UHPC (Ultra High Performance Concrete)-based steel pipe concrete column reinforcing method

Abstract

The invention relates to a UHPC (Ultra High Performance Concrete)-based concrete-filled steel tube column reinforcing method. Specifically, a poured UHPC layer and a concrete-filled steel tube column form a whole by utilizing the ultra-high performance of early-strength UHPC, the constraint of an annular stirrup and the rough polishing treatment of the surface of a steel tube. The UHPC has excellent mechanical property, ultrahigh durability and adhesive property, the ultrahigh performance of the UHPC can be effectively utilized by the annular stirrup and UHPC combined structure, so that the concrete filled steel tubular column is well protected, the overall stress performance after reinforcement is effectively improved, later maintenance is simple and efficient, and the overall cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of building structure reinforcement, and in particular to a UHPC-based steel tube concrete column reinforcement method. Background Art

[0002] In addition to the characteristics of high strength, good ductility, fatigue resistance and impact resistance, steel tube concrete columns also have the advantages of saving labor and materials, easy erection and fast construction. Its external steel tube can exert a strong restraining effect on the internal concrete. When subjected to pressure, the internal concrete is in a three-way compression state, and the strength is greatly improved. Steel pipes can replace the role of steel bars and reduce the amount of steel bars used in the structure. During construction, steel pipes can be directly used as templates for concrete pouring, which greatly saves construction costs and time. In addition, the concrete filled inside can delay the local bulging of steel pipes. Thanks to the above advantages, steel tube concrete columns are widely used in civil engineering, such as large-span bridges, super high-rise buildings, underground buildings, high-speed rail platforms, large factories, etc.

[0003] With the continuous deepening of the application and research of steel tube concrete structures, people have found that steel tube concrete has deficiencies in strength. The concrete inside the steel tube has problems such as plastic shrinkage, autogenous shrinkage, and creep shrinkage. The other steel tube walls are prone to voiding and debonding. At the same time, the shrinkage and creep of concrete produces compressive stress in the steel tube, and the concrete produces tensile stress, which greatly reduces the elastic modulus and bearing capacity of steel tube concrete. In my country, the application of steel tube concrete structures in actual engineering has a history of more than 60 years. Some steel tube concrete structures have insufficient bearing capacity due to corrosion, earthquakes, collisions with vehicles and ships, and improper construction. These problems seriously affect the working performance of steel tube concrete, so that the designed bearing capacity cannot meet the actual use requirements and need to be reinforced.

[0004] Ultra-high performance concrete (UHPC) is a new type of cement-based composite material with ultra-high strength, high toughness and ultra-low porosity. With its excellent mechanical properties, ultra-high durability and bonding properties, UHPC has been put into practical use in structural repair and reinforcement projects, and has produced good social and economic benefits. Summary of the invention

[0005] The purpose of the present invention is to solve the rising problem and provide a reinforcement method for steel tube concrete columns based on UHPC. The purpose of the present invention is achieved through the following technical solutions: A reinforcement method for steel tube concrete columns based on UHPC, specifically comprising the following steps: (1) For the outer surface formwork of the steel tube concrete column, annular stirrups are installed between the formwork and the steel tube. The spacing between each annular stirrup is 100~200mm, and the spacing between the stirrup and the steel tube is 50mm; (2) UHPC is cast on the steel tube concrete column. The thickness of UHPC is 200~400mm. The formwork is removed after curing. After UHPC casting, it is an integral part of the original structure.

[0006] The steel tube concrete column is a steel tube concrete column, which is obtained by pouring concrete inside a hollow steel tube. The strength of the concrete should be C30 or above.

[0007] The formwork described in step (1) is a simple wooden formwork, and annular stirrups are installed between the formwork and the steel pipe. Small concrete blocks are used to separate the annular stirrups, and the spacing between the stirrups is 100-200 mm.

[0008] The thickness of the UHPC layer in step (2) is determined by the diameter of the original steel tube concrete column. When the diameter of the steel tube concrete column exceeds 1500 mm, the thickness of the UHPC layer should be increased accordingly.

[0009] The UHPC is an early-strength UHPC, and its 7-day compressive strength is above 120 MPa.

[0010] When pouring UHPC, due to the different sizes of steel tube concrete columns, when the UHPC layer is larger than 300mm, it is necessary to use vibration and other methods to compact it. After pouring, UHPC becomes a whole with the original structure.

[0011] The curing period after UHPC pouring is 7 days, first 48 hours of standard curing, then 48 hours of steam curing, and finally 72 hours of standard curing. After the curing is completed, traffic can be opened without affecting use.

[0012] Compared with the prior art, the present invention has the following advantages: 1. The UHPC-based steel tube concrete column reinforcement method described in the present invention aims to solve the problems of steel tube bulging, easy corrosion, and large deflection in long span structures in steel tube concrete structures. The method of integral casting of UHPC with annular stirrups is adopted to make the UHPC and the original structure become a whole and the overall bearing capacity is increased by about 2 times compared with the original structure.

[0013] 2. The UHPC-based steel tube concrete column reinforcement method described in the present invention adopts early-strength UHPC as the reinforcement material, which can shorten the maintenance and reinforcement cycle and effectively enhance the durability of steel tube concrete. The low porosity of UHPC makes the reinforced steel tube concrete column have obvious anti-cracking effect, good water seepage resistance and chloride ion penetration resistance, and can prevent steel tube rust. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is a schematic diagram of the cross-sectional structure of an unreinforced circular steel tube concrete column of the present invention; Figure 2 This is a schematic diagram of the structure of a circular steel tube concrete column without stirrup reinforcement of the present invention; Figure 3 This is a schematic diagram of the structure of a circular steel tube concrete column reinforced with stirrups according to the present invention; Figure 4 It is a schematic diagram of the cross-sectional structure of the unreinforced square steel tube concrete column of the present invention; Figure 5 This is a schematic diagram of the structure of the square steel tube concrete column of the present invention without using stirrups for reinforcement; Figure 6 A schematic diagram of the structure of a square steel tube concrete column reinforced with stirrups according to the present invention; In the figure: 1-external steel pipe; 2-internal concrete; 3-annular stirrups; 4-UHPC. DETAILED DESCRIPTION The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] Example 1 A reinforcement method for circular steel tube concrete columns based on UHPC, referring to Figure 1 , 2. When the outer surface of the steel pipe 1 is corroded or bulged, surface repair is required first. The outer surface of the steel pipe is roughened and the corroded part is removed by grinding and other methods to increase the contact area between UHPC4 and the steel pipe 1. When the grinding depth is greater than 20mm and the corrosion range is small, the damaged part can be treated locally. After the surface treatment is completed, the outer mold of the steel pipe 1 is supported for subsequent UHPC4 pouring. The distance between the mold and the outer surface of the steel pipe 1 is determined by the size of the steel tube concrete column, and the reference range of the distance is 200~400mm. When the distance is greater than 400mm, annular stirrups need to be added to the UHPC4 to enhance the repair and reinforcement effect. UHPC4 is poured under pressure, and its excellent fluidity is used for self-compacting, and its excellent bonding performance is used to make UHPC4 and the steel tube concrete column form a whole. After pouring, the UHPC is subjected to 48 hours of standard curing, followed by 48 hours of steam curing, and finally 72 hours of standard curing. After the curing is completed, the reinforcement is completed by removing the formwork. The reinforced UHPC layer and the original structure form a whole. Figure 2 This is a structural schematic diagram of a circular steel tube concrete column without stirrup reinforcement.

[0017] The UHPC used in this embodiment is composed of 840 parts of silicate cement, 200 parts of silica fume, 1100 parts of quartz sand, 5 parts of water reducer, 0.4 parts of defoamer, 80 parts of steel fiber, and 170 parts of water by mass. The strength of UHPC under this mix ratio is 126 MPa.

[0018] Example 2 A reinforcement method for circular steel tube concrete columns based on UHPC, referring to Figure 1 ,3. When the outer surface of the steel pipe 1 is corroded or bulged, surface repair is required first. The outer surface of the steel pipe is made rough by grinding and the corroded part is removed to increase the contact area between UHPC4 and the steel pipe 1. When the grinding depth is greater than 20mm and the corrosion range is small, the damaged part can be treated locally. After the surface treatment is completed, the outer mold of the steel pipe 1 is supported for subsequent UHPC4 pouring. The distance between the mold and the outer surface of the steel pipe 1 is determined by the size of the steel tube concrete column, and the reference range of the spacing is 200~400mm. After the mold is completed, annular stirrups are prevented in the mold. The spacing between each stirrup is 100~200mm. Small concrete blocks are used to separate the annular stirrups. When the UHPC reinforcement thickness exceeds 400mm, the spacing of the annular stirrups should be increased by 50mm for every 100mm increase in UHPC thickness. UHPC4 is poured under pressure, and its excellent fluidity is used for self-compacting, and its excellent bonding performance is used to make UHPC4 and steel tube concrete columns form a whole. After pouring, UHPC is subjected to 48 hours of standard curing, followed by 48 hours of steam curing, and finally 72 hours of standard curing. After curing, the formwork is removed and the reinforcement is completed. The reinforced UHPC layer and the original structure form a whole. Figure 3 Schematic diagram of the structure of circular steel tube concrete column reinforced with stirrups.

[0019] The UHPC used in this embodiment is composed of 750 parts of silicate cement, 220 parts of silica fume, 1200 parts of quartz sand, 4 parts of water reducer, 0.3 parts of defoamer, 70 parts of steel fiber, and 180 parts of water by mass. The strength of UHPC under this mix ratio is 121 MPa.

[0020] Example 3 A reinforcement method for square steel tube concrete columns based on UHPC, referring to Figure 4, 5. When the outer surface of the steel pipe 1 is corroded or bulged, surface repair is required first. The outer surface of the steel pipe is roughened and the corroded part is removed by grinding and other methods to increase the contact area between UHPC4 and the steel pipe 1. When the grinding depth is greater than 20mm and the corrosion range is small, the damaged part can be treated locally. After the surface treatment is completed, the outer mold of the steel pipe 1 is supported for subsequent UHPC4 pouring. The distance between the mold and the outer surface of the steel pipe 1 is determined by the size of the steel tube concrete column, and the reference range of the distance is 200~400mm. When the distance is greater than 400mm, annular stirrups need to be added to the UHPC4 to enhance the repair and reinforcement effect. UHPC4 is poured under pressure, and its excellent fluidity is used for self-compacting, and its excellent bonding performance is used to make UHPC4 and the steel tube concrete column form a whole. After pouring, the UHPC is subjected to 48 hours of standard curing, followed by 48 hours of steam curing, and finally 72 hours of standard curing. After the curing is completed, the reinforcement is completed by removing the formwork. The reinforced UHPC layer and the original structure form a whole. Figure 5 This is a structural schematic diagram of square steel tube concrete columns without stirrup reinforcement.

[0021] The UHPC used in this embodiment is composed of 900 parts of silicate water, 250 parts of silica fume, 900 parts of quartz sand, 7 parts of water reducer, 0.4 parts of defoamer, 150 parts of steel fiber, and 190 parts of water by mass. The strength of UHPC under this mix ratio is 124 MPa.

[0022] Example 4 A reinforcement method for square steel tube concrete columns based on UHPC, referring to Figure 4 ,6. When the outer surface of the steel pipe 1 is corroded or bulged, surface repair is required first. The outer surface of the steel pipe is made rough by grinding and the corroded part is removed to increase the contact area between UHPC4 and the steel pipe 1. When the grinding depth is greater than 20mm and the corrosion range is small, the damaged part can be treated locally. After the surface treatment is completed, the outer mold of the steel pipe 1 is supported for subsequent UHPC4 pouring. The distance between the mold and the outer surface of the steel pipe 1 is determined by the size of the steel tube concrete column, and the reference range of the spacing is 200~400mm. After the mold is completed, annular stirrups are prevented in the mold. The spacing between each stirrup is 100~200mm. Small concrete blocks are used to separate the annular stirrups. When the UHPC reinforcement thickness exceeds 400mm, the spacing of the annular stirrups should be increased by 50mm for every 100mm increase in UHPC thickness. UHPC4 is poured under pressure, and its excellent fluidity is used for self-compacting, and its excellent bonding performance is used to make UHPC4 and steel tube concrete columns form a whole. After pouring, UHPC is subjected to 48 hours of standard curing, followed by 48 hours of steam curing, and finally 72 hours of standard curing. After curing, the formwork is removed and the reinforcement is completed. The reinforced UHPC layer and the original structure form a whole. Figure 6 Schematic diagram of the structure of square steel tube concrete columns reinforced with stirrups.

[0023] The UHPC used in this embodiment is composed of 800 parts of silicate cement, 250 parts of silica fume, 900 parts of quartz sand, 5 parts of water reducer, 0.4 parts of defoamer, 120 parts of steel fiber, and 190 parts of water by mass. The strength of UHPC under this mix ratio is 125 MPa.

[0024] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A reinforcement method for steel tube concrete columns based on UHPC, characterized in that: The specific steps include: (1) Repair the outer surface of the steel tube of the steel tube concrete column by grinding to make the outer surface of the steel tube rough and remove the corroded part. When the grinding depth is greater than 20 mm and the corrosion range is small, the damaged part can be treated locally; (2) For the outer surface of the steel tube concrete column, annular stirrups are installed between the model and the steel tube. The spacing between each annular stirrup is 100-200 mm. Small concrete blocks are used for partitioning. The spacing between the stirrups and the steel tube is 50 mm. (3) UHPC is cast on the steel tube concrete column. The thickness of UHPC is 200~400mm. The formwork is removed after curing. After UHPC casting, it is an integral whole with the original structure.

2. A reinforcement method for steel tube concrete columns based on UHPC according to claim 1, characterized in that: The steel tube concrete column described in step (1) is formed by pouring concrete into a hollow steel tube.

3. A reinforcement method for steel tube concrete columns based on UHPC according to claim 1, characterized in that: The thickness of the UHPC in step (3) is 200-400 mm. When the UHPC reinforcement thickness exceeds 400 mm, the spacing of the annular stirrups should be increased by 50 mm for every 100 mm increase in the UHPC thickness.

4. A reinforcement method for steel tube concrete columns based on UHPC according to claim 1, characterized in that: The UHPC described in step (3) is an ultra-early strength UHPC, and its 7-day compressive strength is above 120 MPa.

5. The ultra-early strength UHPC according to claim 4, characterized in that: The curing conditions for UHPC are 48 hours of standard curing, followed by 48 hours of steam curing at 80°C, and finally 72 hours of standard curing.

6. The ultra-early strength UHPC according to claim 1, characterized in that: By mass fraction, the raw materials for preparation include: 700~950 parts of Portland cement, 100~250 parts of silica fume, 900~1400 parts of quartz sand, 3~7 parts of water reducer, 0.2~0.5 parts of defoamer, 0~250 parts of steel fiber, and 150~200 parts of water.

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