阅读说明：本技术 大体积混凝土浇筑温度和允许最高温度的动态调整方法 (Dynamic adjustment method for pouring temperature and allowable maximum temperature of large-volume concrete ) 是由 王继敏 曾新华 鄢江平 胡书红 魏宝龙 朱振泱 徐建军 刘毅 殷亮 张磊 魏海宁 于 2021-08-13 设计创作，主要内容包括：本发明提供一种大体积混凝土建议浇筑温度和允许最高温度的动态调整方法。该方法在有限元计算分析的基础上确定大体积混凝土建议浇筑温度和允许最高温度,不仅考虑被控区域距离建基面的高度,还考虑该区域混凝土内部的拉应力。本发明在保障施工安全的同时最大限度的节约施工费用。(The invention provides a dynamic adjustment method for recommended pouring temperature and allowable maximum temperature of mass concrete. The method determines the recommended pouring temperature and the allowable maximum temperature of the large-volume concrete on the basis of finite element calculation analysis, and not only considers the height of a controlled area from a building base plane, but also considers the tensile stress in the concrete in the area. The invention can save construction cost to the maximum extent while ensuring construction safety.)

1. A method for dynamically adjusting the pouring temperature and the allowable maximum temperature of large-volume concrete is characterized by comprising the following steps: it comprises the following contents:

A. setting the pouring temperature of the maximum stress point of the constraint area as the lowest achievable pouring temperature T_pc1Maximum allowable temperature T in a strongly restricted area specified by a specification_mc1Establishing a finite element model to calculate the corresponding stress as the maximum stress f (h)₁)；

B. Increasing pouring temperature, and finding a distance building base surface h according to finite element model analysis and calculation_kSuch that it:

f(h_k)＝f(h₁) (1)

C. obtaining a relation graph between the pouring temperature increment, the temperature peak value increment and the distance from the datum plane according to the formula (1)_kPoint of (a) in a standard state of casting temperature T_pckSum distance datum h_kThe maximum allowable temperature T in the standard state of the point of_mck：

T_pck＝T_pc1+ΔT_pk (2)

Wherein: delta T_pkIncreasing the casting temperature;

T_mck＝T_mc1+ΔT_mk (3)

wherein: delta T_mkIs the temperature peak increment;

D. according to the formulas (2) and (3), the casting temperature and the maximum temperature allowed for each elevation can be obtained.

Technical Field

The invention relates to a method for dynamically adjusting recommended pouring temperature and allowable highest temperature in the process of pouring large-volume concrete, and belongs to the technical field of hydraulic and hydroelectric engineering.

Background

At present, in many hydraulic structure design specifications, the provisions on temperature control of mass concrete only specify basic constraint zones (i.e. strong constraints)Zones and weak restraint zones) the allowed temperature difference of the concrete, namely the difference delta T between the maximum temperature and the minimum temperature allowed by the concrete pouring within h height range from the building base plane. The design specification SL319-2005 of the concrete gravity dam also stipulates the temperature difference of the foundation, namely the maximum temperature allowed by the concrete in the foundation constraint area within the height range of 0.4L (L is the long edge size of the pouring block) from the foundation plane and the maximum temperature of the partStable temperatureThe difference between them. During engineering design, designers usually design according to design specifications, so that the basic temperature difference inside concrete is smaller than the allowable temperature difference, and the allowable temperature difference of mass concrete with different heights and lengths is given according to the design specifications in table 1.

TABLE 1 basic restraint area concrete allowable temperature difference DeltaT (. degree. C.)

However, it is generally accepted by those skilled in the art that the proposed placement temperature and the allowable maximum temperature for the bulk concrete cannot be determined by design specifications alone, the height h of the foundation confinement region from the datum plane cannot be considered alone, and the stress of the confinement region should be considered. The temperature crack of the concrete is prevented because the purpose of controlling the temperature of the mass concrete, and the reason of the temperature crack of the concrete is that the tensile stress generated in the concrete is larger than the tensile strength of the concrete, so that the crack is generated.

And the finite element calculation result shows that when the width of the bottom of the dam body is larger, the difference between the temperature and the stress in the constraint area is larger, and the allowable temperature difference of concrete far away from the foundation surface can be further widened. For example, a large ancient hydropower station located in sang ri county in the southern area of the municipality of the Tibetan autonomous region is a second-level power station from sang ri county to canyon valley district of gacharles, deluxe, an upstream distance of which is about 8km from a planned and developed bayu hydropower station, and a downstream distance of which is about 7km and 18km from a planned and developed street demand hydropower station and a built-up zang wood hydropower station, respectively. Taking the temperature control calculation result of the hydropower station as an example, the maximum temperature and the maximum stress inside the concrete with different elevations of the hydropower station and the foundation surface are shown in table 2. The stable temperature near the capital construction surface of the large ancient hydropower station is about 9 ℃, the highest temperature of concrete at a position 10m away from the capital construction surface is slightly higher than the highest temperature of concrete at a position 3m away from the capital construction surface, but the stress of the concrete at a position 10m away from the capital construction surface is obviously smaller than that of the concrete at a position 3m away from the capital construction surface. It can be seen from this that for large-volume concrete works, the maximum temperature allowed inside the concrete and the stress inside the concrete are related!

TABLE 2 temperature at different heights and peak value of stress in the river

Height/m	1.0	2.0	3.0	5.0	10.0	15.0	25.0	35.0	45.0
										Maximum temperature/. degree.C	24.32	21.11	20.55	21.39	21.17	20.49	17.11	17.5	22.09
Maximum stress/MPa	1.02	0.92	0.93	0.91	0.75	0.55	0.12	-0.02	0.20

The internal temperature change process of the mass concrete is temperature rise and temperature drop. The temperature rise stage forms compressive stress, and the temperature reduction stage forms tensile stress; the compressive stress at the temperature rise stage is generally smaller than the tensile stress formed at the temperature drop stage, so that the tensile stress is often internally expressed when the mass concrete reaches a stable temperature. Current design specifications only specify allowable temperature differences, and no relationship between casting temperature and maximum temperature is established. When the highest temperature is consistent with the concrete stabilizing temperature, the stress of the concrete when reaching the stabilizing temperature is closely related to the pouring temperature of the concrete, and when the highest temperature is fixed, the lower the pouring temperature of the concrete is, the larger the compressive stress formed in the temperature rise stage is, and the smaller the tensile stress of the concrete when reaching the stabilizing temperature is.

Therefore, in mass concrete engineering, when the concrete is designed with a proposed pouring temperature and an allowable maximum temperature, not only the allowable temperature difference but also the relationship between the pouring temperature and the maximum temperature, that is, the change process of the internal stress of the mass concrete, need to be considered.

Disclosure of Invention

In view of the deficiencies of the current design specifications, it is an object of the present invention to provide a method for dynamic adjustment of the bulk concrete placement temperature and the allowable maximum temperature. When the method is used for determining the pouring temperature and the allowable highest temperature of the large-volume concrete, the height of the building base planes with different elevations is considered, the distance relation between the highest temperature with different elevations and the building base planes is established, and the internal tensile stress of the elevated concrete, namely the relation between the pouring temperature with the allowable highest temperature, is also considered.

In order to achieve the purpose, the invention adopts the following technical scheme: a method for dynamically adjusting the pouring temperature and the allowable maximum temperature of large-volume concrete comprises the following steps:

A. setting the pouring temperature of the maximum stress point of the constraint area as the lowest achievable pouring temperature T_pc1Maximum allowable temperature T in a strongly restricted area specified by a specification_mc1Establishing a finite element model to calculate the corresponding stress as the maximum stress f (h)₁)；

B. Increasing pouring temperature, and finding a distance building base surface h according to finite element model analysis and calculation_kSuch that it:

f(h_k)＝f(h₁) (1)

C. obtaining a relation graph between the pouring temperature increment, the temperature peak value increment and the distance from the datum plane according to the formula (1)_kPoint of (a) in a standard state of casting temperature T_pckSum distance datum h_kThe maximum allowable temperature T in the standard state of the point of_mck：

T_pck＝T_pc1+ΔT_pk (2)

Wherein: delta T_pkIncreasing the casting temperature;

T_mnck＝T_mc1+ΔT_mk (3)

wherein: delta T_mkIs the temperature peak increment.

D. According to the formulas (2) and (3), the casting temperature and the maximum temperature allowed for each elevation can be obtained.

The method determines the recommended pouring temperature and the allowable maximum temperature of the large-volume concrete on the basis of finite element calculation analysis, and not only considers the height of a controlled area from a building base plane, but also considers the tensile stress in the concrete in the area. The invention can save construction cost to the maximum extent while ensuring construction safety.

Drawings

FIG. 1 is a flow chart of a method for dynamically adjusting the casting temperature and the allowable maximum temperature of large-volume concrete according to the present invention;

FIG. 2 is a graph of elevation versus casting temperature increase for an embodiment of the present invention;

FIG. 3 is a graph of height versus maximum temperature increase for an exemplary embodiment of the present invention.

Detailed Description

The structure and features of the present invention will be described in detail below with reference to the accompanying drawings and examples. It should be noted that various modifications can be made to the embodiments disclosed herein, and therefore, the embodiments disclosed in the specification should not be construed as limiting the present invention, but merely as exemplifications of embodiments thereof, which are intended to make the features of the present invention obvious.

As shown in FIG. 1, the method for dynamically adjusting the casting temperature and the allowable maximum temperature of the large-volume concrete disclosed by the invention comprises the following steps:

A. setting the pouring temperature of the maximum stress point of the constraint area as the lowest achievable pouring temperature T_pc1Maximum allowable temperature T in a strongly restricted area specified by a specification_mc1Establishing a finite element model to calculate the corresponding stress as the maximum stress f (h)₁)；

B. Increasing pouring temperature, and finding a distance building base surface h according to finite element model analysis and calculation_kSuch that it:

f(h_k)＝f(h₁) (1)

C. obtaining a relation graph between pouring temperature increment, temperature peak value increment and distance from the datum plane according to the formula (1), and obtaining the distance from the datum plane h_kPoint of (a) in a standard state of casting temperature T_pckSum distance datum h_kThe maximum allowable temperature T in the standard state of the point of_mck：

T_pck＝T_pc1+ΔT_pk (2)

Wherein: delta T_pkIncreasing the casting temperature;

T_mck＝T_mc1+ΔT_mk (3)

wherein: delta T_mkIs the temperature peak increment.

D. And (4) obtaining the casting temperature and the maximum temperature allowed for each elevation according to the formulas (2) and (3).

Under the condition of different pouring temperatures, the stress is controlled to be f (h) by adjusting temperature control measures (such as water cooling measures, running water maintenance measures, surface heat preservation measures and the like)₁). Obtaining the distance base level h in a list form_kThe point pouring temperature and the maximum temperature.

For example, if a map of casting temperature increase, temperature peak increase and distance from the datum plane is established, the following description is provided. Assuming that the base temperature is 13 ℃ and the ambient temperature is 8 ℃. Characteristic point h_kThe distance from the datum plane is 1.65 m.

Heat dissipation is carried out on the upper surface and the lower surface of the model, heat dissipation is carried out on the ground, the rest surfaces are insulated, and the surface heat release coefficient is 250kJ/m2 d; and carrying out first-stage and second-stage water supply, wherein the water supply temperature is 10 ℃, the target temperature is 8 ℃, the first-stage water supply time is 0-20d, and the second-stage water supply time is 80-170 d. The concrete adiabatic temperature rise is considered according to 28 ℃, and the half-mature age is 4 d; the elastic model is 30Gpa, a is 0.4, and b is 1.0. And calculating the concrete stress caused by the adiabatic temperature rise effect under the condition that the water-feeding cooling measure is certain and the pouring temperature is 13-21 ℃. The relationship of the height to the casting temperature increase and the relationship of the height to the maximum temperature increase resulting from the calculation conditions are shown in fig. 2 and 3.

Finally, it should be noted that: the above-mentioned embodiments are only used for illustrating the technical solution of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.