Hysteresis test device for corrugated steel pipe in axial tension-compression and torsion bearing state

Abstract

The invention relates to the technical field of hysteresis test devices, in particular to a hysteresis test device for a corrugated steel pipe in an axial tension-compression and torsion bearing state, which comprises two groups of supporting seats, a corrugated pipe test piece is arranged between the supporting seats, a measuring piece is arranged on the test piece, and the supporting seats are hinged on a supporting plate. The rotating shaft moving side face of the supporting base is hinged to the supporting plate through a first air cylinder. An opening is formed in the supporting seat, and a first frame body is arranged in the slideway; an actuating mechanism is mounted in the first frame body, one end of a transmission shaft of the actuating mechanism is fixedly connected with a test piece, the other end of the transmission shaft is connected to an axial actuator through a coupling mechanism, and the circumference of the transmission shaft is connected to a torsion actuator through a sliding torsion mechanism; a torsion overshoot protection mechanism is arranged outside the coupling mechanism, axial applied load is cut off in time when torsion overshoot occurs, a non-contact dynamic deformation observation system is additionally arranged on the device, a high-speed camera serves as a core, and the device aims at conducting real-time and dynamic precise monitoring on a test piece in the whole process of a complex loading test.

Description

Technical Field

[0001] This invention relates to the field of hysteresis testing equipment, specifically to a hysteresis testing equipment for corrugated steel pipes under axial tensile, compressive, and torsional load conditions. Background Technology

[0002] In modern bridge engineering, especially in high-intensity earthquake zones or complex geological conditions facing the risk of uneven settlement, increasingly stringent requirements are placed on the seismic performance, energy dissipation capacity, and deformation adaptability of structural components. Developing new structural components that combine high load-bearing capacity with excellent ductility is a key technological direction for improving the safety and toughness of bridge structures.

[0003] Theoretical research shows that corrugated steel pipes, due to their unique structure, exhibit enormous ductile deformation and energy dissipation potential under stress, making them promising candidates for seismic resistance or damping components in bridge structures. However, this innovative application concept differs fundamentally from the traditional applications of corrugated steel pipes in other fields. Traditionally used components cannot meet the stringent requirements of being a primary load-bearing component of a bridge in terms of design philosophy and mechanical performance.

[0004] To safely translate this highly promising new component from theoretical concept to engineering practice, comprehensive and precise experimental verification of its mechanical properties under real service conditions is an indispensable and crucial step. In actual bridges, such components will bear complex composite loads from axial forces, bending moments, and torques, rather than single ideal loads. Therefore, developing experimental methods and devices capable of accurately simulating this multi-dimensional, strongly coupled stress state, and conducting in-depth research on its hysteretic performance, ultimate bearing capacity, and failure modes, is of paramount importance for verifying its design theory, accumulating engineering data, and ultimately achieving its reliable application in bridge engineering.

[0005] Figure 14 The image shows the effect of corrugated steel pipe design in an arch bridge structure. It includes corrugated steel pipe X-braces and K-braces. According to finite element analysis and experiments, compared with the original ordinary steel pipe cross braces, the proposed corrugated steel pipe X-braces save 31% of steel and the corrugated steel pipe K-braces save 62% of steel. At the same time, the bridge's seismic performance is improved by more than 20%.

[0006] Chinese patent document (publication number: CN117554202B) discloses a testing device for local load performance of metal corrugated pipes, relating to the field of metal pipe manufacturing technology. The device includes a support frame, with a testing mechanism fixedly installed above the support frame. A hydraulic testing mechanism is located at the left end of the testing mechanism, and a pneumatic testing mechanism is located at the right end. The testing mechanism includes a testing track. Three sets of hydraulic gripping clamps (first type) are slidably installed above the left end of the testing track, three sets of hydraulic gripping clamps (second type) are slidably installed in the middle of the testing track, and three sets of hydraulic gripping clamps (third type) are slidably installed above the right end of the testing track. Each set of hydraulic gripping clamps (first and third types) can be used to fix the metal corrugated pipe. The testing process uses different testing intensities according to preset metal corrugated pipe quality requirements, ensuring that the metal corrugated pipe is tested at the maximum withstandable testing intensity without damage, resulting in high accuracy of the test results.

[0007] The existing bellows hysteresis test device may experience high sliding friction loss, severe heat generation and jamming, or even impact vibration or rotational jamming when the drive shaft is subjected to combined loading. At the same time, the accumulation of gear meshing clearance and control response delay during repeated torsional loading can easily cause torsional overshoot. The existing device lacks an effective emergency protection mechanism, which may cause the specimen to tear and fail due to the combined effect of axial load and excessive torsion. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a hysteresis test device for corrugated steel pipes under axial tension, compression, and torsional load conditions. A cylindrical roller is installed between the coupling end cap and the limiting block to convert sliding friction into rolling friction. A precise fit of a clearance spring, nut, and guide rod eliminates axial clearance. Simultaneously, an arc-shaped guide groove precisely constrains the rotation trajectory of the drive shaft. Furthermore, a multi-stage linkage torsional overshoot protection mechanism is designed. When the torsional angle exceeds the limit, the convex arc section of the slip ring lifts the locking rod to instantly release the axial load transmission, releasing the axial travel within the buffer cylinder. Mechanical locking is achieved using wedge-shaped contacts and a U-shaped frame, effectively protecting the specimen from tearing damage.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A hysteresis test device for corrugated steel pipe under axial tension, compression, and torsional load conditions includes two sets of support seats mounted at relative intervals on a support plate. A corrugated pipe specimen is installed between the two sets of support seats, and a measuring element is installed on the specimen. The bottoms of the two sets of support seats are hinged to the support plate via rotating shafts. The rotating sides of the support seats are respectively hinged to the support plate via first cylinders for adjusting the tilt angle of the support seats. An opening with a vertical slide rail is provided on the support seat. A first frame is slidably arranged in the slide rail. A second cylinder is installed at the bottom of the first frame for adjusting the lifting height. An actuation mechanism is installed inside the first frame. The actuation mechanism includes an axial actuator, a torsional actuator, and a drive shaft. One end of the drive shaft is fixedly connected to the specimen via a flange. The other end of the drive shaft is connected to the axial actuator via a coupling mechanism. The circumferential direction of the drive shaft is connected to the torsional actuator via a sliding torsional mechanism. A torsional overshoot protection mechanism is provided outside the coupling mechanism to promptly cut off the applied axial load when torsional overshoot occurs.

[0010] Preferably, the sliding torsion mechanism includes a first sleeve, a second sleeve, and a third sleeve. The third sleeve is slidably sleeved on the drive shaft, and the third sleeve and the drive shaft slide relative to each other while maintaining synchronous rotation through a spline structure. The second sleeve is rotatably sleeved on the outside of the third sleeve, and the two ends of the second sleeve extend radially toward the center to form an outer edge, which restricts the axial movement of the third sleeve. A through groove is opened on one side of the second sleeve, and an arc-shaped tooth is fixed on the outer surface of the third sleeve located inside the through groove. The second sleeve is fixedly installed inside the frame through a connecting seat. A torsion actuator is fixed inside the frame, and the output end of the torsion actuator is connected to a rack. The rack meshes with the arc-shaped tooth. The first sleeve is movably sleeved on the drive shaft near one end of the bellows specimen, and the first sleeve is fixed inside the frame through a first bracket.

[0011] Preferably, a support sleeve is movably fitted at the end of the drive shaft away from the bellows. The outer periphery of the support sleeve is fixedly connected to the frame through a second bracket. A buffer cylinder is slidably fitted inside the support sleeve. The buffer cylinder is connected to the drive shaft through a coupling mechanism. An end cap is slidably installed at the other end of the buffer cylinder. The end cap is detachably installed at the end of the buffer cylinder. The radial direction of the end cap is detachably fixedly connected to the buffer cylinder through a limiting component. An axial actuator is fixedly connected to the outer end of the end cap. The axial actuator is fixed inside the frame.

[0012] Preferably, the inner wall of the buffer cylinder has a sliding groove along the axial direction, and a protruding key is provided on the radial outer periphery of the end cap. The end cap slides inside the buffer cylinder, and the protruding key is slidably installed in the sliding groove. A keyway structure is provided between the inner walls of the buffer cylinder and the support sleeve to facilitate the directional sliding of the buffer cylinder. A sliding groove is provided on the inner wall of the support sleeve, and a protruding key is provided on the outer wall of the buffer cylinder corresponding to the sliding groove.

[0013] Preferably, the limiting assembly includes a slip ring and an array of n-shaped frames fixedly arranged on the outer periphery of the buffer cylinder end. A locking unit is provided on the n-shaped frames. The slip ring passes between two legs of several n-shaped frames and rotates circumferentially. The slip ring has several concave arc segments corresponding to the n-shaped frames, with convex arc segments formed between adjacent concave arc segments. A switching unit is fixed on the convex arc segment, and clearance grooves are provided on the slip rings located on both sides of the switching unit. The locking unit includes a locking rod that slides through the cross plate of the n-shaped frame and the side wall of the buffer cylinder. The locking rod is inserted into a limiting hole radially opened on the end cap to form a lock. A second return spring and a baffle are sleeved on the locking rod inside the n-shaped frame. The baffle is fixedly connected to the locking rod, and the two ends of the second return spring are respectively fixedly connected to the baffle and the cross plate of the n-shaped frame. A wedge-shaped contact block is fixed at the top of the n-shaped frame, and the locking rod slides through the wedge-shaped contact block.

[0014] Preferably, the switching unit includes a housing, which is fixed on the convex arc segment of the slip ring. A U-shaped frame is slidably arranged in a guide groove inside the housing. The sliding direction of the U-shaped frame is set along the radial direction of the slip ring. A third return spring is installed at the bottom of the U-shaped frame. The top of the U-shaped frame extends through to the top of the housing. A second hinge is fixed at the top of the housing between the two ends of the U-shaped frame. A connecting block is fixed at the other end of the second hinge. A limiting groove is opened inside the contact block corresponding to the moving end of the U-shaped frame. A second through groove is opened on the upper part of the housing, with the opening of the second through groove facing the rotation direction of the slip ring. A lowering groove is opened on the U-shaped frame corresponding to the second through groove. Under the action of the third return spring, the bottom of the lowering groove coincides with the top of the second through groove. When the wedge-shaped contact block extends into the lowering groove, the U-shaped frame descends and disengages from the limiting groove.

[0015] Preferably, the coupling mechanism includes guide rods, with two guide rods fixedly mounted opposite each other on the bottom plate end face outside the buffer cylinder. A receiving cavity is provided at the end of the transmission shaft away from the specimen, and a coupling end cap is fixed at the end of the receiving cavity. An arc-shaped guide groove is provided on the coupling end cap corresponding to the guide rod. The guide rod enters the receiving cavity after passing through the arc-shaped guide groove. A limiting block, a gap spring, a washer, and a nut are sequentially mounted on the guide rod inside the receiving cavity. The nut is screwed to the threaded end of the guide rod, so that the coupling end cap fits tightly against the bottom plate and rotates. Several cylindrical rollers are arranged circumferentially on the coupling end cap near the bottom plate, and several cylindrical rollers are arranged on the end face of the limiting block near the coupling end cap.

[0016] Preferably, a triggering component is provided between the coupling mechanism and the limiting component. The triggering component includes a ring sleeve that is rotatably fitted onto a support sleeve. Three arc-shaped through slots are spaced apart along the circumference of the support sleeve. Three arc-shaped protrusions extend from the inner wall of the ring sleeve toward the center, with the arc length of the protrusions being less than that of the arc-shaped through slots. Each arc-shaped protrusion is provided with a second spline. A second spline groove is provided on the outside of the drive shaft corresponding to the second spline. The second spline is slidably installed inside the second spline groove. The drive shaft drives the ring sleeve to rotate. Several contact rods are fixed on the outer circumferential surface of the ring sleeve, extending between two contact blocks. When the device experiences torque overshoot, causing the drive shaft to deflect excessively, it drives the ring sleeve and contact rods to rotate together. The contact rods push the contact blocks and slip rings to move together, triggering the switching unit and causing the locking rod in the locking unit to disengage from the end cover, providing a safe movement space for the axial actuator.

[0017] Preferably, a transverse track is provided inside the first frame, and a second frame is slidably installed on the transverse track. A transverse actuator is connected to one side of the second frame to apply a transverse load, which, in conjunction with an axial actuator or a torsional actuator, simulates various stress states of the corrugated pipe on the crossbar of an arch bridge.

[0018] Preferably, the measuring components include a displacement measuring assembly, a strain measuring assembly, and a mechanical parameter measuring assembly; the displacement measuring assembly includes an axial displacement sensor, a torsional angle sensor, and a lateral displacement sensor; the strain measuring assembly includes several resistance strain gauges distributed along the axial direction of the bellows specimen on three key sections: the fixed end, the middle, and the movable end, with longitudinal strain gauges and circumferential strain gauges attached at the crests and troughs, respectively; the mechanical parameter measuring assembly includes an axial force sensor, a torque sensor, and a lateral force sensor.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. In this invention, the coupling mechanism achieves stable and reliable transmission of the drive shaft when simultaneously bearing axial push-pull force and circumferential torsional torque. The cylindrical rollers transform the traditional sliding friction between the coupling end cover and the limiting block into low-resistance rolling friction, greatly reducing friction jamming and heat generation during high-frequency reciprocating torsion. At the same time, the preload of the gap spring, combined with the axial limiting of the nut, ensures that the coupling end cover and the base plate maintain a tight fit while allowing for free and smooth circumferential rotation, avoiding the impact vibration caused by excessive gaps and the jamming caused by interference fits in traditional fixed connections. More importantly, the precise constraint of the arc-shaped guide groove on the coupling end cover ensures that the rotation trajectory of the drive shaft always remains on the preset circumferential path, effectively preventing radial offset and swaying during torsional loading. This ensures that the bellows specimen bears a pure axial and torsional composite load without additional bending moment, significantly improving the accuracy and reliability of the test data.

[0020] 2. In this invention, a multi-stage linkage torsional overshoot protection mechanism is used to achieve rapid identification, load cut-off, and automatic protection of the entire process of mechanical locking for torsional overshoot. Specifically, when the torsional angle exceeds the limit, the protection mechanism uses the convex arc section of the slip ring to lift the locking rod and disengage it from the end cover locking hole, instantly releasing the load transmission connection between the axial actuator and the drive shaft. This releases the axial push-pull force stroke that was originally acting directly on the bellows specimen into the internal space of the buffer cylinder, avoiding tearing damage to the bellows specimen caused by the combined effect of axial load and excessive torsion. The action of the protection mechanism provides valuable buffer time for the control system to stop and respond, reducing the risk of equipment damage and failure of valuable specimens due to torsional overshoot. In addition, the second hinge provides the contact block with a swing avoidance function, enabling the protection mechanism to operate reliably even in multiple overshoot events, improving the fault tolerance and service life of the device.

[0021] 3. In this invention, tilting and coaxial adjustment are achieved by changing the angle of the support seat driven by the first and second cylinders. Combined with the displacement measurement component, strain measurement component, and mechanical parameter measurement component of the measuring device, a system for simulating and evaluating the load-bearing state of corrugated pipes is constructed. This system can accurately reproduce the actual tilt angle and composite load state of corrugated steel pipes in arch bridge structures. The axial actuator, torsional actuator, and lateral actuator work together to apply various load forms such as axial push-pull, circumferential torsion, and lateral displacement independently or in combination, realistically simulating the service environment of corrugated steel pipes under the coupled effects of traffic loads, temperature changes, and foundation settlement. The measuring device records the displacement, strain, and mechanical parameters of the corrugated pipe specimen in real time, plotting force-displacement hysteresis curves and torque-angle hysteresis curves to comprehensively evaluate the load-bearing capacity, deformation characteristics, energy dissipation capacity, and fatigue life of the corrugated pipe, providing reliable experimental data support for the design optimization, safety assessment, and maintenance decisions of corrugated steel pipe arch bridges. Attached Figure Description

[0022] Figure 1 This is a three-dimensional schematic diagram of the overall installation structure of the device of the present invention; Figure 2 This is a three-dimensional schematic diagram of the internal structure of the support base of the device of the present invention; Figure 3 This is a schematic diagram of the overall mounting structure of the drive shaft of the device of the present invention. Figure 1 ; Figure 4 This is a schematic diagram of the overall mounting structure of the drive shaft of the device of the present invention. Figure 2 ; Figure 5 A three-dimensional schematic diagram of the disassembled structure of the sliding torsion mechanism of the device of the present invention. Figure 1 ; Figure 6 A three-dimensional schematic diagram of the disassembled structure of the sliding torsion mechanism of the device of the present invention. Figure 2 ; Figure 7 A three-dimensional schematic diagram of the disassembled structure of the coupling mechanism of the device of the present invention. Figure 1 ; Figure 8 A three-dimensional schematic diagram of the disassembled structure of the coupling mechanism of the device of the present invention. Figure 2 ; Figure 9 A three-dimensional schematic diagram of the disassembled structure of the coupling mechanism of the device of the present invention. Figure 3 ; Figure 10 This is a three-dimensional schematic diagram of the disassembled structure of the trigger component of the device of the present invention; Figure 11 This is a three-dimensional axial view of the triggering component of the device of the present invention; Figure 12 This is a three-dimensional installation diagram of the locking unit and switching unit of the device of the present invention; Figure 13 This is a schematic diagram of the internal cross-sectional structure of the switching unit of the device of the present invention; Figure 14 A schematic diagram showing the connection points of a corrugated pipe in an arch bridge structure. In the diagram: Support plate-11; Support seat-12; First cylinder-13; Bellows specimen-14; Measuring piece-15; Second cylinder-16; First frame-17; Second frame-18; Lateral actuator-19; Axial actuator-20; Torsional actuator-21; Rack-22; Arc tooth-23; Drive shaft-24; First sleeve-25; Support sleeve-26; Second sleeve-27; Connecting seat-28; First bracket-29; Through groove-30; Third sleeve-31; First spline groove-32; First spline-33; Arc through groove-34; Ring sleeve-35; Second spline groove-36; Arc protrusion-37; Contact rod-38; Coupling end cap-39; Arc-shaped guide groove-40; Limiting block-41; Gap spring-42; Washer-43; Nut-44; Guide rod-45; Base plate-46; Buffer cylinder-47; Cylindrical roller-48; End cap-49; Slide groove-50; Convex key-51; Wedge-shaped contact block-52; Housing-53; Contact block-54; Slip ring-55; N-shaped frame-56; Locking rod-57; Second return spring-58; Baffle-59; Clearance groove-60; Second hinge-61; U-shaped frame-62; Limiting groove-63; Lowering groove-64; Second through groove-65; Guide groove-66; Third return spring-67. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

[0024] Contents not described in detail in this specification are prior art known to those skilled in the art. In the description of this invention, it should be understood that terms such as "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, terms such as "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] Figures 1-14 As shown, a hysteresis test device for corrugated steel pipe under axial tension, compression, and torsional load states includes two sets of support seats 12 installed at relative intervals on a support plate 11. A corrugated pipe specimen 14 is installed between the two sets of support seats, and a measuring element 15 is installed on the specimen 14. The bottoms of the two sets of support seats 12 are hinged to the support plate 11 via rotating shafts. The rotating sides of the support seats 12 are respectively hinged to the support plate 11 via first cylinders 13 for adjusting the tilt angle of the support seats 12. An opening with a vertical slide is provided on the support seat 12, and a first frame 17 is slidably arranged in the slide. A second measuring element 15 is installed at the bottom of the first frame 17. Two cylinders 16 are used to adjust the lifting height; an actuation mechanism is installed inside the first frame 17, which includes an axial actuator 20, a torsional actuator 21, and a drive shaft 24. One end of the drive shaft 24 is fixedly connected to the specimen 14 through a flange, and the other end of the drive shaft 24 is connected to the axial actuator 20 through a coupling mechanism. The circumferential direction of the drive shaft 24 is connected to the torsional actuator 21 through a sliding torsional mechanism. A torsional overshoot protection mechanism is set outside the coupling mechanism to cut off the applied axial load in time when torsional overshoot occurs. In the arch bridge structure, a strut is connected between two arch ribs, and a corrugated pipe is installed on the strut. Different struts have different inclination angles and load-bearing methods. The first cylinder 13 and the second cylinder 16 in the two support seats 12 cooperate to adjust the inclination angle of the corrugated pipe specimen 14 to simulate the force and load of the corrugated pipe on different struts. The axial actuator 20 is used to apply axial pushing and pulling force, and the torsional actuator 21 is used to apply circumferential torsional force. The two work together to simulate a stress state of the corrugated pipe on the crossbar of an arch bridge. This application mainly addresses the torsional overshoot protection mechanism for circumferential torsional overshoot under this working condition.

[0026] The device of this invention can also be supplemented with a non-contact dynamic deformation observation system. This system, centered on a high-speed camera, aims to perform real-time, dynamic, and precise monitoring of the specimen throughout the entire process of complex loading tests. Overcoming the limitations of traditional single-point measurement methods, it can capture the full-field deformation of the specimen surface without contact, thereby intuitively and accurately detecting and analyzing the initiation location, propagation path, and dynamic evolution process of stress concentration in local buckling of the structure. This provides comprehensive and crucial visual inspection data for a deep understanding of the failure mechanism of the specimen under complex stress.

[0027] Further, the sliding torsion mechanism includes a first sleeve 25, a second sleeve 27, and a third sleeve 31. The third sleeve 31 is slidably sleeved on the transmission shaft 24. The third sleeve 31 and the transmission shaft 24 slide relative to each other while maintaining synchronous rotation through a spline structure. The second sleeve 27 is rotatably sleeved on the outside of the third sleeve 31. The two ends of the second sleeve 27 extend radially toward the center to form an outer edge, which restricts the axial movement of the third sleeve 31. A through groove 30 is opened on one side of the second sleeve 27. An arc-shaped tooth 23 is fixed on the outer surface of the third sleeve 31 located inside the through groove 30. The second sleeve 27 is fixedly installed inside the frame through a connecting seat 28. A torsion actuator 21 is fixed inside the frame. The output end of the torsion actuator 21 is connected to a rack 22. The rack 22 meshes with the transmission arc-shaped tooth 23. The first sleeve 25 is movably sleeved on the transmission shaft 24 near one end of the bellows specimen 14. The first sleeve 25 is fixed inside the frame through a first bracket 29. The outer periphery of the drive shaft 24 is provided with a first spline 33, and the inner wall of the third sleeve 31 is provided with a first spline groove 32 corresponding to the first spline. The third sleeve 31 and the drive shaft 24 slide together while rotating. The length of the arc-shaped tooth 23 is less than the length of the through groove 30 and extends through to the outside of the second sleeve 27, which is conducive to meshing with the transmission rack 22. The rack 22 is slidably installed inside the frame. The transmission shaft 24 rotates and slides inside the first sleeve 25, and the first sleeve 25 plays a role in stabilizing and limiting the position.

[0028] Furthermore, a support sleeve 26 is movably fitted at the end of the drive shaft 24 away from the bellows. The outer periphery of the support sleeve 26 is fixedly connected to the frame through a second bracket. A buffer cylinder 47 is slidably fitted inside the support sleeve 26. The buffer cylinder 47 is connected to the drive shaft 24 through a coupling mechanism. An end cap 49 is slidably installed at the other end of the buffer cylinder 47. The end cap 49 is detachably installed at the end of the buffer cylinder 47. The radial direction of the end cap 49 is detachably fixedly connected to the buffer cylinder 47 through a limiting component. An axial actuator 20 is fixedly connected to the outer end of the end cap 49. The axial actuator 20 is fixed inside the frame.

[0029] Furthermore, the inner wall of the buffer cylinder 47 has an axially oriented groove 50, and a protruding key 51 is provided on the radial outer periphery of the end cap 49. The end cap 49 slides inside the buffer cylinder 47, and the protruding key 51 is slidably installed in the groove 50. A keyway structure is provided between the inner wall of the buffer cylinder 47 and the inner wall of the support sleeve 26 to facilitate the directional sliding of the buffer cylinder 47. A sliding groove is provided on the inner wall of the support sleeve 26, and a protruding key is provided on the outer wall of the buffer cylinder 47 corresponding to the sliding groove.

[0030] In this invention, a multi-stage linkage torsional overshoot protection mechanism achieves rapid identification, load cut-off, and automatic protection of the entire process of mechanical locking for torsional overshoot. Specifically, when the torsional angle exceeds the limit, the protection mechanism uses the convex arc segment of the slip ring 55 to lift the locking rod 57 out of the locking hole of the end cover 49, instantly releasing the load transmission connection between the axial actuator 20 and the transmission shaft 24. This releases the axial push-pull force stroke that was originally acting directly on the bellows specimen 14 into the internal space of the buffer cylinder 47, avoiding tearing damage to the bellows specimen 14 caused by the combined effect of axial load and excessive torsion. The action of the protection mechanism provides valuable buffer time for the control system to stop and respond, reducing the risk of equipment damage and failure of valuable specimens due to torsional overshoot. In addition, the second hinge 61 gives the contact block 54 a swing avoidance function, enabling the protection mechanism to operate reliably even in multiple overshoot events, improving the fault tolerance and service life of the device.

[0031] Furthermore, the limiting assembly includes a slip ring 55 and an array of n-shaped frames 56 fixedly arranged on the outer periphery of the end of the buffer cylinder 47. A locking unit is provided on the n-shaped frames 56. The slip ring 55 passes between two legs of several n-shaped frames 56 and rotates circumferentially. The slip ring 55 has several concave arc segments corresponding to the n-shaped frames 56, with convex arc segments formed between adjacent concave arc segments. A switching unit is fixed on the convex arc segment, and clearance grooves 60 are provided on the slip rings 55 located on both sides of the switching unit. The locking unit... The system includes a locking rod 57, which slides through the horizontal plate of the n-shaped frame 56 and the side wall of the buffer cylinder 47. The locking rod 57 is inserted into a limiting hole radially opened in the end cap to form a lock. A second return spring 58 and a baffle 59 are sleeved on the locking rod inside the n-shaped frame 56. The baffle 59 is fixedly connected to the locking rod 57. The two ends of the second return spring 58 are respectively fixedly connected to the baffle 59 and the horizontal plate of the n-shaped frame 56. A wedge-shaped contact block 52 is fixedly installed at the top of the n-shaped frame 56, and the locking rod 57 slides through the wedge-shaped contact block 52. When no external force is applied, under the action of the second return spring 58, the locking rod 57 extends into the buffer cylinder 47 and into the radial limiting hole of the end cover 49 to form a fixed connection; the axial actuator 20 pushes and pulls, causing the buffer cylinder 47 and the end cover 49 to move together. When the test device experiences torsional overshoot, the locking rod 57 of the locking unit is triggered to disengage from the end cover 49. The end cover 49 driven by the axial actuator 20 will move inside the buffer cylinder 47, avoiding direct action on the bellows specimen 14 which is subjected to overshoot damage. At the same time, it provides time to cut off the power supply, further ensuring the safety of the test device.

[0032] Furthermore, the switching unit includes a housing 53, which is fixedly mounted on the convex arc segment of the slip ring 55. A U-shaped frame 62 is slidably disposed within a guide groove 66 inside the housing 53. The sliding direction of the U-shaped frame 62 is radially arranged along the slip ring 55. A third return spring 67 is installed at the bottom of the U-shaped frame 62. The top end of the U-shaped frame 62 extends through to the top of the housing 53. A second hinge 61 is fixedly mounted at the top end of the housing 53 between the two ends of the U-shaped frame 62. The other end of the second hinge 61 is fixedly connected to a connecting element. The contact block 54 has a limiting groove 63 inside corresponding to the moving end of the U-shaped frame 62; a second through groove 65 is opened on the housing 53, with the opening of the second through groove 65 facing the rotation direction of the slip ring 55; a lowering groove 64 is opened on the U-shaped frame corresponding to the second through groove 65; under the action of the third return spring 67, the bottom of the lowering groove 64 coincides with the top of the second through groove 65; when the wedge-shaped contact block 52 extends into the lowering groove 64, the U-shaped frame 62 descends and disengages from the limiting groove 63.

[0033] Under the action of the third return spring 67, both ends of the U-shaped frame 62 are pushed into the limiting groove 63, so that the contact block 54 and the housing 53 form a whole; when the U-shaped frame 62 disengages from the limiting groove 63 and retracts into the housing 53, the contact block 54 will rotate under the action of the second hinge 61; wherein, the dimensions of the contact block 54, the U-shaped frame 62 and the second hinge 61 are set according to the actual situation, and the attached drawings of this application are for principle reference; Furthermore, the coupling mechanism includes guide rods 45. Two guide rods 45 are fixedly arranged opposite each other on the end face of the base plate 46 outside the buffer cylinder 47. A receiving cavity is provided at the end of the transmission shaft 24 away from the specimen 14. A coupling end cover 39 is fixedly provided at the end of the receiving cavity. An arc-shaped guide groove 40 is provided on the coupling end cover 39 corresponding to the guide rods 45. The guide rods 45 enter the receiving cavity after passing through the arc-shaped guide groove 40. A limiting block 41, a gap spring 42, a washer 43 and a nut 44 are sequentially sleeved on the guide rods 45 inside the receiving cavity. The nut 44 is screwed to the threaded end of the guide rod 45, so that the coupling end cover 39 is tightly fitted and rotates with the base plate 46. Several cylindrical rollers 48 are arranged around the circumference on the coupling end cover 39 near the base plate 46. Several cylindrical rollers are arranged on the end face of the limiting block 41 near the coupling end cover 39. The coupling end cover 39 is tightly fitted to the base plate 46 by the cooperation of the nut 44 and the gap spring 42, ensuring the push-pull power output of one end of the axial actuator 20; the setting of the cylindrical rollers allows the coupling end cover 39 to rotate freely between the base plate 46 and the limit block 41.

[0034] In this invention, the coupling mechanism enables stable and reliable transmission of the drive shaft 24 when simultaneously bearing axial push-pull force and circumferential torsional torque. The cylindrical roller 48 transforms the traditional sliding friction between the coupling end cover 39 and the limiting block 41 into low-resistance rolling friction, greatly reducing friction jamming and heat generation during high-frequency reciprocating torsion. At the same time, the preload of the gap spring 42, combined with the axial limiting of the nut 44, ensures that the coupling end cover 39 and the base plate 46 maintain a tight fit while allowing for free and smooth circumferential rotation, avoiding the impact vibration caused by excessive gaps and the jamming caused by interference fits in traditional fixed connections. More importantly, the precise constraint of the arc-shaped guide groove 40 on the coupling end cover 39 ensures that the rotation trajectory of the drive shaft 24 always remains on the preset circumferential path, effectively preventing radial offset and swaying during torsional loading. This ensures that the bellows specimen 14 bears a pure axial and torsional composite load without additional bending moment, significantly improving the accuracy and reliability of the test data.

[0035] Furthermore, a triggering component is provided between the coupling mechanism and the limiting component. The triggering component includes a ring 35, which is rotatably fitted onto the support sleeve 26. Three arc-shaped through grooves 34 are spaced apart along the circumference on the support sleeve 26. Three arc-shaped protrusions 37 are formed on the inner wall of the ring 35 extending towards the center. The arc length of the arc-shaped protrusions 37 is less than that of the arc-shaped through grooves 34. A second spline is provided on each of the arc-shaped protrusions 37. A second spline groove 36 is provided on the outside of the drive shaft 24 corresponding to the second spline. The spline is slidably installed inside the second spline groove 36, and the drive shaft 24 drives the ring sleeve 35 to rotate. Several contact rods 38 are fixed on the outer circumferential surface of the ring sleeve 35, and the contact rods 38 extend between the two contact blocks 54. When the device experiences torque overshoot, causing the drive shaft 24 to deflect excessively, it drives the ring sleeve 35 and the contact rods 38 to rotate together. The contact rods 38 push the contact blocks 54 and the slip ring 55 to move together, triggering the switching unit. This causes the locking rod 57 in the locking unit to disengage from the end cover 49, providing a safe movement space for the axial actuator 20.

[0036] Furthermore, a transverse track is provided inside the first frame 17, and a second frame 18 is slidably installed on the transverse track. A transverse actuator 19 is connected to one side of the second frame 18 to apply a transverse load, which works in conjunction with the axial actuator 20 or the torsional actuator 21 to simulate various stress states of the corrugated pipe on the crossbar of an arch bridge.

[0037] In this invention, the first cylinder 13 and the second cylinder 16 drive the support seat 12 to change angles, achieving tilting and coaxial adjustment. Combined with the displacement measurement component, strain measurement component, and mechanical parameter measurement component of the measuring element 15, a system for simulating and evaluating the load-bearing state of corrugated pipes is constructed. This system can accurately reproduce the actual tilt angle and composite load state of the corrugated steel pipe in an arch bridge structure. The axial actuator 20, torsional actuator 21, and lateral actuator 19 work collaboratively, independently or in combination, to apply various load forms such as axial push-pull, circumferential torsion, and lateral displacement, realistically simulating the service environment of the corrugated steel pipe under the coupled effects of traffic loads, temperature changes, and foundation settlement. The measuring element 15 records the displacement, strain, and mechanical parameters of the corrugated pipe specimen 14 in real time, plotting force-displacement hysteresis curves and torque-angle hysteresis curves to comprehensively evaluate the load-bearing capacity, deformation characteristics, energy dissipation capacity, and fatigue life of the corrugated pipe, providing reliable experimental data support for the design optimization, safety assessment, and maintenance decisions of corrugated steel pipe arch bridges.

[0038] Further, the measuring component 15 includes a displacement measuring assembly, a strain measuring assembly, and a mechanical parameter measuring assembly; the displacement measuring assembly includes an axial displacement sensor, a torsional angle sensor, and a lateral displacement sensor; the axial displacement sensor is fixedly mounted on the side bracket of one support base 12, and the measuring rod is connected to the end flange of the bellows specimen 14 at one end of another support base 12, with the measuring direction parallel to the axis of the drive shaft 24, used to monitor the axial expansion and contraction of the bellows specimen 14 when the axial actuator 20 applies a push-pull force; the torsional angle sensor is coaxially connected to the drive shaft 24 through a coupling, and the sensor mounting base is mounted on the support plate 11, used to monitor the circumferential torsional angle of the drive shaft 24 and the bellows specimen 14 in real time; the lateral displacement sensor is fixed on the support plate 11 through a bracket, located in the middle position between the two sets of support bases 12, and measures the lateral deformation of the middle part of the bellows specimen 14 under the action of the lateral actuator 19; The strain measurement assembly includes several resistance strain gauges, distributed along the axial direction of the bellows specimen 14 at three key sections: the fixed end, the middle, and the movable end. Each section is arranged at four circumferential angles: 0°, 90°, 180°, and 270°. Simultaneously, longitudinal and circumferential strain gauges are attached at the crests and troughs of the bellows specimen 14, respectively. The longitudinal strain gauges measure the tensile and compressive strain in the axial direction of the bellows specimen 14, reflecting the stress caused by the axial load applied by the axial actuator 20. The circumferential strain gauges measure the strain in the circumferential direction of the bellows specimen 14. The strain gauges reflect the circumferential stress caused by the torsional load applied by the torsional actuator 21. The crests and troughs are the locations of geometrical abrupt changes in the bellows specimen 14, where stress concentration is obvious. By comparing the strain differences between the crests under tension and the troughs under compression, the stress distribution law is comprehensively evaluated, and the initial location of fatigue failure is predicted. The strain gauges are connected to the data acquisition system through leads to monitor the stress and strain distribution and variation law at different locations of the bellows specimen 14 under combined load, and to evaluate the load-bearing capacity, fatigue life, and failure mode of the bellows specimen 14. The mechanical parameter measurement components include an axial force sensor, a torque sensor, and a lateral force sensor. The axial force sensor is integrated at the connection between the axial actuator 20 and the drive shaft 24 to measure the magnitude of the axial push-pull force in real time. The torque sensor is installed at the output end of the torsion actuator 21 to monitor the circumferential torque value and serve as the basis for judging torsional overshoot. The lateral force sensor is integrated inside the lateral actuator 19 to record the lateral load. All measurement components are synchronously acquired through a data acquisition system, and displacement, strain, and mechanical parameters are used in combination to plot force-displacement hysteresis curves and torque-angle hysteresis curves to comprehensively evaluate the load-bearing capacity and deformation characteristics of the bellows specimen 14.

[0039] It should be noted that both the first cylinder 13 and the second cylinder 16 are connected to an external air source. The specific connection method and operation method are existing technologies and will not be described in detail.

[0040] The axial actuator 20 can be a high-performance electro-hydraulic servo actuator, which is commercially available and belongs to the prior art. The principle will not be elaborated.

[0041] Working principle: During the experiment, firstly, based on the actual tilt angle of the corrugated pipe specimen 14 in the arch bridge structure, the first cylinder 13 and the second cylinder 16 on the two support seats 12 were used to complete the coaxial adjustment, accurately simulating the actual load-bearing posture of the corrugated pipe; then, the corrugated pipe specimen 14 was installed on the drive shaft 24 of the two support seats 12 through the flange, ensuring that it was firmly fixed and the axis was aligned; then, the displacement measurement component, strain measurement component and mechanical parameter measurement component were installed at the designated positions of the device and on the key sections of the corrugated pipe specimen 14, respectively, to complete the arrangement of the measurement system. When the corrugated pipe specimen 14 is subjected to axial and circumferential combined loading test, the axial actuator 20 and the torsional actuator 21 are activated to work together. The axial actuator 20 generates axial push-pull force to simulate the axial force of the arch bridge, and the torsional actuator 21 generates circumferential torsional torque through the meshing transmission of the rack 22 and the arc-shaped tooth 23. The displacement, strain and mechanical parameters of the corrugated pipe specimen 14 are recorded in real time through the measuring device 15, and the force-displacement hysteresis curve and torque-angle hysteresis curve are plotted to comprehensively evaluate the load-bearing performance, deformation characteristics and energy dissipation capacity of the corrugated pipe specimen 14. However, during repeated loading tests, when the control system of the torsion actuator 21 misjudges due to sensor drift or signal interference, it may incorrectly output a torsion command that exceeds the preset range, causing the transmission shaft 24 to exceed the normal torsion angle limit and resulting in command overshoot due to command loss of control. Alternatively, due to the inherent gap of the meshing structure between the rack 22 and the arc tooth 23, the gap gradually accumulates during repeated rotation, and the gap continues to increase, which will produce a "false position" phenomenon, causing the torsion actuator 21 to rotate more than the preset angle. In severe cases, the rack 22 and the arc tooth 23 may even disengage. The torsional inertia causes the transmission shaft 24 to rotate excessively, forming a torsion overshoot phenomenon. At this time, the axial actuator 20 is still applying axial push and pull force. The combined effect of axial load and excessive torsion will cause serious damage to the bellows specimen 14, resulting in test failure and destruction of the valuable specimen.

[0042] This application innovatively designs a torsional overshoot protection mechanism. Through the linkage of components such as the ring sleeve 35, contact rod 38, contact block 54, slip ring 55, U-shaped frame 62 and locking rod 57, when the torsional angle or torque exceeds the set threshold, the protection mechanism automatically cuts off the load transmission path of the axial actuator 20, promptly stops the test and protects the safety of the equipment and the bellows specimen 14, effectively reducing the possibility of serious consequences caused by torsional overshoot, and ensuring the reliable operation of the test device and the rational utilization of specimen resources.

[0043] When the bellows specimen 14 is subjected to axial and circumferential composite loading test, the drive shaft 24 simultaneously realizes reciprocating movement along the axis and rotational movement around the axis; the rack 22 at the output end of the torsion actuator 21 precisely meshes with the arc-shaped tooth 23, driving the third sleeve 31 to generate circumferential rotation. The third sleeve 31 reliably transmits the torsion motion to the drive shaft 24 through the spline connection structure formed by the first spline groove 32 and the first spline 33. At the same time, the coupling end cover 39 fixedly connected to the drive shaft 24 rotates synchronously. During rotation, due to the coordinated limiting effect of the limiting block 41, nut 44 and guide rod 45, the coupling end cover 39 is precisely constrained to run on the circumferential trajectory planned by the arc-shaped guide groove 40, realizing controlled circumferential rotational motion; in particular, the cylindrical roller 48 configured between the limiting block 41 and the coupling end cover 39 cleverly transforms traditional sliding friction into low-resistance rolling friction, greatly reducing the friction loss of the contact surface and enhancing the motion stability and durability of the structure; Through the precise cooperation of components such as nut 44, gap spring 42, guide rod 45 and limit block 41, it is ensured that the coupling end cover 39 and the base plate 46 are tightly fitted without axial movement, and can also freely and smoothly achieve circumferential rotation, thereby stably outputting a composite load of axial push-pull and circumferential torsion.

[0044] When the bellows specimen 14 was subjected to a combined axial and circumferential loading test, rotational overshoot occurred. When the third sleeve 31 rotates excessively, it drives the drive shaft 24 and the coupling end cover 39 to rotate excessively together through the spline connection, entering the response stage of the torsional overshoot protection mechanism. At this time, the ring sleeve 35, which is rotated outside the support sleeve 26, rotates excessively synchronously under the action of the second spline of the arc-shaped protrusion 37 and the second spline groove 36. The contact rod 38 fixedly installed on the ring sleeve 35 gradually contacts and pushes the contact block 54 during the excessive rotation, thus activating the first-level response of the protection mechanism. Under the preload of the third return spring 67, the end of the U-shaped frame 62 remains in the preparatory state of extending into the limiting groove 63. At this time, the housing 53, the contact block 54, and the slip ring 55 are connected by bolts to form a rigid integrated structure. Under the continuous push of the contact rod 38, the entire assembly rotates circumferentially around the axis of the buffer cylinder 47. When the slip ring 55 rotates to a preset angle with the overall structure, the pre-set convex arc segment on the slip ring 55 precisely enters the bottom of the baffle 59. The wedge-shaped inclined surface of the convex arc segment generates an upward component force on the baffle 59, which vertically lifts the baffle 59 and the locking rod 57 together, so that the locking rod 57 completely disengages from the locking hole of the end cover 49, releasing the load transmission connection between the axial actuator 20 and the drive shaft 24. At this time, the convex arc segment of the slip ring 55 forms a stable lifting support for the baffle 59. The axial push-pull stroke that was originally directly acting on the bellows specimen 14 is released into the internal space of the buffer cylinder 47, preventing the axial load from continuing to be applied to the bellows specimen 14 that has experienced rotational overshoot. At the same time, it provides valuable buffer time for the control system to stop, which is conducive to triggering the automatic control switch or the manual emergency stop switch, significantly reducing the risk of damage to the equipment and the bellows specimen 14 due to overshoot.

[0045] Meanwhile, as the slip ring 55 continues to rotate, the inclined guide surface of the fixed wedge-shaped contact 52 gradually extends into the lowering groove 64 of the U-shaped frame 62. The progressive wedge structure of the wedge-shaped contact 52 generates a thrust on the U-shaped frame 62 along the compression direction of the third return spring 67, driving the U-shaped frame 62 to overcome the spring preload and move towards the direction of the third return spring 67. When the U-shaped frame 62 moves to the set position, the horizontal platform section at the bottom of the wedge-shaped contact 52 precisely engages with the second through groove 65 to form a stable snap-fit, reliably locking the U-shaped frame 62 in the disengaged position, so that the end of the U-shaped frame 62 completely disengages from the limiting groove 63 and enters the guide groove 66, realizing the second-level mechanical locking of the protection mechanism. With the second hinge 61 giving the contact block 54 the motion property of free swinging and rotation, the contact block 54 can flexibly swing and form a clearance space in the direction of the continued movement of the contact rod 38, avoiding rigid jamming and continuous squeezing between the contact rod 38 and the contact block 54, increasing the movement stroke and fault tolerance range of the protection mechanism, reducing the impact damage caused by rigid collision between components, protecting the integrity of each part of the protection mechanism, and ensuring that the protection device can still operate reliably in multiple overshoot events.

[0046] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that all related improvements to the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A hysteresis test device for corrugated steel pipe under axial tension, compression and torsional load conditions, comprising two sets of support seats (12) installed at relative intervals on a support plate (11), a corrugated pipe specimen (14) installed between the two sets of support seats, and a measuring element (15) installed on the specimen (14), characterized in that, The bottoms of the two sets of support seats (12) are hinged to the support plate (11) via pivots. The pivot moving side of the support seat (12) is hinged to the support plate (11) via a first cylinder (13) to adjust the tilt angle of the support seat (12). An opening with a vertical slide is provided on the support seat (12). A first frame (17) is slidably installed in the slide. A second cylinder (16) is installed at the bottom of the first frame (17) to adjust the lifting height. The first frame (17) is equipped with an internal cylinder. The actuation mechanism includes an axial actuator (20), a torsional actuator (21), and a drive shaft (24). One end of the drive shaft (24) is fixedly connected to the specimen (14) via a flange, and the other end of the drive shaft (24) is connected to the axial actuator (20) via a coupling mechanism. The circumferential direction of the drive shaft (24) is connected to the torsional actuator (21) via a sliding torsional mechanism. A torsional overshoot protection mechanism is provided outside the coupling mechanism to cut off the applied axial load in time when torsional overshoot occurs.

2. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 1, characterized in that, The sliding torsion mechanism includes a first sleeve (25), a second sleeve (27), and a third sleeve (31). The third sleeve (31) is slidably sleeved on the drive shaft (24). The third sleeve (31) and the drive shaft (24) slide relative to each other while maintaining synchronous rotation through a spline structure. The second sleeve (27) is rotatably sleeved on the outside of the third sleeve (31). The two ends of the second sleeve (27) extend radially toward the center to form an outer edge, which restricts the axial movement of the third sleeve (31). A through groove (30) is opened on one side of the second sleeve (27). An arc-shaped tooth (23) is fixed on the outer surface of the third sleeve (31) inside the through groove (30). The second sleeve (27) is fixedly installed inside the frame through a connecting seat (28). A torsion actuator (21) is fixed inside the frame. The output end of the torsion actuator (21) is connected to a rack (22). The rack (22) meshes with the transmission arc-shaped tooth (23). A first sleeve (25) is movably fitted onto the drive shaft (24) near one end of the bellows specimen (14), and the first sleeve (25) is fixed inside the frame by the first bracket (29).

3. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 2, characterized in that, A support sleeve (26) is movably fitted at the end of the drive shaft (24) away from the bellows. The outer periphery of the support sleeve (26) is fixedly connected to the frame through a second bracket. A buffer cylinder (47) is slidably fitted inside the support sleeve (26). The buffer cylinder (47) is connected to the drive shaft (24) through a coupling mechanism. An end cap (49) is slidably installed at the other end of the buffer cylinder (47). The end cap (49) is detachably installed at the end of the buffer cylinder (47). The radial direction of the end cap (49) is detachably fixedly connected to the buffer cylinder (47) through a limiting component. An axial actuator (20) is fixedly connected to the outer end of the end cap (49). The axial actuator (20) is fixed inside the frame.

4. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 3, characterized in that, The inner wall of the buffer cylinder (47) has an axial groove (50), and a protruding key (51) is provided on the radial outer periphery of the end cap (49). The end cap (49) slides inside the buffer cylinder (47), and the protruding key (51) is slidably installed in the groove (50). A keyway structure is provided between the inner wall of the buffer cylinder (47) and the support sleeve (26) to facilitate the directional sliding of the buffer cylinder (47). A sliding groove is provided on the inner wall of the support sleeve (26), and a protruding key is provided on the outer wall of the buffer cylinder (47) corresponding to the sliding groove.

5. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 3, characterized in that, The limiting assembly includes a slip ring (55) and an array of n-shaped frames (56) fixedly arranged on the outer periphery of the end of the buffer cylinder (47). A locking unit is provided on the n-shaped frames (56). The slip ring (55) passes between two legs of several n-shaped frames (56). The slip ring (55) rotates circumferentially. Several concave arc segments are provided on the slip ring (55) corresponding to the n-shaped frames (56), and convex arc segments are formed between adjacent concave arc segments. A switching unit is fixed on the convex arc segment. Avoidance grooves (60) are provided on the slip rings (55) located on both sides of the switching unit. The locking unit includes a locking rod (57). The locking rod (57) slides through the horizontal plate of the n-shaped frame (56) and the side wall of the buffer cylinder (47). The locking rod (57) is inserted into the limiting hole radially opened in the end cover to form a lock. A second return spring (58) and a baffle (59) are sleeved on the locking rod inside the n-shaped frame (56). The baffle (59) is fixedly connected to the locking rod (57). The two ends of the second return spring (58) are fixedly connected to the baffle (59) and the horizontal plate of the n-shaped frame (56) respectively. A wedge-shaped contact block (52) is fixedly installed at the top of the n-shaped frame (56). The locking rod (57) slides through the wedge-shaped contact block (52).

6. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 5, characterized in that, The switching unit includes a housing (53), which is fixed on the convex arc segment of the slip ring (55). A U-shaped frame (62) is slidably arranged in a guide groove (66) inside the housing (53). The sliding direction of the U-shaped frame (62) is arranged radially along the slip ring (55). A third return spring (67) is installed at the bottom of the U-shaped frame (62). The top end of the U-shaped frame (62) extends through to the top of the housing (53). A second hinge (61) is fixed at the top end of the housing (53) between the two ends of the U-shaped frame (62). A connecting block is fixed at the other end of the second hinge (61). 54), the inside of the contact block (54) is provided with a limiting groove (63) corresponding to the moving end of the U-shaped frame (62); a second through groove (65) is provided on the housing (53), the opening of the second through groove (65) faces the rotation direction of the slip ring (55), a lowering groove (64) is provided on the U-shaped frame corresponding to the second through groove (65), under the action of the third return spring (67), the bottom of the lowering groove (64) coincides with the top of the second through groove (65); when the wedge-shaped contact block (52) extends into the lowering groove (64), the U-shaped frame (62) descends and disengages from the limiting groove (63).

7. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 3, characterized in that, The coupling mechanism includes guide rods (45). Two guide rods (45) are fixedly mounted opposite each other on the end face of the bottom plate (46) outside the buffer cylinder (47). A receiving cavity is provided at the end of the transmission shaft (24) away from the specimen (14). A coupling end cap (39) is fixedly mounted at the end of the receiving cavity. An arc-shaped guide groove (40) is provided on the coupling end cap (39) corresponding to the guide rods (45). The guide rods (45) pass through the arc-shaped guide groove (40) and enter the receiving cavity, and are located inside the receiving cavity. A limiting block (41), a gap spring (42), a washer (43), and a nut (44) are sequentially fitted onto the guide rod (45). The nut (44) is screwed to the threaded end of the guide rod (45), so that the coupling end cover (39) and the base plate (46) are tightly fitted and rotated. Several cylindrical rollers (48) are arranged along the circumference on the coupling end cover (39) near the base plate (46), and several cylindrical rollers are arranged on the end face of the limiting block (41) near the coupling end cover (39).

8. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 7, characterized in that, A triggering component is provided between the coupling mechanism and the limiting component. The triggering component includes a ring sleeve (35), which is rotatably sleeved on the support sleeve (26). Three arc-shaped through grooves (34) are opened at intervals along the circumference on the support sleeve (26). Three arc-shaped protrusions (37) are formed on the inner wall of the ring sleeve (35) extending towards the center. The arc length of the arc-shaped protrusions (37) is less than that of the arc-shaped through grooves (34). A second spline is provided on each of the arc-shaped protrusions (37). A second spline groove (36) is opened on the outside of the drive shaft (24) corresponding to the second spline. The second spline is slidably installed. Inside the second spline groove (36), the drive shaft (24) drives the ring sleeve (35) to rotate; several contact rods (38) are fixed on the outer circumferential surface of the ring sleeve (35), and the contact rods (38) extend between the two contact blocks (54); when the device experiences torque overshoot and causes the drive shaft (24) to deflect excessively, it drives the ring sleeve (35) and the contact rods (38) to rotate together, and the contact rods (38) push the contact blocks (54) and the slip ring (55) to move together to trigger the switching unit, so that the locking rod (57) in the locking unit is disengaged from the end cover (49), providing a safe movement space for the axial actuator (20).

9. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 1, characterized in that, The first frame (17) is provided with a transverse track, and the second frame (18) is slidably installed on the transverse track. One side of the second frame (18) is connected to a transverse actuator (19) for applying a transverse load, which works in conjunction with an axial actuator (20) or a torsional actuator (21) to simulate various stress states of the corrugated pipe on the crossbar of an arch bridge.

10. The hysteresis test apparatus for corrugated steel pipes under axial tension, compression, and torsional bearing conditions according to claim 1, characterized in that, The measuring component (15) includes a displacement measuring component, a strain measuring component, and a mechanical parameter measuring component; the displacement measuring component includes an axial displacement sensor, a torsion angle sensor, and a lateral displacement sensor; the strain measuring component includes several resistance strain gauges, which are distributed along the axial direction of the bellows specimen (14) on three key sections: the fixed end, the middle section, and the movable end, with longitudinal strain gauges and circumferential strain gauges attached at the crest and trough positions, respectively; the mechanical parameter measuring component includes an axial force sensor, a torque sensor, and a lateral force sensor.

Images