A push-out test device and method for shear studs in negative moment regions of corrugated steel web box girders

Abstract

The application discloses a kind of wave-shaped steel web box girder negative bending moment area shear nail push-out test device and method, including wave-shaped steel web composite box girder, loading frame, pulley support, jack and displacement measuring device, wherein the reinforced concrete slab of wave-shaped steel web composite box girder is connected by shear nail wave-shaped steel web, the beam of loading frame is by jack to reinforced concrete slab Symmetrical vertical pressure is applied, column is by jack to lower sliding support Apply horizontal push-out force, reinforced concrete slab is pushed out from steel box girder top surface, and shear slip curve is recorded by displacement measuring device and pressure sensor.The application is more effective by vertical two-way loading mode first, then horizontal, simulate the shear capacity of shear nail under the actual cracking condition of negative bending moment area concrete slab, improve the test device that shear nail only applies unidirectional force, meet the real stress condition of continuous beam bridge negative bending moment area, and the displacement measuring device structure is simple, clamping is stable, effectively measure shear nail relative slip.

Description

Technical Field

[0001] This invention belongs to the field of shear bearing capacity testing devices, specifically relating to a test device and method for shear stud ejection in the negative bending moment zone of a corrugated steel web box girder. Background Technology

[0002] Corrugated steel web PC composite box girder bridges are widely used in practical engineering due to their advantages such as convenient construction, excellent mechanical properties, and crack-free webs. Generally, shear studs are used to firmly connect the reinforced concrete top slab and the corrugated steel web, forming an integral load-bearing structure. This fully utilizes the compressive strength of the reinforced concrete and the shear strength of the steel web, making shear studs crucial components for ensuring the coordinated work of the reinforced concrete slab and corrugated steel web in the composite beam. However, due to the adverse effects of the negative bending moment at the pier tops of continuous beam bridges, the top slab concrete often cracks under tension, leading to a reduction in the shear bearing capacity of the shear studs, altered bond-slip properties, and ultimately, a decrease in the durability of the box girder structure.

[0003] To study the shear stud shear capacity and bond-slip properties, push-out test devices are typically used. Currently, Chinese patent CN111665146B proposes a common testing device for the shear capacity of welded studs under concrete cracking conditions. However, this device cannot account for the wrinkling effect of the corrugated steel web, and therefore cannot directly test the shear capacity of corrugated steel web box girders. Furthermore, this device only has one groove to simulate concrete cracks, and cannot effectively simulate the multiple random crack patterns generated by the tension of the negative moment concrete top slab, resulting in significant differences from real-world engineering. This paper aims to propose a shear stud push-out test device and method for corrugated steel web box girders in the negative moment zone to solve the above problems. Summary of the Invention

[0004] To address the aforementioned issues, this invention discloses a test device and method for shear stud ejection in the negative bending moment zone of a corrugated steel web box girder. By employing a bidirectional loading mode—first vertical and then horizontal—it more effectively simulates the shear bearing capacity of the shear stud under actual cracking conditions in the concrete slab of the negative bending moment zone. The measured shear bearing capacity is more consistent with actual engineering conditions, and the test data is more authentic and reliable.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A test device for shear stud ejection in the negative moment zone of a corrugated steel web box girder, comprising: Corrugated steel web composite box girder, loading frame, upper pulley support, lower pulley support, first jack, second jack, third jack, pressure sensor, jack adapter, displacement gauge, displacement gauge positioning device, strain gauge and base platform; The corrugated steel web composite box girder consists of a top reinforced concrete slab, two symmetrical corrugated steel webs on both sides, and a bottom plate. The reinforced concrete slab is connected to the corrugated steel web by multiple rows of shear studs. The shear studs are vertically welded to the top of the corrugated steel web. The bottom plate is welded to the lower pulley support. The reinforced concrete slab is divided into a cracked area in the middle and uncracked areas at both ends. The surface of the cracked area in the middle is provided with strain rosettes, which measure the cracking strain when a tensile crack is generated. The reinforced concrete slab is composed of reinforced concrete, stirrups and longitudinal bars.

[0006] The loading frame is a "gate"-shaped structure composed of a crossbeam, a left column, and a right column; the lower part of the crossbeam is connected to two first jacks through the upper sliding support. The two first jacks are set on the central axis of the uncracked areas at both ends above the reinforced concrete slab. The first jacks apply symmetrical vertical pressure to the reinforced concrete slab of the corrugated steel web composite box girder. The left column is connected to the second jack via the jack adapter. The second jack is horizontally pressed against the left end face of the reinforced concrete slab, and applies a supporting force to the reinforced concrete slab to keep its horizontal position unchanged. The right column is connected to the third jack via the jack adapter. The third jack horizontally presses against the right end face of the sliding wheel support. The third jack applies a horizontal pushing force to the sliding wheel support, causing it to slide to the left along the base platform, thus performing a push-out test on the shear nail. The third jack is equipped with a pressure sensor at its front end. Displacement gauges are installed above the reinforced concrete slab, at the left end of the reinforced concrete slab, in the middle of the corrugated steel web, and at the center of the left side of the lower sliding support. The pressure sensor records the horizontal pushing force, and the displacement gauges measure the relative slippage between the reinforced concrete slab and the corrugated steel web.

[0007] Furthermore, the upper pulley support consists of an upper top plate and an upper pulley. The upper pulley is positioned above the upper top plate and is attached to the back of the crossbeam. The first jack is pressed against the back of the upper top plate. The sliding wheel support consists of a lower base plate and a sliding wheel. The sliding wheel eliminates the horizontal friction between the bottom of the combined box girder and the base platform. The lower base plate is connected to the third jack.

[0008] Furthermore, the displacement gauge positioning device consists of a positioning plate, a magnetic clamp, and bolts; The positioning plate includes a slide and a positioning groove. The positioning groove is an elliptical hole, symmetrically located at the beam end of the positioning plate, and the center-to-center distance is equal to the distance between the two corrugated steel webs of the composite box girder. The pointer of the horizontally mounted displacement gauge is in perpendicular contact with the positioning groove; The magnetic clamp includes two parallel and symmetrically spaced single clamping plates. The outer side of each single clamping plate is flat, and the inner side has multiple parallel strip-shaped strong magnetic strips. Bolt holes are opened at the root of each single clamping plate, and the distance between the pair of single clamping plates can be adjusted by bolts. The magnetic clip passes through the middle slide of the positioning plate and can slide unidirectionally along the slide of the positioning plate; The displacement gauge positioning device is vertically attached to the middle position of the free end of the corrugated steel web by a pair of magnetic clips.

[0009] Furthermore, a method for testing the shear bearing capacity of a shear stud ejection test device in the negative bending moment zone of a composite box girder includes the following steps: S1. Fix the crossbeam and the left and right columns to the base platform. Install jack adapters on both the left and right columns. Fix the second jack to the left column and the third jack to the right column. S2. Install the lower pulley support of the composite box girder on the base platform. Arrange the first jack and the upper pulley support symmetrically at the two ends of the uncracked area of ​​the reinforced concrete slab of the composite box girder. Adjust the height of the first jack to make it press against the upper pulley support to ensure that the upper pulley support slides freely along the crossbeam. Install two displacement gauges vertically at the position of the first jack. S3. The shear studs are symmetrically and centrally arranged at the top of the corrugated steel web corresponding to the lower wheel support. The reinforced concrete slab generates tensile microcracks under the vertical action of the first jack pressure, and the cracking strain is recorded by the strain rosette to simulate the tensile cracking state of the concrete slab in the negative bending moment zone of the continuous composite beam bridge. S4. According to the force control method, the first jack applies vertical pressure to the reinforced concrete slab, and the concrete cracking strain is detected by strain gauge. When the concrete cracking strain is reached, the vertical pressure of the first jack is kept constant. S5. Multiple displacement gauges are horizontally arranged at the left end of the composite box girder and vertically arranged at the left end of the reinforced concrete slab, the positioning plate, and the left end of the lower base platform, respectively, to measure the shear slip of the shear studs under the action of the horizontal pushing force of the third jack. S6. According to the force control method, the pressure of the third jack is gradually increased from 0. The third jack gradually and evenly applies horizontal thrust to the left, so that the sliding wheel support slides horizontally along the base platform. The sliding direction is consistent with the direction of the crossbeam axis. The shear nails embedded in the reinforced concrete slab bear all the horizontal thrust and gradually undergo shear deformation. S7. When the shear stud is completely ejected from the reinforced concrete slab, or when the shear bearing capacity drops to 85% of the peak bearing capacity, stop the ejection test loading. Obtain the relative bond slip between the reinforced concrete slab and the corrugated steel web using a displacement gauge, and obtain the shear slip curve using a pressure sensor and displacement gauge to provide experimental data for studying the shear bearing capacity of the shear stud in the negative bending moment zone of the composite box girder.

[0010] The beneficial effects of this invention are as follows: (1) The present invention reasonably considers the adverse effects of cracking in reinforced concrete slabs in the negative bending moment zone, and the shear bearing capacity measured by the device is more consistent with actual engineering. The device of the present invention can simulate the shear bearing capacity, stress mechanism, failure mode and other properties of shear studs in the negative bending moment zone under the condition of cracking of reinforced concrete in a more realistic manner through the bidirectional loading mode of vertical first and then horizontal.

[0011] (2) The device of the present invention measures the cracking strain of concrete in the negative bending moment zone of the composite box girder by means of multiple strain rose arrays, quantifies the cracking load of concrete, and keeps the vertical pressure constant during the push-out test, accurately and effectively simulating the actual stress state of shear studs affected by concrete cracking.

[0012] (3) The boundary conditions of the entire push-out test device of the present invention are reasonably set, and the device for measuring shear bearing capacity and bond slip is highly accurate. The upper and lower sliding supports can effectively reduce the friction between the composite box girder and the crossbeam and the base platform, ensuring that the horizontal push-out force output by the jack is completely borne by the shear nail. The positioning device of pressure sensor and displacement gauge effectively improves the accuracy of shear bearing capacity testing.

[0013] (4) Since the thickness of the corrugated steel web of the composite box girder in the test model is generally smaller than the diameter of the displacement gauge pointer, it is very difficult to directly measure the displacement gauge using conventional methods, resulting in large measurement errors. However, the displacement gauge positioning device of this invention is magnetically fixed to the corrugated steel web by magnetic clamps, which is stable, reliable, and easy to install. In order to consider the influence of the corrugated steel web wrinkling effect, the bonding slip of the shear stud measured by the first displacement gauge at the left end of the reinforced concrete slab is recorded. x 1 The second displacement gauge at the positioning plate measures the relative displacement between the corrugated steel web and the shear studs. x 2 Record the displacement of the top of the third jack measured by the third displacement gauge at the lower base. x 3 .like x 1 < x 2 If the wrinkling effect of the corrugated steel web is not negligible, it needs to be considered as an influencing factor in analyzing the shear bearing capacity and shear displacement relationship curve of the shear stud in the negative moment zone.

[0014] (5) The entire push-out test device of the present invention can be used to study the shear stud push-out test of steel-concrete composite beams. It is easy to install, has high measurement accuracy, and does not weaken the corrugated steel web by drilling. The installation is convenient and the measurement results are accurate and reliable. It has wide applicability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a test device for pushing out shear studs in the negative bending moment zone of a corrugated steel web box girder according to the present invention. Figure 2 A front view of the shear pin ejection test device of the present invention; Figure 3 Top view of the shear nail ejection test device of the present invention; Figure 4 for Figure 3 Sectional view at point AA; Figure 5 This is a schematic diagram of the corrugated steel web box girder and the sliding wheel support structure of the present invention; Figure 6 This is a top view of the corrugated steel web box girder and the lower wheel support of the present invention; Figure 7 for Figure 6 Sectional view at CC; Figure 8 This is a plan view of the reinforced concrete slab of the present invention; Figure 9 for Figure 8 Sectional view at point BB; Figure 10 This is a schematic diagram of the bidirectional force exerted by the loading frame of the present invention on the corrugated steel web composite box girder; Figure 11 This is a diagram showing the distribution of tensile cracks and strain rosette in a reinforced concrete slab according to the present invention. Figure 12 This is a schematic diagram of the upper pulley support structure of the present invention; Figure 13 This is a schematic diagram of the upper top plate of the upper pulley support of the present invention; Figure 14 This is a schematic diagram of the upper pulley of the upper pulley support of the present invention; Figure 15 This is a schematic diagram of the displacement gauge positioning device of the present invention installed in the middle of the corrugated steel web; Figure 16 This is a schematic diagram of the displacement gauge positioning device of the present invention; Figure 17 This is a schematic diagram of the positioning plate of the present invention; Figure 18 This is a schematic diagram of the magnetic clip of the present invention.

[0016] List of identifiers in attached diagrams: 1. Reinforced concrete slab; 101. Cracked area in the middle; 102. Uncracked areas at both ends; 103. Crack; 104. Concrete; 105. Stirrups; 106. Longitudinal reinforcement; 2. Corrugated steel web; 201. Top of corrugated steel web; 202. Middle of corrugated steel web; 203. Bottom plate; 204. Shear studs; 3. Lower pulley support; 301. Lower bottom plate; 302. Lower pulley; 4. First jack; 5. Upper pulley support; 501. Upper top plate; 502. Upper pulley; 6. Second jack; 7. Third jack; 8. Pressure sensor; 9. Jack adapter; 10. Crossbeam; 11. Right column; 12. Left column; 13. Displacement gauge; 14. Displacement gauge positioning device; 1401. Positioning plate; 1402. Slide rail; 1403. Positioning groove; 1404. Magnetic clamp; 1405. Bolt; 1406. Strong magnetic strip; 1407. Bolt hole; 15. Strain gauge; 16. Base platform. Detailed Implementation

[0017] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0018] As shown in the figure, the shear nail ejection test device for the negative bending moment zone of a corrugated steel web box girder according to the present invention includes: a corrugated steel web composite box girder, a loading frame, an upper pulley support 5, a lower pulley support 3, a first jack 4, a second jack 6, a third jack 7, a pressure sensor 8, a jack adapter 9, a displacement gauge 13, a displacement gauge positioning device 14, a strain gauge 15, and a base platform 16. like Figure 9 As shown, the reinforced concrete slab 1 is composed of reinforced concrete 104, stirrups 105 and longitudinal bars 106. The strength grade of the reinforced concrete 104 is not lower than C40, which is exactly the same as the reinforced concrete slab used in actual applications, in order to simulate the actual stress conditions.

[0019] like Figure 1 and 11 As shown, the reinforced concrete slab 1 is divided into a cracked area 101 in the middle and an uncracked area 102 at both ends. The surface of the cracked area 101 in the middle is provided with strain rosettes 15. like Figure 4 , Figure 5 and Figure 6As shown, the corrugated steel web composite box girder consists of a top reinforced concrete slab 1, corrugated steel web intermediate 202s on both sides, and a bottom plate 203. A corrugated steel web top 201 is located above the corrugated steel web intermediate 202. The reinforced concrete slab 1 is connected to the corrugated steel web intermediate 202 via multiple rows of shear studs 204. The shear studs 204 are vertically welded to the corrugated steel web top 201. The corrugated steel web bottom 203 is welded to the sliding wheel support 3. The shear studs 204 are common cylindrical head shear studs commonly used in bridge engineering, conforming to the requirements of national standard GB / T10433. The corrugated steel web material is a commonly used specification in bridge engineering, such as type 1000, 1200, 1600, and 2000, conforming to JT / T 784-2022, "Corrugated Steel Webs for Composite Structure Bridges".

[0020] like Figure 2 As shown, the loading frame is a "gate"-shaped structure composed of a crossbeam 10, a left column 11, and a right column 12; the lower part of the crossbeam 10 is connected to two first jacks 4 through the upper sliding support 5. The two first jacks 4 are symmetrically arranged on the central axis of the two uncracked areas 102 above the reinforced concrete slab 1. The first jacks 4 apply symmetrical vertical pressure to the reinforced concrete slab 1 of the corrugated steel web composite box girder. The columns and beams described in this invention are all I-beams commonly used in civil engineering, with a strength grade of not less than Q345. The bottom of the column is firmly connected to the bottom platform, and the column and beam are firmly welded into a whole, without any displacement or deformation under the reaction force of the jack.

[0021] The left column 12 is connected to the second jack 6 through the jack adapter 9. The second jack 6 is horizontally supported on the left end face of the reinforced concrete slab 1. When in use, the second jack 6 applies a supporting force to the reinforced concrete slab 1 to keep its horizontal position unchanged. The right column 11 is connected to the third jack 7 via the jack adapter 9. The third jack 7 horizontally supports the right end face of the sliding wheel support 3. During use, the third jack 7 applies a horizontal pushing force to the sliding wheel support 3, causing it to slide to the left along the base platform 16 to conduct a pushing test on the shear nail 204. The third jack 7 is equipped with a pressure sensor 8 at its front end. Displacement gauges 13 are installed above the reinforced concrete slab 1, at the left end of the reinforced concrete slab 1, at the middle of the corrugated steel web 2, and at the center of the left side of the lower sliding support 3. The pressure sensor 8 records the horizontal thrust, and the displacement gauges 13 measure the relative slippage between the reinforced concrete slab 1 and the corrugated steel web 2.

[0022] As a preferred embodiment, the pressure sensor 8 is a high-precision pressure sensor connected to a display instrument to record pressure values; the displacement gauge 13 is a rod-type displacement gauge with high measurement accuracy and a self-resetting function.

[0023] like Figure 8 , Figure 9 , Figure 10 and Figure 11 As shown, the shear studs 204 are symmetrically and centrally arranged at the top end 201 of the corrugated steel web corresponding to the lower pulley support 3, that is, the shear studs 204 are only arranged in the negative bending moment zone. As a preferred embodiment, the shear stud 204 is automatically welded using a specialized welding machine, and the welding quality is tested by ultrasonic waves to ensure reliable welding quality.

[0024] The strain rosette 15 is arranged in the middle cracking zone (102) of the reinforced concrete slab 1 under negative bending moment, corresponding to the position of the shear nail 204, to record the cracking strain generated by the reinforced concrete slab 1 under the vertical pressure of the first jack 4, and to simulate the tensile cracking state of the concrete slab in the negative bending moment zone of the continuous composite beam bridge. After the reinforced concrete slab 1 cracks, the first jack 4 maintains the magnitude and direction of the vertical pressure unchanged; the end of the second jack 6 is pressed against the left end of the reinforced concrete slab 1. The device of this invention, through a two-way loading mode of first vertical and then horizontal, can realistically simulate the shear bearing capacity, stress mechanism, failure mode, and other properties of shear studs in the negative bending moment zone under the condition of cracking in reinforced concrete.

[0025] like Figure 12 , Figure 13 and Figure 14 As shown, the upper pulley support 5 consists of an upper top plate 501 and an upper pulley 502. The upper pulley 502 is located above the upper top plate 501 and is attached to the back of the crossbeam 10. The first jack 4 is pressed against the back of the upper top plate 501. The upper pulley 502 slides freely along the bottom longitudinal axis of the crossbeam 10, eliminating the horizontal friction between the first jack 4 and the crossbeam 10. like Figure 5 As shown, the sliding wheel support 3 consists of a lower base plate 301 and a sliding wheel 302. The sliding wheel 302 is disposed between the lower base plate 301 and the base platform 16. The third jack 7 faces the end face of the lower base plate 301. The sliding wheel 302 eliminates the horizontal friction between the bottom of the combined box girder and the base platform 16. The lower base plate 301 is connected to the third jack 7 and bears the horizontal pushing force. The upper pulley support 5 and the lower pulley support 3 ensure that the horizontal pushing force applied by the third jack 7 is entirely borne by the shear nail 204, so that the output data of the pressure sensor 8 is the shear bearing capacity of the shear nail 204, thus improving the accuracy of data measurement.

[0026] Both the upper pulley support 5 and the lower pulley support 3 described in this invention are steel supports, with a steel strength grade not lower than Q345. The upper pulley 502 is a rolling bearing, capable of rotating freely around its own bearing. The upper and lower sliding supports effectively reduce the friction between the combined box girder and the crossbeam and base platform, ensuring that the horizontal pushing force output by the jack is entirely borne by the shear stud 204.

[0027] like Figure 15 , Figure 16 , Figure 17 and Figure 18 As shown, the displacement gauge positioning device 14 consists of a positioning plate 1401, a magnetic clamp 1404, and bolts 1405; The positioning plate 1401 includes a slide rail 1402 and a positioning groove 1403. The positioning groove 1403 is an elliptical hole, symmetrically located at the beam end of the positioning plate 1401, and the center distance is equal to the distance between the two corrugated steel webs 2 of the composite box girder. The pointer of the horizontally installed displacement gauge 13 is in vertical contact with the positioning groove 1403. By measuring the horizontal displacement of the positioning plate 1401, the relative slip of the free end of the corrugated steel web 2 relative to the reinforced concrete slab 1 can be obtained, that is, the shear slip of the shear stud. The magnetic clamp 1404 includes two parallel and symmetrically spaced single clamp plates. The outer side of each single clamp plate is flat, and the inner side has multiple parallel strip-shaped strong magnetic strips 1406. Bolt holes 1407 are opened at the root of each single clamp plate, and the spacing between the pair of single clamp plates is adjusted by bolts 1405. The bolts 1405 can manually adjust the spacing between the clamp plates, and the installation and adjustment of the clamp plates can be completed without complicated tools, making disassembly convenient.

[0028] The magnetic clip 1404 passes through the slide 1402 in the middle of the positioning plate 1401 and can slide unidirectionally along the slide 1402 of the positioning plate to change its position and adapt to the spacing and thickness of the corrugated steel web 2. The displacement gauge positioning device 14 is vertically attached to the middle position of the free end of the corrugated steel web by a pair of magnetic clips 1404.

[0029] It should be noted that all displacement gauges 13 are fixed with brackets (existing technology, not shown).

[0030] To account for the effect of the corrugated steel web wrinkling, the bond slip of the shear studs was measured by the first displacement gauge at the left end of the reinforced concrete slab 1. x1 The second displacement gauge at position 1401 measures the relative displacement between the corrugated steel web and the shear studs. x 2 The displacement of the top of the third jack is measured by the third displacement gauge at the left end of the lower base platform 16. x 3 .like x 1 < x 2 If the wrinkling effect of the corrugated steel web is not negligible, it needs to be considered as an influencing factor in analyzing the shear bearing capacity and shear displacement relationship curve of the shear stud in the negative moment zone.

[0031] A measurement method for a shear stud ejection test device in the negative bending moment zone of a corrugated steel web box girder includes the following steps: S1. Fix the crossbeam 10, left column 12, and right column 11 to the base platform 16. Install jack adapters 9 on both left column 12 and right column 11. Fix the second jack 6 to the left column 12 and the third jack 7 to the right column (11). S2. Install the lower pulley support 3 of the composite box girder on the base platform 16. Arrange the first jack 6 and the upper pulley support 5 symmetrically at the two ends of the uncracked area 102 of the reinforced concrete slab 1 of the composite box girder. Adjust the height of the first jack 6 to make it press against the upper pulley support 5, so as to ensure that the upper pulley support 5 can slide freely along the crossbeam 10. Install two displacement gauges 13 vertically at the position of the first jack 4. S3. The shear studs 204 are symmetrically and centrally arranged at the top of the corrugated steel web 201 corresponding to the lower pulley support 3. The reinforced concrete slab 1 generates tensile microcracks 103 under the vertical pressure of the first jack 4, and the cracking strain is recorded by the strain rosette 15 to simulate the tensile cracking state of the concrete slab in the negative bending moment zone of the continuous composite beam bridge. S4. According to the force control method, the first jack 4 applies vertical pressure to the reinforced concrete slab 1, and the concrete cracking strain is detected by the strain gauge 15. When the concrete cracking strain is reached, the magnitude of the vertical pressure of the first jack 4 remains unchanged. S5. Multiple displacement gauges are horizontally arranged at the left end of the composite box girder and vertically arranged at the left end of the reinforced concrete slab 1, the positioning plate 1401, and the left end of the lower base platform 16, respectively, to measure the shear slip of the shear nail 204 under the action of the horizontal pushing force of the third jack 7. S6. According to the force control method, the pressure of the third jack 7 is gradually increased from 0. The third jack 7 gradually and evenly applies horizontal thrust to the left, so that the sliding wheel support 3 slides horizontally along the base platform 16. The sliding direction is consistent with the axis of the crossbeam 10. The shear nail 204 embedded in the reinforced concrete slab 1 bears all the horizontal thrust and gradually undergoes shear deformation. S7. When the shear stud 204 is completely ejected from the reinforced concrete slab 1, or when the shear bearing capacity drops to 85% of the peak bearing capacity, the ejection test loading is stopped. The relative bond slip between the reinforced concrete slab 1 and the corrugated steel web 2 is obtained through the displacement gauge 13. The shear slip curve is obtained through the pressure sensor 8 and the displacement gauge 13, providing experimental data for studying the shear bearing capacity of the shear stud in the negative bending moment zone of the composite box girder.

[0032] It should be noted that the above content merely illustrates the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. For those skilled in the art, various improvements and modifications can be made without departing from the principle of the present invention, and all such improvements and modifications fall within the scope of protection of the claims of the present invention.

Claims

1. A test device for shear stud ejection in the negative bending moment zone of a corrugated steel web box girder, characterized in that, include: Corrugated steel web composite box girder, loading frame, upper pulley support (5), lower pulley support (3), first jack (4), second jack (6), third jack (7), pressure sensor (8), jack adapter (9), displacement gauge (13), displacement gauge positioning device (14), strain gauge (15) and base platform (16); The corrugated steel web composite box girder is composed of a reinforced concrete slab (1) on the top, corrugated steel webs (2) on both sides, and a bottom plate (203). The reinforced concrete slab (1) is connected to the corrugated steel web (2) by multiple rows of shear studs (204). The shear studs (204) are vertically welded to the top end (201) of the corrugated steel web. The bottom plate (203) is welded to the pulley support (3). The reinforced concrete slab (1) is divided into a cracked area in the middle (101) and uncracked areas at both ends (102). The surface of the cracked area (101) is provided with strain rosettes (15). The reinforced concrete slab (1) is composed of reinforced concrete (104), stirrups (105) and longitudinal bars (106). The loading frame is a "gate"-shaped structure composed of a crossbeam (10), a right column (11), and a left column (12); the lower part of the crossbeam (10) is connected to two first jacks (4) through the upper pulley support (5). The two first jacks (4) are symmetrically arranged on the central axis of the two uncracked areas (102) above the reinforced concrete slab (1). The first jacks (4) apply symmetrical vertical pressure to the reinforced concrete slab (1) of the corrugated steel web composite box girder. The left column (12) is connected to the second jack (6) via the jack adapter (9), and the second jack (6) is horizontally pressed against the left end face of the reinforced concrete slab (1). The right column (11) is connected to the third jack (7) through the jack adapter (9). The third jack (7) is horizontally pressed against the right end face of the sliding wheel support (3). The third jack (7) applies a horizontal pushing force to the sliding wheel support (3) so that it slides to the left along the base platform (16) to push out the shear nail (204). The third jack (7) is equipped with a pressure sensor (8) at its front end. Displacement gauges (13) are installed above the reinforced concrete slab (1), at the left end of the reinforced concrete slab (1), at the middle of the corrugated steel web (2), and at the center of the left side of the lower sliding support (3). The pressure sensor (8) records the horizontal pushing force, and the displacement gauges (13) measure the relative slippage between the reinforced concrete slab (1) and the corrugated steel web (2). The displacement gauge positioning device (14) consists of a positioning plate (1401), a magnetic clamp (1404), and bolts (1405); The positioning plate (1401) includes a slide (1402) and a positioning groove (1403). The positioning groove (1403) is an elliptical hole, symmetrically located at the beam end of the positioning plate (1401), and the center spacing is equal to the spacing between the two corrugated steel webs (2) of the composite box girder. The pointer of the horizontally mounted displacement gauge (13) is in perpendicular contact with the positioning groove (1403). The magnetic clamp (1404) includes two parallel and symmetrically spaced single clamp plates. The outer side of the single clamp plate is flat, and the inner side has multiple parallel strip-shaped strong magnetic strips (1406). The root of the single clamp plate has bolt holes (1407), and the distance between the pair of single clamp plates can be adjusted by bolts (1405). The magnetic clip (1404) passes through the slide (1402) in the middle of the positioning plate (1401). The displacement gauge positioning device (14) is vertically attached to the middle position of the free end of the corrugated steel web by a pair of magnetic clips (1404).

2. The shear stud ejection test device for the negative bending moment zone of a corrugated steel web box girder according to claim 1, characterized in that: The shear studs (204) are symmetrically and centrally arranged at the top end (201) of the corrugated steel web corresponding to the lower pulley support (3), that is, the shear studs (204) are only arranged in the negative bending moment area; The strain rosette (15) is arranged in the middle crack zone (101) of the reinforced concrete slab (1), corresponding to the position of the shear stud (204); After the reinforced concrete slab (1) cracks, the first jack (4) maintains the magnitude and direction of the vertical pressure unchanged; the end of the second jack (6) is pressed against the left end of the reinforced concrete slab (1).

3. The shear stud ejection test device for the negative bending moment zone of a corrugated steel web box girder according to claim 2, characterized in that: The upper pulley support (5) consists of an upper top plate (501) and an upper pulley (502). The upper pulley (502) is located above the upper top plate (501) and is attached to the back of the crossbeam (10). The first jack (4) is against the back of the upper top plate (501). The upper pulley (502) slides freely along the bottom longitudinal axis of the crossbeam (10) to eliminate the horizontal friction between the first jack (4) and the crossbeam (10). The sliding wheel support (3) consists of a lower base plate (301) and a sliding wheel (302). The sliding wheel (302) eliminates the horizontal friction between the bottom of the combined box girder and the base platform (16). The right side of the lower base plate (301) is connected to the third jack (7) to bear the horizontal pushing force. The upper pulley support (5) and the lower pulley support (3) together ensure that the horizontal pushing force applied by the third jack (7) is completely borne by the shear nail (204), so that the output data of the pressure sensor (8) is the shear bearing capacity of the shear nail (204), thereby improving the accuracy of data measurement.

4. The method for testing the shear bearing capacity of a corrugated steel web box girder in the negative bending moment zone using a shear stud ejection test device according to claim 3, characterized in that: Includes the following steps: S1. Fix the crossbeam (10), left column (12), and right column (11) to the base platform (16). Install jack adapters (9) on the left column (12) and right column (11). S2. Install the lower pulley support (3) of the combined box girder on the base platform (16). Arrange the first jack (6) and the upper pulley support (5) symmetrically at the two ends of the uncracked area (102) of the reinforced concrete slab (1) of the combined box girder. Adjust the height of the first jack (6) to make it press against the upper pulley support (5) to ensure that the upper pulley support (5) slides freely along the crossbeam (10). Install two displacement gauges (13) vertically at the position of the first jack (4). S3. The shear studs (204) are symmetrically and centrally arranged at the top of the corrugated steel web (201) corresponding to the sliding wheel support (3). The reinforced concrete slab (1) generates tensile microcracks (103) under the vertical pressure of the first jack (4), and the cracking strain is recorded by the strain rosette (15) to simulate the tensile cracking state of the concrete slab in the negative bending moment zone of the continuous composite beam bridge. S4. According to the force control method, the first jack (4) applies vertical pressure to the reinforced concrete slab (1), and the concrete cracking strain is detected by the strain gauge (15). When the concrete cracking strain is reached, the vertical pressure of the first jack (4) remains unchanged. S5. Multiple displacement gauges are horizontally arranged at the left end of the composite box girder and vertically arranged at the left end of the reinforced concrete slab (1), the positioning plate (1401), and the left end of the lower base platform (16) to measure the shear slip of the shear nail (204) under the action of the horizontal pushing force of the third jack (7). S6. According to the force control method, the pressure of the third jack (7) is gradually increased from 0. The third jack (7) gradually and evenly applies horizontal thrust to the left, so that the sliding wheel support (3) slides horizontally along the base platform (16). The sliding direction is consistent with the axis of the crossbeam (10). The shear nail (204) embedded in the reinforced concrete slab (1) bears all the horizontal thrust and gradually undergoes shear deformation. S7. When the shear stud (204) is completely pushed out of the reinforced concrete slab (1), or the shear bearing capacity drops to 85% of the peak bearing capacity, stop the push-out test loading, obtain the relative bond slip of the reinforced concrete slab (1) and the corrugated steel web (2) through the displacement gauge (13), and obtain the shear slip curve through the pressure sensor (8) and the displacement gauge (13) to provide test data for studying the shear bearing capacity of the shear stud in the negative bending moment zone of the composite box girder.

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