Clamping and detecting device for ultra-short exposed prestressed steel strand

Abstract

The device for clamping and detecting the ultra-short exposed prestressed steel strand comprises a front anchor cup, a front clamping piece, a connecting cylinder, a rear anchor cup, a displacement meter, a rear clamping piece, a pressure sensor, a jack, a counter-force supporting cylinder, an extended steel strand and a baffle, one end of the front anchor cup is sleeved on the exposed ultrashort steel strand, the front clamping piece is inserted into an inner cavity at one end of the front anchor cup, and one end of the connecting cylinder is fixed at the other end of the front anchor cup through threads; one end of the rear anchor cup sleeves one end of the extended steel strand, the rear clamping piece is inserted into an inner cavity in one end of the rear anchor cup, and the other end of the connecting cylinder is fixed to the other end of the rear anchor cup through threads; the counter-force supporting cylinder is sleeved outside the rear anchor cup, the front anchor cup, the working anchor and the connecting cylinder from the other end of the extension steel strand, one end of the counter-force supporting cylinder abuts against the end of the anchor bearing plate, the pressure sensor and the jack are sequentially installed on the extension steel strand extending out of the counter-force supporting cylinder, and the jack abuts against the other end of the counter-force supporting cylinder through the pressure sensor. A baffle is arranged on the side wall of the fixed end of the jack, and a displacement meter is arranged on the side wall of the movable end of the jack.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of detection and evaluation of prestressed concrete structures, and particularly relates to a clamping extension device and method for prestress detection in existing unbonded prestressed concrete structures. BACKGROUND

[0002] Unbonded prestressed concrete structures are widely used in engineering practice. The end of the prestressed tendon is usually exposed by about 30-50 mm after construction to meet the needs of anchorage, protection and construction. However, after years of service of existing structures, the actual prestress level of unbonded prestressed tendons often needs to be detected for reasons such as functional adjustment, load change or safety evaluation, so as to judge the residual bearing capacity and service state of the structure.

[0003] For unbonded systems, the prestressed tendon is deeply buried in the concrete. Although there are indirect detection methods such as vibration method and acoustic method, these methods are difficult to accurately reflect the actual prestress of unbonded prestressed tendons. If the true and accurate prestress value is needed in engineering, external force needs to be applied to the end of the prestressed tendon to achieve direct loading detection. However, the current engineering site is generally faced with a fundamental problem: the length of the exposed steel strand at the end is only 30-50 mm, and the existing jacks, tool anchors and their supporting clamps for prestress tension and detection all require sufficient exposed length to complete clamping and tension. The steel strand with a length of a few centimeters cannot meet the effective clamping length requirement of the existing equipment, resulting in the inability to establish the stress system required for tension.

[0004] At present, there is no mature equipment that can apply sufficient tension to the exposed unbonded prestressed tendon with a length of a few centimeters without damaging the end of the component and chiseling the concrete. There is no relevant standard and lack of engineering application cases in the industry. Due to the lack of devices that can effectively clamp the ultra-short end steel strand and establish the loading path, the prestress detection of existing unbonded prestressed structures cannot be carried out in such working conditions.

[0005] Chinese patent CN105675198B discloses a device and method for detecting prestress at the end of unbonded prestressed tendons after cutting. This device detects the prestress at the end of unbonded prestressed tendons fixed to the concrete end face via a fixed anchor and a bearing plate. It includes: a detection anchor, a tensioning screw, a tensioning bracket, a jack, a pressure sensor, a pad, and a nut. The detection anchor includes a cylindrical anchor ring, an annular wedge-shaped clamp, and a clamp locking element. The annular wedge-shaped clamp is inserted between the cylindrical anchor ring and the fixed anchor. The clamp locking element is screwed to the cylindrical anchor ring, thus fixing the detection anchor and the fixed anchor into a single unit. The front end of the tensioning screw is screwed to the clamp locking element. During detection, the detection device is first installed, then tensioned using a jack. When the fixed anchor is pulled, the pressure from the pressure sensor is recorded, which is the prestress at the end of the unbonded prestressed tendon after cutting.

[0006] Existing patents employ the approach of testing a single steel strand by tensioning a single anchorage. Essentially, this relies on controlled tensioning of the target anchorage end and reading the force value to achieve effective prestress detection. This approach has fundamental limitations in group anchorage scenarios: firstly, the resultant force of a group anchorage system is typically very large, making it difficult to configure matching tensioning equipment and reaction systems, thus making it difficult to determine "whether tensioning is possible"; secondly, even if tensioning or traction can be applied to the entire group anchorage, the detection results can only reflect the overall stress state of the group anchorage system, failing to further separate and obtain the effective prestress value of each prestressing tendon within the group anchorage. Therefore, it is difficult to meet the practical needs of identifying the prestress level of each tendon individually before assessing existing structures, partial modifications, or demolition.

[0007] Therefore, there is an urgent need for a device that can reliably clamp ultra-short exposed prestressed steel strands and establish a tensioning force transmission path compatible with conventional jacks, so as to complete prestress testing without damaging the structure, thus filling the current technical gap in the engineering field for this type of working condition. Summary of the Invention

[0008] To address the problem that the exposed length of end steel strands in existing unbonded prestressed concrete structures is only 30-50mm, making them unsuitable for use with existing clamps and tensioning equipment and thus preventing prestress testing, this invention provides a clamping and extension testing device for ultra-short exposed prestressed steel strands. This device reliably clamps the short end steel strands and establishes a loading path compatible with jacks by setting subsequent anchoring units, enabling direct testing of prestress.

[0009] To achieve the objective of this invention, the present invention adopts the following technical solution: This invention discloses a clamping and detection device for ultra-short exposed prestressed steel strands, comprising: a front anchor cup, a front clamping plate, a connecting cylinder, a rear anchor cup, a displacement gauge, a rear clamping plate, a pressure sensor, a jack, a reaction support cylinder, an extension steel strand, and a baffle. The exposed ultra-short steel strand extends from the concrete. An anchor plate, a working anchor, and a wedge-shaped clamping plate are sequentially installed on the extended end of the exposed ultra-short steel strand. The wedge-shaped clamping plate is inserted into the working anchor through an inclined surface that cooperates with the working anchor. One end of the front anchor cup is fitted onto the exposed ultra-short steel strand, and the front clamping plate is inserted into the inner cavity of one end of the front anchor cup through an inclined surface that cooperates with the front anchor cup. One end of the connecting cylinder is threaded to the other end of the front anchor cup. One end of the rear anchor cup is fitted onto... Installed at one end of the extension steel strand, the rear clamp is inserted into the inner cavity of one end of the rear anchor cup through an inclined surface that cooperates with the rear anchor cup. The other end of the connecting cylinder is fixed to the other end of the rear anchor cup by threads. The reaction support cylinder is fitted from the other end of the extension steel strand onto the outside of the rear anchor cup, the front anchor cup, the working anchor and the connecting cylinder, with one end abutting against the end of the anchor plate. The pressure sensor and the jack are installed in sequence on the extension steel strand extending from the reaction support cylinder, and the jack is pressed against the other end of the reaction support cylinder through the pressure sensor. A baffle is installed on the side wall of the fixed end of the jack, and a displacement gauge is installed on the side wall of the moving end of the jack. The moving end of the jack stretches the extension steel strand, and the displacement gauge detects the elongation of the extension steel strand.

[0010] The present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, wherein: the baffle is perpendicular to the side wall of the fixed end of the jack.

[0011] The present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, wherein: the smallest end of the front clamp is close to one end of the reaction support cylinder, and the smallest end of the rear clamp is close to the other end of the reaction support cylinder.

[0012] The present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, wherein the extended steel strand and the exposed ultra-short steel strand are on the same straight line.

[0013] The present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, wherein: the two ends of the connecting cylinder are respectively fixed to the inner walls of the other end of the front anchor cup and the rear anchor cup by threads.

[0014] The present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, wherein the length of the exposed ultra-short steel strands is at least 30 mm.

[0015] The present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, wherein: the displacement gauge is a rod-type displacement gauge, the displacement gauge is fixed to the side of the jack, and one end of the displacement gauge abuts against the baffle.

[0016] Compared with existing technologies and Chinese Patent CN105675198B, the clamping and testing device for ultra-short exposed prestressed steel strands of this invention has the following advantages and brings the following unexpected technical effects: This invention addresses the typical working condition of ultra-short exposed ends in existing unbonded prestressed structures. It proposes a testing device that reliably clamps ultra-short exposed steel strands using a front anchor cup and front clamping plate, and constructs a complete axial loading and testing force transmission path by extending the steel strand. This eliminates the need for tensioning the original working anchor or the entire anchor group, allowing for independent clamping, loading, and measurement of the target steel strand under limited exposed length conditions. Therefore, this invention is applicable to effective prestress testing in single-anchor conditions and can also perform individual testing of steel strands within the anchorage under group anchor conditions. This allows for obtaining the prestress discrimination value of each prestressing tendon without applying a large tension force to the entire anchor group, significantly expanding the scope of engineering applications and better meeting the field conditions for prestress testing of existing structures. Attached Figure Description

[0017] Figure 1 The present invention relates to a clamping and testing device for ultra-short exposed prestressed steel strands. Figure 1 In the process, the hydraulic jacks did not pull the extended steel strand; Figure 2 The present invention relates to a clamping and testing device for ultra-short exposed prestressed steel strands. Figure 2 In the middle, the hydraulic jack pulls the extended steel strand, causing the wedge-shaped clamp to be pulled away from the working anchor; Figure 3 The force-displacement curve for the entire tensioning process.

[0018] exist Figure 1 and Figure 2 In the diagram, 1 is the anchor plate; 2 is the working anchor; 3 is the front anchor cup; 4 is the front clamp; 5 is the connecting cylinder; 6 is the rear anchor cup; 7 is the displacement gauge; 8 is the rear clamp; 9 is the pressure sensor; 10 is the jack; 11 is the exposed ultra-short steel strand; 12 is the reaction support cylinder; 13 is the extension steel strand; 14 is concrete; 15 is the wedge-shaped clamp; 16 is the baffle; and 17 is the tie rod. Detailed Implementation

[0019] like Figure 1 and Figure 2As shown, the present invention provides a clamping and testing device for ultra-short exposed prestressed steel strands, comprising: a front anchor cup 3, a front clamping plate 4, a connecting cylinder 5, a rear anchor cup 6, a displacement gauge 7, a rear clamping plate 8, a pressure sensor 9, a jack 10, a reaction support cylinder 12, an extension steel strand 13, and a baffle 16; the exposed ultra-short steel strand 11 extends from the concrete 14, and the length of the exposed ultra-short steel strand 11 is at least 30mm. Anchor plate 1, working anchor 2, and wedge-shaped clamping plate 15 are sequentially installed on the extended end of the exposed ultra-short steel strand 11. The wedge-shaped clamping plate 15 is inserted into the working anchor 2 through an inclined surface that cooperates with the working anchor 2. One end of the front anchor cup 3 is fitted onto the exposed ultra-short steel strand 11. The front clamping plate 4 is inserted into the inner cavity of one end of the front anchor cup 3 through an inclined surface that mates with the front anchor cup 3. One end of the connecting cylinder 5 is fixed to the inner wall of the other end of the front anchor cup 3 by threads. One end of the rear anchor cup 6 is fitted onto one end of the extension steel strand 13. The rear clamping plate 8 is inserted into the inner cavity of one end of the rear anchor cup 6 through an inclined surface that mates with the rear anchor cup 6. The other end of the connecting cylinder 5 is fixed to the inner wall of the other end of the rear anchor cup 6 by threads. The smallest end of the front clamping plate 4 is close to one end of the reaction support cylinder 12, and the smallest end of the rear clamping plate 8 is close to the other end of the reaction support cylinder 12. The extension steel strand 13 and the exposed ultra-short steel strand 11 are on the same straight line. The reaction support cylinder 12 extends from the other end of the extension steel strand 13. The set is installed on the outside of the rear anchor cup 6, the front anchor cup 3, the working anchor 2 and the connecting cylinder 5, with one end abutting against the end of the anchor plate 1. The pressure sensor 9 and the jack 10 are sequentially installed on the extension steel strand 13 extending from the reaction support cylinder 12, and the jack 10 is pressed against the other end of the reaction support cylinder 12 through the pressure sensor 9. A baffle 16 is installed on the side wall of the fixed end of the jack 10, and the baffle 16 is perpendicular to the side wall of the fixed end of the jack 10. A displacement meter 7 is installed on the side wall of the moving end of the jack 10. The displacement meter 7 is a pull rod type displacement meter, fixed to the top side of the jack 10, with one end abutting against the baffle 16. The moving end of the jack 10 stretches the extension steel strand 13, and the displacement meter 7 detects the extension length of the extension steel strand 13.

[0020] In the testing of existing ultra-short exposed unbonded prestressed concrete structures, the front anchor cup 3 is first fitted onto the end of the exposed ultra-short steel strand 11, and the front clamp 4 is inserted into the inner cavity of the front anchor cup 3, so that the front clamp 4 and the front anchor cup 3 form a wedge clamp, thereby achieving reliable anchoring of the ultra-short exposed steel strand 11; then, the front anchor cup 3 is connected to the rear anchor cup 6 installed at the end of the extension steel strand 13 through the connecting cylinder 5, so that the exposed ultra-short steel strand 11 and the extension steel strand 13 form a continuous force system on the axis.

[0021] Next, the reaction support cylinder 12 is fitted onto the outside of the rear anchor cup 6, connecting cylinder 5, front anchor cup 3 and the original working anchor 2, and one end of the reaction support cylinder 12 is pressed tightly against the end face of the anchor plate 1, thereby establishing a stable reaction force transmission path; pressure sensor 9 and jack 10 are installed in sequence on the outside of the extended steel strand 13, and jack 10 is pressed against the other end of the reaction support cylinder 12 through pressure sensor 9, forming a complete tension-reaction system.

[0022] When the jack 10 is activated and applies axial tension to the extension steel strand 13, the tension is transmitted step by step through the rear clamp 8, rear anchor cup 6, connecting cylinder 5, front anchor cup 3 and front clamp 4 to the exposed ultra-short steel strand 11, causing the original unbonded prestressed tendons to undergo controlled tension. During the tensioning process, the pressure sensor 9 measures the applied tension value in real time, and the displacement gauge 7 measures the axial elongation of the extension steel strand simultaneously, and plots the tension-displacement curve as a basis for judgment.

[0023] When the tension force is less than the existing effective prestress, the wedge-shaped clamp 15 inside the working anchor 2 wedges the exposed ultra-short steel strand 11 tightly, and the exposed ultra-short steel strand 11 does not slip as a whole. Only the finite length exposed at the end can freely extend, and the tension-displacement curve shows a continuous upward trend. As the tension force gradually increases, when it reaches the existing effective prestress level and begins to overcome the frictional resistance between the working anchor 2 and the wedge-shaped clamp 15, the wedge-shaped clamp 15 slips relatively. After reaching the peak point A, the curve shows a significant drop in force value to point B. This drop indicates that the working anchor 2 and the wedge-shaped clamp 15 begin to separate and drive the exposed ultra-short steel strand 11 to participate in the force. When tensioned to point C, it can be observed that the slope of the curve after the anchor is opened is significantly different from that before the anchor is opened. Therefore, the tension force corresponding to the first significant drop to the lowest point after the peak in the tension-displacement curve can be used as the discrimination value of the effective prestress in the existing unbonded prestressed steel strand, thereby realizing intuitive identification and engineering judgment of the prestress state of the existing structure.

[0024] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design methods and embodiments similar to this technical solution without departing from the spirit of the present invention, such methods and embodiments should fall within the protection scope of this patent.

Claims

1. A clamping and testing device for ultra-short exposed prestressed steel strands, comprising: The components include: front anchor cup (3), front clamp (4), connecting cylinder (5), rear anchor cup (6), displacement gauge (7), rear clamp (8), pressure sensor (9), jack (10), reaction support cylinder (12), extension steel strand (13), and baffle (16). An exposed ultra-short steel strand (11) extends from the concrete (14). Anchor plate (1), working anchor (2), and wedge-shaped clamp (15) are sequentially installed at the extended end of the exposed ultra-short steel strand (11). The shaped clamping piece (15) is inserted into the working anchor (2) through an inclined surface that cooperates with the working anchor (2). The features include: one end of the front anchor cup (3) is fitted onto the exposed ultra-short steel strand (11); the front clamping piece (4) is inserted into the inner cavity of one end of the front anchor cup (3) through an inclined surface that cooperates with the front anchor cup (3); one end of the connecting cylinder (5) is fixed to the other end of the front anchor cup (3) by a thread; one end of the rear anchor cup (6) is fitted onto one end of the extended steel strand (13); and the rear clamping piece... The plate (8) is inserted into the inner cavity of one end of the rear anchor cup (6) through the inclined surface that cooperates with the rear anchor cup (6), and the other end of the connecting cylinder (5) is fixed to the other end of the rear anchor cup (6) by threads; the reaction support cylinder (12) is fitted from the other end of the extension steel strand (13) on the outside of the rear anchor cup (6), the front anchor cup (3), the working anchor (2) and the connecting cylinder (5), with one end abutting against the end of the anchor plate (1), and the pressure sensor (9) and the jack (10) are installed in sequence from the end of the anchor plate (1). The extended steel strand (13) extends from the reaction support cylinder (12), and the jack (10) presses against the other end of the reaction support cylinder (12) through the pressure sensor (9). A baffle (16) is installed on the side wall of the fixed end of the jack (10), and a displacement gauge (7) is installed on the side wall of the moving end of the jack (10). The moving end of the jack (10) stretches the extended steel strand (13), and the displacement gauge (7) detects the extension length of the extended steel strand (13).

2. The clamping and testing device for ultra-short exposed prestressed steel strands as described in claim 1, characterized in that: The baffle (16) is perpendicular to the side wall of the fixed end of the jack (10).

3. The clamping and testing device for ultra-short exposed prestressed steel strands as described in claim 2, characterized in that: The smallest end of the front clamp (4) is close to one end of the reaction support cylinder (12), and the smallest end of the rear clamp (8) is close to the other end of the reaction support cylinder (12).

4. The clamping and testing device for ultra-short exposed prestressed steel strands as described in claim 3, characterized in that: The extended steel strand (13) and the exposed ultra-short steel strand (11) are on the same straight line.

5. The clamping and testing device for ultra-short exposed prestressed steel strands as described in claim 4, characterized in that: The two ends of the connecting cylinder (5) are respectively fixed to the inner walls of the front anchor cup (3) and the other end of the rear anchor cup (6) by threads.

6. The clamping and testing device for ultra-short exposed prestressed steel strands as described in claim 5, characterized in that: The length of the exposed ultra-short steel strand (11) is at least 30 mm.

7. The clamping and testing device for ultra-short exposed prestressed steel strands as described in claim 6, characterized in that: The displacement gauge (7) is a rod-type displacement gauge, fixed to the side of the jack (10), with one end abutting against the baffle (16).

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