Method for calculating correction factor for Young's modulus due to temperature stress of concrete, and calculation kit

Abstract

To provide a calculation method for a correction coefficient of a Young's modulus due to a temperature stress of concrete, and a calculation kit for calculating the correction coefficient of the Young's modulus.SOLUTION: A calculation method for a correction coefficient of a Young's modulus due to a temperature stress of concrete includes: a Young's modulus measurement step of measuring a Young's modulus measured value of concrete; a temperature stress calculation step of calculating a concrete temperature stress measured value; a temporary temperature stress calculation step of calculating effective distortion of concrete and a temporary temperature stress of concrete; and a correction coefficient calculation step of calculating a correction coefficient (Ee / Ep) of the Young's modulus from a ratio of an effective Young's modulus (Ee), which is calculated from the concrete temperature stress measured value and the effective distortion of concrete, and a temporary Young's modulus (Ep) which is calculated from the temporary concrete temperature stress and the effective distortion of concrete. A calculation kit for the correction coefficient of the Young's modulus comprises a temperature stress measurement device and a free distortion measurement device.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for calculating a correction factor for Young's modulus due to temperature stress of concrete, and a calculation kit used for calculating a correction factor for Young's modulus due to temperature stress of concrete. [Background technology]

[0002] Concrete generates heat during hydration (hardening), causing its temperature to rise, and then the temperature drops as the heat is released. This deformation of the concrete due to temperature rise and fall is constrained by the external bedrock and existing concrete, and the resulting stress causes thermal cracking. In order to prevent the occurrence of thermal cracks, Non-Patent Document 1 (Japan Society of Civil Engineers' "Standard Specifications for Concrete [Design Edition]") and Non-Patent Document 2 (Japan Concrete Institute's "Guidelines for Crack Control in Mass Concrete 2016") state that the standard is to use three-dimensional finite element analysis (FEM) to calculate the restraint stress that occurs due to volume changes associated with the heat generated by hydration and autogenous shrinkage of concrete, and to predict the probability of crack occurrence and crack width. Although general values ​​are listed as input values ​​for general-purpose cement, it is known that in reality, materials differ from plant to plant, resulting in differences in heat generation characteristics, autogenous shrinkage, strength development, etc. Therefore, in order to improve the accuracy of the analysis, various data may be obtained in advance by measuring the heat generation characteristics of the concrete to be used in construction using mass block specimens, autogenous shrinkage strain after temperature history, compressive strength, splitting tensile strength, Young's modulus, etc. Furthermore, in recent years, methods for measuring the coefficient of thermal expansion from very early material ages and Young's modulus have been developed.

[0003] On the other hand, to calculate the temperature stress of concrete, it is necessary to consider the effects of creep (creep analysis) in addition to autogenous shrinkage strain and Young's modulus. Current guidelines (Non-Patent Documents 1 and 2) consider the effects of creep using the effective elastic modulus method, which uses the effective Young's modulus (effective Young's modulus = Young's modulus correction coefficient × Young's modulus; the Young's modulus correction coefficient is a number less than or equal to 1), obtained by multiplying Young's modulus by a "Young's modulus correction coefficient" as a reduction coefficient. However, the Young's modulus correction coefficient is a fixed value (0.42 when the temperature rises, 0.65 when the temperature falls) regardless of the type of cement, and there are cases where this value is not appropriate. The correction factor for Young's modulus can be calculated by embedding effective stress meters, strain gauges, and stress-free meters when pouring mass concrete for an actual structure and measuring its behavior during hardening. However, when measuring devices are embedded in an actual structure, calculations cannot be made before construction, so it is not possible to prevent or predict the occurrence of thermal cracks using the correction factor for Young's modulus calculated in advance for the actual structure. Also, while it is possible to calculate the correction factor for Young's modulus by installing effective stress meters, strain gauges, and stress-free meters in a mock-up specimen equivalent to the actual size, this requires a great deal of effort and cost, making it unrealistic to implement.

[0004] There is a demand for a method for calculating the correction factor for Young's modulus with high accuracy before construction, but no measurement or evaluation method has been established. For example, in Non-Patent Document 3, the correction factor for Young's modulus is calculated from the results of a laboratory test, but the calculated value may exceed 1. Since the correction factor for Young's modulus is, by definition, 1 or less, it is difficult to say that the accuracy is sufficient. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Japan Society of Civil Engineers "Concrete Standard Specifications [Design Edition]" [Non-patent document 2] Japan Concrete Institute "Guidelines for Crack Control in Mass Concrete 2016" [Non-patent document 3] Ryoichi Ashizawa et al., "Evaluation of the Reduction Factor of Young's Modulus Considering the Effect of Creep at Early Ages," Proceedings of the Cement and Concrete Journal, Vol. 73, No. 1, 2019, pp. 200-207 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention aims to provide a method for calculating a correction factor for Young's modulus due to temperature stress of concrete, and a calculation kit for calculating the correction factor for Young's modulus. [Means for solving the problem]

[0007] The means for solving the problems of the present invention are as follows. 1. A Young's modulus measurement process for measuring the actual Young's modulus of concrete; A temperature stress calculation process in which the strain (εs(t)) of a non-thermal expansion rod placed inside concrete cast in a formwork having the same cross-sectional shape in the longitudinal direction is measured while controlling the temperature, and the concrete temperature stress actual measurement value (σc(t)) is calculated based on the following formula (1); The free strain of concrete (εc) was measured using a strain gauge installed inside concrete placed in a formwork with the same cross-sectional shape in the longitudinal direction. ,free (t)) was measured under the same temperature control conditions as in the temperature stress calculation process, and the effective strain of concrete (Δεc ,res (t)) and further calculate a provisional concrete temperature stress (Δσcp(t)) assuming that the Young's modulus correction coefficient is 1.0 based on the following formula (3); The concrete temperature stress measured value (σc(t)) and the concrete effective strain (Δεc ,res (t)) and the effective Young's modulus (Ee = Δσc(t) / Δεc ,res (t)), the hypothetical concrete temperature stress (Δσcp(t)) and the concrete effective strain (Δεc ,res(t)) and the provisional Young's modulus (Ep = Δσcp(t) / Δεc ,res a correction coefficient calculation step of calculating a correction coefficient (Ee / Ep) for Young's modulus from the ratio of A method for calculating the correction factor for Young's modulus due to temperature stress of concrete. (Formula 1) σc(t)=(εs(t)×Es×As) / Ac σc(t): measured concrete temperature stress εs(t): Strain of non-thermal expansion rod Es: Young's modulus of non-thermal expansion rod material As: Cross-sectional area of ​​non-thermal expansion rod Ac: cross-sectional area of ​​concrete (Formula 2) Δεc ,res (t)=|(εc ,free (t))-εs(t)| Δεc ,res (t): Effective strain of concrete (Absolute value of the difference between the free strain and the strain of a non-thermal expansion rod) εc ,free (t): Free strain εs(t): Strain of non-thermal expansion rod (Formula 3) Δσcp(t)=1.0×Ec(t)×Δεc ,res (t) Δσcp(t): Temporary concrete temperature stress Ec(t): Young's modulus of concrete (Calculated based on the measured Young's modulus of concrete) Δεc ,res (t): Effective strain of concrete 2. A method for calculating a correction factor for Young's modulus of concrete due to temperature stress as described in 1, characterized in that the non-thermal expansion bar material is Invar steel. 3. A method for calculating the correction coefficient for Young's modulus due to temperature stress of concrete described in 1. or 2., characterized in that the correction coefficient for Young's modulus is calculated by dividing it into two or more periods selected from the early age period, the temperature rise period, and the temperature fall period. 4. A temperature stress measuring device having a formwork with the same cross-sectional shape in the longitudinal direction, a non-thermal expansion rod material with its end fixed toward the longitudinal direction of the formwork, and a strain gauge attached to the center of the non-thermal expansion rod material, which can harden concrete in the formwork while controlling the temperature and measure the temperature stress of the concrete during the hardening process; A free strain measurement device has a formwork with a uniform cross-sectional shape in the longitudinal direction and a strain gauge installed inside the formwork, and is capable of hardening concrete inside the formwork while controlling the temperature and measuring the free strain of the concrete during the hardening process; A kit for calculating a correction factor for Young's modulus due to temperature stress of concrete, comprising: 5. A kit for calculating the correction factor for Young's modulus of concrete due to temperature stress as described in 4., characterized in that the non-thermal expansion bar material is Invar steel. 6. The formwork is 150 cm or less in length and has a cross-sectional area perpendicular to the length of 400 cm 2 6. A kit for calculating a correction factor for Young's modulus due to temperature stress of concrete according to 4. or 5., characterized in that:

[0008] Hereinafter, the method for calculating the correction factor for Young's modulus due to temperature stress of concrete and the kit for calculating the correction factor for Young's modulus due to temperature stress of concrete of the present invention will also be simply referred to as the calculation method and the calculation kit. [Effects of the Invention]

[0009] The calculation method and calculation kit of the present invention enable the correction factor for Young's modulus to be calculated with high accuracy before construction. By using the calculated correction factor for Young's modulus, the occurrence of strain due to temperature stress can be predicted with higher accuracy, allowing appropriate countermeasures against temperature cracking to be selected and preventing the occurrence of temperature cracking after construction on-site. The calculation method of the present invention can calculate the correction factor for Young's modulus regardless of the type of concrete, even if the concrete behaves differently during hardening, such as expansive concrete that expands significantly initially, blast-furnace cement concrete that exhibits large autogenous shrinkage strain, or low-heat concrete that develops strength slowly, thereby enabling accurate temperature stress analysis. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram of a temperature stress measuring device in the calculation kit of the present invention. [Figure 2] Schematic diagram of dimensional changes of concrete when the temperature rises and falls. [Figure 3] FIG. 2 is a schematic diagram of a free strain measurement device in the calculation kit of the present invention. [Figure 4] 1 is a graph showing the relationship between age and compressive strength in (N) ordinary cement concrete, which is an example of the relationship between age and compressive strength in the examples. [Figure 5] Graph showing the relationship between the compressive strength (0.75 N / mm2 or less) of all concrete and the measured Young's modulus in the examples. [Figure 6] Graph showing the relationship between the compressive strength (over 0.75 N / mm2) of all concrete and the measured Young's modulus in the examples. [Figure 7] 1 shows temperature control conditions in a temperature stress calculation process and a tentative temperature stress calculation process in an embodiment. [Figure 8] This graph shows the results for specimen 1 of ordinary concrete (N), which is an example of a stress-strain curve in the example, with the vertical axis representing the measured concrete temperature stress (σc(t)) and the hypothetical concrete temperature stress (Δσcp(t)) and the horizontal axis representing the effective concrete strain (Δεc,res(t)). DETAILED DESCRIPTION OF THE INVENTION

[0011] The calculation method of the present invention will be described step by step. The order of the calculation steps of the present invention is not limited, except that the steps are performed in an appropriate order when a value calculated in one step is used in another step. · Young's modulus measurement process Measure the actual Young's modulus of concrete. The Young's modulus can be measured by a conventionally known method. Since the Young's modulus of concrete varies depending on its age, specimens of different ages are used to measure the Young's modulus at various ages. In order to accurately calculate the correction factor for the Young's modulus, it is preferable to measure the Young's modulus at an appropriate frequency. For example, when the compressive strength is 1.0 N / mm 2 It is preferable to measure every 1 to 3 hours when the material is in its early stage (below about 100°C), it is preferable to measure every 2 hours to 1 day when the temperature is rising, and it is preferable to measure every 1 to 14 days when the temperature is falling. The actual Young's modulus can be measured, for example, using a load-controlled method such as JIS A1149:2017, Test method for static elastic modulus of concrete, during the temperature rise and temperature fall periods after the early age of the material, and using a displacement-controlled method during the early age of the material.

[0012] Temperature stress calculation process The strain (εs(t)) of a non-thermal expansion rod placed inside concrete poured into a formwork with the same cross-sectional shape in the longitudinal direction is measured while controlling the temperature, and the measured concrete temperature stress value (σc(t)) is calculated based on the following equation (1). (Formula 1) σc(t)=(εs(t)×Es×As) / Ac σc(t): measured concrete temperature stress εs(t): Strain of non-thermal expansion rod Es: Young's modulus of non-thermal expansion rod material As: Cross-sectional area of ​​non-thermal expansion rod Ac: cross-sectional area of ​​concrete

[0013] The measured concrete thermal stress value (σc(t)) can be measured by the concrete thermal stress measuring device 100 included in the calculation kit of the present invention. FIG. 1 shows a concrete temperature stress measuring device 100. The concrete temperature stress measuring device 100 comprises a formwork 11 having the same cross-sectional shape in the longitudinal direction, a non-thermal-expansion rod 12 whose end is fixed in the longitudinal direction of the formwork 11, and a strain gauge 13 attached to the center of the non-thermal-expansion rod 12. The formwork 11 has the same cross-sectional shape in its length direction. The formwork 11 may be substantially the same in shape, including dimensional errors, manufacturing errors, etc., as long as it can impart uniform stress to the non-thermally expandable rods 12 and does not impart unnecessary restraining force to the concrete hardening inside the formwork 11. By having the formwork 11 have the same (substantially the same) cross-sectional shape in the length direction, it is possible to reduce temperature variations inside the concrete hardening inside the formwork 11, and the concrete can be placed in a more uniform stress state. The cross-sectional shape of the formwork 11 can be, for example, polygonal or circular, with rectangular being preferred as it is easy to manufacture, and square being more preferred.

[0014] The size of the formwork 11 is not particularly limited, but it should be 150 cm or less in length and 400 cm in cross-sectional area in the direction perpendicular to the length. 2 It is preferable that the formwork 11 is 120 cm or less, because it can be easily placed in a temperature-controlled space such as a thermostatic chamber, and furthermore, the temperature distribution in the thickness direction of the concrete can be made more uniform, and the temperature history of the concrete can be precisely controlled. The length of the formwork 11 is preferably 120 cm or less, and more preferably 100 cm or less. If the formwork 11 is too short, it may be difficult to detect strain, so it is preferable that it is 40 cm or more. The cross-sectional area of ​​the formwork 11 is 260 cm 2 Preferably, it is less than 150cm 2If the cross-sectional area of ​​the formwork 11 is too small, the cross-sectional area (Ac) of the concrete hardening in the formwork 11 will be small, and the coarse aggregate may become uneven around the non-thermal expandable bar material, and problems such as excessive stress occurring in the concrete may occur. 2 It is preferable that it is 80cm or more. 2 More preferably, it is equal to or greater than this.

[0015] The non-thermal expansion rod 12 has a thermal expansion coefficient of 5.0×10 -6 The thermal expansion coefficient of the non-thermally expanding rod 12 is preferably small, 4.0×10 -6 / °C or less, and -6 / °C or less, and more preferably 2.0 × 10 -6 / °C or less. Examples of the material for the non-thermal expansion bar 12 include various types of invar steel such as invar steel, super invar steel, and zero invar steel. The shape of the bar is preferably round steel. The non-thermal expansion bar 12 is placed approximately in the center of the formwork 11 when viewed in the longitudinal direction. The non-thermo-expandable bar 12 has attachment sections 121 at both ends that can follow the expansion and contraction of concrete, and a center section that is an attachment removal section 122 that does not follow the expansion and contraction of concrete. The attachment section 121 only needs to follow the expansion and contraction of concrete, and can be provided, for example, by threading the non-thermo-expandable bar 12. The attachment removal section 122 only needs to not follow the expansion and contraction of concrete, and can be provided, for example, by making the surface of the non-thermo-expandable bar 12 flat and covering the periphery with a fluororesin sheet or the like that does not adhere to concrete, or by applying a fluororesin paint or the like that does not adhere to concrete.

[0016] The strain gauge 13 is attached to the longitudinal center of the non-thermal expansion bar 12, which is the adhesion removal portion 122, and detects the amount of strain in the non-thermal expansion bar 12. The strain gauge 13 is attached so as not to detect volumetric changes in the concrete. Any known strain gauge can be used without any particular restrictions, but a three-wire type is preferred, as it can eliminate dimensional changes in the strain gauge itself due to temperature changes.

[0017] Concrete is poured into the formwork 11 of the concrete thermal stress measuring device 100, and the concrete is hardened while being given a predetermined temperature history by controlling the temperature. By controlling the temperature change over time as the concrete hardens, it is possible to give any temperature history that is expected when a large volume of concrete, such as mass concrete, hardens, even with a small measuring device, and it is possible to reproduce the temperature history taking into account the seasons, such as summer and winter, and the regional characteristics of cold regions such as Hokkaido and highlands, and Kyushu and Okinawa.

[0018] Figure 2 shows schematic diagrams of the dimensional changes occurring when the temperature rises and falls. When the temperature rises, the concrete expands, but the attachment portion 121 of the non-thermal-expansion bar is restrained by the concrete and therefore expands in response to the expansion of the concrete (restrained test specimen when the temperature rises in Figure 2). The attachment removal portion 122 does not follow the expansion of the concrete, but is compressed and shortened due to the expansion of the attachment portion 121, and by detecting the amount of deformation with a strain gauge, the strain (εs(t)) of the non-thermal-expansion bar can be calculated. When the temperature drops, the concrete shrinks, and the attachment portion 121 of the non-thermal-expansion bar shortens in response to this shrinkage of the concrete (constrained test specimen when the temperature drops in Figure 2). The attachment removal portion 122 does not follow the shrinkage of the concrete, but is elongated and deformed due to the shortening of the attachment portion 121 that is constrained by the concrete, and by detecting the amount of deformation with the strain gauge 13, the strain (εs(t)) of the non-thermal-expansion bar can be calculated.

[0019] The thermal expansion coefficient of the non-thermal-expansion bar 12 is small, and the difference between this and that of concrete is large, so temperature stress occurs due to temperature changes in the concrete. Note that temperature stress cannot be measured with materials such as ordinary reinforcing bars, whose thermal expansion coefficients are only slightly different from that of concrete. Here, the temperature stress due to the deformation (expansion and contraction) of the concrete and the stress of the non-thermal-expandable bar 12 trying to return to its original shape are balanced and equal, so the actual measured value of the concrete temperature stress (σc(t)) can be calculated from the balance of these two forces using the following equation (1). (Formula 1) σc(t)=(εs(t)×Es×As) / Ac σc(t): Measured concrete temperature stress (N / mm 2 ) εs(t): Strain of non-thermal expansion rod Es: Young's modulus of non-thermal expansion rod material (N / mm 2 ) As: Cross-sectional area of ​​non-thermal expansion rod (mm 2 ) Ac: Cross-sectional area of ​​concrete (mm 2 )

[0020] ·Temporary temperature stress calculation process The free strain of concrete (εc) was measured using a strain gauge installed inside concrete placed in a formwork with the same cross-sectional shape in the longitudinal direction. ,free (t)) was measured under the same temperature control conditions as in the temperature stress calculation process, and the effective strain of concrete (Δεc ,res (t)) is calculated, and then the temporary temperature stress of the concrete (Δσcp(t)) is calculated based on the following equation (3). (Formula 2) Δεc ,res (t)=|(εc ,free (t))-εs(t)| Δεc ,res (t): Effective strain of concrete (Absolute value of the difference between the free strain and the strain of a non-thermal expansion rod) εc ,free (t): Free strain εs(t): Strain of non-thermal expansion rod (Formula 3) Δσcp(t)=1.0×Ec(t)×Δεc ,res (t) Δσcp(t): Temporary concrete temperature stress (N / mm 2 ) Ec(t): Young's modulus of concrete (N / mm 2 ) (Calculated based on the measured Young's modulus of concrete) Δεc ,res (t): Effective strain of concrete

[0021] To calculate the temperature stress of the concrete (Δσcp(t)), the effective strain of the concrete (Δεc ,res (t)) must be calculated. As shown in equation (2), the effective strain of concrete (Δεc ,res (t)) is the free strain (εc ,free The absolute value of the difference between the strain (εs(t)) of the non-thermally expandable rod material calculated in the "temperature stress calculation step" above and the strain (εs(t)) of the non-thermally expandable rod material calculated in the "temperature stress calculation step" above. Free strain of concrete (εc ,free (t)) can be measured by the concrete free strain measuring device 200 of the calculation kit of the present invention. FIG. 3 shows a concrete free strain measuring device 200. The concrete free strain measuring device 200 has a formwork 21 with the same cross-sectional shape in the longitudinal direction, and a strain gauge 22 installed inside the formwork 21. Note that the "same" in this formwork 21 means "approximately the same," as in the formwork 11 of the concrete temperature stress measuring device 100 described above.

[0022] The size of the formwork 21 is not particularly limited, but it should be 150 cm or less in length and 400 cm in cross-sectional area in the direction perpendicular to the length. 2It is preferable that the formwork 21 is 120 cm or less, because it can be easily placed in a temperature-controlled space such as a thermostatic chamber, and furthermore, the temperature distribution in the thickness direction of the concrete can be made more uniform, and the temperature history of the concrete can be precisely controlled. The length of the formwork 21 is preferably 120 cm or less, and more preferably 100 cm or less. If the formwork 21 is too short, it may be difficult to detect the strain in the concrete, so it is preferable that it is 20 cm or more. The cross-sectional area of ​​the formwork 21 is 260 cm 2 Preferably, it is less than 150cm 2 If the cross-sectional area of ​​the formwork 21 is too small, the distribution of the coarse aggregate may become uneven. 2 It is preferable that it is 80cm or more. 2 The above is more preferable. The mold 11 of the temperature stress measuring device 100 and the mold 21 of the free strain measuring device 200 may have the same shape or different shapes.

[0023] Concrete is poured into the formwork 21 of the concrete free strain measuring device 200, and the temperature is controlled to provide the same temperature history as in the temperature stress calculation process described above. By controlling the temperature change over time as the concrete hardens, it is possible to provide any temperature history that is expected when a large volume of concrete, such as mass concrete, hardens, even with a small measuring device, and this can be reproduced taking into account the season, regional characteristics, etc. As shown in the free test specimen when the temperature rises in Figure 2, the concrete expands when the temperature rises and contracts when the temperature drops within the formwork 21. This deformation is detected by a strain gauge 22 installed within the formwork 21, and the free strain of the concrete (εc ,free (t)) can be detected. As shown in the free test specimen during temperature drop in FIG. 2, the concrete in the concrete free strain measuring device 200 is not subjected to any constraints, and therefore can deform more greatly than the concrete constrained by the attachment portion 121 of the non-thermal-expansion bar 12 in the concrete temperature stress measuring device 100. In other words, the concrete in the concrete temperature stress measuring device 100 is essentially subject to the same magnitude of deformation (free strain of concrete (εc ,free Since the concrete is restrained by the attachment part 121 of the non-thermal expansion rod, the amount of deformation is suppressed to the magnitude of the strain (εs(t)) of the non-thermal expansion rod. As shown in equation (2), the original amount of deformation, the free strain of the concrete (εc ,free The difference (absolute value of the difference) between the strain of the non-thermal expansion rod (εs(t)), which is the actual deformation due to the restraint, and the strain of the non-thermal expansion rod (εs(t)), is the effective strain of the concrete (Δεc ,res (t)=|(εc ,free (t))-εs(t)|).

[0024] Then, the effective strain (Δεc ,res This stress is actually the result of creep, but as shown in equation (3), by multiplying it by the Young's modulus of concrete at that age (Ec(t)), it is possible to calculate a tentative concrete temperature stress (Δσcp(t)) that ignores the effect of creep (assuming the Young's modulus correction coefficient is 1.0). (Formula 3) Δσcp(t)=1.0×Ec(t)×Δεc ,res (t) Δσcp(t): Temporary concrete temperature stress Ec(t): Young's modulus of concrete (Calculated based on the measured Young's modulus of concrete) Δεc ,res (t): Effective strain of concrete

[0025] The Young's modulus (Ec(t)) of concrete is calculated based on the Young's modulus measured in the "Young's modulus measurement process" described above. This is because the Young's modulus is the actual value measured at the age at which the concrete was actually measured, and the Young's modulus at ages at which the concrete was not measured is unknown. Therefore, based on the Young's modulus measured value, the Young's modulus (Ec(t)) of concrete, including ages at which the Young's modulus was not measured, is calculated from the relationship between the age and compressive strength, the age and Young's modulus, etc. (a straight line, approximate straight line, approximate curve, etc. connecting the measured values), and this is used to calculate a provisional concrete temperature stress value.

[0026] Correction coefficient calculation process The concrete temperature stress measured value (σc(t)) and the concrete effective strain (Δεc ,res (t)) and the effective Young's modulus (Ee = Δσc(t) / Δεc ,res (t)), the hypothetical concrete temperature stress (Δσcp(t)) and the concrete effective strain (Δεc ,res (t)) and the provisional Young's modulus (Ep = Δσcp(t) / Δεc ,res The correction factor for Young's modulus (Ee / Ep) is calculated from the ratio of Ee to Ep.

[0027] Young's modulus is a value derived from the relationship between strain and stress, and is the slope of a stress-strain curve with stress on the vertical axis and strain on the horizontal axis. Therefore, the measured concrete temperature stress (σc(t)) and the effective concrete strain (Δεc, res (t)) and obtain a stress-strain curve with stress on the vertical axis and strain on the horizontal axis. From the slope of the curve, the effective Young's modulus (Ee = Δσc(t) / Δεc ,res (t)) can be calculated. Similarly, the tentative concrete temperature stress (Δσcp(t)) and the effective concrete strain (Δεc ,res From the slope of the stress-strain curve plotted against the strain (t), the provisional Young's modulus (Ep = Δσcp(t) / Δεc ,res (t)) can be calculated. The effective Young's modulus and the provisional Young's modulus can be calculated as the slope of the tangent to the stress-strain curve, the slope of the approximation line, the slope of the tangent to the approximation curve, or the like.

[0028] Then, the correction coefficient (Ee / Ep) of the Young's modulus can be calculated from the ratio of the effective Young's modulus (Ee) to the provisional Young's modulus (Ep). As is clear from the shape of the obtained stress-strain curve, the early age, temperature rise, and temperature fall periods, which have significantly different hardening behavior, have different slopes of the stress-strain curve and can be clearly distinguished. Therefore, it is preferable to calculate the correction coefficient for Young's modulus in two or more periods selected from the early age, temperature rise, and temperature fall periods, and it is more preferable to calculate the correction coefficient for Young's modulus in the temperature rise and temperature fall periods, which have the greatest impact. [Example]

[0029] The mix proportions of the concrete used are shown in Tables 1 and 2. [Table 1] [Table 2]

[0030] · Young's modulus measurement process The compressive strength of each concrete was measured, and the Young's modulus was calculated. As an example of the relationship between age and compressive strength, the relationship for (N) normal cement concrete is shown in Figure 4. The relationship between compressive strength and the Young's modulus for all concretes was also calculated for a compressive strength of 0.75 N / mm 2 Compression strength below 0.75N / mm 2 The crossing and crossing are shown in Figures 5 and 6, respectively.

[0031] Temperature stress calculation process Length 800cm, cross-sectional area perpendicular to the length is 100cm 2 In a mold (10 cm × 10 cm), a round Invar steel bar (φ32 mm, length 830 mm, thermal expansion coefficient 1.06 × 10-6 A temperature stress measurement device with a fixed temperature (°C / °F) was used. The non-thermal expansion rod was threaded at 265 mm lengths from both ends to form the attachment section. A strain gauge (Tokyo Measuring Instruments Laboratory Co., Ltd., general-purpose strain gauge FLAB-3-11) was attached to the non-threaded central section of the non-thermal expansion rod, and a 0.1 mm thick fluororesin sheet was wrapped around it twice to form the attachment removal section. Each concrete was poured into the formwork of the thermal stress measurement device, and the strain (εs(t)) of the non-thermal expansion rod was measured over time while controlling the temperature, and the actual concrete thermal stress (σc(t)) was calculated based on equation (1) (n=2). The temperature control conditions are shown in Figure 7.

[0032] ·Temporary temperature stress calculation process Length: 400cm, cross-sectional area perpendicular to the length: 100cm 2 A free strain measurement device was used, in which an embedded strain gauge (Tokyo Measuring Instruments Laboratory, KM100BT) was installed in a formwork (10 cm x 10 cm). Each concrete was poured into the formwork of the free strain measurement device, and the free strain of the concrete (εc ,free The temperature control conditions were the same as those in the temperature stress calculation process. Based on equation (2), the free strain (εc ,free The effective strain of concrete (Δεc ,res (t)) was calculated. Furthermore, the effective strain of this concrete (Δεc ,res The tentative temperature stress of concrete (Δσcp(t)) was calculated based on Equation (3) using the temperature (t) of concrete and Young's modulus of concrete (Ec(t)). The Young's modulus of concrete (Ec(t)) is calculated by the relational equation (compressive strength 0.75N / mm) using an approximation curve from the compressive strength (σc) and Young's modulus (Ec) values ​​measured in the "Young's modulus measurement process" above. 2 Below: Ec = 0.008 × exp(5.89 × σc), compressive strength 0.75 N / mm 2The Young's modulus (Ec(t)) of concrete at each age was calculated by combining this formula with the relationship between age and compressive strength, and this was used.

[0033] Correction coefficient calculation process In Fig. 8, the vertical axis shows the measured concrete temperature stress (σc(t)) and the hypothetical concrete temperature stress (Δσcp(t)), and the horizontal axis shows the effective concrete strain (Δεc ,res As an example of the stress-strain curve (t), the results of specimen 1 of ordinary concrete (N) are shown. From the inflection points of each stress-strain curve, (1) the early age period, (2) the temperature rise period, and (3) the temperature fall period were determined, and the effective Young's modulus (Ee) and provisional Young's modulus (Ep) were calculated from the slope of the approximate line in each period. Then, the correction factor for Young's modulus (Ee / Ep) was calculated from the ratio of the effective Young's modulus to the provisional Young's modulus. The results are shown in Tables 3 to 6.

[0034] [Table 3] [Table 4]

[0035] [Table 5] [Table 6]

[0036] The method for calculating the correction factor for Young's modulus of the present invention made it possible to calculate the correction factor for Young's modulus without creating a large mock-up test specimen. Conventionally, a fixed value (0.42 when temperature rises, 0.65 when temperature falls) was used as the correction coefficient for Young's modulus regardless of the type of cement, but the method for calculating the correction coefficient for Young's modulus of the present invention makes it possible to calculate with high accuracy different values ​​of correction coefficient for Young's modulus for each cement that behaves differently. By using the correction coefficient for Young's modulus calculated according to the present invention, it is possible to predict temperature stress strain with higher accuracy, and to select appropriate measures against thermal cracking. [Explanation of symbols]

[0037] 100 Temperature stress measuring device 11 Formwork 12 Non-thermal expansion rod 121 Attachment 122 Adhesion removal section 13 Strain gauge 200 Free strain measurement device 21 Formwork 22 Strain gauge

Claims

1. a Young's modulus measuring step of measuring an actual Young's modulus value of concrete; a temperature stress calculation step of measuring the strain (εs(t)) of a non-thermally expandable rod placed inside concrete cast in a formwork having the same longitudinal cross-sectional shape, while controlling the temperature, and calculating the concrete temperature stress actual measurement value (σc(t)) based on the following formula (1); The free strain of concrete (εc) was measured using a strain gauge installed inside concrete poured into a formwork with the same cross-sectional shape in the longitudinal direction. ，ｆｒｅｅ (t)) was measured while controlling the temperature under the same conditions as in the temperature stress calculation step, and the effective strain of the concrete (Δεc ，ｒｅｓ (t)) and further calculate a provisional concrete temperature stress (Δσcp(t)) assuming that the Young's modulus correction coefficient is 1.0 based on the following formula (3); The concrete temperature stress measurement value (σc(t)) and the concrete effective strain (Δεc ，ｒｅｓ (t)) and the effective Young's modulus (Ee = Δσc(t) / Δεc ，ｒｅｓ (t)), the virtual concrete temperature stress (Δσcp(t)) and the effective strain of the concrete (Δεc ，ｒｅｓ (t)) and the provisional Young's modulus (Ep = Δσcp(t) / Δεc ，ｒｅｓ a correction coefficient calculation step of calculating a correction coefficient (Ee / Ep) of Young's modulus from the ratio of A method for calculating the correction factor for Young's modulus due to temperature stress of concrete. (Formula 1) σc(t)=(εs(t)×Es×As) / Ac σc(t): Measured concrete temperature stress εs(t): Strain of non-thermal expansion rod Es: Young's modulus of non-thermal expansion rod material As: Cross-sectional area of ​​the non-thermal expansion rod Ac: cross-sectional area of ​​concrete (Formula 2) Dec ，ｒｅｓ (t)=|(c) ，ｆｒｅｅ (t))-εs (t)| Δεc ，ｒｅｓ (t): Effective strain of concrete (Absolute value of the difference between the free strain and the strain of a non-thermally expansive bar material) εc ，ｆｒｅｅ (t): Free strain εs(t): Strain of non-thermal expansion rod (Formula 3) Δσcp(t)=1.0×Ec(t)×Δεc ，ｒｅｓ (t) Δσcp(t): Temporary concrete temperature stress Ec(t): Young's modulus of concrete (Calculated based on the measured Young's modulus of concrete) Δεc ，ｒｅｓ (t): Effective strain of concrete

2. 2. The method for calculating a correction factor for Young's modulus of concrete due to temperature stress according to claim 1, wherein the non-thermal expansion bar is Invar steel.

3. 3. A method for calculating the Young's modulus correction coefficient due to temperature stress of concrete according to claim 1 or 2, characterized in that the correction coefficient of the Young's modulus is calculated by dividing the coefficient into two or more periods selected from the early age period, the temperature rising period, and the temperature falling period.

4. a temperature stress measuring device having a formwork with the same cross-sectional shape in the longitudinal direction, a non-thermal expansion rod positioned at the end in the longitudinal direction of the formwork to prevent displacement when concrete is poured, and a strain gauge attached to the center of the non-thermal expansion rod, which hardens the concrete in the formwork while controlling the temperature, and which can measure the temperature stress of the concrete during the hardening process; A free strain measurement device has a formwork with a uniform cross-sectional shape in the longitudinal direction and a strain gauge installed inside the formwork, and is capable of hardening concrete inside the formwork while controlling the temperature and measuring the free strain of the concrete during the hardening process; A kit for calculating a correction factor for Young's modulus due to temperature stress of concrete, comprising:

5. 5. The kit for calculating a correction factor for Young's modulus of concrete due to temperature stress according to claim 4, wherein the non-thermal expansion bar material is Invar steel.

6. The formwork has a length of 150 cm or less and a cross-sectional area perpendicular to the length of 400 cm ２ 6. A kit for calculating a correction factor for Young's modulus due to temperature stress of concrete according to claim 4 or 5, wherein the correction factor is as follows:

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