Prestressed concrete structure and method for constructing the same

Abstract

To provide a prestressed concrete structure which comprises multiple segments and a tensioning material, and in which the reinforcement of the segments can be simplified.SOLUTION: A prestressed concrete structure 1 comprises first and second segments 21 and 22 arranged in the X direction, and a tensioning material 4 that applies compression force in the X direction to the first and second segments 21 and 22. The tensioning material 4 has an inclined part 41 that is inclined with respect to the X-direction, and the first and second segments 21 and 22 have through holes 5 for accommodating the inclined part 41.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a prestressed concrete structure and a construction method thereof. [Background technology]

[0002] In decks used in bridges and other structures, compressive force (prestress) is often applied in the arrangement direction of the deck (in the case of a bridge, in the bridge axis direction). In this case, tendons are sometimes installed so that they penetrate only some consecutive decks, rather than all of the decks. Patent Document 1 describes a deck in which a protrusion is provided at the bottom of the deck and tendons are arranged in the protrusion. The tendons are bent at the protrusion, and the anchoring points of the tendons are provided on the side of the protrusion. The deck adjacent to the deck with the protrusion has a substantially constant thickness, and the tendons extend horizontally in this adjacent deck. Therefore, the inclined portion of the tendon, which is inclined with respect to the arrangement direction of the decks, is accommodated in only one deck. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-200730 Summary of the Invention [Problem to be solved by the invention]

[0004] A tension force is applied obliquely to a deck slab that accommodates the inclined portion of the tendon. Therefore, a vertical tensile force is generated in the deck slab that accommodates the inclined portion. Since the magnitude of this tensile force is roughly proportional to the average inclination angle of the inclined portion, the tensile force can be reduced by increasing the dimensions of the deck slab in the arrangement direction and reducing the inclination angle. However, it may be difficult to ensure sufficient dimensions of the deck slab in the arrangement direction due to constraints on the transportation and installation of the deck slab. For this reason, it is difficult to reduce the vertical tensile force with the deck slab described in Patent Document 1, and the reinforcement structure to withstand the tensile force becomes complex. Similar issues exist in concrete segments other than prestressed decks.

[0005] An object of the present invention is to provide a prestressed concrete structure comprising a plurality of segments and tendons, which allows for simplified reinforcement of the segments. [Means for solving the problem]

[0006] The prestressed concrete structure of the present invention comprises first and second segments arranged in a first direction, and tendons that apply compressive force in the first direction to the first and second segments. The tendons have inclined portions that are inclined with respect to the first direction, and the first and second segments have through holes that accommodate the inclined portions. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a prestressed concrete structure that includes a plurality of segments and tendons and that allows for simplified reinforcement of the segments. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a conceptual diagram showing a prestressed concrete structure according to an embodiment of the present invention. [Figure 2] FIG. 2 is a conceptual diagram showing a prestressed concrete structure in the area where the second tendon is laid. [Figure 3] FIG. 3 is an enlarged view of part A in FIG. 2. [Figure 4] FIG. 3 is a cross-sectional view of part A in FIG. 2. [Figure 5] FIG. 1 is a conceptual diagram showing a prestressed concrete structure of a comparative example. [Figure 6] FIG. 1 is a conceptual diagram showing the construction procedure for a prestressed concrete structure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Embodiments of a prestressed concrete structure and its construction method of the present invention will be described with reference to the drawings. The embodiments described below are directed to deck slabs in bridges and other structures. However, the present invention can also be applied to new construction of prestressed concrete bridges, repair and reinforcement work on bridges, as well as replacement and new construction of deck slabs in bridges and other structures. In the following description and drawings, the bridge axis direction or the arrangement direction of the deck slabs is referred to as the first direction X or X-direction, the bridge width direction or the direction perpendicular to the bridge axis is referred to as the second direction Y or Y-direction, and the direction perpendicular to the X-direction and Y-direction is referred to as the third direction Z or Z-direction. The X-direction and Y-direction are horizontal, but may be slightly inclined from the horizontal, and the Z-direction is vertical, but may be slightly inclined from the vertical.

[0010] FIG. 1 is a conceptual diagram showing the arrangement of deck slabs in a bridge. Bridge 200 has multiple reinforced concrete piers 201, multiple steel beams 203 supported on piers 201 via bearings 202, and multiple concrete deck slabs 2 supported on steel beams 203. The multiple piers 201 are arranged in the X direction, the multiple steel beams 203 are arranged in the Y direction, and the multiple deck slabs 2 are arranged in the X direction via filler material 3. A pavement such as asphalt (not shown) is formed on the top surface of deck slab 2. Although deck slab 2 can be constructed on-site, it is usually produced in a factory. The multiple deck slabs 2 form part of a prestressed concrete structure (hereinafter referred to as structure 1) that uses prestressing forces in the joint structure between the deck slabs.

[0011] A bending moment is applied to the steel beams 203 and the deck slab 2 according to the position of the support 202, resulting in the creation of portions of the deck slab 2 where tension is applied in the X direction. For this reason, the structure 1 has tendons 4 that collectively apply a compressive force (prestress) in the X direction to multiple consecutive deck slabs 2. The tendons 4 are continuous fiber reinforced materials made of fiber-reinforced plastics such as AFRP (aramid fiber reinforced plastic) and CFRP (carbon fiber reinforced plastic). While the tendons 4 may be installed to extend between both ends of the bridge 100 in the X direction, in this embodiment, multiple sections are set in the X direction, and a tendon 4 is installed in each section. Specifically, a first section SA is set between an end SA1 and an intermediate position SA2 in the X direction of the bridge 100, and a first tendon 4A is installed in the first section SA. Furthermore, a second section SB is set between two intermediate positions SB1 and SB2 in the X direction of the bridge 100, and a second tendon 4B is installed in the second section SB. The first section SA and the second section SB partially overlap in the X direction, but may be separated from each other.

[0012] The anchoring portion 6A of the first tendon 4A is provided on the side surface of the deck slab 2 at the end SA1. Since the anchoring portion 6A cannot be provided in a similar position at the intermediate position SA2, a protrusion (described later) is provided on the lower part of the deck slab 2, and the anchoring portion 6A is provided on the side surface of the protrusion. Therefore, the first tendon 4A extends in the X direction from the end SA1 in the X direction and bends downward in the Z direction near the intermediate position SA2. The second tendon 4B has protrusions (described later) on the lower part of the deck slab 2 at intermediate positions SB1 and SB2 on both sides, and anchoring portions 6B are provided on the side surfaces of the protrusions. Therefore, the second tendon 4B extends in the X direction between the intermediate positions SB1 and SB2 on both sides and bends downward in the Z direction near the intermediate positions SB1 and SB2 on both sides. In the following description, the second tendon 4B may be referred to as tendon 4.

[0013] FIG. 2 is a partially enlarged view of FIG. 1, showing the structure 1 in the area where the tendons 4 are installed. The structure 1 has two pairs of slabs 24A and 24B, each consisting of a first slab 21 and a second slab 22. The first slab 21 and the second slab 22 of each pair of slabs 24A and 24B are arranged in the X direction via filler 3. At least one (in this embodiment, multiple) third slabs 23 are disposed between the two pairs of slabs 24A and 24B, and the tendons 4 apply a compressive force in the X direction to the two pairs of slabs 24A and 24B and the at least one third slab 23. The two pairs of slabs 24A and 24B are arranged approximately symmetrically at both end regions of the tendons 4 and have roughly the same structure. Therefore, only one pair of slabs, 24A, will be described below. The portion of the tendon 4 that is bent downward in the Z direction, i.e., the portion that is inclined with respect to the X direction, is referred to as the inclined portion 41. The inclined portion 41 is inclined at an average angle θ with respect to the X direction.

[0014] 3(a) is an enlarged view of part A in FIG. 2, FIG. 3(b) is a partial enlarged view of the first deck slab 21, FIG. 3(c) is a partial enlarged view of the second deck slab 22, FIG. 4(a) is a cross-sectional view of the first deck slab 21 taken along line 4A-4A in FIG. 3(a), and FIG. 4(b) is a cross-sectional view of the second deck slab 22 taken along line 4B-4B in FIG. 3(a). The first deck slab 21 has a first main body 21A having a constant thickness (Z-direction dimension) and a first protruding portion 21B protruding downward in the Z-direction from the first main body 21A. The second deck slab 22 has a second main body 22A having a constant thickness (Z-direction dimension) and a second protruding portion 22B protruding downward in the Z-direction from the second main body 22A. The first main body 21A and the first protrusion 21B are an integral concrete structure, and the second main body 22A and the second protrusion 22B are also an integral concrete structure. As shown in FIG. 3(a), the first protrusion 21B and the second protrusion 22B are adjacent to each other in the X direction via a filler 3. In this embodiment, the first and second deck slabs 21 and 22 are arranged to straddle multiple steel beams 203, so the first and second protrusions 21B and 22B are each divided in the Y direction, and each divided portion is located between the steel beams 203. However, the first protrusion 21B and the second protrusion 22B do not necessarily need to be divided in the Y direction and can have a continuous structure in the Y direction. As shown in FIG. 2, the third deck slab 23 is generally flat. The first main body portion 21A, the second main body portion 22A, and the third deck slab 23 have the same thickness (Z-direction dimension), and their Z-direction upper surfaces are flush with each other. Note that the first main body portion 21A, the second main body portion 22A, and the third deck slab 23 may have rib-like protrusions at the fixing portions to the steel beams 203, but in this specification, the thicknesses of the first main body portion 21A, the second main body portion 22A, and the third deck slab 23 do not include such protrusions.

[0015] The first protrusion 21B has a first hole 21C through which the tendon 4 is inserted, and the second main body 22A and the second protrusion 22B have a second hole 22C through which the tendon 4 is inserted. The first hole 21C and the second hole 22C form part of the through hole 5. The first hole 21C passes through at least the first protrusion 21B and may partially pass through the first main body 21A. The second hole 22C passes through at least the second main body 22A and may partially pass through the second protrusion 22B. The first hole 21C is a hole formed in concrete, and its surface is the concrete surface. The second hole 22C is a sheath embedded in the concrete, and the sheath is made of resin or the like. The first hole 21C extends linearly or curvedly through the first deck slab 21. The second hole 22C extends curvedly through the second deck slab 22. The second hole 22C has a first region 22D that extends linearly or curvedly on the first deck slab 21 side, and a second region 22E that extends linearly in the X direction on the third deck slab 23 side. The first hole 21C and the first region 22D form an inclined region 25 that corresponds to the inclined portion 41 of the tendon 4. The length of the inclined region 25 is not particularly limited.

[0016] As described below, a partition 26 is provided in the second hole 22C (see FIG. 6), and non-shrinkage mortar (including ultra-low shrinkage mortar) is filled in the end region 53 between the partition 26 and the anchoring region 6B. The end region 53 includes at least the entire length of the first hole 21C. As described above, the surface of the first hole 21C is a concrete surface, so the tendon 4 is anchored directly to the concrete via the non-shrinkage mortar. This distributes the anchoring force of the tendon 4 to the first deck slab 21, improving anchoring reliability. The central region 52 between the two partitions 26 (see FIG. 6) is filled with grout to maintain the integrity of the tendon 4 and the second and third decks 22, 23. Because the central region 52 is usually longer than the end regions 53, it is preferable to use PC grout, which has good filling properties.

[0017] The first to third deck slabs 21 to 23 are made of fiber-reinforced concrete and are reinforced with reinforcing members 27. The fibers mixed into the first to third deck slabs 21 to 23 are steel fibers. The fiber diameter is preferably 0.2 mm or more, the fiber length is approximately 15 to 22 mm, and the volume ratio is preferably 0.5% or more. The reinforcing members 27 are rod-shaped continuous fiber reinforcing members, and fiber-reinforced plastics such as GFRP (glass fiber reinforced plastic) can be used. The reinforcing members 27 may also be FRP made from carbon fiber, aramid fiber, polypropylene fiber, polyethylene fiber, or vinylon fiber. As shown in FIGS. 3(b) and 4(a), the reinforcing members 27 include rod-shaped reinforcing members 27X extending in the X direction and rod-shaped reinforcing members 27Y extending in the Y direction. These reinforcing members 27X and 27Y are provided in the first deck slab 21, but may also be provided in the second deck slab 22 if necessary.

[0018] The reinforcement 27 further includes a plurality of first reinforcements 27A provided on the first deck slab 21 and a plurality of second reinforcements 27B provided on the second deck slab 22. The first reinforcement 27A bears the tensile force in the Z direction that occurs between the first main body 21A and the first protruding portion 21B due to the tensile force applied to the tendon 4. The second reinforcement 27B bears the tensile force in the Z direction that occurs between the second main body 22A and the second protruding portion 22B due to the tensile force applied to the tendon 4. As shown in FIGS. 4(a) and 4(b), the first reinforcement 27A and the second reinforcement 27B are rods that have multiple bent portions 28 and are bent into a frame shape when viewed from the X direction. The first reinforcement 27A and the second reinforcement 27B have two end regions 29 that protrude outward in the Y direction in a hook-like shape. The two end regions 29 extend in a direction that overlaps each other. The length of the end regions 29 is at least 10 times the diameter of the reinforcement 27, allowing hook anchoring to the surrounding concrete. As shown in FIG. 4(c), the end regions 29 may extend away from each other in the Y direction. However, this embodiment makes it easier to ensure the length of the end regions 29 while reducing the dimension in the Y direction. Although not shown, the first reinforcement 27A and the second reinforcement 27B can also be formed in a spiral shape. Alternatively, instead of using the reinforcement 27, prestress in the X and Z directions can be applied to the deck slab 2. Alternatively, the first reinforcement 27A and the second reinforcement 27B can be reduced or eliminated by increasing the amount of fiber mixed into the concrete.

[0019] The first reinforcing members 27A have the same height H1 (Z-direction dimension), with a portion of each being located on the first protrusion 21B and the remainder being located on the first main body 21A. Similarly, the second reinforcing members 27B have the same height H2 (Z-direction dimension), with a portion of each being located on the second protrusion 22B and the remainder being located on the second main body 22A. H1 > H2. As shown in FIG. 3, the first protrusion 21B has a constant thickness T1 (Z-direction dimension) in the X direction, and the second protrusion 22B has a constant thickness T2 (Z-direction dimension) in the X direction that is smaller than that of the first protrusion 21B. T1 > T2. The first reinforcing members 27A are produced by filling a mold with resin. Therefore, by making the shapes and dimensions of the first reinforcing members 27A identical, the first reinforcing members 27A can be produced using a single mold, thereby reducing costs. It should be noted that first reinforcing member 27A can also be made by bending reinforcing bars. In this case, even if the shapes of the plurality of first reinforcing members 27A differ from one another, the effect on costs is limited, so the height of first protrusion 21B may be gradually changed in the X direction. The same applies to second reinforcing member 27B.

[0020] As described above, the first to third deck slabs 21-23 and the tendons 4 are made only of non-corrosive materials, which eliminates the possibility of corrosion of corrosive materials such as rebar during use, enabling a longer service life. However, as an alternative, metal materials can also be used; for example, the tendons 4 can be made of steel members such as PC steel strands, or stainless steel can be used to suppress corrosion. The first to third deck slabs 21-23 can be made of ordinary reinforced concrete or metal fiber reinforced concrete.

[0021] Next, the advantages of this embodiment will be described with reference to a comparative example. Figure 5 shows a cross section of a deck slab 102 of the comparative example. The shape of the tendon 104 is similar to that of the tendon 4 of this embodiment, but the inclined portion 141 of the tendon 104 is contained within a single deck slab 102. The deck slab 102 has a main body 121 with a constant thickness in the X direction and a protruding portion 122 with a triangular cross section that protrudes downward in the Z direction from the main body 121. The main body 121 is provided with reinforcing bars 123 extending in the X direction, and reinforcing bars 124 extending in the Z direction are provided between the main body 121 and the protruding portion 122. Because the deck slab 102 is pulled in the X direction near the anchorage portion 6B, a tensile force is applied to the filler material 3 adjacent to the anchorage portion 6B, which may cause openings or cracks in the filler material 3. To prevent this, it is necessary to ensure a certain distance (hereinafter referred to as the anchorage length D) between the anchorage portion B and the end of the deck slab 102 (the filler material 3). In order to ensure the anchorage length D, it is sufficient to increase the average angle θ of the inclined portion 141 so that the tendon 104 bends sharply. However, if the average angle θ of the inclined portion 141 increases, the tensile force in the Z direction between the main body portion 121 and the protruding portion 122 increases, making the arrangement of the reinforcing bars 124 more complicated. In order to ensure the anchorage length D without increasing the average angle θ of the inclined portion 141, it is possible to increase the dimension of the deck slab 102 in the X direction, but this would increase the weight of the deck slab 102 and reduce transportability and installability.

[0022] In this embodiment, the deck slab 102 of the comparative example is divided into two decks (a first deck slab 21 and a second deck slab 22) and integrated on-site, and the inclined portions 141 of the tendons 104 are divided and arranged on the two decks. Therefore, in this embodiment, the average angle θ of the inclined portions 41 or inclined regions 25 of the tendons 4 can be reduced, simplifying the deck reinforcement structure. In the configuration of the comparative example, the average angle θ is generally in the range of 10 to 20 degrees, but in this embodiment, the average angle θ is 7.5 degrees, and can be set in the range of 5 degrees or more and less than 10 degrees.

[0023] In addition, in this embodiment, the degree of freedom in arranging the inclined portion 41 of the tendon 4 in the X direction is substantially increased. As a result, it is easy to ensure the anchorage length D, and openings and cracks in the filler material 3 are less likely to occur. Since it is also easy to reduce the X-direction dimensions of each of the first deck slab 21 and the second deck slab 22, it is possible to prevent a decrease in the transportability and installability of the deck slab. In this embodiment, it is possible to reduce the X-direction length L1 of the first protrusion 21B to approximately two-thirds or less of the X-direction length L2 of the first main body portion 21A. Note that the present invention also includes an embodiment in which the deck slab 102 of the comparative example is divided into three or more deck slabs 2, i.e., the inclined portion 41 is provided across three or more deck slabs 2.

[0024] (Construction method for Structure 1) Next, with reference to FIG. 6, a construction method for the structure 1 described above will be described. First, as shown in FIG. 6(a), the first slab 21, the second slab 22, and the multiple third slabs 23 of one slab pair 24A, and the second slabs 22 and the first slab 21 of the other slab pair 24B are arranged in order in the X direction. At this time, filler material 3 is filled into the gap between adjacent slabs. The dimension of the gap between the slabs (the width of the filler material 3 in the X direction) is not limited, but is selected from a range of several tens to several hundreds of mm. A first hole 21C is pre-formed in the first slab 21, and a second hole 22C (sheath) is pre-formed in the second slab 22. A hole 23C (sheath) similar to that of the second slab 22 is pre-formed in the third slab 23. Therefore, by arranging these slabs 2, a through hole 5 is formed through which the tendon 4 is inserted. In addition, a joint (not shown) is provided between the insertion holes of adjacent deck slabs, so that the filler material 3 does not enter the through-holes 5.

[0025] Next, as shown in FIG. 6(b), a tendon 4 is inserted through the through-hole 5. One end of the tendon 4 protrudes from the first slab 21 of one pair of slabs 24A, and the other end of the tendon 4 protrudes from the first slab 21 of the other pair of slabs 24B. The tendon 4 is then tensioned using the anchoring device 7, and the tendon 4 applies a compressive force in the X direction to the first and second slabs 21, 22 and the third slab 23. Next, as shown in FIG. 6(c), a thickener-based inorganic material is injected through the second injection holes 72 provided in the two second slabs 22 to form partitions 26 inside the hole 22C (sheath). The partitions 26 separate the through-hole 5 into a central region 52 and end regions 53 on both sides. Next, as shown in FIG. 6(d), non-shrink mortar is injected through the first injection holes 71 to fill the end regions 53. Furthermore, PC grout is injected through the third injection hole 73 to fill the central region 52. These steps may be performed in either order, or simultaneously. When PC steel strands are used as the tendons 4, the partitions 26 are not necessary, and PC grout can be injected along the entire length of the tendons 4.

[0026] Although the present invention has been described above using embodiments, the present invention is not limited to the above-described embodiments. For example, the first protrusion 21B can be omitted from the first deck slab 21, and the thickness of the first main body 21A can be the sum of the thicknesses of the first main body 21A and the first protrusion 21B in this embodiment. Similarly, the second protrusion 22B can be omitted from the second deck slab 22, and the thickness of the second main body 22A can be the sum of the thicknesses of the second main body 22A and the second protrusion 22B in this embodiment. Since the thicknesses of the first deck slab 21 and the second deck slab 22 in the X direction are constant, the shape of the formwork can be simplified, and the manufacturing process can be simplified. [Explanation of symbols]

[0027] 1 Prestressed concrete structures 2 Deck (segment) 3. Filling material 4 Tensors 5 through holes 21 First deck (first segment) 21A First body part 21B First protrusion 21C First hole 22 Second deck (second segment) 22A Second body part 22B Second protrusion 22C Second hole 27 Reinforcement 27A First Reinforcement 27B Second Reinforcement

Claims

1. first and second segments aligned in a first direction; a tendon applying a compressive force in the first direction to the first and second segments, the tendon has an inclined portion inclined with respect to the first direction, The first and second segments have through holes to accommodate the ramps.

2. The first segment has a first body portion having a constant thickness and a first protrusion portion protruding downward from the first body portion, The second segment has a second body portion having a constant thickness and a second protrusion portion protruding downward from the second body portion, the first protruding portion and the second protruding portion are adjacent to each other in the first direction via a filler material, 2. The prestressed concrete structure of claim 1, wherein the through holes include a first hole passing through at least the first protrusion portion and a second hole passing through at least the second body portion.

3. 3. The prestressed concrete structure according to claim 2, wherein the length of the first protrusion in the first direction is approximately 2 / 3 or less of the length of the first main body in the first direction.

4. 3. The prestressed concrete structure of claim 2, wherein the first hole extends straight through the first segment and the second hole extends curved through the second segment.

5. the first segment has a plurality of first reinforcements having a plurality of bent portions when viewed from the first direction; the second segment has a plurality of second reinforcing members each having a plurality of bent portions when viewed from the first direction; the plurality of first reinforcing members and the plurality of second reinforcing members are made of fiber-reinforced plastic; the plurality of first reinforcements have the same height, the plurality of second reinforcements have the same height, 3. The prestressed concrete structure of claim 2, wherein the first protrusion has a constant thickness in the first direction and the second protrusion has a constant thickness in the first direction that is smaller than the first protrusion.

6. 6. A prestressed concrete structure according to claim 1, wherein the average angle of the inclined portions with respect to the first direction is less than 10 degrees.

7. 6. The prestressed concrete structure of claim 1, wherein the first and second segments comprise fiber reinforced concrete and fiber reinforced plastic reinforcement.

8. 6. A prestressed concrete structure according to claim 1, wherein the first and second segments are deck slabs.

9. disposing the first and second segments in a first direction; applying a compressive force in the first direction to the first and second segments by tendons; the tendon has an inclined portion inclined with respect to the first direction, A method of constructing a prestressed concrete structure, wherein the first and second segments have through holes to accommodate the inclined portions.

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