Evaluation method for concrete components
A method using multiple regression analyses addresses the inaccuracy of thermal cracking evaluation at high concrete pouring temperatures by deriving equations for maximum temperature rise and stress intensity ratio, ensuring accurate thermal cracking risk assessment in concrete members.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-08-29
- Publication Date
- 2026-03-12
AI Technical Summary
Existing methods for evaluating the risk of thermal cracking in concrete members are inaccurate when concrete pouring temperatures exceed 30°C due to the lack of understanding of the physical properties of mass concrete at these higher temperatures.
A method involving multiple regression analyses to derive equations for calculating the maximum temperature rise and stress intensity ratio, using physical quantities such as unit cement content, rigidity ratio, and temperature rise, allowing for accurate evaluation of thermal cracking risk in concrete members.
Enables precise evaluation of thermal cracking risk in concrete members at temperatures above 30°C, reducing the need for extensive thermal stress analysis and improving the accuracy of quality control during extreme heat periods.
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Abstract
Description
[Technical Field]
[0001] The present invention relates to a method for evaluating a concrete member. [Background technology]
[0002] It is known that in mass concrete with large component thicknesses, there is a risk of harmful thermal cracking due to expansion and contraction caused by temperature changes. The risk of thermal cracking is mainly evaluated using the crack index (splitting tensile strength / temperature stress) and stress strength ratio (temperature stress / splitting tensile strength) obtained by temperature stress analysis using FEM (finite element method). Temperature stress analysis using three-dimensional FEM involves creating an element model and setting analysis parameters.
[0003] Non-Patent Document 1 proposes a nomograph called a chart as a means for easily calculating the stress-intensity ratio. When a thermal stress analysis is performed using a three-dimensional FEM with analytical parameters including the concrete mix at a concrete pouring temperature of 20°C, the shape of the component, and the ground conditions, several hundred thermal stress analysis results are calculated. By performing a multiple regression analysis on the maximum temperature rise and maximum stress-intensity ratio near the center of the component among the calculated results, an estimation formula for the maximum temperature rise and maximum stress-intensity ratio can be derived. By using this estimation formula, the risk of thermal cracking can be accurately evaluated based on the stress-intensity ratio, without performing thermal stress analysis, as long as it is within the applicable range of the chart.
[0004] Due to global warming, concrete temperatures in recent summers often exceed 35°C. However, the chart in Non-Patent Document 1 sets the constitutive law for analysis based on the physical properties of concrete when the temperature is in the range of 10 to 30°C, and even if the estimation formula derived from this chart is applied to concrete temperatures exceeding 30°C, it is difficult to accurately evaluate the maximum temperature rise and maximum stress-strength ratio.
[0005] As shown in Non-Patent Documents 2 and 3, the physical properties of mass concrete when the concrete temperature is 40°C are significantly different from the physical properties at 30°C or below. Therefore, in order to perform thermal stress analysis when the concrete temperature exceeds 30°C, it is necessary to understand the physical properties of mass concrete at that temperature, but this has not yet been fully understood. [Prior art documents] [Non-patent literature]
[0006] [Non-Patent Document 1] Architectural Institute of Japan: Guidelines and Commentary on Thermal Crack Control Design and Construction of Mass Concrete, November 2019 [Non-patent document 2] Toshifumi Kikuchi et al.: Study on the adiabatic temperature rise characteristics of mass concrete in hot weather, Proceedings of the Annual Meeting of the Architectural Institute of Japan, pp.503-504, September 2023 [Non-patent document 3] Japan Concrete Institute Kinki Branch: Guidelines for considering measures against hot weather concreting in civil engineering structures, June 2018 Summary of the Invention [Problem to be solved by the invention]
[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a method for evaluating concrete members that enables accurate evaluation of the risk of thermal cracking in concrete members when the concrete pouring temperature is 30°C or higher. [Means for solving the problem]
[0008] In order to solve the above problems, the present invention employs the following means.
[0009] [1] A method for evaluating a concrete member according to one aspect of the present invention includes measuring the maximum temperature rise T upand the maximum stress intensity ratio η0, and from the results of the calculation in the first step, the physical quantity and the maximum temperature rise amount T up A multiple regression analysis was performed on the relationship between the maximum temperature rise T up A second step of obtaining the following equation (1) regarding the maximum stress intensity ratio η0 from the results of the calculation in the first step, and a third step of performing a multiple regression analysis on the relationship between the physical quantity and the maximum stress intensity ratio η0 to obtain the following equation (2) regarding the maximum stress intensity ratio η0; and M The unit cement content C of the second concrete member and the temperature rise Δt0 from the concrete pouring temperature of 30°C are substituted into the following formula (1) to obtain the maximum temperature rise T of the second concrete member. up a fourth step of calculating the rigidity ratio (E G / E C ), width-to-thickness ratio (L M / H M ), the water-cement ratio (W / C), and the maximum temperature rise T calculated in the fourth step up and a fifth step of calculating the maximum stress strength ratio η0 of the second concrete member by substituting the above into the following equation (2). (a1, b1, c1, d1, and e1 are determined in the process of performing the multiple regression analysis in the second step, and a2, b2, c2, d2, e2, f2, and A are determined in the process of performing the multiple regression analysis in the third step.)
[0010]
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[0011]
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[0012] [2] In the method for evaluating concrete members described in [1] above, it is preferable that the physical quantities include at least one of the type of cement, the unit cement amount, the dimensions of the first concrete member, the rigidity of the ground supporting the first concrete member, and the temperature rise of the concrete member from the pouring temperature of 30°C.
[0013] [3] In the method for evaluating a concrete member described in either [1] or [2] above, it is preferable that the calculation in the first step is performed so that the pouring temperature of the first concrete member is 30°C or higher and 40°C or lower.
[0014] [4] In the method for evaluating concrete members described in either [1] or [2] above, it is preferable that the calculation in the first step is performed so that the difference between the pouring temperature of the first concrete member and the predicted pouring temperature of the second concrete member is 5°C or less. [Effects of the Invention]
[0015] According to the present invention, a method for evaluating concrete members can be provided that makes it possible to accurately evaluate the risk of cracks occurring in concrete members when the pouring temperature of the concrete member is 30°C or higher. [Brief explanation of the drawings]
[0016] [Figure 1] 1 is a process flow of a method for evaluating a concrete member according to one embodiment of the present invention. [Figure 2] 1 is a perspective view of a slab-shaped concrete member used in the calculation of the first step in the method for evaluating a concrete member according to the embodiment, and the ground supporting the concrete member. [Figure 3] 1 is an example of a chart used to calculate the maximum temperature rise of a slab-shaped concrete member. [Figure 4] 1 is an example of a chart used to calculate the stress strength ratio of a slab-shaped concrete member. [Figure 5]1 is a graph for evaluating the maximum temperature rise of a concrete member estimated in the example. More specifically, it is a graph showing the relationship between the result of calculating the maximum temperature rise obtained in the first step and the result of calculating in the fourth step using a1, b1, c1, d1, and e1 obtained in the second step. [Figure 6] 10 is a graph for evaluating the stress-intensity ratio of a concrete member estimated in the examples. More specifically, it is a graph showing the relationship between the result of calculating the maximum stress-intensity ratio obtained in the third step and the result of calculating in the fifth step using a2, b2, c2, d2, e2, f2, and A obtained in the second step. DETAILED DESCRIPTION OF THE INVENTION
[0017] The following describes in detail a concrete member evaluation method according to an embodiment of the present invention, using the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.
[0018] 1 shows a process flow of a method for evaluating concrete members according to one embodiment of the present invention. The method for evaluating concrete members mainly includes a first step, a second step, and a third step for a first concrete member, and a fourth step and a fifth step for a second concrete member.
[0019] (First step) As reference concrete members, we assume multiple slab-shaped first concrete members with different physical quantities (shape, size, material, etc.) (by setting a shape model, physical properties, and boundary conditions), and perform a temperature stress analysis on them. Figure 2 is a perspective view that schematically shows the configuration of a first concrete member 101 and the ground 102 that supports the first concrete member 101.
[0020] The physical quantities constituting the first concrete member are not particularly limited, but may include, for example, the type of cement contained in the first concrete member 101, the unit cement amount, the dimensions of the first concrete member 101, the rigidity of the ground 102, and the temperature rise of the first concrete member 101 from 30°C when it was poured. In the temperature stress analysis using three-dimensional FEM of this embodiment, it is preferable to include at least one of these, it is preferable to include more, and it is most preferable to include all of them.
[0021] In this embodiment, the term "plate-like" refers to a plate-like shape having a pair of substantially flat main surfaces and side surfaces with a smaller area than the main surfaces. As shown in FIG. 2, one main surface 101a of the first concrete member 101 is in contact with the ground 102. The shape of the main surface 101a is not particularly limited, but is preferably rectangular for analytical purposes. The shape of the side surface 101b is rectangular to ensure a uniform thickness (member thickness) of the first concrete member 101.
[0022] A temperature stress analysis was performed on the assumed first concrete member 101 using a three-dimensional FEM within a predetermined temperature range, and the maximum temperature rise T up and the maximum stress intensity ratio η0 are calculated. Maximum temperature rise T up is the maximum temperature rise relative to the temperature at the time of concrete pouring. The maximum stress-strength ratio η0 is the ratio of the temperature stress of concrete to the thermal crack initiation strength.
[0023] In this embodiment, assuming an evaluation during a hot summer, the temperature stress analysis is performed using a three-dimensional FEM assuming that the pouring temperature range of the first concrete member 101 is 30°C or more and 40°C or less. The concrete mix, concrete pouring temperature, member shape, and ground conditions of the second concrete member to be evaluated are set, and an analysis is performed in a temperature range close to the expected pouring temperature, for example, a temperature range where the difference from the expected pouring temperature is 5°C or less, and the maximum temperature rise T up It is preferable to calculate the maximum stress intensity ratio η0 as
[0024] The physical quantities of the first concrete member are assumed for each type of cement, and the maximum temperature rise T is calculated using a predetermined chart created based on the results of temperature stress analysis using three-dimensional FEM. up and the maximum stress intensity ratio η0 is calculated. For example, the unit cement amount C and thickness H of the first concrete member are used as physical quantities. M , width to thickness ratio (L M / H M ), water-cement ratio (W / C), stiffness ratio (E G / E C ) is assumed, the calculation is performed using the following procedure. Here, W indicates the density of water, and C indicates the density of cement (unit cement amount). L M is the width of the two main surfaces of the member (L M , D M ) is the larger width of (L M >D M ).
[0025] First, for each unit cement amount and pouring temperature, the thickness H M The maximum temperature rise T up A chart for determining the thickness H is prepared. M For each, the corresponding maximum temperature rise T up can be calculated.
[0026] Next, the ratio of width to thickness (L M / H M ), maximum temperature rise T up , stiffness ratio (E G / E C A chart is prepared to determine the maximum stress intensity ratio η0 corresponding to a given stiffness ratio (E G / E C ) the corresponding maximum stress intensity ratio η0 can be calculated. G indicates the soil stiffness, and E C indicates the Young's modulus of the second concrete member at 28 days.
[0027] Maximum temperature rise T using chart upThe procedure for calculating the maximum stress strength ratio η0 will be explained using an example in which a concrete member is evaluated under the following conditions. C: 450kg / mm 3 L M :25m H M :2.0m L M / H M :12.5 Δt: 5℃ (casting temperature 35℃) E C :30100N / mm 2 E G :500N / mm 2 E G / E C :0.0166 W / C: 0.389
[0028] Figure 3 is a chart used to analyze the maximum temperature rise of concrete members, showing the relationship between thickness and maximum temperature rise for each cement type and pouring temperature. This chart shows that the unit cement amount corresponding to a thickness of HM 2.0 m is 450 kg / m 3 The pouring temperature corresponding to this unit cement amount is 35°C, and the maximum temperature rise T up The answer is 58.5.
[0029] Figure 4 is a chart used to analyze the maximum stress-strength ratio η0 of concrete members, and shows the relationship between the stiffness ratio and the maximum stress-strength ratio η0 for each dimension ratio, maximum temperature rise, and water-cement ratio. G / E C The width to thickness ratio (L M / H M ) is 12.5, and the ratio of this width to thickness (L M / H M ) the maximum temperature rise T up is 58.5, and the maximum temperature rise T upThe water-cement ratio W / C corresponding to this is 38.9%, and the maximum stress strength ratio η0 corresponding to this water-cement ratio W / C is found to be 0.845.
[0030] (Second process) Maximum temperature rise T up The maximum temperature rise T of the first concrete member 101 is calculated as follows: up From the results of the above calculations, the maximum temperature rise T up is the objective variable, and the thickness H M A multiple regression analysis was performed using the unit cement amount C and the temperature rise from 30°C Δt0 as explanatory variables, and H M , C, Δt0 and T up The following relational expression is derived. It is preferable that Δt0 is equal to or greater than 0°C and equal to or less than 10°C. The derived relational expression is expressed as the following equation (1). The coefficients a1, b1, c1, d1, and e1 of the terms on the right side are determined in the process of performing multiple regression analysis. The multiple regression analysis here may be performed using spreadsheet software such as Excel.
[0031]
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[0032] (Third step) An estimation formula for the maximum stress intensity ratio η0 is derived. From the results of the above calculations of the maximum stress intensity ratio η0 of the first concrete member 101, the maximum stress intensity ratio η0 is used as the objective variable, and the maximum temperature rise T up , thickness H M , stiffness ratio (E G / E C ), width-to-thickness ratio (L M / H M ), and water-cement ratio (W / C) were used as explanatory variables in a multiple regression analysis. up , H M , (E G / E C ), (L M / H M), (W / C), and η0. This relational expression is expressed by the following equation (2). The coefficients a2, b2, c2, d2, e2, and f2 of the terms on the right-hand side are determined during the process of multiple regression analysis. The constant term A on the right-hand side is an adjustment value for a safe evaluation of the analytical value, and is preferably set to a value of about 10% of the analytical value. The multiple regression analysis here may be performed using spreadsheet software such as Excel.
[0033]
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[0034] (Fourth step) The maximum temperature rise T of the second concrete member to be evaluated up Calculate the thickness of the second concrete member H M、 The unit cement content C of the second concrete member is set, and the set value is substituted into the above formula (1) to obtain the maximum temperature rise T of the second concrete member. up Calculate.
[0035] (Fifth step) Calculate the maximum stress strength ratio η0 of the second concrete member. The stiffness ratio between the ground and the second concrete member (E G / E C ), and the dimension ratio of the second concrete member (L M / H M ), and the water-cement ratio (W / C). These set values and the maximum temperature rise T calculated in the fourth step are up is substituted into the above equation (2) to calculate the maximum stress strength ratio η0 of the second concrete member.
[0036] The condition of the second concrete member can be estimated from the maximum temperature rise and maximum stress-intensity ratio calculated in steps 4 and 5, and the risk of cracking in the second concrete member can be evaluated.When evaluating another concrete member, the above equations (1) and (2) can be used in combination, so steps 1 and 2 can be omitted.
[0037] Maximum temperature rise Tup The equation (1) used to estimate the maximum temperature rise T in equation (1) includes the term e·Δt0, which is the temperature rise from 30°C at the time of driving, and takes into account the influence of the driving temperature. up The effect of the pouring temperature is also taken into account in equation (2), which is obtained by substituting the above. Therefore, equations (1) and (2) can also be applied to the evaluation of high-temperature concrete members, such as those with pouring temperatures of 30°C or higher.
[0038] As described above, according to the concrete member evaluation method of this embodiment, the risk of thermal cracking occurring in a slab-shaped concrete member poured within a predetermined temperature range can be evaluated with high accuracy.
[0039] By using an estimation formula for the physical properties (maximum temperature rise, maximum stress intensity ratio) obtained with this evaluation method, it is possible to evaluate the risk of cracking without performing temperature stress analysis using 3D FEM, such as creating a new element model or setting analysis parameters, thereby reducing the amount of work required for evaluation.By reflecting the effect of the pouring temperature on the physical properties of the concrete member being evaluated in the estimation formula, it is possible to improve the accuracy of the risk assessment of cracking based on the estimated physical properties.
[0040] Due to global warming, it is predicted that we will see periods of extreme heat in which pouring temperatures will exceed 38°C. However, with the evaluation of this embodiment, even during periods of extreme heat, it is possible to evaluate with high accuracy the risk of thermal cracking occurring, and to carry out quality control of concrete components to prevent cracking. [Example]
[0041] The effects of the present invention will be more clearly understood from the following examples. Note that the present invention is not limited to the following examples and can be practiced with appropriate modifications within the scope of the present invention.
[0042] In order to verify the accuracy of the estimated values obtained by the evaluation method of the present invention, analysis was performed on all cases (3 x 3 x 2 x 9 x 3 = 486 cases) of slab-shaped concrete members that combined the following conditions, and the analytical values of the maximum temperature rise and maximum stress-intensity ratio were calculated. Cement type: Ordinary Portland cement, Moderate heat Portland cement, Low-heat Portland cement. Unit cement amount: 300 kg / m 3 , 400 kg / m 3 , 500 kg / m 3 . Hammering temperature: 30℃, 40℃. Material thickness: 1.0m, 2.0m, 3.5m. Part width: 10m, 25m, 40m. Ground type (ground rigidity): soft (50N / mm 2 ), normal (500N / mm 3 ), Rock (5000N / mm 2 ).
[0043] In accordance with the evaluation method of the present invention, the maximum temperature rise and maximum stress intensity ratio were estimated using the following procedure. First, a multiple regression analysis was performed on the maximum temperature rise and maximum stress intensity ratio calculated by analysis for 486 cases. The results of the multiple regression analysis are shown in Tables 1 and 2.
[0044] [Table 1]
[0045] [Table 2]
[0046] Next, the coefficients of the explanatory variables a1, b1, c1, d1, e1, a2, b2, c2, d2, e2, f2, and A obtained by multiple regression analysis were substituted into the above equations (1) and (2) for the maximum temperature rise and maximum stress intensity ratio, and estimates of the maximum temperature rise and maximum stress intensity ratio under all of the above conditions were calculated.
[0047] Figure 5 is a graph showing the relationship between analytical and estimated values for the maximum temperature rise under each condition. The horizontal axis of the graph shows the analytical values, and the vertical axis of the graph shows the estimated values obtained using equation (1) above. Plots are displayed separately for each type of cement used (ordinary Portland cement N, moderate-heat Portland cement M, low-heat Portland cement L). Figure 5 shows that the estimated values obtained are generally consistent with the analytical values in all cases, demonstrating good accuracy.
[0048] Figure 6 is a graph showing the relationship between analytical and estimated values of the maximum stress strength ratio under each condition. The horizontal and vertical axes of the graph are the same as those of the graph in Figure 5. A separate plot is shown for each type of cement used. The estimated values obtained are in close agreement with the analytical values in all cases, demonstrating good accuracy overall. Furthermore, even the 90% value of the estimated value, which is a conservative assessment, is close to the analytical value, demonstrating that the safety of the estimated results is ensured.
[0049] These results show that the evaluation method of the present invention can estimate values similar to analytical values for physical properties when the pouring temperature is 30°C to 40°C, and can evaluate with high accuracy the risk of thermal cracking in concrete components during extreme heat. [Explanation of symbols]
[0050] 101 Plate-shaped concrete member 101a... Main surface of slab-shaped concrete member 101b: Side of slab-shaped concrete member 102...ground L M , D M ...Part width H M ···Material thickness
Claims
1. The maximum temperature rise T ｕｐ and maximum stress intensity ratio η ０ A first step of calculating From the results of the calculation in the first step, the physical quantity and the maximum temperature rise T ｕｐ A multiple regression analysis is performed on the relationship between the maximum temperature rise amount T ｕｐ A second step of calculating the following formula (1) regarding From the results of the calculation in the first step, the physical quantity and the maximum stress intensity ratio η ０ A multiple regression analysis was performed on the relationship between the maximum stress intensity ratio η ０ A third step of calculating the following formula (2) regarding Thickness H of the second concrete member to be evaluated Ｍ , the unit cement amount C of the second concrete member, and the temperature rise Δt from the pouring temperature of the concrete member 30 ° C. ０ is substituted into the following formula (1) to obtain the maximum temperature rise T ｕｐ A fourth step of calculating The rigidity ratio (E Ｇ / E Ｃ ), width to thickness ratio (L Ｍ / H Ｍ ), the water-cement ratio (W / C), and the maximum temperature rise T calculated in the fourth step ｕｐ is substituted into the following equation (2) to obtain the maximum stress strength ratio η of the second concrete member. ０ and a fifth step of calculating a value of the concrete member. [Equation 1] [Equation 2] (a １ , b １ , c １ , d １ , e １ is determined in the process of performing the multiple regression analysis in the second step, and a ２ , b ２ , c ２ , d ２ , e ２ , f ２ , A is determined in the process of performing the multiple regression analysis in the third step.)
2. The method for evaluating concrete members described in claim 1, characterized in that the physical quantities include at least one of the type of cement, the unit cement amount, the dimensions of the first concrete member, the rigidity of the ground supporting the first concrete member, and the temperature rise of the concrete member from the pouring temperature of 30°C.
3. A method for evaluating concrete members described in either claim 1 or 2, characterized in that the calculation of the first step is performed so that the pouring temperature of the first concrete member is 30°C or higher and 40°C or lower.
4. A method for evaluating concrete members described in either claim 1 or 2, characterized in that the calculation of the first step is performed so that the difference between the pouring temperature of the first concrete member and the predicted pouring temperature of the second concrete member is 5°C or less.