CN109444387B - Method for realizing engineering restraint degree of mass concrete - Google Patents
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Abstract
The invention discloses a method for realizing the engineering restraint degree of mass concrete, which mainly comprises the following steps: (1) standardizing the degree of constraint, and calculating the degree of constraint of the corresponding position of the mass concrete by combining the elastic modulus of newly-poured concrete and old concrete according to the size of the concrete block of the actual engineering; (2) engineering constraint degree, namely calculating the constraint degree of the corresponding position of the mass concrete according to the relaxation modulus and the free deformation measured on site; (3) actually measuring a time-temperature curve and a time-deformation curve of the large-volume concrete in combination with field construction; (4) inputting the actually measured time-temperature curve and time-deformation curve into a computer system for testing; (5) according to the same temperature history and deformation history, the conversion of the machine constraint degree of the mass concrete engineering constraint degree is realized, and according to the actually measured parameters such as stress, strain and the like and the cracking process, the crack resistance of the concrete is evaluated to make a more accurate standard constraint degree.
Description
Technical Field
The invention relates to a concrete displacement control overall process simulation test device and method, belongs to the technical field of hydraulic and hydroelectric engineering, and particularly relates to a temperature stress simulation test of mass concrete under different restraint degrees.
Background
After concrete is poured, due to the action of hydration heat and the poor heat conducting property of the concrete, most of generated heat cannot be dissipated, so that the temperature of the concrete is increased, and the volume of the concrete is expanded. Generally speaking, the adiabatic temperature rise of concrete in hydraulic engineering can reach 10-40 ℃, even considering surface heat dissipation, the highest temperature in the concrete is still 7-35 ℃ higher than that in pouring, and when the block size is very big, the internal temperature rise can be higher. In the process of temperature reduction and cold contraction, the block body generates tensile stress under the constraint condition, and when the tensile stress exceeds the tensile strength of the concrete, the concrete is cracked. The ratio of the cracking stress to the stress under full restraint at this time is defined as the engineering restraint.
The method mainly focuses on simulation analysis and theoretical calculation, wherein simulation mainly starts from the elastic or viscoelasticity constitutive relation of concrete, simulates the temperature process of the concrete, and obtains the degree of constraint by calculating the maximum temperature stress; the theoretical calculation is mainly to establish an equation through a mechanical means and obtain the degree of constraint by utilizing a solving mode. With the occurrence of the temperature stress testing machine, the field simulation test with adjustable and controllable constraint degree is realized. However, the method for converting the large-volume concrete engineering constraint degree into the temperature stress tester constraint degree is less, and particularly, the relationship between the engineering constraint degree and the simulation test device is realized in the constraint degree controllable process of the temperature stress tester. Therefore, a simulation test device and method for realizing the mass concrete engineering restraint degree is needed by the concrete temperature stress.
Disclosure of Invention
The invention aims to improve the constraint degree method to calculate the temperature stress of the concrete, and from the test angle, the whole development process of factors such as the stress, the strain and the like of the concrete under different constraint degrees is tested, so that a basis is provided for evaluating the cracking capacity of the large-volume concrete.
The technical solution of the invention is as follows: the concrete cracking overall process test device and method under different restraint degrees comprise the following contents:
(1) specification of mass concrete engineering degree of constraint
The method for calculating the constraint degree of the mass concrete engineering specified by the current specification mainly comprises the following steps:
the American ACI Specification:
in the formula, L and H are respectively the length and the height of the pouring block, and H is variable height (H is more than or equal to 0 and less than or equal to H).
The constraint stress of the concrete is reduced in proportion to the reduction of the rigidity of the base material, and the calculated gamma isRIs multiplied by a coefficient.
In the formula ACAnd ECCasting a fast contact area and elastic modulus AFAnd EFIs the contact area and elastic modulus of the foundation. Concrete cast on bedrock, generally referred to as AFIs AC2.5 times of (A)F＝2.5AC。
The domestic specification is as follows:
TABLE 1 engineering restraint value (concrete elastic modulus and foundation rock equal)
Note: l is the length of the long side of the pouring block, m; y is the height of the calculated point from the base surface, m.
TABLE 2 engineering restraint value (concrete elastic modulus and bedrock unequal)
(2) Degree of restraint of temperature stress testing machine
The test device controls two ends of a concrete test piece by using the clamping heads, one end of the concrete test piece is fixed, the other end of the concrete test piece can control the compression and the stretching of the test piece through the clamping heads, and the free deformation of the concrete test piece is epsilon0And (t), according to the actual deformation epsilon (t) generated under different constraint degrees, the free edge of the concrete sample is reduced in proportion through a computer control system, a loading control system and a data acquisition system, and then corresponding constraint, namely machine constraint degree, is generated on the concrete sample.
Wherein t is time, ε0(t) and ε (t) are the free and actual deformation of the concrete mass, respectively.
(3) Engineering restraint degree of mass concrete
Under different temperature histories, the ratio of the temperature stress generated by the restraint of the newly poured concrete block by the bedrock or the old concrete to the theoretical temperature stress under the complete restraint condition obtains the engineering restraint degree. Wherein R (t, t)0) Is the relaxation modulus.
Wherein sigma (t) is the temperature stress generated when the concrete block is restrained by the bed rock live old concrete, and sigma (t) is the temperature stress generated when the concrete block is restrained by the bed rock live old concretefix(t) is the temperature stress generated in the fully confined state of the concrete block, R (t, t)0) Is the relaxation modulus of the concrete block at the moment t.
Drawings
FIG. 1 is a schematic view of a large-volume concrete engineering constraint test flow according to the present invention;
FIG. 2 is a functional schematic of the present invention;
FIG. 3 is a schematic diagram of a whole-process test of the method for realizing the degree of constraint of mass concrete engineering according to the invention;
FIG. 4 is a schematic diagram of a method for implementing the constraint degree of mass concrete engineering according to the present invention;
FIG. 5 is a schematic diagram illustrating actual measurement of the degree of constraint of the mass concrete engineering according to the present invention;
FIG. 6 is a temperature history curve of each measuring point of the concrete block;
FIG. 7 is a deformation curve of each measuring point of the concrete block;
FIG. 8 is a temperature stress curve at different degrees of constraint at various points.
Detailed Description
As shown in fig. 1, fig. 2, fig. 3 and fig. 4, the large-volume concrete engineering constraint degree can be obtained through specification and actual measurement, and can also be realized through the following test modes:
in the large-volume concrete under the actual working condition, the maximum tensile stress, namely the most dangerous part, exists at the central part of the block body, and when the temperature stress of the large-volume concrete is calculated, the central part of the concrete block body is subjected to actual measurement and simulation calculation, so that the anti-cracking capacity of the concrete is evaluated. For the same concrete block body to carry out the restraint degree calculation, the restraint degree not only receives self size influence, and base rock (or old concrete) bullet mould, concreting bullet mould also have very big relation, can calculate the restraint degree of concrete according to current formula: the constraint degree of each part of the concrete block can be calculated by a standard method according to the size and the contact area of the poured block and the elastic modulus of the bedrock; measuring the temperature and deformation history of different points at the center of the block by using an actual measurement method, simultaneously testing each mechanical property parameter of the concrete, including elastic modulus and creep parameter of each age of the concrete, preparing for calculating the relaxation modulus of the concrete, measuring the temperature deformation and free deformation of the concrete under the same condition, and calculating the engineering constraint degree of the concrete; and (2) drawing a time-temperature curve and a time-displacement curve according to the deformation history of the temperature history measured on site by using an indoor test mode, inputting the time-temperature curve and the time-displacement curve into a computer, and controlling the free end of the test piece through a computer control system, a displacement control system, a temperature control system, a loading control system and a data acquisition system to ensure that the free deformation of the test piece follows the change of the time-displacement curve, thereby realizing the large-volume concrete engineering constraint degree. And (3) measuring the machine constraint degree and the temperature stress course according to the calculated standard constraint degree and engineering constraint degree and the test, and with the help of a data processing system, when the stress curve has a mutation to show that the concrete cracks, the temperature and the stress at the moment can be used as the cracking indexes of the concrete under the corresponding constraint degree to be used as reference for evaluating the cracking resistance of the concrete.
Examples
The test method tests the on-site concrete test block, and verifies the effectiveness and the reasonability of the large-volume concrete engineering constraint degree implementation method. Fig. 5 shows the dimensions of the concrete block, points 1,2,3 and 4 are test points of the block, the temperature history and deformation of the block are tested from the beginning of concrete pouring, and the plotted time-temperature curve and time-displacement curve are input into the computer until the end of the test.
The temperature history curves and the deformation curves of the test points 1,2,3 and 4 are shown in figures 6 and 7, except that the temperature history curves and the deformation curves are different, the constraint degree of each test point is reduced along with the increase of the height, and each test point can be regarded as the same concrete material to be poured simultaneously.
Calculating the constraint degrees of the test points 1,2,3 and 4 according to different constraint degree calculation methods, see table 3, wherein the constraint degrees obtained by calculation and the constraint degrees obtained by actual measurement are not greatly different according to the ACI specification, which mainly considers the size of a concrete block and an elastic modulus; the constraint degree of the test point 1 is calculated according to domestic specifications and basically consistent with other two algorithms, the calculation result of the constraint degree of the test point 1 is relatively reliable, the results of the test points 2,3 and 4 are relatively different from the results of the other two algorithms, and the constraint degree of the foundation to the concrete block is underestimated for the block with the length-height ratio of more than 1 mainly due to the fact that the specification aims at the concrete block with the length-height ratio of 1, so that the constraint coefficient is rapidly reduced, the calculated temperature stress is relatively small, and therefore the constraint degree obtained through actual measurement calculation is input into a computer for testing.
It can be seen from the experimental data obtained from the experiment that the time-temperature curve and the time-deformation curve obtained by actual measurement are input into the computer, and the obtained temperature stress removing curve is matched with the actual measurement data. The test point 1 has cracks on the fourth day, the corresponding cracking stress is 3.3MPa, the concrete test piece with the same temperature history and deformation is broken on the fourth day, and the stress during breaking is 3.5 MPa; the test point 2 has cracks on the fourth day, the corresponding cracking stress is 3.0MPa, the concrete test piece with the same temperature history and deformation is broken on the fourth day, and the stress during breaking is 3.4 MPa; the test point 3 has no crack, the stress is 1.7MPa, and the constrained stress of the concrete sample with the same temperature history and deformation is 1.73 MPa; no crack appears in the test point 4, the calculated temperature stress is-0.5 MPa, and the constrained stress of the concrete sample with the same temperature history and deformation is-0.75 MPa. From the temperature stress of a measuring point 1 to the temperature stress of a measuring point 2, which are obtained by field actual measurement, of 3.3MPa, the temperature stress of the measuring point 3 of 1.7MPa and the temperature stress of the measuring point 4 of-0.5 MPa, the constraint capacity of the foundation to the concrete block is reduced and the crack resistance of the block is increased along with the increase of the height. The cracking stress corresponding to the measuring point 1 is 3.5MPa, the cracking stress corresponding to the measuring point 2 is 3.4MPa, the constraint stress corresponding to the measuring point 3 is 1.73MPa, and the constraint stress corresponding to the measuring point 4 is-0.5 MPa, so that the obtained temperature stress is basically consistent with the field measurement result, and the conversion from the large-volume concrete engineering constraint degree to the machine constraint degree is realized. Meanwhile, the crack resistance of the concrete is closely related to the temperature history and the degree of constraint, and cracks can also appear when the degree of constraint is increased to a certain degree under the condition of small temperature difference, so that the conclusion can be obtained by comparing the measuring point 1 with the measuring point 2.
TABLE 3 degree of constraint of test points
Claims (1)
1. The method for evaluating the crack resistance of the large-volume concrete is characterized by comprising the following steps of:
(1) measuring the temperature and deformation history of different points at the center of the block by using an actual measurement method, simultaneously testing each mechanical property parameter of the concrete, including elastic modulus and creep parameter of each age of the concrete, preparing for calculating the relaxation modulus of the concrete, measuring the temperature deformation and free deformation of the concrete under the same condition, and calculating the engineering constraint degree of the concrete;
(2) according to the temperature deformation and free deformation of the concrete measured in the step (1) under the same condition, drawing a time-temperature curve and a time-displacement curve, inputting the time-temperature curve and the time-displacement curve into a computer, and controlling the free end of the test piece through a computer control system, a displacement control system, a temperature control system, a loading control system and a data acquisition system to enable the free deformation of the test piece to follow the change of the time-displacement curve, so that the mechanical restraint degree of the concrete is realized;
(3) drawing a stress-time curve for the concrete engineering constraint degree and the concrete machine constraint degree measured in the step (1) and the step (2) by using a data acquisition system in a computer, comparing the engineering constraint degree and the machine constraint degree measured in the step (1) and the step (2), and if the stress measured by the machine constraint degree is basically consistent with the constraint degree measured by the engineering constraint degree, realizing the conversion from the engineering constraint degree to the machine constraint degree;
(4) and (4) evaluating the crack resistance of the concrete according to a stress-time curve drawn by the machine constraint degree measured in the step (3) to formulate an accurate standard constraint degree.
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| CN110376049A (en) * | 2019-07-19 | 2019-10-25 | 东南大学 | A kind of temperature stress testing machine improving strain acquisition system |
| CN110702886B (en) * | 2019-10-23 | 2020-09-11 | 中国水利水电科学研究院 | Method for inverting parameters of mass concrete material |
| CN110907632A (en) * | 2019-12-27 | 2020-03-24 | 上海建工集团股份有限公司 | Large-volume concrete cracking early warning system and method |
| CN112729082B (en) * | 2020-12-22 | 2022-05-17 | 中交四航工程研究院有限公司 | Entity member external constraint degree evaluation method based on integral deformation monitoring |
| CN112816677B (en) * | 2021-03-04 | 2021-11-30 | 中国水利水电科学研究院 | Method and equipment for testing concrete aging coefficient under variable restraint action |
| CN116644599A (en) * | 2023-06-05 | 2023-08-25 | 重庆大学 | Crack prediction method based on elastic modulus of concrete under capillary pore stress effect |
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| JP2013002904A (en) * | 2011-06-15 | 2013-01-07 | Japan Concrete Institute | Method of preventing cracks in concrete |
| CN103513018A (en) * | 2012-12-31 | 2014-01-15 | 中交四航工程研究院有限公司 | Systematic detection method for anti-cracking performance of concrete |
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| CN106021755A (en) * | 2016-05-26 | 2016-10-12 | 中国核工业第二二建设有限公司 | Simulation analysis method for temperature stress of mass concrete in raft foundations of nuclear island of nuclear power station |
| CN108593770A (en) * | 2018-03-29 | 2018-09-28 | 中国水利水电科学研究院 | Concrete imitation true experiment machine is combined the apparatus and method of monitoring concrete overall process cracking with microseism |
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Patent Citations (5)
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|---|---|---|---|---|
| JP2013002904A (en) * | 2011-06-15 | 2013-01-07 | Japan Concrete Institute | Method of preventing cracks in concrete |
| CN103513018A (en) * | 2012-12-31 | 2014-01-15 | 中交四航工程研究院有限公司 | Systematic detection method for anti-cracking performance of concrete |
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