JP6970887B2 - Precast members for buried formwork, their design methods, and reinforced concrete decks - Google Patents

Description

The present invention relates mainly to a precast member for an embedded formwork applied when constructing a deck, a design method thereof, and a reinforced concrete deck.

The mooring facility, which is one of the port facilities, is for mooring vessels safely and reliably, and proper maintenance and maintenance are indispensable. Since it has been 50 years since its construction, it is aging like other civil engineering structures such as tunnels and bridges, and there is concern that earthquakes and waves will cause great damage.

Therefore, there is an urgent need to take measures according to the progress of aging, but the mooring facilities are placed in a special environment where the reinforcing bars are corroded by chloride ions in seawater, so when taking measures, In addition to improving durability against chloride ions, it is also essential to consider workability and safety during construction because the countermeasure work is done above the seawater surface.

In mooring facilities, the floor slabs that make up the apron, especially the underside of the floor slabs, are exposed to chloride ions for a long period of time, so concrete often peels off due to rebar corrosion. In such cases, the existing floor slabs were removed. Above, it is necessary to rebuild a new floor slab, but if you try to build this with cast-in-place concrete, you will have to assemble and disassemble the scaffold and the formwork at sea, which will of course increase the construction cost. In addition, the period during which the facility cannot be used as a mooring facility will be long, and the impact on logistics will be great.

On the other hand, if the above-mentioned new floor slab is constructed using precast members, the construction period can be shortened, and by using the precast members as half precast members, the transportation cost can be reduced. At the same time, by using it as a buried formwork, it can be used as a work floor during construction, scaffolding can be kept to the minimum necessary, and the burden of assembling and disassembling the formwork is reduced (patented). Document 1).

Japanese Unexamined Patent Publication No. 2011-220059

However, when the half precast member is used as an embedded formwork when constructing the floor slab, it is necessary to manufacture the half precast member with an appropriate thickness in order to support the weight of the concrete cast in the field until the strength is developed. Therefore, the workability during transportation and lifting is limited to the extent that it is reduced compared to the full precast member.

On the other hand, if the procedure of dividing the concrete to be cast on-site into a plurality of times, waiting for the strength of the preceding concrete to be developed, and then casting the next concrete (Patent Document 1), the load of the above-mentioned half precast member is applied. Although the support burden is reduced, dividing the concrete to be cast on-site into multiple times means that measures are immediately required when a horizontal joint is to be provided, and the casting of the preceding concrete is required. Immediately afterwards, a retarding agent is sprayed, and the concrete surface is forced to be treated with high-pressure water at an appropriate time when the lower layer is hardened. At the same time, the reinforcing bar work is divided into multiple times as in the concrete work. Separate construction is forced.

That is, if the half precast member is made thicker, it is possible to avoid the influence on the reinforced concrete work at the site, but there is a limit to the miniaturization or weight reduction, which causes a problem that transportation and installation are costly. If the members are made thinner, the workability during transportation and installation is improved, but there is a problem that the reinforced concrete work at the site is affected and the construction period becomes longer.

Above all, cracks in concrete are the entry route for chloride ions, so in the case of mooring facilities, it is important to minimize cracks. The problem is that the weight of the installed concrete causes cracks, which reduces the durability of the concrete itself, and the chloride ions through the cracks also invade the reinforced concrete constructed on site and reduce the durability. Was occurring.

The present invention has been made in consideration of the above-mentioned circumstances, and it is possible to realize thinning without affecting the reinforced concrete work at the site and to improve the durability against chloride ions by preventing the occurrence of cracks. It is an object of the present invention to provide a possible precast member for an embedded formwork, a design method thereof, and a reinforced concrete deck.

In order to achieve the above object, as described in claim 1, the precast member for an embedded formwork according to the present invention has a grid pattern and is formed on a surface extending to the concrete placing side and a surface on the back side thereof, which is the concrete non-casting side. A grid portion having an expanding surface as a first grid surface and a second grid surface, respectively, a surface extending from the grid portion to each grid space and expanding to the concrete placing side, and a concrete non-casting surface on the back side thereof. It is provided with a plurality of flat plate portions having a surface extending to the concrete side as a first flat plate surface and a second flat plate surface, respectively, and the grid portion and each flat plate portion are provided with the first flat plate surface having the first flat plate surface. It is made of fiber reinforced concrete so as to be flush with the grid surface, the second flat plate surface recedes from the second grid surface, and the grid portion and each flat plate portion are integrated with each other. A rod-shaped or linear tensile resistance material is embedded in the grid portion along the material axis, and the tensile resistance material is placed in the second grid from a position where the center of the cross section corresponds to the second flat plate surface. It is positioned so that it is displaced to the side of the surface.

Further, in the precast member for an embedded formwork according to the present invention, the tensile resistance material is made of a chemical resistant material or a steel material coated with the chemical resistant material.

Further, in the precast member for an embedded formwork according to the present invention, the fiber reinforced concrete is made of a room temperature curing type ultra-high strength fiber reinforced concrete.

Further, as described in claim 4, the reinforced concrete deck according to the present invention uses the buried formwork precast member according to any one of claims 1 to 3 and the buried formwork precast member as a bottom slab. It is composed of a reinforced concrete layer in which concrete is cast on-site on the bottom slab.

Further, as described in claim 5, the method for designing the precast member for buried formwork according to the present invention is the method for designing the precast member for buried formwork according to any one of claims 1 to 3. When concrete is cast on-site on the concrete casting side using the buried formwork precast member as the buried formwork, the tensile strain generated in the flat plate portion due to the weight of the buried formwork precast member and the concrete is generated. The thickness of the flat plate portion, the grid spacing of the grid portion, or the cross-sectional coefficient of the grid portion is determined so as not to exceed the crack strain of the flat plate portion.

The precast member for an embedded formwork according to the present invention includes a grid portion forming a grid shape and a plurality of flat plate portions extending from the grid portion to each of the grid spaces, and includes a grid portion and a plurality of flat plate portions. Since these are made of fiber reinforced concrete so as to be integrated with each other, it is possible to reduce the thickness of the flat plate portion while ensuring sufficient strength, and also constitute these grid portions and a plurality of flat plate portions. On the concrete casting side, the first flat plate surface is flush with the first grid surface, and on the concrete non-casting side, the second flat plate surface recedes from the second grid surface, in other words. Since the grid portion and the plurality of flat plate portions are configured so that the second grid surface protrudes from the second flat plate surface, the grid portion receives the load of the concrete placed on the concrete placing side. It plays a role in increasing the overall bending rigidity.

Further, in the precast member for an embedded formwork according to the present invention, a rod-shaped or linear tensile resistance material is embedded in the grid portion along the material axis, and the tensile resistance material has a second cross-sectional center. It is positioned so as to be offset from the position corresponding to the flat plate surface to the side of the second grid surface.

In this way, the boundary position between the compression side and the tension side in the cross section, in other words, the neutral axis, is a flat plate without a grid portion with respect to the bending moment due to the load of the concrete and the weight of the precast member for the buried formwork. Compared to the case where it is composed of only parts, it shifts significantly to the concrete non-casting side, and even when it is provided with a non-reinforced grid part (grid part without tensile resistance material), it shifts to the concrete non-casting side. Therefore, by appropriately setting the thickness of the flat plate portion, the grid spacing of the grid portion, or the section modulus of the grid portion, tensile strain does not occur in the flat plate portion, or at least tensile strain occurs to the extent that cracks occur. Be prevented.

Therefore, it is possible to prevent the intrusion of chloride ions and carbon dioxide through cracks in the concrete, and it is possible to greatly improve the durability of the precast member for the buried formwork and the reinforced concrete structure using the precast member. ..

It is desirable that the precast member for buried formwork according to the present invention exerts the above-mentioned crack prevention effect when the concrete necessary for constructing the reinforced concrete structure to be applied is cast all at once, but the concrete is provided with a joint. The case of split casting is not excluded, and even in such a case, cracks occur in the conventional precast member for the buried formwork, or the precast member for the buried formwork must be thickened. There is no difference in the above-mentioned anti-cracking effect being exerted in the situation where the above-mentioned is not obtained.

The grid shape referred to in the present invention is not only a grid form in a narrow sense orthogonal to each other and each grid space is a square or a rectangle, but also an arbitrary multiple such as a triangle, a rhombus, a parallelogram, etc. It shall mean a form that intersects so as to form a square.

The grid portion is a component for shifting the neutral axis to the concrete non-casting side by the tensile resistance material embedded in the grid portion so as not to cause cracks in the flat plate portion, and simply stiffens the flat plate. The purpose and action of the beam are essentially different from those of the ribs and beams intended to transmit the load to the columns.

Here, the precast member for an embedded formwork according to the present invention has a reinforced concrete structure of any part such as a pillar, a beam, a wall, etc., as long as it is necessary to prevent cracking due to its own weight and the load of concrete placed on site. It can be applied, and the site and environment to which it is applied are arbitrary, but the application site is applied to the floor slab, that is, the precast member for the buried formwork and the precast member for the buried formwork are used as the bottom slab. A typical example is a reinforced concrete slab composed of a reinforced concrete layer in which concrete is cast on site.

In addition, as a typical application environment, the case where it is applied to a reinforced concrete structure constituting a port facility or an offshore structure is a typical example, and in such a typical example, chloride ions are prevented from entering through cracks and buried. It is possible to improve the durability of precast members for formwork and reinforced concrete structures constructed on-site using them as buried formwork.

In each of the above-mentioned inventions, any rod-shaped or linear tensile resistance material can be adopted, and the tensile resistance material is made of a chemical-resistant material or coated with a chemical-resistant material. If it is made of steel, even if chloride ions or carbon dioxide invade from cracks generated near the second grid surface, corrosion of the tensile resistance material due to the chloride ions or carbon dioxide can be prevented. .. The tensile resistance material made of a chemical resistant material includes stainless steel reinforcing bars, continuous fiber rods, etc., and the tensile resistance material made of a steel material coated with a chemical resistant material includes epoxy resin, nylon, etc. A coated reinforcing bar, a hot-dip galvanized reinforcing bar, a coated PC steel wire, etc., which are covered with a resin, are included. Further, the chemical resistant material includes a salt damage resistant material.

As the fiber reinforced concrete, any composition can be adopted, but it is preferable to use high-strength fiber-reinforced concrete and even ultra-high-strength fiber-reinforced concrete (UFC).

The ultra-high strength fiber reinforced concrete has a compressive strength of 150 N / mm ² or more and a tensile strength of 5 N / mm ² , or a compressive strength of 180 N / mm ² or more and a tensile strength of 8 N / mm ² or more. Is a typical example.

Here, if the above-mentioned fiber reinforced concrete is a room temperature curing type ultra-high-strength fiber reinforced concrete, it becomes possible to manufacture precast members for buried formwork on site, and the precast members for buried formwork can be manufactured at the factory. It is possible to save the trouble of transporting to the site.

In the method for designing a precast member for an embedded formwork according to the present invention, when the above-mentioned precast member for an embedded formwork according to the present invention is used as an embedded formwork and concrete is cast on the concrete casting side, the embedded mold is used. The thickness of the flat plate portion, the grid spacing of the grid portion, or the cross section of the grid portion so that the tensile strain generated in the flat plate portion due to the weight of the precast member for the frame and the concrete does not exceed the crack strain of the flat plate portion. Determine the coefficient.

By doing so, it is possible to prevent the occurrence of cracks in the flat plate portion due to tensile strain, and thus while reducing the thickness of the flat plate portion, the precast member for the embedded formwork, and further, the site as the embedded formwork. It is possible to improve the durability of the reinforced concrete structure to be constructed.

The amount of concrete to be cast used at the time of design is the amount required to cast the concrete required to construct the applicable reinforced concrete structure in a batch, and if it is a reinforced concrete slab, the site required to launch it to the floor surface. Although the total amount of concrete is a typical example, the case where concrete is divided and placed while providing joints is not excluded. In that case, the strength of the first concrete is waited for the second and subsequent times. When concrete is placed, the design may be performed with the amount of concrete for the first time.

It is a figure of the precast member for an embedded formwork which concerns on this embodiment, (a) is a plan view, (b) is a bottom view. Similarly, it is a diagram of a precast member for an embedded formwork, (a) is a cross-sectional view along the AA line, and (b) is a partially enlarged view thereof. Explanatory drawing which showed the operation of the precast member for an embedded formwork which concerns on this embodiment. Explanatory drawing about the design method of the precast member for an embedded formwork which concerns on this embodiment. It is a construction drawing which showed the procedure of constructing the reinforced concrete deck using the precast member for the buried formwork which concerns on this embodiment, (a) is the plan view before removing the deck to be repaired, (b). Is also a vertical cross-sectional view along the BB line. It is a construction drawing showing the construction procedure of the reinforced concrete deck, (a) is a plan view after removing the deck to be repaired, and (b) is a vertical cross-sectional view along the CC line. It is a construction drawing showing the construction procedure of the reinforced concrete deck, (a) is a plan view showing how the precast member for the buried formwork according to this embodiment is arranged, and (b) is the same line DD. Vertical cross-sectional view along. It is a construction drawing showing the construction procedure of the reinforced concrete deck, (a) is a plan view showing how the reinforcing bars are arranged above the precast member for the buried formwork, and (b) is also on the EE line. Vertical cross section along. It is a construction drawing showing the construction procedure of the reinforced concrete deck, (a) is a plan view showing how concrete is placed above the precast member for the buried formwork, and (b) is also the FF line. Vertical cross-sectional view along.

Hereinafter, a precast member for an embedded formwork, a design method thereof, and an embodiment of a reinforced concrete deck according to the present invention will be described with reference to the accompanying drawings.

1 and 2 are a plan view, a bottom view, an AA cross-sectional view, and a partially enlarged view of the cross-sectional view showing the precast member 1 for an embedded formwork according to the present embodiment.

The precast member 1 for an embedded formwork according to the present embodiment is manufactured as an embedded formwork used when constructing a reinforced concrete deck, and has a grid pattern as shown in FIGS. 1 and 2. A grid portion 2 forming a grid portion 2 and a plurality of flat plate portions 3 extending from the grid portion to each of the grid spaces are provided.

The grid portion 2 is configured so as to be orthogonal to each other and the planar shape of each lattice space is square, and the cross section (see FIG. 2B) has, for example, a height of 125 mm and a width of about 100 mm. It has a rectangular cross section and is configured so that the lattice spacing is about 800 mm in each of the two plane directions.

Each flat plate portion 3 has a square planar shape in accordance with the grid portion 2, and the peripheral edge of each flat plate portion 3 is integrally connected to the four side surfaces of the grid portion 2 surrounding the flat plate portion. It is arranged in each lattice space and has a thickness of, for example, about 25 mm.

As can be clearly seen in FIG. 2B, the grid portion 2 and each flat plate portion 3 serve as a first flat plate surface that extends to the concrete casting side (above the precast member 1 for the buried formwork in FIG. 2). The flat plate surface 12a is configured to be flush with the grid surface 11a as the first grid surface, which also extends to the concrete casting side, and on the back side thereof, the concrete non-casting side. The grid as the second grid surface where the flat plate surface 12b as the second flat plate surface, which is the surface extending to (below the precast member 1 for the buried formwork in FIG. 2), also extends to the concrete non-casting side. In other words, the grid surface 11b is configured to protrude from the flat plate surface 12b so as to recede from the surface 11b.

The grid portion 2 and each flat plate portion 3 are made of fiber reinforced concrete so that they are integrated with each other. In the present embodiment, the fiber reinforced concrete is made of a room temperature hardening type ultra-high strength fiber reinforced concrete ( UFC).

Here, the grid portion 2 is formed of a reinforcing bar 13 made of a rod-shaped or linear tensile resistance material, particularly an epoxy resin-coated reinforcing bar as a steel material coated with a chemical-resistant material so as to follow the material axis. And the reinforcing bar is positioned so that the center of the cross section is displaced from the position corresponding to the second flat plate surface 12b to the side of the second grid surface 11b.

Since the reinforcing bars 13 are embedded in the grid portion in two horizontal directions along the material axis of the grid portion 2, the overall planar arrangement form is a grid arrangement orthogonal to each other. As can be seen in FIG. 2 (b), the reinforcing bar diameter may be shifted to the height phrase by the dimension.

Since the reinforcing bar is not embedded in the flat plate portion 2, the flat plate portion 2 is made of unreinforced fiber reinforced concrete.

The precast member 1 for an embedded form according to the present embodiment includes a grid portion 2 forming a grid shape and a plurality of flat plate portions 3 extending from the grid portion to each of the grid spaces, but the grid portion 2 and the precast member 1 are provided. Since the plurality of flat plate portions 3 are made of ultra-high-strength fiber reinforced concrete (UFC) so as to be integrated with each other, it is possible to reduce the thickness of the flat plate portions while ensuring sufficient strength. The grid portion 2 and the plurality of flat plate portions 3 are configured such that the flat plate surface 12a is flush with the grid surface 11a on the concrete casting side and the grid surface 11b protrudes from the flat plate surface 12b on the concrete non-casting side. Therefore, the grid portion 2 plays a role of increasing the overall bending strength against the load of the concrete placed on the concrete placing side.

Further, in the precast member 1 for an embedded formwork according to the present embodiment, a reinforcing bar 13 is embedded in the grid portion 2 along the material axis, and the reinforcing bar is placed from a position where the center of the cross section corresponds to the flat plate surface 12b. Since the position is shifted to the side of the grid surface 11b, the thickness of the flat plate portion 3, the grid spacing of the grid portion 2, the section modulus of the grid portion 2, the cross-sectional area of the reinforcing bar 13, and the like are appropriately set. As a result, it is possible to prevent the flat plate portion 3 from generating tensile strain, or even if it does occur, its magnitude can be suppressed to the extent that cracks do not occur.

That is, when the weight of the fresh concrete cast in the field and the weight of the buried formwork act on the buried formwork to generate a bending moment, the boundary position between the compression side and the tension side in the cross section, in other words, the neutral axis. Is located in the center of the cross section of the flat plate as shown in FIG. 3A in the case of a buried formwork (conventional buried formwork) composed of only the flat plate portion, and tension is applied to the lower half of the flat plate. Distortion occurs. Therefore, even if ultra-high-strength fiber-reinforced concrete having a predetermined tensile strength is used, it is difficult to prevent the occurrence of cracks on the lower surface with the conventional embedded formwork.

Further, assuming an embedded formwork in which a grid portion in which reinforcing bars are not embedded is added to the flat plate portion, in the case of the buried formwork, the grid portion bears the tensile stress as shown in FIG. The neutral axis shifts downward compared to the case of (a), and the area of tensile strain generated in the flat plate portion decreases. It is still difficult to prevent cracks from occurring on the lower surface of the portion.

On the other hand, in the precast member 1 for an embedded formwork in the present embodiment, as shown in FIG. 3C, the grid portion 2 in which the reinforcing bar 13 is embedded sufficiently bears the tensile stress, so that the neutral axis is further lowered. In the vicinity of the grid portion 2 (periphery of the flat plate portion 3) of the flat plate portion 3, tensile strain does not occur.

Therefore, by appropriately setting the thickness of the flat plate portion 3, the grid spacing of the grid portion 2, the section modulus of the grid portion 2, the cross-sectional area of the reinforcing bar 13, and the like, the tensile strain ε is cracked at all the plane positions of the flat plate portion 3. The grid portion 2 and the flat plate portion 3 can be configured so as not to exceed the strain ε _c.

Therefore, in designing the precast member 1 for the buried formwork according to the present embodiment, when the precast member for the buried formwork is used as the buried formwork and concrete is cast on the concrete casting side, the weight of the concrete is applied. The thickness of the flat plate portion 3, the grid spacing of the grid portion 2, the cross-sectional coefficient of the grid portion 2, and the reinforcing bar 13 so that the tensile strain ε generated in the flat plate portion 3 due to its own weight _{does not exceed the crack strain ε c of the flat plate portion.} The cross-sectional area and the like may be determined.

More specifically, as shown in FIG. 4A, the larger the value of the plate thickness t of the flat plate portion 3, the smaller the tensile strain ε. Therefore, the grid spacing L of the grid portion 2 and the cross section of the grid portion 2 When the coefficient Z has already been determined, the plate thickness t of the flat plate portion 3 may be determined with the _{plate thickness t c at} which the tensile strain ε is equal to or less than _{the crack strain ε c as the lower limit.}

Since the flat plate portion 3 is a so-called covering portion of concrete cast on site above the flat plate portion 3, it is desirable that the plate thickness t be 20 mm or more as specified in the guideline for UFC.

Further, as shown in FIG. 4B, the smaller the value of the grid spacing L of the grid portion 2, the smaller the tensile strain ε, so that the plate thickness t of the flat plate portion 3 and the cross-sectional coefficient Z of the grid portion 2 have already been obtained. If it has been determined, the grid spacing L of the grid portion 2 may be determined with the grid spacing L _{c at which the tensile strain ε is equal to or less than the crack strain ε c as the upper limit.}

Further, as the geometrical moment of inertia Z of the grid portion 2 has a larger value as shown in FIG. 4 (c), the tensile strain ε becomes smaller, so that the plate thickness t of the flat plate portion 3 and the lattice spacing L of the grid portion 2 have already been set. If it has been determined, the section coefficient Z of the grid portion 2 may be determined with the section coefficient Z _{c at which the tensile strain ε is equal to or less than the crack strain ε c as the lower limit.}

As for the reinforcing bar 13 of the grid portion 2, a cover of 20 mm or more is secured as specified in the guideline for UFC.

Next, as a measure against the deterioration of the pier, which is a mooring facility, the procedure for repairing the pier 52 shown in FIG. 5 by using the precast member 1 for the buried formwork according to the present embodiment will be described below.

The pier 52 is composed of a pile 53 driven into the sea floor (not shown) in front of the land portion 54, a beam 55 bridged over the upper end of the pile, and a reinforced concrete deck 56 bridged over the beam. Of these, in order to repair the reinforced concrete deck 56 in the form of reconstruction, first, the reinforced concrete deck 56 is removed as shown in FIG.

At this time, of the beams 55, only the concrete is excised above the lower surface level of the reinforced concrete deck 56, and the reinforcing bars 61 are left in order to be integrated with the concrete placed on site in the subsequent process. And expose it.

Next, as shown in FIG. 7, each edge portion of the precast member 1 for the buried formwork according to the present embodiment is hung on the shoulder portion of the beam 55 so as to be bridged between the beams 55 and 55.

Next, as shown in FIG. 8, the lower end bars 81a and 81b are arranged orthogonally above the precast member 1 for the embedded formwork, and the upper end bars are arranged orthogonally in the same manner.

Next, as shown in FIG. 9, the precast member 1 for the buried formwork is used as a bottom slab, and concrete is placed above the bottom slab. The concrete does not have to be fiber reinforced concrete and may be ordinary concrete.

Finally, by curing the cast concrete and paving it as necessary, the precast member 1 for the buried formwork and the reinforced concrete layer 91 having a thickness of, for example, about 175 mm formed on the precast member 1 are formed. Complete the construction of the reinforced concrete floor slab 92.

Here, after the concrete is placed, the weight of the fresh concrete, which is a fluid, is the upper surface of the precast member 1 for the buried formwork composed of the grid surface 11a and the plurality of flat plate surfaces 12a until the strength of the concrete is developed. However, as described above, there is no possibility that the flat plate portion 3 will be cracked.

Further, in the vicinity of the grid surface 11b of the grid portion 2, as can be seen in FIG. 3C, tensile strain may occur, which may cause cracks, but the size thereof is extremely fine.

As described above, according to the precast member 1 for an embedded formwork according to the present embodiment, a reinforcing bar 13 is embedded in the grid portion 2 along the material axis, and the reinforcing bar is provided with a flat plate surface 12b at the center of the cross section. Since the position is shifted from the position corresponding to the grid surface 11b to the side of the grid surface 11b, tensile strain is not generated in the flat plate portion 3 or cracks occur in combination with the flexural rigidity improving effect of the grid portion 2. It is possible to prevent the occurrence of cracks by suppressing the tensile strain to a size that does not occur.

Therefore, it is not necessary to worry about a situation in which chloride ions invade through the flat plate portion 3 and the chloride ions corrode the reinforcing bars of the reinforced concrete layer 91 constructed on site, thus thinning the flat plate portion 3. While trying to do so, it is possible to significantly improve the durability of the precast member 1 for the buried formwork and, by extension, the reinforced concrete deck 92 using the precast member 1.

Further, according to the precast member 1 for the embedded formwork according to the present embodiment, since the reinforcing bar 13 is composed of the epoxy resin coated reinforcing bar, fine cracks are generated on the grid surface 11b of the grid portion 2, and the cracks are chloride. Even if the material ions invade, there is no possibility that the reinforcing bar 13 will corrode, and thus, in combination with the action of the flat plate portion 3, the reinforced concrete layer 91 constructed on site can be reliably and long-term protected from chloride ions. It will be possible.

In the present embodiment, an example in which the precast member 1 for the buried formwork is applied to the construction of the reinforced concrete deck 92 of the pier has been described, but the crack preventing action of the precast member for the buried formwork according to the present invention is the chloride ion. Since it has the effect of blocking not only the intrusion but also the invasion of carbon dioxide in the air and preventing the corrosion of reinforcing bars due to the neutralization of concrete, it can be widely applied to reinforced concrete structures other than port facilities and marine structures. It is possible, and the part is not limited to the floor slab, but can be applied to pillars and walls.

Further, in the present embodiment, the reinforcing bar 13 is composed of the epoxy resin coated reinforcing bar, but since the cracks generated on the grid surface 11b of the grid portion 2 are fine, it is necessary to substantially be concerned about the corrosion of the reinforcing bar due to the intrusion of chloride ions. If there is no such material, the tensile resistance material may be formed of a normal reinforcing bar that is not coated with a chemical resistant material instead of the reinforcing bar 13.

Further, in the present embodiment, the fiber reinforced concrete is a room temperature curing type ultra-high-strength fiber-reinforced concrete, but as long as the wall thickness can be reduced, the high-strength fiber-reinforced concrete is sufficient, and the precast member for the buried formwork. If there is no problem in transportation, it is not necessary to make it a room temperature curing type.

1 Precast member for buried formwork 2 Grid part 3 Flat plate part 11a Grid surface (first grid surface)
12a Flat plate surface (first flat plate surface)
11b grid surface (second grid surface)
12b flat plate surface (second flat plate surface)
13 Reinforcing bar 91 Reinforced concrete layer 92 Reinforced concrete floor slab

Claims (5)

A grid portion having a grid-like shape and a surface extending to the concrete placing side and a surface extending to the concrete non-casting side, which is the back side thereof, as a first grid surface and a second grid surface, respectively, and a grid portion from the grid portion thereof. A plurality of flat plate portions extending in each lattice space and having a surface extending to the concrete placing side and a surface extending to the concrete non-casting side on the back side thereof as a first flat plate surface and a second flat plate surface, respectively. The grid portion and each flat plate portion are provided so that the first flat plate surface is flush with the first grid surface and the second flat plate surface is retracted from the second grid surface. In addition, the grid portion and the flat plate portions are made of fiber reinforced concrete so as to be integrated with each other, and a rod-shaped or linear tensile resistance material is embedded in the grid portion along the material axis to obtain the tensile resistance. A precast member for an embedded formwork, characterized in that the material is positioned so that the center of the cross section is displaced from the position corresponding to the second flat plate surface to the side of the second grid surface. The precast member for an embedded formwork according to claim 1, wherein the tensile resistance material is made of a chemical resistant material or is made of a steel material coated with the chemical resistant material. The precast member for an embedded formwork according to claim 1 or 2, wherein the fiber reinforced concrete is a room temperature curing type ultra-high strength fiber reinforced concrete. It is composed of the precast member for an embedded form according to any one of claims 1 to 3 and a reinforced concrete layer in which concrete is cast on the bottom slab with the precast member for the buried form as a bottom slab. Reinforced concrete floor slab featuring. The method for designing a precast member for an embedded form according to any one of claims 1 to 3, wherein the precast member for the buried formwork is used as an embedded formwork and concrete is cast on the concrete casting side thereof. Then, the thickness of the flat plate portion and the grid spacing of the grid portion so that the tensile strain generated in the flat plate portion due to the weight of the precast member for the embedded formwork and the concrete does not exceed the crack strain of the flat plate portion. Alternatively, a method for designing a precast member for an embedded formwork, which comprises determining the cross-sectional coefficient of the grid portion.

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