Test method for two-way loading test device of large cantilever steel-concrete composite beam

Abstract

This invention relates to a test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam, comprising a transversely arranged large cantilever steel-concrete composite beam, a mid-span loading subsystem positioned at the mid-span of the large cantilever steel-concrete composite beam, and a non-mid-span loading subsystem positioned above the remaining areas of the large cantilever steel-concrete composite beam. The non-mid-span loading subsystem includes at least one pair of vertical loading devices. When the large cantilever steel-concrete composite beam is under negative bending moment stress, the mid-span loading subsystem includes an off-center loading device positioned above and below the large cantilever steel-concrete composite beam under negative bending moment stress, and a mid-span lifting device. When the large cantilever steel-concrete composite beam is under positive bending moment stress, the mid-span loading subsystem includes a mid-span weight loading device positioned on the large cantilever steel-concrete composite beam under positive bending moment stress, and an off-center loading device positioned above the large cantilever steel-concrete composite beam under positive bending moment stress. This invention has a simple structure and reasonable design, and can accurately simulate the positive and negative bending moment stress state and bidirectional live load action, solving the problem that existing test techniques are unable to realistically simulate the bidirectional live load action of large cantilever structures under positive and negative bending moment stress states.

Description

Technical Field

[0001] This invention relates to a test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam. Background Technology

[0002] Large cantilever steel-concrete composite beams are increasingly widely used in modern urban bridge construction due to their excellent mechanical and aesthetic properties and the provision of ample under-bridge space. The core mechanical characteristic of this type of structure lies in the significant negative bending moment generated at the cantilever root under transverse live loads (such as eccentric vehicle loads) on its large cantilever slab; simultaneously, under longitudinal live loads, the main longitudinal beams bear positive bending moments at mid-span and negative bending moments at supports. Therefore, the structure is actually under a complex stress state of coupled longitudinal and transverse loads. The concrete bridge deck, especially in the negative bending moment zone, is highly susceptible to cracking under bidirectional tensile stress, becoming a key issue restricting the structure's durability and safety.

[0003] Currently, experimental research methods for large cantilever structures still largely follow or borrow from the testing methods of traditional composite beams. Traditional structural testing devices mostly employ unidirectional loading methods, such as conducting only longitudinal bending tests or transverse loading tests, which makes it difficult to realistically reproduce their unique and complex stress conditions. Furthermore, in terms of crack monitoring, existing technologies mostly rely on external observations or traditional strain gauges, making it difficult to achieve real-time monitoring of the initiation of microcracks inside the concrete and their propagation path under bidirectional stress conditions.

[0004] Patent document CN118758476A discloses a "structural stress detection device for a steel cantilever beam using a moving trolley," which simulates the tensile stress on the steel cantilever beam under test using a gravity trolley. Although this device attempts to improve the realism of the simulation, its loading method essentially still focuses on unidirectional (longitudinal) moving loads, and cannot simultaneously apply lateral loads to reproduce the most unfavorable bending moment state at the root of the large cantilever, nor does it address the real-time monitoring of the crack development pattern of the concrete bridge deck under bidirectional stress.

[0005] Patent document CN200510031429.8 discloses a "steel-concrete composite spine beam with large cantilever corrugated steel web cantilever beam", which focuses on the lateral force of the large cantilever: the patent improves the lateral force performance and prestressing efficiency of the bridge deck by using corrugated steel web cantilever beam, but its invention content does not mention the need to simulate or test its performance under complex bidirectional load coupling.

[0006] In terms of composite stress, patent document CN108051162A discloses a "torsion test device for concrete-steel truss composite beam". Although the device can test the torsional performance of composite beams with specific cross-sectional forms, its loading method is limited to the single application of torque, and it cannot simultaneously simulate the working condition of a large cantilever composite beam under positive and negative bending moment stress while bearing longitudinal and transverse live loads.

[0007] In summary, existing patents and testing technologies have the following shortcomings: 1. There is a lack of testing equipment capable of simultaneously applying longitudinal and transverse loads, making it impossible to realistically simulate the bidirectional stress conditions faced by large cantilever composite beams in actual operation, especially the complex stress state at the cantilever root under the coupled action of transverse wheel loads and longitudinal bending moments; 2. In simulating negative bending moments, traditional methods often employ inverted loading, resulting in boundary conditions that differ from actual conditions, and they cannot simultaneously apply live loads in other directions while applying pre-negative bending moments; 3. There is a lack of effective monitoring methods for real-time, three-dimensional perception of crack initiation and propagation in concrete bridge decks under bidirectional stress. In particular, there is a lack of technical solutions for identifying and monitoring crack propagation directions (longitudinal or transverse), which is crucial for evaluating the service performance of large cantilever bridge decks. Summary of the Invention

[0008] The present invention improves upon the above-mentioned problems by providing a test method for a bidirectional stress test device for large cantilever steel-concrete composite beams, which can accurately simulate the positive and negative bending moment stress state and bidirectional live load action, thus solving the problem that existing test techniques cannot realistically simulate the simultaneous bidirectional live load action of large cantilever structures under positive and negative bending moment stress states.

[0009] The present invention is constructed as follows: it includes a transversely arranged large cantilever steel-concrete composite beam, a mid-span loading subsystem located at the mid-span of the large cantilever steel-concrete composite beam, and a non-mid-span loading subsystem located above the remaining areas of the large cantilever steel-concrete composite beam. The non-mid-span loading subsystem includes at least one pair of vertical loading devices. When the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under negative bending moment, the mid-span loading subsystem includes an off-center loading device and a mid-span lifting device respectively located above and below the large cantilever steel-concrete composite beam under negative bending moment. When the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under positive bending moment, the mid-span loading subsystem includes a mid-span weight loading device located on the large cantilever steel-concrete composite beam under positive bending moment and an off-center loading device located above the large cantilever steel-concrete composite beam under positive bending moment.

[0010] Furthermore, two vertical loading devices are provided, which are symmetrically arranged on the webs on both sides of the large cantilever steel-concrete composite beam. Each vertical loading device includes a loading reaction frame A, a vertical driving device, a distribution beam, and two force transmission supports A arranged sequentially from top to bottom. The two force transmission supports are respectively located in front of and behind the distribution beam. The vertical driving device is used to drive the distribution beam and the force transmission supports A to rise and fall.

[0011] Furthermore, the off-center loading device includes a loading reaction frame B, an off-center loading drive device, and a force transmission support B arranged sequentially from top to bottom. The off-center loading drive device is used to drive the force transmission support B to move up and down. The force transmission support B is eccentrically mounted on the large cantilever steel-concrete composite beam.

[0012] Furthermore, the mid-span lifting device includes a mid-span jack base below the large cantilever steel-concrete composite beam under negative bending moment stress, a support B set on the mid-span jack base, multi-layer thin pads A and B, and mid-span jacks respectively set at the front and rear of the mid-span jack base. The multi-layer thin pads A are installed at the telescopic end above the mid-span jacks. The lower surface of the mid-span jacks is lower than the upper surface of the mid-span jack base. After the mid-span jacks lift the large cantilever steel-concrete composite beam upwards, the multi-layer thin pads B are added to the gap between the large cantilever steel-concrete composite beam and the support B. Finally, the mid-span jacks are removed.

[0013] Furthermore, the mid-span weight loading device includes two upper crossbeams disposed on the upper surface of the large cantilever steel-concrete composite beam under positive bending moment stress, two lower crossbeams disposed below the large cantilever steel-concrete composite beam under positive bending moment stress, and two connecting longitudinal beams disposed between the front and rear ends of the two lower crossbeams respectively. The two upper crossbeams are perpendicular to the large cantilever steel-concrete composite beam under positive bending moment stress and symmetrically arranged at the mid-span of the large cantilever steel-concrete composite beam under positive bending moment stress. The upper crossbeams and lower crossbeams are connected by multiple connecting bolts. Platform plates are installed on the lower crossbeams and connecting longitudinal beams. The platform plates are used to place weights so that the large cantilever steel-concrete composite beam under positive bending moment stress is subjected to downward force at the mid-span.

[0014] Furthermore, it also includes a restraint system, which comprises a ground anchor system and two restraint beams acting on both ends of the large cantilever steel-concrete composite beam. Each restraint beam is anchored to the ground anchor system via an anchoring device. Each restraint beam includes a metal rod and a restraint steel plate fixed above the metal rod. The anchoring device includes multiple fixing screws, an end base, and supports A set on the end base. The two supports A are used to support the two ends of the large cantilever steel-concrete composite beam. The fixing screws pass through the restraint steel plate and the large cantilever steel-concrete composite beam and are connected to the ground anchor system. A fixing nut is provided at the upper end of the fixing screw.

[0015] Furthermore, the large cantilever steel-concrete composite beam includes a concrete bridge deck and a steel structure, wherein the steel structure consists of a main longitudinal beam and several cantilever beams symmetrically arranged around the axis of the main longitudinal beam. The ratio of the length of the cantilever beam to the span of the main longitudinal beam is not less than 0.3. The steel structure and the concrete bridge deck are connected by a group of studs welded to the upper flange of the steel structure.

[0016] Furthermore, it also includes a monitoring system, which includes a crack monitoring subsystem. The crack monitoring subsystem includes a piezoelectric ceramic smart aggregate sensing layer and a signal excitation and acquisition device built into the concrete bridge deck of the large cantilever steel-concrete composite beam. The piezoelectric ceramic smart aggregate sensing layer and the signal excitation and acquisition device are electrically connected. The piezoelectric ceramic smart aggregate sensing layer includes a transverse bridge sensor layer and a longitudinal bridge sensor layer arranged from top to bottom along the thickness direction of the concrete bridge deck. The transverse bridge sensor layer is mainly used to monitor transverse cracks originating from the cantilever beam, and the bridge sensor layer is mainly used to monitor longitudinal cracks originating from the bending of the longitudinal beam.

[0017] Furthermore, a test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam, when the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under negative bending moment stress, the test steps are as follows: (1) fabricate the large cantilever steel-concrete composite beam under negative bending moment stress; (2) hoist the large cantilever steel-concrete composite beam under negative bending moment stress and fix both ends of the large cantilever steel-concrete composite beam under negative bending moment stress to the constraint system; (3) install the mid-span jacking device at the mid-span position of the large cantilever steel-concrete composite beam under negative bending moment stress; 4) After the mid-span jack of the mid-span lifting device contacts the bottom of the large cantilever steel-concrete composite beam under negative bending moment stress, the mid-span jack is lifted at a constant rate to the target height △h1 to simulate the negative bending moment stress of the original bridge under normal use conditions, keeping the pressure of the mid-span jack stable. At the same time, the support B of the mid-span lifting device is quickly installed and tightened in the lifting position to form a stable stress support point. After that, the mid-span jack is unloaded, and its lifting height (△h1) can be determined by the following formula: △h1=K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target negative bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam; (6) Determine the longitudinal loading point position and the transverse loading point position. After the loading point position is determined, install the vertical loading device and the offset loading device; (7) Start the vertical loading device and the offset loading device to perform pre-loading first to eliminate structural gaps; (8) After pre-loading, start the formal loading work. After the negative bending moment load large cantilever steel-concrete composite beam and each system are working normally, the negative bending moment load large cantilever steel-concrete composite beam is formally loaded by the graded loading method. During the loading process, the mechanical state of the negative bending moment load large cantilever steel-concrete composite beam at each stage is observed and recorded. The load benchmark on which the graded loading is based is analyzed by the internal force of the actual bridge under the actual load. The basic combination internal force values ​​of its normal service limit state and bearing capacity limit state are extracted. According to the equivalent stress principle, the equivalent conversion is performed according to the model scaling ratio: P m = P p / C l 2 M u,m = M u,p / C l 3 ;q m = q p / C l ;q u,m = q u,p / C l Among them, P m For the concentrated load under normal service conditions of the scaled-down large cantilever steel-concrete composite beam, P p For the concentrated force load under normal use conditions of the original bridge, C l M is the geometric similarity constant. u,m For the ultimate bending moment of the reduced-scale large cantilever steel-concrete composite beam, M u,p The bending moment at the ultimate limit state of the original bridge's bearing capacity, q m For the distributed force load of the scaled-down large cantilever steel-concrete composite beam under normal service conditions, q p The distributed force load under the normal service condition of the original bridge, q u,m For the ultimate limit state distributed force load of the scaled-down large cantilever steel-concrete composite beam, q u,p The original bridge bearing capacity ultimate limit state distributed force load; (9) After formal loading, each level is loaded with a 10kN load. After the concrete bridge deck cracks, the load is loaded in 15kN steps to the ultimate load. When approaching the normal service state load and the bearing capacity ultimate state load, the load steps are appropriately densified. After each level of load is stable, the load needs to be held for about 10 minutes before collecting data such as strain, displacement and cracks to complete the test.

[0018] Furthermore, a test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam, when the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under positive bending moment stress, the test steps for simulating the positive bending moment stress state by using a mid-span weight loading device are as follows: (1) Install the mid-span weight loading device on the large cantilever steel-concrete composite beam under positive bending moment stress; (2) Place weights in stages on the platform plate of the weight loading device, so that the large cantilever steel-concrete composite beam under positive bending moment stress deflects downward to the target height at mid-span, so as to simulate the stress in the positive bending moment zone under the normal use state of the original bridge. The deflection height (△h2) is determined by the following formula: △h2=K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target positive bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam.

[0019] Compared with the prior art, the present invention has the following advantages: This device overcomes the problem that traditional tests are difficult to simulate large cantilever steel-concrete composite beams under positive and negative bending moment stresses and bidirectional live loads at the same time. It can monitor the crack development under bidirectional stress in real time, providing more accurate test data support for the design and optimization of large cantilever composite beams. It innovatively proposes a bidirectional stress test method that is different from the traditional stress test that focuses on unidirectional stress behavior. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a bidirectional stress test of a large cantilever steel-concrete composite beam under negative bending moment in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the simulated negative bending moment test of the support lifting of the large cantilever steel-concrete composite beam under negative bending moment in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the mid-span lifting device for a large cantilever steel-concrete composite beam under negative bending moment load according to Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the bidirectional stress on the large cantilever steel-concrete composite beam under positive bending moment in Embodiment 2 of the present invention; Figure 5 This is a schematic diagram of the simulated positive bending moment test of the large cantilever steel-concrete composite beam under positive bending moment force according to Embodiment 2 of the present invention; Figure 6 This is a schematic diagram of the large cantilever steel-concrete composite beam restraint system according to an embodiment of the present invention; Figure 7 This is a plan view of the piezoelectric ceramic smart aggregate sensing layer arrangement in Embodiment 4 of the present invention; Figure 8 This is an elevation view of the piezoelectric ceramic smart aggregate sensing layer arrangement in Embodiment 4 of the present invention; Figure 9 Schematic diagram of the connection of the crack monitoring subsystem in Embodiment 4 of the present invention; In the diagram: 11-Cantilever steel-concrete composite beam under negative bending moment; 12-Cantilever steel-concrete composite beam under positive bending moment; 21-Loading reaction frame A; 22-Vertical drive device; 23-Distribution beam; 24-Force transmission support A; 25-Multi-layer thin pad A; 26-Loading reaction frame B; 27-Force transmission support B; 28-Off-center loading drive device; 201-Upper crossbeam; 202-Lower crossbeam; 203-Connecting longitudinal beam; 204-Platform plate; 205-Connecting bolt; 31-Constraint beam; 32-Fixing bolt; 33-End base; 34-Support A; 35-Mid-span jack base; 36-Support B; 37-Mid-span jack; 38-Constraint steel plate; 41-Transverse bridge sensor layer; 42-Longitudinal bridge sensor layer; 5-Concrete bridge deck; 6-Ground anchor system. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0022] Example: Refer to Appendix Figure 1-3 As shown in Figure 6, a bidirectional stress test device for a large cantilever steel-concrete composite beam is provided, including a large cantilever steel-concrete composite beam arranged laterally, a mid-span loading subsystem arranged at the mid-span of the large cantilever steel-concrete composite beam, and a non-mid-span loading subsystem arranged above the remaining areas of the large cantilever steel-concrete composite beam. The non-mid-span loading subsystem includes at least one pair of vertical loading devices. When the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam 11 under negative bending moment, the mid-span loading subsystem includes an off-center loading device and a mid-span lifting device respectively installed above and below the large cantilever steel-concrete composite beam under negative bending moment.

[0023] When the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under negative bending moment, the test steps are as follows: (1) Fabricate the large cantilever steel-concrete composite beam under negative bending moment; (2) Hoist the large cantilever steel-concrete composite beam under negative bending moment and fix both ends of the large cantilever steel-concrete composite beam under negative bending moment to the constraint system; (3) Install the mid-span jacking device at the mid-span position of the large cantilever steel-concrete composite beam under negative bending moment; (4) When the mid-span jacking device is connected to the mid-span jacking device, the test steps are as follows: (1) Fabricate the large cantilever steel-concrete composite beam under negative bending moment; (2) Hoist the large cantilever steel-concrete composite beam under negative bending moment and fix both ends of the large cantilever steel-concrete composite beam under negative bending moment to the constraint system; (3) Install the mid-span jacking device at the mid-span position of the large cantilever steel-concrete composite beam under negative bending moment; (4) When the mid-span jacking device is connected to the mid-span jacking device, the test steps are as follows: (1) Hoist ... After the bottom of the large cantilever steel-concrete composite beam under negative bending moment stress is reached, the mid-span jacks are raised at a constant rate to the target height Δh1 to simulate the negative bending moment stress of the original bridge under normal use conditions. This maintains stable pressure on the mid-span jacks. Simultaneously, the support B of the mid-span jacking device is quickly installed and secured to the jacking position, forming a stable support point. Afterward, the mid-span jacks are unloaded. The jacking height (Δh1) can be determined using the following formula: Δh1 = K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target negative bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam; (6) Determine the longitudinal loading point position and the transverse loading point position. After the loading point position is determined, install the vertical loading device and the offset loading device; (7) Start the vertical loading device and the offset loading device to perform pre-loading first to eliminate structural gaps; (8) After pre-loading, start the formal loading work. After the negative bending moment load large cantilever steel-concrete composite beam and each system are working normally, the negative bending moment load large cantilever steel-concrete composite beam is formally loaded by the graded loading method. During the loading process, the mechanical state of the negative bending moment load large cantilever steel-concrete composite beam at each stage is observed and recorded. The load benchmark on which the graded loading is based is analyzed by the internal force of the actual bridge under the actual load. The basic combination internal force values ​​of its normal service limit state and bearing capacity limit state are extracted. According to the equivalent stress principle, the equivalent conversion is performed according to the model scaling ratio: P m = P p / Cl 2 M u,m = M u,p / C l 3 ;q m = q p / C l ;q u,m = q u,p / C l Among them, P m For the concentrated load under normal service conditions of the scaled-down large cantilever steel-concrete composite beam, P p For the concentrated force load under normal use conditions of the original bridge, C l M is the geometric similarity constant. u,m For the ultimate bending moment of the reduced-scale large cantilever steel-concrete composite beam, M u,p The bending moment at the ultimate limit state of the original bridge's bearing capacity, q m For the distributed force load of the scaled-down large cantilever steel-concrete composite beam under normal service conditions, q p The distributed force load under the normal service condition of the original bridge, q u,m For the ultimate limit state distributed force load of the scaled-down large cantilever steel-concrete composite beam, q u,p The original bridge bearing capacity ultimate limit state distributed force load; (9) After formal loading, each level is loaded with a 10kN load. After the concrete bridge deck cracks, the load is loaded in 15kN steps to the ultimate load. When approaching the normal service state load and the bearing capacity ultimate state load, the load steps are appropriately densified. After each level of load is stable, the load needs to be held for about 10 minutes before collecting data such as strain, displacement and cracks to complete the test.

[0024] In this embodiment of the invention, two vertical loading devices are provided, symmetrically arranged on both sides of the web of the large cantilever steel-concrete composite beam. Each vertical loading device includes, from top to bottom, a loading reaction frame A21, a vertical drive device 22, a distribution beam 23, and two force transmission supports A24. The two force transmission supports are respectively located below and in front of the distribution beam. The vertical drive device is used to drive the distribution beam and the force transmission supports A24 to rise and fall; the vertical drive device can be a vertical jack. The loading reaction frame A is fixed to the ground anchor system.

[0025] In this embodiment of the invention, the off-center loading device includes a loading reaction frame B26, an off-center loading drive device 28, and a force transmission support B27 arranged sequentially from top to bottom. The off-center loading drive device is used to drive the force transmission support B to move up and down. The force transmission support B is eccentrically mounted on the large cantilever steel-concrete composite beam. The off-center loading drive device can be an off-center loading jack. The loading reaction frame B is fixed to the ground anchor system.

[0026] In this embodiment of the invention, the mid-span lifting device includes a mid-span jack base 35 below the large cantilever steel-concrete composite beam under negative bending moment, a support B36 set on the mid-span jack base, multi-layer thin pads A25 and B26, and mid-span jacks 37 respectively set at the front and rear of the mid-span jack base. The mid-span jack base is convex in shape. The multi-layer thin pads A are installed on the telescopic end above the mid-span jacks. The lower surface of the mid-span jacks is lower than the upper surface of the mid-span jack base. After the mid-span jacks lift the large cantilever steel-concrete composite beam upward, the multi-layer thin pads B are added to the gap between the large cantilever steel-concrete composite beam and the support B. Finally, the mid-span jacks are removed.

[0027] In this embodiment of the invention, a constraint system is also included. The constraint system includes a ground anchor system 6 and two constraint beams 31 that act on both ends of the large cantilever steel-concrete composite beam. Each constraint beam is anchored to the ground anchor system via an anchoring device. The constraint beam includes a metal rod and a constraint steel plate 38 fixed above the metal rod. The anchoring device includes multiple fixing screws 32, an end base 33, and supports A34 set on the end base. The two supports A are used to support both ends of the large cantilever steel-concrete composite beam. The fixing screws pass through the constraint steel plate and the large cantilever steel-concrete composite beam and are connected to the ground anchor system. A fixing nut is provided at the upper end of the fixing screw.

[0028] The aforementioned fixing screws are provided in four parts. The four screws pass through the holes set in the constraint steel plate and the large cantilever steel-concrete composite beam. The upper end of the fixing screw is tightened with a nut, and the lower end is anchored to the ground anchor system. The large cantilever steel-concrete composite beam and the constraint beam are tightly connected by the four screws to prevent the large cantilever steel-concrete composite beam from warping during the mid-span pull-down and jacking process.

[0029] In this embodiment of the invention, the large cantilever steel-concrete composite beam includes a concrete bridge deck 5 and a steel structure, wherein the steel structure consists of a main longitudinal beam and several cantilever beams symmetrically arranged around the axis of the main longitudinal beam. The ratio of the length of the cantilever beam to the span of the main longitudinal beam is not less than 0.3. The steel structure and the concrete bridge deck are connected by a group of studs welded to the upper flange of the steel structure.

[0030] Example 2: Based on Example 1, the specific experimental method is as follows: (1) Fabrication of a large cantilever steel-concrete composite beam under negative bending moment: Steel is cut, welded and bolted to fabricate a steel beam system including main longitudinal beams and cantilever beams, and studs are welded at preset positions on the top plate of the steel beams. The steel mesh is tied and the piezoelectric ceramic smart aggregate is fixed on the steel mesh according to the preset layout. Then the formwork is erected, concrete is poured and cured to the design strength to form a concrete bridge deck that matches the steel beam system. The combination of steel beams and concrete bridge deck is achieved by studs to form a complete large cantilever steel-concrete composite beam under negative bending moment. (2) Install the large cantilever steel-concrete composite beam under negative bending moment: hoist the completed large cantilever steel-concrete composite beam under negative bending moment to the test site, arrange two end bases, fix the end bases to the ground anchor system, place support A on the end bases, use simple support, hoist the large cantilever steel-concrete composite beam under negative bending moment to the support A at both ends, and ensure good support contact; (3) Install the constraint system at both ends: After the negative moment load large cantilever steel-concrete composite beam 11 is installed and stabilized, place the constraint beam at the corresponding positions at both ends of the negative moment load large cantilever steel-concrete composite beam, and then symmetrically arrange the fixing screws through the reserved holes between the constraint beam and the concrete bridge deck, and extend into the ground anchor holes. Tighten the upper end of the fixing screw with a nut, and anchor the lower end to the ground anchor system to ensure that the constraint beam is tightly connected to the negative moment load large cantilever steel-concrete composite beam; (4) Install jacking device: For the large cantilever steel-concrete composite beam under negative bending moment, after the arrangement of the restraint devices at both ends is completed, install the mid-span jack at the bottom of the mid-span of the large cantilever steel-concrete composite beam under negative bending moment. The jack base is fixed to the ground anchor system. Start the mid-span jack until the top surface of the jack contacts the bottom of the large cantilever steel-concrete composite beam under negative bending moment. The top surface of the mid-span jack contacts the bottom of the large cantilever steel-concrete composite beam under negative bending moment through multiple layers of thin pads A to ensure that the contact surface is flat. (5) Lifting device: The mid-span jack is lifted at a constant rate to the target height △h1 to simulate the negative bending moment of the original bridge under normal use, keeping the pressure of the mid-span jack stable. At the same time, the support B of the mid-span jacking device is quickly installed and fastened to the jacking position to form a stable force support point. After that, the mid-span jack is unloaded. Its jacking height (△h1) can be determined by the following formula: △h1=K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target negative bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam; (6) Preliminary installation of vertical loading device and off-center loading device: According to the loading requirements, load reaction frame is arranged in the corresponding position, and the bottom of the load reaction frame is anchored and stable with the ground anchor system. According to the loading requirements, the number of jacks and the approximate arrangement position of the vertical loading device and off-center loading device are determined. The remaining strain and displacement measuring points are arranged on the large cantilever steel-concrete composite beam under negative bending moment. The connection between the built-in piezoelectric ceramic intelligent aggregate sensing layer and the signal excitation and acquisition equipment is completed. (7) Determine the location of the longitudinal loading point: In the positive bending moment zone, the load is mainly transferred to the longitudinal beams through the concrete bridge deck. This type of test focuses on the bending behavior of the main beams. Therefore, the loading point should be applied to the longitudinal beams to simulate the distribution of vehicle loads on the longitudinal main beams of the actual bridge. According to the bridge design specifications, find the most unfavorable location on the bridge deck for the standard vehicle load that generates the maximum positive bending moment, and then perform a scale conversion: Lm =L p / n, where L m L is the distance from the corresponding loading point on the test beam to the centerline of the bridge. p is the distance from the bridge centerline to the most unfavorable load on the actual bridge, and n is the scaling factor; (8) Determine the location of the transverse loading point: For a large cantilever steel-concrete composite beam under negative bending moment, in addition to the stress on the longitudinal beams, the local bending moment at the root of the cantilever beam is the focus. Therefore, in addition to the longitudinal loading on the longitudinal beams, loading must also be applied at specific locations on the cantilever beam to simulate the most unfavorable working condition of a vehicle traveling at the edge of the actual bridge cantilever beam. According to relevant specifications, find the vehicle wheel load location at the root of the actual bridge cantilever beam where the maximum negative bending moment is generated, and then perform a scale conversion: L m =L p / n, where L m L is the distance from the corresponding loading point on the test beam to the centerline of the bridge. p is the distance from the bridge centerline to the most unfavorable load on the actual bridge, and n is the scaling factor; (9) Preloading: After determining the loading point location, preload the large cantilever steel-concrete composite beam under negative bending moment to eliminate structural gaps, and check the working status of each test instrument and loading device. (10) Formal Loading: After preloading, once the normal operation of the negative moment load-bearing large cantilever steel-concrete composite beam 11 and its various systems is confirmed, formal loading of the negative moment load-bearing large cantilever steel-concrete composite beam 11 is carried out using a graded loading method. During the loading process, the mechanical state of the negative moment load-bearing large cantilever steel-concrete composite beam at each stage is observed and recorded. The load reference for graded loading is based on the analysis of the internal forces of the actual bridge under actual load, extracting the basic combination internal force values ​​of its normal service limit state and bearing capacity limit state, and performing equivalent conversion according to the model scaling ratio based on the equivalent stress principle: P m = P p / C l 2 M u,m = M u,p / C l 3 ;q m = q p / C l ;q u,m = q u,p / C l Among them, P m For the concentrated load under normal service conditions of the scaled-down large cantilever steel-concrete composite beam, P p For the concentrated force load under normal use conditions of the original bridge, C l M is the geometric similarity constant. u,mFor the ultimate bending moment of the reduced-scale large cantilever steel-concrete composite beam, M u,p The bending moment at the ultimate limit state of the original bridge's bearing capacity, q m For the distributed force load of the scaled-down large cantilever steel-concrete composite beam under normal service conditions, q p The distributed force load under the normal service condition of the original bridge, q u,m For the ultimate limit state distributed force load of the scaled-down large cantilever steel-concrete composite beam, q u,p The distributed force load represents the ultimate limit state of the original bridge's bearing capacity. (11) Test: After formal loading, a 10kN load was applied in each step. After the concrete bridge deck cracked, the load was applied in 15kN steps until the ultimate load was reached. When approaching the normal service load and the ultimate limit state load, the number of load steps was appropriately increased. After each load was stabilized, the load was held for about 10 minutes before collecting data such as strain, displacement and cracks.

[0031] Example 3: Based on Example 1 or 2, such as Figure 7-9 As shown, this embodiment 3 is basically the same as embodiment 1, except that the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam 12 under positive bending moment. The mid-span loading subsystem includes a mid-span weight loading device set on the large cantilever steel-concrete composite beam under positive bending moment and an off-center loading device set above the large cantilever steel-concrete composite beam under positive bending moment. The positive bending moment stress state is simulated by the mid-span weight loading device.

[0032] In this embodiment of the invention, the mid-span weight loading device includes two upper crossbeams disposed on the upper surface of the large cantilever steel-concrete composite beam under positive bending moment stress, two lower crossbeams disposed below the large cantilever steel-concrete composite beam under positive bending moment stress, and two connecting longitudinal beams disposed between the front and rear ends of the two lower crossbeams respectively. The two upper crossbeams are perpendicular to the large cantilever steel-concrete composite beam under positive bending moment stress and symmetrically arranged at the mid-span of the large cantilever steel-concrete composite beam under positive bending moment stress. The upper and lower crossbeams are connected by four connecting screws, which are evenly disposed between the ends of the upper and lower crossbeams on the same side. A platform plate is installed on the lower crossbeams and the connecting longitudinal beams. The platform plate is used to place weights so that the large cantilever steel-concrete composite beam under positive bending moment stress is subjected to downward force at the mid-span.

[0033] The upper and lower crossbeams are provided with reserved holes. The connecting screw passes through the reserved holes in the flanges of the lower and upper crossbeams to connect the upper and lower crossbeams together.

[0034] The test method of the bidirectional stress test device for large cantilever steel-concrete composite beams, when the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under negative bending moment stress, the test steps for simulating the positive bending moment stress state by using a mid-span weight loading device are as follows: (1) Install the mid-span weight loading device on the large cantilever steel-concrete composite beam under negative bending moment stress; (2) Place weights in stages on the platform plate of the weight loading device, so that the large cantilever steel-concrete composite beam under positive bending moment stress deflects downward to the target height at mid-span, so as to simulate the stress in the positive bending moment zone under the normal use state of the original bridge. The deflection height (△h2) is determined by the following formula: △h2=K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target positive bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam.

[0035] Example 4: Based on Examples 1, 2, and 3, as follows... Figure 9 As shown, in this embodiment of the invention, a monitoring system is also included. The monitoring system includes a strain monitoring subsystem, a displacement monitoring subsystem, and a crack monitoring subsystem installed on the large cantilever steel-concrete composite beam. The strain monitoring subsystem includes a strain gauge sensor, and the displacement monitoring subsystem includes a displacement sensor. The crack monitoring subsystem includes a piezoelectric ceramic smart aggregate sensing layer and a signal excitation and acquisition device built into the concrete bridge deck of the large cantilever steel-concrete composite beam. The piezoelectric ceramic smart aggregate sensing layer and the signal excitation and acquisition device are electrically connected. The piezoelectric ceramic smart aggregate sensing layer includes a transverse bridge sensor layer 41 and a longitudinal bridge sensor layer 42 arranged from top to bottom along the thickness direction of the concrete bridge deck. The transverse bridge sensor layer is mainly used to monitor transverse cracks originating from the cantilever beam, and the longitudinal bridge sensor layer is mainly used to monitor longitudinal cracks originating from the bending of the longitudinal beam.

[0036] The aforementioned piezoelectric ceramic smart aggregate sensing layer is composed of several piezoelectric ceramic smart aggregates and a BNC linear array. The piezoelectric ceramic material is lead zirconate titanate piezoelectric ceramic (PZT). The signal excitation and acquisition equipment includes an arbitrary waveform generator, a power amplifier, a data acquisition card, and a test terminal.

[0037] The arbitrary waveform generator, power amplifier, piezoelectric ceramic smart aggregate sensing layer, data acquisition card, and test terminal are connected via BNC cable.

[0038] The aforementioned piezoelectric ceramic smart aggregate sensing layer employs a specific arrangement: in the bidirectional load coupling region, a sensor network is arranged in two layers along the thickness direction of the concrete bridge deck. The bottom layer consists of longitudinal bridge sensors, and the top layer is a transverse bridge sensor layer. The sensor paths of the two layers form an orthogonal grid on the planar projection. The longitudinal bridge sensor layer is positioned at a certain distance from the bottom of the concrete bridge deck and is primarily used to monitor longitudinal cracks originating from the bending of the longitudinal beams. The transverse bridge sensor layer is positioned at a certain distance from the top of the bridge deck and is primarily used to monitor transverse cracks originating from the cantilever beams.

[0039] This device innovatively employs a layer of longitudinal and a layer of transverse sensors in the bidirectional load coupling region to form an intersecting sensor network for real-time monitoring of crack development in concrete bridge decks.

[0040] Unless otherwise stated, if any technical solution disclosed in this invention discloses a numerical range, then the disclosed numerical range is a preferred numerical range. Anyone skilled in the art should understand that the preferred numerical range is merely a range of numerical values ​​among many implementable values ​​that have a more obvious or representative technical effect. Because there are many numerical values, it is impossible to list them all. Therefore, this invention discloses only some numerical values ​​to illustrate the technical solutions of this invention. Furthermore, the numerical values ​​listed above should not constitute a limitation on the scope of protection of this invention.

[0041] If the terms "first" or "second" are used in this document to specify components, those skilled in the art should know that the use of "first" or "second" is merely for the purpose of distinguishing components in description, and unless otherwise stated, the above terms have no special meaning.

[0042] Meanwhile, if the present invention discloses or relates to mutually fixedly connected parts or structural components, then unless otherwise stated, fixed connection can be understood as: a fixed connection that can be detached (e.g., using bolts or screws), or a fixed connection that cannot be detached (e.g., riveting, welding). Of course, mutually fixed connections can also be replaced by an integral structure (e.g., manufactured by integral molding using a casting process) (except where it is obviously impossible to use an integral molding process).

[0043] In addition, unless otherwise stated, the terms used in any of the technical solutions disclosed in this invention to indicate positional relationships or shapes include states or shapes that are similar to, close to, or approximate with those states or shapes.

[0044] Any component provided by this invention can be assembled from multiple individual components or can be a single component manufactured by a one-piece molding process.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam, characterized in that, The bidirectional stress testing device for a large cantilever steel-concrete composite beam includes a transversely arranged large cantilever steel-concrete composite beam, a mid-span loading subsystem positioned at the mid-span of the large cantilever steel-concrete composite beam, and a non-mid-span loading subsystem positioned above the remaining areas of the large cantilever steel-concrete composite beam. The non-mid-span loading subsystem includes at least one pair of vertical loading devices. When the large cantilever steel-concrete composite beam is under negative bending moment stress, the mid-span loading subsystem includes an off-center loading device positioned above and below the large cantilever steel-concrete composite beam under negative bending moment stress, and a mid-span lifting device. When the large cantilever steel-concrete composite beam is under positive bending moment stress, the mid-span loading subsystem includes a mid-span weight loading device positioned on the large cantilever steel-concrete composite beam under positive bending moment stress, and an off-center loading device positioned above the large cantilever steel-concrete composite beam under positive bending moment stress. The test method for the bidirectional stress test device of the large cantilever steel-concrete composite beam, when the large cantilever steel-concrete composite beam is a negative bending moment large cantilever steel-concrete composite beam, the test steps are as follows: (1) Fabricate the negative bending moment large cantilever steel-concrete composite beam; (2) Hoist the negative bending moment large cantilever steel-concrete composite beam and fix both ends of the negative bending moment large cantilever steel-concrete composite beam to the constraint system; (3) Install the mid-span jacking device at the mid-span position of the negative bending moment large cantilever steel-concrete composite beam; (4) When the span After the mid-span jack of the mid-span lifting device contacts the bottom of the large cantilever steel-concrete composite beam under negative bending moment stress, the mid-span jack is lifted at a constant rate to the target height △h1 to simulate the negative bending moment stress of the original bridge under normal use conditions, maintaining stable pressure on the mid-span jack. At the same time, the support B of the mid-span lifting device is quickly installed and secured to the lifting position to form a stable stress support point. After that, the mid-span jack is unloaded, and its lifting height (△h1) can be determined by the following formula: △h1=K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target negative bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam; (6) Determine the longitudinal loading point position and the transverse loading point position. After the loading point position is determined, install the vertical loading device and the offset loading device; (7) Start the vertical loading device and the offset loading device to perform pre-loading first to eliminate structural gaps; (8) After pre-loading, start the formal loading work. After the negative bending moment load large cantilever steel-concrete composite beam and each system are working normally, the negative bending moment load large cantilever steel-concrete composite beam is formally loaded by the graded loading method. During the loading process, the mechanical state of the negative bending moment load large cantilever steel-concrete composite beam at each stage is observed and recorded. The load benchmark on which the graded loading is based is analyzed by the internal force of the actual bridge under the actual load. The basic combination internal force values ​​of its normal service limit state and bearing capacity limit state are extracted. According to the equivalent stress principle, the equivalent conversion is performed according to the model scaling ratio: P m = P p / C l 2 ; M u,m = M u,p / C l 3 ;q m = q p / C l ;q u,m = q u,p / C l ; Among them, P m For the concentrated load under normal service conditions of the scaled-down large cantilever steel-concrete composite beam, P p For the concentrated force load under normal use conditions of the original bridge, C l M is the geometric similarity constant. u,m For the ultimate bending moment of the reduced-scale large cantilever steel-concrete composite beam, M u,p The bending moment at the ultimate limit state of the original bridge's bearing capacity, q m For the distributed force load of the scaled-down large cantilever steel-concrete composite beam under normal service conditions, q p The distributed force load under normal use conditions of the original bridge, q u,m For the ultimate limit state distributed force load of the scaled-down large cantilever steel-concrete composite beam, q u,p The original bridge bearing capacity ultimate limit state distributed force load; (9) After formal loading, each level is loaded with a 10kN load. After the concrete bridge deck cracks, the load is loaded in 15kN steps to the ultimate load. When approaching the normal service state load and the bearing capacity ultimate state load, the load steps are appropriately densified. After each level of load is stable, the load needs to be held for about 10 minutes before collecting data such as strain, displacement and cracks to complete the test.

2. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, Two vertical loading devices are provided, which are symmetrically arranged on the webs on both sides of the large cantilever steel-concrete composite beam. Each vertical loading device includes a loading reaction frame A, a vertical driving device, a distribution beam, and two force transmission supports A arranged sequentially from top to bottom. The two force transmission supports are respectively located in front of and behind the distribution beam. The vertical driving device is used to drive the distribution beam and the force transmission supports A to rise and fall.

3. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, The off-center loading device includes a loading reaction frame B, an off-center loading drive device, and a force transmission support B arranged sequentially from top to bottom. The off-center loading drive device is used to drive the force transmission support B to move up and down. The force transmission support B is eccentrically mounted on the large cantilever steel-concrete composite beam.

4. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, The mid-span lifting device includes a mid-span jack base below the large cantilever steel-concrete composite beam under negative bending moment stress, a support B set on the mid-span jack base, multi-layer thin pads A and B, and mid-span jacks respectively set at the front and rear of the mid-span jack base. The multi-layer thin pads A are installed at the telescopic end above the mid-span jacks. The lower surface of the mid-span jacks is lower than the upper surface of the mid-span jack base. After the mid-span jacks lift the large cantilever steel-concrete composite beam upwards, the multi-layer thin pads B are filled into the gap between the large cantilever steel-concrete composite beam and the support B. Finally, the mid-span jacks are removed.

5. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, The mid-span weight loading device includes two upper crossbeams disposed on the upper surface of the large cantilever steel-concrete composite beam under positive bending moment stress, two lower crossbeams disposed below the large cantilever steel-concrete composite beam under positive bending moment stress, and two connecting longitudinal beams disposed between the front and rear ends of the two lower crossbeams respectively. The two upper crossbeams are perpendicular to the large cantilever steel-concrete composite beam under positive bending moment stress and are symmetrically arranged at the mid-span of the large cantilever steel-concrete composite beam under positive bending moment stress. The upper and lower crossbeams are connected by multiple connecting bolts. Platform plates are installed on the lower crossbeams and connecting longitudinal beams. The platform plates are used to place weights to make the large cantilever steel-concrete composite beam under positive bending moment stress bear downward force at the mid-span.

6. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, It also includes a restraint system, which comprises a ground anchor system and two restraint beams acting on both ends of the large cantilever steel-concrete composite beam. Each restraint beam is anchored to the ground anchor system via an anchoring device. Each restraint beam includes a metal rod and a restraint steel plate fixed above the metal rod. The anchoring device includes multiple fixing screws, end bases, and supports A set on the end bases. The two supports A are used to support the two ends of the large cantilever steel-concrete composite beam. The fixing screws pass through the restraint steel plate and the large cantilever steel-concrete composite beam and are connected to the ground anchor system. A fixing nut is provided at the upper end of the fixing screw.

7. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, The large cantilever steel-concrete composite beam includes a concrete bridge deck and a steel structure. The steel structure consists of a main longitudinal beam and several cantilever beams symmetrically arranged around the axis of the main longitudinal beam. The ratio of the length of the cantilever beam to the span of the main longitudinal beam is not less than 0.

3. The steel structure and the concrete bridge deck are connected by a group of studs welded to the upper flange of the steel structure.

8. The test method for a bidirectional stress test device for a large cantilever steel-concrete composite beam according to claim 1, characterized in that, It also includes a monitoring system, which includes a crack monitoring subsystem. The crack monitoring subsystem includes a piezoelectric ceramic smart aggregate sensing layer and a signal excitation and acquisition device built into the concrete bridge deck of the large cantilever steel-concrete composite beam. The piezoelectric ceramic smart aggregate sensing layer and the signal excitation and acquisition device are electrically connected. The piezoelectric ceramic smart aggregate sensing layer includes a transverse bridge sensor layer and a longitudinal bridge sensor layer arranged from top to bottom along the thickness direction of the concrete bridge deck. The transverse bridge sensor layer is mainly used to monitor transverse cracks originating from the cantilever beam, and the bridge sensor layer is mainly used to monitor longitudinal cracks originating from the bending of the longitudinal beam.

9. A test method using the bidirectional stress test device for a large cantilever steel-concrete composite beam as described in claim 5, characterized in that, When the large cantilever steel-concrete composite beam is a large cantilever steel-concrete composite beam under positive bending moment stress, the test steps for simulating the positive bending moment stress state using a mid-span weight loading device are as follows: (1) Install the mid-span weight loading device on the large cantilever steel-concrete composite beam under positive bending moment stress; (2) Place weights in stages on the platform plate of the weight loading device, so that the mid-span of the large cantilever steel-concrete composite beam under positive bending moment stress deflects down to the target height, in order to simulate the stress in the positive bending moment zone under the normal use state of the original bridge. The deflection height (△h2) is determined by the following formula: △h2=K·φ·(L1) 2 , where K is an empirical coefficient related to the support conditions, φ is the curvature of the target positive bending moment zone of the actual bridge under the standard combination, and L1 is the calculated span of the test beam.

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