Steel-concrete composite node model test system

Abstract

The invention discloses a steel-concrete combined node model test system, relates to the technical field of model tests, and aims to design a reduced scale model test system to simulate the actual stress state of a combined node of a steel truss web member and a concrete lower chord and provide theoretical and experimental support for the stress of a bridge node. Complex stress conditions of the steel truss web members in actual engineering can be simulated, fixed constraints are provided for the nodes, acting positions are provided for loads when the nodes are loaded, and sensors are arranged according to stress behaviors and damage phenomena of the nodes to monitor the stress conditions of the nodes in the loading process in real time.

Description

Technical Field

[0001] The present invention relates to the technical field of model tests, and particularly to a model test system for a steel-concrete composite joint. Background Art

[0002] In a steel-concrete composite truss bridge, the web members and the concrete lower chord are connected to the lower concrete beam through stud shear keys on the gusset plate, forming a steel-concrete composite joint. The steel-concrete composite joint is a key force transfer part of the composite structure. The stress at the joint part is extremely complex, and the rigidity and strength of the joint have a significant impact on the safe use and stable operation of the whole bridge. Therefore, it is necessary to carry out mechanical property tests on the joint.

[0003] The joints are spliced into a whole by welding stiffening plates to the gusset plates. Part of the gusset plates are placed inside the concrete lower chord. Studs are welded on the part of the gusset plates placed inside the concrete, and the loads on the web members are gradually transmitted to the lower chord. The mechanical properties of the steel used for the studs and the gusset plates are very different from those of the concrete, and their combined strength and the load transfer effect are not yet clear.

[0004] In related tests, a special steel base and a large laboratory shear wall are used for loading, or a reaction pedestal is directly built on the site. The steel base solution is difficult to be universal in similar joint tests. Only a few units are equipped with reaction walls and the cost is high. The reaction pedestal solution requires a large open space, has a long construction period and high cost, and requires multiple jacks to be loaded simultaneously, increasing the complexity of the test process. Therefore, the requirements for joint test conditions are high, the cost is uncontrollable, and the stress behavior and failure phenomenon of the steel-concrete composite joint are not yet clear. Summary of the Invention

[0005] In order to overcome the disadvantages that the stress behavior and failure phenomenon of the steel-concrete composite joint in the above-mentioned prior art are not yet clear, and the test conditions and cost are high, the main object of the present invention is to provide a model test system for a steel-concrete composite joint.

[0006] To achieve the above object, the present invention adopts the following technical solutions. A model test system for a steel-concrete composite joint includes:

[0007] Two joint models, designated as bases;

[0008] Two connection systems, respectively arranged on the two joint models. The connection system includes two side inclined web members and a vertical web member. The vertical web member is vertically arranged on the joint model, and the two side inclined web members are inclined and arranged on both sides of the joint model, and are located on the left and right sides of the vertical web member;

[0009] The reaction force device includes two anchoring cross beams, multiple diaphragm ribs, and multiple anchoring steel shapes. The two anchoring cross beams are arranged side by side in the vertical direction and are connected to the upper end of the connection system through a connection hinge; multiple diaphragm ribs are evenly arranged on the anchoring cross beams, and multiple anchoring steel shapes are evenly arranged on the top of the anchoring cross beams. The distance between adjacent anchoring steel shapes is 8 times the distance between adjacent diaphragm ribs. Each anchoring steel shape is connected to the ground anchor system through a perforated steel plate;

[0010] Three groups of strain gauges. One group is evenly arranged on the two inclined web members and the vertical web member and their extension lines to detect the change of the web member axial force with the load application; one group is evenly arranged on the surface of the joint concrete to detect the change of the concrete deformation with the load application. The remaining group of strain gauges is arranged at the predicted stress concentration area of the joint to detect the change of the joint stress with the load application.

[0011] The inclined web member includes a steel plate welded box section, and stiffeners are arranged inside the steel plate welded box section. The thickness of the inclined web member plate affects the longitudinal stiffness.

[0012] The two inclined web members are respectively a compression inclined web member and a tension inclined web member. The compression inclined web member is made of 8 mm thick steel plate, and the tension inclined web member is made of 30 mm thick steel plate.

[0013] The connection hinge includes an ear plate and a pin shaft. The ear plate is made of 3.5 cm thick steel plate. The ear plates are connected through a pin shaft, and the diameter of the pin shaft is 10 cm.

[0014] It also includes flange plates. Between the anchoring cross beam of the reaction force device and the connection hinge, between the connection hinge and the inclined web member, and between the inclined web member and the joint, flange plates are used for connection.

[0015] It also includes two dial gauges. The two dial gauges are orthogonally arranged on the plane perpendicular to the transverse bridge direction at the load top plate. When loaded to the equivalent standard working condition load, the measured values of the dial gauges should be within a certain range.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This application is a reduced-scale model test system, which simulates the stress state of the combined joint of the actual steel truss web member and the concrete lower chord member, providing theoretical and experimental support for the stress of the bridge joint. It simulates the complex stress conditions of the steel truss web members in the actual project, with some web members in tension and some in compression, and provides fixed constraints for the joint, providing a position for the load to act when loading the joint. And sensors are arranged according to the stress behavior and failure phenomenon of the joint to monitor the stress condition of the joint in real time during the loading process. Moreover, the stress distribution law of the model joint is close to the analysis result of the original bridge model, with stress concentration at the same parts and the stress level close to the actual situation, and it can more accurately simulate the stress distribution law of the key parts of the original bridge joint. Brief Description of the Drawings

[0017] Figure 1 is a schematic structural view of the present invention when using a reaction pedestal;

[0018] Figure 2 is a schematic view of the model node loading device of the present invention;

[0019] Figure 3 is a schematic view of the sensor arrangement of the present invention;

[0020] Figure 4 is a schematic view of the sensor arrangement of the present invention;

[0021] Figure 5 is a schematic structural view of the connecting hinge ear plate of the present invention.

[0022] 1. Node model, 2. Flange plate, 3. Tension-side diagonal web member, 4. Vertical web member, 5. Compression-side diagonal web member, 6. Ear plate, 7. Pin shaft, 8. Anchor cross beam, 9. Diaphragm rib, 10. Anchor section steel, 11. Perforated steel plate, 12. Jack, 13. Load top plate, 14. Unidirectional strain gauge, 15. Triaxial strain gauge, 16. Dial indicator, 17. Concrete strain gauge. Detailed Embodiment

[0023] The present invention will be further described below in conjunction with the drawings and embodiments.

[0024] Embodiment 1:

[0025] Refer to Figures 1-5, A steel-concrete composite joint model test system, including two joint models 1, set as the base; two connecting systems, respectively arranged on the two joint models 1, the connecting system includes two side inclined web members and a vertical web member 4; the vertical web member 4 is vertically arranged on the joint model 1, the two side inclined web members are inclined and arranged on both sides of the joint model 1, and are located on the left and right sides of the vertical web member 4; a reaction force device, including two anchoring cross beams 8, a plurality of diaphragm ribs 9, and a plurality of anchoring steel sections 10, the two anchoring cross beams 8 are arranged in parallel in the vertical direction and are connected to the upper end of the connecting system through a connecting hinge; a plurality of the diaphragm ribs 9 are evenly arranged on the anchoring cross beam 8, a plurality of the anchoring steel sections 10 are evenly arranged on the top of the anchoring cross beam 8, and the distance between adjacent anchoring steel sections 10 is 8 times the distance between adjacent diaphragm ribs 9, each anchoring steel section 10 is connected to the ground anchor system through a perforated steel plate 11; three groups of strain gauges, one group is evenly arranged on the two side inclined web members, the vertical web member 4 and their extension lines to detect the change of the web member axial force with the load loading; one group is evenly arranged on the surface of the joint concrete to detect the change of the concrete deformation with the load loading, and the remaining group of strain gauges is arranged at the predicted stress concentration area of the joint to detect the change of the joint stress with the load loading.

[0026] The two side inclined web members are respectively a compression side inclined web member 5 and a tension side inclined web member 3. The compression side inclined web member 5 is made of 8 mm thick steel plate, and the tension side inclined web member 3 is made of 30 mm thick steel plate. The side inclined web member is a steel plate welded box section, and stiffening ribs are arranged inside the steel plate welded box section. The thickness of the side inclined web member plate affects the longitudinal stiffness.

[0027] The connecting hinge includes an ear plate 6 and a pin shaft 7. The ear plate 6 is made of steel plate, and the ear plate 6 is connected to the upper end of the connecting system through the pin shaft 7.

[0028] It also includes flange plates 2, which are respectively arranged between the anchoring cross beam 8 of the reaction force device and the connecting hinge, between the connecting hinge and the side inclined web member, and between the side inclined web member and the joint, and are connected by flange plates 2.

[0029] In order to more accurately control the load loading during the test, it also includes two dial gauges 16. The two 16 dial gauges are respectively arranged orthogonally on the plane perpendicular to the transverse bridge direction at the load top plate; when the load is loaded to the equivalent standard working condition load, the measured values of the dial gauges 16 should be within a certain range.

[0030] Embodiment 2

[0031] Refer to Figures 1-5, the invention mainly includes a node model 1, a connection system, and a reaction force device. The node model 1 is scaled down based on the actual engineering steel-concrete composite node; the connection system mainly connects the node model 1 and the reaction force device; the reaction force device adopts a self-balanced design. The steel-concrete composite node model 1 test system is as Figure 4 shown. The node can use the same node as the original bridge or a scaled-down node model 1 made of the same materials according to the similarity theory. When performing the scaled-down design, it should be ensured that the shear stiffness of the welded shear studs and PBL shear keys is the same as the selected geometric scaling ratio; if there are longitudinal prestressed steel strands passing through the selected test node, the same level of prestress can be added to the test node or the concrete strength of the node can be compensated by increasing ordinary steel bars, and the transverse prestressed steel strands can be ignored.

[0032] Use a jack to load on the load top plate on the tension inclined web member side of the node model 1. Reinforcing bar grabs are welded at the position of the load top plate and cast into the concrete to make them an integral whole, avoiding the concrete from cracking due to uneven load application during loading.

[0033] The load top plates of the two nodes are welded to make a 50 cm large limiting steel trough, the size of which is equal to the acting surface of the jack, to limit the position of the jack. A 62 cm space is left between the load top plates to place the jack. During loading, the jack should be loaded step by step and maintained for a period of time when each loading gradient is completed. After the deformation sensor reading of the specimen is stable and the record is completed, continue loading.

[0034] The girder part of the reaction force device is composed of double-layer HW400 steel sections arranged on both sides with stiffeners. The diaphragm rib 9 is made of Q235 steel plates with a thickness of 2 cm, and the adjacent steel plates are spaced 10 cm apart. The two layers of steel sections are connected by m18 bolts. An anchoring steel section 10 is arranged every 80 cm. The anchoring steel section 10 is welded to a 2 cm perforated steel plate 11 with an opening of 8.1 cm, and a ground anchor rod is inserted into the steel plate hole, and it is connected to the ground anchor system by using bolts for fastening.

[0035] The web members of the connection system use steel plates welded into box sections, and stiffeners are arranged inside the box sections. Its cross-sectional shape should be similar to that of the original bridge. By adjusting the thickness of the web member plates, the longitudinal stiffness can be affected, and then the force distribution between the web members can be adjusted to simulate the actual stress state of the node. The compression-side inclined web member 5 of the connection system of this model test is made of 8 mm thick steel plates, the vertical web member 4 is made of 12 mm, and the tension-side inclined web member 3 is made of 30 mm thick steel plates.

[0036] The connection system connects the reaction device through a connecting hinge to reduce the bending moment on the joint to simulate the actual stress state. The connecting hinge ear plate 6 is made of 3.5CM steel plate and is connected by a pin shaft 7 with a diameter of 10cm. A total of seven ear plates 6 are used to disperse the shear force. Four of the ear plates 6 are connected to the girder, and three ear plates 6 are connected to the web member. The upper and lower ear plates are inserted alternately at intervals. The pin shaft 7 should adopt a heat treatment process to increase its strength.

[0037] Between the reaction device cross beam and the connecting hinge, between the connecting hinge and the web member, and between the web member and the joint, flange connections are used. Among them, the flange plate 2 between the web member and the joint needs to be perforated for pouring concrete. The perforation is not larger than the box section of the web member. The flange plate 2 is made of 3.5cm Q355 steel plate and is connected by a total of ten 8.8 - grade M36 high - strength bolts arranged on both sides and a pre - tightening force of 382000N is applied. Through the design of the connecting hinge and the flange plate 2, the test joint can be disassembled and replaced more conveniently.

[0038] Two strain gauges are arranged axially along each web member to detect the change of the axial force of the web member with the load. Strain gauges are arranged on the extension line of the web member at the joint plate and the part wrapped by concrete. Data is collected in the order from far to near from the intersection point of the extension line of the chord member of the joint. By analyzing the reduction amount of the strain gauge value, that is, the difference between the value of the previous strain gauge and the value of the next strain gauge, the transfer of the load on the joint is monitored. In the ideal state, the strain gauge value at the steel - concrete combination part should decrease sharply, and the strain gauge value at the intersection point of the extension line of the web member should be less than a certain value. If it is found during the experiment that the reduction amount of the strain gauge value is less than the threshold value or the strain gauge value at the intersection point is greater than the threshold value, it proves that the steel - concrete combination strength is less than expected, and corresponding measures should be taken to increase the combination strength, such as increasing shear studs or PBL shear keys. Through finite - element analysis, three - dimensional strain gauges 15 are arranged at the positions where the stress of the joint plate is predicted to be large to monitor the stress magnitude at the key positions of the joint and its change with the load. During the loading process, the position where the stress of the joint is large generally appears at the position near the intersection of the chord member and the web member outside the concrete interface. During the loading process, the equivalent strain energy stress is calculated and recorded in real time. When the load reaches the equivalent standard working condition load, the equivalent strain energy stress should not exceed the threshold value. If it exceeds the threshold value, it is determined that the strength of the joint does not meet the design requirements, and the loading is terminated at the yield point to protect the safety of the experimental personnel.

[0039] Two dial gauges 16 are arranged orthogonally on the plane perpendicular to the transverse direction of the bridge at the load top plate to monitor the vertical displacement and longitudinal displacement of the joint with respect to the ground during loading. When arranging the dial gauges 16, the base should remain relatively stationary with respect to the ground of the test site. When the load reaches the equivalent standard working condition load, the measured value of the dial gauge 16 should be within a certain range. If it exceeds the established range, it is considered that the design stiffness of the joint of the bridge has not been achieved, and certain measures should be taken to strengthen the joint, such as increasing the thickness of the steel section used.

[0040] It should be noted that in the present invention, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device.

[0041] The above embodiments are merely illustrative examples of the present invention and do not constitute a limitation on the protection scope of the present invention. Any design identical or similar to the present invention falls within the protection scope of the present invention.

Claims

1. A test system for a steel-concrete composite joint model, characterized in that, Comprising: Two node models (1), set as the base; Two connecting systems, respectively arranged on the two node models (1), the connecting system includes two side inclined web members and a vertical web member (4); the vertical web member (4) is vertically arranged on the node model (1), the two side inclined web members are inclined and arranged on both sides of the node model (1), and are located on the left and right sides of the vertical web member (4); A reaction force device, including two anchoring cross beams (8), a plurality of diaphragm ribs (9), and a plurality of anchoring steel sections (10), the two anchoring cross beams (8) are arranged in parallel in the vertical direction and are connected to the upper end of the connecting system through a connecting hinge; a plurality of the diaphragm ribs (9) are uniformly arranged on the anchoring cross beam (8), a plurality of the anchoring steel sections (10) are uniformly arranged on the top of the anchoring cross beam (8), and the distance between adjacent anchoring steel sections (10) is 8 times the distance between adjacent diaphragm ribs (9), and each anchoring steel section (10) is connected to the ground surface through a perforated steel plate (11); Three groups of strain gauges, one group is uniformly arranged on the two side inclined web members, the vertical web member (4) and their extension lines to detect the change of the web member axial force with the load application; one group is uniformly arranged on the surface of the node concrete to detect the change of the concrete deformation with the load application, and the remaining group of strain gauges is arranged at the predicted stress concentration area of the node to detect the change of the node stress with the load application.

2. The steel-concrete composite joint model test system according to claim 1, characterized in that, The two side inclined web members are respectively a compression side inclined web member (5) and a tension side inclined web member (3), the compression side inclined web member (5) is prepared from a steel plate with a thickness of 8 mm, and the tension side inclined web member (3) is prepared from a steel plate with a thickness of 30 mm.

3. The steel-concrete composite joint model test system according to claim 1, characterized in that The side inclined web member is a steel plate welded box section, and stiffening ribs are arranged inside the steel plate welded box section, and the thickness of the side inclined web member plate affects the longitudinal stiffness.

4. The steel-concrete composite joint model test system according to claim 1, wherein The connecting hinge includes an ear plate (6) and a pin shaft (7), the ear plate (6) is made of a steel plate, and the ear plate (6) is connected to the upper end of the connecting system through the pin shaft (7).

5. The steel-concrete composite joint model test system according to claim 1, characterized in that, It further includes a flange plate (2), which is arranged between the anchoring cross beam (8) of the reaction force device and the connecting hinge, and between the connecting hinge and the side inclined web member, and the side inclined web member and the node are connected by the flange plate (2).

6. The steel-concrete composite joint model test system according to claim 1, characterized in that It further includes two dial gauges (16), the two (16) dial gauges are respectively arranged orthogonally on the plane perpendicular to the transverse bridge direction at the load top plate; when the load is applied to the equivalent standard working condition load, the measured values of the dial gauges (16) should be within a certain range.

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