Large cantilever assembled cap beam based on uhpc-nc combined structure

Abstract

The utility model discloses a large cantilever assembly type bent cap based on UHPC-NC combination structure, the assembly type bent cap includes upper UHPC structure and lower NC structure, the upper UHPC structure and the lower NC structure are all the groove prefabricated structure of the section shows " " shape, the upper UHPC structure and the lower NC structure upper and lower superposition connection form the bent cap beam body structure of the middle hollowing out. The utility model solves the material performance utilization rate of large cantilever bent cap structure is low, the self weight is bigger, the on -the -spot operation is complicated and is not favorable to the problem of assembly construction.

Description

Technical Field

[0001] This utility model belongs to the field of bridge engineering, specifically relating to a large cantilever prefabricated cap beam based on a UHPC-NC composite structure. Background Technology

[0002] Traditional cast-in-place concrete cap beams suffer from long construction cycles, cumbersome on-site formwork, and significant environmental disturbances. This is especially true for conventional prestressed concrete (NC) cap beams, where the timing of the initial dead load (beam erection) and the second-stage dead load application often necessitates multiple batches of prestressed steel strand tensioning. This results in complex construction procedures and a long construction period, failing to meet the demands of rapid construction for urban bridges. The reason for this is that existing large-cantilever prestressed concrete cap beams, due to their long cantilever and large loads, often require numerous prestressed steel strands with complex alignments to balance the enormous bending moments during construction and service. To avoid excessive local stress and concrete cracking caused by tensioning all steel strands at once, or excessive camber affecting the bridge deck alignment, a phased tensioning strategy must be adopted during construction. This ensures that structural stress and deformation develop gradually and controllably with the construction progress, guaranteeing that the cap beam meets the requirements for load-bearing capacity and normal use under various working conditions.

[0003] In recent years, prefabricated concrete cap beams have shortened the construction period by assembling precast components on site. However, due to the low strength of ordinary concrete materials, the precast sections are heavy (a single section can exceed 150 tons), making transportation and hoisting difficult. Furthermore, the prestressed steel strands need to be pre-embedded and reserved for tensioning during the prefabrication stage, and multiple tensioning batches are still required after on-site assembly. As a result, the bottleneck of cumbersome procedures and low efficiency cannot be completely eliminated.

[0004] Ultra-high performance concrete (UHPC) boasts the advantages of being lightweight and high-strength, significantly reducing the self-weight of precast components and demonstrating promising application potential. However, its application in precast cap beams still faces several technical limitations in cross-sectional design. Based on existing engineering experience, common cap beam cross-sectional forms mainly include closed and open sections, each with its own construction or structural defects: ① Closed sections (such as rectangular and box-shaped sections): While these sections offer advantages in load-bearing performance, they are prone to mold floating during construction, leading to difficulties in controlling molding accuracy and low demolding efficiency, severely impacting precast production efficiency; ② Open sections (such as channel-shaped, π-shaped, and I-shaped sections): Although formwork fabrication and demolding are relatively simple, their torsional stiffness is low, making them susceptible to torsional deformation under complex stress conditions, affecting the overall performance and durability of the structure. Furthermore, the high cost of UHPC materials and corresponding molding processes further restricts its large-scale application in practical engineering projects.

[0005] The "Semi-precast UHPC-NC Composite Cap Beam Connection Structure" disclosed in Chinese Patent CN113279324A and the "Prestressed UHPC Shell-Concrete Inner Core Composite Cap Beam Structure" disclosed in CN113605246A both improve performance by combining a UHPC shell with normal concrete, but still have the following three shortcomings: first, they rely on a large amount of on-site wet concrete pouring operations, leading to an extended construction period; second, effective optimization of the structural self-weight is not achieved, affecting the feasibility of long-span applications; more importantly, they fail to break through the prefabrication rate bottleneck, and key components still require on-site forming. These technical limitations not only restrict the improvement of construction efficiency, but also make it difficult to give full play to the industrial advantages of prefabricated cap beams in terms of quality control, environmental protection and engineering standardization. Contents of the Utility Model

[0006] The purpose of the utility model is to provide a large cantilever prefabricated cap beam based on a UHPC-NC composite structure, which aims to solve the problems existing in traditional large cantilever cap beam structures, such as low material performance utilization rate, large self-weight, complicated on-site operations, and being unfavorable for prefabricated construction.

[0007] To solve the above technical problems, the technical solution adopted by the utility model is as follows:

[0008] A large cantilever prefabricated cap beam based on a UHPC-NC composite structure comprises an upper UHPC structure and a lower NC structure, both of which are trough-shaped prefabricated structures with a "ㄇ"-shaped cross-section, and the upper UHPC structure and the lower NC structure are connected in an up-down overlapping manner to form a cap beam body structure with a hollowed-out middle part.

[0009] In the cap beam body structure of the utility model, the UHPC material is applied to the top area of the cap beam that mainly bears tensile force, while the NC material is applied to the bottom area that mainly bears compressive force, giving full play to the material advantages of the excellent tensile performance of UHPC and the good compressive performance of NC. To reduce the self-weight, both the upper UHPC structure and the lower NC structure of the utility model adopt a hollowed-out "ㄇ"-shaped cross-section, and the two upper and lower "ㄇ"-shaped cross-section structures are vertically overlapped to form a composite cross-section structure with a "mouth" shape at the upper part and a trough shape at the lower part. This composite cross-section structure has relatively large bending and torsion moments of inertia, which can effectively ensure the overall mechanical performance of the cap beam.

[0010] The prefabricated cap beam of the utility model also has the following preferred designs:

[0011] According to stress requirements, prestressed steel strands may be arranged inside the upper UHPC structure of the utility model.

[0012] The upper UHPC structure of this invention is a constant cross-section structure, while the lower NC structure is a variable cross-section structure. The cross-sectional dimensions and the arrangement of prestressed steel strands and reinforcing bars can be adjusted according to the stress conditions at different parts of the cantilever arm to ensure the compressive strength requirements of the lower NC structure.

[0013] The upper surface of the upper UHPC structure of this invention is provided with support pads, a first partition is provided in the slot of the upper UHPC structure, and a second partition is provided in the slot of the lower NC structure. Both the first and second partitions are positioned directly below each support pad. By installing partitions to address the concentrated force on the support pads at the cut-out section of the cap beam, the problem of localized stress concentration can be improved, enhancing the overall load-bearing capacity of the section.

[0014] This utility model discloses a first construction method for a large cantilever prefabricated cap beam based on a UHPC-NC composite structure. The method includes the following steps:

[0015] S1. First, make a template for the upper UHPC structure, pour the upper UHPC structure, and cure it until the upper UHPC structure reaches the designed strength;

[0016] S2. The upper UHPC structure is placed upside down, and a template for the lower NC structure is made on the upper UHPC structure. Then the lower NC structure is poured to form the cap beam structure.

[0017] S3. After the lower NC structure reaches the design strength, the cap beam structure is flipped upside down and transported to the construction site. The cap beam structure is then hoisted onto the top of the bridge pier column and connected to the bridge pier column through a grouting sleeve.

[0018] As needed, the upper UHPC structure in step S1 can be equipped with prestressed steel strands. After the upper UHPC structure has cured to the designed strength, the prestressed steel strands are tensioned or released to apply prestress to the upper UHPC structure.

[0019] If the prestressed steel strands are constructed using the post-tensioning method, then the prestressed steel strands are tensioned.

[0020] If the prestressed steel strands are constructed using the pre-tensioning method, then the prestressed steel strands are released.

[0021] The first construction method of this utility model enables one-time tensioning of prestressed steel strands. Its core principle lies in the innovative material zoning design and optimization of the structural force path, precisely limiting the application and range of prestress to the upper UHPC region with its superior tensile strength. This avoids the technical constraints of traditional NC cap beams, which require batch tensioning to control stress and deformation due to the low tensile strength of the material. The specific reasons and principles for this achievement are as follows:

[0022] 1. Targeted utilization of material properties and isolation of stress paths.

[0023] This invention, based on the stress pattern of "tension at the top and compression at the bottom" for cap beams, divides the cross-section into material partitions roughly along the neutral axis. The upper part uses ultra-high performance concrete (UHPC), whose ultra-high tensile strength and toughness can withstand the high stress concentration generated by a single tensioning and is not prone to cracking; the lower part uses ordinary concrete (NC), which only bears the compressive stress. This design completely "encapsulates" the tension of the prestressed steel strands and applies it to the upper UHPC section. The resulting elastic compression, arching deformation, and other effects are strictly limited within this area, preventing harmful tensile stress or cracking in the lower NC section. This fundamentally eliminates the primary reason why traditional monolithic NC cap beams must be tensioned in batches.

[0024] 2. Efficient pre-storage of prestress and load offsetting mechanism.

[0025] Before the upper UHPC and lower NC are combined to form an integral composite section, the UHPC section is prestressed separately. This prestressing pre-stores significant compressive stress within the UHPC section. When the composite section is formed and subjected to external forces such as the load from the upper bridge deck, the tensile stress generated at the top of the cap beam is first offset by this pre-stored compressive stress. The high tensile strength of the UHPC material itself provides a solid guarantee, ensuring that the tensile stress in the section remains within the safe bearing range of the UHPC under subsequent service loads. This "pre-stored compressive stress" mechanism ensures that the structure has sufficient tensile reserves in its final stress state, eliminating the need for complex staged tensioning to gradually adjust the stress.

[0026] 3. Precise control of structural separation construction and stress sequence.

[0027] The construction method described above achieves a key breakthrough in its process. By first casting and tensioning the UHPC structure, and then casting the NC structure, the prestress is ensured to be entirely borne by the UHPC structure in an independent state. The lower NC structure is only combined with the upper UHPC structure after the prestressing tension has been completed and the stress state has stabilized. Therefore, the NC structure will not be subject to the adverse effects of prestress. This timing control separates the application of prestress and the final formation of the composite section into two clear and independent stages, making one-time tensioning technically possible without causing any damage to the subsequent composite performance of the structure.

[0028] In summary, this invention precisely limits the prestressing range to the UHPC structural area through material zoning design. It utilizes the high tensile strength of UHPC to safely withstand a single tensioning operation, and effectively resists subsequent tensile stress through a pre-stored compressive stress mechanism. Furthermore, the separate construction sequence ensures that the lower NC structure is not adversely affected by prestressing. The synergistic effect of these innovations constitutes the fundamental principle that allows this invention to replace traditional "batch tensioning" with "single-time tensioning," simplifying the construction process, improving efficiency, and guaranteeing the structural safety and reliability from a mechanical perspective.

[0029] The first construction method of this utility model innovatively realizes the factory-made overall manufacturing of the composite structure under optimal stress state through a unique process of first casting the upper UHPC structure and tensioning it, then casting the lower NC structure and flipping it over as a whole. This fundamentally ensures the quality of the structural interface and the overall integrity of the components, and is especially suitable for large-scale standardized bridge construction with extremely high requirements for structural durability, construction efficiency and quality consistency.

[0030] This utility model discloses a second construction method for a large cantilever prefabricated cap beam based on a UHPC-NC composite structure. The method includes the following steps:

[0031] S1′. The upper UHPC structure and the lower NC structure are prefabricated respectively. The upper sides of the lower NC structure are pre-grooved with side grooves for construction splicing strips.

[0032] S2′. Transport the prefabricated upper UHPC structure and lower NC structure to the construction site;

[0033] S3′. First, construct the lower NC structure, hoist the lower NC structure to the top of the bridge pier column, and connect it to the bridge pier column through a grouting sleeve;

[0034] S4′. Hoist the upper UHPC structure above the lower NC structure, aligning the interface between the upper UHPC structure and the lower NC structure. Use a temporary support device to fix the upper UHPC structure, install the splicing strip, and bond the upper UHPC structure and the lower NC structure together to form a whole.

[0035] If necessary, the upper UHPC structure described in step S1′ may be equipped with prestressed steel strands.

[0036] The splice strip described in step S4′ may be provided with interfacial shear reinforcement to ensure the strength and bonding performance of the splice strip.

[0037] The second construction method of this utility model effectively solves the bottleneck of transportation and hoisting of large components by using a process of prefabrication of upper and lower parts and on-site splicing. It also achieves precise control of key connection interfaces under on-site conditions, and is particularly suitable for bridge projects where transportation conditions are limited and on-site operations need to be flexibly arranged.

[0038] The second construction method of this utility model also precisely limits the application object and scope of prestressing to the upper UHPC region with excellent tensile strength, thereby avoiding the technical constraints of traditional NC cap beams that must rely on batch tensioning to control stress and deformation due to the low tensile strength of the material. Therefore, it is also possible to achieve one-time tensioning of prestressed steel strands during construction.

[0039] Furthermore, in the two construction methods of this utility model, the cap beam is divided into two independent parts for casting: an upper UHPC structure and a lower NC structure. Both independent parts are open-section structures, so during prefabrication, there is no need to set an inner mold as required for casting closed-section structures, resulting in higher prefabrication efficiency and easier control of the forming accuracy of the upper UHPC structure.

[0040] This utility model has the following beneficial effects:

[0041] 1. Lightweight: By hollowing out the cross-sections of the upper UHPC structure and the lower NC structure into a "U" shape, the self-weight of the cap beam is effectively reduced, thus lowering the requirements for the foundation and hoisting equipment.

[0042] 2. Economical construction and full utilization of material properties: UHPC and NC materials are rationally allocated according to the stress pattern. The upper UHPC structure provides tensile strength, while the lower NC structure provides compressive strength, fully utilizing the properties of both materials and achieving optimized material utilization. The stress of the prestressed steel strands is entirely applied to the upper UHPC structure, and the pre-stored large compressive stress effectively resists the tensile stress generated by the upper load, improving the crack resistance and durability of the cap beam. Simultaneously, the amount of material used is reduced, avoiding waste and lowering production costs.

[0043] 3. Small cap beam height: The reasonable cross-sectional design allows the cap beam to be reduced in height while meeting the load-bearing capacity requirements, which can reduce the overall height of the bridge and save space.

[0044] 4. High load-bearing capacity: The composite section has a large bending and torsional moment of inertia, which, combined with the effect of prestressed steel strands, significantly improves the load-bearing capacity of the cap beam.

[0045] 5. Simple construction procedures, fast speed, and high efficiency: Factory prefabrication reduces on-site work, and the prestressed steel strands of the upper UHPC structure are tensioned in one go, simplifying the construction process. Both construction methods have clear operating procedures, which can effectively shorten the construction cycle and improve construction efficiency.

[0046] 6. Less on-site work and controllable quality: In a prefabricated factory environment, construction quality is easier to control, reducing the uncertainty and potential quality problems in on-site construction.

[0047] 7. Less interference with ground traffic: Prefabricated construction methods reduce the use of large equipment on site and the working time of construction personnel, thus reducing interference with ground traffic.

[0048] 8. High degree of prefabrication and full utilization of industrial advantages: The production and installation of prefabricated components meet the requirements of industrialized construction, which can improve the standardization and mechanization of construction and give full play to the advantages of industrialized production. Attached Figure Description

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0050] Figure 1 This is a front view of the large cantilever prefabricated cap beam based on the UHPC-NC combined structure in Example 1;

[0051] Figure 2 for Figure 1 A-A section structural diagram of the prefabricated cap beam;

[0052] Figure 3 for Figure 1 B-B section structural diagram of the prefabricated cap beam;

[0053] Figure 4 This is a construction schematic diagram of the prefabricated cap beam in Example 1;

[0054] Figure 5 This is a front view of the large cantilever prefabricated cap beam based on the UHPC-NC combined structure in Example 2;

[0055] Figure 6 for Figure 5C-C section structural diagram of prefabricated cap beam;

[0056] Figure 7 for Figure 5 D-D section structural diagram of prefabricated cap beam;

[0057] Figure 8 This is a construction schematic diagram of the prefabricated cap beam in Example 2.

[0058] Explanation of reference numerals in the attached figures:

[0059] 1. Upper UHPC structure; 2. Lower NC structure; 2a. Side groove; 3. First diaphragm; 4. Second diaphragm; 5. Pier column; 6. Grouting sleeve; 7. Bearing pad; 8. Stop block; 9. Splicing strip. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this utility model more apparent, exemplary embodiments according to this utility model will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this utility model, and not all embodiments of this utility model. It should be understood that this utility model is not limited to the exemplary embodiments described herein. Based on the embodiments of this utility model described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of this utility model.

[0061] It should be understood that this invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of this invention to those skilled in the art.

[0062] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0063] Example 1

[0064] like Figures 1 to 4 As shown, a large cantilever prefabricated cap beam based on a UHPC-NC combined structure includes an upper UHPC structure 1 and a lower NC structure 2. Both the upper UHPC structure 1 and the lower NC structure 2 are prefabricated structures with a "U"-shaped cross section. The upper UHPC structure 1 and the lower NC structure 2 are stacked and connected to form a cap beam structure with a hollowed-out middle.

[0065] In this embodiment, prestressed steel strands can be installed inside the upper UHPC structure 1 according to the stress requirements.

[0066] The upper UHPC structure 1 is a constant cross-section structure, while the lower NC structure 2 is a variable cross-section structure. The cross-sectional dimensions and the arrangement of prestressed steel strands and reinforcing bars can be adjusted according to the stress conditions of different parts of the cantilever arm to ensure the compressive strength requirements of the lower NC structure.

[0067] The upper surface of the upper UHPC structure 1 is provided with support pads 7, and a first partition 3 is provided in the slot of the upper UHPC structure 1. A second partition 4 is provided in the slot of the lower NC structure 2. The first partition 3 and the second partition 4 are respectively located directly below each support pad 7. The partitions are designed to address the concentrated force at the support pads 7 in the excavated section of the cap beam, which can improve the problem of local stress concentration and enhance the overall load-bearing capacity of the section. In this embodiment, blocks 8 are provided at both ends of the cap beam structure.

[0068] The construction method for the above-mentioned large cantilever prefabricated cap beam based on the UHPC-NC composite structure includes the following steps:

[0069] S1. First, make the template for the upper UHPC structure, pour the upper UHPC structure 1, and cure it until the upper UHPC structure 1 reaches the designed strength;

[0070] S2. Invert the upper UHPC structure 1. Create a template for the lower NC structure 2 on the upper UHPC structure 1. Then, pour the lower NC structure 2 to form the cap beam structure. See the attached image for the cast cap beam structure. Figure 4 When pouring the lower NC, avoid damaging the UHPC structure and ensure that it is tightly integrated with the upper UHPC structure to form a composite section structure.

[0071] S3. After the lower NC structure 2 reaches the design strength, the cap beam structure is flipped up and down and transported to the construction site. The cap beam structure is then hoisted as a whole onto the top of the bridge pier column 5 and connected to the bridge pier column 5 through the grouting sleeve 6.

[0072] As needed, in step S1, the upper UHPC structure 1 can be equipped with prestressed steel strands and reinforcing bars. After the upper UHPC structure 1 has cured to the designed strength, the prestressed steel strands are tensioned or released to apply prestress to the upper UHPC structure 1.

[0073] If the prestressed steel strands are constructed using the post-tensioning method, then the prestressed steel strands are tensioned.

[0074] If the prestressed steel strands are constructed using the pre-tensioning method, then the prestressed steel strands are released.

[0075] Example 2

[0076] like Figures 5 to 8As shown, a large cantilever prefabricated cap beam based on a UHPC-NC combined structure includes an upper UHPC structure 1 and a lower NC structure 2. Both the upper UHPC structure 1 and the lower NC structure 2 are prefabricated structures with a "U"-shaped cross section. The upper UHPC structure 1 and the lower NC structure 2 are stacked and connected to form a cap beam structure with a hollowed-out middle.

[0077] The difference from Embodiment 1 lies in the construction method of the large cantilever prefabricated cap beam based on the UHPC-NC composite structure in this embodiment, which includes the following steps:

[0078] S1′. The upper UHPC structure 1 and the lower NC structure 2 are prefabricated respectively. The upper sides of the lower NC structure 2 are pre-set with side grooves 2a for construction splicing strips 9.

[0079] S2′. Transport the prefabricated upper UHPC structure 1 and lower NC structure 2 to the construction site;

[0080] S3′. First, construct the lower NC structure 2, hoist the lower NC structure 2 to the top of the bridge pier column 5, and connect it to the bridge pier column 5 through the grouting sleeve 6. Adjust the position and elevation during connection to ensure accurate installation.

[0081] S4′. Hoist the upper UHPC structure 1 above the lower NC structure 2, aligning the interface between the upper UHPC structure 1 and the lower NC structure 2. Use temporary support devices to fix the upper UHPC structure 1. Use splicing strip 9 to bond the upper UHPC structure 1 and the lower NC structure 2 into a whole. The splicing strip 9 uses concrete that is compatible with UHPC or NC.

[0082] As needed, prestressed steel strands and reinforcing bars can be installed in the upper UHPC structure 1 in step S1′.

[0083] In step S4′, interfacial shear reinforcement bars can be installed inside the splice strip 9 to ensure the strength and bonding performance of the splice strip.

[0084] During prefabrication, the mix proportions, mixing process, pouring process, and curing conditions of UHPC must be strictly controlled to ensure that the strength and performance of UHPC meet design requirements. During transportation, effective protective measures should be taken to prevent components from being impacted or damaged, ensuring the integrity of the components.

[0085] The above embodiments of this utility model are not intended to limit the scope of protection of this utility model. The implementation of this utility model is not limited thereto. All other modifications, substitutions or alterations made to the above structure of this utility model based on the above content of this utility model and in accordance with the common technical knowledge and conventional means in the field, without departing from the basic technical idea of ​​this utility model, shall fall within the scope of protection of this utility model.

Claims

1. A large cantilever prefabricated cap beam based on a UHPC-NC composite structure, characterized in that: It includes an upper UHPC structure and a lower NC structure. Both the upper UHPC structure and the lower NC structure are prefabricated slotted structures with a "U"-shaped cross-section. The upper UHPC structure and the lower NC structure are stacked and connected to form a cap beam structure with a hollowed-out middle.

2. The large cantilever prefabricated cap beam based on the UHPC-NC composite structure according to claim 1, characterized in that: The upper UHPC structure is equipped with prestressed steel strands.

3. The large cantilever prefabricated cap beam based on the UHPC-NC composite structure according to claim 1, characterized in that: The upper UHPC structure is a constant cross-section structure, and the lower NC structure is a variable cross-section structure.

4. The large cantilever prefabricated cap beam based on the UHPC-NC combined structure according to claim 1, characterized in that: The upper surface of the upper UHPC structure is provided with support pads, the slot of the upper UHPC structure is provided with a first partition, and the slot of the lower NC structure is provided with a second partition. The first partition and the second partition are respectively located directly below each support pad.

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