Optical fiber installation structure, concrete member curing method, breakage evaluation method and structure characteristic evaluation method

Abstract

To provide an optical fiber installation structure which can appropriately detect a temperature crack and its sign during construction of concrete members, and an oblique crack and its sign which may be generated by shear force during a service period, as well as a concrete member curing method, a damage evaluation method and a structural characteristic evaluation method employing the optical fiber installation structure.SOLUTION: An optical fiber installation structure 10 is the optical fiber installation structure that places an optical fiber cable 11 to a column member 1. The optical fiber cable 11 comprises multiple circumferential direction sensor parts 13 extending in a plane orthogonal to a member axis of the column member 1 and inter-sensor connection parts 15 connecting the multiple circumferential direction sensor parts 13 arranged in an axial direction of the member axis.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical fiber installation structure, a concrete member curing method, a damage evaluation method, and a structural characteristic evaluation method. [Background technology]

[0002] A corrosion detection method described in Patent Document 1 below is known as a conventional method for evaluating concrete members using optical fibers as sensors. The corrosion sensor in this detection method includes a steel bar, which corrodes more easily than rebar, and an optical fiber attached to the surface of the steel bar, and is installed inside the reinforced concrete member. By detecting expansion of the steel bar due to corrosion with the optical fiber, a corrosive environment in the reinforced concrete member can be detected early. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6574331 Summary of the Invention [Problem to be solved by the invention]

[0004] Thermal cracking is a problem that can occur during the construction of this type of concrete member. Specifically, concrete expands and contracts with temperature changes after pouring, and cracks can occur if it is constrained by surrounding structures. To prevent cracking, it is important to control the temperature of the concrete during curing after pouring and maintain a stress (strain) state that prevents cracking. While it is possible to measure the temperature and strain of a concrete member using optical fibers installed inside the reinforced concrete member, the sensor in Patent Document 1 cannot necessarily be said to be able to properly measure the information necessary to detect thermal cracks.

[0005] Furthermore, various types of damage occur to concrete components during their service life due to factors such as traffic loads, earthquakes, and environmental influences. For example, diagonal cracks may occur due to shear forces, and large bending moments may cause the cover concrete to peel or rebar to protrude. Since such damage can lead to a decrease in the structural performance of concrete components or brittle fracture, it is necessary to detect it early and take appropriate measures, just as with the corrosive environment described above. However, the sensor in Patent Document 1 cannot necessarily be said to be able to properly measure the information necessary to detect damage.

[0006] Therefore, an object of the present invention is to provide an optical fiber installation structure that can appropriately detect thermal cracks and their precursors during construction of concrete members, as well as damage and its precursors that may occur due to the action of load during service life, and a concrete member curing method, damage evaluation method, and structural characteristic evaluation method that use the same. [Means for solving the problem]

[0007] The gist of the present invention lies in the following [1] to [6].

[0008] [1] An optical fiber installation structure for installing an optical fiber cable in a concrete member, wherein the optical fiber cable comprises a plurality of circumferential sensor units extending in a plane perpendicular to the member axis of the concrete member, and inter-sensor connection units that connect the plurality of circumferential sensor units arranged in the axial direction of the member axis.

[0009] [2] The optical fiber installation structure described in [1], wherein the circumferential sensor section extends in a plane perpendicular to the axis of the member and is installed along a reinforcing bar installed in the concrete member, and the sensor-to-sensor connection section is installed along a reinforcing bar installed in the concrete member.

[0010] [3] A concrete member curing method in which, during the concrete hardening process of the concrete member in which the optical fiber installation structure described in [1] is constructed, the temperature change and strain change of the concrete member are measured by the circumferential sensor part of the optical fiber cable, and the curing specifications of the concrete member during the concrete hardening process are adjusted based on the measured temperature change and strain change.

[0011] [4] A damage assessment method in which damage to a concrete member in which the optical fiber installation structure described in [1] is constructed is assessed based on the strain of the concrete member measured by the circumferential sensor portion of the optical fiber cable.

[0012] [5] The damage assessment method according to [4], wherein corrosion of reinforcing bars installed within the concrete member is detected as damage to the concrete member.

[0013] [6] A structural characteristic evaluation method in which the structural characteristics of a concrete member in which the optical fiber installation structure described in [1] is constructed are evaluated based on the vibration characteristics of the concrete member measured by the optical fiber cable. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an optical fiber installation structure that can appropriately detect thermal cracks and their precursors during construction of concrete members, as well as damage and its precursors that may occur due to external influences during the service period, and a concrete member curing method, damage evaluation method, and structural characteristic evaluation method that use the same. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1(a) is a partially cutaway perspective view of a pole member on which an optical fiber installation structure of a first embodiment is constructed, and FIG. 1(b) is a perspective view showing the optical fiber installation structure extracted from the pole member. [Figure 2] FIG. 10 is a perspective view showing a column member in which thermal cracking has occurred. [Figure 3] FIG. 10 is a perspective view of a reinforcing column on which the optical fiber installation structure of the second embodiment is constructed. [Figure 4] FIG. 10 is a perspective view showing a pillar member in which a diagonal crack has occurred. [Figure 5] This is a horizontal cross-sectional view of the surface of a pillar member where splitting cracks have occurred. [Figure 6] 10 is a graph showing the M-Φ curve and damage level of a pillar member. [Figure 7] 10A is a partially cutaway perspective view of a pole member on which a modified optical fiber installation structure is constructed, and FIG. 10B is a perspective view showing the optical fiber installation structure extracted from the pole member. [Figure 8] FIG. 10 is a partially cutaway perspective view of a pole member on which an optical fiber installation structure of another modified example is constructed. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the optical fiber installation structure and the like according to the present invention will be described in detail with reference to the drawings.

[0017] [First embodiment] FIG. 1(a) is a partially cutaway perspective view of a pillar member 1 on which an optical fiber installation structure 10 according to this embodiment is constructed, with a portion of the concrete cover of the pillar member 1 removed. FIG. 1(b) is a perspective view showing the optical fiber installation structure 10 extracted from the pillar member 1 of FIG. 1(a). The pillar member 1 is a reinforced concrete pillar with a rectangular cross section erected on a footing 2, such as a pier for a road bridge. The pillar member 1 has axial reinforcing bars 7 extending in the axial direction (vertical direction) of the pillar member 1, hoop reinforcing bars 8 extending circumferentially of the pillar member 1, and a concrete section 9 in which these reinforcing bars are embedded. An optical fiber cable 11 is also installed in the pillar member 1. The optical fiber cable 11 is laid while bending along a predetermined path near the surface of the pillar member 1 and embedded in the concrete section 9, thereby constructing the optical fiber installation structure 10 according to this embodiment.

[0018] The optical fiber cable 11 buried in the concrete section 9 deforms in accordance with the deformation of the pillar member 1, and functions as a sensor for measuring the strain or vibration response of the pillar member 1. The optical fiber cable 11 also functions as a sensor for measuring the temperature of the pillar member 1. As the optical fiber cable 11, for example, an optical fiber core wire in which a protective material is attached to an optical fiber strand is used.

[0019] Specifically, one or both ends of the optical fiber cable 11 are pulled out from the pillar member 1 and can be connected to a measuring instrument 21 and an analyzing device 23 for measuring strain, temperature, or vibration response. The measuring instrument 21 inputs pulsed light into the optical fiber cable 11 and receives various scattered lights returning from various positions along the length of the optical fiber cable 11, and transmits information on the intensity, wavelength, etc. of the received scattered light to the analyzing device 23. Examples of the scattered light include Rayleigh scattered light and Brillouin scattered light. Examples of the measuring instrument 21 that can be used include an OTDR (Optical Time Domain Reflectometer) that uses Rayleigh scattered light and a BOTDR (Brillouin Optical Time Domain Reflectometer) that uses Brillouin scattered light.

[0020] The analysis device 23 is a computer including, for example, a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). Based on the principle that the intensity and wavelength of the scattered light depend on the strain and temperature applied to the optical fiber cable 11, the analysis device 23 analyzes the intensity and wavelength of the scattered light at each position along the length of the optical fiber cable 11. Through such analysis, the analysis device 23 acquires the strain and temperature changes occurring at each position along the length of the optical fiber cable 11 at intervals of, for example, several centimeters.

[0021] The optical fiber installation structure 10 includes a plurality of circumferential sensor units 13, which will be described next, and inter-sensor connectors 15 that connect the circumferential sensor units 13 to each other.

[0022] The circumferential sensor unit 13 is composed of a portion of the optical fiber cable 11 that extends in a plane perpendicular to the axis of the pole member 1 (i.e., in a horizontal plane). In this embodiment, the circumferential sensor unit 13 extends in the circumferential direction for a length equivalent to approximately one circumference of the pole member 1. A plurality of circumferential sensor units 13 are arranged parallel to one another in the direction of the pole member 1's axis (i.e., the vertical direction). In this embodiment, there are five circumferential sensor units 13 (five rows), as illustrated in the figure. The circumferential sensor units 13 are fastened intermittently to the hoop reinforcing bars 8 with binding wires or tape. Each circumferential sensor unit 13 is embedded in the concrete section 9 while being fastened to a hoop reinforcing bar 8 in a different row.

[0023] The sensor-to-sensor connection section 15 is formed by a portion of the optical fiber cable 11 sandwiched between two circumferential sensor sections 13, 13 in the longitudinal direction of the optical fiber cable 11. That is, the optical fiber cable 11 has circumferential sensor sections 13 and sensor-to-sensor connection sections 15 connected alternately in series. In the pole member 1 of this embodiment, there is one sensor-to-sensor connection section 15 between each of the five circumferential sensor sections 13, for a total of four sensor-to-sensor connection sections 15. Each sensor-to-sensor connection section 15 extends vertically. As shown in FIG. 1(b), the optical fiber cable 11 is laid in the following order: circumferential sensor sections 13 having a length equivalent to one turn in the circumferential direction, sensor-to-sensor connection sections 15 having a length equivalent to one stage in the vertical direction, circumferential sensor sections 13 having a length equivalent to one turn in the circumferential direction, ... to construct the optical fiber installation structure 10.

[0024] The four inter-sensor connections 15 are aligned in a straight line at predetermined circumferential locations of the pillar member 1, extending vertically. The pillar member 1 has reinforcing bars 17 for installing the inter-sensor connections 15. The reinforcing bars 17 are installed to fasten the inter-sensor connections 15 and are made of, for example, steel bars or FRP bars. The reinforcing bars 17 are fixed to the axial reinforcing bars 7 and the tie bars 8, for example, with binding wires. The reinforcing bars 17 extend vertically in an arrangement that crosses the multiple circumferential sensor units 13, and are provided between two axial reinforcing bars 7, 7. The inter-sensor connections 15 are fastened intermittently to the reinforcing bars 17 with binding wires or tape. Each inter-sensor connection 15 is embedded in the concrete section 9 while fastened to the reinforcing bars 17.

[0025] 1, a plurality of circumferential sensor units 13 and inter-sensor connectors 15 may be provided. The number of stages, range, and intervals at which the circumferential sensor units 13 and inter-sensor connectors 15 are arranged can be set appropriately depending on the dimensions of the column member 1 and the purpose of measurement. Also, the reinforcing bars 17 may be omitted, and the inter-sensor connectors 15 may be fastened to the axial reinforcing bars 7.

[0026] (Construction method for pillar member 1) The method for constructing the pillar member 1 including the optical fiber installation structure 10 is as follows. First, the axial reinforcing bars 7 and tie bars 8 are installed at the planned construction position of the pillar member 1, and reinforcing bars 17 are attached to the axial reinforcing bars 7 and tie bars 8 (reinforcing bar installation process). Then, the optical fiber cable 11 is installed along the predetermined installation path as described above, and the optical fiber cable 11 is intermittently fastened to the tie bars 8 and reinforcing bars 17 (optical fiber placement process). This results in five circumferential sensor units 13 and four inter-sensor connections 15. Here, the circumferential sensor units 13 are preferably arranged along the tie bars 8 and vertically below the tie bars 8. With this arrangement, the circumferential sensor units 13 are protected from impacts during concrete pouring in the concrete pouring process described below, reducing the possibility of the optical fiber cable 11 breaking.

[0027] Next, a concrete formwork is installed so as to surround the axial reinforcing bars 7, tie bars 8, reinforcing bars 17, and optical fiber cable 11 (formwork installation process), and concrete is poured into the formwork (concrete pouring process). After that, the poured concrete portion 9 is cured (curing process), and the concrete formwork is removed (form removal process), completing the pillar member 1. Inside the pillar member 1, an optical fiber installation structure 10 is constructed by the optical fiber cable 11 buried in the concrete portion 9.

[0028] (Construction management of pillar member 1) Here, one of the problems that can occur during the construction of the column member 1 described above is thermal cracking. That is, the concrete poured during the concrete pouring process expands and contracts with temperature changes after pouring while being restrained by the footing 2, and cracks can occur during hardening. To avoid cracking, it is important to control the temperature during the hardening process of the concrete part 9 and maintain a stress (strain) state that does not cause cracks. That is, curing is required so that the stress generated in the hardening concrete part 9 does not exceed the strength that is achieved by hardening.

[0029] Therefore, in this embodiment, the optical fiber installation structure 10 is used to manage the curing process. Specifically, in the curing process, one or both ends of the optical fiber cable 11 are pulled out from the poured concrete section 9 and connected to the measuring instrument 21 and the analyzing device 23. Then, the optical fiber cable 11 measures the temperature change and strain change during the hardening process of the concrete section 9. At this time, the circumferential sensor unit 13 at each stage acquires the temperature change and strain change at each height position of the concrete section 9. Note that here, the "temperature change" and "strain change" refer to the temperature change and strain change from a predetermined reference point in time (for example, immediately after the concrete section 9 is poured). Here, for example, the temperature and strain at each position of the optical fiber cable 11 immediately after the concrete section 9 is poured are measured in advance as a reference.

[0030] Based on the temperature and strain changes of the concrete 9 acquired as described above, the curing specifications for the concrete 9 during its hardening process are adjusted. Here, the curing specifications are adjusted based on a comprehensive judgment that takes into account not only the rate of change in the temperature and strain of the concrete 9 but also the temperature and strain of the concrete 9 at that time. For example, if the temperature of the concrete 9 decreases at a rate greater than a predetermined value and the increase in strain of the concrete 9 is greater than a predetermined value, an adjustment is made, such as adding an insulation mat to cover the concrete 9 to slow the rate of temperature decrease of the concrete 9. Conversely, if the measurement data confirms that the changes in the temperature and strain of the concrete 9 have subsided during the curing period, the curing period can be shortened based on that information. In other words, if the temperature and rate of decrease of the concrete 9 are less than a predetermined value and the strain and increase of the concrete 9 are less than a predetermined value, it is determined that thermal cracking is unlikely to occur. Therefore, adjustments are made, such as removing the insulation mat and curing sheet early and proceeding to the next process.

[0031] The effects of the optical fiber installation structure 10 of this embodiment and the above-described protection method using the same will now be described.

[0032] As mentioned above, the hardening concrete portion 9 expands and contracts with temperature changes after pouring while being restrained by the footing 2, which can cause thermal cracks to occur in the concrete portion 9. In particular, because the bottom end of the concrete portion 9 is restrained by the horizontal footing 2, any thermal cracks 31 that occur tend to extend in a direction with a vertical component, as shown in Figure 2. These thermal cracks 31 and their precursors appear as strain changes in the concrete portion 9 in a direction with a horizontal component.

[0033] In contrast, the circumferential sensor unit 13 of the optical fiber installation structure 10 extends in a plane perpendicular to the axis of the pillar member 1 (i.e., in a horizontal plane). Therefore, as shown in FIG. 2, if thermal cracks 31 occur, the thermal cracks 31 or their precursory portions are likely to cross the circumferential sensor unit 13. The circumferential sensor unit 13 then sensitively detects increases in horizontal strain in the concrete section 9 due to thermal cracks 31 or their precursory portions. Therefore, according to this curing method, the curing specifications for the concrete section 9 can be appropriately adjusted based on the precursory portions of thermal cracks 31, thereby reducing the possibility of thermal cracks occurring.

[0034] Furthermore, since multiple circumferential sensor units 13 are arranged in parallel at multiple stages, there is a high possibility that thermal cracks 31 or their precursory occurrence areas will cross multiple circumferential sensor units 13. Therefore, horizontal strain caused by thermal cracks 31 and their precursory occurrences can be detected at multiple stages, and information from multiple locations can be integrated to detect thermal cracks 31 and their precursory occurrences. As described above, the optical fiber installation structure 10 can appropriately detect thermal cracks 31 and their precursory occurrences during the hardening process of the concrete section 9.

[0035] Depending on the conditions of the structure, thermal cracking may be acceptable. In this case, it is possible to identify the crack location based on the measurement data and understand the crack condition (such as the estimated crack width). Furthermore, the knowledge gained from such measurement data can be used to review the curing method and adjust the concrete mix (addition of expansive agents and shrinkage-reducing agents). Cracks that occur during hardening can also be caused by drying shrinkage or autogenous shrinkage, and for these cracks, it is effective to measure them using the optical fiber mentioned above and adjust the curing method based on the results.

[0036] Furthermore, in the optical fiber installation structure 10 of this embodiment, multiple circumferential sensor units 13 are connected by inter-sensor connectors 15. Therefore, multiple circumferential sensor units 13 can be constructed using a single optical fiber cable 11 connected to the measuring instrument 21 and the analyzing device 23. In other words, it is not necessary to prepare the same number of optical fiber cables 11 to construct multiple stages of circumferential sensor units 13. As a result, the number of channels required for the optical fiber cable 11 connected to the measuring instrument 21 and the analyzing device 23 can be reduced, and the number of joints and fusion points of the optical fiber cable can be reduced. As a result, the effort required for jointing and fusing the optical fiber cables is reduced.

[0037] Another possible method for installing this type of optical fiber cable vertically and horizontally on the pole member 1 is the following. Specifically, optical fiber cables that have been previously integrally adhesively fixed to the surfaces of the axial reinforcing bars 7 and the tie bars 8 can be fusion-spliced ​​together to form a single optical fiber cable 11 after the reinforcing bar installation process. However, the more circumferential sensor units 13 are installed, the more fusion splicing work is required. There is also a risk of the optical fiber cable being damaged or broken during the reinforcing bar installation process. It is also possible to avoid the fusion splicing work and directly connect the circumferential sensor units 13 to the measuring instrument 21 and the analyzing device 23, respectively. However, the more circumferential sensor units 13 are installed, the more channels are required, and the longer the excess length of the optical fiber cable. In contrast, the optical fiber installation structure 10 of this embodiment only requires wiring a single optical fiber cable 11 along a predetermined installation path, thereby avoiding the above-mentioned problems. Furthermore, while it is difficult to integrally adhere the optical fiber cable 11 to the surface of the axial reinforcing bars 7 and the tie bars 8 at the site after the reinforcing bar installation process, in this embodiment, the optical fiber cable 11 only needs to be fastened intermittently to the tie bars 8, auxiliary bars 17, etc., which improves workability.

[0038] Second Embodiment Next, a second embodiment of the optical fiber installation structure etc. according to the present invention will be described. In this embodiment, components that are the same as or equivalent to those in the first embodiment are designated by the same reference numerals in the drawings, and redundant explanations will be omitted.

[0039] FIG. 3 is a perspective view of a reinforcing column 101 on which the optical fiber installation structure 10 of this embodiment is constructed. As shown in FIG. 3, in this embodiment, the optical fiber installation structure 10 similar to that of the first embodiment is constructed on the reinforcing column 101. The reinforcing column 101 is a column reinforced by a winding method, for example, a pier of a road bridge. The reinforcing column 101 is erected on a footing 2 and includes an existing column portion 3 and a reinforcement portion 5 made of reinforced concrete installed on the surface of the existing column portion 3. The existing column portion 3 is an existing column made of reinforced concrete. The reinforcement portion 5 is used to reinforce the existing column portion 3 by winding it, for example, for the purpose of seismic reinforcement of the existing column portion 3, and is provided around the entire periphery of the existing column portion 3.

[0040] The optical fiber installation structure 10 of this embodiment is constructed in a reinforcing section 5. The reinforcing section 5 has axial reinforcing bars 7 extending in the axial direction (vertical direction) of the reinforcing column 101, tie bars 8 extending circumferentially of the reinforcing column 101, and a concrete section 9 in which these reinforcing bars are embedded. Note that the concrete section 9 is indicated by a dashed line in FIG. 3 . The reinforcing section 5 also has reinforcing bars 17. One optical fiber cable 11 is installed in the reinforcing section 5, and multiple circumferential sensor units 13 and multiple inter-sensor connectors 15 are configured and embedded in the concrete section 9. The installation path and fastening structure of the optical fiber cable 11 relative to the axial reinforcing bars 7, tie bars 8, and reinforcing bars 17 are the same as those in the first embodiment.

[0041] In this embodiment, the concrete portion 9 of the reinforcing portion 5 hardens while being restrained not only by the footing 2 but also by the existing column portion 3. The thickness of the reinforcing portion 5 is generally thin, about 250 mm, and the reinforcing portion 5 is restrained over a wide area relative to the existing column portion 3, making it particularly susceptible to cracks due to temperature cracking, autogenous shrinkage, and drying shrinkage. To address this, the above-mentioned curing method using the optical fiber installation structure 10 is applied, as in the first embodiment. This allows signs of cracking during the hardening process of the concrete portion 9 to be properly detected, making it possible to appropriately adjust the curing specifications for the concrete portion 9 and reducing the possibility of cracks occurring.

[0042] Third Embodiment Next, a third embodiment of the optical fiber installation structure etc. according to the present invention will be described. In this embodiment, components that are the same as or equivalent to those in the first embodiment are given the same reference numerals in the drawings, and redundant explanations will be omitted. In this embodiment, the optical fiber installation structure 10 is constructed on a pole member 1 (FIG. 1), as in the first embodiment, but the method of using this optical fiber installation structure 10 differs from that in the first embodiment. The optical fiber installation structure 10 in this embodiment is used to implement a damage assessment method for assessing damage to the pole member 1 during its service life. Specific examples of this damage assessment method will be described below.

[0043] (Evaluation based on diagonal cracks in column member 1) In this example of a damage assessment method, diagonal cracks in a pillar member 1 are detected. Shear forces due to earthquakes, environmental influences, and other factors act on concrete members during their service life. These shear forces can cause diagonal cracks 33 extending diagonally relative to the axis of the pillar member 1, as shown in Figure 4. Because these types of diagonal cracks can lead to brittle fracture of the concrete member, they must be detected early and appropriate measures, such as repair or reinforcement, taken. Therefore, in this damage assessment method, a measuring instrument 21 and an analyzing device 23 are connected to one or both ends of an optical fiber cable 11 in a pillar member 1 during its service life, and diagonal cracks 33 in the pillar member 1 are detected using an optical fiber installation structure 10.

[0044] As described above, the diagonal crack 33 extends diagonally relative to the axis of the column member 1, and signs of the diagonal crack 33 appear as strain changes in the concrete portion 9 in a direction with a horizontal component. Therefore, similar to the thermal cracks in the first embodiment, the diagonal crack 33 or its precursory portion tends to cross the circumferential sensor unit 13. The circumferential sensor unit 13 can sensitively detect increases in horizontal strain in the concrete portion 9 due to the thermal crack 31 or its precursory portion. If a diagonal crack 33 has occurred, its location and crack width can be estimated based on the horizontal strain increase measured by the multiple circumferential sensor units 13. Therefore, damage to the column member 1 can be appropriately evaluated based on the diagonal crack 33 or its precursory portion, and appropriate measures, such as repairs or reinforcement, can be taken. Here, "strain change" refers to the change in strain from a predetermined reference point (for example, immediately after the pole member 1 begins to be used). Here, for example, the strain at each position of the optical fiber cable 11 immediately after the pole member 1 begins to be used is measured in advance as a reference.

[0045] (Evaluation based on splitting cracks in column member 1) In this example of the damage assessment method, splitting cracks are detected in a column member 1. Figure 5 is a horizontal cross-sectional view of the vicinity of the surface of the column member 1, including a possible splitting crack 35. When the axial rebar 7 in the column member 1 yields and the strain increases suddenly, splitting cracks 35 occur around the axial rebar 7 due to the loss of adhesion between the axial rebar 7 and the concrete portion 9, as shown in Figure 5. Alternatively, splitting cracks 35 such as those described above may occur due to corrosion and expansion of the axial rebar 7.

[0046] The axial rebars 7 cross near the horizontally extending hoop rebars 8 and near the circumferential sensor unit 13. Therefore, the area where a splitting crack 35 or its precursor occurs crosses the circumferential sensor unit 13, and the change in circumferential strain is detected by the circumferential sensor unit 13. Therefore, based on the splitting crack 35 or its precursor, damage to the column member 1 can be appropriately evaluated, and appropriate measures such as repair or reinforcement of the column member 1 can be taken. For example, if the circumferential sensor unit 13 detects a local increase in circumferential strain when no external force such as an earthquake is acting, it can be assumed that the axial rebars 7 in that vicinity have previously yielded or have expanded due to corrosion.

[0047] (Evaluation based on the protrusion of axial rebar 7 of column member 1) In this example of the damage assessment method, the bulging of the axial rebars 7 in the column member 1 is detected. When the column member 1 reaches near its maximum strength, the axial rebars 7 may bulge, causing the cover concrete to spall. In this case, the tie bars 8 in the column member 1 restrain the bulging of the axial rebars 7, and an increase in circumferential strain is detected by the circumferential sensor units 13 located along the tie bars 8. Furthermore, when an increase in circumferential strain occurs as a sign of the bulging of the axial rebars 7, this increase in strain is similarly detected by the circumferential sensor units 13. Therefore, based on the bulging of the axial rebars 7 or its signs, the damage to the column member 1 can be appropriately assessed, and appropriate measures, such as repairing or reinforcing the column member 1, can be taken.

[0048] (Evaluation of the structural performance of column member 1) The damage level and structural performance of the column member 1 can be estimated based on damage such as diagonal cracks and the protrusion of axial rebars 7 as described above. Here, the damage levels (L1 to L4) on the M-Φ curve of the column member 1 are estimated, as shown in Figure 6. For example, if the circumferential sensor unit 13 detects signs of cover concrete spalling due to diagonal cracks or the protrusion of axial rebars 7 after a load such as an earthquake, it is estimated that the column member 1 has reached a damage level (L2) at which the rebars will yield and reach their maximum strength. It is then possible to determine whether the column member 1 will be destroyed when subjected to a similar or larger load again, and to determine whether it can continue to be used after an earthquake or whether further reinforcement is necessary.

[0049] (Evaluation based on the vibration characteristics of column member 1) The damage assessment method in this example is a structural characteristic assessment method in which the vibration characteristics of a pole member 1 are detected and the structural characteristics of the pole member 1 are assessed based on these vibration characteristics. Damage and deterioration of the pole member 1 manifest as a decrease in the bending rigidity of the pole member 1, and the vibration characteristics of the pole member 1 change accordingly. That is, the natural frequency of the pole member 1 decreases and the amplitude increases depending on the degree of deterioration in the structural performance of the pole member 1 due to damage and deterioration. Therefore, during the service life of the pole member 1, the vibration characteristics of the pole member 1 are measured by distributed acoustic sensing (DAS) measurement using an optical fiber cable 11. DAS measurement is also sometimes called a "distributed vibration measurement method," "distributed acoustic sensing," or "distributed vibration sensing." In DAS measurement, a DAS measuring device (not shown) is connected to the optical fiber cable 11, and vibration is applied to the pole member 1. Possible methods for applying vibration to the pole member 1 include using traffic loads, or intentionally applying external forces such as impact loads. The vibration of the pole member 1 caused by this vibration application is detected by the optical fiber cable 11, and the vibration waveform is acquired by the DAS measuring instrument. The vibration waveform acquired here is then compared with a vibration waveform measured in advance immediately after the pole member 1 was put into service, and based on the difference, it is possible to estimate the deterioration in the structural performance of the pole member 1 immediately after the pole member 1 was put into service. In this case, the DAS measurement described above was carried out in advance immediately after the pole member 1 was put into service, and the vibration waveform for comparison was acquired.

[0050] The present invention can be implemented in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. It is also possible to configure modified examples by utilizing the technical matters described in the above-described embodiment. The configurations of the respective embodiments may be used in appropriate combination.

[0051] For example, each example of the damage assessment method for the pole member 1 in the third embodiment may be applied to the damage assessment for the reinforcing portion 5 of the reinforcing pole 101 in the second embodiment.

[0052] Furthermore, for example, in the embodiment, the sensor-to-sensor connector 15 (FIG. 1) extends vertically, but is not limited thereto. For example, FIG. 7(a) is a partially cutaway perspective view of a pole member 1 on which a modified optical fiber installation structure 10 is constructed, with part of the concrete cover of the pole member 1 removed. FIG. 7(b) is a perspective view showing the optical fiber installation structure 10 extracted from the pole member 1 of FIG. 7(a). As shown in the figure, the sensor-to-sensor connector 15 may extend obliquely on one side surface of the pole member 1. In the embodiment of FIG. 7, the circumferential sensor unit 13 extends circumferentially, for example, for a length of approximately 3 / 4 of the circumference of the pole member 1. The sensor-to-sensor connector 15 extends across the entire width of one side surface of the pole member 1 and obliquely connects one end of one circumferential sensor unit 13 to the other end of the circumferential sensor unit 13 below it. In this case, the reinforcing bars 17 are installed diagonally along the installation path of the sensor-to-sensor connections 15, and the sensor-to-sensor connections 15 are fastened intermittently to the reinforcing bars 17 with binding wires or tape. The optical fiber installation structure 10 is constructed by installing the optical fiber cable 11 in the following order: circumferential sensor units 13 each having a length equivalent to approximately 3 / 4 of the circumference, sensor-to-sensor connections 15 extending diagonally on the side, and another circumferential sensor unit 13 each having a length equivalent to approximately 3 / 4 of the circumference. The inclination angle of the sensor-to-sensor connections 15 is not limited to that shown in Figures 7(a) and (b), and may be adjusted to an angle that is easy to install depending on the conditions of the structure.

[0053] Furthermore, as shown in Fig. 8, the optical fiber installation structure 10 may further include an axial sensor unit 19 extending in the axial direction. The configuration in Fig. 8 is obtained by adding the axial sensor unit 19 to the optical fiber installation structure 10 in the configuration in Fig. 7. The axial sensor unit 19 extends vertically from near the lower end of the pillar member 1 to near the upper end. The axial sensor unit 19 is fixed integrally to the surface of one axial rebar 7 with an adhesive or the like before the rebar installation process. Then, after the optical fiber cable 11 is laid, the lower end of the axial sensor unit 19 is fusion-spliced ​​to the end of the lowest circumferential sensor unit 13.

[0054] According to this configuration, the strain of the axial rebar 7 can be measured by the axial sensor unit 19, and the yielding of the axial rebar 7 can be directly detected. In addition, since the optical fiber cable 11 is extended by the axial sensor unit 19 and one end of the optical fiber cable 11 (the upper end of the axial sensor unit 19) is located near the upper end of the pillar member 1, it is easy to connect the optical fiber cable 11 to the measuring instrument 21 and the analysis device 23 at the top of the pillar member 1.

[0055] Alternatively, the axial sensor unit 19 may be configured as part of the optical fiber cable 11 and installed continuously with the circumferential sensor unit 13 and the sensor-to-sensor connection unit 15. In this case, the axial sensor unit 19 is not integrally fixed to the surface of the axial rebar 7, but is intermittently fastened to the axial rebar 7 with a tie wire or tape. Alternatively, auxiliary reinforcement bars (not shown) extending in the axial direction may be installed, and the axial sensor unit 19 may be intermittently fastened to the auxiliary reinforcement bars with a tie wire or tape. In this case, the axial sensor unit 19 cannot directly measure the strain of the axial rebar 7, but can detect bending cracks in the column member 1 and estimate the width of bending cracks. Alternatively, the sensor-to-sensor connection unit 15 in the configuration shown in FIG. 1 may be integrally fixed to the surface of the axial rebar 7 and function as the axial sensor unit 19. In this case, the sensor-to-sensor connection unit 15 intermittently measures the strain of the axial rebar 7. [Explanation of symbols]

[0056] 1...Column member (concrete member), 5...Reinforcement part (concrete member), 7...Axial reinforcing bar, 8...Hoop reinforcing bar, 10...Optical fiber installation structure, 11...Optical fiber cable, 13...Circumferential sensor part, 15...Connection part between sensors, 17...Auxiliary bar

Claims

1. An optical fiber installation structure for installing an optical fiber cable in a concrete member, The optical fiber cable comprises: a plurality of circumferential direction sensor units extending in a plane perpendicular to the axis of the concrete member; an inter-sensor connection portion that connects the plurality of circumferential sensor portions arranged in the axial direction of the member axis.

2. The circumferential direction sensor unit extends in a plane perpendicular to the member axis and is installed along a reinforcing bar installed in the concrete member, The optical fiber installation structure according to claim 1 , wherein the sensor-to-sensor connection section is installed along a reinforcing bar installed in the concrete member.

3. During the concrete hardening process of the concrete member in which the optical fiber installation structure according to claim 1 is constructed, the temperature change and strain change of the concrete member are measured by the circumferential sensor portion of the optical fiber cable, A method for curing a concrete member, wherein curing specifications for the concrete member during the concrete hardening process are adjusted based on the measured temperature change and strain change.

4. A damage assessment method in which damage to a concrete member in which the optical fiber installation structure described in claim 1 is constructed is assessed based on the strain of the concrete member measured by the circumferential sensor portion of the optical fiber cable.

5. The damage assessment method according to claim 4 , wherein corrosion of reinforcing bars installed in the concrete member is detected as the damage to the concrete member.

6. A structural characteristic evaluation method in which the structural characteristics of a concrete member in which the optical fiber installation structure described in claim 1 is constructed are evaluated based on the vibration characteristics of the concrete member measured by the optical fiber cable.

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