CN109341923B - Detection structure and stress detection method for internal prestressed tendons - Google Patents
Detection structure and stress detection method for internal prestressed tendons Download PDFInfo
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Abstract
The invention discloses a detection structure and a stress detection method of an in-vivo prestressed tendon, and belongs to the field of civil engineering. The detection structure replaces a section of corrugated pipe of the internal prestressed tendons, and the corrugated pipe is sleeved on the internal prestressed tendons needing to detect stress and comprises two cuffs, a connecting pipe between the cuffs and positioning pipes at two ends. The positioning tube restrains the internal prestressed tendons in the middle of the prestressed duct. At least one side surface of each of the left hoop and the right hoop is exposed, and the left hoop and the right hoop are called passive testing surfaces. After the engineering structure is built, two active testing surfaces of the matched magnetic flux tester are closely attached to corresponding passive testing surfaces, and then the real-time stress in the in-vivo prestressed beam can be tested. The detection structure is simple, low in cost, the service life of the detection structure is the same as that of an engineering structure, detection cost can be reduced, and the detection structure is economical and practical.
Description
Technical Field
The invention relates to a detection structure and a stress detection method of an in-vivo prestressed tendon, belonging to the field of civil engineering.
Background
The prestressed tendons of the prestressed concrete structure are divided into an internal prestressed tendon and an external prestressed tendon, and the invention mainly aims at the former.
During construction, the prestressed pipe is buried and the member is prestressed before loading, so that the section tension area has pre-existing compressive stress. The prestress is generated by stretching the prestress beam in the high-strength body. The current internal prestressed beam is mainly a steel strand beam consisting of a plurality of steel strands. Due to structural characteristics, material characteristics, and the like, a prestressed concrete structure to which a prestress is applied may cause a prestress loss. The magnitude of the loss of prestress affects the established prestress and, of course, the operational performance of the structure. Therefore, how to determine the effective prestress or the permanent prestress, i.e. the stress of the prestressed tendons in the body, is an important matter in the design and use of the prestressed concrete structure.
The factors causing the loss of prestress are more, and it is difficult to accurately calculate. It is desirable that the stress of the tendon be directly detected when necessary. The prestressed tendons of the prestressed structure are positioned in the concrete structure, belong to hidden members, and are difficult to detect by adopting a conventional method.
In recent years, magnetic flux sensors have been developed to solve this problem well. This type of magnetic flux sensor is based on the principle of the magnetoelastic effect of ferromagnetic materials. When the ferromagnetic material is acted by external force, the internal mechanical stress or strain is generated, the magnetic conductivity is changed correspondingly, and the stress change is reflected by measuring the magnetic conductivity change. The pulse current transformer comprises an exciting coil and an induction coil, wherein when the exciting coil is electrified with pulse current, instantaneous current is generated in the induction coil due to the existence of an iron core assembly, and instantaneous voltage is obtained. The magnitude of the voltage generated by electromagnetic induction depends on the magnetic conductivity of the iron core material, the magnetic conductivity of the iron core material is related to the stress state of the iron core, and the stress detection of the internal prestressed beam is realized according to the relation between the induced voltage and the stress. The built-in temperature sensor of the sensor is used for measuring the temperature and correcting the temperature influence. However, the conventional magnetic flux sensors are cylindrical, and need to be sleeved on the prestressed tendons and embedded in the structure when the prestressed tendons are installed. The number of the prestressed tendons of the engineering structure is large, even if only representative prestressed tendons are measured, the number is large, and the total manufacturing cost of the sensor is high; in addition, in the life cycle of the structure, the characteristics of the sensor can be changed, so that the calibration and the maintenance are inconvenient to perform again, and the testing precision is influenced.
Disclosure of Invention
The invention aims to solve the defects and problems in the prior art and provides a structure and a method for detecting internal prestressed tendons. After the detection structure is adopted, the stress in each prestressed tendon of the structure can be detected according to the requirement in the use process of the structure. The detection is carried out by adopting a matched external magnetic flux detector. The detection structure is embedded into the engineering structure and mainly comprises two cuffs, the manufacturing cost is low, and even if the detection structure is adopted for all prestressed tendons of the engineering structure, the increased cost is little and can be almost ignored.
The invention provides a detection structure and a stress detection method of an internal prestressed tendon, wherein the detection structure replaces a section of corrugated pipe of the internal prestressed tendon, is sleeved on the internal prestressed tendon needing stress detection, and mainly comprises a left hoop, a right hoop, a section of connecting pipe for connecting the left hoop and the right hoop, a positioning pipe for connecting the left hoop and a left corrugated pipe, and a positioning pipe for connecting the right hoop and a right corrugated pipe, wherein all connected seams are sealed; the middle part of the positioning pipe is provided with a positioning hole which can restrict the internal prestressed tendons in the middle part of the prestressed duct; the distance between the left hoop and the right hoop is 200mm-400mm, and at least one side surface of each of the left hoop and the right hoop is exposed out of the same side of the engineering structure part, so that the left hoop and the right hoop are called as a passive test surface; the stress detection method of the internal prestressed tendon is characterized in that: a calibrated matched magnetic flux tester is adopted, and two active testing surfaces of the magnetic flux tester are respectively attached to corresponding passive testing surfaces; the magnetic flux tester, the internal prestressed beam and the two cuffs form a magnetic circuit, an exciting coil in the magnetic flux tester generates an exciting magnetic field during detection, and the induced voltage in the induction coil is tested to obtain the stress of the internal prestressed beam, mainly comprising the following implementation steps,
step 1: determining internal prestress tendons needing stress detection in an engineering structure, and designing and manufacturing a detection structure assembly and a magnetic flux tester with corresponding specifications according to the specifications of corrugated pipes adopted by the internal prestress tendons; the magnetic flux tester mainly comprises a left measuring arm, a right measuring arm and a handle for connecting the left measuring arm and the right measuring arm, wherein a left exciting coil is arranged in the left measuring arm, a right exciting coil is arranged in the right measuring arm, an induction coil is arranged in the handle, and the structure of the magnetic flux tester is bilaterally symmetrical; an ammeter for testing the induction voltage is arranged in the handle, and a corresponding display screen is arranged on the handle; a thermometer is also arranged in the handle;
step 2: for the detection structure of each specification, a plurality of prestressed concrete test pieces with unequal tension of the prestressed tendons are manufactured, and sleeve type magnetic flux sensors are installed on the prestressed tendons; calibrating a corresponding flux tester according to a stress test result of the sleeve type flux sensor, and establishing a relation between induced voltage in the flux tester and stress of the prestressed beams in the body;
and step 3: detecting the stress of the prestressed tendons in the body at different temperatures, and establishing the relation between the induced voltage containing temperature correction and the stress of the corresponding magnetic flux tester;
and 4, step 4: when an engineering structure is built, a detection structure assembly with a corresponding specification is installed on a prestressed tendon needing to detect stress;
and 5: after the prestressed duct to be tested is grouted for three days, the stress of the prestressed beam in the corresponding body can be detected by a matched magnetic flux tester.
Furthermore, in the detection structure, the left cuff and the right cuff are completely the same in shape and material, i.e. the same components, which may be collectively referred to as cuffs; the left positioning pipe and the right positioning pipe are also the same components and are collectively called as positioning pipes, and at least one slurry passing hole is formed around the positioning hole in each positioning pipe. This provides for a reduction in the types of components that need to be fabricated. The setting of the grout passing hole can ensure the grouting quality of the prestressed duct without reducing the durability of the prestressed beam in the body.
Furthermore, the connecting pipe in the detection structure is made of engineering plastics; the ferrule is made of ferrite and is hexahedral, and the circular through hole is formed in the middle of two opposite side faces and is called as a connecting hole; the positioning tube is made of steel and is electrically insulated from the hoop through adhesive; the inner diameter of the connecting hole in the hoop is 1mm larger than the outer diameter of the connecting pipe; at the end connected with the hoop, the outer diameter of the positioning tube is the same as that of the connecting tube; the outer end of each positioning tube is provided with a bayonet, and the end part of the corrugated tube can be inserted.
Furthermore, two ends of the positioning hole are respectively provided with an inner diameter change section; the inner diameter of the inner diameter change section is changed slowly, and the two ends are in smooth transition. The measure is to ensure that the steel strand is slowly positioned, prevent edges and corners in the positioning pipe from damaging the steel strand and prevent the lateral pressure of the steel strand bundle from deforming the slurry passing hole as much as possible.
Furthermore, the two exposed ferrule side surfaces of the detection structure are on the same surface of the engineering structure and are level. The purpose is to ensure that the joint surface can be closely attached when an externally matched fluxgate tester detects; during construction, the two ferrules and the connecting pipe in the middle can be assembled and adhered together according to the required distance and relative position. During installation, a specially-made auxiliary tool can be used for positioning the two corresponding ferrules. When the passive testing surface is provided with a template, if a steel template is adopted, the hoop can be fixed on the template from the outer side of the template by using bolts, or the hoop is adsorbed on the steel template by using a strong magnet.
By adopting the scheme, an exciting coil and an induction coil are arranged in an external matched magnetic flux tester, a generated magnetic field starts from one end of the tester, enters the steel strand bundle through one hoop, returns to the matched magnetic flux tester through the other hoop, and is communicated in the matched magnetic flux tester. And the stress of the steel strand can be measured based on the principle of the magneto-elastic effect. And high-permeability powder is added into the mortar, so that the permeability of the mortar can be improved, and the test effect is improved.
Considering that the curved prestressed tendon is extruded to one side after being tensioned and the section shape is changed, the position of the detection structure is carefully selected, and in the case that the prestressed duct close to the anchorage end is a straight line segment in general, the position of the detection structure can be selected to be close to the anchorage at two ends and keeps a distance of at least 30 cm with the anchorage at the end, because the prestressed beam close to the anchorage end is complicated in stress and is likely to be locally changed in the use process. For a number of turns of the tendon in a continuous beam, the tendon does not press the prestressed duct walls on either side between the two bending curves, where the test structure can be placed.
Compared with the prior art, the invention can overcome the defects of the existing cylindrical magnetic flux sensor for testing the stress of the prestressed tendons, and the stress of the prestressed tendons in the body can be detected in the operation process of the engineering structure only by embedding the hoop and other components in the structure. The embedded hoop and the components have low manufacturing cost, the cost for detecting the stress of the prestressed beam is greatly reduced, and the detection structure is effective in the whole service life of the engineering structure and does not influence the precision of the test.
Drawings
FIG. 1 is a schematic view of a detection structure in the present invention.
FIG. 2 is a schematic view of a magnetic flux detector.
FIG. 3 is a schematic structural view of the in-vivo prestressed tendon stress detection system.
FIG. 4 is a schematic cross-sectional view through the left measuring arm for detecting the stress of the tendon in the body.
FIG. 5 is a schematic view of a ferrule.
FIG. 6 is a schematic cross-sectional view of the middle portion of the positioning tube.
FIG. 7 is a schematic longitudinal cross-sectional view of a grout hole in the pilot tube.
The labels in the figure are: 1-left hoop, 2-right hoop, 3-connecting pipe, 4-positioning pipe, 5-bayonet, 6-left measuring arm, 7-right measuring arm, 8-handle, 9-active testing surface, 10-passive testing surface, 11-connecting hole, 12-grout passing hole, 13-corrugated pipe, 14-steel strand bundle, 15-left exciting coil, 16-right exciting coil, 17-induction coil, 18-mortar, 19-concrete and 20-positioning hole.
Detailed Description
The following is a specific embodiment of the present invention, and the technical solution of the present invention is described with reference to the drawings, but the present invention is not limited to this embodiment.
Example one
In the embodiment, for the stress detection of the prestressed tendons in one prestressed concrete box girder, only one type of prestressed tendons is arranged in the engineering structure, the prestressed tendons are straight tendons of a bottom plate, and the number of the steel strands in each tendon is 15. A schematic of the test structure designed to facilitate testing of the stress of the steel strand bundle 14 is shown in fig. 1 and 3. A section of the bellows 13 is removed in the conventional pre-stressed configuration and replaced with a sensing configuration. The steel strand bundle 14 is a floor bundle of the box girder. The main components of the detection structure are a left hoop 1 and a right hoop 2 which are the same components and can be collectively called as hoops, the materials of the left hoop and the right hoop are ferrite, and the inner diameter of a connecting hole 11 is 103mm as shown in figure 5; the thickness of the ferrule is 80mm, and the length and width of the cross section are both 140 mm. The steel strand bundle 14 is composed of 15 steel strands with nominal diameter of 15.2mm, and the corrugated pipe 13 is a plastic corrugated pipe with inner diameter of 100 mm. The connecting pipe 3 is a straight pipe made of high density polyethylene, the outer diameter is 102mm, the wall thickness is 1mm, the inner diameter is also 100mm, the length is 260mm, 20mm are respectively arranged at two ends and are respectively inserted into the left hoop 1 and the right hoop 2, and the two ends are firmly glued by epoxy resin and sealed. The length of the positioning tube 4 is 200mm, the material is high density polyethylene, the inner diameter of the end part is 100mm, the wall thickness is 1mm, the outer diameter of one end is 102mm, and the depth of inserting into the corresponding connecting hole 11 is 20 mm; the other end is provided with a bayonet 5 with the depth of 40mm, the end part of the corrugated pipe 13 is inserted after being expanded, and is firmly glued by epoxy resin and sealed. The structure of the middle section of the positioning pipe 4 is schematically shown in fig. 6 and 7, the diameter of the positioning hole 20 in the middle of the section is 60mm, 6 pulp passing holes 12 which are opposite in pairs are arranged around the positioning hole, and the inner diameter of each pulp passing hole 12 is 15 mm. The left hoop 1 and the right hoop 2 are respectively provided with a corresponding side surface which is a passive testing surface 10, and when the passive testing surface 10 is installed, the design height of the passive testing surface 10 on the upper surface of the bottom plate of the box girder is kept, and after concrete 19 is poured, the passive testing surface is flush with the surface of the concrete 19 at the position. The detection structure is poured with mortar 18 after the steel strand bundle 14 is tensioned. The stress detection method of the internal prestressed tendon comprises the following implementation steps:
step 1: designing and manufacturing components in a plurality of detection structures; and designing and manufacturing a magnetic flux tester matched with the detection structures of various specifications. The magnetic flux tester is shown in fig. 2, fig. 3 and fig. 4, and comprises a left measuring arm 6, a right measuring arm 7 and a handle 8, wherein a left exciting coil 15 is arranged in the left measuring arm 6, a right exciting coil 16 is arranged in the right measuring arm 7, and an induction coil 17 is arranged in the handle 8, and the structure of the magnetic flux tester is bilaterally symmetrical. When testing the stress of the steel strand bundle, the two active testing surfaces 9 are respectively opposite to and closely attached to the passive testing surface 10. Inputting excitation pulse current into the excitation coil, wherein the excitation coil generates an excitation magnetic field to generate induction voltage in the induction coil;
step 2: the prestressed concrete sample is made indoors, 12 prestressed ducts are arranged in the prestressed concrete sample, the type of the prestressed ducts is the same as that of the prestressed ducts in an engineering structure, the tension force of each prestressed tendon is different, and the prestressed concrete sample is grouted. Meanwhile, a sleeve type magnetic flux sensor is installed on the prestressed tendon; calibrating the manufactured magnetic flux tester according to the stress test result of the sleeve type magnetic flux sensor;
and step 3: in a common temperature range, the stress of the steel strand bundle at different temperatures is typically measured, and the relation between the induced voltage and the stress considering temperature correction is established;
and 4, step 4: when an engineering structure is built, the detection structure assembly is installed on a prestressed tendon needing stress measurement, and a temporary tool is adopted to fix the relative positions of two cuffs in the same detection structure; to facilitate the use of a temporary tool, a threaded hole with a diameter of 6mm is drilled in the middle of the passive test surface 10 of the ferrule.
And 5: after the prestressed duct is grouted for three days, the stress of the prestressed strand of the steel strand can be tested by a matched magnetic flux tester, and the stress takes the correction of temperature into consideration.
Example two
This embodiment is a modification of the first embodiment, and the detection structure is simplified. Considering that the tendon to be tested is of a straight type, the steel strand bundle 14 is relatively neat in the cross section of the test section and is no longer positioned. The inner diameter of the positioning pipe 4 is unchanged, and the positioning hole 20 and the pulp passing hole 12 are not arranged any more.
EXAMPLE III
In this embodiment, the second modification is made to the second embodiment, in which the positioning tube 4 in the inspection structure is eliminated, and the inner diameter of the connection hole 11 on the ferrule side 20mm deep from the ferrule side surface is 120mm, which satisfies the insertion and connection of the end portion of the bellows 13.
Example four
The third embodiment is also modified, the positioning tube 4 and the connecting tube 3 are eliminated in the detection structure, and the inner diameter of the connecting hole 11 is 120mm, so that the corrugated tube 13 can penetrate through the connecting hole; the bellows 13 is not broken at the location of the detection structure. That is, the left ferrule 1 and the right ferrule 2 are pierced outside the bellows 13.
The above description of the specific embodiments is intended to be illustrative of the invention and should not be taken to limit the scope of the invention.
Claims (5)
1. A stress detection method of a detection structure of an in-vivo prestressed tendon, the detection structure being characterized in that: the detection structure replaces a section of corrugated pipe of the internal prestressed tendon, is sleeved outside the internal prestressed tendon needing stress detection, and mainly comprises a left hoop, a right hoop, a section of connecting pipe for connecting the left hoop and the right hoop, a positioning pipe for connecting the left hoop and the left corrugated pipe, and a positioning pipe for connecting the right hoop and the right corrugated pipe, wherein all connected joints are sealed; the middle part of the positioning pipe is provided with a positioning hole, and the internal prestressed tendons are restrained in the middle of the prestressed duct; the distance between the left hoop and the right hoop is 200mm-400mm, and at least one side surface of each of the left hoop and the right hoop is exposed out of the same side of the engineering structure part, so that the left hoop and the right hoop are called as a passive test surface; the stress detection method of the internal prestressed tendon is characterized in that: a calibrated matched magnetic flux tester is adopted, and two active testing surfaces of the magnetic flux tester are respectively attached to corresponding passive testing surfaces; the magnetic flux tester, the internal prestressed beam and the two cuffs form a magnetic circuit, an exciting coil in the magnetic flux tester generates an exciting magnetic field during detection, and the induced voltage in the induction coil is tested to obtain the stress of the internal prestressed beam, mainly comprising the following implementation steps,
step 1: determining internal prestress tendons needing stress detection in an engineering structure, and designing and manufacturing a detection structure and a magnetic flux tester with corresponding specifications according to the specifications of corrugated pipes adopted by the internal prestress tendons; the magnetic flux tester mainly comprises a left measuring arm, a right measuring arm and a handle for connecting the left measuring arm and the right measuring arm, wherein a left exciting coil is arranged in the left measuring arm, a right exciting coil is arranged in the right measuring arm, an induction coil is arranged in the handle, and the structure of the magnetic flux tester is bilaterally symmetrical; an ammeter for testing the induction voltage is arranged in the handle, and a corresponding display screen is arranged on the handle; a thermometer is also arranged in the handle;
step 2: for the detection structure of each specification, a plurality of prestressed concrete test pieces with unequal tension of the prestressed tendons are manufactured, and sleeve type magnetic flux sensors are installed on the prestressed tendons; calibrating a corresponding flux tester according to a stress test result of the sleeve type flux sensor, and establishing a relation between induced voltage in the flux tester and stress of the prestressed beams in the body;
and step 3: detecting the stress of the prestressed tendons in the body at different temperatures, and establishing the relation between the induced voltage containing temperature correction and the stress of the corresponding magnetic flux tester;
and 4, step 4: when an engineering structure is built, a detection structure with a corresponding specification is installed on a prestressed tendon needing to detect stress;
and 5: after the prestressed duct to be tested is grouted for three days, the stress of the prestressed beam in the corresponding body is detected by a matched magnetic flux tester.
2. The stress sensing method of a sensing structure of an in-vivo prestressed tendon as claimed in claim 1, wherein: in the detection structure, the left hoop and the right hoop are completely the same in shape and material, namely the left hoop and the right hoop are the same components and are collectively called as hoops; the left positioning pipe and the right positioning pipe are also the same components and are collectively called as positioning pipes, and at least one slurry passing hole is formed around the positioning hole in each positioning pipe.
3. The stress sensing method of a sensing structure of an in-vivo prestressed tendon as claimed in claim 2, wherein: the connecting pipe is made of engineering plastics; the ferrule is made of ferrite and is hexahedral, and the circular through hole is formed in the middle of two opposite side faces and is called as a connecting hole; the positioning tube is made of steel and is electrically insulated from the hoop through adhesive; the inner diameter of the connecting hole in the hoop is 1mm larger than the outer diameter of the connecting pipe; at the end connected with the hoop, the outer diameter of the positioning tube is the same as that of the connecting tube; the outer end of each positioning pipe is provided with a bayonet, and the end part of the corrugated pipe can be inserted.
4. The stress sensing method of a sensing structure of an in-vivo prestressed tendon as claimed in claim 2, wherein: two ends of the positioning hole are respectively provided with an inner diameter change section; the inner diameter of the inner diameter change section is changed slowly, and the two ends are in smooth transition.
5. The stress sensing method of a sensing structure of an in-vivo prestressed tendon as claimed in claim 2, wherein: the exposed two ferrule side surfaces of the detection structure are on the same surface of the engineering structure and are level.
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| 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 |
| CN103528720B (en) * | 2013-10-25 | 2015-04-01 | 交通运输部公路科学研究所 | Precise detection device and detection method for stress of invitro prestressed steel beam |
| CN103557973B (en) * | 2013-11-20 | 2015-09-09 | 重庆交通大学 | Existing structure prestress in situ detection system and method |
| CN105603876B (en) * | 2015-12-24 | 2017-12-15 | 中国铁路总公司 | The dynamic real-time monitor method of prestressed ribs of concrete bridge stretching force and special pre-stress construction system |
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Address after: No.91, Longhai Middle Road, Erqi District, Zhengzhou City, Henan Province, 450000 Patentee after: Zhengzhou Transportation planning Survey, Design and Research Institute Co.,Ltd. Address before: 450000 at the intersection of West Fourth Ring Road and Lianhuo Expressway in High tech Zone, Zhengzhou City, Henan Province Patentee before: ZHENGZHOU COMMUNICATIONS PLANNING SURVEY & DESIGN INSTITUTE |