Steel-UHPC composite beams with multiple PBL connectors and their design method

Abstract

The application discloses a steel-UHPC composite beam connected by mixed PBL connectors and a design method thereof. The steel-UHPC composite beam comprises a UHPC component, an I-beam and multiple cap beams. The cap beams are arranged below the I-beam, and the UHPC component is arranged above the I-beam. A positive bending moment section of the UHPC component is arranged with multiple PBL connectors using NPR steel bars, and a negative bending moment section of the UHPC component is arranged with multiple pull-out resistant and shear resistant PBL connectors. The application applies the PBL connectors using NPR steel bars instead of ordinary steel bars to the positive bending moment section of the composite structure, enhances the continuation ability and bearing capacity of the composite structure, and improves the structural integrity and stability. The application effectively releases the tensile stress of the negative bending moment section of the composite structure, and significantly improves the use performance, long-term performance and durability of the composite structure.

Description

Technical Field

[0001] This invention relates to the field of bridge design technology, and in particular to a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors and its design method. Background Technology

[0002] Steel-concrete composite beam bridges combine steel beams and concrete using various shear connectors, allowing the steel and concrete to work together under stress and deformation. This fully utilizes the high tensile strength of steel and the high compressive strength of concrete, and has been widely used in various beam bridge constructions both domestically and internationally. Compared to ordinary concrete bridges, composite beam bridges have a lower structural height, lighter weight, and less seismic effect, resulting in improved structural ductility and reduced foundation costs. Compared to pure steel beam bridges, the concrete bridge deck enhances the stability of the steel beams, fully leveraging the high strength of steel, significantly improving the flexural capacity of the beam bridge, and reducing steel consumption. Furthermore, composite beam bridges offer numerous advantages, including easier factory production, higher on-site installation quality, lower construction costs, and shorter construction periods.

[0003] Composite structures fully utilize the material advantages of steel and concrete, but their corresponding structural shortcomings are also exposed. In structural systems such as continuous composite beam bridges, composite rigid frame bridges, cable-stayed and suspension bridge composite deck systems, composite frame structures, and large-span load-bearing composites, the concrete is under compression and the steel beams are under tension in the positive bending moment section, resulting in strong load-bearing capacity and high structural stability. However, in the negative bending moment section, the composite structure is in an unfavorable state where the concrete is under tension and the steel components are under compression. Due to the low tensile strength of concrete, cracking occurs even under small loads. This not only reduces the stiffness of the composite structure but also causes corrosion of the reinforcing steel and components, reducing the bridge's durability and posing significant challenges to later maintenance. Furthermore, when composite beam bridges are used in large-span beam bridges, the large self-weight of the concrete bridge deck limits the economically viable span. The two problems faced by the aforementioned composite beam bridges in engineering applications are both due to the low strength of concrete materials, which makes them prone to cracking. Developing new concrete materials with higher mechanical properties and crack control capabilities is an effective way to solve these problems.

[0004] Ultra-high performance concrete (UHPC) is a novel cement-based composite material designed based on principles such as the closest possible particle packing, a water-cement ratio of less than 0.25, and fiber reinforcement. This results in ultra-high mechanical properties, toughness, durability, and excellent workability. Compared to ordinary concrete (NC) and traditional high-performance concrete (HPC), UHPC exhibits orders of magnitude or multiple improvements in strength (compressive and flexural strength, etc.) and durability (resistance to chloride ion intrusion and carbonation, etc.). Furthermore, the high-density UHPC matrix significantly enhances the interfacial bond strength between the UHPC matrix and steel fibers, allowing the UHPC matrix to retain high tensile strength even after cracking. This achieves metal-like tensile and strain-strengthening properties, significantly improving the toughness and ductility of UHPC materials. Due to the superior mechanical and durability properties of UHPC, replacing the concrete layer in a steel-concrete composite structure with UHPC creates a steel-UHPC composite structure. Compared to traditional steel-concrete composite structures, this effectively reduces the cross-sectional dimensions and self-weight of the composite members. When applied to steel-concrete composite beam bridges, the excellent mechanical properties of UHPC not only effectively address the issue of cracking in the negative bending moment section but also improve the load-bearing capacity in the positive bending moment section, further enhancing the stability of the beam bridge structure.

[0005] Besides the inherent effects of steel and concrete materials on steel-concrete composite beam bridges, shear connectors are also a key factor influencing their performance. Horizontally, they bear and transfer longitudinal shear forces between the steel beam and concrete, resisting slippage between them; vertically, their pull-out resistance prevents the concrete and steel beam from lifting or separating. In traditional steel-concrete composite beam bridges, studded connectors and Perfobond Leiste (PBL) connectors are the two most commonly used shear connectors. Studded connectors offer four-way shear resistance, are simple to construct, and perform well, but have lower load-bearing capacity. PBL connectors have higher load-bearing capacity and excellent fatigue performance, but their structure is complex. However, these shear connection methods can lead to excessive tensile stress in the upper concrete slab under negative bending moments. Therefore, eliminating the shear resistance while retaining the pull-out resistance of these connectors, allowing free slippage at the steel-concrete interface without separation, is an effective way to release tensile stress in the concrete slab and reduce the risk of cracking. Therefore, considering the stress characteristics of steel-UHPC composite beams, developing new pull-out but not shear-resistant connectors that match their performance is key to further improving the crack control capability of steel-UHPC composite beam bridges in the negative bending moment zone.

[0006] Figure 1This diagram illustrates a comparison of the stress-strain relationship between existing NPR steel bars and ordinary HRB400 steel bars. In the positive bending moment section of a composite beam bridge, the composite structure is under tension in the steel beam and compression in the concrete. Furthermore, the mechanical properties of UHPC (Ultra-High-Pressure Polymer) and ordinary concrete differ significantly. The steel-UHPC composite structure requires higher shear capacity in the positive bending moment section compared to ordinary shear connectors, which cannot fully utilize the high strength of UHPC and thus fail to meet structural requirements. Stud connectors generally have small diameters and low load-bearing capacity. To achieve a certain load-bearing capacity, the diameter or number of stud connectors needs to be increased. However, excessively large stud diameters and too many connectors reduce the construction area, increase the difficulty of welding procedures, and reduce construction efficiency. Summary of the Invention

[0007] To address the limitations and defects of existing technologies, this invention provides a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, comprising UHPC components, I-beams, and multiple cap beams. The cap beams are disposed below the I-beams, and the UHPC components are disposed above the I-beams. The UHPC components and the cap beams are cuboid structures, and the cross-section of the I-beams is I-shaped.

[0008] The UHPC component has longitudinal and transverse steel mesh inside. The positive bending moment section of the UHPC component is provided with multiple PBL connectors using NPR steel bars, and the negative bending moment section of the UHPC component is provided with multiple pull-out but not shear-resistant PBL connectors.

[0009] The upper flange of the I-beam corresponding to the positive bending moment section of the UHPC component is welded with multiple first perforated steel plates, and a first foam plastic is filled between two adjacent first perforated steel plates. The openings of the first perforated steel plates are circular, and the first foam plastic has a cuboid structure. The upper flange of the I-beam corresponding to the negative bending moment section of the UHPC component is welded with multiple second perforated steel plates, and a second foam plastic is filled between two adjacent second perforated steel plates. The openings of the second perforated steel plates are square, and the second foam plastic has a cuboid structure.

[0010] The PBL connector using NPR reinforcing bars includes a first perforated steel plate, NPR reinforcing bars, and concrete pins. The NPR reinforcing bars pass through an opening in the first perforated steel plate, and the concrete pins surround the NPR reinforcing bars, filling the space between the NPR reinforcing bars and the opening in the first perforated steel plate. The pull-out resistant but not shear resistant PBL connector includes a second perforated steel plate, perforated reinforcing bars, and a modulus of elasticity material. The modulus of elasticity of the modulus of elasticity material is less than a preset value. The perforated reinforcing bars pass through an opening in the second perforated steel plate, and the modulus of elasticity material surrounds the perforated reinforcing bars, filling the space between the perforated reinforcing bars and the opening in the second perforated steel plate.

[0011] Optionally, the PBL connector using NPR steel reinforcement is on the same horizontal plane as the central axis of the pull-out but not shear-resistant PBL connector.

[0012] Optionally, the central axis of the first perforated steel plate, the first foam plastic, the second perforated steel plate, the second foam plastic, the UHPC component, the I-beam, and the cap beam is in the same vertical plane.

[0013] This invention also provides a design method for a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, wherein the steel-UHPC composite beam using a hybrid connection of multiple PBL connectors is the aforementioned steel-UHPC composite beam, and the design method includes:

[0014] Based on the different internal force states of the steel-UHPC composite beam, the section design is carried out for the positive bending moment section and the negative bending moment section when the bearing capacity reaches the bending limit state under the action of bending moment.

[0015] The positive bending moment section of the steel-UHPC composite beam is designed according to the principle of complete shear connection, and the position of the plastic neutral axis of the composite section is determined based on the compressive bearing capacity of the UHPC member and the tensile bearing capacity of the I-beam.

[0016] When Af≤b e f c When xy, the plastic neutral axis of the composite section is located inside the flange of the UHPC member. The height x of the compression zone of the UHPC member is calculated according to formula (1), and the flexural bearing capacity M of the composite section is calculated according to formula (2). u ;

[0017]

[0018] M u =b e f c xy (2)

[0019] Where x is the height of the compression zone of the UHPC component, A is the cross-sectional area of ​​the I-beam, f is the yield strength of the I-beam, and b e f is the flange width of the UHPC component. c M represents the axial compressive strength of the UHPC component. u y represents the flexural bearing capacity of the composite section, and y represents the distance between the resultant stress of the I-beam section and the resultant stress of the UHPC member in the receiving zone section.

[0020] When Af > b e f cWhen xy, the plastic neutral axis of the composite section is located within the section of the I-beam. The compression region A of the I-beam is calculated according to formula (3). b The flexural bearing capacity M of the composite section is calculated according to formula (4). u ;

[0021]

[0022] M u =b e h e f c y1+A b fy2 (4)

[0023] Among them, A b h represents the compression zone of the I-beam. e y1 is the flange thickness of the UHPC member, y2 is the distance between the resultant stress in the tension section of the I-beam and the resultant stress in the compression section of the UHPC member, and y3 is the distance between the resultant stress in the tension section of the I-beam and the resultant stress in the compression section of the I-beam.

[0024] Perform flexural bearing capacity verification, if M u ≥M, the combined section satisfies the structural requirements, if M u ≤M, take M u =M, where M is the design value of the bending moment;

[0025] Calculate the shear capacity V and N of the steel-UHPC composite beam according to formula (5). u =b e f c h e N represents the bearing capacity of the compression zone above the plastic neutral axis of the composite section. p =Af is the bearing capacity of the tension zone below the plastic neutral axis of the composite section;

[0026] V = min[N] u N p (5)

[0027] Wherein, V is the shear bearing capacity of the steel-UHPC composite beam;

[0028] The number of shear connectors n in the positive bending moment section is calculated according to formula (6), and the bearing capacity N of a single PBL connector using NPR steel bars is calculated according to formula (7). v ;

[0029] nN v =V (6)

[0030]

[0031] Where n is the number of shear connectors in the positive bending moment section, N v For the bearing capacity of a single PBL connector using NPR reinforcement, ρ st V represents the reinforcement ratio of the UHPC component. f L represents the volumetric fiber content of steel fibers. f φ is the length of the steel fiber. f f is the diameter of the steel fiber. cu t is the cubic compressive strength of the UHPC component. p Where A is the thickness of the perforated steel plate, D is the diameter of the opening, and A is the diameter of the opening. c Let A be the area of ​​the perforated steel plate, λ be the strength reduction factor of the NPR steel bar, and A be the area of ​​the perforated steel plate. s f is the cross-sectional area of ​​the perforated reinforcing bar. y The yield strength of the perforated steel bar;

[0032] When the negative bending moment section of the steel-UHPC composite beam is in the normal service stage, the elastic modulus material around the perforated steel bar allows the steel-concrete interface to slip by a preset distance. The steel-UHPC composite beam is in a state where the UHPC member is under tension and the I-beam is under compression. The tension zone of the UHPC member is reinforced according to formula (8).

[0033] A r f s =(A1+A2+A3)fb e h e f t (8)

[0034] Among them, A r f is the cross-sectional area of ​​the longitudinal reinforcement within the effective width of the concrete flange in the negative bending moment zone. s Let A1 be the yield strength of the reinforcing steel, A2 be the net cross-sectional area of ​​the web of the I-beam, A3 be the net cross-sectional area of ​​the lower flange of the I-beam, and f be the net cross-sectional area of ​​the upper flange of the I-beam. t The tensile strength of the UHPC component;

[0035] When the negative bending moment section of the steel-UHPC composite beam is at the ultimate limit stage of bearing capacity, the flexural bearing capacity M of the composite section is calculated according to formula (9). u ;

[0036] M u =M a +M r +M t (9)

[0037] The maximum bending moment resisted by the combined section includes the bending moment resisted by the I-beam, M. a The resisting bending moment M of longitudinal reinforcement r and the resisting bending moment M of concrete t ;

[0038] Perform flexural bearing capacity verification, if M u ≥M, the combined section satisfies the structural requirements, if M u ≤M, take M u =M;

[0039] The number of pull-out non-shear connectors n in the negative bending moment section is calculated according to formula (10), the shear capacity V of the steel-UHPC composite beam is calculated according to formula (11), and the bearing capacity N of a single pull-out non-shear PBL connector is calculated according to formula (12). v ;

[0040] nβN v =V (10)

[0041] V = A r f s +b e h e f t (11)

[0042]

[0043] Where β represents the bearing capacity reduction coefficient of the connector, which is taken as 0.9 for the negative bending moment section of the intermediate support and as 0.8 for the negative bending moment section of the cantilever beam; f t The tensile strength of the UHPC component is given.

[0044] The present invention has the following beneficial effects:

[0045] This invention provides a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, comprising UHPC components, I-beams, and multiple cap beams. The cap beams are located below the I-beams, and the UHPC components are located above the I-beams. Multiple PBL connectors using NPR steel reinforcement are arranged in the positive bending moment section of the UHPC components, while multiple pull-out but not shear-resistant PBL connectors are arranged in the negative bending moment section. This invention applies NPR steel reinforcement instead of ordinary steel reinforcement in the PBL connectors of the composite structure, enhancing the continuity and load-bearing capacity of the composite structure, and improving the structural integrity and stability. This invention effectively releases the tensile stress in the negative bending moment section of the composite structure, significantly improving the service performance, long-term performance, and durability of the composite structure. Attached Figure Description

[0046] Figure 1 This is a schematic diagram comparing the stress-strain relationship between NPR steel bars and ordinary HRB400 steel bars in the existing technology.

[0047] Figure 2a The image shows an isometric view of a steel-UHPC composite beam with a hybrid connection of various PBL connectors, as provided in Embodiment 1 of the present invention.

[0048] Figure 2b This is a side view of a steel-UHPC composite beam with a hybrid connection of various PBL connectors, as provided in Embodiment 1 of the present invention.

[0049] Figure 2c This is a top view of a steel-UHPC composite beam using a hybrid connection of various PBL connectors, as provided in Embodiment 1 of the present invention.

[0050] Figure 2d This is a front view of a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, as provided in Embodiment 1 of the present invention.

[0051] Figure 3 This is a schematic diagram of the structure of the pull-out resistant but shear-resistant PBL connector provided in Embodiment 1 of the present invention.

[0052] Figure 4 This is a schematic diagram of the PBL connector using NPR steel bars provided in Embodiment 1 of the present invention.

[0053] Figure 5 This is a schematic diagram of the structure of the first perforated steel plate provided in Embodiment 1 of the present invention.

[0054] Figure 6 This is a schematic diagram of the structure of the second perforated steel plate provided in Embodiment 1 of the present invention.

[0055] Figure 7 This is a schematic diagram of the structure of the cap beam provided in Embodiment 1 of the present invention.

[0056] Figure 8 This is a schematic diagram of the structure of the foam plastic provided in Embodiment 1 of the present invention.

[0057] Figure 9 This is a structural schematic diagram of the perforated steel bar and elastic modulus material provided in Embodiment 1 of the present invention.

[0058] Figure 10 This is a structural schematic diagram of the NPR steel bar and concrete pin provided in Embodiment 1 of the present invention.

[0059] Figure 11 This is a schematic diagram of the two-stage load-slip curves of the pull-out resistant but shear-resistant PBL connector provided in Embodiment 1 of the present invention.

[0060] Figure 12The flowchart illustrates the design method for a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, as provided in Embodiment 2 of the present invention.

[0061] Figure 13 This is a schematic diagram comparing the load-relative slip curves of the PBL connector using NPR steel bars and the traditional PBL connector provided in Embodiment 2 of the present invention.

[0062] Figure 14 This is a schematic diagram comparing the load-relative slip curves of a double-hole PBL connector using NPR steel bars and a single-hole PBL connector, as provided in Embodiment 2 of the present invention.

[0063] Figure 15 This is a schematic diagram comparing the load-relative slip curves of the pull-out resistant but shear-resistant PBL connector provided in Embodiment 2 of the present invention with those of a regular PBL connector.

[0064] Figure 16 This is a schematic diagram comparing the load-relative slip curves of the double-hole pull-out resistant but non-shear resistant PBL connector and the single-hole pull-out resistant but non-shear resistant PBL connector provided in Embodiment 2 of the present invention.

[0065] The attached diagrams are labeled as follows: UHPC component-1; I-beam-2; cap beam-3; second perforated steel plate-4; first perforated steel plate-5; NPR rebar-6; perforated rebar-7; concrete pin-8; elastic modulus material-9; foam plastic-10. Detailed Implementation

[0066] To enable those skilled in the art to better understand the technical solution of the present invention, the following describes in detail, with reference to the accompanying drawings, the steel-UHPC composite beam and its design method that employs a hybrid connection of multiple PBL connectors provided by the present invention.

[0067] Example 1

[0068] PBL connectors offer higher load-bearing capacity and structural stability. To meet the structural requirements of steel-UHPC composite structures, the ordinary reinforcing bars in the PBL connectors are replaced with NPR reinforcing bars. NPR reinforcing bars are a new type of building material with negative Poisson's ratio characteristics, exhibiting slight volume expansion under stress, no necking upon fracture, and excellent properties such as high strength and high ductility. Compared to ordinary reinforcing bars, they possess higher strength, higher ductility, and higher corrosion resistance. Excessive reinforcing bar strength can lead to significant cracking in concrete during service. UHPC's high compressive strength, high tensile strength, and good crack control capabilities make it an excellent carrier for NPR reinforcing bars, improving the structure's load-bearing capacity and ductility. Applying PBL connectors using NPR reinforcing bars in the positive bending moment section of the steel-UHPC composite beam bridge can fully utilize the high strength characteristics of UHPC, improving the structural stability and load-bearing capacity of the steel-UHPC composite beam bridge.

[0069] In the negative bending moment section of a composite beam bridge, the composite structure is in an unfavorable state where the steel beams are under compression and the concrete is under tension. Retaining the tensile strength of traditional connectors while eliminating their shear strength, allowing local slippage at the steel-concrete interface to release tensile stress within the concrete, is key to solving the problem of concrete cracking in the negative bending moment section. By wrapping the perforated reinforcing bars with a low-modulus material, the PBL connector is allowed to slip to a certain extent at the steel-concrete interface, releasing tensile stress in the concrete while ensuring that the steel-concrete interface does not separate. Compared to the standard PBL connector, the pull-out-but-not-shear PBL connector eliminates its shear strength, effectively releasing tensile stress within the concrete. Compared to the pull-out-but-not-shear stud connector, it has a higher load-bearing capacity. Applying the pull-out-but-not-shear PBL connector to the negative bending moment section of a steel-UHPC continuous composite beam bridge can effectively solve the UHPC cracking problem in the negative bending moment section and improve the crack resistance of the negative bending moment section.

[0070] Figure 2a The image shows an isometric view of a steel-UHPC composite beam with a hybrid connection of various PBL connectors, as provided in Embodiment 1 of the present invention. Figure 2b This is a side view of a steel-UHPC composite beam with a hybrid connection of various PBL connectors, as provided in Embodiment 1 of the present invention. Figure 2c This is a top view of a steel-UHPC composite beam using a hybrid connection of various PBL connectors, as provided in Embodiment 1 of the present invention. Figure 2d This is a front view of a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, as provided in Embodiment 1 of the present invention. This embodiment of the steel-UHPC composite beam bridge using a hybrid connection of multiple PBL connectors consists of an I-beam, UHPC components, a cap beam, PBL connectors using NPR reinforcement in the positive bending moment section, and pull-out but not shear-resistant PBL connectors in the negative bending moment section. Longitudinal and transverse steel meshes are arranged in the UHPC components; perforated steel plates are welded to the upper flange of the steel beam, with foam plastic filling between each perforated steel plate. The PBL connectors using NPR reinforcement consist of perforated steel plates, NPR reinforcement passing through the openings, and concrete pins that flow into the holes and wrap around the NPR reinforcement during concrete pouring. The pull-out but not shear-resistant PBL connectors consist of perforated steel plates, reinforcement passing through the openings, and a low-modulus material wrapping around the reinforcement.

[0071] Figure 3 This is a schematic diagram of the structure of the pull-out resistant but shear-resistant PBL connector provided in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the PBL connector using NPR steel bars provided in Embodiment 1 of the present invention. Figure 5 This is a schematic diagram of the structure of the first perforated steel plate provided in Embodiment 1 of the present invention. Figure 6 This is a schematic diagram of the structure of the second perforated steel plate provided in Embodiment 1 of the present invention.

[0072] Figure 7 This is a schematic diagram of the structure of the cap beam provided in Embodiment 1 of the present invention. Figure 8 This is a schematic diagram of the structure of the foam plastic provided in Embodiment 1 of the present invention. Figure 9 This is a structural schematic diagram of the perforated steel bar and elastic modulus material provided in Embodiment 1 of the present invention. Figure 10 This is a schematic diagram of the NPR steel reinforcement and concrete pins provided in Embodiment 1 of the present invention. Because the shear capacity requirements for the positive bending moment section of the composite structure are high, traditional shear connectors cannot meet the structural requirements. NPR steel reinforcement has the characteristics of high strength, high ductility, and high corrosion resistance. By replacing the ordinary steel reinforcement in the PBL connector with NPR steel reinforcement, the PBL connector has higher shear capacity, which can fully utilize the high strength characteristics of UHPC material. At the same time, the presence of perforated steel reinforcement and concrete pins ensures the pull-out resistance of the connector, preventing the UHPC plate from being lifted or separated from the steel beam. This not only meets the structural requirements of the steel-UHPC composite beam bridge, but also further improves the bearing capacity and overall stability of the positive bending moment section of the steel-UHPC composite beam bridge.

[0073] Figure 11 This is a schematic diagram of the two-stage load-slip curves for the pull-out non-shear PBL connector provided in Embodiment 1 of the present invention. In the negative bending moment section of the composite beam bridge, the shear resistance of the traditional shear connector restricts the slippage at the steel-UHPC interface, leading to tensile stress inside the UHPC and making the UHPC prone to cracking. After applying the pull-out non-shear PBL connector to the negative bending moment section, during normal use, the low elastic modulus material around the perforated steel bars allows local slippage at the steel-UHPC interface, releasing the tensile stress inside the UHPC and effectively solving the problem of UHPC cracking in the negative bending moment section. The load-slip curve for this stage is shown below. Figure 11 As shown. In the ultimate bearing capacity stage, the perforated steel bars of the pull-out but not shear-resistant PBL connector begin to bear shear force, exerting the shear resistance of the connector. This ensures the steel-UHPC interface is fully connected, meeting the structural requirements of the steel-UHPC composite beam bridge. The load-slip curve for this stage is shown in the figure. Figure 11 As shown.

[0074] This embodiment provides a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, including UHPC components, I-beams, and multiple cap beams. The cap beams are located below the I-beams, and the UHPC components are located above the I-beams. Multiple PBL connectors using NPR steel reinforcement are arranged in the positive bending moment section of the UHPC components, while multiple pull-out but not shear-resistant PBL connectors are arranged in the negative bending moment section. This embodiment uses PBL connectors with NPR steel reinforcement instead of ordinary steel reinforcement in the positive bending moment section of the composite structure, enhancing the continuity and load-bearing capacity of the composite structure and improving its overall integrity and stability. This embodiment effectively releases the tensile stress in the negative bending moment section of the composite structure, significantly improving its service performance, long-term performance, and durability.

[0075] Example 2

[0076] Figure 12 This is a flowchart illustrating the design method for a steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, as provided in Embodiment 2 of the present invention. The specific steps of the design method for the steel-UHPC composite beam bridge and shear connector using a hybrid connection of multiple PBL connectors in this embodiment are as follows:

[0077] (1) Based on the different internal force states of the composite beam, the section design of the positive bending moment section and the negative bending moment section is carried out respectively when the bearing capacity reaches the bending limit state under the action of bending moment M.

[0078] (2) The positive bending moment section of the composite beam is designed according to the principle of complete shear connection. The position of the plastic neutral axis of the composite section is determined based on the compressive bearing capacity of the UHPC plate and the tensile bearing capacity of the steel beam. There are two cases:

[0079] 1) When Af≤b e f cu When xy, the plastic neutral axis of the composite section is located inside the UHPC flange. The height x of the compression zone of the UHPC plate is calculated according to equation (1), and the flexural bearing capacity M of the composite section is calculated according to equation (2). u .

[0080]

[0081] M u =b e f c xy (2)

[0082] 2) When Af≥b e f cu When xy, the plastic neutral axis of the composite section is located within the steel beam section. The compression zone A of the steel beam is calculated according to equation (3). b The flexural bearing capacity M of the composite section is calculated according to equation (4).u .

[0083]

[0084] M u =b e h e f c y1+A b fy2 (4)

[0085] (3) Perform flexural bearing capacity verification. If M u If M ≥ M, the composite beam section meets the structural requirements. u ≤M, take M u =M.

[0086] (4) According to equation (5), the shear capacity of the composite beam is calculated as N. u =b e f c h e , which represents the bearing capacity of the compression zone above the neutral axis, N p =Af, where Af is the bearing capacity of the tension zone below the neutral axis.

[0087] V = min[N] u N p (5)

[0088] (5) Calculate the number of shear connectors in the positive bending moment section according to equation (6), N v The calculation equation for the bearing capacity of a single PBL connector using NPR steel bars is calculated according to equation (7).

[0089] nN v =V (6)

[0090]

[0091] (7) The negative bending moment section of the composite beam section is designed in two stages. The first stage is the normal service stage, in which the low elastic modulus material around the perforated steel bars allows the steel-concrete interface to slip to a certain extent. This stage is designed as a partial shear connection. The second stage is the ultimate bearing capacity stage, in which the perforated steel bars bear shear force, which restricts the slip of the steel-concrete interface. This stage is designed as a complete shear connection.

[0092] 1) Normal use phase

[0093] The composite structure is in a state of tension of UHPC plate and compression of steel beam. UHPC has good tensile strength and its tensile strength cannot be ignored. The tension zone of UHPC is reinforced according to formula (8).

[0094] A r f s=(A1+A2+A3)fb e h e f t (8)

[0095] 2) Ultimate bearing capacity stage

[0096] Designed according to the principle of complete shear connection, the flexural bearing capacity M of the composite section is calculated according to equation (9). u The maximum bending moment resisted by the cross section is the resisting bending moment M provided by the steel beam. a The resisting bending moment M of longitudinal reinforcement r and the resisting bending moment M of concrete t composition.

[0097] M u =M a +M r +M t (9)

[0098] (8) Perform flexural bearing capacity verification. If M u If M ≥ M, the composite beam section meets the structural requirements. u ≤M, take M u =M.

[0099] (9) Calculate the number n of pull-out non-shear connectors in the negative bending moment section according to formula (10), calculate the shear bearing capacity V of the steel-UHPC composite beam according to formula (11), and calculate the bearing capacity N of a single pull-out non-shear PBL connector according to formula (12). v .

[0100] (10) Shear bearing capacity calculation

[0101] nβN v =V (10)

[0102] V = A r f s +b e h e f t (11)

[0103]

[0104] In the formula: β represents the bearing capacity reduction coefficient of the connector, which is 0.9 for the negative bending moment section of the intermediate support and 0.8 for the negative bending moment section of the cantilever beam; f t The tensile strength of the UHPC component is given.

[0105] Figure 13 This is a schematic diagram comparing the load-relative slip curves of the PBL connector using NPR steel bars and the traditional PBL connector provided in Embodiment 2 of the present invention. Figure 14 This is a comparative schematic diagram of the load-relative slip curves of a double-hole PBL connector using NPR steel reinforcement and a single-hole PBL connector provided in Embodiment 2 of the present invention. In the positive bending moment section, the load-bearing capacity of the PBL connector using NPR steel reinforcement is increased by 24.7% compared to the PBL connector using HRB400 steel reinforcement of the same diameter, and the ultimate slip is increased by 26.6%. It can be seen that applying the PBL connector using NPR steel reinforcement instead of ordinary steel reinforcement in the positive bending section of the composite structure greatly increases the continuity and load-bearing capacity of the composite structure, and significantly improves the overall integrity and structural stability. The comparison diagram of the load-slip curves of the PBL connector using NPR steel reinforcement and the ordinary PBL connector is shown below. Figure 13 As shown. To further improve the bearing capacity of the composite beam in the positive bending moment section, Figure 14 The figure shows a load-slip comparison between single-hole PBL connectors and double-hole connectors using NPR steel bars. It can be seen that the double-hole PBL connector has a 37.8% higher load-bearing capacity and a 7.6% higher ultimate slip than the single-hole connector. The double-hole PBL connector using NPR steel bars exhibits superior mechanical properties.

[0106] The calculation equations for the ultimate bearing capacity of PBL connectors using NPR steel bars are shown in equations (13) and (14).

[0107] (1) Single-hole PBL connector

[0108]

[0109] (2) Double-hole PBL connector

[0110]

[0111] Figure 15 This is a schematic diagram comparing the load-relative slip curves of the pull-out resistant but shear-resistant PBL connector provided in Embodiment 2 of the present invention with those of a regular PBL connector. Figure 16This is a schematic diagram comparing the load-relative slip curves of the double-hole pull-out non-shear PBL connector and the single-hole pull-out non-shear PBL connector provided in Embodiment 2 of the present invention. The pull-out non-shear PBL connector is used in the negative moment section. The shear capacity of the pull-out non-shear PBL connector is approximately 87% of that of a conventional PBL connector, but its ultimate slip is 174% of that of a traditional PBL connector. This effectively releases the tensile stress in the UHPC of the steel-concrete composite member in the negative moment section, significantly improving the service performance, long-term performance, and durability of the composite structure. The relative slip value of the pull-out non-shear PBL connector can reach over 21 mm, clearly meeting the slip requirements of ductile shear connectors specified in European Standard 4. This satisfies the basic concept of "resistance and release combination" in the negative moment section, that is, releasing internal forces horizontally in the longitudinal and transverse directions, while maintaining the anti-lifting function vertically. A comparison of typical load-slip curves of the pull-out non-shear PBL connector and the conventional PBL connector is shown below. Figure 15 As shown. The load-slip curves of the double-hole pull-out non-shear PBL connector and the single-hole pull-out non-shear PBL connector are as follows. Figure 16 As shown, the ultimate bearing capacity of the double-hole pull-out non-shear PBL connector is 141% of that of the single-hole PBL connector, and the ultimate slip is almost unchanged. When the double-hole pull-out non-shear PBL connector is applied to the negative bending moment section of the composite structure, it has higher shear bearing capacity and better ductility compared with the traditional PBL connector.

[0112] The ultimate bearing capacity prediction equations for pull-out resistant but shear resistant PBL connectors are shown in equations (15) and (16):

[0113] (1) Single-hole pull-out resistant but not shear resistant PBL connector

[0114]

[0115] (2) Double-hole pull-out resistant but not shear resistant PBL connector

[0116]

[0117] In this embodiment, the PBL connector using NPR steel reinforcement utilizes perforated steel bars and concrete pins within the holes to provide shear and pull-out resistance, resulting in higher load-bearing capacity and ductility than ordinary perforated connectors. The low elastic modulus material within the holes of the pull-out-resistant but not shear-resistant PBL connector is key to allowing localized slippage at the steel-UHPC interface, releasing tensile stress in the concrete. Compared to pull-out-resistant but not shear-resistant stud connectors, it exhibits higher load-bearing capacity and superior fatigue performance. Compared to ordinary PBL connectors, the PBL connector using NPR steel reinforcement has higher shear resistance and ductility. Applying it to the positive bending moment section of composite beam bridges not only meets structural requirements but also fully leverages the high-strength characteristics of UHPC, further improving the load-bearing capacity and structural stability of the composite beam bridge.

[0118] In this embodiment, the pull-out-resistant but not shear-resistant PBL connector, compared with ordinary PBL connectors, has the characteristic of "combining pull-out and shear resistance," which not only meets structural requirements but also effectively solves the problem of easy cracking of concrete in the negative bending moment section, improves the crack resistance of the negative bending moment section, and enhances the durability of the steel-UHPC composite beam bridge. The use of room-temperature cured UHPC in the superstructure can effectively reduce the cross-sectional dimensions of the components, reduce the self-weight of the components, and further increase the applicable span of the steel-concrete composite beam bridge. At the same time, the excellent crack width control capability of UHPC further benefits the crack control of the concrete in the negative bending moment section of the steel-concrete composite beam bridge. Compared with traditional steel-concrete composite beam bridges, steel-UHPC composite beam bridges using a mixture of various PBL connectors have higher bearing capacity and stronger stability in the positive bending moment section, stronger crack resistance of concrete in the negative bending moment section, better durability, and a longer service life.

[0119] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A steel-UHPC composite beam using a hybrid connection of multiple PBL connectors, characterized in that, It includes UHPC components, I-beams, and multiple cap beams. The cap beams are located below the I-beams, and the UHPC components are located above the I-beams. The UHPC components and the cap beams are cuboid structures, and the cross-section of the I-beams is I-shaped. The UHPC component has longitudinal and transverse steel mesh inside. The positive bending moment section of the UHPC component is provided with multiple PBL connectors using NPR steel bars, and the negative bending moment section of the UHPC component is provided with multiple pull-out but not shear-resistant PBL connectors. The upper flange of the I-beam corresponding to the positive bending moment section of the UHPC component is welded with multiple first perforated steel plates, and a first foam plastic is filled between two adjacent first perforated steel plates. The openings of the first perforated steel plates are circular, and the first foam plastic has a cuboid structure. The upper flange of the I-beam corresponding to the negative bending moment section of the UHPC component is welded with multiple second perforated steel plates, and a second foam plastic is filled between two adjacent second perforated steel plates. The openings of the second perforated steel plates are square, and the second foam plastic has a cuboid structure. The PBL connector using NPR reinforcing bars includes a first perforated steel plate, NPR reinforcing bars, and concrete pins. The NPR reinforcing bars pass through an opening in the first perforated steel plate, and the concrete pins surround the NPR reinforcing bars, filling the space between the NPR reinforcing bars and the opening in the first perforated steel plate. The pull-out resistant but not shear resistant PBL connector includes a second perforated steel plate, perforated reinforcing bars, and a modulus of elasticity material. The modulus of elasticity material is less than a preset value. The perforated reinforcing bars pass through an opening in the second perforated steel plate, and the modulus of elasticity material surrounds the perforated reinforcing bars, filling the space between the perforated reinforcing bars and the opening in the second perforated steel plate. The PBL connector using NPR steel reinforcement is on the same horizontal plane as the central axis of the pull-out but not shear-resistant PBL connector.

2. The steel-UHPC composite beam using a hybrid connection of multiple PBL connectors as described in claim 1, characterized in that, The central axes of the first perforated steel plate, the first foam plastic, the second perforated steel plate, the second foam plastic, the UHPC component, the I-beam, and the cap beam are in the same vertical plane.

3. A design method for steel-UHPC composite beams employing a hybrid connection of multiple PBL connectors, characterized in that, The steel-UHPC composite beam using a hybrid connection of multiple PBL connectors is the steel-UHPC composite beam as described in claim 1 or 2, and the design method includes: Based on the different internal force states of the steel-UHPC composite beam, the section design is carried out for the positive bending moment section and the negative bending moment section when the bearing capacity reaches the bending limit state under the action of bending moment. The positive bending moment section of the steel-UHPC composite beam is designed according to the principle of complete shear connection, and the position of the plastic neutral axis of the composite section is determined based on the compressive bearing capacity of the UHPC member and the tensile bearing capacity of the I-beam. when When the plastic neutral axis of the composite section is located inside the flange of the UHPC component, the height of the compression zone of the UHPC component is calculated according to formula (1). The flexural bearing capacity of the composite section is calculated according to formula (2). ; （1） （2） in, The height of the compression zone of the UHPC component. The cross-sectional area of ​​the I-beam is [area]. The yield strength of the I-beam is given by [the value of the yield strength]. The flange width of the UHPC component. The axial compressive strength of the UHPC component is given. The flexural bearing capacity of the composite section is... The distance between the resultant stress of the section of the I-beam and the resultant stress of the section of the UHPC member in the receiving zone; when When the plastic neutral axis of the composite section is located within the section of the I-beam, the compression zone of the I-beam is calculated according to formula (3). The flexural bearing capacity of the composite section is calculated according to formula (4). ; （3） （4） in, This refers to the compression zone of the I-beam. The flange thickness of the UHPC component. The distance between the resultant stress in the tension zone of the I-beam and the resultant stress in the compression zone of the UHPC member is given. The distance between the resultant stress in the tension zone section of the I-beam and the resultant stress in the compression zone section of the I-beam. Perform flexural capacity verification if The combined cross section meets the structural requirements, if ,Pick , where M is the design value of bending moment; The shear capacity V of the steel-UHPC composite beam is calculated according to formula (5). This represents the bearing capacity of the compression zone above the plastic neutral axis of the composite section. This represents the bearing capacity of the combined cross-section in the tension zone below the plastic neutral axis. （5） Wherein, V is the shear bearing capacity of the steel-UHPC composite beam; The number of shear connectors n in the positive bending moment section is calculated according to formula (6), and the bearing capacity of a single PBL connector using NPR steel bars is calculated according to formula (7). ; （6） （7） Where n is the number of shear connectors in the positive bending moment section. The bearing capacity of a single PBL connector using NPR steel reinforcement. The reinforcement ratio of the UHPC component is given. This refers to the volumetric content of steel fibers. For the length of the steel fiber, The diameter of the steel fiber, The cubic compressive strength of the UHPC component. The thickness of the perforated steel plate is [missing information]. The diameter of the opening. The perforated area of ​​the perforated steel plate. The strength reduction factor for the NPR steel reinforcement is... Let be the cross-sectional area of ​​the perforated reinforcing bar. The yield strength of the perforated steel bar; When the negative bending moment section of the steel-UHPC composite beam is in the normal service stage, the elastic modulus material around the perforated steel bar allows the steel-concrete interface to slip by a preset distance. The steel-UHPC composite beam is in a state where the UHPC member is under tension and the I-beam is under compression. The tension zone of the UHPC member is reinforced according to formula (8). （8） in, This refers to the cross-sectional area of ​​the longitudinal reinforcement within the effective width of the concrete flange in the negative bending moment section. For the yield strength of the steel reinforcement, Let be the net cross-sectional area of ​​the web of the I-beam. Let be the net cross-sectional area of ​​the lower flange of the I-beam. This refers to the net cross-sectional area of ​​the upper flange of the I-beam. The tensile strength of the UHPC component; When the negative bending moment section of the steel-UHPC composite beam is at the ultimate limit stage of bearing capacity, the flexural bearing capacity of the composite section is calculated according to formula (9). ; （9） The maximum bending moment resisted by the combined section includes the bending moment resisted by the I-beam. The bending moment resisted by longitudinal reinforcement and the resistance of concrete to bending moment ; Perform flexural bearing capacity verification, if The combined cross section meets the structural requirements, if ,Pick ; Calculate the number n of pull-out non-shear connectors in the negative moment section according to formula (10), calculate the shear capacity V of the steel-UHPC composite beam according to formula (11), and calculate the bearing capacity of a single pull-out non-shear PBL connector according to formula (12). ; （10） （11） （12） in, The coefficient representing the reduction in bearing capacity of the connecting parts is taken as 0.9 for the negative bending moment section of the intermediate support and 0.8 for the negative bending moment section of the cantilever beam; f t The tensile strength of the UHPC component is given.

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