Construction process of precast and erection of double-track widened simply supported box girder at single and double parallel sections

Abstract

This invention discloses a prefabrication and erection construction process for a double-track variable-width simply supported box girder at a single / double-track junction, relating to the field of construction technology. The process includes obtaining the geometric parameters and spatial constraints of the double-track variable-width simply supported box girder at the single / double-track junction; adaptively modifying the prefabrication beam formwork system and supporting fixtures based on the geometric parameters; calculating the stress state of the box girder structure and implementing prefabrication parameter control during the prefabrication stage; completing the prefabrication, tensioning, and curing of the box girder based on the calculation results; and controlling the stress state under the action of the bridge erecting machine and completing the erection of the box girder during the erection stage. This invention achieves precise prefabrication and safe erection of the double-track variable-width simply supported box girder by parametrically obtaining the box girder's geometry and track conditions, combined with adaptive formwork modification and stress calculation threshold control. It also effectively diverts asymmetrical loads during the erection stage, reducing construction risks, shortening the construction period, and improving project quality and construction safety.

Description

Technical Field

[0001] This invention relates to the field of construction technology, and in particular to the prefabrication and erection process of double-track widened simply supported box girders at single and double parallel sections. Background Technology

[0002] In the construction of railways, urban rail transit, and intercity lines, single- and double-track parallel structures are often set up in station sections, connecting line sections, or line intersection sections. As the line transitions from double track to single track or from single track to double track, the track spacing gradually changes longitudinally within the parallel section. To meet the matching requirements between the line centerline and the bridge load-bearing center, the bridge structure usually adopts a double-track variable-width simply supported box girder form. This type of box girder has an unequal beam width along the longitudinal direction, a complex structural form, and its end construction, reinforcement method, and prestressing arrangement all differ significantly from standard simply supported box girders, making it a typical non-standard beam type.

[0003] In current engineering practice, the in-situ casting method with scaffolding is often used for double-track variable-width simply supported box girders. This method involves setting up scaffolding on-site to complete formwork installation, rebar tying, and concrete pouring. This method has problems such as long construction period, complicated scaffolding erection and dismantling procedures, high safety risks, and quality being greatly affected by the site environment. Especially in the vicinity of existing lines or in parallel sections where site conditions are limited, the difficulty of scaffolding construction and the pressure of safety management are further increased.

[0004] With the development of prefabricated bridge construction technology, precast erection has been widely used in standard simply supported box girders. However, existing precast erection technologies are mostly designed for standard beam types and are difficult to directly apply to double-track variable-width simply supported box girders. The main reasons are: first, the geometric dimensions of the beam change longitudinally, making it difficult to adapt the formwork system; second, the stress state of the beam is complex during the precasting, tensioning, and erection stages, making alignment control difficult; and third, under single-track and double-track conditions, the stress position of the bridge erecting machine columns is asymmetrical, and single-track beams are prone to additional concentrated loads during erection, posing structural safety hazards. Therefore, we propose a precast erection construction process for double-track variable-width simply supported box girders under single-track and double-track conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a prefabrication and erection process for double-line widened simply supported box girders at single and double parallel sections, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a prefabrication and erection process for a double-track variable-width simply supported box girder at a single / double parallel section, comprising the following steps: Step 1: Obtain the geometric parameters and spatial constraints of the double-track variable-width simply supported box girder at the single-double parallel section; Step 2: Adapt the precast beam formwork system and supporting fixtures based on the aforementioned geometric parameters; Step 3: Calculate the stress state of the box girder structure and adjust the prefabrication parameters during the prefabrication stage; Step 4: Based on the calculation results, complete the prefabrication, tensioning, and curing of the box girder; Step 5: Control the stress state under the action of the bridge erecting machine during the erection stage and complete the erection of the box girder.

[0007] Preferably, step 1 includes: Step 1.1: Obtain the beam width variation function along the longitudinal direction of the double-line variable-width simply supported box girder; Step 1.2: Determine the sections where the line spacing changes at the intersection of single and double lines and the corresponding eccentricity characteristics of the box girder. Step 1.3: Establish a model showing the correspondence between the box girder width variation parameters, support arrangement parameters, and erection equipment working parameters.

[0008] Preferably, step 2 includes: Step 2.1: Based on the variation in width at the end of the box girder, a non-standard end mold structure is used to fabricate the end mold; Step 2.2: Adjust the position of the outer mold flange baffle by moving it outward or retracting it to match the shape of the beam; Step 2.3: Reconstruct the position of the inner formwork support legs so that they correspond to the drainage holes at the bottom of the beam and the key stress areas.

[0009] Preferably, step 3 includes: Step 3.1: Establish an equivalent stress model of the box girder during the prefabrication, tensioning, and erection stages before prefabrication; Step 3.2: Calculate the theoretical deflection value δ of the box girder under its own weight and construction loads based on the model. Step 3.3: Preset and adjust the amount of camber in the outer mold based on the deflection value.

[0010] Preferably, the formula for calculating the theoretical deflection value δ of the beam in step 3.2 is: ; Where q is the equivalent construction load per unit length, L is the calculated span of the box girder, E is the elastic modulus of concrete, I is the equivalent moment of inertia of the box girder section, and K is a correction factor related to the support conditions.

[0011] Preferably, step 3.3 includes: The calculated theoretical deflection value δ is compared with the preset deflection threshold δ0; When δ>δ0, increase the outer mold arching amount and adjust the thickness of the bottom mold pad; When δ≤δ0, the original anti-arch parameters are kept unchanged and the prefabrication stage is entered.

[0012] Preferably, the deflection threshold δ0 is set according to the rate of change of the box girder width, and satisfies: When the beam width change rate is greater than the preset change rate threshold, δ0 takes a smaller value to improve control accuracy. When the beam width change rate is less than or equal to the change rate threshold, δ0 is taken as a larger value to reduce the frequency of construction adjustments.

[0013] Preferably, the outer formwork anti-camber is distributed along the longitudinal direction of the box girder in a quadratic parabolic pattern, and a zero anti-camber section is preset at the beam end to reduce the risk of stress concentration at the end.

[0014] Preferably, step 5 includes: Step 5.1: Conduct a stress analysis on the position of the bridge erecting machine's columns before the box girder is erected; Step 5.2: When the bridge erecting machine column is located on the side of the single-line beam, a temporary vertical force transmission structure is set up for the single-line beam; Step 5.3: The load is transferred to the piers or abutments through the force transmission structure.

[0015] Preferably, the temporary vertical force transmission structure in step 5.2 includes: A steel pipe column is installed between the top and bottom plates of a single-line beam, and high-strength concrete is poured into it to form a composite load-bearing component. This is to limit the additional deflection of the single-line beam and improve the overall erection safety during the erection of double-line widened simply supported box girders.

[0016] The technical effects and advantages of this invention are as follows: This invention addresses the challenges of non-standard, complex stress, and high construction safety risks associated with double-track variable-width simply supported box girder structures at single- and double-track junctions. By acquiring the girder's geometric parameters and spatial constraints before construction, the invention adapts the formwork system and tooling. Furthermore, it introduces stress calculation and deflection threshold control mechanisms during the prefabrication stage to achieve precise control over the box girder's alignment and stress state. Simultaneously, during the erection stage, the invention analyzes the stress under the bridge erecting machine and sets up temporary vertical force transmission structures, effectively reducing the additional stress risk on the single-track girder. This process enables safe and high-quality construction of double-track variable-width simply supported box girders using prefabrication and erection methods, significantly shortening the construction period, reducing construction costs, and improving overall construction safety and project quality stability. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides, for example Figure 1 The prefabrication and erection process of the double-track widened simply supported box girder at the single / double parallel section, as shown, includes the following steps: Step 1: Obtain the geometric parameters and spatial constraints of the double-track variable-width simply supported box girder at the single-double parallel section; Step 1 includes: Step 1.1: Obtain the beam width variation function along the longitudinal direction of the double-line variable-width simply supported box girder; Step 1.2: Determine the sections where the line spacing changes at the intersection of single and double lines and the corresponding eccentricity characteristics of the box girder. Step 1.3: Establish a model showing the correspondence between the box girder width variation parameters, support arrangement parameters, and erection equipment working parameters; In this embodiment, considering the engineering characteristics such as the continuous longitudinal variation of the beam width of the double-track widened simply supported box girder at the single-double parallel section, the offset between the center line of the line and the stress center of the beam, and the limited working space of the erection equipment, step 1 is first executed to systematically acquire and model the geometric parameters of the box girder and the spatial constraints of the line, so as to provide basic data support for subsequent template modification, anti-arch setting and erection construction. In step 1.1, by analyzing the design drawings and the longitudinal and horizontal cross-sectional data of the line, the beam width variation function of the double-line variable-width simply supported box girder along the longitudinal direction is obtained. In specific implementation, the mid-span of the box girder is used as the reference position, and discrete sampling is performed along the longitudinal direction of the box girder at a preset interval. The total beam width, the outer edge position of the left and right flange plates and the width variation rate corresponding to each sampling position are extracted. The functional relationship between the beam width and the longitudinal coordinate is established by linear or nonlinear fitting. This variation function can truly reflect the geometric characteristics of the beam body gradually transitioning from the double-line standard width to the single and double parallel area, providing an accurate basis for determining the template adjustment amount and the anti-arch distribution. In step 1.2, based on the line layout and the single / double parallel transition scheme, the specific section range where the line spacing changes is determined, and the offset relationship between the line centerline and the geometric center of the box girder in this section is further analyzed. This helps to identify the force eccentricity characteristics that may occur in the box girder during construction and erection. In practice, based on the position of the double line centerline, the position of the support centerline, and the position of the centroid of the beam section, the eccentricity distance at each key section is calculated, and a force eccentricity distribution curve that varies along the longitudinal direction is formed. Through this analysis, the asymmetric stress state that may occur in the double-line variable-width simply supported box girder under the action of self-weight, tension, and erection loads can be identified in advance, providing a basis for subsequent force control and safety verification. In step 1.3, based on the width variation parameters and force eccentricity characteristics obtained in steps 1.1 and 1.2, a correspondence model between the box girder width variation parameters, support arrangement parameters, and erection equipment working parameters is further established. In specific implementation, parameters such as the beam width variation function, the lateral arrangement position of the supports, the distribution relationship of the support reaction force, as well as the position of the bridge erecting machine column, the position of the lifting point, and the rated bearing capacity are incorporated into a unified model. The formwork displacement, support force adjustment requirements, and erection equipment operation restrictions under different beam segment conditions are determined through parameter mapping. This correspondence model can achieve coordinated matching between beam structure parameters and construction equipment parameters, avoiding construction interference or force abnormalities caused by non-standard beam characteristics. Through the implementation of step 1 and its sub-steps, this invention achieves systematic control over the geometric characteristics, spatial conditions, and eccentricity of the double-track simply supported box girder at the single / double parallel section before construction. This transforms the non-standard box girder construction from "experience-based construction" to "parametric construction." On the one hand, by establishing the beam width variation function, it provides a quantitative basis for formwork modification, anti-arch setting, and rebar positioning, effectively improving prefabrication accuracy. On the other hand, by identifying the eccentricity characteristics in advance, it significantly reduces the risk of uneven deformation or additional internal forces during the tensioning and erection of the box girder. At the same time, by establishing a correspondence model between structural parameters and erection equipment parameters, the erection scheme can automatically adapt to different width sections, avoiding safety hazards in equipment selection and operation, and improving overall construction safety, construction controllability, and project quality stability.

[0020] Step 2: Adapt the precast beam formwork system and support fixtures based on geometric parameters; Step 2 includes: Step 2.1: Based on the variation in width at the end of the box girder, a non-standard end mold structure is used to fabricate the end mold; Step 2.2: Adjust the position of the outer mold flange baffle by moving it outward or retracting it to match the shape of the beam; Step 2.3: Reconstruct the position of the inner formwork support legs so that they correspond to the drainage holes at the bottom of the beam and the key stress areas; After obtaining the geometric parameters and spatial constraints of the double-track variable-width simply supported box girder at the single-double parallel section, proceed to step 2, which is to adapt the precast beam template system and support fixtures based on the geometric parameters. The core of this step is to transform the non-standard width gradient characteristics, end structure differences and internal stress requirements of the box girder into feasible adjustment schemes for the template system and support fixtures, so as to achieve high-quality prefabrication of non-standard box girders using existing beam-making platforms and equipment. In step 2.1, to address the issues of unequal beam widths at the ends of the double-line variable-width simply supported box girder, as well as differences in anchor hole arrangement and prestressing system, a non-standard end mold structure is adopted for end mold fabrication. Specifically, based on the actual design width at both ends of the box girder, the variation in top plate thickness, and the arrangement of anchor plates, a single-hole customized design is carried out for the end mold. The end mold preferably adopts a cuttable and finely adjustable composite wood mold or steel-wood combination mold structure to meet the different geometric size requirements of different beam segments. During the end mold fabrication process, prestressing ducts, anchor holes, and reserved compression control structures are pre-set on the end mold to ensure uniform stress and structural integrity of the end concrete during the tensioning stage. By adopting a non-standard end mold structure, the problem of repeated modification and reinvestment of traditional standard steel end molds in the construction of double-line variable-width beams is avoided, improving the end forming accuracy and construction flexibility. In step 2.2, based on the beam width variation function obtained in step 1, the position of the outer mold flange baffle is adjusted by moving it outward or retracting it to match the gradually changing shape of the beam along the longitudinal direction. Specifically, firstly, the fixed connection between the original outer mold flange baffle and the mold frame is released. Then, according to the design width parameters, the baffle is moved laterally and re-welded or locked onto the outer mold frame to form an outer mold boundary consistent with the outer contour of the beam. After the adjustment is completed, the connection parts of the baffle are ground and sealed to ensure that the template surface is flat and the joints are tight during the concrete pouring process. Through the adaptive adjustment of the outer mold flange baffle, the same set of outer mold systems can meet the forming requirements of box girders of different widths, realizing the efficient reuse of template resources. In step 2.3, the positions of the inner formwork support legs are reconstructed to correspond with the drainage holes at the bottom of the beam and the key stress areas. Specifically, based on the design position of the drainage holes in the bottom plate of the box girder and the stress concentration area of ​​the web plate, the lateral and longitudinal positions of the inner formwork support legs are rearranged so that the legs avoid the drainage hole positions while ensuring the overall stability of the inner formwork, and provide effective support for the bottom plate and web plate areas with greater stress. At the same time, adjustable pads or sleeve structures are set at the contact position between the legs and the bottom formwork to quickly adjust the support height and stress state under different box girder widths and cross sections. Through the above reconstruction method, the inner formwork is ensured to remain stable during concrete pouring and vibration, avoiding local subsidence or displacement. By implementing step 2 and its sub-steps, this invention achieves a systematic adaptation and transformation of the formwork system and supporting fixtures for double-line variable-width simply supported box girders. This enables beam fabrication equipment originally designed for standard beam types to be used efficiently and safely for the prefabrication of non-standard box girders. The introduction of non-standard end formwork structures allows the end structures to precisely match the beam designs of different width sections, significantly improving the quality of end concrete forming and the reliability of prestressed construction. The outward or retraction adjustment of the outer formwork flange baffles makes the outer contour forming of the beam more accurate, avoiding appearance defects and rework risks caused by formwork mismatch. The reconfiguration of the inner formwork frame legs effectively improves the overall stability and stress rationality of the inner formwork, reducing the risk of deformation during concrete pouring. Overall, this step achieves flexible adaptation and efficient reuse of the formwork system without increasing a large amount of fixed investment, providing a reliable guarantee for the factory prefabrication of double-line variable-width simply supported box girders, while reducing construction costs and organizational difficulties, demonstrating significant engineering application value.

[0021] Step 3: Calculate the stress state of the box girder structure and adjust the prefabrication parameters during the prefabrication stage; Step 3 includes: Step 3.1: Establish an equivalent stress model of the box girder during the prefabrication, tensioning, and erection stages before prefabrication; Step 3.2: Calculate the theoretical deflection value δ of the box girder under its own weight and construction loads based on the model; Step 3.3: Preset and adjust the anti-arching amount of the outer mold based on the deflection value.

[0022] In step 3.2, the formula for calculating the theoretical deflection value δ of the beam is as follows: ; Where q is the equivalent construction load per unit length, L is the calculated span of the box girder, E is the elastic modulus of concrete, I is the equivalent moment of inertia of the box girder section, and K is a correction factor related to the support conditions.

[0023] Step 3.3 includes: The calculated theoretical deflection value δ is compared with the preset deflection threshold δ0; When δ>δ0, increase the outer mold arching amount and adjust the thickness of the bottom mold pad; When δ≤δ0, the original anti-arch parameters are kept unchanged and the prefabrication stage is entered.

[0024] The deflection threshold δ0 is set based on the rate of change of the box girder width and satisfies the following: When the beam width change rate is greater than the preset change rate threshold, δ0 takes a smaller value to improve control accuracy. When the beam width change rate is less than or equal to the change rate threshold, δ0 is taken as a larger value to reduce the frequency of construction adjustments.

[0025] Among them, the amount of camber of the outer formwork is distributed along the longitudinal direction of the box girder in a quadratic parabola, and a zero camber section is preset at the beam end to reduce the risk of stress concentration at the end; After completing the adaptive modification of the template system and supporting fixtures, we proceed to step 3, which is to calculate the stress state of the box girder structure and implement prefabrication parameter control during the prefabrication stage. This step introduces an equivalent stress model, deflection calculation and threshold judgment mechanism to transform the structural response of the double-line widened simply supported box girder in the prefabrication stage from experience control to parameterized and quantifiable control, thereby improving the beam alignment accuracy and construction safety. In step 3.1, an equivalent stress model of the box girder during the prefabrication, tensioning and erection stages is established before the box girder is prefabricated. In specific implementation, the box girder is regarded as a simply supported bending member with a gradually changing width along the longitudinal direction. The self-weight of the box girder, the reaction force of the formwork and inner formwork support, the temporary load during the construction stage and the internal force changes caused by prestressing tension are comprehensively considered. In view of the characteristics of the longitudinal change of the cross-sectional geometry of the double-line variable width simply supported box girder, equivalent section parameters are introduced into the model. The stress characteristics of different beam segments are described by segmental equivalent or continuous change, so that the model can truly reflect the stress state of the box girder at each construction stage. In step 3.2, based on the equivalent stress model, the theoretical deflection value δ of the box girder under the combined action of its own weight and construction load is calculated. Through the above calculation, the theoretical deflection value reflecting the overall deflection trend of the box girder in the prefabrication stage can be obtained, providing a quantitative basis for the subsequent anti-arch setting. In step 3.3, the outer formwork camber is preset and adjusted based on the calculated theoretical deflection value δ. Specifically, the theoretical deflection value δ is first compared with the preset deflection threshold δ0. When δ is greater than δ0, it is determined that the box girder has a large risk of downward deflection during the prefabrication stage. At this time, the outer formwork camber is increased, and the thickness of the pad between the bottom formwork and the beam-making platform is adjusted accordingly so that the box girder can offset part of the downward deflection deformation after forming. When δ is less than or equal to δ0, it is determined that the existing camber setting can meet the alignment control requirements. The original camber parameters are kept unchanged, and the subsequent prefabrication process is started. Furthermore, the deflection threshold δ0 is not a fixed value, but is dynamically set according to the rate of change of the box girder width. Specifically, when the rate of change of the beam width is greater than the preset rate of change threshold, it indicates that the box girder cross-section changes drastically and the risk of uneven stress is high. In this case, a smaller δ0 is selected to improve the sensitivity and accuracy of anti-camber control. When the rate of change of the beam width is less than or equal to the rate of change threshold, it indicates that the box girder cross-section changes relatively gently. In this case, a larger δ0 is selected to reduce unnecessary anti-camber adjustments and improve construction efficiency. Regarding the specific setting of the external formwork anti-arch, the anti-arch is set along the longitudinal direction of the box girder in a quadratic parabola distribution, so that the anti-arch at the mid-span is maximized and smoothly transitions to the beam end. At the same time, a zero anti-arch section is preset at the beam end to avoid additional stress concentration caused by the sudden change of anti-arch at the end structure, thereby ensuring the structural safety of the end concrete and prestressed anchorage zone. By implementing step 3, this invention introduces an anti-arch control mechanism based on structural calculation and threshold determination during the prefabrication stage of double-line variable-width simply supported box girders. This transforms the beam alignment control from traditional empirical adjustment to a quantifiable and verifiable technical approach. Through the application of equivalent stress models and deflection calculation formulas, the deflection trend of the box girder under construction loads can be accurately predicted before prefabrication, reducing the risk of alignment deviation after beam completion. By linking the deflection threshold δ0 with the beam width change rate, a dynamic balance between anti-arch control accuracy and construction efficiency is achieved. The introduction of a quadratic parabolic anti-arch distribution and a zero-anti-arch section at the beam end effectively reduces the risk of end stress concentration and local cracks. Overall, this step significantly improves the prefabrication quality, alignment consistency, and construction safety level of double-line variable-width simply supported box girders, providing reliable technical support for the factory-based and standardized production of non-standard box girders.

[0026] Step 4: Based on the calculation results, complete the prefabrication, tensioning, and curing of the box girder; After completing the stress calculation, deflection assessment, and external formwork anti-arch parameter adjustment of the box girder, step 4 is entered, which is to complete the prefabrication, tensioning, and curing of the box girder based on the calculation results. This step is based on the anti-arch parameters, formwork adjustment amount, and stress control results determined in step 3, and the theoretical calculation results are specifically implemented in the actual construction process of the box girder, so as to ensure that the structural performance and alignment quality of the double-line variable width simply supported box girder meet the design requirements in the prefabrication, tensioning, and beam formation stages. During the prefabrication stage, the formwork system is finally checked and locked according to the outer formwork camber, bottom formwork pad thickness and inner formwork support parameters verified in step 3. In specific implementation, the spatial position of the outer formwork, inner formwork and end formwork is checked as a whole before concrete pouring. The focus is on checking whether the camber curve conforms to the preset quadratic parabola distribution form and whether the size of the zero camber section at the beam end meets the design requirements. Then, the concrete is continuously poured in the order of "bottom slab first, then web slab, and finally top slab" to ensure that the box girder is formed in one go. During the pouring process, the attached vibrator and the immersion vibrator are used in combination to make the concrete uniform and dense in the beam section with large width changes, avoiding quality defects such as honeycomb and holes caused by abrupt changes in cross section. During the tensioning stage, based on the development of the concrete strength of the box girder, once the concrete strength reaches the preset proportion of the design strength, the prestressed steel strand tensioning operation is performed. In specific implementation, intelligent tensioning equipment is preferred to be used to manage the tension force and steel strand elongation in a dual-control manner, ensuring that the prestressing application process is consistent with the stress model established in step 3. After the initial tensioning is completed, the box girder alignment and anti-arch recovery are observed and recorded. If the actual alignment is found to deviate from the calculated prediction, the subsequent final tensioning parameters are fine-tuned according to the degree of deviation to further optimize the beam state. After the final tensioning is completed, the duct grouting operation is carried out in a timely manner to make the prestressed system form a stable and complete stress transmission path. During the curing phase, considering the large changes in the cross-sectional dimensions and complex internal structure of the double-line variable-width simply supported box girder, a phased and regional curing approach was adopted. Specifically, during the beam fabrication platform stage, the outer surface of the beam was uniformly cured by covering it with moisture-retaining materials and using an automatic spraying system. At the same time, before the inner formwork was removed, the inner cavity of the box girder was water-filled or sprayed for curing to reduce the temperature difference between the inside and outside of the concrete. After the inner formwork was removed and the beam was transferred to the storage platform, continuous curing was carried out on the top plate, web plate, and internal space of the beam. The concrete temperature was monitored in real time by pre-embedded temperature measuring elements to control the temperature difference between the concrete surface and the interior within the allowable range and prevent cracks caused by temperature stress. By implementing step 4, this invention effectively transforms the stress calculation results and anti-arch control strategy formed in step 3 into specific operations during the actual construction of the box girder. This ensures that the double-line variable-width simply supported box girder maintains consistency in stress state and alignment control throughout the prefabrication, tensioning, and curing processes. By strictly implementing anti-arch parameters and template positioning requirements during the prefabrication stage, the forming accuracy and appearance quality of the box girder are significantly improved. By implementing dual control management of tension force and elongation during the tensioning stage, additional deformation caused by uneven prestressing is effectively avoided. By adopting regional, full-process temperature-controlled curing measures for the width-gradient beam type, early concrete cracking and durability risks are reduced. Overall, this step further consolidates the structural safety, alignment stability, and long-term service performance of the double-line variable-width simply supported box girder, laying a reliable foundation for subsequent erection construction.

[0027] Step 5: Control the stress state under the action of the bridge erecting machine during the erection stage and complete the erection of the box girder.

[0028] Step 5 includes: Step 5.1: Conduct a stress analysis on the position of the bridge erecting machine's columns before the box girder is erected; Step 5.2: When the bridge erecting machine column is located on the side of the single-line beam, a temporary vertical force transmission structure is set up for the single-line beam; Step 5.3: Transfer the erected load to the piers or abutments through the force transmission structure.

[0029] The temporary vertical force transmission structure in step 5.2 includes: A steel pipe column is installed between the top and bottom plates of a single-line beam, and high-strength concrete is poured into it to form a composite load-bearing component. To limit the additional deflection of single-line beams and improve the overall erection safety during the erection of double-line widened simply supported box girders; After completing the prefabrication, tensioning and curing of the double-track widened simply supported box girder, step 5 is entered, which is to control the stress state under the action of the bridge erecting machine and complete the erection of the box girder during the erection stage. This step is designed to address the complex construction conditions at the single and double track junctions, the asymmetrical stress path of the bridge erecting machine columns, and the prominent risk of single-track beam bearing. By combining pre-existing stress analysis with the setting of temporary force transmission structures, the erection process is ensured to be safe and controllable. In step 5.1, a stress analysis is performed on the position of the bridge erecting machine's columns before the box girder is erected. Specifically, based on the structural parameters of the bridge erecting machine, the column spacing, the arrangement of lifting points, and the weight distribution of the box girder, the magnitude of the stress on each column and its position during the erection process are determined. In conjunction with the bridge layout at the single-double parallel section, the working condition of the bridge erecting machine's No. 1 column possibly landing on the top plate area of ​​the single-line beam is analyzed in detail. The vertical concentrated load, additional bending moment, and resulting deflection response borne by the single-line beam under the action of this column are evaluated. Through this stress analysis, the risk of excessive stress that may occur in the single-line beam during the erection of the double-line widened simply supported box girder can be identified in advance, providing a basis for the subsequent arrangement of temporary reinforcement measures. In step 5.2, when the analysis results show that the bridge erecting machine column is located on the side of the single-line beam and the single-line beam itself is not strong enough to directly bear the vertical load, a temporary vertical force transmission structure is set on the single-line beam. Specifically, a steel pipe column is set between the top plate and the bottom plate of the single-line beam at the position corresponding to the axis of the bridge erecting machine column. The two ends of the steel pipe column are tightly attached to the top plate and the bottom plate respectively, and a steel pipe-concrete composite load-bearing member is formed by pouring high-strength concrete. This composite member forms a reliable vertical force-bearing channel in a short time, so that the concentrated load transmitted from the bridge erecting machine column to the single-line beam is no longer borne by the top plate, but is directly transmitted to the bottom plate through the steel pipe column. In step 5.3, the erection load is further transferred to the pier or abutment through a temporary vertical force transmission structure. Specifically, a lifting device or supporting component is set at the corresponding position of the bridge erecting machine column axis between the bottom plate of the single-line beam and the top surface of the pier or abutment. This allows the vertical force transmitted from the steel pipe column to be reliably transmitted to the lower structure through the bottom plate, thus forming a complete force path of "bridge erecting machine column - steel pipe column - bottom plate of single-line beam - pier or abutment". Through this force transmission path, the additional bending moment and deflection of the top plate and web of the single-line beam during the erection process are effectively reduced, avoiding cracks or structural damage. After completing the above temporary stress control measures, the double-line widened simply supported box girder was hoisted, moved longitudinally, lowered and positioned according to the established erection process. After the erection was completed and the stress state was confirmed to have returned to normal, the temporary vertical force transmission structure was dismantled and the original structural state of the single-line beam was restored. By implementing step 5, this invention establishes an active control mechanism for the asymmetrical stress conditions of the bridge erecting machine during the erection stage of the double-track widened simply supported box girder. By performing stress analysis on the action position of the bridge erecting machine's columns before erection, the potential risk conditions that the single-track beam may bear can be identified in advance. By setting up a temporary vertical force transmission structure composed of steel pipe columns and high-strength concrete, the erection load is effectively diverted and transferred downward, significantly reducing the additional deflection and stress level of the single-track beam during the erection process. By directly transferring the erection load to the piers or abutments, the structural safety hazards caused by the single-track beam acting as a temporary load-bearing component are avoided. Overall, this step significantly improves the safety, stability, and controllability of the double-track widened simply supported box girder erection process at the single-double track junction, providing reliable technical support for the smooth erection of non-standard box girders under complex alignment conditions.

[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. The prefabrication and erection construction process of a simply supported box girder with variable width at single and double parallel sections, characterized in that, Includes the following steps: Step 1: Obtain the geometric parameters and spatial constraints of the double-track variable-width simply supported box girder at the single-double parallel section; Step 2: Adapt the precast beam formwork system and supporting fixtures based on the aforementioned geometric parameters; Step 3: Calculate the stress state of the box girder structure and adjust the prefabrication parameters during the prefabrication stage; Step 4: Based on the calculation results, complete the prefabrication, tensioning, and curing of the box girder; Step 5: Control the stress state under the action of the bridge erecting machine during the erection stage and complete the erection of the box girder.

2. The prefabrication and erection construction process of the double-track variable-width simply supported box girder at the single / double parallel section according to claim 1, characterized in that, Step 1 includes: Step 1.1: Obtain the beam width variation function along the longitudinal direction of the double-line variable-width simply supported box girder; Step 1.2: Determine the sections where the line spacing changes at the intersection of single and double lines and the corresponding eccentricity characteristics of the box girder. Step 1.3: Establish a model showing the correspondence between the box girder width variation parameters, support arrangement parameters, and erection equipment working parameters.

3. The prefabrication and erection construction process for a double-track variable-width simply supported box girder at the single / double parallel section according to claim 1, characterized in that, Step 2 includes: Step 2.1: Based on the variation in width at the end of the box girder, a non-standard end mold structure is used to fabricate the end mold; Step 2.2: Adjust the position of the outer mold flange baffle by moving it outward or retracting it to match the shape of the beam; Step 2.3: Reconstruct the position of the inner formwork support legs so that they correspond to the drainage holes at the bottom of the beam and the key stress areas.

4. The prefabrication and erection construction process of the double-track variable-width simply supported box girder at the single / double parallel section according to claim 1, characterized in that, Step 3 includes: Step 3.1: Establish an equivalent stress model of the box girder during the prefabrication, tensioning, and erection stages before prefabrication; Step 3.2: Calculate the theoretical deflection value δ of the box girder under its own weight and construction loads based on the model. Step 3.3: Preset and adjust the amount of camber in the outer mold based on the deflection value.

5. The prefabrication and erection construction process for a double-track variable-width simply supported box girder at the single / double parallel section according to claim 4, characterized in that, The formula for calculating the theoretical deflection value δ of the beam in step 3.2 is as follows: ； Where q is the equivalent construction load per unit length, L is the calculated span of the box girder, E is the elastic modulus of concrete, I is the equivalent moment of inertia of the box girder section, and K is a correction factor related to the support conditions.

6. The prefabrication and erection construction process of the double-track widened simply supported box girder at the single / double parallel section according to claim 5, characterized in that, Step 3.3 includes: The calculated theoretical deflection value δ is compared with the preset deflection threshold δ0; When δ>δ0, increase the outer mold arching amount and adjust the thickness of the bottom mold pad; When δ≤δ0, the original anti-arch parameters are kept unchanged and the prefabrication stage is entered.

7. The prefabrication and erection construction process for a double-track variable-width simply supported box girder at the single / double parallel section according to claim 6, characterized in that, The deflection threshold δ0 is set according to the rate of change of the box girder width and satisfies: When the beam width change rate is greater than the preset change rate threshold, δ0 takes a smaller value to improve control accuracy. When the beam width change rate is less than or equal to the change rate threshold, δ0 is taken as a larger value to reduce the frequency of construction adjustments.

8. The prefabrication and erection construction process for a double-track variable-width simply supported box girder at the single / double parallel section according to claim 7, characterized in that, The external formwork anti-camber is distributed along the longitudinal direction of the box girder in a quadratic parabolic pattern, and a zero anti-camber section is preset at the beam end to reduce the risk of stress concentration at the end.

9. The prefabrication and erection construction process for a double-track variable-width simply supported box girder at the single / double parallel section according to claim 1, characterized in that, Step 5 includes: Step 5.1: Conduct a stress analysis on the position of the bridge erecting machine's columns before the box girder is erected; Step 5.2: When the bridge erecting machine column is located on the side of the single-line beam, a temporary vertical force transmission structure is set up for the single-line beam; Step 5.3: The load is transferred to the piers or abutments through the force transmission structure.

10. The prefabrication and erection construction process for a double-track variable-width simply supported box girder at the single / double parallel section according to claim 9, characterized in that, The temporary vertical force transmission structure in step 5.2 includes: A steel pipe column is installed between the top and bottom plates of a single-line beam, and high-strength concrete is poured into it to form a composite load-bearing component. This is to limit the additional deflection of the single-line beam and improve the overall erection safety during the erection of double-line widened simply supported box girders.

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