CN114034734A - Elastic wave method-based concrete high-temperature damage assessment method - Google Patents
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Abstract
The invention discloses a concrete high-temperature damage assessment method based on an elastic wave method, which comprises the steps of testing the elastic wave velocity V of a concrete structure after high temperature according to the elastic wave method, establishing a test model V (F (T)) of the elastic wave velocity V and the temperature T of the concrete structure after high temperature by adopting a least square method or a Lagrange interpolation method, and according to the actually measured elastic wave velocity ViAnd the inverse function T f of the test model V F (T)‑1And (V) determining the fire temperature T of the concrete structure, so as to construct a temperature field T (x, y, z) in the concrete structure, constructing a damage variable according to the elastic wave velocity V, converting the elastic wave velocity V obtained by testing into the damage degree D of the concrete structure after high temperature, and further evaluating the bearing capacity and damage condition of the concrete structure. The technical scheme provided by the invention can quickly and accurately detect the damage condition of the concrete structure after high temperature through a nondestructive detection method, and avoid a large number of redundant model tests, thereby avoiding purchasing a large-scale testEquipment, effectively reduce engineering cost.
Description
Technical Field
The invention relates to the technical field of civil engineering, in particular to a concrete high-temperature damage assessment method based on an elastic wave method.
Background
Under the normal temperature state, the concrete structure texture is hard, highly dense. However, when concrete is burned at different temperature levels, the structure itself suffers different degrees of damage. With the rise of the temperature and the prolonged constant temperature time, all mechanical indexes of the concrete structure generally show changes of different degrees.
The damage of the concrete structure by the high temperature is extremely serious. In modern engineering, a large number of reinforced concrete structures are adopted, although concrete materials are difficult to burn, the structures are adversely affected due to the high temperature effect, and performance parameters such as the strength and the elastic modulus of the concrete are reduced along with the rise of the temperature; the temperature gradient effect in the structure can cause the structure to crack and bend and deform; although the steel bars in the reinforced concrete structure are protected by concrete, the strength of the steel bars is reduced under the action of high temperature, so that the steel bars yield under initial stress to cause section damage; meanwhile, due to the thermal expansion of the structures, the adjacent structures may generate excessive displacement, so that the cross section is damaged or deformed excessively to fail and collapse.
The damage grading of the concrete structure after high temperature is mainly influenced and controlled by the bearing capacity, and the reduction of the bearing capacity of the structure is mainly related to two aspects: firstly, the mechanical property of the structural material is reduced; secondly, the effective stress area of the structure is reduced. Both of these reductions or reductions are directly related to the high temperature temperatures experienced at the surface of the structure and the temperature profile experienced within the structure. Therefore, the key for researching the high-temperature damage assessment of the concrete structure lies in accurately determining the fire temperature experienced by the structure and the temperature field in the member, then determining the reduction of the mechanical property of the structural material and the reduction of the effective stress area of the structure on the basis, further assessing the damage condition of the bearing capacity of the structure, and finally assessing the damage grade of the concrete structure after high temperature.
At present, the determination method of the high-temperature damage degree of the concrete mainly comprises the observation of the color change of the surface of the concrete and the investigation of on-site residues. The surface color of the concrete is changed into: (1) at 20-100 ℃, the concrete structure is dark gray; (2) when the temperature is 200-300 ℃, the surface color of the test block is whitened; (3) part of the surface appears light pink at 400 ℃; (4) the surface color changed to light yellow at 500 ℃ and 600 ℃; (5) after the test block is subjected to high temperature of 700 ℃, the surface of the test block is light white. The investigation of the on-site residues is mainly directed to the combustion characteristics of common combustibles and incombustibles, such as the ignition point of the common combustibles, the transformation temperature of the common incombustibles, and the like. The common method at the present stage can only qualitatively judge the experienced temperature and cannot accurately judge.
Disclosure of Invention
In order to solve the limitations and defects in the prior art, the invention provides a concrete high-temperature damage assessment method based on an elastic wave method, which comprises the following steps:
manufacturing a concrete sample meeting preset regulations;
firing the concrete test piece, and recording a temperature rise curve of the concrete test piece by using a standard temperature rise curve;
testing the elastic wave velocity V of the concrete structure after high temperature by using an elastic wave method to obtain test data of the elastic wave velocity V;
judging whether the suspicious value is an abnormal value or not according to the test data through a Grabas criterion, and removing all the suspicious values with the judgment results of the abnormal values;
establishing a test model V (F (T)) of the elastic wave velocity V and the temperature T of the concrete structure after high temperature by using a least square method or a Lagrange interpolation method;
according to the actual elastic wave velocity ViAnd the inverse function T f of said test model V f (T)-1(V) determining the temperature T of the concrete structure subjected to fire, constructing a temperature field T (x, y, z) in the concrete structure, defining the domain A and the domain C for the test model V (F (T), and defining the domain F for the inverse function T (f)-1(V), the definition domain is C, the value domain is A;
converting the elastic wave velocity V obtained by testing into the damage degree D of the concrete structure after the concrete structure is subjected to high temperature according to the temperature field T (x, y, z);
and carrying out damage assessment on the concrete structure according to the damage degree D.
Optionally, the concrete test piece is prepared according to a preset test index type and a preset test method, and the concrete test piece includes any one of a cubic test piece, a prismatic test piece and a cylindrical test piece.
Optionally, the firing is performed on the concrete sample, and the step of recording the temperature rise curve of the concrete sample by using a standard temperature rise curve includes:
when a building is in fire, the fuel is fibrous material, and the temperature rise curve is an ISO834 curve, and the expression is as follows:
T＝345log(8t+1)+T0 (1)
when an oil fire breaks out, the expression of the temperature rise curve is as follows:
T＝T0+1296(1-0.325e-0.167t-0.675e-2.5t) (2)
in the formulae (1) and (2), T0Is the initial temperature in degrees celsius; t is the duration of the fire in minutes; t is the average temperature of the air at time T, in degrees Celsius.
Optionally, the step of determining whether the "suspicious value" is an "abnormal value" according to the test data by using a grassbs criterion, and removing all the "suspicious values" with the determination result being the "abnormal value" includes:
obtaining test data A of the concrete structure after high temperaturei(i-1, 2, …, n) and the mean value of the test data is
The deviation of the test data is
The standard deviation of the test data is s, and for each test data, the expression defining the statistics is as follows:
if g isi＞gα(n) identifying that the test data contains an "outlier" at a level of significance of α, and rejecting the test data, wherein giTo test data, gα(n) is a critical value;
if gi＞gα(n) the test data contains when the significance level is assumed to be alphaIf there is an "abnormal value", the step of removing the test data comprises:
arranging the test data under the preset temperature level in the order from small to big, wherein the expression is as follows:
A1≤A2...≤An-1≤An (4)
calculating mean of sample data using mathematical statistics
And standard deviation s;
according to the number n of the test data and the selected significance level alpha, searching a Grabbs test critical value table to obtain a critical value gα(n)；
For test data A with the maximum standard deviation siMaking a judgment if AiCorresponding gi≤gα(n) identifying the test data AiJudging to be finished without gross errors; if AiCorresponding gi＞gα(n) identifying the test data AiHaving a gross error, rejecting the test data;
re-executing the step g on the rest n-1 measurement datai＞gαAnd (n) when the significance level is alpha, determining that the test data contains an abnormal value, and rejecting the test data.
Optionally, the step of using an elastic wave method to test the elastic wave velocity V of the concrete structure after high temperature to obtain the test data of the elastic wave velocity V includes:
taking the molded bottom surface of the concrete test piece as a test surface;
drawing a positioning line on the test surface in advance, setting 4 to 5 test points on each test surface, and acquiring data for 3 times at each test point;
fixing an acceleration sensor and a vibration source on the test surface in a pressing manner;
exciting the concrete test piece by using the vibration source to enable the concrete test piece to vibrate and excite a stress wave, wherein the propagation characteristic of the stress wave in the concrete test piece reflects the mechanical characteristic of the concrete structure after high temperature;
and converting the propagation parameters of the stress wave in the concrete test piece into the mechanical parameters of the concrete structure after high temperature, and obtaining the test data of the elastic wave velocity V.
Optionally, the step of establishing a test model V ═ f (T) of the elastic wave velocity V and the temperature T of the concrete structure after the high temperature by using a least square method or a lagrange interpolation method includes:
drawing the elastic wave velocity V and the temperature T in a two-dimensional coordinate system at each temperature level, and setting a curve equation as V ═ F (T) ═ Sigma (M) according to the curve distribution of the elastic wave velocity V and the temperature TiTi) Wherein M isiIs an arbitrary real number, TiV ═ f (t) for temperature constants;
setting N ═ Sigma (V)i-F(Ti))2In which V isiFor the actual elastic wave velocity, F (T)i) The calculated value of the model corresponding to the preset temperature is obtained, and N is the square of the difference between the actually measured wave speed and the calculated value of the model and a function formed by the square of the difference;
f (T)i) Substituting N ═ Σ (V)i-F(Ti))2Obtaining N ═ Sigma (V)i-∑(MiTi))2；
When N takes the minimum value, N pairs of M are usediCalculating a partial derivative;
when the partial derivative is zero, obtaining the inclusion unknown number MiThe system of equations is solved to obtain Mi；
Will MiSubstituted into the equation V ═ f (t) ═ Σ (M)iTi) Obtaining the test model V ═ f (t).
Optionally, the step of converting the elastic wave velocity V obtained by the test into the damage degree D of the concrete structure after the concrete structure is subjected to high temperature according to the temperature field T (x, y, z) includes:
the expression of the damage degree D of the concrete structure after high temperature is as follows:
wherein, ViIs the elastic wave velocity, V, of the concrete structure after the concrete structure is subjected to high temperature0The elastic wave velocity before the concrete structure is subjected to high temperature.
The invention has the following beneficial effects:
the invention provides a concrete high-temperature damage assessment method based on an elastic wave method, which is characterized in that aiming at a concrete structure, the elastic wave velocity V of the concrete structure after high temperature is tested according to the elastic wave method, a large amount of test data is judged whether a suspicious value is an abnormal value or not according to the Graves criterion, the abnormal value is completely removed, a test model V (F) (T) of the elastic wave velocity V and the temperature T of the concrete structure after high temperature is established by adopting a least square method or a Lagrange interpolation method, and the measured elastic wave velocity V is measured according to the actual elastic wave velocity ViAnd the inverse function T f of the test model V F (T)-1And (V) determining the fire temperature T of the concrete structure, so as to construct a temperature field T (x, y, z) in the concrete structure, constructing a damage variable according to the elastic wave velocity V, converting the elastic wave velocity V obtained by testing into the damage degree D of the concrete structure after high temperature, and further evaluating the bearing capacity and damage condition of the concrete structure. The concrete high-temperature damage assessment method based on the elastic wave method can quickly and accurately detect the damage condition of the concrete structure after high temperature through a nondestructive detection method, and avoids a large number of redundant model tests. The technical scheme provided by the invention is simple to operate and low in cost, large-scale test equipment can be avoided from being purchased, and the engineering cost is effectively reduced.
Drawings
Fig. 1 is a schematic view of a concrete high-temperature damage assessment method based on an elastic wave method according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a linear variation curve of the elastic wave velocity with temperature according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a quadratic curve of the elastic wave velocity varying with temperature according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of a cubic curve of the elastic wave velocity varying with temperature according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a Fourier function variation curve of the elastic wave velocity varying with temperature according to an embodiment of the present invention.
Fig. 6 is a schematic diagram of a Fourier function variation curve of the damage degree varying with temperature according to an embodiment of the present invention.
Wherein the reference numerals are: : 1-a concrete structure; 2-measuring points of a sensor; 3-exciting the vibration hammer; 4-a vibration measuring sensor; 5-a signal transmission line; 6-multifunctional detector.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the concrete high temperature damage assessment method based on the elastic wave method provided by the present invention is described in detail below with reference to the accompanying drawings.
Example one
The invention provides a concrete high-temperature damage assessment method based on an elastic wave method, which comprises the steps of manufacturing a concrete test piece meeting the requirements specified in GB/T50081-2002 of general concrete mechanical property test method standard, placing the test piece meeting the requirements in an experimental resistance furnace for burning, testing the elastic wave velocity V of a concrete structure after high temperature by using the elastic wave method, judging whether a suspicious value is an abnormal value or not by using a Grubbs criterion for a large amount of test data, removing all the abnormal values, establishing a test model V (F) (T) of the elastic wave velocity V and the temperature T of the concrete after high temperature by using a least square method or a Lagrange interpolation method, and establishing a test model V (F) (T) of the elastic wave velocity V and the temperature T of the concrete after high temperature by using the actual elastic wave velocity V (T)iAnd the inverse function T f of the test model V F (T)-1And (V) determining the fire temperature T experienced by the structure, constructing a temperature field T (x, y, z) inside the structure, constructing a damage variable through the elastic wave velocity V, converting the concrete elastic wave velocity V obtained through testing into the damage degree D of the concrete after high temperature, and evaluating the damage of the structure.
In this embodiment, the concrete test piece needs to be prepared according to a specific test index type and a specific test method, and the concrete test piece is a cube test piece, a prism test piece or a cylinder test piece. The temperature rise profile is selected based on the characteristics of the structure, such as the temperature change of a typical building fire, and the fuel is a fibrous material, such as wood, paper, fabric, and the like. The temperature rise curve is an ISO834 curve, and the calculation formula is as follows:
T＝345log(8t+1)+T0 (6)
for example, describing the combustion characteristics of oil fires, such as gasoline tanks, chemical transport tanks, etc., which can be used to simulate more severe fire conditions, the formula is:
T＝T0+1296(1-0.325e-0.167t-0.675e-2.5t) (7)
in formulae (6) and (7), T0Initial temperature (. degree. C.); t is duration of fire (min); t is the average temperature in air (DEG C) at time T.
In this embodiment, the actual measurement index a of the concrete after high-temperature damagei(i-1, 2, …, n) with a mean value of
Deviation is as
The standard deviation is s. For each test data, the statistics are defined as:
selecting a level of significance α, e.g. a certain test data gi＞gα(n), when the significance level is alpha, the measured data contains an abnormal value, and the abnormal value is removed, and the specific implementation steps are as follows:
firstly, the test data at a certain temperature level are arranged from small to big in sequence as follows:
A1≤A2…≤An-1≤An (9)
calculating the mean value of sample data by using related contents of mathematical statistics
And standard deviation s;
according to the number n of the test data and the selected significance level alpha, searching a Grabbs test critical value table to obtain a critical value g of the test dataα(n)；
For mean value
Data A with the largest deviationi(A1Or An) Making a judgment if AiCorresponding gi≤gα(n), if the data does not contain a gross error, judging to be finished; if g isi＞gα(n), if the data contains a gross error, the data is to be eliminated, and the rest n-1 measurement data are judged again according to the steps.
In this embodiment, the elastic wave velocity V after high temperature was measured based on the elastic wave method. Specifically, the elastic wave method adopts single-sided reflection to perform testing, namely, the acceleration sensor and the vibration source are on the same testing surface, and the propagation time and the elastic wave velocity V of the elastic wave in the tested concrete sample can be measured by using repeated reflection of the elastic wave on the premise that the thickness of the tested object is known.
In the embodiment, when a single-side reflection method is adopted for testing, the bottom surface of the test piece during molding is used as a test surface, 4 to 5 test points are arranged on each test surface, and each test point is collected for 3 times. The tested object is excited to vibrate and excite stress wave, and the propagation characteristic of the stress wave in the tested object can reflect the mechanical characteristic of the structure after high temperature. And converting the propagation parameters of the waves in the measured object into mechanical parameters of the structure, thereby obtaining target data. The method is characterized in that a positioning line is drawn on a test surface in advance during elastic wave speed collection, a pressing type is adopted as a fixing method of a sensor during collection, the sensor is pressed on the surface of a test object manually or mechanically, the method is highest in test efficiency, and an elastic wave speed value at each measuring point is measured and recorded.
In this embodiment, a least square method or a lagrange interpolation method is used to establish a test model V ═ f (T) of the elastic wave velocity V and the temperature T of the concrete after the high temperature, specifically, the present embodiment applies each temperatureDrawing the data of the concrete elastic wave velocity V and the temperature value T in a two-dimensional coordinate system under the degree grade, and enabling the curve equation to be V ═ F (T) ═ Sigma (M) according to the curve distribution of the pointsiTi) Wherein M isiIs an arbitrary real number, TiFor temperature constants, V ═ f (t) is the test model. Let N be ═ Sigma (V)i-F(Ti))2In which V isiMeasuring the wave velocity, F (T), for the concretei) And N is a function formed by the sum of squares of the difference between the measured wave speed of the concrete and the wave speed value calculated by the model at a certain temperature. F (T)i) Substituting into the above formula to obtain N ═ Sigma (V)i-∑(MiTi))2When N is minimum, use N to MiAnd (5) calculating a partial derivative. Making partial derivative zero to obtain inclusion unknown number MiSolving the system of equations to obtain MiWill MiSubstituted into equation f (t) ═ Σ (M)iTi) To obtain the test model.
This embodiment is implemented by actually measuring the elastic wave velocity ViAnd the inverse function T f of the test model V F (T)-1(V) determining the temperature T of the fire experienced by the structure and the temperature field T (x, y, z) inside the component. The function V ═ F (T), the domain is defined as A, and the value domain is C; inverse function T ═ f-1And (V), the definition domain is C, and the value domain is A.
In this embodiment, the concrete elastic wave velocity V obtained by the test is converted into the damage degree D of the concrete after high temperature by a method of constructing a damage variable by the elastic wave velocity V. The calculation formula of the damage degree D of the concrete after high temperature is as follows:
wherein D is the damage degree of the concrete structure after fire loss, ViAnd V0The elastic wave velocities after and without fire damage, respectively.
The embodiment provides a concrete high-temperature damage assessment method based on an elastic wave method, which is characterized in that the elastic wave velocity V of a concrete structure after high temperature is tested according to the elastic wave method, and the height is established by adopting a least square method or a Lagrange interpolation methodTesting model V ═ F (T) of elastic wave velocity V and temperature T of the warmed concrete structure according to the actually measured elastic wave velocity ViAnd the inverse function T ═ f-1And (V) determining the fire temperature T of the concrete structure, so as to construct a temperature field T (x, y, z) in the concrete structure, constructing a damage variable according to the elastic wave velocity V, converting the elastic wave velocity V obtained by testing into the damage degree D of the concrete structure after high temperature, and further evaluating the bearing capacity and damage condition of the concrete structure. The embodiment can quickly and accurately detect the damage condition of the concrete structure after high temperature, and avoid a large number of redundant model tests. The embodiment is simple to operate and low in cost, can avoid purchasing test equipment such as large-scale instruments and equipment, and effectively reduces the test cost. The technical scheme provided by the embodiment comprises the following specific steps:
1. and (3) manufacturing a standard prism test piece meeting the requirements of standard GB/T50081-2002 for the mechanical property test method of common concrete.
2. The test piece is placed in a resistance furnace for ablation, the test is performed by taking the formula (7) as a temperature rise curve, the test piece is divided into 8 groups, and the test piece is divided at room temperature and 100 ℃ to 700 ℃.
3. And judging whether the suspicious value is an abnormal value according to the Grabbs criterion. The results of the y-test are shown in Table 1, taking the measured value at 20 ℃ as an example.
120 ℃ elastic wave speed change meter
| Serial number | Wave speed (Km/m) | Serial number | Wave speed (Km/s) |
| 1 | 4.388 | 9 | 4.298 |
| 2 | 4.412 | 10 | 4.201 |
| 3 | 4.392 | 11 | 4.479 |
| 4 | 4.403 | 12 | 4.386 |
| 5 | 4.398 | 13 | 4.407 |
| 6 | 4.360 | 14 | 4.320 |
| 7 | 4.397 | 15 | 4.316 |
| 8 | 4.408 | 16 | 4.449 |
The test data at the temperature level of 20 ℃ are arranged from small to large.
Calculating the mean value of sample data
Standard deviation s ═ 0.0659.
According to the number n of the test data and the selected significance level alpha of the test data, the number n is 16 and the selected significance level alpha is 0.05, and the Grubbs test critical value table is searched to obtain the critical value g of the test dataα(n) ═ 2.44, the grabbs test critical value table is shown in table 2.
TABLE 2 Grubbs test Critical value Table
To and mean value
Big data A with maximum deviationi(A1Or An) Is judged as gi＞gα(n), then, is discarded, example AiWhen the data is 4.261, the data is eliminated, and the rest 15 measurement data are judged again according to the steps.
The remaining 15 test data AiCorresponding gi≤gα(n) meets the requirements.
The outlier in this example is 4.201, the number is truncated and the remaining data is taken into account.
4. And according to the steps, removing abnormal values of all temperature levels in sequence. And taking the average value of the elastic wave speed at each temperature grade as a test value at the temperature grade. The results are shown in Table 3, giving a test model.
TABLE 3 temperature-dependent change of elastic wave speed of concrete structure
5. Adopting a least square method or a Lagrange interpolation method to establish a test model F (T) of the elastic wave velocity of the concrete structure along with the temperature change after the high temperature:
Linear model 1：F(T)＝p1T+p2
Coefficients(with 95％confidence bounds)：
p1＝-0.005896,p2＝4.514,R2＝0.9608。
Linear model 2：F(T)＝p1T2+p2T+p3
Coefficients(with 95％confidence bounds)：
p1＝4.113e-6,p2＝-0.008834,p3＝4.83,R2＝0.978。
Linear model 3：F(T)＝p1T3+p2T2+p3T+p4
Coefficients(with 95％confidence bounds)：
p1＝2.306e-08,p2＝-2.082e-05,p3＝-0.001872,p4＝4.48,R2＝0.9956。
General model Fourier 4：F(T)＝a0+a1*cos(w*T)+b1*sin(w*T)
Coefficients(with 95％confidence bounds)：
a0＝2.667，a1＝1.802，b1＝-0.3881，w＝0.004539，R2＝0.9965。
of the four analytical models, the General model Fourier 4 has the highest fitting degree and is recommended to be adopted.
By measuring the elastic wave velocity ViAnd the inverse function T f of the test model V F (T)-1And (V) determining the fire temperature T experienced by the structure, and constructing a temperature field T (x, y, z) in the structure.
6. And converting the concrete elastic wave velocity V obtained by testing into the damage degree D of the concrete after high temperature.
TABLE 4 Damage Change Table for concrete Structure at different temperature levels
In this embodiment, the correlation function between the damage degree D and the temperature level T adopts the following formula:
General model Fourier5:D(T)＝a0+a1*cos(ω*T)+b1*sin(ω*T)
Coefficients(with 95％confidence bounds):
a0＝0.3913，a1＝-0.4462，b1＝0.3977，ω＝0.004041，R2＝0.9932
as can be seen from table 4, the damage degree D was 0.000 at 20 ℃; the damage degree D is 0.850 at 400 ℃.
The embodiment provides a concrete high-temperature damage assessment method based on an elastic wave method, and aims at a concrete structure, the elastic wave velocity V of the concrete structure after high temperature is tested according to the elastic wave method, a large amount of test data is judged whether a suspicious value is an abnormal value or not according to the Graves criterion, all the abnormal values are eliminated, a test model V (F (T)) of the elastic wave velocity V and the temperature T of the concrete structure after high temperature is established by adopting a least square method or a Lagrange interpolation method, and the measured elastic wave velocity V is measured according to the measured elastic wave velocity ViAnd the inverse function T f of the test model V F (T)-1And (V) determining the fire temperature T of the concrete structure, so as to construct a temperature field T (x, y, z) in the concrete structure, constructing a damage variable according to the elastic wave velocity V, converting the elastic wave velocity V obtained by testing into the damage degree D of the concrete structure after high temperature, and further evaluating the bearing capacity and damage condition of the concrete structure. According to the concrete high-temperature damage assessment method based on the elastic wave method, the fire temperature T experienced after the concrete structure is high in temperature can be quickly and accurately estimated, the temperature field T (x, y, z) inside the structure is constructed, the concrete structure damage degree is further identified, a large number of redundant tests are avoided, the operation is simple, the cost is low, the purchase of test equipment such as a large-scale testing machine can be avoided, and the engineering cost is effectively reduced.
It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (7)
1. A concrete high-temperature damage assessment method based on an elastic wave method is characterized by comprising the following steps:
manufacturing a concrete sample meeting preset regulations;
firing the concrete test piece, and recording a temperature rise curve of the concrete test piece by using a standard temperature rise curve;
testing the elastic wave velocity V of the concrete structure after high temperature by using an elastic wave method to obtain test data of the elastic wave velocity V;
judging whether the suspicious value is an abnormal value or not according to the test data through a Grabas criterion, and removing all the suspicious values with the judgment results of the abnormal values;
establishing a test model V (F (T)) of the elastic wave velocity V and the temperature T of the concrete structure after high temperature by using a least square method or a Lagrange interpolation method;
according to the actual elastic wave velocity ViAnd the inverse function T f of said test model V f (T)-1(V) determining the temperature T of the concrete structure subjected to fire, constructing a temperature field T (x, y, z) in the concrete structure, defining the domain A and the domain C for the test model V (F (T), and defining the domain F for the inverse function T (f)-1(V), the definition domain is C, the value domain is A;
converting the elastic wave velocity V obtained by testing into the damage degree D of the concrete structure after the concrete structure is subjected to high temperature according to the temperature field T (x, y, z);
and carrying out damage assessment on the concrete structure according to the damage degree D.
2. The method for evaluating the high-temperature damage of the concrete based on the elastic wave method according to claim 1, wherein the concrete test piece is prepared according to a preset test index type and a preset test method, and the concrete test piece comprises any one of a cubic test piece, a prism test piece and a cylindrical test piece.
3. The method for evaluating the high-temperature damage of the concrete based on the elastic wave method as claimed in claim 1, wherein the step of burning the concrete sample and recording the temperature rise curve of the concrete sample by using a standard temperature rise curve comprises the following steps:
when a building is in fire, the fuel is fibrous material, and the temperature rise curve is an ISO834 curve, and the expression is as follows:
T＝345log(8t+1)+T0 (1)
when an oil fire breaks out, the expression of the temperature rise curve is as follows:
T＝T0+1296(1-0.325e-0.167t-0.675e-2.5t) (2)
in the formulae (1) and (2), T0Is the initial temperature in degrees celsius; t is the duration of the fire in minutes; t is the average temperature of the air at time T, in degrees Celsius.
4. The method for evaluating concrete high-temperature damage based on the elastic wave method according to claim 1, wherein the step of judging whether the "suspicious value" is an "abnormal value" or not by the Grabbs criterion based on the test data and eliminating all the "suspicious values" having the judgment result of the "abnormal value" comprises:
obtaining test data A of the concrete structure after high temperaturei(i-1, 2, …, n) and the mean value of the test data is
The deviation of the test data is
The standard deviation of the test data is s, and for each test data, an expression for the statistics is defined asThe following:
if g isi＞gα(n) identifying that the test data contains an "outlier" at a level of significance of α, and rejecting the test data, wherein giTo test data, gα(n) is a critical value;
if gi＞gα(n) identifying that the test data contains an "outlier" at a level of significance α, the step of rejecting the test data comprising:
arranging the test data under the preset temperature level in the order from small to big, wherein the expression is as follows:
A1≤A2…≤An-1≤An (4)
calculating mean of sample data using mathematical statistics
And standard deviation s;
according to the number n of the test data and the selected significance level alpha, searching a Grabbs test critical value table to obtain a critical value gα(n)；
For test data A with the maximum standard deviation siMaking a judgment if AiCorresponding gi≤gα(n) identifying the test data AiJudging to be finished without gross errors; if AiCorresponding gi＞gα(n) identifying the test data AiHaving a gross error, rejecting the test data;
re-executing the step g on the rest n-1 measurement datai＞gαAnd (n) when the significance level is alpha, determining that the test data contains an abnormal value, and rejecting the test data.
5. The method for evaluating the high-temperature damage of the concrete based on the elastic wave method as claimed in claim 1, wherein the step of testing the elastic wave velocity V of the concrete structure after the high temperature by using the elastic wave method comprises the steps of:
taking the molded bottom surface of the concrete test piece as a test surface;
drawing a positioning line on the test surface in advance, setting 4 to 5 test points on each test surface, and acquiring data for 3 times at each test point;
fixing an acceleration sensor and a vibration source on the test surface in a pressing manner;
exciting the concrete test piece by using the vibration source to enable the concrete test piece to vibrate and excite a stress wave, wherein the propagation characteristic of the stress wave in the concrete test piece reflects the mechanical characteristic of the concrete structure after high temperature;
and converting the propagation parameters of the stress wave in the concrete test piece into the mechanical parameters of the concrete structure after high temperature, and obtaining the test data of the elastic wave velocity V.
6. The method for evaluating the high temperature damage of the concrete based on the elastic wave method as claimed in claim 1, wherein the step of establishing a test model of the elastic wave velocity V and the temperature T of the concrete structure after the high temperature by using a least square method or a lagrange interpolation method comprises:
drawing the elastic wave velocity V and the temperature T in a two-dimensional coordinate system at each temperature level, and setting a curve equation as V ═ F (T) ═ Sigma (M) according to the curve distribution of the elastic wave velocity V and the temperature TiTi) Wherein M isiIs an arbitrary real number, TiV ═ f (t) for temperature constants;
setting N ═ Sigma (V)i-F(Ti))2In which V isiFor the actual elastic wave velocity, F (T)i) The calculated value of the model corresponding to the preset temperature is obtained, and N is the square of the difference between the actually measured wave speed and the calculated value of the model and a function formed by the square of the difference;
f (T)i) Substituting N ═ Σ (V)i-F(Ti))2Obtaining N ═∑(Vi-∑(MiTi))2；
When N takes the minimum value, N pairs of M are usediCalculating a partial derivative;
when the partial derivative is zero, obtaining the inclusion unknown number MiThe system of equations is solved to obtain Mi；
Will MiSubstituted into the equation V ═ f (t) ═ Σ (M)iTi) Obtaining the test model V ═ f (t).
7. The method for evaluating the high temperature damage of the concrete based on the elastic wave method as claimed in claim 1, wherein the step of converting the elastic wave velocity V obtained by the test into the damage degree D of the concrete structure after the high temperature according to the temperature field T (x, y, z) comprises:
the expression of the damage degree D of the concrete structure after high temperature is as follows:
wherein, ViIs the elastic wave velocity, V, of the concrete structure after the concrete structure is subjected to high temperature0The elastic wave velocity before the concrete structure is subjected to high temperature.
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