A steel pipe concrete shear connector with a restraining formation

Abstract

The application discloses a steel pipe concrete shearing connecting piece with a constraint structure, which comprises a steel pipe concrete component for connecting a steel structure and a reinforced concrete structure and a tensile constraint structure thereof, the steel pipe concrete component comprises a steel pipe welded at one end with the steel structure, a high-strength and high-performance concrete filling layer poured in the steel pipe, and a steel cap embedded in the reinforced concrete structure and fixedly connected with the other end of the steel pipe, the constraint structure comprises a high-strength and high-performance concrete ring arranged on the outer periphery of the steel pipe, a tensile unit arranged on the outer periphery of the high-strength and high-performance concrete ring, and spiral reinforcement arranged around the tensile unit and the outer side of the steel pipe. The application can greatly improve the shearing strength and rigidity of the shearing connecting piece, ensure that the welding position is not a shearing weak position of the steel-concrete composite structure, effectively inhibit the splitting of the reinforced concrete and development thereof, and make the bearing capacity of each structure fully play; the shearing connecting piece has excellent structural toughness and can coordinate the deformation difference between the steel-concrete composite structures.

Description

A steel-concrete composite shear connector with a constrained structure Technical Field

[0001] This invention relates to the field of building structure technology, and in particular to a shear connector for the interface of steel-concrete composite structures. It is especially suitable for large steel-concrete composite structures with insufficient shear stiffness, easy splitting of concrete, and insufficient anti-slip performance. Specifically, it is a steel-concrete composite shear connector with a restrained structure. Background Technology

[0002] Steel-concrete composite structures, as a structural form that fully utilizes the tensile strength of steel and the compressive strength of concrete, have gained widespread acceptance in the modern bridge and construction field. In this composite system, shear connectors are key components enabling the steel beams and concrete flanges to work together, bearing the important functions of transmitting longitudinal shear force at the interface and resisting vertical uplift forces. Among various shear connector types, ordinary studs have become the most widely used connector type in engineering applications due to their simple manufacturing process, convenient construction, isotropy, and ease of on-site welding. However, traditional studs are prone to problems such as concrete splitting, weld fatigue, and insufficient stiffness under high stress, repeated loading, thin-plate structures, or ultra-high performance concrete (UHPC) scenarios, which restrict the load-bearing efficiency and durability of composite beams.

[0003] Chinese invention patent CN106088469B discloses a shear-resistant stud connector, which is an ultra-large head stud, belonging to the geometrically optimized type. Its technical principle is to increase the concrete bearing area by enlarging the stud head diameter (e.g., stud head diameter ≥ 1.6 times stud rod diameter), thereby improving anchoring force and shear resistance. The advantages of this technical solution are: it constrains concrete splitting through the stud head pressure field; and it is suitable for thin-plate structures (the length-to-diameter ratio can be relaxed to 2~4). Its limitations are: limited improvement in shear stiffness, making it difficult to meet the needs of thicker, higher-strength steel-concrete composite structures; limited improvement in shear strength and fatigue resistance at welded positions; and insufficient utilization of the high-strength steel's potential, resulting in inadequate material performance utilization.

[0004] Chinese invention patent CN106969975B discloses a shear stud in a steel-concrete composite structure, which is a stress-optimized type. Its technical principle is to design the lower part of the stud as a trumpet-shaped cone (the diameter of the stud base is 2 to 2.5 times the stud rod diameter), transferring stress to the more ductile middle part of the stud and reducing stress concentration at the weld point. Through geometric reconstruction, plastic strain is transferred to areas outside the weld point, reducing the risk of ultra-low cycle fatigue. The shear bearing capacity is 2 to 3 times that of ordinary studs; material utilization is improved (saving approximately 30% of steel). Limitations include: the risk of concrete splitting is not completely eliminated; the increase in shear stiffness is limited (only 2 to 3 times); the advantages of high-strength steel cannot be fully utilized; stress is still concentrated at the stud root, and the concrete flange is prone to longitudinal splitting under cyclic loads, restricting the performance of the composite structure.

[0005] Chinese invention patent publication CN111155718B discloses a split-type stud, which is a structural innovation. Its technical principle is to divide the stud into multiple split parts, with the gaps filled with elastic material to promote the redistribution of internal forces in the concrete. The split parts deform independently, adapting to the brittleness of high-strength concrete; the overall length-to-diameter ratio can be reduced to 2, making it suitable for thin slabs. Its advantages include improved ductility, leveraging the properties of high-strength materials; and convenient construction (direct casting is possible). Its disadvantages include: the split structure weakens the overall stiffness, resulting in limited improvement in overall shear stiffness; aging of the elastic material may affect long-term performance; base expansion may exacerbate local compressive stress; and the risk of concrete splitting remains unresolved.

[0006] In recent years, steel-concrete composite structures have become increasingly large-scale, with spans approaching or even exceeding 60m. Large composite structures have thick concrete slabs (thickness can reach over 700mm, while existing floor slabs are 120-150mm thick and existing bridge decks are typically 250-350mm thick), requiring high shear stiffness at the joint surfaces and necessitating shear-resistant connectors that match the thickness of the slabs. If existing stud shear connectors are used, the following problems may exist: (1) The shear stiffness of the stud shear connectors themselves is insufficient. The studs will bend and deform under greater shear force, which cannot meet the use requirements of large steel-concrete composite structures, and the compressive performance of concrete will not be fully utilized; (2) If only the design size of the stud shear connectors is increased, the studs (i.e. steel bars) after the size is increased have excessive stiffness, which is not coordinated with the stiffness of the surrounding reinforced concrete. It still cannot effectively solve the splitting risk of reinforced concrete structures, or the stress is concentrated at the root of the stud shear connectors, which can easily lead to brittle shear failure of the steel-concrete interface, which seriously threatens the safety of steel-concrete composite structures; (3) Existing stud shear connectors are subjected to complex forces, and it is difficult to accurately calculate the actual shear stiffness that they can withstand. The design pressure and safety risks are high, and they cannot be widely promoted and applied. Their economic value is not fully utilized; (4) The shear slip limit of the shear connectors is very small, but the actual shear deformation of large steel-concrete composite structures is much greater than the slip limit. The slip resistance is insufficient and the toughness is insufficient.

[0007] Therefore, it is necessary to propose a steel-concrete composite shear connector with a constrained structure to solve one of the aforementioned technical problems. Summary of the Invention

[0008] To address one of the problems in existing technologies, this invention proposes a steel-concrete composite shear connector with a constrained structure. This connector effectively suppresses the development of splitting cracks in reinforced concrete structures, stably and effectively improves the shear strength and shear stiffness of the interface, reduces excessive interface slip, increases material utilization, and enhances the toughness of the shear connector. It also considers ease of construction and economy, making it suitable for larger steel-concrete composite structures and promoting the wider application of steel-concrete composite structures in engineering projects.

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

[0010] A steel-concrete composite shear connector with a constraint structure includes a steel-concrete composite member for connecting a steel structure and a reinforced concrete structure, and a constraint structure disposed on the outer periphery of the steel-concrete composite member. The constraint structure includes a high-strength, high-performance concrete ring disposed on the outer periphery of the steel-concrete composite member, a tensile unit disposed on the outer periphery of the high-strength, high-performance concrete ring, and spiral reinforcements surrounding the tensile unit and the outer side of the steel-concrete composite member. The steel-concrete composite member includes a steel pipe welded to the steel structure at one end, a high-strength, high-performance concrete filling layer poured inside the steel pipe, and a steel pipe cap embedded inside the reinforced concrete structure and fixedly connected to the other end of the steel pipe.

[0011] As a preferred technical solution of the present invention, the steel pipe is a round steel pipe or a rectangular steel pipe, and the steel pipe material can be one of carbon structural steel or low alloy high strength structural steel.

[0012] As a preferred embodiment of the present invention, the length of the steel pipe is not less than 90% of the height of the reinforced concrete structure and not greater than the height of the reinforced concrete structure minus the thickness of the steel pipe cap and the thickness of the concrete protective layer of the reinforced concrete structure. Preferably, the length of the steel pipe is the height of the reinforced concrete structure minus the thickness of the steel pipe cap and the thickness of the concrete protective layer of the reinforced concrete structure.

[0013] As a preferred embodiment of the present invention, for a round steel pipe, the outer diameter of the steel pipe is 1 / 8 to 1 / 4 of the length of the steel pipe; the wall thickness of the steel pipe is 1 / 15 to 1 / 5 of the outer diameter of the steel pipe, preferably 1 / 10, and not less than 4 mm.

[0014] As a preferred technical solution of the present invention, for a round steel pipe, the thickness of the steel pipe cap is not less than twice the wall thickness of the steel pipe and not less than 1 / 5 of the outer diameter of the steel pipe; the outer diameter of the steel pipe cap is 1.4 to 1.7 times the outer diameter of the steel pipe; designing the diameter and thickness of the steel plate of the steel pipe cap can increase the embedding capacity of the steel pipe concrete component.

[0015] As a preferred embodiment of the present invention, for rectangular steel pipes, the long side is arranged parallel to the shearing direction, the short side of the steel pipe is 1 / 8 to 1 / 6 times the length of the steel pipe, the long side of the steel pipe is 1.5 to 2 times the short side; the wall thickness of the steel pipe is 1 / 15 to 1 / 6 of the short side, preferably 1 / 10.

[0016] As a preferred technical solution of the present invention, for rectangular steel pipes, the thickness of the steel pipe cap is not less than twice the wall thickness of the steel pipe and not less than 1 / 5 of the short side length of the steel pipe; the short side length of the steel pipe cap is 1.4 to 1.7 times the short side length of the steel pipe, and the long side length of the steel pipe cap is 1.4 to 1.7 times the long side length of the steel pipe; by designing the diameter and thickness of the steel plate of the steel pipe cap, the embedding capacity of the shear connector of the steel pipe concrete component in the reinforced concrete structure can be increased.

[0017] As a preferred embodiment of the present invention, the steel pipe cap is provided with a pouring hole at its center. The diameter or side length of the pouring hole is 0.3 to 0.5 times the outer diameter or short side length of the steel pipe, and not less than 25 mm.

[0018] As a preferred technical solution of the present invention, the high-strength and high-performance concrete filling layer adopts high-strength and high-performance fine stone concrete or UHPC (ultra-high performance concrete), with a strength of not less than C80 and the nominal particle size of coarse aggregate not greater than 0.4 times the diameter of the pouring hole.

[0019] As a preferred embodiment of the present invention, the high-strength, high-performance concrete ring is made of high-strength, high-performance fine aggregate concrete or UHPC (ultra-high performance concrete), which has a strength higher than that of reinforced concrete structures, preferably not lower than C80. The outer diameter of the high-strength, high-performance concrete ring is not less than 1.4 to 1.7 times the outer diameter of the steel pipe, and its wall thickness is not less than 25 mm and not greater than the minimum spacing of the main reinforcement in the reinforced concrete structure. The maximum nominal particle size of the coarse aggregate in the high-strength, high-performance concrete ring is 10 mm. The tensile unit is a high-strength prestressed steel wire, elastic fiber rope, or high-strength fiber fabric wrapped around the outer cylindrical surface of the high-strength, high-performance concrete ring.

[0020] As a preferred technical solution of the present invention, in application, multiple steel-concrete composite shear connectors with constraint structure are provided at the connection between the steel structure and the reinforced concrete structure. The number of such connectors should be determined according to relevant calculation requirements. The net distance between adjacent steel pipes should not be less than 100mm, and the center distance between adjacent steel pipes should not be greater than the thickness of the reinforced concrete structure.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] (1) Compared with traditional studs, this invention increases the shear stiffness of shear connectors by about 30 times through the strong shear stiffness and ductility of steel-concrete composite members, achieving a qualitative leap in shear stiffness. The slippage of the steel-concrete interface after deformation under load can be transformed from the original observation after loading into a quantifiable structural physical calculation index. The increase in total stiffness transforms the slippage of the interface from nonlinear to linear quantifiable index (such as inter-story shear angle), which helps to realize the quantitative design of shear strength and stiffness of the shear surface and ensures the interface strength and stiffness requirements that match the design requirements of the composite structure.

[0023] (2) Effectively suppressing splitting of ordinary reinforced concrete structures: Tensile units and spiral reinforcement limit the development of splitting in reinforced concrete structures to the core area (25-30mm), improve the durability of reinforced concrete in steel-concrete composite structures, and the shear bearing capacity is controlled by the nominal shear stress strength of the steel pipe section (the safety factor depends on the steel pipe material).

[0024] (3) Improved material utilization and applicability: High-strength steel pipes (carbon structural steel, low alloy high-strength structural steel) can be welded to Q235B / Q345B steel structures. The material of the steel pipe breaks through the limitation of ML15 grade stud material. Moreover, the cross-sectional area and rotational inertia of the steel pipe are much greater than the physical and mechanical properties of the cross-section of the traditional stud. It can fully realize the shear stiffness of the shear connection by tens of times on the basis of complete shear connection, greatly reduce the shear deformation of the joint surface, and improve the combination performance and durability of the composite components. It is particularly suitable for heavy-load structures, long-span bridges, trusses, high-rise buildings and other common steel-concrete composite and hybrid structures, which is very beneficial to improving the overall performance of the strength and toughness of steel-concrete prefabricated structures.

[0025] (4) The present invention uses steel-concrete composite members as shear connectors, which can effectively ensure the strength and stiffness of the welded joint between the steel-concrete composite structure and the steel structure, and ensure that it does not become a weak shear position in the steel-concrete composite structure, and can give full play to the bearing capacity of the steel-concrete composite; the steel pipe itself has a large stiffness, plus the stiffness provided by the high-strength concrete filling layer inside, the total shear stiffness of the steel-concrete composite member is large, which can meet the use requirements; and the steel pipe in the present invention has a certain elasticity, which can realize the redistribution of internal forces between connectors and can realize the coordination of the deformation difference between the steel structure and the reinforced concrete structure.

[0026] (5) Since the average elastic modulus of the steel-concrete composite member is close to that of its confined structure and the surrounding reinforced concrete structure, the steel-concrete composite member can produce coordinated deformation with its confined structure and the surrounding reinforced concrete structure. Thus, the steel-concrete composite member can exert a certain elasticity. On the one hand, the shear load borne by the welded weak position is transformed to be borne by the steel-concrete composite member, which can effectively prevent the welded position from becoming a shear weak position. On the other hand, when the steel pipe undergoes a certain deformation in the shear direction, the confined structure can diffuse the stress and deformation borne by the steel-concrete composite member, avoiding the concentrated transfer to the ordinary reinforced concrete structure behind the steel-concrete composite member, and avoiding its splitting. Traditional stud shear connectors, even when combined with the confined structure, do not give full play to the advantages of studs and confined structures. This invention can give full play to the advantages of steel-concrete composite and confined structure, so that the shear connector can provide sufficient shear strength and stiffness while having a certain shear deformation bearing capacity (i.e. anti-slip capacity) and strong toughness, thereby ensuring the safety and stability of large steel-concrete composite structures. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0028] Figure 1 is a structural schematic diagram of the circular steel tube concrete shear connector with constraint structure of the present invention.

[0029] Figure 2 is a schematic diagram of the cross-section of a circular steel tube concrete shear connector with a constrained structure.

[0030] Figure 3 is a top view of a circular steel tube concrete shear connector with a constrained structure; D1 is the outer diameter of the steel tube (inner diameter of the high-strength, high-performance concrete filling layer); D2 is the outer diameter of the steel tube cap; D3 is the outer diameter of the high-strength, high-performance concrete filling layer (i.e., the inner diameter of the steel tube); D4 is the diameter of the pouring hole; D5 is the outer diameter of the high-strength, high-performance concrete ring; D6 is the outer diameter of the tensile unit; D7 is the diameter of the spiral reinforcement.

[0031] Figure 4 shows the plan layout of the circular steel tube concrete shear connector with constraint structure.

[0032] Figure 5 is a schematic diagram of the neutral axis shear deformation of a circular steel tube concrete shear connector with a constrained structure; where L is the distance between the neutral axis of the reinforced concrete slab and the neutral axis of the steel beam flange plate, L=(d+h) / 2, ΔL is the shear deformation of the neutral axis of the reinforced concrete slab, d is the thickness of the steel beam flange plate, h is the thickness of the neutral axis of the reinforced concrete slab, and the neutral axis is represented by a dashed line.

[0033] Figure 6 is a structural schematic diagram of a rectangular steel tube concrete shear connector with a constrained structure; where A1 is the length of the long side of the rectangular steel tube and B1 is the length of the short side of the rectangular steel tube.

[0034] Figure 7 is a schematic diagram of the shear force ratio of steel-concrete composite tubes relative to 22mm diameter studs.

[0035] Figure 8 is a schematic diagram showing the ratio of the shear stiffness of concrete-filled steel tubing to that of a 22mm diameter stud.

[0036] Figure 9 shows the relationship between shear stiffness and cross-sectional area.

[0037] Figure 10 is a comparison of the load-slip (Vs) curves of ordinary studs and steel-concrete composite shear connectors.

[0038] Figure 11 shows the simulation results of a 300mm thick reinforced concrete slab using traditional studs, and the internal force cloud diagram of the traditional stud shear connector when the slip displacement is 2mm.

[0039] Figure 12 shows the simulation results of a 300mm thick reinforced concrete slab using steel-concrete composite members, and the internal force cloud diagram of the steel-concrete composite shear connector when the slip displacement is 2mm.

[0040] Figure 13 is a schematic diagram of the structural model for the rollout test; where Figure (a) is a schematic diagram of the vertical section and Figure (b) is a schematic diagram of the horizontal section.

[0041] Among them: 1. Steel pipe; 2. Steel pipe cap; 3. High-strength and high-performance concrete filling layer; 4. Pouring hole; 5. High-strength and high-performance concrete ring; 6. Tensile unit; 7. Spiral reinforcement; 10. Steel beam flange; 11. Reinforced concrete slab flange. Detailed Implementation

[0042] The present invention will be further described below with reference to embodiments.

[0043] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "provided with" and "connected" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0044] It should be noted that the steel-concrete composite shear connector with a constrained structure proposed in this invention is particularly suitable for large steel-concrete composite structures with insufficient shear stiffness, easy splitting of concrete, and insufficient anti-slip performance, i.e., situations where steel structures are combined with ordinary reinforced concrete structures. The steel structure includes, but is not limited to, steel beams and steel plates, while the ordinary reinforced concrete structure includes, but is not limited to, reinforced concrete slabs and reinforced concrete beams.

[0045] Implementation method one;

[0046] This embodiment uses a large steel-concrete composite structure composed of steel beams and reinforced concrete slabs as an example to explain in detail the specific structural construction of the shear connector. It should be noted that the "steel-concrete composite member" in this embodiment is not an ordinary solid stud, but a steel-concrete composite member obtained through the inventor's technological innovation. After the steel pipe 1 and the steel pipe cap 2 are connected, it has an appearance similar to a large stud, but it is not a large solid stud or a solid steel bar. Instead, it uses a hollow steel pipe 1 as the core component, and then fills the inside of the hollow steel pipe 1 with high-strength, high-performance concrete. In this embodiment, the steel-concrete composite is not used as one of the main structural components of the building, but as a shear connector between structural components of different materials, representing an innovation in the application of steel-concrete composite. This embodiment uses the steel-concrete composite shear connector for connecting the flange 10 of the steel beam and the flange 11 of the reinforced concrete slab.

[0047] Please refer to Figures 1-3. This embodiment provides a steel-concrete composite shear connector with a constrained structure. The connector's structure, from the inside out, consists of: an inner layer with a steel pipe 1 as its core; a high-strength, high-performance concrete filling layer 3 filling the inside of the steel pipe 1; a high-strength, high-performance concrete ring 5 tightly surrounding the outer periphery of the steel pipe 1; tensile units 6 tightly surrounding the outer periphery of the high-strength, high-performance concrete ring 5; and spiral reinforcement 7 arranged at certain intervals around the outer side of the tensile units 6. The bottom of the steel pipe 1 is welded to the flange 10 of the steel beam, and the top of the steel pipe 1 is connected to a steel pipe cap 2, which is embedded in the flange 11 of the reinforced concrete slab.

[0048] Specifically, a steel cap 2 with a diameter of 85mm and a thickness of 15mm is welded to the top of the steel pipe 1. The thickness of the steel cap 2 must be at least twice the pipe thickness and 1 / 5 of the pipe diameter (the diameter and thickness of the steel plate of the steel cap 2 are used to increase the embedding capacity of the connector in the concrete slab). The steel cap 2 is embedded in the flange 11 of the reinforced concrete slab. The steel cap 2 has a pouring hole 4 with a diameter or side length of about 25-30mm. High-strength fine stone concrete or high-strength high-performance concrete such as UHPC is poured into the steel pipe 1 through the pouring hole 4 on the steel cap 2. The high-strength, high-performance concrete filling layer 3 is used. The high-strength, high-performance concrete ring 5 at the force transmission contact area of ​​the steel pipe 1 is made of high-strength, high-performance fine aggregate concrete or UHPC ring, with a strength higher than that of the reinforced concrete slab flange 11. An outer constraint system is set outside this high-strength, high-performance concrete ring 5, including tensile units 6 that directly encircle the high-strength, high-performance concrete ring 5 in the circumferential direction, and spiral reinforcement 7 tied to the outside of the tensile units 6. The spiral reinforcement 7 is finally cast into the reinforced concrete slab flange 11 to form an integral whole with the reinforced concrete slab flange 11. The length of the steel pipe 1 is as close as possible to the thickness of the reinforced concrete slab, only needing to deduct the thickness of the steel pipe cap 2 and the thickness of the concrete protective layer of the steel pipe cap 2.

[0049] Specifically, the steel pipes used are round or rectangular steel pipes. The steel pipe material can conform to national standards for carbon structural steel and low-alloy high-strength structural steel, as well as other special steel materials that have passed relevant inspections. The specific design and selection of steel-concrete shear connectors must be based on the minimum bearing capacity requirements of both the connected steel and reinforced concrete materials. The connectors should be selected within the recommended range according to the combined structural performance requirements, such as bearing capacity and connection stiffness. Their quantity and arrangement must be determined according to relevant calculation regulations. Furthermore, the combined structural members must be verified under different design stress states based on the selection and design arrangement of the connectors, ensuring that the reinforced concrete and steel structures in the combined structural members meet the relevant structural design specifications for reinforced concrete and steel structures, respectively.

[0050] Specifically, the high-strength, high-performance concrete ring 5 is made of high-strength, high-performance fine-aggregate concrete, with an outer diameter 25mm larger than the outer diameter of the steel pipe. The minimum spacing requirement for reinforcing bars is still met between the steel pipe 1 and the connecting parts after the constraint structure is completed. High-strength, high-performance fine-aggregate concrete of grade C80 or higher is preferred, with a maximum nominal particle size of 10mm for the pebbles or crushed stone (coarse aggregate). High-strength, high-performance concrete refers to concrete with a large number of micro-units such as tiny tensile fibers added to compensate for low tensile strength and improve or enhance the crack resistance of the concrete.

[0051] Specifically, the tensile element 6 is a high-strength prestressed steel wire, elastic fiber rope, or high-strength fiber fabric wrapped around the outer cylindrical surface of the high-strength, high-performance concrete ring 5. The carbon fiber fabric is tightly wrapped around the outer cylindrical surface of the high-strength, high-performance concrete ring 5 2-3 times, and the density of the carbon fiber fabric is 200-300 g / m³. 2 Preferably 300g / m 2 High-strength steel wires are formed on the outer surface of the high-strength, high-performance concrete ring 5 using a winding method, effectively constraining and anchoring it. Furthermore, to reduce the possibility of splitting at the flange 11 of the reinforced concrete slab near the steel pipe 1, circumferential prestress can be applied to the high-strength, high-performance concrete ring 5. This circumferential prestress is achieved through an anchor embedded in the high-strength, high-performance concrete ring 5. The anchor is a rectangular block structure, positioned along the length of the high-strength, high-performance concrete ring 5, with several groups of holes on its left and right sides for the prestressed steel wires to pass through. These holes are used for the helical tensioning and anchoring of the prestressed steel wires, as well as for anchoring the anchoring clips that provide circumferential prestress. This prestressed anchor structure applies circumferential prestress to the high-strength concrete cylinder within the core area surrounding the steel pipe, preventing splitting of the concrete within the core area surrounding the steel pipe concrete member, thereby improving the load-bearing capacity of the connector and significantly reducing slippage caused by splitting. The spiral reinforcement is preferably made of Ф4 spiral reinforcement, with no less than 4 turns. The spiral reinforcement is concentrically wrapped around the outside of the high-strength and high-performance concrete ring 5 and formed in the flange 11 of the reinforced concrete slab by casting. The inner diameter of the spiral reinforcement 7 is 25-30mm larger than the diameter of the tensile unit 5.

[0052] Specifically, the connection between steel pipe 1 and steel beam flange 10 is butt welding. When using butt welding, the steel pipe cap 2 must first be connected to steel pipe 1, and then steel pipe 1 and upper flange steel plate of steel beam are butt welded together.

[0053] Specifically, round steel pipes are used. The length of steel pipe 1 is the height of the reinforced concrete slab minus the thickness of the steel pipe cap and the thickness of the concrete protective layer of the reinforced concrete slab; the outer diameter of the steel pipe is 1 / 8 to 1 / 4 of the length of the steel pipe, and the wall thickness of the steel pipe is 1 / 10 of the outer diameter of the steel pipe, and not less than 4mm; the outer diameter of the steel pipe cap is 1.4 to 1.7 times the outer diameter of the steel pipe, and the thickness of the steel pipe cap is not less than 2 times the wall thickness of the steel pipe and not less than 1 / 5 of the outer diameter of the steel pipe, but should not be too thick.

[0054] In application, multiple steel-concrete composite shear connectors with restraint structures are installed at the connection between the steel beam flange and the reinforced concrete slab flange, arranged in a rectangular array. The number should be determined according to relevant calculations. The clear distance between adjacent steel pipes should not be less than 60mm, and the center distance between adjacent steel pipes should not be greater than the thickness of the reinforced concrete slab. The spacing between the steel pipes is generally consistent with the spacing of the main reinforcement bars in its arrangement direction.

[0055] Implementation method two;

[0056] Unlike embodiment one, this embodiment uses a rectangular steel pipe as the core component. The length of the steel pipe 1 is the height of the reinforced concrete slab minus the thickness of the steel pipe cap and the thickness of the concrete protective layer of the reinforced concrete slab. The long side of the steel pipe 1 is parallel to the shear direction of the steel-concrete composite structure. The short side of the steel pipe is 1 / 8 to 1 / 6 of the length of the steel pipe, and the long side of the steel pipe is 1.5 to 2 times the length of the short side. The wall thickness of the steel pipe is 1 / 10 of the length of the short side. The short side of the steel pipe cap is 1.4 to 1.7 times the length of the short side of the steel pipe, and the long side of the steel pipe cap is 1.4 to 1.7 times the length of the long side of the steel pipe.

[0057] In application, multiple steel-concrete composite shear connectors with restraint structure are provided at the connection between the steel beam flange and the reinforced concrete slab flange, arranged in a rectangular array. The number should be determined according to relevant calculation requirements. The net distance between adjacent steel pipes should not be less than 60mm, and the center-to-center distance between adjacent steel pipes should not be greater than the thickness of the reinforced concrete slab.

[0058] Next, the technical principles and basis of the steel-concrete composite structure used in this invention will be explained.

[0059] (1) The reason for replacing the original cylindrical steel solid stud connector with a steel-concrete shear connector is as follows:

[0060] Using formulas from mechanics of materials and structural mechanics It can be seen that the shear stiffness K of a single shear connector is inversely proportional to the cube of the distance L between the neutral axis of the reinforced concrete slab and the neutral axis of the steel beam flange 10, and directly proportional to the moment of inertia I of the shear connector. When the distance L between the neutral axis of the reinforced concrete slab and the neutral axis of the steel beam flange 10 is greater than 2 to 3 times the diameter of the solid shear connector, the shear stiffness of the shear connector shows a rapid decreasing trend, and the "shear-pry" mechanical behavior exhibits obvious nonlinear mechanical behavior.

[0061] When using traditional solid studs (maximum diameter d is only 25mm) to connect relatively thick ordinary reinforced concrete slabs (e.g., 150-700mm), the thickness of the ordinary reinforced concrete slab is large and the L / d ratio reaches more than 3 times. Due to the insufficient rotational stiffness of the studs, the respective properties and interaction capabilities of steel and concrete cannot be fully utilized. However, the rotational inertia of steel-concrete composite members is proportional to the fourth power of their width B or diameter D. Increasing the width B or diameter D on the basis of the constrained structure has the following technical and theoretical advantages and breakthroughs: steel-concrete composite members can effectively solve the problem of insufficient shear stiffness of steel solid studs. While increasing the shear strength by about 4 times, the shear stiffness can be increased by more than 30 times, which greatly improves the working performance and efficiency of steel-concrete composite shear connectors.

[0062] When steel-concrete composite shear connectors possess sufficient shear stiffness, the nonlinear mechanical behavior between the joint surfaces can be transformed into approximately linear mechanical behavior. The slippage of the joint surface after loading deformation can be converted from an observational measure under load into a quantifiable structural physical calculation index (such as inter-story shear angle) of the neutral axis shear deformation between the concrete slab and the connecting steel plate. This lays a fundamental technical foundation for establishing digital standards for composite components. For specific quantitative calculation methods, please refer to "Analysis Method for Calculation Model of Steel-Concrete Composite Beam Based on Shear Stud Connection" (CN108614936B).

[0063] (2) The reason for not replacing the original cylindrical steel solid stud connector with a steel bar as a shear connector is as follows:

[0064] Given the trend towards larger steel-concrete composite structures, simply enlarging traditional stud shear connectors into giant steel studs is insufficient to meet the actual performance requirements of steel-concrete composite structures. However, compared to giant steel studs (or bars) of the same diameter, steel-concrete composite shear connectors with confined structures significantly improve the shear stiffness of the connectors while also possessing a certain degree of elasticity. This allows for the redistribution of internal forces between the connectors and the coordination of deformation differences between the steel beams and concrete. Regardless of the deformation, the high-strength concrete filling layer inside the steel tube and the high-strength, high-performance concrete ring within the confined structure can effectively transfer the interaction to the outer ordinary reinforced concrete slab flange 11 without affecting the durability of the ordinary reinforced concrete.

[0065] When giant steel solid studs are used to fix solid steel bars with a diameter of 60mm to steel beams by welding, the enormous welding heat will severely alter the metallic properties of the steel in the weld area of ​​the steel plate flange 10 of the steel beam, causing the steel to deteriorate, become brittle, or experience a decline in performance. While the welding strength of giant steel solid studs is not significantly different from that of steel pipes, using giant steel solid studs will make the welded connection between the stud and the steel structure a weak point in shear resistance, creating potential problems. In practice, it is difficult to achieve good welding, and the excessive shear strength of giant steel solid studs is unnecessary. When the studs are replaced with steel-concrete composite members, the elastic modulus of steel-concrete composite members is similar to that of reinforced concrete structures (superior to steel bars). Steel-concrete composite members can coordinate some deformation, making the welded connection less likely to become a weak point in shear resistance. The use of beveled butt welding with equal or super strength for the thick-walled steel pipe 1 and the steel plate of the steel beam flange 10 is a simple, mature, and low-cost technology that is easy to implement for quality acceptance and inspection. The shear connection of the steel pipe concrete component with restraint structure is a key tool for improving the composite performance of thick plate composite components while ensuring the durability of concrete. It is also a key tool for digitally quantifying the working state and structural calculation of thick plate composite components.

[0066] Specific Implementation Example 1;

[0067] Please refer to Figures 1-3. This embodiment provides a steel-concrete composite shear connector with a constrained structure. In this embodiment, the steel-concrete composite shear connector is manufactured using steel pipe 1 as the connection base. The steel pipe 1 is a commercially available 60mm diameter steel pipe with a thickness of 6mm. Simultaneously, pipe welding is used to connect the steel pipe 1 to the steel plate of the steel beam flange 11. A cylindrical mold with an inner diameter of 110mm is concentrically fitted onto the outside of the steel pipe 1. A C80 high-strength, high-performance concrete ring 5 (using high-strength fine-aggregate concrete ring) is poured inside the cylindrical mold. The maximum nominal particle size of the pebbles or crushed stone in the poured high-strength, high-performance concrete ring 5 is 10mm. UHPC concrete is poured into the pouring hole 4. After the UHPC concrete hardens, the cylindrical mold is removed, and it is cured for 28 days. Then, 300g / m³ concrete is used. 2 Carbon fiber fabric (the density of carbon fiber fabric is 200-300 g / m³) 2 Preferably 300g / m 2The high-strength, high-performance concrete ring 5, acting as tensile element 6 (meeting the relevant requirements for important components in the "Code for Design of Strengthening Concrete Structures" (GB50367-2013), is wrapped around the side surface of the column 2-3 times. This tensile element is designed to address the defects caused by concentrated local pressure on the concrete within a 25mm radius around the steel pipe 1. In this way, on the one hand, the locally placed high-strength, high-performance concrete ring 5 improves the splitting resistance; on the other hand, the carbon fiber fabric, acting as tensile element 6, provides circumferential restraint, effectively constraining the splitting and splitting development of the flange of the reinforced concrete slab at the outer edge of the steel pipe 1, thus solving the problem of easy splitting of concrete by studs in traditional steel-concrete composite structures from the source.

[0068] Before welding the steel pipe concrete shear connector to the steel beam flange 10 according to the butt welding specifications and before pouring the reinforced concrete slab flange 11, a Ф4 spiral bar 7 with an inner diameter of 140mm is fixed on the outside of the high-strength and high-performance concrete ring 5 with the same center. The spiral bar 7 is wound 4 times. After the spiral bar 7 is fixed, the concrete is poured and finally formed in the reinforced concrete slab flange 11. The thickness of the concrete protective layer above the steel pipe cap 2 only needs to meet the specifications.

[0069] At this point, the high-strength, high-performance concrete ring 5 in the steel-concrete composite shear connector is formed in the reinforced concrete slab flange 11, acting as a shear connector at the steel-concrete composite interface. Its outer side is effectively constrained by the carbon fiber fabric, effectively improving its resistance to local compressive stress in the steel-concrete composite member. The local compressive stress concentration effect of the steel pipe 1 is diffused through the high-strength, high-performance concrete ring 5 within a 25mm radius around the steel pipe 1, and then transferred to the reinforced concrete slab flange 11, where the local compressive stress extends beyond the carbon fiber fabric (tensile unit 6) by an additional 25mm, significantly reducing the stress. The spiral reinforcement 7 is used to resist the local compressive stress diffused to the area beyond the diameter of the carbon fiber fabric by an additional 25mm, preventing longitudinal splitting failure of the reinforced concrete slab flange 11. The number of these reinforcements should be determined according to relevant calculations, with a minimum clear distance between the steel pipes of not less than 100mm, and the center-to-center spacing of the steel pipes should preferably not exceed the thickness of the concrete slab.

[0070] The force analysis can be performed by referring to Figure 1-3.

[0071] The shearing and prying effect of steel pipe 1 causes the concrete within a 25mm radius (30mm in Example 1) of steel pipe 1 to split under stress. However, the high-strength, high-performance concrete ring 5 and the effective constraint of the carbon fiber fabric prevent further outward expansion of the split. This significantly increases the local compressive bearing capacity of the concrete within the 25mm radius of steel pipe 1. When the local compressive force from steel pipe 1 diffuses through the 25mm of high-strength, high-performance concrete to the ordinary concrete of the reinforced concrete slab flange 11 (25mm beyond the diameter of the carbon fiber fabric), the stress on the ordinary concrete is greatly reduced. Simultaneously, the diffusion of longitudinal shear force within the reinforced concrete slab flange 11 between adjacent steel pipe concrete shear connectors is also strongly constrained by the spiral reinforcement 7 (25mm beyond the diameter of the inner carbon fiber fabric), preventing longitudinal splitting cracks between adjacent shear connectors. This essentially solves the problem of longitudinal splitting cracks along the central axis of steel pipe 1 in the reinforced concrete slab flange 11 caused by shearing of the steel pipe concrete shear connectors. Therefore, the cracks caused by the negative bending moment at the support of the reinforced concrete slab flange 11 can only occur 25mm away from the centerline of the steel pipe 1, and it is basically no longer necessary to configure more transverse main reinforcement at the top and bottom of the reinforced concrete slab flange 11.

[0072] The number of transverse main reinforcement bars at the top of the reinforced concrete slab flange 11 can be determined by calculating the negative bending moment at the reinforced concrete slab support, while the number of transverse main reinforcement bars at the bottom is determined by calculating the mid-span bending moment of the reinforced concrete slab. However, it is required that the transverse main reinforcement bars at the bottom of the reinforced concrete slab be anchored at the support as continuous tension reinforcement bars or separately as tension reinforcement bars, just like the transverse main reinforcement bars at the top. In the negative bending moment zone of the composite beam, the longitudinal reinforcement bars at the top of the reinforced concrete slab flange 11 along the longitudinal shear direction can be determined by calculating the rotation requirements and capacity of the negative bending moment tension zone of the composite beam. Under the normal serviceability limit state, the calculation of the crack width in the negative bending moment zone of the composite beam (structure) can refer to the comprehensive force ratio (Rp) of the reinforcement in the negative bending moment tension zone of the composite beam (structure) and convert the composite beam (structure) into a reinforced concrete structure for verification by equivalent conversion of the bending stiffness. The longitudinal main reinforcement at the bottom of the reinforced concrete slab along the longitudinal shear direction can be configured according to the requirement that the minimum reinforcement ratio of the tensile reinforcement is not less than 0.20% to ensure good connection with the current steel structure and concrete codes.

[0073] The calculation methods for the shear design value, shear stiffness of the steel pipe, shear stiffness of the concrete filling inside the steel pipe, stiffness of the concrete confining outside the steel pipe, and total shear stiffness of the steel pipe shear connector in this invention are as follows.

[0074] Shear design value of steel-concrete composite shear connector Calculate using the following formula:

[0075] ;

[0076] In the formula, This is the design value for shear force. For cross-sectional area, The shear stress is given; the wall thickness of the steel pipe is taken as 0.1d of the outer diameter (taking 0.1d can reduce the shear stress and ensure the rigidity and elasticity of the steel pipe).

[0077] Shear stiffness of steel pipe Calculate using the following formula:

[0078] ;

[0079] In the formula, For the shear stiffness of the steel pipe itself, The elastic modulus of the steel pipe is... Let be the moment of inertia of the steel pipe section. This is the distance between the neutral axis of the concrete slab and the connecting steel plate.

[0080] The moment of inertia of steel pipes of different shapes is calculated using the following formula:

[0081] , , ;

[0082] In the formula, Let be the moment of inertia of the cross section of the circular steel pipe. Where is the diameter of the round steel pipe. Let be the moment of inertia of the square steel tube section. Let be the side length of the square steel pipe. The moment of inertia of the rectangular steel tube section, For the shorter side length, The length of the longer side.

[0083] shear stiffness of concrete Calculate using the following formula:

[0084] ;

[0085] In the formula, This refers to the shear stiffness of concrete. This refers to the shear stiffness of the high-strength concrete filling layer inside the steel pipe. This refers to the elastic modulus of the high-strength concrete filling layer inside the steel pipe. The moment of inertia of the high-strength concrete filling layer inside the steel pipe. This is the distance between the neutral axis of the concrete slab and the neutral axis of the connecting steel plate. The shear stiffness of the high-strength concrete ring outside the steel pipe. The elastic modulus of the high-strength concrete ring surrounding the steel pipe. The high-strength moment of inertia is represented by the high-strength concrete outside the steel pipe.

[0086] ;

[0087] In the formula, This refers to the shear stiffness of the steel-concrete composite shear connector.

[0088] The high-strength concrete outside the steel pipe has a diameter of 110mm. Due to the excessive shear stiffness of the concrete, a reduction factor α is applied to ensure deformation compatibility. Considering the stiffness degradation characteristics of the steel pipe and the concrete within and outside the pipe working together, a reduction factor α is introduced to the overall shear stiffness of the steel-concrete shear connector under working conditions. α is typically taken as 0.1, thus obtaining the equivalent lateral stiffness between the centroidal axis of the reinforced concrete slab flange and the centroidal axis of the upper flange of the steel beam. :

[0089] ;

[0090] Equivalent moment of inertia of the circular steel tube in a short steel beam unit :

[0091] ;

[0092] Equivalent moment of inertia of square steel tube in short steel beam unit :

[0093] ;

[0094] Equivalent moment of inertia of short steel beam unit steel tube :

[0095] ;

[0096] The equivalent diameter of the circular steel tube in the short steel beam element Calculate using the following formula:

[0097] ;

[0098] The equivalent diameter of the square steel tube in a short steel beam element is calculated using the following formula:

[0099] ;

[0100] The equivalent diameter of the rectangular steel tube in a short steel beam element is calculated using the following formula:

[0101] .

[0102] Based on the above formula, the shear mechanical parameters of the steel-concrete shear connector (excluding restraint structures) of the present invention can be calculated when using different types of steel pipes. Specifically, see Tables 1a, 1b, 2, 3a, and 3b. In Tables 1a, 1b, 2, 3a, and 3b, (i=1, 2, 3, 4, j=f, y, jx, jy) represent the shear force ratios in the x and y directions for square steel tube concrete shear connectors, round steel tube concrete shear connectors, and rectangular steel tube concrete shear connectors, respectively. (i=1, 2, 3, 4, j=af, ay, ajx, ajy) represent the stiffness ratios in the x and y directions of square steel tube concrete shear connectors, round steel tube concrete shear connectors, and rectangular steel tube concrete shear connectors compared to ordinary stud shear connectors, respectively (where 106kN is the shear force design value of the largest diameter 22mm stud used in actual engineering, and 8kN / mm is the shear stiffness value corresponding to a distance L of 150mm between the neutral axis of the largest diameter 22mm stud used in actual engineering and the neutral axis of the steel beam flange 10). The elastic modulus of the constrained steel tube is taken as Es=2.06×10⁻⁶. 10 Pa, the elastic modulus Ec of the concrete filling around the steel pipe is 3.6 × 10 Pa. 10 Pa, the elastic modulus Ec of the concrete filling the steel pipe is 3.8 × 10 Pa. 10 Pa, the distance L = 150 mm between the neutral axis of the reinforced concrete slab and the neutral axis of the steel plate flange 10 of the steel beam. 0.1D b1 This represents the shear stiffness of the high-strength concrete filling layer inside the steel pipe multiplied by a reduction factor of 0.1, which represents 0.1D. b2 The shear stiffness of the high-strength concrete ring outside the steel pipe is represented by a reduction factor of 0.1.

[0103] Square steel pipes are isotropic along the X and Y principal axes, except for the 45-degree diagonal. Round steel pipes are also isotropic, but round steel pipes can act as a constrictor for the internal high-strength and high-performance concrete filling layer 3, allowing the performance of the high-strength and high-performance concrete filling layer 3 to be fully utilized. Therefore, round steel pipes are more recommended for practical engineering applications, while rectangular steel pipes are suitable for thick plates with different requirements for shear stiffness and strength in different directions at the joint surface.

[0104]

[0105] From the data in Tables 1a, 1b, 2, 3a, and 3b, it can be seen that: (1) When the cross-sectional area is almost the same, the shear stiffness of the square steel tube concrete member is about 6 times that of the ordinary stud, the shear stiffness of the round steel tube stud is about 4 times that of the ordinary stud, and the shear stiffness of the rectangular steel tube concrete member in the x direction is about 10 times that of the ordinary stud, and in the y direction it reaches about 30 times. The steel tube concrete connector with the constrained structure has a substantial leap in shear stiffness of the steel tube concrete itself compared with the traditional stud by 4 to 30 times (without considering the contribution of the high-strength and high-performance concrete filling layer 3 inside the steel tube and the high-strength and high-performance concrete ring 5 outside the tube to the shear stiffness). Obviously, this steel-concrete composite shear connector with a constrained structure can not only effectively suppress concrete splitting and its development at the interface and improve the durability of the concrete at the interface, but also increase the shear stiffness of the interface by orders of magnitude, fundamentally and significantly improving the combined performance and effective load-bearing capacity of thick concrete slabs with steel beams and steel trusses; (2) Compared with traditional shear connectors, the steel-concrete composite shear connector proposed in this invention effectively constrains and limits concrete splitting and its development within a 25mm-30mm radius around the steel-concrete composite member, which can greatly improve the effective load under normal service limit state, increase the design value of the shear bearing capacity of the flange 11 of the reinforced concrete slab, and broaden the application range of large-diameter connectors.

[0106] The following conclusions can be drawn from the data patterns in Tables 1a, 1b, 2, 3a, and 3b: (1) When the stress on the connector increases to the point that the steel pipe 1 fails under shear tension, the reinforced concrete slab flange 11 does not experience local pressure splitting failure. Even if it does, the splitting is reliably limited to the range of 25mm-30mm, which is completely within the allowable range of the project. The concrete splitting and crack development inside the steel pipe are constrained by the high tensile strength of the steel pipe wall itself, and the concrete splitting and crack development outside the steel pipe are constrained by the high tensile strength of the steel pipe wall, such as carbon fiber. Thus, the local pressure splitting failure and crack development occurring in each part will be limited to a reasonable range by the targeted structural construction. (2) The design value of the ultimate shear bearing capacity of the steel pipe concrete shear connector proposed in this invention depends entirely on the ultimate bearing capacity when the steel pipe fails under shear tension. There is no need to consider the random and uncertain effects caused by the splitting of the concrete. (3) The connection reliability and safety factor of the shear connector depend entirely on the reliability and safety factor of the steel pipe and its connection method with the steel beam flange 10.

[0107] The advantages of concrete-filled steel tubular (CFST) shear connectors lie not only in their exceptionally high strength and rigidity, but also in their ability to effectively coordinate the deformation between the steel and concrete materials. The reinforced concrete strength is taken as C80. The material properties of CFST shear connectors are as follows:

[0108] ;

[0109] ;

[0110] ;

[0111] ;

[0112] ;

[0113] With Φ60 6. Taking the steel pipe as an example, consider the consequences of the concrete inside the steel pipe breaking. Reduced to 0.1 Then the comprehensive elastic modulus for:

[0114] ;

[0115] ;

[0116] The shear modulus of the steel pipe is The shear modulus of the high-strength, high-performance concrete inside the pipe is: Comprehensive shear modulus of concrete-filled steel tube members The overall shear modulus of the connector is twice that of pure steel, while the deformation moduli of steel and concrete are more similar. Absolute value of shear modulus and compressive elastic modulus of concrete ;and ; The ratio of the comprehensive shear modulus of steel-concrete composite studs to the compressive elastic modulus of reinforced concrete structures is 0.78~0.81. The ratio of the comprehensive shear modulus of steel-concrete composite stud shear connectors to the compressive elastic modulus of concrete is very close, making it easier to coordinate the deformation of materials between steel-concrete composite members.

[0117] .

[0118] The main advantage of using concrete-filled steel tubes (CFST) as shear connectors lies in the coordination of stiffness and deformation, as shown in Table 4, which displays the deformation modulus of different shear connectors. Table 4 shows that while mega-studs (steel bars) have sufficient connection strength, they are ineffective at coordinating the deformation between steel and concrete as shear connectors. Ordinary studs have too weak bending stiffness to effectively leverage the thick concrete structure for combined action. The ratio of the comprehensive shear modulus of CFST shear connectors to the compressive elastic modulus of reinforced concrete structures is between 0.78 and 0.81. This indicates that CFST shear connectors can highly coordinate the deformation capacity between steel and concrete materials. In conclusion, CFST as a shear connector for steel-concrete composite members can achieve both sufficient shear stiffness and a high degree of coordination in deformation between steel and concrete materials. CFST shear connectors are the highest quality connector products, possessing both high connection stiffness and high capacity for coordinated deformation.

[0119] To verify the significant advantage of the constrained steel-concrete composite shear connector in shear stiffness, computer finite element simulation analysis (MIDAS) was conducted on basic push-out tests of both traditional studs and steel-concrete composite shear connectors. The shear stiffness results for traditional studs and steel-concrete composite connectors are shown in Table 5, the simulation results are shown in Figures 11-12, and the test model is shown in Figure 13. The steel pipe diameter was 60 mm, the wall thickness was 6 mm, and the length was 270 mm, with a total of 2×2 connectors arranged at a center-to-center distance of 200 mm. The concrete slab thickness was 300 mm, and the steel beam height was 300 mm. The concrete slabs were symmetrically arranged on both sides of the steel beam.

[0120] .

[0121] The following conclusions can be drawn from the data in Table 5: (1) When the plate thickness is 300 mm and the slippage is 4 mm, the maximum shear force of the traditional stud is 789 kN, while when the plate thickness is 120 mm and the slippage is 4 mm, the maximum shear force of the traditional stud is 3320.6 kN. Obviously, the shear stiffness of the traditional stud at a plate thickness of 300 mm is much smaller than that of the steel-concrete composite column stud connector with restraint structure; (2) When the plate thickness is 300 mm and the slippage is 4 mm, the maximum shear force of the traditional stud is 789 kN and the maximum shear force of a single stud is 98.6 kN, while the maximum shear force of the steel pipe stud is 3790.4 kN and the maximum shear force of a single stud is 473.8 kN. Under the same conditions, the steel pipe stud is 5 times that of the traditional stud. The steel pipe stud can also play a full role in thick plates.

[0122] The main improvements of this invention are shown in Table 6.

[0123] .

[0124] By replacing the original cylindrical steel solid studs (diameters of 16, 19, 22, and 25 mm) with steel-concrete composite shear connectors and combining them with restraint structures, the following key technical effects are achieved:

[0125] (1) Achieving a qualitative leap in shear stiffness: The stiffness of the steel pipe itself is 4-30 times higher than that of traditional studs (about 4 times for round steel pipes and 30 times for rectangular steel pipes in the y direction). The increase in total stiffness transforms the slip of the joint surface from nonlinear to linear and quantifiable index (such as inter-layer shear angle), which helps to realize the quantitative design of shear strength and stiffness of the shear surface and ensures the strength and stiffness requirements of the joint surface that match the design requirements of the composite structure.

[0126] (2) Effectively suppress concrete splitting: Carbon fiber fabric (tensile unit) and spiral reinforcement limit the development of splitting to within 25-30mm in the core area, improve durability, and the load-bearing capacity is controlled by the steel pipe (the safety factor depends on the material of the steel pipe).

[0127] (3) Improved material utilization and applicability: The pipe material breaks through the limitation of ML15 grade stud material, and the cross-sectional area and rotational inertia of the steel pipe are much larger than the physical and mechanical properties of the cross-section of the traditional stud. It can fully realize the shear stiffness of the shear connection by tens of times on the basis of complete shear connection, greatly reduce the shear deformation of the joint surface, and improve the combination performance and durability of the composite component.

[0128] (4) The comprehensive elastic modulus of the steel-concrete composite member in this invention is similar to that of reinforced concrete, and much lower than the difference or ratio of the elastic modulus of steel bars and reinforced concrete. The use of steel-concrete composite members can realize the redistribution of internal forces between the connectors and can achieve coordination between the deformation difference between steel structures and reinforced concrete structures.

[0129] The steel-concrete composite shear connector with restraint structure described in this invention can be applied to existing steel-concrete composite beams, and can also be widely applied to steel-concrete composite trusses, steel-concrete composite columns, steel-reinforced concrete columns, and various high-rise steel-concrete hybrid structures. It is particularly suitable for heavy-load structures, long-span bridges, trusses, high-rise buildings, and other common steel-concrete composite and hybrid structures. It is very beneficial to improve the overall strength and toughness of steel-concrete prefabricated structures, and can generate huge engineering economic and social benefits.

[0130] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A steel-concrete composite shear connector with a restraint structure, comprising a steel-concrete composite member for connecting a steel structure and a reinforced concrete structure, and a restraint structure disposed around the outer periphery of the steel-concrete composite member, the restraint structure comprising a high-strength, high-performance concrete ring disposed around the outer periphery of the steel-concrete composite member, a tensile element disposed around the outer periphery of the high-strength, high-performance concrete ring, and spiral reinforcement surrounding the tensile element and the outer side of the steel-concrete composite member; characterized in that: The steel-concrete composite member includes a steel pipe welded to a steel structure at one end, a high-strength, high-performance concrete filling layer poured inside the steel pipe, and a steel pipe cap embedded inside the reinforced concrete structure and fixedly connected to the other end of the steel pipe; the length of the steel pipe is not less than 90% of the height of the reinforced concrete structure and not greater than the height of the reinforced concrete structure minus the thickness of the steel pipe cap and the thickness of the concrete protective layer of the reinforced concrete structure.

2. The steel-concrete composite shear connector with a constrained structure according to claim 1, characterized in that: The steel pipe can be round or rectangular, and the material can be either carbon structural steel or low-alloy high-strength structural steel.

3. The steel-concrete composite shear connector with a constrained structure according to claim 2, characterized in that: For round steel pipes, the outer diameter of the pipe is 1 / 8 to 1 / 4 of the pipe length; the wall thickness of the pipe is 1 / 15 to 1 / 5 of the outer diameter, and not less than 4 mm.

4. The steel-concrete composite shear connector with a constrained structure according to claim 3, characterized in that: For round steel pipes, the thickness of the steel pipe cap shall be no less than twice the wall thickness of the steel pipe and no less than one-fifth of the outer diameter of the steel pipe; the outer diameter of the steel pipe cap shall be 1.4 to 1.7 times the outer diameter of the steel pipe.

5. The steel-concrete composite shear connector with a constrained structure according to claim 2, characterized in that: For rectangular steel pipes, the long side is arranged parallel to the shearing direction, the short side is 1 / 8 to 1 / 6 of the length of the steel pipe, the long side is 1.5 to 2 times the short side, and the wall thickness is 1 / 15 to 1 / 6 of the short side.

6. The steel-concrete composite shear connector with a constrained structure according to claim 3, characterized in that: For rectangular steel pipes, the thickness of the steel pipe cap shall be no less than twice the wall thickness of the steel pipe and no less than one-fifth of the shorter side length of the steel pipe; the shorter side length of the steel pipe cap shall be 1.4 to 1.7 times the shorter side length of the steel pipe, and the longer side length of the steel pipe cap shall be 1.4 to 1.7 times the longer side length of the steel pipe.

7. The steel-concrete composite shear connector with a constrained structure according to claim 4 or 6, characterized in that: The steel pipe cap has a pouring hole at its center. The diameter or side length of the pouring hole is 0.3 to 0.5 times the outer diameter or short side length of the steel pipe, and not less than 25 mm.

8. The steel-concrete composite shear connector with a constrained structure according to claim 7, characterized in that: The high-strength, high-performance concrete filling layer is made of high-strength, high-performance fine aggregate concrete or UHPC, with a strength not lower than C80; the high-strength, high-performance concrete ring is made of high-strength, high-performance fine aggregate concrete or UHPC, with a strength higher than that of reinforced concrete structures; the outer diameter of the high-strength, high-performance concrete ring is not less than 1.4 to 1.7 times the outer diameter of the steel pipe, and its wall thickness is not less than 25 mm and not greater than the minimum spacing of the main reinforcement in the reinforced concrete structure; the tensile unit is a high-strength prestressed steel wire, elastic fiber rope, or high-strength fiber fabric wrapped around the outer cylindrical surface of the high-strength, high-performance concrete ring.

9. The steel-concrete composite shear connector with a constrained structure according to claim 8, characterized in that: In application, multiple steel-concrete composite shear connectors with constraint structures are provided at the connection between the steel structure and the reinforced concrete structure. The net distance between adjacent steel pipes is not less than 100mm, and the center distance between adjacent steel pipes is not greater than the thickness of the reinforced concrete structure.

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