Residual prestress force estimation method for PC structure and strain measurement device for estimating residual prestress force in PC structure

Abstract

To provide a residual prestress force estimation method for a PC structure capable of estimating residual prestress force without breaking down a PC structure, and a strain measurement device for estimating residual prestress force in a PC structure.SOLUTION: A method for estimating residual prestress force in a PC structure comprises: generating strain at a specific location; measuring strain using a strain measurement device; obtaining relation between change in stress and change in strain at the specific location; identifying an inflection point where the relation between the change in stress and the change in strain at the specific location changes as a characteristic point; and estimating residual prestress force in a PC structure based on the relation between compressive stress at dead load, which has been prepared in advance, and the change in strain at the characteristic point.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the residual prestress force of a PC structure and a strain measuring device for estimating the residual prestress force of a PC structure. [Background technology]

[0002] Prestressed concrete (PC) has tendons such as prestressing steel bars embedded inside the concrete, and compressive stress is applied to the concrete beforehand. It is used as concrete for bridges (PC girders) and building beams. In PC structures constructed using PC, the prestress may decrease after construction due to factors such as fracture of tendons. Therefore, there have been methods for estimating the residual prestress remaining in PC structures in order to determine the need for reinforcement of PC structures, the amount of reinforcement required, and to evaluate the soundness of PC structures.

[0003] For example, Patent Document 1 discloses a method in which multiple circumferential strain gauges are attached around the circumference of a hole in concrete, with radial strain gauges attached to the outside of them, and then the hole is drilled, and the stress acting on the concrete structure is estimated from the pattern of combinations of the strain gauge measurement values ​​after drilling.

[0004] Furthermore, Patent Document 2 discloses a method for estimating the residual prestress by attaching a biaxial strain gauge to the surface of concrete and cutting into it with a concrete core cutter. The strain released by the cutting is measured, and the difference between the released strain in the direction in which the residual prestress acts and the released strain in the perpendicular direction is used to eliminate most of the strain components due to internal constraints (the effects of drying shrinkage and creep strain), and the effective stress is calculated using the proposed formula.

[0005] Furthermore, Patent Document 3 discloses a method of measuring stress by drilling a hole in the center of the measurement area of ​​a structure to release the stress acting on the structure, detecting the strain changes that occur around the hole due to the release of stress, and analyzing the current stress in the measurement area based on this. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-60490 [Patent Document 2] Patent No. 5095258 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-303916 Summary of the Invention [Problem to be solved by the invention]

[0007] However, because all of the above-mentioned conventional methods for estimating the residual prestress of PC structures estimate compressive stress from measuring the strain in concrete that accompanies the release of stress at specific locations, estimating the residual prestress requires partially destroying the PC structure by drilling a core to release the stress, etc. Therefore, it is not possible to drill a core to measure strain at a location where strain has already been measured, which creates the problem that it is not possible to measure strain over time or estimate the residual prestress at the same location.

[0008] An object of the present invention is to provide a method for estimating the residual prestress force of a PC structure, which can estimate the residual prestress force without destroying the PC structure, and a strain measurement device for estimating the residual prestress force of a PC structure. [Means for solving the problem]

[0009] The premise of the present invention for solving the above problem is a method for estimating the residual prestress force of a PC structure into which prestress has been introduced.

[0010] The method for estimating the residual prestress force of a PC structure of the present invention based on the above premise comprises a strain measurement process in which strain is generated at a specific location and the strain is measured using a strain measurement means; a characteristic point identification process in which the relationship between the change in stress intensity and the change in strain at the specific location is determined and the bending point where the relationship between the change in stress intensity and the change in strain at the specific location changes is identified as the characteristic point; and an estimation process in which the remaining prestress force of the PC structure is estimated based on the relationship between the compressive stress intensity at dead load and the change in strain at the characteristic point, which has been prepared in advance.

[0011] In one example of the method for estimating the residual prestress force of a PC structure according to the present invention, the strain measuring step includes a step of generating strain at a specific location by loading and measuring the strain.

[0012] In another example of the method of estimating the residual prestress force of a PC structure of the present invention, the strain measurement process includes a cooling process in which strain is generated by cooling a specific location, and also includes a process in which, when the direction in which prestress is introduced is the x direction and the direction perpendicular to the x direction is the y direction, the x-direction strain and the y-direction strain of the specific location cooled in the cooling process are measured, and the characteristic point identification process includes a process in which the relationship between the x-direction strain and the y-direction strain is determined, and the bending point where the relationship between the x-direction strain and the y-direction strain changes is identified as the characteristic point.

[0013] In another example of the method for estimating the residual prestress force of a PC structure according to the present invention, the characteristic point specifying step calculates the change in strain at the characteristic point based on the following equation (1). (1)ε0'=Δε B / 0.3 ε0' is the compressive strain value under dead load (μ), Δε B is the value of the change distortion (μ) at the feature point.

[0014] In another example of the method for estimating the residual prestress force of a PC structure of the present invention, the estimation step calculates the compressive stress at dead load from the characteristic points based on the following equation (2), and estimates the residual prestress force based on the compressive stress at dead load. (2)σ0'=0.1×Δε B σ0' is the compressive stress under dead load (N / mm 2 ), Δε B is the value of the change distortion (μ) at the feature point.

[0015] In another example of the method for estimating the residual prestress force of a PC structure according to the present invention, the characteristic point identification step determines a linear relationship between the secant elastic modulus and the change in strain based on the relationship between the change in stress intensity and the change in strain at a specific location, and identifies the bending point where the linear relationship changes as the characteristic point.

[0016] In another example of the method for estimating the residual prestress force of a PC structure according to the present invention, the x-direction length and the y-direction length measured at a specific point are set to be the same length.

[0017] The premise of the present invention for solving the above-mentioned problems is a strain measurement device that is attached to a PC structure in order to estimate the remaining prestress force of the PC structure to which prestress has been introduced.

[0018] The strain measuring device of the present invention based on the above premise is characterized in that it comprises a specific location where a strain measuring means is attached, and a heat conducting member that is arranged to cover the specific location and can change the temperature, the specific location is cooled or heated via the heat conducting member, and the strain measuring means measures the strain generated at the specific location by the cooling or heating.

[0019] In one example of the strain measuring device of the present invention, the strain measuring means further includes a heat insulating material arranged on the outer periphery of the specific location.

[0020] Another example of the strain measuring device of the present invention further includes a lubricating oil filled between the specific location and the heat conducting member.

[0021] In another example of the strain measuring device of the present invention, when the direction in which prestress is introduced is defined as the x direction and the direction perpendicular to the x direction is defined as the y direction, the x-direction length and y-direction length measured at a specific location are set to the same length.

[0022] The method for estimating the residual prestress force of a PC structure of the present invention based on the above premise comprises a strain measurement step of generating strain at a specific location by heating and measuring the strain using a strain measurement means, a feature point identification step of identifying a feature point, which is a numerical value of the strain of the PC structure at which the relationship between the strain measured in the strain measurement step and the newly measured acoustic emission changes, and a residual prestress force estimation step of estimating the residual prestress force of the PC structure using the maximum compressive strain, which is the sum of the strain at the feature point and the compressive strain at dead load, and the Young's modulus of the PC structure.

[0023] The method for estimating the residual prestress force of a PC structure of the present invention based on the above premise comprises a heating process in which strain is generated by heating specific locations, and a cooling process in which strain is generated by cooling specific locations at a timing different from the heating process, a strain measurement process in which strain in the heating process and the cooling process is measured using a strain measurement means, a feature point identification process in which a feature point is identified, which is a numerical value of the strain of the PC structure at which the relationship between the strain measured in the heating process and the strain measured in the cooling process changes, and a residual prestress force estimation process in which the strain at the feature point and the Young's modulus of the PC structure are used to estimate the residual prestress force of the PC structure.

[0024] The method for estimating the residual prestress force of a PC structure of the present invention based on the above premise comprises a strain measurement process in which strain is generated at a specific location and the strain is measured by a strain measurement means; a feature point identification process in which first information, which is information about the strain measured in the strain measurement process, and feature points, which are numerical values ​​of the strain of the PC structure that change in relationship with second information that is different from the first information and is obtained by multiplying the first information by a specific coefficient, or that is newly measured; and a residual prestress force estimation process in which a predetermined calculation process is performed on the numerical values ​​of the feature points to estimate the remaining prestress force of the PC structure. [Effects of the Invention]

[0025] According to the present invention, the residual prestress force can be estimated using characteristic points identified by measuring strain generated at specific locations, so that the residual prestress force can be estimated without destroying the PC structure. [Brief explanation of the drawings]

[0026] [Figure 1] Diagram showing PCT digits. [Figure 2] 1 shows an example of a test specimen, where (1) is a front view showing a schematic cross-sectional structure of the test specimen, and (2) is a cross-sectional view of the test specimen in the XX direction. [Figure 3] Schematic diagram showing the stress-strain relationship. [Figure 4] Schematic diagram showing the change stress-change strain relationship. [Figure 5] A diagram showing the relationship between change in stress and change in strain. [Figure 6] FIG. 6 is a diagram illustrating a method for identifying feature points using a secant elastic modulus. [Figure 7] FIG. 10 is a diagram showing the relationship between the secant elastic modulus and the change in strain at a characteristic point. [Figure 8] 1 is a graph showing the relationship between compressive stress under dead load and strain change at characteristic points. [Figure 9] 3 is a flowchart showing the flow of processing in the method for estimating the residual prestress force of a PC structure according to the first embodiment of the present invention. [Figure 10] 6 is a flowchart showing the processing flow of a method for estimating the residual prestress force of a PC structure according to a second embodiment of the present invention. [Figure 11] FIG. 10 is a cross-sectional view showing the installation state of a strain measurement device for estimating the remaining prestress force of a PC structure according to a second embodiment of the present invention. [Figure 12] A view of the strain measurement device shown in Figure 11 as seen from a direction opposite to a specific location. [Figure 13] FIG. 12 is a plan view showing the strain measurement device shown in FIG. 11 with a heat conduction member removed. [Figure 14] FIG. 1 is a diagram showing the relationship between x-direction strain and y-direction strain. [Figure 15] 10 is a flowchart showing the processing flow of a method for estimating the residual prestress force of a PC structure according to a third embodiment of the present invention. [Figure 16] Time series diagram of change in strain εx, AE peak amplitude, AE energy, etc. [Figure 17] 10 is a flowchart showing the processing flow of a method for estimating a residual prestress force of a PC structure according to a fourth embodiment of the present invention. [Figure 18] FIG. 10 is a graph showing the εx-εy relationship during heating and cooling. [Figure 19] 3 is a flowchart showing the processing flow of a method for estimating the residual prestress force of a PC structure according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The method for estimating the residual prestress of a PC structure according to the present invention will be described in detail below with reference to the accompanying drawings: Figure 1 is a diagram showing a PCT girder as an example.

[0028] PCT girder 1 is a concrete block used in the construction of a PC bridge, which is an example of a PC structure. PCT girder 1 has a T-shaped cross section perpendicular to the axial direction (x direction in Figure 1). PCT girder 1 has tendons such as PC steel embedded in the axial direction, and prestress (force acting on the concrete by the tendons) is introduced.

[0029] When constructing PC bridges, the post-tensioning method is sometimes used, in which concrete is poured and cured at the construction site, and after the concrete has developed its strength, the PC steel strands are tensioned with hydraulic jacks or other tools to introduce prestress. The PC steel strands are placed inside sheaths, and after tensioning the PC steel strands, PC grout is filled into the sheaths. In existing PC bridges built using this post-tensioning method, depending on the technological level at the time of construction, there is a possibility that the PC grout was insufficiently filled. If the PC grout is insufficient, water may seep into the sheath, causing corrosion or fracture of the PC steel strands. If the PC steel strands fracture, the prestress introduced into the PC bridge may decrease, potentially reducing its load-bearing capacity. For this reason, the integrity of PC bridges must be evaluated periodically after construction.

[0030] The method for estimating the residual prestress force of a PC structure according to the present invention generates strain (surface strain) at a specific location of the PC structure, measures the strain, and then estimates the remaining prestress force using the characteristic points (described below). A PC structure refers to a structure constructed using PC (prestressed concrete), including bridge girders and beams. The specific location refers to the portion where strain is measured to estimate the remaining prestress force. In Figure 1, the lower edge of the PCT girder 1 is designated as the specific location 2, but the specific location may be another portion of the lower edge, or a portion other than the lower edge, such as the upper edge if prestress force remains. Furthermore, while Figure 1 shows a PCT girder 1, other shapes, such as an I-girder or a box girder, may also be used.

[0031] Next, a method for estimating the residual prestress force of a PC structure according to a first embodiment of the present invention will be explained, but before that, the underlying concept will be explained.

[0032] FIG. 2 shows an example of a test specimen, where (1) is a front view of the test specimen and (2) is a cross-sectional view of the test specimen taken along the XX direction.

[0033] In order to examine a method for estimating the residual prestress of a PC structure, a test piece 3 was prepared and a loading test was carried out. From the results of the loading test, the relationship between the compressive stress at dead load and the strain change at characteristic points, which will be described later, was prepared in advance.

[0034] First, the procedure for the loading test will be explained. Referring to Figure 2, specimen 3 is a PC simple girder with a rectangular cross section perpendicular to the axial direction (left-right direction in Figure 2(1)), and is set to a girder length of 8.0 m, a span of 7.5 m, a rectangular cross section girder height (vertical direction in Figure 2(2)) of 1.0 m, and a cross section width (left-right direction in Figure 2(2)) of 0.35 m. Two prestressing tendons 4a and 4b are embedded vertically inside specimen 3 in the axial direction (left-right direction in Figure 2(1)), and prestress is introduced into the concrete of specimen 3 by applying tension to the prestressing tendons 4a and 4b. The level of prestress introduced into specimen 3 (prestress level) is a lower edge compressive stress of 7.5 N / mm at the center cross section of the span under dead load. 2 The prestress level at which the load is applied is set to 100%, and three levels of prestress application rates are set: 100%, 75%, and 50 percent.

[0035] The load was applied at one point in the center of the span, and in order to prevent bending cracks from occurring in the specimen due to the load, the composite bending stress at the lower edge of the center of the span at the time of maximum load application was set to -1.0 N / mm 2 The maximum load was determined by a plane frame analysis so that the maximum load, dead load, and concrete stress at the maximum load for each prestress level are shown in Table 1.

[0036] [Table 1] Figure 3 is a schematic diagram showing the stress-strain relationship, Figure 4 is a schematic diagram showing the change stress-change strain relationship, Figure 5 is a diagram showing the relationship between change stress and change strain, and Figure 6 is a diagram showing the relationship between compressive stress at dead load and change strain at a characteristic point.

[0037] The loading test was conducted by applying a load to a single point in the center of the span (arrow in Figure 2(1)), which was designated as the cross section where a large tensile stress would occur due to the live load. The stress change Δσ on the tensile side of the cross section due to the applied load was estimated. The strain change Δε on the tensile side of the cross section due to the applied load was also measured. The stress change Δσ on the tensile side of the cross section due to the applied load can be estimated using structural calculations or from the strain change on the compressive side of the cross section. The strain change Δε on the tensile side of the cross section due to the applied load can be measured using strain gauges or optical fiber sensors. In this loading test, the lower edge of specimen 3 was designated as specific point 5. A strain gauge (strain measurement device) was attached to specific point 5, and strain was generated at specific point 5 by loading, and the amount of strain change was measured. The maximum load was applied and then unloaded three times for each prestress level. As a result, referring to Figure 3, it was confirmed that when prestress was introduced into Specimen 3, the relationship between stress (tensile stress) and strain (tensile strain) decreased parabolically during the compressive stress reduction process. The stress-strain relationship of concrete shown in Figure 3 is a coordinate system in which the compression direction is positive. In contrast, Figure 4 shows a coordinate system in which the coordinate origin O is at the time of dead load (starting point of measurement), the tensile direction is positive, the horizontal axis is the strain change due to loading Δε, and the vertical axis is the changed stress intensity due to loading Δσ.

[0038] Next, referring to Figure 5, it was confirmed that the relationship between the change in stress Δσ and the change in strain Δε at specific point 5 consists of two types of parabolas. The starting point of parabola 1 passes through the origin O, and the end point of parabola 2 passes through (ε0, σ0). The bending point where the relationship changes from parabola 1 to parabola 2 is called the characteristic point (Δε B , Δσ B ) from Figure 5. B = 0.3 × ε0, where ε0 is the strain value (μ) at the end point of parabola 2, and Δε B is the value of the change distortion (μ) at the feature point.

[0039] Here, a method for identifying feature points using the secant elastic modulus will be described.

[0040] FIG. 6 is a diagram illustrating a method for identifying characteristic points using the secant elastic modulus, and FIG. 7 is a diagram illustrating the relationship between the secant elastic modulus and the change in strain at the characteristic points.

[0041] Referring to Figure 6(1), the secant elastic modulus E d This refers to the gradient of a line connecting the origin of the relationship between the change stress Δσ and the change strain Δε shown in Figure 5 and an arbitrary point on the Δσ-Δε curve.

[0042] Referring to Figure 6(2), the secant elastic modulus E d The relationship between the strain change Δε and the secant elastic modulus E is shown on the horizontal axis. d If the function form of Δσ-Δε is f(X), the secant elastic modulus E d The relationship between the strain and the change in strain Δε is as follows: E d =f(X) / X If f(X)=aX, then E d (X)=aX / X=a(constant value) f(X)=aX 2 +bX, E d (X)=(aX 2 +bX) / X=aX+b(straight line) f(X)=aX 2 +bX+c, E d (X)=(aX 2 +bX+c) / X=aX+b+c / X(hyperbola) 5 and 7, the relationship between the change in stress Δσ and the change in strain Δε at the specific point 5 was obtained, and then the secant elastic modulus E d The relationship between the strain and the change in strain Δε is obtained.

[0043] The horizontal axis represents the change in strain Δε, and the vertical axis represents the secant elastic modulus E d When the two types of parabolas (parabola 1 and parabola 2) shown in Figure 5 are taken, they become linear as shown in Figure 7. Then, the change strain Δε B As shown in Figure 7, the change in strain at the break point ΔεB It was confirmed that can be calculated from 0.3 × strain ε0.

[0044] As mentioned above, the secant elastic modulus E d By using this, the secant elastic modulus E is calculated based on the relationship between the change in stress Δσ and the change in strain Δε at the specific point 5. d The relationship between the strain change Δε and the linear relationship can be linearly calculated, and the bending points where the linear relationship changes can be identified as the characteristic points. This makes it easier to identify the characteristic points because the characteristic points are identified from the bending points where the linear relationship changes.

[0045] Next, the change strain Δε at the characteristic points B In order to obtain the relationship between the compressive strain ε0' at dead load and the stress change Δσ-strain change Δε relationship at the characteristic point when compressive stress is released, the stress change Δσ at the characteristic point was calculated from the stress change Δσ-strain change Δε relationship at the time of release of compressive stress. B The results of the reconfirmation are shown in Table 2.

[0046] [Table 2] For Reference Example 1, the prestress levels were set as follows: 100%, 75%, 50%, cross-sectional shape: rectangular, girder height-span ratio: 1 / 7.5, PC steel type: SWPR7AL (7Φ12.4), bottom edge rebar amount: 3-D13 (three D13 rebars inserted), and grouting: none.

[0047] For Reference Example 2, the prestress levels were set as follows: 100%, 70%, 50%, cross-sectional shape: rectangular, girder height-span ratio: 1 / 6.4, PC steel type: SBPR930 / 1180 (Φ32), amount of lower edge reinforcement: 3-D13 (three D13 reinforcement bars inserted), and grouting: none.

[0048] For Reference Example 3, the prestress levels were set as follows: 100%, 70%, 50%, cross-sectional shape: rectangular, girder height-span ratio: 1 / 6.4, PC steel type: SBPR930 / 1180 (Φ32), amount of lower edge reinforcement: 3-D13 (three D13 reinforcement bars inserted), and grouting: present.

[0049] For Reference Example 4, the prestress levels were set as follows: 100%, 70%, 50%, cross-sectional shape: rectangular, girder height-span ratio: 1 / 14.5, PC steel type: SWPR7AL (7Φ12.4), amount of lower edge reinforcement: 3-D13 (three D13 reinforcement bars inserted), and grouting: none.

[0050] For Reference Example 5, the prestress levels were set as follows: 100%, 70%, 50%, cross-sectional shape: rectangular, girder height-span ratio: 1 / 14.5, PC steel type: SWPR7AL (7Φ12.4), amount of lower edge reinforcement: 3-D19 (three D19 reinforcement bars inserted), and grouting: none.

[0051] For Reference Example 6, the prestress levels were set as follows: 100%, 80%, 60%, cross-sectional shape: T-girder, girder height-span ratio: 1 / 17, PC steel type: SWPR7BL (7Φ9.5), amount of lower edge reinforcement: 4-D13 (four D13 reinforcement bars inserted), and grouting: none.

[0052] From Table 1, the change strain Δε at the characteristic points B is in the range of 28.4% to 40.0% of the dead load strain ε0' (Δε B It was confirmed that the average value of / ε0' was 29.7%). That is, 0.28ε0' ≦ the change strain Δε at the characteristic point B Therefore, regardless of the prestress level, cross-sectional shape, girder height-span ratio, type of PC steel, amount of bottom edge reinforcing bars, or whether or not grout is used, ε0' ≒ Δε B It can be seen that there is a relationship of equation (1) shown as / 0.3. ε0' is the value of compressive strain under dead load (μ), Δε B is the value of the change distortion (μ) at the feature point.

[0053] As described above, the residual prestress force estimation method of the present invention uses the amount of reduction in stress and strain from the time of dead load, and therefore uses coordinate axes in which the coordinate origin O is set at the time of dead load (measurement start point), the X axis represents the strain change Δε due to loading, and the Y axis represents the stress change Δσ due to loading (both with the tensile direction being positive).

[0054] Next, referring to Figure 8, the compressive stress intensity σ0' under dead load and the change in strain Δε at the characteristic point B Specifically, the vertical axis represents the compressive stress σ0' under dead load, and the horizontal axis represents the change in strain Δε at the characteristic point. B As a result, the concrete nominal strength (36-40N / mm 2 ), the characteristic point Δε B Based on the compressive stress under dead load σ0', the following equation (2) was obtained: σ0' is the compressive stress under dead load (N / mm 2 ), Δε B is the value of the change distortion (μ) at the feature point. σ0'=0.1×Δε B (2) Since the compressive stress under dead load is a parameter determined by the sum of the dead load and prestress force, as shown in Table 1 above, the remaining prestress force of a PC structure can be estimated by eliminating the influence of the dead load.

[0055] Next, a method for estimating the residual prestress force of a PC structure according to the first embodiment of the present invention will be described.

[0056] FIG. 9 is a flowchart showing the flow of processing in the method for estimating the residual prestress force of a PC structure according to the first embodiment of the present invention.

[0057] First, a strain measuring means 11 (strain gauge) is attached to the lower edge of the PCT girder.

[0058] Next, referring to Figure 8, strain is generated at a specific location 2 on the lower edge of the PCT girder 1 by live load, and the strain in the x direction (axial direction, the direction in which prestress is introduced) and the strain in the y direction (direction perpendicular to the x direction) are measured (step S10).

[0059] Next, the relationship between the change in stress intensity Δσ and the change in strain Δε at the specific point 2 is found, and the bending point where the relationship between the change in stress intensity Δσ and the change in strain Δε at the specific point 2 changes is identified as a characteristic point (step S11). Specifically, the horizontal axis is the change in strain Δε, and the vertical axis is the change in stress Δσ. This makes it possible to confirm two types of parabolas. The bending point where the relationship between the two types of parabolas changes is identified as a characteristic point. Note that the change in strain Δε at the characteristic point is calculated based on equation (1). B In this case, it is not necessary to create a stress-strain diagram, and it is easier to identify the characteristic points.

[0060] Next, the change strain Δε at the characteristic points B The value of is introduced into equation (2) to estimate the compressive stress intensity σ0' under dead load. Then, the residual prestress force of the PC structure can be estimated from the compressive stress intensity σ0' under dead load (step S12).

[0061] As described above, the method for estimating the residual prestress of a PC structure of the present invention involves determining the relationship between the change in stress and the change in strain at a specific location to identify a characteristic point, and then estimating the residual prestress of the PC structure based on the previously prepared relationship between the compressive stress under dead load and the change in strain at the characteristic point. This configuration allows the residual prestress to be estimated without destroying the PC structure. Unlike conventional methods that require drilling cores to measure strain, this method enables time-dependent strain measurement and estimation of the residual prestress at the same location. Furthermore, the remaining prestress can be estimated at any desired timing, regardless of the condition of the PC structure, regardless of the number of years since construction, making this a highly versatile estimation method.

[0062] The method for estimating the residual prestress of a PC structure of the present invention is configured to generate strain at specific locations by loading and measure the strain, thereby making it possible to estimate the residual prestress based on the measurement results of the strain caused by loading the PC structure. Therefore, the residual prestress can be estimated without destroying the PC structure. Furthermore, when strain is measured using traffic loads, the residual prestress can be estimated with a simple device configuration.

[0063] The method for estimating the residual prestress force of a PC structure of the present invention is to estimate the characteristic points (the change in strain at the characteristic points Δε B ), the residual prestress force can be easily estimated. Moreover, the estimation step is configured to calculate the residual prestress force based on equation (2) from the characteristic points. As a result, the compressive stress at dead load is calculated based on equation (2) from the characteristic points, and the residual prestress force is estimated based on the compressive stress at dead load, so the residual prestress force can be easily estimated. Incidentally, in the method for estimating the residual prestress force of a PC structure according to the first embodiment of the present invention, strain is generated by loading, but strain can also be generated by temperature changes. Means for generating strain by temperature changes include cooling and heating.

[0064] Next, before explaining the method for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention, we will explain the strain measurement device used to estimate the residual prestress force of a PC structure according to the second embodiment of the present invention.

[0065] FIG. 10 is a flowchart showing the processing flow of the method for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention, FIG. 11 is a cross-sectional view showing the installation state of a strain measurement device for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention, FIG. 12 is a view from the direction facing a specific location of the strain measurement device shown in FIG. 11, FIG. 13 is a plan view showing the strain measurement device shown in FIG. 11 with the heat conduction member removed, and FIG. 14 is a diagram showing the relationship between x-direction strain and y-direction strain.

[0066] 11 to 13, a strain measuring device 10 is attached to a specific location 6 of a PC structure to estimate the remaining prestress force of the PC structure to which prestress has been introduced. The strain measuring device 10 is mainly composed of a strain measuring means 11, a heat conducting member 12, and a heat insulating material 13.

[0067] The strain measurement means 11 is a strain gauge that measures strain at a specific location. When the direction in which prestress is applied is defined as the x direction and the direction perpendicular to the x direction is defined as the y direction, the strain in the x direction and the strain in the y direction at a specific location are measured. Note that strain can be measured using a biaxial strain gauge, or two uniaxial strain gauges that are orthogonal to each other.

[0068] The heat conducting member 12 is made of a copper plate, is temperature-changeable, and has a disk shape larger than the range of the specific location 6. The effect of this design will be described later. The size of the heat conducting member 12 is set to a diameter of 90 mm and a thickness of 5 mm.

[0069] The heat insulating material 13 has a disk shape and has a circular opening in its center that corresponds to the specific location 6. The size of the heat insulating material 13 is set to an outer diameter of 200 mm, an inner diameter of 70 mm, and a thickness of 10 mm. The size of the specific location 6 is set to a diameter of 70 mm. When installed, the heat insulating material 13 is placed on the outer periphery of the specific location 6. This configuration suppresses heat transfer between the specific location 6 and the outside, thereby stabilizing the surface temperature of the specific location 6.

[0070] Referring to Figure 11, the installation of the strain measuring device 10 involves first attaching the strain measuring means 11 to a specific location 6 of the PC structure. Then, a heat insulating material 13 is placed around the periphery of the specific location 6 and attached to the surface of the PC structure. Next, a heat conducting member 12 is placed so as to cover the specific location 6 and attached to the heat insulating material 13.

[0071] As described above, the heat conduction member 12 has a disk shape larger than the specific location 6 and is arranged to reliably cover the entire specific location 6. With this configuration, the specific location 6 is entirely covered by the heat conduction member 12, allowing the entire specific location 6 to be cooled or heated. However, an excess portion 16 of the heat conduction member 12 protrudes from the specific location 6. The temperature of this excess portion 16 may change due to external influences, and the specific location 6 may not be uniformly cooled or heated due to the temperature change of the excess portion 16. Therefore, the heat insulating material 13 is arranged around the periphery of the specific location 6 so as to abut the PC structure side of the excess portion 16. With this configuration, the heat conduction member 12 is arranged to entirely cover the specific location 6, allowing the specific location 6 to be cooled or heated via the heat conduction member 12 without being affected by external influences. Therefore, the specific location 6 can be uniformly cooled or heated without any omissions.

[0072] The structure is configured so that lubricating oil 14 is filled between the specific location 6 and the heat conducting member 12. The lubricating oil 14 is filled within an area of ​​70 mm in diameter and 10 mm in thickness. This allows the strain measuring means 11 to be covered with lubricating oil, allowing the strain measuring means 11 to accurately measure strain regardless of the cooling or heating temperature. This completes the installation of the strain measuring device 10. With this configuration, when the heat conducting member is cooled or heated by a coolant or a hot air dryer, etc., the specific location 6 is cooled or heated through the heat conducting member, causing strain. Therefore, strain can be measured without destroying the PC structure.

[0073] Next, the principle of the method for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention will be described.

[0074] First, the relationship between surface temperature and strain was determined through a preliminary analysis performed using an analytical model. Specifically, the measurement point was cooled in the analytical model to generate strain. Then, the x-direction strain was plotted on the horizontal axis and the temperature at the measurement point on the vertical axis. Also, the y-direction strain was plotted on the horizontal axis and the temperature at the measurement point on the vertical axis. After that, the x-direction strain was plotted on the horizontal axis and the y-direction strain on the vertical axis. As a result, it was confirmed that up to an generated strain of approximately 180 μm, there was a direct proportional relationship between the y-direction strain at the measurement point and the x-direction strain. Therefore, it can be said that the y-direction strain can be used as an alternative indicator of stress intensity.

[0075] In addition, in the loading test conducted in advance, load was applied to the measurement points A and B of the specimen shown in Figure 2 to generate strain. The compressive stress at the dead load was almost zero at measurement point A and 5.5 N / mm at measurement point B. 2 Therefore, in the preliminary tests, measurement point A was assumed to be concrete without prestressing, and measurement point B was assumed to be PC with prestressing.

[0076] After that, a partial cooling test was conducted. Measurement points A and B were cooled to generate strain, which was then measured. The horizontal axis represents the x-direction strain, and the vertical axis represents the temperature at the measurement points. The horizontal axis also represents the y-direction strain, and the vertical axis represents the temperature at the measurement points.

[0077] In Figure 14, the left side shows the relationship between the x-direction strain and the y-direction strain at measurement point A, and the right side shows the relationship between the x-direction strain and the y-direction strain at measurement point B. Because the compressive stress at measurement point A under dead load is almost zero, we confirmed that the relationship between the y-direction strain and the x-direction strain at measurement point A is directly proportional, just as in the case of the analytical model.

[0078] On the other hand, at measurement point B, because there is an initial compressive stress in the x direction, it was confirmed that a break point occurs in the relationship between the x-direction strain and the y-direction strain even above the proportional limit temperature (within the proportional range).

[0079] Here, when strain is generated by cooling a circular shape, the stress and strain in the x and y directions are equal (σx = σy, εx = εy). Furthermore, stress and strain are proportional (σx ∽ εx, σy ∽ εy). Therefore, the relationship between stress and strain in the x and y directions is σy ∽ εx, εy ∽ εx. Therefore, the relationship between Δσx and Δεx and the relationship between Δεy and Δεx are similar, so if there is a break point, it will occur at the same position. Therefore, the break point (inflection point) that occurs within the proportional range in the relationship between the y-direction strain and the x-direction strain at measurement point B can be said to correspond to the characteristic point identified when strain is generated by loading.

[0080] Next, a method for estimating the residual prestress force of a PC structure according to a second embodiment of the present invention will be described.

[0081] 10, first, strain is generated by cooling specific location 6 of the PC structure, and the strain is measured (step S50). When measuring the strain, a coolant such as dry ice (with a surface temperature of, for example, -50°C) is applied to the surface of heat conductive member 12. This causes specific location 6 to be cooled via heat conductive member 12 so that its surface temperature drops by, for example, about 10 to 15°C, generating strain. Then, strain measuring means 11 measures the x-direction strain and y-direction strain generated at specific location 6 by cooling.

[0082] Next, the relationship between the x-direction strain and the y-direction strain is calculated, and the inflection points where the relationship between the x-direction strain and the y-direction strain changes are identified as characteristic points (step S51). Specifically, the x-direction strain is plotted on the horizontal axis, and the y-direction strain is plotted on the vertical axis. Two types of curves then appear, and the inflection points where the relationship between them changes are identified as characteristic points.

[0083] Finally, the remaining prestress is estimated using equation (2) (step S52). Specifically, the strain value at the characteristic point is substituted into equation (2) to calculate the compressive stress under dead load. Then, the remaining prestress is estimated based on the compressive stress under dead load.

[0084] The method for estimating the residual prestress of a PC structure according to the second embodiment of the present invention is configured to generate strain at a specific location 6 by cooling and measure the strain, thereby making it possible to estimate the residual prestress based on the measurement results of the strain caused by cooling the PC structure. Therefore, it is possible to estimate the residual prestress without destroying the PC structure.

[0085] Furthermore, in the method for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention, the x-direction length and the y-direction length measured at the specific point 6 are set to be the same. This configuration creates conditions similar to those in the x-direction and y-direction of the circular part measured in the preliminary partial cooling test, and the x-direction stress and y-direction stress measured at the specific point 6 become equal, making it easier to identify the characteristic point from the relationship between the x-direction strain and the y-direction strain.

[0086] In the above embodiments, strain gauges are used as the strain measuring means, but other measuring devices may be used as long as they are capable of measuring strain.

[0087] In addition, in each of the above embodiments, the feature points are identified using the secant elastic modulus, but the secant elastic modulus may not be used. If the secant elastic modulus is used, the relationship curve can be expressed linearly, making it easier to obtain the feature points.

[0088] Furthermore, in each of the above embodiments, the characteristic points are identified using the secant elastic modulus for the relationship between stress and strain in the first embodiment, but the characteristic points can also be identified using the secant elastic modulus for the relationship between the x-direction strain and the y-direction strain in the second embodiment. In this case, considering K=Δεy / Δεx for the relationship between the x-direction strain and the y-direction strain, the relationship between the secant elastic modulus and the change in strain can be linearly obtained, and the bending point where the linearity changes can be identified as the characteristic point.

[0089] Furthermore, in each of the above embodiments, the specific location is a circular location at the lower edge of the PCT girder, but other locations may be selected, and other shapes may also be used.

[0090] Furthermore, in each of the above embodiments, the y direction is a direction perpendicular to the x direction, but it may be a direction substantially perpendicular to the x direction or a direction intersecting the x direction.

[0091] Furthermore, in the second embodiment, the x-direction length and y-direction length measured at the specific location are set to be the same, but they may be different lengths.

[0092] Furthermore, in the second embodiment, the specific location is circular, but it does not have to be circular. For example, it may be a polygonal shape such as a square, octagon, or dodecagon. In this case, the measured x-direction length and y-direction length will be the same, making it easier to identify the feature point.

[0093] Furthermore, in the second embodiment, a copper plate is used as the heat conducting member, but it may be made of other materials, such as aluminum. In this case, it is preferable that the thermal conductivity of the material is 100 (W / m K) or more.

[0094] Furthermore, in the second embodiment, dry ice is used as the coolant, but it may be cooled by other members such as a Peltier element.

[0095] Furthermore, in the second embodiment, the heat insulating material has a specific shape, size, and thickness, but it may have other shapes. Also, the heat insulating material may not be present.

[0096] Furthermore, in the second embodiment, the heat insulating material is arranged on the periphery of the specific location, but it may be arranged in other ways, such as being arranged on a part of the specific location.

[0097] Furthermore, in the second embodiment, the size of the specific location was set to 70 mm in diameter, but it may be larger or smaller, or may have other sizes and shapes, or if circular, may have other diameters. A shape and size that can accommodate the strain measurement means and that facilitates uniform cooling is preferred, for example, a circle with a diameter of 35 mm to 140 mm is preferred.

[0098] Furthermore, in the second embodiment described above, low-temperature lubricant oil is provided in a specific thickness in a specific range, but other materials that protect the strain measurement means may be filled. Also, instead of filling, it may be applied, etc. Furthermore, low-temperature lubricant oil may not be necessary. Furthermore, it may be filled in a different location. Furthermore, it may be filled to a different thickness.

[0099] Furthermore, in the second embodiment, the heat conducting member is formed to be larger than the specific portion, but it may be of other size, such as the same size as the specific portion.

[0100] Furthermore, in the second embodiment, the heat insulating material, heat conducting material, and other members are formed to a specific thickness, but they may be formed to a different thickness.

[0101] In the second embodiment, the surface temperature of the dry ice or the like is set to -50°C, but it may be set to another temperature. Furthermore, it is preferable to lower the surface temperature of the specific location by 10 to 15°C. In this way, a strain of about 100 to 150 μm, which is necessary for identifying the characteristic points, can be obtained, making it easier to estimate the remaining prestress force. Furthermore, the surface temperature of the specific location is lowered by 10 to 15°C to generate strain, but it may be set to another numerical range, such as less than 10°C or more than 15°C.

[0102] Next, we will explain a method for estimating the residual prestress of a PC structure according to a third embodiment of the present invention. The method for estimating the residual prestress of a PC structure according to the third embodiment of the present invention estimates the residual prestress by utilizing the Kaiser effect, a phenomenon in which, when concrete is repeatedly compressed, acoustic emissions (AE) are barely detected until the prestress is reached when the prestress is removed and then reapplied.

[0103] FIG. 15 is a flowchart showing the process flow of the method for estimating the residual prestress force of a PC structure according to the third embodiment of the present invention, and FIG. 16 is a flowchart showing the process flow of the method for estimating the residual prestress force of a PC structure according to the third embodiment of the present invention. x 10 is a time series diagram of AE peak amplitude, AE energy, etc.

[0104] Referring to Fig. 15, first, a specific location 6 of the PC structure is heated to generate strain, and the strain is measured (step 60). When measuring the strain, a strain measuring device similar to the strain measuring device 10 used in the method for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention is used, and the surface of the heat conducting member 12 is heated with a hot air dryer such as a hairdryer. As a result, the specific location 6 is heated via the heat conducting member 12, and strain is generated. Then, the strain measuring device 10 measures the x-direction strain generated at the specific location 6 by heating.

[0105] Next, acoustic emission measurement (AE measurement) is used to detect elastic waves associated with microscopic destruction phenomena during heating (step 61).

[0106] Next, a characteristic point, which is a numerical value of the strain of the PC structure where the relationship between the strain measured in the strain measurement process and the newly measured acoustic emission changes, is identified (step 62). Specifically, referring to FIG. 16, the change in strain ε x Create a time series diagram of the AE peak amplitude, AE energy, etc. The AE measurement value begins to increase at time t1, and the change in strain at that time is ε1' (the "'" indicates that compressive strain or compressive stress is to be interpreted as a positive value). According to the Kaiser effect, when the compressive strain increases by ε1' from the initial strain ε0 (compressive strain under dead load = strain at the start of measurement; unknown), the maximum compressive strain experienced ε max (i.e., ε0+ε1'=ε max ).

[0107] Experienced maximum compressive stress σ of concrete max If the calculated value immediately after the introduction of prestress in the design calculation sheet is used, ε max =σ max / E c E c refers to Young's modulus, which is the proportional constant between stress and strain in PC structures.

[0108] From the above, the following equation is obtained: Finally, the remaining prestress force is estimated using the following equation (step S62).

[0109] ε0=σ max / E c -ε1' Residual prestress (compressive stress at dead load) σ0=E c ×ε0=σ max -E c ×ε1' The method for estimating the residual prestress of a PC structure according to the third embodiment of the present invention is configured to generate strain by heating, measure the strain, identify characteristic points that are numerical values ​​of the strain of the PC structure where the relationship between the strain and acoustic emission changes, and estimate the residual prestress of the PC structure using the maximum compressive strain and the Young's modulus of the PC structure, thereby making it possible to estimate the residual prestress using the strain generated by heating. As a result, the residual prestress can be estimated without destroying the PC structure.

[0110] Next, a method for estimating the residual prestress force of a PC structure according to a fourth embodiment of the present invention will be described.

[0111] FIG. 17 is a flowchart showing the flow of processing of the method for estimating the residual prestress force of a PC structure according to the fourth embodiment of the present invention, and FIG. 18 is a flowchart showing the flow of processing of the residual prestress force of a PC structure according to the fourth embodiment of the present invention. x -ε y FIG.

[0112] 17, first, a specific location 6 of the PC structure is heated to generate strain, and the strain in the x direction (the direction in which prestress is introduced) and the strain in the y direction (the direction perpendicular to the x direction) are measured (step 70). Note that the measurement of strain due to heating is performed in the same manner as in the method for estimating the residual prestress force of a PC structure according to the third embodiment of the present invention, and therefore the description thereof will not be repeated here.

[0113] Next, strain is generated by cooling a specific location 6 of the PC structure, and the x-direction strain and y-direction strain are measured (step 71). Note that the measurement of strain due to cooling is performed in the same manner as in the method for estimating the residual prestress force of a PC structure according to the second embodiment of the present invention, and therefore the description thereof will not be repeated here.

[0114] Next, a characteristic point, which is a numerical value of the strain of the PC structure where the relationship between the strain measured in the heating process and the strain measured in the cooling process changes, is identified (step 72). Specifically, referring to FIG. 18, ε x -ε y If a graph showing the relationship is drawn and approximated with a quadratic curve passing through the origin, the strain (ε x ) represents the initial strain ε0 (compressive strain under dead load = strain at the start of measurement; unknown). Finally, the remaining prestress force is estimated using the following equation (step S72).

[0115] Residual prestress (compressive stress at dead load) σ0=E c ×ε0 The method for estimating the residual prestress of a PC structure according to the fourth embodiment of the present invention is configured to generate strain by heating and generate strain by cooling at a timing separate from the heating, and measure the strain in each case of heating and cooling, thereby making it possible to estimate the residual prestress using the strain generated by heating and cooling. As a result, the residual prestress can be estimated without destroying the PC structure.

[0116] FIG. 19 is a flowchart showing the process flow of the method for estimating the residual prestress force of a PC structure according to an embodiment of the present invention.

[0117] While the first to fourth embodiments of the present invention have been described above, referring to Fig. 19, the present invention can be said to be a method for estimating the residual prestress force in a prestressed PC structure, comprising: a strain measurement step (step 80) of generating strain at specific locations and measuring the strain using a strain measurement device; a feature point identification step (step 81) of identifying feature points, which are numerical values ​​of strain in the PC structure that have a changing relationship with first information, which is information related to the strain measured in the strain measurement step, obtained by multiplying the first information by a specific coefficient, or with second information, which is newly measured and different from the first information; and a residual prestress force estimation step (step 82) of performing a predetermined calculation process on the numerical values ​​of the feature points to estimate the residual prestress force in the PC structure. This configuration allows the residual prestress force to be estimated using the feature points identified by measuring the strain generated at the specific locations, thereby making it possible to estimate the residual prestress force without destroying the PC structure.

[0118] There are several possible methods for generating strain. For example, strain may be generated by loading as in the first embodiment, or by cooling as in the second embodiment. Strain may also be generated by heating as in the third embodiment, or by cooling at a timing different from the heating timing as in the fourth embodiment. In the first and second embodiments, the first information is the change in strain, and the second information is the change in stress. The characteristic point identification step determines the relationship between the change in stress and the change in strain at a specific location and identifies, as the characteristic point, a bending point where the relationship between the change in stress and the change in strain at the specific location changes. The residual prestress estimation step estimates the residual prestress of the PC structure based on the previously prepared relationship between the compressive stress at dead load and the change in strain at the characteristic point. In a third embodiment, the first information is strain due to heating, and the second information is acoustic emission, and the residual prestress force estimation step can estimate the residual prestress force of the PC structure using the maximum compressive strain, which is the sum of the strain at the characteristic point and the compressive strain at dead load, and the Young's modulus of the PC structure.In a fourth embodiment, the first information is strain due to heating, and the second information is strain due to cooling, and the residual prestress force estimation step can estimate the residual prestress force of the PC structure using the strain at the characteristic point and the Young's modulus of the PC structure.

[0119] In the third and fourth embodiments, strain gauges are used as the strain measuring means, but other measuring devices may be used as long as they are capable of measuring strain.

[0120] Furthermore, in the third and fourth embodiments, heating is performed by a specific method, but the heating method is not particularly limited as long as it is possible to heat a specific location.

[0121] Furthermore, in the fourth embodiment, the strain is measured in the heating step and the cooling step, but the order of the heating step and the cooling step may be any. [Explanation of symbols]

[0122] 1...PCT digit 2...Specific location 3...Specimen 4…PC steel material 5...Specific location 6...Specific location 10...Strain measurement device 11...Strain measurement means 12...Heat conductive material 13...Insulation material 14…Low temperature lubricating oil 16...Excess part In addition, the same reference numerals in each drawing indicate the same or corresponding parts.

Claims

1. A method for estimating the remaining prestress force of a PC structure into which prestress is introduced, comprising: a strain measurement step of generating a strain at a specific location and measuring the strain with a strain measurement means; a characteristic point identifying step of determining a relationship between the change in stress intensity and the change in strain at the specific location and identifying a bending point at which the relationship between the change in stress intensity and the change in strain at the specific location changes as a characteristic point; A method for estimating the residual prestress force of a PC structure, comprising an estimation step of estimating the residual prestress force of the PC structure based on a relationship between a previously prepared compressive stress intensity under dead load and the change in strain at the characteristic point.

2. 2. The method for estimating a residual prestress force of a PC structure according to claim 1, wherein the strain measuring step includes a step of generating strain at the specific location by loading and measuring the strain.

3. the strain measuring step includes a cooling step of generating the strain by cooling the specific location, and also includes a step of measuring the x-direction strain and the y-direction strain of the specific location cooled in the cooling step, where the direction in which the prestress is introduced is defined as the x-direction and the direction perpendicular to the x-direction is defined as the y-direction; 2. The method for estimating the residual prestress force of a PC structure according to claim 1, wherein the characteristic point identifying step includes a step of determining the relationship between the x-direction strain and the y-direction strain, and identifying, as the characteristic point, a bending point where the relationship between the x-direction strain and the y-direction strain changes.

4. 3. The method for estimating a residual prestress force of a PC structure according to claim 1, wherein the step of identifying the characteristic points calculates a change in strain at the characteristic points based on the following formula (1): (1)e ０ '=No Ｂ / 0.3 ε ０ ' is the value of compressive strain under dead load (μ), Δε Ｂ is the value of the change distortion (μ) at the feature point.

5. 4. The method for estimating the residual prestress force of a PC structure according to claim 1, wherein the estimation step calculates the compressive stress intensity under dead load from the characteristic points based on the following formula (2), and estimates the residual prestress force based on the compressive stress intensity under dead load. (2)s ０ '=0.1×No Ｂ σ ０ ' is the compressive stress at dead load (N / mm ２ ), Δε Ｂ is the value of the change distortion (μ) at the feature point.

6. 2. The method for estimating the residual prestress force of a PC structure according to claim 1, wherein the characteristic point identifying step linearly determines the relationship between the secant elastic modulus and the change in strain based on the relationship between the change in stress intensity and the change in strain at the specific location, and identifies the bending point at which the linear relationship changes as the characteristic point.

7. 4. The method for estimating the residual prestress force of a PC structure according to claim 3, wherein the x-direction length and the y-direction length measured at the specific location are set to be the same length.

8. A strain measurement device attached to a specific location of a PC structure in order to estimate a residual prestress force of the PC structure into which prestress is introduced, a strain measuring means attached to the specific location; a heat conduction member that is arranged to cover the specific location and can change the temperature, the specific location is cooled or heated via the heat conduction member, The strain measuring means is a strain measuring device that measures strain generated at the specific location due to cooling or heating.

9. The strain measurement device according to claim 8 , further comprising a heat insulating material arranged on an outer periphery of the specific location.

10. The strain measurement device according to claim 8 or 9, further comprising a lubricant oil filled between the specific location and the heat conducting member.

11. 9. The strain measuring device according to claim 8, wherein the x-direction length and the y-direction length measured at the specific location are set to be the same length, when the direction in which the prestress is introduced is defined as the x-direction and the direction perpendicular to the x-direction is defined as the y-direction.

12. A method for estimating the remaining prestress force of a PC structure into which prestress is introduced, comprising: a strain measurement step of generating the strain at a specific location by heating and measuring the strain with a strain measurement means; a feature point identifying step of identifying a feature point, which is a numerical value of the strain of the PC structure, at which a relationship between the strain measured in the strain measuring step and a newly measured acoustic emission changes; A method for estimating the residual prestress force of a PC structure, comprising a residual prestress force estimation step of estimating the residual prestress force of the PC structure using a maximum compressive strain which is the sum of the strain at the characteristic point and the compressive strain under dead load, and the Young's modulus of the PC structure.

13. A method for estimating the remaining prestress force of a PC structure into which prestress is introduced, comprising: a strain measuring step including a heating step of heating a specific location to generate the strain, and a cooling step of cooling the specific location at a timing different from that of the heating step to generate the strain, and measuring the strain in the heating step and the cooling step by a strain measuring means; a feature point identifying step of identifying a feature point, which is a numerical value of the strain of the PC structure, at which a relationship between the strain measured in the heating step and the strain measured in the cooling step changes; A method for estimating a residual prestress force of a PC structure, comprising a residual prestress force estimation step of estimating a residual prestress force of the PC structure using the strain at the characteristic point and the Young's modulus of the PC structure.

14. A method for estimating the remaining prestress force of a PC structure into which prestress is introduced, comprising: a strain measurement step of generating a strain at a specific location and measuring the strain with a strain measurement means; a feature point identifying step of identifying a feature point, which is a numerical value of the strain of the PC structure, that changes in relationship between first information, which is information about the strain measured in the strain measuring step, and second information, which is obtained by multiplying the first information by a specific coefficient or is newly measured differently from the first information; a residual prestress force estimation step of estimating the residual prestress force of the PC structure by performing a predetermined calculation process on the numerical values ​​of the characteristic points.

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