A monitoring method for the temperature difference between upper and lower layers of mass concrete that is convenient to implement

Abstract

A method for monitoring the temperature difference between upper and lower layers of mass concrete that is easy to implement, belonging to the field of concrete construction monitoring, includes: simulating and calculating the temperature field and creep stress field of mass concrete under different construction conditions; designing different calculation methods for the temperature difference between upper and lower layers to obtain samples of the maximum temperature difference and maximum tensile stress between upper and lower layers of concrete under different calculation methods; determining the failure probability of the maximum tensile stress between upper and lower layers of concrete under different calculation methods based on the allowable tensile stress of concrete; obtaining the allowable temperature difference between upper and lower layers of mass concrete by combining the determined failure probability feedback; selecting a calculation method that is easy to calculate and on-site monitoring and the corresponding allowable temperature difference between upper and lower layers of concrete for temperature control and crack prevention of mass concrete. This method addresses the problems that the existing definition of the temperature difference between upper and lower layers is not convenient for monitoring and the control range of the allowable temperature difference between upper and lower layers is not representative. Based on the principle of matching the calculation method and monitoring index, it gives a calculation method for the allowable temperature difference between upper and lower layers under the corresponding monitoring method.

Description

Technical Field

[0001] The present invention belongs to the field of temperature control of mass concrete, and particularly relates to a method for monitoring the temperature difference between upper and lower layers of mass concrete that is easy to implement. Background Art

[0002] The allowable temperature difference of the foundation, the allowable temperature difference between upper and lower layers, and the allowable temperature difference between inside and outside are three important temperature control criteria for temperature control and crack prevention of mass concrete. When there is a long intermittent period exceeding 28 days during the pouring process of mass concrete, if the temperature gradient near the contact surface between new and old concrete is not properly controlled, it is easy to cause cracks in the mass concrete structure. At this time, it is necessary to monitor the temperature difference between upper and lower layers. However, the existing specifications define the temperature difference between upper and lower layers of mass concrete as the difference between the highest average temperature of the upper layer of newly poured concrete and the average temperature of the lower layer at the start of pouring of the previously poured concrete. It can be seen from the definition that there is no clear solution method for the highest average temperature of the upper layer of newly poured concrete, resulting in large differences in simulation calculation and temperature monitoring: should we take the highest average temperature of the entire upper layer? Or should we take the highest average temperature of the temperatures at different positions of the central section of the upper layer by referring to the calculation method of the temperature difference between inside and outside of the concrete? The same problem also exists in the specific solution method for the average temperature of the previously poured concrete. In addition, in the specification, the average temperature of the previously poured concrete is taken as the temperature at the start of opening the warehouse, which results in a fixed value for the calculated temperature difference between upper and lower layers of concrete and is difficult to reflect the change of the temperature difference between upper and lower layers of concrete within a period of time after pouring. There are great inconveniences in both the layout of temperature sensors for monitoring the temperature difference between upper and lower layers and the specific calculation of the temperature difference between upper and lower layers.

[0003] At the same time, the allowable range of the temperature difference between upper and lower layers of concrete given in the current specifications is mainly for pouring bins with a length-height ratio greater than 0.5, which is 15 - 20 °C. For pouring bins that do not meet the above size requirements, the allowable temperature difference between upper and lower layers needs to be demonstrated in detail in combination with temperature stress. In actual projects, there are many pouring bins with a length-height ratio much less than 0.5, that is, the existing control range of the allowable temperature difference between upper and lower layers has certain limitations. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for monitoring the temperature difference between upper and lower layers of mass concrete that is easy to implement. Aiming at the problems that the existing definition of the temperature difference between upper and lower layers is not convenient for monitoring and the control range of the allowable temperature difference between upper and lower layers is not representative, based on the principle of matching the calculation method and the monitoring index, a calculation method for the allowable temperature difference between upper and lower layers under the corresponding monitoring method is given.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a method for monitoring the temperature difference between upper and lower layers of mass concrete that is easy to implement, including the following steps:

[0006] Step 1. Simulation calculation of the temperature field and creep stress field of mass concrete under different construction conditions;

[0007] Step 2. Design different calculation methods for the upper and lower layer temperature difference, and obtain samples of the maximum temperature difference and maximum tensile stress between the upper and lower layers of concrete under different calculation methods;

[0008] Step 3. Determine the probability distribution function of the maximum tensile stress samples between the upper and lower layers of concrete under different calculation methods, and determine the failure probability of the maximum tensile stress between the upper and lower layers of concrete under different calculation methods based on the allowable tensile stress of concrete;

[0009] Step 4. Determine the probability distribution function of the maximum temperature difference samples between the upper and lower layers of concrete under different calculation methods, and obtain the allowable temperature difference between the upper and lower layers of mass concrete by combining with the determined failure probability feedback;

[0010] Step 5. Select a calculation method that is convenient for calculation and on-site monitoring and the corresponding allowable temperature difference between the upper and lower layers of concrete for temperature control and crack prevention of mass concrete.

[0011] In the preferred solution, in the step 1, first establish a three-dimensional finite element model of the concrete project, apply calculation parameters, boundaries and initial conditions, and carry out simulation calculations of the temperature field and creep stress field of new and old concrete in different seasons and different construction intermittent periods.

[0012] In the preferred solution, in the step 2, after determining different calculation methods for the temperature difference between the upper and lower layers of concrete, calculate the sample set of the calculated values of the temperature difference between the upper and lower layers and the corresponding sample set of the maximum tensile stress under different calculation methods in combination with the simulation calculation results of the temperature field and creep stress field under different construction conditions in the step 1;

[0013] The calculation methods for the temperature difference between the upper and lower layers include the following four types:

[0014] Method 1: The temperature of the upper layer of concrete is taken as the highest average temperature T u1 of the upper layer of concrete in the middle section area within the main influence range of the upper and lower layer temperature difference, and the temperature of the lower layer of concrete is taken as the average temperature T d1 of the lower layer of concrete in the middle section area at the start of pouring of the newly poured concrete within the main influence range of the upper and lower layer temperature difference. The difference between the two, T u1 - T d1 ;

[0015] Method 2: The temperature of the upper layer of concrete is taken as the real-time average temperature (T u2 ) t of the upper layer of concrete in the middle section area within the main influence range of the upper and lower layer temperature difference, and the average temperature of the lower layer of concrete is taken as the real-time average temperature (T d2 ) t, the maximum value of the difference between the two, Max{(T u2 ) t -(T d2 ) t};

[0016] Method 3: The temperature of the upper-layer concrete is taken as the highest average temperature T u3 of the upper-layer concrete within the main influence range of the temperature difference between the upper and lower layers in the overall area. The temperature of the lower-layer concrete is taken as the average temperature T d3 of the lower-layer concrete within the main influence range of the temperature difference between the upper and lower layers at the start of pouring of the newly poured concrete in the overall area. The difference between the two, T u3 -T d3 ;

[0017] Method 4: The temperature of the upper-layer concrete is taken as the real-time average temperature (T u4 ) t of the upper-layer concrete within the main influence range of the temperature difference between the upper and lower layers in the overall area. The temperature of the lower-layer concrete is taken as the real-time average temperature (T d4 ) t of the lower-layer concrete within the main influence range of the temperature difference between the upper and lower layers in the overall area. The maximum value of the difference between the two, Max{(T u4 ) t -(T d4 ) t}.

[0018] In the preferred solution, in step 3, it specifically includes the following steps:

[0019] S301. Organize the simulation calculation results of the creep stress field under different construction conditions to obtain the sample of the maximum tensile stress of concrete at the mature age, and calculate the mean and variance σ σ of the maximum tensile stress sample, and conduct a distribution test on it using statistical test methods to determine its probability density function f(σ);

[0020] S302. Obtain the allowable tensile stress of concrete: The expression of the allowable tensile stress of concrete is:

[0021]

[0022] In the formula: [σ(τ)] is the allowable tensile stress, MPa; ε p is the ultimate tensile value of concrete corresponding to the age; E(τ) is the elastic modulus of concrete corresponding to the age, GPa; K f is the safety factor;

[0023] S303. Obtain the failure probability based on the allowable tensile stress of concrete and the probability density function f(σ) of the maximum tensile stress of concrete at the mature age under different working conditions. When σ>[σ(τ)], the failure risk of the concrete structure is relatively large, and its probability is:

[0024]

[0025] Wherein: P α is the failure probability of the structural concrete.

[0026] In the preferred solution, in step four, it specifically includes the following steps:

[0027] S401. For the upper and lower layer temperature difference calculation method i, organize the temperature field simulation calculation results of different construction conditions to obtain the upper and lower layer temperature difference samples of the concrete, and calculate the mean value and variance σ T of the upper and lower layer temperature difference samples of the concrete, and conduct a distribution test on it using a statistical test method to determine its probability density function f i (T);

[0028] S402. Let the allowable upper and lower layer temperature difference corresponding to the upper and lower layer temperature difference calculation method i be [T] i . When the upper and lower layer temperature difference T > [T] i , the structural concrete will have the maximum tensile stress exceeding the allowable tensile stress of the concrete due to the upper and lower layer temperature difference exceeding the allowable upper and lower layer temperature difference. Since the variation laws of the upper and lower layer temperature differences and the corresponding maximum tensile stress of the concrete at 28d age are very consistent for different calculation conditions and different upper and lower layer temperature difference calculation methods, it is assumed that the probability of the upper and lower layer temperature difference exceeding the allowable upper and lower layer temperature difference is equal to the failure probability P α of the structural concrete, that is:

[0029]

[0030] Substitute the failure probability P α corresponding to the allowable tensile stress of the concrete into f i (T), and calculate the allowable upper and lower layer temperature difference [T] i corresponding to the calculation method i:

[0031]

[0032] S403. Repeat S401 and S402 to calculate and obtain the allowable upper and lower layer temperature differences corresponding to the other three upper and lower layer temperature difference calculation methods.

[0033] In the preferred solution, in step five, the calculation method uses method 1 and method 2 to bury temperature sensors, and monitors the upper and lower layer concrete temperature difference with an intermittent period exceeding 28d in combination with the corresponding allowable upper and lower layer temperature difference.

[0034] A large-volume concrete upper and lower layer temperature difference monitoring method provided by the present invention that is easy to implement has the following beneficial effects:

[0035] 1. This method addresses the issue of unclear definitions for the upper layer temperature and lower layer temperature in the temperature difference definition of mass concrete. It clarifies the values of the upper layer temperature and lower layer temperature under four different calculation methods, and determines the allowable temperature difference between the upper and lower layers under the above four different calculation methods in combination with the allowable tensile stress of concrete.

[0036] 2. Based on the principle of matching calculation methods and monitoring indicators, this method invents an easy-to-operate monitoring method for the temperature difference between the upper and lower layers of mass concrete, which solves the shortcomings of vague definition and difficult operation and implementation of the temperature difference between the upper and lower layers in existing concrete projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below with reference to the drawings and embodiments:

[0038] Figure 1 is a schematic flow chart of the method of the present invention;

[0039] Figure 2 is a schematic diagram of calculating the temperature difference between different upper and lower layers;

[0040] Figure 3 is a finite element model of the lock floor - chamfer in the embodiment;

[0041] Figure 4 is a schematic diagram of the node positions in the embodiment;

[0042] Figure 5 is the temperature distribution and stress distribution of the floor - chamfer under typical working conditions in the embodiment;

[0043] Figure 6 is the temperature change process line at a depth of 1.5 m from the new - old concrete interface inside the floor and chamfer under typical working conditions in the embodiment;

[0044] Figure 7 is the sample distribution diagram of the maximum tensile stress of the chamfer concrete at 28 d in the embodiment;

[0045] Figure 8 is the corresponding distribution diagram of different upper - lower layer temperature difference samples in the embodiment;

[0046] Figure 9 is the variation law diagram of the temperature difference between the upper and lower layers of concrete and its maximum tensile stress under different working conditions;

[0047] Figure 10 is the schematic diagram of the embedding of temperature sensors for the temperature difference between the upper and lower layers in the embodiment;

[0048] Figure 11 The temperature distribution between the upper and lower layers of the typical lock chamber in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] Combined with Figures 1 to 11Further detailed description of the specific embodiments of the present invention.

[0050] A monitoring method for the temperature difference between upper and lower layers of mass concrete that is easy to implement, as Figure 1 shown, includes the following steps:

[0051] Step 1: Simulation calculation of the temperature field and creep stress field of mass concrete under different construction conditions.

[0052] First, establish a three-dimensional finite element model of the concrete project, apply calculation parameters, boundaries, and initial conditions, and carry out simulation calculations of the temperature field and creep stress field of new and old concrete under different seasons and different construction intermittent periods.

[0053] Through the analysis of the simulation calculation results, obtain the distance from the position where the upper-layer concrete reaches the highest temperature to the interface between new and old concrete, and the depth of the temperature rise of the lower-layer concrete caused by the upper-layer concrete reaching the highest temperature, so as to obtain the main influence range of the temperature difference between the upper and lower layers of new and old concrete.

[0054] Step 2: Design different calculation methods for the temperature difference between upper and lower layers to obtain samples of the maximum temperature difference and maximum tensile stress between upper and lower layers of concrete under different calculation methods.

[0055] After determining different calculation methods for the temperature difference between upper and lower layers of concrete, combine the simulation calculation results of the temperature field and creep stress field under different construction conditions in Step 1 to calculate the sample set of the calculated values of the temperature difference between upper and lower layers and the corresponding sample set of the maximum tensile stress under different calculation methods.

[0056] Combined with the definition of the temperature difference between upper and lower layers in the existing specifications, since the value of the highest average temperature of the upper-layer concrete is not clear enough and it is difficult to reflect the law of the temperature difference between upper and lower layers changing with time when the initial value of the lower-layer concrete temperature is taken, in the present invention, the calculation methods for the temperature difference between upper and lower layers include the following four, as detailed in Figure 2 :

[0057] Method 1: The temperature of the upper-layer concrete is taken as the highest average temperature T u1 in the middle cross-section area of the upper-layer concrete within the main influence range of the temperature difference between upper and lower layers, and the temperature of the lower-layer concrete is taken as the average temperature T d1 of the lower-layer concrete in the middle cross-section area within the main influence range of the temperature difference between upper and lower layers at the start of pouring of the newly poured concrete. The difference between the two, T u1 - T d1 ;

[0058] Method 2: The temperature of the upper-layer concrete is taken as the real-time average temperature (T u2 ) t in the middle cross-section area of the upper-layer concrete within the main influence range of the temperature difference between upper and lower layers, and the average temperature of the lower-layer concrete is taken as the real-time average temperature (Td2 ) t , the maximum value of the difference between the two, Max{(T u2 ) t -(T d2 ) t};

[0059] Method 3: The temperature of the upper-layer concrete is taken as the highest average temperature T of the upper-layer concrete in the overall area within the main influence range of the temperature difference between the upper and lower layers u3 , and the temperature of the lower-layer concrete is taken as the average temperature T of the lower-layer concrete in the overall area at the start of pouring of the newly poured concrete within the main influence range of the temperature difference between the upper and lower layers d3 . The difference T u3 -T d3 ;

[0060] Method 4: The temperature of the upper-layer concrete is taken as the real-time average temperature (T u4 ) t of the upper-layer concrete in the overall area within the main influence range of the temperature difference between the upper and lower layers, and the temperature of the lower-layer concrete is taken as the real-time average temperature (T d4 ) t of the lower-layer concrete in the overall area within the main influence range of the temperature difference between the upper and lower layers. The maximum value of the difference between the two, Max{(T u4 ) t -(T d4 ) t}.

[0061] Among the above four calculation methods, Method 1 and Method 3 calculate by taking the area with higher internal temperature and the inter-layer area of the entire pouring block according to the definition of the temperature difference between the upper and lower layers in the existing mass concrete construction specifications. Method 2 and Method 4 calculate considering that the temperature difference between the upper and lower layers of concrete changes in real time.

[0062] After determining the different calculation methods for the temperature difference between the upper and lower layers of concrete, combined with the simulation calculation results of the temperature field and creep stress field under the aforementioned different construction conditions, the sample sets of the calculated values of the temperature difference between the upper and lower layers and the corresponding sample sets of the maximum tensile stress are calculated under the four different calculation methods.

[0063] Step Three: Determine the probability distribution function of the maximum tensile stress samples of the upper and lower layers of concrete under different calculation methods, and determine the failure probability of the maximum tensile stress of the upper and lower layers of concrete under different calculation methods based on the allowable tensile stress of concrete.

[0064] Specifically, it includes the following steps:

[0065] S301. Organize the simulation calculation results of the creep stress field under different construction conditions to obtain the maximum tensile stress samples of concrete at the mature age, and calculate the mean value and variance σ σ, perform a distribution test on it using statistical test methods (such as the K-S method, etc.), and determine its probability density function f(σ), such as normal distribution and lognormal distribution, etc.

[0066] S302. Obtain the allowable tensile stress of concrete: The expression for the allowable tensile stress of concrete is:

[0067]

[0068] In the formula: [σ(τ)] is the allowable tensile stress, MPa; ε p is the ultimate tensile value of concrete corresponding to the age, generally taking (0.7 - 1.0)×10 -4 ; E(τ) is the elastic modulus of concrete corresponding to the age, GPa; K f is the safety factor, which depends on the importance of the project and the harmfulness of cracking, and generally takes 1.5 - 2.0.

[0069] Determine the allowable tensile stress of concrete at the maturity age according to the actual situation of the project. For general concrete projects, 28d is generally taken as the maturity age, and for dam projects, 90d is generally taken as the maturity age.

[0070] S303. Obtain the failure probability based on the allowable tensile stress of concrete and the probability density function f(σ) of the maximum tensile stress of concrete at the maturity age under different working conditions. When σ > [σ(τ)], the failure risk of the concrete structure is relatively large, and its probability is:

[0071]

[0072] In the formula: P α is the failure probability of the structural concrete.

[0073] Step Four. Determine the probability distribution function of the maximum temperature difference sample between the upper and lower layers of concrete under different calculation methods, and obtain the allowable temperature difference between the upper and lower layers of mass concrete by combining with the determined failure probability feedback.

[0074] Specifically, it includes the following steps:

[0075] S401. For the upper and lower layer temperature difference calculation method i, organize the temperature field simulation calculation results of different construction working conditions to obtain the upper and lower layer temperature difference sample of concrete, and calculate the mean value and variance σ T , perform a distribution test on it using statistical test methods (such as the K-S method, etc.), and determine its probability density function f i (T), such as normal distribution and lognormal distribution, etc.

[0076] S402. Let the allowable temperature difference between the upper and lower layers corresponding to the upper and lower layer temperature difference calculation method i be [T] i , when the upper and lower layer temperature difference T > [T]i When the temperature difference between the upper and lower layers of the structural concrete exceeds the allowable temperature difference between the upper and lower layers, the maximum tensile stress will exceed the allowable tensile stress of the concrete. Since the variation laws of the temperature difference between the upper and lower layers and the corresponding maximum tensile stress of the concrete at 28 days of age obtained under different calculation conditions and different calculation methods of the temperature difference between the upper and lower layers are very consistent, it is assumed that the probability of the temperature difference between the upper and lower layers exceeding the allowable temperature difference between the upper and lower layers is equal to the failure probability P of the structural concrete α That is:

[0077]

[0078] Substitute the failure probability P corresponding to the allowable tensile stress of the concrete α into f i (T), and calculate the allowable temperature difference [T] between the upper and lower layers corresponding to the calculation method i i :

[0079]

[0080] S403. Repeat S401 and S402 to calculate the allowable temperature differences between the upper and lower layers corresponding to the other three calculation methods of the temperature difference between the upper and lower layers

[0081] Step Five: Select a calculation method and the corresponding allowable temperature difference between the upper and lower layers of the concrete that are convenient for calculation and on-site monitoring to control and prevent cracking of mass concrete

[0082] From the above four calculation methods of the temperature difference between the upper and lower layers

[0083] For calculation methods 3 and 4, it is necessary to monitor the temperature of the upper or lower layer concrete in the overall area within the main influence range of the temperature difference between the upper and lower layers. This requires burying a large number of temperature sensors for temperature monitoring, which is not only costly but also inconvenient for calculation and monitoring, and is difficult to operate and implement in actual projects

[0084] For calculation methods 1 and 2, only by burying temperature sensors in the middle cross-section area within the main influence range of the temperature difference between the upper and lower layers can the temperature difference between the upper and lower layers of the concrete be monitored well. At this time, combining the allowable temperature differences between the upper and lower layers corresponding to calculation methods 1 and 2 can effectively monitor the temperature difference between the upper and lower layers of the concrete with an intermittent period exceeding 28 days

[0085] Therefore, calculation methods 1 and 2 are used to bury temperature sensors and cooperate with the corresponding allowable temperature differences between the upper and lower layers to monitor the temperature difference between the upper and lower layers of the concrete with an intermittent period exceeding 28 days

[0086] Case analysis:

[0087] A large ship lock project is a Class - II ship lock. The bottom slab is cast in 3 parts: the middle, the south, and the north. The upper parts of the south and north bottom slabs are chamfer and side - wall concrete. When pouring concrete, after the bottom - slab concrete is poured, it is necessary to wait for 28 days or more before starting to pour the chamfer concrete on the bottom slab. At this time, the monitoring of the temperature difference between the upper and lower layers of concrete is concerned by the engineering unit. The following monitors the temperature difference between the upper and lower layers of the bottom slab - chamfer of this large ship lock project.

[0088] Step 1: Simulation calculation of temperature field and creep stress field under different construction conditions

[0089] According to the actual dimensions of the ship - lock bottom slab and chamfer, first establish a 3D finite - element model of the ship - lock foundation - bottom slab - chamfer, as shown in the appendix Figure 3 ; Then set the thermal and mechanical parameters of the concrete, and apply different boundary conditions for different boundaries. Among them, the bottom of the foundation is completely displacement - constrained, and all around are link - constrained. When designing the calculation conditions, referring to the construction organization design, the ship - lock project has bottom - slab pouring in all four seasons of spring, summer, autumn, and winter, and the upper - layer chamfer concrete of the bottom slab is poured after an interval of 30d - 180d. Therefore, the designed calculation conditions are 24 groups of calculation conditions for pouring the bottom slab in the four seasons of spring, summer, autumn, and winter, and pouring the chamfer after intervals of 30d, 60d, 90d, 120d, 150d, and 180d. Since this ship lock uses C25 pumped concrete with a high hydration - heat rate and the 28 - day age has reached the mature age, the simulation calculation ends when the chamfer reaches 28 - day age.

[0090] The simulation calculation of the temperature field and creep stress field is mainly to obtain the temperature and stress magnitudes in typical areas, as well as the main influence range of the temperature difference between the upper and lower layers. When specifically analyzing, take the node temperature and stress at the center of the bottom - slab - chamfer concrete for analysis. The schematic diagram of the specific node positions is shown in the appendix Figure 4 as shown. Since there are 24 groups of calculation conditions, only the temperature and stress distributions of typical conditions are given in this embodiment, as shown in the appendix Figure 5 as shown, and the process line of the temperature change of typical measuring points over time is shown in the appendix Figure 6 as shown. In the appendix Figure 6 , U30d and D30d respectively represent the temperature - process lines of the measuring points at a depth of 1.5m from the new - old concrete interface of the chamfer and the bottom slab when pouring the chamfer after an interval of 30d.

[0091] Step 2: Design of different calculation methods for the temperature difference between the upper and lower layers and obtaining samples of the maximum temperature difference and its maximum tensile stress

[0092] From the analysis of the temperature field and creep stress field results, it can be seen that after the chamfered concrete is poured, the temperature gradient within a depth range of 1.5 m above and below the interface between the new and old concrete is very large. The temperature of the lower floor slab concrete within this range is significantly affected by the temperature of the upper chamfered concrete. In addition, when the chamfered concrete reaches its temperature peak at the age of 3 days, the temperature of the measuring point at a depth of 1.5 m from the interface between the new and old concrete in the floor slab concrete only has a very small increase. From the range of the area with a large temperature gradient and the temperature rise of the old concrete, it can be seen that the main range affected by the temperature difference between the upper and lower layers in the floor slab-chamfer area of this ship lock project is about 1.5 m above and below the interface between the new and old concrete. Therefore, according to the four calculation methods for the temperature difference between the upper and lower layers proposed in this patent, the four calculation methods for the temperature difference between the upper and lower layers of this ship lock are as follows:

[0093] Method 1: The temperature of the upper concrete is taken as the highest average temperature T of the 1.5 m range of the upper concrete at the interface between the new and old concrete in the middle section area u1 , and the temperature of the lower concrete is taken as the average temperature T of the 1.5 m area of the lower concrete at the interface between the new and old concrete in the middle section when the upper concrete starts to be poured d1 . The difference between the two is T u1 - T d1 .

[0094] Method 2: The temperature of the upper concrete is taken as the real-time average temperature (T u2 ) t of the 1.5 m range of the upper concrete at the interface between the new and old concrete in the middle section area, and the average temperature of the lower concrete is taken as the real-time average temperature (T d2 ) t of the 1.5 m range of the lower concrete at the interface between the new and old concrete in the middle section when the upper concrete starts to be poured. The maximum temperature difference between the two is Max{(T u2 ) t - (T d2 ) t}.

[0095] Method 3: The temperature of the upper concrete is taken as the overall highest average temperature T of the 1.5 m area of the upper concrete at the interface between the new and old concrete for the temperature difference between the upper and lower layers u3 , and the temperature of the lower concrete is taken as the overall average temperature T of the 1.5 m area of the lower concrete at the interface between the new and old concrete when the upper concrete starts to be poured d3 . The difference between the two is T u3 - T d3 .

[0096] Method 4: The temperature of the upper concrete is taken as the overall real-time average temperature (T u4 ) t, the temperature of the lower-layer concrete is the overall real-time average temperature of the 1.5m area of the lower-layer concrete at the interface between the upper and lower layers, taking the temperature difference between the upper and lower layers (T d4 ) t , and the maximum value of the temperature difference between the two is Max{(T u4 ) t -(Td4) t}.

[0097] Extract the temperature data of the finite element nodes according to the four calculation methods of the temperature difference between the upper and lower layers. The samples of the temperature difference between the upper and lower layers under the four different calculation methods for different calculation conditions are shown in Tables 1 to 4 in the appendix.

[0098] Table 1 Temperature difference between upper and lower layers obtained by calculation method 1 (°C) in different seasons

[0099]

[0100] Table 2 Temperature difference between upper and lower layers obtained by calculation method 2 (°C) in different seasons

[0101]

[0102] Table 3 Temperature difference between upper and lower layers obtained by calculation method 3 (°C) in different seasons

[0103]

[0104] Table 4 Temperature difference between upper and lower layers obtained by calculation method 4 (°C) in different seasons

[0105]

[0106] Step 3: Determine the concrete failure probability based on the allowable tensile stress of concrete

[0107] The determination of the structural concrete failure probability is divided into the following three steps:

[0108] S301. First, extract the stress field data from the simulation calculation to obtain the sample of the maximum tensile stress of the concrete. The mean value of the sample of the maximum tensile stress of the concrete is 1.633, and the variance is 0.285. The K-S method is used to conduct a statistical test on the sample. As shown in Table 5, the analysis shows that the sample of the maximum tensile stress of the concrete follows a normal distribution. The normal distribution histogram of the sample is shown in the appendix Figure 7 .

[0109] Table 5 K-S test results of the sample of the maximum tensile stress of the concrete

[0110]

[0111] Thus, the probability density function of the maximum tensile stress of the concrete obtained is

[0112]

[0113] S302. Obtain the allowable tensile stress of concrete.

[0114] The concrete used in this project is pumped concrete. Taking 28 days as the mature age, according to relevant concrete test data, the ultimate tensile value of the concrete at the age of 28 days is taken as 0.85×10 -4 , the elastic modulus of the concrete at the age of 28 days is taken as 31.20 GPa, and the safety factor is taken as 1.6. The allowable tensile stress of the concrete at the age of 28 days is 1.66 MPa.

[0115] S303. Obtain the failure probability based on the allowable tensile stress of concrete and the probability density function f(σ) of the maximum tensile stress of concrete at the mature age under different working conditions. When σ > [σ(τ)] = 1.66, the structural concrete will fail, and its probability is:

[0116]

[0117] The failure probability P obtained after integration a is 0.486.

[0118] Step 4. Determine the allowable temperature difference between the upper and lower layers of concrete under different calculation methods

[0119] S401. For the temperature difference calculation method 1 between the upper and lower layers, organize the simulation calculation results of the temperature field under different construction working conditions to obtain the temperature difference samples between the upper and lower layers of concrete. The mean value of the samples is 29.025 and the variance is 3.360. Then, use the K-S method for statistical testing. As shown in Table 6, the analysis shows that the temperature difference samples between the upper and lower layers under the four different calculation methods all satisfy the normal distribution.

[0120] Table 6 K-S test results of the samples of the calculated values of the temperature difference between the upper and lower layers

[0121]

[0122] The histogram of the assumed sample normal distribution is shown in the appendix Figure 8 as shown. The probability density functions of the calculated values of the temperature difference between the upper and lower layers obtained by the four calculation methods are as follows.

[0123] Method 1:

[0124] S402. The variation laws of the temperature difference between the upper and lower layers of concrete and its maximum tensile stress under different working conditions are shown in the appendix Figure 9 as shown. Substitute the failure probability P corresponding to the allowable tensile stress of concrete α into the probability density function f(T) of Equation (7), and the allowable temperature difference [T] between the upper and lower layers under different calculation methods can be obtained. The calculation expression is:

[0125]

[0126] The calculated allowable temperature difference between the upper and lower layers, for specific results, see Appendix 7.

[0127] S403. Repeat S401 and S402 to calculate the probability density functions corresponding to the other three calculation methods of the temperature difference between the upper and lower layers as

[0128] Method 2:

[0129] Method 3:

[0130] Method 4:

[0131] The calculated allowable temperature difference between the upper and lower layers, for specific results, see Appendix 7.

[0132] Table 7 Allowable temperature differences between the upper and lower layers corresponding to different calculation methods (°C)

[0133]

[0134] Step 5. Selection of the calculation method for the temperature difference between the upper and lower layers

[0135] During the process of monitoring the temperature of the bottom slab and the guide angle of this ship lock project, point-type temperature sensors were used for temperature monitoring work. Therefore, when monitoring the temperature difference between the upper and lower layers, calculation methods 1 and 2 were used for monitoring. The layout of the temperature sensors is shown in the appendix Figure 10 as shown, and the typical chamber temperature distribution is shown in the appendix Figure 11 as shown. The temperature differences between the upper and lower layers obtained by using calculation methods 1 and 2 are shown in Appendix 8.

[0136] Table 8 Temperature differences between the upper and lower layers on both the north and south sides of the typical chamber for different calculation methods (°C)

[0137]

[0138] The temperature differences between the upper and lower layers obtained by using calculation method 1 on both the north and south sides of the typical chamber are 26.13 °C and 27.84 °C respectively, and the temperature differences between the upper and lower layers obtained by using calculation method 2 are 19.27 °C and 19.55 °C respectively, neither of which exceeds the allowable temperature differences under the corresponding calculation methods as previously determined. No harmful cracks were found during the actual construction process, indicating that the calculation method for the temperature difference between the upper and lower layers proposed in this method and the proposed method for determining the allowable temperature difference between the upper and lower layers are practical and feasible.

Claims

1. A monitoring method for the temperature difference between upper and lower layers of mass concrete that is easy to implement, characterized in that, It includes the following steps: Step 1: Simulate and calculate the temperature field and creep stress field of mass concrete under different construction conditions; Step 2: Design different calculation methods for the temperature difference between upper and lower layers of concrete. After determining different calculation methods for the temperature difference between upper and lower layers of concrete, combine the simulation calculation results of the temperature field and creep stress field under different construction conditions in Step 1 to calculate the sample set of the temperature difference calculation values between upper and lower layers and the corresponding sample set of the maximum tensile stress under different calculation methods, and obtain the samples of the maximum temperature difference and maximum tensile stress between upper and lower layers of concrete under different calculation methods; The calculation methods for the temperature difference between upper and lower layers include the following four: Method 1: The upper layer concrete temperature is taken as the highest average temperature T of the upper layer concrete in the middle cross-section area within the main influence range of the upper and lower layer temperature difference u1 , and the lower layer concrete temperature is taken as the average temperature T of the lower layer concrete in the middle cross-section area at the start of the newly poured concrete pouring within the main influence range of the upper and lower layer temperature difference d1 . The difference between the two is T u1 - T d1 ; Method 2: The temperature of the upper-layer concrete is taken as the real-time average temperature (T u2 ) t of the upper-layer concrete within the main influence range of the upper and lower layer temperature difference in the middle cross-section area, and the average temperature of the lower-layer concrete is taken as the real-time average temperature (T d2 ) t of the lower-layer concrete within the main influence range of the upper and lower layer temperature difference in the middle cross-section area. The maximum value of the difference between the two is Max{(T u2 ) t -(T d2 ) t}; Method 3: The temperature of the upper-layer concrete is taken as the highest average temperature T of the upper-layer concrete within the overall area within the main influence range of the temperature difference between the upper and lower layers u3 , and the temperature of the lower-layer concrete is taken as the average temperature T of the lower-layer concrete within the overall area within the main influence range of the temperature difference between the upper and lower layers at the start of pouring of the newly poured concrete d3 . The difference between the two is T u3 - T d3 ; Method 4: The temperature of the upper-layer concrete is taken as the real-time average temperature (T u4 ) t of the upper-layer concrete within the main influence range of the upper and lower layer temperature difference in the overall area, and the temperature of the lower-layer concrete is taken as the real-time average temperature (T d4 ) t of the lower-layer concrete within the main influence range of the upper and lower layer temperature difference, and the maximum value of the difference between the two is Max{(T u4 ) t -(T d4 ) t}; Step 3: Determine the probability distribution function of the maximum tensile stress samples between upper and lower layers of concrete under different calculation methods, and determine the failure probability of the maximum tensile stress between upper and lower layers of concrete under different calculation methods based on the allowable tensile stress of concrete; Step 4: Determine the probability distribution function of the maximum temperature difference samples between upper and lower layers of concrete under different calculation methods, and obtain the allowable temperature difference between upper and lower layers of mass concrete by combining the determined failure probability feedback; Step 5: Select a calculation method that is convenient for calculation and on-site monitoring and the corresponding allowable temperature difference between upper and lower layers of concrete to control and prevent cracking of mass concrete.

2. The large-volume concrete upper and lower layer temperature difference monitoring method according to claim 1, characterized in that In the said Step 1, first establish a three-dimensional finite element model of the concrete project, apply calculation parameters, boundaries and initial conditions, and carry out simulation calculations of the temperature field and creep stress field of new and old concrete in different seasons and different construction intervals.

3. The large-volume concrete upper and lower layer temperature difference monitoring method according to claim 1, characterized in that, In the said Step 3, it specifically includes the following steps: S301. Organize the simulation calculation results of the creep stress field under different construction conditions to obtain the maximum tensile stress samples of concrete at the mature age, and calculate the mean value of the maximum tensile stress samples and variance , and conduct a distribution test on them using statistical test methods to determine their probability density function f ( σ ); S302. Obtain the allowable tensile stress of concrete: The expression of the allowable tensile stress of concrete is: (1)； Where: [σ(τ)] is the allowable tensile stress, MPa; ε p is the ultimate tensile value of concrete at the corresponding age; E ( τ ) is the elastic modulus of concrete at the corresponding age, GPa; K f is the safety factor; S303. Probability density function of the maximum tensile stress of concrete at the maturity age based on the allowable tensile stress of concrete and different working conditions f ( σ ) Obtain the failure probability. When , the failure risk of the concrete structure is high, and its probability is: (2)； In the formula: P α is the failure probability of structural concrete.

4. A method for monitoring the temperature difference between upper and lower layers of mass concrete that is easy to implement according to claim 1, characterized in that, In the said Step 4, it specifically includes the following steps: S401. For the calculation method of the temperature difference between the upper and lower layers i , organize the simulation calculation results of the temperature field under different construction conditions to obtain the sample of the temperature difference between the upper and lower layers of concrete, and calculate the mean value and variance of the sample of the temperature difference between the upper and lower layers of concrete, and conduct a distribution test on it using statistical test methods to determine its probability density function f i ( T ); S402. Set the calculation method for the temperature difference between the upper and lower layers i The corresponding allowable temperature difference between the upper and lower layers is T i , when the temperature difference between the upper and lower layers T > T i , the structural concrete will have a maximum tensile stress exceeding the allowable tensile stress of the concrete due to the temperature difference between the upper and lower layers exceeding the allowable temperature difference between the upper and lower layers. Assume that the probability of the temperature difference between the upper and lower layers exceeding the allowable temperature difference between the upper and lower layers is equal to the failure probability of the structural concrete P α That is:​​ (3)； The failure probability corresponding to the allowable tensile stress of concrete P α Substitute into f i ( T ) to calculate the calculation method i The allowable temperature difference between the upper and lower layers corresponding to T i :​ (4)； S403. Repeat S401 and S402 to calculate the allowable temperature difference between upper and lower layers corresponding to the other three calculation methods for the temperature difference between upper and lower layers.

5. The method for monitoring the temperature difference between upper and lower layers of mass concrete that is easy to implement according to claim 1, wherein In the said Step 5, the calculation method uses Method 1 and Method 2 to bury temperature sensors, and monitors the temperature difference between upper and lower layers of concrete with an interval exceeding 28 days in combination with the corresponding allowable temperature difference between upper and lower layers.

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