Repair system and construction method of reinforced concrete column based on triple cooperative constraints

Abstract

The invention relates to the technical field of concrete structure repairing, in particular to a repairing system of a reinforced concrete column based on triple cooperative constraint, which comprises a core area concrete column formed by removing a failed concrete protection layer from a rusted reinforced concrete column; the longitudinal bars are arranged on the peripheral side of the core area concrete column; the four-corner star-shaped stirrups are hooped on the outer side of the core area concrete column at intervals in the axial direction of the core area concrete column and are fixed to the longitudinal bars; the anti-stress pieces are arranged at the four corners of the core area concrete column and fixedly connected with the four corner ends of the four-corner star-shaped stirrups; and the FRP grid-ECC composite sandwich structure is arranged on the outer side of the core area concrete column. According to the method, through a material performance complementation and interface stress coordination mechanism, the purpose of multi-target collaborative optimization of axial compression-bending shear coupling bearing capacity reconstruction, interface durability improvement, secondary corrosion inhibition and the like of the repaired concrete column is achieved. The invention further correspondingly discloses a construction method of the repairing system.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete structure repair, and particularly to a repair system and construction method for reinforced concrete columns based on triple cooperative constraints. Background Art

[0002] Reinforced concrete structures are widely used in various buildings due to their advantages such as low cost, good moldability, and strong durability. As the core load-bearing unit of building structures, the safety and stability of reinforced concrete columns play a decisive role in the entire building structure. However, in high-salt fog areas such as coastal areas, reinforced concrete columns are in a wet-dry alternating environment for a long time and may be affected by seismic motion. Under such complex service conditions, various typical damage modes are likely to occur in reinforced concrete columns.

[0003] Electrochemical corrosion of stirrups is one of the most prominent problems. Chloride ions in the high-salt fog environment will penetrate the concrete protective layer, damage the passivation film on the surface of the steel bars, and cause steel bar corrosion. As an important component in concrete columns that restrains the core concrete and bears shear force, once the stirrups are corroded, the effective cross-sectional area is reduced, resulting in a weakened restraint on the core concrete, and then reducing the bearing capacity and ductility of the concrete column. At the same time, the volume expansion of the steel bar corrosion products will generate huge internal stresses, causing stress cracking of the concrete protective layer. The appearance of cracks not only further accelerates the penetration of external corrosive media into the concrete interior but also reduces the durability of the concrete column. In addition, under the long-term action of various adverse factors, the cross-sectional resistance of the concrete column will deteriorate over time, seriously threatening the safety of the building structure.

[0004] Regarding the reinforcement of reinforced concrete columns, various existing reinforcement systems have been developed, including the section enlargement method, the technique of externally bonding carbon fiber reinforced polymer (CFRP) laminates, the method of externally wrapping steel, and the ECC wrapping method, etc. The externally bonded CFRP technique has been widely applied in engineering practice due to its high specific strength, excellent specific modulus, and convenient construction. However, this technique has many insurmountable defects. Its mechanical transfer mechanism highly depends on the bonding integrity of the epoxy-based interface adhesive, and the epoxy resin adhesive is sensitive to the humid and hot environment. Under the coupled action of humidity cycling (-20°C - 60°C) and relative humidity fluctuation (40% - 95% RH), the interfacial debonding strength between the FRP and concrete shows significant time-varying attenuation, with an average annual decline rate of about 15%. This attenuation not only reduces the reinforcement effect but also poses a risk of type II fracture caused by interfacial stress concentration. When applying this technique to severely corroded columns in coastal areas, due to the loss of effective confinement of stirrups, the core concrete is in an unconfined state, and single FRP reinforcement is prone to brittle debonding failure, leading to sudden structural failure. The data simulation results show that under the working condition where the corrosion rate of stirrups > 25%, the ductility improvement rate of the traditional reinforcement system is less than 20%, and there is a risk of activating secondary corrosion, seriously affecting the long-term safety of the structure after reinforcement.

[0005] In addition, the traditional FRP grid - ECC reinforcement system also faces a series of technical bottlenecks when solving the problem of the degradation of the axial compressive bearing capacity of corroded reinforced concrete columns. This system often relies on the section enlargement method to increase stiffness, usually requiring a section increase of ≥ 20%. However, in working conditions where building space is limited, such as dense column grids, this method is difficult to implement. Although using ultra-high-strength ECC materials can increase the section resistance, when the compressive strength ≥ 80 MPa, the material cost will increase exponentially, resulting in too high economic costs. When enhancing the confinement effect by superimposing multiple layers of FRP grids, it is easy to cause interfacial shear slip and imbalance of stress redistribution, affecting the reliability of the reinforcement effect.

[0006] To sum up, the existing reinforced concrete column reinforcement technologies have many deficiencies when dealing with structural damage under the coupled action of high salt spray wet-dry alternation and seismic motion in coastal areas, and it is difficult to meet the requirements of the actual project for structural safety, durability, and economy. Summary of the Invention

[0007] In order to solve at least one of the above technical problems, the present invention proposes a repair system and construction method for reinforced concrete columns based on triple cooperative constraints, so as to achieve the purpose of multi-objective cooperative optimization of the reconstructed axial compression - flexure - shear coupling bearing capacity, improved interfacial durability, and secondary corrosion inhibition of the repaired concrete columns.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides a repair system for reinforced concrete columns based on triple cooperative constraints, including:

[0010] The core area concrete column, which is formed by removing the failed concrete protective layer from the corroded reinforced concrete column;

[0011] Longitudinal bars, arranged on the periphery of the core area concrete column;

[0012] Four - corner star - shaped stirrups, spaced along the axial direction of the core area concrete column and hoop - installed on the outside of the core area concrete column, and fixed to the longitudinal bars;

[0013] Stress - preventing members, used to prevent stress concentration at the corner ends of the four - corner star - shaped stirrups. The stress - preventing members are arranged at the four corners of the core area concrete column and fixedly connected to the four corner ends of the four - corner star - shaped stirrups;

[0014] FRP grid - ECC composite sandwich structure, arranged on the outside of the core area concrete column;

[0015] Through the four - corner star - shaped stirrups with negative Poisson's ratio effect combined with the FRP grid - ECC composite sandwich structure with active constraint mechanism and multi - crack control mechanism, a triple cooperative constraint repair system is formed to repair the structural performance of corroded reinforced concrete columns.

[0016] Preferably, the FRP grid - ECC composite sandwich structure includes:

[0017] The ECC inner layer, arranged on the outside of the core area concrete column. The four - corner star - shaped stirrups and the stress - preventing members are located in the ECC inner layer;

[0018] The FRP grid layer, wound on the outside of the ECC inner layer;

[0019] The ECC outer layer, arranged on the outside of the FRP grid layer.

[0020] Preferably, the stress - preventing member is an arc - shaped steel plate. The inner arc surface of the arc - shaped steel plate faces the center of the core area concrete column, and the four non - closed corner ends of the four - corner star - shaped stirrups are welded and fixed to the inner arc surface of the arc - shaped steel plate.

[0021] Preferably, the edges and corners of the ECC inner layer are rounded.

[0022] Preferably, the FRP grid layer is at least one layer and is provided with a lap layer. The length of the lap layer is 1 / 2 or 1 / 3 of the single - layer length of winding the ECC inner layer.

[0023] Preferably, the FRP grid layer is made of CFRP or BFRP material, and the grid shape is a square grid.

[0024] Preferably, the core area concrete column is square or rectangular.

[0025] The second aspect of the present invention provides a construction method for the repair system of a reinforced concrete column based on triple co - restraint as described in the first aspect, including the following steps:

[0026] S1. Chisel out the crack area and corroded stirrups of the corroded reinforced concrete column to form a core area concrete column with a square or rectangular cross - section, and pre - process the longitudinal bars.

[0027] S2. Bind four - corner star - shaped stirrups and fixedly connect the four - corner star - shaped stirrups with the pre - processed longitudinal bars.

[0028] S3. Weld and fix the stress - proof member to the four unclosed corner ends of the four - corner star - shaped stirrups to form an integral structure.

[0029] S4. Set up formwork on the outside of the four - corner star - shaped stirrups and the stress - proof member, and pour ECC between the formwork and the core area concrete column. After initial setting, an ECC inner layer is formed.

[0030] S5. Remove the formwork, and continuously wind the FRP grid in a single layer or multiple layers on the outside of the ECC inner layer to form an FRP grid layer. Before cutting the FRP grid, a lapping layer is reserved.

[0031] S6. Set up formwork outside the FRP grid layer, and pour ECC between the formwork and the FRP grid layer to form an ECC outer layer.

[0032] Preferably, the mass loss rate of the corroded stirrups ≥ 20%.

[0033] Preferably, one or more of polyvinyl alcohol fiber, steel fiber, polypropylene fiber, and carbon fiber are added to the ECC.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] Through the strain - hardening effect of the four - corner star - shaped stirrups with negative Poisson's ratio effect and the FRP grid - ECC composite sandwich structure with active restraint mechanism and multi - crack control mechanism, the present invention forms a triple co - restraint repair system. Under the condition of maintaining the original cross - section size of the concrete column and the conventional material grade, by using the material property complementarity and interface stress coordination mechanism, the maximum utilization of material efficiency is achieved, and the axial compression - flexure - shear coupling bearing capacity reconstruction and systematic restoration of the structural performance of the corroded reinforced concrete column are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural schematic diagram of a repair system for a reinforced concrete column based on triple co - restraint.

[0037] Figure 2 The side view of a repair system for reinforced concrete columns based on triple collaborative constraints;

[0038] Figure 3 The top view of a repair system for reinforced concrete columns based on triple collaborative constraints;

[0039] Figure 4 The connection schematic diagram of the four - corner star - shaped stirrups, longitudinal bars and arc - shaped steel plates in the present invention;

[0040] Figure 5 The top view of the connection state of the four - corner star - shaped stirrups, longitudinal bars and arc - shaped steel plates in the present invention;

[0041] Figure 6 The three - dimensional view of the FRP grid - ECC composite sandwich structure in the present invention;

[0042] Figure 7 The perspective view of the FRP grid - ECC composite sandwich structure in the present invention;

[0043] Figure 8 The top view of the FRP grid - ECC composite sandwich structure in the present invention;

[0044] Figure 9 The lapping schematic diagram of the FRP grid layer in the present invention;

[0045] Figure 10 The construction method flow chart of the repair system for reinforced concrete columns based on triple collaborative constraints in the present invention.

[0046] In the figure: 10, core area concrete column; 20, longitudinal bar; 30, four - corner star - shaped stirrup; 40, arc - shaped steel plate; 50, FRP grid - ECC composite sandwich structure; 501, inner ECC layer; 502, FRP grid layer; 5021, lapping layer; 503, outer ECC layer. Detailed implementation manners

[0047] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments of the present invention.

[0048] Embodiment 1

[0049] Please refer to Figures 1 - 8 as shown, the repair system for reinforced concrete columns based on triple collaborative constraints includes:

[0050] The concrete column 10 in the core area is formed by removing the ineffective concrete protective layer from the corroded reinforced concrete column;

[0051] The longitudinal reinforcement 20 is arranged on the peripheral side of the concrete column 10 in the core area;

[0052] The four - corner star - shaped stirrups 30 are spaced and hooped on the outer side of the concrete column 10 in the axial direction of the concrete column 10 in the core area and are fixed to the longitudinal reinforcement 20;

[0053] The stress - proof member is used to prevent stress concentration at the corner ends of the four - corner star - shaped stirrups 30. The stress - proof member is arranged at the four corners of the concrete column 10 in the core area and is fixedly connected to the four corner ends of the four - corner star - shaped stirrups 30;

[0054] The FRP grid - ECC composite sandwich structure 50 is arranged on the outer side of the concrete column 10 in the core area.

[0055] In this embodiment, through the strain - hardening effect of the four - corner star - shaped stirrups 30 with negative Poisson's ratio effect combined with the FRP grid - ECC composite sandwich structure 50 with active constraint mechanism and multi - crack control mechanism, a triple - coordinated constraint repair system is formed. Under the condition of keeping the original cross - sectional size of the concrete column and the conventional material grade, by using the complementary material properties and interface stress coordination mechanism, the maximum utilization of material efficiency is achieved, and the axial compression - flexure - shear coupling bearing capacity reconstruction of the corroded reinforced concrete column and the systematic restoration of the structural performance are realized.

[0056] It can be understood that the negative Poisson's ratio effect means that for general materials, when subjected to axial tension, the transverse dimension will shrink, showing a positive Poisson's ratio. While for materials with negative Poisson's ratio effect, when subjected to axial tension, their transverse dimension will instead increase; when subjected to axial compression, the transverse dimension will decrease.

[0057] Specifically, in this embodiment, the four - corner star - shaped stirrups 30 with negative Poisson's ratio effect, when the concrete column is in the axial tension state, the concrete column shows transverse expansion, which enhances the biting effect between the four - corner star - shaped stirrups 30 and the concrete column; while when the concrete column is under axial pressure, the concrete column shows transverse contraction, providing effective transverse restraint to the concrete column and improving the compressive strength and ductility of the concrete column. In this embodiment, the four - corner star - shaped stirrups 30 provide a more effective restraint to the concrete column 10 in the core area through their unique deformation mechanism.

[0058] It should be noted that, as shown in Figure 1 、 Figure 4 and Figure 5 , in this embodiment, the four - corner star - shaped stirrups 30 are composed of four hoop limbs connected end to end. However, since the longitudinal reinforcement 20 in this embodiment adopts an existing structure, for the convenience of installation and fixation of the four - corner star - shaped stirrups 30, the four corner ends of the four - corner star - shaped stirrups 30 are all in an unclosed state.

[0059] Specifically, in this embodiment, 8 longitudinal bars 20 are evenly distributed outside the core area concrete column 10, including corner longitudinal bars 20 at the four corners of the core area concrete column 10 and central longitudinal bars 20 at the midpoints of the four sides. The midpoint position of each hoop limb is fixed to the side of the central longitudinal bar 20 close to the core area concrete column 10, and both ends of the hoop limb are respectively fixed to the corner longitudinal bar 20 and the anti-stress member. In this way, a star shape with a concave center is formed, thus forming a stable structure with a negative Poisson's ratio effect, effectively avoiding the bond slip phenomenon of the concrete column under the stress state.

[0060] Please refer to Figure 6 , Figure 7 and Figure 8 as shown, the above-mentioned FRP grid - ECC composite sandwich structure 50 includes:

[0061] The ECC inner layer 501 is arranged outside the core area concrete column 10, and the four-corner star-shaped stirrups 30 and the anti-stress member are located in the ECC inner layer 501; the FRP grid layer 502 is wound outside the ECC inner layer 501; the ECC outer layer 503 is arranged outside the FRP grid layer 502.

[0062] It should be noted that in this embodiment, the ECC in the composite sandwich structure has quasi-strain hardening characteristics, multi-crack cracking mechanism and ultra-high tensile ductility (ultimate tensile strain > 3%), which can effectively coordinate the structural deformation, enable the entire composite sandwich structure to distribute stress more evenly when stressed, and reduce the damage caused by local stress concentration. Through the fiber bridging effect (such as PVA fibers), multiple cracks are formed instead of a single wide crack when in tension. The width of the micro-cracks is usually less than 100 microns, significantly reducing the permeability, reducing the diffusion rate of oxygen and moisture, effectively blocking the penetration path of corrosive media such as chloride ions, and enhancing the durability of the structure. As a wrapping material, it can completely wrap the FRP grid and the negative Poisson's ratio star-shaped stirrups, realizing the collaborative work of the three materials and giving full play to the mechanical properties of each material.

[0063] At the same time, the FRP grid forms an active constraint on the core concrete through a triaxial stress state, significantly improving the axial bearing capacity and ductility of the core concrete, making the internal concrete in a triaxial compression state, increasing the strength of the core concrete. Its high tensile strength can inhibit the lateral deformation of the concrete caused by rust expansion, reduce the crack width or even avoid cracking, reduce the connectivity of the diffusion channels, and further prevent external corrosive media from entering the concrete interior, protecting the steel bars from rust.

[0064] Based on the functional characteristics of the above-mentioned ECC and FRP grids, the composite sandwich structure used in this embodiment is composed of an ECC inner layer 501, an FRP grid and an ECC outer layer 503 from the inside to the outside. This composite sandwich structure effectively improves the mechanical properties and durability of the concrete column, and can meet the reinforcement and repair needs of concrete structures in harsh environments such as coastal areas.

[0065] Specifically, in terms of enhancing constraints and bearing capacity, the FRP grid has high tensile strength and is arranged between the ECC inner layer 501 and the outer layer, which can actively constrain the core concrete through a triaxial stress state. This constraint puts the internal concrete in a triaxial compressive state, significantly improving the axial bearing capacity and ductility of the core concrete. When subjected to pressure, the FRP grid limits the lateral deformation of the concrete, allowing the concrete to better exert its compressive properties, thereby improving the bearing capacity of the entire concrete column.

[0066] In terms of crack control and permeability reduction, FRP mesh can inhibit the lateral deformation of concrete caused by corrosion and expansion, reduce crack width, even avoid cracking, and reduce the connectivity of diffusion channels. At the same time, ECC materials form multiple cracks when tensile through fiber bridging, and the width of micro cracks is usually less than 100 microns, which significantly reduces permeability. FRP mesh works with the inner and outer layers of ECC to further prevent the penetration of corrosive media such as oxygen, moisture and chloride ions, effectively control the corrosion rate of steel bars, and enhance the durability of the structure.

[0067] In addition, the ECC completely wraps the FRP grid, making the three form a whole. The ECC inner layer 501 is in close contact with the core area concrete, which can coordinate the deformation of the concrete; the ECC outer layer 503 forms a continuous wrapping layer with the FRP grid, forming a physical barrier. The FRP grid in the middle not only uses the characteristics of ECC to achieve better bonding, but also cooperates with the inner and outer layers of ECC to give full play to their respective mechanical properties, achieve complementary material properties and interface stress coordination, and improve the comprehensive performance of the structure in terms of force performance, durability, fire resistance and impact resistance.

[0068] Based on the structural characteristics of the above-mentioned four-pointed star stirrup 30 with negative Poisson's ratio and the FRP grid-ECC composite sandwich structure 50, the present invention innovatively combines the two to form a repair system of four-pointed star stirrup 30-FRP grid-ECC triple collaborative constraints. The structural performance of the concrete column repaired by the repair system is significantly improved, achieving the purpose of multi-objective collaborative optimization such as constraint force reconstruction, interface durability improvement and secondary corrosion inhibition.

[0069] Specifically, in terms of improving mechanical properties, the four - corner star - shaped stirrup 30 has a negative Poisson's ratio effect, expanding laterally during tension and contracting laterally during compression. This characteristic enables it to provide strong lateral restraint to the core - area concrete when the concrete column is stressed, significantly increasing the peak load and flexural capacity of the concrete column, and changing its failure mode from brittle failure to ductile failure. The FRP grid in the composite sandwich structure forms an active restraint on the core concrete through a tri - axial stress state, further enhancing the axial bearing capacity and ductility of the core concrete; the ECC material, with its quasi - strain - hardening characteristic, multi - crack cracking mechanism, and ultra - high tensile ductility, effectively coordinates the structural deformation. The three work together to enhance the bearing capacity and deformation performance of the repaired concrete column, realizing the reconstruction of the axial compression - flexure - shear coupling bearing capacity of the corroded column, with a promotion rate ≥ 40%. The axial bearing capacity recovery coefficient of the repaired component reaches 1.18, and the displacement ductility coefficient μ ≥ 5.2.

[0070] In terms of the complementary and synergistic restraint mechanisms, the four - corner star - shaped stirrup 30 generates a radial expansion effect when stressed, forming a self - tightening restraint and initially restraining and strengthening the core - area concrete. In the composite sandwich structure, the FRP grid provides additional restraint to the concrete from the outside, complementing the restraint effect of the four - corner star - shaped stirrup 30, making the internal concrete in a more favorable tri - axial compression state, and enhancing the strength and ductility of the concrete. The ECC material tightly wraps the four - corner star - shaped stirrup 30 and the FRP grid, ensuring the coordinated work between all parts and making the restraint effect more stable and lasting.

[0071] In terms of the synergistic enhancement of durability, the special deformation mechanism of the four - corner star - shaped stirrup 30 can reduce the diffusion rate of oxygen and moisture, playing a certain role in inhibiting steel bar corrosion. The continuous wrapping layer formed by the outer - layer ECC matrix and the FRP grid in the composite sandwich structure constitutes a physical barrier, effectively blocking the penetration path of corrosive media such as chloride ions. The two work together to build a double - protection mechanism. Through experimental verification, it can improve the structural durability by more than 60%, effectively controlling the steel bar corrosion rate and meeting the long - life maintenance requirements of concrete structures in harsh coastal environments.

[0072] Please refer to Figure 1 、 Figure 3 and Figure 5 As shown, considering that the four corner ends of the four - corner star - shaped stirrup 30 are protruding parts relative to the overall structure, in order to avoid stress concentration at the corner ends after stress application, in this embodiment, the stress - proof part is the arc - shaped steel plate 40. The inner arc surface of the arc - shaped steel plate 40 faces the center of the core - area concrete column 10, and the four non - closed corner ends of the four - corner star - shaped stirrup 30 are welded and fixed to the inner arc surface of the arc - shaped steel plate 40.

[0073] Specifically, in this embodiment, the curved steel plate 40 is made of high-strength steel plate, for example, low-alloy high-strength structural steel (such as Q345), alloy structural steel (such as 40Cr) or high-strength stainless steel (such as 316L). In this embodiment, the curved steel plate 40 is arranged in the ECC inner layer 501. By utilizing the curvature of the curved steel plate 40 itself, the concentrated stress generated at the corner end of the four-pointed star-shaped stirrup 30 can be effectively dispersed through its curved surface, so that the stress distribution at the corner end is uniform, thereby avoiding local damage to the concrete column and ensuring the integrity of the structure.

[0074] In order to reduce the corrosion phenomenon in the harsh environment, the surface of the curved steel plate 40 in this embodiment is subjected to anti-corrosion treatment, such as hot-dip galvanizing, coating with anti-corrosion coating, etc. At the same time, the weld is subjected to anti-corrosion treatment such as coating with zinc-rich primer and sealant, thereby effectively preventing the weld from reducing strength due to corrosion.

[0075] Please refer to Figure 1 and Figure 6 As shown, in order to avoid stress concentration at the corners of the core area concrete column 10 and the ECC inner layer 501, in this embodiment, the corners of the core area concrete column 10 and the ECC inner layer 501 are rounded. Specifically, in the repair system of corroded reinforced concrete columns, from the perspective of stress distribution, right-angled corners are prone to stress concentration when subjected to force, reducing the bearing capacity and stability of the structure, while rounded corners can change the geometric shape of the corners, making the stress distribution more uniform, effectively dispersing the stress, reducing the risk of structural damage, and improving the overall bearing capacity.

[0076] In terms of structural integrity, the rounded ECC inner layer 501 and the arc-starting steel plate form a stable whole, which improves the stress transfer efficiency and avoids the reduction of structural performance due to poor coordination.

[0077] Considering durability, right-angled corners are easily affected by corrosive media, which accelerates concrete deterioration and steel corrosion. Rounded corners reduce the accumulation points of media and reduce the possibility of penetration. The ECC material is more evenly distributed at the rounded corners, which can better play the role of blocking corrosive media, enhance structural durability and extend service life.

[0078] In terms of construction operation, the rounded corners of the ECC inner layer 501 are easier to construct than right angles, which is beneficial to the flow and filling of ECC materials, reduces defects such as voids and bubbles, ensures the casting quality, and improves the construction quality of the entire structure.

[0079] Please refer to Figure 6 , Figure 7 and Figure 9 As shown, the FRP mesh layer 502 is at least one layer, and is provided with an overlap layer 5021 , and the length of the overlap layer 5021 is 1 / 2 or 1 / 3 of the length of a single layer wrapped around the ECC inner layer 501 .

[0080] It can be understood that the above FRP grid can be wound in multiple single layers or continuously multiple layers. The above overlapping layer 5021 makes the tail end of the FRP grid have an overlapping area relative to the head end, enhancing the overall connection strength of the FRP grid. When the concrete column is subjected to dynamic loads, the overlapping layer 5021 prevents the FRP grid from becoming disconnected due to excessive stress, maintains a tight bond with the ECC layer, and avoids situations such as separation and slippage between the FRP grid layer 502 and the ECC layer, ensuring the stability and reliability of the repaired structure.

[0081] It should be noted that in this embodiment, the FRP grid layer 502 is made of CFRP or BFRP material, and the grid shape is a square grid. As is well known, CFRP (carbon fiber reinforced composite material) has extremely high strength, elastic modulus, and excellent corrosion resistance, and BFRP (basalt fiber reinforced composite material) has relatively high strength, elastic properties, and excellent high-temperature resistance. Using the above materials to make the FRP grid layer 502 can significantly improve the axial compressive and flexural capacities of the post-repair concrete column, and at the same time can also well meet the usage requirements in a corrosive environment.

[0082] Embodiment 2

[0083] Please refer to Figure 10 , this example provides a construction method for a repair system of a reinforced concrete column based on triple cooperative constraints, including the following steps:

[0084] S1, chisel off the crack area and corroded stirrups of the corroded reinforced concrete column to form a core area concrete column 10 with a square or rectangular cross-section, and preprocess the longitudinal bars 20.

[0085] It should be noted that due to the typical damages such as electrochemical corrosion of stirrups, stress cracking of the protective layer, and time-varying deterioration of the cross-section resistance easily caused by the coupled action of coastal high-salt fog wet-dry alternation and seismic vibration, the stirrups mainly play the roles of shear resistance and longitudinal reinforcement confinement in concrete columns. When the mass loss rate of stirrup corrosion reaches 20% or more, its effective cross-sectional area is greatly reduced, the shear resistance ability is significantly decreased, and it cannot effectively make the concrete and longitudinal reinforcement work together, resulting in a decline in the overall bearing capacity of the structure. At the same time, the confinement effect of the corroded stirrups on the concrete is weakened, and the concrete column is prone to lateral expansion and cracking when compressed, thereby reducing the ductility of the structure. When the structure of the concrete column is subjected to dynamic loads such as earthquakes, it is difficult to dissipate energy through plastic deformation, increasing the risk of brittle failure of the structure and reducing the seismic performance of the structure. In addition, stirrup corrosion will cause the volume expansion of rust, generating expansion pressure on the surrounding concrete, causing the concrete protective layer to crack and spall, further accelerating the erosion of internal steel bars in the concrete by external corrosive media such as air, moisture, and chloride ions. Under the vicious cycle, the durability of the structure is severely damaged, shortening the service life of the structure. Therefore, when the mass loss rate of stirrup corrosion reaches ≥20%, the concrete column needs to be repaired.

[0086] S2. Bind the four-corner star-shaped stirrups 30, and fixedly connect the four-corner star-shaped stirrups 30 with the pre-treated longitudinal reinforcement 20.

[0087] It should be noted that there is rust on the surface of the above-mentioned longitudinal reinforcement 20. In this embodiment, mechanical grinding or chemical rust removal treatment is adopted to remove the rust and other attachments, so as to facilitate the welding and fixing of the four-corner star-shaped stirrups 30 and the longitudinal reinforcement 20.

[0088] S3. Weld and fix the stress prevention member to the four unclosed corner ends of the four-corner star-shaped stirrups 30 to form an integral structure.

[0089] It can be understood that as described above, the stress prevention member can adopt an arc-shaped steel plate 40. By fixing the unclosed corner ends of the four-corner star-shaped stirrups 30 to the inner arc surface of the arc-shaped steel plate 40, the four-corner star-shaped stirrups 30, the arc-shaped steel plate 40, and the longitudinal reinforcement 20 are connected into an integral structure. While improving the overall structure bearing capacity and anti-deformation ability of the concrete column, it can effectively disperse and transfer stress, reducing the stress concentration phenomenon.

[0090] S4. Set up formwork on the outer sides of the four-corner star-shaped stirrups 30 and the stress prevention member, and pour ECC between the formwork and the core area concrete column 10. After initial setting, an ECC inner layer 501 is formed.

[0091] It should be noted that the components of ECC in this embodiment mainly include cement, sand, water reducer, fly ash, silica fume and fibers. Among them, the added fibers can be one or more of polyvinyl alcohol fibers, steel fibers, polypropylene fibers, and carbon fibers. The specific ratio can be adjusted according to construction needs to meet construction requirements. For example, for ECC with high impermeability requirements, it is necessary to appropriately increase the dosage of silica fume and reduce the water-binder ratio; for projects that require rapid construction, it is necessary to adjust the ratio of cement and mineral admixtures to shorten the setting time.

[0092] S5, Demolish the formwork, and continuously wind the FRP grid in a single layer or multiple layers on the outer side of the inner layer 501 of ECC to form the FRP grid layer 502. Before cutting the FRP grid, a lap layer 5021 is reserved.

[0093] It should be noted that the FRP grid used in this embodiment is a square grid. Obviously, according to construction needs, the shape of the FRP grid can be diamond-shaped, hexagonal, circular, etc.

[0094] S6, Set up formwork outside the FRP grid layer 502, and pour ECC between the formwork and the FRP grid layer 502 to form the outer layer 503 of ECC.

[0095] The present invention provides a repair system and construction method for corroded reinforced concrete columns with triple synergistic constraints. Through the strain hardening effect of the four-corner star-shaped stirrups 30 with a negative Poisson's ratio effect and the FRP grid-ECC composite sandwich structure 50 with an active constraint mechanism and a multi-crack control mechanism, a triple synergistic constraint repair system with a gradient is formed. Under the condition of maintaining the cross-sectional size and conventional material grade of the original concrete column, by utilizing the complementary material properties and the interface stress coordination mechanism, the maximum utilization of material efficiency is achieved. Thus, the purposes of multi-objective collaborative optimization such as the reconstruction of the axial compression-bending shear coupling bearing capacity, the improvement of interface durability, and the inhibition of secondary corrosion of corroded reinforced concrete columns are realized.

[0096] The above is the specific implementation manner of the embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of this application.

Claims

1. Repair system for reinforced concrete columns based on triple collaborative constraints, characterized in that Including: The core area concrete column (10) is formed by removing the ineffective concrete cover layer from the corroded reinforced concrete column; Longitudinal reinforcement bars (20) are arranged on the periphery of the core area concrete column (10); Four-corner star-shaped stirrups (30) are spaced along the axial direction of the core area concrete column (10) and are hooped outside the core area concrete column (10), and are fixed to the longitudinal reinforcement bars (20); A stress prevention member is used to prevent stress concentration at the corner ends of the four-corner star-shaped stirrups (30). The stress prevention member is arranged at the four corners of the core area concrete column (10) and is fixedly connected to the four corner ends of the four-corner star-shaped stirrups (30); The FRP grid-ECC composite sandwich structure (50) is arranged outside the core area concrete column (10); Through the four-corner star-shaped stirrups (30) with negative Poisson's ratio effect and the FRP grid-ECC composite sandwich structure (50) with active constraint mechanism and multi-crack control mechanism, a triple collaborative constraint repair system is formed to repair the structural performance of the corroded reinforced concrete column.

2. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 1, wherein, The FRP grid-ECC composite sandwich structure (50) includes: The ECC inner layer (501) is arranged outside the core area concrete column (10). The four-corner star-shaped stirrups (30) and the stress prevention member are located in the ECC inner layer (501); The FRP grid layer (502) is wound outside the ECC inner layer (501); The ECC outer layer (503) is arranged outside the FRP grid layer (502).

3. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 1, wherein The stress prevention member is an arc-shaped steel plate (40). The inner arc surface of the arc-shaped steel plate (40) faces the center of the core area concrete column (10). The four non-closed corner ends of the four-corner star-shaped stirrups (30) are welded and fixed to the inner arc surface of the arc-shaped steel plate (40).

4. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 2, characterized in that The edges and corners of the ECC inner layer (501) are rounded.

5. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 2, characterized in that, The FRP grid layer (502) is at least one layer and is provided with a lapping layer (5021). The length of the lapping layer (5021) is 1 / 2 or 1 / 3 of the single-layer length of winding the ECC inner layer (501).

6. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 2, wherein The FRP grid layer (502) is made of CFRP or BFRP material, and the grid shape is a square grid.

7. The repair system for reinforced concrete columns based on triple collaborative constraints according to any one of claims 1-6, characterized in that, The core area concrete column (10) is square or rectangular.

8. The construction method of the repair system for reinforced concrete columns based on triple collaborative constraints according to any one of claims 1-7, characterized in that, Including the following steps: S1. Chisel the crack area and corroded stirrups of the corroded reinforced concrete column to form a core area concrete column (10) with a square or rectangular cross-section, and pre-treat the longitudinal reinforcement bars (20); S2. Bind the four-corner star-shaped stirrups (30) and fixedly connect the four-corner star-shaped stirrups (30) to the pre-treated longitudinal reinforcement bars (20); S3. Weld and fix the stress prevention member to the four unclosed corner ends of the four-corner star-shaped stirrups (30) to form an integral structure; S4. Set up a formwork outside the four-corner star-shaped stirrups (30) and the stress prevention member, and pour ECC between the formwork and the core area concrete column (10). After initial setting, an ECC inner layer (501) is formed; S5. Demolish the formwork, and continuously wind a single layer or multiple layers of FRP grids on the outer side of the inner layer (501) of the ECC to form an FRP grid layer (502). Before cutting the FRP grids, a lapping layer (5021) is reserved. S6. Set a formwork outside the FRP grid layer (502), and pour ECC between the formwork and the FRP grid layer (502) to form an outer layer (503) of ECC.

9. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 8, characterized in that, The mass loss rate of the corroded stirrups is ≥20%.

10. The repair system for reinforced concrete columns based on triple collaborative constraints according to claim 1, characterized in that, One or more of polyvinyl alcohol fibers, steel fibers, polypropylene fibers, and carbon fibers are added to the ECC.

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