Joint structure for precast floor slabs

Abstract

To provide a joint structure for precast floor slabs capable of preventing the destruction of concrete around a reinforcing bar while reducing thickness and improving workability.SOLUTION: A joint part has a joint part concrete in which reinforcement protruding parts 54 of bridge-axis direction reinforcements 52 of the respective precast floor slabs to be joined to each other are disposed and the reinforcement protruding parts 54 are embedded; the reinforcement protruding parts 54 has a base part 57 on the joining end surface side, a first enlarged diameter part 55 located on the distal end side in the protruding direction with respect to the base part 57 and having an outer diameter larger than that of the base part 57, and a second enlarged diameter part 56 located on the distal end side with respect to the first enlarged diameter part 55 and having an outer diameter larger than that of the first enlarged diameter part 55, the first enlarged diameter part 55 has the same outer diameter over the entire protruding direction of the reinforcement protruding parts 54, the second enlarged diameter part 56 has the same outer diameter over the entire protruding direction of the reinforcement protruding parts 54, a first step part 58 is formed at a connection portion between the base part 57 and the first enlarged diameter part 55, and a second step part 59 is formed at a connection part between the first enlarged diameter part 55 and the second enlarged diameter part 56.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a joint structure for a precast deck. [Background technology]

[0002] A known joint structure for joining precast decks together involves providing loop-shaped loop joints at the ends of the precast decks that protrude from the concrete part, arranging the loop joints of each of the precast decks being joined alternately at the joints between the precast decks, inserting reinforcing bars into these loop joints, and filling them with concrete (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5337122 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when loop joints are installed at the joints of precast decks, the deck thickness is determined by the constraints of the inner bending radius of the semicircular hooks of the loop joints, and it may be difficult to make the precast decks thinner. Also, when inserting reinforcing bars inside the loop joints, the internal reinforcing bars of the loop joints are inserted from the ends of the arranged loop joints in the arrangement direction, so it is necessary to secure construction space, which creates the problem of poor workability.

[0005] In response to this, a joint structure for precast decks has been proposed in which, instead of loop joints, a rebar is provided at the end of the precast deck that protrudes linearly from the concrete part, and the tip of the rebar is provided with an enlarged part with a tapered outer periphery. This eliminates the restriction on deck thickness due to the bending radius of the protruding rebar, and makes it possible to arrange the reinforcing bars at the joints in advance before installing the rebar, improving workability.

[0006] However, in this type of precast deck joint structure, a bearing resistance force is generated from the tapered outer surface of the enlarged portion of the reinforcing bar in a direction intersecting the axial direction of the reinforcing bar, which may destroy the concrete around the reinforcing bar.

[0007] Therefore, an object of the present invention is to provide a joint structure for a precast deck slab that can prevent destruction of the concrete around the reinforcing bars while achieving thinner walls and improved workability. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides a joint structure for precast floor slabs, in which precast floor slabs are joined via joints, the precast floor slabs having a concrete portion and a reinforcing bar embedded in the concrete portion and protruding from a joint end surface of the concrete portion on the other precast floor slab side, the joints being located between the joint end surfaces of the precast floor slabs to be joined together, a reinforcing bar protruding portion protruding from the joint end surface of the reinforcing bar of each of the precast floor slabs to be joined together is disposed, and a joint concrete in which the reinforcing bar protruding portion is embedded is provided. The reinforcing bar protrusion has a base on the joint end face side, a first enlarged diameter portion located toward the tip side in the protruding direction from the base and having a larger outer diameter than the base, and a second enlarged diameter portion located toward the tip side from the first enlarged diameter portion and having a larger outer diameter than the first enlarged diameter portion, the first enlarged diameter portion has the same outer diameter throughout the protruding direction of the reinforcing bar protrusion, and the second enlarged diameter portion has the same outer diameter throughout the protruding direction of the reinforcing bar protrusion, a first step portion is formed at the connection portion between the base and the first enlarged diameter portion, and a second step portion is formed at the connection portion between the first enlarged diameter portion and the second enlarged diameter portion.

[0009] In the present invention, the first enlarged portion has the same outer diameter over the entire protruding direction of the rebar protrusion, and the second enlarged portion has the same outer diameter over the entire protruding direction of the rebar protrusion. That is, the outer peripheral surfaces of the first enlarged portion and the second enlarged portion do not have a tapered surface inclined with respect to the axial direction of the rebar protrusion. Therefore, during bending deformation of the concrete floor slab, the bearing resistance force generated from the first enlarged portion and the second enlarged portion on the concrete of the joint acts in the axial direction of the rebar protrusion, and hardly acts on the concrete around the rebar protrusion. As a result, the bearing resistance force generated from the first enlarged portion and the second enlarged portion on the concrete of the joint is borne by the rebar protrusion, and destruction of the concrete around the rebar protrusion can be prevented. In addition, compared to conventional loop joints, the protruding reinforcing bar does not have any constraints on deck thickness due to bending radius, and it is possible to pre-arrange the reinforcing bars at the joint before installing them, improving workability.

[0010] In addition, in the precast deck joint structure of the present invention, the outer diameter of the first expansion portion may be greater than 1.1 times and less than 2.4 times the outer diameter of the base, and the outer diameter of the second expansion portion may be greater than 1.5 times and less than 2.5 times the outer diameter of the base.

[0011] With this configuration, the bearing resistance force generated in the concrete of the joint from the first enlarged diameter portion and the second enlarged diameter portion can be efficiently transmitted to the reinforcing bar protruding portion.

[0012] In addition, in the precast deck joint structure of the present invention, the end face on the base side of the first expansion portion and the end face on the first expansion portion side of the second expansion portion may be flat surfaces perpendicular to the axial direction of the reinforcing bar protrusion.

[0013] With this configuration, the bearing resistance force generated in the concrete of the joint from the first enlarged diameter portion and the second enlarged diameter portion can be efficiently transmitted to the reinforcing bar protruding portion. Effect of the Invention

[0014] According to the present invention, it is possible to prevent destruction of concrete around protruding reinforcing bars while achieving thinner walls and improved workability. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a vertical cross-sectional view showing a joint structure of a precast deck according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a horizontal cross-sectional view showing a joint structure of a precast deck according to an embodiment of the present invention. [Diagram 3] FIG. 13 is a diagram showing the shape of the tip of a reinforcing bar protrusion. [Figure 4] FIG. 13 is a diagram showing the shape of a tip portion of a conventional reinforcing bar protrusion. [Diagram 5] FIG. 2 is a vertical cross-sectional view of a test specimen. [Figure 6] FIG. 2 is a horizontal cross-sectional view of the test specimen. [Figure 7] 1 is a graph showing the relationship between load and displacement at the center of the span (joint). [Figure 8] 1 is a graph showing the ultimate state of a test specimen of a conventional precast deck joint structure. [Figure 9] 1 is a graph showing bond splitting failure that occurred in a test specimen of a conventional precast deck joint structure. [Figure 10] 1 is a graph showing the ultimate state of a test specimen of a joint structure of a precast deck according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a joint structure for precast decks according to an embodiment of the present invention will be described with reference to Figs. 1 to 10. As shown in Figures 1 and 2, the precast deck joint structure 1 according to this embodiment is provided on a bridge and is a joint structure for adjacent precast decks 2, 3 in the bridge axis direction. The adjacent precast decks 2, 3 in the bridge axis direction are joined via a joint 4 provided between them. In the following, the precast deck 2 located on one side of the bridge axis direction may be referred to as the first precast deck 2, and the precast deck 3 located on the other side of the bridge axis direction may be referred to as the second precast deck 3.

[0017] The precast decks 2, 3 have a concrete portion 51, bridge axis direction reinforcing bars 52 extending in the bridge axis direction, and bridge axis perpendicular direction reinforcing bars 53 extending in a direction perpendicular to the bridge axis. The concrete portion 51 is formed in a plate shape. The concrete portion 51 of the first precast floor slab 2 and the concrete portion 51 of the second precast floor slab 3 are arranged with a gap in the bridge axis direction. A joint portion 4 is provided between the concrete portion 51 of the first precast floor slab 2 and the concrete portion 51 of the second precast floor slab 3. An end surface 511 of the concrete portion 51 in the bridge axis direction is formed into a surface that gradually slopes from the lower side to the upper side toward the joint 4. The end surface 511 of the concrete portion 51 in the bridge axis direction is referred to as a joint end surface 511.

[0018] A plurality of bridge axis direction reinforcing bars 52 are provided at intervals in the direction perpendicular to the bridge axis on both the upper and lower sides of the concrete portion 51. The bridge axis direction reinforcing bars 52 are longer than the length dimension of the concrete portion 51 in the bridge axis direction, and protrude in the bridge axis direction from the joint end surface 511 of the concrete portion 51. The part of the bridge axis direction reinforcing bars 52 protruding from the concrete portion 51 is referred to as a reinforcing bar protruding part 54. The bridge axis direction reinforcing bars 52 correspond to reinforcing bars in the claims.

[0019] Multiple reinforcing bars 53 orthogonal to the bridge axis are provided at intervals in the bridge axis direction on both the upper and lower sides of concrete section 51. Reinforcing bars 53 orthogonal to the bridge axis provided on the upper side of concrete section 51 are provided below bridge axis direction reinforcing bars 52 provided on the upper side of concrete section 51. Reinforcing bars 53 orthogonal to the bridge axis provided on the lower side of concrete section 51 are provided above bridge axis direction reinforcing bars 52 provided on the lower side of concrete section 51. Reinforcing bars 53 orthogonal to the bridge axis are reinforcing bars.

[0020] 3, a first enlarged diameter portion 55 and a second enlarged diameter portion 56 having a larger outer diameter than the base end side are formed at the tip end of the reinforcing bar protruding portion 54. The base end side of the reinforcing bar protruding portion 54, i.e., the portion on the concrete portion 51 side, is referred to as a base portion 57. The base portion 57 has the same outer diameter as the portion of the bridge axis direction reinforcing bar 52 that is embedded in the concrete portion 51. The rebar protruding portion 54 is arranged in the order of the base portion 57, the first enlarged diameter portion 55, and the second enlarged diameter portion 56 from the base end side to the tip end side. The outer diameter D1 of the first enlarged diameter portion 55 is larger than the outer diameter D of the base portion 57. The outer diameter D2 of the second enlarged diameter portion 56 is larger than the outer diameter D1 of the first enlarged diameter portion 55. The base portion 57, the first enlarged diameter portion 55, and the second enlarged diameter portion 56 each have the same outer diameter in the protruding direction, i.e., throughout the entire bridge axis direction. In other words, the outer peripheral surfaces of the base portion 57, the first enlarged diameter portion 55, and the second enlarged diameter portion 56 do not have a tapered surface in which the outer diameter increases from one side to the other side in the protruding direction.

[0021] At the boundary between the base 57 and the first enlarged diameter portion 55, a first step 58 is formed by an outer peripheral surface 571 of the base 57, an end face 552 of the first enlarged diameter portion 55 on the base 57 side, and the outer peripheral surface 551 of the first enlarged diameter portion 55. The end face 552 of the first enlarged diameter portion 55 on the base 57 side is a flat surface perpendicular to the protruding direction of the rebar protruding portion 54. At the boundary between the first enlarged diameter portion 55 and the second enlarged diameter portion 56, a second step portion 59 is formed by an outer peripheral surface 551 of the first enlarged diameter portion 55, an end face 562 of the second enlarged diameter portion 56 on the first enlarged diameter portion 55 side, and an outer peripheral surface 561 of the second enlarged diameter portion 56. The end face 562 of the second enlarged diameter portion 56 on the first enlarged diameter portion 55 side is a flat surface perpendicular to the protruding direction of the rebar protruding portion 54.

[0022] As described above, if the outer diameter of the base 57 is D, the outer diameter of the first enlarged portion 55 is D1, and the outer diameter of the second enlarged portion 56 is D2, in this embodiment, the relationship between D1, D2, and D is set as follows. The outer diameter D of the base 57 corresponds to the reinforcing bar diameter of the bridge axis direction reinforcing bar 52. D1 <D2 1.1D <D1<2.4D 1.5D <D2<2.5D

[0023] In the joint 4, the rebar protrusions 54 of the first precast slab 2 and the rebar protrusions 54 of the second precast slab 3 are alternately arranged at intervals in the direction perpendicular to the bridge axis. The rebar protrusions 54 of the first precast slab 2 and the rebar protrusions 54 of the second precast slab 3 are arranged overlapping each other when viewed from the direction perpendicular to the bridge axis. That is, the first enlarged portion 55 and the second enlarged portion 56 of the rebar protrusions 54 of the first precast slab 2 are adjacent to the base 57 of the rebar protrusions 54 of the second precast slab 3 in the direction perpendicular to the bridge axis with an interval. The first enlarged portion 55 and the second enlarged portion 56 of the rebar protrusions 54 of the second precast slab 3 are adjacent to the base 57 of the rebar protrusions 54 of the joint structure 1 in the direction perpendicular to the bridge axis with an interval.

[0024] The joint 4 is provided with joint bridge axis perpendicular direction rebar 41 extending in a direction perpendicular to the bridge axis, and joint concrete 42 in which the joint bridge axis perpendicular direction rebar 41 and the rebar protrusions 54 of the first precast deck 2 and the second precast deck 3 are embedded. Multiple joint reinforcing bars 41 orthogonal to the bridge axis are provided at intervals in the bridge axis direction on both the upper and lower sides of joint 4. Reinforcing bar 53 orthogonal to the bridge axis provided on the upper side of joint 4 is provided below reinforcing bar protrusion 54 provided on the upper side. Reinforcing bar 53 orthogonal to the bridge axis provided on the lower side of joint 4 is provided above reinforcing bar protrusion 54. Reinforcing bar 53 orthogonal to the bridge axis is a reinforcing bar. The joint concrete 42 is filled in the entire space between the concrete portion 51 of the first precast floor slab 2 and the concrete portion 51 of the second precast floor slab 3. The joint concrete 42 is cast-in-place concrete.

[0025] Loading tests were carried out using specimens for the joint structure of the precast floor slab according to this embodiment and the joint structure of a conventional precast floor slab in which a tapered enlarged diameter portion 155 (see FIG. 4) is provided at the tip of the rebar protruding portion 154. The outer diameter of the enlarged diameter portion 155 is larger than the outer diameter of the base portion 157 of the rebar protruding portion 154. The shape of the RC slab test specimen is shown in Figures 5 and 6. The rebar protrusion 54 in Figure 5 shows a first enlarged portion 55 and a second enlarged portion 56 of this embodiment. The test specimen for the conventional precast slab joint structure is a test specimen in which the rebar protrusion 54 in the RC slab test specimen shown in Figures 5 and 6 has been replaced with a rebar protrusion 154 as shown in Figure 4. The test specimen for the conventional precast slab joint structure is referred to as test specimen 1, and the test specimen for the precast slab joint structure according to this embodiment is referred to as test specimen 2.

[0026] The relationship between the load and the displacement at the center of the span (joint) is shown in Figure 7. Figure 7 also shows the relationship between the load and the displacement at the center of the span (joint) for a one-piece cast-in-place RC deck without joints (joints). In the case of specimen 1 of the conventional precast floor slab joint structure, after yielding, a brittle final state was reached due to bond splitting failure of the tapered enlarged portion 155 of the rebar protrusion 154, as shown in Figures 8 and 9. In the case of specimen 2 of the precast floor slab joint structure according to this embodiment, it was confirmed that the structural performance was equivalent to that of a one-piece cast RC slab without joints. In addition, in the case of specimen 2 of the precast floor slab joint structure according to this embodiment, as shown in Figure 10, the final state was reached due to the crushing of the upper edge concrete near the loading point.

[0027] In the joint structure of a precast deck in which the conventional expansion portion 155 is tapered, the bearing resistance force from the outer surface of the expansion portion 155 occurs in the direction of the covering concrete around the reinforcing bar protrusion 154, whereas in the joint structure of a precast deck in this embodiment, the bearing resistance force from the first expansion portion 55 and the second expansion portion 56 is guided to the reinforcing bar protrusion 54, i.e., the bridge axis direction reinforcing bar 52, which is thought to be because an adhesion resistance mechanism with excellent deformation performance has been formed that can prevent destruction of the concrete around the reinforcing bar protrusion 54.

[0028] Next, the action and effect of the precast floor slab joint structure 1 according to this embodiment will be described. In the joint structure 1 of the precast floor slab according to this embodiment, the first enlarged diameter portion 55 has the same outer diameter over the entire protruding direction of the reinforcing bar protrusion 54, and the second enlarged diameter portion 56 has the same outer diameter over the entire protruding direction of the reinforcing bar protrusion 54. That is, the outer peripheral surface 551 of the first enlarged diameter portion 55 and the outer peripheral surface 561 of the second enlarged diameter portion 56 do not have a tapered surface inclined with respect to the axial direction of the reinforcing bar protrusion 54. For this reason, during bending deformation of the concrete floor slabs 2 and 3, the bearing resistance force generated from the first enlarged diameter portion 55 and the second enlarged diameter portion 56 on the joint concrete 42 acts in the axial direction of the reinforcing bar protrusion 54, and hardly acts on the joint concrete 42 around the reinforcing bar protrusion 54. As a result, the bearing resistance force generated from the first enlarged diameter portion 55 and the second enlarged diameter portion 56 on the joint concrete 42 is borne by the reinforcing bar protrusion 54, and the destruction of the joint concrete 42 around the reinforcing bar protrusion 54 can be prevented. In addition, compared to conventional loop joints, the reinforcing bar protrusion 54 does not restrict the deck thickness due to the bending radius, and it makes it possible to arrange the reinforcing bars at the joint in advance before installing the reinforcing bar protrusion 54, i.e., before installing the precast decks 2, 3, thereby improving workability.

[0029] In addition, in the precast deck joint structure 1 according to this embodiment, the outer diameter of the first expansion portion 55 is set to be greater than 1.1 times and less than 2.4 times the outer diameter of the base portion 57, and the outer diameter of the second expansion portion 56 is set to be greater than 1.5 times and less than 2.5 times the outer diameter of the base portion 57. With this configuration, the bearing resistance force generated in the joint concrete 42 from the first enlarged diameter portion 55 and the second enlarged diameter portion 56 can be efficiently transmitted to the reinforcing bar protruding portion 54.

[0030] In addition, in the precast deck joint structure 1 according to this embodiment, the end face 552 on the base 57 side of the first expansion portion 55 and the end face 562 on the first expansion portion 55 side of the second expansion portion 56 are flat surfaces perpendicular to the axial direction of the reinforcing bar protrusion 54. With this configuration, the bearing resistance force generated in the joint concrete 42 from the first enlarged diameter portion 55 and the second enlarged diameter portion 56 can be efficiently transmitted to the reinforcing bar protruding portion 54.

[0031] The above describes an embodiment of the joint structure of a precast deck according to the present invention, but the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the spirit of the present invention. For example, in the above embodiment, the precast decks 2, 3 are provided on a bridge, but they may be provided on something other than a bridge. In the above embodiment, the outer diameter of the first enlarged diameter portion is set to be greater than 1.1 times and less than 2.4 times the outer diameter of the base, and the outer diameter of the second enlarged diameter portion is set to be greater than 1.5 times and less than 2.5 times the outer diameter of the base. In contrast, if the outer diameter of the first enlarged diameter portion is greater than the outer diameter of the base and the outer diameter of the second enlarged diameter portion is greater than the outer diameter of the first enlarged diameter portion 155, the magnification of the outer diameter of the first enlarged diameter portion and the outer diameter of the second enlarged diameter portion to the outer diameter of the base may be set appropriately.

[0032] The Sustainable Development Goals (SDGs) are among the 17 international goals adopted at the United Nations Summit in September 2015. The joint structure of the precast deck in this embodiment can contribute to achieving one of the 17 SDGs goals, such as goal 9, "Create inclusive and sustainable infrastructure for industry, innovation and sustainable development." [Explanation of symbols]

[0033] 1 Joint structure 2,3 Precast deck 4 Joint 42 Concrete joints 51 Concrete Section 52 Bridge Axial Reinforcement (Reinforcement) 54 Reinforcement bar protrusion 55 1st enlarged diameter section 56 Second enlarged diameter section 57 Base 58 First Stage 59 Second Stage 511 Joint end face 551 Outer surface

Claims

1. The precast deck slabs are joined together through joints, The precast deck is Concrete section, A reinforcing bar is embedded in the concrete portion and protrudes from a joint end surface of the other precast floor slab side of the concrete portion, The joint is Located between the joint end faces of the precast floor slabs that are joined to each other, A reinforcing bar protrusion protruding from the joint end surface of each of the reinforcing bars of the precast floor slabs to be joined to each other is arranged, The joint concrete in which the reinforcing bar protrusion is embedded is provided, The reinforcing bar protruding portion has a base portion on the joint end surface side, a first enlarged diameter portion located on a tip side of the base portion in a protruding direction and having an outer diameter larger than that of the base portion; a second enlarged diameter portion located on a tip side of the first enlarged diameter portion and having an outer diameter larger than that of the first enlarged diameter portion, The first enlarged diameter portion has a constant outer diameter throughout the entire protruding direction of the reinforcing bar protruding portion, The second enlarged diameter portion has a constant outer diameter throughout the entire protruding direction of the reinforcing bar protruding portion, A first step portion is formed at a connection portion between the base portion and the first enlarged diameter portion, A joint structure for precast decks, in which a second step portion is formed at the connection portion between the first expansion portion and the second expansion portion.

2. The outer diameter of the first expanded portion is greater than 1.1 times and smaller than 2.4 times the outer diameter of the base portion, The precast deck joint structure according to claim 1 , wherein the outer diameter of the second expanded portion is greater than 1.5 times and less than 2.5 times the outer diameter of the base portion.

3. A precast deck joint structure as described in claim 1 or 2, wherein the end face on the base side of the first expansion section and the end face on the first expansion section side of the second expansion section are flat surfaces perpendicular to the axial direction of the reinforcing bar protrusion.

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