Study on seismic strengthening of CFRP sheets

1 carbon fiber reinforced polymer(CFRP) for strengthening the frame

Reinforced concrete frame structure has become one of the most common structural forms in China. It has shown good seismic performance in many earthquakes, guaranteed the safety of people's lives and property, and played an important role in China's economic construction.

Wang Xinling and others designed and manufactured a reinforced concrete frame based on a frame structure of a two-storey reinforced concrete industrial factory building. Carbon fiber sheet was pasted on the beam end, column end and joint of the frame. The test results show that the RC frame strengthened with CFRP sheets has good seismic performance and hysteretic energy dissipation capacity.

After the earthquake, the frame structure belongs to the category of "repairable". Reasonable reinforcement and restoration can save more manpower and financial resources than push-down reconstruction. At the same time, it can speed up the recovery and reconstruction of the disaster area. In order to study the seismic behavior of reinforced concrete frames strengthened with CFRP sheets after earthquake damage, some domestic scholars have done corresponding research and obtained certain research results. Wang Xinling and others used CFRP sheets to reinforce damaged reinforced concrete frame structures. The sequence and location of cracks and plastic hinges under CFRP sheets were analyzed. The results show that the energy dissipation mechanism is "the mixed mechanism of yielding of beam end and casting and forging". It is suggested that CFRP sheets be used to reinforce the frame to columns and foundations. The root. Based on the fact that the damage degree of the damaged concrete structure has little influence on the reinforced structure, Wang Xinling and others have carried out pseudo-static tests on the three frames. Among them, two frames are pre-damaged, which are pre-damaged to the section cracking and the steel bar yielding, and are strengthened by CFRP without unloading. The results show that with the increase of damage degree, the maximum crack width and strain lag of CFRP strengthened frame increase. Generally speaking, the RC frame reinforced by CFRP has good seismic performance under different degree of damage. Zheng Qizhen and others designed and manufactured three single-story reinforced concrete frame specimens. Low-cycle cyclic loading tests were carried out to compare the intact frame, the frame strengthened by CFRP and the damaged frame strengthened directly. The results show that the CFRP reinforced frame can effectively improve the mechanical performance and seismic capacity, and can improve the collapse resistance of the structure.

2 Carbon fiber sheet reinforcing joints

Frame joint is an indispensable part of the whole reinforced concrete frame structure, which plays an important role in transmitting and distributing internal forces. The investigation of post-earthquake disasters shows that although the designers follow the principles of "strong nodes and weak members" and "strong columns and weak beams", the failure modes of the joints are embodied in the compression and bending failure at the end of columns, the bending failure at the end of beams and the shear failure at the core area. Therefore, strengthening the joints is very important for improving the seismic performance of the whole structure.

Luzhou Dao et al. have studied the seismic behavior of CFRP reinforced concrete Beam-slab-column joints. It is found that the ultimate bearing capacity and seismic performance of the joints have been greatly improved after strengthening, and the performance indexes have reached and exceeded the requirements of the existing seismic code. Four full-scale beam-column joints (two of them strengthened with CFRP) were tested under low cyclic loading. The results show that the seismic behavior of the joints strengthened with CFRP can be significantly improved. Wu Bo et al. compared the reinforcement effect of different reinforcement methods and analyzed the corresponding reinforcement mechanism through the seismic performance tests of three CFRP reinforcement points and one comparative joint. On the basis of the test, the calculation method of shear capacity of Reinforced Concrete Frame Joints Strengthened with CFRP sheets is put forward. Xian Qiaoling and others put forward a new method of strengthening the intermediate joints of plane frame and space frame with CFRP, and verified the effectiveness of the method. Based on the test results, the design methods and suggestions for strengthening joints are put forward. Peng Shuquan and other researchers studied the seismic behavior of the joints in the frame strengthened with bonded steel and CFRP. The results show that bonded steel can obviously improve the shear capacity of the mid-joints, and CFRP can effectively improve the seismic performance of the mid-joints.

3 Carbon fiber reinforced polymer column

Reinforced concrete column is the lateral resistance component of the whole frame structure. When subjected to earthquake, the collapse of load-bearing column will cause the collapse of the whole building, and bring great threat to the safety of people's lives and property. Therefore, when the seismic capacity of the column can not meet the requirements of the code, it needs to be reinforced to meet the use requirements.

Lu Yiyan et al. put forward a new method of strengthening reinforced concrete columns. The whole process analysis program of reinforced concrete columns strengthened by steel wrapped with CFRP was compiled. The influence of axial compression ratio, CFRP dosage and angle steel dosage on the strengthening effect was studied. Yang Jian carried out the experimental study and numerical simulation of CFRP reinforced concrete columns, analyzed the mechanism of CFRP confined concrete columns and the reinforcement effect of defective concrete columns. Wang Jialei and so on studied the seismic behavior of reinforced concrete columns strengthened with CFRP sheets. In order to improve the seismic strengthening of the special-shaped column structure, Zhou Mingjie and others adopted three methods to reinforce the special-shaped column: sticking steel plate, sticking carbon fiber cloth and the combination of them. The test results show that the ultimate load and ductility and seismic energy dissipation capacity of the steel plate strengthened with CFRP are improved significantly, and the ductility is improved greatly. Composite reinforcement can not only improve the bearing capacity but also enhance ductility, which is an effective reinforcement method. Wang Suyan and other researchers have studied the seismic performance of high-strength concrete square columns strengthened by transverse CFRP cloth and L-type CFRP cloth. The results show that the seismic performance of the columns strengthened by the two methods has been significantly improved. Among them, the specimens with lateral combination of L type CFRP cloth have better seismic performance. In order to find an effective method to reinforce damaged RC columns, the seismic performance of three damaged RC columns strengthened with CFRP and one comparative column under low-cycle horizontal repeated loading was studied. The main parameters of the study were axial compression ratio and pre-crack width.

Conclusion

Although CFRP has made a lot of achievements in strengthening frames, joints and columns, there are still some defects and shortcomings.

(1) With the popularization and application of special-shaped structure, the problem of strengthening special-shaped structure with CFRP will be encountered in the future. How to ensure the good reinforcement effect of CFRP is still scarce, and more in-depth theoretical analysis and experimental research are needed.

(2) The structural adhesive used in the pasting of CFRP sheets is not heat-resistant, although fire prevention treatment is required in the code, in practical engineering, the thermal colloid of structural adhesive will be destroyed, resulting in ineffective reinforcement of CFRP sheets. Therefore, the future research emphasis should pay attention to the CFRP should continue to play a reinforcing effect in the case of fire.

(3) The damage index is not clear, and how many CFRP sheets can be used to reinforce the damage degree to obtain the best reinforcement effect, which is not yet known accurately, but also needs to be solved in the future.