A method for controlling the smooth temperature drop rate curve of a large-volume thin-wall structure concrete

Abstract

The application discloses a control method of a large-volume thin-wall structure concrete smooth temperature drop rate curve, which comprises the following steps: S1, judging whether a temperature drop stage starts or not, and calculating a temperature drop duration when the temperature drop starts; S2, calculating a concrete adiabatic temperature rise value; S3, calculating a temperature drop rate index of the moment according to the temperature drop duration and a temperature drop rate curve fitting formula and a temperature drop rate proportion; S4, calculating an actual temperature drop rate Δt, and adjusting a cooling water flow rate according to comparison of the actual temperature drop rate Δt of the moment with the temperature drop rate index; and S5, calculating a valve operation time of an electromagnetic valve. The application can more accurately control the temperature drop rate of the large-volume thin-wall structure concrete at each moment during a temperature drop period, obviously reduces an over-standard amplitude of the temperature drop rate of the concrete during a construction period, controls the temperature drop rate in a reasonable range, and further reduces a maximum tensile stress in the concrete.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of temperature control during the construction period of mass concrete, and particularly relates to a control method for smooth temperature drop rate curve of mass thin-wall structure concrete. BACKGROUND

[0002] Mass thin-wall structure concrete is widely used in the fields of water conservancy and hydropower, transportation, municipal administration, industrial construction, etc. Because of its high cement consumption and large heat generation, the cracking of concrete caused by temperature stress is one of the problems faced by engineering construction. According to the investigation data at home and abroad, about 20% of the cracks in concrete structures are caused by load, and 80% of the cracks are caused by shrinkage and uneven deformation, temperature change, etc. In the early stage of concrete construction, the hydration heat reaction of cement will release a large amount of heat, which will cause the basic temperature difference and the internal and external temperature difference of the concrete. When these temperature differences are too large, the concrete will crack with the change of temperature. At present, the temperature control of mass concrete mainly controls the internal and external temperature difference and the maximum temperature, and the control of temperature drop rate is not enough. Practice shows that too fast temperature drop rate will cause the temperature stress in the structure to exceed the ultimate tensile stress of concrete, and then internal cracks will be generated; and too slow temperature drop rate will cause the internal and external temperature difference to exceed the standard for a long time and surface cracks will be generated. Therefore, it is necessary to optimize and automatically control the temperature drop rate during the construction period of concrete.

[0003] In the patent of "Concrete Construction Period Temperature Automatic Control System", the intelligent temperature control system of mass concrete is composed of an upper computer system and three subsystems, and can realize the automatic control of the temperature drop rate during the construction period of concrete. However, from the actual effect of the system in the past in the pump station type mass thin-wall concrete structure, the stepwise temperature drop algorithm of the system is not accurate enough for the control of the temperature drop rate of concrete, and the controlled temperature drop rate is sometimes quite different from the temperature drop rate index. SUMMARY

[0004] The purpose of the present application is to provide a control method for smooth temperature drop rate curve of mass thin-wall structure concrete, which can enhance the accuracy of the actual temperature drop rate during temperature control and avoid the cracking problem caused by early age stress exceeding the standard.

[0005] Technical scheme: A control method for smooth temperature drop rate curve of mass thin-wall structure concrete, comprising the following steps:

[0006] S1, judging whether the temperature drop stage starts, and calculating the temperature drop duration when the temperature drop starts;

[0007] S2, calculating the adiabatic temperature rise value of concrete;

[0008] S3, according to the temperature drop duration and the temperature drop rate curve fitting formula, the temperature drop rate ratio, calculate the temperature drop rate index at this time;

[0009] S4, calculate the actual temperature drop rate Δt, according to the comparison between the actual temperature drop rate Δt at this time and the temperature drop rate index, adjust the cooling water flow;

[0010] S5, calculate the valve operating time of the electromagnetic valve.

[0011] Further, the criterion for judging the start of the temperature drop stage is that the age of the concrete is greater than zero and the internal temperature tn at this time is less than the internal temperature tnq at the previous time.

[0012] Further, the calculation formula of the adiabatic temperature rise value of the concrete is as follows:

[0013]

[0014] Where, θ(n) is the adiabatic temperature rise value of the concrete, n represents the age of the concrete, and the unit is h; e is the natural constant.

[0015] Further, in step S3, a temperature duration curve with minimum temperature stress is obtained by simulation calculation, the temperature drop stage of the temperature duration curve is cut off for fitting, and the fitting formula is as follows:

[0016] y = 13.38 + 47.62*0.89x

[0017] In the formula, y is the temperature, ℃; x is the temperature drop time, d;

[0018] Take the derivative of the fitting formula and take the negative value to obtain the temperature drop rate curve:

[0019] y' = -47.62*ln(0.89)*0.89^x

[0020] In the formula, y' is the temperature drop rate, ℃ / d;

[0021] Further, the upper and lower limits [a, b] of the temperature drop rate index at this time are obtained.

[0022] Further, in step S4, the actual temperature drop rate Δt at this time is compared with the temperature drop rate index: if the actual temperature drop rate Δt is not within the corresponding temperature drop rate index range [a, b], the cooling water flow is adjusted to the target flow Q 新 , the calculation formula of the target flow Q 新 is:

[0023] Q 新 = Q 旧 / (Δt+j)*(j+(a+b) / 2)

[0024] j = theta (n+1) - theta (n)

[0025] In the formula, Q 新 , Q 旧 are target flow and previous time flow respectively; Delta t is actual temperature drop rate; a is lower limit value of temperature drop rate index, value is 0.9*M, unit is DEG C / h; b is upper limit value of temperature drop rate index, value is 1.1*M, unit is DEG C / h, and M is corresponding temperature drop rate index.

[0026] Further, in step S5, target flow Q 新 corresponding to electromagnetic valve flow opening degree relationship curve is obtained. 目标 Then, the calculation formula of valve operation time of electromagnetic valve is as follows:

[0027] T 阀 = KD 目标 -KD 原

[0028] In the formula, T 阀 is valve operation time, unit is s, and negative value indicates valve closing |T 阀 |, and positive value indicates valve opening T 阀 ; KD 目标 is target valve opening degree, unit is s; and KD 原 is previous time valve opening degree value, unit is s.

[0029] Compared with the prior art, the present application has the following remarkable effects:

[0030] The present application optimizes the original stepped line segment temperature drop rate curve into a smooth curve temperature drop rate curve, can enhance the precision of actual temperature drop rate during temperature control, more accurately controls the temperature drop rate at each time during the temperature drop period of large-volume thin-wall structure concrete, obviously reduces the over-standard amplitude of concrete construction period temperature drop rate, controls it in a reasonable range, and then reduces the maximum tensile stress in the concrete; compared with the previous stepped temperature drop, the cracking problem caused by early-age stress over-standard is avoided to a greater extent. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The flow chart of the present application;

[0032] Figure 2 The temperature drop rate index diagram of the present application. DETAILED DESCRIPTION

[0033] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0034] The application obtains a relatively optimal temperature drop rate curve through simulation calculation, and applies the optimal temperature drop rate curve to actual engineering, so that the temperature drop rate of concrete during construction period can be more accurately controlled.

[0035] As Figure 1 Fig. 1 is a control algorithm flow chart of a mass concrete smooth temperature drop curve according to the application, and the implementation steps are as follows:

[0036] Step 1, judge whether the temperature drop stage starts, and calculate the temperature drop duration when the temperature drop starts.

[0037] The criterion for judging whether the temperature drop stage starts is that the age of the concrete is greater than zero and the internal temperature tn at this moment is less than the internal temperature tnq at the previous moment.

[0038] After judging that the temperature drop stage starts, the temperature drop rate proportion is calculated according to the actual maximum temperature of the concrete and the maximum temperature index.

[0039] Step 2, calculate the adiabatic temperature rise value of the concrete, and the calculation formula of the adiabatic temperature rise value of the concrete is as follows:

[0040]

[0041] Wherein, θ(n) is the adiabatic temperature rise value of the concrete, n represents the age of the concrete, and the unit is h; e is a natural constant.

[0042] Step 3, calculate the temperature drop rate index at this moment according to the temperature drop duration T and the temperature drop rate curve fitting formula and the temperature drop rate proportion, and then obtain the upper and lower limits [a, b] of the temperature drop rate index at this moment, Figure 2 Fig. 2 is a temperature drop rate index schematic diagram.

[0043] Through simulation calculation of multiple different temperature drop rates of multiple different working conditions, the stress sizes under several working conditions are compared, and a temperature duration curve with the minimum temperature stress is obtained. The temperature drop stage of the temperature duration curve is cut off for fitting, and a fitting formula can be obtained:

[0044] y = 13.38 + 47.62*0.89^x (2)

[0045] In the formula, y is temperature (℃), and x is temperature drop time (d).

[0046] The derivative of formula (2) is taken and then the negative value is taken, so that the temperature drop rate curve can be obtained:

[0047] y' = -47.62*ln(0.89)*0.89^x (3)

[0048] In the formula, y' is temperature drop rate (℃ / d), and x is temperature drop time (d).

[0049] Step 4, calculate the actual temperature drop rate Δt, and compare the actual temperature drop rate Δt at this moment with the temperature drop rate index: if the actual temperature drop rate Δt is not within the range [a, b] corresponding to the temperature drop rate index, adjust the cooling water flow to the target flow Q 新 . The calculation formula of the target flow Q 新 is as follows:

[0050] Q 新 = Q 旧 / (Δt+j)*(j+(a+b) / 2) (4)

[0051] j=θ(n+1)-θ(n) (5)

[0052] In the formula, Q 新 , Q 旧 are the target flow and the flow at the previous moment respectively; Δt is the actual temperature drop rate; a is the lower limit value of the temperature drop rate index, with a value of 0.9*M and a unit of ℃ / h; b is the upper limit value of the temperature drop rate index, with a value of 1.1*M and a unit of ℃ / h, and M is the corresponding temperature drop rate index.

[0053] Step 5, calculate the valve operation time of the electromagnetic valve;

[0054] After the target flow Q 新 is calculated, the target valve opening KD 目标 corresponding to the target flow can be obtained according to the flow opening relationship curve of the electromagnetic valve. Finally, the valve operation time of the electromagnetic valve is calculated, and the calculation formula is as follows:

[0055] T 阀 = KD 目标 - KD 原 (6)

[0056] In the formula, T 阀 is the valve operation time, with a unit of s, and a negative value indicates that the valve is closed |T 阀 |(s), and a positive value indicates that the valve is opened T 阀 (s); KD 目标 is the target valve opening, with a unit of s; KD 原 is the valve opening value at the previous moment, with a unit of s, and the upper computer system control program can obtain KD 原 by reading the intermediate data file of the system.

[0057] In this embodiment, a certain large-scale drainage pump station is taken as an example, and five vertical shaft tubular pump groups are used, with a single machine design flow of 40m 3The flow channel structure of the pump station is complex, and the pump station is a vertical shaft through-flow type. The flow channel structure is three-hole + two-hole, and the size of the three-hole inlet section is relatively large (29.25 m in the river direction * 35.5 m in the transverse river direction). The concrete grade is C30, and the final value of the adiabatic temperature rise is 50°C. Since the high-grade normal concrete is different from the low-grade concrete and low-heat cement concrete commonly used in dams, the temperature rise and fall rate is often larger, and the fluctuation range of the temperature fall rate is also significantly higher than the fluctuation range of the temperature fall rate of the dam concrete.

[0058] In this embodiment, 12 temperature measuring points in the flow channel mass concrete are selected as test samples, and the temperature drop rate during the construction period is shown in Table 1.

[0059] Table 1 Temperature drop rate during construction period of flow channel part

[0060]

[0061]

[0062] As shown in Table 1, the maximum over-standard range of the temperature drop rate is 20%, and the average over-standard range of the temperature drop rate is 8.7%, which is less than the expected target of 10%.

Claims

1. A method for controlling the smooth temperature drop rate curve of large-volume thin-walled concrete structures, characterized in that, The steps include the following: S1, determine whether the temperature drop phase has started, and calculate the temperature drop duration when the temperature drop begins; S2, calculates the temperature rise of concrete adiabatic properties; S3. Calculate the temperature drop rate index at this moment based on the temperature drop duration, the temperature drop rate curve fitting formula, and the temperature drop rate ratio. S4, Calculate the actual temperature drop rate Based on the actual rate of temperature drop at that moment Compare the cooling water flow rate with the temperature drop rate index and adjust accordingly; S5, calculate the valve operation time of the solenoid valve; The formula for calculating the thermal temperature rise of concrete is as follows: in, This represents the adiabatic temperature rise of concrete, where n represents the age of the concrete in hours (h), and e is the natural constant. In step S3, a temperature duration curve with minimum temperature stress is obtained through simulation calculation. The temperature drop phase of this temperature duration curve is extracted and fitted to obtain the following fitting formula: y = 13.38 + 47.62 * 0.89^x In the formula, y is the temperature, °C; x is the temperature drop time, d; Taking the derivative of the fitted formula and then taking its negative value yields the temperature drop rate curve: y' = -47.62 * ln(0.89) * 0.89^x In the formula, y' is the rate of temperature drop, ℃ / d; This allows us to obtain the upper and lower limits of the temperature drop rate index at that moment. a , b ]; In step S4, the actual temperature drop rate at that moment is calculated. Compare with the temperature drop rate index: if the actual temperature drop rate Not within the corresponding temperature drop rate index range [ a , b If the target flow rate is reached, adjust the cooling water flow rate accordingly. Q 新 Target traffic Q 新 The calculation formula is: In the formula, Q 新 , Q 旧 These are the target traffic and the traffic from the previous moment, respectively. 1 represents the actual temperature drop rate; 'a' is the lower limit of the temperature drop rate index, with a value of 0.9*M, and the unit is ℃ / h; 'b' is the upper limit of the temperature drop rate index, with a value of 1.1*M, and the unit is ℃ / h, where M is the corresponding temperature drop rate index.

2. The method for controlling the smooth temperature drop rate curve of large-volume thin-walled concrete structures according to claim 1, characterized in that, The criteria for determining the start of the temperature drop stage are: the concrete age is greater than zero and the internal temperature tn at this moment is less than the internal temperature tnq at the previous moment.

3. The method for controlling the smooth temperature drop rate curve of large-volume thin-walled concrete structures according to claim 1, characterized in that, In step S5, the target flow rate is obtained based on the flow-opening relationship curve of the solenoid valve. Q 新 The corresponding target valve opening KD 目标 The formula for calculating the valve operating time of a solenoid valve is: T 阀 =KD 目标 -KD 原 In the formula, T 阀 This refers to the valve operating time, measured in seconds (s). A negative value indicates that the valve is closed. A positive value indicates that the valve is open. T 阀 ; KD 目标 The target valve opening degree is expressed in seconds (s). KD 原 This represents the valve opening value at the previous moment, expressed in seconds (s).

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