Composite repairing and reinforcing technology for concrete filled steel tubular column subjected to non-uniform fire after fire

Abstract

The invention discloses a composite repairing and reinforcing technology for a non-uniform fire-receiving concrete-filled steel tubular column after a fire, which comprises a concrete-filled steel tubular column, a wall body, CFRP cloth, a GFRP plate, SMA ribs, a fiber grid net and a UHPC surface layer, the concrete-filled steel tubular column after the fire is detected and identified, the CFRP cloth is adhered to a serious damage part such as bulging of a steel tube, and an adhering area extends to the wall bodies on the two sides; studs are welded to the surfaces of the steel pipes, and L-shaped GFRP plates are arranged at the joints of the columns and the wall and fixed through split bolts; the SMA ribs are fixed to the studs through wire locking devices, the SMA ribs are energized to reach the preset temperature, and circumferential constraining force is applied to the concrete-filled steel tubular column; a fiber grating net is hung on the surface of a wall body and fixed through screws, and the surfaces of the wall and columns are sprayed with hybrid fiber UHPC with the thickness of 30 mm. Due to the fact that the CFRP cloth, the SMA ribs and the UHPC provide three defense line protection for the structure, the mechanical property of the concrete filled steel tubular column after the fire disaster can be effectively improved, meanwhile, the durability requirement of the reinforced structure is met, and the fire resistance of the reinforced structure after secondary fire disaster can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of building structures, in particular to a composite repair and reinforcement technology for non-uniformly-fired steel tube concrete columns after fire. Background Art

[0002] Steel tube concrete columns have been widely used in high-rise, super-high-rise buildings and large-span structures due to their good bearing capacity, seismic performance and construction convenience. Fire is a common and frequent form of disaster. The steel tubes of steel tube concrete columns may be directly affected by fire. Under the coupling of load and temperature rise and fall fire, the material properties of steel tubes and concrete are seriously deteriorated. The steel tubes may be partially buckled or even separated from the core concrete. Even if the steel tube concrete column does not fail as a whole under fire, its mechanical properties such as bearing capacity, stiffness, and ductility after the fire may be significantly reduced, resulting in the fire-affected structure being unable to continue to be used or posing serious safety hazards, requiring damage assessment and repair and reinforcement. In particular, in actual building fires, the walls adjacent to the columns block the spread of fire, and the column components are affected by non-uniform fire, forming real non-uniform fire boundaries on two or three sides, resulting in non-uniform stress and non-uniform material degradation caused by non-uniform temperature field in the fire column, which in turn causes non-uniform constraint effect, additional eccentricity, non-uniform residual deformation of the components after the fire, making the damage assessment and repair and reinforcement of non-uniformly fired steel tube concrete columns more complicated and difficult, and the relevant technology is still blank.

[0003] For steel tube concrete columns that have been exposed to fire, the post-fire repair and reinforcement needs to comprehensively consider many factors. In addition to the degree of fire, structural deformation, interface damage, etc., the mechanical properties of the reinforced structure exposed to secondary fire must also be considered. At present, the commonly used structural reinforcement technology at room temperature can improve the mechanical properties of the structure, but when used for steel tube concrete structures that have been exposed to non-uniform fire and may be exposed to secondary fire, there are certain limitations:

[0004] 1) FRP cloth reinforcement: FRP is lightweight, high-strength, corrosion-resistant, easy to construct, easy to maintain, and has good fatigue resistance. It can be flexibly constructed as the structure changes. However, the epoxy resin glue used to stick FRP loses its adhesion at a conversion temperature of about 100°C, causing the performance of the FRP reinforced structure to be greatly reduced during secondary fire. In addition, due to the existence of partition walls, it is difficult for FRP cloth to be effectively bonded to the reinforced surface at the inner corner where the wall and the column are connected, and it is easy to bulge and fall off. It is urgent to propose an FRP cloth wrapping method and technology that can effectively reinforce three-sided and two-sided non-uniformly exposed columns that take into account the influence of the wall.

[0005] 2) Steel plate reinforcement: It can effectively improve the bearing capacity of components without significantly increasing the cross-section of components. However, the fire resistance of steel without fire protection is poor, the thermal conductivity of steel is large, and its mechanical properties will deteriorate significantly at high temperatures, affecting the effect of the reinforced structure when it is subjected to fire for the second time. It is difficult to meet the first-level fire resistance requirements of column components, and an additional fire protection layer needs to be set up, which is time-consuming, labor-intensive, and increases costs.

[0006] 3) Prestressed reinforcement: By applying circumferential prestress, the bearing capacity and seismic performance of the structure are improved. However, traditional prestressed reinforcement technology has high requirements on the original shape and stress state of the structure. When subjected to secondary fire, the prestressed structure may be exposed to high temperature, and the loss of prestress may cause brittle failure of the structure, making it difficult to use in steel tube concrete structures that lack a second line of fire protection.

[0007] 4) Strengthening by increasing the cross-section: The bearing capacity and rigidity of the components are increased by outsourcing concrete, but the concrete pouring on site is a wet operation, which requires additional support formwork, and the newly added cross-section size is large and occupies the building space. Using ultra-high performance concrete instead of ordinary concrete to strengthen the existing structure can effectively reduce the newly added cross-sectional area and have little effect on the rigidity of the original structure. However, ultra-high performance concrete has dense pores and is prone to bursting and falling off at high temperatures, affecting the fire resistance of the reinforced structure.

[0008] It can be seen that the current single traditional reinforcement method cannot achieve the ideal repair effect for steel tube concrete columns with non-uniform fire damage. There is an urgent need for a composite reinforcement technology that is easy to operate, effective in repair, and can meet the structural durability and secondary fire resistance. In recent years, a variety of new high-performance materials have emerged in the field of civil engineering, such as ultra-high performance concrete (UHPC), shape memory alloy (SMA), fiber reinforced composite material (FRP), etc., which have broad prospects for post-fire repair and reinforcement of steel tube concrete columns with non-uniform fire damage. They can significantly improve the mechanical properties of the fire-damaged structure and meet the first-level fire resistance requirements of the reinforced column without applying fireproof protective materials. Summary of the invention

[0009] In view of the deficiencies in the prior art, the present invention discloses a composite repair and reinforcement technology for non-uniformly exposed steel tube concrete columns after fire, so as to solve the problems raised in the above background technology.

[0010] To achieve the above object, the present invention provides the following technical solution: A composite repair and reinforcement technology for non-uniformly exposed steel tube concrete columns after fire, comprising the following steps:

[0011] S1. First, after the fire, the damaged area of ​​the steel tube concrete column is inspected and identified, and the wall with surface peeling after the fire is cleaned and leveled with repair mortar;

[0012] S2. Then, epoxy resin glue is applied to the damaged parts of the steel tube concrete column such as bulging to paste the CFRP cloth, and the pasting area extends to the walls on both sides;

[0013] S3. At the inner corner where the steel tube concrete column and the wall meet, studs are locally welded in the non-reinforced area on the steel tube surface, holes are punched in the non-reinforced areas of the walls on both sides to reserve tension bolt holes for installing tension bolts, and an L-shaped GFRP plate is set at the inner corner where the steel tube concrete column and the wall meet. The GFRP plate has a hole on the side connected to the steel tube and the wall, and epoxy resin glue is applied on the back of the GFRP plate in the area not in contact with the CFRP cloth as a flexible cushion layer, and the GFRP plate is fixed by the tension bolts on the wall side.

[0014] S4, mechanically stretch the SMA tendons, slowly unload them after reaching a certain strain, fix the SMA tendons on the studs at the inner corner where the steel tube and the wall meet through the provided wire lockers, and conduct electrical excitation at both ends of the SMA tendons to heat them to a preset temperature, so that the SMA tendons generate prestress and then exert circumferential constraint force on the steel tube concrete column;

[0015] S5. A mounting slot is provided at the connection between the horizontal and vertical bars of the fiber grid net. Holes are drilled on the wall surface, and screws are screwed into the slots to fix the fiber grid net on the wall surface. In the overlapping area with the CFRP cloth, epoxy resin glue is applied on the CFRP cloth to adhere the fiber grid net to the CFRP cloth.

[0016] S6. Weld short steel bars on the surface of the steel tube, spray UHPC containing mixed fibers on the surface of the steel tube concrete column and the wall to form a reinforced surface layer, and finally complete the repair and reinforcement of the steel tube concrete column.

[0017] Preferably, step S1 specifically includes the following steps: according to the actual non-uniform fire boundary of the building, including the situation of two-sided fire or three-sided fire, a post-fire reinforcement scheme for steel tube concrete columns is selected, and a non-destructive testing method for steel tube concrete columns is used to determine the seriously damaged parts such as steel tube bulging and steel tube-concrete debonding, and then determine the CFRP cloth reinforcement position; clean the oxide layer produced by the fire on the surface of the steel tube at the reinforcement position, and for the steel tube concrete structure with a fireproof protective layer, if it is confirmed after the fire that the structure does not need to be reinforced, the original fireproof protective layer is still used to repair the small amount of fireproof protective material missing in the burned area. Repair and strengthen. If the fireproof protective layer is damaged and fallen off on a large scale after the fire, replace the fireproof protective material in the burned area, remove the original fireproof protective material and re-construct. For the unburned area of ​​the steel tube concrete column, repair the materials that are not water-resistant after being soaked in water. The fireproof protection structure and materials should be the same as the original components. If changes are necessary, the fire resistance limit of the repaired components should not be lower than that of the original components. Clean and polish the surface peeling area of ​​the wall connected to the steel tube concrete column caused by fire, remove impurities and dust, fill cracks and defects with repair mortar or repair glue, and ensure that the wall surface is flat.

[0018] Preferably, the nondestructive testing method for the steel tube concrete column includes traditional methods such as manual tapping method, induced vibration method, ultrasonic testing method and infrared thermal imaging method, as well as emerging technologies such as ultrasonic phased array.

[0019] Preferably, in step S2, several groups of CFRP sheets are pasted at intervals along the height direction of the steel tube concrete column, and at the same time, the CFRP sheets are pasted in the middle and end parts of the steel tube concrete column where the force is greater. The pasting direction of the CFRP sheets is horizontal and extends to the walls on both sides.

[0020] Preferably, precise and targeted reinforcement is carried out according to the actual degree of damage of the steel tube concrete column, that is, the number of CFRP cloth pasting layers is determined according to the degree of damage, and the CFRP cloth is extended to the areas where the walls on both sides are more seriously damaged. When the wall damage after the fire is not serious, the extension length of the CFRP cloth is 1000mm, and the CFRP cloth is pasted with the formulated epoxy resin glue, which includes colorless and transparent epoxy glue and light yellow curing agent.

[0021] Preferably, in step S3, studs are locally welded on the surface of the non-CFRP cloth reinforced area of ​​the steel pipe inner corner. The welding studs can be welded by manual arc welding. The welding equipment is simple and convenient and flexible to operate. Holes are punched in the non-CFRP cloth reinforced area of ​​the wall to reserve tension bolt holes. Holes are opened in the L-shaped GFRP plate. The position and size of the hole diameters are respectively consistent with the ends of the welding studs on the steel pipe surface and the tension bolt holes on the wall. Epoxy resin glue is applied to the area on the back of the L-shaped GFRP plate that is not in contact with the CFRP cloth as a flexible cushion layer. The long side of the L-shaped GFRP plate is fixed to the wall by tension bolts, and the short side is fixed to the surface of the steel pipe. The reinforced steel tube concrete column includes a two-sided non-uniformly fired column and a three-sided non-uniformly fired column.

[0022] 1) When repairing and reinforcing a column that is not uniformly exposed to fire on both sides, the studs are respectively fixed to the non-CFRP cloth reinforced areas on the adjacent sides of the concrete-filled steel tube column;

[0023] 2) When repairing and reinforcing a column that is non-uniformly exposed to fire on three sides, the studs are respectively fixed on the non-CFRP cloth reinforced areas on the opposite sides of the steel tube concrete column.

[0024] Preferably, in step S4, the SMA tendon is an iron-based SMA (Fe-SMA) tendon. Fe-SMA is inexpensive, cost-effective, and has good fatigue resistance. Other types of shape memory alloys may also be used. At a temperature lower than the phase transition temperature of the SMA tendon, a jack is used to mechanically stretch the SMA tendon to 6%, and the stretching length does not exceed the recoverable range. The SMA tendon is fixed to the bolt through the wire locker proposed by the present invention. The wire locker has two holes. One end of the SMA tendon is inserted into the upper hole and out of the lower hole to form a ring-shaped sleeve. The SMA bars are fixed on the bolts on the surface of the steel pipe by tightening the wire lock; the two ends of the SMA bars are electrified by an arc welding machine. When the SMA bars reach 200°C and show a shrinkage and tightening trend and begin to stabilize, the heating is stopped, so that the SMA bars produce a certain degree of prestress, thereby exerting annular constraint force on the steel tube concrete column; when the reinforced steel tube concrete column is subjected to secondary fire, the SMA bars are indirectly heated by fire to reach the complete phase change temperature (400°C), and a secondary constraint force is generated on the steel tube concrete column, thereby improving the fire resistance limit of the column subjected to fire.

[0025] Preferably, in step S5, the fiber grid mesh is arranged along the wall, with a width extending to the severely damaged area of ​​the wall or not less than 1m. The fiber grid mesh is a bidirectional glass fiber grid. Installation slots are provided at the connection between the horizontal bars and the vertical bars of the fiber grid mesh. Holes are drilled at suitable installation locations on the wall, residual debris in the holes are cleaned, structural adhesive is injected into the holes, and screws are screwed into the holes in the wall to fix the fiber grid mesh.

[0026] Preferably, in step S6, the welded steel bar head is welded in the non-CFRP cloth reinforcement area on the surface of the steel pipe, using a small diameter threaded steel bar for welding, so as to achieve a reliable connection between the UHPC surface layer and the interface of the steel tube concrete column. The sprayed UHPC adopts a rapid spraying equipment such as a hose peristaltic mortar sprayer. The thickness of the UHPC does not exceed 30 mm, and the mixed fibers therein include recycled tire polymer (RTP) fibers, polyvinyl alcohol (PVA) fibers and polyethylene (PE) fibers. While ensuring the reinforcement effect of UHPC, the incorporation of the mixed fibers can significantly reduce the density and thermal conductivity of the UHPC, and can melt to form channels when the reinforced structure is subjected to a secondary fire, thereby discharging the internal high-temperature water vapor and preventing the UHPC from bursting.

[0027] Compared with the existing single structure normal temperature reinforcement technology, the present invention has the following beneficial effects:

[0028] 1. The composite reinforcement technology proposed by the present invention for the repair of steel tube concrete columns after fire can realize the rapid and effective repair of composite columns under the actual non-uniform fire conditions of the wall, while eliminating the adverse effects of additional eccentricity and non-uniform constraint effects inside the fire column caused by non-uniform fire.

[0029] 2. The present invention adopts CFRP cloth, SMA tendons, UHPC and other new high-performance materials to form three lines of defense for repair and reinforcement, which provide sufficient redundancy and safety for improving the mechanical properties of the structure after the fire and the fire resistance of the secondary fire. The UHPC surface layer is the first line of defense for reinforcement and repair and secondary fire, which improves the bearing capacity and stiffness of the column components after the fire, while reducing the newly added cross-sectional area. The mixed fibers such as RTP, PVA and PE are added to UHPC to effectively prevent the occurrence of bursting, and can also reduce the thermal conductivity of UHPC, effectively reducing the heating rate of the internal structure when the fire occurs again, while meeting the thermal insulation performance requirements of the structure during normal use; SMA tendons For the second line of defense of reinforcement and repair and secondary fire, the SMA bars are heated by electricity to generate partial prestress, and the first stage of circumferential constraint force is applied to the steel tube concrete column to improve its mechanical properties after the fire. At the same time, when the steel tube concrete column is subjected to the fire for the second time, the SMA heats up but the rate is controllable, and the temperature can be controlled at around the complete phase change temperature, providing secondary circumferential constraint force for the fire column; CFRP cloth is the third line of defense for reinforcement and repair and secondary fire, which directly improves the mechanical properties of the steel tube concrete column after the fire, and when the external structure is subjected to the fire for the second time, due to the heat insulation effect of the UHPC surface layer, the CFRP cloth can be kept at a low temperature for a long time, and continuously and effectively constrain the steel tube concrete column. The three lines of defense are organically combined, work together, and reinforce each other, forming a new trinity composite reinforcement technology, which realizes the improvement of the mechanical properties of the steel tube constrained concrete column after non-uniform fire and the consideration of the fire resistance performance of the secondary fire.

[0030] 3. The present invention uses CFRP cloth to reinforce the fire surface of the non-uniformly fired steel tube concrete column and extends it to the walls on both sides. According to the stress characteristics and damage degree of the fired column, the pasting area and number of CFRP cloth are comprehensively determined, which can effectively improve the bearing capacity, stiffness and ductility of the steel tube concrete column after fire, while achieving the effects of saving materials, reducing costs and facilitating construction.

[0031] 4. The present invention arranges unequal-sided L-shaped GFRP plates at the inner corners of the steel tube concrete column and the wall to fix the CFRP cloth, which effectively solves the problems of difficult bonding and fixing of the CFRP cloth at the inner corners, poor reinforcement effect, and easy loosening and falling off. The GFRP plate is effectively connected to the wall and the fire-affected column by tension bolts and studs respectively. The tension bolts anchor the FRP plate on the wall side. For the irregular deformation of the fire-affected surface of the steel tube concrete column, the GFRP plate can be effectively connected with the structure to constrain and limit the deformation. Among them, the FRP material has the characteristics of light weight, high strength, corrosion resistance, etc., and its thermal conductivity is small, which avoids the problem of using angle steel to fix in the structure to form a thermal bridge, and effectively takes into account the structural bearing capacity and thermal performance during normal use.

[0032] 5. In the present invention, compared with ordinary prestressed steel bars, Fe-SMA prestressed bars with a high cost-effectiveness are provided, which can achieve a two-stage prestressing effect on the fire column, thereby taking into account the normal temperature mechanical properties and secondary fire resistance of the component: since the SMA bar does not have an obvious yield point, the prestressing strain is firstly applied to 6%, and the two ends of the SMA bar are fixed after unloading, and the SMA bar is electrically excited at both ends, and the SMA bar is heated to more than 200°C, so that it generates the maximum restoring force during the heating process. In addition, during the cooling stage of the SMA bar, its restoring stress continues to increase, further applying the first stage circumferential constraint force to the steel tube concrete column, thereby effectively improving the bearing capacity of the reinforced component at room temperature; when the structure is subjected to fire for the second time, after the whole process of heating and cooling, the SMA bar is heated again to the complete phase change temperature, and the restoring force generated can be used as a permanent prestress to improve the structural performance, thereby applying a secondary circumferential constraint force to the steel tube concrete column, and improving the fire resistance of the structure when it is subjected to fire again and the mechanical properties after the secondary fire. In addition, the wire lock has a simple structure and is easy to construct, and can achieve reliable fixation of SMA tendons and effective application of two-stage prestressing.

[0033] 6. The present invention sprays a layer of UHPC surface layer on the surface of the steel tube concrete column and the wall. UHPC has the advantages of high strength, impact resistance, good durability, etc. The construction is fast and convenient. The thickness of the UHPC surface layer does not exceed 30 mm. Under the premise of not affecting the use space of the building, it can effectively improve the mechanical properties of the fire-affected column and have a beautiful appearance. It can also serve as a fireproof protective layer to reduce the temperature of the internal steel pipe, CFRP cloth and SMA reinforcement and significantly improve their durability. At the same time, it can also increase the thermal resistance of the wall and reduce the overall energy consumption of the building.

[0034] 7. In the present invention, mixed fibers of RTP fiber, PVA fiber and PE fiber are added to the UHPC surface layer. While ensuring the strength and reinforcement effect of UHPC, the mixed fibers can melt at high temperature to form channels, emit internal high-temperature water vapor, prevent the UHPC layer from bursting, and at the same time reduce the thermal conductivity of UHPC and the heating rate under fire, effectively reduce the temperature of the internal SMA tendons and CFRP cloth, ensure that they can still play a role when the structure is subjected to fire for the second time, and can also reduce the dead weight of the structure and reduce the reinforcement cost; at the same time, recycled tire fibers can realize solid waste utilization, carbon reduction and energy saving, green environmental protection, and meet the national dual carbon strategic needs.

[0035] 8. In order to ensure that the UHPC reinforced surface layer plays an effective role, the present invention welds the steel bar head on the surface of the steel tube concrete column to enhance the interface connection performance between the steel tube and the UHPC, and uses the fiber grid mesh to enhance the bonding performance of the interface between the UHPC surface layer and the reinforced wall. In addition, the studs and tension bolts used to fix the GFRP plate can also serve as connectors to further enhance the interface performance between the UHPC surface layer and the wall and the steel tube concrete column. The fiber grid mesh is a bidirectional glass fiber with the characteristics of high strength, light weight, corrosion resistance, good thermal stability, and low thermal conductivity. The fiber grid mesh has installation slots at the connection between the horizontal and vertical bars, making the installation process more convenient and quick, and also helping to improve the accuracy and stability of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0037] In the attached picture:

[0038] Figure 1 It is a plan view of the composite reinforcement method of a three-sided fire-exposed steel tube concrete column of the present invention;

[0039] Figure 2 It is an overall schematic diagram of the composite reinforcement method of a three-sided fire-exposed steel tube concrete column of the present invention;

[0040] Figure 3 It is a plan view of the composite reinforcement method of the steel tube concrete column exposed to fire on both sides of the present invention;

[0041] Figure 4 It is an overall schematic diagram of the composite reinforcement method of the steel tube concrete column exposed to fire on both sides of the present invention;

[0042] Figure 5 It is a cross-sectional view of the composite reinforcement tension bolts of the steel tube concrete column of the present invention;

[0043] Figure 6 It is a schematic diagram of SMA tendon fixation;

[0044] Figure 7 It is a schematic diagram of the connection structure between the steel tube concrete column and the wall;

[0045] Figure 8 is a schematic diagram of a fiber grid mesh;

[0046] Fig. 9 This is a diagram of the hydraulic jack equipment for tensioning SMA tendons.

[0047] Numbers in the figure: 1. core concrete; 2. steel pipe; 3. wall; 4. flexible joint; 401. PE rod; 402. alkali-resistant glass fiber mesh cloth; 403. special sealant; 5. CFRP cloth; 6. tension bolts; 601. tension screw rods; 602. nuts; 603. cross braces; 7. L-shaped GFRP plates; 8. studs; 9. wire lockers; 10. SMA bars; 11. steel bar heads; 12. fiber grid mesh; 13. screws; 14. UHPC; 15. arc welder; 16. jack; 16-a. fixing plate; 16-b. reaction plate; 16-c. hydraulic jack; 16-d. displacement meter. DETAILED DESCRIPTION

[0048] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0049] Example: Figure 1-Figure 9 As shown, a composite repair and reinforcement technology for non-uniformly exposed steel tube concrete columns after fire includes the following steps:

[0050] S1. First, after a fire, a damaged area of ​​a steel tube concrete column is detected, wherein the steel tube concrete column comprises a core concrete 1 and a steel tube 2, the steel tube 2 is located between two walls 3 and fixed to the wall 3 via a flexible seam 4, the core concrete 1 is located inside the steel tube 2, and the internal structure of the flexible seam 4 comprises a PE rod 401 arranged on the surface of the steel tube, an alkali-resistant glass fiber mesh cloth 402 is laid on the surface, and a layer of special sealant 403 is arranged;

[0051] Specifically according to the actual non-uniform fire boundary of the building, including three-sided fire or two-sided fire, the post-fire reinforcement plan of the steel tube concrete column is judged, and the non-destructive detection method of the steel tube concrete column is adopted. The non-destructive detection method of the steel tube concrete column includes traditional methods such as manual tapping method, induced vibration method, ultrasonic detection method, infrared thermal imaging method or emerging technologies such as ultrasonic phased array, to detect the positions of steel tube bulging, steel tube-concrete debonding, etc., and then select the key reinforcement position of the CFRP cloth 5, clean the detached oxide layer produced by the fire on the surface of the steel tube 2 at the reinforcement position, and for the wall 3 whose surface has peeled off after the fire, chisel out the severely damaged and cracked parts, clean the chiseled interface, and fill the cracks and defects with repair mortar or repair glue.

[0052] S2. Then, CFRP cloth 5 is pasted on the parts of the steel tube concrete column where the steel tube 2 is seriously damaged such as buckling, and several groups of CFRP cloth 5 are pasted at intervals along the height direction of the steel tube concrete column. At the same time, CFRP cloth 5 is pasted on the middle and end parts of the steel tube 2 where the force is greater, and the number of pasted layers of CFRP cloth 5 is determined according to the degree of damage. The pasting direction of CFRP cloth 5 is horizontal and extends to the seriously damaged areas of the walls 3 on both sides. When the wall 3 is not seriously damaged after the fire, the extension length of CFRP cloth 5 is 1000mm, and it is pasted by using the prepared epoxy resin glue, and the epoxy resin glue includes A colorless transparent epoxy glue and B light yellow curing agent.

[0053] S3. Studs 8 are welded at the inner corner where the steel tube 2 of the steel tube concrete column is connected to the wall 3. Holes are punched on the side of the wall 3 to reserve holes for tension bolts 6 for installing the tension bolts 6. Holes are opened at specific positions on the L-shaped GFRP plate 7, which is set at the inner corner where the steel tube 2 and the wall 3 intersect. The GFRP plate 7 is pressed on the surface of the CFRP cloth 5. The tension bolts 6 are installed. The tension screws 601 are first inserted into the wall, and the two ends are inserted into the cross braces 603. The nuts 602 are screwed in to fix the tension screws 601. The GFRP plate 7 is anchored by the tension bolts 6 and the studs 8 to achieve compaction and fixation of the CFRP cloth 5 at the inner corner.

[0054] Among them, the treated CFST columns include two-side fire-exposed surfaces and three-side fire-exposed surfaces;

[0055] 1) When repairing and reinforcing a column exposed to fire on both sides, the studs 8 are respectively fixed to the non-CFRP cloth 5 reinforcement area on the adjacent sides of the steel tube concrete column steel tube 2;

[0056] 2) When repairing and reinforcing a column exposed to fire on three sides, the bolts 8 are respectively fixed to the non-CFRP cloth 5 reinforcement area on the opposite side of the steel tube 2 of the concrete-filled steel tube column.

[0057] S4. The SMA tendon 10 is tensioned to 6% by a hydraulic jack 16. The working principle of the jack 16 is as follows: the SMA tendon 10 is inserted into the fixed plates 16-a at both ends, one end of which is fixed and the other end is fixed to the reaction plate 16-b. The hydraulic jack 16-c is started, and the tension strain is observed by the displacement meter 16-d to slowly unload when it reaches 6%. The SMA tendon 10 is a Fe-SMA tendon, and both ends are fixed to the bolt 8 by a wire locker 9, and the wire locker 9 has two holes. The hole diameter is slightly larger than the diameter of the SMA tendon 10. One end of the SMA tendon 10 is inserted into the upper hole of the wire locker 9 and comes out from the lower hole to form a ring-shaped sleeve on the bolt 8 on the surface of the steel pipe. The wire locker 9 is tightened to fix the SMA tendon 10. The two ends of the SMA tendon 10 are energized by the arc welder 15. When the SMA tendon 10 reaches 200°C and produces a shrinkage and tightening trend and begins to stabilize, the heating is stopped, so that the SMA tendon 10 generates prestress and then applies the first stage of annular constraint force to the steel tube concrete column.

[0058] S5. The fiber grid mesh 12 is a bidirectional glass fiber grid. The connection between the horizontal bars and the vertical bars of the fiber grid mesh is provided with installation slots. A hole is drilled at the installation position of the wall 3, and debris in the hole of the wall 3 is cleaned. Structural adhesive is injected into the hole. Screws 13 are screwed into the hole of the wall to fix the fiber grid mesh 12. In the overlapping area between the fiber grid mesh 12 and the CFRP cloth 5, epoxy resin adhesive is applied on the CFRP cloth 5 to make the fiber grid mesh 12 evenly adhered to the CFRP cloth 5.

[0059] S6. Weld and connect the steel bar head 11 on the surface of the steel pipe 2 to enhance the interface performance between UHPC14 and the steel pipe 2. Spray UHPC14 on the surface of the steel pipe 2 and the wall 3 to form a reinforced surface layer. The spraying of UHPC14 adopts a hose peristaltic mortar sprayer. The thickness of the UHPC14 reinforced surface layer does not exceed 30 mm. The UHPC14 includes mixed fibers such as RTP fiber, PVA fiber and PE fiber. At high temperature, the mixed fibers in the UHPC14 reinforced surface layer melt to form channels, discharge the internal high-temperature water vapor, prevent the UHPC from bursting, and finally complete the repair and reinforcement of the steel tube concrete column.

[0060] The specific working principle is to improve the mechanical properties of the steel tube concrete column after non-uniform fire exposure and take into account the secondary fire resistance by setting up three lines of defense. By inspecting and identifying the damaged area of ​​the steel tube concrete column after the fire, the scope and method of reinforcement are determined, the damaged area of ​​the wall 3 is cleaned and leveled with repair mortar to restore the integrity and continuity of the structure; CFRP cloth 5 is pasted in the middle, end and severely damaged areas of the steel tube concrete column where the force is greater. The pasting direction is horizontal and extends to the wall 3 areas on both sides to ensure reliable connection and coordinated force between the wall and the column; in the non-CFRP cloth 5 pasting area at the inner corner where the steel tube 2 and the wall 3 are connected, studs 8 are welded on the surface of the steel tube 2, and holes are drilled in the wall 3 to reserve the tension bolts 6 channels, L-type GFR After the P plate 7 is opened, the CFRP cloth 5 is pressed and fixed, which effectively solves the problems of difficult bonding and fixing of the CFRP cloth 5 at the inner corner, poor reinforcement effect, easy bulging and debonding, etc. The short side of the L-shaped GFRP plate 7 is inserted into the stud 8, and the long side is fixed with the tension bolt 6, so that the L-shaped GFRP plate 7 is effectively connected with the wall and the fire column; the SMA bar 10 is inserted into the locking device 9 to form a ring on the stud 8, and the arc welding machine 15 is connected to the two ends of the SMA bar 10 for power-on excitation, so that the SMA bar 10 generates the first stage of circumferential constraint force on the steel tube concrete column, which effectively improves the bearing capacity of the component after the fire, and the steel tube concrete structure is subjected to secondary stress. During a fire, the SMA tendons 10 heat up to the complete phase change temperature to generate recovery stress, thereby applying secondary circumferential restraint to the steel tube concrete column to prevent the component from being damaged by fire for the second time, and after the structure is cooled down, a permanent effective prestress is applied to the steel tube concrete column; a steel bar head 11 is welded to the non-CFRP cloth 5 reinforcement area on the surface of the steel tube 3, and a fiber grid mesh 12 is arranged on the surface of the wall 3, and studs and tension bolts are used to enhance the interface connection performance between the UHPC 14 and the steel tube 2 and the wall 3; installation slots are provided at the connection between the horizontal bars and the vertical bars of the fiber grid mesh 12, which is convenient for screws 13 to install and fix the fiber grid mesh The UHPC14 surface layer has high strength, impact resistance and good durability. It is mixed with mixed fibers such as RTP fiber, PVA fiber, PE fiber, etc., which can ensure the strength and reinforcement effect of UHPC14. The mixed fibers melt at high temperature to form channels to discharge internal high-temperature water vapor, prevent the UHPC14 layer from bursting, reduce the thermal conductivity of UHPC and the heating rate under fire, and effectively reduce the temperature of the internal SMA tendons 10 and CFRP cloth 5 to ensure that they can still play a role when the structure is subjected to fire for the second time, thereby improving the fire resistance of the steel tube concrete column subjected to secondary fire, and can also reduce the dead weight of the structure and reduce the reinforcement cost.

[0061] It should be noted that the above description is only used to illustrate the preferred examples of the present invention and is not used to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A composite repair and reinforcement technology for non-uniformly exposed steel tube concrete columns after fire, characterized in that: The following steps are involved: S1. First, after the fire, the damaged area of ​​the steel tube concrete column is inspected and identified, and the wall with surface peeling after the fire is cleaned and leveled with repair mortar; S2. Then, epoxy resin glue is applied to the damaged part of the steel tube concrete column where the steel tube is buckled, and the CFRP cloth is pasted, and the pasting area extends to the walls on both sides; S3. At the inner corner where the steel tube concrete column and the wall meet, studs are locally welded in the non-CFRP cloth reinforced area on the steel tube surface, holes are punched in the non-reinforced areas of the walls on both sides to reserve tension bolt holes for installing tension bolts, and an L-shaped GFRP plate is arranged at the inner corner where the steel tube concrete column and the wall meet. The GFRP plate has a hole on the side connected to the steel tube and the wall, and epoxy resin glue is applied on the back of the GFRP plate in the area not in contact with the CFRP cloth as a flexible cushion layer, and the GFRP plate is fixed by the tension bolts on the wall side; S4, mechanically stretch the SMA tendons, slowly unload them after reaching a certain strain, fix the SMA tendons on the studs at the inner corner where the steel tube and the wall meet through the provided wire lockers, and conduct electrical excitation at both ends of the SMA tendons to heat them to a preset temperature, so that the SMA tendons generate prestress and then exert circumferential constraint force on the steel tube concrete column; S5. A mounting slot is provided at the connection between the horizontal and vertical bars of the fiber grid net. Holes are drilled on the wall surface, screws are screwed into the slots, and the fiber grid net is fixed to the GFRP board and the wall surface. In the overlapping area with the CFRP cloth, epoxy resin glue is applied on the CFRP cloth to adhere the fiber grid net to the CFRP cloth. S6. Weld short steel bars on the surface of the steel tube, spray UHPC containing mixed fibers on the surface of the steel tube concrete column and the wall to form a reinforced surface layer, and finally complete the repair and reinforcement of the fire-damaged steel tube concrete column.

2. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 1 is characterized by: In step S1, the following steps are specifically included: according to the actual non-uniform fire boundary of the building, including two-sided fire or three-sided fire, a post-fire reinforcement plan for the steel tube concrete column is selected, and a non-destructive testing method for the steel tube concrete column is used to determine the seriously damaged parts of the steel tube bulging and steel tube-concrete debonding, and then determine the CFRP cloth reinforcement position, clean the oxide layer produced by the fire on the surface of the steel tube at the reinforcement position, clean and polish the surface peeling area produced by the fire on the wall connected to the steel tube concrete column, remove impurities and dust, fill the cracks and defects with repair mortar or repair glue, and ensure that the wall surface is flat.

3. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 2 is characterized in that: The nondestructive testing method for the steel tube concrete column includes the traditional methods of manual knocking method, induced vibration method, ultrasonic testing method and infrared thermal imaging method and the emerging technology of ultrasonic phased array.

4. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 1 is characterized in that: In step S2, CFRP sheets are pasted on the outer surface of the steel tube in the severely damaged area of ​​the steel tube concrete column. Several groups of CFRP sheets are pasted at intervals along the height direction of the steel tube concrete column. At the same time, CFRP sheets are pasted on the middle and end parts of the steel tube concrete column where the force is greater. The pasting direction of the CFRP sheets is horizontal and extends to the walls on both sides.

5. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 4 is characterized in that: Accurate and targeted reinforcement is carried out according to the actual degree of damage of the steel tube concrete column, that is, the number of CFRP cloth pasting layers is determined according to the degree of damage. The CFRP cloth is extended to the areas where the walls on both sides are more seriously damaged. When the wall damage after the fire is not serious, the extension length of the CFRP cloth is 1000mm, and the CFRP cloth is pasted with the formulated epoxy resin glue, which includes colorless and transparent epoxy glue and light yellow curing agent.

6. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 1 is characterized by: In step S3, an L-shaped GFRP plate is set to fix the CFRP cloth, the L-shaped GFRP plate has unequal sides, the long side is arranged along the wall direction, and the short side is arranged along the steel tube concrete column direction. The L-shaped GFRP plate is pre-drilled at a specific position using an electric drill, and the GFRP plate hole diameter is consistent with the wall hole diameter. The reinforced steel tube concrete column includes a two-sided non-uniform fire column and a three-sided non-uniform fire column; 1) When repairing and reinforcing a column that is not uniformly exposed to fire on both sides, the studs are respectively fixed on the wall surfaces on adjacent sides of the steel tube concrete column; 2) When repairing and reinforcing a column that is non-uniformly exposed to fire on three sides, the studs are respectively fixed on the wall surfaces on opposite sides of the steel tube concrete column.

7. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 1, characterized in that: In step S4, the SMA tendon is a Fe-SMA tendon, and a jack device is used to tension the SMA tendon to 6% strain, and then slowly unload the tendon, and the SMA tendon is fixed on the bolt through a wire locker, the wire locker has two holes, one end of the SMA tendon is inserted into the upper hole, and comes out from the lower hole to form a ring sleeve on the bolt on the surface of the steel pipe, and the wire locker is tightened to fix the SMA tendon, and the two ends of the SMA tendon are energized by an arc welder. When the temperature of the SMA tendon reaches 200°C, a shrinkage and tightening trend is generated, and the heating is stopped after it begins to stabilize, so that the SMA tendon undergoes a partial phase change to generate prestress and then exerts a circumferential constraint force on the steel tube concrete column. When the steel tube concrete column is subjected to fire for the second time, the SMA tendon is heated to a complete phase change temperature, and a secondary constraint force is generated on the steel tube concrete column.

8. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 1 is characterized by: In step S5, the fiber grid mesh is set along the wall, and the width extends to the severely damaged area of ​​the wall or is not less than 1m. The fiber grid mesh is a bidirectional glass fiber grid. Installation slots are opened at the connection between the horizontal bars and the vertical bars of the fiber grid mesh. Holes are drilled at suitable installation locations on the wall, residual debris in the holes are cleaned, structural glue is injected into the holes, and screws are screwed into the wall holes to fix the fiber grid mesh.

9. The composite repair and reinforcement technology for non-uniformly exposed concrete-filled steel tube columns after fire according to claim 1, characterized in that: In step S6, the welded short steel bar head is arranged at the center of the steel tube surface and the upper and lower areas of the SMA ribs, and avoids the CFRP cloth pasting area to enhance the interface connection performance between the UHPC surface layer and the steel tube concrete column. UHPC is sprayed using equipment such as a hose peristaltic mortar sprayer. The spraying thickness of UHPC on the steel tube concrete column and the wall surface does not exceed 30 mm. The spraying width along the wall direction covers the fiber grid mesh. The mixed fibers in the UHPC include recycled tire polymer fibers, PVA fibers and PE fibers. When the structure is subjected to fire for the second time, the fibers in the UHPC surface layer melt to form channels, thereby discharging the internal high-temperature water vapor and preventing the UHPC from bursting.

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