How to build it

Abstract

To provide a method for determining the necessity of a crack suppression member capable of rationally suppressing the crack of a concrete structure by appropriately arranging the crack suppression member and a method for constructing the concrete structure.SOLUTION: A determination method according to one embodiment is the determination method for determining the necessity of a crack suppression member embedded in the concrete 8. A determination method comprises the steps of: placing concrete 8 in a concrete placing area A by placing optical fiber sensors 11 at multiple positions in the concrete placing area A; measuring distortion amounts at the plurality of positions by the optical fiber sensors 11 after placing the concrete 8; and determining the necessity of the crack suppression member from the magnitude of the difference between the distortion amounts at the plurality of positions.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a method for determining whether or not a crack suppression member is required when constructing a concrete structure, and a method for constructing a concrete structure. [Background technology]

[0002] Methods for predicting and estimating cracks in concrete in concrete structures are known. For example, Patent Document 1 describes a method for estimating the maximum crack width of a wall-shaped reinforced concrete structure. The reinforced concrete structure is a plurality of wall-like bodies constructed on a footing. Joint materials are arranged between the plurality of wall-like bodies. For this type of structure, the maximum crack is estimated.

[0003] In this estimation method, first, measured crack data is collected from multiple existing structures that are subject to external restraints. Next, from the measured crack data, an estimated unit crack width, which indicates the total crack width per unit length of the structure's wall, and an estimated unit crack number, which indicates the number of cracks per unit length of the structure's wall, are calculated. The maximum crack width of the structure is estimated from the calculated estimated unit crack width and estimated unit crack number.

[0004] Patent Document 2 describes a method for predicting maximum crack width. The target structure of this prediction method is a reinforced concrete structure, and a crack dispersion material is placed between the reinforcing bar and the surface of the concrete. In this prediction method, the maximum crack width is calculated using the average reinforcing bar strain, distribution coefficient, net cover of the crack dispersion material, gap of the crack dispersion material, net cover of the reinforcing bar, and gap of the reinforcing bar as parameters. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-19472 A [Patent Document 2] JP 2015-117954 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in the method for predicting and estimating cracks in concrete, the maximum crack width of a structure is estimated from the measured data of the cracks. However, although this method estimates the maximum crack width, there are cases where specific means and methods for suppressing the cracks are not required.

[0007] In the above-mentioned method for predicting the maximum crack width, the maximum crack width is calculated using a crack dispersion material. However, although Patent Document 2 describes the placement of crack suppression members such as crack dispersion materials, it is unclear where in the concrete structure the crack suppression members should be placed, and whether or not the crack suppression members are necessary. Therefore, there is a demand for the placement of crack suppression members appropriately to rationally suppress cracks in concrete structures.

[0008] The present disclosure aims to provide a method for determining the need for crack-suppression members that can appropriately position the crack-suppression members to rationally suppress cracks in concrete structures, and a method for constructing a concrete structure. [Means for solving the problem]

[0009] The method for determining whether or not a crack suppression member is necessary according to the present disclosure is a method for determining whether or not a crack suppression member embedded inside concrete is necessary, and includes the steps of placing optical fiber sensors at multiple positions in the concrete pouring area and pouring concrete into the concrete pouring area, measuring the amount of strain at the multiple positions using the optical fiber sensors after the concrete has been poured, and determining whether or not a crack suppression member is necessary based on the magnitude of the difference in the amount of strain at the multiple positions.

[0010] In this determination method, optical fiber sensors are placed at a plurality of positions in a concrete pouring area, and concrete is poured at the plurality of positions. The optical fiber sensors measure the time that has elapsed since concrete was poured (more specifically, the time that has elapsed since concrete was poured) and the amount of strain at the plurality of positions. In this way, the optical fiber sensors measure the amount of strain at the plurality of positions, so that the amount of strain at the plurality of positions can be measured with high accuracy along the length direction of the optical fiber. The necessity of a crack suppression member that suppresses cracks in the concrete is determined from the magnitude of the difference in the amount of strain at the plurality of positions measured by the optical fiber sensor. Therefore, since the necessity of the crack suppression member is determined from the difference in the amount of strain at the plurality of positions, the crack suppression member can be appropriately arranged. Therefore, cracks in the concrete structure can be reasonably suppressed by appropriately arranging the crack suppression member.

[0011] The concrete may have a portion that is erected on the base slab and extends vertically, and the multiple positions may include a center portion in the thickness direction of the portion and a surface layer portion in the thickness direction of the portion. In this case, optical fiber sensors are disposed in the center portion in the thickness direction of the portion that extends vertically and in the surface layer portion in the thickness direction of the portion, respectively, and the optical fiber sensors measure the strain in the center portion and the surface layer portion. Therefore, the need for a crack suppression member can be determined from the difference in strain between the center portion and the surface layer portion.

[0012] This determination method may include a step of measuring temperatures at a plurality of positions with an optical fiber sensor after pouring the concrete, and a step of controlling the temperature of the concrete in accordance with the measured temperatures. In this case, the temperature of the concrete can be controlled using the temperature measurement results by the optical fiber sensor, so that the occurrence of cracks can be reduced by temperature control.

[0013] A method for constructing a concrete structure according to one aspect of the present disclosure is a method for constructing a concrete structure by pouring concrete sequentially into a first section and a second section to construct a structure, the method comprising the steps of: placing optical fiber sensors at multiple positions in the first section and pouring the first concrete; measuring the amount of strain at the multiple positions using the optical fiber sensor after pouring the first concrete; determining whether or not a crack-suppression member is needed based on the magnitude of the difference in the amount of strain at the multiple positions; and if it is determined that a crack-suppression member is needed in the step of determining whether or not a crack-suppression member is needed, placing a crack-suppression member in the second section and pouring the second concrete.

[0014] In this construction method, an optical fiber sensor is placed in a first section of multiple sections in which concrete is poured, and the first concrete is poured. The optical fiber sensor then measures the amount of strain at multiple positions in the first section, and the need for placing a crack-suppressing member is determined from the magnitude of the difference between the multiple amounts of strain. Therefore, it is possible to rationally determine whether or not a crack-suppressing member is needed in the first section. Furthermore, if it is determined that a crack-suppressing member is needed in the first section, a crack-suppressing member is placed in the second section, and the second concrete is poured. Therefore, in the second section, the crack-suppressing member can be appropriately placed to rationally suppress cracks in the structure.

[0015] A method for constructing a concrete structure according to another aspect of the present disclosure is a method for constructing a concrete structure by pouring concrete sequentially into a first section and a second section to construct a structure, the method comprising the steps of: placing optical fiber sensors at multiple positions in the first section and pouring the first concrete; measuring the amount of strain at the multiple positions using the optical fiber sensor after pouring the first concrete; placing a crack-suppression member inside the first concrete in advance; determining the effectiveness of the crack-suppression member from the magnitude of the difference in the amount of strain at the multiple positions; and if it is determined in the step of determining the effect of the crack-suppression member that it is necessary to correct the position of the crack-suppression member, placing the crack-suppression member at the corrected position in the second section and pouring the second concrete.

[0016] In this construction method, an optical fiber sensor is placed in the first section and the first concrete is poured, and a crack-suppressing member is placed inside the first concrete in advance. The optical fiber sensor measures the amount of strain at multiple positions in the first section as time elapses after the concrete is poured, and the effectiveness of the crack-suppressing member is determined from the magnitude of the difference between the multiple amounts of strain. Then, if it is determined that the position of the crack-suppressing member needs to be corrected as a result of the determination of the effectiveness of the crack-suppressing member, the crack-suppressing member is placed in the corrected position in the second section and the second concrete is poured. Therefore, by placing the crack-suppressing member in the corrected position, the crack-suppressing member can be placed in a more effective position, thereby rationally suppressing cracks. Effect of the Invention

[0017] According to the present disclosure, cracks in concrete structures can be rationally suppressed by appropriately arranging crack-suppressing members. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1A is a side view showing a concrete structure as an example to which a determination method and a construction method according to an embodiment are applied, FIG. 1B is a perspective view showing a part of the concrete structure of FIG. 1A, and FIG. 1C is a schematic diagram showing a cross section of the concrete structure. [Diagram 2] 1 is a flowchart illustrating steps of a determination method and a construction method according to an embodiment. [Diagram 3] 1A is a diagram for explaining a process of placing an optical fiber sensor and pouring concrete, and FIG. 1B is a diagram for illustrating a cross section of concrete for explaining the placement of the optical fiber sensor. [Figure 4] 11A, 11B, 11C, and 11D are graphs showing examples of the measurement results of the amount of strain measured by the optical fiber sensor. [Diagram 5] 13 is a graph showing the results of the difference in the amount of distortion at multiple positions for each elapsed time after pouring concrete, obtained in an embodiment. [Figure 6] (a) and (c) are cross-sectional views showing the arrangement of reinforcing bars or crack suppression members in a concrete structure, and (b) and (d) are diagrams showing the results of a simulation of cracks in a concrete structure in which reinforcing bars are arranged as in (a) or (c). [Figure 7] (a) and (c) are cross-sectional views showing the arrangement of reinforcing bars and crack suppression members in a concrete structure, and (b) and (d) are diagrams showing the results of a simulation of cracks in a concrete structure in which reinforcing bars and crack suppression members are arranged as in (a) or (c). [Figure 8] 10 is a flowchart showing steps of a method for constructing a concrete structure according to a second embodiment. [Figure 9] FIG. 1 is a diagram showing an embodiment in which an optical fiber sensor is arranged to control the temperature of poured concrete. [Figure 10] 1 is a flowchart showing an example of steps in a method for controlling the temperature of concrete. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the determination method and construction method according to the present disclosure will be described with reference to the drawings. In the description of the drawings, the same or corresponding elements are given the same reference numerals, and duplicated descriptions are omitted as appropriate. In addition, the drawings may be partially simplified or exaggerated for ease of understanding, and the dimensional ratios and the like are not limited to those shown in the drawings.

[0020] (First embodiment) FIG. 1(a) shows a concrete structure 1 as an example to which the determination method and construction method according to the first embodiment are applied. FIG. 1(b) is a perspective view showing a part of the concrete structure 1. As shown in FIG. 1(a) and FIG. 1(b), for example, the concrete structure 1 is a box culvert. The concrete structure 1 has a base slab 2 extending in a first direction D1 and a second direction D2, and a part 3 erected in a third direction D3 at a central part of the base slab 2 in the first direction D1. For example, the first direction D1 and the second direction D2 are horizontal directions, and the third direction D3 is a vertical direction.

[0021] For example, the concrete structure 1 has an inclined surface 4 that extends obliquely from the base slab 2 toward the portion 3 at a boundary portion B between the base slab 2 and the portion 3. The concrete structure 1 has a pair of inclined surfaces 4 aligned in a first direction D1. Each inclined surface 4 extends obliquely with respect to both the first direction D1 and the third direction D3 between an upper surface 2b of the base slab 2 and a side surface 3b of the portion 3.

[0022] The concrete structure 1 has, for example, a plurality of pouring joints 5. The pouring joints 5 are provided at the center of the portion 3 in the third direction D3 and at the boundary portion B (the upper portion of the inclined surface 4). The concrete structure 1 is constructed by pouring the base slab 2, the lower portion of the portion 3 (the portion between a pair of upper and lower pouring joints 5), and the upper portion of the portion 3 in this order. The concrete structure 1 also has a first section A1 and a second section A2 which are concrete pouring areas A aligned along the second direction D2. A pouring joint 5 is also provided between the first section A1 and the second section A2, and concrete is poured, for example, in the order of the first section A1 and the second section A2.

[0023] Fig. 1(c) is a cross-sectional view of the concrete structure 1 cut along a plane extending in the first direction D1 and the third direction D3. As shown in Fig. 1(c), the concrete structure 1 comprises a plurality of main reinforcements 6, a plurality of distribution reinforcements 7, and concrete 8. The main reinforcements 6 and the distribution reinforcements 7 are embedded in the concrete 8, with the main reinforcements 6 extending in the third direction D3 and the distribution reinforcements 7 extending in the second direction D2.

[0024] The concrete structure 1 further includes a crack suppression member 10. The crack suppression member 10 is provided to suppress cracks in the concrete 8. Cracks may occur in the concrete 8, for example, when heat generated by the hydration reaction of the concrete is cooled by the outside air, but in order to suppress corrosion of the main reinforcement bars 6 and the distribution bars 7, it is necessary to suppress the width of the cracks in the concrete 8.

[0025] The crack-suppressing member 10 resists cracks in the concrete 8, thereby suppressing the expansion of crack width in the concrete 8. The crack-suppressing member 10 is, for example, a crack-suppressing rebar. As an example, the crack-suppressing member 10 includes a plurality of first rebars 12 extending along the third direction D3 and a plurality of second rebars 13 extending along the second direction D2.

[0026] The crack-suppressing member 10 is disposed, for example, in a central portion 8c in the first direction D1 at the boundary portion B between the base slab 2 and the portion 3. This central portion 8c (center of the member) is considered to be a location where stress is likely to be predominant compared to the surface layer portion 8b (cover) of the concrete 8, so disposing the crack-suppressing member 10 in the central portion 8c can effectively suppress cracks in the concrete 8.

[0027] However, it is not always sufficient to arrange the crack-suppressing members 10 as described above, and how to arrange the crack-suppressing members 10 may differ depending on the type of concrete structure 1, etc. Therefore, it has been unclear where and to what extent the crack-suppressing members 10 should be arranged to be effective. In the method for determining whether or not the crack-suppressing members 10 are necessary and the method for constructing the concrete structure 1 according to the present embodiment, it is possible to determine whether or not the crack-suppressing members 10 are necessary using an optical fiber sensor 11 (see FIG. 3(a)) that measures the amount of strain in the concrete 8, and to arrange the crack-suppressing members 10 rationally and economically to suppress cracks in the concrete 8.

[0028] A method for constructing a concrete structure 1 and a method for determining whether or not a crack suppression member 10 is required according to this embodiment will be described with reference to Fig. 2 and Fig. 3(a). Fig. 2 is a flowchart showing an example of steps of the method for constructing a concrete structure 1. Fig. 3(a) is a schematic diagram showing an example of the arrangement of a first section A1 and a second section A2 of the concrete structure 1 and an optical fiber sensor 11. In this embodiment, the need for a crack suppression member 10 is determined while the concrete structure 1 is being constructed.

[0029] 2 and 3(a), first, the optical fiber sensor 11 is placed at each of a plurality of positions in the first section A1 (step of placing the optical fiber sensor, step S1). In Fig. 3(a), the optical fiber sensor 11 is shown diagrammatically by a solid line, and a measuring instrument is placed at the end of the optical fiber sensor 11. This measuring instrument measures the strain of the cast concrete 8 by, for example, Rayleigh measurement using the optical fiber sensor 11.

[0030] However, this measuring instrument may use the optical fiber sensor 11 to measure the strain by Brillouin measurement. When the measuring instrument inputs measurement light to the optical fiber sensor 11, backscattered light is generated in the optical fiber sensor 11. The spectrum (intensity per frequency) of this backscattered light changes depending on the strain. The intensity of the backscattered light is smaller than the intensity of the measurement light. In Rayleigh measurement, the strain generated in the optical fiber sensor 11 is detected by measuring the change in the spectrum of the backscattered light. The Rayleigh measurement using the backscattered light has the advantages of being highly accurate and resistant to light loss. The optical fiber sensor 11 can detect the strain of the concrete 8 with an accuracy of, for example, 1 μm.

[0031] Fig. 3(b) is an enlarged view of an example of the arrangement of the optical fiber sensors 11. As shown in Fig. 3(a) and Fig. 3(b), a plurality of optical fiber sensors 11 are arranged above and below the joint 5 on the upper side of the portion 3. Above and below the joint 5 of the portion 3, the optical fiber sensors 11 are arranged in a central portion 8c in the first direction D1 (thickness direction) of the portion 3, a surface layer portion 8b in the first direction D1 of the portion 3, and a spaced portion 8d provided at a position spaced vertically upward from the central portion 8c.

[0032] The optical fiber sensors 11 are arranged to extend in the second direction D2 in the surface layer 8b, the central portion 8c, and the spaced portion 8d, respectively. In this embodiment, an optical fiber sensor 11 is further arranged between the surface layer 8b and the central portion 8c. As a result, the three optical fiber sensors 11 are arranged in line along the first direction D1 near the joint 5 (above the joint 5), so that the strain of the concrete 8 at the joint 5 can be detected with higher accuracy. An example of the arrangement of the optical fiber sensors 11 has been described above. However, the arrangement and number of the optical fiber sensors 11 are not limited to the examples in Figs. 3(a) and 3(b) and can be changed as appropriate.

[0033] After the optical fiber sensor 11 is placed in the first section A1 as described above, concrete 8 is poured in the first section A1 (first concrete pouring process, step S2). At this time, the concrete 8 is poured into the base slab 2, and then, after a predetermined time has elapsed, concrete 8 is poured into the lower part of the portion 3 and concrete 8 is poured into the upper part of the portion 3, in that order. Note that since the concrete of the base slab 2 is poured after the concrete of the portion 3 has hardened, strain and a bias in strain are generated inside the concrete of the portion 3 that is restrained by the base slab 2. The base slab 2 does not necessarily have to be a concrete structure, and may be bedrock or ground.

[0034] After the concrete 8 has been poured into the first section A1, the amount of strain of the concrete 8 in the first section A1 is measured with the passage of time after pouring by the multiple optical fiber sensors 11 (a step of measuring the amount of strain). At this time, for example, the amount of strain of the surface layer 8b of the concrete 8 and the amount of strain of the central portion 8c of the concrete 8 are measured as the amount of strain at multiple positions.

[0035] Fig. 4(a) shows data on the amount of strain in the surface layer 8b and the central portion 8c one day after the concrete 8 is poured, Fig. 4(b) shows data on the amount of strain in the surface layer 8b and the central portion 8c one day after the concrete 8 is poured, Fig. 4(c) shows data on the amount of strain in the surface layer 8b and the central portion 8c five days ...d) shows data on the amount of strain measured by the optical fiber sensor 11. In each of the graphs in Fig. 4(a) to Fig. 4(d), the vertical axis shows strain (unit: μ), and the horizontal axis shows distance (unit: m) from the end of the concrete 8 in the second direction D2.

[0036] As shown in Figures 4(a) to 4(d), one day after the concrete 8 was poured, the difference between the amount of strain in the surface layer 8b and the amount of strain in the central portion 8c was small. In contrast, five days after the concrete 8 was poured, the difference between these amounts of strain became larger, and the amount of strain (absolute value) in the central portion 8c became larger than the amount of strain in the surface layer 8b. This shows that the concrete 8 was strained earlier in the central portion 8c than in the surface layer 8b.

[0037] The difference between the amount of strain in the central portion 8c and the amount of strain in the surface layer portion 8b became larger 7 days after the concrete 8 was poured. However, the difference between the amount of strain in the central portion 8c and the amount of strain in the surface layer portion 8b became smaller 28 days after the concrete 8 was poured.

[0038] The peaks in Fig. 4(a) to Fig. 4(d) indicate the locations where cracks have occurred. The positions of the peaks in Fig. 4(a) to Fig. 4(d) coincide with the locations where cracks have occurred. As shown in Fig. 4(b) to Fig. 4(d), it can be seen that cracks occurred first in the central portion 8c, and cracks occurred later in the surface layer portion 8b than in the central portion 8c. Specifically, five days after the concrete 8 was poured, cracks occurred in the central portion 8c, but no cracks occurred in the surface layer portion 8b. In contrast, seven days after the concrete 8 was poured, cracks occurred in both the central portion 8c and the surface layer portion 8b. This shows that cracks progress from the central portion 8c to the surface layer portion 8b. The cracks occur in locations where the amount of strain is large, where the absolute value of the amount of strain is large, or where the amount of change in the amount of strain is large.

[0039] Fig. 5 is a graph showing the relationship between the number of days after pouring of the concrete 8 and the amount of strain at the location of the displacement of the concrete 8 of 15.45 m in Fig. 4(a) to Fig. 4(d). As shown in Fig. 5, four days after pouring the concrete 8, cracks appear in the central portion 8c, and the amount of strain in the central portion 8c increases.

[0040] On the other hand, in the surface layer 8b, there was almost no change in the amount of strain until six days after the concrete 8 was poured, and after six days, cracks appeared and the amount of strain increased. As described above, the increase in the amount of strain and cracks appeared first in the central portion 8c of the concrete 8, and the increase in the amount of strain and cracks appeared later (two days later) in the surface layer 8b than in the central portion 8c.

[0041] As described above, the amount of distortion in the surface layer 8b and the amount of distortion in the central portion 8c are measured, and the necessity of the crack suppression member 10 is judged by measuring these amounts (step S4 for judging the necessity of the crack suppression member). For example, as described above, the distortion in the surface layer 8b is compared with the distortion in the central portion 8c over time, and if the difference between the distortion in the surface layer 8b and the distortion in the central portion 8c (hereinafter simply referred to as the "difference") is equal to or greater than a predetermined threshold, it is judged that the crack suppression member 10 needs to be added between the central portion 8c and the surface layer 8b (more specifically, the central portion 8c or a position closer to the central portion 8c) or that the position of the crack suppression member 10 needs to be corrected (moved). On the other hand, when the difference between the distortion in the surface layer 8b and the distortion in the central portion 8c is compared and is smaller than a predetermined threshold, it is judged that the addition of the crack suppression member 10 is not necessary.

[0042] In step S4 (a process for determining whether or not a crack suppression member is required), in this embodiment, the distortion of the surface layer 8b is compared with the distortion of the central portion 8c, and the distortion of the central portion 8c increases, followed by a delay in the distortion of the surface layer 8b. At the time when the distortion of the central portion 8c increases, the amount of distortion of the surface layer 8b is small, resulting in a difference. In this embodiment, if the difference is equal to or greater than a predetermined threshold value, it is determined that the addition of the crack suppression member 10 or the correction (movement) of its position is required. In other cases, if the distortion of the surface layer 8b increases and, at the same time or with a delay, the distortion of the central portion 8c increases, it is determined that the addition of the crack suppression member 10 or the correction (movement) of its position is required to the surface layer 8b or a position closer to the surface layer 8b.

[0043] If it is determined in step S4 that the crack-suppressing member 10 is not required, the concrete 8 is poured (step S6), and then the series of steps is completed. On the other hand, if it is determined that the crack-suppressing member 10 is required to be added or its position is corrected, the crack-suppressing member 10 is added or its position is corrected in a predetermined position of the second section A2 (for example, a position between the surface layer 8b and the central portion 8c) (step of placing the crack-suppressing member, step S5). Then, the concrete 8 is poured in the second section A2 (step of pouring the second concrete, step S6), and the series of steps is completed.

[0044] Next, the effects obtained from the method for assessing the crack suppression member 10 and the method for constructing the concrete structure 1 according to this embodiment will be described. In this assessment method, optical fiber sensors 11 are placed at multiple positions in concrete pouring zone A, and concrete 8 is poured in concrete pouring zone A. The optical fiber sensor 11 measures the amount of strain at the multiple positions after the concrete 8 is poured. By measuring the amount of strain at the multiple positions in this way with the optical fiber sensor 11, the amount of strain at the multiple positions can be measured with high accuracy along the length direction of the optical fiber.

[0045] The necessity of the crack-suppressing member 10 for suppressing cracks in the concrete 8 is determined from the magnitude of the difference in the amount of strain at a plurality of positions measured by the optical fiber sensor 11. Therefore, since the necessity of the crack-suppressing member 10 is determined from the difference in the amount of strain at a plurality of positions, the crack-suppressing member 10 can be appropriately positioned. Therefore, by appropriately positioning the crack-suppressing member 10, cracks in the concrete structure 1 can be reasonably suppressed.

[0046] In this embodiment, the concrete 8 has a base slab 2 extending horizontally and a portion 3 extending vertically from the base slab 2. The above-mentioned multiple positions include a central portion 8c in the thickness direction of the portion 3 and a surface layer portion 8b in the thickness direction of the portion 3. Thus, optical fiber sensors 11 are disposed in the central portion 8c in the thickness direction of the portion 3 and the surface layer portion 8b in the thickness direction of the portion 3, respectively, and the optical fiber sensors 11 measure the strain of the central portion 8c and the surface layer portion 8b. Therefore, the need for a crack suppression member 10 can be determined from the difference between the strain of the central portion 8c and the strain of the surface layer portion 8b.

[0047] In this embodiment, the central portion 8c and the surface portion 8b are provided at the boundary portion B between the base slab 2 and the portion 3, and the above-mentioned multiple positions further include a spaced portion 8d provided at a position spaced apart in the vertical direction from the central portion 8c. Thus, the optical fiber sensor 11 is disposed at the spaced portion 8d spaced apart in the vertical direction from the central portion 8c. The optical fiber sensor 11 disposed at the spaced portion 8d can predict the progression of cracks in the concrete 8. In addition, by checking the progression of cracks from the central portion 8c to the spaced portion 8d, the height at which the crack suppression member 10 is required can be determined.

[0048] In the method for constructing the concrete structure 1 according to the present embodiment, the optical fiber sensor 11 is placed in a first section A1 of the multiple sections in which the concrete 8 is poured, and the concrete 8 is poured. The optical fiber sensor 11 then measures the amount of strain at multiple positions in the first section A1, and the necessity of placing the crack suppression member 10 is determined based on the magnitude of the difference between the multiple amounts of strain. Therefore, the necessity of the crack suppression member 10 in the first section A1 can be reasonably determined. Furthermore, if it is determined that the crack suppression member 10 is necessary in the first section A1, the crack suppression member 10 is placed in the second section A2, and the concrete 8 is poured. Therefore, in the second section A2, the crack suppression member 10 can be appropriately placed to reasonably suppress cracks in the structure.

[0049] Next, the results of a simulation of cracks in concrete 8 when the crack suppression member 10 is arranged and when the crack suppression member 10 is not arranged will be described with reference to Figs. 6(a) to 6(d) and Figs. 7(a) to 7(d). Fig. 6(a) shows concrete without the crack suppression member 10 arranged, Fig. 6(b) shows the simulation result of Fig. 6(a), Fig. 6(c) shows concrete with multiple crack suppression members 10 arranged in the surface layer 8b (between a pair of reinforcing bars 7), and Fig. 6(d) shows the simulation result of Fig. 6(c). Fig. 7(a) shows concrete with multiple crack suppression members 10 arranged between the surface layer 8b and the central portion 8c, Fig. 7(b) shows the simulation result of Fig. 7(a), Fig. 7(c) shows concrete with multiple crack suppression members 10 arranged in the central portion 8c, and Fig. 7(d) shows the simulation result of Fig. 7(c). In each simulation result, cracks are indicated by thick solid lines.

[0050] As shown in Figures 6(a) to 6(d) and Figures 7(a) to 7(d), it can be seen that cracks are more effectively suppressed when the crack-suppression member 10 is placed (Figures 6(d), 7(b) and 7(d)) ​​compared to when the crack-suppression member 10 is not placed (Figure 6(b)).

[0051] Furthermore, it was found that cracks can be further suppressed when multiple crack-suppressing members 10 are arranged between the surface layer 8b and the central portion 8c (Fig. 7(b)) than when multiple crack-suppressing members 10 are arranged on the surface layer 8b (Fig. 6(d)). On the other hand, in this simulation, it was found that when multiple crack-suppressing members 10 are arranged on the central portion 8c (Fig. 7(d)), more cracks occur than when multiple crack-suppressing members 10 are arranged between the surface layer 8b and the central portion 8c (Fig. 7(b)).

[0052] From the above, it has been found that when the concrete 8 has a certain thickness (when the length in the first direction D1 is relatively long), placing the crack-suppressing member 10 between the central portion 8c and the surface layer portion 8b is more effective at suppressing cracks than placing the crack-suppressing member 10 in the central portion 8c. In this way, by measuring the amount of strain in the surface layer portion 8b and the central portion 8c, etc. of the concrete 8 in advance with the optical fiber sensor 11 and calculating the difference between the amounts, it is possible to know where to place the crack-suppressing member 10.

[0053] Second embodiment Next, a method for constructing a concrete structure according to the second embodiment will be described with reference to Fig. 8. Fig. 8 is a flow chart showing steps of the method for constructing a concrete structure 1 according to the second embodiment. In the following, the same reference numerals are used to designate the same contents as those in the first embodiment, and the description thereof will be omitted as appropriate.

[0054] First, optical fiber sensors 11 are placed at multiple positions in the first section A1 (for example, the surface layer 8b and the central section 8c) (step of placing optical fiber sensors, step S21), and crack suppression members 10 are placed in advance in the first section A1 (step of placing crack suppression members in advance). In the following, an example in which the crack suppression members 10 are placed in advance in the central section 8c of the concrete 8 as shown in Fig. 7(c) will be described.

[0055] After arranging the optical fiber sensor 11 and the crack suppression member 10 as described above, concrete 8 is poured in the first section A1 (step of pouring first concrete, step S23), and similarly to the above, the optical fiber sensor 11 measures the amount of strain of the concrete 8 (step of measuring the amount of strain, step S24). Then, from the magnitude of the difference in the amounts of strain at a plurality of positions (the difference between the amount of strain at the surface layer 8b and the amount of strain at the central portion 8c), the effect of the crack suppression member 10 is judged (step S25), and it is determined whether or not the position of the crack suppression member 10 needs to be adjusted (step S26).

[0056] For example, if the crack-suppressing member 10 is placed in the central portion 8c, as shown in Fig. 7(d), cracks are not suppressed very much, so it is determined that correction is necessary in step S26 (YES in step S26). In this case, the crack-suppressing member 10 is placed in the corrected position (for example, a position between the surface layer 8b and the central portion 8c) in the second section A2 (step S27), and concrete 8 is poured (step of pouring second concrete, step S29).

[0057] On the other hand, if it is determined in step S26 that correction is not necessary (NO in step S26), for example, in the second section A2, crack suppression members 10 are placed in the same positions as in the first section A1 (step S28), and concrete 8 is poured (step S29). After going through the above steps, construction of the concrete structure 1 is completed.

[0058] As described above, in the method for constructing the concrete structure 1 according to the second embodiment, the optical fiber sensor 11 is placed in the first section A1, and before the concrete 8 is poured, the crack suppression member 10 is placed inside the concrete 8 in advance. The optical fiber sensor 11 measures the amount of strain at multiple positions in the first section A1 after the concrete 8 is poured, and the effectiveness of the crack suppression member 10 is determined from the magnitude of the difference between the multiple amounts of strain.

[0059] Then, if it is determined as a result of judging the effectiveness of the crack-suppressing member 10 that it is necessary to correct the position of the crack-suppressing member 10, the crack-suppressing member 10 is placed at the corrected position in the second section A2 and the concrete 8 is poured. Therefore, by placing the crack-suppressing member 10 at the corrected position, the crack-suppressing member 10 can be placed at a more effective position, so that cracks can be rationally suppressed.

[0060] Third embodiment Next, a construction method according to a third embodiment will be described with reference to Fig. 9 and Fig. 10. Fig. 9 is a diagram that illustrates monitoring of a concrete structure 1 according to the third embodiment. Fig. 10 is a flow chart that illustrates steps of the construction method for a concrete structure 1 according to the third embodiment. As shown in Figs. 9 and 10, in the construction method according to the third embodiment, the temperature of the concrete structure 1 is controlled.

[0061] For example, a monitoring room R is provided in a remote location away from the concrete structure 1. The monitoring room R has a measurement data acquisition unit R1 that acquires measurement data from the optical fiber sensor 11, and a temperature adjustment unit R2 that adjusts the temperature of the concrete 8. In the third embodiment, a plurality of pipes P are buried in the concrete structure 1, and the water temperature is indicated by the temperature adjustment unit R2 to a device that adjusts the water temperature, and cold water or hot water is supplied from the device to the pipes P. The temperature of the concrete 8 is adjusted by supplying cold water or hot water to the pipes P.

[0062] Next, a method for constructing the concrete structure 1 will be described. First, the optical fiber sensor 11 is placed (a step of placing the optical fiber sensor, step S11). At this time, for example, a plurality of pipes P are placed together with the optical fiber sensor 11. Then, concrete 8 is poured (a step of pouring concrete, step S12).

[0063] Next, the temperature of the concrete 8 is measured by the optical fiber sensor 11 (step of measuring the temperature of concrete, step S13). At this time, for example, the measurement data acquisition unit R1 inputs measurement light to the optical fiber sensor 11, and backscattered light generated from the optical fiber sensor 11 by the input of the measurement light is input to the measurement data acquisition unit R1.

[0064] The measurement data acquisition unit R1 measures the change in the spectrum of the input backscattered light to measure the temperature of the concrete around the optical fiber sensor 11. The measurement data acquisition unit R1 may measure the strain as well as the temperature of the concrete. The measured temperature (and strain) of the concrete is stored in, for example, a computer in the monitoring room R.

[0065] Then, based on the measured concrete temperature, the temperature adjustment unit R2 adjusts the temperature of the concrete 8 (concrete temperature control process, step S14). Specifically, the temperature adjustment unit R2 indicates the water temperature to a device for adjusting the water temperature, which supplies cold water or hot water to the pipe P, and the optical fiber sensor 11 measures the temperature of the concrete after supply. The supply of cold water or hot water and measurement by the optical fiber sensor 11 are repeated to control the temperature of the concrete structure 1. A series of processes are completed through the above steps.

[0066] As described above, the construction method according to the third embodiment includes a step of measuring temperatures at a plurality of positions using the optical fiber sensor 11 after pouring the concrete, and a step of controlling the temperature of the concrete 8 in accordance with the measured temperatures. Therefore, the temperature of the concrete can be controlled using the results of temperature measurement by the optical fiber sensor 11, and thus it is possible to make cracks less likely to occur by controlling the temperature.

[0067] Various embodiments of the method for constructing a concrete structure and the method for determining the necessity of a crack suppression member according to the present disclosure have been described above. However, the construction method and the determination method according to the present disclosure are not limited to the various embodiments described above, and can be modified as appropriate within the scope of the gist of the claims. In other words, the content and order of the steps of the construction method and the determination method are not limited to the embodiments described above, and can be modified as appropriate. The construction method and the determination method according to the present disclosure may be a combination of two or more of the first embodiment, the second embodiment, and the third embodiment described above.

[0068] For example, in the above embodiment, an example was described in which the crack suppression member 10 was a crack suppression rebar. However, the crack suppression member according to the present disclosure may be something other than a crack suppression rebar. For example, the crack suppression member according to the present disclosure may be a mesh member such as a crack reduction net made of alkali-resistant glass fiber, a perforated steel strip, or fiber-reinforced concrete that is stronger than concrete 8, and may be changed as appropriate.

[0069] In the above embodiment, an example was described in which the concrete structure 1 is a box culvert. However, the concrete structure to which the determination method and construction method according to the present disclosure are applied is not limited to a box culvert. For example, the concrete structure may be a caisson foundation, and the determination method and construction method according to the present disclosure can be applied to various concrete structures. [Explanation of symbols]

[0070] 1...concrete structure, 2...base slab, 2b...top surface, 3...part, 3b...side, 4...inclined surface, 5...construction joint, 6...main reinforcement, 7...distribution reinforcement, 8...concrete (first concrete, second concrete), 8b...surface part, 8c...central part, 8d...separation part, 10...crack suppression member, 11...optical fiber sensor, 12...first reinforcing bar, 13...second reinforcing bar, A...concrete pouring area, A1...first section, A2...second section, B...boundary part, D1...first direction, D2...second direction, D3...third direction, P...pipe, R...monitoring room, R1...measurement data acquisition unit, R2...temperature adjustment unit.

Claims

1. A method for constructing a concrete structure by sequentially pouring concrete into a first section and a second section, comprising the steps of: placing optical fiber sensors at a plurality of positions in the first section and pouring a first concrete; A step of measuring the amount of strain at the multiple positions by the optical fiber sensor after the first concrete is poured; A step of determining whether or not a crack suppression member is required based on the magnitude of the difference in the amount of strain at the multiple positions; When it is determined that the crack suppression member is necessary in the step of determining whether the crack suppression member is necessary, a step of placing the crack suppression member in the second section and pouring a second concrete; A method of construction comprising:

2. A method for constructing a concrete structure by sequentially pouring concrete into a first section and a second section, comprising the steps of: placing optical fiber sensors at a plurality of positions in the first section and pouring a first concrete; A step of measuring the amount of strain at the multiple positions by the optical fiber sensor after the first concrete is poured; A step of previously disposing a crack suppression member inside the first concrete; A step of determining an effect of the crack suppression member based on a magnitude of a difference in the amount of strain at the plurality of positions; When it is determined that the position of the crack suppression member needs to be corrected in the step of determining the effect of the crack suppression member, a step of placing the crack suppression member at the corrected position in the second section and pouring a second concrete; A method of construction comprising:

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