Multi-wave fish belly door rigid frame bridge with post-poured belt and construction method thereof

Abstract

This invention discloses a multi-wave fish-belly portal rigid frame bridge with post-cast strips and its construction method, belonging to the field of bridge engineering technology. The rigid frame bridge includes a substructure, a main beam structure, and abutment structures on both sides. The substructure includes pile foundations and abutments. The main beam structure consists of at least two fish-belly-shaped beams arranged laterally. The longitudinal section of the fish-belly-shaped beams varies in height from high at mid-span to low at both ends. Post-cast strip slots are reserved between adjacent fish-belly-shaped beams, and the post-cast strips are poured. The main beam has variable-height sections at both longitudinal ends, gradually transitioning from a fish-belly-shaped section to a rectangular section before being fixed to the abutments, forming a portal rigid frame system. During construction, the substructure is constructed first, then the fish-belly-shaped beams are poured in sections, followed by the post-cast strips. Finally, the supports are removed to complete the system conversion. This invention uses multiple fish-belly-shaped beams combined with post-cast strips to create a multi-wave landscape, and the variable-height sections are fixed to the abutments to form a portal rigid frame, combining good aesthetics, controllable construction quality, and excellent structural performance.

Description

Technical Field

[0001] This invention belongs to the field of bridge engineering technology, specifically relating to a multi-wave fish-belly portal rigid frame bridge with post-cast strips and its construction method. Background Technology

[0002] Fish-belly girder bridges, with their smooth, light curves at the bottom and strong visual transparency, have been widely used in urban landscape bridges. Fish-belly cast-in-place box girders are characterized by smooth lines, good aesthetic appeal, and strong applicability in span, but the construction control of their variable curvature curved formwork is quite challenging, and the shape and stress of the fish-belly concrete box girder are also relatively complex. With the continuous improvement of urban infrastructure quality, the requirements for the synergy between aesthetics and structural performance in wide urban bridges spanning rivers and roads are increasingly demanding.

[0003] The existing fish-belly beam bridges mainly suffer from the following technical shortcomings: Firstly, the landscape design is monotonous and lacks a sense of rhythm in the horizontal direction. Existing fish-belly beams are mostly single-span integral sections or parallel beams of equal height, resulting in a visually monotonous and oppressive appearance under the beams on wide bridges, lacking continuous, undulating horizontal variations. Some multi-beam designs use fish-belly prestressed concrete box girders where the side beams and middle beams are connected by transverse wet joints, and the webs are connected by a steel transverse support system. While this solves the transverse connection problem, it fails to create a continuous and smooth undulating landscape effect, making it difficult to fully meet the high visual quality requirements of urban water systems and landscape corridors for bridges.

[0004] Secondly, the construction quality of large-width, monolithic casting is difficult to control. When casting large-width fish-belly box girders in one continuous span, the large temperature difference in concrete hydration heat and uneven shrinkage and creep deformation make the beam prone to transverse through cracks, affecting its long-term durability. Existing post-cast strip technology is mostly applied to ordinary building beams and slabs or box girders with uniform cross-sections. It does not have a suitable post-cast strip structure designed for the curved bottom surface and variable cross-section characteristics of fish-belly beams, and cannot achieve precise control of stress during construction through segmented casting.

[0005] Third, stress concentration exists at the end rigid frame nodes. Existing fish-belly beams mostly employ simply supported systems, resulting in insufficient end stiffness and limited overall bending and torsional resistance, thus restricting their spanning capacity. If the fish-belly beam is directly fixed to the abutment to form a portal rigid frame system, the abrupt change in cross-section occurs when the fish-belly-shaped variable cross-section connects to the rectangular abutment, leading to severe stress concentration in the node area and a high risk of cracking. Furthermore, the shear reinforcement structures in the node areas of existing rigid frame bridges are typically designed for beams with uniform or regular variable cross-sections, making it difficult to directly adapt to the non-uniform stress characteristics and gradually changing cross-sectional shape of the fish-belly beam.

[0006] In summary, existing fish-belly bridges cannot simultaneously achieve the goals of improving landscape quality, controlling stress during construction, and optimizing the stress performance of end rigid frame nodes, thus failing to meet the construction requirements of high-quality urban bridges. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, this invention provides a multi-wave fish-belly portal rigid frame bridge with post-cast strips and its construction method.

[0008] The objective of this invention can be achieved through the following technical solutions: A multi-wave fish-belly portal rigid frame bridge with post-cast strips includes a substructure, a main beam structure, and abutment structures on both sides. The lower foundation structure includes a pile group embedded in the ground and a pile cap fixed on top of the pile group; The main beam structure is composed of at least two fish-belly shaped beams arranged side by side at intervals along the bridge width; the longitudinal section height of the fish-belly shaped beams varies with a smooth curve that is high at the mid-span and low at both ends along the span direction. A post-cast strip groove is reserved between two adjacent fish-belly shaped beams, which runs along the longitudinal length of the bridge, and a post-cast strip is poured into the post-cast strip groove. Both ends of the main beam structure are provided with variable height sections. Along the longitudinal direction of the bridge, the variable height section smoothly transitions from a fish-belly shaped variable cross section on the mid-span side to a rectangular cross section of equal thickness towards the abutment side. The abutment structures on both sides are respectively fixed on the two side piers. The rectangular cross-section ends of the variable height sections at both ends of the main beam structure are integrally cast and solidified with the corresponding abutment structures, together forming a portal rigid frame load-bearing system.

[0009] As a preferred embodiment of the present invention, a concave arc transition section extending smoothly towards the top surface of the fish-belly shaped beams on both sides is provided at the bridge deck position at the top of the post-cast strip groove, with an arc radius of 150mm to 500mm; a stress relief groove extending longitudinally along the bridge is provided on the bottom surface of the bridge deck directly below the arc transition section, the stress relief groove having a semi-circular or trapezoidal cross-section, a groove depth of 10mm to 30mm, and a groove width of 20mm to 50mm.

[0010] As a preferred technical solution of the present invention, a prestressed tendon guide duct is provided inside the variable height section, which is arranged longitudinally along the bridge. The guide duct is an arc-shaped steel duct, which is fixed inside the concrete of the variable height section by positioning steel bars, and is used to guide the longitudinal prestressed tendons in the fish belly beam to smoothly transition to the corresponding height position of the rectangular section.

[0011] As a preferred technical solution of the present invention, a vertical prestressed anchoring system is provided at the connection node between the variable height section and the abutment structure, including vertical prestressed steel strands and matching anchors; the vertical prestressed steel strands are arranged vertically upward from the top surface of the abutment, embedded in the abutment structure throughout and extending into the variable height section beam, with the lower end anchored to the top surface of the abutment and the upper end anchored to the top plate of the variable height section beam.

[0012] As a preferred embodiment of the present invention, the post-cast strip is made of micro-expansion concrete with a concrete strength grade one grade higher than that of the fish-belly shaped beams on both sides; the micro-expansion concrete contains steel fibers with a volume content of 0.5% to 1.5%, and the steel fibers are oriented along the width of the bridge.

[0013] As a preferred embodiment of the present invention, the concrete contact surfaces on both sides of the post-cast strip groove are provided with a rectangular cross-section toothed convex-concave interface. The teeth of the toothed convex-concave interface extend along the width of the bridge, and the convex-concave structure is arranged longitudinally along the bridge. The height of the toothed protrusion is 20mm to 50mm, and the tooth spacing is 100mm to 200mm. The post-cast strip is provided with transverse connecting steel bars, and the two ends of the transverse connecting steel bars are respectively embedded in the fish-belly-shaped beams on both sides, with an anchorage length of not less than 35 times the diameter of the steel bar. The toothed convex-concave interface and the transverse connecting steel bars cooperate to form a transverse shear force transmission system adapted to the stress of multiple fish-belly beams.

[0014] As a preferred embodiment of the present invention, a corrugated steel plate shear key is provided inside the consolidation node between the variable-height section and the abutment structure. The corrugated steel plate is a vertically arranged corrugated steel plate with its surface extending laterally along the bridge. The corrugated steel plate is embedded in the abutment structure and extends into the beam body of the variable-height section. Its crests extend longitudinally along the bridge, and its troughs and crests are alternately arranged laterally along the bridge. The wave height of the corrugated steel plate shear key is 30mm to 80mm, the wavelength is 150mm to 300mm, and the steel plate thickness is 10mm to 20mm. The wave height changes synchronously along the beam height gradient direction of the variable-height section, with the largest wave height on the abutment side and the smallest wave height on the mid-span side. The consolidation node area is also equipped with dense stirrups and shear reinforcement, and the stirrup spacing in the node area is not greater than 1 / 2 of the stirrup spacing in the standard mid-span section of the beam body.

[0015] A construction method for a multi-wave fish-belly portal rigid frame bridge with post-cast strips includes the following steps: S1 Substructure Construction: Construct the pile foundation group according to the designed pile positions, and construct the pile cap after the pile body concrete reaches the design strength; then pour the bridge abutment structure on both sides, and pre-embed connecting components at the positions of the bridge abutments corresponding to the main beams. S2 main beam segmented casting: erect construction scaffolding and pre-stress, install beam formwork, tie steel reinforcement cage and prestressing duct; symmetrically cast multiple fish-belly shaped beams in batches along the bridge width, with an interval of no less than 3 days between adjacent batches; leave post-cast strip slots between adjacent fish-belly shaped beams. Construction of the S3 end height change section and the consolidation node: Tie the steel reinforcement cage of the height change section, install the prestressed guide structure and node reinforcement components; connect and fix the longitudinal reinforcing steel bars of the height change section to the bridge abutment embedded components, lay out the node reinforcement steel bars, check the position of the shear-resistant components, and pour concrete simultaneously with the fish belly beam to complete the consolidation construction of the beam end and the bridge abutment. S4 Post-Pouring Strip Delayed Pouring: After the shrinkage and creep of the fish-belly beams on both sides have completed more than 60%, clean and moisten the contact surface of the post-pouring strip groove. After confirming that there are no defects through ultrasonic non-destructive testing, tie the post-pouring strip reinforcement, embed monitoring components, and install the top formwork with a rounded shape; pour the micro-expansion concrete of the post-pouring strip, monitor the hydration heat temperature field throughout the process, and control the temperature difference between the inside and outside of the concrete to not exceed 25℃; after curing to the design strength, tension the transverse prestressing tendons. S5 System Conversion and Bridge Completion: After the post-cast strip concrete and the consolidation node concrete have reached their design strength, and all prestressed tensioning and grouting have been completed, the construction supports are removed according to the principle of graded and symmetrical dismantling to complete the system conversion of the portal frame.

[0016] As a preferred technical solution of the present invention, in step S4, the transverse prestressed tendons adopt a graded tensioning process: firstly, initial tensioning is performed with a control stress of 30%; after the concrete of the post-cast strip reaches 70% of the design strength, secondary tensioning is performed with a control stress of 50%; after the concrete of the post-cast strip reaches 100% of the design strength, final tensioning is completed with a control stress of 100%.

[0017] As a preferred technical solution of the present invention, in step S2, the multiple fish-belly-shaped beams are cast in an alternating and symmetrical sequence: when the total number of fish-belly-shaped beams is even, they are cast symmetrically in batches from the outermost side to the middle; when the total number of fish-belly-shaped beams is odd, the middle beam is cast first, and then the two side beams are cast symmetrically in batches from the inside to the outside; the interval between adjacent batches of casting is not less than 3 days.

[0018] The beneficial effects of this invention are as follows: A continuous wave-shaped bottom surface is formed by arranging multiple fish-belly-shaped beams laterally, enhancing the rhythmic feel of the landscape beneath the bridge. Post-cast strips are reserved between adjacent beams and poured laterally, allowing for independent construction in sections to release hydration heat and reduce the risk of cracking. The post-cast strips use high-grade micro-expansion concrete mixed with directional steel fibers to compensate for shrinkage and enhance tensile strength, balancing stress release during construction with the overall integrity of the completed bridge. Gradual height-changing sections are provided at both ends of the main beam and are fixed to the abutments to form a portal frame, alleviating stress concentration caused by abrupt changes in cross-section and improving the overall structural stiffness and node durability. Prestressed tendon guide ducts are installed within the height-changing sections, and vertical prestressed anchorage systems are provided at the fixed nodes to ensure smooth prestress transfer and node crack resistance. The post-cast strip features a toothed, keyed interface on both sides of the groove, complemented by transverse connecting reinforcement. The height of the toothed key varies synchronously with the bending moment (maximum at mid-span, minimum at both ends), forming a regular mechanical interlocking force transmission path. A corrugated steel plate shear key is installed within the consolidation node, with the wave height gradually varying synchronously with the beam height (maximum at the abutment side, minimum at mid-span), dispersing and transmitting concentrated shear stress along the corrugated contact surface. A concave arc transition section is provided at the top of the post-cast strip, and a stress relief groove at the bottom, eliminating corner stress concentration and buffering shrinkage and temperature deformation. This invention solves the technical challenge of simultaneously achieving aesthetic appeal, construction controllability, and load-bearing performance through a synergistic design of landscape aesthetics, stress regulation, and rigid frame optimization. Attached Figure Description

[0019] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 This is a schematic front elevation view of the bridge structure of the present invention; Figure 2 This is a schematic diagram of the bridge structure of the present invention from an oblique upward view; Figure 3 This is a top-view axonometric schematic diagram of the bridge structure of the present invention.

[0021] Attached diagram labels: 1. Pile foundation group; 2. Pile cap; 3. Fish belly-shaped beam; 4. Post-cast strip; 5. Abutment structure; 6. Variable height section. Detailed Implementation

[0022] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0023] Please see Figures 1 to 3 This invention provides a multi-wave fish-belly portal rigid frame bridge with post-cast strips, including a substructure, a main beam structure, and abutment structures 5 on both sides. The substructure includes a pile group 1 embedded in the ground and a pile cap 2 fixedly installed on top of the pile group 1.

[0024] The pile foundation group 1 uses bored cast-in-place piles. Multiple piles can be arranged under each side of the pile cap 2 according to the bridge width and geological conditions, and the depth of the pile tip into the bearing stratum meets the design requirements. The pile cap 2 is a reinforced concrete structure used to evenly distribute and transfer the load of the superstructure to the pile foundation group 1.

[0025] The main girder structure is composed of at least two fish-belly shaped beams 3 arranged side-by-side at intervals along the bridge width. In this embodiment, four fish-belly shaped beams 3 are preferably arranged side-by-side. The longitudinal section height of the fish-belly shaped beams 3 varies smoothly along the span direction, with a higher height at the mid-span and lower height at both ends. The bottom curve of the beam can be fitted with a quadratic parabola or a circular arc to match the curve shape with the bending moment distribution law of the main girder, thus fully utilizing the mechanical properties of the material. After the four fish-belly shaped beams 3 are arranged side-by-side along the bridge width, the bottom surface of the bridge's transverse section forms three continuous undulating wave-like shapes, giving the space under the bridge a rich visual rhythm and layered variation.

[0026] Between two adjacent fish-belly shaped beams 3, there is a pre-reserved groove for a post-cast strip that runs along the longitudinal length of the bridge. The post-cast strip 4 is poured into the groove. The width of the post-cast strip groove is 0.8m, and it runs along the longitudinal length of the bridge.

[0027] The concrete contact surfaces on both sides of the post-cast strip groove are equipped with rectangular cross-section toothed convex-concave interfaces. The teeth of the toothed convex interface extend continuously along the bridge width, and the convex-concave structure is arranged longitudinally along the bridge. The height of the tooth protrusions ranges from 20mm to 50mm, and the tooth spacing ranges from 100mm to 200mm. The toothed convex interface is formed using custom-made steel templates, resulting in a regular rectangular toothed convex-concave structure on the concrete contact surfaces on both sides of the post-cast strip groove. Compared to traditional roughening treatment, this regular toothed interface provides more reliable mechanical interlocking force and a clear shear force transmission path.

[0028] The shear transfer mechanism of the toothed-key type concave-convex interface is as follows: When the old and new concrete interfaces on both sides of the post-cast strip groove are subjected to transverse shear force, the protruding part of the toothed key is embedded in the concave concrete on the opposite side, forming a regular mechanical interlock. The shear force is first transferred through the concrete bearing surface at the root of the toothed key. When the shear force increases, bending stress and shear stress are generated at the root of the toothed key. The height of the toothed key protrusion varies synchronously with the magnitude of the transverse bending moment of the fish-belly beam 3 along the bridge span direction. The bending moment is the largest at the mid-span, and the height of the toothed key protrusion is correspondingly the largest to provide a larger mechanical interlocking area and shear bearing capacity; the bending moment is smaller at both ends, and the height of the toothed key protrusion is correspondingly smaller. The toothed-key type concave-convex interface works in conjunction with the transverse connecting reinforcement that penetrates the post-cast strip 4: The transverse connecting reinforcement passes through the old and new concrete interface, and on the basis of the mechanical interlocking of the toothed key, the reinforcement dowel action is added, forming a dual shear transfer mechanism of toothed key interlocking and reinforcement dowel.

[0029] The height of the toothed key protrusion varies synchronously with the magnitude of the lateral bending moment of the fish-belly beam 3 along the bridge span direction. The toothed key protrusion height is the largest at the mid-span and the smallest at both ends, thus matching the wavy bending moment distribution of the multi-wave fish-belly beam. The post-cast strip 4 is equipped with transverse connecting reinforcement bars, both ends of which are pre-embedded inside the fish-belly beams 3 on both sides, with an anchorage length not less than 35 times the diameter of the reinforcement bar. The toothed key-type concave-convex interface, in conjunction with the transverse connecting reinforcement bars, forms a transverse shear force transmission system adapted to the stress of multiple fish-belly beams, which helps ensure the shear force transmission capacity of the interface between the old and new concrete after the delayed pouring of the post-cast strip 4.

[0030] Post-cast strip 4 is constructed using micro-expansion concrete, with a strength grade one level higher than that of the fish-belly beams 3 on both sides. For example, if the fish-belly beams on both sides use C45 concrete, post-cast strip 4 uses C50 micro-expansion concrete. The micro-expansion concrete incorporates steel fibers, with a volumetric fiber content of 0.5%–1.5%, and the steel fibers are oriented along the bridge width direction. The oriented arrangement of the steel fibers can be achieved by controlling the concrete flow direction during casting or by using an electromagnetic orientation device, ensuring that the orientation of the steel fibers is consistent with the transverse stress direction. This effectively improves the crack resistance and transverse tensile strength of the post-cast strip 4 concrete, and compensates for concrete shrinkage deformation.

[0031] At the top of the post-cast strip groove, on the bridge deck, there is a concave arc transition section that extends smoothly towards the top surface of the fish-belly beams 3 on both sides, with an arc radius of 150mm to 500mm. This concave arc transition section eliminates the corner stress concentration at the top of the bridge deck at the top of the post-cast strip groove, while improving the ride comfort.

[0032] A stress relief groove, running longitudinally along the bridge, is installed on the bottom surface of the bridge deck directly below the arc transition section. The cross-section of the stress relief groove is semi-circular or trapezoidal, with a depth of 10mm to 30mm and a width of 20mm to 50mm. The stress relief groove is formed by an arc-shaped protrusion at the bottom of the top template of the post-cast strip 4. It is used to buffer the tensile stress generated by the shrinkage and temperature deformation of the concrete in the post-cast strip 4. Together with the concave arc transition section of the top bridge deck, it forms a dual crack-resistant structure that eliminates angular stress at the top and buffers shrinkage deformation at the bottom.

[0033] Both ends of the main girder structure are equipped with variable height sections 6. Along the longitudinal direction of the bridge, the variable height sections 6 smoothly transition from a fish-belly shaped cross-section on the mid-span side to a uniformly thick rectangular cross-section towards the abutment side. The length of the variable height sections 6 is not less than 1 / 8 of the calculated span of the main girder, and the beam height transition rate is 1:3 to 1:8, achieving a seamless transition of the cross-section and effectively reducing the stress concentration in the joint area.

[0034] The variable-height section 6 is equipped with prestressed tendon guide ducts arranged longitudinally along the bridge. These guide ducts are arc-shaped steel ducts, fixed to the concrete interior of the variable-height section 6 by positioning reinforcing bars. The guide ducts guide the longitudinal prestressed tendons within the fish-belly-shaped beam 3 to smoothly transition from the height of the fish-belly section to the corresponding height of the rectangular section, preventing abrupt bends and interruptions in the prestressed tendons within the variable-height section 6 and ensuring effective force transmission. The longitudinal prestressed tendons are made of high-strength, low-relaxation steel strands, arranged along the entire length of both the fish-belly-shaped beam 3 and the variable-height section 6.

[0035] The abutment structures 5 on both sides are fixed to the bearing caps 2 on both sides respectively. The rectangular sections of the variable height sections 6 at both ends of the main beam structure are integrally cast and solidified with the corresponding abutment structures 5, together forming a portal rigid frame load-bearing system.

[0036] A vertical prestressed anchorage system, including vertical prestressed steel strands and matching anchorages, is installed at the fixed joint between the variable-height section 6 and the abutment structure 5. The vertical prestressed steel strands are arranged vertically upward from the top surface of the abutment 2, embedded entirely within the abutment structure 5 and extending into the beam of the variable-height section 6. The lower end is anchored to the top surface of the abutment 2, and the upper end is anchored to the top plate of the beam of the variable-height section 6. The vertical prestressed steel strands are used to resist the negative bending moment tensile stress in the fixed joint area of ​​the portal frame, suppress cracking at the top of the beam end and the junction of the abutment, and significantly improve the crack resistance and overall stiffness of the joint.

[0037] Corrugated steel plate shear keys are installed inside the fixed joint between the variable-height section 6 and the abutment structure 5. The corrugated steel plate is a vertically arranged corrugated steel plate, with its surface extending laterally along the bridge, embedded in the abutment structure 5 and extending into the beam body of the variable-height section 6. The crests of the corrugated steel plate extend longitudinally along the bridge, while the troughs and crests are arranged alternately laterally along the bridge. The wave height of the corrugated steel plate shear key is 30mm to 80mm, the wavelength is 150mm to 300mm, and the steel plate thickness is 10mm to 20mm.

[0038] The wave height changes synchronously along the beam height gradient direction of the variable-height section 6, with the largest wave height on the abutment side and the smallest on the mid-span side. This gradual wave height design matches the waveform amplitude of the corrugated steel plate shear key with the shear stress distribution law of the fixed node, effectively dispersing and transferring concentrated shear stress along the corrugated contact surface, which helps to alleviate local shear stress concentration. The corrugated steel plate shear key is pre-embedded in the abutment structure 5 and extends into the beam body of the variable-height section 6, forming a combined shear-resistant structure with the fixed node concrete.

[0039] The stress dispersion and transfer mechanism of the corrugated steel plate shear key is as follows: The shear stress borne by the fixed node is non-uniformly distributed along the gradual change direction of the beam height in the variable-height section 6. The shear stress concentration is highest at the abutment side section, while it is relatively dispersed at the mid-span side section. The crests and troughs of the corrugated steel plate are alternately arranged along the transverse direction of the bridge. When subjected to shear force, the inclined surface of the corrugated steel plate decomposes the longitudinal shear stress into a distributed force along the plate surface direction, and transfers the shear force to the surrounding concrete through the concrete bearing surfaces at the crests and troughs. The wave height changes synchronously along the gradual change direction of the beam height in the variable-height section 6. The shear stress concentration is highest at the abutment side, and the wave height is correspondingly the largest, providing a larger contact area between the steel plate and the concrete and increasing the shear bearing capacity. The shear stress is relatively smaller at the mid-span side, and the wave height is correspondingly smaller. This gradual wave height design makes the shear stiffness of the corrugated steel plate shear key gradient-distributed along the longitudinal direction of the bridge, precisely matching the shear stress distribution law of the fixed node.

[0040] The consolidated joint area is also equipped with denser stirrups and shear reinforcement. The stirrup spacing in the joint area is no more than 1 / 2 of the stirrup spacing in the standard section at the mid-span of the beam, further enhancing the shear and bending resistance of the rigid frame joint. The corrugated steel plate shear key works in conjunction with the denser stirrups and shear reinforcement to form multiple shear defense lines, jointly improving the load-bearing capacity and ductility of the consolidated joint.

[0041] This invention also provides a construction method for a multi-wave fish-belly portal rigid frame bridge with post-cast strips, comprising the following steps: Construction of the S1 substructure: Following the design pile locations, pile group 1 was constructed using rotary drilling. After drilling, the reinforcing cage was lowered, and underwater concrete was poured. Once the pile concrete reached its design strength, the laitance at the pile head was removed, and the pile integrity was checked. Subsequently, the abutment reinforcement was tied, bridge abutment reinforcing bars were pre-embedded, and after formwork was erected, the abutment 2 concrete was poured. After curing, the bridge abutment structures 5 on both sides were constructed. Longitudinal connecting reinforcing bars, positioning embedded parts, and corrugated steel plate shear keys were precisely pre-embedded at the positions corresponding to the main beams of the abutments. The corrugated steel plate shear keys were precisely positioned and fixed during the abutment construction stage to ensure that their pre-embedded positions and extension directions met the design requirements.

[0042] S2 main beam segmented casting: A full-span cup-lock scaffold was erected, and the scaffold foundation was hardened. Preloading was carried out according to specifications to eliminate inelastic deformation of the scaffold and collect elastic deformation data for setting the construction pre-camber. After successful preloading, steel formwork was installed according to the designed fish-belly shape, and the beam reinforcement cage was tied to the longitudinal prestressing ducts, guide pipes, and embedded parts. The guide pipes were fixed inside the concrete of the height-changing section 6 by positioning steel bars, and their arc shape was consistent with the design alignment of the prestressing tendons.

[0043] Multiple fish-belly shaped beams 3 are poured symmetrically in batches along the width of the bridge. The fish-belly shaped beams 3 are poured in an alternating symmetrical sequence: when the total number of fish-belly shaped beams 3 is even, they are poured symmetrically in batches from the outermost part towards the middle; when the total number of fish-belly shaped beams 3 is odd, the middle beam is poured first, and then the two side beams are poured symmetrically in batches from the inside out. The interval between adjacent batches is no less than 3 days. For example, when there are four fish-belly shaped beams, the first batch consists of the symmetrical beams No. 1 and No. 4, and the second and third symmetrical beams are poured after a 3-day interval. This avoids deformation due to eccentric load on the supports and reduces mutual interference from concrete shrinkage.

[0044] Each beam is cast independently, with a groove reserved between adjacent fish-belly beams 3 for post-casting. The concrete contact surfaces on both sides of the groove are formed into a rectangular cross-section toothed key-type concave-convex interface using custom steel templates, with protruding transverse connecting steel bars reserved inside the groove. The toothed key protrusion height is 20mm to 50mm, and the tooth spacing is 100mm to 200mm. The toothed key extends along the entire length of the bridge width, and the concave-convex structure is arranged longitudinally along the bridge. The toothed key protrusion height is the largest at the mid-span and the smallest at both ends to accommodate the wavy bending moment distribution of the fish-belly beam.

[0045] While pouring the fish-belly-shaped beam 3, the variable-height sections 6 at both ends of the main beam were poured simultaneously. The reinforcing steel cage of the variable-height sections 6 was tied, and prestressed tendon guide ducts, vertical prestressed steel tendon ducts, and anchorages were installed within the variable-height sections 6. The guide ducts and vertical prestressed ducts were installed and positioned before concrete pouring to ensure smooth threading and tensioning of the subsequent prestressed tendons. The longitudinal reinforcing steel of the variable-height sections 6 was connected and fixed to the pre-embedded connecting steel of the abutment. Denser stirrups and shear reinforcement were installed. After verifying the position of the shear keys of the pre-embedded corrugated steel plates in the abutment and completing the butt joint fixing, concrete was poured simultaneously with the fish-belly-shaped beam 3, completing the consolidation construction between the beam ends and the abutment.

[0046] S3 Post-Pouring Strip 4 Delayed Pouring: Construction of the post-pouring strip 4 will commence after the concrete of the fish-belly beams 3 on both sides has reached the design age and more than 60% of the shrinkage and creep have been completed. The degree of completion of concrete shrinkage and creep can be determined by comprehensively considering the age and shrinkage test data of test blocks cured under the same conditions. Generally, when the age reaches more than 60 days, more than 60% of the shrinkage and creep can be completed. First, the toothed concrete contact surfaces on both sides of the post-pouring strip groove should be cleaned and moistened to remove slag and dust. The contact surfaces should be fully moistened 24 hours before pouring.

[0047] Ultrasonic non-destructive testing was used to inspect the toothed key concrete contact surface for microcracks or defects. Subsequent construction could only proceed after the inspection was passed. Ultrasonic testing can effectively identify casting defects at the root of the toothed key, ensuring the reliability of force transmission at the contact surface. Subsequently, the transverse reinforcement of the post-cast strip, the bridge deck reinforcement, and the transverse prestressed ducts were tied, temperature sensors were embedded, and a top formwork with a rounded shape was installed to ensure a smooth transition.

[0048] The post-pouring strip 4 micro-expansion concrete was poured during nighttime or cloudy days when the ambient temperature was between 10℃ and 25℃. The micro-expansion concrete contained steel fibers, with a volumetric fiber content of 0.5% to 1.5%. During pouring, the steel fibers were oriented along the bridge width by controlling the concrete flow direction. Layered pouring and immersion vibrator compaction were used to ensure concrete density.

[0049] During the pouring process, the hydration heat temperature field inside the post-pouring strip 4 and the beams on both sides is monitored in real time using pre-embedded temperature sensors to control the temperature difference between the inside and outside of the concrete to not exceed 25℃. When the temperature difference exceeds the limit, temperature control can be adjusted by adjusting the thickness of the curing cover layer or by using cooling water pipes for circulation. During the pouring process, test blocks cured under the same conditions are simultaneously prepared to determine the demolding and tensioning times. After pouring, the concrete is covered with geotextile for moisturizing and curing for no less than 14 days.

[0050] After the concrete in post-cast strip 4 reaches its design strength, the transverse prestressing tendons are tensioned. A staged tensioning process is used: initial tensioning is performed at 30% control stress to ensure the tendons are initially attached to the duct and to eliminate slack; after the concrete in post-cast strip 4 reaches 70% of its design strength, secondary tensioning is performed at 50% control stress; finally, after the concrete in post-cast strip 4 reaches 100% of its design strength, final tensioning is performed at 100% control stress. Staged tensioning avoids excessive early stress on the concrete in post-cast strip 4 caused by a single tensioning, preventing cracking of post-cast strip 4, while ensuring the effective establishment of transverse prestress. Grouting of the ducts is carried out promptly after tensioning.

[0051] S4 System Conversion and Bridge Completion: After the post-cast strip 4 concrete and the consolidation node concrete reached 100% of their design strength, and all prestressing tensioning and grouting were completed, the scaffolding was dismantled. The dismantling of the construction scaffolding strictly followed the principles of dismantling from the mid-span outwards, in stages, symmetrically, and slowly. The scaffolding reaction force was released gradually in three stages. After each stage of scaffolding removal, the beam deformation and node stress were observed to ensure a smooth and controllable system conversion. After scaffolding removal, a portal frame system with integrated load-bearing capacity was formed. Finally, the bridge deck paving, crash barriers, lighting, drainage, and other ancillary facilities were constructed to complete the entire bridge construction. Testing revealed no transverse through cracks in the beams after completion, uniform stress distribution in the node areas, and a visually rhythmic wavy cross-section beneath the bridge, meeting the design requirements for an urban landscape bridge.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A multi-wave fish-belly portal rigid frame bridge with post-cast strips, comprising a substructure, a main beam structure, and abutment structures on both sides, characterized in that: The lower foundation structure includes a pile group embedded in the ground and a pile cap fixed on top of the pile group; The main beam structure is composed of at least two fish-belly shaped beams arranged side by side at intervals along the bridge width; the longitudinal section height of the fish-belly shaped beams varies with a smooth curve that is high at the mid-span and low at both ends along the span direction. A post-cast strip groove is reserved between two adjacent fish-belly shaped beams, which runs along the longitudinal length of the bridge, and a post-cast strip is poured into the post-cast strip groove. Both ends of the main beam structure are provided with variable height sections. Along the longitudinal direction of the bridge, the variable height section smoothly transitions from a fish-belly shaped variable cross section on the mid-span side to a rectangular cross section of equal thickness towards the abutment side. The abutment structures on both sides are respectively fixed on the two side piers. The rectangular cross-section ends of the variable height sections at both ends of the main beam structure are integrally cast and solidified with the corresponding abutment structures, together forming a portal rigid frame load-bearing system.

2. A multi-wave fish-belly portal rigid frame bridge with post-cast strip as described in claim 1, characterized in that, The bridge deck at the top of the post-cast strip groove is provided with a concave arc transition section that extends smoothly to the top surface of the fish-belly shaped beams on both sides, with an arc radius of 150mm to 500mm; the bottom surface of the bridge deck directly below the arc transition section is provided with a stress relief groove that runs longitudinally along the bridge, the cross-section of the stress relief groove is semi-circular or trapezoidal, the groove depth is 10mm to 30mm, and the groove width is 20mm to 50mm.

3. A multi-wave fish-belly portal rigid frame bridge with post-cast strip as described in claim 1, characterized in that, The variable-height section is equipped with a prestressed tendon guide duct that is arranged longitudinally along the bridge. The guide duct is an arc-shaped steel duct that is fixed inside the concrete of the variable-height section by positioning steel bars. It is used to guide the longitudinal prestressed tendons in the fish-belly beam to smoothly transition to the corresponding height position of the rectangular section.

4. A multi-wave fish-belly portal rigid frame bridge with post-cast strip as described in claim 1, characterized in that, A vertical prestressed anchorage system is provided at the connection node between the variable height section and the abutment structure, including vertical prestressed steel strands and matching anchors; the vertical prestressed steel strands are arranged vertically upward from the top surface of the abutment, embedded in the abutment structure throughout and extending into the variable height section beam, with the lower end anchored to the top surface of the abutment and the upper end anchored to the top plate of the variable height section beam.

5. A multi-wave fish-belly portal rigid frame bridge with post-cast strip as described in claim 1, characterized in that, The post-cast strip is made of micro-expansion concrete with a concrete strength grade one level higher than that of the fish-belly shaped beams on both sides. The micro-expansion concrete contains steel fibers with a volume content of 0.5% to 1.5%, and the steel fibers are oriented along the width of the bridge.

6. A multi-wave fish-belly portal rigid frame bridge with post-cast strip as described in claim 1, characterized in that, The concrete contact surfaces on both sides of the post-cast strip groove are provided with a rectangular cross-section toothed convex-concave interface. The teeth of the toothed convex-concave interface extend along the width of the bridge, and the concave-convex structure is arranged along the longitudinal direction of the bridge. The height of the tooth protrusion is 20mm to 50mm, and the tooth spacing is 100mm to 200mm. The post-cast strip is provided with transverse connecting steel bars. The two ends of the transverse connecting steel bars are respectively embedded in the fish-belly beams on both sides, and the anchorage length is not less than 35 times the diameter of the steel bar. The toothed convex-concave interface and the transverse connecting steel bars cooperate to form a transverse shear force transmission system adapted to the stress of multiple fish-belly beams.

7. A multi-wave fish-belly portal rigid frame bridge with post-cast strip as described in claim 1, characterized in that, The shear key of corrugated steel plate is provided inside the fixed joint between the variable height section and the abutment structure. The corrugated steel plate is a vertically arranged corrugated steel plate that extends laterally along the bridge. The corrugated steel plate is embedded in the abutment structure and extends into the beam of the variable height section. Its crests extend longitudinally along the bridge, and the troughs and crests are alternately arranged laterally along the bridge. The wave height of the shear key of corrugated steel plate is 30mm to 80mm, the wavelength is 150mm to 300mm, and the steel plate thickness is 10mm to 20mm. The wave height changes synchronously with the beam height gradient direction of the variable height section, with the largest wave height on the abutment side and the smallest wave height on the mid-span side. The fixed joint area is also equipped with dense stirrups and shear reinforcement. The stirrup spacing in the joint area is not greater than 1 / 2 of the stirrup spacing in the standard mid-span section of the beam.

8. A construction method for a multi-wave fish-belly portal rigid frame bridge with post-cast strips, applicable to a multi-wave fish-belly portal rigid frame bridge with post-cast strips as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1 Substructure Construction: Construct the pile foundation group according to the designed pile positions, and construct the pile cap after the pile body concrete reaches the design strength; then pour the bridge abutment structure on both sides, and pre-embed connecting components at the positions of the bridge abutments corresponding to the main beams. S2 main beam segmented casting: erect construction scaffolding and pre-stress, install beam formwork, tie steel reinforcement cage and prestressing duct; symmetrically cast multiple fish-belly shaped beams in batches along the bridge width, with an interval of no less than 3 days between adjacent batches; leave post-cast strip slots between adjacent fish-belly shaped beams. Construction of the S3 end height change section and the consolidation node: Tie the steel reinforcement cage of the height change section, install the prestressed guide structure and node reinforcement components; connect and fix the longitudinal reinforcing steel bars of the height change section to the bridge abutment embedded components, lay out the node reinforcement steel bars, check the position of the shear-resistant components, and pour concrete simultaneously with the fish belly beam to complete the consolidation construction of the beam end and the bridge abutment. S4 Post-Pouring Strip Delayed Pouring: After the shrinkage and creep of the fish-belly beams on both sides have completed more than 60%, clean and moisten the contact surface of the post-pouring strip groove. After confirming that there are no defects through ultrasonic non-destructive testing, tie the post-pouring strip reinforcement, embed monitoring components, and install the top formwork with a rounded shape; pour the micro-expansion concrete of the post-pouring strip, monitor the hydration heat temperature field throughout the process, and control the temperature difference between the inside and outside of the concrete to not exceed 25℃; after curing to the design strength, tension the transverse prestressing tendons. S5 System Conversion and Bridge Completion: After the post-cast strip concrete and the consolidation node concrete have reached their design strength, and all prestressed tensioning and grouting have been completed, the construction supports are removed according to the principle of graded and symmetrical dismantling to complete the system conversion of the portal frame.

9. A construction method for a multi-wave fish-belly portal rigid frame bridge with post-cast strips according to claim 8, characterized in that, In step S4, the transverse prestressed tendons are tensioned in stages: firstly, they are tensioned with 30% control stress; after the concrete in the post-cast strip reaches 70% of the design strength, they are tensioned a second time with 50% control stress. After the post-cast strip concrete reaches 100% of its design strength, the final tensioning is completed with 100% controlled stress.

10. A construction method for a multi-wave fish-belly portal rigid frame bridge with post-cast strips according to claim 8, characterized in that, In step S2, the multiple fish-belly-shaped beams are poured in an alternating and symmetrical sequence: when the total number of fish-belly-shaped beams is even, they are poured symmetrically in batches from the outermost side to the middle; when the total number of fish-belly-shaped beams is odd, the middle beam is poured first, and then the two side beams are poured symmetrically in batches from the inside to the outside; the interval between adjacent batches of pouring is no less than 3 days.

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