Reinforcement cage for attaching reinforcing bars

Abstract

This prevents serious damage to the tops of columnar structures during massive earthquakes. [Solution] When connecting the head of a columnar structure such as a foundation pile to a superstructure such as a foundation footing, a reinforcing cage 1 for attaching reinforcing bars 20 to the head of the columnar structure is constructed of a reinforcing cage body 10 inserted into the hollow space 52 at the head of the main body 51 of the columnar structure, and reinforcing bars 20 that are detachably attached to the reinforcing cage body 10. A locking part 15 is provided on the upper end side of the reinforcing cage body 10, which consists of an annular outer hoop bar 16 and an inner angle ring 17, for locking the reinforcing bars 20 in an upright position. When the columnar structure with the reinforcing bars 20 attached is connected to the superstructure using this reinforcing cage 1, the inner angle ring 17 is embedded in the concrete, and in the event of a massive earthquake, the concrete is divided above and below the inner angle ring 17, thereby mitigating the stress applied to the main body 51 of the columnar structure 5 and preventing serious damage.

Description

Technical Field

[0001] The present invention relates to a reinforcing bar cage for attaching reinforcing bars, such as pile head reinforcing bars, embedded in the concrete of an upper structure, to the head of a columnar structure, such as a foundation pile or a column, by a filling method when connecting the head of the columnar structure to an upper reinforced concrete (RC) structure, such as a foundation or a beam, constructed on the head of these structures.

Background Art

[0002] As an example of a structure composed of the aforementioned columnar structure and upper structure, a "pile foundation" composed of a foundation pile as the columnar structure and a foundation as its upper structure will be described as an example.

[0003] This pile foundation is formed by constructing and connecting a foundation footing, which is the bottom part of the foundation, on the head of the foundation pile driven into the ground until it reaches the supporting layer. By constructing structures such as buildings and bridge piers on the pile foundation thus formed, it is possible to construct structures on soft ground or liquefiable ground.

[0004] As a method of connecting the head of such a foundation pile and the foundation footing, conventionally, a method of embedding the head of the foundation pile into the foundation footing at a depth greater than or equal to the diameter of the foundation pile has also been adopted. In recent years, however, a method of connecting by embedding reinforcing bars (pile head reinforcing bars) attached to the head of the foundation pile into the foundation footing while minimizing the embedding depth of the head of the foundation pile has been generally adopted.

[0005] And as one method of attaching reinforcing bars to the head of the foundation pile, a method called the so-called "filling method" is adopted.

[0006] In this "filling method," a pile body 151, which has a hollow space 152 at least at its head, such as a hollow pile as illustrated in Figure 5, is erected in the ground. Then, the lower end of a reinforcing bar 120 is embedded in the filling concrete poured into the hollow space 152 at the head of the pile body 151, thereby forming a foundation pile 150 with a reinforcing bar 120 attached to its head.

[0007] For the installation of reinforcing bars 120 using this filling method, the use of a reinforcing cage 100, as shown in Figure 5, has also been proposed as an example.

[0008] This reinforcing cage 100 is formed by arranging pile head reinforcing bars 120 at regular intervals in the circumferential direction and restraining a predetermined area on the lower end side of these pile head reinforcing bars 120 by welding them to a spiral hoop 160. By inserting this reinforcing cage 100 into the hollow space 152 at the top of the pile body 151 for a predetermined length and then pouring infill concrete, a foundation pile 150 with pile head reinforcing bars 120 attached to its top can be obtained.

[0009] Furthermore, as explained with reference to Figure 5, when installing the pile head reinforcing bars 120 using a reinforcing cage 100 in which the pile head reinforcing bars 120 and spiral hoops 160 are pre-welded, even if it is discovered through marking out or the like that a part of the pile head reinforcing bars 120 will interfere with the reinforcement in the foundation footing, it is difficult to avoid interference by moving only a part of the pile head reinforcing bars 120. In light of this, as shown in Figure 6, a method has also been proposed in which the reinforcing cage body 210 and the pile head reinforcing bars 220 are formed as separate components, and the pile head reinforcing bars 220 can be attached to and detached from the reinforcing cage body 210 (see Patent Document 1).

[0010] The reinforcing cage 200 described in Patent Document 1 comprises a reinforcing cage body 210 which is constructed by restraining the upper ends of multiple inverted L-shaped suspension reinforcing bars 211 with guide bodies 230 and restraining the lower ends with bottom-side restraining bodies 240.

[0011] Furthermore, the aforementioned guide body 230 that restrains the upper end of the suspension reinforcement bar 211 is formed by an annular inner guide body 231 (which is shown as a flat bar in Figure 6, but may also be a hoop made of reinforcement bar) and an outer guide body 232 positioned on the outer circumference of the inner guide body 231 with a gap δ that allows for the insertion of the pile head reinforcement bar 220. By inserting the reinforcement bar 220 into the aforementioned gap δ and placing its lower end on the bottom restraint body 240, the pile head reinforcement bar 220 can be locked at any position in the circumferential direction of the guide body 230. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2019-082103 [Overview of the project] [Problems that the invention aims to solve]

[0013] As explained above, the heads of the foundation piles 150 and the foundation footing are connected by embedding the pile head reinforcing bars 120 and 220 attached to the heads of the foundation piles 150 using the infill method into the foundation footing. As a result, when a large force is applied horizontally to the foundation piles and foundation footing during a massive earthquake, stress concentrates near the heads of the foundation piles 150 that are connected to the foundation footing.

[0014] Furthermore, if deformation exceeding the deformation capacity of the foundation pile 150 occurs near the head, serious damage may occur, such as crushing of the concrete wall thickness t of the pile body 151 near the head if the pile body is a concrete pile (PC pile, PHC pile, PRC pile, etc.), or bulging of the reinforcing bars if reinforcing bars are placed within the wall thickness t, or buckling or other deformation of the wall thickness t near the head of the steel pipe if the pile body 151 is a steel pipe pile or a concrete pile with an outer steel pipe (SC pile), etc.

[0015] If serious damage occurs to the top of the pile body 151 in this manner, settlement or tilting of the foundation constructed above it may occur. Even if such settlement or tilting does not occur, it will be difficult to continue using a structure supported by a foundation pile 150 that has suffered serious damage to the pile body 151, such as concrete collapse or buckling of the steel pipe.

[0016] Therefore, even in the event of a massive earthquake, it is desirable to eliminate or minimize damage to the head of the foundation pile 150, particularly to the thickness t portion of the head of the pile body 151.

[0017] In this configuration, where the head of the foundation pile 150 and the foundation footing are rigidly connected using the pile head reinforcing bars 120 and 220 installed by the infill method, the thickness t portion of the pile body 151 at the head is firmly connected to the foundation footing by the pile head reinforcing bars 120 and 220 and the infill concrete. As a result, the stress received by the pile head reinforcing bars 120 and 220 from the foundation footing in response to a horizontal load is directly transmitted to the thickness t portion of the pile body 151 via the infill concrete, causing the thickness t portion of the pile body 151 at the head to deform significantly in the bending direction.

[0018] Furthermore, it is considered that when the thickness t portion at the top of the pile body 151 deforms in the bending direction beyond its deformation capacity, brittle fracture of the concrete, bulging of the reinforcing bars, buckling of the steel pipe, etc., occur in the thickness t portion of the pile body 151.

[0019] Based on the above considerations, the inventors of the present invention considered that, under normal circumstances or during relatively minor earthquakes, the head of the foundation pile 150 and the foundation footing are rigidly connected (jointed) by pile head reinforcing bars and concrete, so that the pile head reinforcing bars 120 and 220 receive the stress from the foundation footing across the entire head of the foundation pile. However, in the event of a massive earthquake, if the horizontal force applied is so large that it exceeds the deformation capacity of the thickness t portion of the pile body 151's head, then if the connection between the head of the foundation pile and the foundation footing can be relaxed from the aforementioned "rigid connection" to something closer to a "pin connection," then the stress received by the pile head reinforcing bars 120 and 220 from the foundation footing is less likely to be transmitted to the thickness t portion of the pile body 151's head, thereby preventing damage to the thickness t portion of the pile body 151's head that supports the foundation footing, or reducing damage as much as possible.

[0020] On the other hand, if no significant damage occurs to the thickness t portion at the top of the pile body 151, the thickness t portion of the pile body 151 will still exert its effect of restraining the inner concrete. Therefore, even if cracks occur in the infill concrete, for example, the overall strength of the foundation pile 150 is unlikely to be significantly impaired.

[0021] In the above explanation, the connection between the head of the foundation pile 150 and the foundation footing was considered as an example. However, similar damage is not limited to the connection between the head of the foundation pile and the foundation footing, but can occur in any case where a superstructure such as a beam is rigidly connected to the upper end of a reinforced concrete column via reinforcing bars installed in a filler method.

[0022] Therefore, the present invention aims to reduce damage to the thickened portion of the main body at the top of a columnar structure, such as a foundation pile, even during a massive earthquake, by devising the structure of the reinforcing cage used when installing reinforcing bars in a filling method into the hollow space provided at the top of the main body of the columnar structure. [Means for solving the problem]

[0023] Means for solving the problems will be described below together with reference numerals used in the mode for carrying out the invention. This reference numeral is for clarifying the correspondence between the description of the claims and the description of the mode for carrying out the invention, and of course, is not used restrictively for interpreting the technical scope of the present invention.

[0024] In order to achieve the above object, the reinforcing bar cage 1 for attaching reinforcing bars according to the present invention is In the reinforcing bar cage 1 for attaching a reinforcing bar 20 such as a pile head reinforcing bar to the head of a columnar structure (for example, a foundation pile) 5 for joining the head of the columnar structure 5 and an upper structure (for example, a foundation footing) 6 of a reinforced concrete structure constructed on the head of the columnar structure 5 {reference numerals 5 and 6 are shown in FIGS. 4(F) and (G); hereinafter, the same}, The reinforcing bar cage 1 includes a reinforcing bar cage main body 10 inserted into a head hollow space 52 of a main body of the columnar structure 5 (for example, a pile main body such as a hollow pile) 51, and a plurality of reinforcing bars 20 detachably attached to the reinforcing bar cage main body 10, and The reinforcing bar cage main body 10 includes a locking portion 15 for locking the reinforcing bar 20 in a standing state on the upper end side of the reinforcing bar cage main body 10, The locking portion 15 includes an annular outer hoop bar 16 and an inner angle ring 17 having an outer peripheral shape similar to the inner peripheral shape of the outer hoop bar 16 in a plan view, which is disposed on the inner peripheral side of the outer hoop bar 16 with an interval δ allowing insertion of the reinforcing bar 20, The inner angle ring 17 is formed in an L-shaped cross section, which is composed of a cylindrical cylindrical portion 17a forming the outer diameter of the inner angle ring 17 and an endless annular flange portion 17b protruding inward in the orthogonal direction from the lower end edge of the cylindrical portion 17a (Claim 1).

[0025] In the reinforcing bar cage 1 having the above configuration, the outer hoop bar 16 and the inner angle ring 17 may be connected by a connecting plate 18 at a plurality of locations in the circumferential direction (Claim 2).

[0026] The inner angle ring 17 may be provided on the reinforcing cage body 10 such that the bottom surface of the flange portion 17b of the inner angle ring 17 is at the same height or higher as the upper end opening edge of the main body 51 of the columnar structure 5 (Claim 3).

[0027] Furthermore, the inner angle ring 17 may be configured to be positioned within the hollow space 52 at the top of the main body 51 of the columnar structure 5. In this case, the inner angle ring 17 may be provided on the reinforcing cage body 10 such that the bottom surface of the flange portion 17b of the inner angle ring 17 is at or above the same height as the bottom surface of the upper structure 6 {Figure 4(G)} (Claim 4).

[0028] Furthermore, if the main body 51 of the columnar structure 5 is a steel pipe pile, the inner angle ring 17 may be provided on the reinforcing cage body 10 such that the bottom surface of the flange portion 17b of the inner angle ring 17 is at or above the same height as the uppermost position of the slip stopper 53 among the slip stoppers 53, 53 attached to the inner wall surface of the steel pipe pile (Claim 5).

[0029] Furthermore, if the reinforcing bar 20 is a threaded reinforcing bar, It is preferable that the distance δ between the outer hoop reinforcement 16 and the inner angle ring 17 be wider than the width W of the two planes 21 and 22 provided on the threaded reinforcement bar which is the reinforcing bar 20, and narrower than the diameter D of the threaded reinforcement bar (Claim 6). [Effects of the Invention]

[0030] By using the reinforcing cage 1 of the present invention described above to attach reinforcing bars 20 to the top of a columnar structure (for example, a foundation pile) 5 and connecting it to a superstructure (for example, a foundation footing) 6, it was possible to prevent damage to the thickness t portion of the top of the main body 51 of the columnar structure 5, or to reduce the damage that does occur as much as possible, in the event of a massive earthquake.

[0031] In other words, when connecting the head of a columnar structure 5 to a superstructure 6 using the reinforcing cage 1 of the present invention, the concrete filling the hollow space 52 at the head of the main body 51 of the columnar structure 5 is in communication with the concrete of the superstructure 6 through an opening provided in the center of the flange portion 17b of the inner angle ring 17, but many other parts are separated from the concrete of the superstructure by the inner angle ring 17.

[0032] As a result, under normal circumstances or during relatively minor earthquakes, the connection (rigid joint) between the top of the columnar structure 5 and the superstructure 6 is maintained, and the stress received by the reinforcing bars 20 from the superstructure 6 is borne by the entire upper end portion of the columnar structure 5. However, when a large earthquake occurs and a large horizontal force is applied to the columnar structure 5 and the superstructure 6, and a large bending force is applied near the top of the columnar structure 5, cracks may form in the concrete starting from the mounting position of the inner angle ring 17, causing the infill concrete placed in the hollow space 52 at the top of the main body 51 of the columnar structure 5 to separate from the concrete of the superstructure 6.

[0033] In this way, as the infill concrete separates from the upper concrete, the rigid connection between the head of the columnar structure 5 and the superstructure 6, which was previously established by the synergistic effect of the reinforcing bars 20 and the concrete, is eased. At the same time, the separation of the concrete as described above causes the reinforcing bars 20 in contact with the inner angle ring 17 to concentrate and repeatedly receive positive and negative loads, leading to the formation of a plastic hinge due to the yielding of the reinforcing bars 20 at this location.

[0034] The formation of this plastic hinge reduces the transmission of stress to the thickness t portion at the top of the main body 51 of the columnar structure 5, thereby reducing the amount of deformation in this portion. This effectively prevents damage to the thickness t portion of the outer hoop reinforcement 16 at the top of the main body 51 of the columnar structure 5, or minimizes any damage that may occur.

[0035] This ensures that the columnar structure 5's function of supporting the superstructure 6 is maintained without being impaired, thereby suppressing the occurrence of settlement and tilting of the superstructure.

[0036] In the embodiment in which the outer hoop reinforcement 16 and inner angle ring 17 constituting the aforementioned locking portion 15 are connected by connecting plates 18 at multiple locations in the circumferential direction, it is possible to accurately position the outer hoop reinforcement 16 and inner angle ring 17 through the aforementioned interval δ.

[0037] In a configuration in which the inner angle ring 17 is provided on the reinforcing cage body 10 such that the bottom surface of the flange portion 17b of the inner angle ring 17 is at or above the same height as the upper opening edge of the main body 51 of the columnar structure 5, the entire infill concrete is separated from the concrete of the superstructure 6, making it easier to prevent damage to the wall thickness t portion at the top of the main body 51 of the columnar structure 5.

[0038] Furthermore, the aforementioned inner angle ring 17 may be attached to the reinforcing cage body 10 during construction so as to be positioned within the hollow space 52 at the top of the main body 51 of the columnar structure 5. In this case, by providing the reinforcing cage body 10 so that the bottom surface of the flange portion 17b of the inner angle ring 17 is positioned at a height equal to or greater than the bottom surface of the upper structure 6, it is possible to block or mitigate stress transmission to the portion of the wall thickness t at the top of the main body 51 of the columnar structure 5 where the greatest strain occurs, thereby preventing failure from the plastic hinge during a massive earthquake.

[0039] Furthermore, when the main body 51 of the columnar structure 5 is a steel pipe pile, by positioning the bottom surface of the flange portion 17b of the inner angle ring 17 on the reinforcing cage body 10 at the same height or higher as the uppermost position of the uppermost shear stopper 53 among the shear stoppers 53 attached to the inner wall surface of the steel pipe pile, it is possible to separate the portion of the infill concrete that has a high bonding force with the pile body (steel pipe) from the concrete of the superstructure 6, thereby making it difficult for stress from the reinforcing bars 20 to be transmitted to the wall thickness t portion at the top of the pile body 51.

[0040] Furthermore, in a configuration where the reinforcing bar 20 is a threaded reinforcing bar, and the distance δ between the outer hoop bar 16 and the inner angle ring 17 is wider than the two-sided width W of the two planes 21 and 22 provided on the threaded reinforcing bar 20, and narrower than the diameter D of the threaded reinforcing bar, the reinforcing bar (threaded reinforcing bar) 20 can be inserted into the distance δ such that the two planes 21 and 22 face the outer hoop bar 16 and the inner angle ring 17, and the threaded reinforcing bar 20 can be easily locked to the locking part 15 by rotating the threaded reinforcing bar 20 at an angle of 90° or less. [Brief explanation of the drawing]

[0041] [Figure 1] (A) is a plan view of the reinforcing cage of the present invention when inserted into a hollow pile (pile body), and (B) is a cross-sectional view of (A) along line BB. [Figure 2] (A) is a perspective view of the locking mechanism, and (B) is an enlarged cross-sectional view of the section B in the direction of arrow B in (A). [Figure 3] This is an explanatory diagram of the method for securing reinforcing bars to the locking part, where (A) is the state before locking and (B) is the state after locking. [Figure 4] This diagram illustrates a method for attaching pile head reinforcement to a steel pipe pile using the reinforcing cage of the present invention, showing (A) the state after dislodgement welding is completed, (B) the state in which the reinforcing cage body is inserted into the pile head, (C) the state in which the insertion of the reinforcing cage body into the pile head is completed, (D) the state in which the reinforcement bars (pile head reinforcement bars) are attached to the reinforcing cage body, (E) the state in which the pile head reinforcement bars are moved to avoid interference with the reinforcement of the foundation footing, (F) the state in which the infill concrete has been poured, and (G) the state in which the head of the foundation pile and the foundation footing are joined. [Figure 5] An explanatory diagram of the method for installing pile head reinforcement bars using the conventional method of filling with steel cages. [Figure 6] An explanatory diagram of a method for installing pile head reinforcement using a conventional reinforcing cage with separate reinforcing cage body and pile head reinforcement bars (corresponding to Figure 2 of Patent Document 1). [Modes for carrying out the invention]

[0042] Next, embodiments of the present invention will be described below with reference to the attached drawings.

[0043] In the following description, the installation of reinforcing bars 20 using the reinforcing cage 1 of the present invention will be explained using the example of installing reinforcing bars (pile head reinforcing bars) 20 to the head of a foundation pile 5, and also using the example of connecting a foundation footing 6 to the head of this foundation pile 5. However, the reinforcing cage 1 of the present invention is not limited to these examples and can be widely used for connecting the head of a columnar structure 5 to a reinforced concrete superstructure 6 constructed on top of it, such as a column of a building and a reinforced concrete beam connected to this column.

[0044] [Overall structure of the reinforced concrete cage] As shown in Figure 1, the reinforcing cage 1 of the present invention consists of a reinforcing cage body 10 that is inserted into the hollow space 52 at the top of a pile body 51 such as a hollow pile that forms a foundation pile 5, and reinforcing bars (pile head reinforcing bars) 20 that can be attached to and removed from the reinforcing cage body 10.

[0045] [Reinforced steel cage body] The aforementioned reinforcing cage body 10 is a cylindrical cage as an example formed by combining deformed reinforcing bars, and is formed by restraining multiple suspension reinforcing bars 11, which are arranged at approximately equal intervals in the circumferential direction, with hoop reinforcing bars 12 at multiple locations in the longitudinal direction (height direction), as shown in Figure 1(B).

[0046] A cross-shaped reinforcing bar, or cross bar, is attached to the upper end of the reinforcing cage body 10. When the reinforcing cage body 10 is inserted into the hollow space 52 at the top of the pile body 51 from the lower end, the ends of the cross bar, or cross bar, are locked to the opening edge of the top of the pile body 51, allowing the reinforcing cage body 10 to be suspended and installed within the hollow space 52 at the top of the pile body 51.

[0047] A bottom plate 14 may be provided at the bottom of the steel cage body 10. By configuring it in this way, it is possible to prevent the concrete poured into the hollow space 52 at the top from falling below the bottom plate 14 without providing a separate bottom plate to prevent the concrete from falling in addition to the steel cage body 10.

[0048] The steel cage body 10 configured in this way is provided with a locking part 15 that allows the reinforcing bars (pile head reinforcing bars) 20, which will be described later, to be locked in an upright position at any position in the circumferential direction.

[0049] As shown in Figures 1 and 2, the locking portion 15 comprises an annular outer hoop reinforcement 16 and an inner angle ring 17 positioned on the inner circumference side of the outer hoop reinforcement 16. In a plan view, the inner circumferential shape of the outer hoop reinforcement 16 and the outer circumferential shape of the inner angle ring 17 are similar, and the two are positioned such that a gap δ is formed between the outer hoop reinforcement 16 and the inner angle ring 17, allowing for the insertion of a reinforcing bar 20, which will be described later.

[0050] The aforementioned inner angle ring 17 consists of a cylindrical portion 17a formed in a cylindrical shape and an endless annular flange portion 17b that protrudes inward in a direction perpendicular to the lower edge of the cylindrical portion 17a, and has an L-shaped cross-section in the vertical direction. In the illustrated embodiment, the outer hoop reinforcement 16 and the inner angle ring 17 are connected at the aforementioned interval δ by placing and fixing both the outer hoop reinforcement 16 and the flange portion 17b of the inner angle ring 17 on the connecting plate 18.

[0051] Alternatively, instead of connecting with the connecting plate 18, the outer hoop reinforcement 16 and the inner angle ring 17 may be fixed together on the cross reinforcement 13, thereby connecting them at the aforementioned interval δ.

[0052] Furthermore, when using threaded reinforcing bars 20, the spacing δ between the outer hoop bars 16 and the inner angle ring 17 may be made wider than the two-sided width W of the planes 21 and 22 provided on the threaded reinforcing bar 20 for gripping the jaws of a wrench, while being narrower than the diameter D of the threaded reinforcing bar 20. This allows the threaded reinforcing bar 20 to be locked at any position in the circumferential direction of the reinforcing cage body 10 by inserting the threaded reinforcing bar 20 at spacing δ such that the planes 21 and 22 of the threaded reinforcing bar 20 face the outer hoop bars 16 and the inner angle ring 17, respectively, and then rotating the threaded reinforcing bar 20 at an angle of 90° or less.

[0053] Furthermore, in the illustrated embodiment, a hoop reinforcement 12 is provided to restrain the suspension reinforcement 11 from the inner circumference, and the aforementioned outer hoop reinforcement 16 is provided separately from the hoop reinforcement 12. However, instead of this configuration, if a hoop reinforcement 12 is provided to restrain the suspension reinforcement 11 from the outside, the outer hoop reinforcement 16 may be shared with the uppermost hoop reinforcement 12 among the hoop reinforcements 12 used to restrain the suspension reinforcement 11.

[0054] Furthermore, in this embodiment, as shown in Figure 1(B), the inner angle ring 17 is positioned on the cross reinforcement 13. This configuration ensures that when the reinforcing cage body 10 is inserted into the hollow space 52 at the top of the pile body 51, the bottom surface of the flange portion 17b of the inner angle ring 17 is positioned higher than the upper opening edge of the pile body 51. However, the mounting position of the inner angle ring 17 is not limited to this position. The inner angle ring 17 may be attached to the reinforcing cage body 10 such that it is positioned within the hollow space 52 at the top of the pile body 51 when the reinforcing cage body 10 is inserted into the hollow space 52 at the top of the pile body 51.

[0055] When the inner angle ring 17 is attached to the reinforcing cage body 10 in such a way that it is positioned within the hollow space 52 at the top of the pile body 51, it is desirable to attach it so that the height of the bottom surface of the flange portion 17b of the inner angle ring 17 is close to the height of the upper end opening edge of the pile body 51. For example, it is preferable to attach the inner angle ring 17 to the reinforcing cage body 10 so that the bottom surface of the flange portion 17b of the inner angle ring 17 is at the same height as or greater than the bottom surface of the foundation footing 6.

[0056] Furthermore, when the pile body 51 is a steel pipe pile, it is preferable to attach the inner angle ring 17 to the reinforcing cage body 10 such that the bottom surface of the flange portion 17b of the inner angle ring 17 is positioned at a height equal to or greater than the upper end position of the uppermost of the shear stoppers 53 attached to the inner wall of the steel pipe pile.

[0057] In the illustrated embodiment, in addition to the aforementioned locking portion 15, a lower end locking portion 19 is also provided on the lower end side of the reinforcing cage body 10 to lock the lower end of the reinforcing bar 20, so that the reinforcing bar 20 can be locked at two locations, the upper end and the lower end of the reinforcing cage body 10.

[0058] As such a lower end locking portion 19, in the illustrated embodiment, an outer hoop reinforcement 19a is provided on the outer circumference of the lowest hoop reinforcement 12 among the hoop reinforcements 12 that restrain the suspension reinforcement from the inner circumference side, with an interval δ wider than the width W of the two planes 21 and 22 provided on the threaded reinforcement 20 and narrower than the diameter D.

[0059] [Reinforcement bars for pile heads (reinforcement bars)] The pile head reinforcing bars (reinforcement bars) 20 attached to the aforementioned reinforcing cage body 10 can be made from various types of reinforcing bars, such as deformed reinforcing bars, which are commonly used as reinforcement in reinforced concrete structures. In this embodiment, threaded reinforcing bars are used as the reinforcement bars 20.

[0060] As shown in Figure 2(B), the threaded reinforcing bar 20 has threads along its entire length, and as shown in Figures 2(B) and 3(A) and (B), two planes 21 and 22 are formed parallel to each other along its entire length so that a wrench jaw can be placed on the threaded reinforcing bar 20. As mentioned above, the spacing δ between the outer hoop reinforcement 16 and the inner angle ring 17 of the locking portion 15 is made wider than the two-sided width W of the aforementioned planes 21 and 22, and narrower than the diameter D of the threaded reinforcing bar, so that the planes of the threaded reinforcing bar 20 can be formed as shown in Figure 3(A). The locking device 15 is configured such that the threaded reinforcing bars 20 are inserted into the gap δ between the outer hoop reinforcement 16 and the inner angle ring 17, respectively, so that the surfaces 21 and 22 face the outer hoop reinforcement 16 side and the inner angle ring 17 side in a plan view, allowing the threaded reinforcing bars 20 to be moved to any position in the circumferential direction of the locking device 15 along the gap δ, and that the threaded reinforcing bars 20 can be firmly clamped and locked between the outer hoop reinforcement 16 and the inner angle ring 17 by rotating the threaded reinforcing bars 20 at a rotation angle of 90° or less.

[0061] [Construction method, etc.] The installation of the pile head reinforcing bars 20 using the reinforcing cage 1 of the present invention, configured as described above, can be performed on either precast piles or cast-in-place piles, as long as it is on a pile body 51 that has a hollow space 52 at its head.

[0062] Furthermore, it can be applied to any type of precast pile, including steel pipe piles, concrete piles (PC piles, PHC piles, PRC piles), and concrete piles with outer steel pipes (SC piles).

[0063] In the following description, we will use the example of using the reinforcing cage 1 of the present invention to attach pile head reinforcing bars 20 to a cylindrical foundation pile 5. However, the reinforcing cage 1 of the present invention can be used in general to attach reinforcing bars 20 to the heads of columnar structures other than foundation piles 5, and can also be used to attach reinforcing bars 20 to columnar structures other than cylindrical ones, such as rectangular columnar structures.

[0064] In this case, the shape of the reinforcing cage body 10 may be adapted to the shape of the columnar structure to be attached, and if necessary, the shape of the reinforcing cage body 10 may be adapted not only to a cylindrical shape but also to a shape such as a rectangular tube, depending on the shape of the target columnar structure 5.

[0065] Below, as an example, the process of attaching the pile head reinforcing bars 20 to the foundation pile 5 using the reinforcing cage 1 of the present invention will be described with reference to Figure 4.

[0066] In the illustrated embodiment, the pile body 51 to which the pile head reinforcing bars 20 are attached is a steel pipe pile. In this case, a so-called "slip-prevention welding" is performed, in which a bent strip of steel plate or the like is welded circumferentially to the inner wall of the hollow space 52 at the top of the pile body 51 as a slip-prevention 53 {Figure 4(A)}.

[0067] Furthermore, the illustrated example describes a case where a reinforcing cage body 10 equipped with a bottom plate 14 at its lower end is used. However, when using a reinforcing cage body 10 that does not have such a bottom plate 14, a bottom plate (not shown) may be attached to a predetermined height position within the hollow space 52 at the top of the pile body 51 before installing the reinforcing cage body 10, as needed, to prevent the concrete poured into the hollow space 52 at the top of the pile body 51 from falling below this bottom plate.

[0068] Subsequently, the reinforcing cage body 10 is inserted into the hollow space 52 at the top of the pile body 51 from the bottom side {Figure 4(B)}, and the cross-shaped reinforcement bars 13 are secured to the opening edge of the pile head, thereby suspending the reinforcing cage body 10 within the hollow space 52 at the top of the pile body 51 {Figure 4(C)}.

[0069] The attachment of the pile head reinforcing bars 20 to the reinforcing cage body 10 may be done in advance before inserting the reinforcing cage body 10 into the hollow space 52 at the top of the pile body 51. However, in this embodiment, only the reinforcing cage body 10 is installed first into the hollow space 52 at the top of the pile body 51, and the pile head reinforcing bars 20 are attached to the reinforcing cage body 10 afterward.

[0070] In this manner, the pile head reinforcing bars 20 are attached to the reinforcing cage body 10 by first inserting the lower end of the threaded reinforcing bar 20, which is the pile head reinforcing bar, into the gap δ between the outer hoop reinforcing bar 16 and the inner angle ring 17 of the locking part 15 provided on the upper end side of the reinforcing cage body 10 (above the cross reinforcing bar 13 in the illustrated embodiment), then dropping the threaded reinforcing bar 20 until its lower end abuts against the bottom plate 14, and then temporarily attaching it by rotating the threaded reinforcing bar 20 at an angle of 90° or less using a hand or a tool such as a wrench.

[0071] Furthermore, the lower end of the threaded reinforcing bar 20 is not limited to being placed on the bottom plate 14 provided on the reinforcing cage body 10, but may also be placed on the hoop reinforcing bar 14' provided below the lower end locking portion 19, as shown as a "modified example" in Figure 1(B).

[0072] The temporary attachment of reinforcing bars 20 to the steel cage body 10 is carried out until the required number of bars, which is determined in advance based on strength calculations, is reached.

[0073] In this manner, the pile head reinforcing bars 20, which have been temporarily attached to the reinforcing cage body 10, are not yet completely fixed in place before the concrete filling is poured into the hollow space 52 at the top of the pile body 51. By rotating the pile head reinforcing bars 20 in the opposite direction to when they were temporarily fixed, the temporary fixing can be released, and the pile head reinforcing bars 20 can be moved along the interval δ provided in the locking portion 15.

[0074] Therefore, when the position of the lateral reinforcement bars to be placed within the foundation footing is determined by marking out the foundation footing, or when the foundation footing is actually reinforced, if there are pile head reinforcement bars 20 in a position that interferes with the reinforcement within the foundation footing, the corresponding pile head reinforcement bars 20 are moved to a position that avoids this interference {Figure 4(E)}.

[0075] After avoiding interference in this manner, concrete is poured into the hollow space 52 at the top of the pile body 51, and together with the reinforcing cage body 10, the lower end of the pile head reinforcing bar 20 attached to the reinforcing cage body 10 is embedded in the poured concrete, thereby completing the foundation pile (columnar structure) 5 with the pile head reinforcing bar 20 attached {Figure 4(F)}.

[0076] Subsequently, by forming a foundation footing 6 on the foundation pile 5 to which the pile head reinforcing bars 20 have been attached in this manner, and constructing the foundation footing 6 with the pile head reinforcing bars 20 embedded in the concrete of the foundation footing 6, a pile foundation can be formed in which the head of the foundation pile 5 and the foundation footing 6 are connected.

[0077] [Effects and Effects] In the configuration described above, in which the head of the foundation pile 5 and the foundation footing 6 are connected using the reinforcing cage 1 of the present invention, under normal circumstances or during relatively minor earthquakes, the infill concrete and the concrete of the foundation footing 6 are integrally connected by the embedding of the inner angle ring 17. When a horizontal force is applied to the foundation pile 5 or the foundation footing 6, the stress borne by the pile head reinforcing bars 20 is transmitted to the thickened portion of the pile body 51 head via the infill concrete, so that the stress against the horizontal load is borne by the entire head of the foundation pile 5.

[0078] However, in the foundation pile 5 constructed using the reinforcing cage 1 of the present invention, as shown in Figure 4(G), the inner angle ring 17 provided in the locking portion 15 is embedded in the concrete. Although the infill concrete poured into the hollow space 52 at the top of the pile body 51 and the concrete of the foundation footing 6 are in communication through an opening provided in the center of the flange portion 17b of the inner angle ring 17, many parts are separated vertically by the inner angle ring 17.

[0079] As a result, when a massive earthquake occurs and a large horizontal force is applied to the foundation piles 5 and foundation footings 6, cracks appear in the concrete, causing the concrete to separate above and below the inner angle ring 17.

[0080] In this way, as the concrete is separated above and below the inner angle ring 17 and subjected to repeated horizontal loads, stress concentrates in the reinforcing bars 20 in contact with the inner angle ring 17, causing that portion to yield and form a plastic hinge. As a result, the rigid connection between the head of the foundation pile 5 and the foundation footing 6 is lost, and the stress received by the pile head reinforcing bars 20 from the foundation footing 6 is less likely to be transmitted to the thickness t portion of the head of the pile body 51.

[0081] As a result, the deformation in the bending direction of the wall thickness t portion at the top of the pile body 51 can be made as small as possible, and by sacrificing the concrete in the inner angle ring 17 portion, damage to the wall thickness t portion at the top of the pile body 51, and in this embodiment where the pile body 51 is a steel pipe pile, buckling at the top of the steel pipe pile can be effectively prevented.

[0082] In the illustrated embodiment, the inner angle ring 17 is positioned on the cross reinforcement 13, so that the bottom surface of the flange portion 17b of the inner angle ring 17 is positioned higher than the upper end opening edge of the pile body 51. However, the arrangement of the inner angle ring 17 is not limited to the illustrated configuration, and it may be positioned within the hollow space 52 at the top of the pile body 51, as long as it is positioned near the top of the pile body 51.

[0083] When the inner angle ring 17 is placed in the hollow space 52 at the top of the pile body 51 in this manner, it is preferable that the bottom surface of the flange portion 17b of the inner angle ring 17 be positioned at a height equal to or greater than the bottom surface of the foundation footing 6.

[0084] If no cracks or other defects occur in the concrete, and the head of the foundation pile 5 and the foundation footing 6 are tightly connected (rigidly joined), and a horizontal force is applied to the foundation pile 5 and the foundation footing 6, the strain generated at the head of the foundation pile 5 will be maximum at the height of the bottom surface of the foundation footing 6.

[0085] Therefore, by arranging the bottom surface of the flange portion 17b of the inner angle ring 17 at a position higher than this position and cutting the concrete above and below during the occurrence of a huge earthquake, the stress received by the pile head reinforcing bars 20 with respect to the thick portion of the pile body 51 of this portion is inhibited from being transmitted, and the occurrence of damage to the pile body 51 can be suppressed.

[0086] Also, when the pile body 51 is a steel pipe pile, it is preferable that the bottom surface of the flange portion 17b of the inner angle ring 17 is arranged at a height equal to or higher than the upper end position of the uppermost anti-slip member 53 among the anti-slip members 53 attached to the inner wall of the steel pipe pile.

[0087] Among the filled concrete, the filled concrete below the uppermost anti-slip member is more firmly bonded to the steel pipe pile compared to the filled concrete above it. By cutting the filled concrete in the portion firmly bonded to the steel pipe pile like this due to the occurrence of cracks starting from the inner angle ring 17, from the filled concrete in this portion, the transmission of stress to the pile head of the steel pipe pile is inhibited, and while maintaining the restraint effect of the filled concrete possessed by the steel pipe pile, by suppressing deformation in the bending direction, the occurrence of damage to the main body portion of the steel pipe pile can be reduced.

Explanation of Reference Signs

[0088] 1 Steel cage 5 Columnar structure (foundation pile) 6 Upper structure (foundation footing) 10 Steel cage body 11 Suspension reinforcing bars 12 Hoop bars 13 Cross bars 14 Bottom plate 14’ Hoop bars 15 Locking portion 16 Outer hoop bars 17 Inner angle ring 17a Cylindrical portion 17b Flange portion 18 Connecting plate 19 Lower end side locking portion 19a Lateral hoop muscle 20 (Pile head) Reinforcement bars (threaded rebar) 21,22 plane 51. Main body of columnar structure (pile body) 52 Head hollow space 53 Anti-slip 100 Reinforced Steel Cage 120 Pile head reinforcement bars 150 Foundation piles 151 Pile body 152 Head hollow space 160 Spiral Hoop 200 Reinforced Steel Cage 210 Reinforced Steel Cage Body 211 Suspension Reinforcement Bars 220 Pile head reinforcement bars 230 Guide Body 231 Inner guide body 232 Outer guide body 240 Bottom side restraint body W threaded rebar width D Diameter of threaded rebar δ interval t Thickness of the pile body

Claims

1. In order to connect the top of a columnar structure to a reinforced concrete superstructure constructed on the top of the columnar structure, a reinforcing cage for attaching reinforcing bars to the top of the columnar structure, The aforementioned reinforcing cage comprises a reinforcing cage body inserted into the hollow space at the top of the main body of a columnar structure, and a plurality of reinforcing bars detachably attached to the reinforcing cage body, The reinforcing cage body is provided with a locking portion on the upper end side of the reinforcing cage body for locking the reinforcing bars in an upright position, The locking portion comprises an annular outer hoop reinforcement and an inner angle ring having an outer shape similar to the inner shape of the outer hoop reinforcement in a plan view, which is arranged on the inner circumference side of the outer hoop reinforcement with a gap that allows for the insertion of the reinforcing reinforcement. The reinforcing cage for attaching reinforcing bars is characterized in that the inner angle ring is formed in an L-shape in cross-section, comprising a cylindrical portion that forms the outer diameter of the inner angle ring and an endless annular flange portion that protrudes inward in a direction perpendicular to the lower edge of the cylindrical portion.

2. The reinforcing cage for attaching reinforcing bars according to claim 1, characterized in that the outer hoop reinforcement and the inner angle ring are connected by connecting plates at multiple locations in the circumferential direction.

3. The reinforcing cage for attaching reinforcing bars according to claim 1 or 2, characterized in that the inner angle ring is provided on the reinforcing cage body such that the bottom surface of the flange portion of the inner angle ring is at the same height or higher as the upper end opening edge of the main body of the columnar structure.

4. The reinforcing cage for attaching reinforcing bars according to claim 1 or 2, characterized in that the inner angle ring is provided on the reinforcing cage body such that the bottom surface of the flange portion of the inner angle ring is at or above the same height as the bottom surface of the superstructure.

5. The main body of the columnar structure is a steel pipe pile, The reinforcing cage for attaching reinforcing bars according to claim 1 or 2, characterized in that the inner angle ring is provided on the reinforcing cage body such that the bottom surface of the flange portion of the inner angle ring is at the same height as or higher than the upper end position of the uppermost anti-slip stopper among the anti-slip stops attached to the inner wall surface of the steel pipe pile.

6. The reinforcing bars are threaded bars. The reinforcing cage for attaching reinforcing bars according to claim 1 or 2, characterized in that the distance between the outer hoop reinforcement and the inner angle ring is formed to be wider than the width of the two planes provided on the threaded reinforcing bar which is the reinforcing bar, and narrower than the diameter of the threaded reinforcing bar.

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