Stress transfer structure of cast-in-place steel pipe concrete piles

Abstract

To provide a stress transmission structure of a cast-in-place steel pipe concrete pile which can be easily formed, in which bleeding affection does not occur, and which is preferable in stress transmission performance.SOLUTION: In a stress transmission structure of a cast-in-place steel pipe concrete pile 1 formed of a steel pipe and concrete, a plurality of through holes 22 with a substantially circular shape in side view is provided at an end 21a of a cylindrical steel pipe 21 around and inside which concrete is filled with an interval in a circumference direction. Four to thirty-two through holes can be provided with a constant interval in a circumference direction according to a steel pipe size. The through holes can be provided by arbitrary steps of one to ten steps with an interval in an axial direction of the steel pipe.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a stress transmission structure for cast-in-place steel pipe concrete piles formed from steel pipes and concrete. [Background technology]

[0002] Cast-in-place steel pipe concrete piles are known, in which the upper part of the pile is made of steel pipe concrete and the lower part is made of cast-in-place concrete (see Patent Documents 1-3, etc.). In such composite pile structures, a joint is created at the boundary between the steel pipe concrete section and the reinforced concrete section.

[0003] Normally, piles are primarily subjected to vertical loads, and the presence of joints does not impede the vertical load. However, during an earthquake, if a large horizontal force acts on the pile head, bending moments and shear forces act on the pile, potentially making the joint a weak point.

[0004] Therefore, Patent Documents 1-3 provide a joint structure for reinforcing the joint between the steel pipe concrete section and the reinforced concrete section. Specifically, protrusions are provided on the inner surface of the steel pipe to increase the adhesion force (frictional resistance) with the concrete filling the inside of the steel pipe. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 5717118 [Patent Document 2] Japanese Patent Publication No. 2006-138095 [Patent Document 3] Special Publication No. 5-62171 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, creating a protrusion on the inner surface of a steel pipe can be difficult and time-consuming during manufacturing. On the other hand, Patent Document 3 describes a structure in which a rectangular opening in side view is provided in the peripheral wall of a steel pipe so that concrete can also be poured around the outer surface of the steel pipe.

[0007] A rectangular opening in side view allows drilling from the outside of the steel pipe, which is more efficient than creating a protrusion on the inner surface of the steel pipe. However, it requires cutting all four sides, resulting in a high number of steps per opening, and creating multiple openings is quite time-consuming.

[0008] Furthermore, a challenge exists in that concrete bleeding tends to accumulate in the corners of rectangular openings, leading to the formation of voids in the hardened concrete. To prevent such voids from forming in the concrete, measures such as mixing special additives into the concrete during filling are necessary.

[0009] Therefore, the present invention aims to provide a stress transmission structure for cast-in-place steel pipe concrete piles that is easy to manufacture, does not suffer from bleeding effects, and has excellent stress transmission performance. [Means for solving the problem]

[0010] To achieve the above objective, the stress transmission structure for a cast-in-place steel pipe concrete pile of the present invention is a stress transmission structure for a cast-in-place steel pipe concrete pile formed by a steel pipe and concrete, characterized in that a plurality of through holes, which are approximately circular in side view or polygonal in side view with their vertices facing upward in side view, are provided at intervals in the circumferential direction at the end of a cylindrical steel pipe filled with concrete around and inside.

[0011] Here, the through-holes can be configured to be provided at equal intervals in the circumferential direction, from 4 to 32 locations, depending on the size of the steel pipe. Furthermore, the through-holes can be configured to be provided in any number of stages, from 1 to 10, at intervals along the axial direction of the steel pipe.

[0012] Furthermore, in such cast-in-place steel pipe concrete piles, it is preferable that the end of the steel pipe be positioned near the boundary between the steel pipe concrete section and the reinforced concrete section, at the enlarged base of an enlarged base pile, or at the enlarged diameter section of an intermediate enlarged diameter pile.

[0013] Furthermore, the structure can be configured such that reinforcing pipes protruding from the outer circumference and into the interior of the steel pipe are inserted into the through-hole. Alternatively, the structure can be configured such that a reinforcing section for the opening is provided by welding steel material around the through-hole. [Effects of the Invention]

[0014] The stress transmission structure for the cast-in-place steel pipe concrete pile of the present invention, configured in this way, has multiple through holes at the end of a cylindrical steel pipe, which is filled with concrete around its periphery and interior, spaced apart in the circumferential direction. These holes are approximately circular in side view or polygonal in shape, with their vertices facing upwards in side view.

[0015] Through-holes that are roughly circular in side view or polygonal with their vertices on the upper side in side view can be easily drilled from the outside of the steel pipe, and even if concrete is filled around these circular or polygonal through-holes, bleeding does not accumulate. Furthermore, the connection between the concrete inside and outside the steel pipe through the through-hole increases the adhesion between the steel pipe and the concrete.

[0016] Furthermore, if four to 32 through-holes are provided at equal intervals in the circumferential direction depending on the size of the steel pipe, the adhesion force can be obtained without bias in the circumferential direction of the pile, and the reduction in the load-bearing capacity of the steel pipe 21 can be kept within an acceptable range.

[0017] Furthermore, by positioning the end of the steel pipe, which has a through hole, near the boundary between the steel pipe concrete section and the reinforced concrete section, it becomes possible to effectively transmit the tensile force of the reinforcing bars in the reinforced concrete section to the steel pipe in the steel pipe concrete section, thereby improving stress transmission performance.

[0018] On one hand, by arranging the end of the steel pipe provided with a through hole at the enlarged bottom part of the under-reamed pile or the enlarged diameter part of the intermediate enlarged diameter pile, the pull-out resistance of the inclined part that is widened and contacts the ground can be effectively transmitted to the steel pipe of the steel pipe concrete part.

[0019] Moreover, if a reinforcing pipe protruding to the outer peripheral side and the inside of the steel pipe is inserted into the through hole, it is possible to suppress the reduction of the bearing capacity of the steel pipe due to the drilling of the through hole and increase the bearing resistance. Here, by providing an opening reinforcement part by welding steel materials around the through hole, it is also possible to suppress the reduction of the bearing capacity of the steel pipe.

Brief Description of the Drawings

[0020] [Figure 1] It is an explanatory drawing showing the overall configuration of the cast-in-place steel pipe concrete pile of the present embodiment. [Figure 2A] It is an explanatory drawing showing the configuration of the steel pipe concrete part of the cast-in-place steel pipe concrete pile. [Figure 2B] FIG. 2A is an explanatory drawing exemplifying the configuration of a steel pipe concrete part with a different number of through holes. [Figure 3] It is an explanatory drawing showing the configuration near the enlarged bottom part of the under-reamed pile of Example 1. [Figure 4] It is a drawing for explaining a test specimen of a model experiment for confirming the effect of providing a through hole. (a) is an explanatory drawing of a test specimen of a straight pile, and (b) is an explanatory drawing of a test specimen of an under-reamed pile. [Figure 5] It is a graph showing the experimental results in relation to displacement and load. [Figure 6] It is a graph showing the experimental results in relation to the width of the through hole (total window area) and the maximum load. [Figure 7] It is a graph showing the experimental results in relation to the width of the through hole (total window area) and the shear stress. [Figure 8] It is an explanatory drawing showing the configuration near the enlarged diameter part of the intermediate enlarged diameter pile of Example 2. [Figure 9] It is an explanatory drawing showing the overall configuration of another intermediate enlarged diameter pile of Example 2. [Figure 10]This is an explanatory diagram showing the configuration in which a reinforcing pipe is inserted into the through-hole of the steel pipe in Example 3. [Figure 11] This is an explanatory diagram conceptually illustrating the function of the reinforcing pipe in Example 3. [Figure 12] This is a conceptual diagram illustrating the function of reinforcing pipes in the case of enlarged-base piles. [Figure 13A] This is a conceptual diagram illustrating the function of a through-hole without reinforcing pipes. [Figure 13B] This is a conceptual diagram illustrating the function of a through-hole without reinforcing pipes in the case of an enlarged-base pile. [Figure 14] This is an explanatory diagram showing a configuration in which an opening reinforcement portion is provided around the through-hole of the steel pipe in Example 4. [Modes for carrying out the invention]

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is an explanatory diagram showing the overall configuration of the cast-in-place steel pipe concrete pile 1 of this embodiment. Figure 2A is an explanatory diagram showing the configuration of the steel pipe concrete section 2 of the cast-in-place steel pipe concrete pile 1.

[0022] First, to explain the overall structure, the cast-in-place steel pipe concrete pile 1, as shown in Figure 1, comprises a steel pipe concrete section 2 formed at the top and a reinforced concrete section 3 formed at the bottom. Furthermore, the cast-in-place steel pipe concrete pile 1 described in this embodiment is an enlarged-base pile in which a truncated cone-shaped enlarged base section 11 is provided at the lower end of the reinforced concrete section 3.

[0023] The head of the cast-in-place steel pipe concrete pile 1 is connected to a reinforced concrete footing 6. The superimposed load acting on the foundation of a building or other structure is transmitted to the cast-in-place steel pipe concrete pile 1 via this footing 6.

[0024] The steel pipe concrete section 2 formed below the footing 6 is mainly composed of a cylindrical steel pipe 21 and concrete 4 that fills its interior and exterior. Here, for the steel pipe 21, for example, a steel pipe material with a diameter of about 600 mm to 2500 mm can be used.

[0025] Furthermore, multiple pile head anchoring bars 12 are attached to the outer surface of the upper end of the steel pipe 21 by welding or other means. The pile head anchoring bars 12 that protrude upward from the steel pipe 21 are embedded in the footing 6.

[0026] On the other hand, during an earthquake, the footing 6 moves horizontally significantly from the bottom of the pile, causing bending moments and shear forces to act on the joint between the steel pipe concrete section 2 and the reinforced concrete section 3.

[0027] Therefore, in order to counteract such forces, through holes 22 are drilled near the lower end 21a of the steel pipe 21 to increase the adhesion strength with the concrete 4. These through holes 22 are approximately circular in side view and are provided in multiples at intervals in the circumferential direction of the steel pipe 21.

[0028] The diameter of the through-hole 22 is preferably set to at least three times the maximum aggregate diameter of the concrete 4, taking into consideration factors such as the ease with which the concrete 4 can pass through and the magnitude of the adhesion force obtained at one location. As a guideline, a through-hole 22 with a diameter of approximately 75 mm to 250 mm can be provided, for example, with a diameter of approximately 150 mm.

[0029] Furthermore, if multiple through holes 22 are provided at intervals in the circumferential direction, then any number of through holes, from one to five, can be provided at intervals in the axial direction (pile axis direction) of the steel pipe 21 at the end 21a of the steel pipe 21. Figure 1 illustrates an example in which three stages of through holes 22 are provided at the lower end 21a of the steel pipe 21.

[0030] As shown in Figure 2A, the through holes 22 are provided at equal intervals in the circumferential direction. This figure illustrates an example where four through holes 22 are provided at equal intervals in the circumferential direction. The number of through holes 22 is not limited to this. For example, as shown in Figure 2B, eight through holes 22 can be provided at equal intervals in the circumferential direction at the lower end 21a of the steel pipe 21A.

[0031] In other words, the through-holes 22 can be provided at equal intervals in the circumferential direction in any number from 4 to 32, depending on the size of the steel pipe. By providing the through-holes 22 at equal intervals, the adhesion force obtained in the circumferential direction of the pile can be made even. For example, a steel pipe 21 with a diameter of 600 mm can have 4 through-holes 22 per row, and a steel pipe 21 with a diameter of 2500 mm can have 24 through-holes 22 per row. Typically, about 4 to 8 through-holes 22 are provided at equal intervals in the circumferential direction.

[0032] On the other hand, the reinforced concrete section 3 formed at the lower part of the cast-in-place steel pipe concrete pile 1 comprises a reinforcing cage 31 extending in the axial direction and concrete 4 filled around it, as shown in Figure 1.

[0033] This reinforcing cage 31 is manufactured in a cylindrical shape and is mainly composed of a plurality of main reinforcing bars 31b arranged at intervals in the circumferential direction as shown in Figure 2A, and annular stirrup reinforcing bars 31c arranged at intervals in the pile axis direction as shown in Figure 1.

[0034] Furthermore, the upper end portion 31a of the reinforcing cage 31 is housed inside the steel pipe 21. The upper end portion 31a housed inside the lower part (end portion 21a) of the steel pipe 21 is wrapped around the area where the three layers of through holes 22 are provided, as shown in Figure 1.

[0035] For example, if the diameter of the main reinforcement bar 31b is d, the axial range (length) of the end 21a of the steel pipe 21 where the through-hole 22 is provided can be in the range of approximately 40d-45d. The diameter of the through-hole 22 can also be set considering a size that can be appropriately provided without compromising the load-bearing capacity of the steel pipe 21, depending on the diameter (steel pipe size) of the steel pipe 21. Furthermore, the area around the through-hole 22 can be reinforced as needed, as will be described later.

[0036] Furthermore, by positioning the upper end portion 31a of the reinforcing cage 31 in approximately the same area as the area where the through-hole 22 is provided and overlapping it, the tensile force of the main reinforcing bars 31b can be effectively transmitted to the steel pipe 21.

[0037] Furthermore, as shown in Figure 1, even when the upper end 21b of the steel pipe 21 is connected to the reinforced concrete section, the stress transfer performance with the reinforcement can be improved by providing a through-hole 22. Specifically, the lower part of the pile head reinforcement bar 121, whose upper part is embedded in the footing 6, is inserted into the interior of the upper end 21b of the steel pipe 21 and overlaps with the area where the through-hole 22 is provided. In this way, the tensile force of the pile head reinforcement bar 121 can be effectively transferred to the steel pipe 21.

[0038] Furthermore, Figure 1 illustrates a case where three through-holes 22 are provided in the upper end 21b of the steel pipe 21. However, if there is concern about a reduction in the load-bearing capacity of the steel pipe 21 due to the drilling of the through-holes 22, the reduction in load-bearing capacity of the end 21b can be suppressed by providing an opening reinforcement section 23, such as by welding an annular steel plate around the through-holes 22. This opening reinforcement section 23 can be provided by fixing an annular steel plate to either the outer or inner surface of the steel pipe 21, or by fixing an annular steel plate to both the outer and inner surfaces of the steel pipe 21.

[0039] Next, the construction method for the cast-in-place steel pipe concrete pile 1 of this embodiment will be described. First, before construction, through holes 22, which are roughly circular in shape when viewed from the side, are drilled near the lower end 21a of the steel pipe 21, at the designed number and intervals.

[0040] The through-hole 22, which is roughly circular in side view, can be easily drilled by simply marking the center of the circle on the outer surface of the steel pipe 21, then punching a punch at that center point and automatically rotating the gas cutting machine.

[0041] Meanwhile, at the construction site, pile holes 5 are excavated in the ground G using methods such as earth drilling or reverse drilling. Then, a steel pipe 21 is lifted above the pile holes 5 by a crane and installed in the upper part of the pile holes 5. At this stage, the inside of the steel pipe 21 is either hollow or filled with stabilizing fluid for excavation.

[0042] Next, the reinforcing cage 31 is lifted above the pile hole 5, inserted into the steel pipe 21, and then lowered. Although not shown in the diagram, a suspension bar longer than the steel pipe 21 is connected to the upper end 31a of the reinforcing cage 31, and by suspending the reinforcing cage 31 via this suspension bar, the reinforcing cage 31 can be lowered to the position shown in Figure 1.

[0043] Then, by measuring the amount of protrusion of the suspension reinforcement from the pile hole 5, the upper end 31a of the reinforcing cage 31 can be aligned with the range in which the through-hole 22 of the end 21a of the steel pipe 21 is provided. After positioning the steel pipe 21 and the reinforcing cage 31 in the predetermined positions in the pile hole 5 in this manner, a tremie pipe is erected in the pile hole 5, and concrete 4 is poured using the tremie pipe. The concrete 4 is poured continuously from the bottom of the hole up to the upper end of the steel pipe 21.

[0044] Then, by pouring this concrete 4, a stress transmission structure for a cast-in-place steel pipe concrete pile 1 is constructed, comprising a reinforced concrete section 3 and a steel pipe concrete section 2, and ensuring the load-bearing capacity of the bond between the concrete 4 and the steel pipe 21 through a through hole 22 drilled in the end 21a of the steel pipe 21.

[0045] Next, the operation of the stress transfer structure of the cast-in-place steel pipe concrete pile 1 of this embodiment will be described. In this embodiment, the stress transmission structure of the cast-in-place steel pipe concrete pile 1 is configured such that a plurality of through holes 22, which are approximately circular in side view, are provided at intervals in the circumferential direction at the end 21a of the cylindrical steel pipe 21, which is filled with concrete 4 around and inside.

[0046] The through-hole 22, which is roughly circular in side view, can be drilled from the outside of the steel pipe 21 using a gas cutting machine or the like with minimal effort and ease. Furthermore, even if concrete 4 is filled around the circular through-hole 22, bleeding will not accumulate around it, preventing the formation of voids in the concrete 4.

[0047] Furthermore, the concrete 4 inside and outside the steel pipe 21 is connected through the through-hole 22, thereby increasing the adhesion between the steel pipe 21 and the concrete 4. In other words, by positioning the end 21a of the steel pipe 21 near the boundary between the reinforced concrete section 3 and the steel pipe concrete section 2, the tensile force of the main reinforcement 31b of the reinforcing cage 31 can be effectively transmitted to the steel pipe 21 of the steel pipe concrete section 2, thereby improving the stress transmission performance.

[0048] Furthermore, if four to 32 through-holes 22 are provided at equal intervals in the circumferential direction of the steel pipe 21, depending on the size of the steel pipe, the adhesion force can be obtained without bias in the circumferential direction of the pile, and the reduction in the load-bearing capacity of the steel pipe 21 due to drilling the through-holes 22 can be kept within an acceptable range. [Examples]

[0049] Hereinafter, a cast-in-place steel pipe concrete pile of a different embodiment from the cast-in-place steel pipe concrete pile 1 of the above-described embodiment will be described with reference to Figure 3. Note that the same or equivalent parts as those described in the above embodiment will be described using the same terms or reference numerals.

[0050] This embodiment 1 describes an enlarged-base pile 1A as a cast-in-place steel pipe concrete pile. The enlarged-base pile 1A of this embodiment 1 comprises a steel pipe concrete section 2A formed at the top and a truncated conical enlarged-base section 11A formed at the bottom.

[0051] The steel pipe concrete section 2A is mainly composed of a cylindrical steel pipe 21 and concrete 4 filled inside it. Here, for the steel pipe 21, for example, a steel pipe material with a diameter of about 600 mm to 2500 mm can be used.

[0052] Furthermore, near the lower end 21a of the steel pipe 21, through holes 22 are drilled to transmit the pull-out strength of the enlarged base inclined portion of the enlarged base 11A to the steel pipe 21 via the concrete 4. These through holes 22 are approximately circular in side view, and multiple holes are provided at intervals around the circumferential direction of the steel pipe 21.

[0053] In this embodiment 1, the end 21a of the steel pipe 21 embedded inside the enlarged base 11A has six layers of through holes 22, spaced apart in the circumferential direction, arranged in a single layer.

[0054] With a stress transmission structure for an enlarged-base pile 1A having such a configuration, the end portion 21a of the steel pipe 21, which is provided with the through hole 22, is positioned at the enlarged base portion 11A of the enlarged-base pile 1A, thereby effectively transmitting the pull-out resistance of the inclined portion of the enlarged base portion 11A to the steel pipe 21.

[0055] In other words, as the concrete 4 poured into the pile hole 5 using a tremie pipe or the like is poured up from below, it fills the inside and outside of the steel pipe 21 through the through hole 22, and the concrete 4 also fills the inclined portion of the enlarged base 11A that is in contact with the ground G, thereby creating a structure in which the pull-out resistance is reliably transmitted to the steel pipe 21.

[0056] In order to effectively transmit the pull-out strength of the enlarged base 11A to the steel pipe 21, the end 21a of the steel pipe 21 is buried down to the bottom of the enlarged base 11A, and through holes 22 are provided in approximately 3 to 5 stages, and in some cases, approximately 10 stages.

[0057] In the following, we will describe the experiments conducted to confirm the effect of the through-holes 22 in the cast-in-place steel pipe concrete pile 1 described in the above embodiment and in the enlarged-base pile 1A of this embodiment 1, with reference to Figures 4-7.

[0058] Figure 4 illustrates the steel pipe concrete section 2 (straight pile) of the cast-in-place steel pipe concrete pile 1 of the above embodiment and the test specimens used in the experiment, which are modeled after the enlarged-base pile 1A of this embodiment 1. Figure 4(a) shows four straight pile test specimens. These test specimens are model-sized test specimens scaled down to about 1 / 10 the size of an actual pile.

[0059] The specimen labeled "Straight-10" on the far left of Figure 4(a) is a specimen in which a steel pipe 21 with a diameter of 101.6 mm is embedded in a cylindrical concrete 4 with a diameter of 125.0 mm. A through hole 22 with a diameter of 15.0 mm is drilled 23.0 mm above the lower edge of the steel pipe 21 in the axial direction. There are eight through holes 22 at equal intervals in the circumferential direction (eight directions), and the specimen is configured with a single layer of through holes 22.

[0060] On the other hand, test specimen "Cho-11," located to the right of "Cho-10," has a configuration in which two more through-holes 22 are provided at 65.0 mm intervals in the axial direction from the lowest through-hole 22, for a total of three through-holes 22. The rest of the configuration is the same as "Cho-10."

[0061] Furthermore, the "Straight-12" specimen has a configuration in which four more through-holes 22 are provided at 32.0 mm intervals in the axial direction from the lowest through-hole 22, for a total of five stages. The rest of the configuration is the same as "Straight-10". In contrast, the "Straight-13" specimen has a configuration in which four through-holes 22 are provided at equal intervals in the circumferential direction (four locations in four directions), and the rest of the configuration is the same as "Straight-12".

[0062] The specimen labeled "Expand-4" in Figure 4(b) is a test specimen that mimics an expanded-base pile 1A, in which the lower part of a 101.6 mm diameter steel pipe 21 is embedded in concrete 4 of a truncated conical expanded base section 11A with a base diameter of 265.0 mm and a height of 145.0 mm.

[0063] The lower end of the enlarged base 11A is provided with a disc-shaped base with a height of 25.0 mm. From a position 23.0 mm above the lower edge of the steel pipe 21 embedded in the enlarged base 11A, a total of five through holes 22 are provided at 32.0 mm intervals in the axial direction. In each step, eight through holes 22 are provided at equal intervals in the circumferential direction (eight directions).

[0064] Compression tests and pure bending tests were performed using these specimens. The reason for performing the compression test was that, given the shape of the specimens, applying compressive force would be disadvantageous for confirming the adhesion strength. In the pure bending test, if the required adhesion strength was present, failure would occur at reinforced concrete section 3, so the failure mode was confirmed.

[0065] Figure 5 is a graph summarizing the experimental results of the pure bending test using each specimen, showing the relationship between displacement and load. These results show that yield strength was observed in all specimens. Furthermore, it was found that the "Straight-12" specimen, which had the most through holes 22, obtained the greatest yield strength among the straight piles. In addition, it was found that the "Enlarged-4" specimen of the enlarged-base pile 1A obtained an even greater yield strength than "Straight-12".

[0066] On the other hand, in Figures 6 and 7, the results of the compression test are shown as the total opening area of ​​the through-holes 22, which is the total window area (mm²). 2 The horizontal axis represents the total window area ΣW. In other words, Figure 6 shows the total window area ΣW. A and maximum load P max This graph shows the experimental results in relation to (kN). Figure 7 shows the total window area ΣW. A and shear stress τ max (mm 2 This graph shows the experimental results in relation to ).

[0067] As can be seen from the graph in Figure 6, in the case of straight piles, there is a linear proportional relationship between the increase in total window area and the increase in maximum load. Furthermore, it can be seen that with enlarged-base piles ("Enlarged-4"), a larger maximum load can be obtained than that of straight piles.

[0068] Furthermore, the graph in Figure 7 shows that, among straight piles, the shear stress tends to decrease as the total window area increases. However, it can be seen that enlarged-base piles ("Enlarged-4") can be subjected to considerably larger shear stresses than straight piles.

[0069] Thus, it was confirmed that whether it is a cast-in-place steel pipe concrete pile 1 or an enlarged-base pile 1A, by providing a through hole 22 in the end 21a of the steel pipe 21 embedded in the concrete 4, an increase in bond strength and pull-out strength can be expected.

[0070] Furthermore, the other configurations and effects are substantially the same as those of the above embodiment or other examples, so their explanation will be omitted. [Examples]

[0071] Hereinafter, a cast-in-place steel pipe concrete pile of an embodiment different from the cast-in-place steel pipe concrete pile 1 of the above-described embodiment and the enlarged-base pile 1A of Example 1 will be described with reference to Figures 8 and 9. Note that the same or equivalent parts described in the above-described embodiment or Example 1 will be denoted by the same terms or reference numerals.

[0072] This second embodiment describes intermediate enlarged diameter piles 1B and 1C as cast-in-place steel pipe concrete piles. As shown in Figures 8 and 9, the intermediate enlarged diameter piles 1B and 1C of this second embodiment are provided with an enlarged diameter section 13 in the middle section, not at the end in the pile axis direction.

[0073] The intermediate enlarged diameter pile 1B shown in Figure 8 comprises a steel pipe concrete section 2B formed at the top of the pile, a reinforced concrete section 3B formed at the bottom, and an enlarged diameter section 13 formed in the intermediate section that forms the boundary between them.

[0074] In other words, a widened diameter section 13 is provided between the straight pile-shaped steel pipe concrete section 2B and the reinforced concrete section 3B. The upper part of this widened diameter section 13, which is connected to the steel pipe concrete section 2B, is formed in a truncated cone shape, and the lower part is formed in a shape that gradually decreases toward the diameter of the reinforced concrete section 3B.

[0075] The steel pipe concrete section 2B is mainly composed of a cylindrical steel pipe 21 and concrete 4 filled inside it. Here, for the steel pipe 21, for example, a steel pipe material with a diameter of about 600 mm to 2500 mm can be used.

[0076] Then, near the lower end 21a of the steel pipe 21, through holes 22 are drilled to transmit the pull-out strength of the enlarged diameter inclined portion of the enlarged diameter portion 13 to the steel pipe 21 via the concrete 4. These through holes 22 are approximately circular in side view, and multiple holes are provided at intervals around the circumferential direction of the steel pipe 21.

[0077] In the intermediate enlarged diameter pile 1B of this embodiment 2, the end 21a of the steel pipe 21 embedded inside the enlarged diameter section 13 has four rows of through holes 22 spaced apart in the axial direction of the steel pipe 21, with multiple through holes 22 spaced apart in the circumferential direction forming one row.

[0078] On the other hand, the intermediate enlarged diameter pile 1C shown in Figure 9 comprises a steel pipe concrete section 2C formed at the top of the pile, a reinforced concrete section 3C formed at the bottom, an enlarged diameter section 13 formed in the intermediate section that forms the boundary between them, and a truncated conical enlarged base section 11 formed at the lower end of the pile.

[0079] Furthermore, near the end 21a of the steel pipe 21 in the steel pipe concrete section 2C, through holes 22 are drilled to transmit the pull-out strength of the enlarged diameter inclined section of the enlarged diameter section 13 to the steel pipe 21 via the concrete 4. These through holes 22 are approximately circular in side view and multiple holes are provided at intervals around the circumferential direction of the steel pipe 21.

[0080] In the intermediate enlarged diameter pile 1C of this embodiment 2, the end 21a of the steel pipe 21 embedded inside the enlarged diameter section 13 has four rows of through holes 22 spaced apart in the axial direction of the steel pipe 21, with multiple through holes 22 spaced apart in the circumferential direction forming one row.

[0081] With a stress transmission structure for intermediate enlarged diameter piles 1B and 1C configured in this way, the end portion 21a of the steel pipe 21, which has a through hole 22, is positioned in the enlarged diameter portion 13 of the intermediate enlarged diameter piles 1B and 1C, thereby effectively transmitting the pull-out resistance of the inclined portion of the enlarged diameter portion 13 that is in contact with the ground G to the steel pipe 21.

[0082] Furthermore, if the upper end portion 31a of the reinforcing cage 31 in the reinforced concrete sections 3B and 3C overlaps with the end portion 21a of the steel pipe 21, which is provided with the through hole 22, the tensile force of the main reinforcement 31b can be effectively transmitted to the steel pipe 21 in the steel pipe concrete sections 2B and 2C.

[0083] Furthermore, the other configurations and effects are substantially the same as those of the above embodiment or other examples, so their explanation will be omitted. [Examples]

[0084] Hereinafter, a cast-in-place steel pipe concrete pile 1 of an embodiment different from the cast-in-place steel pipe concrete pile 1 (1A-1C) of the above-described embodiment and Examples 1 and 2 will be described with reference to Figures 10-13B. Note that the same or equivalent parts as those described in the above embodiment or Examples 1 and 2 will be described using the same terms or reference numerals.

[0085] In the cast-in-place steel pipe concrete pile 1 of the above embodiment, when there is concern about a reduction in the load-bearing capacity of the steel pipe 21 due to the drilling of the through hole 22, an opening reinforcement portion 23 is provided by welding an annular steel plate around the through hole 22.

[0086] This third embodiment describes the configuration of the opening reinforcement for the through-hole 22, which can suppress the reduction in the load-bearing capacity of the steel pipe 21 due to the drilling of the through-hole 22, and is also expected to increase the bearing resistance of the cast-in-place steel pipe concrete pile 1.

[0087] In other words, in the cast-in-place steel pipe concrete pile 1 of Example 3, reinforcing pipes 24 protruding from the outer circumference and into the interior of the steel pipe 21 are inserted into through holes 22 drilled in the steel pipe 21 and fixed to the steel pipe 21 by welding or the like.

[0088] In detail, as shown in Figure 11, the reinforcing pipe 24 is a pipe material such as a steel pipe having an outer diameter (d2) about the same as the diameter of the through hole 22 drilled in the steel pipe 21, and has a length (t1 + t2 + t3) that protrudes outward from the outer side of the steel pipe 21 (see t2) and also protrudes inward from the inner side of the steel pipe 21 (see t3).

[0089] As described in the above embodiment, the diameter of the through hole 22 is preferably set to three times or more the maximum aggregate diameter of the concrete 4, taking into consideration the ease with which the concrete 4 can pass through and the relationship with the magnitude of the adhesion force obtained at one location. Therefore, when inserting a reinforcing pipe 24 into the through hole 22, it is preferable that the inner diameter (d1) of the reinforcing pipe 24 is set to three times or more the maximum aggregate diameter of the concrete 4.

[0090] For example, a reinforcing pipe 24 with an inner diameter (d1) of about 150 mm and a length of about 50 mm is inserted into a through hole 22 with a diameter of about 167.5 mm, causing a protrusion of about t2 = 20 mm on the outer circumference side of the steel pipe 21, and also causing a protrusion of about t3 = 20 mm on the inner side of the steel pipe 21. The lengths (t2, t3) of the protrusions of the reinforcing pipe 24 can be set considering the relationship with the gap between the pile hole 5 and the outer surface of the steel pipe 21, and the size of the reinforcing cage 31 that passes through the steel pipe 21.

[0091] On the one hand, FIG. 12 is an explanatory diagram conceptually showing the action of the reinforcing pipe 24 in the case of the under-reamed pile 1A described in Example 1. As shown in FIGS. 13A and 13B, even if only a through-hole 22 is provided in the steel pipe 21 having a wall thickness t1 of about 10 mm, the compressive stress degree σ B and the shear stress degree τ can construct the stress transmission structure of the cast-in-place steel pipe concrete pile 1, 1A.

[0092] Furthermore, as in Example 3 of the present embodiment, by passing the reinforcing pipe 24 through the through-hole 22, as shown by the upward arrow in FIG. 11, the compressive stress degree σ B of the concrete 4 on the center side of the through-hole 22 can be widened according to the length of the reinforcing pipe 24.

[0093] In addition, since the protruding portions (t2, t3) of the reinforcing pipe 24 can also receive the compressive stress degree σ B of the concrete 4, the bearing resistance of the cast-in-place steel pipe concrete pile 1 can be significantly increased.

[0094] Particularly, as shown in FIG. 12, in the enlarged bottom portion 11A of the under-reamed pile 1A, since the concrete 4 is sufficiently filled around the reinforcing pipe 24 protruding on the outer peripheral side of the steel pipe 21 (refer to the symbol in FIG. 11 for t2), the compressive stress degree σ B of the protruding portion can be more reliably expected.

[0095] Regarding other configurations and effects, since they are substantially the same as those in the above-described embodiment or other examples, the description thereof is omitted.

Example

[0096] Hereinafter, the cast-in-place steel pipe concrete pile 1 of another embodiment different from the cast-in-place steel pipe concrete piles 1 (1A - 1C) of the above-described embodiment and Examples 1 - 3 will be described with reference to FIG. 14. Regarding the description of the parts that are the same as or equivalent to those described in the above-described embodiment or Examples 1 - 3, the same terms or the same reference numerals will be used for the description.

[0097] In the cast-in-place steel pipe concrete pile 1 of the above embodiment, when there is concern about a reduction in the load-bearing capacity of the steel pipe 21 due to the drilling of the through hole 22, an opening reinforcement portion 23 is provided by welding an annular steel plate around the through hole 22. In this embodiment 4, this will be explained in more detail with reference to Figure 14.

[0098] Figure 14 shows a configuration in which an opening reinforcement portion 23 is provided on the outer surface of the steel pipe 21 by welding an annular steel plate around the through hole 22. In short, the opening reinforcement portion 23 is made up of an annular steel plate having an inner diameter equal to the diameter of the through hole 22 and a width suitable for reinforcement.

[0099] Furthermore, although not shown in the illustration, the opening reinforcement is not limited to annular steel plates. For example, if the through holes 22 are densely drilled in the steel pipe 21, the opening reinforcement can be created by drilling multiple holes of the same diameter as the through holes 22 in a single rectangular steel plate, aligning the holes with the positions of the through holes 22, and welding the steel plate to the steel pipe 21. In this case, a single strip-shaped steel plate may be fixed to the through holes 22 arranged in the axial direction of the steel pipe 21, or a single ring-shaped or arch-shaped steel material may be fixed to the through holes 22 arranged in the circumferential direction of the steel pipe 21.

[0100] In this way, by welding steel material around the through hole 22 to provide an opening reinforcement section, the reduction in the load-bearing capacity of the steel pipe 21 due to the drilling of the through hole 22 can be suppressed. Furthermore, the other configurations and effects are substantially the same as those of the above embodiment or other examples, so their explanation will be omitted.

[0101] While embodiments and examples of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and examples, and any design modifications that do not depart from the spirit of the present invention are included in the present invention.

[0102] For example, in the above embodiments and examples, cases in which four or eight through holes 22 are provided at equal intervals in the circumferential direction of the steel pipe 21 have been described. However, the invention is not limited to these cases, and the number of through holes 22 provided at intervals in the circumferential direction can be set to any number between four and 32, depending on the size of the steel pipe.

[0103] Furthermore, while the above embodiments and examples described an example of a cast-in-place steel pipe concrete pile 1 (1A, 1B, 1C) in which three, four, and six through holes 22 are provided at axial intervals in the end 21a of the steel pipe 21, the invention is not limited to this, and the number of through holes 22 provided at intervals in the pile axis direction can be set to any number between one and ten.

[0104] Furthermore, while the above embodiments and examples describe the case in which through holes 22 with a substantially circular shape in side view are provided at the ends 21a and 21b of the steel pipe 21, the invention is not limited to this, and polygonal through holes with vertices formed on the upper side in side view can also be provided at the ends 21a and 21b of the steel pipe 21. For example, even if the vertices of a polygon such as a triangle, rhombus, pentagon, or hexagon are positioned on the upper side of the through hole, bleeding cannot accumulate around the vertices of the through hole, thus preventing the formation of voids in the concrete. [Explanation of symbols]

[0105] 1: Cast-in-place steel pipe concrete piles 1A: Enlarged-base pile (cast-in-place steel pipe concrete pile) 11A: Enlarged base 1B, 1C: Intermediate enlarged diameter pile (cast-in-place steel pipe concrete pile) 13: Expanded diameter part 2,2A-2C: Steel pipe concrete section 21,21A: Steel pipe 21a: End 21b: End 22: Through hole 23: Opening reinforcement section 24: Reinforcement pipe 3,3B,3C: Reinforced concrete section 4: Concrete

Claims

1. A stress transmission structure for a cast-in-place steel pipe concrete pile formed by steel pipes and concrete, The end of the cylindrical steel pipe, which is filled with concrete around and inside, is provided with multiple through holes that are approximately circular in side view or polygonal in side view with their vertices facing upwards, spaced apart in the circumferential direction. A stress transmission structure for a cast-in-place steel pipe concrete pile, characterized in that reinforcing pipes protruding from the outer circumference and into the interior of the steel pipe are inserted into the aforementioned through-hole.

2. The stress transmission structure for a cast-in-place steel pipe concrete pile according to claim 1, characterized in that the through holes are provided at equal intervals in the circumferential direction from 4 to 32 locations depending on the size of the steel pipe.

3. The end of the steel pipe is positioned near the boundary between the concrete steel pipe section and the reinforced concrete section. The stress transmission structure for a cast-in-place steel pipe concrete pile according to claim 1 or 2, characterized in that the through holes are provided in any number of stages, from one to five, at intervals in the axial direction of the steel pipe, in order to improve the stress transmission performance between the steel pipe and the reinforcing bars of the reinforced concrete section.

4. The end of the steel pipe is positioned at the enlarged base portion of the enlarged base pile or the enlarged diameter portion of the intermediate enlarged diameter pile, The stress transmission structure for a cast-in-place steel pipe concrete pile according to claim 1 or 2, characterized in that the through holes are provided in any number of stages from one to ten at intervals in the axial direction of the steel pipe in order to transmit the pull-out strength of the enlarged base or the enlarged diameter to the steel pipe.

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