A terminal control structure applicable to a single prestressed steel bar under an anchor

Abstract

A terminal control structure applicable to a single prestressed steel bar under an anchor, comprising a force transfer backing plate, a "[["-shaped support frame and a tapered sleeve. The force transfer backing plate is a rigid rectangular backing plate structure, and its two sides are fixed to the surface of a concrete member through threaded fasteners. The force transfer backing plate is provided with a force transfer backing plate through hole and symmetric sector-shaped blind grooves, and sector-shaped force transfer steel plates are fixed in the blind grooves. The two legs of the "[["-shaped support frame are fixed to the two sector-shaped force transfer steel plates, and a support frame steel bar through hole is provided. The tapered sleeve has its tapered bottom fitting the working anchor, and its tapered top abuts against the inner surface of the "[["-shaped support frame. A sleeve steel bar through hole that is collinear with the support frame steel bar through hole and the force transfer backing plate through hole is provided at the axial center position of the tapered sleeve. The materials of the present invention are simple, the cost is low, and it can be recycled after removal, which is green and economical.

Description

Technical Field

[0001] The invention belongs to the field of prestressed bridge construction, and particularly relates to a terminal control structure suitable for detecting the prestress of a single reinforcing bar under an anchor Background Technique

[0002] Prestressed concrete components are one of the most important structural forms used in large and medium-span bridges. Among them, the effective prestress value under the anchor is a key parameter affecting the project quality, and has a close causal relationship with the formation and development of cracks in prestressed concrete structures, the size of deflections, and the bearing capacity of components.

[0003] In the existing research methods, the reverse tension method is a relatively advanced method for detecting the effective prestress under the anchor. The basic principle of the reverse tension method is largely based on the tension test method and is an extension of the tension test method, that is, a prestress detector under the anchor is used to apply a tensile force in the direction opposite to the prestress direction under the anchor by a jack, with single-strand unidirectional tension or full-hole unidirectional tension. The reverse tension method has the advantages of reliable principle and convenient operation, and has been partially applied in projects in provinces and cities such as Yunnan, Fujian, Guizhou, Sichuan, and Zhejiang. However, during the implementation of single-strand unidirectional tension of the prestressed steel bars under the anchor, the following technical problems exist:

[0004] During the detection process, due to some objective reasons, the prestressed steel bars will have adverse phenomena such as corrosion, insufficient effective cross-section, entanglement, broken wires, and wire slippage, resulting in different degrees of connection loosening between the prestressed steel bars and the anchor. If this loosening phenomenon is not effectively constrained and compensated at the boundary terminal of the anchor during the detection process, this phenomenon is very likely to cause stress concentration at the contact part between the anchor and the concrete component, and the phenomenon of relative displacement with the jack, resulting in too large measurement errors and the generation of fine cracks on the surface of the concrete component. Under the long-term action of the natural environment and traffic loads, these fine cracks will develop into irreversible crack diseases that are long and wide.

[0005] In the prior art, the boundary terminal of the anchor is mainly directly connected to the detection device (jack) through a limiting plate and a support frame. The main technical effect of the limiting plate is to limit the displacement of the jack during tensioning, and it cannot effectively constrain and compensate between the prestressed steel bar and the anchor when the above-mentioned adverse phenomena occur. Moreover, in actual operation, due to the design factors of the size of the limiting plate, construction workers cannot directly judge the contact situation between the boundary terminal of the anchor and the limiting plate. In addition, the purpose of using the support frame is to provide a mechanical support point for applying a reverse force to the jack during the pulling process on the basis of limiting the displacement of the jack. Similar to the limiting plate, the support frame's constraint and compensation for the boundary terminal of the anchor are very limited. In the prior art solution, there is a certain free area between the inside of the support frame and the boundary terminal of the anchor. Under the action of the pulling force of the jack, it provides a relatively large development space for the aggravated damage of the anchor jaw along the direction of the prestressed steel bar. If the anchor jaw is damaged, after the detection is completed, the boundary control terminal of the prestressed steel bar will also basically fail, which is very unfavorable to the strength development of concrete components and brings potential safety hazards to the project.

[0006] Therefore, aiming at the technical defects of the single - root unidirectional tensioning method in the above-mentioned reverse tensioning method, it is of great significance to develop a terminal control structure for single - root prestressed steel bars under the anchor to effectively control the terminal strength of prestressed steel bars with corrosion, insufficient effective cross - section, entanglement, broken wires, and wire slippage, so as to solve the problem that the boundary control terminal fails due to the loosening of the prestressed steel bar under the anchor during the tensioning process and the relative displacement with the jack. Summary of the Invention

[0007] The technical problem solved by the present invention is to provide a terminal control structure suitable for single - root prestressed steel bars under the anchor. This structure can achieve constraint reinforcement for the boundary terminal of the prestressed steel bar with loose anchor, and effectively control the terminal strength of prestressed steel bars with corrosion, insufficient effective cross - section, entanglement, broken wires, and wire slippage, so as to solve the problem that the boundary control terminal fails due to the loosening of the prestressed steel bar under the anchor during the tensioning process and the relative displacement with the jack, and improve the measurement accuracy of the effective prestress value in the single - root unidirectional tensioning method.

[0008] The technical problem solved by the present invention is achieved by adopting the following technical solutions:

[0009] A terminal control structure applicable to a single prestressed steel bar under an anchor, comprising a force-transmitting backing plate, a "[-]" shaped support frame, and a tapered sleeve. Among them, the force-transmitting backing plate is a rigid rectangular backing plate structure, and its two sides are fixed to the surface of the concrete member through threaded fasteners. A force-transmitting backing plate through-hole for the steel bar to be detected to pass through is provided in the middle of the force-transmitting backing plate, and fan-shaped blind grooves are symmetrically arranged on both sides of the force-transmitting backing plate through-hole, and fan-shaped force-transmitting steel plates that match the fan-shaped blind grooves and are independently formed are fixed in the blind grooves; and the two legs of the "[-]" shaped support frame are respectively fixed to the two fan-shaped force-transmitting steel plates through threaded connectors, and a support frame steel bar through-hole is provided in the middle of the cross beam of the "[-]" shaped support frame corresponding to the extension line of the force-transmitting backing plate through-hole; and the tapered sleeve has its tapered bottom fitting the working anchor, and its tapered top abuts against the inner surface of the "[-]" shaped support frame, and a sleeve steel bar through-hole that is collinear with the support frame steel bar through-hole and the force-transmitting backing plate through-hole is provided at the axial center position of the tapered sleeve.

[0010] As a further limitation, the length of the force-transmitting backing plate is not less than 1.5 times the longest side length of the working anchor, and the thickness is not less than 3 times the thickness of the fan-shaped force-transmitting steel plate, which can provide sufficient bottom support area for the jack, expand the distribution range of stress dispersion, effectively avoid the occurrence of stress concentration near the working anchor, and also reduce the probability of relative slip between the jack and the "[-]" shaped support frame.

[0011] As a further limitation, a reserved groove is provided at the tapered bottom of the tapered sleeve. The reserved groove is a blind groove with a circular cross-section, and the height of the reserved groove is the same as the height of the working anchor fixture exposed on the surface of the working anchor; an annular thread is engraved along the radial direction on the inner side surface of the reserved groove, and the inner diameter of the thread is the same as the outer diameter of the working anchor fixture.

[0012] As a further limitation, the inner diameter of the support frame steel bar through-hole is 1-2 mm larger than the outer diameter of the steel bar to be detected, and an internal thread is provided in the support frame steel bar through-hole; and the inner diameter of the sleeve steel bar through-hole is 1-2 mm larger than the outer diameter of the steel bar to be detected, and an internal thread is provided in the sleeve steel bar through-hole; and the internal threads in the sleeve steel bar through-hole and the support frame steel bar through-hole are consistent in both direction and size.

[0013] Beneficial effects: The terminal control structure applicable to a single prestressed steel bar under an anchor of the present invention can realize constraint reinforcement for the boundary terminal of the prestressed steel bar with loose anchor, and effectively control the terminal strength of the prestressed steel bar with corrosion, insufficient effective cross-section, entanglement, broken wire, and wire slipping, thereby solving the problem that the prestressed steel bar under the anchor loosens and has relative displacement with the jack during the tensioning process, resulting in the failure of the boundary control terminal, and improving the measurement accuracy of the effective prestress value in the single-strand unidirectional tensioning method;

[0014] In terms of its overall structure, the terminal control strength of the anchor is triple-compensated by restricting the contact surfaces of the force-transferring backing plate with the concrete member, the conical sleeve with the working anchor fixture, and the "["-shaped support frame with the force-transferring backing plate. This greatly reduces the possibility of instantaneous relative displacement between the anchoring fixture of the jack and the steel bar to be tested during the tensioning process. Therefore, the vicious cycle phenomenon of "loosening - slipping - loosening" during the tensioning process is effectively reduced. At the same time, the effective compensation of the terminal control strength provides displacement constraints for the entire section of the steel bar to be tested between the "["-shaped support frame and the working anchor. When the steel bar to be tested suffers from corrosion, insufficient effective cross-section, entanglement, broken wires, wire slipping, etc., the inner diameters of the perforations of the sleeve steel bar and the perforations of the support frame steel bar are both larger than the diameter of the steel bar to be tested. It can achieve the effect of ensuring the normal passage of the steel bar to be tested while leaving a certain gap between the inner walls of the perforations of the sleeve steel bar and the support frame steel bar. This design can prevent the steel bar to be tested from being subjected to excessive frictional force and avoid affecting the accuracy of the test results due to frictional force during the testing process. Description of the Drawings

[0015] Figure 1 is a schematic diagram of the overall structure of the present invention.

[0016] Figure 2 is a schematic diagram of the force-transferring backing plate of the present invention.

[0017] Figure 3 is a schematic diagram of the "["-shaped support frame of the present invention.

[0018] Figure 4 is a schematic sectional view of the conical sleeve of the present invention.

[0019] Figure 5 is a top view of the structural diagram of the conical sleeve of the present invention.

[0020] Wherein: 1. Working anchor; 2. Steel bar to be tested; 3. Working anchor fixture; 4. Force-transferring backing plate; 5. Force-transferring backing plate fixing bolt; 6. "["-shaped support frame fixing bolt; 7. "["-shaped support frame; 8. Conical sleeve; 9. Concrete member; 10. Force-transferring backing plate bolt hole; 11. Force-transferring backing plate through hole; 12. Sector-shaped force-transferring steel plate; 13. "["-shaped support frame bolt hole; 14. Support frame steel bar perforation; 15. Sleeve steel bar perforation; 16. Reserved groove. Detailed Embodiment

[0021] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below with reference to specific drawings.

[0022] See Figures 1 to 5A preferred embodiment of a terminal control structure suitable for a single prestressed steel bar under an anchor. In this embodiment, the terminal control structure includes a force transfer backing plate 4, force transfer backing plate fixing bolts 5, "[ "-shaped support fixing bolts 6, a "[ "-shaped support 7, and a tapered sleeve 8; the force transfer backing plate 4 is connected to the "[ "-shaped support 7 through the "[ "-shaped support fixing bolts 6. The outside of the working anchor clamp 3 is tightly nested with the tapered sleeve 8. The right side of the tapered sleeve 8 is in close contact with the "[ "-shaped support 7, and the left side of the tapered sleeve 8 is in close contact with the working anchor 1.

[0023] Referring to Figure 1 and Figure 2 , the force transfer backing plate 4 is a rigid rectangular backing plate. The length of the backing plate is not less than 1.5 times the longest side length of the working anchor 1. The thickness of the backing plate should not be less than 3 times the thickness of the fan-shaped force transfer steel plate 12. The purpose is that during the detection process, the pulling force of the jack acting on the "[ "-shaped support 7 can be evenly distributed on the surface layer of the concrete member 9 through the force transfer backing plate 4, avoiding stress concentration near the working anchor 1 and developing into cracks; there are force transfer backing plate bolt holes 10 and force transfer backing plate through holes 11 inside the force transfer backing plate 4. There is a fan-shaped force transfer steel plate 12 inside the force transfer backing plate 4, and the fan-shaped force transfer steel plate 12 is fixed through the force transfer backing plate fixing bolts 5; and during the detection, the force transfer backing plate 4 is in close contact with the concrete member 9.

[0024] Referring to Figure 1 and Figure 3 , there are "[ "-shaped support bolt holes and support steel bar through holes 14 inside the "[ "-shaped support 7. The inside of the "[ "-shaped support bolt holes is engraved with threads, and the thread size matches the thread of the "[ "-shaped support fixing bolts 6; the inside of the support steel bar through holes 14 has threads, and the inner diameter of the support steel bar through holes 14 is 1 - 2 mm larger than that of the steel bar 2 to be detected.

[0025] Referring to Figure 1 and Figure 4 , there are sleeve steel bar through holes 15 and reserved grooves 16 inside the tapered sleeve 8. The upper and lower bottom surfaces of the reserved grooves 16 are circular, and the height is the same as the distance that the working anchor clamp 3 is exposed outside the working anchor 1. The inner side surface of the reserved grooves 16 is engraved with annular threads along the radial direction, and the inner diameter of the threads is the same as the outer diameter of the working anchor clamp 3, ensuring that during the detection, the working anchor clamp 3 can be tightly nested in the reserved grooves 16; the inside of the sleeve steel bar through holes 15 has threads, and the inner diameter of the sleeve steel bar through holes 15 is 1 - 2 mm larger than that of the steel bar 2 to be detected. The internal threads of the sleeve steel bar through holes 15 are consistent with the internal threads of the support steel bar through holes 14 in terms of direction and size.

[0026] This invention is applicable to the method of detecting the effective prestress of prestressed concrete structures by the reverse tension method. When implemented, it includes the following steps:

[0027] Step S1: During the single-way tension of the prestressed steel bars under the anchor, mark the steel bars 2 to be detected that show adverse phenomena such as rust, insufficient effective cross-section, entanglement, broken wires, and wire slippage.

[0028] Step S2: Install the tapered sleeve 8. Refer to Figure 1 and Figure 4 , from the free end of the steel bar 2 to be detected, insert the steel bar 2 to be detected into the sleeve steel bar through-hole 15, and slowly rotate and screw the tapered sleeve 8 along the steel bar 2 to be detected, so that the working anchor clamp 3 is nested in the reserved groove 16 of the tapered sleeve 8.

[0029] Step S3: Initially place the force transfer plate 4. Insert the force transfer plate 4 through the force transfer plate through-hole 11 along the free end of the steel bar 2 to be detected, and place it on the working anchor 1. In order to avoid the force transfer plate 4 interfering with subsequent operations due to inclination or slipping, the force transfer plate 4 does not have to be in close contact with the concrete member 9 in this step.

[0030] Step S4: Initially install the "[ "-shaped support frame 7. First, from the free end of the steel bar 2 to be detected, insert the steel bar 2 to be detected into the support frame steel bar through-hole 14, and slowly rotate and screw the "[ "-shaped support frame 7 along the steel bar 2 to be detected, so that the sleeve steel bar through-hole 15 on the tapered sleeve 8 is centered with the support frame steel bar through-hole 14 on the "[ "-shaped support frame 7, and slowly push it in; at this time, due to the thrust of the "[ "-shaped support frame 7, the force transfer plate 4 is basically parallel to the outer edge of the concrete member 9 in the vertical direction. Use visual estimation to judge that when the gap between the force transfer plate 4 and the concrete member 9 is reduced to 1 - 2 mm, the initial installation of the "[ "-shaped support frame 7 is completed.

[0031] Step S5: Fix the "[ "-shaped support frame 7 and the force transfer plate 4. Refer to Figure 1 , rotate the force transfer plate 4 axially along the steel bar 2 to be detected so that the force transfer plate bolt hole 10 is aligned with the support frame bolt hole 13 of the "[ "-shaped support frame 7, and slowly screw in the support frame fixing bolt 6 of the "[ "-shaped support frame 7. During the screwing-in process, when the contact surface between the tapered sleeve 8 and the working anchor clamp 3 is completely and closely in contact, and the sleeve steel bar through-hole 15 is centered with the support frame steel bar through-hole 14, the support frame fixing bolt 6 of the "[ "-shaped support frame 7 can be completely tightened. When the above requirements are not met, the positions of the tapered sleeve 8, the working anchor clamp 3, and the "[ "-shaped support frame 7 need to be adjusted in real time.

[0032] Step S6: According to the operation steps in the reverse tension method in the specification requirements, after fixing the jack used for detection, check the three contact surfaces: the contact surface between the force transfer plate 4 and the concrete member 9, the contact surface between the tapered sleeve 8 and the working anchor clamp 3, and the contact surface between the "[ "-shaped support frame 7 and the force transfer plate 4. After ensuring close contact, the test can be started.

[0033] In the present invention, a tapered sleeve 8 is arranged outside the working anchor fixture 3. The tapered sleeve 8 supplements the free area between the working anchor fixture 3 and the "[-]" type support frame 7 in space. After the installation of the terminal control structure is completed, under the action of the jacking force, the development space for the aggravated damage of the working anchor fixture 3 is blocked along the free end direction of the reinforcing bar 2 to be detected. Through the reserved groove 16, the working anchor fixture 3 can be tightly nested in the tapered sleeve 8, and the contact surface between the tapered sleeve 8 and the working anchor fixture 3 is closely fitted, limiting the lateral displacement of the loose working anchor 1 and the working anchor clip of the working anchor 3.

[0034] In the present invention, outside the concrete member 9, the force transfer plate 4 and the "[-]" type support frame 7 are fixed into a frame structure by using the fixing bolts 6 of the "[-]" type support frame. A sector-shaped force transfer steel plate 12 is arranged inside the force transfer plate 4, enabling most of the reverse pressure of the jack to be transmitted in the order of the "[-]" type support frame 7, the sector-shaped force transfer steel plate 12, and the force transfer plate 4, and obvious stress dispersion and attenuation occur at the sector-shaped force transfer steel plate 12. Therefore, the surface stress distribution transmitted to the concrete member 9 is more uniform, effectively avoiding the stress concentration phenomenon near the working anchor 1.

[0035] In the present invention, force transfer plate bolt holes 10 are arranged inside the force transfer plate 4, and force transfer plate fixing bolts 5 are installed. On the one hand, it increases the overall structural stability of the force transfer plate 4. On the other hand, when the reverse pressure of the jack is transmitted to the sector-shaped force transfer steel plate 12, the force transfer plate fixing bolts 5 can help disperse the stress on the sector-shaped force transfer steel plate 12 on one side of the force transfer plate 4 close to the "[-]" type support frame 7, that is, enable the stress of the sector-shaped force transfer steel plate 12 to be transmitted in two opposite directions, achieving the purpose of stress dispersion and attenuation during the force transmission through the structural design.

[0036] The size design of the force transfer plate 4 provided by the present invention has a length not less than 1.5 times the longest side length of the working anchor 1, and the thickness of the pad should not be less than 3 times the thickness of the sector-shaped force transfer steel plate 12. The purpose is to ensure that during the detection process, the force transfer plate 4 can provide sufficient bottom support area for the jack, expand the distribution range of stress dispersion, and on the technical effect of effectively avoiding the stress concentration phenomenon near the working anchor 1, it can also reduce the probability of relative slip between the jack and the "[-]" type support frame.

[0037] In the present invention, force transfer plate through holes 11 are arranged inside the force transfer plate 4, which can provide a larger effective contact area for the reinforcing bar 2 to be detected, limit the relative displacement of the reinforcing bar 2 to be detected during tensioning, and reduce the measurement error.

[0038] In terms of the overall structure of the present invention, through the constraints: the contact surface between the force transfer cushion plate 4 and the concrete member 9, the contact surface between the conical sleeve 8 and the working anchor fixture 3, and the contact surface between the "[-]" type support frame 7 and the force transfer cushion plate 4, the terminal control strength of the anchor is compensated three times, greatly reducing the possibility of instantaneous relative displacement between the anchoring fixture of the jack and the steel bar 2 to be detected during the tensioning process. Therefore, the vicious cycle phenomenon of "loosening - slipping - loosening" during the tensioning process is effectively reduced; at the same time, the effective compensation of the terminal control strength provides full-segment displacement constraint for the steel bar 2 to be detected between the "[-]" type support frame and the working anchor 1. When the steel bar 2 to be detected undergoes conditions such as corrosion, insufficient effective cross-section, entanglement, broken wires, or wire slipping, the inner diameters of the sleeve steel bar perforation 15 and the support frame steel bar perforation 14 are both 1 - 2 mm larger than the diameter of the steel bar 2 to be detected, which can achieve the effect of ensuring the normal passage of the steel bar 2 to be detected while leaving a certain gap between the inner walls of the sleeve steel bar perforation 15 and the support frame steel bar perforation 14. This design can prevent the excessive friction force on the steel bar 2 to be detected and avoid affecting the accuracy of the test results due to friction during the detection process.

[0039] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art of this industry should understand that the uses of these embodiments are only for illustrating the present invention rather than intending to limit the protection scope of the present invention. In addition, it should also be understood that after reading the technical content of the present invention, those skilled in the art can make various changes, modifications and / or variations to the present invention, and all these equivalent forms also fall within the protection scope defined by the appended claims of this application.

Claims

1. A terminal control structure applicable to a single prestressed steel bar under an anchor, comprising a force transmission backing plate, a "[”-shaped support frame, and a tapered sleeve, characterized in that, The force transfer cushion plate is of a rigid rectangular cushion plate structure, and its two sides are fixed to the surface of the concrete member through threaded fasteners. A force transfer cushion plate through hole for the steel bar to be detected to pass through is arranged in the middle of the force transfer cushion plate, and fan-shaped blind grooves are symmetrically arranged on both sides of the force transfer cushion plate through hole. Fan-shaped force transfer steel plates that match the fan-shaped blind grooves and are independently formed are fixed in the blind grooves. The two legs of the "[“-shaped support frame are respectively fixed to the two fan-shaped force transfer steel plates through threaded connectors, and a support frame steel bar through hole is arranged in the middle of the cross beam of the "[“-shaped support frame corresponding to the extension line of the force transfer cushion plate through hole. The conical sleeve has its conical bottom fitting the working anchor, and its conical top abuts against the inner surface of the "[“-shaped support frame. A sleeve steel bar through hole that is collinear with the support frame steel bar through hole and the force transfer cushion plate through hole is arranged at the axial center position of the conical sleeve.

2. The terminal control structure applicable to a single prestressed steel bar under an anchor according to claim 1, characterized in that, The length of the force transfer cushion plate is not less than 1.5 times the longest side length of the working anchor, and the thickness is not less than 3 times the thickness of the fan-shaped force transfer steel plate.

3. The terminal control structure applicable to a single prestressed steel bar under an anchor according to claim 1, characterized in that A reserved groove is arranged at the conical bottom of the conical sleeve, and the reserved groove is a blind groove with a circular cross-section.

4. The terminal control structure applicable to a single prestressed steel bar under an anchor according to claim 3, characterized in that, The height of the reserved groove is the same as the height of the working anchor fixture exposed on the surface of the working anchor; and annular threads are engraved on the inner side surface of the reserved groove along the radial direction, and the inner diameter of the threads is the same as the outer diameter of the working anchor fixture.

5. The terminal control structure applicable to a single prestressed steel bar under an anchor according to claim 1, characterized in that, The inner diameter of the support frame steel bar through hole is 1-2 mm larger than the outer diameter of the steel bar to be detected, and internal threads are arranged in the support frame steel bar through hole.

6. The terminal control structure applicable to a single prestressed steel bar under an anchor according to claim 5, characterized in that The inner diameter of the sleeve steel bar through hole is 1-2 mm larger than the outer diameter of the steel bar to be detected, and internal threads are arranged in the sleeve steel bar through hole; and the internal threads in the sleeve steel bar through hole and the support frame steel bar through hole are consistent in both direction and size.

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