CN113252446B - Concrete beam prestressed tendon tension testing device and method - Google Patents

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

Concrete Beam Prestressed Tendon Tensile Testing Device and Method

technical field

The invention relates to the technical field of tension testing of prestressed tendons of concrete beams, in particular to a tension testing device and method for prestressed tendons of concrete beams.

Background technique

During the construction stage and static load test of prestressed concrete beams, sometimes it is necessary to measure the tension of prestressed tendons. The accuracy of the measurement data is directly related to the calculation and evaluation of the stress state of concrete beams. Therefore, effective and accurate prestressed tendons Testing is especially important. The longitudinal prestressed tendons of prestressed concrete beams are generally prestressed bundles made of standard steel strands. A single standard steel strand is twisted by 6 steel wires around a central steel wire, and the outer steel wires are made by Arranged in a spiral winding manner.

In related testing technologies, the method of pasting resistance strain gauges on the surface of steel wires, vibration frequency testing methods, anchoring end pressure sensor testing methods, fixed gauge elongation measuring methods, and fiber Bragg grating strain gauge methods are generally used. When the method of sticking the resistance strain gauge on the surface of the steel wire is adopted, the resistance strain gauge is bonded together with the steel wire by glue, and its waterproofness, insulation and durability are all poor. Resistance strain gauges are greatly affected by temperature and humidity, so they are not suitable for protection and cannot be used for a long time. Moreover, the strain value of the test is only the strain in the helical direction of a steel wire, not the strain in the straight line direction of the steel strand, nor the average strain of the steel strand bundle, so the test error is large and the measuring range is small. When the vibration frequency method is used to test, the vibration sensor is wound on the outside of the prestressed tendons, which is suitable for external prestressed tendons suspended in the air for a long time, but not suitable for internal prestressed tendons. For external prestressed tendons with short suspension, the vibration frequency is high and the test error is large. When the anchor end pressure sensor is used for testing, the through-type pressure sensor is installed between the anchor plate and the working anchor, and only the tension of the prestressed tendon at the anchor hole can be tested, and the tension at the mid-span position of the prestressed tendon cannot be obtained. When using the method of measuring elongation with fixed gauge distance, this method is only applicable to external prestressed tendons. Select a fixed length to mark the straight section of external prestressed tendons, and use a ruler, tape measure or extensometer to measure the elongation of the fixed length. Then convert to pulling force. When the fiber grating strain gauge method is used, the side wires of a single steel strand are first broken up, the center wire is taken out, an inclined groove is set on the center wire, the fiber grating is pasted in the inclined groove with an adhesive, and then the edge The wire and the central wire are twisted and shaped, and the end is encapsulated for protection. Steel strands with fiber grating sensors need to be specially customized by manufacturers, which is expensive and takes a long time. Therefore, when measuring the tensile force of prestressed tendons, there are problems such as low test accuracy, large error, high cost, and long cycle. pull.

Contents of the invention

The present invention aims to solve the problems existing in the prior art. For this reason, the present invention proposes a kind of concrete beam prestressed tendon tension testing device. The prestressed tendon is a magnetic material. Under the external load, the internal stress will change, and the magnetic permeability will also change accordingly. The test device includes a magnetic flux sensor, which reflects the change of the internal stress through the change of the magnetic permeability of the prestressed tendon, and then indirectly measures the tensile force of the prestressed tendon. The testing device has high precision, is less disturbed by external environmental factors, can reflect the overall stress level of the prestressed tendon, and can reflect the real tensile force of the prestressed tendon.

At the same time, the invention also provides a method for testing the tension of the prestressed tendon of the concrete beam.

The concrete beam prestressed tendon tension test device provided according to the embodiment of the first aspect of the present invention includes:

The magnetic flux sensor includes a cylindrical housing with a through hole in the center and a test coil and a magnetic excitation coil arranged between the inner wall and the outer wall of the housing, the test coil is arranged around the inner wall of the housing, The magnetic excitation coil is wound around the outside of the test coil;

The tester is electrically connected to the test coil and the magnetic excitation coil through a data line.

According to an embodiment of the present invention, a centering rigid support is provided in the through hole, and a perforation is provided at the center of the centering rigid support, and the perforation is used for placing prestressing tendons.

According to an embodiment of the present invention, the difference between the diameter of the through hole and the diameter of the prestressing tendon is 2-6 cm.

The concrete beam prestressed tendon tension test method provided according to the second aspect embodiment of the present invention comprises the following steps:

A cavity is preset at the bottom of the mid-span position of the beam body, the cavity corresponds to the prestressed pipe of the prestressed tendon to be measured, and the magnetic flux sensor is placed in the cavity;

passing the prestressed tendons to be measured in the prestressed pipeline and the magnetic flux sensor, stretching the prestressed tendons to be tested and reading the tension of the prestressed tendons to be measured;

injecting grout into the prestressed pipe, and sealing the cavity;

A static load bending test was performed on the beam body.

According to an embodiment of the present invention, placing the magnetic flux sensor in the cavity also includes:

Calibrate the relationship between prestressing tendon tension and flux sensor voltage.

According to an embodiment of the present invention, the relationship between the calibration prestressed tendon tension and the magnetic flux sensor voltage specifically includes:

Select prestressed tendons with the same batch, same quantity, same cross section, same elastic modulus, and same tensile strength standard value as the prestressed tendons to be tested, and calibrate the relationship between the tension of prestressed tendons and the voltage of the magnetic flux sensor.

According to an embodiment of the present invention, the relationship between the calibration prestressed tendon tension and the magnetic flux sensor voltage specifically includes:

Within the range of 0.8 times the standard value of the tensile strength of the prestressed tendon, stretch it in 8-10 levels, and record the tension value and the voltage value of the magnetic flux sensor at each level;

Calibrate the relationship between prestressing tendon tension and flux sensor voltage.

According to an embodiment of the present invention, within the range of 0.8 times the standard value of the tensile strength of the prestressed tendon, the tension is divided into 8-10 levels, and the force value of the tension and the voltage value of the magnetic flux sensor are recorded at each level, and then Also includes:

The graded stretching process was carried out at least 2 cycles, and the recorded values of each stage in different cycles were averaged, and then the relationship between the tension of the prestressed tendon and the voltage of the magnetic flux sensor was fitted.

According to an embodiment of the present invention, the prestressed tendons to be tested are penetrated in the prestressed pipeline and the magnetic flux sensor, the prestressed tendons to be tested are stretched and the prestressed tendons to be tested are read pull, including:

passing the prestressed tendon to be measured in the prestressed pipeline and the magnetic flux sensor;

Stretching and anchoring the prestressed tendons to be measured according to the design sequence, and reading the initial effective tension of the prestressed tendons to be measured;

After tensioning and anchoring all the prestressed tendons, read the final effective tensile force 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 includes:

grouting into the prestressed pipeline and preventing the grouting material from entering the magnetic flux sensor;

Concrete with the same strength as the beam body is poured in the cavity.

The above-mentioned one or more technical solutions in the present invention have at least one of the following technical effects:

The prestressed tendon is a magnetic material. Under the external load, the internal stress will change, and the magnetic permeability will also change accordingly. The tension test device for prestressed tendons of concrete beams includes a magnetic flux sensor, which reflects the change of internal stress through the change of magnetic permeability of prestressed tendons, and then indirectly measures the tensile force of prestressed tendons. The tensile test device for prestressed tendons of concrete beams is less disturbed by external environmental factors, can reflect the overall stress level of prestressed tendons, and can reflect the real tensile force of prestressed tendons. The test device is not affected by the structural form and section change of the concrete beam, and is suitable for the tensile test of the prestressed tendon in the straight section of the bridge with any span. The test device is easy to install on site, simple to operate, high in test accuracy, convenient in data collection, and high in work efficiency.

Description of drawings

1 is a cross-sectional view of a magnetic flux sensor provided by an embodiment of the present invention;

Fig. 2 is the left side view of the magnetic flux sensor provided by the embodiment of the present invention;

Fig. 3 is a schematic structural diagram of a calibration test beam provided by an embodiment of the present invention;

Fig. 4 is the schematic structural diagram of the internal prestressed concrete beam provided by the embodiment of the present invention;

5 is a schematic structural diagram of an externally prestressed concrete beam provided by an embodiment of the present invention;

Fig. 6 is the flowchart one of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 7 is the flow chart two of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 8 is the flowchart three of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 9 is a flow chart four of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 10 is the flow chart five of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 11 is the flow chart six of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 12 is the flow chart seven of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 13 is the measured data figure one of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention;

Fig. 14 is the actual measured data Fig. 2 of the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention.

Reference signs:

1. Magnetic flux sensor; 10. Through hole; 11. Shell; 12. Test coil; 13. Magnetic excitation coil; 14. Centering rigid support; 2. Tester; 3. Data line; 4. Prestressed rib ; 40, prestressed tendon to be calibrated; 5, beam body; 50, cavity; 51, prestressed pipe; 52, grouting pipe; 6, calibration test beam.

Detailed ways

In order to make the purpose of the invention, technical solutions and advantages clearer, the technical solutions in the invention will be clearly described below in conjunction with the accompanying drawings in the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and Not all examples. Based on the embodiments of the invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the invention.

In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right" , "vertical", "horizontal", "top", "bottom", "inner", "outer" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing this The embodiments and simplified descriptions of the invention do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be construed as limiting the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and should not be construed as indicating or implying relative importance.

In the description of the embodiments of the present invention, it should be noted that unless otherwise specified and limited, the terms "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection, Or integrated connection; it can be mechanical connection or electrical connection; it can be direct connection or indirect connection through an intermediary. Those skilled in the art can understand the specific meanings of the above terms in the embodiments of the present invention according to specific situations.

In the embodiments of the present invention, unless otherwise specified and limited, the first feature may be in direct contact with the first feature or the first feature and the second feature may pass through the middle of the second feature. Media indirect contact. Moreover, "above", "above" and "above" the first feature on the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. "Below", "beneath" and "beneath" the first feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is less horizontally than the second feature.

In the description of this specification, descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific examples", or "some examples" mean that specific features described in connection with the embodiment or example , structure, material or feature, included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the described specific features, structures, materials or characteristics may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine or combine different embodiments or examples and features of different embodiments or examples described in this specification without conflicting with each other.

In related technologies, when measuring the tensile force of prestressed tendons, there are problems such as low measurement accuracy, large error, high cost, and long cycle. real stress state.

The concrete beam prestressed tendon tension testing device provided according to the embodiment of the first aspect of the present invention, as shown in FIGS. 1 to 5 , includes a magnetic flux sensor 1 and a tester 2 .

The prestressed tendon is a magnetic material. Under the external load, the internal stress will change, and the magnetic permeability will also change accordingly.

The prestressed tendon tension test device for concrete beams, hereinafter referred to as the test device, includes a magnetic flux sensor 1. The magnetic flux sensor 1 reflects the change of internal stress by detecting the change of the magnetic permeability of the prestressed tendon, and then indirectly measures the tensile force of the prestressed tendon.

According to an embodiment of the present invention, the magnetic flux sensor 1 includes a cylindrical housing 11 with a through hole 10 in the center, a test coil 12 and a magnetic excitation coil 13 .

The casing 11 includes an inner wall and an outer wall surrounding the through hole 10 , and the test coil 12 and the magnetic excitation coil 13 are disposed between the inner wall and the outer wall. The test coil 12 is wound around the inner wall of the casing 11 , and the magnetic excitation coil 13 is wound around the outside 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 to apply a voltage to the magnetic excitation coil 13, so that the magnetic excitation coil 13 generates a magnetic field, and simultaneously receives the voltage value on the test coil 12, The voltage value across the test coil 12 is related to the magnetic flux through the test coil 12 .

The diameter of the test coil 12 is smaller than that of the magnetic excitation coil 13 , and the test coil 12 is arranged in the magnetic excitation coil 13 .

When 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 senses 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 an external load, the internal stress of the prestressed tendon 4 to be tested will change, and the magnetic permeability will also change. At this time, the prestressed tendon 4 to be tested changes the test coil The magnetic flux in the test coil 12 and the induced voltage generated by the test coil 12 will also change accordingly. Therefore, the relationship between the tensile force 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 can be indirectly reflected by the voltage value of the magnetic flux sensor 1 .

The magnetic flux sensor 1 is less disturbed by external environmental factors, can reflect the overall stress level of the prestressed tendons, and can reflect the real stress state of the prestressed tendons. The test device is not affected by the structural form and section change of the concrete beam, and is suitable for the tensile test of the prestressed tendon in the straight section of the bridge with any span. The test device is easy to install on site, simple to operate, high in test accuracy, convenient in data collection, and high in work efficiency.

In one embodiment, a centering rigid support 14 is provided in the through hole 10, and a perforation is provided at the center of the centering rigid support 14, and the perforation is used for placing the prestressed tendons 4 to be tested. The centering rigid support 14 can locate the prestressed tendon 4 to be tested at the center of the through hole 10, so as to prevent the placement position or placement angle of the prestressed tendon 4 to be tested from affecting the measurement accuracy.

In one embodiment, the centering rigid support 14 is provided along the axial direction of the through hole 10 to form a rigid support for the prestressed tendon 4 to be tested in the entire through hole 10 . It can also be a support with a certain width, evenly distributed in the through hole 10 .

According to an embodiment of the present invention, the difference between the diameter of the through hole 10 and the diameter of the prestressed tendon 4 to be measured is between 2-6 cm, which can avoid the contact between the inner side wall of the housing 11 and the prestressed tendon 4, and reduce interference factors , to make the test results more accurate.

At the same time, the embodiment of the second aspect of the present invention provides a method for testing the tensile force of prestressed tendons of concrete beams, see Figure 3 to Figure 14, the test method is realized by using the testing device provided by the embodiment of the first aspect of the present invention, including the following step:

S1. A cavity is preset at the bottom of the mid-span of the beam body, the cavity corresponds to the prestressed pipe of the prestressed tendon to be measured, and the magnetic flux sensor is placed in the cavity.

It can be understood that a prestressed pipe 51 is arranged inside the beam body 5 , and the prestressed pipe 51 is arranged in a straight line at the lower edge of the mid-span position of the beam body 5 . A cavity 50 is preset at the bottom of the mid-span position of the beam body 5, and the cavity 50 is set corresponding to the prestressing pipe 51 of the prestressing tendon 4 to be tested. The magnetic flux sensor 1 is placed in the cavity 50 , and the prestressed tendons 4 to be tested pass through the prestressed pipe 51 and the through hole 10 of the magnetic flux sensor 1 in a straight line.

It can be seen from the above that the test method requires the condition that the prestressed tendon 4 to be tested is in a straight line state, so this test method can also be extended to the situation where the prestressed tendon is outside the beam. The prestressed tendons are in a tensioned state outside the beam, and the tension of the prestressed tendons can be indirectly measured through the magnetic flux sensor 1 .

S2. Thread the prestressed tendons to be tested in the prestressed pipe and the magnetic flux sensor, stretch the prestressed tendons to be tested, and read the tension of the prestressed tendons to be tested.

It can be understood that when the magnetic flux sensor 1 is placed in the cavity 50 , 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 straight line. After the prestressed tendons 4 to be tested are stretched and anchored, the prestressed tendons 4 to be tested are in an elastic tension state in the beam body 5 .

S3. Injecting grout into the prestressed pipe, and sealing the cavity.

It can be understood that after the prestressed tendons 4 to be tested are tensioned and anchored, grouting is injected into the prestressed pipeline 51, and after the grouting material solidifies and reaches the design strength, the prestressed tendons 4 to be tested can be anchored in the prestressed pipeline 51 Inside.

The sealed cavity 50 can reduce the interference of the external environment on the magnetic flux sensor 1 and prevent the magnetic flux sensor 1 from being damaged.

S4. Perform a static load bending test on the beam body.

It can be understood that when the static load bending test is performed on the beam body 5, the beam body 5 is placed on the test stand and loaded in multiple stages to complete the static load bending test.

The concrete beam prestressed tendon tension testing method that the embodiment of the present invention provides, the principle of utilization is:

The prestressed tendon is a magnetic material. Under the external load, the internal stress will change, and the magnetic permeability will also change accordingly. The change of the magnetic permeability of the prestressed tendon is detected by the magnetic flux sensor to reflect the change of the internal stress, and then the tensile force of the prestressed tendon is indirectly measured.

It should be noted that before the magnetic flux sensor 1 detects the change in the magnetic permeability of the prestressed tendons, the relationship between the tensile force of the prestressed tendons and the voltage of the magnetic flux sensor needs to be established, and the voltage value measured by the magnetic flux sensor 1 is used to read indirectly. Take the tensile force of the prestressed tendon 4 to be tested.

According to an embodiment of the present invention, before placing the magnetic flux sensor in the cavity, the step further includes:

S11. Calibrate the relationship between the tensile force of the prestressed tendon and the voltage of the magnetic flux sensor.

It can be understood that, to calibrate the relationship between the tensile force of the prestressed tendon and the voltage of the magnetic flux sensor, the calibration test beam 6 can be produced in advance before the beam body 5 is produced, and the test data of the calibration test beam 6 can be collected and organized to form a complete data correspondence.

In one embodiment, the corresponding relationship between the tensile force of the prestressed tendon and the voltage of the magnetic flux sensor can be made into an operation manual or a user guide and sent to the operator.

The concrete beam prestressed tendon tension test method provided by the embodiment of the present invention uses the prestressed tendon other than the prestressed tendon 4 to calibrate the relationship between the tension and the voltage of the magnetic flux sensor, and the prestressed tendon is the prestressed tendon to be calibrated 40.

In the production process, the physical and mechanical properties of prestressed tendons are closely related to raw materials and processing techniques. In order to avoid excessive material performance differences between the prestressed tendons 40 to be calibrated and the prestressed tendons 4 to be tested, it is necessary to screen the prestressed tendons 40 to be calibrated to reduce interference factors and increase the reliability of measurement results.

According to an embodiment of the present invention, the relationship between the calibration prestressed tendon tension and the magnetic flux sensor voltage specifically includes:

S111. Select prestressed tendons with the same batch, same quantity, same cross section, same elastic modulus, and same tensile strength standard value as the prestressed tendons to be tested, and calibrate the relationship between prestressed tendon tensile force and magnetic flux sensor voltage.

It can be understood that the material properties of prestressed tendons with the same batch, same quantity, same cross section, same elastic modulus, and same tensile strength standard value are basically the same as those of prestressed tendons 4 to be tested, and the calibration results have reliability.

In the method for testing the tensile force of prestressed tendons in concrete beams provided by the embodiment of the present invention, the prestressed tendons 40 to be calibrated reflect the real stress state of the prestressed tendons 4 to be tested by simulating the working conditions of the prestressed tendons 4 to be tested.

According to an embodiment of the present invention, the relationship between the calibration prestressed tendon tension and the magnetic flux sensor voltage specifically includes:

S1121. Within the range of 0.8 times the standard value of the tensile strength of the prestressed tendons, perform tensioning in 8-10 levels, and record the tensioning force value and the voltage value of the magnetic flux sensor at each level.

S1123. Calibrate the relationship between the tensile force of the prestressed tendon and the voltage of the magnetic flux sensor.

According to the regulations in "Anchors, Fixtures and Connectors for Prestressed Tendons" (GB/T 14370-2015), the maximum tensile stress value of prestressed tendons static load test is 0.80f _ptk , f _ptk refers to the tensile strength of prestressed tendons Strength standard value.

Tensioning is carried out within the range of 0.8 times the standard value of the tensile strength of the prestressed tendon, which basically covers the normal use range of the prestressed tendon, can simulate the working conditions of the prestressed tendon 4 to be tested, and then reflect the performance of the prestressed tendon 4 to be tested real stress state.

In the method for testing the tensile force of prestressed tendons of concrete beams provided by the embodiments of the present invention, when the prestressed tendons are stretched in stages, if the test data is single or small, accidental errors are prone to occur, resulting in the calibration of the prestressed tendon tension and the voltage of the magnetic flux sensor. The error of the relationship between is relatively large, and it is difficult to reflect the real stress state of the prestressed tendon 4 to be tested. Therefore, the error can be reduced by multiple loop tests.

According to an embodiment of the present invention, within the range of 0.8 times the standard value of the tensile strength of the prestressed tendon, the tension is divided into 8-10 levels, and the force value of the tension and the voltage value of the magnetic flux sensor are recorded at each level, and then Also includes:

S1122. Perform at least 2 cycles of the staged tensioning process, average the recorded values of each stage in different cycles, and then fit the relationship between the tensile force of the prestressed tendons and the voltage of the magnetic flux sensor.

It can be understood that after averaging multiple test data, accidental errors are reduced, so that the relationship between the tensile force 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 tested.

In the concrete beam prestressed tendon tensile test method provided by the embodiment of the present invention, the beam body 5 is provided with multiple bundles of prestressed tendons, and the multi-bundles of prestressed tendons are symmetrically distributed in the beam body 5, and are stretched symmetrically according to the design sequence during tensioning. Ensure that the beam body 5 is balanced in force. After the 4 prestressed tendons to be tested are stretched and anchored, other prestressed tendons need to be stretched, which will cause the tension of the prestressed tendons 4 to be measured to relax, and the relaxed tension is the final effective tension.

According to an embodiment of the present invention, the prestressed tendons to be tested are penetrated in the prestressed pipeline and the magnetic flux sensor, the prestressed tendons to be tested are stretched and the prestressed tendons to be tested are read pull, including:

S21, passing the prestressed tendon to be tested in the prestressed pipeline and the magnetic flux sensor.

S22. Tensing and anchoring the prestressed tendons to be tested according to the design sequence, and reading the initial effective tension of the prestressed tendons to be tested.

S23. After stretching and anchoring all the prestressed tendons, read the final effective tension of the prestressed tendons to be tested.

It can be understood that after all the prestressed tendons are stretched and anchored, the tension value of the prestressed tendons 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. By comparing the initial effective tension of the prestressed tendon 4 to be tested with the final effective tension, the amount of relaxation of the prestressed tendon after gradual stretching can be obtained, and the relationship between the initial effective tension and the final effective tension can also be established.

According to the measured tensile force of prestressed tendons, the stress state of prestressed concrete beams can be accurately calculated or evaluated.

In the method for testing the tension of prestressed tendons of concrete beams provided by the embodiments of the present invention, when grouting into the prestressed pipe 51, it is necessary to prevent the grouting material from entering the magnetic flux sensor 1, to avoid affecting the test coil 12 and the circuit, and to reduce interference factors. , to ensure the accuracy of the measurement data.

According to an embodiment of the present invention, the grouting into the prestressed pipe and sealing the cavity specifically includes:

S31. Inject grout into the prestressed pipeline and prevent the grouting material from entering the magnetic flux sensor.

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, and the position where the cavity 50 is connected to the prestressed pipeline 51 is blocked, and the cavity 50 is injected into the prestressed pipeline 51 on both sides to ensure Cavity 50 is free of grouting material.

At the same time, the cavity 50 is located at the bottom of the mid-span of the beam body 5, and grouting is injected from the cavity 50 into the prestressed pipes 51 on both sides, and the grouting material flows from low to high, reducing air bubbles and increasing compactness.

Concrete with the same strength as the beam body 5 is poured in the cavity 50 , and the thermal expansion and contraction effect of the concrete and the dry shrinkage effect are kept in sync with the beam body 5 .

According to the concrete beam prestressed tendon tension test method provided by the embodiment of the present invention, the following two tests were carried out.

In test one:

For a prestressed concrete beam with a span of 24m, the tensile force of the prestressed tendon was tested during the tension stage and under the static test load.

The prestressed tendons of the concrete beam adopt standard steel strands with a standard value of tensile strength of 1860Mpa and a nominal diameter of 15.2mm. There are bonded prestressed tendons.

In order to facilitate the installation of the magnetic flux sensor, the prestressed tendons numbered N2 (sample-1) and N3 (sample-2) in the bottom plate bundle were selected for testing. The schematic diagram of the test structure is shown in Figure 4.

In the concrete beam pouring stage, a cavity 50 is preset at the position where the N2 and N3 bundles of prestressed tendons pass through the lower edge of the mid-span floor, and the cavity 50 is used for installing the magnetic flux sensor 1 . The length, width and height of the cavity 50 are 240mm, 120mm and 170mm respectively. The length, outer diameter, and inner diameter of the magnetic flux sensor 1 used in the test are 200 mm, 100 mm, and 56 mm, respectively.

Refer to Fig. 3 to prefabricate a calibration test beam 6 of concrete material at the construction site, penetrate 7 steel strands consistent with the beam body 5 in the calibration test beam 6, install the magnetic flux sensor 1 to the middle part of the calibration test beam 6, and use The jack at one end of the calibration test beam 6 is used for single-end tensioning with a maximum tension of 1458kN, which is divided into 10 levels. The tension value and the voltage value of the magnetic flux sensor 1 are recorded at each level, and a total of 2 cycles are performed. Take the average value of the recorded values of each level in 2 cycles to fit the tension and voltage relationship curve, and input the fitting parameters into the tester 2 as the benchmark for the tension test of the prestressed tendon of the 24m concrete beam.

Before the prestressed tendon 4 to be measured is pierced in the prestressed pipe 51 of the concrete beam, 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 is passed through Inside the through hole 10 of the magnetic flux sensor 1 . After the N2 and N3 bundles are tensioned and anchored separately, the tension test is carried out to obtain the initial effective tension of the mid-span section of the bundle of prestressed tendons.

Because the prestressed tendons are stretched in batches, the lower edge of the beam body 5 is gradually compressed, resulting in loss of the tensile force of the prestressed tendons that were stretched earlier. After the stretching of all prestressed tendons is completed, a tensile test of the bundle can be performed to obtain the final effective tensile force of the mid-span section of the prestressed tendons.

After all the prestressed tendons are stretched, the prestressed pipeline 51 is grouted to form bonded prestressed tendons in the body, and the magnetic flux sensor 1 must not inject grouting materials. The opening of the cavity 50 is sealed with concrete of the same strength as the beam body 5, and the magnetic flux sensor 1 should not be damaged.

After the grouting material in the prestressed pipe 51 reaches the design strength, the static load bending test is carried out on the 24m concrete beam on the test bench. There are 24 levels, graded loading. During the test, two samples of N2 and N3 bundles were tested for tensile force, and the test results are shown in Figure 13.

In test two:

For a prestressed concrete beam with a span of 8m, the tensile force of the prestressed tendons was tested during the tension stage and under the static test load.

The prestressed tendons of the concrete beam adopt standard steel strands with a standard value of tensile strength of 1860Mpa and a nominal diameter of 15.2mm. There are bonded prestressed tendons.

In order to facilitate the installation of the magnetic flux sensor, the prestressed tendon with the number N1 (sample-3) of the bottom plate bundle was selected for testing. The schematic diagram of the test structure is shown in Figure 4.

In the pouring stage of the concrete beam, a cavity 50 is preset at the passage position of the N1 bundle of prestressed tendons on the lower edge of the mid-span floor, 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 in the test are 200mm, 100mm, and 56mm, respectively.

Refer to Fig. 3 to prefabricate a calibration test beam 6 of concrete material at the construction site, penetrate 6 steel strands consistent with the beam body 5 in the calibration test beam 6, install the magnetic flux sensor 1 to the middle part of the calibration test beam 6, and use The jack at one end of the calibration test beam 6 is tensioned at one end, with a maximum tension of 1250kN, and the tension is divided into 10 levels. The tension value and the voltage value of the magnetic flux sensor 1 are recorded at each level, and a total of 2 cycles are performed. Take the average value of the recorded values of each level in 2 cycles to fit the tension and voltage relationship curve, and input the fitting parameters into the tester 2 as the benchmark for the tension test of the prestressed tendon of the 8m concrete beam.

Before the prestressed tendon to be measured is pierced in the prestressed pipe 51 of the concrete beam, 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 to be measured is passed through the magnetic flux sensor 1 through hole 10. After the tension and anchorage of bundle N1 is completed, the tensile test is carried out to obtain the initial effective tension of the mid-span section of the bundle of prestressed tendons.

Because the prestressed tendons are stretched in batches, the lower edge of the beam body 5 is gradually compressed, resulting in loss of the tensile force of the prestressed tendons that were stretched earlier. After the stretching of all the prestressed tendons is completed, the tensile test of the bundle of prestressed tendons can be carried out again, and the final effective tensile force of the mid-span section of the prestressed tendons can be obtained.

After all the prestressed tendons are stretched, the prestressed pipeline is grouted to form a bonded prestressed beam in the body, and no grouting material is injected into the magnetic flux sensor 1 . The opening of the cavity 50 is sealed with concrete of the same strength as the beam body 5, and the magnetic flux sensor 1 should not be damaged.

After the grouting material in the prestressed pipeline 51 reaches the design strength, the static load bending test is carried out on the 8m concrete beam on the test bench. The test adopts the longitudinal two-point loading method on the top surface of the beam body, and the maximum single point load is 449kN. It is level 25 and loaded in stages. During the test, a tensile test of a sample of the N1 bundle was carried out, and the test results are shown in Figure 14.

To sum up, the embodiments of the present invention provide a tensile test device and method for prestressed tendons of concrete beams. The prestressed tendon is a magnetic material. Under the external load, the internal stress will change, and the magnetic permeability will also change accordingly. The test device includes a magnetic flux sensor, which reflects the change of the internal stress through the change of the magnetic permeability of the prestressed tendon, and then indirectly measures the tensile force of the prestressed tendon. The test device is less disturbed by external environmental factors, can reflect the overall stress level of the prestressed tendons, and can reflect the real stress state of the prestressed tendons. The test device is not affected by the structural form and section change of the concrete beam, and is suitable for the tensile test of the prestressed tendon in the straight section of the bridge with any span. The test device is easy to install on site, simple to operate, high in test accuracy, convenient in data collection, and high in work efficiency.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

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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