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Carbon fiber wrapping for beam
Insufficient bending and shearing capacity of beam
Through the calculation analysis and engineering application of the concrete structure strengthened by bonded CFRP wrap, it is shown that the CFRP wrap strengthening method is an effective strengthening technology for concrete structure.
A comprehensive building project of a Nanjing development company is located in the eastern suburb of the city. It has six floors. The bottom two floors are frames, and the top four floors are special-shaped frame columns. The total floor area is 8 000 M. The original design floor is a shopping mall, and the function of the above two floors is residential. Because of the change of using function, the floor load increases. According to the increased load, the whole structure is checked and calculated. The results show that the bending and shearing capacity of beams in the local scope of the second floor structure is insufficient, and the flexural bearing capacity of slabs is insufficient.
As the building has been built and used, the rest of the floors must be in normal operation during the reinforcement period. After a comprehensive comparison of the schemes (see table 1), it was finally decided to use carbon fiber wrap paste and local bonded steel reinforcement method.
| Item | Structural strengthening methods | ||
| FRP strengthening | Steel jacketing | Enlarged section | |
| Application | Widely | Restricted | -- |
| Weight | Light | Heavier | Heavier |
| Strength | High strength | High | -- |
| Reinforcement coordination | Good | Good | Good |
Length and lap | The length is arbitrary, and the lap is convenient. | Limited length, welded connection | -- |
| Price | High | High | Lower |
Durability | Good | Lower | Good |
Construction period | Short perio | Longer period | Longer period |
Difficulty of operation | Simple operation | Complex | Complex |
| Impact on the outside world | Small | Big | Big |
Reinforcing material
The bonded steel F W B adopts Q345 4 m steel plate, carbon fiber reinforced wrap 0.167 m thick (or 300 g/m) type fiber and matching adhesive grade A. The matching adhesive includes bottom adhesive, leveling epoxy putty and bonding resin.
Reinforcement design
In the reinforced plane of the second floor, the bearing capacity of the negative bending distance of the floor should be increased by 25. According to the calculation and analysis, the shortage of the negative bending distance of the floor is that the CFRP wrap with a width of 200 m and a distance of 400 m is used as one layer, which is 2 500 m long. Liang Shouwan bearing capacity needs to be increased by 2O%, and 3 layers of fiber cloth with Liang Kuan should be adhered along the bottom of the beam. In addition, "U" shaped hoops are pasted on the brackets at both ends of the beam and on both sides of the secondary beam for shear reinforcement, and 200 m wide longitudinal bar entry anchorage is pasted on both ends of the "U" shaped hoops.
Reinforcement construction process and reinforcement effect
The surface of the steel plate pasted on the surface of the concrete component should be rust-proof, and the rust-proof material should be harmless to the steel plate and the adhesive.
The project actually pasted carbon fiber reinforced wrap about 145 m, completed within 15 working days. The thickest paste is the "U" - shaped hoop at the bottom of the beam, and 3 layers of 0.167 m m thick carbon fiber reinforced wrap. It basically does not increase the weight and geometric size of the structure, and meets the requirements of the owner from the aspects of time limit, use space and construction quality. Moreover, the bond between CFRP wrap and concrete surface is intact, the durability is good, and the reinforcement effect is remarkable.
Concluding remarks
Through the calculation analysis and engineering application of the concrete structure strengthened by bonded CFRP wrap, it is shown that the CFRP wrap strengthening method is an effective strengthening technology for concrete structure. Compared with the traditional reinforcement technology, carbon fiber wrap reinforced concrete technology has a good comprehensive economic performance. The application of carbon fiber reinforced concrete structure has broad application prospects.
