Hybrid girder cable-stayed bridge concrete side span and cast-in-place support interactive design method

Abstract

The application relates to the technical field of bridges, and provides a mixed beam cable-stayed bridge concrete side span and cast-in-place support interactive design method, which realizes the unity of structural safety, structural economy and support cost saving through interactive design of the concrete side span and the cast-in-place support, and saves the construction whole-process cost; in the interactive design process, a support batched dismantling scheme, prestressed beam arrangement and three-level adjustment priority of the main beam geometric size are established, the influence of concrete side span parameter adjustment on the mid-span steel beam is reduced to the minimum; the application comprehensively considers the structural new cost and the support amortization cost of the support meeting the stress requirement and the flood season demand, selects the most economical combination scheme, realizes the minimization of the whole life cycle cost of the project under the premise of guaranteeing safety, and can completely avoid the risk of a large number of supports blocking and piling up water in the flood period under the premise of guaranteeing the stress safety of the structure, and ensures smooth flood discharge and support structure safety.

Description

Technical Field

[0001] This invention relates to the field of bridge technology, and in particular to a method for interactive design of concrete side spans and cast-in-place supports in a hybrid beam cable-stayed bridge. Background Technology

[0002] Hybrid beam cable-stayed bridges have been widely used due to their strong span capacity and high stiffness. The side spans of hybrid beam cable-stayed bridges are usually made of heavy and stiff concrete structures, which serve to anchor and counterweight the middle span.

[0003] Due to the significant difference in self-weight between the side spans and the middle span, conventional symmetrical cantilever construction is not feasible. In existing technologies, the concrete side spans are typically poured and prestressed on supports; as the main span and main beam segments are installed sequentially, the stay cables of the side spans and the middle span are also tensioned symmetrically; the cast-in-place supports for the side spans are then removed all at once after the main span is closed and all the stay cables of the bridge are tensioned.

[0004] However, the side span supports of long-span hybrid beam cable-stayed bridges have a high water resistance rate and a long construction period, making it usually impossible to complete the main beam construction and support dismantling in one dry season. Conventional construction procedures have the following problems and shortcomings:

[0005] (1) According to the local regulations on water conservancy technology for bridges across rivers, the allowable water obstruction area of ​​bridges across rivers is generally between 3.5% and 7%. A large number of cast-in-place supports will cause the water obstruction rate in the river channel to exceed the allowable water obstruction rate, which will seriously hinder the normal flow of floodwater during floods, causing backwater and potentially posing a serious danger to the structures on both sides of the river.

[0006] (2) During sudden floods, there are usually a large number of floating objects, and the dense temporary supports greatly increase the water-blocking effect; in severe cases, the temporary supports are at risk of being washed away by the flood, which further damages the completed bridge structure. The existing technology lacks a precise means of simulating the stress state of the structure during the dismantling of the supports. Relevant personnel cannot predict whether the main beam will crack or whether the remaining supports will become unstable during the dismantling of the supports in batches. Therefore, they can only adopt a conservative one-time dismantling strategy.

[0007] (3) The strength of the natural foundation is greatly affected by floods. For cast-in-place supports that need to survive the flood season, bored piles or driven steel pipe piles are usually used. The construction period of the support pile foundation is long, the driven steel pipe piles cannot be effectively recovered, and the cost of the support foundation is high.

[0008] Therefore, it is necessary to propose an interactive design method for the concrete side spans and cast-in-place supports of hybrid beam cable-stayed bridges to solve or at least alleviate the above-mentioned defects. Summary of the Invention

[0009] The main objective of this invention is to provide an interactive design method for the concrete side span and cast-in-place supports of a hybrid beam cable-stayed bridge, in order to solve the technical problems in the prior art where the timing of the removal of the cast-in-place supports for the concrete side span of a hybrid beam cable-stayed bridge is rigid (it must be removed all at once after the entire bridge is closed, and it cannot dynamically adapt to flood warnings) and the main beam structure is designed according to the completed bridge state, without considering the stress requirements of the supports being removed in batches during construction.

[0010] To achieve the above objectives, the present invention provides a method for the interactive design of concrete side spans and cast-in-place supports in a hybrid beam cable-stayed bridge, comprising the following steps:

[0011] S1, obtain the initial structural parameters of the concrete side span main beam, the maximum allowable water-blocking area of ​​the conventional support, and the actual water-blocking area of ​​the conventional support;

[0012] S2, If the actual water-blocking area is greater than the maximum allowable water-blocking area, various plans for dismantling the supports in batches shall be proposed.

[0013] S3. Establish a full-bridge structural analysis model, divide the construction into stages according to the actual construction sequence, input the initial structural parameters and various batch dismantling schemes for supports, and calculate the stress state of the concrete side span main beam and the stress state of the supports under each construction stage.

[0014] S4. Determine whether the stress state of the concrete side span main beam and the stress state of the support meet the preset safety standards at each construction stage. If yes, mark the current support batch dismantling plan as a feasible plan and proceed to step S7; otherwise, proceed to step S5.

[0015] S5. Keep the main beam dimensions unchanged, adjust the arrangement parameters of the prestressed tendons, generate multiple prestressed adjustment sub-schemes, and return to step S3 for recalculation; if there is a prestressed adjustment sub-scheme that makes all construction stages meet the safety standards, then mark the combination of the current support batch dismantling scheme and the prestressed adjustment sub-scheme as a feasible scheme and proceed to step S7; otherwise, proceed to step S6.

[0016] S6. Adjust the geometric dimensions of the concrete side span main beam step by step according to the preset priority. After each adjustment, return to step S5 for prestress optimization and verification until a combination of geometric dimensions and prestress parameters that meets the safety standard is found. Mark it as a feasible solution and proceed to step S7.

[0017] S7 summarizes all feasible solutions, calculates the comprehensive cost of each feasible solution, and selects the feasible solution with the lowest comprehensive cost as the optimal construction solution output.

[0018] Preferably, obtaining the initial structural parameters of the concrete side span main beam in step S1 includes the following steps:

[0019] A finite element model of the entire bridge was established based on the material and geometric properties of the bridge structure. The preliminary structural dimensions of the concrete side span main beam and the preliminary arrangement of the prestressed tendons were obtained by calculating the construction method of the bridge in one step based on the principle of minimum bending energy.

[0020] The construction phases are divided according to the conventional construction procedures. The full span concrete support is simulated in the finite element model of the whole bridge. The full span support is set as a spring unit that is only subjected to compression. The spring unit is passively removed in sequence at the moment of removal, and at the same node position before passive removal, a node force with the same magnitude and opposite direction as the spring support reaction force is applied.

[0021] The entire bridge finite element model was run to perform full-process construction simulation calculations, and the structural stress state of each construction stage was accumulated to obtain the stress distribution of the concrete side span main beam during the entire construction process.

[0022] The stress distribution is compared with the preset stress safety standard. For parts that do not meet the stress safety standard, the preliminary structural dimensions and the preliminary arrangement of the prestressing tendons are optimized and adjusted according to the stress distribution, and the optimized initial structural parameters of the concrete side span main beam are output. The initial structural parameters include beam height, web thickness, top plate thickness, bottom plate thickness and prestressing tendon arrangement parameters.

[0023] Preferably, obtaining the maximum permissible water-blocking area of ​​a conventional support in step S1 includes the following steps:

[0024] Obtain the allowable flood obstruction rate at the bridge site, the water obstruction area of ​​the permanent bridge piers, and the cross-sectional area of ​​the river channel corresponding to the design flood level at the bridge site;

[0025] Calculate the maximum allowable total water obstruction area based on the allowable flood obstruction rate and the cross-sectional area of ​​the river channel.

[0026] The difference between the maximum allowable total water-blocking area and the water-blocking area of ​​the permanent pier is calculated to obtain the maximum allowable water-blocking area of ​​the conventional support.

[0027] Preferably, step S2 includes the following steps:

[0028] S21, if the actual water-blocking area is greater than the maximum allowable water-blocking area, several batch dismantling schemes for the supports are proposed; wherein, each batch dismantling scheme for the supports is generated according to the following principles: at least two steel pipe columns form a support group as the smallest unit for support dismantling; each support group is symmetrically arranged from the middle of the side span towards the bridge piers on both sides; the spatial position coordinates of each support group and the dismantling sequence of each support group are determined;

[0029] S22, For each batch removal scheme of the support, calculate the maximum instantaneous water blocking area at each removal stage, and verify whether the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area.

[0030] S23, filter out all support batch dismantling schemes that satisfy the condition that the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area, and obtain multiple support batch dismantling schemes.

[0031] Preferably, step S3 includes the following steps:

[0032] S31. Establish a full bridge structural analysis model, divide the construction stages according to the actual construction sequence, and input the initial structural parameters and various support batch dismantling schemes into the full bridge structural analysis model.

[0033] S32, In each construction stage, the cast-in-place support is simulated as a spring unit under compression only, and according to the dismantling sequence in the dismantling plan of each support in batches, the spring unit at the corresponding position is blunted in the corresponding dismantling stage. At the same time, a node force with the same magnitude and opposite direction as the supporting reaction force of the spring unit is applied at the same node position before blunting, so as to simulate the load transfer during the dismantling process of the support.

[0034] S33, run the full bridge structure analysis model, calculate and output the normal compressive stress and normal tensile stress at the edge of the concrete section of the main beam of the concrete side span under each construction stage, as well as the axial force and bending moment values ​​of each steel pipe column, as the stress state of the main beam of the concrete side span and the stress state of the support.

[0035] Preferably, step S4, determining whether the stress state of the concrete side span main beam and the stress state of the support meet the preset safety standards at each construction stage, includes the following steps:

[0036] Determine whether the following conditions are met simultaneously at each construction stage:

[0037] Condition 1: The concrete side span main beam satisfies: ; and satisfy: ;in This refers to the normal compressive stress at the edge of the concrete section of the main beam in the side span during the construction phase. This refers to the normal tensile stress in the concrete edge section of the main beam in the concrete side span during the construction phase. This is the design value of the axial compressive strength of concrete. This is the design value for the axial tensile strength of concrete;

[0038] Condition 2: The steel pipe support meets the following strength requirements: ;in, The importance coefficient of the steel pipe support structure. This represents the axial force value of the steel pipe support under load. The effective cross-sectional area of ​​the steel pipe support should take into account the impact of local stability. The design allowable strength of steel as specified in the standard;

[0039] Condition 3: The stability of the steel pipe support meets the following requirements: ;in Let be the bending moment of the steel pipe support about the y-axis under load. The bending moment of the steel pipe support about the z-axis under load. The overall stability reduction factor for axially compressed members , These are the section moduli of the effective section relative to the y-axis and z-axis, respectively, considering the effects of local stability.

[0040] If all construction stages simultaneously meet conditions one, two, and three, then the current phased dismantling plan for the support is deemed to meet the preset safety standards; otherwise, it is deemed not to meet the preset safety standards.

[0041] Preferably, in step S5, keeping the main beam dimensions unchanged and adjusting the prestressing tendon arrangement parameters to generate multiple prestressing adjustment sub-schemes includes the following steps:

[0042] S51, obtain the main beam geometry corresponding to the current support batch dismantling plan that is determined by step S4 to not meet the preset safety standards; wherein, the main beam geometry includes beam height, web thickness, top plate thickness and bottom plate thickness;

[0043] S52, keeping the main beam geometry unchanged, adjust the prestressing tendon arrangement parameters in the following priority order: first adjust the prestressing tensioning sequence; second adjust the prestressing tendon alignment; and finally adjust the prestressing tendon steel strand type.

[0044] S53, Each time the layout parameters are adjusted, a prestressing adjustment sub-scheme is generated; wherein, the prestressing adjustment sub-scheme includes the adjusted tensioning sequence, alignment, and steel strand type;

[0045] S54, the generated multiple prestress adjustment sub-schemes are combined with the current support batch dismantling scheme to form the multiple prestress adjustment sub-schemes.

[0046] Preferably, step S6 includes the following steps:

[0047] S61, Obtain the main beam geometry corresponding to the current support batch dismantling scheme that still does not meet the preset safety standard after adjusting the prestressed tendons in step S5;

[0048] S62, adjust the main beam geometry step by step in the following priority order: first adjust the web thickness, with an adjustment increment of 5cm~10cm; second adjust the top plate thickness or bottom plate thickness, with an adjustment increment of 5cm~10cm; finally adjust the beam height, with an adjustment increment of 5cm~10cm.

[0049] S63, after each size adjustment, a new main beam structure scheme is generated, and the process returns to step S5 to re-optimize and verify the prestressed tendon parameters;

[0050] S64. Repeat steps S62 to S63 until a combination of geometric dimensions and prestressed tendon parameters is found that meets the safety criteria. Mark the combination as a feasible solution and proceed to step S7.

[0051] Preferably, step S7 includes the following steps:

[0052] S71, summarize all feasible solutions; each feasible solution includes the final geometric dimensions of the concrete side span main beam, the final arrangement parameters of the prestressed tendons, and the final phased removal plan of the cast-in-place support.

[0053] S72, obtain the benchmark main beam material cost and benchmark support service life corresponding to the conventional construction scheme;

[0054] S73, for each feasible option, calculate the increase in main beam material cost relative to the baseline main beam material cost;

[0055] S74. For each feasible scheme, calculate the actual service life of each support group according to the dismantling sequence in the final batch dismantling scheme, and calculate the amortization cost of support materials.

[0056] S75, For each feasible solution, calculate the comprehensive cost based on the increase and the amortization cost of the support material;

[0057] S76 compares the overall cost of all feasible solutions and selects the feasible solution with the lowest overall cost as the optimal construction solution output.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] This application achieves a balance between structural safety, structural economy, and cost savings in support structures through the interactive design of concrete side spans and cast-in-place supports, thus reducing costs throughout the construction process. During the interactive design process, this application establishes a three-tiered priority system for adjusting the phased removal of supports, the arrangement of prestressed tendons, and the geometric dimensions of the main beam. This minimizes the impact of adjusting the parameters of the concrete side spans on the mid-span steel beams, breaking the rigid constraint of one-time removal and enabling dynamic, phased early removal of supports before the flood season. For supports that meet structural requirements and flood control needs, this application comprehensively considers the additional structural costs and support amortization costs, selecting the most economical combination scheme to minimize the project's life-cycle cost while ensuring safety. Through interactive design, this application determines the construction method for early removal of some supports, enabling the early removal of some supports before the flood season while ensuring structural structural safety. This completely avoids the risk of water blockage and backlog caused by a large number of supports during the flood season, ensuring smooth flood discharge and structural safety. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0061] Figure 1 This is a schematic flowchart of one embodiment of the present invention;

[0062] Figure 2 This is a schematic diagram of the structure after erecting a cast-in-place support for the side span in one embodiment of the present invention, casting a concrete main beam for the side span on the support, and tensioning the prestressed steel strands after the concrete strength reaches the design requirements.

[0063] Figure 3 This is a schematic diagram of the structure after the early removal of the cast-in-place support for the side span in one embodiment of the present invention;

[0064] Figure 4 This is a schematic diagram of the structure after the simultaneous installation and tensioning of the stay cables in the side span and the middle span, according to one embodiment of the present invention;

[0065] Figure 5 This is a schematic diagram of the main span structure after closure in one embodiment of the present invention;

[0066] Figure 6 This is a schematic diagram of the structure after removing the remaining side span cast-in-place support in one embodiment of the present invention;

[0067] Figure 7This is a schematic diagram of a side span support system in the prior art;

[0068] Figure 8 This is a schematic diagram of the support structure that was removed in advance.

[0069] Figure 9 A schematic diagram of the brackets that were later removed;

[0070] Figure 10 This is a schematic diagram of the Bailey beam before its separation and dismantling in one embodiment of the present invention;

[0071] Figure 11 This is a schematic diagram of the structure after the Bailey beam is separated and dismantled in one embodiment of the present invention;

[0072] Figure 12 This is a schematic diagram of the structure of the bracket graded unloading block assembly in one embodiment of the present invention;

[0073] Figure 13 for Figure 12 A view along the AA direction;

[0074] Figure 14 for Figure 13 A view along the BB direction;

[0075] Figure 15 for Figure 12 A view along the CC direction.

[0076] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0077] Explanation of icon numbers:

[0078] 10. First support unit; 110. First I-beam; 120. Second I-beam; 130. First detachable connector; 20. Second support unit; 210. Third I-beam; 220. Fourth I-beam; 230. Second detachable connector; 30. Third connector; 310. Rectangular slot; 320. Nut; 40. Filling layer; 50. Base connecting plate; 610. First batch of cutting seams; 620. Second batch of cutting seams; 710. Bailey beam lower chord; 720. Connecting pin; 81. Foundation; 82. Steel pipe column; 83. Horizontal bracing; 84. Diagonal brace; 85. Pier top steel plate; 86. Bailey beam; 87. Lower crossbeam; 91. Pre-removed support; 92. Post-removed support; 93. Concrete side span main beam; 94. Stay cable. Detailed Implementation

[0079] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0080] 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 a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0081] In this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0082] Please refer to Figures 1 to 15 The present invention provides a method for interactive design of concrete side spans and cast-in-place supports in a hybrid beam cable-stayed bridge, comprising the following steps:

[0083] S1, obtain the initial structural parameters of the concrete side span main beam 93, the maximum allowable water-blocking area of ​​the conventional support, and the actual water-blocking area of ​​the conventional support;

[0084] S2, If the actual water-blocking area is greater than the maximum allowable water-blocking area, various plans for dismantling the supports in batches shall be proposed.

[0085] S3, establish a full bridge structure analysis model, divide the construction stages according to the actual construction sequence, input the initial structural parameters and various support batch removal schemes, and calculate the stress state of the concrete side span main beam 93 and the support under each construction stage;

[0086] S4, determine whether the stress state of the concrete side span main beam 93 and the stress state of the support meet the preset safety standards at each construction stage; if yes, mark the current support batch dismantling plan as a feasible plan and proceed to step S7; otherwise, proceed to step S5.

[0087] S5. Keep the main beam dimensions unchanged, adjust the arrangement parameters of the prestressed tendons, generate multiple prestressed adjustment sub-schemes, and return to step S3 for recalculation; if there is a prestressed adjustment sub-scheme that makes all construction stages meet the safety standards, then mark the combination of the current support batch dismantling scheme and the prestressed adjustment sub-scheme as a feasible scheme and proceed to step S7; otherwise, proceed to step S6.

[0088] S6. Adjust the geometric dimensions of the concrete side span main beam 93 step by step according to the preset priority. After each adjustment, return to step S5 for prestress optimization and verification until a combination of geometric dimensions and prestress parameters that meets the safety standard is found. Mark it as a feasible solution and proceed to step S7.

[0089] S7 summarizes all feasible solutions, calculates the comprehensive cost of each feasible solution, and selects the feasible solution with the lowest comprehensive cost as the optimal construction solution output.

[0090] In a preferred embodiment, obtaining the initial structural parameters of the concrete side span main beam 93 in step S1 includes the following steps:

[0091] A finite element model of the entire bridge was established based on the material and geometric properties of the bridge structure. The preliminary structural dimensions and preliminary arrangement of prestressed tendons of the concrete side span main beam 93 were obtained by calculating the minimum bending energy according to the one-time bridge construction method.

[0092] First, a finite element model of the entire bridge is established based on the material properties of the bridge structure (such as the elastic modulus and compressive strength standard value of concrete, and the yield strength of steel) and geometric characteristics (such as the main span, side span, tower height, and cable arrangement). In the full-bridge finite element model, the minimum bending energy method, well-known in the field, is used to determine the reasonable completed bridge state of the hybrid beam cable-stayed bridge. The principle of this method is: using cable force distribution, main beam bending moment, main tower bending moment, and side pier reaction force as control targets, the initial tension of the cable-stayed cables 94 is optimized to minimize the bending strain energy of the main beam under dead load, thereby obtaining a stress-balanced and smoothly aligned completed bridge state. Through this calculation, the preliminary structural dimensions of the concrete side span main beam 93 (including beam height, web thickness, top plate thickness, and bottom plate thickness) and the preliminary arrangement of the prestressed tendons (including tendon type, alignment, and tensioning sequence) can be obtained.

[0093] The construction phases are divided according to the conventional construction procedures. The full span concrete support is simulated in the finite element model of the whole bridge. The full span support is set as a spring unit that is only subjected to compression. The spring unit is passively removed in sequence at the moment of removal, and at the same node position before passive removal, a node force with the same magnitude and opposite direction as the spring support reaction force is applied.

[0094] Using the preliminary structural dimensions and prestressed tendon arrangement as input, the finite element model of the entire bridge is divided into detailed construction stages according to conventional construction procedures. For example... Figures 2 to 6 The typical construction stages are divided into:

[0095] Stage (1): Erect the cast-in-place support for the side span, pour concrete main beam 93 on the support, and tension the prestressed steel strands after the concrete strength reaches the design requirements; Stage (2): Remove the cast-in-place support for the side span in advance; Stage (3): Install and tension the cable stays 94 of the side span and the middle span simultaneously; Stage (4): Close the main span structure; Stage (5): Remove the remaining cast-in-place support for the side span.

[0096] In this embodiment, the simulation of the cast-in-place support uses compression-only spring units. Specifically, a spring unit is placed below each node of the concrete side span main beam 93. This spring unit only functions when under pressure (i.e., simulating the support of the beam). When the beam detaches from the support, the spring unit automatically disengages. During support dismantling, the spring units are sequentially deactivated according to the dismantling steps. At the same node position before deactivation, a node force equal in magnitude and opposite in direction to the supporting reaction force of the spring unit is applied. This simulates the smooth transfer of load from the support to the main beam and cable-stayed cable 94 system during support dismantling, solving the technical problem of accurately simulating the sudden change in stress during support dismantling in traditional finite element analysis.

[0097] The entire bridge finite element model was run to perform full-process construction simulation calculations, and the structural stress state of each construction stage was accumulated to obtain the stress distribution of the concrete side span main beam 93 during the entire construction process.

[0098] The finite element model of the entire bridge was run to perform full-process construction simulation calculations according to the construction stages. During the calculation, the finite element program automatically accumulated the structural stress state of each construction stage, taking into account time-dependent effects such as geometric nonlinearity and concrete shrinkage and creep, and finally output the stress distribution of the concrete side span main beam 93 in each construction stage.

[0099] The stress distribution is compared with a preset stress safety standard (preferably the safety standard required by current domestic specifications). For parts that do not meet the stress safety standard, the preliminary structural dimensions and the preliminary arrangement of the prestressing tendons are optimized and adjusted according to the stress distribution, and the optimized initial structural parameters of the concrete side span main beam 93 are output. These initial structural parameters include beam height, web thickness, top slab thickness, bottom slab thickness, and prestressing tendon arrangement parameters. The obtained stress distribution throughout the process is compared with the preset stress safety standard stage by stage and part by part. For parts that do not meet the stress safety standard, the preliminary structural dimensions and the preliminary arrangement of the prestressing tendons are optimized and adjusted specifically according to the degree and location of stress exceeding the limit. The adjustment principle is: priority is given to adjusting the prestressing (such as adjusting the tensioning sequence, alignment, and tendon type); if this is still not met, then the geometric dimensions are adjusted (prioritizing the web, top and bottom slabs, and beam height). After optimization and adjustment, return to step S3 to perform full-process simulation until all construction stages and all parts meet the stress safety standards. At this point, the dimensional parameters and bundle parameters obtained after iterative convergence are used as the initial structural parameters of the optimized concrete side span main beam 93.

[0100] In a preferred embodiment, obtaining the maximum permissible water-blocking area of ​​a conventional support in step S1 includes the following steps:

[0101] Obtain the allowable flood obstruction rate at the bridge site, the water obstruction area of ​​the permanent bridge piers, and the cross-sectional area of ​​the river channel corresponding to the design flood level at the bridge site;

[0102] The allowable flood obstruction rate is a control indicator determined based on the river class, flood control planning, and relevant specifications. The obstruction area of ​​permanent bridge piers can be calculated based on the size, number, and layout of the permanent bridge piers in the preliminary bridge design scheme, and is the sum of the projected areas of all permanent bridge piers in the direction of water flow under the design flood level. The cross-sectional area of ​​the river channel corresponding to the design flood level at the bridge site can be determined based on the hydrological analysis report of the river section at the bridge site and the river topographic survey data, and is the total cross-sectional area of ​​the river channel under the design flood level of a certain return period (such as once in 100 years) corresponding to the bridge flood control standard.

[0103] The maximum allowable total water obstruction area is calculated based on the allowable flood obstruction rate and the cross-sectional area of ​​the river channel. The total cross-sectional area of ​​the river channel at the bridge site under the design flood level is the total flood passage. The allowable flood obstruction rate specifies the maximum proportion that permanent piers and temporary supports can occupy. Therefore, the maximum allowable total water obstruction area is the product of the allowable flood obstruction rate and the cross-sectional area of ​​the river channel.

[0104] The difference between the maximum permissible total water-blocking area and the water-blocking area of ​​the permanent pier is calculated to obtain the maximum permissible water-blocking area of ​​the conventional support. After obtaining the maximum permissible total water-blocking area, the water-blocking area of ​​the permanent pier already occupied is subtracted. The remaining space is the space that the temporary support can occupy. This value is used as a constraint for the subsequent phased dismantling plan of the support. The maximum instantaneous water-blocking area of ​​the phased dismantling plan must not exceed this value at any stage of dismantling.

[0105] In a preferred embodiment, step S2 includes the following steps:

[0106] S21, if the actual water-blocking area is greater than the maximum allowable water-blocking area, several batch dismantling schemes for the supports are proposed; wherein, each batch dismantling scheme for the supports is generated according to the following principles: at least two steel pipe columns form a support group as the smallest unit for support dismantling; each support group is symmetrically arranged from the middle of the side span towards the bridge piers on both sides; the spatial position coordinates of each support group and the dismantling sequence of each support group are determined;

[0107] If the actual water-blocking area is greater than the maximum allowable water-blocking area, flood discharge is deemed restricted, and the design process for a phased dismantling plan for the support structures needs to be initiated. When formulating the plan, the following principles are followed to generate multiple phased dismantling schemes for the support structures:

[0108] (1) Grouping principle of supports: At least two steel pipe columns are used to form a support group, which serves as the smallest unit for support dismantling. The purpose of setting up groups instead of dismantling single columns is that: the lateral stability of a single steel pipe column is poor and it is easy to overturn during the dismantling process; by forming a group of two or more steel pipe columns, a stable spatial force system can be formed, ensuring the overall stability of the remaining supports during the dismantling process.

[0109] (2) Symmetrical arrangement principle: Each support group is arranged symmetrically from the mid-span of the side span towards the piers on both sides. The purpose of symmetrical dismantling is to ensure that the main beam is subjected to balanced forces during the unloading process of the support, and to avoid excessive additional torsional moment or lateral deformation of the main beam due to excessive unloading on one side.

[0110] (3) Parameter determination: Determine the spatial coordinates of each support group and the dismantling sequence of each support group to form a preliminary support batch dismantling plan.

[0111] S22, For each batch removal scheme of the support, calculate the maximum instantaneous water blocking area at each removal stage, and verify whether the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area.

[0112] For each type of phased dismantling scheme, the entire construction process is divided into several dismantling stages based on the dismantling sequence. In each dismantling stage, the number of steel pipe columns still in service is counted, and the maximum instantaneous water-blocking area is calculated. This verifies whether the maximum instantaneous water-blocking area is less than or equal to the maximum allowable water-blocking area. This step ensures that the water-blocking area at any given moment does not exceed the maximum allowable water-blocking area through stage-by-stage verification. If the calculated value of a scheme exceeds the maximum allowable water-blocking area in a certain stage, the scheme is deemed unsuitable for flood control and is discarded.

[0113] S23, filter out all support batch dismantling schemes that satisfy the condition that the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area, and obtain multiple support batch dismantling schemes.

[0114] After completing the phased verification of all proposed support dismantling schemes, all support dismantling schemes that satisfy the condition that the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area are selected, resulting in a variety of support dismantling schemes.

[0115] In a preferred embodiment, step S3 includes the following steps:

[0116] S31. Establish a full bridge structural analysis model, divide the construction stages according to the actual construction sequence, and input the initial structural parameters and various support batch dismantling schemes into the full bridge structural analysis model.

[0117] Establish a full-bridge structural analysis model (e.g., using common commercial finite element software), divide the construction into stages according to the actual construction sequence, and input the initial structural parameters and various support batch removal schemes into the full-bridge structural analysis model as the basis for subsequent simulation calculations.

[0118] S32, In each construction stage, the cast-in-place support is simulated as a spring unit under compression only, and according to the dismantling sequence in the dismantling plan of each support in batches, the spring unit at the corresponding position is blunted in the corresponding dismantling stage. At the same time, a node force with the same magnitude and opposite direction as the supporting reaction force of the spring unit is applied at the same node position before blunting, so as to simulate the load transfer during the dismantling process of the support.

[0119] In each construction phase, the cast-in-place support is simulated as a spring unit subjected only to compression. The spring unit only functions when subjected to pressure and automatically ceases operation when the beam detaches from the support, simulating the actual physical characteristic of the support only supporting and not pulling. According to the dismantling sequence in the phased dismantling plan for each support, the spring units at the corresponding positions are deactivated sequentially in the corresponding dismantling phase. At the same node position before deactivation, a nodal force equal in magnitude and opposite in direction to the supporting reaction force of the spring unit is applied to simulate the load transfer during the dismantling process.

[0120] S33, run the full bridge structure analysis model, calculate and output the normal stress of the concrete section and the bearing capacity of the concrete structure under the long-term condition of the concrete side span main beam 93 under each construction stage, as well as the strength and stability of the steel pipe support of each steel pipe column, as the stress state of the concrete side span main beam 93 and the stress state of the support.

[0121] The full-bridge structural analysis model is run to perform full-process construction simulation calculations. During the calculation, the program automatically accumulates the structural stress state at each construction stage and considers time-dependent effects such as geometric nonlinearity and concrete shrinkage and creep. It outputs the normal stress of the concrete section of the main beam 93 of the concrete side span and the bearing capacity of the concrete structure under the long-term condition, as well as the strength and stability of the steel pipe supports of each steel pipe column at each construction stage.

[0122] In a preferred embodiment, step S4, determining whether the stress state of the concrete side span main beam 93 and the stress state of the support meet the preset safety standards at each construction stage, includes the following steps:

[0123] Determine whether the following conditions are met simultaneously at each construction stage:

[0124] Condition 1: The 93mm concrete side span main beam satisfies the following: ; and satisfy: ;in The normal compressive stress (MPa) at the edge of the concrete section of the main beam 93 of the concrete side span during the construction stage. The normal tensile stress (MPa) at the edge of the concrete section of the main beam 93 of the concrete side span during the construction stage. This represents the design value of the axial compressive strength of concrete (MPa). The design value of the axial tensile strength of concrete (MPa);

[0125] Condition 2: The steel pipe support meets the following strength requirements: ;in, The importance coefficient of the steel pipe support structure. MN represents the axial force (MN) of the steel pipe support under load. The effective cross-sectional area (m²) of the steel pipe support considering local stability effects 2 ), The design allowable strength (MPa) of steel as specified in the standard;

[0126] Condition 3: The stability of the steel pipe support meets the following requirements: ;in Let MN be the bending moment (MN·m) of the steel pipe support about the y-axis under load. Let MN be the bending moment (MN·m) of the steel pipe support about the z-axis under load. The overall stability reduction factor for axially compressed members , These are the section moduli (m) of the effective section relative to the y-axis and z-axis, respectively, considering the effects of local stability. 3 If all construction stages simultaneously meet conditions one, two, and three, then the current phased dismantling plan for the support is deemed to meet the preset safety standards; otherwise, it is deemed not to meet the preset safety standards.

[0127] Preferably, the overall stability reduction factor of the axially compressed member Calculate using the following formula:

[0128] ;

[0129] in, , ;in, The slenderness ratio under axial compression can be directly selected according to the specifications; E is the yield strength of the steel; E is the elastic modulus of the steel. The calculation parameter for the overall stability reduction factor of an axially compressed member can be directly obtained by referring to the specifications. For relative slenderness ratio, Intermediate parameters for calculating the reduction factor (no explicit definition).

[0130] As a preferred embodiment, step S5, which keeps the main beam dimensions unchanged and adjusts the prestressing tendon arrangement parameters to generate multiple prestressing adjustment sub-schemes, includes the following steps:

[0131] S51, obtain the main beam geometry corresponding to the current support batch dismantling plan that is determined by step S4 to not meet the preset safety standards; wherein, the main beam geometry includes beam height, web thickness, top plate thickness and bottom plate thickness;

[0132] S52, keeping the main beam's geometric dimensions unchanged, adjust the prestressed tendon arrangement parameters in the following priority order: first, adjust the prestressing tensioning sequence; second, adjust the prestressed tendon alignment; and finally, adjust the prestressed tendon steel strand type. Adjusting the tensioning sequence does not increase material costs, only changes the construction sequence, and has the most direct impact on structural stress and is the most economical. Adjusting the alignment involves ductwork arrangement, which has a moderate cost. Adjusting the steel strand type involves changes in material specifications, which has the highest cost and should be used as a last resort.

[0133] S53, Each time the layout parameters are adjusted, a prestressing adjustment sub-scheme is generated; wherein, the prestressing adjustment sub-scheme includes the adjusted tensioning sequence, alignment, and steel strand type;

[0134] S54, the generated multiple prestress adjustment sub-schemes are combined with the current support batch dismantling scheme to form the multiple prestress adjustment sub-schemes.

[0135] As a preferred example, step S6 includes the following steps:

[0136] S61, Obtain the main beam geometry corresponding to the current support batch dismantling scheme that still does not meet the preset safety standard after adjusting the prestressed tendons in step S5;

[0137] S62. Adjust the main beam's geometric dimensions step by step according to the following priority order: First, adjust the web thickness in increments of 5cm to 10cm; second, adjust the top or bottom slab thickness in increments of 5cm to 10cm; finally, adjust the beam height in increments of 5cm to 10cm. Adjusting the web thickness first, in increments of 5cm to 10cm, is crucial because the web contributes the most to the shear strength and stiffness of the section, and prioritizing its adjustment can quickly improve the structural stress while having the least impact on the bridge deck system. Adjusting the top or bottom slab thickness in increments of 5cm to 10cm affects the bridge deck elevation or lower edge alignment. Finally, adjusting the beam height in increments of 5cm to 10cm has the greatest impact on the overall bridge stiffness and may affect the clearance under the bridge; it should be used as a last resort. The increments of 5cm to 10cm are engineering experience values ​​determined based on the minimum structural dimensions of the concrete structure and the modularity of the construction formwork, ensuring the adjustment effect while avoiding over-adjustment.

[0138] S63, after each size adjustment, a new main beam structure scheme is generated, and the process returns to step S5 to re-optimize and verify the prestressed tendon parameters;

[0139] S64. Repeat steps S62 to S63 until a combination of geometric dimensions and prestressed tendon parameters is found that meets the safety criteria. Mark the combination as a feasible solution and proceed to step S7.

[0140] In a preferred embodiment, step S7 includes the following steps:

[0141] S71, summarize all feasible solutions; each feasible solution includes the final geometric dimensions of the concrete side span main beam 93, the final arrangement parameters of the prestressed tendons, and the final phased removal plan of the cast-in-place support.

[0142] S72, obtain the material cost of the benchmark main beam and the service life of the benchmark support corresponding to the conventional construction scheme; the material cost of the benchmark main beam can be calculated based on the conventional design dimensions and bundle arrangement, according to the market material unit price. The service life of the benchmark support is the total number of days from the erection of the support to its one-time dismantling in the conventional scheme.

[0143] S73, for each feasible option, calculate the increase in main beam material cost relative to the baseline main beam material cost;

[0144] S74. For each feasible scheme, calculate the actual service life of each support group according to the dismantling sequence in the final batch dismantling scheme, and calculate the amortization cost of support materials.

[0145] S75, For each feasible solution, calculate the comprehensive cost based on the increase and the amortization cost of the support material;

[0146] S76 compares the overall cost of all feasible solutions and selects the feasible solution with the lowest overall cost as the optimal construction solution output.

[0147] As another preferred embodiment, this application also provides a design and dismantling construction plan for the cast-in-place support system for the side span. For the cast-in-place support design, the side span support system of this application consists of foundations, steel pipe columns, horizontal bracing, diagonal bracing, pier top steel plates, lower crossbeams, unloading blocks, Bailey bridges, I-beams, square timber, and formwork. According to the proposed support dismantling plan, the side span support foundation is divided into two types: supports to be dismantled later use driven steel pipe pile foundations, while supports that can be dismantled earlier use strip spread foundations.

[0148] The connection point between the driven steel pipe pile and the steel pipe column is a high-stress area, and the two are welded together using a single-sided bevel weld. Four reinforcing connecting plates are evenly arranged around the connection point and welded to the steel pipe pile and steel pipe column using a circumferential fillet weld. The same connection method can be used for steel pipe columns that need to be extended.

[0149] Please see the appendix Figures 7 to 15 In another embodiment, the present invention also provides a bracket-stage unloading block assembly for a hybrid beam cable-stayed bridge, comprising:

[0150] The first support unit 10 includes two opposing I-beams 110 and 120, with their webs facing each other and fixedly connected by a first detachable connector 130 to form a first box-shaped structure. Further, the first and second detachable connectors 130 are first screws, each with a fastening nut 320 at both ends. The first screws pass through corresponding connecting holes (not shown in the figure) on the webs of the two I-beams and are locked at both ends by the fastening nuts 320. Through this connection method, the first and second I-beams 110 and the space between them together form a box-shaped structure, i.e., the first box-shaped structure. This first box-shaped structure has a closed cross-section, effectively bearing vertical loads and possessing a certain bending stiffness.

[0151] The second support unit 20 includes two opposing third I-beams 210 and fourth I-beams 220, the webs of the third I-beams 210 and the fourth I-beams 220 are opposite to each other, and the two are fixedly connected by a second detachable connector 230 to enclose and form a second box-shaped structure.

[0152] A third connecting member 30 connects the first support unit 10 and the second support unit 20, detachably linking the first box-shaped structure and the second box-shaped structure into an integral support structure, and forming a filling cavity between the first support unit 10 and the second support unit 20. Further, the third detachable connecting member is a second screw, with fastening nuts 320 at both ends, and the length of the second screw is greater than the length of the first screw. The second screw passes through the webs of the first I-beam 110, the second I-beam 120, the third I-beam 210, and the fourth I-beam 220, and is locked at both ends by fastening nuts 320. Through the connection of the third connecting member 30, the first box-shaped structure and the second box-shaped structure are detachably connected into an integral support structure. At this time, a closed cavity, i.e., a filling cavity, is formed between the first support unit 10 and the second support unit 20.

[0153] A filler layer 40 is disposed within the filled cavity. The filler layer 40 transmits pressure under normal load conditions and provides thermal insulation and buffering during unloading.

[0154] Furthermore, the second I-beam 120 and the third I-beam 210 are arranged adjacent to each other, forming the filling cavity between them. The upper and lower flanges of the second I-beam 120 and the third I-beam 210 are arranged side by side and adjacent to each other.

[0155] In a preferred embodiment, the upper flange of the second I-beam 120 is provided with a first slot (not shown in the figure) that connects to the filling cavity, and the upper flange of the third I-beam 210 is provided with a second slot (not shown in the figure) that connects to the filling cavity. The first slot and the second slot are provided correspondingly and together form a rectangular slot 310.

[0156] Specifically, before installing the bracket-type unloading block assembly, construction workers can fill the cavity with fine sand through the rectangular groove to ensure a dense filling. When cutting the web of the I-beam, the cutting point is in direct contact with the fine sand, and the heat is quickly absorbed and diffused by the sand, thus providing insulation. Simultaneously, the rectangular groove allows for direct observation of the fine sand's flow during the cutting operation. When cutting the web causes fine sand to flow out, operators can observe its descent through the rectangular groove to judge the unloading progress. For example, after removing the first support unit 10, one side of the cavity is open, and the fine sand flows outward through the first groove under gravity, which is beneficial for subsequent cutting.

[0157] In another preferred embodiment, the lower end of the first support unit 10 and / or the second support unit 20 is provided with a base connecting plate 50, and the base connecting plate 50 has bolt holes for connecting with the lower steel pipe column 82. The base connecting plate 50 enables a detachable connection between the bracket graded unloading block assembly and the lower steel pipe column 82.

[0158] In a preferred embodiment, the webs of the first I-beam 110, the second I-beam 120, the third I-beam 210, and the fourth I-beam 220 are provided with cutting guide marking lines (not shown in the figure), and the cutting guide marking lines are located in the upper middle region of the webs.

[0159] Specifically, cutting guide marking lines are provided on the webs of the first I-beam 110, the second I-beam 120, the third I-beam 210, and the fourth I-beam 220. These cutting guide marking lines are located in the upper-middle region of the webs, specifically at 2 / 3 to 4 / 5 of the web height, and on both sides of the support center line of the lower chord 710 of the Bailey beam. This position avoids the high-stress area at the bottom of the webs and ensures a smooth change in stress at the support point of the lower chord 710 when cutting the first batch of areas. Furthermore, the cutting guide marking lines are located on both sides of the support center line of the lower chord 710, and the spacing between the two marking lines is preferably equal to twice the width of the lower chord.

[0160] The cutting guide markings are pre-set on the web surface using either stamping or high-temperature resistant coating. When operators are cutting at height, there is no need for temporary measurements or marking; they can directly cut according to the pre-set markings. This avoids cutting position deviations caused by manual measurement errors, ensuring that the first batch of cuts always falls within the predetermined range. Furthermore, it standardizes operations, guaranteeing consistent unloading results even when different work teams are involved.

[0161] Preferably, the first support unit 10 and the second support unit 20 are symmetrically arranged about the central plane of the filled cavity. Under normal load-bearing conditions, the load transmitted from the Bailey beam 86 is evenly distributed to the lower structure through the four I-beams, ensuring uniform stress distribution under normal load-bearing conditions. The symmetrical design allows the first support unit 10 and the second support unit 20 to be used interchangeably without the need to distinguish left from right on site.

[0162] As a preferred example, the filling layer 40 is fine sand with a particle size ranging from 0.15 mm to 2.36 mm. The lower limit of 0.15 mm ensures sufficient voids between particles, maintaining a certain degree of fluidity under pressure. Particles larger than 2.36 mm have better fluidity but a higher void ratio, easily leading to bridging. Therefore, this embodiment uses a particle size range of 0.15 mm to 2.36 mm. Furthermore, during the cutting of the web of the inner I-beam and the descent of the Bailey beam 86, the fine sand acts as a buffer medium, being gradually compacted and providing a cushioning effect.

[0163] Workflow:

[0164] Before the support structure is removed, the tiered unloading block assembly has been installed between the steel pipe column 82 and the Bailey beam 86 and is under load. At this time, the first support unit 10 and the second support unit 20 are connected as a whole by the third connector 30, and the cavity is filled with fine sand, which is poured in through a rectangular groove.

[0165] When dismantling the support structure, first remove the connecting pin 720 of Bailey beam 86, and then separate and unload the dismantled and retained support structures. After separation and unloading, the Bailey beam 86 to be dismantled is removed, and the retained Bailey frame remains in its original support state.

[0166] During unloading, first remove the second screw and its nut 320, then remove the first screw and nut 320 of one of the box-shaped structures. At this time, the mechanical connection between the first support unit 10 and the second support unit 20 is released, but the fine sand in the cavity still transmits pressure, the upper structure remains stable, and the initial unloading is achieved.

[0167] Select the side to be demolished (e.g., the first support unit 10) according to construction needs, and remove the first detachable connector 130 and the second detachable connector 230 (i.e., the first screw) and its nut 320 from the first support unit 10. Remove the two I-beams from the first screw by cutting the web. Cut and remove the two I-beams sequentially from the outside in.

[0168] When cutting the web of the I-beam, to prevent sudden damage during the cutting process, the cutting position is located at the upper part of the web, and the horizontal cutting area is divided into two batches. The first batch of cutting areas is the area on both sides of the support centerline of the lower chord member 710 of the Bailey beam, which is one width of the lower chord member; the remaining area is the second batch of cutting areas. When cutting the external I-beam, the first batch of areas is cut first to cause some deformation in a local area of ​​the top plate supporting the lower chord member 710 of the Bailey beam, achieving initial unloading of the I-beam; then the second batch of areas is cut to complete the unloading of the entire I-beam; the unloaded I-beam is then removed.

[0169] After the outer I-beams are removed, the lower chord 710 of the Bailey beam rests on the inner I-beam. The web of the inner I-beam is cut in the same way as the outer I-beam. Once the web is cut, the top plate of the I-beam deforms and moves downward as a whole, causing the Bailey beam 86 and the upper formwork system supported on the top plate to move downward simultaneously, thus separating them from the concrete structure and allowing for the further removal of the partial support system.

[0170] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A design method for the interaction between concrete side spans and cast-in-place supports in a hybrid beam cable-stayed bridge, characterized in that, Includes the following steps: S1, obtain the initial structural parameters of the concrete side span main beam, the maximum allowable water-blocking area of ​​the conventional support, and the actual water-blocking area of ​​the conventional support; S2, If the actual water-blocking area is greater than the maximum allowable water-blocking area, various plans for dismantling the supports in batches shall be proposed. S3. Establish a full-bridge structural analysis model, divide the construction into stages according to the actual construction sequence, input the initial structural parameters and various batch dismantling schemes for supports, and calculate the stress state of the concrete side span main beam and the stress state of the supports under each construction stage. S4. Determine whether the stress state of the concrete side span main beam and the stress state of the support meet the preset safety standards at each construction stage. If yes, mark the current support batch dismantling plan as a feasible plan and proceed to step S7; otherwise, proceed to step S5. S5. Keep the main beam dimensions unchanged, adjust the arrangement parameters of the prestressed tendons, generate multiple prestressed adjustment sub-schemes, and return to step S3 for recalculation; if there is a prestressed adjustment sub-scheme that makes all construction stages meet the safety standards, then mark the combination of the current support batch dismantling scheme and the prestressed adjustment sub-scheme as a feasible scheme and proceed to step S7; otherwise, proceed to step S6. S6. Adjust the geometric dimensions of the concrete side span main beam step by step according to the preset priority. After each adjustment, return to step S5 for prestress optimization and verification until a combination of geometric dimensions and prestress parameters that meets the safety standard is found. Mark it as a feasible solution and proceed to step S7. S7 summarizes all feasible solutions, calculates the comprehensive cost of each feasible solution, and selects the feasible solution with the lowest comprehensive cost as the optimal construction solution output.

2. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 1, characterized in that, The initial structural parameters of the concrete side span main beam obtained in step S1 include the following steps: A finite element model of the entire bridge was established based on the material and geometric properties of the bridge structure. The preliminary structural dimensions of the concrete side span main beam and the preliminary arrangement of the prestressed tendons were obtained by calculating the construction method of the bridge in one step based on the principle of minimum bending energy. The construction phases are divided according to the conventional construction procedures. The full span concrete support is simulated in the finite element model of the whole bridge. The full span support is set as a spring unit that is only subjected to compression. The spring unit is passively removed in sequence at the moment of removal, and at the same node position before passive removal, a node force with the same magnitude and opposite direction as the spring support reaction force is applied. The entire bridge finite element model was run to perform full-process construction simulation calculations, and the structural stress state of each construction stage was accumulated to obtain the stress distribution of the concrete side span main beam during the entire construction process. The stress distribution is compared with the preset stress safety standard. For parts that do not meet the stress safety standard, the preliminary structural dimensions and the preliminary arrangement of the prestressing tendons are optimized and adjusted according to the stress distribution, and the optimized initial structural parameters of the concrete side span main beam are output. The initial structural parameters include beam height, web thickness, top plate thickness, bottom plate thickness and prestressing tendon arrangement parameters.

3. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 1, characterized in that, The step S1 of obtaining the maximum permissible water-blocking area of ​​a conventional support includes the following steps: Obtain the allowable flood obstruction rate at the bridge site, the water obstruction area of ​​the permanent bridge piers, and the cross-sectional area of ​​the river channel corresponding to the design flood level at the bridge site; Calculate the maximum allowable total water obstruction area based on the allowable flood obstruction rate and the cross-sectional area of ​​the river channel. The difference between the maximum allowable total water-blocking area and the water-blocking area of ​​the permanent pier is calculated to obtain the maximum allowable water-blocking area of ​​the conventional support.

4. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 1, characterized in that, Step S2 includes the following steps: S21, if the actual water-blocking area is greater than the maximum allowable water-blocking area, several batch dismantling schemes for the supports are proposed; wherein, each batch dismantling scheme for the supports is generated according to the following principles: at least two steel pipe columns form a support group as the smallest unit for support dismantling; each support group is symmetrically arranged from the middle of the side span towards the bridge piers on both sides; the spatial position coordinates of each support group and the dismantling sequence of each support group are determined; S22, For each batch removal scheme of the support, calculate the maximum instantaneous water blocking area at each removal stage, and verify whether the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area. S23, filter out all support batch dismantling schemes that satisfy the condition that the maximum instantaneous water blocking area is less than or equal to the maximum allowable water blocking area, and obtain multiple support batch dismantling schemes.

5. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 4, characterized in that, Step S3 includes the following steps: S31. Establish a full bridge structural analysis model, divide the construction stages according to the actual construction sequence, and input the initial structural parameters and various support batch dismantling schemes into the full bridge structural analysis model. S32, In each construction stage, the cast-in-place support is simulated as a spring unit under compression only, and according to the dismantling sequence in the dismantling plan of each support in batches, the spring unit at the corresponding position is blunted in the corresponding dismantling stage. At the same time, a node force with the same magnitude and opposite direction as the supporting reaction force of the spring unit is applied at the same node position before blunting, so as to simulate the load transfer during the dismantling process of the support. S33, run the full bridge structure analysis model, calculate and output the normal compressive stress and normal tensile stress at the edge of the concrete section of the main beam of the concrete side span under each construction stage, as well as the axial force and bending moment values ​​of each steel pipe column, as the stress state of the main beam of the concrete side span and the stress state of the support.

6. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 5, characterized in that, The step S4, which determines whether the stress state of the concrete side span main beam and the stress state of the support meet the preset safety standards at each construction stage, includes the following steps: Determine whether the following conditions are met simultaneously at each construction stage: Condition 1: The concrete side span main beam satisfies: ; and satisfy: ;in, This refers to the normal compressive stress at the edge of the concrete section of the main beam in the side span during the construction phase. This refers to the normal tensile stress in the concrete edge section of the main beam in the concrete side span during the construction phase. This is the design value of the axial compressive strength of concrete. This is the design value for the axial tensile strength of concrete; Condition 2: The steel pipe support meets the following strength requirements: ;in, The importance coefficient of the steel pipe support structure. This represents the axial force value of the steel pipe support under load. The effective cross-sectional area of ​​the steel pipe support should take into account the impact of local stability. The design allowable strength of steel as specified in the standard; Condition 3: The stability of the steel pipe support meets the following requirements: ;in, Let be the bending moment of the steel pipe support about the y-axis under load. Let be the bending moment of the steel pipe support about the z-axis under load. This is the overall stability reduction factor for axially compressed components. , These are the section moduli of the effective section relative to the y-axis and z-axis, respectively, considering the effects of local stability. If all construction stages simultaneously meet conditions one, two, and three, then the current phased dismantling plan for the support is deemed to meet the preset safety standards; otherwise, it is deemed not to meet the preset safety standards.

7. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 6, characterized in that, Step S5, which involves keeping the main beam dimensions constant and adjusting the prestressing tendon arrangement parameters to generate multiple prestressing adjustment sub-schemes, includes the following steps: S51, obtain the main beam geometry corresponding to the current support batch dismantling plan that is determined by step S4 to not meet the preset safety standards; wherein, the main beam geometry includes beam height, web thickness, top plate thickness and bottom plate thickness; S52, keeping the main beam geometry unchanged, adjust the prestressing tendon arrangement parameters in the following priority order: first adjust the prestressing tensioning sequence; second adjust the prestressing tendon alignment; and finally adjust the prestressing tendon steel strand type. S53, Each time the layout parameters are adjusted, a prestressing adjustment sub-scheme is generated; wherein, the prestressing adjustment sub-scheme includes the adjusted tensioning sequence, alignment, and steel strand type; S54, the generated multiple prestress adjustment sub-schemes are combined with the current support batch dismantling scheme to form the multiple prestress adjustment sub-schemes.

8. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 6, characterized in that, Step S6 includes the following steps: S61, Obtain the main beam geometry corresponding to the current support batch dismantling scheme that still does not meet the preset safety standard after adjusting the prestressed tendons in step S5; S62, adjust the main beam geometry step by step in the following priority order: first adjust the web thickness, with an adjustment increment of 5cm~10cm; second adjust the top plate thickness or bottom plate thickness, with an adjustment increment of 5cm~10cm; finally adjust the beam height, with an adjustment increment of 5cm~10cm. S63, after each size adjustment, a new main beam structure scheme is generated, and the process returns to step S5 to re-optimize and verify the prestressed tendon parameters; S64. Repeat steps S62 to S63 until a combination of geometric dimensions and prestressed tendon parameters is found that meets the safety criteria. Mark the combination as a feasible solution and proceed to step S7.

9. The interactive design method for concrete side spans and cast-in-place supports of a hybrid beam cable-stayed bridge according to claim 1, characterized in that, Step S7 includes the following steps: S71, summarize all feasible solutions; each feasible solution includes the final geometric dimensions of the concrete side span main beam, the final arrangement parameters of the prestressed tendons, and the final phased removal plan of the cast-in-place support. S72, obtain the benchmark main beam material cost and benchmark support service life corresponding to the conventional construction scheme; S73, for each feasible option, calculate the increase in main beam material cost relative to the baseline main beam material cost; S74. For each feasible scheme, calculate the actual service life of each support group according to the dismantling sequence in the final batch dismantling scheme, and calculate the amortization cost of support materials. S75, For each feasible solution, calculate the comprehensive cost based on the increase and the amortization cost of the support material; S76 compares the overall cost of all feasible solutions and selects the feasible solution with the lowest overall cost as the optimal construction solution output.

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