A method for internal force conversion and anchor bar design at a hole connection of an existing station

Abstract

The application relates to the technical field of anchoring design, in particular to a method for internal force conversion and anchoring design at a hole connecting position of an existing station. In the design method, a stress concentration area is determined by comparing and analyzing a simplified model and a solid model, and a mapping coefficient of internal forces of a ring beam node in the stress concentration area and internal forces of an anchoring interface is determined, so that the internal forces of the anchoring interface in the stress concentration area are corrected, the anchoring in the stress concentration area is designed to be densified, and the anchoring in the remaining area is designed according to a standard; thus, the anchoring is arranged differently according to the shear force peak value / stress concentration, blind densification in the whole range is avoided, the anchoring is arranged according to needs, material and construction costs are saved, the precision and efficiency of the anchoring design are greatly improved, rapid scheme comparison and selection and conventional engineering design are realized, and the method can provide a theoretical basis and practical reference for design optimization of similar structures in the reconstruction and expansion of a subway station.

Description

A method for internal force conversion and rebar installation at the connection of openings in existing railway stations Technical Field

[0001] This application relates to the field of rebar installation design technology, and in particular to a method for internal force conversion and rebar installation design at the opening connection of an existing railway station. Background Technology

[0002] In the renovation and expansion of existing subway stations, a common construction method for adding transfer / connecting passages is "opening the side wall + pouring reinforced concrete reinforcing ring beams around the opening + rebar connection between the old and new structures". Currently, in the engineering design stage, a simplified finite element model (shell elements to simulate the wall and beam elements to simulate the reinforcing ring beam) is usually used to analyze the internal forces of the reinforcing ring beam, which serves as the basis for the rebar design.

[0003] However, the connection point is the boundary between the old and new structures, with complex force paths and various coupling effects such as shearing, pull-out, and bending. Because simplified models cannot accurately simulate local stress concentration areas, there is a discrepancy between the internal forces in the ring beam and the actual rebar stress at the connection point. In engineering practice, it is often impossible to accurately determine the required anchorage strength and quantity of rebar, and design must be based on experience according to the structural requirements of relevant specifications, with an appropriate increase in safety margin, resulting in waste or insufficient safety redundancy.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this application is to provide a method for internal force conversion and rebar installation design at the opening connection of existing stations, so as to solve or alleviate the problems existing in the prior art.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] A method for internal force conversion and rebar installation design at the opening connection of an existing railway station, the method comprising the following steps:

[0008] Step 1: Obtain project input parameters;

[0009] Step 2: Substitute the engineering input parameters into the finite element software, and establish a simplified shell-beam model and a solid model respectively, and establish a global coordinate system;

[0010] The simplified shell-beam model includes at least beam elements and shell elements, while the solid model includes at least sidewalls and reinforced ring beams.

[0011] Step 3: Set the load under the condition of no opening and the load under the condition of opening. Apply the load under the condition of no opening and the load under the condition of opening to the simplified shell-beam model respectively.

[0012] Apply loads to the solid model under both unopened and open conditions.

[0013] Step 4: Establish the mapping relationship between the internal forces of the simplified shell-beam model and the internal forces at the rebar interface. Substitute the internal forces of the simplified shell-beam model into the mapping relationship to obtain the internal forces at the rebar interface.

[0014] Step 5: Compare and analyze the stress conditions of the simplified shell-beam model and the solid model to determine the stress concentration area and obtain the mapping coefficient between the internal forces of the ring beam nodes and the internal forces of the rebar interface in the stress concentration area. This is used to amplify the internal forces of the rebar interface in Step 4 by the corresponding mapping coefficient to obtain the rebar internal force correction result.

[0015] Step 6: Based on the internal force of the rebar interface in Step 4 and the correction results of the internal force of the rebar in the stress concentration area in Step 5, design the rebar installation scheme.

[0016] As described above, the design method for internal force conversion and rebar installation at the opening connection of existing stations is preferably implemented in a simplified shell-beam model. Shell elements are used to simulate the side walls of the existing stations, and beam elements are used to simulate the reinforcing ring beams. The shell elements and beam elements are connected by sharing nodes to ensure coordinated node displacement.

[0017] As described above, the design method for internal force conversion and rebar installation at the opening connection of existing stations preferably involves setting material properties, structural boundaries, and connection methods in the solid model based on actual engineering parameters.

[0018] As described above, the existing station opening connection internal force conversion and rebar design method preferably includes, in step 3, the unopened working condition load is used to simulate the external load condition of the structure before the opening of the reinforced ring beam, and the opening working condition load is based on the unopened working condition load to simulate the stress redistribution process after the local opening of the side wall.

[0019] As described above, the internal force conversion and rebar design method for the opening connection of existing stations is preferably such that, in step 4, the mapping relationship is: internal force at the end of the beam element in the simplified shell-beam model ≡ force transmitted to the beam from the interface ≡ interface internal force required for rebar installation.

[0020] As described above, the preferred method for internal force conversion and rebar design at the opening connection of existing stations is to compare and analyze the stress conditions of the simplified shell-beam model and the solid model in step 5. The analysis results show that the stress on the reinforced ring beam before the opening is mainly shear force; after the opening, the shear force and pull-out force at the joint increase, and local shear force peak concentration and stress gradient are large. Based on the specific experimental results, the mapping coefficient relationship between the internal force of the ring beam joint and the internal force of the rebar interface is determined.

[0021] As described above, in the existing station opening connection method for internal force conversion and rebar design, preferably, in step 6, the ring beam and the existing side wall form a rigid connection, wherein the rebar acts as a force transmission medium. The rebar design verification formula is calculated according to the tension-shear composite stress state as follows:

[0022] ;

[0023] In the formula, —Tensile bearing capacity of a single rebar; —All shear capacity of the rebar; N—Normal force perpendicular to the joint surface; V—Combined shear force.

[0024] The preferred method for calculating the tensile bearing capacity of a single rebar in the existing station opening connection, as described above, is as follows:

[0025] ;

[0026] In the formula: —Rebar diameter; —Effective anchorage depth (>15d); —The bond strength between the rebar adhesive and the concrete.

[0027] As described above, the internal force conversion and rebar design method at the opening connection of the existing station is preferably such that the shear bearing capacity of all rebars is equal to the shear bearing capacity of a single rebar multiplied by the number of rebars. The shear bearing capacity of a single rebar is the smaller value among the following two formulas.

[0028] ; ;

[0029] In the formula: — Yield strength of steel reinforcement; —Cross-sectional area of ​​the reinforcing steel; —Concrete cube compressive strength; —Effective anchorage depth of rebar.

[0030] As described above, the preferred method for internal force transformation and rebar installation design at the opening connection of existing stations requires the following formula to be satisfied in the shear resistance calculation of the interface between the old and new concrete:

[0031] ;

[0032] In the formula: —Existing concrete tensile strength; —Area of ​​the mating surface; μ—Coefficient of friction; N—Normal force perpendicular to the mating surface; V—Shear force parallel to the mating surface.

[0033] Compared with the closest prior art, the technical solution of this application has the following beneficial effects:

[0034] This design method identifies stress concentration areas by comparing and analyzing simplified and solid models. It also determines the mapping coefficient between the internal forces of the ring beam nodes and the internal forces of the rebar interface within the stress concentration areas. This allows for the correction of the internal forces at the rebar interface within the stress concentration areas, enabling denser rebar design within these areas, while rebar in other areas is designed according to standards. This allows for differentiated arrangement based on peak shear force / stress concentration, avoiding blind densification across the entire range, achieving on-demand reinforcement, and saving material and construction costs.

[0035] This design method, without requiring the creation of a fully detailed 3D solid model, compares and analyzes the internal forces between the simplified model and the solid model, and establishes the conversion relationship between the internal forces of the ring beam nodes and the actual stress at the rebar interface. This yields interface stress data that can be used for rebar design, greatly improving the accuracy and efficiency of rebar design and enabling rapid scheme comparison and finalization of conventional engineering designs. Furthermore, this design method can provide theoretical basis and practical reference for the design optimization of similar structures in the renovation and expansion of subway stations. Attached Figure Description

[0036] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. Wherein:

[0037] Figure 1 is a load diagram of a simplified shell-beam model provided according to some embodiments of this application;

[0038] Figure 2 is a load diagram of a solid model provided according to some embodiments of this application;

[0039] Figure 3 is a comparison diagram of the normal pull-out force of two models under unopened working condition load according to some embodiments of this application;

[0040] Figure 4 is a comparison diagram of the combined shear force of two models under unopened working load according to some embodiments of this application;

[0041] Figure 5 is a comparison of the normal pull-out forces of two models under working load after opening, according to some embodiments of this application;

[0042] Figure 6 is a comparison diagram of the combined shear force of two models under the working load after the opening is provided according to some embodiments of this application. Detailed Implementation

[0043] The present application will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of interpretation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present application without departing from the scope or spirit thereof. For example, a feature represented or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present application encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0044] In the following description, the terms "first / second / third" are used merely to distinguish similar objects and do not represent a specific order of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used herein is for the purpose of describing embodiments of this disclosure only and is not intended to limit this disclosure.

[0046] In the description of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and do not require that this application be constructed and operated in a specific orientation, and therefore should not be construed as limiting this application. The terms "connected," "linked," and "set up" used in this application should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; direct connections or indirect connections through intermediate components; wired connections, radio connections, or wireless communication signal connections. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0047] The present application will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present application can be combined with each other.

[0048] According to specific embodiments of this application, as shown in Figures 1-6, this application provides a method for internal force conversion and rebar installation design at openings in existing railway stations. The method includes the following steps:

[0049] Step 1: Obtain engineering input parameters; In this embodiment, engineering input parameters include determining the thickness of the existing station sidewall, concrete strength grade, opening shape (arch / rectangular, etc.), reinforced ring beam section and material, new passage geometry and expansion joint setting method; and determining the load combination and boundary constraint conditions during the construction / operation phase.

[0050] Step 2: Substitute the engineering input parameters into the finite element software, and establish a simplified shell-beam model and a solid model respectively, and establish a global coordinate system; in this embodiment, the finite element software is ABAQUS.

[0051] The simplified shell-beam model includes at least beam elements and shell elements, while the solid model includes at least sidewalls and reinforced ring beams.

[0052] Step 3: Set the load under the condition of no opening and the load under the condition of opening. Apply the load under the condition of no opening and the load under the condition of opening to the simplified shell-beam model respectively.

[0053] Apply loads to the solid model under both unopened and opened conditions.

[0054] Step 4: Establish the mapping relationship between the internal forces of the simplified shell-beam model and the internal forces at the rebar interface. Substitute the internal forces of the simplified shell-beam model into the mapping relationship to obtain the internal forces at the rebar interface.

[0055] Step 5: Compare and analyze the stress conditions of the simplified shell-beam model and the solid model to determine the stress concentration area and obtain the mapping coefficient between the internal forces of the ring beam nodes and the internal forces of the rebar interface in the stress concentration area. This is used to amplify the internal forces of the rebar interface in Step 4 by the corresponding mapping coefficient to obtain the corrected rebar internal forces.

[0056] Step 6: Based on the internal forces at the rebar anchoring interface in Step 4 and the correction results of the internal forces in the stress concentration area in Step 5, design the rebar anchoring scheme.

[0057] In this design method, conventional rebar installation schemes are designed based on the internal forces at the rebar interface determined in step 4. However, these conventional rebar installation schemes cannot meet the requirements of stress concentration areas. This design method, by comparing and analyzing the simplified model and the solid model, identifies stress concentration areas and determines the mapping coefficient between the internal forces at the ring beam nodes and the internal forces at the rebar interface within these stress concentration areas. This allows for the correction of the internal forces at the rebar interface within the stress concentration areas, enabling denser rebar installation in these areas while standard rebar installation is used in other areas. This achieves differentiated arrangement based on shear peak value / stress concentration, avoiding blind densification across the entire range, enabling on-demand reinforcement, and saving material and construction costs.

[0058] In this study, a simplified shell-beam model and a solid model were established using finite element software. Through internal force comparison analysis between the two models, the peak shear force location of the ring beam in the shell-beam model closely matches the stress concentration area in the solid model, indicating that the simplified shell-beam model has good engineering applicability. In contrast, the normal pull-out force generated by stress concentration in some local locations of the solid model is significantly higher than the overall level. A mapping coefficient for the normal pull-out force was obtained, which can be used to correct the normal pull-out force by multiplying the mapping coefficient. This can cover the influence of stress concentration, improve the safety reserve of key parts such as the arch foot, and provide a more realistic safety correction. Based on the modified internal forces, the rebar installation design was carried out, thus making the rebar installation design results more reasonable and adaptable to engineering.

[0059] This design method, without requiring the creation of a fully detailed 3D solid model, compares and analyzes the internal forces between the simplified model and the solid model, and establishes the conversion relationship between the internal forces of the ring beam nodes and the actual stress at the rebar interface. This yields interface stress data that can be used for rebar design, greatly improving the accuracy and efficiency of rebar design and enabling rapid scheme comparison and finalization of conventional engineering designs. Furthermore, this design method can provide theoretical basis and practical reference for the design optimization of similar structures in the renovation and expansion of subway stations.

[0060] In the simplified shell-beam model, shell elements are used to simulate the existing station sidewalls, and beam elements are used to simulate the reinforced ring beams. The shell elements and beam elements are connected by sharing nodes to ensure coordinated node displacement.

[0061] In this embodiment, the simplified shell-beam model can effectively simplify the calculation scale and facilitate rapid analysis and internal force extraction in the preliminary design stage of the project.

[0062] In this model, the side wall area of ​​the station structure is selected as the main analysis object, and the contact layer connected to the reinforcing ring beam is extracted. A global coordinate system is established, with the X-axis perpendicular to the wall outward (normal direction), the Y-axis vertically upward, and the Z-axis horizontally to the right. The reinforcing ring beam consists of horizontal beams, vertical beams, and arch beams. Shell elements and beam elements are connected through shared nodes to ensure coordinated node displacements. The simplified model can quickly output the internal force information of the beam elements through slicing, including: Fx: normal pull-out force, Fy: vertical shear force, and Fz: horizontal shear force. The simplified shell-beam model is suitable for structural scheme comparison and preliminary stress judgment, but it is difficult to reflect the true stress state at the connection.

[0063] In the solid model, material properties, construction boundaries, and connection methods are all set according to actual engineering parameters.

[0064] In this embodiment, in terms of contact relationship, the side wall and the reinforcing ring beam are connected by a "Tie" connection (i.e., a tie / tie connection) to achieve a rigid connection between the two structural parts at the ring beam node. All materials in the solid model are C30~C40 grade concrete, and the steel bars are treated as equivalent distribution.

[0065] This solid model can output the stress distribution in various directions of the structure, mainly including: Fx (X direction): reflecting the normal pull-out force at the connection surface; Fy (Y direction): reflecting the vertical shear force at the connection surface; Fz (Z direction): reflecting the transverse shear force at the connection surface. The solid model can display the stress concentration areas, structural weaknesses, and multiaxial coupled force characteristics of the connection area, and is an important tool for detailed analysis and design verification.

[0066] In step 3, the unopened working condition load is used to simulate the external load on the structure of the reinforced ring beam before the opening, and the working condition load after the opening is based on the unopened working condition load to simulate the stress redistribution process after the local opening of the side wall.

[0067] In this embodiment, the load under the condition of no opening includes: vertical load on the top slab (cover and operation load); lateral load on the wall (lateral earth pressure), which is linearly distributed; the load under the condition of opening can be used to evaluate the stress change at the connection between the reinforced ring beam and the existing structure and the evolution of the stress state of the rebar.

[0068] For the constraints, the simplified shell-beam model and the solid model are kept consistent: fixed constraints are set at the bottom of the station structure; directional constraints are set in the longitudinal direction (Z direction) of the station to simulate the overall stability conditions of the structure.

[0069] In step 4, the mapping relationship is: internal force at the end of the beam element in the simplified shell-beam model ≡ force transmitted to the beam from the interface ≡ interface internal force required for rebar installation.

[0070] To convert the simplified model to the actual internal forces at the connection interface, it is necessary to clarify the correspondence between the internal forces of the beam elements and the internal forces at the rebar anchoring interface. The rebar anchoring design is performed using MIDAS software. However, because MIDAS uses shell elements to simulate the side walls and beam elements to simulate the reinforcing ring beam in the simplified model, and lacks built-in functions for the section method or rigid connection elements, it cannot directly output the actual internal force distribution at the interface between the ring beam and the wall. Therefore, based on the internal force output of the beam element end nodes and combined with the principle of force equilibrium, it is necessary to deduce the actual internal forces transmitted at the interface, thereby guiding the rebar anchoring design.

[0071] (1) Interface force transfer principle: In shell-beam modeling, the interface between the ring beam and the wall achieves nodal displacement coordination through "shared node connection". According to the principle of structural mechanics equilibrium, in the absence of local nonlinearity, the internal forces (shear force, bending moment, axial force) on the end nodes of the beam element are the resultant forces borne by the section where it is located, and these internal forces are also equal to the interface internal forces transferred to the beam at that interface. Therefore, the internal force at the end of the beam element is always equal to the force transferred to the beam from the interface ≡ the interface internal force required to be borne by the rebar; that is, the internal force at the end of the beam element is always equal to the interface internal force required to be borne by the rebar.

[0072] (2) Explanation of beam element internal force output (local coordinate system): In MIDAS, the beam element internal force is output according to the local coordinate system, and the direction is defined as follows: Fx: axial force along the beam axis (t-axis direction); Fy, Fz: shear force in the two principal axis directions n1 and n2 within the section (n1 and n2 directions are the local orthogonal directions of the section, i.e., the principal axis directions of the section, usually corresponding to the strong axis and weak axis of the section); My, Mz: bending moment about the principal axis of the section; Mx: torque about the beam axis (if it exists).

[0073] (3) Correspondence between interface internal forces and rebar direction: Since the rebar is anchored along the wall thickness direction, the key is to clarify the mapping relationship between the rebar direction and the local coordinates of the beam element. The correspondence is shown in Table 1.

[0074]

[0075] Step 5: A comparative analysis of the stress conditions of the simplified shell-beam model and the solid model reveals that: before the opening, the stress on the reinforced ring beam is mainly shear force; after the opening, the shear force and pull-out force at the joints increase, and local shear force peak concentration and stress gradient are observed. Based on specific experimental results, the mapping coefficient relationship between the internal forces at the ring beam joints and the internal forces at the rebar interface is determined.

[0076] In this embodiment, to derive the internal forces and design the rebar anchoring from the simplified model to the actual structural interface, it is necessary to compare and analyze the stress characteristics of the shell-beam element model and the solid element model at key components. By extracting the internal forces and stress distributions of the beam element and the solid model under typical working conditions, the conversion relationship between the internal forces of the ring beam node and the actual stress at the rebar anchoring interface is established, and finally, an internal force conversion method that is easy to apply in engineering is proposed.

[0077] Based on working condition 1 (without opening) and working condition 2 (after opening), the internal forces of the beam elements at the connection nodes of the reinforcing ring beam with the side wall are extracted, as shown in Figure 5 and Figure 6, respectively.

[0078] Analysis results show that before the opening, the reinforced ring beam was mainly subjected to shear force; after the opening, the shear force at the joints increased significantly, and the pull-out force increased. Especially at the arch foot of the opening, the peak shear force was concentrated, and the stress gradient was large, requiring close attention. The solid model output shows that in load case two, significant stress concentration occurred in the arch foot area of ​​the opening. After the opening in the sidewall, the stress changed from a uniform distribution to a typical opening effect of concentrated stress at the arch foot and weakened stress at the arch crown. The shear force at the contact surface increased significantly after the opening, potentially indicating a risk of insufficient shear capacity of the structure.

[0079] Fx exhibits tensile stress concentration at the interface, reflecting that the rebar must bear a large normal tensile force.

[0080] Fy exhibits shear stress concentration at the arch foot of the interface, indicating significant in-plane shear force at the interface.

[0081] The ring beam bears a significant amount of load redistribution pressure after the opening, forming a typical "shear-tension-bending" composite action zone in the contact area with the sidewall. This area should be the focus of reinforcement and rebar control. Comparison reveals that the peak shear force location of the ring beam in the simplified beam element model closely matches the stress concentration area in the solid model, indicating that the actual stress state at the interface can be inferred from the nodal shear force.

[0082] In step 6, the ring beam forms a rigid connection with the existing side wall, where the rebar acts as a force transmission medium. The rebar design verification formula is calculated based on a tension-shear composite stress state, and is as follows:

[0083] ;

[0084] In the formula, —Tensile bearing capacity of a single rebar; —All shear capacity of the rebar; N—Normal force perpendicular to the joint surface; V—Combined shear force.

[0085] In this embodiment, V is and The square root of the sum of the squares is the resultant shear force, which runs along the joint surface; horizontal shear force ( ), that is, shear force parallel to the joint surface and along the channel axis; vertical shear force ( This refers to the shear force parallel to the interface and perpendicular to the channel axis. The interface is the surface where the ring beam and the side wall meet, which is also the interface between the old and new concrete.

[0086] The formula for calculating the tensile bearing capacity of a single rebar is as follows:

[0087] ;

[0088] In the formula: —Rebar diameter; —Effective anchorage depth (>15d); —The bond strength between the rebar adhesive and the concrete.

[0089] The shear capacity of all anchored bars is equal to the shear capacity of a single anchored bar multiplied by the number of anchored bars. The shear capacity of a single anchored bar is the smaller value among the following two formulas.

[0090] ; ;

[0091] In the formula: — Yield strength of steel reinforcement; —Cross-sectional area of ​​the reinforcing steel; —Concrete cube compressive strength; —Effective anchorage depth of rebar.

[0092] In this embodiment, Used to calculate the shear strength of a single steel bar. The smaller of the two formulas is used to calculate the shear bearing capacity of a single rebar.

[0093] The shear strength calculation of the interface between new and old concrete must satisfy the following formula:

[0094] ;

[0095] In the formula: —Existing concrete tensile strength; —Area of ​​the mating surface; μ—Coefficient of friction; N—Normal force perpendicular to the mating surface; V—Shear force parallel to the mating surface. In this embodiment, the coefficient of friction μ is taken as 0.6-0.7. Rebar spacing and edge distance: Minimum center distance =4d, margin =3d, to avoid concrete splitting failure caused by dense reinforcement.

[0096] Taking a real-world project as an example, the calculation of rebar installation design parameters is explained:

[0097] In Figures 3-6, the red lines represent the solid model, and the blue lines represent the beam elements in the simplified shell-beam model.

[0098] The analysis results of the refined model of the solid element reflect that the local internal forces are large due to stress concentration. The mapping coefficient is determined to be 2. Therefore, for safety considerations, the normal pull-out force can be multiplied by the mapping coefficient of 2. Accordingly, when arranging the rebar, the shear peak / stress concentration areas such as the arch foot are set as the densification zone. The mapping coefficient of the densification zone is 2, which means that the rebar in the densification zone is arranged according to twice the design standard value. The remaining areas are set as the standard zone. The mapping coefficient of the standard zone is 1, which means that the rebar in the standard zone is arranged according to the design standard value. This achieves differentiated arrangement of rebar, avoids blind densification across the entire range, realizes reinforcement as needed, and saves material and construction costs. The tensile-shear composite stress state verification takes the maximum pull-out force and shear force value. When the pull-out force is the maximum, the shear force is exactly the maximum: N=97.2kN; V=1025.4kN.

[0099] Substituting the internal force values ​​at the rebar anchoring interface determined in the above process with the mapping coefficient for the emergency concentration area into the MIDAS software for rebar anchoring design, we obtain: rebar diameter d = 28mm; according to the specifications, the bond strength between the rebar anchoring adhesive and concrete is... Take 4.0 MPa as the effective anchorage depth. =31d=868 mm>800 mm, based on the anchorage distance C≥3d, the effective anchorage depth is taken. =710mm; Reinforcing bar yield strength Take 360 ​​MPa, cross-sectional area of ​​the reinforcing bar The concrete cube compressive strength is 615.8 mm². The tensile strength of existing concrete is 45 MPa. The strength is 1.8 MPa; the area of ​​the interface between the old and new concrete is... 2.2×10 7 mm²; the coefficient of friction μ is taken as 0.65.

[0100] The calculation process for the tensile bearing capacity of a single rebar is as follows:

[0101] ;

[0102] The shear bearing capacity of a single rebar is determined by taking the smaller of the following two formulas:

[0103] ;

[0104] ;

[0105] The formula for checking the rebar installation design is as follows:

[0106] In this design, the shear force is not borne independently by a single rebar, but rather resisted jointly by the concrete friction at the interface and the rebars within the interface area. The shear force corresponding to the maximum shear force value is borne jointly by 24 rebars within the range of the bottom slab at that interface. The shear capacity caused by concrete friction is considered by introducing a mapping coefficient of 2; the verification results show that the requirements are met.

[0107] The shear strength calculation of the interface between the old and new concrete is as follows:

[0108] The verification results show that the requirements are met.

[0109] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for internal force conversion and rebar installation design at the connection of openings in existing railway stations, characterized in that, The method includes the following steps: Step 1, obtaining engineering input parameters; Step 2, substituting the engineering input parameters into the finite element software, and establishing a simplified shell-beam model and a solid model respectively, and establishing a global coordinate system; the simplified shell-beam model includes at least beam elements and shell elements, and the solid model includes at least side walls and reinforcing ring beams; Step 3, setting the load under the condition of no opening and the load under the condition of opening, applying the load under the condition of no opening and the load under the condition of opening to the simplified shell-beam model respectively; applying the load under the condition of no opening and the load under the condition of opening to the solid model; Step 4, establishing the internal coordinate system of the simplified shell-beam model. The mapping relationship between the force and the internal force at the rebar interface is established by substituting the internal forces of the simplified shell-beam model into the mapping relationship to obtain the internal forces at the rebar interface; Step 5: The stress conditions of the simplified shell-beam model and the solid model are compared and analyzed to determine the stress concentration area, and the mapping coefficient between the internal forces of the ring beam nodes and the internal forces at the rebar interface in the stress concentration area is obtained. The internal forces at the rebar interface in Step 4 are amplified by the corresponding mapping coefficient to obtain the corrected internal forces of the rebar; Step 6: Based on the internal forces at the rebar interface in Step 4 and the corrected internal forces of the rebar in the stress concentration area in Step 5, the rebar installation scheme is designed.

2. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 1, characterized in that, In the simplified shell-beam model, shell elements are used to simulate the existing station sidewalls, and beam elements are used to simulate the reinforced ring beams. The shell elements and beam elements are connected by sharing nodes to ensure coordinated node displacement.

3. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 2, characterized in that, In the solid model, material properties, construction boundaries, and connection methods are all set according to actual engineering parameters.

4. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 3, characterized in that, In step 3, the unopened working condition load is used to simulate the external load on the structure of the reinforced ring beam before the opening, and the working condition load after the opening is based on the unopened working condition load to simulate the stress redistribution process after the local opening of the side wall.

5. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 4, characterized in that, In step 4, the mapping relationship is: internal force at the end of the beam element in the simplified shell-beam model ≡ force transmitted to the beam from the interface ≡ interface internal force required for rebar installation.

6. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 5, characterized in that, Step 5: A comparative analysis of the stress conditions of the simplified shell-beam model and the solid model reveals that: before the opening, the stress on the reinforced ring beam is mainly shear force; after the opening, the shear force and pull-out force at the joints increase, and local shear force peak concentration and stress gradient are observed. Based on specific experimental results, the mapping coefficient relationship between the internal forces at the ring beam joints and the internal forces at the rebar interface is determined.

7. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 6, characterized in that, In step 6, the ring beam forms a rigid connection with the existing side wall, where the rebar acts as a force transmission medium. The rebar design verification formula is calculated based on a tension-shear composite stress state, and is as follows: In the formula, —Tensile bearing capacity of a single rebar; —All shear capacity of the rebar; N—Normal force perpendicular to the joint surface; V—Combined shear force.

8. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 7, characterized in that, The formula for calculating the tensile bearing capacity of a single rebar is as follows: In the formula: —Rebar diameter; —Effective anchorage depth (>15d); —The bond strength between the rebar adhesive and the concrete.

9. The method for internal force conversion and rebar installation design at the opening connection of existing stations according to claim 8, characterized in that, The shear capacity of all anchored bars is equal to the shear capacity of a single anchored bar multiplied by the number of anchored bars. The shear capacity of a single anchored bar is the smaller value among the following two formulas. ； In the formula: — Yield strength of steel reinforcement; —Cross-sectional area of ​​the reinforcing steel; —Concrete cube compressive strength; —Effective anchorage depth of rebar.

10. The method for internal force conversion and rebar installation design at the opening connection of an existing station, as described in claim 9, is characterized in that... The shear strength calculation of the interface between new and old concrete must satisfy the following formula: In the formula: —Existing concrete tensile strength; —Area of ​​the mating surface; μ—Coefficient of friction; N—Normal force perpendicular to the mating surface; V—Shear force parallel to the mating surface.

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