JP7626686B2 - How to build it - Google Patents

Description

This 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.

Methods for predicting and estimating cracks 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 made up of multiple wall-like bodies built on a footing. Joint material is placed between the multiple wall-like bodies. For this type of structure, the maximum crack is estimated.

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 that occurs per unit length of the structure's wall, and an estimated unit crack number, which indicates the number of cracks that occur 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.

Patent Document 2 describes a method for predicting maximum crack width. The structure targeted by this prediction method is a reinforced concrete structure, in which a crack dispersion material is placed between the reinforcing bars 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 bars, and gap of the reinforcing bars as parameters.

JP 2009-19472 A JP 2015-117954 A

As mentioned above, in the method of predicting and estimating cracks in concrete, the maximum crack width of a structure is estimated from actual crack measurement data. However, while this method estimates the maximum crack width, it may not require specific means or methods for suppressing cracks.

In the above-mentioned method for predicting 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, or whether or not the crack suppression members are even necessary. Therefore, there is a demand for the crack suppression members to be placed appropriately in order to rationally suppress cracks in concrete structures.

The present disclosure aims to provide a method for determining the necessity of crack suppression members that can be appropriately positioned to rationally suppress cracks in concrete structures, and a method for constructing concrete structures.

The method of determining whether or not a crack suppression member is required according to the present disclosure is a method of determining whether or not a crack suppression member embedded inside concrete is required, 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 pouring the concrete, and 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.

In this determination method, optical fiber sensors are placed at multiple positions in the concrete pouring area, and concrete is poured at the multiple positions. The optical fiber sensors measure the time that has elapsed since the concrete was poured (more specifically, the time that has elapsed since the concrete was poured) and the amount of strain at the multiple positions. By having the optical fiber sensor measure the amount of strain at multiple positions in this way, the amount of strain at the multiple positions can be measured with high accuracy along the length of the optical fiber. The need for 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 multiple positions measured by the optical fiber sensor. Therefore, since the need for a crack suppression member is determined from the difference in the amount of strain at the multiple positions, the crack suppression member can be appropriately positioned. Therefore, cracks in the concrete structure can be rationally suppressed by appropriately positioning the crack suppression member.

The concrete has a portion that stands on the base slab and extends vertically, and the multiple positions may include a central 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 placed in the central portion in the thickness direction of the portion extending 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 central portion and the surface layer portion. Therefore, the need for a crack suppression member can be determined from the difference in strain between the central portion and the surface layer portion.

This determination method may include a step of measuring the temperature at multiple positions using an optical fiber sensor after the concrete is poured, and a step of controlling the temperature of the concrete in accordance with the measured temperature. In this case, the temperature measurement results from the optical fiber sensor can be used to control the temperature of the concrete, making it possible to make cracks less likely to occur through temperature control.

A method for constructing a concrete structure according to one aspect of the present disclosure is a method for constructing a concrete structure by sequentially pouring concrete into a first section and a second section, and includes 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 sensors after pouring the first concrete, 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, and, if it is determined in the step of determining whether or not a crack suppression member is required that a crack suppression member is required, placing the crack suppression member in the second section and pouring the second concrete.

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 suppression member is determined from the magnitude of the difference between the multiple strain amounts. Therefore, it is possible to rationally determine whether or not a crack suppression member is needed in the first section. Furthermore, if it is determined that a crack suppression member is needed in the first section, a crack suppression member is placed in the second section and the second concrete is poured. Therefore, in the second section, cracks in the structure can be rationally suppressed by appropriately placing the crack suppression member.

A method for constructing a concrete structure according to another aspect of the present disclosure is a method for constructing a concrete structure by sequentially pouring concrete into a first section and a second section, and includes 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 sensors after pouring the first concrete, placing a crack suppression member inside the first concrete in advance, determining the effectiveness of the crack suppression member based on 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.

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

According to the present disclosure, cracks in concrete structures can be rationally suppressed by appropriately positioning crack suppression members.

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. 1 is a flowchart illustrating steps of a determination method and a construction method according to an embodiment. 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. 6A, 6B, 6C, and 6D are graphs showing examples of the measurement results of the amount of strain measured by the optical fiber sensor. 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. (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). (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). 10 is a flowchart showing steps of a method for constructing a concrete structure according to a second embodiment. FIG. 1 is a diagram showing an embodiment in which an optical fiber sensor is arranged to control the temperature of poured concrete. 1 is a flowchart showing an example of steps in a method for controlling the temperature of concrete.

Below, 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 will be omitted as appropriate. In addition, the drawings may be partially simplified or exaggerated to facilitate understanding, and the dimensional ratios and the like are not limited to those shown in the drawings.

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.

For example, the concrete structure 1 has an inclined surface 4 that extends obliquely from the base slab 2 toward the portion 3 at the 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 the first direction D1. Each inclined surface 4 extends obliquely between the top surface 2b of the base slab 2 and the side surface 3b of the portion 3 with respect to both the first direction D1 and the third direction D3.

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 the pair of upper and lower pouring joints 5), and the upper portion of the portion 3 in that 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.

Figure 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 Figure 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.

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.

The crack suppression member 10 suppresses the expansion of crack width in the concrete 8 by resisting cracks in the concrete 8. The crack suppression member 10 is, for example, a crack suppression rebar. As an example, the crack suppression 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.

The crack suppression member 10 is placed, for example, in the 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 more likely to predominate than the surface portion 8b (cover) of the concrete 8, so placing the crack suppression member 10 in the central portion 8c can effectively suppress cracks in the concrete 8.

However, it is not always sufficient to place the crack suppression members 10 as described above, and the manner in which the crack suppression members 10 should be placed may differ depending on the type of concrete structure 1, etc. Therefore, it is currently unclear where and to what extent the crack suppression members 10 should be placed to be effective. In the method for determining whether or not a crack suppression member 10 is required and the method for constructing a concrete structure 1 according to this embodiment, the need for a crack suppression member 10 is determined using an optical fiber sensor 11 (see FIG. 3(a)) that measures the amount of strain in the concrete 8, and the crack suppression members 10 can be placed rationally and economically to suppress cracks in the concrete 8.

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

As shown in Figures 2 and 3(a), first, optical fiber sensors 11 are placed at each of multiple positions in the first section A1 (step of placing optical fiber sensors, step S1). In Figure 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 poured concrete 8 by, for example, Rayleigh measurement using the optical fiber sensor 11.

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 backscattered light has the advantage of being highly accurate and resistant to light loss. The optical fiber sensor 11 can detect the strain in the concrete 8 with an accuracy of, for example, 1 μm.

Figure 3(b) is an enlarged view of an example of the arrangement of the optical fiber sensors 11. As shown in Figures 3(a) and 3(b), a plurality of optical fiber sensors 11 are arranged above and below the upper joint 5 of the part 3. Above and below the joint 5 of the part 3, the optical fiber sensors 11 are arranged in the central part 8c in the first direction D1 (thickness direction) of the part 3, the surface layer 8b in the first direction D1 of the part 3, and the spaced part 8d located vertically above the central part 8c.

Each optical fiber sensor 11 is arranged to extend in the second direction D2 in each of the surface layer 8b, the central portion 8c, and the spaced portion 8d. In this embodiment, an optical fiber sensor 11 is also 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. Above, an example of the arrangement of the optical fiber sensors 11 has been described. However, the arrangement and number of the optical fiber sensors 11 are not limited to the examples in Figures 3(a) and 3(b) and can be changed as appropriate.

After arranging the optical fiber sensor 11 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, concrete 8 is poured into the base slab 2, and then, after a predetermined time has passed, concrete 8 is poured into the lower part of portion 3 and then into the upper part of portion 3, in that order. Note that since the concrete of portion 3 is poured after the concrete of base slab 2 has hardened, distortion and distortion bias occur inside the concrete of portion 3 that is restrained by base slab 2. Base slab 2 does not necessarily have to be a concrete structure, and may be bedrock or ground.

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

Figure 4(a) shows data on the amount of strain in the surface layer 8b and the central layer 8c one day after pouring the concrete 8, Figure 4(b) shows data on the amount of strain five days after pouring the concrete 8, Figure 4(c) shows data on the amount of strain seven days after pouring the concrete 8, and Figure 4(d) shows data on the amount of strain 28 days after pouring the concrete 8. Figures 4(a) to 4(d) show data on the amount of strain measured by the optical fiber sensor 11. In each graph of Figures 4(a) to 4(d), the vertical axis shows strain (unit: μ), and the horizontal axis shows the distance (unit: m) from the end of the concrete 8 in the second direction D2.

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, after five days, the difference between these amounts of strain became larger, and the amount of strain (absolute value) in the central portion 8c was greater 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.

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

The peaks in Figures 4(a) to 4(d) indicate the locations where cracks have occurred. The positions of the peaks in Figures 4(a) to 4(d) correspond to the locations where cracks have occurred. As shown in Figures 4(b) to 4(d), it can be seen that cracks occurred first in the central portion 8c, and later in the surface layer portion 8b. Specifically, five days after the concrete 8 was poured, cracks occurred in the central portion 8c, but not 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. Note that 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.

Figure 5 is a graph showing the relationship between the number of days after pouring of concrete 8 and the amount of strain at the location of the displacement of concrete 8 of 15.45 m in Figures 4(a) to 4(d). As shown in Figure 5, four days after pouring of concrete 8, cracks have appeared in central portion 8c, and the amount of strain in central portion 8c has increased.

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, after which cracks appeared and the amount of strain increased. From the 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.

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 (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, if 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.

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 to a position closer to the surface layer 8b.

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

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

The need for a crack suppression member 10 to suppress cracks in the concrete 8 is determined from the magnitude of the difference in the amount of strain at multiple positions measured by the optical fiber sensor 11. Therefore, since the need for a crack suppression member 10 is determined from the difference in the amount of strain at multiple positions, the crack suppression member 10 can be appropriately positioned. Therefore, by appropriately positioning the crack suppression member 10, cracks in the concrete structure 1 can be rationally suppressed.

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 in 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 in the central portion 8c and the strain in the surface layer portion 8b.

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 vertically from the central portion 8c. Thus, the optical fiber sensor 11 is disposed at the spaced portion 8d spaced vertically 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.

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

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

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-suppressing member 10 is placed (Figures 6(d), 7(b) and 7(d)) compared to when the crack-suppressing member 10 is not placed (Figure 6(b)).

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

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 suppression member 10 between the central portion 8c and the surface layer 8b is more effective at suppressing cracks than placing the crack suppression member 10 in the central portion 8c. In this way, by measuring the amount of strain in the surface layer 8b and central portion 8c, etc. of the concrete 8 in advance using the optical fiber sensor 11 and calculating the difference between the amounts, it is possible to determine where the crack suppression member 10 should be placed.

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.

First, optical fiber sensors 11 are placed at multiple positions in the first section A1 (e.g., the surface layer 8b and the central portion 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). Below, an example in which the crack suppression members 10 are placed in advance in the central portion 8c of the concrete 8 as shown in Figure 7(c) is described.

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

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

On the other hand, if it is determined in step S26 that no correction is required (NO in step S26), for example, in the second section A2, the crack suppression member 10 is placed in the same position as in the first section A1 (step S28), and concrete 8 is poured (step S29). After going through the above steps, the construction of the concrete structure 1 is completed.

As described above, in the method for constructing a 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.

If it is determined that the crack suppression member 10 needs to be corrected as a result of judging the effectiveness of the crack suppression member 10, the crack suppression member 10 is placed in the corrected position in the second section A2 and concrete 8 is poured. Therefore, by placing the crack suppression member 10 in the corrected position, the crack suppression member 10 can be placed in a more effective position, thereby rationally suppressing cracks.

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 Fig. 9 and Fig. 10, in the construction method according to the third embodiment, the temperature of the concrete structure 1 is controlled.

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, multiple pipes P are buried in the concrete structure 1, and the temperature adjustment unit R2 indicates the water temperature 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.

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

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

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 also measure the strain along with the temperature of the concrete. The measured temperature (and strain) of the concrete is stored, for example, in a computer in the monitoring room R.

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

As described above, the construction method according to the third embodiment includes a process in which the optical fiber sensor 11 measures the temperature at multiple positions after the concrete is poured, and a process in which the temperature of the concrete 8 is controlled in accordance with the measured temperature. Therefore, the temperature measurement results by the optical fiber sensor 11 can be used to control the temperature of the concrete, so that the occurrence of cracks can be reduced by temperature control.

Various embodiments of the method for constructing a concrete structure and the method for determining whether or not a crack suppression member is required 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, second, and third embodiments described above.

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 modified as appropriate.

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

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

Claims (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 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: 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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