Method for manufacturing precast floor slab

Abstract

To provide a manufacturing method based on an unconventional idea, which was made by focusing on the point that a "box body" with an opening at the bottom is installed so as to cover a part of reinforcing steel, and then concrete is placed.SOLUTION: A method for manufacturing a precast floor slab comprises a bar arrangement step, a form step, a box body installation step, and a concrete placing step. In the box body installation step, a box body with an open bottom part is installed to cover a part of the reinforcing bars, and in the concrete placing step, concrete is placed in a form with the box body installed. When the box body is removed after the concrete is hardened, the reinforcing bars are arranged to pass through the opening part of the box.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to technology related to precast concrete slabs such as steel-concrete composite slabs, PC (Prestressed Concrete) slabs, and RC (Reinforced Concrete) slabs, and more specifically to a manufacturing method for precast slabs that allows rebar to be placed in the box-cut sections of the slab. [Background technology]

[0002] It has been pointed out that the construction infrastructure (hereafter referred to as "construction infrastructure"), which was developed intensively during the period of high economic growth, is already showing signs of considerable deterioration. In 2014, the Council for Social Capital Development compiled a "Recommendation for Full-scale Implementation of Measures to Counteract Aging Roads," which cited the Sasago Tunnel ceiling collapse accident of 2012 as an example, sounding the alarm that "in the near future, this will lead to fatal incidents, such as the collapse of bridges, affecting human lives and social infrastructure," and strongly advocated the importance of maintaining and managing construction infrastructure.

[0003] Against this background, the government has promulgated a ministerial ordinance amending part of the Road Act Enforcement Regulations, formulating periodic inspection guidelines that outline specific construction infrastructure inspection methods, areas to look out for in major abnormalities, and photographs of case studies. These periodic inspection guidelines apply to bridges with a length of 2.0m or more, which is said to number around 700,000, and stipulate that the first inspection should be carried out within two years of opening to service, with periodic inspections thereafter to be carried out once every five years.

[0004] Meanwhile, the "Highway Bridge Specifications," which are the standards for designing road bridges, have been revised from time to time since the draft of the Steel Highway Bridge Design Specifications was published in 1939, and were significantly revised in particular after the Hyogo-ken Nanbu Earthquake. As a result, there are many cases where bridges that previously had sufficient strength are found to have insufficient strength in light of current design standards.

[0005] Due to the two reasons mentioned above, namely deterioration and insufficient strength, bridges are now frequently reinforced or rebuilt. Furthermore, even if the girder members are sound, if the deck that supports the vehicle load deteriorates, the deck is repaired or deck renewal work is carried out to replace the deteriorated deck with a new one.

[0006] However, current road bridges ensure a large volume of traffic, meaning they support the movement of people and the distribution industry, and so cannot be easily taken out of service. In particular, viaducts for expressways and other roads exclusively for automobiles carry tens of thousands of vehicles per day, and if they were to be closed to traffic, the economic losses would be immeasurable, and if emergency patients could not be transported, it could become a social problem. For this reason, when construction is carried out on a road bridge that is in service, it is always necessary to reopen it to traffic as soon as possible, and contractors are working hard to shorten the construction period in order to achieve this.

[0007] Traditionally, the cast-in-place concrete method has been used to construct concrete decks. This method requires assembling formwork on-site, pouring fresh concrete, and then allowing it to cure for a specified period of time. This means that the site is occupied for a long period of time, and when replacing the deck of a road bridge in service, traffic is restricted for an equally long period of time.

[0008] Therefore, in recent years, there has been an increase in the use of precast concrete slabs instead of cast-in-place concrete construction methods. Because these precast concrete slabs are manufactured in factories, quality control is easy, and what's more, the on-site process is mainly installation, which means that the time required for construction on-site can be shortened.

[0009] Furthermore, with the increase in usage, various technologies related to precast concrete decks have been proposed. For example, Patent Document 1 proposes a precast deck with a storage section formed so that a top plate remains above the box cutout section that stores the dowels of the main girders to prevent water from entering the box cutout section. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 2018-40168 Summary of the Invention [Problem to be solved by the invention]

[0011] Precast decks are often integrated with the main girders, and therefore shear stoppers (dowels) installed on the top surface of the main girders are sometimes used. Specifically, the dowels are inserted into the box cutouts in the precast deck, and then concrete is filled in the box cutouts to integrate the precast deck with the main girders. Conventional precast decks, however, were unable to place rebar in the box cutouts that penetrated the slab thicknesswise. Therefore, the rebar was either placed to avoid the box cutouts without bending, or bent rebar was placed to bypass the box cutouts. However, if the rebar was not bent, it was sometimes not possible to secure the required amount of rebar, and the rebar placement was also sparse. On the other hand, using bent rebar to avoid the box cutouts required additional processing work, and the placement of excessive rebar in a narrow space made the rebar placement process complicated.

[0012] The object of the present invention is to solve the problems associated with the prior art, that is, to provide a method for manufacturing precast deck slabs that allows reinforcing bars to be placed in box cutout sections. [Means for solving the problem]

[0013] The present invention was made by focusing on the fact that a "box" with an open bottom is placed over part of the reinforcing bars and then concrete is poured into it, and is an invention based on an unprecedented idea.

[0014] The method for manufacturing a precast deck slab of the present invention is a method for manufacturing a precast deck slab, and includes a reinforcement process, a formwork process, a box installation process, and a concrete pouring process. In the reinforcement process, the rebar is assembled, and in the formwork process, the formwork is assembled. In the box installation process, a box with an open bottom is installed so as to cover a portion of the rebar, and in the concrete pouring process, fresh concrete is poured into the formwork with the box installed. The box has slits on its sides to accommodate the rebar. In the box installation process, the rebar is inserted from below the slits and then dropped from above to install the box. When the box is removed after the concrete has hardened, a box cutout is formed that penetrates the slab thickness, and the rebar is placed so as to pass through the box cutout.

[0015] The precast deck manufacturing method of the present invention can also be a method using a box consisting of a main body and a top cover. The main body is composed of side surfaces. In this case, in the box installation process, the main body is installed so as to cover part of the reinforcing bars, and the top cover is then placed over the top opening of the main body.

[0016] The method for manufacturing a precast deck slab of the present invention can further include a covering material attachment step. In this covering material attachment step, after the box body installation step, covering materials are attached to the slits from the inside of the box body. In this case, after the concrete hardens, the top cover is removed, the covering materials are removed from the inside of the box body, and the box body is then removed.

[0017] The manufacturing method of the precast deck slab of the present invention can also be a method of placing the first rebar in the bridge axis direction and the second rebar perpendicular to the bridge axis. In this case, the first rebar and the second rebar are placed in the box cutout part so that they are approximately perpendicular (including perpendicular). [Effects of the Invention]

[0018] The method for manufacturing precast deck slabs according to the present invention has the following advantages: (1) Main reinforcement and distribution reinforcement can be placed in the box-out section that accommodates the main girder dowels. As a result, the degree of freedom in rebar placement is increased compared to conventional technology, and quality defects due to overcrowded rebar placement can be avoided. (2) Furthermore, since main reinforcement and distribution reinforcement can be placed in the box-out section that accommodates the main girder dowels, there is greater freedom in planning the position and size of the box-out section. (3) No special process or special equipment is required; simply by using a box body with a slit, reinforcing bars can be easily placed in the box cutout portion. (4) By attaching a covering material to the slit, the box cutout portion can be formed more reliably. [Brief explanation of the drawings]

[0019] [Figure 1] A perspective view showing the installation of a PC deck on top of the main girder. [Figure 2] (a) is a vertical cross-sectional view showing the main girder and steel-concrete composite deck slab as viewed in the direction of the bridge axis, and (b) is a plan view showing the steel-concrete composite deck slab as viewed from above. [Figure 3] FIG. 1 is a flow chart showing the flow of the main steps in the manufacturing method of a precast composite floor slab, one of the precast floor slabs of the present invention. [Figure 4] (a) is a side view showing the housing in a schematic manner, and (b) is a plan view showing the housing in a schematic manner. [Figure 5] FIG. 3 is a side view schematically showing a housing including a top cover. [Figure 6] FIG. 10 is a step diagram showing the procedure for installing the box. [Figure 7] FIG. 10 is a side view schematically showing a box with two levels of reinforcing bars housed in the slits. [Figure 8] FIG. 2A is a perspective view showing a box placed at a predetermined position, and FIG. 2B is a plan view showing a schematic view of the box placed at a predetermined position. [Figure 9] A schematic plan view showing a box body covered with reinforcing bars in the bridge axis direction and reinforcing bars perpendicular to the bridge axis. [Figure 10]A cross-sectional view showing the state in which a precast deck manufactured according to the present invention is installed on the main girder. [Figure 11] Plan view showing a precast deck slab with straight reinforcement arranged to avoid the box cutout area. [Figure 12] A plan view showing a precast deck slab reinforced with bent rebar to avoid the box cutout area. DETAILED DESCRIPTION OF THE INVENTION

[0020] An example of an embodiment of the precast deck manufacturing method of the present invention will be described with reference to the drawings. The present invention is a method for manufacturing a precast deck 200 to be installed on a main girder MG, as shown in FIG. 1. FIG. 1 is a perspective view schematically showing the installation of a PC deck (precast deck 200) on the main girder MG. However, this precast deck 200 has a box cutout 210. This box cutout 210 is a space that accommodates the dowels JB fixed to the top surface of the main girder MG, as shown in FIG. 2. The precast deck 200 and the main girder MG are integrated by filling the box cutout 210 that accommodates the dowels JB with concrete or the like. FIG. 2(a) is a vertical cross-sectional view schematically showing the main girder MG and the steel-concrete composite deck (precast deck 200) as viewed in the bridge axis direction, and FIG. 2(b) is a plan view schematically showing the steel-concrete composite deck as viewed from above.

[0021] The manufacturing method for the precast deck 200 of the present invention will be described with reference to Figure 3. Figure 3 is a flow diagram showing the flow of the main steps in the manufacturing method for the precast deck 200 of the present invention. Note that the present invention is a method for manufacturing various precast decks 200, such as steel-concrete composite decks, PC decks, and RC decks, but for convenience, the example of manufacturing a steel-concrete composite deck will be described here. The manufacturing method for the precast deck 200 of the present invention can be carried out in a dedicated manufacturing factory, or in a yard installed near the bridge construction site.

[0022] A steel-concrete composite deck (precast deck 200) is a composite deck consisting of a two-layer structure of steel plate panels and concrete. Therefore, first, the steel plate panels are placed in the designated positions as shown in Figure 3 (Step 101 in Figure 3). At this time, if the precast deck 200 is a PC deck or RC deck, it is recommended to place steel plate formwork or wooden formwork instead of the steel plate panels. Next, main reinforcement bars, distribution bars, etc. are assembled on top of the steel plate panels (Step 102 in Figure 3), and the concrete formwork is assembled to achieve the planned shape (Step 103 in Figure 3).

[0023] After assembling the rebar and concrete formwork, the "box 300" shown in FIG. 4 is installed (Step 104 in FIG. 3). FIG. 4 is a schematic diagram of the box 300, with (a) being a side view and (b) being a plan view. The box 300 is a hollow, box-like structure consisting of side surfaces 320 and a top surface 330, with an open bottom. Two opposing side surfaces 320 have slits 310 with open bottoms. When the box 300 is composed of four side surfaces 320, there are two sets of opposing side surfaces 320. Slits 310 can be formed on only one set, or on both sets. The box 300 is made of a material that can withstand the lateral pressure of fresh concrete, such as steel or resin.

[0024] The case 300 can be configured such that the top surface 330 is fixed to the side surface 320, or such that the top surface 330 and the side surface 320 are separate. For example, the case 300 shown in Fig. 5 is configured with a "main body 350" made up of the side surface 320 and a top lid 340, the main body 350 being cylindrical with openings at the bottom and top, and the top lid 340 being detachably disposed in the top opening of the main body 350.

[0025] The procedure for installing the box body 300 will be described below with reference to Fig. 6. Fig. 6 is a step diagram showing the procedure for installing the box body 300. Once the reinforcing bars 220 have been assembled, the main body 350, from which the top lid 340 has been removed, is placed at the planned position of the box cutout section 210 in the precast deck 200. Then, as shown in Fig. 6(a), the main body 350 is lowered from above, and the reinforcing bars 220 are inserted from the bottom (opening) of the slit 310.

[0026] Once the reinforcing bar 220 has been inserted into the slit 310, the main body 350 is further lowered while being guided along the slit 310 by the reinforcing bar 220, and is placed on the steel plate panel as shown in Fig. 6(b). At this time, it is advisable to form the slit 310 so that the reinforcing bar 220 comes into contact with the top of the slit 310.

[0027] Once the main body 350 is placed on the steel panel, as shown in FIG. 6(c), tape, a thin plate, or the like (hereinafter referred to as "covering material 360") is attached to the gaps in the slits 310 where the reinforcing bars 220 are not placed. At this time, since the top surface of the main body 350 is still open, the worker may attach the covering material 360 from the inside of the main body 350. Note that in FIG. 6, one slit 310 accommodates one row of reinforcing bars 220, but the slit 310 may accommodate two or more rows of reinforcing bars 220. In that case, it is preferable to attach a covering material 360 to each gap. For example, in FIG. 7, two rows of reinforcing bars 220 are accommodated in the slit 310, and therefore covering materials 360 are attached at two locations, the upper and lower.

[0028] Once the covering material 360 is attached, the top lid 340 is placed over the top opening of the main body 350, as shown in Figure 6(d). Note that up to this point, the example of the box 300 made up of the main body 350 and the top lid 340 has been explained, but in the case of a box 300 in which the top surface 330 and the side surface 320 are integrated, the box 300 itself is lowered. Furthermore, in cases where an extremely narrow slit 310 is formed, the attachment of the covering material 360 can be omitted.

[0029] When the box body 300 is placed on the steel panel with the reinforcing bars 220 housed in the slits 310, the box body 300 covers a portion of the reinforcing bars 220, as shown in FIG. 8. FIG. 8 shows the box body 300 placed in a predetermined position, with (a) being a perspective view and (b) being a plan view seen from above. Note that in FIG. 8(b), the slits 310 are formed only on the two opposing side surfaces 320, so that only the reinforcing bars 220 in one direction are covered. However, this is not limited to this, and the box body 300 can also cover the reinforcing bars 220 in two directions. For example, in FIG. 9, a reinforcing bar in the bridge axis direction (hereinafter referred to as the "first reinforcing bar 221") and a reinforcing bar perpendicular to the bridge axis (hereinafter referred to as the "second reinforcing bar 222") are arranged, and the box body 300 covers these first reinforcing bars 221 and second reinforcing bars 222. In this case, slits 310 are formed on two side surfaces 320 of the box body 300 that face each other in the bridge axis direction, and slits 310 are also formed on two side surfaces 320 that face each other in the direction perpendicular to the bridge axis.

[0030] Once the box body 300 is installed at the planned location of the box punch section 210, fresh concrete is poured into the concrete formwork (Step 105 in Figure 3), and the concrete is allowed to cure for the planned period of time. The formwork is then removed (Step 106 in Figure 3), and the box body 300 is removed (Step 107 in Figure 3). Note that it is advisable to apply a release agent to the surface of the box body 300 (particularly the side surface 320) before installation, so that the box body 300 can be easily removed from the hardened concrete.

[0031] Removal of the box 300 can be achieved by roughly reversing the installation procedure. That is, first, remove the top cover 340 from the top opening of the main body 350, then reach inside the main body 350 and remove the covering material 360. Then, peel the main body 350 from the concrete and remove it.

[0032] Figure 10 is a cross-sectional view showing a precast deck 200 manufactured according to the present invention installed on a main girder MG. As shown in this figure, a box cutout 210 is formed in the precast deck 200, penetrating in the thickness direction of the deck, and reinforcing bars 220 are arranged in the box cutout 210 so that they pass through it. When the precast deck 200 is installed in the planned position of the main girder MG, the dowel JB of the main girder MG is accommodated in the box cutout 210. When installing the precast deck 200 on the main girder MG, it is recommended to adjust the height using the height adjustment bolts AB shown in Figure 10.

[0033] So far, we have explained a precast slab 200 in which reinforcing bars 220 are placed in the box cutout section 210. On the other hand, a precast slab that is reinforced with reinforcing bars without placing reinforcing bars in the box cutout section is also possible. For example, the precast slab shown in Figure 11 has straight bars arranged to avoid the box cutout section, so that the reinforcing bars avoid the box cutout section in a planar manner, while the precast slab shown in Figure 12 has reinforcing bars arranged to bend down halfway, so that the reinforcing bars avoid the box cutout section in a planar manner. This allows reinforcing bars to be placed around the box cutout section, resulting in a precast slab in which the box cutout section is reinforced with reinforcing bars. [Industrial Applicability]

[0034] The precast deck manufacturing method of the present invention can be used for bridges of all types, including road bridges and railway bridges, as well as for bridges that cross various types of terrain, such as river bridges, overpasses, and railway bridges. Furthermore, the present invention can be used not only for deck replacement of existing bridges, but also for new bridge construction. Considering that the present invention can provide safer transportation and ultimately extend the lifespan of bridges, it can be said to be an invention that can be expected to not only be used industrially but also make a significant contribution to society. [Explanation of symbols]

[0035] 200 Precast deck manufactured according to the present invention 210 Box removal section 220 Reinforced concrete 221 First Reinforcement Bar 222 Second Reinforcement Bar 300 box 310 Slit 320 Side 330 Top 340 Top lid 350 body 360 Covering material AB height adjustment bolt JB Zibel MG main girder

Claims

1. A method for manufacturing a precast deck, comprising: The reinforcing bar arrangement process, a formwork process for assembling formwork; a box installation process for installing a box having an open bottom so as to cover a portion of the reinforcing bar; a concrete pouring step of pouring concrete into the formwork with the box body installed, A slit for accommodating the reinforcing bar is provided on the side surface constituting the box body, In the box installation step, the reinforcing bar is inserted from below the slit, and then the box is installed by dropping it from above. When the box body is removed after the concrete has hardened, a box cutout portion penetrating in the thickness direction of the slab is formed, and the reinforcing bar is arranged to pass through the box cutout portion. A method for manufacturing precast deck slabs.

2. The housing includes a main body having the side surface and a top cover, In the box installation step, the main body is installed so as to cover a portion of the reinforcing bar, and then the top cover is placed on an upper opening of the main body. The method for manufacturing a precast deck according to claim 1.

3. Further provided is a covering material attaching step of attaching a covering material to the slit from the inside of the case after the case installation step, After the concrete has hardened, the top cover is removed, and the covering material is removed from the inside of the box, and the box is then removed.

3. The method for manufacturing a precast deck according to claim 2.

4. In the reinforcing bar arrangement process, a first reinforcing bar in the bridge axis direction and a second reinforcing bar in the direction perpendicular to the bridge axis are arranged, The first reinforcing bar and the second reinforcing bar that are orthogonal or approximately orthogonal to each other are arranged in the box cutout portion. The method for manufacturing a precast deck according to claim 1.

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