CN113252446B - Concrete beam prestressed tendon tension testing device and method - Google Patents
Concrete beam prestressed tendon tension testing device and method Download PDFInfo
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- CN113252446B CN113252446B CN202110610051.6A CN202110610051A CN113252446B CN 113252446 B CN113252446 B CN 113252446B CN 202110610051 A CN202110610051 A CN 202110610051A CN 113252446 B CN113252446 B CN 113252446B
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- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- G01N2203/0014—Type of force applied
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- G01N2203/0017—Tensile
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
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Abstract
The invention provides a device and a method for testing the tension of a prestressed tendon of a concrete beam, which comprises the following steps: the magnetic flux sensor comprises a cylindrical shell, a test coil and a magnetic excitation coil, wherein the center of the cylindrical shell is provided with a through hole, the test coil and the magnetic excitation coil are arranged between the inner side wall and the outer side wall of the shell, the test coil is wound on the inner side wall of the shell, and the magnetic excitation coil is wound on the outer side of the test coil; and the tester is electrically connected with the test coil and the magnetic excitation coil through data wires. When the testing device and the method are used for testing the tension of the prestressed tendon of the concrete beam, the interference of external environmental factors is small, the overall stress level of the prestressed tendon can be reflected, and the real tension of the prestressed tendon can be reflected. The testing device is not influenced by the structural form and the section change of the concrete beam, and is suitable for the tension test of the straight-line prestressed tendon of the bridge with any span. The testing device is convenient to install on site, simple to operate, high in testing precision, convenient to acquire data and high in working efficiency.
Description
Technical Field
The invention relates to the technical field of concrete beam prestressed tendon tension testing, in particular to a concrete beam prestressed tendon tension testing device and method.
Background
In the construction stage and the static load test process of the prestressed concrete beam, the tension of the prestressed tendons sometimes needs to be measured, and the accuracy of the measured data is directly related to the calculation and evaluation of the stress state of the concrete beam, so that the effective and accurate tension test of the prestressed tendons is very important. The longitudinal prestressed tendons of the prestressed concrete beam generally adopt prestressed bundles woven by standard steel strands, a single standard steel strand is formed by twisting 6 steel wires around 1 central steel wire, and the outer steel wires are all arranged in a spiral winding mode.
In the related testing techniques, a resistance strain gauge method, a vibration frequency testing method, an anchoring end pressure sensor testing method, a fixed-scale distance measurement and elongation method, a fiber grating strain gauge method, and the like are generally adopted. When the method of sticking the resistance strain gauge on the surface of the steel wire is adopted, the resistance strain gauge is stuck with the steel wire by glue, and the water resistance, the insulativity and the durability of the resistance strain gauge are poor. The resistance strain gauge is greatly influenced by temperature and humidity, is not suitable for protection and cannot be used for a long time. And the tested strain value is only the strain of one steel wire in the spiral direction, not the strain of the steel strand in the linear direction, not the average strain of the steel strand bundle, and the test error is large and the measuring range is small. When the vibration frequency method is adopted for testing, the vibration sensor is wound on the outer side of the prestressed tendons, so that the vibration sensor is suitable for suspending long external prestressed tendons and is not suitable for internal prestressed tendons. For the short suspended external prestressed tendons, the vibration frequency is high, and the test error is large. When the pressure sensor at the anchoring end is used for testing, the straight-through pressure sensor is arranged between the anchor backing plate and the working anchorage device, only the tension of the prestressed tendon at the anchor recess position can be tested, and the tension at the middle position of the prestressed tendon cannot be obtained. When a fixed gauge length elongation measurement method is adopted, the method is only suitable for the external prestressed tendons, fixed length of straight line sections of the external prestressed tendons are selected to be marked, and the elongation with fixed length is measured by a plate ruler, a tape measure or an extensometer and then converted into tension. When the fiber grating strain gauge method is adopted, firstly, the side wires of the single steel stranded wire are scattered, the central wire is taken out, the inclined groove is arranged on the central wire, the fiber grating is stuck in the inclined groove by using an adhesive, then, the side wires and the central wire are twisted and formed, and the end part is packaged and protected. The steel strand with the fiber grating sensor needs to be specially customized by a manufacturer, so that the cost is high and the period is long. Therefore, when the tension of the prestressed tendon is measured, the problems of low testing precision, large error, high cost, long period and the like exist, and meanwhile, the overall stress level of the prestressed tendon is difficult to reflect, and the real tension of the prestressed tendon is difficult to reflect.
Disclosure of Invention
The present invention is directed to solving the problems of the prior art. Therefore, the invention provides a concrete beam prestressed tendon tension testing device. The prestressed tendons are made of magnetic materials, and under the action of external load, the internal stress can be changed, and the magnetic conductivity can be changed accordingly. The testing device comprises a magnetic flux sensor, and reflects the internal stress change through the magnetic conductivity change of the prestressed tendon, so as to indirectly measure the tension of the prestressed tendon. The testing device is high in accuracy, is less interfered by external environmental factors, can embody the overall stress level of the prestressed tendon, and can reflect the real tension of the prestressed tendon.
Meanwhile, the invention also provides a method for testing the tension of the prestressed tendon of the concrete beam.
According to a first aspect of the present invention, an apparatus for testing a tension of a prestressed tendon of a concrete beam includes:
the magnetic flux sensor comprises a cylindrical shell, a testing coil and a magnetic excitation coil, wherein the center of the cylindrical shell is provided with a through hole, the testing coil and the magnetic excitation coil are arranged between the inner side wall and the outer side wall of the shell, the testing coil is wound on the inner side wall of the shell, and the magnetic excitation coil is wound on the outer side of the testing coil;
and the tester is electrically connected with the test coil and the magnetic excitation coil through data wires.
According to one embodiment of the invention, a centering rigid support is arranged in the through hole, and a through hole is arranged in the center of the centering rigid support and used for placing a prestressed tendon.
According to one embodiment of the invention, the difference between the diameter of the through hole and the diameter of the tendon is 2-6cm.
According to the embodiment of the second aspect of the invention, the method for testing the tension of the prestressed tendon of the concrete beam comprises the following steps:
a cavity is preset at the bottom of the midspan position of the beam body, the cavity corresponds to a prestressed pipeline of a prestressed tendon to be tested, and a magnetic flux sensor is placed in the cavity;
penetrating a prestressed tendon to be tested into the prestressed pipeline and the magnetic flux sensor, tensioning the prestressed tendon to be tested and reading the tension of the prestressed tendon to be tested;
grouting into the prestressed pipeline and sealing the cavity;
and carrying out static load bending test on the beam body.
According to an embodiment of the invention, said positioning a magnetic flux sensor within said cavity further comprises:
and calibrating the relation between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
According to an embodiment of the present invention, the calibrating the relationship between the tendon tension and the magnetic flux sensor voltage specifically includes:
selecting the prestressed tendons with the same batch, the same quantity, the same cross section, the same elastic modulus and the same tensile strength standard value as the prestressed tendons to be tested, and calibrating the relation between the tension of the prestressed tendons and the voltage of the magnetic flux sensor.
According to an embodiment of the present invention, the calibrating the relationship between the tendon tension and the magnetic flux sensor voltage specifically includes:
stretching in 8-10 stages within the range of 0.8 times of the standard tensile strength value of the prestressed tendon, and recording the stretching force value and the voltage value of the magnetic flux sensor at each stage;
and calibrating the relation between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
According to an embodiment of the invention, the stretching is performed in 8-10 stages within 0.8 times of the standard value of the tensile strength of the prestressed tendon, each stage records the value of the stretching force and the voltage value of the magnetic flux sensor, and then the method further comprises the following steps:
and (3) performing at least 2 cycles in the stage tensioning process, averaging the recorded values of each stage of different cycles, and fitting the relationship between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
According to an embodiment of the present invention, the penetrating the tendon to be tested into the prestressed pipe and the magnetic flux sensor, tensioning the tendon to be tested, and reading the tension of the tendon to be tested specifically includes:
penetrating a prestressed tendon to be tested into the prestressed pipeline and the magnetic flux sensor;
tensioning the prestressed tendon to be tested according to a design sequence, anchoring, and reading the initial effective tension of the prestressed tendon to be tested;
and after tensioning and anchoring all the prestressed tendons, reading the final effective tension of the prestressed tendons to be tested.
According to an embodiment of the present invention, the grouting into the prestressed pipe and sealing the cavity specifically include:
grouting into the prestressed pipeline and preventing grouting materials from entering the magnetic flux sensor;
and pouring concrete with the same strength as the beam body in the cavity.
One or more technical schemes in the invention have at least one of the following technical effects:
the prestressed tendons are made of magnetic materials, and under the action of external load, the internal stress can be changed, and the magnetic conductivity can be changed accordingly. The concrete beam prestressed tendon tension testing device comprises a magnetic flux sensor, and the internal stress change is reflected through the magnetic conductivity change of the prestressed tendon, so that the tension of the prestressed tendon is indirectly measured. The concrete beam prestressed tendon tensile force testing device is less interfered by external environment factors, can reflect the overall stress level of the prestressed tendon, and can reflect the real tensile force of the prestressed tendon. The testing device is not influenced by the structural form and the section change of the concrete beam, and is suitable for the tension test of the straight-line prestressed tendon of the bridge with any span. The testing device is convenient to install on site, simple to operate, high in testing precision, convenient to acquire data and high in working efficiency.
Drawings
FIG. 1 is a cross-sectional view of a magnetic flux sensor provided in accordance with an embodiment of the present invention;
FIG. 2 is a left side view of a magnetic flux sensor provided by an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a calibration test beam provided by an embodiment of the invention;
FIG. 4 is a schematic structural diagram of an in-vivo prestressed concrete girder according to an embodiment of the present invention;
fig. 5 is a schematic structural view of an in vitro prestressed concrete girder provided in an embodiment of the present invention;
fig. 6 is a first flowchart of a method for testing a tensile force of a prestressed tendon of a concrete beam according to an embodiment of the present invention;
fig. 7 is a second flowchart of a method for testing a tensile force of a prestressed tendon of a concrete beam according to an embodiment of the present invention;
fig. 8 is a third flowchart of a method for testing a tensile force of a prestressed reinforcement of a concrete beam according to an embodiment of the present invention;
fig. 9 is a fourth flowchart of a method for testing a tensile force of a prestressed reinforcement of a concrete beam according to an embodiment of the present invention;
fig. 10 is a flow chart of a fifth method for testing the tensile force of a prestressed reinforcement of a concrete beam according to an embodiment of the present invention;
fig. 11 is a sixth flowchart of a method for testing a tensile force of a prestressed tendon of a concrete beam according to an embodiment of the present invention;
fig. 12 is a seventh flowchart of a method for testing a tensile force of a prestressed tendon of a concrete beam according to an embodiment of the present invention;
fig. 13 is a first actually measured data diagram of the method for testing the tensile force of the prestressed reinforcing steel of the concrete beam according to the embodiment of the present invention;
fig. 14 is a second measured data diagram of the method for testing the tensile force of the prestressed reinforcing steel of the concrete beam according to the embodiment of the present invention.
Reference numerals are as follows:
1. a magnetic flux sensor; 10. a through hole; 11. a housing; 12. testing the coil; 13. a magnetic excitation coil; 14. centering the rigid support; 2. a tester; 3. a data line; 4. the prestressed tendons to be tested; 40. the prestressed tendon is to be calibrated; 5. a beam body; 50. a cavity; 51. a prestressed pipe; 52. a grouting pipe; 6. and calibrating the test beam.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described below with reference to the accompanying drawings, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the scope of protection of the present invention.
In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the embodiments of the present invention and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the embodiments of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the embodiments of the present invention, it should be noted that the terms "connected" and "connected" are to be interpreted broadly, and may be, for example, a fixed connection, a detachable connection, or an integral connection, unless explicitly stated or limited otherwise; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. Specific meanings of the above terms in the embodiments of the present invention can be understood by those skilled in the art according to specific situations.
In embodiments of the invention, unless expressly stated or limited otherwise, a first feature may be "on" or "under" a second feature such that the first and second features are in direct contact, or the first and second features are in indirect contact via an intermediary. Also, a first feature "on," "above," and "over" a second feature may be directly on or obliquely above the second feature, or simply mean that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of various embodiments or examples described in this specification can be combined or combined by those skilled in the art without contradiction.
In the related technology, when the tension of the prestressed tendon is measured, the problems of low measurement precision, large error, high cost, long period and the like exist, and meanwhile, the overall stress level of the prestressed tendon is difficult to reflect, and the real stress state of the prestressed tendon is difficult to reflect.
The concrete beam prestressed tendon tensile testing device provided by the embodiment of the first aspect of the invention, referring to fig. 1 to 5, comprises a magnetic flux sensor 1 and a tester 2.
The prestressed tendons are made of magnetic materials, and under the action of external load, the internal stress can be changed, and the magnetic conductivity can be changed accordingly.
A concrete beam prestressed tendon tension testing device is hereinafter referred to as a testing device for short and comprises a magnetic flux sensor 1, wherein the magnetic flux sensor 1 reflects internal stress change by detecting magnetic conductivity change of prestressed tendons, and then tension of the prestressed tendons is indirectly measured.
According to one embodiment of the present invention, the magnetic flux sensor 1 includes a cylindrical case 11 provided with a through hole 10 at the center, and a test coil 12 and a magnetic excitation coil 13.
The housing 11 includes an inner side wall and an outer side wall which enclose the through-hole 10, and the test coil 12 and the magnetic excitation coil 13 are disposed at positions between the inner side wall and the outer side wall. The test coil 12 is wound around the inner wall of the housing 11, and the magnetic excitation coil 13 is wound around the outer side of the test coil 12.
The tester 2 is electrically connected with the test coil 12 and the magnetic excitation coil 13 through the data line 3, and the tester 2 is used for applying voltage to the magnetic excitation coil 13 to enable the magnetic excitation coil 13 to generate a magnetic field and simultaneously receiving a voltage value on the test coil 12, wherein the voltage value on the test coil 12 is related to magnetic flux passing through the test coil 12.
The diameter of the test coil 12 is smaller than the diameter of the magnetic excitation coil 13, and the test coil 12 is disposed inside the magnetic excitation coil 13.
In use, the magnetic excitation coil 13 is energized to form a magnetic field in the magnetic excitation coil 13. When the test coil 12 induces a magnetic field, an induced voltage is generated. The prestressed tendon 4 to be tested passes through the through hole 10, under the action of external load, the internal stress of the prestressed tendon 4 to be tested can be changed, the magnetic conductivity can be changed, at the moment, the magnetic flux in the test coil 12 is changed by the prestressed tendon 4 to be tested, and the induction voltage generated by the test coil 12 can be changed accordingly. Therefore, the relation between the tension of the prestressed tendon 4 to be measured and the voltage of the magnetic flux sensor 1 can be established, and the tension value of the prestressed tendon 4 is indirectly reflected through the voltage value of the magnetic flux sensor 1.
The magnetic flux sensor 1 is less interfered by external environmental factors, can reflect the whole stress level of the prestressed tendon, and can reflect the real stress state of the prestressed tendon. The testing device is not influenced by the structural form and the section change of the concrete beam, and is suitable for the tension test of the straight-line prestressed tendon of the bridge with any span. The testing device is convenient to install on site, simple to operate, high in testing precision, convenient to acquire data and high in working efficiency.
In one embodiment, a centering rigid support 14 is disposed in the through hole 10, and a through hole is disposed at a central position of the centering rigid support 14, and the through hole is used for placing the tendon 4 to be tested. The centering rigid support 14 can position the tendon 4 to be measured at the center of the through hole 10, so as to avoid the influence of the placement position or the placement angle of the tendon 4 to be measured on the measurement accuracy.
In one embodiment, the centering rigid support 14 is arranged along the axial direction of the through hole 10, and forms a rigid support for the tendon 4 to be tested in the whole through hole 10. Or may be a support member having a certain width and uniformly distributed in the through-hole 10.
According to one embodiment of the invention, the difference between the diameter of the through hole 10 and the diameter of the prestressed tendon 4 to be tested is 2-6cm, so that the contact between the inner side wall of the shell 11 and the prestressed tendon 4 can be avoided, interference factors are reduced, and the test result is more accurate.
Meanwhile, the embodiment of the second aspect of the present invention provides a method for testing a tensile force of a prestressed tendon of a concrete beam, and referring to fig. 3 to 14, the testing method is implemented by using the testing apparatus provided in the embodiment of the first aspect of the present invention, and includes the following steps:
s1, a cavity is preset at the bottom of a span center position of a beam body, the cavity corresponds to a prestressed pipeline of a prestressed tendon to be tested, and a magnetic flux sensor is placed in the cavity.
It is understood that the inside of the girder 5 is provided with the prestressed pipe 51, and the prestressed pipe 51 is arranged in a straight line at the lower edge of the midspan position of the girder 5. A cavity 50 is preset at the bottom of the midspan position of the beam body 5, and the cavity 50 is arranged corresponding to a prestressed pipeline 51 of the prestressed tendon 4 to be tested. The magnetic flux sensor 1 is placed in the cavity 50, and the prestressed tendon 4 to be tested passes through the prestressed pipe 51 and the through hole 10 of the magnetic flux sensor 1 in a linear state.
It can be known from the above that the testing method requires that the tendon 4 to be tested is in a linear state, so the testing method can also be extended to the case that the tendon is outside the beam body. The prestressed tendon is in a tense state outside the beam body, and the tension of the prestressed tendon can be indirectly measured through the magnetic flux sensor 1.
S2, the prestressed tendons to be tested penetrate through the prestressed pipeline and the magnetic flux sensor, and the prestressed tendons to be tested are tensioned and the tension of the prestressed tendons to be tested is read.
It can be understood that when the magnetic flux sensor 1 is placed in the cavity 50, the tendon 4 to be tested passes through the prestressed pipe 51 and the through hole 10 of the magnetic flux sensor 1 in a straight line. And after the prestressed tendon 4 to be tested is tensioned and anchored, the prestressed tendon 4 to be tested is in an elastic tension state in the beam body 5.
And S3, grouting into the prestressed pipeline, and sealing the cavity.
It can be understood that after the tendon 4 to be tested is tensioned and anchored, grouting is performed in the prestressed pipe 51, and after the grouting material is solidified and reaches the designed strength, the tendon 4 to be tested can be anchored in the prestressed pipe 51.
The cavity 50 is sealed, so that the interference of the external environment to the magnetic flux sensor 1 can be reduced, and the magnetic flux sensor 1 is prevented from being damaged.
And S4, carrying out static load bending test on the beam body.
It can be understood that when the beam body 5 is subjected to the static bending test, the beam body 5 is placed on a test bed, and the static bending test is completed by multi-stage loading.
The method for testing the tension of the prestressed tendon of the concrete beam provided by the embodiment of the invention utilizes the following principle:
the prestressed tendons are made of magnetic materials, and under the action of external load, internal stress can be changed, and magnetic conductivity can be changed accordingly. The magnetic conductivity change of the prestressed tendon is detected by the magnetic flux sensor to reflect the internal stress change, so that the tension of the prestressed tendon is indirectly measured.
It should be noted that, before the magnetic flux sensor 1 detects the change of the magnetic permeability of the tendon, a relationship between the tension of the tendon and the voltage of the magnetic flux sensor needs to be established, and when the device is used, the tension of the tendon 4 to be detected is indirectly read according to the voltage value measured by the magnetic flux sensor 1.
According to an embodiment of the invention, before placing the magnetic flux sensor in the cavity, further comprises:
s11, calibrating the relation between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
It can be understood that the relationship between the calibrated tendon tension and the magnetic flux sensor voltage can be manufactured in advance before the beam body 5 is manufactured, and a complete data corresponding relationship is formed by collecting and sorting the test data of the calibrated test beam 6.
In one embodiment, the corresponding relationship between the tension of the tendon and the voltage of the magnetic flux sensor can be made into an operation manual or an instruction manual and sent to an operator.
According to the method for testing the tension of the prestressed tendon of the concrete beam, provided by the embodiment of the invention, the relationship between the tension and the voltage of the magnetic flux sensor is calibrated through the prestressed tendon outside the prestressed tendon 4 to be tested, wherein the prestressed tendon is the prestressed tendon 40 to be calibrated.
In the production process, the physical and mechanical properties of the prestressed tendon are closely related to raw materials, processing technology and the like. In order to avoid the overlarge material performance difference between the tendon 40 to be calibrated and the tendon 4 to be measured, the tendon 40 to be calibrated needs to be screened, so that interference factors are reduced, and the reliability of the measurement result is improved.
According to an embodiment of the present invention, the calibrating the relationship between the tendon tension and the magnetic flux sensor voltage specifically includes:
and S111, selecting the prestressed tendons with the same batch, quantity, cross section, elastic modulus and tensile strength standard value as those of the prestressed tendons to be detected, and calibrating the relation between the tension of the prestressed tendons and the voltage of the magnetic flux sensor.
It can be understood that the material performance of the prestressed tendon with the same batch, the same quantity, the same cross section, the same elastic modulus and the same standard value of the tensile strength is basically the same as the material performance of the prestressed tendon 4 to be measured, and the calibration result has reliability.
According to the method for testing the tension of the concrete beam prestressed tendon provided by the embodiment of the invention, the prestressed tendon 40 to be calibrated reflects the real stress state of the prestressed tendon 4 to be tested by simulating the working condition of the prestressed tendon 4 to be tested.
According to an embodiment of the present invention, the calibrating the relationship between the tendon tension and the magnetic flux sensor voltage specifically includes:
and S1121, stretching in 8-10 stages within the range of 0.8 times of the standard tensile strength value of the prestressed tendon, and recording the stretching force value and the voltage value of the magnetic flux sensor at each stage.
S1123, calibrating the relation between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
According to the stipulations in anchorage device, clamp and connector for prestressed tendon (GB/T14370-2015), the maximum tensile stress value of the prestressed tendon in static load test is 0.80f ptk ，f ptk The standard value of the tensile strength of the prestressed tendon is indicated.
Tensioning is carried out within the range of 0.8 times of the standard tensile strength value of the prestressed tendon, the normal use range of the prestressed tendon is basically covered, the working condition of the prestressed tendon 4 to be tested can be simulated, and the real stress state of the prestressed tendon 4 to be tested is further reflected.
When the prestressed reinforcing steel is tensioned in a grading manner, if the test data are single or less, accidental errors are easy to occur, so that the relationship error between the calibrated prestressed reinforcing steel tension and the voltage of the magnetic flux sensor is large, and the real stress state of the prestressed reinforcing steel 4 to be tested is difficult to reflect. Thus, errors can be reduced by multiple cycle testing.
According to an embodiment of the invention, the stretching is performed in 8-10 stages within 0.8 times of the standard value of the tensile strength of the prestressed tendon, each stage records the value of the stretching force and the voltage value of the magnetic flux sensor, and then the method further comprises the following steps:
and S1122, performing at least 2 cycles in the step tensioning process, averaging the recorded values of each stage of different cycles, and fitting the relationship between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
It can be understood that the condition of accidental errors is reduced after the test data are averaged for a plurality of times, so that the relation between the tension of the prestressed tendon and the voltage of the magnetic flux sensor can reflect the real stress state of the prestressed tendon 4 to be measured.
The method for testing the tension of the prestressed tendons of the concrete beam, provided by the embodiment of the invention, has the advantages that a plurality of prestressed tendons are arranged in the beam body 5 and are symmetrically distributed in the beam body 5, and the beam body 5 is symmetrically tensioned according to a design sequence during tensioning, so that the stress balance of the beam body 5 is ensured. After the prestressed tendon 4 to be tested is tensioned and anchored, other prestressed tendons need to be tensioned, so that the tension of the prestressed tendon 4 to be tested is loosened, and the loosened tension is the final effective tension.
According to an embodiment of the present invention, the penetrating the tendon to be tested into the prestressed pipe and the magnetic flux sensor, tensioning the tendon to be tested, and reading the tension of the tendon to be tested specifically includes:
s21, the prestressed tendons to be tested penetrate through the prestressed pipeline and the magnetic flux sensor.
S22, tensioning the prestressed tendons to be tested according to a design sequence, anchoring, and reading the initial effective tension of the prestressed tendons to be tested.
And S23, after all the prestressed tendons are tensioned and anchored, reading the final effective tension of the prestressed tendons to be tested.
It can be understood that after all the prestressed tendons are tensioned and anchored, the tension value of the prestressed tendon 4 to be tested is read again through the magnetic flux sensor 1, and the tension value at this time is the final effective tension. The initial effective tension of the prestressed tendon 4 to be tested is compared with the final effective tension, so that the relaxation amount of the prestressed tendon after gradual tensioning can be obtained, and the relationship between the initial effective tension and the final effective tension can also be established.
According to the actually measured tension of the prestressed reinforcement, the stress state of the prestressed concrete beam can be accurately calculated or evaluated.
According to the method for testing the tensile force of the prestressed reinforcing steel of the concrete beam, provided by the embodiment of the invention, when grouting is carried out in the prestressed pipeline 51, a grouting material is required to be prevented from entering the magnetic flux sensor 1, the influence on the test coil 12 and a circuit is avoided, interference factors are reduced, and the accuracy of measured data is ensured.
According to an embodiment of the present invention, the grouting into the prestressed pipe and sealing the cavity specifically include:
and S31, grouting into the prestressed pipeline and preventing grouting materials from entering the magnetic flux sensor.
And S32, pouring concrete with the same strength as the beam body in the cavity.
It can be understood that the grouting pipe 52 is inserted before grouting, the position where the cavity 50 is connected with the prestressed pipe 51 is blocked, and grouting is performed from the cavity 50 to the prestressed pipe 51 at two sides, so as to ensure that no grouting material exists in the cavity 50.
Meanwhile, the cavity 50 is positioned at the bottom of the span-middle position of the beam body 5, grouting is performed from the cavity 50 to the prestressed pipelines 51 on two sides, and grouting materials flow from low to high, so that bubbles are reduced, and compactness is improved.
Concrete with the same strength as the beam body 5 is poured in the cavity 50, and the expansion and contraction effect and the dry shrinkage effect of the concrete are kept synchronous with the beam body 5.
According to the method for testing the tension of the prestressed tendons of the concrete beam, provided by the embodiment of the invention, the following two tests are carried out.
In test one:
the method is characterized in that the tensile force of a prestressed tendon is tested under the action of a tension stage and a static test load aiming at a prestressed concrete beam with a 24m span.
The prestressed tendon of the concrete beam adopts standard steel stranded wires with the standard tensile strength value of 1860Mpa and the nominal diameter of 15.2mm, and the prestressed tendons of the web plate and the bottom plate are formed by weaving 7 steel stranded wires and are designed as a bonded prestressed tendon in the body.
In order to facilitate installation of the magnetic flux sensor, the prestressed tendons numbered as N2 (sample-1) and N3 (sample-2) in the bottom plate bundle are selected for testing, and a schematic diagram of a test structure is shown in fig. 4.
In the concrete beam pouring stage, a cavity 50 is preset at the position where the N2 and N3 bundles of prestressed tendons on the lower edge of the mid-span bottom plate pass through, and the cavity 50 is used for installing the magnetic flux sensor 1. The length, width and height dimensions of the cavity 50 are 240mm, 120mm and 170mm respectively. The magnetic flux sensor 1 used for the test had a length, an outer diameter, and an inner diameter of 200mm, 100mm, and 56mm, respectively.
A calibration test beam 6 made of concrete materials is prefabricated in a construction site by referring to fig. 3, 7 steel strands consistent with a beam body 5 are inserted into the calibration test beam 6, the magnetic flux sensor 1 is installed in the middle of the calibration test beam 6, a jack at one end of the calibration test beam 6 is used for single-end tensioning, the maximum tensioning force is 1458kN, and tensioning is carried out in 10 grades. Each stage records the tension force value and the voltage value of the magnetic flux sensor 1 for 2 cycles. And (3) taking the average value of the recorded values of each stage of 2 cycles to perform tension and voltage relation curve fitting, and inputting fitting parameters into the tester 2 to be used as the reference of the tension test of the prestressed tendon of the 24m concrete beam.
Before the prestressed tendon 4 to be measured is arranged in the prestressed pipeline 51 of the concrete beam in a penetrating manner, the calibrated magnetic flux sensor 1 is placed in the cavity 50 at the lower edge of the beam body 5, and then the prestressed tendon 4 to be measured penetrates through the through hole 10 of the magnetic flux sensor 1. And after the N2 and N3 bundles are respectively tensioned and anchored, performing tension test to obtain the initial effective tension of the intermediate section of the prestressed tendon.
Because the prestressed tendons are tensioned in batches, the lower edge of the beam body 5 is gradually compressed, and the tension of the prestressed tendons tensioned firstly is lost. And after all the prestressed tendons are tensioned, performing a tension test on the tendon again to obtain the final effective tension of the prestressed tendon across the middle section.
After all the prestressed tendons are tensioned, grouting is carried out on the prestressed pipeline 51 to form the prestressed tendons bonded in the body, and grouting materials cannot be injected into the magnetic flux sensor 1. The opening of the cavity 50 is sealed by concrete with the same strength as the beam body 5, and the magnetic flux sensor 1 is not damaged.
After the mortar material in the prestressed pipeline 51 reaches the designed strength, a static load bending test is carried out on the 24m concrete beam on a test bench, the test adopts a longitudinal 5-point loading mode on the top surface of the beam body, the single-point maximum load is 1955kN, and the 24-level concrete beam is divided into 24-level concrete beams and is loaded in a grading mode. During the test, tensile tests of two samples of N2 and N3 bundles were performed, and the test results are detailed in fig. 13.
In test two:
the tension of the prestressed reinforcement is tested under the action of a tension stage and a static test load aiming at a prestressed concrete beam with a span of 8 m.
The prestressed tendon of the concrete beam adopts a standard steel strand with a tensile strength standard value of 1860Mpa and a nominal diameter of 15.2mm, and the prestressed tendons of the web plate and the bottom plate are formed by weaving 6 steel strands and are designed as a bonded prestressed tendon in the body.
In order to conveniently install the magnetic flux sensor, the prestressed tendon with the number of the bottom plate bundle N1 (sample-3) is selected for testing, and the schematic diagram of the testing structure is shown in FIG. 4.
In the concrete beam pouring stage, a cavity 50 is preset at the passing position of the N1-beam prestressed tendons at the lower edge of the mid-span bottom plate, and the cavity 50 is used for installing a magnetic flux sensor. The length, width and height of the cavity are 240mm, 120mm and 170mm respectively. The length, outer diameter and inner diameter of the magnetic flux sensor used for the test are respectively 200mm, 100mm and 56mm.
A calibration test beam 6 made of concrete materials is prefabricated on a construction site by referring to fig. 3, 6 steel strands consistent with a beam body 5 are inserted into the calibration test beam 6, the magnetic flux sensor 1 is installed in the middle of the calibration test beam 6, a jack at one end of the calibration test beam 6 is used for single-end tensioning, the maximum tensioning force is 1250kN, and tensioning is carried out in 10 grades. Each stage records the tension force value and the voltage value of the magnetic flux sensor 1 for 2 cycles. And taking the average value of the recorded values of each stage of 2 cycles to perform curve fitting on the relation between the tension and the voltage, and inputting fitting parameters into the tester 2 to be used as the reference of the tension test of the prestressed reinforcing steel of the 8m concrete beam.
Before the prestressed tendon to be measured is arranged in the prestressed pipeline 51 of the concrete beam in a penetrating manner, the calibrated magnetic flux sensor 1 is placed in the cavity 50 of the lower edge of the beam body 5, and then the prestressed tendon to be measured penetrates through the through hole 10 of the magnetic flux sensor 1. And after the N1 bundles of tension anchors are finished, performing a tension test to obtain the initial effective tension of the intermediate section of the prestressed tendon.
Because the prestressed tendons are tensioned in batches, the lower edge of the beam body 5 is gradually compressed, and the tension of the prestressed tendons tensioned before is lost. And after all the prestressed tendons are tensioned, performing a tension test on the prestressed tendon bundle again to obtain the final effective tension of the prestressed tendon across the middle section.
After all the prestressed tendons are tensioned, grouting is carried out on the prestressed pipeline to form a bonded prestressed tendon in the body, and grouting materials cannot be injected into the magnetic flux sensor 1. The opening of the cavity 50 is sealed by concrete with the same strength as the beam body 5, and the magnetic flux sensor 1 is not damaged.
After the mortar material in the prestressed pipeline 51 reaches the design strength, a static load bending test is carried out on the 8m concrete beam on a test bench, the test adopts a longitudinal 2-point loading mode on the top surface of the beam body, the single-point maximum load is 449kN, the load is divided into 25 grades, and the load is graded. During the test, a tensile test of one sample of N1 bundles was performed, and the test results are detailed in fig. 14.
In summary, the embodiment of the invention provides a device and a method for testing the tension of a prestressed tendon of a concrete beam. The prestressed tendons are made of magnetic materials, and under the action of external load, internal stress can be changed, and magnetic conductivity can be changed accordingly. The testing device comprises a magnetic flux sensor, and the internal stress change is reflected through the magnetic conductivity change of the prestressed tendon, so that the tension of the prestressed tendon is indirectly measured. The testing device is less interfered by external environmental factors, can reflect the overall stress level of the prestressed tendon, and can reflect the real stress state of the prestressed tendon. The testing device is not influenced by the structural form and the section change of the concrete beam, and is suitable for the tension test of the straight-line prestressed tendon of the bridge with any span. The testing device is convenient to install on site, simple to operate, high in testing precision, convenient to acquire data and high in working efficiency.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the scope of the present invention, which is intended to cover any modifications, equivalents, improvements, etc. within the spirit and scope of the present invention.
Claims (4)
1. A concrete beam prestressed tendon tensile force test method is characterized by comprising the following steps:
manufacturing a calibration test beam, reflecting the real stress state of the prestressed tendon to be tested by simulating the working condition of the prestressed tendon to be tested by the prestressed tendon to be calibrated, and calibrating the relation between the tension of the prestressed tendon and the voltage of a magnetic flux sensor;
a cavity is preset at the bottom of the midspan position of the beam body, the cavity corresponds to a prestressed pipeline of a prestressed tendon to be tested, and a magnetic flux sensor is placed in the cavity;
penetrating a prestressed tendon to be tested into the prestressed pipeline and the magnetic flux sensor, wherein the prestressed tendon to be tested is in a linear state;
tensioning the prestressed tendon to be tested according to a design sequence, anchoring, and reading the initial effective tension of the prestressed tendon to be tested;
after all the prestressed tendons are stretched and anchored, reading the final effective tension of the prestressed tendons to be tested;
grouting into the prestressed pipeline and preventing grouting materials from entering the magnetic flux sensor, and pouring concrete with the same strength as the beam body in the cavity;
and carrying out static load bending test on the beam body.
2. The concrete beam prestressed tendon tension test method according to claim 1, wherein the relationship between the calibrated prestressed tendon tension and the magnetic flux sensor voltage specifically comprises:
selecting the prestressed tendons with the same batch, the same quantity, the same cross section, the same elastic modulus and the same tensile strength standard value as the prestressed tendons to be detected, and calibrating the relation between the tension of the prestressed tendons and the voltage of the magnetic flux sensor.
3. The concrete beam prestressed tendon tension test method according to claim 1, wherein the calibration of the relationship between the prestressed tendon tension and the magnetic flux sensor voltage specifically includes:
stretching in 8-10 stages within the standard value range of 0.8 times of the tensile strength of the prestressed tendon, and recording the force value of each stage of stretching and the voltage value of the magnetic flux sensor;
and calibrating the relation between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
4. The method for testing the tensile force of the prestressed tendon of the concrete beam according to claim 3, wherein the prestressed tendon is tensioned in 8-10 stages within the range of 0.8 times of the standard value of the tensile strength of the prestressed tendon, the value of the tension force of each stage and the voltage value of the magnetic flux sensor are recorded, and then the method further comprises the following steps:
and (3) performing at least 2 cycles in the stage tensioning process, averaging the recorded values of each stage of different cycles, and fitting the relationship between the tension of the prestressed tendon and the voltage of the magnetic flux sensor.
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| DE19749907C1 (en) * | 1997-11-11 | 1999-10-14 | Suspa Spannbeton Gmbh | Method and device for determining tensile or compressive stresses in a ferromagnetic element, in particular a tendon, tensile or compressive element for the building industry |
| CN102426070B (en) * | 2011-12-31 | 2013-03-27 | 交通运输部公路科学研究所 | Device and method for testing along-path stress distribution state of prestressed steel beam |
| CN103048066A (en) * | 2012-12-17 | 2013-04-17 | 江苏省交通科学研究院股份有限公司 | Monitoring method for prestress state of side slope anchor cable |
| CN203490007U (en) * | 2013-10-25 | 2014-03-19 | 交通运输部公路科学研究所 | Accurate detecting device for external prestress steel beam stress |
| CN107290091B (en) * | 2017-06-22 | 2023-06-02 | 广西大学 | Tension force measurement system and method for prestressed steel strand |
| CN112683425A (en) * | 2021-01-21 | 2021-04-20 | 交通运输部公路科学研究所 | Method for detecting effective stress of longitudinal prestressed tendon in bridge body |
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