Composite loading device and loading method for concrete i-shaped beam

Abstract

The application belongs to the technical field of bridge structure test loading device, and discloses a concrete I-shaped beam composite loading device and a loading method, which comprises a spherical hinge support, the spherical hinge support is supported at both ends of the I-shaped beam, a plurality of out-of-plane loading devices are arranged equidistantly in the axial direction of the I-shaped beam, and a vertical loading device is arranged at the midspan of the I-shaped beam; the out-of-plane loading device comprises lever arms above and below the I-shaped beam, bidirectional jacks are arranged on both sides of the I-shaped beam, the two ends of the bidirectional jacks are respectively hinged to two lever arms, and the bidirectional jacks respectively apply pressure and tension to the I-shaped beam; two distribution beams are hinged to one side of the lever arms towards the I-shaped beam, a rubber pad is connected between the pressure distribution beam and the I-shaped beam, a U-shaped swing arm is rotationally connected to the end of the tension distribution beam, the flange plate of the I-shaped beam is inserted into the U-shaped swing arm, and a rubber pad is connected between the inner side of the flange plate and the U-shaped swing arm; the spacing of the rubber pads along the axial direction and the transverse direction of the I-shaped beam is consistent. The application can simulate the actual response of the bridge web plate under the composite stress state.

Description

Technical Field

[0001] This invention belongs to the technical field of bridge structure test loading devices, specifically relating to a composite loading device and loading method for concrete I-beams. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, differential shear cracking on both sides of the web of long-span prestressed concrete box girder bridges and the resulting structural safety problems have become quite common. The main cause of these problems stems from the spatial stress characteristics of bridges. In addition to bearing the in-plane bending and shear of the bridge, the web also bears additional out-of-plane bending moments from loads such as vehicle wheel loads on the bridge deck and temperature differences between the inside and outside of the box girder. These out-of-plane bending moments generate gradient vertical normal stresses along the thickness of the web, which in turn disturb the principal stress states on the inner and outer sides of the web, causing differential cracking and affecting structural safety.

[0004] In bridge structural testing, I-beams are generally used to simplify box girder bridges to save testing costs. For out-of-plane loading and combined loading of the web of I-beams, existing technology discloses a distortion fatigue test loading device for steel plate girder bridges. The test beam is mounted on a support structure at both ends via auxiliary beams. The support structure restricts the cross-sectional deflection of the test beam through lateral constraint triangular supports. Fixed hinge supports and sliding hinge supports are respectively provided between the constraint triangular supports of the auxiliary beams at both ends of the test beam. A K-shaped cross brace is provided on one side of the test beam, and a load distribution beam is vertically mounted at the free end of the K-shaped cross brace. A hydraulic servo fatigue testing machine actuator is mounted on the top of the load distribution beam to withstand vertical cyclic loading. The out-of-plane load is applied to the vertical stiffening ribs and horizontal node plates through the K-shaped cross brace, which can simulate the stress characteristics of the web gap of a steel plate girder bridge under the coupled effects of bending, constrained torsion, and distortion deformation.

[0005] The above solution has the following drawbacks:

[0006] The above scheme applies eccentric force to the test beam by placing a K-shaped cross brace on one side of the test beam, thereby generating out-of-plane action on the web. This out-of-plane action is a local torque at the K-shaped cross brace, which cannot generate or can be modified to generate a uniform transverse out-of-plane bending moment. It cannot achieve the composite loading of transverse out-of-plane bending moment and vertical in-plane bending shear, and cannot meet the testing requirements for differential cracking on both sides of the web of a large-span prestressed concrete box girder bridge.

[0007] In addition, when subjected to combined loading of out-of-plane bending moment and in-plane bending-shear in the vertical direction, the I-beam may undergo bending deformation in the length or width direction at the same time. Although the test beam in the above scheme is equipped with fixed hinge supports and sliding hinge supports at both ends, it is also equipped with lateral constraint triangular supports to restrict the cross-sectional deflection of the test beam. This results in a discrepancy with the actual stress condition of the bridge, making it impossible for the test personnel to make a correct judgment on the performance of the test component and the safety of the test. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a composite loading device and loading method for concrete I-beams. The composite loading device of the present invention can solve the technical problems in the prior art that it is impossible to apply a uniform out-of-plane bending moment in the transverse direction to the web of the I-beam, impossible to achieve composite loading of out-of-plane bending moment in the transverse direction and in-plane bending and shear in the vertical direction, and impossible to truly reflect the actual stress condition of the bridge.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, a composite loading device for a concrete I-beam is provided, including a ball joint support, the ball joint support being supported on the bottom surfaces of both ends of the I-beam, a plurality of out-of-plane loading devices being equally spaced along the axial direction of the I-beam, and a vertical loading device being provided at the mid-span of the upper flange of the I-beam.

[0011] The out-of-plane loading device includes lever arms on the top and bottom surfaces of the I-beam. There are bidirectional jacks on both sides of the I-beam connected between the lever arms, and the two ends of the bidirectional jacks are respectively hinged to the two lever arms. The bidirectional jacks on both sides of the I-beam apply pressure and tension to the flange plate of the I-beam respectively.

[0012] The lever arm is hinged to the pressure distribution beam and the tension distribution beam on the side facing the I-beam. A rubber pad is connected between the pressure distribution beam and the I-beam. The end of the tension distribution beam is rotatably connected to the U-shaped swing arm. The flange of the I-beam is inserted into the U-shaped swing arm. A rubber pad is connected between the inner side of the flange and the U-shaped swing arm.

[0013] The rubber pads maintain a consistent spacing along the axial and width directions of the I-beam.

[0014] Preferably, the ball joint support is mounted on a fixed base. The ball joint support includes a fixed ball joint support and a sliding ball joint support. The sliding ball joint support includes a base plate on the bottom surface of the ball joint support. The base plate and the fixed base are provided with multiple rollers. Thin cylinders are symmetrically arranged on both sides of the base plate of the fixed ball joint support or the sliding ball joint support. The top of the thin cylinder is provided with a ball joint flange, and the upper surface of the ball joint flange abuts against the lower flange of the I-beam.

[0015] Preferably, the centers of both the fixed ball joint support and the sliding ball joint support are located directly below the web of the I-beam; the line connecting the thin cylinders on the same side ball joint support is perpendicular to the axial direction of the I-beam and passes through the center of either the fixed ball joint support or the sliding ball joint support.

[0016] Preferably, the vertical loading device includes a loading ball seat installed in the middle of the upper flange span of the I-beam, an actuator connected to the upper part of the loading ball seat, the actuator being perpendicular to the I-beam from top to bottom, and the actuator cooperating with the reaction frame.

[0017] Preferably, the two ends of the tension distribution beam are fixedly connected to end plates, and the end plates are fixedly connected to semi-threaded bolts parallel to the I-beam. The unthreaded section of the semi-threaded bolts is rotatably connected to a U-shaped swing arm.

[0018] Preferably, both the lever arm and the distribution beam are ribbed I-beams, with the lever arm positioned perpendicular to the axial direction of the I-beam and the distribution beam positioned parallel to the axial direction of the I-beam.

[0019] Secondly, a loading method for the aforementioned composite loading device for concrete I-beams is provided, the specific steps of which include:

[0020] The two ends of the I-beam are placed on ball joint supports, and the posture of the I-beam is adjusted by thin cylinders. Then, the out-of-plane loading device and the vertical loading device are assembled.

[0021] The bidirectional jacks of the out-of-plane loading device load the I-beam through rubber pads, while the actuators of the vertical loading device load the I-beam through a loading ball seat.

[0022] When performing composite loading, dual-mode loading can be used simultaneously, or single-mode loading can be used followed by composite loading.

[0023] During the loading process, the loading data were recorded when the diagonal cracks appeared in the web of the I-beam and when the specimen failed.

[0024] Preferably, the vertical loading device uses force or displacement control, with force control used in the initial stage of loading and displacement control used when near failure; the out-of-plane loading device uses force control.

[0025] Preferably, the relationship between the loading force q at the rubber pad and the output force F of the bidirectional jack is as follows: ;

[0026] In the formula:

[0027] S1 is the distance between the bidirectional jack and the distribution beam;

[0028] S2 is the spacing of the distribution beams;

[0029] θ is the angle of inclination between the upper or lower flange and the horizontal axis after lateral bending deformation;

[0030] The applied force q is calculated based on the output force F, and the out-of-plane bending moment is further deduced. The magnitude of the out-of-plane bending moment per unit longitudinal length is: ;

[0031] In the formula:

[0032] S3 is the axial spacing of the rubber pads along the I-beam.

[0033] Preferably, during the composite loading process, a thin-walled cylinder is driven to adjust the lateral posture of the I-beam, so that the loading ball seat and the ball hinge support are always in the vertical plane.

[0034] Compared with the prior art, the advantages and positive effects of this invention are:

[0035] This invention utilizes lever arms perpendicular to the axial direction of the I-beam, installed on the top and bottom surfaces, to transmit and amplify the force from the jacks on both sides of the I-beam. This force is then evenly distributed to multiple sets of rubber pads via a distribution beam. This applies a uniform out-of-plane bending moment to the web of the I-beam, creating a gradient of vertical normal stress along the thickness direction. This realistically simulates the differentiated stress characteristics on both sides of the bridge web. The use of lever arms and distribution beams reduces the number and tonnage requirements of the jacks, and installation and disassembly are simple and convenient. Combined with a vertical loading device, it enables independent control and composite loading of the out-of-plane bending moment and the in-plane bending shear, replicating the actual spatial stress characteristics of a bridge under multiple loads such as its own weight, vehicle wheel loads, and box girder temperature differences. Furthermore, by installing ball joint supports at both ends of the I-beam, this invention provides rotational freedom to accommodate the bidirectional bending deformation requirements of the I-beam under composite loading.

[0036] In addition, the present invention also symmetrically arranges thin cylinders on both sides of the ball joint support to adjust the lateral attitude of the I-beam under composite loading, so that the tilt angle of the upper and lower flanges of the I-beam after lateral bending deformation is consistent with the horizontal axis, thereby ensuring that the loading ball seat and the ball joint support are always in the same vertical plane, avoiding the generation of additional torque to interfere with the test results, ensuring the accuracy of the test data, and providing a reliable basis for web performance evaluation. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0038] Figure 1 This is a three-dimensional schematic diagram of a composite loading device for a concrete I-beam according to Embodiment 1 or 2 of the present invention;

[0039] Figure 2 This is a front view of a concrete I-beam composite loading device according to Embodiment 1 or 2 of the present invention;

[0040] Figure 3 This is a rear view of a concrete I-beam composite loading device according to Embodiment 1 or 2 of the present invention;

[0041] Figure 4 This is a top view of a concrete I-beam composite loading device according to Embodiment 1 or 2 of the present invention;

[0042] Figure 5 This is in embodiment 1 or 2 of the present invention. Figure 2 Sectional view of section AA;

[0043] Figure 6 It is in embodiment 1 or 2 of the present invention Figure 2 BB section sectional view;

[0044] Figure 7 It is in embodiment 1 or 2 of the present invention Figure 2 CC section sectional view;

[0045] Figure 8 This is a schematic diagram of the lateral posture adjustment of the I-beam by the thin cylinder in Embodiment 1 or 2 of the present invention;

[0046] Figure 9 This is a schematic diagram of the force distribution of a concrete I-beam composite loading device under composite loading in Embodiment 2 of the present invention;

[0047] In the picture:

[0048] 1. I-beam; 2. Fixed ball joint support; 3. Sliding ball joint support; 4. Loading ball seat; 5. Lever arm; 51. First stiffening rib; 6. First hinge; 7. Pressure distribution beam; 71. Second stiffening rib; 8. Tension distribution beam; 81. End plate; 82. Half-threaded bolt; 83. U-shaped swing arm; 9. Second hinge; 10. Two-way jack; 11. Thin cylinder; 12. Rubber pad. Detailed Implementation

[0049] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0050] The present invention will now be described in detail with reference to the accompanying drawings.

[0051] Example 1

[0052] This embodiment discloses a composite loading device for concrete I-beams, such as... Figure 1 , Figure 2 , Figure 3As shown, the test includes ball joint supports, which are supported on the bottom surfaces of both ends of the I-beam 1, providing a stable support foundation for the I-beam 1. At the same time, the ball joint supports allow the ends of the I-beam 1 to rotate in any direction, providing rotational freedom to adapt to the bidirectional bending deformation requirements of the I-beam 1 under loading, thereby improving the reliability of the test results.

[0053] like Figure 1 As shown, several out-of-plane loading devices are uniformly arranged along the axial direction of the I-beam 1 to continuously and uniformly distribute transverse out-of-plane bending moments on the I-beam 1. Figure 1 As shown, it also includes a vertical loading device set at the mid-span of the upper flange of the I-beam. By loading the I-beam 1 together with the vertical loading device and the out-of-plane loading device, the composite loading of the transverse out-of-plane bending moment and the vertical in-plane bending shear of the I-beam 1 can be achieved.

[0054] like Figure 1 , Figure 4 , Figure 5 As shown, the out-of-plane loading device includes lever arms 5 on the top and bottom surfaces of the I-beam 1. On both sides of the I-beam 1, a bidirectional jack 10 is connected between the two lever arms 5 on the top and bottom surfaces of the I-beam 1. Specifically, the top end of the bidirectional jack 10 is hinged to the lever arm 5 on the top surface of the I-beam 1, and the bottom end of the bidirectional jack 10 is hinged to the lever arm 5 on the bottom surface of the I-beam 1.

[0055] It should be noted that, in this embodiment, the bidirectional jack 10 on one side of the I-beam 1 applies pressure to the flange plate of the I-beam by retracting its output end, while the bidirectional jack on the other side applies tension to the flange plate of the I-beam by extending its output end. Figures 1 to 5 As shown, two distribution beams are hinged to the side of the lever arm 5 facing the I-beam 1. The edges of the distribution beams are flush with the edges of the I-beam 1. The distribution beam near the pressure side of the bidirectional jack 10 is the pressure distribution beam 7, and the distribution beam near the tension side of the bidirectional jack 10 is the tension distribution beam 8.

[0056] It is understandable that when the bidirectional jack 10 retracts or extends through the output end, since the output end is hinged to the lever arm 5 and the lever arm 5 is hinged to the distribution beam, the jack force can be transmitted to the I-beam 1 through the distribution beam, thus achieving effective application of the load.

[0057] In this embodiment, the distribution beam is connected to the flange plate (upper or lower flange plate) of the I-beam 1 via corresponding force transmission components. A rubber pad 12 is bonded between the pressure distribution beam 7 and the I-beam, and the pressure distribution beam 7 applies pressure to the I-beam 1 through the rubber pad 12. A U-shaped swing arm 83 is rotatably connected to the end of the tension distribution beam 8. The flange plate of the I-beam 1 is inserted into the U-shaped swing arm 83, and a rubber pad 12 is bonded between the inner side of the flange plate of the I-beam 1 and the U-shaped swing arm 83. The rubber pad can be a rectangular block made of vulcanized rubber, such as a 20mm thick pad, primarily for uniform pressure distribution and preventing localized stress concentration.

[0058] like Figure 1 , Figure 5 As shown, the pressure distribution beam 7 applies pressure inward to one side of the I-beam 1, while the tension distribution beam 8 applies tension outward to the other side of the I-beam 1 via the U-shaped swing arm 83. In this embodiment, by simultaneously applying inward pressure and outward tension to both sides of the I-beam 1, forces of equal magnitude and opposite direction are generated, achieving self-balancing of internal forces within the device and eliminating interference with vertical loading.

[0059] It should be noted that several out-of-plane loading devices are arranged at equal intervals along the axial (longitudinal) direction of the I-beam 1. The rubber pads 12 maintain consistent spacing along the axial and width directions of the I-beam 1. Under a load diffusion angle of 45°, the loading force (compression or tension) at the rubber pads 12 can generate a constant and uniform transverse bending moment in the web of the I-beam 1, causing a gradient distribution of vertical normal stress in the web of the I-beam 1 along the thickness direction. This can reproduce the differentiated stress characteristics on both sides of the web of the bridge under the action of vehicle wheel load and box girder temperature difference.

[0060] like Figure 1 , Figure 5 As shown, the vertical loading device includes a loading ball seat 4 installed at the mid-span position of the upper flange of the I-beam 1. An actuator (not shown) is connected to the upper part of the ball hinge. The actuator is perpendicular to the I-beam 1 from top to bottom. Figure 8 , Figure 9 As shown, the actuator and reaction frame (not shown in the figure) work together to apply a vertical force Fn to the loading ball seat 4, thereby subjecting the I-beam 1 to vertical in-plane bending and shear loading. It should be noted that the loading ball seat 4 is used to perform vertical in-plane bending and shear loading on the I-beam 1 because it can adapt to the dynamic deformation angle changes of the upper flange of the I-beam during transverse bending, and always transmits the vertical force Fn applied by the actuator, thus achieving independent control of the vertical in-plane bending and shear and the transverse out-of-plane bending moment.

[0061] In this embodiment, as Figures 1 to 5As shown, the ball joint support is installed on a fixed base. The ball joint support includes a fixed ball joint support 2 and a sliding ball joint support 3. One end of the I-beam 1 is supported on the fixed ball joint support 2, and the other end is supported on the sliding ball joint support 3. The sliding ball joint support 3 is formed by connecting a base plate to the bottom surface of the ball joint support, and adding multiple rollers between the base plate and the fixed base. It can be understood that the fixed base refers to the basic support platform used to install the ball joint support. It can be made of concrete blocks to provide a stable initial support environment and avoid initial deflection problems caused by uneven ground.

[0062] In this embodiment, as Figures 1 to 5 As shown, the left end ball joint support of the I-beam 1 is a fixed ball joint support 2. The fixed ball joint support 2 allows the left end of the I-beam 1 to rotate in any direction, providing rotational freedom to accommodate the bending deformation requirements of the I-beam 1 under loading, without generating additional bending moment; the right end ball joint support of the I-beam 1 is a sliding ball joint support 3, as shown... Figure 2 , Figure 3 As shown, the sliding ball joint support 3 provides axial displacement freedom to accommodate the expansion and contraction displacements caused by loading, avoiding the accumulation of axial force due to displacement restriction. In this embodiment, the ball joint support can simultaneously meet the deformation constraint requirements of in-plane bending shear and out-of-plane bending moment loading on the beam end, allowing the I-beam 1 to deform naturally during loading, eliminating the interference of additional constraint stress, ensuring the independence of in-plane bending shear loading and out-of-plane bending moment loading, improving the reliability of test results, and enabling the composite loading process to truly reflect the response characteristics of the bridge web under actual stress conditions.

[0063] like Figure 1 , Figure 2 , Figure 6 , Figure 7 As shown, thin cylinders 11 are symmetrically arranged on both sides of the base plate of the fixed ball joint support 2 or the sliding ball joint support 3, i.e., in the width direction of the I-beam 1. Each thin cylinder has a ball joint flange at its top, and the upper surface of the ball joint flange abuts against the lower flange of the I-beam 1. A ball joint flange refers to a flange connection structure integrating a ball joint, which can be implemented using a ball bearing assembly or a universal joint mechanism. Its purpose is to allow the flange to rotate freely in three-dimensional space, adapting to the dynamic deformation angle changes when the lower flange of the I-beam bends vertically and laterally.

[0064] In this embodiment, as Figure 8As shown, when the out-of-plane loading device applies load to the I-beam 1, the I-beam 1 may deflect laterally when a transverse out-of-plane bending moment is applied, causing a lateral offset of the vertical loading ball seat. This generates additional torque that interferes with the accuracy of the vertical in-plane bending and shear loading, thus affecting the authenticity of the test results. During the loading process, by adjusting the extension of the top of the thin cylinders 11 on both sides of the ball joint support, the lateral posture of the I-beam 1 is kept in balance, ensuring that the inclination angles of the upper and lower flanges are consistent. This ensures that the loading ball seat 4 and the ball joint support (including the fixed ball joint support 2 and the sliding ball joint support 3) are always in the same vertical plane, avoiding the generation of additional torque on the I-beam 1 due to the lateral offset of the vertical force, which would interfere with the test results.

[0065] like Figures 1 to 7 As shown, in this embodiment, the centers of the fixed ball joint support 2 and the sliding ball joint support 3 are both located directly below the web of the I-beam 1; the line connecting the thin cylinders 11 on the same side of the ball joint support is perpendicular to the axial direction (longitudinal direction) of the I-beam 1 and passes through the center of either the fixed ball joint support 2 or the sliding ball joint support 3. During loading, because the line connecting the thin cylinders 11 is strictly perpendicular to the axial direction of the I-beam 1 and passes through the center of the ball joint support, the line of force coincides with the geometric center of the ball joint support, thus avoiding the generation of eccentric torque.

[0066] It should also be noted that the thin cylinder 11 not only plays a role in lateral posture stabilization and adjustment during loading, but also plays a role in lateral posture stabilization and adjustment during the installation of the I-beam 1, thereby preventing the I-beam 1 from rotating and overturning during installation and loading.

[0067] like Figures 1 to 5 As shown, the force transmission component on the tension side also includes an end plate 81, which is fixedly connected to both ends of the tension distribution beam 8. A half-threaded bolt 82 is fixedly connected (threaded or welded) on the end plate 81. The half-threaded bolt 82 is parallel to the I-beam 1. A U-shaped swing arm 83 is rotatably connected to the unthreaded section of the half-threaded bolt 82. The U-shaped swing arm 83 applies pressure by abutting against the inner side of the flange of the I-beam 1 through the rubber pad 12.

[0068] Understandably, the threaded section of the half-threaded bolt 82 is used for bolt connection, while the unthreaded section serves as the axis of rotation, allowing the U-shaped swing arm 83 to rotate freely around the axis to adapt to angular changes during flange deformation. The U-shaped swing arm 83 can be made of cast steel or forged steel. The rubber pad 12 can be made of natural or synthetic rubber, with the purpose of buffering and ensuring stable transmission of pressure or tension. When the flange of the I-beam 1 undergoes lateral bending deformation, the U-shaped swing arm 83 can adjust its angle, and the rubber pad 12 can maintain uniform contact pressure, thereby ensuring uniform application of lateral out-of-plane bending moment and avoiding stress concentration.

[0069] It should be noted that in this embodiment, both the lever arm 5 and the distribution beam are ribbed I-beams. Ribbed I-beams refer to I-beams whose bending stiffness is significantly improved by adding stiffening ribs, such as... Figure 1 , Figure 2 , Figure 3 , Figure 5 As shown, along the axial direction of the lever arm 5 or the distribution beam, there are first stiffening ribs 51 or second stiffening ribs 71 arranged at intervals. The stiffening ribs can be T-shaped or L-shaped. The purpose is to enhance the overall stiffness and stability of the lever arm 5 or the distribution beam, and to avoid bending deformation of the lever arm 5 or the distribution beam during loading, which would affect the transmission effect of the influence and thus affect the test results.

[0070] like Figures 1 to 5 As shown, lever arm 5 is positioned perpendicular to the axial direction of I-beam 1, and distribution beam is positioned parallel to the axial direction of I-beam 1. The purpose is to ensure that the applied lateral force is completely confined within the lateral plane, avoiding the introduction of axial (longitudinal) components.

[0071] In this embodiment, as Figures 1 to 5 As shown, the lever arm 5 is hinged to the distribution beam via the first hinge 6, and the lever arm 5 is hinged to the output end of the bidirectional jack 10 via the second hinge 9. Both the first hinge 6 and the second hinge 9 are lug pin type hinges.

[0072] In this embodiment, the I-beam 1 is made of concrete.

[0073] Example 2

[0074] This embodiment discloses a loading method for a composite loading device for concrete I-beams, which utilizes a composite loading device for concrete I-beams disclosed in Embodiment 1. The specific steps include:

[0075] First, place both ends of the I-beam 1 on the ball joint support, and adjust the posture of the I-beam 1 by using the thin cylinder 11 to ensure that the I-beam 1 has no lateral deflection; then assemble the out-of-plane loading device and the vertical loading device.

[0076] Specifically, first place the rubber pad 12 and the distribution beam on the top surface of the I-beam 1. The pressure distribution beam 7 can be directly supported on the rubber pad 12. The tension distribution beam 8 can be temporarily supported by square timber, etc. Rotate the U-shaped swing arm 83 to the inside of the flange of the I-beam 1, and place the rubber pad 12 between the inside of the flange and the U-shaped swing arm 83.

[0077] Next, the lever arm 5 on the top surface is connected to the distribution beam on the top surface of the I-beam 1 through the first hinge 6, and then the lever arm 5 on the top surface is connected to the top of the double-acting jack 10 through the second hinge 9.

[0078] Then, the lever arm 5 on the bottom surface of the I-beam 1 is connected to the bottom end of the bidirectional jack 10 through the second hinge 9. The lever arm 5 on the bottom surface is connected to the distribution beam on the bottom surface of the I-beam 1 through the first hinge 6. Then, the rubber pad 12 and the U-shaped swing arm 83 on the bottom surface of the I-beam 1 are placed.

[0079] Then, the bidirectional jack 10 is pre-pressurized and the temporary support is removed. The output end of one jack retracts to apply internal tension, and the output end of the other jack extends to apply external thrust, so that all the rubber pads 12 in the out-of-plane loading device abut against the flange of the I-beam 1.

[0080] A loading ball seat 4 is installed on the top surface of the I-beam 1 at the mid-span, so that the loading ball seat 4 is connected to the actuator (perpendicular to the I-beam 1 from top to bottom), and the actuator cooperates with the reaction frame.

[0081] Finally, composite loading was applied to I-beam 1; during the loading process, the loading data were recorded when the diagonal cracks appeared in the web of the I-beam and when the specimen failed.

[0082] In this embodiment, the vertical in-plane bending shear loading uses an actuator to apply a vertical force to the mid-span loading ball seat of the I-beam specimen, using force or displacement control. Generally, force control is used in the early stage of loading, and displacement control is used when the failure is near. The transverse out-of-plane bending moment loading uses an out-of-plane loading device, using force control. The magnitude of the jack output force is changed by adjusting the oil pressure of the jack oil pump. During out-of-plane bending moment loading, one side of the jack applies an internal tension force, and the other side applies an external thrust force. The two are always equal in magnitude and opposite in direction. The force is transmitted and amplified to the distribution beam through the lever arm 5, and then evenly distributed to the rubber pad 12 at a predetermined interval through the distribution beam, and then transmitted to the I-beam 1.

[0083] In this embodiment, as Figure 8 , Figure 9 As shown, the relationship between the loading force q at the rubber pad 12 and the output force F of the two-way jacks 10 on both sides is as follows: ;

[0084] In the formula:

[0085] S1 is the distance between the bidirectional jack and the distribution beam;

[0086] S2 is the spacing of the distribution beams;

[0087] θ is the angle of inclination between the upper or lower flange and the horizontal axis after lateral bending deformation.

[0088] At a load diffusion angle of 45°, the loading force at rubber pad 12 is uniformly diffused to the web of the I-beam 1, thereby generating a uniform out-of-plane bending moment in the transverse direction and forming a vertical normal stress with a gradient distribution along the web thickness, realistically simulating the differentiated stress characteristics on both sides of the bridge web. The loading force q is calculated based on the output force F, and then the corresponding data is obtained based on the dimensions of the I-beam 1 to further calculate the out-of-plane bending moment in the transverse direction. The magnitude of the transverse bending moment per unit longitudinal length is... .

[0089] In the formula:

[0090] S3 is the axial spacing of the rubber pads 12 along the I-beam 1.

[0091] In this embodiment, the I-beam 1 can be simultaneously subjected to vertical in-plane bending shear and transverse out-of-plane bending moment loading, or a single-mode loading can be performed first, followed by a combined loading.

[0092] Specifically, the in-plane vertical bending shear load on the I-beam 1 can be applied first using an actuator until the web of the I-beam 1 shows diagonal cracks. Then, the out-of-plane loading device is activated to apply a constant transverse bending moment to the web of the I-beam 1. After that, the in-plane vertical bending shear load is applied until the specimen fails.

[0093] It should be noted that, regardless of the composite loading mode used, the thin cylinder 11 needs to be driven during the loading process to adjust the lateral attitude of the I-beam 1, so that the loading ball seat 4 and the ball hinge support are always in the vertical plane, that is, the tilt angle of the upper and lower flanges of the I-beam 1 after lateral bending deformation is consistent with the horizontal axis, so as to avoid generating additional torque that interferes with the test results.

[0094] Understandably, position sensors can be installed on the upper and lower flanges of the I-beam 1 to detect deformation.

[0095] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A composite loading device for concrete I-beams, characterized in that, It includes a ball joint support, which is supported on the bottom surfaces of both ends of the I-beam. Several out-of-plane loading devices are evenly spaced along the axial direction of the I-beam, and a vertical loading device is provided at the mid-span of the upper flange of the I-beam. The out-of-plane loading device includes lever arms on the top and bottom surfaces of an I-beam. Bi-directional jacks are connected between the lever arms on both sides of the I-beam, and the two ends of the bi-directional jacks are respectively hinged to the two lever arms. The bi-directional jacks on both sides of the I-beam apply pressure and tension to the flange plate of the I-beam, respectively. The lever arm is hinged to a pressure distribution beam and a tension distribution beam on the side facing the I-beam. A rubber pad is connected between the pressure distribution beam and the I-beam. The end of the tension distribution beam is rotatably connected to a U-shaped swing arm. The flange of the I-beam is inserted into the U-shaped swing arm, and a rubber pad is connected between the inner side of the flange and the U-shaped swing arm. The rubber pads maintain a consistent spacing along the axial and width directions of the I-beam.

2. The composite loading device for concrete I-beams as described in claim 1, characterized in that, The ball joint support is mounted on a fixed base. The ball joint support includes a fixed ball joint support and a sliding ball joint support. The sliding ball joint support includes a base plate on the bottom surface of the ball joint support. The base plate and the fixed base are provided with multiple rollers. Thin cylinders are symmetrically arranged on both sides of the base plate of the fixed ball joint support or the sliding ball joint support. The top of the thin cylinder is provided with a ball joint flange. The upper surface of the ball joint flange abuts against the lower flange of the I-beam.

3. The composite loading device for concrete I-beams as described in claim 2, characterized in that, The centers of both the fixed ball joint support and the sliding ball joint support are located directly below the web of the I-beam; the line connecting the thin cylinders on the same side ball joint support is perpendicular to the axial direction of the I-beam and passes through the center of either the fixed ball joint support or the sliding ball joint support.

4. The composite loading device for a concrete I-beam as described in claim 1, characterized in that, The vertical loading device includes a loading ball seat installed in the middle of the upper flange span of the I-beam. An actuator is connected to the upper part of the loading ball seat. The actuator is perpendicular to the I-beam from top to bottom and cooperates with the reaction frame.

5. The composite loading device for a concrete I-beam as described in claim 1, characterized in that, Both ends of the tension distribution beam are fixedly connected to end plates, and semi-threaded bolts parallel to the I-beam are fixedly connected to the end plates. The unthreaded section of the semi-threaded bolts is rotatably connected to a U-shaped swing arm.

6. The composite loading device for a concrete I-beam as described in claim 1, characterized in that, Both the lever arm and the distribution beam are reinforced I-beams. The lever arm is set perpendicular to the axial direction of the I-beam, and the distribution beam is set parallel to the axial direction of the I-beam.

7. The loading method of the composite loading device for concrete I-beams as described in any one of claims 1-6, characterized in that, The specific steps include: The two ends of the I-beam are placed on the ball joint support, and the posture of the I-beam is adjusted by a thin cylinder. Then the out-of-plane loading device and the vertical loading device are assembled. The bidirectional jacks of the out-of-plane loading device load the I-beam through rubber pads, and the actuators of the vertical loading device load the I-beam through a loading ball seat. When performing composite loading, dual-mode loading can be used simultaneously, or single-mode loading can be used followed by composite loading. During the loading process, the loading data were recorded when the diagonal cracks appeared in the web of the I-beam and when the specimen failed.

8. The loading method of the composite loading device for concrete I-beams as described in claim 7, characterized in that, The vertical loading device uses force or displacement control, with force control used in the initial loading stage and displacement control used when near failure; the out-of-plane loading device uses force control.

9. The loading method of the composite loading device for concrete I-beams as described in claim 7, characterized in that, The relationship between the loading force q at the rubber pad and the output force F of the bidirectional jack is as follows: ; In the formula: S1 is the distance between the bidirectional jack and the distribution beam; S2 is the spacing of the distribution beams; θ is the angle of inclination between the upper or lower flange and the horizontal axis after lateral bending deformation; The applied force q is calculated based on the output force F, and the out-of-plane bending moment is further deduced. The magnitude of the out-of-plane bending moment per unit longitudinal length is: ; In the formula: S3 is the axial spacing of the rubber pads along the I-beam.

10. The loading method of the composite loading device for concrete I-beams as described in claim 7, characterized in that, During the composite loading process, the thin cylinder is driven to adjust the lateral posture of the I-beam, so that the loading ball seat and the ball hinge support are always in the vertical plane.

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