JP2006257710A - Joint structure of cast-in-situ concrete pile to foundation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joint structure of a cast-in-situ concrete pile to a foundation capable of preventing a resistance body from being damaged in earthquake and reducing a pile head stress on the foundation of a building and coping with the large rotation of a pile head part produced when a big earthquake occurs without lowering workability. <P>SOLUTION: In this joint structure of the cast-in-situ concrete pile 1 to the foundation 2 for connecting, with semi-rigidity, the pile head 1a of the cast-in-situ concrete pile 1 to the concrete foundation formed on the upper side of the pipe head 1a through a joint member 7 having one end part 7a buried in the center part of the pile head 1a and the other end part 7b buried in the foundation 2, the one end part 7a of the joint member 7 is adhered to the concrete of the pile head 1a and fixed to the inside of the pile head 1a. In the other end part of the joint member 7, a fixed part 7 fixed into the foundation 2 is formed at the tip of the other end part and a covering material 8 cutting off the adhesion of the foundation 2 to the concrete is put on the outer peripheral surface of the other end part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a joint structure between a cast-in-place concrete pile and a foundation that semi-rigidly join the cast-in-place concrete pile and the foundation.

  Conventionally, a cast-in-place concrete pile method has been widely used as a method for constructing a large-diameter pile at a low cost. In normal cast-in-place concrete piles, the upper end of the pile main reinforcement is fixed in the building foundation and the pile head is often rigidly connected (fixed) to the building foundation such as footing. In order to improve the earthquake resistance, a method of semi-rigid joining without fixing the pile head to the building foundation has been proposed. This semi-rigid joint structure has a pile main bar that is not anchored in the building foundation but stopped in the pile head, and a joint member (rebar material) that is arranged from the center of the pile head to the building foundation. This is a joint structure in which the pile head and the building foundation are connected via

On the other hand, in recent years, a joining structure has been proposed in which a cylindrical ready-made pile such as a steel pipe pile and a building foundation are semi-rigidly joined via a joining member. In this joint structure, a steel plate (bearing plate) with an area smaller than the top surface of the pile head is interposed between the upper surface of the pile head and the lower surface of the building foundation. A rod-shaped joining member is provided which is embedded in the interior and the upper portion is embedded in the building foundation. The upper and lower ends of this joining member are formed with enlarged diameter portions (nuts) that serve as anchors, and the joining member is coated with a covering material on the side surface so as not to bear compressive force. Adhesion is cut, and a cushioning material is disposed so as to surround the outer periphery of the steel sheet (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2002-356861 (page 3-4, FIG. 4)

  However, in the conventional joint structure of cast-in-place concrete pile and foundation described above, since the joint member embedded in the foundation is attached to the concrete of the foundation, the axial rigidity of the joint member is increased, and the cast-in-place concrete pile However, there is a problem that the foundation is difficult to rotate and cracks may occur in the concrete of the foundation when the joining member expands and contracts with the rotation of the foundation with respect to the cast-in-place concrete pile. In addition, in the above-described conventional prefabricated pile-to-foundation joint structure, the outer peripheral surface of the joint member in the pile head is coated with the coating material, but the outer peripheral surface of the joint member in the pile head is coated with the coating material. Since the work to be performed is a considerable effort, there is a problem that workability is deteriorated.

  The present invention takes the above-mentioned conventional problems into consideration, and while preventing damage to pile bodies during earthquakes and reducing pile head stress to building foundations, large earthquakes can occur without reducing workability. The purpose of the present invention is to provide a joint structure between a cast-in-place concrete pile and a foundation that can cope with the occurrence of a large rotation in the pile head.

  The invention according to claim 1 is characterized in that a pile head of a cast-in-place concrete pile and a concrete foundation formed above the pile head are embedded at one end in the center of the pile head and the other end. In a joint structure between a cast-in-place concrete pile and a foundation to be semi-rigidly joined via a joint member embedded in the foundation, one end of the joint member is attached to the concrete of the pile head and The other end portion of the joining member is fixed at the tip, and a fixing portion for fixing in the foundation is formed at the tip, and the outer peripheral surface is coated with a covering material that cuts off adhesion to the foundation concrete. It is characterized by.

  Due to such a feature, a fixing part that is fixed in the foundation is formed at the tip of the other end of the joining member embedded in the foundation, so that the tensile strength of the joining member is reduced at the joint between the pile and the foundation. Acts as a tensile resistance. Further, since the outer peripheral surface of the other end portion of the joining member is coated with a covering material that cuts off the adhesion to the concrete of the foundation, it is possible to reduce the shaft rigidity while ensuring the tensile strength of the joining member. Even when the foundation is rotated with respect to the cast-in-place concrete pile, the joining member is expanded and contracted without affecting the concrete of the foundation. Furthermore, the covering material that cuts off the adhesion with concrete is covered only on the other end portion of the joining member embedded in the foundation, and the covering material is not covered on one end portion of the joining member embedded in the pile head. The covering work of the covering material in the pile head which is difficult to construct is eliminated, and the work is facilitated.

  The invention according to claim 2 is the joint structure between the cast-in-place concrete pile and the foundation according to claim 1, wherein the covering material is disposed with a space between the upper end surface of the pile. It is said.

  With such a feature, a portion on the base side (joint side between the pile and the foundation) of the other end of the joining member is fixed in the concrete. Thereby, in a junction part of a pile and a foundation, a joining member exhibits a dowel effect.

  According to the joining structure of the cast-in-place concrete pile and the foundation according to the present invention, it is possible to realize the prevention of damage to the pile body and the reduction of the pile head stress to the foundation by the semi-rigid joining by the joining member. In addition, it can resist axial force even when tension is applied to the pile, can reduce the rotational rigidity against pile head bending, and further suppress the occurrence of cracks in the foundation concrete due to expansion and contraction of the joining members. be able to. Moreover, workability does not deteriorate and construction can be easily performed.

  In addition, since the covering member is arranged at an interval from the upper end surface of the pile, the joining member exerts a dowel effect at the joint between the pile and the foundation, so even if a tensile force acts on the pile Stable shear resistance can be ensured, and excessive stress concentration on a specific pile can be avoided.

  Hereinafter, 1st, 2nd embodiment of the joining structure of the cast-in-place concrete pile and foundation which concerns on this invention is each demonstrated based on drawing.

[First embodiment]
First, the first embodiment will be described.
FIG. 1 is a longitudinal sectional view showing a joint structure between a cast-in-place concrete pile (hereinafter simply referred to as a pile 1) and a foundation 2 in the first embodiment, and FIG. FIG. 3 is a cross-sectional view taken along the line bb shown in FIG.

  As shown in FIGS. 1, 2, and 3, the pile 1 is constructed substantially vertically in the ground G, and is built into a cylindrical pile concrete 3 and a cylindrical concrete pile 3 embedded in the pile concrete 3. It consists of a rebar bar 4. The reinforcing bar 4 is composed of a plurality of pile main bars 5 extending in the vertical direction and a plurality of pile hoop bars 6 surrounding and restraining the plurality of pile main bars 5. The plurality of pile main bars 5 are arranged circumferentially at intervals, and are not protruded from the upper end surface 1c of the pile 1 but are stopped in the pile head 1a. The plurality of pile hoop bars 6 are arranged at intervals in the vertical direction, and the pitch of the pile hoop bars 6 in the pile head 1a is narrower than the pitch of the pile hoop bars 6 in the other general portion 1b. It has become.

  On the other hand, the foundation 2 is a reinforced concrete structure such as a footing, and is constructed immediately above the pile 1.

  The pile 1 and the foundation 2 have a lower end portion 7a (one end portion) embedded in the center portion of the pile head 1a with a sufficient fixing length and an upper end portion 7b (other end portion) sufficient in the foundation 2. Semi-rigid joining is performed via a plurality of joining members 7 embedded with a fixing length. The joining member 7 is a rod-shaped member in which an enlarged diameter portion 7c (fixing portion) that is fixed in the foundation 2 is formed at the upper end (tip) of the upper end portion 7b embedded in the foundation 2. Since the upper end portion 7b of the joining member 7 is fixed in the foundation 2 by the enlarged diameter portion 7c, an interference problem with other reinforcing bars arranged in the foundation 2 is less likely to occur. The enlarged diameter portion 7c is, for example, a method (T head bar method) in which the end of the reinforcing bar is subjected to high frequency induction heating to expand the end of the reinforcing bar without a plate, or a method in which the fixing plate is friction-welded to the tip of the deformed reinforcing bar. (Mighty head method) or a method (plate nut method) in which a nut is screwed into the end of a threaded joint.

  Further, the outer peripheral surface of the joining member upper end portion 7b excluding the enlarged diameter portion 7c is coated with a covering material 8 that cuts off the adhesion of the foundation 2 to the concrete, and the upper end portion 7b of the joining member 7 is unbonded. The covering material 8 is made of, for example, a well-known unbonded sheath that is vertically divided into two, and covers the outer peripheral surface of the joining member 7 from both sides. In addition, as the covering material 8, a vinyl tape, a vinyl sheet, or other coating material may be used. Moreover, the coating | covering material 8 is arrange | positioned in the position which opened the predetermined space | interval upward from the upper end surface 1c of the pile 1, and the length dimension of the coating | covering material 8 is adjusted suitably.

On the other hand, the lower end part of the joining member 7 is attached to the pile concrete 3 of the pile head 1a over the whole, and is fixed in the pile head 1a. Moreover, the lower end part of the joining member 7 embed | buried in the pile head 1a is restrained by the several hoop muscle 9 arranged in the vertical direction at intervals.
The plurality of joining members 7 are not arranged in an arc shape in a plan view, but are arranged in a polygonal shape such as a quadrangle or an octagon.

  A rubber sheet 10 is interposed between the upper end surface 1c of the pile 1 and the bottom surface 2a of the foundation 2 as a cushioning material. The rubber sheet 10 is elastic and durable. For example, a general-purpose chloroprene rubber that is easily cut into an arbitrary shape and is widely used at low cost is used. The rubber sheet 10 is formed in an annular shape along the outer edge of the upper end surface 1c of the pile 1, and is installed in a region other than the central portion of the pile upper end surface 1c where a plurality of joining members 7 are arranged. The inner edge of the rubber sheet 10 is formed along the planar arrangement of the plurality of joining members 7 arranged in a polygonal shape, with a predetermined interval between the outermost joining members 7. Yes. The rubber sheet 10 may be formed using a single annular sheet, or may be formed by arranging a plurality of divided rubber sheet pieces in an annular shape. Further, by forming the rubber sheet 10 using the divided rubber sheet pieces, the yield can be improved and the cost can be reduced.

  Further, an axial force transmission portion 11 that is interposed between the upper end surface 1 c of the pile 1 and the bottom surface 2 a of the foundation 2 and transmits an axial force from the foundation 2 to the pile 1 is formed inside the annular rubber sheet 10. ing. The axial force transmission unit 11 is a part that joins the pile head 1 a and the foundation 2, and is made of concrete formed integrally with the concrete of the foundation 2. The cross-sectional area of the axial force transmission portion 11 in plan view is smaller than the cross-sectional area of the pile 1, and specifically, the size is 1/4 to 2/3 of the axial cross-sectional area of the pile head 1a.

  Next, the construction method of the joining structure of the pile 1 and the foundation 2 which consist of an above-described structure is demonstrated.

First, a pile placing process for placing the pile 1 on the ground G by a well-known cast-in-place concrete pile construction method is performed. At this time, a plurality of joining members 7 are arranged on the pile head 1c.
Next, after the completion of the placement of the pile 1, the ground G is excavated to expose the upper end portion of the pile 1, and a pile head processing step is performed for scooping the surplus portion at the upper end of the pile 1. By this step, the upper end portion 7b of the joining member 7 is exposed, and the upper end portions 7b of the plurality of joining members 7 protrude from the center of the upper end surface 1c of the pile 1. In addition, the pile main reinforcement 5 is stopped within the pile head 1 a and is not protruded from the upper end surface 1 c of the pile 1.

Next, the cushioning material installation process which installs the rubber sheet 10 in the upper end surface 1c of the pile 1 is performed. At this time, even if there is some unevenness on the upper end surface 1c of the pile 1, there is no problem because the rubber sheet 10 is adapted.
Next, an unbonding process for covering the outer peripheral surface of the upper end portion 7b of the joining member 7 with the covering material 8 is performed. Specifically, the unbonded sheath divided in two on the outer peripheral surface of the upper end portion 7b of the joining member is respectively covered from both sides, and the unbonded sheath divided in two is further taped so as not to come off. At this time, the covering material 8 is attached to a position floating from the upper end surface 1c of the pile 1 so that there is a predetermined interval between the lower end of the covering material 8 and the upper end surface 1c of the pile 1 so that it does not fall after the attachment. Temporarily fix. Note that a vinyl sheet may be used as the covering material 8 and the vinyl tape may be wound around the outer peripheral surface of the joining member upper end portion 7b. Alternatively, the vinyl sheet may be used as the covering material 8 and the vinyl sheet may be attached to the joining member upper end portion. It may be wrapped around the outer peripheral surface of 7b and stopped with tape.
Next, a foundation reinforcing step (not shown) is arranged, a foundation form (not shown) is built, concrete is placed, and a foundation forming step for forming the foundation 2 is performed.

  According to the joining structure of the pile 1 and the foundation 2 having the above-described configuration, the semi-rigid joining by the joining member 7 reduces the pile head fixing degree, so that the pile head moment is significantly reduced. The generated maximum stress is not the pile head 1a but the general portion 1b. This is because the bending stress concentrated on the pile head in the pile head fixed joint is smoothed, and the value of the maximum stress is 2/3 or less of the maximum stress generated in the conventional pile head. Therefore, the cross-sectional dimension of the pile 1 can be reduced by the cast-in-place concrete pile construction method, and the cost can be reduced. Moreover, since a pile head moment becomes small, the stress which acts on the foundation 2 also becomes small, can reduce the cross-section of the frame of the foundation 2, and can aim at cost reduction. Furthermore, if the cross-section of the foundation 2 is reduced, the excavation depth can be reduced and the retaining can be rationalized, so that further cost reduction can be achieved.

  Moreover, since the enlarged diameter part 7c fixed in the foundation 2 is formed in the front-end | tip of the upper end part 7b of the joining member 7 embed | buried in the foundation 2, the tensile strength of the joining member 7 is the pile 1 and the foundation 2. It acts as a tensile resistance force at the joint part, and the axial force can be processed at the joint part even if a tensile force acts on the pile.

  Further, since the outer peripheral surface of the upper end portion 7b of the joining member 7 is coated with the covering material 8 that cuts off the adhesion of the foundation 2 to the concrete, the shaft rigidity is reduced while securing the tensile strength of the joining member, and the pile head Rotational rigidity against bending can be reduced. Moreover, since the joining member 7 is expanded and contracted without affecting the concrete of the foundation 2 even when the foundation 2 is rotated with respect to the pile 1, it is possible to prevent the occurrence of cracks in the foundation concrete due to the expansion and contraction of the joining member. .

  Moreover, it is only the joining member upper end part 7b embed | buried in the foundation 2, and the lower end part 7a of the joining member 7 embed | buried in the pile head 1a is coat | covered with the coating | covering material 8 which cuts adhesion with concrete. Since the covering material 8 is not covered, the covering work of the covering material 8 in the pile head 1a which is difficult to perform is eliminated, and the work can be easily performed without deteriorating workability.

  Further, the covering material 8 is disposed at a position spaced apart from the upper end surface 1c of the pile 1 by a predetermined distance. And since it is fixed in the concrete of the foundation 2, the joining member 7 exhibits the dowel effect at the joint between the pile 1 and the foundation 2. Thereby, the dowel effect of the joining member 7 (the shear shear resistance of the joining member 7) and the frictional force of the compression part between the upper surface of the axial force transmission part 11 and the bottom face 2a of the foundation 1 Even if a compressive force acts on the pile 1 or a tensile force acts on the pile 1, a stable shear resistance force can be secured and excessive stress concentration on a specific pile 1 can be avoided. .

  Further, since the rigidity of the rubber sheet 10 is overwhelmingly smaller than that of concrete, the rigidity of the rubber sheet 10 can be ignored in the assumed earthquake range, and the rotation at the joint between the pile head 1a and the foundation 2 during the earthquake. Is not restrained. Moreover, at the time of an extremely large earthquake, the rotation amount of the joint becomes excessive, the rubber sheet 10 is crushed, and the reaction force from the foundation 2 acts on the pile head 1a, thereby compressing the concrete section of the pile head 1a. Stress is relieved and concrete collapse can be prevented. Furthermore, since it is easy to cut out the inner peripheral shape of the annular rubber sheet 10 into a predetermined shape, the axial force transmission portion 11 formed inside the rubber sheet 10 can be easily formed into a predetermined shape.

  Further, since the plurality of pile main bars 5 are respectively stopped in the pile head 1a, the pile main bars 5 interfere with the reinforcing bars of the foundation 2 arranged in the horizontal direction and the reinforcing bars of the foundation beam and the foundation slab (not shown). Can be solved. Moreover, in the case of the cast-in-place concrete pile construction method, pile heading work is usually performed to pile up the pile concrete of the surplus portion, but the pile main reinforcement 5 is stopped in the pile head 1a, respectively. The construction can be done easily.

  In addition, since the plurality of joining members 7 are not arranged in an arc shape in a plan view but are arranged in a polygonal shape such as a quadrangle or an octagon, Interference can be avoided.

  Moreover, since the pitch of the pile hoop reinforcement 6 of the pile head 1a is narrow, the restraint effect in the pile head 1a increases, and the tensile split which arises in the pile concrete 3 when concentrated load is received in the center part of the pile head 1a. Destruction can be prevented.

  Further, since the length of the covering material 8 is appropriately adjusted, the length of the unbonded range can be adjusted by the length dimension of the covering material 8, and the axial rigidity of the joining member 7 can be freely controlled.

[Second Embodiment]
Next, a second embodiment will be described. In addition, description of the part which consists of the structure similar to 1st embodiment is abbreviate | omitted suitably.
FIG. 4 is a longitudinal sectional view showing a joint structure between a cast-in-place concrete pile (hereinafter simply referred to as a pile 101) and a foundation 102 in the second embodiment, and FIG. 5 is a perspective view showing a pile head 101a. is there.

  As shown in FIGS. 4 and 5, an axial force transmission portion 111 made of a plate-shaped steel plate 120 is formed inside the annular rubber sheet 110. The steel plate 120 has a plurality of through holes 120a through which the plurality of joining members 107 are respectively inserted. The diameter of the through hole 120a is a dimension obtained by adding a clearance of about 2 mm to the diameter of the enlarged portion 107c when the enlarged portion 107c of the joining member 107 is formed by the T head bar method or the mighty head method. In the case where the enlarged diameter portion 107c is formed by the plate nut method, it is a dimension obtained by adding a clearance of about 5 mm to the shaft diameter dimension of the joining member 107.

  Further, the covering material 108 is disposed at a position spaced apart from the upper end surface 101c of the pile 101 (the upper end surface of the axial force transmission unit 111) by a predetermined distance, and the lower side (joining part side) of the joining member upper end part 107b. Is fixed to the concrete of the foundation 102.

  Next, the construction method of the joining structure of the pile 101 which consists of an above-described structure and the foundation 102 is demonstrated.

First, as in the first embodiment, a pile driving process and a pile head processing process are performed.
Next, a pile upper end surface leveling process for smoothening the upper end surface 101c of the pile 101 is performed. Specifically, leveling mortar such as self-leveling mortar is applied to make the upper end surface 101c of the pile 101 horizontal and smooth. In addition, the pile upper end surface leveling process should just be performed only at the center part in which the steel plate 120 is installed, and does not need to be performed to the part in which the surrounding rubber sheet 110 is installed.

  Next, while performing the buffer material installation process which installs the rubber sheet 110 in the upper end surface 101c of the pile 101, the steel plate installation process which installs the steel plate 120 in the upper end surface 101c of the pile 101 smoothed is performed. The steel plate 120 is installed on the upper end surface 101c of the pile 101 while the plurality of joining member upper end portions 107b protruding from the upper end surface 101c of the pile 101 are inserted through the plurality of through holes 120a formed in the steel plate 120, respectively.

Next, an unbonding process for covering the outer peripheral surface of the upper end portion 107b of the joining member 107 with the covering material 108 is performed. At this time, the covering material 108 is attached at a position where the covering material 108 is floated so as to have a predetermined gap between the lower end of the covering material 108 and the upper end surface of the axial force transmission portion 111, and is temporarily fixed so as not to fall after the attachment. .
Then, the foundation formation process is performed similarly to 1st embodiment.

According to the joint structure between the pile 101 and the foundation 102 having the above-described configuration, the following effects can be achieved in addition to the effects similar to those of the first embodiment described above.
First, since the axial force transmission part 111 is made of the steel plate 120, the axial force transmission part 111 has sufficient compressive strength and does not undergo compression failure even when there is a risk of crushing in concrete with a small cross-sectional area.
Further, since the steel plate 120 constituting the axial force transmission unit 111 is installed inside the rubber sheet 110 and the steel plate 120 is surrounded by the rubber sheet 110, corrosion of the steel plate 120 and the joining member 107 is suppressed. be able to.

  In addition, the shape of the steel plate 120 does not need to be a shape along the bar arrangement shape of the plurality of joining members 107, and the plurality of joining members 107 are arranged in a quadrangular or octagonal manner with respect to the circular steel plate 120. Also good.

  Further, a shear connector may be attached by welding a steel material such as a stud or a reinforcing bar to the steel plate 120. As a result, the shear strength at the joint between the pile 101 and the foundation 102 can be increased. Furthermore, a screw reinforcing bar may be used for the joining member 107 and may be fixed on the steel plate 120 via a lock nut. Thereby, the steel plate 120 is integrated with the pile, and the effect of the shear connector can be increased.

  Further, when the enlarged diameter portion 107c is formed by the T head bar method or the mighty head method, the diameter of the through hole 120a formed in the steel plate 120 must be large enough to allow the enlarged diameter portion 107c to be inserted. The diameter of the through hole 120a formed in the steel plate 120 can be reduced by forming the enlarged diameter portion 107c by the plate nut method.

  Further, instead of the plurality of through holes 120a through which the plurality of joining members 107 are respectively inserted, a large through hole through which the plurality of joining members 107 are collectively inserted may be formed in the central portion of the steel plate 120.

  As mentioned above, although embodiment of the joining structure of the cast-in-place concrete pile and foundation which concerns on this invention was described, this invention is not limited to above-described embodiment, In the range which does not deviate from the meaning, it changes suitably. Is possible. For example, in the first and second embodiments described above, the enlarged diameter portions 7c and 107c are formed as the fixing portions for fixing in the foundations 2 and 102, but the present invention provides an upper end portion of the joining member. The fixing portion may be formed by bending the lens into an L shape or a hook shape.

  Further, in the first and second embodiments described above, the covering materials 8 and 108 are arranged with an interval between the upper end surfaces 1c and 101c of the piles 1 and 101. In order to facilitate the installation work of the materials 8 and 108, the covering materials 8 and 108 may be attached in a state where the lower ends of the covering materials 8 and 108 are attached to the upper end surfaces 1 c and 101 c of the piles 1 and 101.

It is a longitudinal cross-sectional view for demonstrating 1st embodiment which concerns on this application. It is a cross-sectional view between aa shown in FIG. It is a cross-sectional view between bb shown in FIG. It is a longitudinal cross-sectional view for demonstrating 2nd embodiment which concerns on this application. It is a perspective view for demonstrating 2nd embodiment which concerns on this application.

Explanation of symbols

1,101 pile (cast-in-place concrete pile)
1a, 101a Pile head 2,102 Foundation 7a Lower end (one end) of joint member
7b, 107b (joining member) upper end (other end)
7, 107 Joining member 7c, 107c Wide diameter part (fixing part)
8,108 Coating material

Claims (2)

The pile head of the cast-in-place concrete pile and the concrete foundation formed above the pile head have one end embedded in the center of the pile head and the other end embedded in the foundation. In the joint structure of cast-in-place concrete piles and foundations that are semi-rigidly joined via joint members,
One end of the joining member is attached to the pile head concrete and fixed in the pile head,
The other end portion of the joining member is formed with a fixing portion for fixing in the foundation at the tip, and an outer peripheral surface is covered with a covering material that cuts off the adhesion to the concrete of the foundation. Joint structure between cast-in-place concrete pile and foundation. In the joint structure of the cast-in-place concrete pile according to claim 1 and the foundation,
The said covering material is arrange | positioned at intervals between the upper end surfaces of the said pile, The joining structure of the cast-in-place concrete pile and the foundation characterized by the above-mentioned.

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