Application status of CFRP composite material in strengthening concrete structure

1 Beam

Mainly the bending and shear strengthening of simply supported beams. Including the dynamic load fatigue performance of the beam, the prestressed reinforcement performance of the beam, etc., the cracks, deformation and stiffness of the beam after the reinforcement were observed. Sheng Guangfu et al. strengthened the shear bending section of reinforced concrete beams by externally pasting carbon fiber cloth, and studied the shear failure characteristics, shear capacity and influencing factors of the beams with different bonding heights of carbon fiber strips and whether there are beads at the open end. And analysis, and the test results are compared with the design calculation value of the regulation. Li Zhongxian et al. used the variable-angle space truss model to theoretically calculate the torsional bearing capacity of the box girder model by studying the torsion resistance of the carbon fiber reinforced beam, and compared it with the test results. Li Yuan et al. conducted fatigue test research on ordinary reinforced concrete beams and prestressed concrete beams after reinforcement. Experimental research shows that after 2 million fatigue cycles, the strength and rigidity of the concrete beams reinforced with carbon fiber cloth will not decrease, spalling and brittle fracture will not occur, which fully meets the practical requirements

2 Slabs

As an important bending member, slab has also been reviewed by researchers and engineers in the field of reinforcement. Mainly study the improvement of the bearing capacity of the board and the improvement of the deflection and cracks after the use of carbon fiber and guts

3 Columns

Mainly study the stress-strain curve under the axial compression of the reinforced concrete column. After reinforcement, the shear and bending resistance are improved. The improvement of seismic performance includes hysteretic energy dissipation capacity, ductility performance, bending moment-curvature relationship, etc. Wang Suyan and others considered the influence of factors such as the amount of carbon fiber cloth, the bonding method, and the spacing of the fiber cloth strips on the restraint effect, and gave the calculation formula of the peak stress and peak strain of the high-strength concrete square column confined by carbon fiber cloth and the stress-strain relationship. model. The test shows that the compressive strength of the reinforced high-strength concrete column has been improved to a certain extent. When the amount of fiber cloth increases, the compressive strength increases. The all-inclusive test piece has a more significant enhancement effect than the strip-type package. After the reinforcement, the falling section of the stress-strain curve of the specimen tends to be flat, and the roof property is improved, but it is still brittle when broken. Cheng Yapeng et al. proposed an index describing the carbon fiber content in strip reinforcement, that is, the relative fiber strip width ‘frp, and using this as a parameter to conduct experimental research on circular concrete axially compressed short columns reinforced with different ‘frp values. Experimental research shows that this reinforcement method can effectively improve the bearing capacity of concrete columns. Wang Suyan et al. tested the mechanical performance of high-strength concrete columns under low-cycle cyclic loading, and discussed the effect of carbon fiber cloth on improving the ductility of high-strength concrete columns, including the failure form, hysteresis curve, skeleton curve, Performance characteristics such as court coefficient. Tests have shown that the use of carbon fiber cloth to wrap high-strength concrete columns transversely can significantly increase the ductility of the column and improve the seismic performance of the column.

4 Nodes

Due to the complex structure at the node, the current various reinforcement methods (including CFRP reinforcement) have not well solved the construction problem of node reinforcement. Wang Bu et al. used two methods of reinforcing the outer beams and column ends of the core area with carbon fiber cloth, and conducted low-cycle repeated loading tests on five full-scale concrete frame joints. In order to test the effect of improving the shear performance of the core area of the node after reinforcement, and according to different reinforcement methods, the reinforcement mechanism of carbon fiber cloth was analyzed and studied.

5 Structure connection

Mainly research the reasonable lap length and anchorage length of carbon fiber cloth for bending reinforcement, and the influence of different anchoring forms at the end on the reinforcement effect during shear reinforcement. The effect of different types of adhesives on the interface bonding performance. Yao Jian and Teng Jinguang used the single-shear test method of FRP board-concrete seven-piece lap joint, taking into account the lap length of the FRP board, the change of the support height, the deviation of the test piece, the width ratio of the FRP board and the concrete block, etc. factor, in-depth study of the bond strength between FRP and concrete.

6 Masonry structure and steel structure

In addition to the research and application of concrete upper structures, some scholars have studied the use of carbon fiber to strengthen masonry structures and steel structures. Mainly study the ultimate load, deformation capacity and improvement of structural performance of block walls after reinforcement. Yu Jinghai et al. tested the mechanical performance of small concrete hollow block walls reinforced by carbon fiber cloth under repeated loads. The effectiveness of the reinforcement method of sticking carbon fiber cloth to enhance the seismic capacity of small concrete hollow block walls is studied.

7 Mechanical analysis

The research mainly focuses on the establishment of interface peeling mechanism model and finite element analysis, the establishment of shear model and some simplified algorithms. For example, Ye Lieping has studied the anti-stripping mechanism and setting position of the U-shaped hoop through experiments, and the influence of the amount and form of the U-shaped hoop on the anti-stripping performance of the carbon fiber cloth at the bottom of the beam, and according to the experimental research results, the setting of the U-shaped hoop is given. Relevant suggestions. Huang Yuli et al. used the commercial finite element program MSC. Marc established a finite element model and performed a nonlinear calculation analysis. According to the analysis and test results, the concepts of "effective anchorage bond length" and "anchorage bond stress" are introduced, and calculation suggestions for anchorage bond stress under ultimate load are given.

8 Durability and long-term performance

The main research is the atmospheric corrosion resistance and water resistance of concrete members reinforced with carbon fiber cloth. Such as the change of the positive tensile bond strength, in-plane shear bond strength, and flexural bond strength of the concrete after the resin is bonded to the concrete after the rapid exposure test. Ren Huitao and others studied the effect of corrosive environment on the mechanical properties of fiber-reinforced polymer composites through rapid freeze-thaw tests, alkalization tests, water immersion tests, and damp heat tests. The test results show that the durability of carbon fiber reinforced polymer (CFRP) is better, and the mechanical properties are not significantly degraded under various exposure conditions. Using rapid freeze-thaw cycle test and damp heat test, the comprehensive influence of corrosive environment on the bonding performance of FRP and concrete and the mechanical performance of FRP reinforced concrete beams and columns are studied. The results show that the bonding performance between FRP and concrete is greatly reduced, and FRPJill concrete structure has better durability.