CN109374452B - Fatigue damage state characterization method and test device for prestressed concrete beam - Google Patents
Fatigue damage state characterization method and test device for prestressed concrete beam Download PDFInfo
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Abstract
The invention discloses a fatigue damage state characterization method of a prestressed concrete beam, which comprises the following steps: measuring initial dynamic parameters of the prestressed concrete beam and performing a first static load test; static load test and dynamic test of prestressed concrete beams in fatigue loading process; analyzing the vibration mode parameters of the prestressed concrete beam; and (5) evaluating the fatigue damage state of the prestressed concrete beam. The invention also discloses a measuring device for realizing the scheme. According to the invention, the dynamic test is carried out in the fatigue test process of the prestressed concrete beam structure, and the position of the fatigue damage of the prestressed concrete beam and the damage degree thereof are analyzed based on the vibration mode parameters, so that the fatigue damage state of the prestressed concrete beam is represented based on the mode parameters, and a new thought is provided for the research and test of the fatigue performance of the prestressed concrete beam.
Description
Technical Field
The invention belongs to the technical field of engineering structure fatigue damage testing, and particularly relates to a method and a device for representing a fatigue damage state of a prestressed concrete beam.
Background
The prestressed concrete beam is widely applied to civil large-span engineering structures such as highway, railway and bridge and the like. The prestressed concrete beams can bear the repeated action of fatigue load of vehicles for a long time in the designed service life. Fatigue loading effects will cause structural fatigue damage to occur and develop, and as damage accumulates, normal service performance of the structure will be affected and even the safety of the structure will be compromised. Therefore, the fatigue performance of the prestressed concrete beam is a common concern for many scholars and engineering technicians at home and abroad.
In the traditional test of the fatigue performance of the prestressed concrete beam, a pulsating fatigue testing machine is generally adopted to apply constant-amplitude fatigue load, and a static loading and unloading experiment is stopped and carried out at a typical moment in the fatigue loading process, so that the fatigue damage development process of the prestressed concrete beam is estimated according to the deflection, stress, strain and other static characteristics of the prestressed concrete beam. The method has single cutting points, can not reflect the stress characteristics of the structure under the action of fatigue dynamic load, is difficult to reveal the development process of the fatigue damage and the fatigue failure mechanism of the prestressed concrete beam, and needs to be researched and developed for a new method for researching the fatigue problem of the prestressed concrete beam based on a dynamic test means.
Disclosure of Invention
The first technical problem to be solved by the invention is to provide a method for representing the fatigue damage state of the prestressed concrete beam based on modal parameters.
The second technical problem to be solved by the invention is to provide a testing device for realizing the fatigue damage state characterization method.
In order to solve the first technical problem, the invention adopts the following technical scheme:
the method for representing the fatigue damage state of the prestressed concrete beam is characterized by comprising the following steps of:
step 1: placing the prestressed concrete beam to be tested on two simply supported supports, and firstly, performing power test on the initial intact prestressed concrete beam to be tested to obtain the initial modal frequency w of the prestressed concrete beam to be tested 0 ；
Step 2: starting a fatigue testing machine to perform fatigue test on the prestressed concrete beam to be tested, stopping the machine after a certain number of fatigue cycles to perform power test, and obtaining the modal frequency w of the prestressed concrete beam to be tested when the number of fatigue cycles is n ten thousand times n ；
Step 3: obtaining damage variables of the prestressed concrete beam to be tested under different circulation times according to the following formula:
wherein: w (w) 0 For the initial modal frequency, w N The mode frequency of the prestressed concrete beam to be tested in fatigue failure is N, which is the cycle number of the prestressed concrete beam to be tested in fatigue failure;
step 4: fitting the damage variables of the prestressed concrete beam to be tested under different circulation times obtained in the step 3 to obtain a fatigue whole-process damage variable evolution rule based on modal frequency, thereby representing the fatigue damage state of the prestressed concrete beam to be tested.
Further, the damage variable and the cycle number are fitted by adopting the following formula:
wherein: alpha and beta are parameters to be fitted, N is the cycle number, and N is the cycle number when the prestressed concrete beam to be tested is subjected to fatigue failure.
Further, the dynamic test adopts an excitation method, the vibration exciter is moved to the vicinity of the maximum amplitude point of the theoretical amplitude of each stage of the prestressed concrete beam to be tested to carry out sweep frequency excitation, and the vibration exciter is used for collecting acceleration signals and then transmitting the acceleration signals to a modal test analysis system to carry out modal analysis.
Further, the lesion variable defined by the modal frequency selects a first order modal frequency.
Further, during power test, the vibration exciter and the vibration pickup are staggered.
In order to solve the second technical problem, the invention adopts the following technical scheme:
the testing device for realizing the characterization method comprises two simply supported supports oppositely arranged on the ground, a prestressed concrete beam to be tested arranged on the two simply supported supports, an excitation system and a modal test analysis system;
the vibration excitation system comprises a vibration exciter, a power amplifier and a signal amplifier which are sequentially connected, wherein the vibration exciter is arranged between two simple support seats below the prestressed concrete beam to be tested in a free moving way;
the modal test analysis system comprises a vibration pickup, a signal acquisition system and a modal analysis system which are connected in sequence, wherein the vibration pickup is arranged on the top surface of the prestressed concrete beam to be tested.
Further, the vibration pickers are equally arranged along the length direction of the prestressed concrete beam to be tested.
Further, the vibration exciter is arranged on the travelling trolley.
Further, a fatigue testing machine is arranged above the prestressed concrete beam to be tested, the fatigue testing machine is fixedly arranged on the ground through a reaction frame, a load distribution beam is arranged below an actuating head of the prestressed concrete beam to be tested, and the central point of the actuating head of the fatigue testing machine is opposite to the central point of the prestressed concrete beam to be tested and the central point of the load distribution beam.
Further, displacement meters are arranged at the upper parts of the two ends of the prestressed concrete beam to be tested and at the positions of the simple support seat and the Liang Kuazhong and the bottom of the load loading point.
Further, two ends of the load distribution beam are connected with the prestressed concrete beam to be tested through simple supports.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, by utilizing a good mapping relation between the fatigue damage state of the structure and the modal parameters in the fatigue loading and damage process of the prestressed concrete beam, the structure fatigue test and the dynamic test of the prestressed concrete beam are combined, and the position of the fatigue damage of the prestressed concrete beam and the damage degree thereof are analyzed based on the vibration modal parameters, so that the fatigue damage state of the prestressed concrete beam is represented based on the modal parameters, and a new thought is provided for the research and test of the fatigue performance of the prestressed concrete beam.
2. The testing device improves the traditional fixed vibration excitation equipment into the movable vibration excitation equipment, can be quickly transported according to the position of the vibration excitation point, ensures that the test is more convenient to carry out, and has the advantages of simple structure and convenient test.
Drawings
FIG. 1 is a flow chart of a characterization method of the present invention;
FIG. 2 is a schematic diagram of a power test according to the present invention;
FIG. 3 is a schematic diagram of a fatigue testing process device according to the present invention;
FIG. 4 is a cross-sectional view of the present invention;
FIG. 5 is a schematic view of excitation position selection;
FIG. 6 is a graph showing the measured frequency degradation ratio in fatigue history;
fig. 7 is a graph of fatigue damage evolution law of a prestressed concrete beam characterized by a first-order modal frequency.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1, a method for representing fatigue damage state of a prestressed concrete beam includes the following steps:
step 1: placing the prestressed concrete beam to be tested on two simply supported supports, and firstly, performing power test on the initial intact prestressed concrete beam to be tested to obtain the initial modal frequency w of the prestressed concrete beam to be tested 0 ；
Step 2: starting a fatigue testing machine to perform fatigue test on the prestressed concrete beam to be tested, stopping the machine after a certain number of fatigue cycles to perform power test, and obtaining the modal frequency w of the prestressed concrete beam to be tested when the number of fatigue cycles is n ten thousand times n ；
Step 3: obtaining damage variables of the prestressed concrete beam to be tested under different circulation times according to the following formula:
wherein: w (w) 0 For the initial modal frequency, w N The mode frequency of the prestressed concrete beam to be tested in fatigue failure is N, which is the cycle number of the prestressed concrete beam to be tested in fatigue failure;
step 4: fitting the damage variables of the prestressed concrete beam to be tested under different circulation times obtained in the step 3 to obtain a fatigue whole-process damage variable evolution rule based on modal frequency, thereby representing the fatigue damage state of the prestressed concrete beam to be tested.
Further, the damage variable and the cycle number are fitted by adopting the following formula:
wherein: alpha and beta are parameters to be fitted, N is the cycle number, and N is the cycle number when the prestressed concrete beam to be tested is subjected to fatigue failure.
Further, the dynamic test adopts an excitation method, the vibration exciter is moved to the vicinity of the maximum amplitude point of the theoretical amplitude of each stage of the prestressed concrete beam to be tested to carry out sweep frequency excitation, and the vibration exciter is used for collecting acceleration signals and then transmitting the acceleration signals to a modal test analysis system to carry out modal analysis.
Further, the lesion variable defined by the modal frequency selects a first order modal frequency.
Further, during power test, the vibration exciter and the vibration pickup are staggered.
During modal testing, the excitation position is selected according to the following principle: 1) Moving the vibration exciter to the vicinity of the maximum amplitude point of each-order theoretical amplitude value of the beam to be tested to perform sweep frequency vibration excitation; 2) The vibration exciter placing position should avoid the position right below the vibration pickup placing position so as to avoid the distortion of the vibration signal measured at the point due to overload.
The mode analysis method selected by the mode test analysis system is a random subspace SSI method, and the method can effectively extract structural mode parameters from structural response of environmental excitation without inputting external excitation or being undetectable.
Referring to fig. 2-5, a testing device for implementing the above characterization method includes two simply supported supports 1 oppositely disposed on the ground 10, a prestressed concrete beam 2 to be tested disposed on the two simply supported supports 1, an excitation system 3, and a modal test analysis system 4.
Specifically, the excitation system 3 includes an exciter 301, a power amplifier 302 connected to the exciter 301, and a signal amplifier 303 connected to the power amplifier 302, where the exciter 301 is freely movably disposed below the prestressed concrete beam 2 to be measured and between the two simply supported supports 1. The modal test analysis system 4 includes a vibration pickup 401, a signal acquisition system 402 connected with the vibration pickup 401, and a modal analysis system 403 connected with the signal acquisition system 402, where components such as the modal analysis system 403 connected with the signal acquisition system 402 are all existing structures, and are not described herein.
The vibration pickup 401 is arranged on the top surface of the prestressed concrete beam 2 to be tested, the vibration pickup 401 is adsorbed on a magnetic support, and the magnetic support is fixedly arranged on the prestressed concrete beam 2 to be tested. The fatigue testing machine 5 of which the actuating head is opposite to the prestressed concrete beam 2 to be tested is also arranged above the prestressed concrete beam 2 to be tested, and the fatigue testing machine 5 is fixedly arranged on the ground through the reaction frame 6.
Preferably, the vibration pickup 401 is equally arranged along the length direction of the prestressed concrete beam 2 to be tested, the output end of the vibration pickup 401 is connected with the input end of the signal acquisition system 402, the output end of the signal acquisition system 402 is connected with the input end of the modal analysis system 403, the signal acquisition system 402 acquires the vibration signal measured by the vibration pickup 401 and transmits the vibration signal to the modal analysis system 403, and the modal analysis system 403 obtains the modal parameters of the beam to be tested through analysis.
It is conceivable that in practical design, the vibration exciter 301 is arranged on the traveling trolley 11, the traveling trolley 11 is arranged on the ground, and each time of modal test, the vibration exciter is rapidly transported to a designated excitation point through the traveling trolley, so that the modal test is more convenient and effective.
In practical application, the simply supported support 1 includes a base 101 fixedly installed on the ground and a hinge support 102 provided on the base 101, the two hinge supports 102 are used for supporting a beam to be tested (prestressed concrete beam), and the base 101 is fixedly installed on the laboratory ground 10 by fastening bolts. The top of the prestressed concrete beam 2 to be tested is also provided with a load distribution beam 7 for transmitting the load applied by the fatigue testing machine 5 to the beam to be tested, two ends of the load distribution beam 7 are connected with the prestressed concrete beam 2 to be tested through hinged supports 8, and the positions of the upper ends of the beams, liang Kuazhong corresponding to the simply supported supports at the two ends of the prestressed concrete beam to be tested and the bottom of the load loading point are provided with displacement meters 9. And during the test, according to a loading program of the static monotonic loading test, carrying out graded loading to the fatigue upper limit load, and measuring the strain, crack, deflection and the like under each level of load and the development condition thereof.
The invention will be further illustrated with reference to specific examples.
Examples
A prestressed concrete simply supported T beam of a railway bridge with the standard height of 32m is selected as a prototype beam, a 1:6 reduced scale model of the prototype beam is manufactured according to a similar theory to serve as a prestressed concrete beam 3 to be tested, and design parameters are shown in the table 1 below. In this example, a total of 3 model beams were prepared, one of which (No. 1) was used for the static load test toDetermination of the static limiting load P required for fatigue test u Actual measurement of P u =265 kN; the other two (No. 2, no. 3) were used for fatigue test.
TABLE 1 modelBeam designParameters (parameters)
The concrete mixing ratio is cement: water: stone: sand: water reducer = 460:118:1092:735:4.2, reserving concrete test blocks when pouring each test beam, wherein the mechanical property test and the model beam test are carried out simultaneously, and the measured mechanical properties are shown in the following table 2:
table 2 actual measurement of parameters of mechanical properties of concrete
The longitudinal bars adopt HRB335 grade steel bars with the diameter of 10mm; according to the design and construction requirements of the railway bridge, hoops with the diameter of 8mm (HPB 300) and the spacing of 100mm are arranged in a Liang Chun bent section, and the hoops with the spacing of 50mm are arranged in other sections. The measured mechanical properties of the steel bars are shown in table 3 below:
table 3 actual measurement of the mechanical properties parameters of the reinforcing bars
The prestress steel bar adopts 2 bundles of 7 phi 5 steel strands, the nominal diameter d=15.2 mm and the ultimate strength standard value f ptk =1860 MPa, a parabolic arrangement was employed. The prestressed tendons are tensioned at two ends (single steel strand of a single-hole jack is pulled in pairs and is completed in two times), and the tensioning control stress sigma is achieved con =1116 MPa, 5% overstretched, the concrete age exceeded 28 days at tensioning.
A fatigue damage state characterization method of a prestressed concrete beam mainly comprises the following steps:
1) Initial dynamic parameter measurement and first static load test of prestressed concrete beams: placing a prestressed concrete beam 2 to be tested on a simple support 1, firstly, performing power test on the prestressed concrete beam 2 to be initially detected perfectly, performing sweep frequency excitation by moving an exciter 301 to the vicinity of the maximum amplitude point of each order of theoretical vibration mode amplitude, collecting acceleration signals by a vibration pickup 401, and then transmitting the acceleration signals to a modal test analysis system for modal analysis to obtain modal parameters of each order; then arranging load distribution beams 7 according to a four-point bending loading mode, placing the load distribution beams 7 on the prestressed concrete beam 2 to be tested through a hinged support 8, and ensuring that the center point of an actuating head of the fatigue testing machine 5 is opposite to the center point of the prestressed concrete beam 2 to be tested and the center point of the load distribution beams 7; according to a loading program of a static monotonic loading test, carrying out graded loading to the fatigue upper limit load, and measuring strain, cracks, deflection and the like under each level of load and the development condition thereof;
2) Static load test and dynamic test of prestressed concrete beams in fatigue loading process: after the step 1) is completed, starting the fatigue testing machine 5 to carry out fatigue loading, stopping after the fatigue loading cycle times reach 1 ten thousand times, 5 ten thousand times, 10 ten thousand times, 25 ten thousand times and the like (and so on until the prestressed concrete beam 2 to be tested is close to fatigue damage), and respectively carrying out a power test and a static load test loaded to the fatigue upper limit load as described in the step 1); and after the prestressed concrete beam 2 to be tested is subjected to fatigue failure, carrying out a power test and a static load test.
The fatigue test adopts constant amplitude sine wave loading with loading frequency of 3.5Hz, the main parameters of the test are shown in the following table 4, and the lower limit value of the fatigue load is P min ＝0.2P u Upper limit value P of fatigue load max Respectively take 0.45P u And 0.5P u 。
Table 4 model beam test parameters and fatigue life
3) And (3) analyzing the vibration modal parameters of the prestressed concrete beam: and as shown in the step 1) and the step 2), respectively carrying out dynamic tests on the prestressed concrete beam 2 to be detected in the initial perfect state before the initial static load and in the fatigue process, and carrying out vibration mode parameter analysis through a mode test analysis system to obtain mode parameters of each stage in the fatigue process.
During initial power parameter measurement, the load distribution beam 7 and the simple support 8 are removed, a magnetic support matched with the vibration pickup 401 is stuck on the prestressed concrete beam 2 to be measured, and the vibration pickup 401 is fixed on the prestressed concrete beam 2 to be measured by being adsorbed on the magnetic support; in the cyclic loading of the fatigue test, the vibration pickup 401 is taken down for storage, and when the power test is carried out by stopping the machine for a certain number of times in fatigue, the vibration pickup 401 is taken out and adsorbed on the magnetic support for re-measurement.
The mode analysis method selected by the mode test analysis system is a random subspace SSI method, and the method can effectively extract structural mode parameters from structural response of environmental excitation without inputting external excitation or being undetectable.
4) And (3) evaluating fatigue damage states of the prestressed concrete beam: and 3) carrying out fatigue damage state evaluation on the prestressed concrete beam 2 to be tested through relevant analysis by analyzing the modal parameters of each step in the fatigue process.
The instrument model and manufacturer used in this example are shown in table 5 below:
table 5 test instrument
Based on the characterization method and the testing device for the fatigue damage state of the prestressed concrete beam based on the modal parameters, the frequencies of the two fatigue test beams in the fatigue process are obtained as shown in the following table 6.
TABLE 6 fatigue history actual measurement and degradation ratio summary table
Defining the frequency degradation ratio under fatigue:
γ(n)＝w n /w 0
wherein omega is 0 Is the initial frequency of the sound beam; omega n The frequency of the back beam is n ten thousand times fatigue. The frequency degradation ratio of the first three-order measured frequency in the fatigue history is obtained as shown in the table 6, and the frequency degradation ratio curve is drawn as shown in fig. 6.
As can be seen from table 6 and fig. 6 above, the first third order frequency of the prestressed concrete girder is decreased with the increase of the fatigue frequency. The loading is started, and the modal frequency is obviously reduced; after entering the middle fatigue stage, the frequency reduction rate becomes slow, gradually decreases with a smaller value, and has fluctuation but basically keeps stable; when the fatigue life is reached, the amplitude is reduced slightly once, the amplitude of the third-order frequency reduction before the final beam No.2 is 19.5%,15.8% and 9.0%, and the amplitude of the third-order frequency reduction before the beam No.3 is 19.4%,13.6% and 7.4%. It can be seen that the frequency of the first order frequency is reduced to the greatest extent under the action of fatigue; second order frequency order; while the frequency reduction amplitude of the third order frequency is minimal.
It can also be seen from fig. 6 that: the degradation process of the modal frequency of the prestressed concrete beam also has a three-stage rule similar to fatigue stiffness degradation. The mode frequency in the initial fatigue stage is greatly reduced because of the development of concrete cracks and great effective prestress loss at the beginning of loading, so that the rigidity of the test beam is greatly reduced, and the mode frequency of the beam is rapidly reduced. After entering the middle fatigue stage, the crack slowly stretches and expands, the effective prestress loss rate is reduced and tends to be stable, local bonding slip damage occurs between the reinforced steel bar and the concrete, the beam rigidity is in an approximately linear development state, the modal frequency is also approximately linearly reduced, and the relative development is relatively stable. At the end of fatigue, the concrete cracks again rapidly develop and dendritic cracks appear, and at the moment, the rigidity of the beam body is reduced again, so that the frequency is reduced again.
Defining a lesion variable based on modal frequencies:
wherein w is 0 For the initial modal frequency, w N The mode frequency of the prestressed concrete beam to be tested in fatigue failure is N, which is the cycle number of the prestressed concrete beam to be tested in fatigue failure. The variation range of the damage variable D defined by the formula is between 0 and 1; d=0 corresponds to the lossless state of the test beam; d=1 corresponds to complete fatigue failure of the beam. The damage variable D is a monotonically increasing function, i.e. the degree of fatigue damage of the test beam increases with increasing load cycles, and the damage is irreversible.
In consideration of bridge dynamic test of actual engineering, the damage variable is defined by adopting the first-order modal frequency because the energy and the like of the first-order modal frequency occupy a larger proportion, have higher accuracy, and meanwhile, the frequency degradation amplitude of the first-order modal frequency is found to be the largest by the previous research. Comprehensive many scholars study the damage accumulation fitting curve, and after comparison and selection, the following formula is selected for fitting:
wherein: alpha and beta are parameters to be fitted, N is the cycle number, and N is the cycle number when the prestressed concrete beam to be tested is subjected to fatigue failure. From the test results, nonlinear regression analysis was performed using the least squares method, and the parameters were obtained as shown in table 7 below. Fitting degree R of two beams 2 All approach 100%, which indicates that the model has better fitting degree.
TABLE 7 nonlinear model fitting parameters for fatigue damage
According to the fitting curve and the fitting parameters, the fatigue accumulated damage evolution rule of the two beams based on the first-order modal frequency can be obtained, and the fatigue accumulated damage evolution rule is shown in the figure 7.
As can be seen from fig. 7, the fatigue damage evolution rule of each test beam has obvious nonlinearity. The whole fatigue damage evolution can be divided into 3 stages. In stage 1 of the initial development of the injury, the fatigue accumulation injury increases sharply to reach a stable level; stage 2, the fatigue accumulation damage steadily and slowly increases; as the cycle times increase, the fatigue accumulation damage enters the 3 rd stage, and the fatigue accumulation damage starts to increase sharply on the basis of the 2 nd stage accumulation damage in the 3 rd stage until the test beam is completely destroyed and the bearing capacity is lost.
It can also be seen by comparing the fatigue damage evolution curves of the two beams that the greater the fatigue stress amplitude is, the more severe the damage is developed. In the early stage of fatigue, the damage development degree of the beam No.2 with larger stress amplitude is faster than that of the beam No.3, and when two beams respectively reach the damage threshold values of about 0.68 and 0.56, the two beams enter the middle stage of fatigue in which the damage stably develops; the threshold for end of damage beam No.2 is about 0.85, greater than the threshold of beam No.3 by 0.82. Throughout the development process, the beam damage development with larger stress amplitude always leads the beam with smaller stress amplitude, and the low life characteristics of the compared large stress amplitude beam also show the rationality of the evolution rule.
According to the method, the first-order natural frequency is used as a damage variable, and the three-stage nonlinear fatigue damage evolution rule of the prestressed concrete beam is effectively simulated. Therefore, by researching the fatigue damage accumulation curve and combining the recognition of the fatigue damage three-stage threshold value, a research foundation can be provided for judging the structural performance degradation degree and predicting the residual life, a certain application prospect is provided, and a new thought is provided for the research of the fatigue performance of the prestressed concrete beam.
The above examples are only illustrative of the invention and are not intended to be limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. Nor is it necessary or impossible to exhaust all embodiments herein. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (9)
1. The method for representing the fatigue damage state of the prestressed concrete beam is characterized by comprising the following steps of:
step 1: placing the prestressed concrete beam to be tested on two simply supported supports, and firstly, performing power test on the initial intact prestressed concrete beam to be tested to obtain the initial modal frequency w of the prestressed concrete beam to be tested 0 ；
Step 2: starting a fatigue testing machine to perform fatigue test on the prestressed concrete beam to be tested, stopping the machine after a certain number of fatigue cycles to perform power test, and obtaining the modal frequency w of the prestressed concrete beam to be tested when the number of fatigue cycles is n ten thousand times n ；
Step 3: obtaining damage variables of the prestressed concrete beam to be tested under different circulation times according to the following formula:
wherein: w (w) 0 For the initial modal frequency, w N The mode frequency of the prestressed concrete beam to be tested in fatigue failure is N, which is the cycle number of the prestressed concrete beam to be tested in fatigue failure;
step 4: fitting the damage variables of the prestressed concrete beam to be tested under different cycle times obtained in the step 3 to obtain a fatigue whole-process damage variable evolution rule based on modal frequency, thereby representing the fatigue damage state of the prestressed concrete beam to be tested;
the damage variable and the cycle number are fitted by adopting the following formula:
wherein: alpha and beta are parameters to be fitted, N is the cycle number, and N is the cycle number when the prestressed concrete beam to be tested is subjected to fatigue failure.
2. The method for characterizing the fatigue damage state of the prestressed concrete beam according to claim 1, wherein: the dynamic test adopts an excitation method, and the vibration exciter is moved to the vicinity of the maximum amplitude point of the theoretical amplitude of each order of the prestressed concrete beam to be tested to carry out sweep frequency excitation, and the vibration exciter is used for collecting acceleration signals and then transmitting the acceleration signals to a modal test analysis system to carry out modal analysis.
3. The method for characterizing the fatigue damage state of the prestressed concrete beam according to claim 1, wherein: and the damage variable selects a first-order modal frequency.
4. The method for characterizing the fatigue damage state of the prestressed concrete beam according to claim 1, wherein: during power test, the vibration exciter and the vibration pickup are staggered.
5. A testing device for realizing the characterization method according to any one of claims 1-4 is characterized by comprising two simply supported supports oppositely arranged on the ground, a prestressed concrete beam to be tested arranged on the two simply supported supports, an excitation system and a modal test analysis system;
the vibration excitation system comprises a vibration exciter, a power amplifier and a signal amplifier which are sequentially connected, wherein the vibration exciter is arranged between two simple support seats below the prestressed concrete beam to be tested in a free moving way;
the modal test analysis system comprises a vibration pickup, a signal acquisition system and a modal analysis system which are connected in sequence, wherein the vibration pickup is arranged on the top surface of the prestressed concrete beam to be tested.
6. The test device of claim 5, wherein: the vibration pickers are equally arranged along the length direction of the prestressed concrete beam to be tested, and the vibration exciter is arranged on the travelling trolley.
7. The test device of claim 5, wherein: a fatigue testing machine is arranged above the prestressed concrete beam to be tested, the fatigue testing machine is fixedly arranged on the ground through a reaction frame, a load distribution beam is arranged below an actuating head of the prestressed concrete beam to be tested, and the central point of the actuating head of the fatigue testing machine is opposite to the prestressed concrete to be tested
A beam center point and a load distribution beam center point.
8. The test device of claim 5, wherein: and displacement meters are arranged at the upper parts of two ends of the prestressed concrete beam to be tested, at the positions of the simple support and Liang Kuazhong and at the bottom of the load loading point.
9. The test device of claim 5, wherein: and two ends of the load distribution beam are connected with the prestressed concrete beam to be tested through simple supports.
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| CN110455650A (en) * | 2019-07-10 | 2019-11-15 | 河海大学 | A method of quickly determining prefabricated cracked concrete beam fatigue life |
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| CN113092290B (en) * | 2021-03-26 | 2022-05-20 | 太原理工大学 | External prestress reinforced concrete beam fatigue test device and method |
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