A method for installing a bridge pier anti-collision device

Abstract

This invention discloses a method for installing anti-collision facilities on bridge piers. Addressing the problems of existing technologies relying on large floating cranes, high-altitude assembly risks, and conflicts with main tower construction, this method divides the annular anti-collision steel casing into multiple arc-shaped segments along the circumference. Each segment is then vertically divided into multiple blocks, making the weight of each block suitable for on-site lifting equipment. After installing a lowering support and continuous lowering device on the top of the pier cap, the bottom blocks are first assembled into a ring and connected to the lifting points, then lowered by one block height. The lifting points are then temporarily fixed and changed, and the upper blocks are assembled to form a new ring. This cycle of lowering, changing, and assembling is repeated until all blocks are assembled, and finally, the entire structure is lowered to the design elevation. This method confines all assembly work to the low position of the pier cap, eliminates the need for large floating cranes, reduces the risks of high-altitude operations, achieves safe cross-construction with the main tower, and offers low construction costs and controllable construction period.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and in particular to a method for installing anti-collision facilities for bridge piers. Background Technology

[0002] As crucial structures in waterways, the piers of cross-sea and cross-river bridges typically require collision protection devices to withstand the impact forces of ships. Large pier collision protection devices are mostly integral steel cofferdam structures, with diameters reaching tens of meters and total weights exceeding a thousand tons. Installation is a critical and challenging aspect of bridge construction, characterized by high risk and difficulty. Given the complex hydrological and meteorological conditions at the bridge site and the confined working space, how to safely and economically and precisely position these ultra-large collision protection steel cofferdams has always been a major challenge in the field of construction technology.

[0003] Taking the No. 4 main tower of the Xihoumen Railway-Highway Bridge on the newly built Ningbo-Zhoushan Railway as an example, its anti-collision device adopts a fixed double-walled steel box design, circular in shape, with a diameter of 64.32 meters, a total height of 15.3 meters, and a total weight of approximately 1518 tons. It is divided into 20 standard segments in plan. The bridge site area has rapid water flow, significant lake tides, and frequent typhoons and monsoons, making the construction environment harsh. More importantly, this anti-collision device must be installed simultaneously and concurrently during the construction of the No. 4 main tower. The main tower construction platform is only equipped with luffing jib tower cranes and crawler cranes, with limited single-machine lifting capacity, making it impossible to directly lift entire segments weighing over 75 tons. Furthermore, once the main tower is capped, the 68-meter-wide main beam to be constructed above it will completely cover the vertical projection area of ​​the anti-collision device, resulting in a complete loss of installation space.

[0004] In existing technologies, such extra-large collision avoidance facilities are mostly installed as a whole using large floating cranes or barges, or in sections, lifted to a high altitude, assembled into a whole, and then lowered in one go. However, the large floating crane solution is not only difficult to schedule and extremely expensive, but also has irreconcilable time and space conflicts with the ongoing main tower construction process, making it basically infeasible in engineering. The conventional section-by-section high-altitude assembly solution requires the assembly of all height segments on the assembly support, resulting in a tall construction platform and a large windward area, which greatly increases the risk during typhoon and monsoon seasons. Moreover, its assembly operation also relies on large crane vessels that exceed the capabilities of existing equipment on site. Therefore, there is an urgent need for an installation method for ultra-large collision avoidance facilities that can completely eliminate the need for large floating crane equipment, utilize only existing construction machinery, and can safely be carried out in conjunction with the main tower structure. Summary of the Invention

[0005] In view of the above problems, a method for installing bridge pier anti-collision facilities is proposed to overcome or at least partially solve the above problems, including: S1. Divide the annular anti-collision steel casing into several arc-shaped segments along the circumferential direction, and divide each arc-shaped segment into several blocks along the vertical direction; wherein the weight of a single block shall not exceed the maximum lifting capacity of the lifting equipment on the construction platform; S2. Install a lowering support on the top of the pier cap and configure a continuous lowering device on the lowering support; S3. Use lifting equipment to hoist the bottom layer segments into place and connect adjacent bottom layer segments into a ring structure; S4. Operate the continuous lowering device to lower the assembled ring structure as a whole by one segment vertical height; S5. Temporarily fix the lowered ring structure, disconnect the continuous lowering device from the ring structure, and change the lifting point of the continuous lowering device to another preset lifting point position on the ring structure. S6. Use lifting equipment to hoist the upper layer segment to the top surface of the lowered ring structure, and connect the adjacent segments and the upper and lower layer segments to form a new ring structure. S7. Repeat steps S4 to S6 until all blocks are assembled and the final ring structure is lowered to the design elevation.

[0006] Optionally, the lowering supports include type A, type B, type C, and type D supports; type A supports are used to install the continuous lowering device; type B supports are set in areas without a construction platform to assist in segment positioning and enhance the stability of the assembled ring structure; type C supports are set at the bottom of the construction platform to assist in positioning and support the temporary beam passage; and type D supports are set at the bottom of the guide frame platform to assist in segment positioning and enhance the stability of the assembled ring structure.

[0007] Optionally, before step S3, the method further includes: pre-embedding several sets of pre-embedded parts around the pier cap, and welding and fixing a horizontal cantilever beam on each set of pre-embedded parts. The horizontal cantilever beams are arranged radially around the pier cap. The horizontal cantilever beams are used to support the bottom block during the assembly stage.

[0008] Optionally, the continuous lowering device includes 16 continuous jacks, 4 hydraulic pump stations, and 1 computer control system; the rated load capacity of each continuous jack is not less than 1.2 times the weight it bears; the computer control system collects the vertical displacement and load values ​​of each lifting point in real time through displacement sensors and pressure sensors, takes one lifting point as the master lifting point and the other lifting points as follower lifting points, and dynamically adjusts the lowering speed of each follower lifting point through electro-hydraulic proportional control technology so that the synchronous displacement deviation between each lifting point is not greater than 5mm.

[0009] Optionally, before step S3, the method further includes: welding several sets of rigid guide structures to the inner wall of the bottom section of the annular anti-collision steel casing, with each set of guide structures corresponding to the position of an A-type bracket; during the lowering process, the guide structures maintain sliding contact with the outer wall of the pier caisson to limit the radial displacement of the annular structure.

[0010] Optionally, several reinforced rubber water bladders are also installed on the inner wall of the annular anti-collision steel casing, and each water bladder is equipped with a water injection valve at the top. After the final annular structure is lowered to the design elevation in step S7, water is injected into the water bladder to make it expand and fill the annular gap between the annular structure and the outer wall of the pier caisson. The water bladder is vacuum treated before installation to make it in a contracted state.

[0011] Optionally, before step S1, the method further includes: dismantling the Bailey beam connection platforms between the No. 1, No. 3 and No. 5 guide frames and the pier cap in batches on the pier construction platform; and after completing one or more overall lowering operations, restoring part of the Bailey beam connection platforms using temporary beam structures composed of H-beams to maintain at least one passage for personnel and material transportation.

[0012] Optionally, the connection between adjacent bottom blocks in step S3, and the connection between adjacent upper blocks and between upper blocks and the lowered ring structure in step S6, shall all adopt the following process: the horizontal plate of the lower block at the segmentation position shall be extended outward by 2cm as a welding backing during the processing stage, and CO2 gas shielded welding shall be used for welding during on-site assembly; the outer side plate and the transverse partition shall be butt welded with a single-sided bevel weld, and the remaining parts shall be connected with fillet welds, and the weld leg height of the fillet weld shall not be less than 6mm.

[0013] Optionally, in step S5, the lowered annular structure is temporarily fixed, including: installing several sets of temporary hanging legs between the vertical partition of the inner wall of the annular structure and the pier cap, with the lower end of the temporary hanging legs being supported on the top surface of the pier cap by means of a support plate and a pad; and setting a set of square timber pads every 2m along the inner circumference of the annular structure to transfer the load of the annular structure from the continuous lowering device to the pier cap.

[0014] Optionally, after step S6, the method further includes: performing on-site anti-corrosion coating repair work on the connecting welds between adjacent segments in the new annular structure. The anti-corrosion coating repair work includes, in sequence, applying zinc-rich anti-rust primer, applying epoxy micaceous iron oxide intermediate paint, and applying polysiloxane topcoat.

[0015] This invention fundamentally solves the installation problem of bridge pier anti-collision facilities in complex and overlapping construction environments through a process path of "vertical segmented load reduction, low-level cyclic assembly, synchronous lowering, and lifting point conversion." By further dividing each arc-shaped segment vertically into multiple blocks, the weight of a single block can be limited to the lifting capacity of the tower cranes and crawler cranes on the construction site, thus completely eliminating reliance on large floating cranes or external lifting vessels. This significantly saves on high vessel and machinery rental costs and eliminates the irreconcilable temporal and spatial conflicts between floating crane operations and the main tower construction. All assembly operations are always carried out at a low level above the pier cap. After each layer of the ring structure is completed, multiple continuous jacks are used to synchronously lower the entire structure and change the lifting points, ensuring that the assembled structure remains within a safe height range, with a small windward area, significantly reducing construction risks under adverse weather conditions such as typhoons and monsoons. The synchronous lowering control system adjusts the displacement and load of each lifting point in real time to ensure the ring structure is lowered smoothly and centrally, avoiding structural deformation or jamming due to uneven stress. The cyclical assembly and lowering processes can be completed concurrently with the main tower construction without affecting critical construction schedules, ensuring a controllable construction cycle. This method requires fewer large temporary facilities and allows for the reuse of existing construction platforms and conventional lifting equipment, further reducing project costs and providing a reliable construction approach for the safe, efficient, and economical installation of bridge pier anti-collision facilities. Attached Figure Description

[0016] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart of a method for installing anti-collision facilities for bridge piers provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the planar segmentation of the anti-collision facility provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the synchronous deployment of monitoring points for the anti-collision facilities provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of a cantilever beam provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the guide structure provided in an embodiment of the present invention. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0019] This invention provides a method for installing anti-collision facilities on bridge piers, which may specifically include: S1. Divide the annular anti-collision steel casing into several arc-shaped segments along the circumferential direction, and divide each arc-shaped segment into several blocks along the vertical direction; wherein the weight of a single block shall not exceed the maximum lifting capacity of the lifting equipment on the construction platform; S2. Install a lowering support on the top of the pier cap and configure a continuous lowering device on the lowering support; S3. Use lifting equipment to hoist the bottom layer segments into place and connect adjacent bottom layer segments into a ring structure; S4. Operate the continuous lowering device to lower the assembled ring structure as a whole by one segment vertical height; S5. Temporarily fix the lowered ring structure, disconnect the continuous lowering device from the ring structure, and change the lifting point of the continuous lowering device to another preset lifting point position on the ring structure. S6. Use lifting equipment to hoist the upper layer segment to the top surface of the lowered ring structure, and connect the adjacent segments and the upper and lower layer segments to form a new ring structure. S7. Repeat steps S4 to S6 until all blocks are assembled and the final ring structure is lowered to the design elevation.

[0020] Reference Figure 1 This method for installing bridge pier anti-collision facilities is applicable to the installation of large-diameter, high-tonnage anti-collision steel caissons at the bridge pier abutment under existing construction platforms and conventional lifting equipment conditions. The implementation steps of this method are explained in detail below with specific engineering examples.

[0021] In step S1, the anti-collision steel casing is first designed in sections according to the lifting capacity of the construction site's equipment. The lifting equipment at the construction site includes one 150-ton crawler crane and two luffing tower cranes. The crawler crane has a rated lifting capacity of approximately 23 tons at a working radius of 24 meters, and the tower cranes have a maximum lifting capacity of 50 tons. To ensure the weight of the component is compatible with the lifting capacity of the equipment, the annular anti-collision steel casing is evenly divided into 20 arc-shaped segments along the circumference, with each arc segment corresponding to a central angle of 18 degrees. Figure 2Each arc-shaped segment is further divided vertically into 6 blocks, numbered F, E, D, C, B, and A from bottom to top. The bottom F and top A layers are 3.35 meters high and weigh approximately 15.3 tons each; the middle B, C, D, and E layers are 2.15 meters high and weigh approximately 11.3 tons each.

[0022] All the aforementioned segments weigh less than the crawler crane's rated lifting capacity at the corresponding operating radius. The segments are assembled and welded in the factory using an arc-shaped jig. The jig's base is an I-beam frame, with a welded arc-shaped steel plate on top to match the curvature of the caisson. After fabrication, the segments undergo shot blasting for rust removal and are coated with an anti-corrosion coating. Adjacent segments are pre-assembled in the factory, and after passing inspection, they are transported in sections by flatbed trucks to the storage area at the bridge site.

[0023] In step S2, a lowering support frame and a continuous lowering device are installed on top of the pier cap. Before the cap concrete is poured, multiple sets of annular steel plates and anchor bars are pre-embedded at the designed locations. After the cap construction is completed, the lowering support frame is arranged in a ring along the outer edge of the cap using the pre-embedded parts and welded on. The lowering support frame consists of steel pipe columns, steel beams, and scissor braces, with the bottom of the columns fully welded to the pre-embedded parts. The support frame is divided into two types along the circumferential direction: one type has a top beam for installing the continuous lowering device, with a larger beam cross section and stiffening ribs; the other type has multiple layers of steel brackets pre-embedded at different heights on the sides, with the top surface elevation of the brackets corresponding to the bottom surface elevation of each segment during assembly, used to support the annular structure during assembly and temporary fixing stages.

[0024] The continuous lowering device mainly consists of continuous hydraulic jacks, steel strand bundles, hydraulic pump stations, and a synchronous control cabinet. The continuous hydraulic jacks are positioned on the top beam of the support frame, with the jack cylinders pointing vertically downwards. A bundle of steel strands, composed of multiple low-relaxation prestressed steel strands, passes through the center of the jack. The upper end of the steel strand bundle is held by an upper anchor, which sits on the upper part of the jack cylinder. The lower end of the steel strand bundle passes through the jack, is held by a lower anchor, and connected to a lifting device. The lifting device is then connected to a lifting lug on the structure to be lowered via a pin. The hydraulic pump station supplies oil to the main cylinder, upper anchor cylinder, and lower anchor cylinder of the continuous hydraulic jacks via high-pressure hoses. Each pump station controls one set of jacks. The synchronous control cabinet has a built-in programmable controller that communicates with the proportional valves and sensors of each hydraulic pump station. Based on real-time feedback signals, it performs closed-loop adjustment of the lowering speed at each lifting point to ensure the stability of the ring structure during the lowering process.

[0025] In step S3, the bottom F-layer blocks are hoisted one by one to the assembly position using on-site lifting equipment. Before hoisting, lifting points are set at the center of gravity of the blocks, and a spreader-type gantry crane is used for four-point balanced hoisting to prevent the blocks from twisting or deforming during hoisting. The F-layer blocks are hoisted to the outside of the foundation and placed on the lowest steel bracket on the side of the lower support. Steel pads are placed on the brackets beforehand to adjust the elevation. The inner arc surface of the block is pressed against the positioning block on the support to determine the radial position; the flange at the end of the block is aligned with the flange of the adjacent already positioned block, and the circumferential gap is adjusted with steel wedges. After the position adjustment is qualified, the flange plates at the ends of adjacent blocks are temporarily welded and fixed with clamps. After each two adjacent blocks are temporarily fixed, the verticality and splicing misalignment of the blocks are measured. If the deviation exceeds the tolerance, fine adjustments are made using jacks or hand-operated hoists.

[0026] After all 20 segments of the entire layer were in place and temporarily fixed, a suspended welding operation platform was erected at the weld locations. Semi-automatic CO2 gas shielded welding was used to weld the joints between the segments, following the principles of symmetry, layering, and segmentation to control residual welding deformation. During welding, the diameter and ellipticity of the annular structure were monitored, and the welding sequence was adjusted as necessary. After welding, all welds underwent visual inspection, and some welds were subjected to ultrasonic non-destructive testing. Welds that passed inspection were then cleaned with an angle grinder and manually recoated with an anti-corrosion coating. The recoating process involved first applying one coat of zinc-rich primer, then two coats of epoxy micaceous iron oxide intermediate paint, and finally one coat of polysiloxane topcoat. The dry film thickness of each coating was measured using a thickness gauge after it had fully dried.

[0027] At this point, the 20 segments of the bottom F layer are connected into a single closed ring structure. During the prefabrication stage of the F layer segments, lifting lugs with pin holes were welded to the top of the vertical partitions of each segment. The lifting equipment of the continuous lowering device is then lowered to the lifting lug position, the pin is inserted, and a cotter pin is installed, connecting the ring structure to the continuous lowering device. Afterwards, all temporary support plates are cut off, and the steel pads on the brackets are removed, allowing the self-weight load of the ring structure to be entirely borne by the steel strand bundle.

[0028] In step S4, the continuous lowering device is used to lower the assembled ring structure as a whole by one segment vertically. Before the lowering begins, a trial lowering is conducted. The synchronous control cabinet sets the target load and allowable deviation of synchronous displacement for each lifting point. The hydraulic pump station is operated to apply load in stages, sequentially applying the estimated load at 20%, 40%, 60%, 80%, and 100%. After each stage of loading, the process is paused to check the deformation of the support frame, the stress on the lifting lugs, the slippage of the steel strands, and the posture of the ring structure. After loading reaches 100%, the hydraulic pressure is increased until the ring structure is about 10 cm away from the corbel support surface. It is then suspended for 15 minutes to fully observe the working status of each mechanism. After confirming that everything is normal, the formal lowering begins.

[0029] During the actual lowering, the continuous hydraulic jack operates in the following cycle: the lower anchor clamps the steel strand bundle, the upper anchor releases, oil enters the rod chamber of the main cylinder, causing the piston rod to retract, driving the steel strand bundle and the annular structure down one stroke; after the piston rod retracts to the end of its stroke, the upper anchor clamps the steel strand bundle, the lower anchor releases, oil enters the rodless chamber of the main cylinder, causing the piston rod to extend without load, and the lower anchor moves up with the piston rod to the next working position; the lower anchor clamps the steel strand bundle again, the upper anchor releases, and the next lowering stroke begins. This process repeats, with the steel strand bundle driving the annular structure to descend continuously. During the lowering process, the synchronous control cabinet collects data in real time through displacement and pressure sensors installed at each lifting point, using one lifting point as the master lifting point and the others as follower lifting points. When the displacement of a follower lifting point lags behind or leads the master lifting point, the synchronous control cabinet adjusts the oil flow of the continuous hydraulic jack corresponding to that lifting point through a proportional valve, accelerating or decelerating that lifting point until the displacement difference returns to the set allowable deviation range. Simultaneously, pressure sensors monitor the load at each lifting point. When the load at any lifting point suddenly changes and exceeds a preset threshold, the system automatically alarms and stops lowering, only resuming after the cause has been identified. Through this closed-loop synchronous control, the ring structure is smoothly and synchronously lowered one segment vertically. Taking the lowering of layer F as an example, the entire ring structure is lowered by approximately 3.35 meters, reducing the top surface of layer F to a height suitable for subsequent assembly of layer E. During the lowering process, the attitude is monitored in real-time through monitoring points at the top of the ring structure, referencing... Figure 3 .

[0030] In step S5, the lowered annular structure is temporarily fixed, the connection between the continuous lowering device and the annular structure is disconnected, and the lifting point conversion is completed. After the annular structure is lowered into place, the synchronous control cabinet stops the extension and retraction of each continuous hydraulic jack, maintaining the load. The operator quickly inserts wedge-shaped steel blocks between the inner wall of the annular structure and the upper layer of steel brackets on the side of the lowering support, and drives the steel wedges in to tighten them, so that the self-weight load of the annular structure is transferred from the steel strand bundle to the brackets of the lowering support. After checking that each set of blocks is in close contact with the brackets, the synchronous control cabinet slowly unloads the oil pressure of each continuous hydraulic jack, the steel strand bundle gradually loosens, and the load is fully borne by the brackets. Then, the connecting pin between the continuous hydraulic jack lifting device and the current lifting lug is removed, and the lifting device is retrieved.

[0031] During the prefabrication of the blocks, multiple layers of lifting lugs are installed on the inner wall of each arc-shaped segment from bottom to top. Each layer of lifting lugs corresponds to one block, and the planar positions of each layer of lifting lugs are aligned vertically. For example, the lifting lugs of layer F are located at the top of layer F, the lifting lugs of layer E are located at the top of layer E, and so on. When the ring structure of layer F is lowered by one layer, the lifting lugs of layer E, which were originally above it, descend with the structure to a range accessible to the operators. The operators then lower the lifting device of the continuous hydraulic jacks back down, connect it to the lifting lugs of layer E via pins, and install cotter pins to prevent loosening. After this operation, the continuous lowering device has established a connection with the new lifting point on the ring structure, and subsequent lowering operations will use the new lifting point as the force application point. At this point, a complete lifting point conversion is completed, preparing for the next cycle of lowering work.

[0032] In step S6, the upper layer segment (E layer segment) is hoisted to the top surface of the lowered annular structure using lifting equipment and connected to form a new annular structure. The hoisting method for the E layer segment is similar to that of the F layer, using a special lifting frame for balanced hoisting. After the E layer segment is hoisted to the top surface of the F layer annular structure, its bottom horizontal partition overlaps the extended steel plate at the top of the F layer. This extended steel plate is prefabricated in the factory and serves as a backing for on-site welding. The circumferential and radial positions of the E layer segment are adjusted using pry bars and positioning pins to align the end flanges of the E layer segment with the adjacent E layer segment and to make the inner side of the E layer segment flush with the inner side of the F layer segment. After adjustment, temporary welding plates are used to simultaneously fix the end flanges and the joints between the upper and lower layers. After hoisting the entire E layer segment piece by piece, the circumferential butt joints between the E layer segments are welded first, followed by the horizontal circumferential butt joints between the E layer and the F layer. The welding method also uses semi-automatic carbon dioxide gas shielded welding, and the welding sequence follows the principle of symmetrical welding. After welding, a visual inspection and non-destructive testing of the weld are performed, and an anti-corrosion coating is applied. At this point, layer E and layer F form a new, elevated ring structure.

[0033] In step S7, steps S4 to S6 are repeated until all segments are assembled and the final ring structure is lowered to the design elevation. Specifically, after assembling the ring in layer E, step S4 is repeated to lower the new ring structure by one segment's vertical height, i.e., the height of layer E is 2.15 meters; then step S5 is repeated for temporary fixing and lifting point conversion, changing the lifting points of the continuous lowering device to the lifting lugs in layer D; then step S6 is repeated to assemble the segments in layer D. This cycle of assembly, lowering, fixing, and conversion is repeated layer by layer to complete the installation of layers D, C, B, and A. After assembling the last layer, layer A, into a ring and completing the weld inspection, the lifting point conversion is no longer performed. Instead, the final complete ring structure is lowered to the design elevation through the operation in step S4. Synchronous control is maintained during the lowering process until the bottom surface of the ring structure reaches the design bottom elevation and the top surface reaches the design top elevation. After being lowered to the design elevation, the ring structure is finally positioned and finely adjusted, and then permanently fixed to the bridge pier abutment or caisson to complete the transformation of the load-bearing system.

[0034] During the aforementioned cyclical construction process, to ensure overall stability, after each layer of the ring structure is lowered, the ring structure can be temporarily connected to the support using bolts or welding, utilizing the pre-set brackets and bolt holes on the side of the lowering support. This connection helps resist water flow forces and wind loads during construction. All high-altitude assembly and welding operations are carried out within a welding operation platform, which is erected and dismantled layer by layer as the ring structure is lowered, ensuring the safety of the workers.

[0035] In one or more embodiments of the present invention, the lowering support includes type A support, type B support, type C support and type D support; type A support is used to install the continuous lowering device, type B support is set in the area without construction platform to assist in segment positioning and enhance the stability of the assembled ring structure, type C support is set at the bottom of the construction platform to assist in positioning and support the temporary beam passage, and type D support is set at the bottom of the guide frame platform to assist in segment positioning and enhance the stability of the assembled ring structure.

[0036] In the specific implementation of the scaffolding deployment, all scaffolding columns were fixed to the top surface of the foundation using pre-embedded annular steel plates and anchor bars during the foundation construction phase. The planar position deviation of the pre-embedded parts was controlled within 20mm by measurement. After the columns were hoisted into place, they were temporarily fixed with installation bolts, and then fully welded around the perimeter with fillet welds. Based on the location of the scaffolding around the foundation and its main function, the 20 scaffolding units were configured into four structural types: Type A, Type B, Type C, and Type D.

[0037] Eight A-type supports are installed, arranged circumferentially along the outer edge of the foundation. Each A-type support is located directly below a set of continuous lowering devices, serving as the main vertical load-bearing structure during the lowering process. The main body of the A-type support consists of steel pipe columns and box-shaped beams. The steel pipe columns are 630mm in diameter and 10mm thick, welded to the pre-embedded parts A at the bottom. Horizontal tie rods are welded between the columns to improve overall lateral stiffness. The beams are made of two hot-rolled H-beams welded side by side, with both ends resting on top of the columns and reinforced at the joints with stiffening plates. Bolt holes are provided on the top surface of the beams for fixing the bases of the continuous hydraulic jacks. Several layers of brackets are welded below the beams at different heights along the columns. The brackets are made of steel plates cut into right-angled triangles and welded to the flanges of the columns. The top elevation of each layer of brackets is consistent with the bottom elevation of the corresponding segment requiring support during the assembly or temporary fixing stage. When the anti-collision facility blocks are hoisted, the outer arc surface of the block can be placed against the positioning block on the A-type bracket column to determine the radial position; when the ring structure is lowered by one block height, the bracket can be used as a load-bearing point for temporary fixation, and the self-weight load of the ring structure can be transferred to the A-type bracket through the wedge-shaped pad.

[0038] Six Type B supports are installed, concentrated in the arched section of the pier without direct coverage by a construction platform. This area lacks the shelter of a jacket platform, and during typhoons or monsoons, wind loads act directly on the assembled ring-shaped anti-collision structure. The Type B support columns are made of H-beams with a cross-section of 700mm × 300mm and a height of approximately 7.3 meters. The bottom is fully welded to the embedded part B. Horizontal support arms are installed at regular intervals along the column height, with removable temporary connecting plates welded to the ends of the arms. When the bottom section is hoisted into place, the pre-set ear plates on the inner wall of the section can be overlapped with the connecting plates and spot-welded. The lateral stiffness of the Type B supports constrains the circumferential and radial displacement of the section, thus aiding in positioning. As the ring structure is assembled and lowered layer by layer, once it reaches a certain height, the connecting plate on the upper layer of the B-type support can be welded and fixed to the corresponding elevation of the lowered ring structure. This creates a rigid connection between the ring structure and the B-type support at multiple height levels, increasing the overall lateral stiffness of the structure and improving its wind resistance stability during construction. Patterned steel plates are also laid on the support arms of the support as temporary walkways for personnel, and ladders are welded to the sides of the columns to facilitate workers' access for connection operations.

[0039] Two C-type supports are installed, one on the left and one on the right of the pier line, directly below the No. 3 guide frame construction platform. Due to the constraint of the upper platform beam, the vertical space of the supports is limited; therefore, the total height of the C-type support columns is lower than that of the A-type supports, approximately 6 meters. The columns still use 630mm diameter, 10mm wall thickness steel pipes, welded and fixed to the pre-embedded part A at the bottom. A temporary beam support is installed at the top of the crossbeam of the C-type support. The temporary beam support is a channel-shaped steel plate component that restricts displacement. After the partial dismantling of the construction platform, the H-shaped steel temporary beam used to restore the passage can be lowered into the support and a lateral limiter installed, allowing the temporary beam to be reliably placed on the C-type support. At this time, the C-type support not only bears the live load of the passage transmitted by the temporary beam, but also serves as a lateral auxiliary positioning point for the assembled ring structure. The limiting plate welded to the side of the column keeps it in close contact with the outer wall of the ring structure, preventing excessive radial sway of the ring structure during the assembly stage.

[0040] Four D-type supports are installed, two at each of the bottom edge of the foundation of the jacket platform (platforms 1 and 5). The uprights of the D-type supports also use H-section steel, approximately 4.4 meters high, and are welded to the embedded part B at the bottom. Because the D-type supports are located below the jacket platform and close to the temporary beam passage, the orientation and elevation of their horizontal support arms have been adjusted to avoid existing diagonal braces and pipelines below the platform. The temporary connecting plates at the ends of the support arms are used as guides during segment hoisting. After the segment is hoisted to the predetermined elevation, the segment's posture is finely adjusted so that its inner wall is flush with the connecting plate. Then, clamps are used to temporarily fix the segment to the connecting plate, thus aiding in determining the segment's installation position. After the ring structure is formed, the D-type support is locked to the ring structure through a code plate and fillet weld. When locking, welding is performed between the end of the support arm of the support and the inner wall reinforcement of the block. The weld leg height of the fillet weld is 10mm, and the welding length covers the full width of the support arm, thereby reliably connecting the ring structure and the D-type support into one, enhancing the local wind resistance of the structure at the bottom of the jacket platform.

[0041] Before construction, the brackets, connecting plates, and positioning blocks of the above four types of supports were all laid out in three dimensions based on the measured shape of the foundation and the segmented dimensions of the anti-collision facilities to ensure that all contact surfaces could effectively fit during installation. As the ring structure was lowered layer by layer, the connecting parts on the sides of the supports were gradually activated as the height of the ring structure changed. Before each activation, the relative position between the connecting parts and the ring structure was measured and checked. If there were any deviations, fine adjustments were made by adding steel shims or using flame straightening to ensure that the positioning and constraint effect of the supports on the ring structure met expectations.

[0042] In one or more embodiments of the present invention, before step S3, the method further includes: pre-embedding several sets of pre-embedded parts around the pier cap, and welding and fixing a horizontal cantilever beam on each set of pre-embedded parts, the horizontal cantilever beams being arranged radially around the pier cap; the horizontal cantilever beams are used to support the bottom block during the assembly stage.

[0043] Before step S3, multiple sets of embedded parts are pre-installed around the top perimeter of the pier cap for subsequent welding and installation of the horizontal cantilever beam. The embedded parts are positioned and fixed before the cap concrete is poured. Each set of embedded parts includes a horizontal steel plate and several anchor bars. The horizontal steel plate is square, 20mm thick, with anchor bars welded vertically to its bottom surface. The length and spacing of the anchor bars are determined based on the arrangement of the main reinforcement bars of the cap. After the cap reinforcement bars are tied and formed, the plane position control line of the embedded parts is marked on the top of the formwork according to the design position of the cantilever beam. After inserting the anchor bars of the embedded parts into the gaps in the reinforcement cage, short steel bars are used to spot weld the anchor bars to the main reinforcement bars of the cap, ensuring the horizontal steel plate remains at the design elevation. The top surface of the horizontal steel plate is controlled to be flush with the finished surface of the cap concrete, with a plane position deviation of no more than 20mm. During the pouring of the cap concrete, auxiliary vibration is applied to the area of ​​the embedded parts to ensure a tight bond between the bottom surface of the steel plate and the concrete.

[0044] Once the foundation concrete reaches its design strength, the horizontal cantilever beams can be installed. The horizontal cantilever beams are made of hot-rolled H-beams with a cross-section of 700mm × 300mm, as per reference. Figure 4 During installation, a tower crane or crawler crane is used to lift each horizontal cantilever beam above its corresponding embedded part, ensuring that the root end face is flush with the upper surface of the horizontal steel plate of the embedded part. The elevation of the cantilever beam's overhang is measured using a level, and thin steel shims of varying thicknesses are inserted between the root and the steel plate for fine-tuning, ensuring that the top surface of the entire cantilever beam falls on the same horizontal plane, with a height difference of no more than 5mm between adjacent cantilever beams. After adjustment, manual arc welding is performed on the contact edges between the cantilever beam's flange and web and the embedded steel plate. The weld is a fillet weld with a weld leg height of no less than 10mm, and the weld length covers the entire contact line. A triangular stiffening plate is also welded between the cantilever beam's root and the embedded steel plate to enhance the bending and torsional stiffness of the cantilever beam's root. A total of 40 horizontal cantilever beams are installed around the circumference of the foundation, with two cantilever beams supporting each arc segment.

[0045] When the bottom blocks are assembled on-site, the horizontal cantilever beams directly support the weight of each block as vertical load-bearing points. After the blocks are hoisted to the assembly position, their bottom outer wall panels and horizontal partitions are placed on the top surface of the corresponding cantilever beams. The top surface of the cantilever beams is pre-coated with a release agent to reduce sliding friction during minor adjustments of the blocks. Operators use the radial and circumferential scale lines pre-drawn on the top surface of the cantilever beams to initially align the planar position of the blocks, and then use pry bars or small hydraulic jacks to apply horizontal thrust to bring the blocks close to the design edge lines. Before the blocks are connected to each other, the self-weight of a single block is entirely borne by the two cantilever beams below, and the cantilever force of the cantilever beams is transferred to the embedded parts and the foundation concrete through the root weld. After the entire layer of blocks is assembled into a closed ring structure, the self-weight of the ring structure begins to be borne by the circumferential load-bearing system, and the support of the cantilever beams gradually degenerates into auxiliary safety. Before the overall lowering in step S4, all horizontal cantilever beams must be removed to avoid interference between the cantilever beams and the descending outer wall of the ring structure. During dismantling, the welds on the flanges and web of the cantilever beam are cut section by section using an oxy-acetylene torch, with the flanges cut first and then the web. A skip-cutting method is used to reduce the impact of thermal deformation on the embedded parts. The stiffening plate is cut off along with the cantilever beam. After the cantilever beam is cut off, it is removed from the work surface by a crane, completing the removal of the entire temporary support.

[0046] In one or more embodiments of the present invention, the continuous lowering device includes 16 continuous jacks, 4 hydraulic pump stations and 1 computer control system; the rated load capacity of each continuous jack is not less than 1.2 times the weight it bears; the computer control system collects the vertical displacement and load values ​​of each lifting point in real time through displacement sensors and pressure sensors, takes one lifting point as the master lifting point and the other lifting points as follower lifting points, and dynamically adjusts the lowering speed of each follower lifting point through electro-hydraulic proportional control technology so that the synchronous displacement deviation between each lifting point is not greater than 5mm.

[0047] Sixteen continuous hydraulic jacks are installed in pairs on the top beams of eight A-frame supports. The cylinders of the jacks are fixed to the beams via bolt holes in the bases, ensuring verticality. Each lifting point has a bottom anchor installed at its base. The inner cavity of the bottom anchor and the central through-hole of the jack piston rod together form a through-channel for the steel strand bundle. The steel strand bundle consists of multiple low-relaxation prestressed steel strands with a nominal diameter of 15.2 mm and a tensile strength of 1860 MPa. The number of strands is configured according to the design load of each lifting point. The upper end of the steel strand bundle is held by an upper anchor clamp located above the jack cylinder, and the lower end passes through the piston rod and the bottom anchor, then is held by a lower anchor clamp located below the bottom anchor. A lifting device is connected to the lower end of the lower anchor clamp, which is hinged to a lifting lug at the top of the annular structural block via a pin, thus transferring the load from the jacks to the annular structure. Each continuous hydraulic jack has a rated load capacity of 350 tons, which is more than 1.2 times the single-point load obtained by distributing the total weight of the anti-collision facility evenly among the 16 lifting points, thus providing sufficient load redundancy during the lowering process.

[0048] Four hydraulic pump stations are centrally located in a temporary hydraulic power station on the top surface of the pier near the A-type support area. Each pump station supplies pressurized oil to the four continuous hydraulic jacks via multiple high-pressure hoses. The main oil circuit of each pump station is equipped with a proportional directional valve. The valve opening of this valve can be continuously adjusted by an electrical signal, thereby providing stepless control over the flow of hydraulic oil into the main cylinder of the jack. Simultaneously, the pump station also has an independent control oil circuit and a solenoid directional valve to supply oil to the drive cylinders of the upper and lower anchor clamps of the jacks, enabling the clamping and releasing actions of the anchor clamps. Through the combined action of the proportional and solenoid directional valves, each continuous hydraulic jack can be controlled to independently complete work cycles such as clamping the steel strand bundle, extending or retracting the piston rod, and alternating the anchor clamps, thereby driving the annular structure to achieve continuous lowering motion.

[0049] The computer control system includes a main control cabinet located in the field control room, an industrial control host computer, multiple signal acquisition modules arranged near the jacks, and sensor groups installed at each lifting point. The sensor groups consist of two main categories: displacement sensors and pressure sensors. At each lifting point, the displacement sensor uses a pull-wire absolute encoder. The encoder body is fixed to the side of the jack cylinder, and its pull wire end is fixed to a measuring block at the end of the lifting device or steel strand. When the lifting device descends with the ring structure, the pull wire is pulled out, and the encoder outputs a pulse signal proportional to the pulled-out length. After conversion by the signal acquisition module, the current vertical displacement value of the lifting point is obtained. The pressure sensor is installed at the oil port on the large cavity side of the jack's main cylinder, measuring the hydraulic oil pressure in the working chamber of the cylinder in real time. After conversion using the piston area of ​​the cylinder, the actual load value currently borne by the lifting point is obtained. Each lifting point is also equipped with proximity switches to detect the status of the upper and lower anchor clamps, used in the control logic to determine whether the steel strand bundle is in a safe clamping state.

[0050] Before the actual lowering begins, the operator selects one lifting point as the master lifting point via the industrial control computer, while the remaining 15 lifting points are automatically identified as follow-up lifting points. The lowering speed of the master lifting point is set by the operator, typically choosing a speed value that is compatible with the construction progress and hydrological window. The control system synchronously reads the displacement sensor data of all lifting points at a set sampling frequency, using the current displacement value of the master lifting point as the reference value, and calculates the displacement deviation of each follow-up lifting point in each control cycle. When the displacement of a following lifting point lags behind that of the master lifting point, the control system generates a control output through a built-in proportional-integral-derivative adjustment algorithm. This output is converted into an electrical signal and sent to the proportional directional valve amplifier of the hydraulic pump station corresponding to that following lifting point. This increases the valve core opening, increasing the flow rate into the jack's main cylinder, thus slightly accelerating the piston rod retraction speed of the jack and gradually catching up with the lowering displacement of the master lifting point. When the displacement of the following lifting point leads that of the master lifting point, the flow output of the proportional valve is reduced accordingly, decreasing the piston rod retraction speed until the displacement deviation is reduced to within the set range. Through this electro-hydraulic proportional synchronous control strategy, which uses the master lifting point as the displacement reference and adjusts the following lifting points in real time, the maximum synchronous displacement deviation between each lifting point remains within 5mm throughout the entire lowering process of the ring structure.

[0051] Meanwhile, the load values ​​transmitted in real time by the pressure sensors are continuously monitored. The host computer software has preset upper load thresholds and load drop thresholds for each lifting point. When the load value at any lifting point exceeds the upper threshold, the system determines that jamming or local overload may occur, immediately issues a stop command to all hydraulic pump stations, locks all anchor clamps, suspends the ring structure in its current position, and triggers an audible and visual alarm to prompt the operator to inspect. When the load value at a lifting point suddenly drops significantly and falls below the drop threshold, the system determines that there may be a risk of steel strand slack or lifting device detachment at that point, and similarly executes the emergency suspension and alarm procedures. In addition, the control cabinet panel is equipped with an independent emergency stop button, which can be pressed directly by the operator in the event of a sudden abnormal working condition to cut off the main power supply to all hydraulic pump stations. At this time, the hydraulic control check valves and balance valves of each hydraulic circuit automatically close, locking the ring structure's posture and preventing accidental fall.

[0052] In one or more embodiments of the present invention, before step S3, the method further includes: welding several sets of rigid guide structures to the inner wall of the bottom section of the annular anti-collision steel casing, each set of guide structures corresponding to the position of an A-type bracket; during the lowering process, the guide structures maintain sliding contact with the outer wall of the pier caisson to limit the radial displacement of the annular structure.

[0053] The number of guide structures is the same as the number of A-type supports. The circumferential position of each guide structure corresponds to the radial projection position of an A-type support. Each guide structure consists of a guide plate and several stiffening plates. The guide plate is made of Q235B steel, the same material as the main body of the anti-collision steel caisson. Its inner edge is attached to the vertical partition or outer plate on the inner side of the bottom segment. The joint is connected by double-sided fillet welds using CO2 gas shielded welding, with a weld leg height of 8mm. The stiffening plates are welded to both sides of the guide plate. The right-angled edges of the stiffening plates are welded to the guide plate surface and the inner wall of the segment, respectively, to enhance the bending stiffness of the guide plate under radial compression. The outer edge arc of the guide plate is CNC cut according to the measured contour of the outer wall of the pier caisson at that elevation. After cutting, the outer edge is ground to remove cutting marks and oxides to reduce frictional resistance during subsequent sliding contact.

[0054] After the bottom segment blocks have completed the welding of the guide structure and undergone dimensional verification, they are transported to the site to participate in the assembly of the bottom ring structure in step S3. When the bottom segments are connected to form a closed ring structure and lowered as a whole by the continuous lowering device in step S4, these guide structures move downward synchronously with the ring structure. During the lowering process, if the ring structure is subjected to water flow thrust or uneven load on the lifting points and shifts radially in a certain direction, the outer edges of several sets of guide plates on one side of the shift direction will first touch the outer wall surface of the pier caisson. The contact between the guide plates and the outer wall of the caisson is a sliding contact between steel and concrete. The radial reaction force generated by the contact is transmitted to the vertical and horizontal partitions of the ring structure through the guide plates and stiffening plates, thus forming a rigid constraint on further shifts in that direction. At this time, due to the circumferential stiffness of the ring structure itself, the constraint force on one side will be redistributed along the circumferential direction, causing the ring structure to return to its central position. The arc-shaped contour of the outer edge of the guide plate makes the contact area distribution more uniform during the sliding process, avoiding jamming caused by local stress concentration. As the lowering process continues, the guide structure slides downwards along the outer wall of the caisson. During this process, the designed gap between the annular structure and the caisson is always passively limited and controlled by the guide structure. The radial displacement of the annular structure is constrained within the allowable deviation range throughout the entire lowering phase. Figure 5 .

[0055] In one or more embodiments of the present invention, a plurality of reinforced rubber water bladders are also installed on the inner wall of the annular anti-collision steel casing, and each water bladder is provided with a water injection valve at the top; after the final annular structure is lowered to the design elevation in step S7, water is injected into the water bladder to make the water bladder expand and fill the annular gap between the annular structure and the outer wall of the pier caisson; the water bladder is vacuum treated before installation to make the water bladder in a contracted state.

[0056] The water bladder is made of fiber-reinforced rubber-based composite material with a total wall thickness of 10mm. It features an internal reinforcing layer of fabric and an outer layer of weather-resistant rubber. The water bladder is rectangular and vertically installed between the vertical partitions on the inner wall of the enclosure. During installation, the skirt of the water bladder fits against the steel plate of the inner wall of the enclosure, and the skirt is secured externally by segmented steel pressure plates. These pressure plates are bolted to pre-drilled bolt holes on the inner wall of the enclosure. Each segment of the pressure plate is disconnected at the bolt holes to accommodate on-site assembly conditions of the enclosure. A water injection valve is located at the top of the water bladder. This valve is a two-way valve, model DN25, and its base is vulcanized integrally with the water bladder body to ensure a tight seal at the connection.

[0057] Before all water bladders are installed and secured but transported to the site, each bladder undergoes vacuum treatment. During vacuum treatment, the vacuum equipment's extraction pipe is connected to the water injection valve. After opening the valve, the vacuum pump is started to extract the air from the bladder's cavity. As the air pressure inside the cavity decreases, the bladder walls contract inward under atmospheric pressure, sticking together and resulting in a flattened, contracted state. Once the vacuum gauge reaches the set value, the water injection valve is closed, and then the vacuum equipment's extraction pipe is removed. The vacuum treatment significantly reduces the thickness of the water bladders, preventing premature contact and scratches with the outer wall of the bridge pier caisson during the assembly and phased lowering of the ring structure.

[0058] In step S7, after the final annular anti-collision steel casing is lowered to the design elevation and the plane position and elevation are verified to meet the requirements, water is injected into the water bladder. During injection, clean water is drawn from the on-site tap water pipeline and connected to the injection valve via a hose. The injection valves of each section of the water bladder are opened sequentially, using a low-head submersible pump or directly utilizing the head difference to inject water into the bladder cavity. As clean water gradually fills the bladder cavity, the water bladder gradually expands from a contracted state, with the bladder wall bulging outwards. It first contacts the outer wall surface of the pier caisson, and then, with the continuous action of the injection pressure, the water bladder tightly fills the annular gap between the inner wall of the annular anti-collision steel casing and the outer wall of the pier caisson. During the injection process, care must be taken to control the injection rate to avoid excessively high rates, so that the bladder wall can extend evenly and fully adhere to the concrete surface of the caisson's outer wall. When water overflows from the injection valve and the bladder wall is tightly adhered to both side walls without visible gaps, the injection is stopped and the valve is closed, completing the water filling of a single water bladder. After all the water bladders are filled with water, the water bladders form a uniform and continuous annular flexible filling layer between the casing and the caisson, which firmly embeds the annular anti-collision steel casing around the pier caisson.

[0059] In one or more embodiments of the present invention, before step S1, the method further includes: dismantling the Bailey beam connection platforms between the No. 1, No. 3 and No. 5 guide frames and the pier cap in batches on the pier construction platform; after completing one or more overall lowering operations, restoring part of the Bailey beam connection platforms using a temporary beam structure composed of H-beams to maintain at least one passage for personnel and material transportation.

[0060] Before step S1, the existing Bailey bridge connection platforms between the No. 1, No. 3, and No. 5 guide frames and the pier caps of the existing pier construction platform need to be dismantled in batches. These connection platforms are assembled into load-bearing trusses by ZB200 Bailey bridge panels and reinforcing chords, with steel bridge decks and I-beam distribution beams laid on top, serving as the main passage for personnel and material transportation during construction. Due to the large vertical dimensions of the crash barrier segments, and the need to lower the assembled ring structure as a whole in subsequent steps, the clearance under the original Bailey bridge connection platforms is insufficient to accommodate the hoisting path of the segments and the vertical movement of the ring structure. If they are not dismantled, the upper edge of the assembled structure will interfere with the bottom of the platform beams, making it impossible to install the crash barrier.

[0061] The dismantling operation is scheduled to take place during the construction phase of the main tower's middle columns. At this stage, the main tower's demand for the three connecting platforms mentioned above is relatively reduced, and the dismantling will not interrupt the progress of the main construction process. During dismantling, the connecting welds between the bridge deck and the distribution beams will be cut first. The bridge deck and distribution beams will then be lifted off the work surface in sections using a tower crane. Next, the pins between the Bailey bridge sections will be removed in sequence, and the Bailey bridge sections will be lifted one by one to the designated stacking location on the pier cap. In terms of the dismantling sequence, a phased approach will be adopted, ensuring that at least one connecting platform remains in its original state at any given time to maintain basic personnel access and limited material handling conditions from the jacket structure to the pier cap.

[0062] During the S7 cycle, after one or more overall lowering operations are completed and the top surface of the assembled annular structure is lowered below the original connecting platform position, the passageway in the partially dismantled platform area can be restored. At this time, the original Bailey beam structure is no longer used; instead, a temporary beam structure composed of hot-rolled H-beams is adopted to control the net distance between the bottom of the beam and the lowered structure after the passageway is restored, reducing the space occupied by subsequent operations. The main beam of the temporary beam consists of two HN700×300 steel sections arranged side-by-side, with the beam ends resting on the existing crossbeam on one side of the jacket and on the pile caps of the steel pipe piles on the top surface of the pier cap, respectively. 20a I-beams are laid transversely on the temporary beam deck as distribution beams, and roadbed box slabs are laid on top of the distribution beams as walking panels, forming a low-height temporary beam passageway that accommodates personnel passage and the installation of facilities such as ground pump pipes. The restoration of this temporary beam passageway allows construction personnel to directly access the pier cap work area from the jacket side without affecting the subsequent hoisting and final lowering of sections. By dismantling the Bailey bridge connecting platform in batches and restoring the temporary beam access, the vertical space required for the installation of the crash barrier is guaranteed, while ensuring the continuous availability of at least one passageway for personnel and materials during the construction period.

[0063] In one or more embodiments of the present invention, the connection between adjacent bottom blocks in step S3, and the connection between adjacent upper blocks and between upper blocks and the lowered annular structure in step S6, are all carried out using the following process: the horizontal plate of the lower block at the segmentation position is extended outward by 2cm as a welding backing during the processing stage, and CO2 gas shielded welding is used for welding during on-site assembly; the outer side plate and the transverse partition are butt welded with a single-sided bevel weld, and the remaining parts are connected with fillet welds, and the weld leg height of the fillet weld is not less than 6mm.

[0064] During the factory fabrication of the segments, each layer of the arc-shaped segment has a pre-extension portion (20mm) pre-cut on the horizontal partition at the segmentation point. This extension serves as a welding backing during on-site assembly. When the upper and lower segments are butt-jointed, the extended portion of the lower segment's horizontal partition extends into the projection range of the upper segment's horizontal partition, filling the root gap of the butt joint. As the welding arc melts and fills the metal on the front side of the joint, the extended backing provides a continuous metal support for the back of the molten pool, preventing the molten metal from flowing through large gaps and ensuring the fusion quality at the weld root. This avoids the difficulty of setting independent backings inside the segments during high-altitude welding in the field. This extended backing is not removed after welding and remains as a permanent component of the weld root within the structure.

[0065] All on-site welding employs a semi-automatic CO2 gas shielded welding process. The shielding gas is CO2 with a purity of not less than 99.5%. Parameters such as welding wire diameter, welding current, arc voltage, and welding speed are set according to the pre-qualified welding procedure specifications based on the plate thickness and welding position. Before formal welding of all joints, two sections to be connected are temporarily welded and fixed at the end flanges using tie plates. The tie plate spacing is controlled at 400mm to 600mm along the joint direction. The weld leg height of the tie plate does not exceed half the designed weld leg height, and the tie plate position avoids the designed arc start and end points of the formal weld, with a spacing of not less than 30mm. After temporary fixing, the joint gaps and misalignments between the sections are re-measured to confirm that they meet the welding requirements.

[0066] Different joint types are used for the joints in different parts based on their stress characteristics and accessibility. The circumferential butt joints between the outermost plates of the anti-collision steel casing, as well as the interlayer butt joints between the outermost plates and the transverse diaphragms, are implemented using single-sided bevel welding. The bevel angle and blunt edge dimensions of the single-sided bevel are pre-formed by a planer during the block processing stage, with the bevel facing the outer operating side to facilitate welding operations on the outside of the casing. During welding, multiple layers and passes are first filled within the bevel, with the thickness of each weld pass not exceeding 1.2 times the diameter of the electrode core, and the interpass temperature controlled within the specified range. When welding to the cover layer, the weld reinforcement is controlled between 1mm and 2mm, and the weld surface has a slightly convex shape, smoothly transitioning with the base material on both sides.

[0067] The connections between vertical and horizontal partitions and stiffening ribs inside the enclosure, as well as the connections between the inner side plates and partitions, are completed using fillet welds. The weld leg height of the fillet weld is not less than 6mm. When the two plates being connected have different thicknesses, the upper limit of the weld leg height is determined based on the thickness of the thinner plate to avoid excessive burning of the thinner base material. The welding sequence of the fillet welds follows the principle of symmetrical development from the inside out and from the center to both sides to reduce the wavy deformation of the enclosure wall panels.

[0068] Environmental conditions during welding must be continuously monitored. When the wind speed in the work area exceeds 2 meters per second, a three-sided windbreak made of fireproof canvas should be erected on the windward side of the weld joint, and an arc-blocking curtain should be hung inside the windbreak to ensure effective coverage of the molten pool by the shielding gas. When the ambient humidity in the work area exceeds 80%, or the ambient temperature is below 5°C, the area to be welded and a 100mm radius on both sides should be preheated with a flame torch. The preheating temperature should be controlled between 80°C and 120°C, and a temperature pen or surface thermometer should be used to measure the temperature 30mm to 50mm from the edge of the weld joint. Arc ignition and welding can only begin after confirming that the preheating temperature has been reached. Outdoor welding operations should be suspended in rainy, snowy, or foggy weather.

[0069] After all welds are completed and cooled to ambient temperature, a visual inspection of the welds is conducted. The inspection includes checking for defects such as cracks, lack of fusion, porosity, undercut, and weld beads on the weld surface. For welds that pass the visual inspection, ultrasonic non-destructive testing is performed according to a specified ratio. This testing is scheduled 24 hours after welding to cover potential delayed cracking. Welds that pass the inspection proceed to the anti-corrosion coating touch-up process. During touch-up, the weld surface and the heat-affected zones on both sides are first polished to a metallic luster with a wire wheel to remove oxide scale and spatter particles. Then, a zinc-rich primer, an epoxy micaceous iron oxide intermediate coat, and a polysiloxane topcoat are applied sequentially, with the number of coating layers and the dry film thickness consistent with the anti-corrosion system completed at the factory for this section.

[0070] In one or more embodiments of the present invention, the temporary fixing of the lowered annular structure in step S5 includes: installing several sets of temporary hanging legs between the vertical partition of the inner wall of the annular structure and the pier abutment, with the lower end of the temporary hanging legs being supported on the top surface of the pier abutment by means of a support plate and a pad; and setting a set of square timber pads every 2m along the inner circumference of the annular structure to transfer the load of the annular structure from the continuous lowering device to the pier abutment.

[0071] Temporary fixation primarily relies on several sets of temporary support legs installed between the inner wall of the annular structure and the pier cap. These temporary support legs are pre-welded to the inner wall of the vertical partitions of each relevant segment during the segment manufacturing stage. Each set of temporary support legs consists of a vertical load-bearing plate, a horizontal base plate, and two triangular stiffening plates, all welded together. The material is the same Q235B steel as the main body of the anti-collision steel casing. The upper part of the vertical load-bearing plate is connected to the segment's vertical partition via double-sided fillet welds with a weld leg height of 8mm and a weld length covering the entire height of the load-bearing plate. The horizontal base plate is located at the lower end of the vertical load-bearing plate, with its bottom surface facing the top surface of the pier cap after the annular structure is lowered into place. The stiffening plates are symmetrically arranged on both sides of the vertical load-bearing plate and welded to both the vertical load-bearing plate and the horizontal base plate, respectively, to enhance the bending resistance at the base of the support legs. Each set of temporary hanging legs is arranged circumferentially along the inner wall of the annular structure. The circumferential position of each set of hanging legs corresponds to the radial position of an A-type bracket, so that the hanging legs can directly transfer the load through the corbel of the A-type bracket or the stress area on the top surface of the pier after being stressed.

[0072] After the ring structure is lowered to the designated elevation, continuous hydraulic jacks maintain the load, keeping the ring structure suspended and preventing displacement. Operators insert steel clamps into the gap between the horizontal base plate of the temporary support leg and the top surface of the support platform, through the gap between the inner wall of the ring structure and the top surface of the support platform. The clamps are rectangular steel plates of varying thicknesses. During operation, a thinner clamp is first wedged into the gap by gently tapping with a hammer, and then clamps of appropriate thickness are stacked according to the measured gap size until the clamps are simultaneously in contact with the bottom surface of the horizontal base plate and the top surface of the support platform. After the clamps are tightened, a short fillet weld is applied to the side joint between the clamps and the horizontal base plate of the temporary support leg to temporarily spot weld the clamps to the base plate, preventing slippage under stress during subsequent unloading. Steel pads, square steel plates larger than the projected area of ​​the horizontal base plate of the temporary support leg, are then placed on the outside of the clamps to increase the local bearing area of ​​the top surface of the support platform.

[0073] While installing temporary hanging legs and stacking plates, a set of square timber pads is installed every 2 meters along the inner circumference of the ring structure. The square timber has a cross-section of 100mm × 100mm and is made of pine or hardwood of equivalent density. Before use, the surface is checked for through cracks and rot. The square timber pads are placed on the flat surface of the inner side panel of the casing, avoiding the installation positions of vertical partitions and temporary hanging legs, so that the square timber directly supports the bottom surface of the inner side panel of the casing. When the height of a single square timber pad is insufficient, multiple square timbers are stacked in a cross shape and aligned, with each layer of square timber fixed with diagonal nails. The top surface of the top layer of square timber is in close contact with the bottom surface of the inner side panel of the casing, and the bottom surface of the bottom layer of square timber rests flat on the top surface of the foundation. The square timber pads will undergo a certain degree of compression deformation after being compressed by the weight of the casing. This deformation helps to form a uniform bonding stress between the square timber and the two contact surfaces of the casing and the foundation, thus playing a role in assisting in distributing the load.

[0074] After all temporary support legs, pads, and timber supports have been installed, inspected, and confirmed to be secure, the continuous lowering device is operated to slowly and synchronously unload the load. During unloading, the main cylinder pressure of each continuous hydraulic jack gradually decreases, causing the steel strand bundle to loosen. The annular structure begins to transfer its own weight load from the lifting point to the temporary support legs and timber supports below. During unloading, the operator continuously observes whether there are signs of slippage or uneven settlement between the horizontal base plate and the support plate of each set of temporary support legs, and between the timber and the top surface of the pier. If a gap appears at a certain set of support legs, the corresponding jack is reloaded until the support leg just leaves contact, the support plate is re-tightened, or steel shims are added before unloading. After unloading is completed, the load reading of the continuous hydraulic jack returns to zero or drops to the value corresponding to the self-weight of the steel strand. At this point, the annular structure is completely supported by the support system on the top surface of the pier, completing the transfer of the lowering load. Subsequently, the lifting equipment of the continuous lowering device can be released, and subsequent lifting point switching operations can be performed.

[0075] In one or more embodiments of the present invention, after step S6, the method further includes: performing on-site anti-corrosion coating repair work on the connecting weld between adjacent segments in the new annular structure, wherein the anti-corrosion coating repair work sequentially includes applying zinc-rich anti-rust primer, applying epoxy micaceous iron oxide intermediate paint and applying polysiloxane topcoat.

[0076] On-site anti-corrosion coating touch-up is carried out in the order from base to top, applying zinc-rich anti-rust primer, epoxy micaceous iron oxide intermediate paint, and polysiloxane topcoat in sequence, so as to ensure that the anti-corrosion system at the weld joint is continuous and equivalent to the anti-corrosion system completed in the factory.

[0077] Before starting the touch-up coating operation, the surface of the weld and the steel surface within a 50mm width on both sides should be treated. Use an electric wire wheel and angle grinder to clean and grind the weld area to remove weld slag, spatter, oxide scale, and the heat-induced discoloration layer generated during welding, until the surface has a uniform metallic luster, meeting the St3 treatment requirements specified in ISO 8501-1 standard. After grinding, use dry, oil-free compressed air or a clean brush to remove surface dust and debris, and wipe both sides of the weld with a cotton cloth dampened with thinner to remove any residual oil. The treated area should proceed to the coating process as soon as possible. If the interval exceeds 4 hours or rust has appeared on the surface, it needs to be re-grinded before proceeding with the coating.

[0078] At the start of the coating operation, a zinc-rich anti-rust primer is applied first. This primer is an epoxy zinc-rich type coating. The zinc powder in the coating forms an electrochemical contact with the steel substrate after film formation. When the coating is partially damaged, the zinc powder acts as a sacrificial anode, preferentially corroding and providing cathodic protection to the exposed steel surface. Before coating, the main agent and hardener of the paint are mixed according to the proportions specified in the product instructions and thoroughly stirred with an electric mixer until the color is uniform. It is then allowed to mature for a certain period before use. Because the weld seams on site are scattered and relatively small, a roller brush is used for primer application. Before use, the roller brush is repeatedly rolled and cleaned in clean water to remove loose fibers and impurities, then shaken dry before dipping it in paint. When applying the paint, first roll it two to three times vertically in a "W" shaped path on both sides of the weld seam to spread the paint evenly. Then, lightly press the roller horizontally, controlling the width of each section to be within four times the length of the roller. The overlap between adjacent sections should be about one-third of the width to eliminate overlapping roller marks. The primer coating should achieve a dry film thickness of at least 75 μm after drying. If a single coat fails to reach the specified thickness, an additional coat can be applied after the previous coat is surface dry but before it is fully dry, until the dry film thickness meets the requirements. After the primer is fully dry, the weld area should be randomly inspected using a wet film thickness gauge or a magnetic dry film thickness gauge. If any measuring point is less than 85% of the specified thickness and still fails to meet the standard after retesting, the area should be re-coated with primer.

[0079] After the primer layer has passed inspection and fully cured, the epoxy micaceous iron oxide intermediate coat is applied. The film-forming material of the epoxy micaceous iron oxide intermediate coat is epoxy resin, and the pigment contains micaceous iron oxide. The micaceous iron oxide has a lamellar structure and is arranged in layers within the coating, which can extend the path of corrosive media penetrating the coating, thus providing shielding protection. The intermediate coat also uses a two-component formulation, and is thoroughly stirred after mixing. Two coats of the intermediate coat are required, each with a dry film thickness of 200μm, for a total dry film thickness of 400μm. The first coat of the intermediate coat is applied using a roller, with the application method the same as the primer, but in a direction perpendicular to the primer layer to eliminate potential pinholes. After the first coat of the intermediate coat has completely dried, the film thickness is checked with a thickness gauge. Only after confirming it is acceptable can the second coat of the intermediate coat be applied. The application method for the second coat is the same as the first coat, with sufficient interval between the two coats to avoid blistering or decreased adhesion due to solvent retention. If air bubbles are found in the coating during the intermediate paint application process, after the coating has dried slightly, use a small amount of the same type of paint to press and fill the air bubble area.

[0080] After the intermediate paint system reaches the specified total dry film thickness and cures, the polysiloxane topcoat is applied. The film-forming material of the polysiloxane topcoat is an organosilicon-modified acrylic polysiloxane resin. After curing, it forms a chemically stable coating that maintains its gloss and color under sunlight and marine atmospheric conditions, providing long-term UV aging and corrosion protection for the underlying coating. During topcoat application, the roller is dipped in the topcoat and evenly rolled over the weld area, alternating light pressure in both horizontal and vertical directions to ensure uniform coating thickness. One coat of topcoat should achieve a dry film thickness of 100μm. After application, the paint film surface should have smooth lines and a color consistent with adjacent painted areas.

[0081] All painting operations are conducted under natural or mechanical ventilation conditions, with continuous monitoring of environmental conditions in the work area during operation. The relative humidity of the air during painting operations must be below 85%, the surface temperature of the steel plate must be at least 3°C ​​above the dew point temperature, and the ambient temperature must be above 5°C. When wind speeds are high and dust may be stirred up, dust barriers must be erected around the work area; when rain or dense fog is forecast, outdoor painting operations must be stopped in advance, and uncured coating areas must be covered with waterproof tarpaulins. After all on-site anti-corrosion coating touch-ups are completed, the total dry film thickness of the coating is finally inspected. A magnetic dry film thickness gauge is used to measure the film thickness at several points per meter along the weld length, and the film thickness value at each measuring point is recorded. The adhesion of the coating system is tested using the pull-out method. Test points are selected near the weld area, and the tensile strength between the coating and the steel surface is measured using a pull-out tester, requiring an adhesion of not less than 5.0 MPa. Areas that pass the test are repaired by recoating the test points as needed to maintain the overall continuity of the coating. The on-site anti-corrosion coating repair completed through the above steps ensures that the anti-corrosion performance of the newly added welds in the new ring structure is consistent with that of the main body of the anti-collision steel tank, meeting the requirements for long-term use in marine environments.

[0082] This invention fundamentally solves the installation problem of bridge pier anti-collision facilities in complex and overlapping construction environments through a process path of "vertical segmented load reduction, low-level cyclic assembly, synchronous lowering, and lifting point conversion." By further dividing each arc-shaped segment vertically into multiple blocks, the weight of a single block can be limited to the lifting capacity of the tower cranes and crawler cranes on the construction site, thus completely eliminating reliance on large floating cranes or external lifting vessels. This significantly saves on high vessel and machinery rental costs and eliminates the irreconcilable temporal and spatial conflicts between floating crane operations and the main tower construction. All assembly operations are always carried out at a low level above the pier cap. After each layer of the ring structure is completed, multiple continuous jacks are used to synchronously lower the entire structure and change the lifting points, ensuring that the assembled structure remains within a safe height range, with a small windward area, significantly reducing construction risks under adverse weather conditions such as typhoons and monsoons. The synchronous lowering control system adjusts the displacement and load of each lifting point in real time to ensure the ring structure is lowered smoothly and centrally, avoiding structural deformation or jamming due to uneven stress. The cyclical assembly and lowering processes can be completed concurrently with the main tower construction without affecting critical construction schedules, ensuring a controllable construction cycle. This method requires fewer large temporary facilities and allows for the reuse of existing construction platforms and conventional lifting equipment, further reducing project costs and providing a reliable construction approach for the safe, efficient, and economical installation of bridge pier anti-collision facilities.

[0083] The above provides a detailed description of the installation method for a bridge pier anti-collision facility. Specific examples have been used to illustrate the principle and implementation of the invention. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​the invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the invention. Therefore, the content of this specification should not be construed as a limitation of the invention.

Claims

1. A method for installing anti-collision facilities on bridge piers, characterized in that, The method includes: S1. Divide the annular anti-collision steel casing into several arc-shaped segments along the circumferential direction, and divide each arc-shaped segment into several blocks along the vertical direction; wherein, the weight of a single block does not exceed the maximum lifting capacity of the lifting equipment on the construction platform; S2. Install a lowering support on the top of the pier cap, and configure a continuous lowering device on the lowering support; S3. Use the lifting equipment to hoist the bottom block into place and connect adjacent bottom blocks into a ring structure; S4. Operate the continuous lowering device to lower the assembled ring structure as a whole by one segment vertical height; S5. Temporarily fix the lowered ring structure, disconnect the continuous lowering device from the ring structure, and change the lifting point of the continuous lowering device to another preset lifting point position on the ring structure. S6. Using the lifting equipment, the upper layer segment is hoisted to the top surface of the lowered ring structure, and adjacent segments and upper and lower layer segments are connected to form a new ring structure. S7. Repeat steps S4 to S6 until all blocks are assembled and the final ring structure is lowered to the design elevation.

2. The method according to claim 1, characterized in that, The lowering support includes type A, type B, type C, and type D supports. Type A supports are used to install the continuous lowering device. Type B supports are set in areas without a construction platform to assist in segment positioning and enhance the stability of the assembled ring structure. Type C supports are set at the bottom of the construction platform to assist in positioning and support the temporary beam passage. Type D supports are set at the bottom of the guide frame platform to assist in segment positioning and enhance the stability of the assembled ring structure.

3. The method according to claim 1, characterized in that, Before step S3, the method further includes: pre-embedding several sets of pre-embedded parts around the pier cap, and welding and fixing a horizontal cantilever beam on each set of pre-embedded parts, wherein the horizontal cantilever beam is arranged radially around the pier cap; the horizontal cantilever beam is used to support the bottom block during the assembly stage.

4. The method according to claim 3, characterized in that, The continuous lowering device includes 16 continuous jacks, 4 hydraulic pump stations, and 1 computer control system. The rated load capacity of each continuous jack is not less than 1.2 times the weight it bears. The computer control system collects the vertical displacement and load values ​​of each lifting point in real time through displacement sensors and pressure sensors. One lifting point is the master lifting point, and the other lifting points are the follow-up lifting points. The lowering speed of each follow-up lifting point is dynamically adjusted through electro-hydraulic proportional control technology so that the synchronous displacement deviation between each lifting point is not greater than 5mm.

5. The method according to claim 4, characterized in that, Before step S3, the method further includes: welding several sets of rigid guide structures to the inner wall of the bottom section of the annular anti-collision steel casing, with each set of guide structures corresponding to the position of an A-type bracket; during the lowering process, the guide structures maintain sliding contact with the outer wall of the pier caisson to limit the radial displacement of the annular structure.

6. The method according to claim 5, characterized in that, Several reinforced rubber water bladders are also installed on the inner wall of the annular anti-collision steel casing, and each water bladder is equipped with a water injection valve at the top. In step S7, after the final annular structure is lowered to the design elevation, water is injected into the water bladder to make it expand and fill the annular gap between the annular structure and the outer wall of the pier caisson. The water bladder is vacuum treated before installation to make it in a contracted state.

7. The method according to claim 6, characterized in that, Before step S1, the process also includes: dismantling the Bailey beam connection platforms between the No. 1, No. 3 and No. 5 guide frames and the pier cap in batches on the pier construction platform; after completing one or more overall lowering operations, restoring part of the Bailey beam connection platforms using temporary beam structures composed of H-beams to maintain at least one passage for personnel and material transportation.

8. The method according to claim 7, characterized in that, The connection between adjacent bottom blocks in step S3, and the connection between adjacent upper blocks and between upper blocks and the lowered ring structure in step S6, all adopt the following process: the horizontal plate of the lower block at the segment position is extended outward by 2cm as a welding backing during the processing stage, and CO2 gas shielded welding is used for welding during on-site assembly; the outer plate and the transverse partition are butt welded with a single-sided bevel weld, and the remaining parts are connected with fillet welds, and the weld leg height of the fillet weld is not less than 6mm.

9. The method according to claim 8, characterized in that, The temporary fixing of the lowered annular structure in step S5 includes: installing several sets of temporary hanging legs between the vertical partition on the inner wall of the annular structure and the pier cap; the lower end of the temporary hanging legs is supported on the top surface of the pier cap by means of a support plate and a pad; and setting a set of square timber pads every 2m along the inner circumference of the annular structure to transfer the load of the annular structure from the continuous lowering device to the pier cap.

10. The method according to claim 9, characterized in that, After step S6, the process further includes: performing on-site anti-corrosion coating repair work on the connecting welds between adjacent segments in the new annular structure. The anti-corrosion coating repair work includes, in sequence, applying zinc-rich anti-rust primer, applying epoxy micaceous iron oxide intermediate paint, and applying polysiloxane topcoat.

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