Pile head joint structure and joint method

Abstract

To provide a joint structure between a sheath pipe and a pile head block that is rationalized so that the shape and dimensions of the pile head block can be rationalized and the weight of the member can be reduced. [Solution] The pile comprises a steel pile (1), a sheath pipe (5) fixed to the top of the steel pile (1) and filled with concrete, a precast concrete pile head block (3) fixed to the top of the sheath pipe (5), and a PC beam (2) extending horizontally from the pile head block (3), and is PC-pressed and joined using a post-tensioning method with PC steel (9) arranged to penetrate the PC beam (2) and the pile head block (3), and the sheath for inserting the PC steel (9) is arranged to penetrate the top of the sheath pipe (5), and at least part of the sheath is a steel pipe sheath (4b) welded rigidly to the sheath pipe (5), and the PC steel (9) and the steel pipe sheath (4b) bear part of the bending moment transmitted between the sheath pipe (5) and the pile head block (3), and the steel pipe sheath (4b) bears part of the axial force transmitted between the sheath pipe (5) and the pile head block (3).

Description

[Technical Field]

[0001] The present invention relates to a joint structure and a joining method between a sheath pipe extended from a sheath pipe joint at the head of a steel pipe pile and a pile head block, regardless of whether the structure is for the renovation of an existing pier or for the construction of a new pier. [Background technology]

[0002] A well-known joint structure for the head of a steel pipe pile is a joint structure (hereinafter referred to as "sheath pipe joint") in which a steel pipe pile with a smaller diameter is fitted into a larger diameter sheath pipe (also called a "socket steel pipe") at a predetermined length, and the annular gap is filled with concrete or mortar to form an integrated structure. An example of this joint structure is disclosed in Figure 2 of Patent Document 1.

[0003] On the other hand, Patent Documents 2 and 3 disclose a PC pressure-bonded joint structure for PC piers, which uses precast concrete PC beams and pile head blocks and integrates the PC beams and pile head blocks by tension-bonding them together using PC steel.

[0004] Regarding the connection between the pile head block and the head of the steel pipe pile, Patent Document 2 describes a method in which a reinforcing bar is placed in the central hole of the pile head block, and filled with concrete to integrate the block, and a lateral tightening cable is provided at the bottom of the pile head block to tension and secure the block, thereby firmly joining the pile head block to the head of the steel pipe pile. However, the lateral tightening cables are arranged on both sides of the pile head without penetrating it to prevent cross-sectional defects in the steel pipe pile.

[0005] In Patent Document 3, the above-mentioned sheath pipe joint structure is utilized. A sheath pipe, which is previously fitted to a joint member (corresponding to a pile cap block), is fitted into the head of a pile columnar body (corresponding to a steel pipe pile). The gap between the joint member and the sheath pipe is filled with high-flow concrete or grout, and the joint member is fixed to the pile columnar body. The pile columnar body and the sheath pipe are then filled with concrete and allowed to solidify, thereby joining the pile columnar body and the joint member. Furthermore, a precast concrete member (corresponding to a precast concrete steel member) that connects the precast concrete beam member and the joint member is tensioned and fixed to the precast concrete beam member. However, the precast concrete member is positioned on both sides of the pile columnar body without penetrating it. For ease of explanation, the terminology is standardized below: the joint member is referred to as a pile cap block, the pile columnar body is referred to as a steel pipe pile, and the precast concrete member is referred to as a precast concrete steel member. Furthermore, the term "steel pile" used herein includes steel pipe piles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7185499 [Patent Document 2] Patent No. 7554445 [Patent Document 3] Patent No. 7178050 Summary of the Invention [Problem to be solved by the invention]

[0007] The techniques disclosed in Patent Documents 2 and 3 make it possible to form the framework of the superstructure of a PC pier by joining precast concrete members (beams, pile head blocks) together using the PC pressure joining method.

[0008] However, the connection between the pile head block and the steel pipe pile head has the following problems: The invention described in Patent Document 2 not only increases on-site work and costs, such as placing rebar in the central hole of the pile head block, but also means that the horizontal tightening cables are placed on both sides of the bottom of the pile head block without passing through the pile head, which forces the height and planar dimensions of the pile head block to be increased, making it impossible to reduce the weight of the PC member, which exceeds the general weight limit (about 20 tons) set forth in the Road Act, making it difficult to transport the member.

[0009] In the invention described in Patent Document 3, the pile head is placed within the pile head block, and the PC steel is placed on both sides of the sheath pipe in the planar direction so that it does not penetrate the steel pipe pile.As a result, the width of the PC beam must be made larger than the diameter of the sheath pipe, making it impossible to rationalize the shape and dimensions of the precast members (beams, pile head blocks) and reduce their weight.

[0010] There is no problem with joining a steel pipe pile and a sheath pipe using the sheath pipe joining method, but the connection between the sheath pipe and the pile head block must be a rigid connection in accordance with current port facility technical standards, and the acting bending moment and axial force must be smoothly transmitted between the sheath pipe and the pile head block.

[0011] The bending moment that can be transmitted to the pile head block is determined by the following formula as the bending moment that can be transmitted by the sheath pipe embedded in the pile head block.

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[0012] The above formula was derived from the bending stress resistance model due to concrete bearing pressure shown in Figure 3, according to the following relationship.

[0013] The bearing resistance cross section of the concrete is rectangular, width = diameter D of the sheath pipe, height = embedded length L of the sheath pipe, distance yc from the neutral axis to the edge of the cross section = L / 2, maximum edge stress σmax of the cross section = f' cd Then, the above Mud formula can be derived as follows: Moment of inertia: I0=D·L 3 / 12 Section modulus: Z=I0 / yc = 2·I0 / L Bending moment: Mud=σmax·Z=f' cd 2 I0 / L

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[0014] The axial force is transmitted only through the bond between the outer surface of the sheath pipe and the vertical ribs (if necessary) and the pile head concrete. When no vertical ribs are provided, the axial force Pud that can be transmitted can be calculated using the following formula:

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[0015] From the above, the embedment length of the sheath pipe into the pile head block is determined so as to satisfy both of the above two equations for transmission confirmation. Also, if the embedment length is short, there is a risk that the rotational rigidity of the pile head block will become extremely small, so the relationship between the embedment length (L) of the sheath pipe and the sheath pipe diameter (D) is generally set to L = 1D.

[0016] One of the advantages of PC structures is that the cross section of PC beams can usually be made smaller than that of RC beams, due to the prestressing of PC members and the use of high-strength concrete. To take advantage of this, the depth (h) of the PC beam can sometimes be made smaller than the diameter (D) of the steel pipe pile, as shown in Figure 1. In this case, in order to satisfy L = 1D, an unnecessarily large increase in height occurs in the height of the pile cap block, making it impossible to make it reasonably small, and therefore making it impossible to reduce the weight of the precast members.

[0017] The present invention solves the above-mentioned problems of the conventional technology, and aims to provide a rational joint structure between the sheath pipe and the pile head block so that the shape and dimensions of the pile head block can be rationally formed and the component can be made lighter. [Means for solving the problem]

[0018] The joining structure of the present invention is Steel piles and a sheath pipe fixed to the top of the steel pile and filled with concrete; a precast concrete pile cap block fixed to an upper portion of the sheath pipe; A PC beam extending horizontally from the pile head block, The PC beam and the pile head block are connected by PC pressure using a post-tensioning method with PC steel members arranged to penetrate the PC beam and the pile head block, The PC steel insertion sheath is disposed so as to penetrate through an upper portion of the sleeve pipe, At least a portion of the sheath is a steel pipe sheath rigidly connected to the sleeve pipe by welding, The PC steel member and the steel pipe sheath bear a part of the bending moment transmitted between the sheath pipe and the pile cap block, The steel pipe sheath bears part of the axial force transmitted between the sheath pipe and the pile cap block.

[0019] The joining structure of the present invention preferably comprises: The bending moment that can be transmitted between the sheath pipe and the pile head block is the smaller of the values ​​calculated by the following formulas (1) and (2).

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[0020] The joining structure of the present invention preferably comprises: The axial force that can be transmitted between the sheath pipe and the pile head block is calculated using the following equation (3).

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[0021] The joining structure of the present invention preferably comprises: If the diameter of the sheath pipe is larger than the diameter of the PC beam, The embedding length L of the sheath pipe into the pile head block is given by the following formula (4).

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[0022] The joining method of the joining structure of the present invention includes the steps of: Steel piles and a sheath pipe fixed to the top of the steel pile and filled with concrete; a precast concrete pile cap block fixed to an upper portion of the sheath pipe; A PC beam extending horizontally from the pile head block, The PC beam and the pile head block are connected by PC pressure using a post-tensioning method with PC steel members arranged to penetrate the PC beam and the pile head block, The PC steel insertion sheath is disposed so as to penetrate through an upper portion of the sleeve pipe, The coil is disposed within a steel pipe sheath welded to the sleeve pipe, At least a part of the sheath is welded to the sleeve pipe to form a rigidly connected steel pipe sheath. The PC steel member and the steel pipe sheath bear a part of the bending moment transmitted between the sheath pipe and the pile cap block, The steel pipe sheath bears part of the axial force transmitted between the sheath pipe and the pile cap block. [Effects of the Invention]

[0023] 1. By placing the prestressing steel member through the sheath pipe, the width of the PC beam can be rationally reduced. 2. By arranging the PC steel and steel pipe sheath so that they penetrate the sheath pipe in a straight line, the performance of the bending resistance cross section obtained by using the Young's modulus ratio of different materials is improved, and the bending moment that can be transmitted between the sheath pipe and the pile head block is increased.In addition, by adding the allowable shear force of the steel pipe sheath to the conventional sheath pipe adhesion force, the axial force that can be transmitted is improved, making it possible to shorten the embedded length L of the sheath pipe within a reasonable range, and thereby making it possible to rationally reduce the weight of PC components such as pile head blocks. 3. By improving the axial force that can be transmitted, there is no need to install vertical ribs or shear keys to increase the adhesion force of the sheath pipe, as was previously the case, and the shape, dimensions, and reinforcement of the pile head block can be made more rational. 4. The steel pipe sheath can also be used as a reinforcement for the through-hole, and can be used in combination with other reinforcing materials to alleviate stress concentration. 5. The steel pipe sheath penetrates the cross section of the sheath pipe and is anchored to the filled concrete and pile head block, which increases the resistance to pulling out of the sheath pipe and prevents it from coming loose. 6. By using a highly rigid steel pipe sheath, there is no risk of deformation or damage to the sheath when filling the sheath pipe with concrete, and temporary support materials are not required, which improves the filling ability of the concrete and significantly reduces the construction effort. [Brief explanation of the drawings]

[0024] [Figure 1] 1A and 1B are cross-sectional views of an example for explaining the basic configuration of the present invention and problems with the prior art, where (a) shows a cross section cut in the horizontal direction and (b) shows a cross section cut in the direction of gravity. [Figure 2] 1A and 1B are cross-sectional views showing a joint structure according to an embodiment, in which (a) shows a cross section cut in the horizontal direction and (b) shows a cross section cut in the gravity direction. [Figure 3] FIG. 10 is a diagram showing a bending resistance model due to concrete bearing pressure. [Figure 4] FIG. 10 is a diagram for explaining a method for calculating the bending moment that can be transmitted between the sheath pipe and the pile head block. [Figure 5] FIG. 10 is a diagram for explaining a method for calculating the axial force that can be transmitted between the sheath pipe and the pile head block. DETAILED DESCRIPTION OF THE INVENTION

[0025] The embodiments of the present application will be described in detail with reference to the drawings. Note that since the embodiments of the present application are an evolution of the proposal of the applicant disclosed in Patent Document 2, a description of the same configuration as in Patent Document 2 will be omitted.

[0026] FIG. 1 shows an example illustrating the basic configuration of the present invention and problems with the prior art. Similar to Patent Document 2, multiple steel pipe piles 1 are erected as foundation piles at a predetermined interval (span) in two directions, X and Y, to form a straight-pile horizontal pier. Precast PC beams 2 are arranged in both the X and Y directions. A pile head block 3 is installed at the top of each pile, and the PC beams 2 are installed on the sides of the pile head block 3 as X and Y beams. A composite deck 11 is provided between the X and Y beams. Sub-girders may also be provided between the PC beams 2 (main beams). Similar to Patent Document 2, PC beams 2 and pile head block 3 are joined by PC compression joints, with PC steel members 9 inserted into sheaths 4a that penetrate the PC beams 2 and pile head block 3. The PC steel members 9 are then tension-fixed by post-tensioning at anchorages (not shown) located at the center cross section of the span of the PC beams 2. The shape and dimensions of the PC beams 2 and pile head block 3 at the PC compression joints are also similar to Patent Document 2. In Figures 1(a) and 2(a), the dotted center line is the dividing line, and half of the figure shows the upper part of the pile head block 3 (the jaw protrusion at the tip of the PC beam 2 and the beam end intake part of the pile head block 3), and the other half shows the lower part of the pile head block 3 (the tip of the PC beam 2 and the surface of the pile head block 3).

[0027] This embodiment is an improvement on the joint structure between the pile head block 3 and the steel pipe pile head in order to further reduce on-site work based on Patent Document 2. This will be explained in detail below.

[0028] In this embodiment, the upper part of the sheath pipe 5 is embedded in the pile head block 3 beforehand, the lower part of the sheath pipe 5 is extended a predetermined length outside the cross-section of the pile head block 3, and fitted onto the head of the steel pipe pile 1. A filler material is then filled between the sheath pipe 5 and the pile head, solidified, and the sheath pipe 5 and the pile head are integrally joined. This is the same as the prior art disclosed in Patent Documents 1 and 3, but the joint between the steel pipe pile 1 and the sheath pipe 5 is offset outside the cross-section of the pile head block 3, and the PC steel member 9 is positioned to penetrate the upper part of the sheath pipe 5. As mentioned above, if the depth (h) of the PC beam 2 is smaller than the diameter (D) of the steel pipe pile 1, there is a problem that an unnecessary height increment 3a occurs in the height of the pile head block 3 to satisfy L = 1D. The following mainly describes how to rationalize the joint structure between the upper part of the sheath pipe 5 and the pile cap block 3.

[0029] First, we will explain the sheaths 4a and 4b shown in Figures 1 and 2. In order to apply prestress to PC members using the post-tensioning method, a sheath is generally embedded in the PC member to form holes for inserting PC steel strands. In order to accommodate the curved arrangement of the PC steel strands, the sheaths used in conventional technology are highly flexible spiral sheaths (steel sheaths or PE sheaths) (hereinafter referred to as "general sheaths 4a"), and materials with high bending rigidity, such as steel pipes, are generally not suitable for sheaths.

[0030] To solve the above-mentioned problems, as shown in Figure 2, a steel pipe that has not been used conventionally is used as a sheath (hereinafter referred to as "steel pipe sheath 4b") to be placed on the pile head block 3, and the upper part of the sheath pipe is placed in a straight line. This makes it possible to make the height of the pile head block 3 equal to the height of the PC beam 2. The sheath 4a to be placed on the PC beam 2 can be a general sheath as in the past.

[0031] The examples shown in Figures 1 and 2 have similar configurations, except that the type of sheath placed in the pile head block 3 is different, and in the example shown in Figure 1, there is a height increment 3a in the pile head block 3 to make the relationship between the embedded length (L) of the sheath pipe 5 and the sheath pipe diameter (D) L = 1D.

[0032] Multiple layers of sheaths 4a and 4b are embedded in advance through a precast concrete PC beam 2 and a pile head block 3. The upper part of a sheath pipe 5 is embedded and integrally joined to the pile head block 3, and the lower part of the sheath pipe 5 extends a predetermined length outside the cross section of the pile head block 3. In the example shown in Figure 1, the sheath placed on the pile head block 3 is also a general sheath 4a. In this case, although not shown, longitudinal ribs or shear keys are often provided on the outer surface of the sheath pipe 5 to increase the adhesive bonding strength between the upper part of the sheath pipe 5 and the concrete of the pile head block 3. When using the steel pipe sheath 4b of the present application shown in Figure 2, longitudinal ribs and shear keys are not required, reducing manufacturing effort and cost compared to conventional types. However, a shear key is provided on the outer surface of the lower part of the sheath pipe 5. The following describes the details of the joint structure between the PC beam 2 and pile head block 3 and the head of the steel pipe pile 1 shown in Figure 2.

[0033] The allowable tolerance for flat driving of steel pipe piles is ±100 mm, so the diameter of the sheath pipe 5 is selected to absorb construction errors, and the top of the sheath pipe 5 is embedded in the pile cap block 3 to prefabricate the pile cap block 3 with the sheath pipe 5. A shear key is provided to the outer surface of the top of the driven steel pipe pile 1 to a specified length. In addition, a partition plate 7 is provided inside the steel pipe pile 1 below the sheath pipe 5. The lower part of the sheath pipe 5 joined to the pile cap block 3 is fitted onto the head of the driven steel pipe pile 1, and the head of the steel pipe pile 1 is inserted into the sheath pipe 5 up to the level of the lower end of the PC beam 2. Non-shrinkage mortar 6 is filled between the sheath pipe 5 and the head of the steel pipe pile 1 and allowed to harden, joining the sheath pipe 5 and the head of the steel pipe pile 1 together. The length of the sheath pipe 5 joint should, as a general rule, be at least 1.5 times the diameter (D) of the steel pipe pile 1. Next, the PC steel members 9 are inserted into the general sheath 4a from the anchorage at one end of the PC beam (not shown), and then passed through the steel pipe sheath 4b of the sheath pipe 5 to the anchorage at the other end of the PC beam 2. Before tensioning, filler concrete 8 is poured into the hollow portion of the sheath pipe 5 and the steel pipe pile 1 and allowed to harden. The hardened concrete 8 firmly anchors the steel pipe sheath 4. The PC steel members 9 are then tensioned and fixed, forming a PC pressure-bonded joint between the pile cap block 3 and the PC beam 2. The pile is rigidly connected to the steel pipe pile 1 via the joint of the sheath pipe 5, forming the superstructure framework of the PC pier. A composite deck slab is then formed to complete the PC pier, as shown in Patent Document 2. A composite deck 11 is then formed to complete the PC pier, as shown in Patent Document 2.

[0034] Next, the contribution of the steel pipe sheath 4b to improving the performance of the joint structure between the sheath pipe 5 and the pile cap block 3 will be described.

[0035] In order to compare the present invention with the prior art, a bending moment transmission model (bending resistance due to concrete bearing pressure) between the sheath pipe 5 and the head concrete 8 of the prior art is shown in Figure 3, focusing on the sheath pipe joint structures shown in Figure 2 of Patent Document 1 and Patent Document 3. Note that the joint between the sheath pipe 5 and the steel pipe pile 1 (sheath pipe joint) shown in Figure 3 is the same as that of the prior art, and a description thereof will be omitted.

[0036] As shown in Figure 3, the planar distribution of the concrete bearing resistance stress is equal to the diameter (D) of the sheath pipe 5, the cross section of the concrete bearing resistance is rectangular, the cross section width = diameter D of the sheath pipe 5, height = embedded length L of the sheath pipe 5, due to the symmetry, the distance from the neutral axis to the edge of the cross section yc = L / 2, and the maximum edge stress of the cross section σmax = f' cd Then, from these relationships, the following cross-sectional constants and bending moment M are obtained. Moment of inertia: I0=D·L 3 / 12 Section modulus: Z=I0 / yc = 2·I0 / L Bending moment:

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[0037] In an embodiment of the present application, as shown in Fig. 2, a steel pipe sheath 4b is used as the insertion sheath for the PC steel strands 9, and is arranged to penetrate the sheath pipe 5. This adds an equivalent cross-sectional area of ​​the PC steel strands 9 and the steel pipe sheath 4b to the conventional concrete bearing resistance cross section in response to the bending moment M acting on the pile head of the steel pipe 1, and the moment of inertia and section modulus can be set from the total cross-sectional area, thereby improving the bending moment M (bending strength of the cross section) that can be transmitted. The following will explain this based on the embodiment shown in Fig. 4.

[0038] For ease of understanding, the embedded length (L) of the sheath pipe 2 in the pile head block 3 is set to equal the height of the pile head block 3 = the depth (h) of the PC beam 2, and the PC steel member 9 that passes straight through the sheath pipe 2 is set to a PC cable made up of multiple PC steel strands, with two rows (top and bottom) and two cables per row, for a total of four cables on the cross section. All sheaths placed on the pile head block 3 are steel pipe sheaths 4b welded rigidly to the sheath pipe 2. This is used as a bending resistance model due to the concrete bearing pressure of the pile head block 3, and the method for setting the various cross-sectional constants will be explained based on the following assumed conditions.

[0039] The cross-sectional area of ​​the PC steel 9 (PC cable) is Apc, and the effective cross-sectional area of ​​the steel pipe sheath 4b is As. Total cross-sectional area A1 = Apc + As, The design Young's modulus of the PC steel 9 and the steel pipe sheath 4b is Es, The design Young's modulus of concrete 8 and PC grout 10 is Ec, Here, since the PC grout 10 is a cement-based solidification material similar to the concrete 8, the slight difference in the design Young's modulus is ignored and they are considered to be the same. Using the Young's modulus ratio n = Es / Ec, A1 can be converted to the concrete equivalent cross-sectional area (Ac1). Ac1= ( n - 1 )·A 1 The centroid position of the equivalent cross-sectional area (Ac1) is assumed to be equal to the centroid position of the PC steel member 8 or the steel pipe sheath 4b (because the centroid positions of both are the same).

[0040] Adding the equivalent cross-sectional area (Ac1) to the concrete cross-sectional area (Ac = L·D) gives the total concrete cross-sectional area ΣA. ΣA=Ac+Ac1·q q: number of equivalent cross-sectional areas

[0041] The above concrete total cross section ΣA is set as the bending resistance cross section, and the cross section constants (Ic, Zc) are set, and the bending moment (Mud) that can be transmitted is determined using the obtained cross section constants (Ic, Zc).

[0042] In the example shown in Figure 4, the total cross-sectional area is calculated by adding equivalent cross-sectional areas (Ac1) at four locations to the concrete cross-section (Ac = D·L), and the centroid of the equivalent cross-sectional area is located on the neutral axis from the shape formed at a distance a from the neutral axis. Based on the elastic theory of material mechanics, the second moment of area (Ic) and section modulus (Zc) can be calculated as follows: Total cross section ΣA=Ac+4·Ac1 (Ac=D·L) Centroid position yc′=(Ac·yc+4·Ac1·yc) / ΣA (yc': distance from the upper edge of the cross section to the neutral axis of the total cross section) Moment of inertia Ic=Ac·yc 2 +4·Ac1·yc 2 +Σ(I0+4·Ipc+4·Is)-ΣA·yc′ 2 where: I0: Moment of inertia of concrete section (Ac) Ipc: Moment of inertia of PC steel 9 (PC cable) Is: Moment of inertia of steel pipe sheath 4b The section modulus is Upper edge Zc′=Ic / yc′ Lower edge Zc =Ic / yc In the example, the cross section is symmetrical and the neutral axis is at the centroid of the cross section, so The section modulus is Zc = Ic·L / 2.

[0043] A comparison between Mud (RC) with a conventional concrete bending resistance cross section and Mud (PC) in which the PC steel member 9 is inserted through the sheath pipe 5 using the steel pipe sheath 4b of the present invention is shown below.

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[0044] From the above, it can be seen that by using the steel pipe sheath 4b and passing the PC steel material 9 through the sheath pipe 5, the bending moment that can be transmitted (the bending moment resistance of the joint structure in this application) is improved. Although not shown in the figure, the effect of increasing the bending moment that can be transmitted as described above may be taken into consideration by adding the prestress introduced into the concrete cross section of the pile head block 3 to the concrete bearing stress.

[0045] Next, the contribution of the steel pipe sheath 4b to the axial force that can be transmitted between the sheath pipe 5 and the pile cap block 3 will be described.

[0046] As shown in FIG. 5, when the steel pipe sheath 4b is disposed so as to penetrate the sheath pipe 5, the axial force Pud that can be transmitted between the sheath pipe 5 and the pile cap block 3 is as follows.

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[0047] Equation 19 shows that the axial force that can be transmitted by the joint structure of the present invention (the tensile (compression) strength of the joint structure) is improved compared to the axial force transmitted only by conventional RC bond strength.

[0048] As a result, it is possible to shorten the embedded length L of the sheath pipe 5 within a reasonable range, and the weight of PC members such as the pile head block 3 can be reduced in a reasonable manner.

[0049] However, if the embedded length of the sheath pipe 5 is too short, the rotational rigidity of the pile head block 3 may be extremely reduced. Therefore, the embedded length (L) of the sheath pipe 5 is set as follows. When the diameter (D) of the sheath pipe 5 is greater than the height (h) of the PC beam 2, It is assumed that the steel pipe sheath 4b contributes to the strength, and L is set to be equal to or greater than h. When the diameter of the sheath pipe (D) is less than or equal to the depth of the PC beam (h), The contribution of the steel pipe sheath 4b to the strength is not taken into consideration, and L is set to 1D or more.

[0050] By using the steel pipe sheath 4b, when transmitting the axial force of the sheath pipe 5, shear resistance is achieved using only the allowable shear force of the steel pipe sheath 4b, and the PC steel 9 inside the steel pipe sheath 4b is not subjected to shear force. PC steel wires, PC steel rods, and reinforcing bars are wire materials that are only effective against tensile forces in the axial direction of the steel material. On the other hand, steel pipes and sectional steel are face materials that can be subjected to bending moments and axial forces in the axial direction as well as shear forces in the cross-sectional direction. However, in certain cases, prior art has used reinforcing bars as dowels to provide shear resistance in the cross-sectional direction, taking into account the dowel action. In this application, the PC steel material 9 is always subjected to tensile forces in the axial direction of the steel material, and does not provide shear resistance in the cross-sectional direction. In other words, the axial force transmission of the sheath pipe 5 is borne by the steel pipe sheath 4b, and only the tension force is borne by the PC steel material 9. When axial force is transmitted to the sheath pipe 5, a high bearing pressure restraint force is generated in the concrete around the steel pipe sheath 4b, and by anchoring the steel pipe to the concrete, it provides resistance to the pull-out of the sheath pipe 5 and also prevents the sheath pipe 5 from coming loose. In addition, by using a steel pipe sheath 4b at the joint between the upper part of the sheath pipe 5 and the pile head block 3, it is no longer necessary to provide vertical ribs or shear keys to increase the adhesion strength of the sheath pipe 5 as in the past. Furthermore, by welding the steel pipe sheath 4b to the sleeve pipe 5 and rigidly connecting them, the steel pipe can be used in combination with other reinforcing materials as a reinforcing material for the hole where the steel pipe penetrates the sleeve pipe 5.

[0051] As shown in Figure 1, when a general sheath 4a is installed inside the pile head block 3, the general sheath 4a is flexible and has very little rigidity. Therefore, when filling the sheath pipe 5 with concrete 8, it is necessary to install rebars or other temporary support materials to prevent deformation or damage to the sheath 4a. Not only is installing the rebars time-consuming, but they often interfere with the anchor reinforcement from the cast-in-place deck slab. As shown in Figure 2, by installing a highly rigid steel pipe sheath 4b inside the pile head block 3, the installation of rebars or other materials is unnecessary, improving the concrete filling ability and significantly reducing construction work. The PC steel material 9 may be a PC cable made up of a plurality of PC steel strands, or may be a PC steel rod. When the PC steel members 9 are arranged in multiple vertical stages, only a portion of the steel sheath 4b can be used as a steel pipe sheath 4b as needed to reduce costs. In this case, it is preferable that at least the top and bottom stages of the cross section be made of steel pipe sheath 4b. [Explanation of symbols]

[0052] 1 steel pipe pile 2 PC beams 3 Pile cap block 3a Height increment 4a General sheath 4b Steel pipe sheath 5 Sheath tube 6. Non-shrinkage mortar 7 Partition 8. Concrete 9 PC steel material 10 PC grout 11 Composite floor slab

Claims

1. Steel piles and a sheath pipe fixed to the top of the steel pile and filled with concrete; a precast concrete pile cap block fixed to an upper portion of the sheath pipe; A PC beam extending horizontally from the pile head block, The PC beam and the pile head block are connected by PC pressure using a post-tensioning method with PC steel material arranged to penetrate the PC beam and the pile head block, The PC steel insertion sheath is disposed so as to penetrate through an upper portion of the sheath pipe, At least a portion of the sheath is a steel pipe sheath rigidly connected to the sleeve pipe by welding, The PC steel member and the steel pipe sheath bear a part of the bending moment transmitted between the sheath pipe and the pile head block, A joint structure in which the steel pipe sheath bears part of the axial force transmitted between the sheath pipe and the pile cap block.

2. 2. The joint structure according to claim 1, wherein the bending moment that can be transmitted between the sheath pipe and the pile head block is the smaller of the values ​​calculated by the following equations (1) and (2): [Equation 1] [Equation 2] where: Mud: Bending moment transmitted between the sheath pipe and the pile cap block yc': Distance from the neutral axis of the portion of the sheath pipe embedded in the pile cap block to the upper edge of the cross section yc: Distance from the neutral axis of the portion of the sheath pipe embedded in the pile cap block to the lower edge of the cross section f' ｃｄ : Allowable compressive strength of pile head block concrete gamma ｂ : Material coefficient of the concrete filled in the sheath pipe Ic: Moment of inertia due to the total concrete cross section calculated by adding the concrete equivalent cross-sectional area of ​​the PC steel and the steel pipe sheath, calculated from the Young's modulus ratio (n = Es / Ec) between the design Young's modulus Es of the PC steel and the steel pipe sheath and the design Young's modulus Ec of the concrete of the pile head block, to the concrete cross section (cross-sectional area Ac = D L) that transmits the bending moment between the top of the sheath pipe and the pile head block where: L: Embedded length of the sheath pipe into the pile head block D: diameter of the sheath tube

3. 2. The joint structure according to claim 1, wherein the axial force that can be transmitted between the sheath pipe and the pile head block is calculated using the following formula (3). [Equation 3] where: Pud: The axial force that can be transmitted between the sheath pipe and the pile cap block gamma ｂ : Material coefficient of the concrete filled in the sheath pipe L: Embedded length of the sheath pipe into the pile head block φ: outer circumferential length of the sheath tube f ｂｏｄ : Allowable bond strength between the sheath pipe and the pile head block As: Effective cross-sectional area of ​​the steel pipe sheath f ｓａ : Allowable shear stress of the steel pipe sheath q: Quantity of the steel pipe sheath in the axial force region that can be transmitted from the sleeve pipe

4. If the diameter of the sheath pipe is larger than the diameter of the PC beam, 4. The joint structure according to claim 2 or 3, wherein the embedded length L of the sheath pipe into the pile head block is determined by the following formula (4). [Equation 4] where: L1: Length calculated using M = Mud L2: Length calculated as N = Pud L3: Length equal to the width of the PC beam where: M: Bending moment generated at the head of the steel pile due to the expected applied load Mud: The smaller of the values ​​calculated using the following formulas (1) and (2) [Equation 5] [Equation 6] N: Axial force generated at the head of the steel pile due to the expected applied load Pud: Axial force calculated by the following formula (3) [Equation 7] where: Mud: Bending moment transmitted between the sheath pipe and the pile cap block yc': Distance from the neutral axis of the portion of the sheath pipe embedded in the pile cap block to the upper edge of the cross section yc: Distance from the neutral axis of the portion of the sheath pipe embedded in the pile cap block to the lower edge of the cross section f' ｃｄ : Allowable compressive strength of pile head block concrete gamma ｂ : Material coefficient of the concrete filled in the sheath pipe Ic: Moment of inertia due to the total concrete cross section calculated by adding the concrete equivalent cross-sectional area of ​​the PC steel and the steel pipe sheath, calculated from the Young's modulus ratio (n = Es / Ec) between the design Young's modulus Es of the PC steel and the steel pipe sheath and the design Young's modulus Ec of the concrete of the pile head block, to the concrete cross section (cross-sectional area Ac = D L) that transmits the bending moment between the top of the sheath pipe and the pile head block Pud: The axial force that can be transmitted between the sheath pipe and the pile cap block gamma ｂ : Material coefficient of the concrete filled in the sheath pipe L: Embedded length of the sheath pipe into the pile head block φ: outer circumferential length of the sheath tube f ｂｏｄ : Allowable bond strength between the sheath pipe and the pile head block As: Effective cross-sectional area of ​​the steel pipe sheath f ｓａ : Allowable shear stress of the steel pipe sheath q: Quantity of the steel pipe sheath in the axial force region that can be transmitted from the sleeve pipe where: L: Embedded length of the sheath pipe into the pile head block D: diameter of the sheath tube

5. Steel piles and a sheath pipe fixed to the top of the steel pile and filled with concrete; a precast concrete pile cap block fixed to an upper portion of the sheath pipe; A PC beam extending horizontally from the pile head block, The PC beam and the pile head block are connected by PC pressure using a post-tensioning method with PC steel material arranged to penetrate the PC beam and the pile head block, The PC steel insertion sheath is disposed so as to penetrate through an upper portion of the sheath pipe, The coil is disposed within a steel pipe sheath welded to the sleeve pipe, At least a part of the sheath is welded to the sleeve pipe to form a rigidly connected steel pipe sheath. The PC steel member and the steel pipe sheath bear a part of the bending moment transmitted between the sheath pipe and the pile head block, A joining method in which the steel pipe sheath bears part of the axial force transmitted between the sheath pipe and the pile cap block.

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