A method for dismantling discontinuous sections of a multi-span cast-in-place box girder pier top without scaffolding.

Abstract

This invention discloses a method for dismantling discontinuous sections of a multi-span cast-in-place box girder pier top without scaffolding. First, the base surface of the discontinuous section area at the pier top is surveyed and cleaned. Then, the gaps in the pier top supports and expansion joints are backfilled, creating a close-fitting force-transfer structure between the bottom of the discontinuous girder and the top surface of the pier. Next, holes are drilled from the top plate of the box girder into the solid area at the pier top, anchors are inserted, and the anchors are tensioned and anchored, making the discontinuous box girder and pier an integral load-bearing structure. Finally, after anchoring, the discontinuous section at the pier top is cut and hoisted for dismantling. Based on this, this invention completely eliminates the need for the entire process of erecting, reinforcing, and dismantling steel pipe supports and brackets for discontinuous sections at the pier top of side spans. It eliminates the need for large-scale steel rental and labor / machinery investment, significantly reducing the construction cost of dismantling a single discontinuous section and greatly improving the economic benefits of old bridge demolition projects.

Description

Technical Field

[0001] This invention relates to the field of bridge reconstruction and expansion, and old bridge demolition construction technology, specifically a method for demolishing discontinuous sections of a multi-span cast-in-place box girder pier top without scaffolding. Background Technology

[0002] Multi-span cast-in-place reinforced / prestressed concrete box girders generally adopt a combined structural form of "continuously fixed at the pier top in the middle span and simply supported discontinuous at the pier top in the side spans". In the middle span, the beams at the top of each pier are fixed to the piers to form a continuous section at the pier top, which has good structural integrity and continuous and stable stress. However, the pier tops of the side spans at both ends of the bridge are equipped with supports and expansion joints, forming discontinuous sections at the pier tops. In this area, the beams are not rigidly fixed to the piers and rely only on the vertical support of the supports and the expansion joint gaps to adapt to deformation. This results in a strong structural independence but poor overall stability.

[0003] During the demolition and reconstruction of the old bridge, the conventional demolition sequence is to first demolish the continuous section at the top of the mid-span piers and the standard segments of each span, and finally demolish the discontinuous sections at the top of the end span piers. After the continuous section of the mid-span and the standard segments of the main span are completely demolished, the remaining discontinuous sections at the top of the end span piers become isolated, cantilevered structures with no constraint from adjacent beams. Relying only on single-point support, they are extremely prone to overturning, torsion, and slippage under their own weight, making them the highest-risk construction part during the box girder demolition process.

[0004] To address the risk of instability in discontinuous sections at the pier top, existing traditional construction techniques employ a passive support and stabilization scheme: full-span steel pipe scaffolds and temporary support brackets are erected on both sides of the side span pier. This external support system bears the self-weight of the discontinuous section, resists the overturning moment, and prevents the beam from overturning and falling. The support system is then dismantled after the discontinuous section is cut and hoisted. This traditional construction process is a common industry practice and is adopted by the conventional support requirements of the "Technical Specification for Construction of Highway Bridge Demolition Engineering JTG / T3650-2020". Various published patents and construction documents also use the conventional "scaffold support + cutting and demolition" model.

[0005] Based on a review of existing technologies and a summary of engineering applications, the traditional dismantling process for discontinuous support structures on pier tops has the following significant technical defects and industry pain points: First, the scaffolding erection project is large in scale and has high construction costs. A full-coverage steel pipe support system needs to be erected for each discontinuous section of the side span pier top. The total scaffolding volume for multi-span bridges and multiple endpoints is huge, requiring a large amount of steel rental, labor for erection and dismantling, which significantly increases the cost of demolishing the old bridge and makes it uneconomical.

[0006] Secondly, the preparatory procedures are cumbersome and the construction period is lengthy. Traditional processes require multiple preparatory procedures to be completed in advance, such as site leveling, scaffolding layout, layered erection, stress calculation, and reinforcement acceptance. The erection, maintenance, and dismantling of scaffolding occupy a large amount of critical construction time, resulting in an uncontrollable overall bridge demolition schedule and making it unsuitable for the rapid construction needs of urban reconstruction and expansion projects.

[0007] Third, poor site adaptability and severe construction limitations. Urban bridge piers generally have dense underground pipelines, narrow construction space, limited ground hardening, and mountainous bridges are limited by terrain, making it impossible to set up large-area scaffolding. This makes it impossible to implement traditional support techniques and greatly limits the applicable scenarios for the demolition of discontinuous sections of side spans.

[0008] Fourth, the safety of passive support is insufficient. Temporary steel pipe supports are prefabricated structures erected manually, which have hidden dangers such as node gaps, uneven stress, foundation settlement, and local instability. Moreover, the supports can only provide vertical support and cannot restrain the horizontal sliding and torsion of the beam. There is still a risk of slight swaying and displacement during the dismantling of discontinuous sections, which can easily cause beam cracking and structural disturbance, resulting in low construction safety redundancy.

[0009] In summary, the current industry relies entirely on external scaffolding for the passive support of discontinuous sections at the top of piers of multi-span box girders. There is no technical solution to achieve self-stabilizing dismantling without scaffolding through active structural anchoring and reinforcement. This approach suffers from numerous technical shortcomings, such as high cost, long construction period, limited site space, and poor safety and stability. Therefore, a scaffolding-free construction method for dismantling discontinuous sections at the top of piers of multi-span cast-in-place box girders is invented. Summary of the Invention

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for dismantling discontinuous sections at the pier top of a multi-span cast-in-place box girder without scaffolding includes the following steps: Pre-construction preparation and base surface cleaning: Survey the base surface of the discontinuous section at the top of the pier and clean it; Fine aggregate concrete backfilling: Backfilling the gaps in the pier top support and expansion joints to create a close-fitting force-transfer structure between the bottom of the discontinuous beam section and the top surface of the pier top. Drilling and rebar installation, tensioning and anchoring: Drill holes from the top plate of the box girder to the solid area at the top of the pier, insert anchors, and tension and anchor the anchors to make the discontinuous box girder and the pier anchored as an integral load-bearing structure. Cutting and hoisting dismantling: After anchoring is completed, the discontinuous section on the top of the pier is cut and hoisted for dismantling.

[0011] As a preferred embodiment of the construction method for dismantling the non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the specific steps of the pre-construction preparation and base surface cleaning include: surveying the non-continuous section area of ​​the multi-span cast-in-place box girder pier top and checking the debris in the gap between the supports and expansion joints; cleaning the garbage, laitance, and accumulated water on the pier top base surface to ensure that the supports and expansion joint areas are clean and dry; and simultaneously verifying the dimensions and self-weight parameters of the non-continuous section beam to determine the subsequent drilling and rebar installation positions and anchorage depths.

[0012] As a preferred embodiment of the construction method for dismantling the non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the specific steps of the fine stone concrete backfilling include: using fine stone concrete to backfill and compact the support suspension gap and expansion joint hollow area of ​​the non-continuous section of the pier top, so as to eliminate the gap between the beam and the pier top and limit the slippage and misalignment deformation of the beam.

[0013] As a preferred embodiment of the construction method for dismantling a non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the specific steps of drilling, rebar installation, tensioning, and anchoring include: positioning and drilling holes at the top of the top slab of the non-continuous section of the cast-in-place box girder pier top, with the drilling depth extending to the solid area of ​​the pier top; after cleaning dust and debris from the holes, inserting anchors, and tensioning, anchoring, and locking the anchors, so as to actively counteract the overturning moment, horizontal sliding force, and torsional shear force generated by the self-weight of the non-continuous section through the tensioning and anchoring force of the anchors.

[0014] As a preferred embodiment of the construction method for dismantling a non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the specific steps of cutting and hoisting dismantling include: after the concrete backfill strength and the tensioning and anchoring performance of the anchors have been verified as qualified, a crane is placed at the un-dismantled bridge span structure, and the non-continuous section to be dismantled is connected by a lifting tool or rope; after applying the hoisting force, a wire saw is used to cut the non-continuous section, and the anchors are cut synchronously with the section; and the crane is used to complete the hoisting and removal of the cut section.

[0015] As a preferred embodiment of the construction method for dismantling the non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, after the cutting and hoisting dismantling steps, a post-completion finishing process is also included: performing a finishing process to remove the residue on the pier top.

[0016] As a preferred embodiment of the construction method for dismantling the non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the specific steps of the post-construction finishing process include: recycling or cutting the remaining anchor components after the complete dismantling of the non-continuous section at the pier top, and cleaning up the remaining concrete and construction waste at the pier top; repeating the pre-construction preparation and base cleaning, fine stone concrete backfilling, drilling and rebar installation, tensioning and anchoring, cutting and hoisting dismantling, and post-construction finishing process to carry out the dismantling operation of the next section of the bridge.

[0017] As a preferred embodiment of the construction method for dismantling the non-continuous section of the pier top of a multi-span cast-in-place box girder without support as described in this invention, the fine stone concrete is set as C50 high-strength fine stone concrete.

[0018] As a preferred embodiment of the construction method for dismantling the non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the anchor is set as a finely rolled threaded steel bar.

[0019] As a preferred embodiment of the construction method for dismantling a non-continuous section of a multi-span cast-in-place box girder pier top without support as described in this invention, the drilling depth extends to 1-2m below the solid area of ​​the pier top, and the drilling depth is determined according to the self-weight of the dismantled non-continuous section.

[0020] Compared with existing technologies: 1. Completely eliminate the temporary support system and significantly reduce project costs: This invention completely eliminates the entire process of erecting, reinforcing and dismantling the steel pipe supports and support brackets for the discontinuous sections of the side span pier top. It eliminates the need for large-scale steel rental and labor and machinery investment, greatly reducing the construction cost of demolishing a single discontinuous section and greatly improving the economic benefits of old bridge demolition projects. 2. Streamlined construction procedures and significantly shortened construction period: Eliminates cumbersome pre-construction procedures such as site leveling, scaffold erection, stress calculation, acceptance and dismantling, greatly shortens the construction period of non-continuous sections, avoids the problem of uncontrollable construction period of traditional scaffold construction, and perfectly adapts to the construction needs of bridge reconstruction and expansion projects for rapid construction and time-limited completion. 3. Active anchoring and stabilization significantly improves construction safety: Traditional supports can only provide passive vertical support and cannot restrain slippage and torsion; This invention achieves bottom compaction and force transmission through concrete backfilling and achieves overall rigid connection through deep tensioning and rebar installation, actively resisting multi-dimensional loads such as overturning, slippage, and torsion, and completely eliminating the safety hazards of swaying, shifting, overturning, and falling during the dismantling of discontinuous sections. The construction safety redundancy is far higher than that of traditional processes. 4. Breaking through site limitations and highly adaptable to working conditions: This invention does not require a large area of ​​flat construction site, does not occupy the passage space under the bridge, and does not touch underground pipelines. It is perfectly adapted to the demolition of discontinuous sections on the top of piers in narrow urban spaces and restricted sites, solving the industry problem that traditional processes cannot be carried out in complex urban conditions. 5. Minimal structural disturbance and controllable construction quality: This invention adopts active anchoring and static cutting and dismantling methods, eliminating problems such as support settlement, sudden stress changes, and structural impact. The stress in the beam is stable, maximizing the protection of the integrity of the original pier and surrounding structure. It features high construction precision and minimal structural disturbance, meeting the green, safe, and refined construction standards for urban bridges. Attached Figure Description

[0021] Figure 1 This is a general diagram showing the dismantling sequence of the present invention; Figure 2 For the present invention Figure 1 Section AA; Figure 3 This is a diagram of a segment (bridge span segment) to be dismantled in sequence according to the present invention; Figure 4 This is a diagram of the second-order dismantling segment (segment at the bridge span support) of the present invention; Figure 5 This is a diagram of the three-stage demolition segment (continuous segment at the pier top) of the present invention; Figure 6 This is a diagram of the four-stage dismantling segments (non-continuous segments) of the present invention; Figure 7 This is a schematic diagram of the overall process of the present invention.

[0022] In the diagram: cyan refers to the first-order demolition segment (bridge span segment); magenta refers to the second-order demolition segment (segment at the bridge span support); green refers to the third-order demolition segment (continuous segment at the pier top); and yellow refers to the fourth-order demolition segment (discontinuous segment). Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0024] This invention relates to a method for dismantling discontinuous sections at the pier top of a multi-span cast-in-place box girder without scaffolding. Please refer to [link to relevant documentation]. Figures 1-7 The core technical principle is as follows: Addressing the independent and easily overturned structural characteristics of the discontinuous section at the pier top in a bearing + expansion joint configuration, high-strength fine-aggregate concrete is first used to backfill the area from the pier top bearing to the bottom of the discontinuous cast-in-place box girder, eliminating structural voids and achieving initial force transmission through a close fit at the pier top. Then, by drilling holes in the top slab, deeply embedding precision-rolled threaded steel bars, and tensioning and anchoring, the discontinuous box girder is rigidly anchored to the pier top of the lower pier as a whole, actively resisting overturning, slippage, and torsional moments due to its own weight. No temporary steel pipe supports are required, allowing for direct completion of the discontinuous section cutting, hoisting, and dismantling operations. Specific construction steps are as follows: Pre-construction preparation and base surface cleaning: Before the bridge demolition, a comprehensive survey was conducted on the discontinuous section of the multi-span cast-in-place box girder pier top. Debris was inspected in the bearings and expansion joint gaps, and garbage, laitance, and water were removed from the pier top surface to ensure the bearing and expansion joint areas were clean and dry, providing a good interface for subsequent concrete backfilling. Simultaneously, the dimensions and self-weight parameters of the discontinuous girder section were verified to determine the drilling and anchoring depth of the reinforcing bars.

[0025] Fine aggregate concrete backfill: For the gaps in the supports and the open areas of the expansion joints in the discontinuous section at the pier top, C50 high-strength fine aggregate concrete was used for overall backfilling and compaction. By replacing the original open gaps with high-strength concrete, the gap between the beam and the pier top is eliminated, ensuring that the bottom of the discontinuous beam is fully in contact with the top surface of the pier, and that force is transmitted evenly. This prevents localized suspension and stress concentration, and provides preliminary rigid support and restraint at the bottom of the discontinuous section at the pier top, limiting minor slippage and misalignment deformation of the beam.

[0026] Drilling and rebar installation, tensioning and anchoring: (1) Drill holes precisely at the top of the cast-in-place box girder top plate in the discontinuous section of the pier. The drilling depth is controlled to be 1-2m below the pier top (the depth of rebar installation is determined by removing the self-weight of the segment). The holes penetrate the top plate of the box girder and extend to the solid area of ​​the pier top. After drilling, clean the dust and debris in the holes, insert fine-rolled threaded steel bars, and tension, anchor and lock the fine-rolled threaded steel bars.

[0027] (2) By planting deep reinforcement at the top of the pier and tensioning and anchoring, the upper discontinuous box girder structure is rigidly connected to the lower pier body to form an overall anchoring system from top to bottom. The tensioning and anchoring force of the fine-rolled threaded steel bars is used to actively offset the overturning moment, horizontal sliding force and torsional shear force generated by the self-weight of the discontinuous section, so that the originally isolated and unstable discontinuous section is completely locked into an overall self-stable structure.

[0028] Cutting and hoisting dismantling: (1) After the demolition of the continuous section of the pier top and the standard bridge span segments of the whole bridge are completed, the demolition of the non-continuous section of the pier top cast-in-place box girder segments can only be carried out after the concrete backfill consolidation strength reaches the standard, the fine-rolled threaded steel bar anchoring tension is completed, and the structural self-stability performance is verified as qualified.

[0029] (2) Place the crane at the bridge span that has not been demolished, and use special lifting tools or ropes to connect the crane and the demolition segment. After being stressed, use wire saw cutting equipment to cut and demolish the discontinuous section on the top of the pier. The fine-rolled threaded steel bars are cut and demolished simultaneously with the segment.

[0030] (3) The crane is used to directly complete the smooth hoisting and removal of the cut segments. The entire process relies on the active reinforcement system of "concrete backfilling + rebar tensioning and anchoring" to maintain structural stability and eliminate the risk of overturning and sliding.

[0031] Post-production finishing touches: (1) After the discontinuous section of the bridge pier top is completely demolished, the rebar components are recycled or cut and treated, the residual concrete and construction waste on the pier top are cleaned up, and all construction procedures for the dismantling of the discontinuous section of the pier top without support are completed.

[0032] (2) After the first section of the bridge is demolished, repeat the above construction steps to demolish the remaining sections of the bridge.

[0033] Based on the above, the present invention also includes equivalent alternative embodiments. Based on the core technical mechanism of "backfilling and force transfer in the pier top support area + deep rebar tensioning and anchoring to achieve self-stabilizing demolition without support", the following equivalent adjustments can be made according to the actual engineering conditions, all of which fall within the protection scope of this invention: Material parameter equivalent adjustment For discontinuous sections with large cross-sections and beam heights ≥ 2.5m and self-weights > 120t, the backfill concrete strength grade can be upgraded to C55, the rebar installation depth can be adjusted to 2m below the pier top, the precision-rolled threaded steel bar specification can be upgraded to φ32mm, and the single-bar tension control stress can be correspondingly increased to 330MPa to ensure that the anchorage force meets the anti-overturning requirements under heavy self-weight conditions. For discontinuous sections with small box girders and spans ≤ 20m and self-weights < 40t, C40 fine aggregate concrete can be used for backfilling, the rebar installation depth can be reduced to 1m below the pier top, and the number of rebars can be reduced accordingly, thereby reducing construction costs while ensuring safety.

[0034] equivalent replacement of anchor type High-strength prestressed steel bars can be used to replace finely rolled threaded steel bars as anchoring components, and corresponding anchors can be used for tensioning and locking. The anchoring force transmission mechanism is completely consistent with the present invention. For discontinuous sections of lightweight box girders with small self-weight, high-strength chemical anchors can also be used to replace tensioned rebars. The anchoring force is provided by the bonding force of the rebar adhesive, omitting the tensioning process and further simplifying the construction process.

[0035] Equivalent replacement of backfill materials For applications with small support gaps (≤10cm), high-strength non-shrink grout can be used to replace fine aggregate concrete for pressure grouting backfilling, improving the filling density of narrow gaps and shortening the curing period. For low-temperature construction environments, early-strength admixtures can be added to fine aggregate concrete to prepare early-strength backfill concrete, accelerating the strength growth rate and meeting the needs of rapid construction in urban renovation and expansion projects.

[0036] Equivalent adjustment of cutting process For small, discontinuous sections that need to be demolished in sections, diamond circular saws can be used instead of wire saws for section cutting; for cases where surrounding buildings have extremely high requirements for vibration control, static fracturing agents can be used in conjunction with mechanical cutting to further reduce construction vibration and disturbance. The above process adjustments do not change the core construction logic of the supportless active anchoring of this invention.

[0037] In conjunction with the above, the present invention includes, but is not limited to, the following embodiments: This embodiment is a concrete application of the above construction method in a real project, used to further illustrate the feasibility and technical effectiveness of this solution: This embodiment is applied to a city expressway reconstruction and expansion project. The object to be demolished is a four-span cast-in-place prestressed concrete box girder with a span combination of 30m+35m+35m+30m. The box girder height is 1.8m, the top slab width is 25m, and the bottom slab width is 12m. The tops of the end spans of the bridge are discontinuous sections, with a single-sided cantilever length of 2.2m. The self-weight of a single discontinuous section is approximately 95t (considering the box girder's hollowness and the reduction of the flange's gradually changing cross-section). Plate rubber bearings and modular expansion joints are installed on the tops of the piers. The area beneath the bridge is an existing main urban road with multiple underground pipelines for rainwater, sewage, electricity, and communications. The construction space is narrow, and full-span scaffolding cannot be erected. Therefore, the scaffold-free demolition method of this invention is adopted. The specific implementation process is as follows: Pre-construction preparation and base surface cleaning Before construction, a total station was used to re-measure the profile of the discontinuous section at the top of the two end spans of the pier to confirm that the actual dimensions of the beam deviated from the design documents by ≤2cm. Deposits and grout and water accumulation in the expansion joints and on the surface of the pier top were cleaned manually. An air compressor was used to blow away the gaps around the supports to ensure that the backfill interface was dry and free of dust. Based on the calculation results of the self-weight and overturning moment of the discontinuous section, it was determined that 8 rebars would be arranged at the top of each end of the pier, in a double-row rectangular symmetrical arrangement, with the anchoring depth set at 1.5m below the top of the pier.

[0038] Fine aggregate concrete backfill C50 fine aggregate concrete (5-10mm aggregate size) with added micro-expansion agent was used to backfill the gaps in the pier top support and the hollow areas of the expansion joints in layers. The thickness of each layer was controlled within 15cm, and compaction was carried out using a small immersion vibrator. The backfilling area covered the entire width of the bottom of the discontinuous beam section and the corresponding pier top area, as well as the gaps in the surrounding support and the expansion joint area. The filling thickness was based on densely filling the gaps, without raising the original design elevation of the beam. After backfilling, geotextile was covered and water was sprayed for curing. During the curing period, the strength was tested according to the specifications. When using C50 fine aggregate concrete, the next process could proceed only after the rebound test showed that the strength reached 90% of the design strength after 7 days of curing. When using early-strength grouting material, the next process could proceed only after the compressive strength reached 40MPa or more after 24 hours.

[0039] Drilling and rebar installation, tensioning and anchoring A rebar detector was used to determine the distribution of the main reinforcing bars inside the pier top, and the drilling points were adjusted to avoid the main reinforcing bars. Then, a diamond water drill was used to drill holes in the top slab of the box girder at the adjusted points, with a hole diameter of φ30mm. Special epoxy anchoring adhesive (Grade A, tensile strength ≥30MPa) was used, with an injection fullness of ≥90%. The vertical deviation of the drilling was controlled within 1°, and the hole depth penetrated the top slab of the box girder and reached 1.5m into the solid area of ​​the pier top. The holes were cleaned with a high-pressure water gun and then dried with an air compressor to ensure that there was no dust or residue on the hole wall. φ25mm precision-rolled threaded steel bars were then inserted, and Grade A epoxy anchoring adhesive was used for injection, with an injection fullness of ≥90%. After the anchoring adhesive has cured to the required standard, the fine-rolled threaded steel bars are tensioned in stages using a through-hole jack. The tensioning stress of a single bar is controlled at 750MPa (corresponding to 0.75 times the yield strength of fine-rolled threaded steel bar PSB830, and the stress loss is controlled within 10% after locking). After tensioning, the matching nuts are used to lock the system, forming a rigid anchoring system from top to bottom.

[0040] Cutting and hoisting dismantling After the continuous section at the top of the mid-span pier and all standard segments of the bridge were demolished, on-site testing confirmed that the backfill concrete strength and rebar anchoring force met the design requirements, and the self-stabilizing performance of the discontinuous section structure was verified as qualified, demolition work commenced. A 200t truck crane (with a rated lifting capacity ≥120t under main boom conditions, meeting the 1.5 times safety factor requirement) was selected and parked on the hardened roadbed of the adjacent demolished span. The discontinuous segment was bound using a four-point lifting device, with the pre-lifting force taken as 1.3 times the segment's self-weight, and considering a dynamic load factor of 1.2 and an imbalance factor of 1.1, the overall safety factor was not less than 1.5. After confirming that the lifting points were evenly stressed, a diamond wire saw was used to cut the discontinuous section as a whole along the preset dividing line, simultaneously cutting the precision-rolled threaded steel bars during the cutting process. After cutting, the section was lifted smoothly and transported to the designated crushing site.

[0041] Post-production finishing touches After the discontinuous section was hoisted, the exposed ends of the fine-threaded steel bars on the pier top were cut using an angle grinder. Excess backfilled fine aggregate concrete on the pier top surface was removed, construction waste was cleaned up, and the pier top base surface was restored to flatness. After the construction of this section was completed, the dismantling of the remaining box girder sections was carried out using the same procedures.

[0042] Compared with traditional support technology, this embodiment reduces the construction cost and shortens the construction period for dismantling single-end discontinuous sections. It does not occupy the passage space under the bridge, does not touch underground pipelines, and there is no structural shaking or displacement during the construction process, which verifies the economy, adaptability and safety of this method.

[0043] Although the present invention has been described above with reference to embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of the invention. In particular, as long as there is no structural conflict, the features in the disclosed embodiments can be combined with each other in any manner. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, the present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, characterized in that, Includes the following steps: Pre-construction preparation and base surface cleaning: Survey the base surface of the discontinuous section at the top of the pier and clean it; Fine aggregate concrete backfilling: Backfilling the gaps in the pier top support and expansion joints to create a close-fitting force-transfer structure between the bottom of the discontinuous beam section and the top surface of the pier top. Drilling and rebar installation, tensioning and anchoring: Drill holes from the top plate of the box girder to the solid area at the top of the pier, insert anchors, and tension and anchor the anchors to make the discontinuous box girder and the pier anchored as an integral load-bearing structure. Cutting and hoisting dismantling: After anchoring is completed, the discontinuous section on the top of the pier is cut and hoisted for dismantling.

2. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 1, is characterized in that... The specific steps for pre-construction preparation and base surface cleaning include: surveying the discontinuous section area at the top of the pier of a multi-span cast-in-place box girder and checking the debris in the gap between the support and the expansion joint; cleaning up the garbage, laitance and water accumulation on the base surface at the top of the pier to ensure that the support and expansion joint area are clean and dry; and at the same time, verifying the dimensions and self-weight parameters of the discontinuous section of the beam to determine the subsequent drilling and anchoring depth of the rebar.

3. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 1, is characterized in that... The specific steps of the fine aggregate concrete backfilling include: using fine aggregate concrete to backfill and compact the gaps in the support suspension space and the hollow area of ​​the expansion joint in the discontinuous section of the pier top, so as to eliminate the gaps between the beam and the pier top and limit the slippage and misalignment deformation of the beam.

4. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 1, is characterized in that... The specific steps of drilling, rebar installation, tensioning and anchoring include: drilling a hole at the top of the cast-in-place box girder top slab in the discontinuous section of the pier top, with the drilling depth extending to the solid area of ​​the pier top; after cleaning the dust and debris in the hole, inserting anchors, and tensioning, anchoring and locking the anchors, so as to actively counteract the overturning moment, horizontal sliding force and torsional shear force generated by the self-weight of the discontinuous section through the tensioning and anchoring force of the anchors.

5. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 1, is characterized in that... The specific steps of cutting and hoisting demolition include: after the concrete backfill strength and the anchoring performance of the anchors have been verified as qualified, the crane is placed at the undemolished bridge span structure, and the discontinuous segments to be demolished are connected by lifting tools or ropes; after applying the hoisting force, the discontinuous segments are cut by wire saw cutting equipment, and the anchors are cut synchronously with the segments; and the crane is used to complete the hoisting and removal of the cut segments.

6. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 5, is characterized in that... Following the cutting and hoisting dismantling steps, post-construction finishing work is also included: performing finishing work to remove residue from the top of the pier.

7. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 6, is characterized in that... The specific steps of the post-construction finishing process include: recycling or cutting the remaining anchor components after the complete demolition of the discontinuous section at the top of the pier, and cleaning up the remaining concrete and construction waste at the top of the pier; repeating the pre-construction preparation and base cleaning, fine stone concrete backfilling, drilling and rebar installation, tensioning and anchoring, cutting and hoisting demolition, and post-construction finishing process to carry out the demolition work of the next section of the bridge.

8. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 3, is characterized in that... The fine aggregate concrete is designated as C50 high-strength fine aggregate concrete.

9. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 4, is characterized in that... The anchor is made of finely rolled threaded steel bar.

10. The method for dismantling a discontinuous section of a multi-span cast-in-place box girder pier top without scaffolding, as described in claim 4, is characterized in that... The drilling depth extends 1-2m below the solid area of ​​the pier top, and the drilling depth is determined according to the self-weight of the discontinuous segments being demolished.

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