Precast concrete member joint structure and precast concrete member joint method

Abstract

To provide a precast concrete member joint structure and a precast concrete member joint method which inhibit reinforcement bars from becoming congested in a filled concrete and enable efficient construction.SOLUTION: A joint structure 1 comprises: axial-direction reinforcement bars 3 that are arranged protruding from an end surface of a precast slab 2; joint reinforcement bars 4 that are arranged parallel to the axial-direction reinforcement bars 3 between adjacent two precast slabs 2; transverse-direction reinforcement bars 5 that are arranged in a direction across the axial-direction reinforcement bars 3 and the joint reinforcement bars 4; and a filled concrete 6 placed between the adjacent two precast slabs 2. The axial-direction reinforcement bars 3 of one precast slab 2 and the axial-direction reinforcement bards 3 of the other precast slab 2 are arranged on an identical axis. Anchor bodies 31, 41 are formed at the tip of the axial-direction reinforcement bar 3 and at both ends of the joint reinforcement bar 4. The transverse-direction reinforcement bars 5 are arranged in positions away from each anchor body 31, 41.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a joint structure for precast concrete members and a method for joining precast concrete members. [Background technology]

[0002] Precast concrete members arranged side by side are often connected via filler concrete or filler mortar (hereinafter simply referred to as "filler") poured into the joints. At the joint portion, axial reinforcing bars are protruding from the end faces of both precast concrete pieces, and it is common for these axial reinforcing bars to serve as joint members. When connecting rebars, it is common to use lap joints, but to ensure the necessary joint length for the rebars, the width of the joint becomes larger. When the joint width becomes larger, the amount of filling material that needs to be poured increases, and the effort required for pouring it also increases.

[0003] In some cases, the width of the joint can be reduced by processing the reinforcing bar serving as the joint member in the joint into a loop shape. For example, Patent Document 1 discloses a deck joint structure in which the end faces of precast decks with protruding loop reinforcements are butted together with a specified gap between them, distribution bars are arranged to cross the loop reinforcements, and filler concrete is poured into the gap between the end faces. However, when loop reinforcements are used as joint members, the member height may increase depending on the diameter of the loop. In addition, in order to obtain a strength equivalent to the tensile strength of the rebar base material using a loop joint, it is necessary to arrange the horizontal reinforcement within the loop, but this arrangement is time-consuming. Furthermore, when PC steel is arranged, the loop reinforcement and horizontal reinforcement may interfere with the PC steel.

[0004] In addition, the width of the joint may be reduced by forming a widened portion (anchoring portion) at the end of the reinforcing bar as a joint member. For example, Patent Document 2 discloses a joint structure in which axial rebars protruding from the end faces of opposing precast concrete members are arranged on the same axis at the joint portion, anchors are formed at the ends, and further, joint rebars with anchors formed at both ends are arranged between adjacent axial rebars in parallel to the axial rebars. In the joint structure of Patent Document 2, reinforcing bars are provided that extend in a direction intersecting the axial rebars and joint rebars, and this reinforcing bar is connected to at least one of the upper and lower sides of the axial rebars and joint rebars, so that the reinforcing bars are engaged with the widening portion, thereby restricting the axial movement of the axial rebars and joint rebars. However, when reinforcing bars are connected to axial bars or connecting bars, especially at the ultimate limit state, instead of the reinforcing bars restraining the axial displacement of the axial bars and connecting bars, large bending stresses are generated in the reinforcing bars (local bending deformation occurs). Therefore, when lateral tensile forces (tensile forces in a direction intersecting the axial bars) act on the reinforcing bars, in addition to the reinforcing bars, it is necessary to place separate bars to resist the lateral tensile forces. Also, Patent Document 3 discloses a joint structure in which axial reinforcing bars, each having an anchor formed at an end protruding from the end face of an opposing precast member, are joined together by a lap joint. However, in the joint structure of Patent Document 3, when the axial reinforcing bars are arranged vertically and horizontally, such as in a box culvert, the axial reinforcing bars interfere with each other when the precast concrete member is moved vertically and horizontally during positioning, so that the precast concrete member must be positioned vertically and horizontally and then slid from the axial direction to position it, which can make efficient construction difficult. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2010-236258 A [Patent Document 2] JP 2020-063617 A [Patent Document 3] Patent Publication No. 2021-055531 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to propose a joint structure for precast concrete members and a method for joining precast concrete members that prevent over-dense reinforcement in the fill concrete and enables efficient construction. [Means for solving the problem]

[0007] In order to solve such problems, the joint structure of the precast concrete members of the present invention comprises axial reinforcing bars protruding from the end faces of the precast concrete members, connecting reinforcing bars arranged parallel to the axial reinforcing bars between the precast concrete members, transverse reinforcing bars arranged in a direction intersecting the axial reinforcing bars and the connecting reinforcing bars, and filling concrete filled between the precast concrete members, wherein the axial reinforcing bars of one precast concrete member and the axial reinforcing bars of the other precast concrete member are arranged coaxially, an anchor having an outer shape larger than the cross-sectional shape of the axial reinforcing bars is formed at the tip of the axial reinforcing bars, anchors having an outer shape larger than the cross-sectional shape of the connecting reinforcing bars are formed at both ends of the connecting reinforcing bars, and the transverse reinforcing bars are arranged at a position away from the anchors of the axial reinforcing bars and the anchors of the connecting reinforcing bars.

[0008] The method for joining precast concrete members of the present invention is a method for joining a pair of precast concrete members having axial reinforcing bars protruding from their end faces, and includes an arrangement step of arranging one of the precast concrete members at a distance from the other precast concrete member, an arrangement step of arranging joint reinforcing bars and transverse reinforcing bars between the precast concrete members, and a pouring step of pouring filler concrete between the precast concrete members. An anchor having an outer shape larger than the cross-sectional shape of the axial reinforcing bars is formed at the tip of the axial reinforcing bars, and an anchor having an outer shape larger than the cross-sectional shape of the joint reinforcing bars is formed at both ends of the joint reinforcing bars. In the arrangement step, the precast concrete members are arranged so that the anchor of the axial reinforcing bars of one of the precast concrete members faces the anchor of the axial reinforcing bars of the other precast concrete member. In addition, in the reinforcing bar arrangement process, the transverse reinforcing bars are arranged at positions away from the anchors of the axial reinforcing bars and the anchors of the joining reinforcing bars.

[0009] According to the joint structure of the precast concrete members and the joining method of the precast concrete members, the axial reinforcing bars are connected to each other through the joint reinforcing bars shorter than the interval between the precast concrete members with the end faces of the axial reinforcing bars facing each other, so that the installation method of the precast concrete members is not limited to sliding from the axial direction. In addition, the transverse reinforcing bars are arranged at a position away from the anchorage and are not connected to the axial reinforcing bars, so they do not contribute to the axial slippage or bending restraint of the axial reinforcing bars and the joint reinforcing bars. When the transverse reinforcing bars are in contact with the anchorage of the axial reinforcing bars and the joint reinforcing bars, a large bending stress is generated in the transverse reinforcing bars (bending deformation occurs locally) instead of restraining the axial displacement of the axial reinforcing bars and the joint reinforcing bars, especially in the ultimate limit state. Therefore, when a large tensile force acts on the transverse reinforcing bars, it is necessary to separately arrange the reinforcing bars for restraining the displacement of the axial reinforcing bars and the joint reinforcing bars and the reinforcing bars for resisting the lateral tensile force. In this case, if the amount of reinforcing bars required to resist the lateral tensile force is large, the concrete will become over-crowded, causing problems in workability and quality. On the other hand, if the lateral reinforcing bars are arranged so as not to restrict the axial movement of the axial reinforcing bars and the joint reinforcing bars, over-crowding can be avoided.

[0010] If the rebar diameter of the joining rebar is larger than the rebar diameter of the axial rebar, the propagation of cracks due to axial tensile force can be suppressed. In the thickness direction of the filler concrete, it is desirable that the cover of the joint reinforcing bars is equal to or greater than the cover of the axial reinforcing bars. In this way, the thickness of the member does not increase even when the joint reinforcing bars are arranged. It is desirable to place tension members through both precast concrete members at the middle of the thickness of the filler concrete. This will reduce the crack width at the service limit. In addition, by increasing the tension, the occurrence of cracks can be suppressed. Furthermore, the tension members function effectively as tensile steel against torsion. Effect of the Invention

[0011] According to the joint structure for precast concrete members and the method for joining precast concrete members of the present invention, the progression of cracks due to axial tensile force can be suppressed and efficient construction can be performed. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a plan view showing the joint structure of the present embodiment. [Diagram 2] FIG. 2 is a side view showing the joint structure of the present embodiment. [Diagram 3] 2 is a flowchart showing the steps of a precast deck joining method according to the present embodiment. [Figure 4] FIG. 1 shows an analytical model of a numerical analysis conducted to confirm the effect of transverse reinforcement bars, where (a) is a plan view and (b) is a side view. [Diagram 5] 13 is a graph showing the results of a numerical analysis performed to confirm the effect of transverse reinforcement bars. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In this embodiment, a joint structure 1 for joining a plurality of precast decks 2 laid continuously in the bridge axis direction in bridge construction will be described. The joint structure 1 is shown in FIGS. As shown in Figures 1 and 2, the joint structure 1 joins a pair of precast deck slabs 2, 2 arranged with a gap 11 between them, and includes axial reinforcing bars 3, joining reinforcing bars 4, transverse reinforcing bars 5, filling concrete 6, and tendons 7.

[0014] The precast slab 2 is a precast concrete member made of reinforced concrete. As shown in Figures 1 and 2, inside the precast slab 2, two tiers of vertical slab reinforcements 21 are arranged along the bridge axis direction (left and right direction in the drawings), and horizontal slab reinforcements 22 are arranged to intersect with the vertical slab reinforcements 21. In addition, axial reinforcing bars 3 are provided to protrude from end faces 23 of the precast slab 2.

[0015] As shown in Fig. 2, the axial rebars 3 in this embodiment are the parts of the deck vertical bars 21 that protrude from the end faces 23 and are disposed in the gaps 11. The axial rebars 3 in this embodiment are SD345. The axial rebars 3 may be embedded in the end faces 23 of the precast deck 2 separately from the deck vertical bars 21. The standard of the rebars that constitute the axial rebars 3 is not limited. As shown in FIG. 1, in the joint structure 1, the axial reinforcing bar 3 of one precast floor slab 2 and the axial reinforcing bar 3 of the other precast floor slab 2 are arranged coaxially. An anchor 31 having an outer shape larger than the cross-sectional shape of the axial reinforcing bar 3 is formed at the end of the axial reinforcing bar 3. The anchor 31 in this embodiment is formed by fixing a rectangular steel plate to the end of the axial reinforcing bar 3. The method of fixing the anchor 31 to the axial reinforcing bar 3 is not limited, and may be, for example, welding, friction welding, or gas pressure welding. In addition, when the axial reinforcing bar 3 is threaded, a nut that can be screwed into the axial reinforcing bar 3 may be used as the anchor 31, or a steel plate with a female thread may be used. In addition, the anchor 31 is not limited to one formed by joining a separate member (steel plate) to the axial reinforcing bar 3, and may be, for example, an enlarged diameter portion (so-called a knob) formed by forging the end of the reinforcing bar. A gap is secured between the anchors 31 of the axial reinforcing bars 3 of one precast deck 2 and the anchors 31 of the axial reinforcing bars 3 of the other precast deck 2. The anchors 31 of the axial reinforcing bars 3 protruding from the opposing precast decks 2, 2 may face each other in an abutting state, or may face each other with a gap therebetween.

[0016] As shown in FIG. 1 , the connecting rebars 4 are rebars arranged parallel to the axial rebars 3 in the gaps 11 between the precast floor slabs 2. In this embodiment, the rebar diameter of the connecting rebars 4 is larger than the rebar diameter of the axial rebars 3. The cover of the connecting rebars 4 in the thickness direction of the interfacial concrete 6 is equal to or greater than the cover of the axial rebars 3. In other words, the central axis of the connecting rebars 4 is located closer to the center of the interfacial concrete 6 in the thickness direction than the central axis of the axial rebars 3. An anchor 41 having an outer shape larger than the cross-sectional shape of the joint rebar 4 is formed on both ends of the joint rebar 4. The anchor 41 of the joint rebar 4 is formed by fixing a rectangular steel plate to the end of the joint rebar 4. The method of fixing the anchor 41 to the joint rebar 4 is not limited, and may be, for example, welding, friction welding, or gas pressure welding. In addition, when the joint rebar 4 is threaded, a nut that can be screwed into the joint rebar 4 may be used as the anchor 41, or a steel plate with a female thread may be used. In addition, the anchor 41 is not limited to one formed by fixing a separate member (steel plate) to the joint rebar 4, and may be, for example, an enlarged diameter portion (so-called a knob) formed by forging the end of the rebar.

[0017] The transverse reinforcing bars 5 are reinforcing bars arranged in a direction intersecting the axial reinforcing bars 3 and the joint reinforcing bars 4 between the precast floor slabs 2 (gaps 11). The transverse reinforcing bars 5 are arranged at positions away from the anchors 31 of the axial reinforcing bars 3 and the anchors 41 of the joint reinforcing bars 4. In other words, the transverse reinforcing bars 5 are arranged so as not to come into contact with the anchors 31, 41.

[0018] The filler concrete 6 is a hardened concrete body filled between the precast deck slabs 2 (gaps 11). For the filler concrete 6, a material having the same compressive strength as the precast deck slab 2 is used. Note that the material constituting the filler concrete 6 is not limited, and for example, mortar may be used. The mix proportions of the filler concrete 6 may be determined appropriately. The tendons 7 are inserted through both precast floor slabs 2, 2 and disposed at the middle in the thickness direction of the filling concrete 6. The tendons 7 are made of, for example, PC steel bars, PC steel wires, PC strands, or the like.

[0019] Next, a method for joining precast floor slabs 2 (precast concrete members) will be described. Figure 3 shows the steps of the method for joining precast floor slabs 2. As shown in Figure 3, the method for joining precast floor slabs 2 includes a placement process S1, a reinforcing bar arrangement process S2, a casting process S3, and a tensioning process S4. In the installation step S1, one precast slab 2 is installed at a distance (gap 11) from the other precast slab 2. In the installation step S1, the precast slab 2 is laid so that the anchors 31 of the axial reinforcing bars 3 of one precast slab 2 face the anchors 31 of the axial reinforcing bars 3 of the other precast slab 2. The precast slab 2 is laid by suspending the other precast slab 2 from above after placing one precast slab 2 in a predetermined position. After laying the precast slab 2, the tension members 7 are inserted through the precast slabs 2, 2. After laying the precast slab 2, the side and bottom of the gap 11 are covered with formwork (not shown) as necessary. Note that, in cases where there is no risk of the filling concrete 6 flowing out from the bottom of the gap 11, such as when a main girder is arranged below the gap 11, the formwork on the bottom of the gap 11 may be omitted.

[0020] In the reinforcement arrangement process S2, joint rebars 4 and transverse rebars 5 are arranged between the precast floor slabs 2 (gaps 11). The joint rebars 4 are arranged on the sides of a pair of opposing axial rebars 3,3 so as to straddle both axial rebars 3,3 and to be parallel to both axial rebars 3,3. In other words, the joint rebars 4 are arranged between the axial rebars 3 arranged side by side with a gap in the direction intersecting the axial direction. Also, in the reinforcement arrangement process S2, the transverse rebars 5 are arranged at positions axially away from the anchors 31 of the axial rebars 3 and the anchors 41 of the joint rebars 4. In the pouring process S3, filler concrete 6 is poured between the precast floor slabs 2 (in the gaps 11). The filler concrete 6 is poured into a formwork that covers the gaps 11. The filler concrete 6 is cured, and when it has developed a predetermined strength, the formwork is removed. In the tensioning process S4, the tensioning material 7 is tensioned to introduce prestress into the precast deck 2.

[0021] According to the joint structure 1 and the joining method of the precast floor slabs 2 of this embodiment, the axial rebars 3 are connected to each other via the joint rebars 4 that are shorter than the distance (width of the gap 11) between the precast floor slabs 2 with the end faces 23 of the axial rebars 3 facing each other, so the installation method when installing the precast floor slabs 2 is not limited to sliding from the axial direction. Even when the precast floor slab 2 to be installed later is lowered from above, the axial rebars 3 will not come into contact with each other.

[0022] In addition, the transverse reinforcing bars 5 are arranged at a position away from the anchors 31 and 41 and are not connected to the axial reinforcing bars 3, so they do not contribute to the axial slippage or bending restraint of the axial reinforcing bars 3 and the connecting reinforcing bars 4. When the transverse reinforcing bars 5 are in contact with the anchors 31 of the axial reinforcing bars 3 and the anchors 41 of the connecting reinforcing bars 4, a large bending stress is generated in the transverse reinforcing bars 5 (bending deformation occurs locally) instead of restraining the axial displacement of the axial reinforcing bars 3 and the connecting reinforcing bars 4, especially in the ultimate limit state. Therefore, when a large tensile force acts on the transverse reinforcing bars 5, it is necessary to separately arrange reinforcing bars for restraining the displacement of the axial reinforcing bars 3 and the connecting reinforcing bars 4 and reinforcing bars for resisting the lateral tensile force. In this case, if the amount of reinforcing bars required to resist the lateral tensile force is large, the filling concrete 6 will be over-densely arranged, causing problems in workability and quality. On the other hand, in this embodiment, the lateral reinforcing bars 5 are arranged so as not to restrict the axial movement of the axial reinforcing bars 3 and the joint reinforcing bars 4, so that over-dense reinforcing bars can be avoided.

[0023] Since the rebar diameter of the joint rebar 4 is larger than the rebar diameter of the axial rebar 3, the progression of cracks in the filling concrete 6 due to axial tensile force can be suppressed. In addition, since the cover of the connecting bars 4 in the thickness direction of the interfacial concrete 6 is equal to or greater than the cover of the axial bars 3, the thickness of the precast deck 2 or the interfacial concrete 6 does not increase even when the connecting bars 4 are arranged. Since the tension members 7 inserted through both precast floor slabs 2 are disposed in the middle of the thickness direction of the filling concrete 6, it is possible to reduce the crack width at the service limit state. Furthermore, by increasing the tension of the tension members 7, it is possible to suppress the occurrence of cracks in the filling concrete 6. Furthermore, the tension members 7 effectively function as tensile steel against torsion.

[0024] The results of a numerical analysis performed on the joint structure of this embodiment are shown below. In this analysis, the relationship between the axial displacement of the axial rebar 3 and the tensile stress of the axial rebar 3 when the transverse rebar 5 is arranged so as not to contact the anchors 31, 41 of the axial rebars 3 and the joint rebars 4 is calculated by an elastic-plastic FEM analysis, and it was confirmed that the transverse rebar 5 does not contribute to the axial slippage or bending restraint of the axial rebars 3 and the joint rebars 4. Table 1 shows the analysis cases, and Figure 4 shows the analysis model. In this analysis, as shown in Figures 4(a) and (b), the gap 11 between the precast floor slabs 2 is set to 600 mm in width and 500 mm in height (thickness), and four horizontal reinforcements 5 of D25 are arranged at intervals of 150 mm. As shown in Figure 4(a), the distance from the center of the horizontal reinforcement 5 arranged on the outside (precast floor slab 2 side) to the end face 23 of the precast concrete member is set to 75 mm. As shown in Figure 4(b), the horizontal reinforcement 5 is set to a distance of 15 mm from the nearest anchors 31, 41. In addition, the cover (net cover) of the axial reinforcement 3 and the joint reinforcement 4 is set to 75 mm, and the cover (net cover) of the horizontal reinforcement 5 is set to 50 mm. The axial reinforcement 3 is set to D25, and the joint reinforcement 4 is set to D29. As comparative examples 1, 2, and 3, analyses were also performed for cases where the horizontal reinforcing bars 5 were not placed and the cover (net cover) of the connecting reinforcing bars 4 was set to 75, 80, and 110 (see Table 1).

[0025] [Table 1]

[0026] The analysis results are shown in Figure 5. As shown in Figure 5, there was almost no difference between Comparative Example 1 and the Example. In addition, the stress of the transverse reinforcing bar 5 in the Example was 3N / mm 2Therefore, it was confirmed that the horizontal reinforcing bars 5 separated from the anchors 31 and 41 did not contribute to the axial slippage or bending restraint of the axial reinforcing bars 3 and the connecting reinforcing bars 4.

[0027] Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and each component can be appropriately modified without departing from the spirit of the present invention. In the above embodiment, the joint structure 1 of the precast floor slab 2 has been described, but the precast concrete member is not limited to a floor slab and may be, for example, a box culvert. The rebar diameter of the joining rebar 4 does not necessarily have to be larger than the rebar diameter of the axial rebar 3, and can be the same as the rebar diameter of the axial rebar 3. The tendons 7 may be disposed as required. Similarly, the tensioning step S4 may be performed as required. The shape of the fixing bodies 31 and 41 is not limited to a rectangle, but may be, for example, another polygon, circle, ellipse, or the like. [Explanation of symbols]

[0028] 1 Joint structure (joint structure of precast concrete members) 11. Gap 2 Precast floor slabs (precast concrete components) 21 Deck vertical reinforcement 22 Deck slab horizontal reinforcement 23 End face 3 Axial reinforcement 31 Fixer 4. Jointed Reinforcement Bars 41 Fixer 5 Transverse Reinforcement 6. Filling concrete 7 Tensors

Claims

1. A joint structure for precast concrete members for joining precast concrete members arranged at intervals, comprising: An axial reinforcing bar protruding from an end surface of the precast concrete member; A joint reinforcing bar is arranged between the precast concrete members in parallel with the axial reinforcing bar; A transverse reinforcing bar arranged in a direction intersecting the axial reinforcing bar and the joint reinforcing bar; and filling concrete filled between the precast concrete members, The axial reinforcing bars of one of the precast concrete members and the axial reinforcing bars of the other precast concrete member are arranged coaxially, An anchor having an outer shape larger than the cross-sectional shape of the axial reinforcing bar is formed at the tip of the axial reinforcing bar, An anchor having an outer shape larger than the cross-sectional shape of the joint rebar is formed on both ends of the joint rebar, A joint structure of a precast concrete member, characterized in that the transverse reinforcement is arranged at a position away from the anchors of the axial reinforcement and the anchors of the joining reinforcement.

2. 2. A joint structure for precast concrete members according to claim 1, wherein the reinforcing bar diameter of the joint reinforcing bar is larger than the reinforcing bar diameter of the axial reinforcing bar.

3. 2. A joint structure for a precast concrete member as described in claim 1, characterized in that the cover of the joining reinforcing bars in the thickness direction of the filler concrete is equal to or greater than the cover of the axial reinforcing bars.

4. 2. A joint structure for precast concrete members as described in claim 1, characterized in that a tension member inserted into both of the precast concrete members is arranged in the middle of the thickness direction of the filling concrete.

5. A method for joining precast concrete members, comprising the steps of: connecting a pair of precast concrete members each having an axial reinforcing bar protruding from an end face of the precast concrete member; a placement step of placing one of the precast concrete members at a distance from the other of the precast concrete members; A reinforcing bar arrangement process of arranging joint reinforcing bars and transverse reinforcing bars between the precast concrete members; A pouring step of pouring filler concrete between the precast concrete members, An anchor having an outer shape larger than the cross-sectional shape of the axial reinforcing bar is formed at the tip of the axial reinforcing bar, An anchor having an outer shape larger than the cross-sectional shape of the joint rebar is formed on both ends of the joint rebar, In the disposing step, the precast concrete members are disposed so that the anchors of the axial reinforcing bars of one of the precast concrete members face the anchors of the axial reinforcing bars of the other precast concrete member; A method for joining precast concrete members, characterized in that in the reinforcement process, the transverse reinforcement is arranged at a position away from the anchors of the axial reinforcement and the anchors of the joining reinforcement.

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