Construction method of column core cage joint of large-size steel pipe concrete column based on top-down method

Abstract

The application discloses a construction method of a column core cage joint of a large-size steel pipe concrete column based on a reverse construction method, and comprises the following steps: S1, preliminary preparation, preparing a steel pipe column, concrete, connecting pieces and construction equipment; S2, measurement positioning and steel pipe column correction, accurately controlling the position, perpendicularity and top elevation of the steel pipe column; S3, on-site lower pile foundation construction of the steel pipe column, hoisting and inserting a prefabricated steel pipe column before the final setting of the pile foundation concrete, and the top of the steel pipe column extending to the position of the top slab structure elevation of the basement; a stiffening plate is fixedly arranged at the top of the steel pipe concrete column and arranged around the outer wall of the steel pipe concrete column. The application effectively increases the net distance between longitudinal reinforcements by optimizing the reinforcement form of the column core cage (such as adopting double-layer reinforcement or adding a steel core column), creates a spacious channel for the smooth penetration of beam reinforcements, overcomes the construction difficulty of the cross-penetration of reinforcements, guarantees the bearing performance of concrete and the pouring construction quality, and ensures that the design stress path can be accurately realized.

Description

Technical Field

[0001] This invention relates to the field of column core cage joint construction technology, and in particular to a column core cage joint construction method for large-size steel tube concrete columns based on the reverse construction method. Background Technology

[0002] The cut-and-cover method is a widely used construction method in deep foundation pit engineering in urban centers of my country. Its process of "vertical support first, then horizontal excavation" can effectively control the deformation of the foundation pit and reduce the impact on the surrounding environment. In this method, the steel-concrete composite columns, which are the main vertical load-bearing components, need to be constructed before the basement roof structure. The node area where the columns are connected to the main beam (top longitudinal beam) of the roof is the key part for transferring the load of the beam to the column. Its load transfer reliability and construction quality are directly related to the safety of the overall structure. Currently, this node often uses a core cage (i.e., a steel cage placed inside a steel pipe column) connected to the top longitudinal beam reinforcement. According to the current cut-and-cover construction design specifications and guidelines, in order to meet the extremely high bearing capacity and seismic requirements of the column, the core cage usually adopts a single-layer, densely reinforced design scheme. However, this traditional approach has revealed the following prominent technical problems in actual construction: First, in large-scale construction projects, the insertion of reinforcing bars is extremely difficult, and because it requires manual operation by workers, the construction quality is hard to guarantee. During the stage of binding the top longitudinal beam reinforcing bars, the dense main beam bars (especially the bottom bars) need to pass through the equally dense longitudinal bars of the column core cage. The spacing between the bars is very small, and the spatial conflict is very serious. During construction, the main beam bars are often forced to be bent or even cut on site because they cannot be inserted smoothly, which seriously damages the pre-set stress path of the structure and leaves safety hazards. In addition, the excessive density of reinforcing bars seriously leads to the concrete pouring not being dense, resulting in phenomena such as concrete slurry segregation, which seriously affects the quality of the project.

[0003] In summary, while the traditional single-layer densely reinforced column core cage joint design can theoretically meet the calculation requirements, there is a sharp contradiction between construction operability and the final actual structural performance. How to fundamentally solve the construction bottleneck of difficult reinforcement insertion without sacrificing or even improving the mechanical performance of the column has become a key technical problem to promote the development of the cut-and-cover reverse construction method towards higher quality and higher safety level. Therefore, this application proposes a column core cage joint construction method for large-size steel tube concrete columns based on the reverse construction method. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings and technical difficulties existing in the prior art by proposing a construction method for the core cage joint of large-size steel tube concrete columns based on the reverse construction method.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method is characterized by the following steps: S1: Preliminary preparation: Prepare steel pipe columns, concrete, connectors and construction equipment. Weld support plates and stiffening plates to the top of the steel pipe columns. The support plates and stiffening plates are installed around the outer wall of the top of the steel pipe columns (this process is completed in advance in the factory). S2: Measurement and positioning and steel pipe column correction, precisely controlling the position, verticality and top elevation of the steel pipe column; S3: On-site construction of the lower pile foundation of the steel pipe column is carried out. The precast steel pipe column is hoisted and inserted before the final setting of the pile foundation concrete. The top of the steel pipe column extends to the structural elevation of the basement roof slab. S4: Pour concrete into the steel pipe on site to about 0.5m above the bottom of the column core cage; S5: Insert the core cage into the steel pipe column before the concrete inside the column has fully set; In step S5, one of the following two parallel schemes is used to optimize the structure of the core cage: Option A: Adopt a double-layer column core cage structure. The number of longitudinal steel bars in the outer column core cage is reduced to increase the clear spacing of the steel bars. At the same time, an inner column core cage is added. The inner column core cage is composed of ring-shaped closed stirrups or spiral stirrups and vertical longitudinal bars arranged in a circle. The total cross-sectional area of ​​the longitudinal steel bars in the inner and outer column core cages is not less than the original design value. Option B: A steel core column composite structure is adopted. The number of longitudinal steel bars in the original column core cage is reduced to increase the clear spacing of the steel bars. At the same time, a steel core column is added at the center of the steel pipe column. The cross-sectional area of ​​the steel core column is determined by calculation. In Option B, the longitudinal steel bars at the bottom of the top longitudinal beam that are blocked by the steel core column are handled by cutting them off and welding them to the connecting plate on the steel core column, bypassing the steel core column, or connecting them to the steel core column through a mechanical connecting sleeve. S6: Construction of node connectors: Treatment of top longitudinal beam reinforcement, anchor bars and formwork installation. The top longitudinal beam reinforcement and anchor bars are interleaved. The formwork is installed and the node area and top slab beam concrete are poured.

[0006] As a further embodiment of the present invention: in embodiment A, there is a radial spacing between the inner and outer core cages.

[0007] As a further embodiment of the present invention: In embodiment B, the cross-sectional form of the steel core column is a square steel tube, an I-beam, or a cross-shaped steel.

[0008] As a further aspect of the present invention: the square steel tube selected for the steel core column has an outer contour dimension smaller than the inner diameter of the original column core cage, and maintains a net distance of not less than 50mm from the surrounding longitudinal steel bars.

[0009] As a further aspect of the present invention: the steel pipe column correction in step S2 includes: a. Baseline layout: Control stakes are set around the foundation pit, and the center coordinates of the steel pipe column and the axis of the top longitudinal beam are measured using a total station; b. Installation and alignment: After the steel pipe column is hoisted into place, the verticality is monitored using a laser plumb line and fixed by lateral supports; c. Elevation control: Use a level to control the elevation of the top of the steel pipe column. If it exceeds the tolerance, mechanical cutting is performed for correction. d. Permanent fixation: After verification, weld the fixed support.

[0010] As a further aspect of the present invention: the construction of the node connector in step S6 adopts one of the following methods: (1) When processing steel pipe columns in the factory: a flange is installed on the top of the steel pipe column, and the two are fixed by welding before construction. (2) On-site construction method: Weld pressure flanges on the outside of the steel pipe column on site.

[0011] As a further aspect of the present invention, the stirrups of the top longitudinal beam are densified in the node area (within a range of not less than 1.5 times the beam height on both sides of the column).

[0012] As a further aspect of the present invention: the concrete pouring in step S4 adopts a layered pouring method from the side away from the steel pipe column toward the node, and the node area is vibrated with a small diameter vibrator.

[0013] As a further aspect of the present invention: the column core cage is constructed using prefabricated column core cage modules or / and adjustable column core cages.

[0014] Compared with the prior art, the present invention provides a construction method for the core cage joint of large-size steel tube concrete columns based on the reverse construction method, which has the following beneficial effects: 1. By optimizing the reinforcement configuration of the column core cage (such as using double-layer reinforcement or adding steel core columns), the clear distance between longitudinal bars is effectively increased, creating a spacious passage for the beam reinforcement to pass through smoothly. This fundamentally overcomes the construction difficulties of cross-penetration of reinforcement bars and ensures that the designed stress path can be accurately realized.

[0015] 2. Increasing the spacing between reinforcing bars provides the necessary conditions for the smooth flow and full vibration of the concrete mixture (especially coarse aggregate), which can effectively ensure the compactness and uniformity of the concrete in the joint area, thereby ensuring that the concrete and reinforcing bars work together reliably and ensuring the quality of concrete pouring.

[0016] 3. The favorable spatial conditions created make operations such as rebar positioning and binding more convenient, which not only greatly improves construction efficiency, but also reduces the quality risks caused by human intervention. It can effectively avoid structural hazards such as reduced durability and seismic performance caused by insufficient rebar spacing and loose concrete.

[0017] The parts of this device not covered herein are the same as or can be implemented using existing technologies. This invention has a simple structure and is easy to operate. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings: Figure 1 This is a top view of the construction method for the inner and outer double-layer column core cage method of the column core cage joint of large-size steel tube concrete column based on the reverse construction method proposed in this invention. Figure 2 This is a side view of the construction method for the inner and outer double-layer column core cage method of the column core cage node construction method for large-size steel tube concrete columns based on the reverse construction method proposed in this invention. Figure 3 The top view of the construction method of the column core cage and steel core column combination method of the column core cage node construction method of large-size steel tube concrete column based on the reverse construction method proposed in this invention. Figure 4 This is a side view of the construction method of the column core cage and steel core column combination method for the column core cage node construction method of large-size steel tube concrete column based on the reverse construction method proposed in this invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0021] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0022] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain circumstances to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0023] In addition, the term "multiple" should mean two or more.

[0024] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments. Example

[0025] The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method is shown in the figure, and includes the following steps: S1: Preliminary Preparation Stage Materials include: Steel pipe columns: Provide material certificates (yield strength, tensile strength), the top end face needs to be pre-processed in the factory (flatness error ≤2mm / m), and burrs and rust removed; Concrete: The core grouting of steel pipe columns (if designed) should use high-strength, low-shrinkage plain concrete (such as C40-C60) with added crack-resistant fibers; the top longitudinal beams should be made of high-strength concrete; Connecting components: Flanges must conform to national standards; Equipment: Total station (positioning accuracy ±2mm), laser plumb bob (verticality monitoring), concrete vibrator (φ50mm, to ensure compaction); S2: Measurement and Positioning and Steel Pipe Column Alignment In the cut-and-cover construction method, steel pipe columns must be installed before the top longitudinal beams. Their position, verticality, and top elevation directly determine the accuracy of the end-bearing connection. The construction steps include: Excavate pile hole → enlarge pile bottom → clean pile hole using mud slurry wall protection method → ​​pour plain concrete → insert steel pipe pile (before initial setting) → insert column core reinforcement cage (and steel core column) (before initial setting) → reach strength → excavate earthwork at beam and slab location → formwork → tie top longitudinal beam → tie slab reinforcement → pour concrete. The steel pipe column correction steps include: a. Baseline layout Control piles were set around the foundation pit, and the center coordinates of the steel pipe column and the axis of the top longitudinal beam were measured using a total station. b. Steel pipe column installation and correction After the steel pipe column is hoisted into place, the verticality is monitored with a laser plumb line (allowable deviation ≤ 1 / 500 column height), and it is fixed by lateral support (such as steel diagonal bracing); c. Use a level to control the top elevation of the steel pipe column (error ≤ ±3mm). If the elevation deviation exceeds the tolerance, the top of the column must be mechanically cut (gas cutting is strictly prohibited to avoid end face carbonization). d. Permanent fixing: After the bottom of the steel pipe column is firmly connected to the pile foundation (or foundation cap), the verticality and elevation are checked again. After confirming that there are no errors, the support is welded and fixed. S3: On-site construction of the lower pile foundation of steel pipe columns is carried out. Before the final setting of the pile foundation concrete, the precast steel pipe columns are hoisted and inserted. The top of the steel pipe columns extends to the structural elevation of the basement roof slab. S4: Pour concrete into the steel pipe column to about 0.5 meters above the bottom of the column core cage; S5: Binding of top longitudinal beam reinforcement and installation of formwork The reinforcement bars of the top longitudinal beam need to be installed in conjunction with the node connectors to ensure a continuous load transfer path. The specific sub-steps include: a. Reinforcing bar binding The main reinforcement bars of the top longitudinal beam must pass through the longitudinal reinforcement bars of the steel pipe column core cage and be tied to the longitudinal reinforcement bars of the column core cage. The stirrup reinforcement zone must cover the node area (≥1.5 times the beam height on both sides of the column), and the stirrups must be firmly tied to the main reinforcement to prevent displacement during pouring; Template installation Steel formwork is used (high rigidity and small deformation). The formwork size must match the beam cross section, and the contact surface with the steel pipe column is sealed with sponge strips (to prevent grout leakage). The formwork support system (such as cup-lock scaffolding) needs to be verified for its load-bearing capacity, and the spacing should be ≤600mm to prevent the formwork from sinking during pouring; Key points for acceptance: verticality of the template (deviation ≤3mm / m), cross-sectional dimensions (deviation ±5mm), and tightness of the joints; c. Concrete pouring and curing (key to end bearing quality) The density and strength of concrete directly determine the bearing capacity of the end bearing surface, and the pouring process must be strictly controlled. Before pouring, it is necessary to clean the debris and water inside the formwork and blow the dust off the top of the steel pipe column with high-pressure air; pour concrete into the steel pipe column to 50mm below the top surface of the column, and pour concrete for other parts and beams. d Layered casting Concrete is delivered using a truck-mounted pump and poured from the side furthest from the steel pipe column toward the joint, with each layer being ≤500mm thick. The joint area (within 500mm of the column circumference) is vibrated with a small-diameter vibrator (φ30mm) for 20-30 seconds (until no air bubbles appear on the concrete surface and it settles), to avoid missed vibration that could lead to honeycomb or voids on the end bearing surface. Self-compacting concrete should be used as much as possible for pouring. Precautions: It is strictly forbidden to pour concrete into the formwork to prevent aggregate concentration; if the pouring interval exceeds the initial setting time (generally 2-3 hours), it must be treated as a construction joint (roughening, brushing with cement slurry); e-Maintenance Cover the concrete with geotextile and plastic film within 12 hours after pouring, and use water spraying to keep it moist. The curing time is ≥14 days (≥21 days for C60 concrete). During the curing period, it is strictly forbidden to disturb the top longitudinal beam (such as by stacking loads or colliding with the formwork) to prevent concrete cracking. f. Formwork Removal and Quality Acceptance Formwork removal must wait until the concrete strength meets the standard, and acceptance must cover all aspects of the quality of the nodes.

[0026] g formwork removal Side formwork: Can only be removed when the concrete strength is ≥2.5MPa (2~3 days after pouring). Avoid damaging the beam corners during removal. Bottom formwork: It is strictly forbidden to remove the formwork prematurely until the concrete strength reaches 100% of the design value (confirmed by compressive strength test of test blocks under the same conditions).

[0027] S6: Construction of node connectors, treatment of top longitudinal beam reinforcement and anchor bars and formwork installation, the top longitudinal beam reinforcement and anchor bars are interleaved and formwork is installed; pour concrete in the node area and top slab beam.

[0028] End-bearing connections require the use of flanges to achieve a rigid beam-column connection, avoiding joint cracking caused by relying solely on concrete end bearings. There are two specific structural forms: (1) Prefabrication in the factory, the key technical points are: During the prefabrication of steel pipe columns in the factory, a flange is welded to the top end face (the center of the steel plate is aligned with the center of the column, the weld height is ≥10mm, and penetrant testing is required); longitudinal reinforcement bars of the column core cage are welded below the flange (length ≥40d, where d is the diameter of the longitudinal reinforcement bar), and the longitudinal reinforcement bars of the column core cage are evenly distributed along the circumference of the column (e.g., 8 bars / column), extending into the interior of the top longitudinal beam; the plane position of the flange is checked on site (deviation ≤5mm), and if it is offset, it needs to be adjusted by welding. (2) The key technical points are as follows: Welding pressure-bearing flanges on the outside of the steel pipe column on site: After cleaning the top end face of the steel pipe column, weld the flange (with the center of the steel plate aligned with the center of the column, weld height ≥10mm, requiring penetrant testing) to the side wall of the steel pipe column with equal strength. Then, weld a stiffening plate between the top plate flange and the bottom plate flange, with fillet welds between the stiffening plate and the top and bottom plates. Weld longitudinal reinforcement bars of the column core cage (length ≥40d, where d is the diameter of the longitudinal reinforcement bar) below the flange. The longitudinal reinforcement bars of the column core cage are evenly distributed around the column (e.g., 8 bars / column) and extend into the interior of the top longitudinal beam. Check the plane position of the flange on site (deviation ≤5mm). If it is offset, it needs to be adjusted by welding. Example

[0029] The construction method of column core cage joint for large-size steel tube concrete columns based on the reverse construction method, in step S4, the binding of the top longitudinal beam reinforcement and the installation of the formwork, in large underground projects, the traditional densely reinforced column core cage design, due to its small reinforcement spacing and complex joints, causes frequent spatial conflicts when various types of reinforcement such as beams, slabs and walls cross and intersect in the joint area, often requiring on-site forced bending or cutting of the main reinforcement, thus destroying the force path; at the same time, the extremely narrow clear spacing of the reinforcement seriously hinders the flow of concrete, causing coarse aggregate to be filtered and retained by the reinforcement mesh, and even with repeated vibration, it is still easy to form honeycomb, voids and other non-dense defects inside. These problems weaken the effective force transmission capacity of the joint, reduce the actual bearing capacity and ductility of the column, and provide channels for chloride ions and moisture to penetrate, accelerating the corrosion of the reinforcement and freeze-thaw damage of the concrete, fundamentally endangering the seismic safety and long-term durability of the structure; In sub-step a, when the main reinforcement of the top longitudinal beam needs to pass through the longitudinal reinforcement of the steel pipe column core cage, in order to ensure the smooth insertion of the bottom steel reinforcement of the basement top slab beam and the longitudinal reinforcement of the top column core cage under the cut-and-cover reverse construction method, and to fully ensure the compactness of the concrete pouring at the joint position of the basement top beam slab structure, the following method is adopted to ensure the smooth insertion of the bottom steel reinforcement of the top slab beam and the longitudinal reinforcement of the top column core cage under the cut-and-cover reverse construction method: While reducing the longitudinal reinforcement of the original column core cage, an inner column core cage is added. The inner column core cage still consists of ring-shaped closed stirrups or spiral stirrups and multiple vertical longitudinal bars arranged in a circle. This compensates for the reduced longitudinal reinforcement area of ​​the original outer column core cage, ensuring that the total cross-sectional area of ​​the longitudinal reinforcement of the column core cage remains unchanged. See the attached instruction manual for details. Figures 1 to 2 ; The inner and outer core cages together form a dual constraint system. The inner ring-shaped closed stirrups or spiral stirrups can exert a strong lateral constraint force on the core concrete, significantly improving its compressive strength and ultimate compressive strain. The outer stirrups expand the effective constraint area. This enhanced constraint transforms concrete from a brittle material into a material with a certain degree of ductility, thereby greatly improving the axial compressive bearing capacity and deformation capacity of the column. By keeping the total cross-sectional area of ​​the longitudinal reinforcement constant, the theoretical value of the column's flexural bearing capacity is not reduced. Although reducing the outer layer of longitudinal reinforcement will slightly reduce the flexural arm, this effect can be controlled within a safe range by reasonably designing the position of the inner layer of longitudinal reinforcement. The most direct benefit of increasing the clear spacing of longitudinal reinforcement is that it creates a wider concrete flow channel, allowing the concrete mixture (especially coarse aggregate) to pass smoothly through the gaps between the reinforcement bars and reach the core area of ​​the component. This can effectively avoid defects such as concrete segregation, honeycombing, and voids caused by excessive reinforcement, ensuring the uniformity and compactness of the core concrete, thereby ensuring that the concrete can fully realize its design strength and form a reliable bond with the reinforcement bars to achieve joint work. The aforementioned dual constraint effect and improved concrete density are key to seismic performance. Under seismic action, columns can withstand greater repeated deformation without sudden brittle shear failure or crushing failure. Their ductility and energy dissipation capacity are greatly improved. Denseer concrete means lower permeability, which can more effectively resist the intrusion of harmful substances (such as chloride ions and carbon dioxide), slow down steel corrosion, and thus improve the long-term durability of the structure. By increasing the radial spacing between the inner and outer core cages, a smooth annular operating channel is created inside the steel cage. This space greatly improves construction conditions: workers can more easily tie stirrups and position steel bars, significantly improving the efficiency of insertion; at the same time, it provides an ideal main flow path for concrete pouring, ensuring that coarse aggregates pass through smoothly and are evenly distributed, and allowing vibrators to fully penetrate the core area for vibration, thereby completely avoiding defects such as honeycomb and voids, achieving extremely high density and uniformity of concrete, and fundamentally guaranteeing the final forming quality and design strength of the structure. Through systematic finite element analysis and physical model test comparison, the double-layer column core cage component exhibits comprehensive mechanical performance advantages: under low-cycle cyclic loading, its hysteresis curve is full without significant pinching, and its energy dissipation capacity is increased by more than 30% compared with traditional single-layer reinforced columns; the displacement ductility coefficient is increased by 20%-40%, and the failure mode changes from brittle shear to ductile bending failure; the finite element stress cloud diagram clearly reveals the strong confinement effect of the inner stirrups on the core concrete, and the test data confirms that the concrete crush strain is significantly increased and the rate of stiffness and strength degradation is slowed down, which together proves that the reliability of this structure in significantly improving seismic performance and deformation capacity through the dual confinement mechanism. Example

[0030] A construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method is proposed. In step S4, the binding of the top longitudinal beam reinforcement and formwork installation, specifically in sub-step a, where the main reinforcement of the top longitudinal beam needs to pass through the longitudinal reinforcement of the steel-concrete composite column core cage, is described. An alternative method is proposed to ensure the compactness of the concrete pouring at the joint location of the basement top beam slab structure. The operational steps include: While reducing the longitudinal reinforcement of the original column core cage, a steel core column is added at the center of the steel pipe column. The steel core column can be made of square steel pipe, I-beam, or cross-shaped steel with the same strength grade as the outer steel pipe of the steel-concrete composite column, ensuring that the total cross-sectional area of ​​the longitudinal reinforcement of the column core cage is not lost. In practice, to fully ensure the coordinated work between the inserted steel and the original column core cage, it is generally ideal to increase the cross-sectional area of ​​the required steel by 10%. Therefore, the required cross-sectional area of ​​the inserted steel can be calculated using the following formula.

[0031] ;

[0032] In the above formula: The required cross-sectional area of ​​the inserted steel core column; This represents the cross-sectional area of ​​the steel tube on the outer side of the concrete-filled steel tube column. is the cross-sectional area of ​​a single steel bar in the original column core cage; n is the number of longitudinal steel bars in the original column core cage. Please refer to the attached instruction manual for details. Figure 3-4 Under the premise that all other conditions remain unchanged, the original 36C32 longitudinal steel bars in the column core cage are reduced by 206C32, and 200 (length) x 200 (width) x 20 (wall thickness) welded square steel pipes are added to ensure that the total cross-sectional area of ​​the longitudinal steel bars in the column core cage is not lost. The steel bar arrangement of the column core cage improved by method two can fully meet the requirements for the insertion of the steel bars under the basement top beam; In practice, it should be noted that the inserted steel core column may block a small number of longitudinal and longitudinal reinforcement bars at the bottom of the beam from passing through. Depending on the actual size, it can be cut off, bypassed, or welded to the inserted steel core column through a mechanical connecting sleeve. When selecting steel core columns, square steel tubes are preferred because their isotropic properties (same moment of inertia on the x and y axes) provide uniform and strong bidirectional bending and shear resistance for the column members. When combined with circular steel tube columns, they can form a perfect double-confined concrete system with the best synergistic performance. As a secondary option, cross-shaped steel can be used. Its biaxially symmetrical cross-section can also provide good bidirectional bending performance, and its large cross-sectional development length results in good bonding with the core concrete. In terms of size selection, the outer contour dimension of the steel core column must be smaller than the inner diameter of the original column core cage to ensure that there is a sufficient minimum clear distance (usually ≥50-80mm) between the core column and the original column longitudinal reinforcement, so as to ensure the fluidity of concrete pouring, so that the concrete can fully fill and wrap the steel section and achieve overall stress. The height-to-thickness ratio or width-to-thickness ratio of the steel core column should meet the requirements for "local stability" of compression members in the "Steel Structure Design Standard" to prevent premature local buckling of its plates under compression; the steel core column should be reliably connected to the outer beam reinforcement at the floor level, usually by welding connecting plates or studs on the steel section to ensure that the bending moment and shear force of the beam can be effectively transferred to the core column; The bonding and cohesion of concrete connects the outer steel-concrete tube and the inner steel column into a whole for joint deformation; the dual constraint effect (the outer steel tube and the inner steel column constrain the concrete respectively) significantly improves the strength and ductility of the core concrete, laying the foundation for ultra-high load-bearing capacity; while the multi-line defense design (the load is borne by the outer concrete, steel tube, and inner steel column in sequence) ensures that the structure still has excellent internal force redistribution ability and ductility under extreme loads, greatly enhancing seismic performance and overall safety redundancy; The connection between the steel core column and the lower longitudinal reinforcement of the beam requires flexible selection of three typical schemes based on the actual needs of the project: the welded connection plate scheme involves welding a connection plate with stiffening ribs at a predetermined position on the steel section in the factory, and then using bevel welding or high-strength bolts on site to achieve equal strength connection of the reinforcement, which is the most reliable force transmission method; the bypass scheme achieves the continuity of the reinforcement by large-radius bending or pre-drilling reinforcement holes in the factory, but additional stirrups are required to strengthen the bending area or ring plate to reinforce the opening area; the mechanical connection scheme relies on pre-welded sleeves in conjunction with grouting / extrusion process, which significantly improves assembly efficiency while ensuring quality; The three schemes can be combined to use welding of main reinforcement plates, selection of bypass or perforation of secondary reinforcement, and priority mechanical connection of prefabricated nodes. Through precise positioning and process control by BIM, the stress requirements of the nodes are met while achieving construction convenience. Example

[0033] This embodiment of the construction method for column core cage nodes of large-size steel tube concrete columns based on the reverse construction method introduces prefabricated column core cage modules and adjustable column core cages to improve the construction efficiency of column core cages. The prefabricated column core cage modules are steel cage units in which longitudinal bars, stirrups and additional steel bars are precisely welded or tied into a whole in the factory. Standardized design ensures accurate dimensions and controllable quality. During construction, they are directly hoisted into place, which greatly reduces the amount of on-site tying work and improves construction efficiency and accuracy. Adjustable column core cages, through the use of threaded connections, sliding sleeves, or telescopic components, allow for on-site adjustment of their height, diameter, or reinforcement density within a certain range. This effectively absorbs construction errors (such as rebar misalignment and elevation deviations), adapts to minor changes in structural dimensions, and enhances construction tolerance and flexibility. The combined application of these two technologies, with prefabricated modules serving as the main body to ensure core quality and efficiency, and adjustable design handling of variability in nodes and interfaces, collectively achieves high-quality and high-efficiency industrialized construction of reinforced concrete structures. Example

[0034] This document describes a construction method for column core cage joints of large-size steel-concrete composite columns based on the reverse construction method. To evaluate the effectiveness of methods one and two, this example serves as a comparative example, testing the bearing capacity and seismic performance of column core cage joints constructed using methods one and two, as well as those constructed using the traditional guideline method (single-layer dense reinforcement). Conclusion: Both new methods are superior to traditional methods in terms of seismic performance. Method 2 (steel core column) has the most significant improvement in bearing capacity and ductility, but the cost is higher. Method 1 (double-layer column core cage) achieves excellent performance optimization without significantly increasing costs, and is a highly cost-effective solution.

[0035] Meanwhile, tests were conducted on the reinforcement binding efficiency and concrete pouring quality of column core cage joints constructed using Method 1 and Method 2, as well as column core cage joints constructed using the traditional "Guideline" method (single-layer dense reinforcement). Conclusion: Although the initial material costs are high, the extremely high load-bearing capacity and seismic performance it provides make it suitable for projects with extreme performance requirements, such as super high-rise buildings and super large public buildings.

[0036] 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 construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method, characterized in that, Includes the following steps: S1: Preliminary preparation: Prepare steel pipe columns, concrete, connectors and construction equipment. Weld support plates and stiffening plates to the top of the steel pipe columns. The support plates and stiffening plates are installed around the outer wall of the top of the steel pipe columns (this process is completed in advance in the factory). S2: Measurement and positioning and steel pipe column correction, precisely controlling the position, verticality and top elevation of the steel pipe column; S3: On-site construction of the lower pile foundation of steel pipe columns is carried out. Before the final setting of the pile foundation concrete, the precast steel pipe columns are hoisted and inserted. The top of the steel pipe columns extends to the structural elevation of the basement roof slab. S4: Pour concrete into the steel pipe on site to about 0.5m above the bottom of the column core cage; S5: Insert the core cage into the steel pipe column before the concrete inside the column has fully set; In step S5, one of the following two parallel schemes is used to optimize the structure of the core cage: Option A: Adopt a double-layer column core cage structure. The number of longitudinal steel bars in the outer column core cage is reduced to increase the clear spacing of the steel bars. At the same time, an inner column core cage is added. The inner column core cage is composed of ring-shaped closed stirrups or spiral stirrups and vertical longitudinal bars arranged in a circle. The total cross-sectional area of ​​the longitudinal steel bars in the inner and outer column core cages is not less than the original design value. Option B: A steel core column composite structure is adopted. The number of longitudinal steel bars in the original column core cage is reduced to increase the clear spacing of the steel bars. At the same time, a steel core column is added at the center of the steel pipe column. The cross-sectional area of ​​the steel core column is determined by calculation. In Option B, the longitudinal steel bars at the bottom of the top longitudinal beam that are blocked by the steel core column are handled by cutting them off and welding them to the connecting plate on the steel core column, bypassing the steel core column, or connecting them to the steel core column through a mechanical connecting sleeve. S6: Construction of node connectors: Treatment of top longitudinal beam reinforcement, anchor bars and formwork installation. The top longitudinal beam reinforcement and anchor bars are interleaved and formwork is installed; pour concrete in the node area and top slab beam.

2. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, In Scheme A, there is a radial spacing between the inner and outer core cages.

3. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, In Scheme B, the cross-sectional form of the steel core column is a square steel tube, an I-beam, or a cross-shaped steel.

4. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 3, characterized in that, The square steel tubes used for the steel core columns have an outer contour dimension smaller than the inner diameter of the original column core cage, and maintain a net distance of not less than 50mm from the surrounding longitudinal reinforcing bars.

5. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, The steel pipe column correction in step S2 includes: a. Baseline layout: Control stakes are set around the foundation pit, and the center coordinates of the steel pipe column and the axis of the top longitudinal beam are measured using a total station; b. Installation and alignment: After the steel pipe column is hoisted into place, the verticality is monitored using a laser plumb line and fixed by lateral supports; c. Elevation control: Use a level to control the elevation of the top of the steel pipe column. If it exceeds the tolerance, mechanical cutting is performed for correction. d. Permanent fixation: After verification, weld the fixed support.

6. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, The construction of the node connectors in step S6 shall be carried out in one of the following ways: (1) When processing steel pipe columns in the factory: a flange is installed on the top of the steel pipe column, and the two are fixed by welding before construction. (2) On-site construction method: Weld pressure flanges on the outside of the steel pipe column on site.

7. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, In step S6, the stirrups of the top longitudinal beam are densified in the node area.

8. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, In step S4, the concrete is poured in layers from the side away from the steel pipe column toward the node, and the node area is vibrated with a small-diameter vibrator.

9. The construction method for the core cage joint of a large-size steel-concrete composite column based on the reverse construction method according to claim 1, characterized in that, The column core cage is constructed using prefabricated column core cage modules and / or adjustable column core cages.

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