A reinforced structure of a trestle and a construction method thereof

Abstract

The application discloses a kind of existing trestle reinforcing structure, including existing trestle and reinforcing component, the reinforcing component uses following any reinforcing type: reinforcing type I, the reinforcing type I is suitable for existing trestle upstream and downstream without support trestle, or the section of support trestle distance main trestle interval >6m.A kind of construction method of existing trestle reinforcing structure, including the following steps: S1, construction preparation;S2, steel pipe pile is sunk;S3, flat link and inclined brace processing;S4, flat link and inclined brace installation;S5, acceptance and use.The application is aimed at the problem of mud surface overdeep scour caused by strong tide and rapid current, three kinds of differentiated reinforcing types are used, the upstream side is uniformly reinforced by newly added pile foundation, the downstream side is flexibly selected by newly added pile foundation or cooperatively stressed by support trestle according to the interval between main trestle and support trestle, a triangular support structure is formed by flat link and inclined brace, which significantly improves the anti-scouring capacity and overall stiffness of the trestle, and ensures the stress balance of the structure.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and in particular to a reinforcement structure and construction method for existing trestle bridges. Background Technology

[0002] Piers are indispensable key facilities in waterway engineering projects in shallow waters and nearshore areas. They are widely used in bridge construction, material transportation, and personnel passage. Their structural stability is directly related to project progress and operational safety. The substructure of these facilities mostly adopts steel pipe pile foundations, relying on the embedment effect of the surrounding soil to bear vertical and horizontal loads. The original design has fully considered the impact of mud erosion under normal hydrological conditions.

[0003] However, in areas with strong tidal currents, the high-speed water flow carries sediment, creating a continuous and intense scouring effect that significantly erodes the mud surface where the trestle bridge foundation is located. As service time progresses, the actual scouring depth gradually exceeds the original design safety control value, with some sections experiencing scouring elevations as low as -7.5 to -15 meters. This phenomenon directly leads to insufficient effective embedment depth of the steel pipe piles, a significant decrease in pile side friction and pile end bearing capacity, and disrupts the original structural stress balance.

[0004] Structural stress imbalance can lead to a series of safety hazards, such as pile foundation tilting, structural deformation, and bridge deck settlement, and in severe cases, even collapse. Furthermore, the trestle must bear the loads of construction vehicles and machinery; overloading or improper stress will exacerbate structural damage, not only disrupting construction and causing economic losses, but also posing a serious threat to the lives of passing vehicles and personnel.

[0005] Therefore, in response to the problem of deep mud erosion caused by strong tidal currents, it is urgent to develop a scientific, reasonable, and targeted reinforcement scheme for existing trestle bridges. By optimizing the reinforcement design and construction process, the load-bearing capacity and erosion resistance of the trestle bridge structure can be restored and improved to ensure that it meets the structural stress requirements during its subsequent service life and to guarantee the continued safety of construction and traffic. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a design and construction method for reinforcing existing trestle bridges.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: An existing trestle reinforcement structure includes the existing trestle and reinforcement components, wherein the reinforcement components adopt any of the following reinforcement types: Reinforcement Type I is applicable to sections where there are no supporting trestle bridges upstream and downstream of existing trestle bridges, or where the distance between the supporting trestle bridge and the main trestle bridge is greater than 6m. Reinforcement Type I includes two Φ1000×10mm steel pipe piles and two Φ630×8mm diagonal braces. One of the Φ1000×10mm steel pipe piles is installed on the outer side of the upstream main trestle bridge steel pipe pile, with a center-to-center distance of 3.5m between the two piles. The other Φ1000×10mm steel pipe pile is installed on the outer side of the downstream main trestle bridge steel pipe pile, with a center-to-center distance of 2.5m between the two piles. The lower ends of the two Φ630×8mm diagonal braces are welded to the sidewall of the newly added steel pipe piles, and the upper ends are welded to the sidewall of the main trestle bridge steel pipe piles, forming a triangular support structure. Reinforcement Type II is applicable to sections where a branch bridge exists downstream of an existing trestle bridge, and the distance between the main trestle bridge and the branch bridge is ≤3.3m. Reinforcement Type II includes one Φ1000×10mm steel pipe pile, one Φ800×8mm horizontal brace, one Φ630×8mm horizontal brace, and two Φ630×8mm diagonal braces. One of the Φ1000×10mm steel pipe piles is installed outside the main trestle bridge steel pipe pile on the upstream side, with a center-to-center distance of 3.5m between the two piles. The lower end of one of the Φ630×8mm diagonal braces is welded... The high end of the Φ800×8mm horizontal bracing is welded to the side wall of the newly added steel pipe pile, forming a triangular support structure; the Φ630×8mm horizontal bracing is welded to the side wall of the main trestle steel pipe pile on the downstream side and the steel pipe of the nearby branch trestle; the Φ630×8mm horizontal bracing is welded to the side wall of the main trestle steel pipe pile on the downstream side and the steel pipe of the distant branch trestle; the low end of one Φ630×8mm diagonal brace is welded to the side wall of the nearby branch trestle steel pipe, and the high end is welded to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure. Reinforcement Type III is applicable to sections where a secondary trestle exists downstream of an existing trestle, and the distance between the main trestle and the secondary trestle is between 3.3m and 6.0m. Reinforcement Type III includes one Φ1000×10mm steel pipe pile, one Φ800×8mm horizontal brace, one Φ630×8mm horizontal brace, two Φ630×8mm diagonal braces, and one Φ426×6mm diagonal brace. One of the Φ1000×10mm steel pipe piles is installed on the outer side of the main trestle steel pipe pile upstream, with a center-to-center distance of 3.5m between the piles. The lower end of one of the Φ630×8mm diagonal braces is welded to the sidewall of the newly added steel pipe pile, and the upper end is welded... A triangular support structure is formed on the side wall of the main trestle steel pipe pile on the upstream side; the Φ800×8mm horizontal bracing is welded between the main trestle steel pipe pile on the downstream side and the steel pipe of the nearby branch trestle; the Φ630×8mm horizontal bracing is welded between the main trestle steel pipe pile on the downstream side and the steel pipe of the distant branch trestle; the lower end of one Φ630×8mm diagonal brace is welded to the side wall of the nearby branch trestle steel pipe, and the upper end is welded to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure; the lower end of the Φ426×6mm diagonal brace is welded to the side wall of the distant branch trestle steel pipe, and the upper end is welded to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure.

[0008] Preferably, the horizontal spacing between the main trestle bridge steel pipe piles and the branch trestle bridge steel pipe piles is not less than 1m, and the inclination angle of the diagonal bracing is adjusted according to the actual pile spacing.

[0009] A construction method for reinforcing an existing trestle bridge includes the following steps: S1. Construction preparation: Strictly control the types of equipment entering the trestle bridge, strictly prohibit overloading, limit the load of trailers and other tire equipment to 65t, formulate and implement a monitoring plan, closely monitor the scouring situation, and select the smallest model of reinforcement equipment that meets safety requirements. S2. Steel pipe pile driving: A 75t crawler crane and ZJ-90 vibratory hammer are used for construction. The newly added steel pipe piles are welded on site into 20m+20m segments. They are then hoisted and driven in two stages during the low tide period to ensure that the longitudinal axis inclination deviation of the pile body is not greater than 1% and the horizontal deviation of the pile top is not greater than 100mm. S3. Processing of horizontal and diagonal bracing: The horizontal bracing uses Φ800×8mm steel pipe, and the diagonal bracing uses Φ630×8mm steel pipe. On the same side of the horizontal bracing, two lifting lugs are made of steel plate and welded to both ends of the horizontal bracing. The material is cut 10cm shorter than the design spacing of the two steel pipes, and one end is processed into a vertical section. The diagonal bracing is cut to length according to the pipe pile spacing and the pre-installation position of the horizontal bracing. S4. The horizontal bracing and diagonal bracing are installed using a 50t crawler crane. A suspended working platform is attached to the steel pipe piles. The horizontal bracing and each steel pipe pile are welded together through a Haval joint. Each horizontal bracing is equipped with one Haval joint. The horizontal bracing is cut to a length 10cm shorter than the design spacing between the two steel pipes. One end is processed into a vertical section. The diagonal bracing and the horizontal bracing are pre-welded to form a whole before being hoisted to the steel pipe piles of the main trestle for installation. S5. Acceptance and Use: This is divided into sub-item acceptance and overall acceptance. Sub-item acceptance includes acceptance of the quality of steel pipe pile sinking, acceptance of the quality of horizontal bracing and diagonal bracing processing, and acceptance of welding quality. Overall acceptance includes verification of structural dimensions, bearing capacity test, and scour protection effect test. The acceptance standards shall comply with the "Code for Acceptance of Construction Quality of Steel Structures" (GB50205-2020), "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020), and the requirements of the design documents. The structure can only be put into use after passing the acceptance.

[0010] Preferably, the monitoring scheme in step S1 has the following specific requirements: Increase the monitoring frequency of scour of steel pipe piles in section 1 to one cycle every 7 days; Before reinforcing the trestle bridge, the mud surface scouring elevation of the steel pipe piles in the crawler crane station section was verified in advance to ensure the safety of the reinforcement operation. In response to the on-site hydrology and mud scour, the system formulated the order of cofferdam insertion and removal. Before the cofferdam insertion and removal, the mud scour elevation of the steel pipe piles in the crawler crane station section was verified in advance to ensure the safety of the cofferdam insertion and removal operation. During the removal of the cofferdam, closely monitor changes in scour. If scour intensifies, promptly report back to the site for further investigation and handling. For the newly added cofferdam area, closely monitor the scouring of the steel pipe piles of the surrounding trestle and abutment trestle, provide real-time feedback to the back site, summarize the patterns, and adopt emergency plans in advance.

[0011] Preferably, step S1 further includes the following control measures: Before the reinforcement is completed, 12m³ concrete mixer trucks can pass through the trestle bridge normally, but trucks weighing 65t or more are restricted from passing through, and crawler cranes weighing 100t or more are prohibited from passing through or operating. If passage is necessary, the counterweight must be reduced and approved by the project chief engineer and project manager. During the reinforcement period, steel pipe pile bearing capacity tests will be carried out simultaneously to verify the reliability of the reinforcement plan. Traffic control measures are in place. Construction vehicles and machinery must travel at a constant speed, not exceeding 15 km / h. Within 60 meters of the trestle, only two 12 m³ concrete mixer trucks or one freight vehicle weighing less than 65 tons are allowed to pass. Vehicles in other areas must maintain a safe distance of more than 15 meters. Load limit and speed limit signs, as well as "Safety Instructions for Use of Construction Trestle" signs, must be set up. For corrosion prevention and protection, anti-corrosion measures should be taken when storing steel pipe piles to avoid damage to the anti-corrosion coating. Damaged areas should be coated in time. The trestle should be protected against wind, rain and snow. Life rings, lighting facilities, fire-fighting equipment, navigation warning lights and various warning signs set on the trestle should not be moved or damaged at will. Electrical equipment should be protected against rain, moisture and grounding. A dedicated person should be assigned to traffic control and trestle inspection and maintenance.

[0012] Preferably, when implementing reinforcement type II scheme, in step S3, the horizontal bracing uses Φ800×8mm and Φ630×8mm steel pipes, and the diagonal bracing uses Φ630×8mm steel pipes; when implementing reinforcement type III scheme, in step S3, the horizontal bracing uses Φ800×8mm and Φ630×8mm steel pipes, and the diagonal bracing uses Φ630×8mm and Φ426×6mm steel pipes.

[0013] Preferably, the welding quality control during welding in steps S3 and S4 is as follows: the quality grade of butt welds with full penetration and partial penetration is level 2, the quality grade of fillet welds is level 3, the weld height unless otherwise specified is the thickness of the thinner component plate, rust and dirt are removed from the surface of the steel before cutting, and burrs, slag and spatter are removed after cutting.

[0014] Preferably, the specific requirements for acceptance in step S6 are as follows: The acceptance of steel pipe pile driving quality involves checking the inclination of the longitudinal axis of the pile, the horizontal deviation of the pile top, the depth of penetration into the mud, the pile length and the elevation of the pile bottom. The deviations must meet the design and specification requirements; among them, the deviation of the pile inclination is ≤1%, the horizontal deviation of the pile top is ≤100mm, and the deviation of the pile length is 0-300mm. Acceptance of the processing quality of horizontal bracing and diagonal bracing: check the specifications of steel pipes, the welding quality of lifting lugs, the cutting dimensions and the flatness of the cross section. The cutting dimension deviation of horizontal bracing should be ≤ ±5mm, and the verticality deviation of the cross section should be ≤ 2mm / m. Welding quality acceptance adopts a combination of visual inspection and non-destructive testing. There are no defects such as cracks, porosity, or slag inclusions in the appearance. The pass rate of non-destructive testing for secondary welds is ≥95%, and the visual inspection of tertiary welds is qualified. Structural dimensions were checked, including the spacing of newly added pile foundations, the installation elevation of horizontal and diagonal braces, and the dimensions of node connections. Deviations were found to be in accordance with the design drawings. The load-bearing capacity test was conducted using a 12m³ concrete mixer truck with a load capacity of 48t and a 65t freight vehicle. The structural deformation was monitored. The deformation was ≤ the span of the trestle bridge / 500. There was no residual deformation after unloading. The scour protection effect was tested, and the mud surface scour elevation was continuously monitored after acceptance. The scour depth did not increase significantly for three consecutive monitoring cycles, which met the design scour resistance requirements.

[0015] The present invention has the following beneficial effects: 1. The design scheme of this invention is highly targeted and the reinforcement system is stable and reliable. In response to the problem of ultra-deep mud scouring caused by strong tides and rapid currents, three different reinforcement types are adopted. On the upstream side, new pile foundations are added to strengthen the bearing capacity. On the downstream side, new pile foundations are added or the support trestle is used to share the load flexibly according to the distance between the main trestle and the support trestle. A triangular support structure is formed by horizontal bracing and diagonal bracing, which significantly improves the trestle's scouring resistance and overall stiffness and ensures the structural stress balance.

[0016] 2. This invention has high adaptability and is applicable to a wide range of scenarios. The three reinforcement types correspond to trestle sections with different spacing conditions. It not only solves the independent reinforcement needs of sections without trestle support or with long spacing, but also reduces material consumption and construction difficulty through trestle support and collaborative reinforcement. It is suitable for various trestle scour reinforcement scenarios in shallow water areas and has strong practicality.

[0017] 3. The construction process of this invention is scientific and efficient, with strong quality control. It optimizes the process of segmented sinking of steel pipe piles, horizontal connection and diagonal bracing, factory processing and overall on-site installation. It utilizes the low tide period to reduce the impact of tides. Through the welding connection of Haver joints and clear weld quality standards, it ensures construction accuracy and connection reliability, and greatly improves construction efficiency and project quality.

[0018] 4. This invention provides comprehensive construction safety management and effective risk control. Throughout the construction process, control measures such as equipment load limits, scour monitoring, and traffic control are implemented. Combined with a targeted acceptance process, a full-cycle safety guarantee is formed from construction preparation to commissioning. This effectively reduces the safety risks caused by overloading, increased scour, and construction operations, ensuring the long-term safe and stable operation of the trestle bridge. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of reinforcement type I proposed in this invention; Figure 2 This is a plan view of the pile foundation layout for reinforcement type I proposed in this invention; Figure 3 This is a plan view of the horizontal bracing arrangement of reinforcement type I proposed in this invention; Figure 4 This is a schematic diagram of the cross-sectional structure of reinforcement type II proposed in this invention; Figure 5 This is a plan view of the pile foundation layout for reinforcement type II proposed in this invention; Figure 6 This is a plan view of the horizontal bracing arrangement of reinforcement type II proposed in this invention; Figure 7 This is a schematic diagram of the longitudinal section structure of reinforcement type II proposed in this invention; Figure 8 This is a schematic diagram of the cross-sectional structure of reinforcement type III proposed in this invention; Figure 9 This is a plan view of the pile foundation for reinforcement type III proposed in this invention; Figure 10 This is a plan view of the horizontal bracing arrangement of reinforcement type III proposed in this invention; Figure 11 This is a schematic diagram of the longitudinal section structure of reinforcement type III proposed in this invention. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] An existing trestle reinforcement structure includes the existing trestle and reinforcement components, wherein the reinforcement components adopt any of the following reinforcement types: Reinforcement Type I is applicable to sections of existing trestle bridges where there are no supporting trestle bridges upstream or downstream, or where the distance between the supporting trestle bridge and the main trestle bridge is greater than 6 meters. Reinforcement Type I includes two Φ1000×10mm steel pipe piles and two Φ630×8mm diagonal braces. (Refer to...) Figure 1-3 One Φ1000×10mm steel pipe pile is installed on the outer side of the main trestle bridge steel pipe pile on the upstream side, with a center-to-center distance of 3.5m between the two piles. Another Φ1000×10mm steel pipe pile is installed on the outer side of the main trestle bridge steel pipe pile on the downstream side, with a center-to-center distance of 2.5m between the two piles. The lower ends of two Φ630×8mm diagonal braces are welded to the side wall of the newly added steel pipe pile, and the upper ends are welded to the side wall of the main trestle bridge steel pipe pile, forming a triangular support structure.

[0022] Reinforcement Type II is applicable to sections where a secondary trestle bridge exists downstream of the existing trestle bridge, and the distance between the main trestle bridge and the secondary trestle bridge is ≤3.3m. Reinforcement Type II includes one Φ1000×10mm steel pipe pile, one Φ800×8mm horizontal brace, one Φ630×8mm horizontal brace, and two Φ630×8mm diagonal braces. (Refer to...) Figure 4-7 A Φ1000×10mm steel pipe pile is installed on the outside of the main trestle steel pipe pile on the upstream side, with a center-to-center distance of 3.5m between the two piles. A Φ630×8mm diagonal brace is welded at its low end to the side wall of the newly added steel pipe pile and at its high end to the side wall of the main trestle steel pipe pile on the upstream side, forming a triangular support structure. A Φ800×8mm horizontal brace is welded between the main trestle steel pipe pile on the downstream side and the nearby branch trestle steel pipe, and a Φ630×8mm horizontal brace is welded between the main trestle steel pipe pile on the downstream side and the distant branch trestle steel pipe. A Φ630×8mm diagonal brace is welded at its low end to the side wall of the nearby branch trestle steel pipe and at its high end to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure. Reinforcement Type III is applicable to sections where a secondary trestle bridge exists downstream of the existing trestle bridge, and the distance between the main trestle bridge and the secondary trestle bridge is between 3.3m and 6.0m. Reinforcement Type III includes one Φ1000×10mm steel pipe pile, one Φ800×8mm horizontal brace, one Φ630×8mm horizontal brace, two Φ630×8mm diagonal braces, and one Φ426×6mm diagonal brace. (Refer to...) Figure 8-11 A Φ1000×10mm steel pipe pile is installed on the outer side of the upstream main trestle bridge steel pipe pile, with a center-to-center distance of 3.5m between the two piles. A Φ630×8mm diagonal brace is welded at its low end to the side wall of the newly added steel pipe pile and at its high end to the side wall of the upstream main trestle bridge steel pipe pile, forming a triangular support structure. A Φ800×8mm horizontal brace is welded between the downstream main trestle bridge steel pipe pile and the nearby branch trestle bridge steel pipe, and a Φ630×8mm horizontal brace is welded between the downstream main trestle bridge steel pipe pile and the distant branch trestle bridge steel pipe. A Φ630×8mm diagonal brace is welded at its low end to the side wall of the nearby branch trestle bridge steel pipe and at its high end to the side wall of the downstream main trestle bridge steel pipe pile, forming a triangular support structure. A Φ426×6mm diagonal brace is welded at its low end to the side wall of the distant branch trestle bridge steel pipe and at its high end to the side wall of the downstream main trestle bridge steel pipe pile, forming a triangular support structure.

[0023] A construction method for reinforcing an existing trestle bridge includes the following steps: S1. Construction preparation: Strictly control the types of equipment entering the trestle bridge, strictly prohibit overloading, limit the load of trailers and other tire equipment to 65t, formulate and implement a monitoring plan, closely monitor the scouring situation, and select the smallest model of reinforcement equipment that meets safety requirements. The specific requirements of the monitoring plan are as follows: Increase the monitoring frequency of scour of steel pipe piles in section 1 to one cycle every 7 days; Before reinforcing the trestle bridge, the mud surface scouring elevation of the steel pipe piles in the crawler crane station section was verified in advance to ensure the safety of the reinforcement operation. In response to the on-site hydrology and mud scour, the system formulated the order of cofferdam insertion and removal. Before the cofferdam insertion and removal, the mud scour elevation of the steel pipe piles in the crawler crane station section was verified in advance to ensure the safety of the cofferdam insertion and removal operation. During the removal of the cofferdam, closely monitor changes in scour. If scour intensifies, promptly report back to the site for further investigation and handling. For the newly added cofferdam area, closely monitor the scouring of the steel pipe piles of the surrounding trestle and abutment trestle, provide real-time feedback to the back site, summarize the patterns, and adopt emergency plans in advance.

[0024] It also includes the following control measures: Before the reinforcement is completed, 12m³ concrete mixer trucks can pass through the trestle bridge normally, but trucks weighing 65t or more are restricted from passing through, and crawler cranes weighing 100t or more are prohibited from passing through or operating. If passage is necessary, the counterweight must be reduced and approved by the project chief engineer and project manager. During the reinforcement period, steel pipe pile bearing capacity tests will be carried out simultaneously to verify the reliability of the reinforcement plan. Traffic control measures are in place. Construction vehicles and machinery must travel at a constant speed, not exceeding 15 km / h. Within 60 meters of the trestle, only two 12 m³ concrete mixer trucks or one freight vehicle weighing less than 65 tons are allowed to pass. Vehicles in other areas must maintain a safe distance of more than 15 meters. Load limit and speed limit signs, as well as "Safety Instructions for Use of Construction Trestle" signs, must be set up. For corrosion prevention and protection, anti-corrosion measures should be taken when storing steel pipe piles to avoid damage to the anti-corrosion coating. Damaged areas should be coated in time. The trestle should be protected against wind, rain and snow. Life rings, lighting facilities, fire-fighting equipment, navigation warning lights and various warning signs set on the trestle should not be moved or damaged at will. Electrical equipment should be protected against rain, moisture and grounding. A dedicated person should be assigned to traffic control and trestle inspection and maintenance.

[0025] S2. Steel pipe pile driving: A 75t crawler crane and ZJ-90 vibratory hammer are used for construction. The newly added steel pipe piles are welded on site into 20m+20m segments. They are then hoisted and driven in two stages during the low tide period to ensure that the longitudinal axis inclination deviation of the pile body is not greater than 1% and the horizontal deviation of the pile top is not greater than 100mm. S3. Fabrication of horizontal and diagonal bracing: Horizontal bracing uses Φ800×8mm steel pipe, and diagonal bracing uses Φ630×8mm steel pipe. Two lifting lugs are made from steel plates on the same side of the horizontal bracing and welded to both ends of the horizontal bracing. The material is cut 10cm shorter than the design spacing between the two steel pipes, and one end is processed into a vertical section. The diagonal bracing is cut to size according to the spacing of the pipe piles and the pre-installation position of the horizontal bracing. When implementing reinforcement type II scheme, horizontal bracing uses Φ800×8mm and Φ630×8mm steel pipe, and diagonal bracing uses Φ630×8mm steel pipe. When implementing reinforcement type III scheme, horizontal bracing uses Φ800×8mm and Φ630×8mm steel pipe, and diagonal bracing uses Φ630×8mm and Φ426×6mm steel pipe.

[0026] S4. The horizontal bracing and diagonal bracing are installed using a 50t crawler crane. A suspended working platform is attached to the steel pipe piles. The horizontal bracing and each steel pipe pile are welded together using a Halfer joint. Each horizontal bracing is equipped with one Halfer joint. The horizontal bracing is cut to a length 10cm shorter than the designed spacing between the two steel pipes. One end is machined into a vertical section. The contact parts of the diagonal bracing and the horizontal bracing are pre-welded to form a whole before being hoisted to the steel pipe piles of the main trestle for installation. The welding quality control is as follows: the quality grade of the butt welds with full penetration and partial penetration is grade II, and the quality grade of the fillet welds is grade III. The weld heights not specified are the thickness of the thinner components. Before cutting, rust and dirt are removed from the surface of the steel. After cutting, burrs, slag and spatter are removed.

[0027] S5. Acceptance and Use: This is divided into sub-item acceptance and overall acceptance. Sub-item acceptance includes acceptance of the quality of steel pipe pile sinking, acceptance of the quality of horizontal bracing and diagonal bracing processing, and acceptance of welding quality. Overall acceptance includes verification of structural dimensions, bearing capacity test, and scour protection effect test. The acceptance standards shall comply with the "Code for Acceptance of Construction Quality of Steel Structures" (GB50205-2020), "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020), and the requirements of the design documents. The structure can only be put into use after passing the acceptance.

[0028] The specific requirements for acceptance are as follows: The acceptance of steel pipe pile driving quality involves checking the inclination of the longitudinal axis of the pile, the horizontal deviation of the pile top, the depth of penetration into the mud, the pile length and the elevation of the pile bottom. The deviations must meet the design and specification requirements; among them, the deviation of the pile inclination is ≤1%, the horizontal deviation of the pile top is ≤100mm, and the deviation of the pile length is 0-300mm. Acceptance of the processing quality of horizontal bracing and diagonal bracing: check the specifications of steel pipes, the welding quality of lifting lugs, the cutting dimensions and the flatness of the cross section. The cutting dimension deviation of horizontal bracing should be ≤ ±5mm, and the verticality deviation of the cross section should be ≤ 2mm / m. Welding quality acceptance adopts a combination of visual inspection and non-destructive testing. There are no defects such as cracks, porosity, or slag inclusions in the appearance. The pass rate of non-destructive testing for secondary welds is ≥95%, and the visual inspection of tertiary welds is qualified. Structural dimensions were checked, including the spacing of newly added pile foundations, the installation elevation of horizontal and diagonal braces, and the dimensions of node connections. Deviations were found to be in accordance with the design drawings. The load-bearing capacity test was conducted using a 12m³ concrete mixer truck with a load capacity of 48t and a 65t freight vehicle. The structural deformation was monitored. The deformation was ≤ the span of the trestle bridge / 500. There was no residual deformation after unloading. The scour protection effect was tested, and the mud surface scour elevation was continuously monitored after acceptance. The scour depth did not increase significantly for three consecutive monitoring cycles, which met the design scour resistance requirements. Example 1

[0029] Reinforcement project of existing trestle bridge using reinforcement type I Project Overview The original trestle bridge, a supporting structure for a bridge project in a shallow water area, had a top elevation of 7.5m and a deck width of 10.5m. Its surface layer consisted of 10mm thick checkered steel plates and 12×25cm I-beams; the transverse distribution beams used 22×75cm I-beams; the substructure was composed of Φ1000×10mm steel pipe piles, with horizontal bracing using Φ426×6mm and Φ630×8mm steel pipes, and diagonal bracing using Φ325×6mm steel pipes. The area where the original trestle bridge was located experienced significant strong tidal currents, with measured mudslide erosion reaching -12.000m, exceeding the design erosion depth, necessitating reinforcement. Since there were no supporting trestle bridges on the upstream and downstream sides of this section, reinforcement type I was adopted.

[0030] reinforcement design On the upstream side, a new Φ1000×10mm steel pipe pile will be added outside the existing main trestle bridge steel pipe piles, with a center-to-center distance of 3.5m between the two piles. On the downstream side, a new Φ1000×10mm steel pipe pile will be added outside the existing main trestle bridge steel pipe piles, with a center-to-center distance of 2.5m between the two piles. The top elevation of the new steel pipe piles is tentatively set at +5.000m, the depth into the mud is 20m, the bottom elevation is -35.000m, and the pile length is 40m.

[0031] The main trestle bridge steel pipe piles on both the upstream and downstream sides are welded to the newly added steel pipe piles via Φ800×8mm horizontal bracing and Φ630×8mm diagonal bracing. The Φ800×8mm horizontal bracing is arranged horizontally, and the lower end of the Φ630×8mm diagonal bracing is welded to the side wall of the newly added steel pipe pile, while the upper end is welded to the side wall of the main trestle bridge steel pipe pile, forming a triangular support structure. The horizontal bracing is spaced at 3500mm and 6000mm intervals, and the angle between the diagonal bracing and the horizontal bracing is 50°.

[0032] Construction process 1. Construction preparation: Strictly control the equipment entering the trestle bridge. Trailers and other tire equipment are limited to a load of 65t or less. Develop a monitoring plan and adjust the monitoring frequency of the steel pipe pile scour in section 1 to one cycle every 7 days. Before reinforcement, verify the mud scour elevation of the steel pipe pile in the section where the crawler crane is located. Select the smallest model of equipment that meets the safety requirements, such as 75t crawler crane or 50t crawler crane.

[0033] 2. Steel pipe pile driving: A 75t crawler crane and a DZJ-90 vibratory hammer were used to weld the newly added steel pipe piles into 20m+20m sections on site. These sections were then lowered in two stages during the low tide period. Initially, a low excitation force was used. Once the pile body, guide frame, and vibratory hammer were aligned, normal driving was resumed. When the pile entered the hard soil layer, a high excitation force was used. This high excitation force was maintained until the pile reached the designed top elevation. Ultimately, the longitudinal axis inclination deviation of the pile was 0.8%, and the horizontal deviation of the pile top was 80mm, meeting the requirements.

[0034] 3. Processing of horizontal and diagonal bracing: The horizontal bracing uses Φ800×8mm steel pipe, with two steel plate lifting lugs welded on the same side. The material is cut 10cm shorter than the design spacing of the two steel pipes, and one end is processed into a vertical section. The diagonal bracing uses Φ630×8mm steel pipe, and the material is cut to length according to the spacing of the pipe piles and the pre-installation position of the horizontal bracing.

[0035] 4. Installation of horizontal bracing and diagonal bracing: A 50t crawler crane is used for hoisting. A suspended working platform is attached to the steel pipe pile. The horizontal bracing is welded to each steel pipe pile through a Haval joint. Each horizontal bracing is equipped with one Haval joint. The contact parts between the diagonal bracing and the horizontal bracing are pre-welded to form a whole before being hoisted to the installation position.

[0036] 5. Acceptance and Use: During the sub-item acceptance, the quality of steel pipe pile sinking, the processing quality of horizontal bracing and diagonal bracing, and the welding quality all met the standards; during the overall acceptance, the structural dimensions were verified as qualified, and load tests were conducted using a 12m³ 48t concrete mixer truck and a 65t freight vehicle. The structural deformation was ≤ the span of the trestle bridge / 500, there was no residual deformation after unloading, and the scour depth did not increase significantly for three consecutive monitoring cycles. After passing the acceptance, it was put into use.

[0037] After the reinforcement was completed, the key indicator data of the reinforcement process were statistically analyzed. The specific results are shown in the table below: Table 1: Key Indicator Recording Table for Example 1

[0038] This embodiment employs a symmetrical double-steel pipe pile reinforcement type I. Although the construction cost is relatively high (850,000 yuan per span) and the construction period is long (28 days), the reinforcement effect is significant. During the load test, the structure remained stable under the stress of a 65t vehicle, with a maximum deformation of only 51.7mm and no residual deformation. The mud scour depth increase was controlled within 0.05m over three monitoring periods, indicating stable scour. This type is suitable for sections with unsupported trestle bridges or trestle bridge spacing >6m. The symmetrical triangular support structure significantly improves the trestle bridge's resistance to lateral displacement and overall stability, effectively resisting the scour effects of strong tides and rapid currents, ensuring the long-term safe operation of the trestle bridge. Example 2

[0039] Reinforcement project of existing trestle bridge using reinforcement type II Project Overview The main trestle of a near-shore bridge project has a top elevation of 8.0m and a deck width of 10.5m, with structural parameters consistent with Example 1. A secondary trestle exists downstream of the main trestle, with a distance of 3.0m between the main trestle and the secondary trestle, less than 3.3m. Due to strong tidal currents, the mudslide depth reaches -10.500m, exceeding the design value, requiring reinforcement. Reinforcement type II is adopted.

[0040] reinforcement design The upstream reinforcement method is the same as in Example 1, namely, adding Φ1000×10mm steel pipe piles 3.5m outside the existing main trestle bridge steel pipe piles. These are connected by Φ800×8mm horizontal bracing and Φ630×8mm diagonal bracing to form a triangular support structure. The top elevation of the new steel pipe piles is +5m, the depth into the mud is 20m, and the pile length is 40m. No new steel pipe piles are added on the downstream side. Φ800×8mm horizontal bracing is horizontally welded between the main trestle bridge steel pipe piles and the nearby branch trestle bridge steel pipe piles. Φ630×8mm horizontal bracing is horizontally welded between the main trestle bridge steel pipe piles and the distant branch trestle bridge steel pipe piles. The lower end of the Φ630×8mm diagonal bracing is welded to the side wall of the nearby branch trestle bridge steel pipe pile, and the upper end is welded to the side wall of the main trestle bridge steel pipe pile, forming a triangular support structure. A 10mm thick stiffening plate is installed at the connection node between the diagonal bracing and the branch trestle bridge steel pipe piles, and the spacing between adjacent horizontal bracing is 6000mm.

[0041] Construction process Construction preparation: Similar to Example 1, additionally verify the actual distance between the main trestle bridge and the branch trestle bridge and the integrity of the steel pipe piles of the branch trestle bridge to ensure that the branch trestle bridge has the conditions for coordinated stress.

[0042] Steel pipe pile driving: Only new steel pipe piles were added on the upstream side. The driving process was the same as in Example 1. The longitudinal axis inclination of the pile body was 0.7%, and the horizontal deviation of the pile top was 75mm, which met the requirements.

[0043] Processing of horizontal bracing and diagonal bracing: The horizontal bracing includes two specifications: Φ800×8mm and Φ630×8mm. The diagonal bracing is Φ630×8mm steel pipe. The processing requirements are the same as in Example 1. At the same time, a 10mm thick stiffening plate is also processed.

[0044] Installation of horizontal bracing and diagonal bracing: The installation process on the upstream side is the same as in Example 1; on the downstream side, first weld the stiffening plate to the connection position of the steel pipe pile of the trestle bridge, then hoist the horizontal bracing and diagonal bracing, and weld and fix them to the steel pipe pile of the main trestle bridge and the steel pipe pile of the trestle bridge through the Haval joint to ensure a firm connection.

[0045] Acceptance and Use: During the sub-item acceptance, the welding quality was inspected by appearance and non-destructive testing, and the pass rate of non-destructive testing of the secondary weld was 96%; during the overall acceptance, the structural deformation met the requirements, the scour protection effect met the standards, and it was put into use after passing the acceptance.

[0046] After the reinforcement was completed, the key indicator data of the reinforcement process were statistically analyzed. The specific results are shown in the table below: Table 2: Key Indicator Recording Table for Example 2

[0047] This embodiment employs reinforcement type II, utilizing the existing trestle bridge for collaborative stress distribution, demonstrating significant economic efficiency and effectiveness. The construction cost per span is only 580,000 yuan, a 31.8% reduction compared to type 1, and the construction period is shortened to 20 days. This is attributed to the elimination of the need for additional steel pipe piles on the downstream side, reducing the amount of construction work. During the load test, the main trestle bridge and the trestle bridge exhibited good collaborative stress distribution with no localized stress concentration issues, and the maximum deformation was 48.4 mm, superior to reinforcement type I.

[0048] The scour depth increase over three monitoring cycles did not exceed 0.04m, demonstrating excellent scour control. This type of system is suitable for sections where the downstream trestle bridge spacing is relatively close (≤3.3m). While ensuring reinforcement quality and structural safety, it effectively reduces engineering costs and shortens the construction period, demonstrating high engineering application value. Example 3

[0049] Reinforcement project of existing trestle bridge using reinforcement type III Project Overview The main trestle bridge of a cross-river bridge project has a top elevation of +7.2m and a bridge deck width of 10.5m, with structural parameters consistent with Example 1. Downstream of this trestle bridge is a branch trestle bridge. The distance between the main trestle bridge and the branch trestle bridge is 4.5m, ranging from 3.3m to 6m. Due to the strong tidal current, the mud surface erosion depth reaches -13.000m, requiring reinforcement. Reinforcement type III is adopted.

[0050] reinforcement design The upstream reinforcement scheme is the same as in Examples 1 and 2, adding Φ1000×10mm steel pipe piles. These are connected to the main trestle bridge steel pipe piles via Φ800×8mm horizontal bracing and Φ630×8mm diagonal bracing, forming a triangular support structure. The new steel pipe piles are driven into the mud to a depth of 22m, with a top elevation of +5m, a bottom elevation of -37m, and a length of 42m. No new steel pipe piles are added to the downstream side. Φ800×8mm horizontal bracing is horizontally welded between the main trestle bridge steel pipe piles and the near-side abutment bridge steel pipe piles. The Φ630×8mm diagonal bracing is welded at its lower end to the side wall of the near-side abutment bridge steel pipe pile and at its upper end to the side wall of the main trestle bridge steel pipe pile. Similarly, the Φ426×6mm diagonal bracing is welded at its lower end to the side wall of the far-side abutment bridge steel pipe pile and at its upper end to the side wall of the main trestle bridge steel pipe pile, all forming a triangular support structure. The horizontal bracing between the main trestle and the branch trestle is spaced 1.2m apart. The inclination angle of the diagonal bracing is adjusted to 55° according to the actual pile spacing. In some sections, Φ426×6mm reinforced horizontal bracing is added at a spacing of 15000mm.

[0051] Construction process Construction preparation: In addition to routine preparations, the focus is on measuring the actual pile spacing between the main trestle bridge and the branch trestle bridge, determining the inclination angle of the diagonal bracing and the location of the reinforced horizontal bracing, and developing a specific installation plan.

[0052] Steel pipe pile driving: The driving process of the newly added steel pipe piles on the upstream side is the same as that of the previous two examples. The driving depth is 22m, the longitudinal axis inclination deviation of the pile body is 0.9%, and the horizontal deviation of the pile top is 90mm, which meets the standards.

[0053] Processing of horizontal bracing and diagonal bracing: Horizontal bracing includes three specifications: Φ800×8mm, Φ630×8mm and Φ426×6mm. Diagonal bracing is made of Φ630×8mm and Φ426×6mm steel pipes. The material is cut to length according to the actual measured size, and the processing accuracy is controlled within the required range.

[0054] Installation of horizontal bracing and diagonal bracing: First, install the downstream side Φ800×8mm horizontal bracing, then hoist the Φ630×8mm and Φ426×6mm diagonal bracing respectively, and weld and fix them to the horizontal bracing, the main trestle bridge steel pipe piles, and the branch trestle bridge steel pipe piles. Finally, install the Φ426×6mm reinforced horizontal bracing to ensure the overall structural rigidity.

[0055] Acceptance and Use: During the sub-item acceptance, the dimensional deviation of the horizontal bracing and diagonal bracing is ≤ ±5mm, and the verticality deviation of the cross section is ≤ 2mm / m; during the overall acceptance, the load-bearing capacity test and the scour protection effect test are both qualified, and the product is put into use after passing the acceptance.

[0056] After the reinforcement was completed, the key indicator data of the reinforcement process were statistically analyzed. The specific results are shown in the table below: Table 3: Key Indicator Recording Table for Example 3

[0057] This embodiment employs reinforcement type III, featuring double diagonal bracing and reinforced horizontal bracing, which offers the best overall performance. The construction cost per span is 660,000 yuan, with a construction period of 24 days, placing it in the middle of the three types. It avoids the high cost and long construction period of type 1 while incorporating reinforced horizontal bracing and double diagonal bracing. During load tests, the structure exhibited the best stability, with a maximum deformation of only 46.2 mm, the smallest among the three. The combination of double diagonal bracing and reinforced horizontal bracing significantly improved structural stiffness and deformation resistance. Even in areas with the deepest initial mudslide depth, the increase in scour depth was controlled within 0.07 m over three monitoring periods, demonstrating significant scour resistance. This type is suitable for sections where the distance between the main trestle and the auxiliary trestle is between 3.3 m and 6.0 m, balancing economy, construction efficiency, and reinforcement quality. It is particularly suitable for reinforcing trestle bridges in areas with strong tidal currents where high structural stiffness is required.

[0058] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A reinforcement structure for an existing trestle bridge, comprising the existing trestle bridge and reinforcement components, characterized in that, The reinforcement component adopts any of the following reinforcement types: Reinforcement Type I is applicable to sections where there are no supporting trestle bridges upstream and downstream of existing trestle bridges, or where the distance between the supporting trestle bridge and the main trestle bridge is greater than 6m. Reinforcement Type I includes two Φ1000×10mm steel pipe piles and two Φ630×8mm diagonal braces. One of the Φ1000×10mm steel pipe piles is installed on the outer side of the upstream main trestle bridge steel pipe pile, with a center-to-center distance of 3.5m between the two piles. The other Φ1000×10mm steel pipe pile is installed on the outer side of the downstream main trestle bridge steel pipe pile, with a center-to-center distance of 2.5m between the two piles. The lower ends of the two Φ630×8mm diagonal braces are welded to the sidewall of the newly added steel pipe piles, and the upper ends are welded to the sidewall of the main trestle bridge steel pipe piles, forming a triangular support structure. Reinforcement Type II is applicable to sections where a branch bridge exists downstream of an existing trestle bridge, and the distance between the main trestle bridge and the branch bridge is ≤3.3m. Reinforcement Type II includes one Φ1000×10mm steel pipe pile, one Φ800×8mm horizontal brace, one Φ630×8mm horizontal brace, and two Φ630×8mm diagonal braces. One of the Φ1000×10mm steel pipe piles is installed outside the main trestle bridge steel pipe pile on the upstream side, with a center-to-center distance of 3.5m between the two piles. The lower end of one of the Φ630×8mm diagonal braces is welded... The high end of the Φ800×8mm horizontal bracing is welded to the side wall of the newly added steel pipe pile, forming a triangular support structure; the Φ630×8mm horizontal bracing is welded to the side wall of the main trestle steel pipe pile on the downstream side and the steel pipe of the nearby branch trestle; the Φ630×8mm horizontal bracing is welded to the side wall of the main trestle steel pipe pile on the downstream side and the steel pipe of the distant branch trestle; the low end of one Φ630×8mm diagonal brace is welded to the side wall of the nearby branch trestle steel pipe, and the high end is welded to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure. Reinforcement Type III is applicable to sections where a secondary trestle exists downstream of an existing trestle, and the distance between the main trestle and the secondary trestle is between 3.3m and 6.0m. Reinforcement Type III includes one Φ1000×10mm steel pipe pile, one Φ800×8mm horizontal brace, one Φ630×8mm horizontal brace, two Φ630×8mm diagonal braces, and one Φ426×6mm diagonal brace. One of the Φ1000×10mm steel pipe piles is installed on the outer side of the main trestle steel pipe pile upstream, with a center-to-center distance of 3.5m between the piles. The lower end of one of the Φ630×8mm diagonal braces is welded to the sidewall of the newly added steel pipe pile, and the upper end is welded... A triangular support structure is formed on the side wall of the main trestle steel pipe pile on the upstream side; the Φ800×8mm horizontal bracing is welded between the main trestle steel pipe pile on the downstream side and the steel pipe of the nearby branch trestle; the Φ630×8mm horizontal bracing is welded between the main trestle steel pipe pile on the downstream side and the steel pipe of the distant branch trestle; the lower end of one Φ630×8mm diagonal brace is welded to the side wall of the nearby branch trestle steel pipe, and the upper end is welded to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure; the lower end of the Φ426×6mm diagonal brace is welded to the side wall of the distant branch trestle steel pipe, and the upper end is welded to the side wall of the main trestle steel pipe pile on the downstream side, forming a triangular support structure.

2. The existing trestle bridge reinforcement structure according to claim 1, characterized in that: The horizontal spacing between the main trestle bridge steel pipe piles and the branch trestle bridge steel pipe piles shall not be less than 1m, and the inclination angle of the diagonal bracing shall be adjusted according to the actual pile spacing.

3. A construction method for reinforcing an existing trestle bridge as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Construction preparation: Strictly control the types of equipment entering the trestle bridge, strictly prohibit overloading, limit the load of trailers and other tire equipment to 65t, formulate and implement a monitoring plan, closely monitor the scouring situation, and select the smallest model of reinforcement equipment that meets safety requirements. S2. Steel pipe pile driving: A 75t crawler crane and ZJ-90 vibratory hammer are used for construction. The newly added steel pipe piles are welded on site into 20m+20m segments. They are then hoisted and driven in two stages during the low tide period to ensure that the longitudinal axis inclination deviation of the pile body is not greater than 1% and the horizontal deviation of the pile top is not greater than 100mm. S3. Processing of horizontal and diagonal bracing: The horizontal bracing uses Φ800×8mm steel pipe, and the diagonal bracing uses Φ630×8mm steel pipe. On the same side of the horizontal bracing, two lifting lugs are made of steel plate and welded to both ends of the horizontal bracing. The material is cut 10cm shorter than the design spacing of the two steel pipes, and one end is processed into a vertical section. The diagonal bracing is cut to length according to the pipe pile spacing and the pre-installation position of the horizontal bracing. S4. The horizontal bracing and diagonal bracing are installed using a 50t crawler crane. A suspended working platform is attached to the steel pipe piles. The horizontal bracing and each steel pipe pile are welded together through a Haval joint. Each horizontal bracing is equipped with one Haval joint. The horizontal bracing is cut to a length 10cm shorter than the design spacing between the two steel pipes. One end is processed into a vertical section. The diagonal bracing and the horizontal bracing are pre-welded to form a whole before being hoisted to the steel pipe piles of the main trestle for installation. S5. Acceptance and Use: This is divided into sub-item acceptance and overall acceptance. Sub-item acceptance includes acceptance of the quality of steel pipe pile sinking, acceptance of the quality of horizontal bracing and diagonal bracing processing, and acceptance of welding quality. Overall acceptance includes verification of structural dimensions, bearing capacity test, and scour protection effect test. The acceptance standards shall comply with the "Code for Acceptance of Construction Quality of Steel Structures" (GB50205-2020), "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020), and the requirements of the design documents. The structure can only be put into use after passing the acceptance.

4. The construction method for reinforcing an existing trestle bridge according to claim 3, characterized in that: The specific requirements for the monitoring scheme in step S1 are as follows: Increase the monitoring frequency of scour of steel pipe piles in section 1 to one cycle every 7 days; Before reinforcing the trestle bridge, the mud surface scouring elevation of the steel pipe piles in the crawler crane station section was verified in advance to ensure the safety of the reinforcement operation. In response to the on-site hydrology and mud scour, the system formulated the order of cofferdam insertion and removal. Before the cofferdam insertion and removal, the mud scour elevation of the steel pipe piles in the crawler crane station section was verified in advance to ensure the safety of the cofferdam insertion and removal operation. During the removal of the cofferdam, closely monitor changes in scour. If scour intensifies, promptly report back to the site for further investigation and handling. For the newly added cofferdam area, closely monitor the scouring of the steel pipe piles of the surrounding trestle and abutment trestle, provide real-time feedback to the back site, summarize the patterns, and adopt emergency plans in advance.

5. The construction method for reinforcing an existing trestle bridge according to claim 3, characterized in that: Step S1 also includes the following control measures: Before the reinforcement is completed, 12m³ concrete mixer trucks can pass through the trestle bridge normally, but trucks weighing 65t or more are restricted from passing through, and crawler cranes weighing 100t or more are prohibited from passing through or operating. If passage is necessary, the counterweight must be reduced and approved by the project chief engineer and project manager. During the reinforcement period, steel pipe pile bearing capacity tests will be carried out simultaneously to verify the reliability of the reinforcement plan. Traffic control measures are in place. Construction vehicles and machinery must travel at a constant speed, not exceeding 15 km / h. Within 60 meters of the trestle, only two 12 m³ concrete mixer trucks or one freight vehicle weighing less than 65 tons are allowed to pass. Vehicles in other areas must maintain a safe distance of more than 15 meters. Load limit and speed limit signs, as well as "Safety Instructions for Use of Construction Trestle" signs, must be set up. For corrosion prevention and protection, anti-corrosion measures should be taken when storing steel pipe piles to avoid damage to the anti-corrosion coating. Damaged areas should be coated in time. The trestle should be protected against wind, rain and snow. Life rings, lighting facilities, fire-fighting equipment, navigation warning lights and various warning signs set on the trestle should not be moved or damaged at will. Electrical equipment should be protected against rain, moisture and grounding. A dedicated person should be assigned to traffic control and trestle inspection and maintenance.

6. The construction method for reinforcing an existing trestle bridge according to claim 3, characterized in that: When implementing reinforcement type II scheme, in step S3, the horizontal bracing uses Φ800×8mm and Φ630×8mm steel pipes, and the diagonal bracing uses Φ630×8mm steel pipes; when implementing reinforcement type III scheme, in step S3, the horizontal bracing uses Φ800×8mm and Φ630×8mm steel pipes, and the diagonal bracing uses Φ630×8mm and Φ426×6mm steel pipes.

7. The construction method for reinforcing an existing trestle bridge according to claim 3, characterized in that: The welding quality control during steps S3 and S4 is as follows: the quality grade of butt welds with full penetration and partial penetration is level 2, the quality grade of fillet welds is level 3, and the weld height without specification is the thickness of thinner component plates. Before cutting, remove rust and dirt from the surface of the steel, and after cutting, remove burrs, slag and spatter.

8. The construction method for reinforcing an existing trestle bridge according to claim 3, characterized in that: The specific requirements for acceptance in step S6 are as follows: The acceptance of steel pipe pile driving quality involves checking the inclination of the longitudinal axis of the pile, the horizontal deviation of the pile top, the depth of penetration into the mud, the pile length and the elevation of the pile bottom. The deviations must meet the design and specification requirements; among them, the deviation of the pile inclination is ≤1%, the horizontal deviation of the pile top is ≤100mm, and the deviation of the pile length is 0-300mm. Acceptance of the processing quality of horizontal bracing and diagonal bracing: check the specifications of steel pipes, the welding quality of lifting lugs, the cutting dimensions and the flatness of the cross section. The cutting dimension deviation of horizontal bracing should be ≤ ±5mm, and the verticality deviation of the cross section should be ≤ 2mm / m. Welding quality acceptance adopts a combination of visual inspection and non-destructive testing. There are no defects such as cracks, porosity, or slag inclusions in the appearance. The pass rate of non-destructive testing for secondary welds is ≥95%, and the visual inspection of tertiary welds is qualified. Structural dimensions were checked, including the spacing of newly added pile foundations, the installation elevation of horizontal and diagonal braces, and the dimensions of node connections. Deviations were found to be in accordance with the design drawings. The load-bearing capacity test was conducted using a 12m³ concrete mixer truck with a load capacity of 48t and a 65t freight vehicle. The structural deformation was monitored. The deformation was ≤ the span of the trestle bridge / 500. There was no residual deformation after unloading. The scour protection effect was tested, and the mud surface scour elevation was continuously monitored after acceptance. The scour depth did not increase significantly for three consecutive monitoring cycles, which met the design scour resistance requirements.

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