How to form a reverse taper cotter

Abstract

To provide a method for forming a reverse taper cotter easily and economically. [Solution] The method includes the steps of preparing a core set 1 including a high-elasticity core 2 and a high-rigidity core 3 inserted into the high-elasticity core 2; positioning the core set 1 with its opening facing the surface of the concrete and its bottom facing inside the concrete before pouring a precast concrete element 9; pouring the precast concrete element 9; removing the high-rigidity core 3 after the poured concrete has hardened; elastically deforming the high-elasticity core 2 to remove it from the concrete after removing the high-rigidity core 3; and filling the recesses formed in the concrete by the core set with filler.

Description

[Technical Field]

[0001] The present invention relates to a method for forming a cotter used for joining precast concrete members, etc. [Background technology]

[0002] A known method for joining precast concrete members, such as precast deck slabs, involves providing a predetermined gap between adjacent precast deck slabs, passing PC steel or rebar or other joining material through the deck slabs in the longitudinal direction, and pouring concrete or grout to join them together. One such method, which involves providing shear cotters in the lateral direction of the deck slab to improve shear strength, has been disclosed as prior art (see Figure 1 of Patent Document 1).

[0003] In addition, shear cotters are often installed on the top surface of precast decks to improve the joining strength, not only between precast components but also in composite decks, which are integrated by pouring concrete on top of precast decks (see Patent Document 2).

[0004] In most cases, shear cotters are trapezoidal or arc-shaped, with the width on the surface of the concrete wider than the width on the inside of the concrete, to allow precast members to be demolded. Cotters formed in this way may experience peeling or chipping of the bonding material at the cotter's uneven surface when subjected to repeated loads. Patent Documents 2 and 3 disclose a method of improving this by forming a reverse taper. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-190103 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-62155 [Patent Document 3] Japanese Patent Application Publication No. 52-74614 Summary of the Invention [Problem to be solved by the invention]

[0006] The forming method disclosed in Patent Document 2 involves pressing a convex mold against the top surface of the concrete being continuously poured by a mobile pouring machine before the concrete hardens to form a groove, and then pressing a dovetail-shaped mold into the groove to form a dovetail groove.

[0007] However, this method not only increases costs and reduces workability due to the use of specialized machinery, but also has the disadvantage that it can only be applied to the pouring surface of precast members. In other words, this method cannot be used when forming cotters on formwork surfaces, such as the bottom or side surfaces of members.

[0008] Patent document 3 discloses a molding method that can be adapted to formwork surfaces, in which a rubber elastic body with a hollow structure whose cross section is an inverted trapezoidal shape and whose wall thickness at the four corners is gradually increased compared to the other parts is used as a spacer for forming joint grooves between concrete segments.

[0009] However, this method has the following problems. 1. When forming a reverse taper joint trench, first pour the first layer of concrete using a steel core to form half of the trench, then press a rubber elastic core into place and pour the second layer of concrete to form the trench. This method makes the concrete pouring process complicated, and requires the use of many different types of cores and formwork, significantly increasing costs and the amount of work involved. Not only that, pouring the concrete in two stages creates unnecessary pouring joints in the precast members, which can easily become weak points in the structure. 2. The required performance of rubber elastic cores is that they must be able to withstand the concrete pouring pressure and at the same time be able to be easily removed from the concrete after it has hardened. However, in reality, the pouring pressure (lateral pressure) of the concrete varies depending on the size of the components and the spacing of the joint grooves, so it is extremely difficult to select a material for the rubber elastic core that will not deform due to the pouring pressure (lateral pressure) and will also be easy to deform so that it can be easily removed when demolding, making it difficult to put this technology into practical use.

[0010] Therefore, an object of the present invention is to provide a method for easily and economically forming a reverse tapered cotter on the surface of a precast concrete member. [Means for solving the problem]

[0011] The method for forming a reverse taper cotter of the present application includes the steps of: a step of preparing a core set including: a high-elasticity core having a cylindrical portion, an opening formed at one end of the cylindrical portion and a bottom formed at the other end, wherein the distance from the outer surface of the cylindrical portion to the central axis of the cylindrical portion in the direction of the central axis of the cylindrical portion decreases from the bottom side toward the opening side; and a high-rigidity core having a cylindrical shape and a through-hole formed in a side surface thereof that penetrates in the radial direction, and inserted into the cylindrical portion through the opening; Before pouring the precast concrete member, positioning the core set so that the opening is on the surface side of the precast concrete member and the bottom is on the inside of the precast concrete member, and so that the top surface of the core set on the opening side protrudes from the surface of the precast concrete member; A step of placing the precast concrete member; removing the high-rigidity core after the poured concrete has hardened; After removing the high-rigidity core, the high-elasticity core is elastically deformed and removed from the concrete. and filling the recesses formed in the precast concrete member by the core set with a filler material. [Effects of the Invention]

[0012] According to the present invention, the following effects can be obtained. (1) By placing a high-rigidity core inside a high-elasticity core, the cotter formed on the surface of the precast concrete member can be ensured to have the desired shape without being affected by the concrete pouring pressure (lateral pressure). (2) Unlike conventional technology, deformation due to pouring pressure is prevented, and removal after concrete hardens is also easy, making it possible to freely select the material and hardness, thereby making the technology more practical. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view showing a core set according to Example 1, where (a) is a perspective view cut along the central axis, and (b) is a perspective view of the entire core set. [Figure 2] 1 is a perspective view showing a core set according to Example 2. (a) is a perspective view cut along the central axis, and (b) is a perspective view of the entire core set. [Figure 3] 10A and 10B are perspective views showing a core set according to Example 3. (a) is a perspective view cut along the central axis, and (b) is a perspective view of the entire core set. [Figure 4] 10A and 10B are diagrams showing a procedure for forming a recess for a cotter using the core sets of Examples 1 and 2. [Figure 5] 1A and 1B are diagrams showing an example of use of a reverse taper cotter 8 formed using Example 1 or Example 2. (a) shows a horizontal cross section, (b) shows an AA cross section, and (c) shows a BB cross section. [Figure 6] FIG. 10 is a cross-sectional view showing an example of application to a composite deck. [Figure 7] FIG. 10 is a diagram illustrating an example of use of the second embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of use of the third embodiment. [Figure 9] FIG. 10 is a diagram illustrating an example of use of the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION [Example]

[0014] The present invention will be described in detail based on the illustrated embodiments. Figure 1 shows a core set 1 according to Example 1 of the present invention. The core set 1 consists of a high-elasticity core 2 and a high-rigidity core 3. Figure 1(a) is a perspective view cut along the central axis, and Figure 1(b) is a perspective view showing the overall shape. In order to form a reverse tapered cotter in a precast concrete member, the highly elastic core 2, which is easily deformed, is combined with a high-rigidity core 3, which is placed inside it and is sufficiently able to withstand pouring pressure (lateral pressure).

[0015] The high-elasticity core 2 has a cylindrical portion 2a, with an opening 2b formed at one end of the cylindrical portion 2a and a bottom 2c formed at the other end. The outer surface of the cylindrical portion 2a is inclined with respect to the central axis, and the distance from the outer surface of the cylindrical portion 2a to the central axis decreases from the bottom 2c side toward the opening 2b side in the direction of the central axis of the cylindrical portion 2a.

[0016] The high-rigidity core 3 is cylindrical, with a through-hole 3a formed in the side surface that penetrates in the radial direction. The through-hole 3a makes it easy to remove the high-rigidity core 3 from the high-elasticity core 2 by hooking it with a finger or a tool.

[0017] In the illustrated embodiment, the outer shapes of the high-elasticity core 2 and the high-rigidity core 3 when viewed in the direction of the central axis are circular, but this is not limited to a circular shape and they may be rectangular, polygonal, etc. Furthermore, the portions forming the inner surfaces of the high-elasticity core 2 and the high-rigidity core 3 do not need to be circular when viewed in the direction of the central axis and may have other shapes.

[0018] The through hole 3a is a hook provided to make it easier to remove the high-rigidity core 3, but is not limited to this and may be changed to another shape, such as a groove or a protrusion. [Example]

[0019] FIG. 2 is a diagram showing a core set 1 according to Example 2. Example 2 was devised assuming a case in which the method of fixing to the formwork during pouring and the use of the cotter formation are different from those of Example 1. Example 2 differs from Example 1 in that a circular hole 2d is formed in the center of the bottom 2c of the high-elasticity core 2. The high-rigidity core 3 is the same as that of Example 1. [Example]

[0020] Figure 3 is a diagram showing a core set 1 according to Example 3. Example 3 was devised to accommodate an application that is even different from Examples 1 and 2. Example 3 differs from Example 2 in that a cylindrical protrusion 2e is provided on the side of the high-elasticity core 2 opposite the opening 2b from the bottom 2c in the central axis direction. The high-rigidity core 3 is the same as in Examples 1 and 2. The protrusion 2e has a smaller diameter than the cylindrical portion 2 and is cylindrical in shape, sharing a common central axis with the cylindrical portion 2. [Example]

[0021] Figure 4 shows the procedure for forming cotters on the surface of a precast concrete member 9, for example, a deck (hereinafter also referred to as a precast deck 9), using the core set 1 of Examples 1 and 2. This is the case when a shear cotter is provided on the joint surface (side surface) between precast concrete members 9 (deck slabs), and Figure 4 shows a bed formwork 4 and side frame 5, with the upper surface serving as the concrete pouring surface. The procedure is explained below.

[0022] In step (1), thread taps are drilled into the side frame 5, and with the top end of the core set 1 flush with the surface of the precast deck 9, the surface of the side frame is temporarily fixed with bolts 6, and concrete is poured. Although not shown in the figure, in this case, it is preferable to fix it to the side frame 5 using adhesive tape as well. In step (2), once the concrete has hardened and the precast deck 9 has been formed, the bolts 6 are removed and the side frame 5 is demolded. In step (3), a finger or a tool is hooked into the through hole 3a of the high-rigidity core 3 to remove the high-rigidity core 3a. In step (4), a finger or a tool is inserted between the highly elastic core 2 and the precast deck 9, and the highly elastic core 2 is elastically deformed and removed. Step (5) shows the completed cotter recess on the surface of the precast deck 9.

[0023] Although the illustration shows an example in which the bolt 6 is used for temporary fixation, the present invention is not limited to this, and other fixing methods may be appropriately selected from the prior art and used.

[0024] Next, a method of using the second embodiment shown in FIG. 4 will be described as step (1)-a. When using Example 2, holes are drilled in the side frames 5, bolts 6 are inserted into the holes in the side frames 5, core set 1 is passed through, and nuts 7 are screwed in to temporarily fix core set 1 to the side frames 5, and concrete is then poured. The subsequent steps (2) to (5) are not shown in the drawings, but are the same as those in Example 1.

[0025] In Example 2, the highly elastic core 2 has a hole 2d in the bottom 2c thereof, so that the highly elastic core 2 is more easily deformed when removed than in Example 1, and the range of choices for material and hardness is increased.

[0026] Figure 5 shows an example of the use of a reverse taper cotter 8 formed using Example 1 or Example 2. When used for road bridge decks, port container decks, or airport runway pavement decks, as shown in Figure 5(a), precast decks 9 are joined at a required distance to absorb construction errors, and PC steel wires 10 are inserted longitudinally as connecting steel. Multiple reverse taper cotters 8 are provided at predetermined intervals in the width direction.

[0027] (b) AA cross section shows the PC steel wires 10 arranged inside the sheath. Generally, the thickness of the deck slab 9 is limited, unlike girders or beams, so in most cases only one level of connecting steel is arranged in the center in the height direction. Similar to the example shown, the case where reinforcing bars or steel rods are used as connecting steel instead of the PC steel wires 10 is also applicable.

[0028] (c) Cross section B-B shows the cotter formed with the filled mortar and the joint, along with the image of load and stress transfer. When wheel load P is applied, a bending moment M and a shear force Q are most commonly generated in the precast deck slabs at both ends of the joint. The stress intensity due to the bending moment along the height of the cross section is distributed triangularly around the neutral axis (centroid of the cross section), with the resultant forces acting on the cross section as a tensile force T on the tension side and a compressive force C on the compression side. As can be seen from the illustration, the resultant tensile force T acts on the cotter before the connecting steel. Therefore, with conventional tapered cotter fillers, whose surface width is wider than the base, repeated wheel loads can cause the filler forming the cotter to peel off, potentially resulting in damage to the cotter. In contrast, the use of the reverse tapered cotter 8 of the present invention prevents cotter peeling and damage.

[0029] Figure 6 shows an application to a composite deck. As is well known, composite decks, formed by pouring in-place top concrete 12 onto a precast deck 9 that also serves as formwork, are commonly used in buildings and bridges. For composite decks, it is important to integrate the precast deck and the top concrete. By using the reverse taper cotter 8 of the present invention, it is possible to overcome the weaknesses of conventional taper cotters as mentioned above and achieve integration.

[0030] Figure 7 shows an example of the use of Example 2. It is common to hammer inserts into the surface of a deck slab as anchors for mounting metal fittings, such as lifting jigs used during construction, removal from formwork, moving, and transportation. After construction is complete, the insert heads are treated with anti-corrosion agents and then filled with mortar. However, if the filled mortar is subjected to repeated loads and peels off from the concrete, the cotter becomes hollow and breaks, inevitably affecting the durability of the deck slab. The use of the reverse taper cotter of the present invention significantly reduces the likelihood of this happening.

[0031] In step (1), inserts 13 are placed, and temporary positioning plates 14 are placed as fixing hardware in a position overlapping the top surface of the precast member, and bolts 15 are inserted into temporary plates 14, passed through core set 1, and screwed into inserts 13 to secure them in place. Concrete is then poured in this state. In step (2), after the precast members are formed, the bolts 15 and the temporary plates 14 are removed. Steps (3) and (4) are the same as steps (3) and (4) in Figure 4. In step (5), a metal fitting for construction, such as a hanging jig 16, is attached and work is carried out. In step (6), after the construction is completed, the lifting jig 16 is removed, and the recess for the cotter is filled with mortar 17, which hardens to form a reverse tapered cotter.

[0032] Figure 8 shows an example of use of Example 3. A well-known method for joining precast deck slabs 9 together involves placing a sheath inside the member, inserting connecting steel materials 18 such as PC steel wires or slip bars into the sheath, filling the sheath with grout 19 and allowing it to harden, thereby integrating the connecting steel materials 18 with the member. A steel pipe or steel sheath, for example, is placed as a vertical sheath 20 that connects the grout injection or discharge port to the sheath. The procedure for using a reverse taper cotter in this method is described below.

[0033] In step (1), the protrusion 2e provided on the bottom 2c of Example 3 is inserted into the vertical sheath 20, a temporary positioning plate 14 is placed in a position overlapping the top surface of the precast member, the core set 1 is temporarily fixed with bolts 15, and concrete is poured. In step (2), after the concrete has hardened and the precast concrete member 9 has been formed, the bolts 15 and the temporary plate 14 are removed. Steps (3) and (4) are the same as steps (3) and (4) in Figure 7. In step (5), grout is filled into the sheath from the vertical sheath 20, and it is confirmed that it overflows to the top surface of the vertical sheath 20. After the grout hardens, mortar 17 is filled into the recess for the cotter, and as the mortar 17 hardens, a reverse tapered cotter is formed on the surface of the precast concrete member 9.

[0034] Figure 9 shows an example of use of Example 4. To make it easier to remove the highly elastic core 2 during demolding, Example 2 has been improved by making the height of the core set 1 slightly higher than the depth of the reverse tapered cotter 8 to be formed, and making the top surface of the core set 1 protrude by this amount above the surface of the precast concrete member 9. The protruding height may be such that it can be grasped with fingers. By doing this, it is easier to grasp the protruding part with just the fingers, deform it, and remove it without using a tool, compared to inserting a finger or tool between the high-elasticity core 2 and the precast deck 9 and elastically deforming the high-elasticity core 2 to remove it, as shown in step (4) of Figure 4. In this case, as shown in Figure 9 as an example of a formwork, a hole is drilled in the side frame 5 to match the size of the protrusion, a temporary plate 14 is attached on top of it, and it is fixed with a bolt 6 via a larger washer. In the illustration, both the high-elasticity core 2 and the high-rigidity core 3 are similarly longer in the central axis direction than in other embodiments, but it is also possible to have only the high-elasticity core 2 protrude and the high-rigidity core 3 not protrude, making them the same length as in other embodiments. Steps (1) to (5) are the same as described above. Also, although not shown in the illustration, the same method can be applied to Examples 1 and 3. Usage examples are also similar. It is preferable that the material of the high-elasticity core 2 is soft rubber, and the material of the high-rigidity core 3 is synthetic resin, but the materials are not limited to these and may be selected appropriately from various commercially available materials. [Explanation of symbols]

[0035] 1 core set 2 High elasticity core 2a Side 2b opening 2c bottom 2d hole 2e Protrusion 3 High rigidity core 3a through hole 4 Bed formwork 5 side frame 6 volts 7 Nuts 8 Reverse Taper Cotter 9 Precast concrete members (floor slabs) 10 PC steel wire 12 Top Concrete 13 Insert 14 Temporary Plate 15 volts 16 Lifting jig 17 Mortar 18 Joined steel materials 19 Grout 20 Vertical sheath

Claims

1. preparing a core set including: a high-elasticity core having a cylindrical portion, an opening formed at one end of the cylindrical portion and a bottom formed at the other end, the distance from the outer surface of the cylindrical portion to the central axis of the cylindrical portion decreasing from the bottom side toward the opening side in the direction of the central axis of the cylindrical portion; and a high-rigidity core having a cylindrical shape and a through-hole formed in a side surface thereof that penetrates radially, the high-elasticity core being inserted into the cylindrical portion through the opening; Before pouring the precast concrete member, positioning the core set so that the opening is on the surface side of the precast concrete member and the bottom is on the inside of the precast concrete member, and so that the top surface of the core set on the opening side protrudes from the surface of the precast concrete member; pouring concrete into the precast concrete members; removing the high-rigidity core after the poured concrete has hardened; After removing the high-rigidity core, elastically deforming the high-elasticity core and removing it from the concrete; and filling the recess formed in the precast concrete member by the core set with a filler material.

2. The method for forming a reverse taper cotter according to claim 1 , wherein the bottom has a hole.

3. The method for forming a reverse taper cotter according to claim 2 , wherein the cylindrical portion has a protrusion extending from the hole to a side opposite to the opening in the direction of the central axis of the cylindrical portion.

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