Method for different span bridge special-shaped splicing and staggered hole arrangement

Abstract

The application relates to a method for different-span bridge abnormal splicing and staggered-hole arrangement, which comprises the following steps: S1, an old bridge foundation data collection stage; S2, a new bridge main girder structure selection stage, wherein the structure type of the new bridge main girder is determined through span matching degree analysis, rigidity coordination evaluation and main girder type decision; S3, a staggered-hole arrangement condition identification stage, wherein obstacle conditions of new bridge pier position arrangement are identified, the necessity of staggered-hole arrangement is determined, and the staggered-hole arrangement type is divided into a micro-staggered-hole type, a moderate-staggered-hole type and a large-staggered-hole type; S4, a splicing feasibility evaluation stage, wherein a finite element analysis model of the new and old bridges is established, the vertical deflection difference Delta delta and the horizontal relative displacement Delta d of the splicing position are calculated, and the splicing feasibility is determined by comparing with preset limit values; S5, a splicing scheme design stage; and S6, a scheme output stage. Compared with the prior art, the application has the advantages of high system integration, wide span adaptability, fine staggered-hole classification, high rigidity analysis rigor and strong construction feasibility.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering construction, and in particular to a method for irregular splicing and staggered arrangement of spans of bridges with different spans. Background Technology

[0002] With the continuous growth of traffic volume, early-built highway bridges generally face insufficient traffic capacity. Widening existing bridges is an economical and efficient option. Widening typically involves constructing a new bridge on one side of the old one and then laterally connecting the superstructures of the old and new bridges so that they can share the load and work together.

[0003] However, in actual widening projects, new and old bridges often face the following difficulties: First, the old bridge was built earlier, and its span arrangement, structural form, and material properties may differ from those of the new bridge. Direct splicing will lead to excessive differences in the stress state and structural stiffness of the new and old bridges, resulting in a large difference in deflection under the same load, thus causing cracks at the joint. Second, due to external conditions such as road traffic, river navigation, and underground pipelines under the bridge, the piers of the new bridge cannot be aligned with those of the old bridge, resulting in a misaligned arrangement and a deviation in pier position in the longitudinal direction. Third, after the misaligned arrangement, the vertical deformation of the new and old bridges under live loads is not coordinated in the lateral direction, and the conventional ordinary concrete splicing wet joint scheme is difficult to meet the lateral tensile stress generated by vehicle loads.

[0004] CN202511582470.8 discloses a design method for staggered splicing of multi-beam bridges with differential vertical deformation, including the following steps: S1: Based on the staggered relationship between old bridge A, old bridge B, new bridge C, and new bridge D in the multi-beam bridge, calculate the maximum value of the vertical deformation difference; S2: Design the structural forms of rigid splicing structures A and B; S3: According to the settings in S2, calculate the maximum value of the vertical deformation difference in the section where the flexible splicing structure is located; S4: If 90%×Dmax-(i) ≤ Dmax-(i+1) ≤ 110%×Dmax-(i), then the preliminary design is completed and proceeds to step S5; otherwise, return to step S3; if L1 cannot satisfy a value greater than 1 / 2 of min(LA,LC), or L3 cannot satisfy a value greater than 1 / 2 of min(LB,LD), then return to step S2; S5: Further verify whether the transverse stress of the multi-beam bridge meets the design requirements. However, the splicing structure form is singular, and its application scenarios are limited.

[0005] In existing technologies, the design of bridge widening and reconstruction schemes largely relies on experience-based judgment, lacking a systematic and standardized pre-span design methodology. In particular, it lacks an integrated design process capable of simultaneously addressing the two core issues of main girder irregularity selection and staggered span configuration. Therefore, there is an urgent need to develop a pre-span design methodology for bridges of different spans that incorporates main girder selection and staggered span configuration, providing a scientific, systematic, and operable design solution for widening and reconstruction of bridges of varying spans. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for irregular splicing and staggered arrangement of bridges with different spans. The method has high system integration, wide span adaptability, refined staggered hole classification, high mechanical analysis rigor, strong construction feasibility, and guaranteed durability and structural transition.

[0007] The objective of this invention can be achieved through the following technical solutions: This invention provides a method for irregular splicing and staggered span arrangement of bridges with different spans, comprising the following steps: S1: Data collection phase for the old bridge foundation, collecting design parameters, current status inspection data, bridge site environmental conditions data, and design objectives for the reconstruction and expansion project of the old bridge. S2: In the new bridge main girder structure selection stage, based on the span range of the old bridge, the current status of the old bridge main girder and the reconstruction and expansion goals, the new bridge main girder structure type is determined through span matching degree analysis, stiffness coordination assessment and main girder type decision. S3: In the stage of identifying the conditions for misaligned pier placement, the obstacles to the placement of the new bridge piers are identified, the necessity of misalignment is determined, and the misaligned pier placement type is classified into micro misalignment, moderate misalignment, and large misalignment based on the ratio of the deviation between the new and old bridge piers ΔL to the span of the old bridge L_span. Based on the specific location and constraint requirements of the obstacles, the longitudinal offset direction and offset amount of the new bridge piers relative to the old bridge piers are determined. S4: During the feasibility assessment stage of splicing, a finite element analysis model of the new and old bridges is established, the vertical deflection difference Δδ and the lateral relative displacement Δd at the splicing position are calculated, and compared with the preset limit values ​​to determine the feasibility of splicing. If it is a staggered hole arrangement, an additional special analysis of staggered hole splicing is conducted. S5: During the splicing scheme design phase, select the splicing mode and design the splicing seam structure based on the splicing feasibility assessment results; S6: Solution output stage, integrate the design results of steps S1 to S5 and output them as a pre-assembly solution design file.

[0008] Furthermore, step S2 specifically includes: S21: Span matching degree analysis: The span of the old bridge is compared with the preset span range. Based on the comparison results, the span matching relationship between the old and new bridges is divided into: Type I - complete span matching, Type II - similar span (span deviation ≤ 5%), and Type III - significant span deviation (span deviation > 5%). S22: Stiffness compatibility assessment: Calculate the bending stiffness EI_old of the old bridge main girder and the bending stiffness EI_new of the candidate main girder of the new bridge, calculate the stiffness ratio K = EI_new / EI_old of the old and new bridges, and determine whether the value of K is within the preset compatibility range K∈[0.8, 1.2]. S23: Main beam type decision: If the spans of the new and old bridges belong to type I and K∈[0.8, 1.2], then the main girder of the new bridge adopts the same type of main girder structure as the old bridge; If the span of the new and old bridges belongs to type II and K∈[0.8,1.2], then the main beam of the new bridge adopts the same type of main beam structure as the old bridge, but a stiffness transition structure needs to be set at the splice joint; If the span of the new and old bridges belongs to type III, or K∉[0.8, 1.2], then the main beam of the new bridge should be selected with a different structural type than that of the old bridge (such as replacing the hollow slab with a small box girder or T-beam), and K should be adjusted to the preset coordination range by adjusting the cross-sectional form and the amount of bundled beams. S24: Durability Matching Verification: Verify whether the material durability indicators (freeze-thaw resistance, impermeability, chloride ion diffusion coefficient) of the new bridge main beam meet the durability requirements for matching with the old bridge. If not, add a protective coating to the surface of the main beam or adjust the concrete mix ratio.

[0009] Furthermore, in S3, the misalignment type is specifically classified as follows: based on the ratio of the deviation between the old and new bridge pier positions ΔL to the span L_span of the old bridge, the misalignment arrangement type is classified as follows: Micro-faulted hole type: ΔL / L_span ≤ 0.1; Moderately misaligned hole type: 0.1 < ΔL / L_span ≤ 0.3; Large misalignment type: ΔL / L_span > 0.3.

[0010] Furthermore, in S4, the feasibility determination for splicing is specifically as follows: If max(Δδ) ≤ δ_limit and max(Δd) ≤ d_limit, then the splicing is deemed feasible, and proceed to step S5; If max(Δδ) > δ_limit or max(Δd) > d_limit, then the splicing is deemed infeasible. Return to step S2 to adjust the main beam selection scheme, or return to step S3 to adjust the staggered hole arrangement scheme, until the deformation coordination requirements are met. Wherein, δ_limit is the preset vertical deflection difference limit, and d_limit is the preset lateral relative displacement limit.

[0011] Furthermore, in S4, the specific analysis of misaligned joints is as follows: if the joints are arranged in a misaligned manner, the stress characteristics of the joints between the old and new bridges under the misaligned joint conditions are analyzed in addition, including: the mismatch effect of the lateral stiffness of the old and new bridges caused by the misaligned joints, the stress concentration effect in the misaligned joint area under vehicle load, and the stress performance of the flange plates of the old and new bridges under support settlement and vehicle load.

[0012] Furthermore, in S5, the splicing mode selection is specifically as follows: based on the evaluation results of step S4, select one of the following three splicing modes: The upper part is connected and the lower part is not connected, which is suitable for situations with staggered hole layout and large differences in geological conditions; The upper connection and lower connection modes are suitable for situations where the borehole layout or slightly misaligned borehole type and geological conditions are similar. The longitudinal expansion joint splicing mode is suitable for situations with large misaligned spans or significant differences between the old and new bridge structures.

[0013] Furthermore, in S5, the specific design of the splice seam structure is as follows: For hole arrangement or slightly staggered hole type: use conventional reinforced concrete wet joint or UHPC wet joint for rigid connection. For moderate misaligned holes: UHPC wet joint combined with shear key structure is adopted to resist the transverse tensile stress caused by misalignment by utilizing the high tensile strength (≥130MPa) and excellent bonding performance of UHPC; For large misaligned spans: longitudinal expansion joints are used for splicing, and the old and new bridge structures are separated.

[0014] Furthermore, in S5, the pre-splicing design documents include: main beam selection scheme, staggered hole layout diagram, splicing mode selection instructions, splicing joint construction details, substructure avoidance scheme, and construction sequence arrangement; The construction schedule is as follows: the connection construction between the new and old bridges will begin 90 to 180 days after the new bridge is installed. The proposed substructure avoidance scheme is as follows: when there is a spatial conflict between the new bridge pier and the old bridge foundation, one or a combination of the following measures shall be taken: adjusting the coordinates of the new bridge pier (to stagger its arrangement with the old bridge pier), changing the form of the new bridge foundation (such as changing the bored piles to steel pipe piles or enlarging the foundation), or removing or reinforcing the old bridge foundation.

[0015] Furthermore, S1 specifically includes: Collect the design parameters of the old bridge, including: the span of the old bridge, structural form, main beam type, concrete strength grade, prestressing tendon arrangement, and design load level; Collect current status inspection data of the old bridge, including: the condition of the bridge, the condition of cracks in the main beam, the depth of concrete carbonation, and the degree of steel corrosion; Collect data on the environmental conditions of the bridge site, including: clearance under the bridge, traffic requirements, distribution of underground pipelines, navigation conditions of the river, and geological and hydrological conditions; The design objectives of the expansion and renovation project include: widening width, design load level, and design service life.

[0016] Furthermore, in S3, obstacle condition identification specifically refers to: identifying the types of obstacle conditions for the layout of new bridge piers, including but not limited to: traffic requirements for roads under the bridge, navigation clearance requirements for waterways, avoidance requirements for underground pipelines, avoidance requirements for existing building foundations, and geological condition restrictions; The necessity of staggered hole arrangement is determined as follows: if the obstacle conditions prevent the new bridge pier from being laterally aligned with the old bridge pier, then staggered hole arrangement is deemed necessary; if the obstacle conditions can be resolved through local adjustments (such as minor adjustments to the pier position or changes in the foundation form), then staggered hole arrangement or aligned hole arrangement can be chosen.

[0017] Compared with the prior art, the present invention has the following advantages: (1) High system integration. For the first time, the two core issues of selecting irregular spliced ​​main beam structure and setting staggered holes, which were originally separate, are integrated into the same design process. This overcomes the design conflicts caused by the separate decision-making of the two in the existing technology and realizes the whole-chain systematic design from old bridge data collection to scheme output.

[0018] (2) Wide span adaptability. Through span matching degree classification and stiffness coordination assessment, it can cope with splicing scenarios of new and old bridges with different span deviations, and solve the technical problem of main beam structure matching in the widening of bridges with different spans.

[0019] (3) Refined classification of misaligned spans. Based on the ratio of the deviation ΔL between the old and new bridge pier positions to the span L_span of the old bridge, misaligned spans are quantitatively classified (micro-misaligned spans ≤0.1, moderate misaligned spans 0.1~0.3, and large misaligned spans >0.3). Different splicing construction schemes are matched for different types (such as conventional wet joints, UHPC wet joints combined with shear keys, and longitudinal expansion joints). This greatly improves the scientific nature and pertinence of splicing design under misaligned span conditions.

[0020] (4) High rigor in mechanical analysis. Deformation compatibility analysis (calculating vertical deflection difference Δδ and lateral relative displacement Δd) and finite element simulation are the core judgment criteria, and additional special analysis (lateral stiffness mismatch effect, stress concentration effect, and flange stress performance) is performed when there are misaligned holes. This avoids structural safety hazards caused by decision-making based solely on experience, and makes the determination of splicing feasibility more reliable.

[0021] (5) Strong construction feasibility. The output includes substructure avoidance design (adjusting pier coordinates, changing foundation type, removing or reinforcing old bridge foundations, etc.) and specific construction sequence arrangements (preferably connecting construction 90 to 180 days after the new bridge is installed). Consideration of actual construction issues such as site space conflicts and differences in shrinkage and creep between new and old concrete ensures the feasibility of the design scheme.

[0022] (6) Durability and structural transition assurance. Through durability matching verification (freezing resistance, impermeability, chloride ion diffusion coefficient) and irregular splicing transition structure (such as thickness gradient section, stiffness transition structure), the collaborative working performance and durability of the new and old bridges under long-term use are guaranteed. Attached Figure Description

[0023] Figure 1 A flowchart illustrating the overall process for irregular splicing and staggered span arrangement of bridges with different spans; Figure 2 This is a schematic diagram of the widening of the staggered holes in the concrete T-beams in Example 1; Figure 3 This is a schematic diagram of the staggered hole width of the concrete T-beam and small box girder in Example 2; Attached diagram labels: 1-First old bridge T-beam; 2-New bridge T-beam; 3-500mm wide joint; 4-Second old bridge T-beam; 5-New bridge small box girder; 6-600mm wide joint. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0025] Example 1 The 3×30m prestressed concrete T-beam bridge was widened by widening the staggered spans, such as... Figure 1 , 2 As shown.

[0026] The following is a detailed explanation using the example of widening the misaligned spans of a 3×30m prestressed concrete T-beam bridge in a highway reconstruction and expansion project.

[0027] Step S1 (Basic Data Acquisition): The old bridge is a 3×30m prestressed concrete T-beam bridge, with a design load of vehicle-super 20 and trailer-120. The main beam concrete strength grade is C50. There is an existing urban road under the bridge, with a clearance requirement of no less than 5m. The reconstruction and expansion target is to widen one side by 8.25m and increase the design load to Highway-I level.

[0028] Step S2 (Main Girder Selection): The old bridge has a span of 30m, which is a medium span. Calculate the flexural stiffness EI_old of the first old bridge T-beam 1. The candidate T-beam types for the new bridge include prestressed concrete T-beams and prestressed concrete small box girders. Calculations show that if the new bridge uses the same type of T-beam, the stiffness ratio K=1.08, satisfying K∈[0.8, 1.2]. Therefore, the main girder of the new bridge will be a prestressed concrete T-beam of the same type as the old bridge. In terms of durability, the new bridge will use C50 high-performance concrete, matching the old bridge.

[0029] Step S3 (Identification of Misalignment Conditions): Due to the traffic requirements of the existing urban road under the bridge, the piers of the new bridge cannot be aligned with the piers of the old bridge, and a misalignment arrangement must be adopted. The position of the new bridge pier is offset by 2.0m relative to the position of the old bridge pier along the longitudinal direction of the bridge. The span of the old bridge is 30m, and ΔL / L_span=2 / 30≈0.067≤0.1, which belongs to the micro misalignment type.

[0030] Step S4 (Feasibility Assessment of Splicing): A finite element analysis model of the beam grid of the old and new bridges was established using Midas Civil. The vertical deflection difference Δδ at the splicing position was calculated under various load combinations. The maximum value max(Δδ) was 3.2 mm, which is less than the preset limit δ_limit of 5.0 mm. The maximum value of the lateral relative displacement Δd max(Δd) was 1.8 mm, which is less than the preset limit d_limit of 3.0 mm, indicating that splicing is feasible. At the same time, the analysis found that the staggered hole arrangement caused the vertical deformation of the old and new bridges under live loads to be inconsistent in the lateral direction, and the conventional C50 concrete wet joint could not meet the lateral tensile stress requirements.

[0031] Step S5 (Splicing Scheme Design): This is a micro-misaligned hole type, so a splicing pattern of upper connection and lower non-connection is selected. The splice joint adopts a UHPC wet joint construction: 500mm wide joint 3, cast with ultra-high performance concrete with a compressive strength ≥130MPa and a tensile strength ≥8MPa. Shear keys are installed on both sides of the 500mm wide joint 3 to reinforce the connection. Regarding substructure clearance, the new bridge's pile foundation uses bored cast-in-place piles. Calculations show a minimum clear distance of 2.5m from the old bridge's pile foundation, meeting construction requirements and requiring no special clearance. In terms of construction sequence, the new bridge will be allowed to stand for 120 days after installation before the 500mm wide joint 3 is poured to reduce the impact of the difference in shrinkage and creep between the new and old concrete.

[0032] Step S6 (Scheme Output): Output the scheme design documents before splicing, including the main beam selection scheme (prestressed concrete T-beam), staggered hole layout diagram (offset 2.0m), splicing mode selection instructions (upper connection + lower non-connection), splicing joint construction details (UHPC wet joint), substructure avoidance scheme (no special treatment required), and construction sequence arrangement (the new bridge will be left to stand for 120 days after installation).

[0033] Example 2 Modification of the 3×30m prestressed concrete T-beam and small box girder bridge with staggered spans, such as... Figure 1 , 3 As shown.

[0034] Taking a 3×30m prestressed concrete T-beam bridge in a national highway reconstruction and expansion project as the engineering background, the old and new bridges have the same span but different main beam structures, and due to the traffic conditions under the bridge, a staggered span arrangement must be adopted. The method of the present invention will be specifically explained.

[0035] Step S1 (Basic Data Collection) The old bridge is a 3×30m prestressed concrete T-beam bridge, built in 2005. Its design load is for vehicles exceeding Class 20 and trailers exceeding Class 120. The main beam concrete strength grade is C50, the beam height is 1.8m, and the T-beam flange width is 1.6m, totaling 10 T-beams. The bridge has a total width of 12.0m and two lanes in both directions. Current condition inspection results show that no structural cracks were found in the main beams, the average carbonation depth of the concrete is 3.2mm, and there is no significant corrosion of the reinforcing steel. The bridge's technical condition is assessed as Class II, meeting the conditions for widening and reconstruction.

[0036] Bridge site environmental conditions: The riverbed beneath the bridge is an existing waterway with navigation clearance requirements of ≥15m width and ≥3.5m height. There is a deviation between the river centerline and the existing bridge piers, preventing the new bridge piers from being laterally aligned with the old ones. The expansion and reconstruction target is to widen one side by 4.5m (adding one lane), increase the design load to Highway-I level, and design service life of 50 years.

[0037] Step S2 (Main beam structure selection - irregular splicing decision) S2.1 Span matching analysis: The old bridge has a span of 30m, and the new bridge is also designed to have a span of 30m, which means they are in a perfectly matched span type.

[0038] S2.2 Stiffness Compatibility Assessment: Calculate the flexural stiffness EI_old of T-beam 4 of the second old bridge. The moment of inertia of section 4 of T-beam 4 of the second old bridge is I_old ≈ 0.152m. 4 The elastic modulus of C50 concrete, E_old, is 3.45 × 10⁻⁶. 4 MPa, get EI_old=5.244×10 9 N·m 2 .

[0039] The candidate main girder type for the new bridge is a prestressed concrete small box girder (single box, single cell), with a girder height of 1.6m, a top slab width of 2.4m, a bottom slab width of 1.2m, and a moment of inertia of I_new ≈ 0.198m. 4 The elastic modulus of C50 concrete is E_new = 3.45 × 10⁻⁶. 4 MPa, resulting in EI_new = 6.831 × 10 9 N·m2 .

[0040] The stiffness ratio K = EI_new / EI_old = 6.831 / 5.244 ≈ 1.303, K ∉ [0.8, 1.2], indicating that the stiffness of the small box girder 5 of the new bridge is significantly greater than that of the T-beam 4 of the second old bridge.

[0041] S2.3 Main Girder Type Decision: Since the spans are perfectly matched but K∉[0.8,1.2], this falls under the category of "spans perfectly matched but stiffness deviation is significant". According to the method of this invention, instead of directly using the same type of main girder, the stiffness of the selected irregular main girder (small box girder) is adjusted: Adjustment measures: By reducing the cross-sectional dimensions of the small box girder and adjusting the prestressing tendon quantity, the moment of inertia of section 5 of the new bridge's small box girder was reduced from 0.198m. 4 Reduced to 0.168m 4 After adjustment, EI_new = 5.796 × 10 9 N·m 2 The stiffness ratio K = 5.796 / 5.244 ≈ 1.105, which falls within the compatibility range of 0.8 to 1.2.

[0042] Section adjustment details: Maintaining the beam height at 1.6m, the top slab width was narrowed from 2.4m to 2.1m, the web thickness was reduced from 0.35m to 0.28m, and the bottom slab thickness was reduced from 0.30m to 0.25m. Simultaneously, the number of prestressed steel strands was reduced from 12 strands (φ15.2mm) to 10 strands, lowering the initial prestressing force to match the stiffness of the new bridge with the old bridge during operation.

[0043] Irregular splicing determination: The T-beam 4 of the second old bridge and the small box girder 5 of the new bridge have different structural forms, which belong to the irregular splicing scenario. A stiffness transition structure needs to be set at the splicing joint.

[0044] S2.4 Durability Matching Verification: The new bridge's small box girder 5 uses C55 high-performance concrete (to match the old bridge's C50 and compensate for the strength loss caused by the section thinning), with a frost resistance grade of F300, a permeability grade of P12, and a chloride ion diffusion coefficient ≤1.5×10⁻⁶. - 12 m 2 / s, meeting the durability requirements for matching the C50 concrete of the old bridge. A penetrating crystalline waterproof coating is applied to the joint between the new and old bridges to prevent chloride ions from seeping in along the joint.

[0045] Step S3 (Identification of Misaligned Hole Arrangement Conditions) S3.1 Obstacle Condition Identification: There is a deviation between the centerline of the river channel under the bridge and the location of the old bridge piers. The old bridge piers are symmetrically arranged on both sides of the river channel centerline. If the new bridge piers are aligned with the old bridge piers, the new bridge piers will fall within the main channel area of ​​the river, affecting the flood control and navigation safety of the river. Therefore, the obstacle condition type is the river channel navigation clearance requirement and flood control requirement.

[0046] S3.2 Necessity of staggered hole arrangement: Since the position of the river centerline is fixed and cannot be solved by local adjustment (such as fine adjustment of the pier position), it is determined that staggered hole arrangement must be adopted.

[0047] S3.3 Classification of Misalignment Type: The new bridge pier is offset by 3.5m relative to the old bridge pier along the longitudinal direction. The old bridge span L_span = 30m, and ΔL / L_span = 3.5 / 30 ≈ 0.117. Since 0.1 < 0.117 ≤ 0.3, it belongs to the moderate misalignment type.

[0048] S3.4 Determination of the misalignment position: Based on the position of the river centerline, the new bridge pier is offset 3.5m downstream relative to the old bridge pier. After the offset, the new bridge pier avoids the main channel of the river and falls into the river beach area, and the foundation construction conditions are feasible.

[0049] Step S4 (Feasibility Assessment of Splicing) S4.1 Deformation Compatibility Analysis: A spatial solid finite element model of the old and new bridges was established using the solid finite element method. The model includes: The second old bridge's T-beam 4 (10 pieces) was simulated using solid elements; The new bridge's small box girder 5 (3 pieces) was simulated using solid elements; The splicing seam area (proposed to use UHPC wet joints) will be divided using a fine mesh.

[0050] The calculation of load combinations includes: Operating Condition 1: Self-weight + Secondary Dead Load; Working condition 2: Self-weight + secondary dead load + vehicle load (Highway-Class I, most unfavorable lateral load distribution). Operating condition 3: Operating condition 2 + temperature gradient (positive temperature difference 15℃); Condition 4: Condition 2 + foundation settlement (differential settlement of 5mm between adjacent piers).

[0051] Calculation results: Under working condition 2, the maximum vertical deflection difference Δδ at the splicing position occurs at the mid-span, Δδ_max=4.2mm, which is less than the preset limit δ_limit=5.0mm; Under operating condition 3, the relative lateral displacement of the old and new bridges caused by the temperature gradient is Δd_max = 2.6 mm, which is less than the preset limit d_limit = 3.0 mm; Under operating condition 4, the additional bending moment at the splice location caused by foundation settlement is approximately 45 kN·m / m, which is within the bearing capacity of the UHPC wet joint.

[0052] S4.2 Feasibility of splicing: max(Δδ)=4.2mm ≤ 5.0mm, max(Δd)=2.6mm ≤ 3.0mm, splicing is deemed feasible.

[0053] S4.3 Specific Analysis of Misaligned Hole Joints: A specific analysis is conducted for moderately misaligned holes (offset 3.5m): Lateral stiffness mismatch effect: Since the stiffness of the small box girder 5 of the new bridge is slightly greater than that of the T-beam 4 of the second old bridge (K=1.105), and the staggered hole arrangement causes the crossbeams of the new and old bridges to be misaligned, the peak lateral tensile stress in the staggered hole area under live load is 2.8MPa, which cannot be met by conventional C50 concrete (tensile strength of about 2.0MPa), and UHPC wet joints must be used.

[0054] Stress concentration effect: At the new bridge pier location in the misaligned area, the shear stress concentration factor of the vehicle load transmitted to the splice joint through the bridge deck is 1.35, and shear keys need to be set in the splice joint to disperse the shear stress.

[0055] Flange plate stress performance: The bending moment at the cantilever end of the fourth flange plate of the second old bridge under the staggered hole arrangement is about 22% higher than that under the same hole arrangement. According to the calculation, the reinforcement of the flange plate meets the stress requirements and no reinforcement is required.

[0056] Step S5 (Splicing Scheme Design) S5.1 Selection of splicing mode: It belongs to the moderate misaligned hole type, and the geological conditions of the new and old bridge foundations are similar. However, in order to reduce the impact of the settlement difference between the new and old bridge foundations on the splicing joint, the splicing mode of upper connection and lower non-connection is selected.

[0057] S5.2 Joint Construction Design: For moderately staggered and irregularly shaped splices (T-beams + small box girders), a UHPC wet joint combined with shear key construction is adopted. Wet joint width: 600mm wide joint 6, which is wider than the conventional wet joint to accommodate the deformation caused by misaligned holes; UHPC material properties: compressive strength ≥130MPa, tensile strength ≥8MPa, elastic modulus approximately 42GPa, shrinkage and creep approximately 1 / 3 of ordinary concrete; Shear key setting: On the side of the 4th flange of the T-beam of the second old bridge and the side of the 5th flange of the small box girder of the new bridge, a rectangular shear key (30mm deep × 50mm high) is set every 500mm along the beam length to enhance the mechanical interlocking between the UHPC and the precast beam; Reinforcing bar connection: The pre-embedded reinforcing bars in the flange plates of the new and old bridges extend into the wet joint, with a lap length ≥35d (d is the diameter of the reinforcing bar), and are arranged in a staggered manner; Irregular splicing transition structure: A thickness gradient section is set within the splicing joint area, transitioning from the thickness of 180mm of the old bridge side flange plate to the thickness of 200mm of the new bridge side flange plate, smoothly eliminating stress concentration caused by abrupt changes in cross section.

[0058] S5.3 Substructure Avoidance Design: After the new bridge piers are offset by 3.5m, there is no spatial conflict with the old bridge piers. The new bridge foundation uses bored cast-in-place piles (pile diameter 1.2m, pile length 35m), and the old bridge foundation is an enlarged foundation. The minimum clear distance between the two is 4.2m, which meets the construction and stress requirements and does not require special avoidance treatment.

[0059] S5.4 Construction Sequence Design: The prefabrication and installation of the five small box girders for the new bridge have been completed. Construction of new bridge deck paving and crash barriers; The new bridge will be left to cure statically for 120 days (considering that the amount of concrete used after the adjustment of the small box girder section is reduced and the shrinkage and creep period is slightly shorter, 120 days is taken), during which settlement will be monitored. After the settlement stabilizes (settlement rate <0.01mm / d for two consecutive months), the splicing joint is constructed. The joints are cast in one go using UHPC, and then kept moist for 14 days after casting. Finally, the waterproof layer and asphalt pavement were installed on the bridge deck above the splicing joints.

[0060] Step S6 (Solution Output) Output the pre-assembly design documents, which mainly include: Main girder selection scheme: The new bridge adopts prestressed concrete small box girders (irregular splicing), and after section adjustment, the stiffness ratio K=1.105, which meets the coordination requirements; Misalignment layout diagram: The new bridge pier is offset 3.5m downstream, and the misalignment type is moderate misalignment (ΔL / L_span=0.117). Splicing mode selection instructions: Top connected + Bottom not connected; Detailed construction of splice joint: UHPC wet joint (600mm wide) + shear key (500mm spacing) + thickness gradient transition section; Substructure avoidance scheme: No special treatment required; Construction schedule: After the new bridge is installed, it will be left to stand for 120 days before the splicing joints are constructed.

[0061] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0062] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for irregular splicing and staggered span arrangement of bridges with different spans, characterized in that, Includes the following steps: S1: Data collection phase for the old bridge foundation, collecting design parameters, current status inspection data, bridge site environmental conditions data, and design objectives for the reconstruction and expansion project of the old bridge. S2: In the new bridge main girder structure selection stage, based on the span range of the old bridge, the current status of the old bridge main girder and the reconstruction and expansion goals, the new bridge main girder structure type is determined through span matching degree analysis, stiffness coordination assessment and main girder type decision. S3: In the stage of identifying the conditions for misaligned pier placement, the obstacles to the placement of the new bridge piers are identified, the necessity of misalignment is determined, and the misaligned pier placement type is classified into micro misalignment, moderate misalignment, and large misalignment based on the ratio of the deviation between the new and old bridge piers ΔL to the span of the old bridge L_span. Based on the specific location and constraint requirements of the obstacles, the longitudinal offset direction and offset amount of the new bridge piers relative to the old bridge piers are determined. S4: During the feasibility assessment stage of splicing, a finite element analysis model of the new and old bridges is established, the vertical deflection difference Δδ and the lateral relative displacement Δd at the splicing position are calculated, and compared with the preset limit values ​​to determine the feasibility of splicing. If it is a staggered hole arrangement, an additional special analysis of staggered hole splicing is conducted. S5: During the splicing scheme design phase, select the splicing mode and design the splicing seam structure based on the splicing feasibility assessment results; S6: Solution output stage, integrate the design results of steps S1 to S5 and output them as a pre-assembly solution design file.

2. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, Step S2 specifically includes: S21: Span Matching Analysis: The span of the old bridge is compared with the preset span range. Based on the comparison results, the span matching relationship between the old and new bridges is divided into: Type I - complete span matching, Type II - span deviation ≤ 5%, and Type III - span deviation > 5%. S22: Stiffness compatibility assessment: Calculate the bending stiffness EI_old of the old bridge main girder and the bending stiffness EI_new of the candidate main girder of the new bridge, calculate the stiffness ratio K = EI_new / EI_old of the old and new bridges, and determine whether the value of K is within the preset compatibility range K∈[0.8, 1.2]. S23: Main beam type decision: If the spans of the new and old bridges belong to type I and K∈[0.8, 1.2], then the main girder of the new bridge adopts the same type of main girder structure as the old bridge; If the span of the new and old bridges belongs to type II and K∈[0.8,1.2], then the main beam of the new bridge adopts the same type of main beam structure as the old bridge, but a stiffness transition structure needs to be set at the splice joint; If the span of the new and old bridges belongs to type III, or K∉[0.8, 1.2], then the main beam of the new bridge should be selected with a different structural type than that of the old bridge. K should be adjusted to the preset coordination range by adjusting the cross-sectional form and the amount of bundle. S24: Durability Matching Verification: Verify whether the material durability index of the new bridge main beam meets the durability requirements for matching with the old bridge. If not, add a protective coating to the surface of the main beam or adjust the concrete mix ratio.

3. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S3, the misalignment type is specifically classified as follows: based on the ratio of the deviation between the old and new pier positions ΔL to the span L_span of the old bridge, the misalignment arrangement type is classified as follows: Micro-faulted hole type: ΔL / L_span ≤ 0.1; Moderately misaligned hole type: 0.1 < ΔL / L_span ≤ 0.3; Large misalignment type: ΔL / L_span > 0.

3.

4. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S4, the feasibility of splicing is determined as follows: If max(Δδ) ≤ δ_limit and max(Δd) ≤ d_limit, then the splicing is deemed feasible, and proceed to step S5; If max(Δδ) > δ_limit or max(Δd) > d_limit, then the splicing is deemed infeasible. Return to step S2 to adjust the main beam selection scheme, or return to step S3 to adjust the staggered hole arrangement scheme, until the deformation coordination requirements are met. Wherein, δ_limit is the preset vertical deflection difference limit, and d_limit is the preset lateral relative displacement limit.

5. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S4, the specific analysis of misaligned joints is as follows: If the joints are arranged in a misaligned manner, the stress characteristics of the joints between the old and new bridges under the misaligned joint conditions will be analyzed in addition, including: the mismatch effect of the lateral stiffness of the old and new bridges caused by the misaligned joints, the stress concentration effect in the misaligned joint area under vehicle load, and the stress performance of the flanges of the old and new bridges under support settlement and vehicle load.

6. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S5, the splicing mode selection is as follows: Based on the evaluation results of step S4, select one of the following three splicing modes: The upper part is connected and the lower part is not connected, which is suitable for situations with staggered hole layout and large differences in geological conditions; The upper connection and lower connection modes are suitable for situations where the borehole layout or slightly misaligned borehole type and geological conditions are similar. The longitudinal expansion joint splicing mode is suitable for situations with large misaligned spans or significant differences between the old and new bridge structures.

7. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S5, the splice seam construction design is as follows: For hole arrangement or slightly staggered hole type: use conventional reinforced concrete wet joint or UHPC wet joint for rigid connection. For moderate misaligned holes: UHPC wet joint combined with shear key structure is adopted to resist the transverse tensile stress caused by misalignment by utilizing the high tensile strength and excellent bonding performance of UHPC. For large misaligned spans: longitudinal expansion joints are used for splicing, and the old and new bridge structures are separated.

8. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S5, the pre-splicing design documents include: main beam selection scheme, staggered hole layout diagram, splicing mode selection instructions, splicing joint construction details, substructure avoidance scheme, and construction sequence arrangement. The construction schedule is as follows: the connection construction between the new and old bridges will begin 90 to 180 days after the new bridge is installed. The proposed substructure avoidance scheme is as follows: when there is a spatial conflict between the new bridge pier and the old bridge foundation, one or a combination of adjusting the coordinates of the new bridge pier, changing the form of the new bridge foundation, or clearing or reinforcing the old bridge foundation shall be adopted.

9. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, S1 specifically includes: Collect the design parameters of the old bridge, including: the span of the old bridge, structural form, main beam type, concrete strength grade, prestressing tendon arrangement, and design load level; Collect current status inspection data of the old bridge, including: the condition of the bridge, the condition of cracks in the main beam, the depth of concrete carbonation, and the degree of steel corrosion; Collect data on the environmental conditions of the bridge site, including: clearance under the bridge, traffic requirements, distribution of underground pipelines, navigation conditions of the river, and geological and hydrological conditions; The design objectives of the expansion and renovation project include: widening width, design load level, and design service life.

10. The method for irregular splicing and staggered span arrangement of bridges with different spans according to claim 1, characterized in that, In S3, obstacle condition identification specifically refers to identifying the types of obstacle conditions for the layout of new bridge piers, including but not limited to: traffic requirements for roads under the bridge, navigation clearance requirements for waterways, avoidance requirements for underground pipelines, avoidance requirements for existing building foundations, and geological condition restrictions. The necessity of staggered hole arrangement is determined as follows: if the obstacle conditions prevent the new bridge pier from being laterally aligned with the old bridge pier, then staggered hole arrangement is deemed necessary; if the obstacle conditions can be resolved through local adjustments (such as minor adjustments to the pier position or changes in the foundation form), then staggered hole arrangement or aligned hole arrangement can be chosen.

Images