10 having a sufficiently large allowable bending moment sMa can be realized with low-cost specifications.

The analysis method used in the design of the pile foundation 8 includes a spring element with discrete ground, a multi-layer ground analysis model in which the pile 2 is replaced with a beam element, and a solution of elastic bearing beams in a semi-infinite uniform ground. There is a method (Chang's method). The former is positioned as a detailed method and the latter as a simplified method. In the case of the detailed method, it is possible to evaluate the elastic rotational rigidity by providing a rotary spring directly on the pile head joint 10. On the other hand, in the simple method, in order to consider the elastic rotational rigidity of the pile head joint 10, it is necessary to introduce a fixing degree α ₀ . There are several calculation methods for calculating the pile head fixing degree α ₀ , but in the fourth embodiment described above, a method related to the solution of the elastic bearing beam by using the equation shown in [Equation 8]. Is used to calculate the pile head fixing degree α ₀ .
Under such circumstances, the elastic rotational rigidity K ₀ can be evaluated by using a formula other than that shown in [Equation 8], and can be evaluated not only by another simple method but also by a detailed method.

[Pile head joint design method according to the fifth embodiment]
Hereinafter, a method for designing a pile head joint according to the fifth embodiment will be described. Design method of pile joint according to the fifth embodiment, in the specification appropriateness determination step S3, and calculates the elastic rotational stiffness K ₀ with the larger one of the first allowable bending moment sMaA and second allowable bending moment sMaB In the point, it differs from the design method of the pile head junction part of 4th Embodiment.
FIG. 29 is a flowchart showing a schematic procedure of a method for designing a pile head joint according to the fifth embodiment. The pile head joint design method according to the fifth embodiment selects the larger one of the first allowable bending moment sMaA and the second allowable bending moment sMaB (maximum allowable bending moment: sMah = max (sMaA, sMaB)). Step S13 is further included. Then, an elastic rotational stiffness calculation step S10 ', by dividing the maximum allowable bending moment sMah in pile rotation angle theta _0, computes the elastic rotational stiffness K _0.

According to the method for designing a pile head joint according to the fifth embodiment described above, as in the case of the fourth embodiment, the bending moment generated under the condition that no axial compressive force is acting on the pile head 12. it is possible to reduce the M _theta, it is possible to reduce the bending moment M _theta generation than the allowable bending moment SMA.
On the other hand, when the elastic rotational rigidity K ₀ is evaluated as being underestimated, that is, when the fixing degree α ₀ is evaluated as being underestimated, the calculated generated bending moment M _θ is too small. When comparing the such generated bending moment M _theta an allowable bending moment SMA, there is a fear that there is a problem in the validity of the comparison result.
In this regard, according to the method for designing a pile head joint according to the above-described fifth embodiment, the maximum allowable bending moment sMah and the pile head which is the larger of the first allowable bending moment sMaA and the second allowable bending moment sMaB. Since the elastic rotational rigidity K ₀ of the pile head joint 10 is calculated based on the rotational angle θ _{0 of} 12, the magnitude of the elastic rotational rigidity K ₀ is prevented from being evaluated too low. As a result, according to the design method of the pile joint according to the fifth embodiment, the result of the validity collateral when comparing generated bending moment M _theta and allowable bending moment SMA, large enough The pile head joint 10 having the allowable bending moment sMa can be reliably realized with low-cost specifications.
Preferably, the maximum allowable bending moment sMah is an allowable bending moment obtained by accumulating all of the mechanisms I, II, and III. That is, the maximum allowable bending moment sMah is the sum of the first allowable bending moment component sMa1, the second allowable bending moment component sMa2, and the third allowable bending moment component sMa3.

  Preferably, in the elastic rotational rigidity calculation steps S10 and S10 ′, as shown in the above [Equation 6] or [Equation 7], the adhesion of the foundation concrete portion 4 to the shaft portion 20 of the reinforcing bar 16 is considered. It includes a step of calculating the amount of elongation δb of the reinforcing bar 16 located on the pull side.

When the elongation amount δb is calculated excessively, the rotation angle θ ₀ of the pile head 12 is evaluated excessively, and the elastic rotational rigidity K ₀ of the pile head joint 10 is evaluated excessively. When the elastic rotational stiffness K ₀ is evaluated as being underestimated, that is, when the fixing degree α ₀ is evaluated as being underestimated, the calculated bending moment M _θ is too small. When comparing the such generated bending moment M _theta an allowable bending moment SMA, there is a fear that there is a problem in the validity of the comparison result.
In this regard, according to the above configuration, the elongation amount δb of the reinforcing bar 16 is calculated in consideration of the adhesion of the foundation concrete portion 4 to the shaft portion 20 of the reinforcing bar 16, and therefore the elongation amount δb may be excessively calculated. Is prevented. As a result, according to the above arrangement, the validity of results when comparing generated bending moment M _theta allowable bending moment sMa is secured, pile head joint 10 with acceptable bending moment sMa large enough Can be reliably realized with low-cost specifications.

[Pile head joint design method according to the sixth embodiment]
Hereinafter, a method for designing a pile head joint according to the sixth embodiment will be described. The design method of the pile head joint according to the sixth embodiment is that the bending moment (rigid joint generated bending moment) M ₀ and the allowable bending moment obtained without considering the pile head rotation angle θ ₀ in the specification suitability determination step S3. In the point which compares sMa, it differs from the design method of the pile head junction part of 4th Embodiment.
FIG. 30 is a flowchart showing a schematic procedure of a method for designing a pile head joint according to the sixth embodiment. The pile head joint design method according to the sixth embodiment further includes a rigid joint occurrence bending moment comparison determination step S14. In rigid connections generated bending moment comparison judgment step S14, it is calculated by ignoring the elastic rotational stiffness K ₀ of the pile head joint 10, to the pile head 12 when assuming the horizontal force H is applied to the pile head 12 is rigidly joined generate the bending moment M ₀ for generating determines whether greater than the allowable bending moment SMA.
One of the conditions for determining that the specifications of the pile head 12, the joining member 14, the reinforcing bar 16, and the foundation concrete portion 4 are appropriate is that the rigid joint generated bending moment is determined in the rigid joint generated bending moment comparison determination step S <b> 14. It is determined that M ₀ is larger than the allowable bending moment sMa.

According to the method for designing a pile head joint according to the sixth embodiment described above, when the rigid joint generated bending moment M ₀ calculated by ignoring the rotation angle θ ₀ of the pile head 12 is larger than the allowable bending moment sMa. Since it is determined that the specifications of the pile head 12, the joining member 14, the reinforcing bar 16 and the foundation concrete part 4 are appropriate, the specifications of the pile head 12, the joining member 14, the reinforcing bar 16 and the foundation concrete part 4 are determined. Is prevented from becoming excessive. As a result, according to the method for designing a pile head joint according to the sixth embodiment, the pile head joint 10 having a sufficiently large allowable bending moment sMa can be reliably realized with low-cost specifications.

[Pile head joint design method according to the seventh embodiment]
Hereinafter, a method for designing a pile head joint according to the seventh embodiment will be described. Design method of pile joint according to the seventh embodiment, as allowable bending moment sMa approaches bending moment M _theta occurs, the specification selection step S1, the allowable bending moment calculation step S2, the specification appropriateness determination process S3 In the point which repeats, it differs from the design method of the pile head junction part which concerns on 1st thru | or 6th embodiment.
Preferably, as shown in FIG. 31, until the evolution bending moment M _theta is less than the allowable bending moment SMA, specification selection step S1, the allowable bending moment calculation step S2 and specifications appropriateness determination step S3 is repeated.
More preferably, rigid to the joining generating the bending moment M ₀ becomes larger than the allowable bending moment SMA, specification selection step S1, the allowable bending moment calculation step S2 and specifications appropriateness determination step S3 is repeated.

[Method for Manufacturing Pile Head Joint According to Eighth Embodiment]
Hereinafter, the manufacturing method of the pile head junction part concerning an 8th embodiment is explained. The method for manufacturing a pile head joint according to the eighth embodiment is appropriate according to the method for designing a pile head joint according to any one of the first to seventh embodiments described above, as shown in FIG. The pile head joint construction step S16 for constructing the pile head joint 10 is provided based on the specifications of the pile head 12, the joint member 14, the reinforcing bars 16, and the foundation concrete part 4 determined as follows.
In the pile head joint construction step S16, at least the pile 2 is built in the ground, the joint member 14 is welded to the outer peripheral surface of the pile head 12, the reinforcing bar 16 is joined to the joint member 14, and the pile head 12 is provided with a step of placing concrete around the periphery.

  According to the method for manufacturing a pile head joint according to the eighth embodiment, the pile head determined to be appropriate by the method for designing a pile head joint according to any one of the first to seventh embodiments described above. Since the pile head joint portion 10 is constructed based on the specifications of the portion 12, the joining member 14, the reinforcing bar 16, and the foundation concrete portion 4, the pile head joint portion 10 having a sufficiently large allowable bending moment sMa is reduced in cost. Can be realized with various specifications.

〔Example〕
1. Confirmation of validity of allowable bending moment and elastic rotational stiffness Repeated pile head horizontal force tests were conducted to verify the bending performance of pile head joints and the validity of the design method.
1) Test method and specifications of test body Table 1 shows the specifications of the test body, and FIG. 13 shows a horizontal force test apparatus 50 for the pile head joint 10. The test was carried out in a total of 6 pieces, taking the pile diameter (φ400 and φ600), axial force (0 kN and 1500 kN), reinforcing bar diameter (D35 and D41) and the number of reinforcing bars (6 and 10) as verification parameters. . The pile was a concrete-filled steel pipe simulating an outer shell steel pipe wound concrete pile (SC pile). The steel pipe was provided with an end plate corresponding to the wall thickness of the SC pile having the same diameter, and the same concrete as the foundation concrete portion was placed (filled) inside the steel pipe. The concrete-filled steel pipe is designed so that it does not break before the pile head joint breaks.
In order to measure the strain distribution of the reinforcing bars in the joining member, a plurality of strain gauges were attached to each reinforcing bar.
Further, the vertical displacements d2 and d3 were measured in order to measure the rotation angle θ ₀ of the pile head and to obtain the experimental value eK ₀ of the elastic rotational rigidity K ₀ .

As shown in FIG. 13, the upper part of the pile was joined to the horizontal force test device 50 by high-strength anchor joining by providing a square steel pipe from a position 100 mm above the foundation concrete surface. As a manufacturing method of the test body, the pile was placed on the upper side, the foundation concrete part was placed on the lower side, the formwork was assembled, and the concrete was cast to a predetermined height in the pile. After concrete curing, non-shrink mortar was cast at the flange position of the square steel pipe.
And with respect to each test body, horizontal force was performed with the horizontal force pattern shown in FIG.

2) Test result (1) Allowable bending moment Table 2 shows the experimental value Me of the allowable bending moment obtained from the test result and the allowable bending moment sMa (calculated value) obtained based on the mechanisms I, II, and III. .

As shown in Table 2, the test body 3 is a test body in which yielding of the reinforcing bar screw portion preceded the occurrence of oblique cracking. The ratio between the experimental value and the calculated value of the short-term allowable bending moment is 1.12 to 1.50 (average 1.28), and the short-term allowable bending moment can be accurately calculated based on the mechanisms I, II, and III. I understand that.
The calculated value is smaller than the experimental value. This is considered to be an effect that the resistance force of the mechanism II increases due to the bearing pressure effect and an effect that does not consider the frictional resistance around the embedded pile. It is considered preferable that the calculated value is smaller than the experimental value because safety is expected.

(2) the elastic rotational stiffness Table 3 shows a comparison of the rotational stiffness eK ₀ when short allowable bending moment at the time of the experiment and calculated cK ₀ of elastic rotational stiffness K ₀ (design value). The fixed degree α ₀ in the table defines the ratio of the equivalent value when considering the theoretical solution of the pile head bending moment when the pile head is completely fixed and the rotational rigidity of the pile head, and the N value of the ground = 1. 0 is a value obtained from the equation shown in the above [Equation 8]. Table 3 shows the following.
(I) The ratio of the elastic rotational stiffness cK ₀ obtained by the calculation to the rotational stiffness eK ₀ at the short-term tolerance obtained in the experiment is 1.00 to 2.85.
(Ii) The ratio of the elastic fixing degree α ₀ obtained by the calculation to the fixing degree α ₀ obtained in the experiment is 1.00 to 1.16.
(Iii) Since the ratio of the elastic fixing degree α ₀ obtained by the calculation with respect to the fixing degree α ₀ obtained by the experiment is substantially higher than 1.0, the elastic rotational rigidity cK ₀ obtained by the calculation is taken into consideration. It can be confirmed that the calculated generated bending moment _Mθ gives a safety evaluation at the time of design.

2. Confirmation of effectiveness of allowable bending moment, virtual RC cross-sectional diameter and elastic rotational stiffness 1) Pile stress integrated analysis Pile stress integrated analysis at pile head joints using joint members was performed under the following conditions.
(1) Building Superstructure: RC structure 12F scale Pile arrangement: 12 m x 36 m (1 x 6 span) (See Fig. 32)
(2) Design axial force Table 4 shows the design axial force.

(3) External force for design Horizontal force of upper part and foundation part: 66000 × 0.15 = 9900kN
Horizontal force of basic weight: 1862 × 0.1 = 186kN
External force for design 10100kN
(4) Ground conditions The ground conditions, pile specifications, and reinforcing bar specifications are shown in Tables 5 to 7 below.
As ground conditions, two cases with an N value of 1 or 3 at a depth of 0 to 8 m were set, and pile specifications and reinforcing bar specifications were selected for each case. Table 7 also shows pile head displacement, pile head bending, and shear force.

(5) Analytical method ・ The elastic rotation stiffness is calculated assuming that the location where the pull-out has occurred is fixed at 0.9. The other parts are regarded as having a fixed degree of 0.999, and the elastic rotational rigidity is calculated.
・ The short-term variable axial force at the four corners (Y1-X1 etc.) is set as 130% of the long-term axial force including the pile cap weight. The center pillar is reduced.
・ Surface layer ground N value is 1.0 and 3.0.
(6) Analysis Result FIG. 33 shows an NM curve of the pile P1 when the N value = 3.0. FIG. 34 shows an NM curve of the pile P1 when the N value = 1.0. FIG. 35 shows an NM curve of the pile P2 when the N value = 1.0.
(I) As shown in FIGS. 33 and 34, in a range where the compressive force is less than 0, the generated bending moment _Mθ is calculated in consideration of the elastic rotational rigidity, thereby reducing the generated bending moment _Mθ in the short-term allowable bending. It can be seen that the moment sMa can be made smaller.
As shown in (ii) Figure 35, also in the piles P2 constantly compressive force acts, by selecting the specification of Reinforcement (the shank diameter) appropriate, generates bending moment M _theta than short allowable bending moment sMa It can be seen that it can be made smaller.
In FIG. 35, when the shaft portion diameter of reinforcement is D41, it generates bending moment M _theta is but smaller than the short-term permissible bending moment SMA, which as this assumption, considering virtual RC sectional diameter D You must keep in mind. Considering the virtual RC cross-sectional diameter D, the first allowable bending moment component sMa1 by the mechanism I can be increased, and as a result, the allowable bending moment sMa can be increased. Under this assumption, the shank diameter of the reinforcement is in the case of D41, generating bending moment M _theta is smaller than the short-term permissible bending moment SMA.

The present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.
For example, according to the method for designing a pile head joint described above, a pile head joint other than the above-described pile head joint 10 can also be designed. FIG. 36 schematically shows a part of a pile head joint 100a that can be designed by the method for designing a pile head joint according to the first embodiment.
The pile head joint portion 100 a is different from the pile head joint portion 10 in that the pile head joint portion 100 a further includes a plurality of partition members 102 a corresponding to the joint member 14.
The partition member 102a has a bowl shape (groove shape) as shown in FIG. 37, for example, a U-shaped cross-sectional shape. The partition member 102a has a pair of rectangular side walls (first side walls) 104 and a semi-cylindrical side wall (second side wall) 106 that connects the first side walls 104 to each other. As shown in FIGS. 38 and 39, the first side walls 104 are arranged on both sides of the corresponding joining member 14 in the circumferential direction of the pile head 12, and are arranged in parallel with each other with the joining member 14 interposed therebetween. Is done. The partition member 102 a is fixed to the pile head 12 by welding the side edge of the first side wall 104 to the outer peripheral surface of the pile head 12, for example, spot welding or spot welding. The second side wall 106 is disposed to face the outer peripheral surface of the pile head 12 with the joining member 14 interposed therebetween.

The first side wall 104 and the second side wall 106 are laterally separated from the joining member 14 and the portion 20a of the shaft portion 20 (the joining member inner portion) 20a extending between the lower projection 23 and the upper end surface of the upper projection 24. There is a space inside the partition member 102a, that is, between the first side wall 104 and the second side wall 106 and the joining member inner portion 20a. The space is filled with concrete constituting the foundation concrete portion 4.
In addition, when the space inside the partition member 16a is narrow and it is difficult to fill with concrete, the hardener material such as mortar and grout is filled inside the partition member 102a before placing concrete in the foundation concrete portion 4. May be.

  According to the pile head joint portion 100a described above, one partition member 102a constitutes one partition wall 108 disposed on the side of the joint member inner portion 20a of the shaft portion 20 of the corresponding one reinforcing bar 16. The foundation concrete portion 4 can be partitioned into the inner side and the outer side in the radial direction of the reinforcing bar 16 at the side of the joint member inner portion 20 a of the shaft portion 20. By partitioning the foundation concrete portion 4 in this way, as shown in FIG. 40, the portion of the foundation concrete portion 4 (attachment portion) attached to the joint member inner portion 20 a of the shaft portion 20 in the radial direction of the reinforcing bar 16. (Proximal part)) 110 and the connection (distal part) 112 of the foundation concrete part 4 outside the partition wall 108 are cut off. Thereby, when a bending moment acts on the pile head joint part 100a, the adhesion part 110 of the foundation concrete part 4 is easy to be relatively displaced with respect to the distal part 112, and as shown in FIG. A force (resistance force due to adhesion) Fsb acting on the upper protrusion 24 is generated.

  As a result, in calculating the allowable bending moment sMa, the resistance force Fsb can be considered in addition to the tensile yield strength Tsy of the screw portion 21, but the relationship represented by Tby ≦ Tsy + Fsb is usually established. As a result, when calculating the allowable bending moment sMa, it is possible to consider the tensile yield strength Tby of the shaft portion 20 of the reinforcing bar 16 regardless of whether or not cracking has occurred in the foundation concrete portion 4, and the allowable bending moment. Can be easily calculated. That is, the second allowable bending moment sMaB can be calculated as the allowable bending moment sMa, and the pile head joint design method according to the first embodiment can be employed.

FIG. 41 schematically shows a part of a pile head joint 100b that can be designed by the method for designing a pile head joint according to the first embodiment.
The pile head joint portion 100b is different from the pile head joint portion 100a in that it has a partition member 102b instead of the plurality of partition members 102a.
As shown in FIGS. 41 to 43, the partition member 102 b has a cylindrical peripheral wall 114, and the peripheral wall 114 is arranged so as to surround the pile head 12 with a predetermined space. The peripheral wall 114 is disposed so as to collectively surround the joint member inner portions 20a of the plurality of joining members 14 and the plurality of reinforcing bars 16, and within the joint members of the plurality of joining members 14 and the plurality of reinforcing bars 16. One partition wall 116 disposed on the side of the portion 20a is formed.

  According to the above-described pile head joint portion 100b, the peripheral wall 114 disposed so as to surround the pile head portion 12 and the attached portion 110 of the foundation concrete portion 4 and the foundation concrete portion 4 in the radial direction of the reinforcing bar 16 The connection with the distal portion 112 can be interrupted with a simple configuration.

Preferably, as illustrated in FIGS. 41 to 43, the partition member 102 b includes an annular plate 118 that is continuous with the upper end of the peripheral wall 114 and is disposed along the end surface of the pile head 12. The annular plate 118 has a plurality of openings 120 through which the reinforcing bars 16 are inserted.
According to the said structure, the partition wall 116 can be arrange | positioned easily by arrange | positioning the cyclic | annular board 118 on the end surface of the pile head part 12. FIG. For example, the partition member 102b can be easily fixed to the pile head 12 by fixing the annular plate 118 to the pile head 12 with a bolt (not shown).

  Finally, the method for designing a pile head joint according to the above-described embodiment is an invention related to the method. However, according to the present invention, a program for causing a computer to execute the method is also provided as an invention of an object. Of course it is possible.

DESCRIPTION OF SYMBOLS 1 Structure 2 Pile 4 Foundation concrete part 4a Pile cap 5 Beam 6 Superstructure 8 Pile foundation 10,100a, 100b Pile head joint 12 Pile head 14 Joint member (joint coupler)
16 Reinforcing bar 17 Concrete part 18 End plate 19 Outer steel pipe 20 Shaft part 20a Joining member inner part 21 Screw part 22 Fixing body 23 Lower projection part 24 Upper projection part 26 Screw hole 28 Notch 29 Fork part 30 Connecting part 32 Reinforcement Beam portion 34 Reinforcing rib portion 35 Curved surface 36 Groove surface 38 Weld bead 40 Upper portion 42 Lower portion 44 Crack 50 Horizontal force test device 51 Actuator 52 Crack 102a, 102b Partition member 104 First side wall 106 Second side wall 108 Partition Wall 110 attachment part (proximal part)
112 Distal portion 114 Peripheral wall 116 Partition wall 118 Annular plate 120 Opening

Claims (11)

A pile head,
A plurality of joining members fixed to the outer peripheral surface of the pile head;
A plurality of reinforcing bars respectively attached to the pile head via the joining member;
A foundation concrete portion constituted by concrete surrounding the pile head, the plurality of joining members, and the plurality of reinforcing bars,
The reinforcing bar is
A shaft portion having irregularities on the surface;
A screw portion connected to one end side of the shaft portion and having a smaller cross-sectional area than the shaft portion, and
The joining member is
A lower protrusion fixed to the outer peripheral surface of the pile head;
An upper protrusion fixed to the outer peripheral surface of the pile head, and an upper protrusion disposed above the lower protrusion in the axial direction of the pile head;
A screw portion of the reinforcing bar is coupled to the lower protrusion,
The shaft portion of the reinforcing bar extends between the lower protrusion portion and the upper protrusion portion in the axial direction of the pile head portion, and protrudes upward from the end surface of the pile head portion. ,
In the design method of the pile head joint,
A specification selection step of selecting specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part;
Based on the specification selected in the specification selection step, an allowable bending moment calculation step for calculating an allowable bending moment of the pile head joint,
A specification suitability determination step for determining suitability of the specification selected in the specification selection step based on the allowable bending moment, and
In the allowable bending moment calculation step,
A portion of a foundation concrete portion surrounding a portion of a shaft portion of the reinforcing bar protruding upward from an end surface of the pile head, and a shaft portion of the reinforcing bar extending between the lower protrusion portion and the upper protrusion portion. Assuming that cracks occur between the part of the foundation concrete part surrounding the part,
While taking into account the tensile yield strength of the shaft portion of the reinforcing bar, the allowable bending moment is calculated by ignoring the resistance acting on the foundation concrete portion from the joint member. Design method. A pile head,
A plurality of joining members fixed to the outer peripheral surface of the pile head;
A plurality of reinforcing bars respectively attached to the pile head via the joining member;
A foundation concrete portion constituted by concrete surrounding the pile head, the plurality of joining members, and the plurality of reinforcing bars,
The reinforcing bar is
A shaft portion having irregularities on the surface;
A screw portion connected to one end side of the shaft portion and having a smaller cross-sectional area than the shaft portion, and
The joining member is
A lower protrusion fixed to the outer peripheral surface of the pile head;
An upper protrusion fixed to the outer peripheral surface of the pile head, and an upper protrusion disposed above the lower protrusion in the axial direction of the pile head;
A screw portion of the reinforcing bar is coupled to the lower protrusion,
The reinforcing bar extends between the lower protrusion and the upper protrusion in the axial direction of the pile head, and extends upward from an end surface of the pile head.
In the design method of the pile head joint,
A specification selection step of selecting specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part;
Based on the specification selected in the specification selection step, an allowable bending moment calculation step for calculating an allowable bending moment of the pile head joint,
A specification suitability determination step for determining suitability of the specification selected in the specification selection step based on the allowable bending moment, and
In the allowable bending moment calculation step,
A portion of a foundation concrete portion surrounding a portion of a shaft portion of the reinforcing bar protruding upward from an end surface of the pile head, and a shaft portion of the reinforcing bar extending between the lower protrusion portion and the upper protrusion portion. Assuming that no cracks occur between the foundation concrete part surrounding the part,
Considering the tensile yield strength of the screw part of the reinforcing bar and calculating the allowable bending moment in consideration of the resistance acting on the foundation concrete part from the joint member, Design method. A pile head,
A plurality of joining members fixed to the outer peripheral surface of the pile head;
A plurality of reinforcing bars respectively attached to the pile head via the joining member;
A foundation concrete portion constituted by concrete surrounding the pile head, the plurality of joining members, and the plurality of reinforcing bars,
The reinforcing bar is
A shaft portion having irregularities on the surface;
A screw portion connected to the lower end side of the shaft portion and having a smaller cross-sectional area than the shaft portion, and
The joining member is
A lower protrusion fixed to the outer peripheral surface of the pile head;
An upper protrusion fixed to the outer peripheral surface of the pile head, and an upper protrusion disposed above the lower protrusion in the axial direction of the pile head;
A screw portion of the reinforcing bar is coupled to the lower protrusion,
The reinforcing bar extends between the lower protrusion and the upper protrusion in the axial direction of the pile head, and extends upward from an end surface of the pile head.
In the design method of the pile head joint,
A specification selection step of selecting specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part;
Based on the specification selected in the specification selection step, an allowable bending moment calculation step for calculating an allowable bending moment of the pile head joint,
A specification suitability determination step for determining suitability of the specification selected in the specification selection step based on the allowable bending moment, and
The allowable bending moment calculation step includes:
Considering the tensile yield strength of the screw portion of the reinforcing bar and calculating the first allowable bending moment as the allowable bending moment in consideration of the resistance acting on the foundation concrete portion from the joint member Bending moment calculation process;
While considering the tensile yield strength of the shaft portion of the reinforcing bar, the second permissible bending moment is calculated as the permissible bending moment ignoring the resistance acting on the foundation concrete portion from the joining member Bending moment calculation process;
An allowable bending moment selection step of comparing the first allowable bending moment and the second allowable bending moment and selecting a smaller one of the first allowable bending moment and the second allowable bending moment as the allowable bending moment; A method for designing a pile head joint, comprising: In the allowable bending moment selection step, when the yield strength of the upper protrusion is smaller than the difference between the tensile yield strength of the shaft portion and the tensile yield strength of the screw portion, the first allowable bending moment is the allowable bending moment. The pile head joint design method according to claim 3, wherein the pile head joint is selected as a moment. The specification suitability determination step includes
Based on the rotation angle of the pile head corresponding to the allowable bending moment and the allowable bending moment, an elastic rotation stiffness calculation step of calculating the elastic rotation stiffness of the pile head joint,
The pile head when an assumed horizontal force is applied to the pile head in consideration of the elastic rotational rigidity of the pile head joint, under the condition that no axial compression force is applied to the pile head. The generated bending moment calculation process for calculating the generated bending moment generated in the part,
A bending moment comparison and determination step for determining whether or not the generated bending moment calculated in the generated bending moment calculation step is smaller than the allowable bending moment,
One of the conditions for determining that the specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part are appropriate is that the generated bending moment is the allowable bending moment in the bending moment comparison determining step. Is determined to be smaller than the
The design method of the pile head junction part of any one of Claims 1 thru | or 4 characterized by the above-mentioned. The specification suitability determination step includes
Elastic rotation for calculating the elastic rotational rigidity of the pile head joint based on the larger of the first allowable bending moment and the second allowable bending moment and the rotation angle of the pile head corresponding to the allowable bending moment Stiffness calculation process;
The pile head when an assumed horizontal force is applied to the pile head in consideration of the elastic rotational rigidity of the pile head joint, under the condition that no axial compression force is applied to the pile head. The generated bending moment calculation process for calculating the generated bending moment generated in the part,
A bending moment comparison determination step of determining whether or not the generated bending moment of the pile head calculated in the generated bending moment calculation step is smaller than the allowable bending moment,
One of the conditions for determining that the specifications of the pile head, the joining member, the reinforcing bar, and the foundation concrete part are appropriate is that the generated bending moment is the allowable bending moment in the bending moment comparison determining step. Is determined to be smaller than the
The pile head joint design method according to claim 3 or 4, characterized in that The elastic rotational rigidity calculation step includes a step of calculating an extension amount of a reinforcing bar located on a tension side among the reinforcing bars in consideration of adhesion of the foundation concrete portion to a shaft portion of the reinforcing bar,
The pile head joint design method according to claim 5 or 6, characterized in that The bending bending moment generated at the pile head when the assumed horizontal force is applied to the pile head, calculated by ignoring the elastic rotational rigidity of the pile head joint, is the allowable bending moment. Further comprising a rigid joint occurrence bending moment comparison and determination step of determining whether or not greater than
One of the conditions for determining that the specifications of the pile head, the joint member, the reinforcing bar, and the foundation concrete part are appropriate is that the rigid joint generated bending moment is determined in the rigid joint generated bending moment comparison determination step. , Is determined to be greater than the allowable bending moment.
The method for designing a pile head joint according to any one of claims 5 to 7. In the allowable bending moment calculation step,
It is assumed that the resistance bending moment of the reinforcing concrete projecting upward from the end of the pile head and the foundation concrete portion surrounding the reinforcement is the bending moment borne by the virtual RC section including the end face of the pile head,
The diameter of the pile head is Dp,
The diameter of the virtual RC cross section is D,
When the length of the foundation concrete portion attached to the shaft portion of the reinforcing bar between the lower protrusion portion and the upper end of the upper protrusion portion in the axial direction of the pile head is defined as Le:
Dp + Le ≦ D ≦ Dp + 2Le
The method for designing a pile head joint according to any one of claims 1 to 8, wherein the diameter D of the virtual RC cross section is set and calculated so as to satisfy the relationship represented by:   10. The method according to claim 1, wherein the specification selection step, the allowable bending moment calculation step, and the specification suitability determination step are repeated so that the allowable bending moment approaches the generated bending moment. The design method of the pile head joint part as described in a term.   Based on the specifications of the pile head, the joint member, the reinforcing bar, and the foundation concrete part determined to be appropriate by the method for designing a pile head joint according to any one of claims 1 to 10. A method for manufacturing a pile head joint comprising a pile head joint construction step for constructing the pile head joint.

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