CN112729082B - Entity member external constraint degree evaluation method based on integral deformation monitoring - Google Patents
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- 238000012544 monitoring process Methods 0.000 title claims abstract description 36
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- 239000007787 solid Substances 0.000 claims abstract description 85
- 239000004567 concrete Substances 0.000 claims abstract description 59
- 238000000034 method Methods 0.000 claims abstract description 9
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- G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
- G01B5/30—Measuring arrangements characterised by the use of mechanical techniques for measuring the deformation in a solid, e.g. mechanical strain gauge
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- G—PHYSICS
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N25/00—Investigating or analyzing materials by the use of thermal means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/38—Concrete; Lime; Mortar; Gypsum; Bricks; Ceramics; Glass
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Abstract
The invention discloses an entity component external constraint degree evaluation method based on integral deformation monitoring, which comprises the following steps of: (1) pre-embedding temperature sensors in the concrete solid member and on the surface of the concrete solid member, and calculating the average temperature of the solid member; (2) according to the temperature monitoring result, calculating the free deformation epsilon caused by the temperature reduction of the solid member1t(ii) a (3) According to the concrete mixing proportion and the reinforcement ratio of the solid member, forming a concrete sample, and calculating the free deformation epsilon caused by self-shrinkage and dry shrinkage1s(ii) a (4) According to epsilon1tAnd ε1sCalculating the total free deformation epsilon 1 of the entity structure; (5) actually measuring actual deformation epsilon 2 of the solid member in different ages after pouring on site; (6) taking the difference value of the total free deformation epsilon 1 and the actual deformation epsilon 2 as a constraint deformation epsilon 3; (7) and solving the constraint degree R of the entity structure. The method is beneficial to improving the accuracy of early constraint stress calculation of the concrete structure and provides support for establishment of concrete structure crack control measures.
Description
Technical Field
The invention relates to the technical field of concrete structure cracking risk assessment, in particular to an evaluation method for the external restraint degree of a concrete structure.
Technical background
A large number of engineering crack investigation results show that 80% -90% of cracks of a concrete structure, particularly an ultra-long large-volume concrete structure, are caused by the fact that the temperature reduction shrinkage and the drying shrinkage of concrete are restrained by the outside, and the generated restrained stress exceeds the ultimate tensile strength of the concrete, namely the restrained tensile strain of the concrete exceeds the ultimate tensile of the concrete.
According to the Chinese standard of Mass concrete construction Standard (GB 50496-2018), the external constraint stress generated by the constraint of the bottom, end or side of the deformation of the member is related to the free deformation, elastic modulus, constraint degree and creep coefficient of the member, and the constraint degree of the member is related to the length L, height H and basic horizontal resistance coefficient C of the memberxCorrelation can be calculated as in equation (1):
in the formula: l is the length (mm) of the concrete casting;
h is the height of the concrete pouring body, when H is more than 0.2L, 0.2L (mm) is taken;
Cxthe basic horizontal resistance coefficient (MPa/mm) of the external restraint medium can be generally taken according to the value in the table 1.
TABLE 1 different external restraint media CxValue (MPa/mm)
According to the Chinese standard, the constraint degree of the member is closely related to the basic horizontal resistance coefficient, and the specification only gives the empirical range of the value of the basic horizontal resistance coefficient under different conditions, for example, when concrete is poured on a reinforced concrete foundation, the reference value given by the specification is 1.0-1.5 MPa/mm, the value is adjusted from 1.0 to 1.5, the constraint degree is multiplied, and the reliability of the calculation result of the constraint stress is low.
The degree of constraint of the component by external constraint according to the european standard is shown in table 2.
TABLE 2 empirical values of degree of external constraint given by European Standard
European regulations only give the empirical value range of the degree of constraint outside the component under different constraint conditions.
The difference between the european standard and the chinese standard with respect to the fundamental degree of constraint is mainly reflected in: the restriction degree in the European standard is irrelevant to the length and the height of a new pouring member, and has a larger relation with the section size of a new concrete member and an old concrete member. The Chinese standard considers that the constraint degree of the member is closely related to the length and height of a new cast concrete member, and is not greatly related to the section size of the new and old concrete members.
Whether a constraint degree calculation method is given according to the Chinese standard or a constraint degree experience value is given according to the European standard, only the experience range of the constraint degree can be obtained, and when the tensile stress of the solid structure is calculated, larger deviation exists, so that the accuracy of the crack risk evaluation result of the concrete structure is influenced.
Disclosure of Invention
In order to make up for the defects of the existing standard, the invention develops an entity structure external constraint degree evaluation method based on integral deformation monitoring.
In order to achieve the purpose, the invention adopts the following technical scheme: a solid member external constraint degree evaluation method based on integral deformation monitoring comprises the following steps:
(1) embedding temperature sensors in the concrete solid member and on the surface of the concrete solid member, monitoring temperature fields of the central temperature, the upper surface temperature and the lower surface temperature of the solid member after the concrete solid member is poured, and calculating the average temperature of the solid member according to the formula (I);
in the formula: t isav(t) is the average temperature of the solid member; t ism(t) is the core temperature of the solid member; t isbm(t) is the upper surface temperature of the solid member; t isdm(t) is the lower surface temperature of the solid member;
(2) according to the temperature monitoring result, taking the maximum average temperature of the solid member as a starting point, and calculating the free deformation epsilon caused by the temperature reduction of the solid member according to a formula (II)1t；
ε1t＝α×[Tav,max-Tav(t)] (II)
In the formula: epsilon1tAmount of free deformation, T, due to temperature reduction of solid memberav(t) is the average temperature of the solid member at time t; t isav,maxThe maximum value of the average temperature of the solid member; alpha is the coefficient of thermal expansion of the concrete;
(3) according to the concrete mix proportion and the reinforcement ratio of the solid member, a concrete sample is formed and erected, a moisturizing curing film is adopted to carry out package curing after the sample is formed, the humidity field of the solid member is simulated, dial indicators or dial indicators are erected on two sides of the sample to monitor the deformation of the sample, and the free deformation epsilon caused by self-shrinkage and dry shrinkage is calculated1s；
(4) Comprehensively calculating total free deformation epsilon 1 of the member in different ages after pouring according to the free deformation caused by temperature reduction of the solid member obtained in the step (2) and the free deformation numerical values caused by self-shrinkage and dry shrinkage obtained in the step (3), and obtaining the total free deformation epsilon 1 of the solid structure according to a formula (III);
ε1＝ε1t+ε1s (III)
in the formula: ε 1 is the total free deflection of the member; epsilon1tThe amount of free deformation due to a decrease in the temperature of the component; epsilon1sThe amount of free deformation caused by self-shrinkage and dry shrinkage of the member;
(5) actually measuring actual deformation epsilon 2 of the solid member in different ages after pouring on site;
(6) taking the difference value of the total free deformation epsilon 1 and the actual deformation epsilon 2 as a constraint deformation epsilon 3, and obtaining a formula (IV);
ε3＝ε1-ε2 (IV)
(7) obtaining the constraint degree R of the entity structure according to a formula (V),
R＝ε3/ε1 (V)
in the formula: epsilon 1 is the total free deformation of the solid member; epsilon 2 is the actual deformation of the solid member; epsilon 3 is the constrained deformation of the solid component; r is the degree of constraint of the solid member.
The thermal expansion coefficient alpha of the concrete in the formula (II) is 10 mu epsilon/DEG C.
Preferably, the temperature sensors on the upper surface and the lower surface of the concrete solid member are respectively embedded at positions 5cm away from the concrete surface.
Preferably, the temperature field monitoring interval time is 1h, and the monitoring is continuously carried out until the temperature of the concrete center is reduced to the ambient temperature.
Preferably, in the step (5), the actual deformation epsilon 2 of the solid member in different ages after casting is actually measured on site, when the average temperature of the section of the concrete member reaches the maximum value, deformation monitoring is started, and the monitoring frequency is once a day.
The method comprises the steps of monitoring the temperature field change of the concrete member by embedding a temperature sensor in the concrete, obtaining the free deformation of the member caused by the temperature change in the temperature reduction stage of the member, taking the free deformation of a free deformation test piece beam body with the same mixing ratio and the same reinforcement ratio in an absolute wet curing environment as the self-shrinkage and dry-shrinkage free deformation of the member, and taking the sum of the temperature deformation, the self-shrinkage and the dry-shrinkage deformation as the total free deformation of the member. Monitoring points are embedded at two ends along the length direction of the solid member, and the deformation of the member actually generated under the actual constraint condition is monitored. And calculating the constraint degree of the solid member through the free deformation amount and the actual deformation amount.
The invention establishes a method for calculating the degree of constraint of an entity component according to the actual temperature and the deformation monitoring result, and can obtain the actual value of the degree of constraint of the component under the actual working condition. The current specification can only derive a rough range of constraints based on the empirical parameters of equation (1) and table 1. Therefore, the method is beneficial to improving the accuracy of calculation of early constraint stress of the concrete structure, so that the cracking risk of the structure is more accurately evaluated, and support is provided for formulation of concrete structure crack control measures.
Detailed Description
The present invention is described in further detail below to facilitate the implementation of the inventive concepts on site by those skilled in the art.
(1) Embedding temperature sensors in the concrete solid member and on the surface of the concrete solid member, monitoring temperature fields of the central temperature, the upper surface temperature and the lower surface temperature of the solid member after the concrete solid member is poured, and calculating the average temperature of the solid member according to the formula (I);
in the formula: t isav(t) is the average temperature of the solid member; t ism(t) is the core temperature of the solid member; t isbm(t) is the upper surface temperature of the solid member; t isdm(t) is the lower surface temperature of the solid member;
the upper surface temperature sensor and the lower surface temperature sensor are respectively embedded at the position 5cm away from the concrete surface. The temperature monitoring interval time is 1h, and the monitoring is continuously carried out until the central temperature of the concrete is reduced to the ambient temperature.
(2) According to the temperature monitoring result, taking the maximum average temperature of the solid member as a starting point, and calculating the free deformation epsilon caused by the temperature reduction of the solid member according to a formula (II)1t；
ε1t＝α×[Tav,max-Tav(t)] (II)
In the formula: epsilon1tAmount of free deformation, T, due to temperature reduction of solid memberav(t) is the average temperature of the solid member at time t; t isav,maxThe maximum value of the average temperature of the solid member; alpha is the coefficient of thermal expansion of concrete, generally 10 mu epsilon/DEG C;
taking the monitoring result of a pier breast wall as an example, the maximum value T of the average temperature of the concrete memberav,maxAt 60 deg.C, calculating the accumulated cooling of different ages with the maximum value of the average temperature of the member section as the starting point, and converting into cooling shrinkage epsilon1tSee table 3.
TABLE 3 calculation of shrinkage strain due to chest wall cooling at a dock
(3) According to the concrete mix proportion and the reinforcement ratio of the solid member, a concrete sample is formed and erected, a moisturizing curing film is adopted to carry out package curing after the sample is formed, the humidity field of the solid member is simulated, dial indicators or dial indicators are erected on two sides of the sample to monitor the deformation of the sample, and the free deformation epsilon caused by self-shrinkage and dry shrinkage is calculated1s；
(4) Comprehensively calculating the total free deformation epsilon 1 of the member in different ages after pouring according to the free deformation caused by temperature reduction of the solid member obtained in the step (2) and the free deformation numerical values caused by self-shrinkage and dry shrinkage obtained in the step (3), and obtaining the total free deformation epsilon 1 of the solid structure according to a formula (III);
ε1＝ε1t+ε1s (III)
in the formula: ε 1 is the total free deflection of the member; epsilon1tThe amount of free deformation due to a decrease in the temperature of the component; epsilon1sThe amount of free deformation caused by self-shrinkage and dry shrinkage of the member;
(5) actually measuring actual deformation epsilon 2 of the solid member in different ages after pouring on site;
the method is characterized in that the monitoring points of the convergence meter are embedded in the top of the member before concrete pouring, the monitoring points are embedded in pairs, hard materials are selected and are 10cm higher than the top surface of the concrete, and the monitoring points have enough rigidity and cannot deform due to the tension of the convergence meter. When the average temperature of the section of the concrete member reaches the maximum value, generally 24-48 h after the concrete is poured, deformation monitoring is started, the monitoring frequency is generally once a day, and monitoring is preferably carried out at the same time every day.
(6) Taking the difference value of the total free deformation epsilon 1 and the actual deformation epsilon 2 as a constraint deformation epsilon 3, and obtaining a formula (IV);
ε3＝ε1-ε2 (IV)
(7) obtaining the constraint degree R of the entity structure according to a formula (V),
R＝ε3/ε1 (V)
in the formula: epsilon 1 is the total free deformation of the solid member; epsilon 2 is the actual deformation of the solid member; epsilon 3 is the constrained deformation of the solid member; r is the degree of constraint of the solid member.
The evaluation of the degree of restraint of a certain wharf breast wall is shown in a table 4, the degree of restraint is actually measured to have certain fluctuation in the early stage, and after 14d, the degree of restraint is basically stable at 0.52. Calculated according to the current specification, due to the basic horizontal drag coefficient C given in the specificationxThe recommended value is 1.0-1.5 MPa/mm, and the constraint degree range of the 30d age calculated according to the upper and lower limit values is 0.67-0.77. According to the actual measurement constraint degree, the basic horizontal resistance coefficient C in the specification can be correctedxAnd (6) correcting.
TABLE 4
Claims (4)
1. A solid member external constraint degree evaluation method based on integral deformation monitoring is characterized by comprising the following steps:
(1) embedding temperature sensors in the concrete solid member and on the surface of the concrete solid member, monitoring temperature fields of the central temperature, the upper surface temperature and the lower surface temperature of the solid member after the concrete solid member is poured, and calculating the average temperature of the solid member according to the formula (I);
in the formula: t isav(t) is the average temperature of the solid member; t ism(t) is the core temperature of the solid member; t isbm(t) is the upper surface temperature of the solid member; t isdm(t) is the lower surface temperature of the solid member;
(2) according to the temperature monitoring result, taking the maximum average temperature of the solid member as a starting point, and calculating the free deformation epsilon caused by the temperature reduction of the solid member according to a formula (II)1t；
ε1t＝α×[Tav,max-Tav(t)] (II)
In the formula: epsilon1tThe amount of free deformation, T, due to a decrease in temperature of the solid memberav(t) is the average temperature of the solid member at time t; t isav,maxThe maximum value of the average temperature of the solid member; alpha is the coefficient of thermal expansion of the concrete;
(3) according to the concrete mix proportion and the reinforcement ratio of the solid member, a concrete sample is formed and erected, a moisturizing curing film is adopted to carry out package curing after the sample is formed, the humidity field of the solid member is simulated, dial indicators or dial indicators are erected on two sides of the sample to monitor the deformation of the sample, and the free deformation epsilon caused by self-shrinkage and dry shrinkage is calculated1s；
(4) Comprehensively calculating the total free deformation epsilon 1 of the member in different ages after pouring according to the free deformation caused by temperature reduction of the solid member obtained in the step (2) and the free deformation numerical values caused by self-shrinkage and dry shrinkage obtained in the step (3), and obtaining the total free deformation epsilon 1 of the solid structure according to a formula (III);
ε1＝ε1t+ε1s (III)
in the formula: ε 1 is the total free deflection of the member; epsilon1tThe amount of free deformation due to a decrease in the temperature of the component; epsilon1sThe amount of free deformation caused by self-shrinkage and dry shrinkage of the member;
(5) actually measuring actual deformation epsilon 2 of the solid member in different ages after pouring on site;
(6) taking the difference value of the total free deformation epsilon 1 and the actual deformation epsilon 2 as a constraint deformation epsilon 3, and obtaining a formula (IV);
ε3＝ε1-ε2 (IV)
(7) obtaining the constraint degree R of the entity structure according to a formula (V),
R＝ε3/ε1 (V)
in the formula: epsilon 1 is the total free deformation of the solid member; epsilon 2 is the actual deformation of the solid member; epsilon 3 is the constrained deformation of the solid member; r is the degree of constraint of the solid member.
2. The method for evaluating the degree of constraint outside a solid member based on integral deformation monitoring according to claim 1, wherein the method comprises the following steps:
the monitoring interval time of the temperature field is 1h, and the monitoring is continuously carried out until the central temperature of the concrete is reduced to the ambient temperature.
3. The method for evaluating the degree of constraint outside a solid member based on integral deformation monitoring according to claim 1, wherein the method comprises the following steps:
and (5) actually measuring actual deformation epsilon 2 of the solid member in different ages after pouring on site, and starting deformation monitoring when the average temperature of the section of the concrete member reaches the maximum value, wherein the monitoring frequency is once a day.
4. The entity component external constraint degree evaluation method based on integral deformation monitoring as claimed in claim 1, wherein:
the thermal expansion coefficient alpha of the concrete in the formula (II) is 10 mu epsilon/DEG C.
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