Pier PC beam-end joint structure and joining method therefor

Abstract

To provide a beam-end joint structure which, when forming the framework of a pier superstructure using precast PC beams, minimizes offshore operations with cast-in-place concrete and is substantially stronger than conventional technology against large-scale tsunamis caused by massive earthquakes, and a joining method therefor.SOLUTION: Provided is a pier PC beam-end joint structure in which precast PC beams (X-beam 1, Y-beam 2) are provided between pile heads in two respective planar directions, and a deck slab is formed thereon. The structure has a pile-head block 3 fixed to the pile heads and comprising beam-end receiving portions 5 each recessed to a predetermined depth at a position corresponding to a beam end 5a of a PC beam and formed in a recessed shape in plan view so as to surround three sides of the beam end 5a of the PC beam. The beam end 5a is inserted into the beam-end receiving portion 5. PC steel members 6 that penetrate both the PC beam and the pile-head block 3 are tensioned and anchored, thereby achieving PC pressure joining of the PC beams and the pile-head block 3.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a beam end joint structure and a joining method for constructing a straight pile horizontal pier in which the beam end and pile head block are integrated using precast PC beams with PC pressure joints, regardless of whether the pier is being renovated or newly constructed. [Background technology]

[0002] Conventional techniques relating to a method for installing precast PC beams (girders) on foundation piles and joining and integrating the PC beams (girders) with the pile heads in a concrete pier are disclosed in several patent documents.

[0003] Patent Document 1 describes a method in which precast concrete vertical and horizontal beams are hung between the heads of the foundation piles, with reinforcing bars protruding from both end faces of each beam and exposed to the outside, and the beams and piles are integrated with cast-in-place concrete pile heads.This means that only the pile head concrete is cast in place, significantly reducing the amount of work at sea.

[0004] Patent Document 2 describes a method in which steel frames and reinforcing bars are protruded from the end face of the precast part of the beam, and the steel frames and reinforcing bars are placed on a support base on the pile, and then the space between the pile and the end face of the precast part of the beam is filled with cast-in-place concrete to join the pile and the beam, thereby minimizing work on site and eliminating the effort required to construct the joint.

[0005] In Patent Document 3, after installing a precast PC main beam at the pile head, the space between the main beam and the pile head is filled with filler concrete to join them together, and precast PC cross beams are erected on supports protruding from the sides of the main beam, with PC steel wires passing through and tensioned to integrate the main beam and cross beam. Because the lattice frame is a precast product, there is no need for offshore scaffolding or shoring that is required for cast-in-place concrete, and further, there is no need to assemble and remove formwork, allowing for rapid construction.

[0006] Patent Document 4 describes a method for inserting a connecting member into the pile head, forming a prefabricated beam member with a flat top plate and side walls hanging down from both edges, forming an inverted U-shaped cross section. The end of the top plate is placed on a support shelf attached to the connecting member, and the penetrating prestressed concrete (PC steel) member is tensioned and fixed. The prefabricated beam and connecting member are joined together by PC pressure welding. Then, the opening or sheath pipe that fits the pile head at the center of the connecting member is filled with cast-in-place concrete to join the connecting member to the pile head. A precast concrete deck or cast-in-place concrete deck is then formed on top of the beam portion, completing the pile-supported structure. The inverted U-shaped cross section of the prefabricated beam reduces the weight of the precast member, facilitating transportation even when manufactured in a factory, and eliminating the need for large cranes. Furthermore, even if the prefabricated beam member is temporarily installed and the pile sways due to waves or other factors, it is said to be possible to prevent the prefabricated beam member from falling off.

[0007] Furthermore, the applicant has already disclosed prior art related to PC pressure bonding in numerous patent documents, the most representative of which is the PC pressure bonding joint construction method. In order to explain the differences between the present invention and the prior art, which will be described later, Patent Document 5 will be taken up here. The characteristics of the prior art PC pressure bonding joint are as shown in Figures 1, 2 and 4 of Patent Document 5. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 7-207641 [Patent Document 2] Japanese Patent Application Publication No. 8-120638 [Patent Document 3] Patent No. 4597921 [Patent Document 4] Patent No. 7178050 [Patent Document 5] Patent No. 5612231 Summary of the Invention [Problem to be solved by the invention]

[0009] The methods disclosed in Patent Documents 1 and 2 involve protruding rebar or steel frames from the ends of precast beams to serve as pile head concrete, or pouring cast-in-place concrete between the end faces of the pile and the precast beam to join the pile head and the precast beam. This cast-in-place concrete work is carried out offshore, and the processes of erecting shoring and formwork, laying reinforcement, pouring concrete, and curing it are all carried out offshore, which not only lengthens the construction period and increases costs, but also makes quality control more difficult. In particular, salt damage from seawater splashes can quickly corrode rebar even during the construction stage, resulting in problems such as a significant decrease in the strength and durability of the constructed structure.

[0010] Patent Documents 3 and 4 disclose inventions that solve the above problems and further reduce on-site offshore work.

[0011] Specifically, in Patent Document 3, the precast PC main beam and the portion equivalent to the concrete (footing) of a conventional pile head are integrated in the longitudinal (normal) direction to form a single continuous piece spanning multiple spans. In the transverse direction (perpendicular to the normal), precast PC cross beams are erected on supports protruding from the sides of the PC main beam, and the PC steel wires that pass through both beams are tensioned and fixed, and the two are integrated by PC pressure bonding.

[0012] However, there are the following problems. 1. The main beam body is made into a single continuous piece spanning multiple spans, resulting in considerable weight and length. As a normal precast factory product, it is difficult to transport and install, and can only be manufactured on-site. However, due to significant constraints on on-site manufacturing and the capacity of heavy equipment for installation, it is difficult to adapt to various span divisions and floor plans. 2. The precast PC cross beams are erected on supports protruding from the sides of the PC main beams, and the PC steel wires that pass through them are tensioned and fixed to form an integrated structure. This creates a strong connection in the longitudinal direction (beam axis direction) of the cross beams, just like conventional PC pressure joints. However, the connection in the lateral direction (perpendicular to the beam axis) is weaker than in the longitudinal direction. If a large tsunami caused by a major earthquake were to strike from the side, there is a risk that the cross beams would fall and be swept away. 3. Since the precast PC main beam is essentially a combination of the conventional concrete pile head (footing) and the PC beam body, the width of the beam must be adjusted to match the required size of the concrete pile head (footing), resulting in wasted space in the component.

[0013] In Patent Document 4, the cross section of the prefabricated beam is made in an inverted U shape, thereby achieving weight reduction and solving the problems of weight and length caused by the extra-large precast members in Patent Document 3. However, the prefabricated beam and the connecting member are connected by tensioning and fixing the prefabricated beam members (PC steel members) that penetrate the beam members and connecting member. While this provides a strong connection in the longitudinal direction (beam axis direction) like conventional PC pressure connections, the connection in the lateral direction (perpendicular to the beam axis) remains weak. Furthermore, at the PC pressure connection surface between the beam end of the prefabricated beam and the connecting member, the PC steel members (PC steel members) pass only through the side wall portions hanging down from both edges. Therefore, only the side wall portions of the prefabricated beam are actually PC pressure-connected to the connecting member. The top plate portion simply rests on the support shelf and is not directly connected to the connecting member. The document also states, "When a prefabricated beam is loaded onto a connecting member, a gap forms between the inner surface of the side wall of the prefabricated beam and the side of the support ledge of the connecting member. It is desirable to fill this gap with grout. Alternatively, instead of filling the gap with grout, rubber may be attached to the side of the support ledge in advance, measuring the size of the gap, and then the prefabricated beam is loaded onto the support ledge. Alternatively, a water-repellent paint may be applied instead of grouting or attaching rubber." However, even if the gap between the inner surface of the side wall and the side of the support ledge at the connecting member is filled with grout, because the PC members (PC steel members) are not directly penetrated and pressure-bonded, the constant vibrations from large cranes traveling on the pier's superstructure could cause the grout to fall, creating a gap. Furthermore, even if rubber is attached instead of grout and water-repellent paint is applied, the document allows for gaps to form after the project is essentially completed. Therefore, the joints in the horizontal direction (perpendicular to the beam axis) are as weak as conventional PC pressure joints, and because there is a gap between the support shelf and the prefabricated beam, when a large tsunami caused by a major earthquake strikes the prefabricated beam from the side, it will not function to prevent the prefabricated beam from falling, and there is still a risk that the prefabricated beam will fall.In the first place, Patent Document 4 states that "after erection, before the connecting member and the prefabricated beam are integrated, the prefabricated beam can be prevented from falling off even if the pile column-shaped body sways due to waves or the like." However, even if the gaps are filled and the prefabricated beam (under its own weight alone) can be prevented from falling off due to small lateral swaying caused by waves, it will not be able to withstand a large tsunami caused by a major earthquake when the structure is in service after being joined, and is no different from conventional technology. This is because Patent Document 4 states that since the superstructure is integrated with the upper deck slab, no special consideration is required, and that "the support shelf portion is shown as having a shape with a downward inclined surface from the protruding edge of the support surface to reduce weight, but it is sufficient that the upper surface has a support surface that supports the top plate end of the prefabricated beam." This is because the PC member (PC steel) does not penetrate the support shelf portion, and the prefabricated beam and the support shelf portion are not joined by PC pressure bonding.

[0014] Conventional techniques for integrating precast concrete members, such as beams and columns, using PC pressure joints include, as shown in Figures 1, 2, and 4 of Patent Document 5, a method in which a barb is extended from the column surface, the beam end is placed on the barb, and PC steel wires pass through the barb to join the column and beam together. This is the basic configuration of the PC pressure joint construction method developed by the applicant. Conventional PC pressure joints also include joints without a barb. In either case, these are architectural structures constructed on land, and lateral loads, such as strong winds and earthquakes, act on the entire structure, with little risk of beam members being subjected to localized strong impact loads. Therefore, there is no need to worry about lateral collapse of individual beams. However, in the case of piers, depending on the usage environment, there is a risk of beams collapsing and being swept away when a large tsunami caused by a massive earthquake strikes from the side. This point is not taken into account in the prior art.

[0015] Therefore, the present invention aims to minimize the amount of on-shore work using cast-in-place concrete when forming the framework of a pier superstructure using precast PC beams, and to provide a beam-end joint structure and joint method that is significantly stronger than conventional technology against large-scale tsunamis caused by major earthquakes. [Means for solving the problem]

[0016] The PC beam end joint structure of the pier of this invention is as follows: A PC beam end joint structure for a pier in which precast PC beams are installed between pile heads in two directions on a plane, and a deck slab is formed on top of them. The pile head block has a height dimension approximately equal to the beam configuration of the PC beam, is recessed to a predetermined depth at a position corresponding to the end of the PC beam, and is provided with a beam end capture portion formed in a concave shape that surrounds the beam end of the PC beam on three sides in a plan view, and is fixed to the pile head; A portion of the beam end excluding a lower portion thereof protrudes toward the corresponding beam end intake portion, and the beam end is inserted into the beam end intake portion; The pile head block has a surface facing the lower part of the beam end and forms a joint between the lower part of the beam end and the pile head block, The PC beam and the PC steel member that penetrates the pile head block are tensioned and fixed, and the PC beam and the pile head block are joined by PC pressure bonding.

[0017] The PC beam end joining method for a pier of the present invention is as follows: A PC beam end connection method for a pier in which precast PC beams are installed between pile heads in two directions on a plane and a deck slab is formed on top of them, A pile head block is fixed to the pile head, and is recessed to a predetermined depth at a position corresponding to the end of the PC beam, and is provided with a concave beam end capture portion that surrounds the beam end of the PC beam on three sides in a plan view, has approximately the same height as the beam configuration of the PC beam, and has a surface facing the lower part of the beam end. The beam end has a portion excluding a lower portion protruding toward the corresponding beam end intake portion, After the PC beam is placed with the portion of the beam end other than the lower part inserted into the beam end intake section, the joints between the beam end intake section and the beam end and between the lower part of the beam end and the face of the pile head block facing the lower part of the beam end are filled with joint mortar and allowed to harden, The PC beam and the pile head block are joined together by tensioning and fixing the PC steel wires that pass through the PC beam and the pile head block. [Effects of the Invention]

[0018] According to the present invention, the following effects can be obtained. (1) The PC beam end joint structure that is formed is strong not only in the longitudinal direction (in the direction of the beam axis) but also in the lateral direction (perpendicular to the beam axis). Even if a large tsunami caused by a major earthquake strikes from the side, the beams will not fall and be washed away, significantly improving both earthquake resistance and tsunami resistance. (2) By constructing and forming the pile cap block and the beam member separately, it is possible to adapt it to various span divisions and floor plans without difficulty. (3) By using precast beam members and pile cap blocks, the amount of on-site concrete work at sea can be significantly reduced and construction time can be shortened, making this method particularly suitable for repair work on aging existing piers. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a plan view showing a PC beam end joint structure of a pier according to Example 1 of the present application. [Figure 2] 1. (b) is a cross-sectional view taken along the line AA shown in (a). [Figure 3] 10(a) is a partially enlarged plan view of a PC beam end joint structure of a pier according to Example 2 of the present application, and FIG. 10(b) is a BB cross-sectional view shown in FIG. [Figure 4] (a) is a plan view of a pile cap block according to Example 3 of the present application, (b) is a CC sectional view shown in (a), (c) is a plan view showing a PC beam end joint structure of a pier according to Example 3 of the present application, and (d) is a DD sectional view shown in (c). [Figure 5] FIG. 10 is a perspective view showing a PC beam end joint structure of a pier according to Example 3 of the present application. [Figure 6] (a) is a diagram showing the standards for seismic performance verification of specific facilities. (b) is a diagram showing the standards for seismic performance verification of standard facilities. [Figure 7] This is an image of local buckling of a steel pipe pile. [Figure 8] This is a side view showing the joint spacing at the PC pressure joint (surface) between the beam end and the pile cap block. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in detail based on the illustrated embodiments. In this application, a straight pile horizontal pier will be mainly shown as an example. Figures 1 and 2 show Example 1 of the present invention. Figure 1 shows part of the planar layout of the pier. Here, the normal direction is the X direction, and the direction perpendicular to the normal is the Y direction. The beam arranged parallel to the X direction is called X beam 1, and the beam arranged parallel to the Y direction is called Y beam 2.

[0021] A number of steel pipe piles 7 are erected as foundation piles at a predetermined interval (span) in two directions, X and Y. A pile head block 3 of the required size is formed in advance at the head of each pile. X beams 1 and Y beams 2, which serve as precast PC beams, are installed between each pile head block 3. The central section surrounded by X beams 1 and Y beams 2 is a concrete floor slab 4.

[0022] Although not shown in the drawings as it is not directly related to the problem of this application, small beams may be installed between PC beams (girders) depending on the pile arrangement interval (span). As in the past, stirrup reinforcement is placed in advance from the top of the precast PC beam to a specified height and integrated with the top concrete, but the stirrup reinforcement is not shown in the drawings.

[0023] The precast PC beams (X beam 1, Y beam 2) referred to in this invention are precast products, and are beam members into which prestress is introduced. Note that sheaths for inserting PC steel wires are embedded and arranged in advance in the beam members and pile head blocks 3, but are not shown in the figure.

[0024] The pile head block 3 is recessed to a predetermined depth at a position corresponding to the PC beam (X beam 1, Y beam 2), and has a beam end capture section 5 that surrounds the beam end 5a on three sides in a plan view. The PC beam is installed by inserting its beam end 5a into the beam end capture section 5, and PC steel wires 6 are inserted into sheaths (not shown) that are pre-placed on the beam member and the pile head block 3, and are then tensioned and fixed, thereby integrating the PC beam and pile head block 3 with a PC pressure joint.

[0025] As a detailed enlarged view of one of these, the plan view and AA side view of the area indicated by the dashed circle in Figure 1 are shown in Figure 2. The pile head block 3 is a precast member that is installed and integrated at the head of the pile 7 before the installation of the beam. The planar shape is not limited to the octagonal shape shown in the figure, and may be changed as long as it satisfies the structural performance and the arrangement of the PC steel wires.

[0026] In plan view, the beam end intake 5 has a predetermined gap from the peripheral surface (three sides) of the beam end 5a of the PC beam (X beam 1, Y beam 2) to form a joint 14, absorbing construction errors. Similarly, joints 14 are provided below the beam end 5a on the side (beam direction). After the PC beam is fitted into the beam end intake 5 and erected, joint mortar (not shown) is filled into the joint 14 and allowed to harden. After hardening, PC steel wires 6 are inserted into pre-embedded sheaths (not shown) and fixed in place under tension, forming a beam end joint structure. A concrete deck 4 is then formed on the top end of the beam to form a PC pier.

[0027] The beam-end joint structure formed in this way is strong not only in the longitudinal direction (beam axis direction) but also in the lateral direction (direction perpendicular to the beam axis), eliminating the risk of the beam falling even when struck laterally by a large tsunami caused by a massive earthquake. Furthermore, because prestress is introduced between the beam ends 5a of the PC beams (X beam 1, Y beam 2) and the pile head block 3, and the PC beams are joined by pressure bonding, the joint mortar between the beam ends 5a of the PC beams and the pile head block 3 will not fall off even under constant vibration loads. Because the pile head block 3 supports the bottom of the joint mortar, the joint mortar on both sides of the beam ends 5a will not fall off under constant vibration loads. In the structure described in Patent Document 4, grout (joint mortar) is filled in the gap between the inner surface of the side wall and the side of the support shelf. However, because the PC member (PC steel member) does not penetrate through the gap, there is a risk that the grout (joint mortar) will fall off and create a gap under constant vibration loads. The configuration of the present application eliminates this problem.

[0028] Next, a second embodiment will be described with reference to Fig. 3. Note that a description of the same configuration as that of the first embodiment shown in Figs. 1 and 2 will be omitted. In Fig. 3 as well, sheaths for inserting PC steel wires provided on the beam members and the pile head block 3 are omitted from illustration. Also, the joint mortar filled in the joints 14 is omitted from illustration.

[0029] If the height (also called thickness) of the pile head block 3 is approximately the same as or slightly larger than the beam configuration of the PC beams (X beam 1, Y beam 2), it will be impossible to insert the entire cross section of the beam end 5a into the pile head block 3. In other words, if the cross section of the concrete member in the height direction of the pile head block 3 remaining below the beam end 5a is small, the shear strength will be insufficient. In such cases, only a portion of the cross section of the member in the height direction of the beam end 5a is inserted into the beam end inlet 5. It is desirable that this portion have a cross-sectional area of more than half the cross section of the member in the beam end 5a. Furthermore, it is preferable that a portion of the beam protrudes from the adjacent portion toward the pile head block 3 and is supported by the jaw 8 protruding from the side of the pile head block 3 toward the beam end 5a via joint mortar filled in the joint 14. In this case, the "portion" includes the portion inserted into the pile head block 3 and the portion not inserted into the pile head block 3 but placed on the jaw 8, thereby increasing the stability of the beam member. The pile head block 3 and the beam member are joined by tensioning and fixing the PC steel wire 6 passed through the upper part of the beam end 5a and the PC steel wire 6 passed through the lower part of the beam end 5a and the jaw 8. The configuration of Example 2 also achieves the same effect as Example 1 against large-scale tsunamis from the lateral direction.

[0030] Next, as Example 3, a PC beam end joining method for a pier will be explained with reference to Fig. 4. Note that the sheaths for inserting PC steel wires are omitted from the illustration of the beam member and the pile head block 3. Also, the joint mortar filled in the joint 14 of the beam end 5a is omitted from the illustration.

[0031] First, as shown in Figure 4(a) and (b), 1. A prefabricated pile head block 3 is installed on the head of a steel pipe pile 7. An upper hole 3a and a lower hole 3b are formed in the center of the pile head block 3. The inner diameter of the lower hole 3b is made larger than the pile diameter to take into account any misalignment of the pile head during construction. It is preferable that the inner diameter of the upper hole 3a is made smaller than the pile diameter so that the pile head block 3 can be placed directly on the pile head. This allows the pile head block 3 to be temporarily installed freestanding on the pile head without the need for shoring or support materials. 2. A beam end intake section 5 and reinforcing bars 9 are provided in advance on the top of the pile head block 3, and a sheath for inserting the pile head horizontal tightening cable 10 and a notch 10b for installing the fixing device 10a are provided on the bottom. The pile head horizontal tightening cable 10 is placed on both sides of the pile head without penetrating the pile head so as not to cause cross-sectional defects in the steel pipe pile 7. 3. After the pile head block 3 is installed on the pile head, the joint 14 between the lower hole 3b and the pile head is filled with joint mortar 11. 4. By inserting the pile head horizontal tightening cable 10 and attaching the fixing device 10a to the end and fixing it in place, the pile head block 3 is firmly integrated with the pile head. 5. Place the reinforcing bar 9 in the central hole of the pile head, and a sheath (not shown) and other necessary reinforcing bars (not shown) at the position of the PC steel wire 6 that is planned to pass through from the beam. 6. Fill the central hole in the pile head with concrete 12 to a specified depth and allow it to cure. The depth should preferably be twice the pile diameter.

[0032] However, the construction procedure is not limited to the above, and for example, step 4 may be performed after step 6, with the fill concrete 12 poured first, and then the pile head horizontal tightening cable 10 tensioned and fixed.

[0033] Next, as shown in Figure 4(c) and (d), 7. Precast PC beams in two directions on the plane are placed by inserting each beam end 5a into the beam end intake section 5, and joint mortar is filled into the beam ends 5a and surrounding joints 14 and allowed to harden. 8. The PC steel wire 6 is inserted into a pre-buried sheath (not shown), passed through the pile head, and fixed under tension, and the beam end 5a and the pile head block 3 are joined together by PC pressure bonding. 9. Finally, the top concrete main reinforcement is inserted through the stirrups that have been placed in advance to protrude from the top end of the PC beam and the reinforcing bars 9 that have been placed in advance on the top surface of the pile cap block, and the top concrete is poured to integrate them. However, it is more efficient to pour the top concrete at the same time as pouring the concrete deck slab 4.

[0034] Although not shown in the figures, the concrete slab 4 is constructed by bridging a precast PC slab with ribs between precast PC beams, placing reinforcement on top of it, and pouring top concrete to integrate it. This allows the precast PC slab to double as formwork, reducing the labor required for on-site work. To make the work procedures for the above-mentioned embodiments 1 to 8 easier to understand, they are all shown together in Figure 5 (perspective view). However, some steps and details are not shown.

[0035] A prefabricated pile head block 3 is installed on the head of the steel pipe pile 7. The pile head block 3 is provided with a beam end intake portion 5, a sheath 13 for inserting the PC steel wire 6, and a notch 10b for fixing the pile head horizontal tightening cable 10.

[0036] The upper opening of the pile head block 3 is placed on the top surface of the steel pipe pile 7. For ease of understanding, a cross section of one pile head block 3 cut approximately in half is shown. The gap between the lower opening and the steel pipe pile head is filled with joint mortar (not shown), the pile head horizontal fastening cable 10 is inserted into the sheath 13 and arranged in two horizontal directions, and fixing device 10a (not shown in Figure 5) is attached to the notch 10b at the end to tension and fix it, and prestress is introduced into the pile head in two horizontal directions and tightened, thereby firmly joining the pile head block 3 to the head of the steel pipe pile 7.

[0037] A precast PC beam, which is provided with a sheath 13 for inserting PC steel wires in advance, is spanned between pile head blocks 3 with its beam end 5a inserted into the beam end intake section 5 of the pile head block 3 installed on the steel pipe pile 7.

[0038] A sheath for the PC steel wire and a reinforcing bar (not shown) are placed in the central hole of the pile head block 3 , and the PC steel wire 6 is inserted into the sheath of the beam and passed through the pile head block 3 .

[0039] After filling the central hole of the pile head block 3 with filler concrete 12 and allowing it to harden, the PC steel wire 6 is tensioned and fixed (fixing device not shown) and the PC beam and pile head block 3 are joined together by PC pressure bonding to form a single unit.

[0040] The above construction procedure is a rough explanation, but is not limited to this. For example, if a rebar is placed in the central hole of the pile head block 3 and then filled with concrete 12, it can be reliably integrated with the pile head block 3, and the illustrated pile head horizontal fastening cable 10 may not need to be placed or tensioned. In this case, the configuration will be as shown in Figures 1 to 3, and the pile head block 3 can have an octagonal top and bottom in plan view, which is also applicable to the present invention.

[0041] In the current technology, the seismic performance verification of a straight pile horizontal pier is carried out based on the technical standards of port facilities, and a method is adopted in which the deformation performance of the pier is verified by allowing localized damage during an earthquake that does not lead to the collapse of the entire structure. Specifically, as shown in Figure 6, the contingency state verification for level 2 earthquake motion of an earthquake-resistant reinforced facility is as follows: In the case of specific facilities, (1) The design section force acting on the superstructure must not exceed the design section strength. (2) There are no piles that have reached the limit curvature in more than two places per pile. (3) The design value of the axial force acting on the pile does not exceed the design value of the resistance force based on the failure of the ground. For standard facilities, Regarding (2) above, it is required that there are no more than two piles that have reached the limit curvature per pile.

[0042] In other words, in the event of a massive earthquake (level 2 earthquake load), the superstructure of any facility may not be destroyed, and all pile heads may yield in bending, reaching full plastic moment and forming plastic hinges. For special facilities, it is acceptable for plastic hinges not to occur in two or more locations per pile (pile head and underground), while for standard facilities, it is acceptable for plastic hinges not to occur in two or more locations per pile (pile head and underground). Therefore, the current state of structural design emphasizes the degree of fixation between the superstructure, which is reinforced concrete or prestressed concrete, and the pile heads (degree of rotational restraint of the pile heads), and provides ample structural margin to prevent the pile heads from dropping to the point where full plastic moment is reached and plastic hinges occur.

[0043] However, as shown in Figure 7, it has been reported that during a large-scale earthquake (level 2 earthquake load), after a steel pipe pile reaches the bending yield moment (My), local buckling may occur at the head of the steel pipe pile, causing it to lose its strength before reaching the full plastic moment (Mu).

[0044] Therefore, in order to solve this problem, the present invention goes against the current design method in which the superstructure (beam) excessively restrains the pile head, and instead, based on the earthquake-resistant design method using the PC pressure joint method shown in Patent Document 5, the joints at the PC pressure joints (surfaces) between precast PC members are kept rigidly connected without opening up until a specified design load is reached, and when the specified design load is exceeded, the joints are separated (opened) to protect the structural members around the joints from damage. An image of this is shown in Figure 8.

[0045] Specifically, prestress is introduced by the tension anchoring force of the PC steel wire 6 at the beam end 5a of the PC beam (X beam 1, Y beam 2), the pile head block 3, and the PC pressure joint (surface) so that the relationship shown in the following equation holds. Me≦My Joints remain rigid without any gap Me>My Joint spacing Me: Bending moment due to earthquake load acting on the beam end My: Yield bending moment of steel pipe pile head

[0046] As described above, by separating the joints after the steel pipe pile head reaches the yield bending moment, the PC beam reduces the restraint on the steel pipe pile head, preventing local buckling at the steel pipe pile head and ensuring that the pile head's strength reaches the full plastic moment (Mu) as designed, even during a large-scale earthquake. Also, if the type and number of PC steel wires 6 are designed so that the PC steel wires at the end of the PC beam do not yield during a massive earthquake (level 2 earthquake load), after the earthquake, the PC steel wires 6 will remain in their elastic range, so the separated joints will close and return to their original state, maintaining the superstructure and the steel pipe pile 7 in good condition.

[0047] To summarize the above, in the present invention, in the PC pressure joint at the beam end 5a, prestress is introduced by the tension anchoring force of the PC steel wire 6 in the longitudinal direction (direction of the beam axis) so that local buckling does not occur after the yield bending moment at the pile head of the steel pipe pile 7 and joint separation is possible, and in the lateral direction (direction perpendicular to the beam axis), it is a PC beam end joint structure for a pier that is designed to prevent the beam from falling due to a large tsunami.

[0048] Therefore, the conventional PC pressure joint construction method has been further evolved to create a pier structure that can be safely used in the specific usage environment of a PC pier, and has significantly improved earthquake resistance and durability.

[0049] The present invention has been described in more detail and specifically above by showing the embodiments, but the embodiments are merely illustrative and do not limit the present invention. [Explanation of symbols]

[0050] 1X Beam 2 Y beam 3 Pile cap block 3a Upper hole 3b Lower hole 4 Concrete deck 5 Beam end intake 5a beam end 6 PC steel wire 7 Piles (steel pipe piles) 8 Jaw 9. Reinforced concrete 10 Pile head horizontal fastening cable 10a Fixing device 10b Notch 11 Joint mortar 12 Filling concrete 13 Sheath 14 Joint

Claims

1. A PC beam end joint structure for a pier in which precast PC beams are provided between pile heads in two directions on a plane, and a deck slab is formed on top of them. The pile head block has a height dimension approximately equal to the beam length of the PC beam, is recessed to a predetermined depth at a position corresponding to the beam end of the PC beam, and is provided with a beam end capture portion formed in a concave shape that surrounds the beam end of the PC beam on three sides in a plan view, and is fixed to the pile head; A portion of the beam end excluding the lower portion protrudes toward the corresponding beam end intake portion and is inserted into the beam end intake portion, The pile head block has a surface facing the lower part of the beam end and forms a joint between the lower part of the beam end and the pile head block, A PC beam end joint structure for a pier, characterized in that the PC steel material passing through the PC beam and the pile head block is tensioned and fixed, and the PC beam and the pile head block are PC pressure-jointed.

2. The beam end joint structure of a pier as described in claim 1, characterized in that at least half of the beam end cross section perpendicular to the longitudinal direction of the PC beam is inserted into the beam end intake portion.

3. The pile head block has a jaw protruding below the PC beam, The beam end joint structure of a pier as described in claim 2, characterized in that the PC beam is installed on the jaw, the PC steel material passing through the PC beam and the jaw is tensioned and fixed, and the PC beam and the pile head block are connected by PC pressure bonding.

4. A PC beam end joining method for a pier in which precast PC beams are provided between pile heads in two directions in a plane and a deck slab is formed on the precast PC beams, The pile head block is fixed to the pile head, and is provided with a beam end capture portion that is recessed to a predetermined depth at a position corresponding to the beam end of the PC beam and that is formed in a concave shape surrounding the beam end of the PC beam on three sides in a plan view, has a height dimension approximately the same as the beam configuration of the PC beam, and has a surface facing the lower part of the beam end. The beam end has a portion excluding a lower portion protruding toward the corresponding beam end intake portion, After the PC beam is placed with the portion of the beam end other than the lower part inserted into the beam end intake portion, the joints between the beam end intake portion and the beam end and between the lower part of the beam end and the face of the pile head block facing the lower part of the beam end are filled with joint mortar and allowed to harden, A method for joining PC beam ends of a pier, characterized in that the PC beam and the pile head block are joined together by tensioning and fixing the PC steel wire that passes through the PC beam and the pile head block.

5. 5. The method for joining beam ends of a pier according to claim 4, wherein at least half of the cross section of the beam end perpendicular to the longitudinal direction of the PC beam is inserted into the beam end intake portion.

6. A jaw protruding from the lower side of the beam end intake portion is formed on the pile head block, The method for joining beam ends of a pier as described in claim 5, characterized in that the PC beam is installed on the jaw, the PC steel wire passing through the PC beam and the jaw is tensioned and fixed, and the PC beam and the pile head block are joined by PC pressure bonding.

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