Earthquakes are one of the most serious natural disasters faced by mankind. They occur suddenly and have great destructive power. They can instantly turn a bustling city into ruins, causing huge casualties and economic losses. Since earthquakes cannot be accurately predicted so far, from the perspective of structural reinforcement, it is the focus of attention of engineers from all over the world to ensure that buildings will not collapse during earthquakes or can continue to be used after earthquakes.、
Taking the 2008 Wenchuan earthquake as an example, according to statistics from relevant departments, the area of urban housing damage after the earthquake reached 135 million m2, of which 18.88 million m2 collapsed, 58.37 million m2 was severely damaged, and 58.07 million m2 was generally damaged. After on-site inspection and evaluation, most buildings were moderately or severely damaged and did not collapse, and basically reached the three-level seismic fortification target of "small earthquakes are not damaged, moderate earthquakes can be repaired, and large earthquakes are not collapsed" required by the code. A large number of severely damaged and generally damaged building structures can continue to be used after proper maintenance and reinforcement. Therefore, how to choose the most appropriate earthquake damage reinforcement method is the primary consideration for post-disaster reconstruction in the earthquake area.
An overview of seismic damage reinforcement methods for concrete structures
Enlarged section reinforcement method
External bonding steel reinforcement method
Sticking steel plate reinforcement method
Externally bonded fiber reinforced composite material reinforcement method
Crack repair technology
Research progress on performance after reinforcement of various methods
The various reinforcement methods in my country's existing reinforcement codes introduced above are basically aimed at building structures whose performance is insufficient and needs to be improved through reinforcement. And in GB 50367, only the newly-added steel bar strength utilization factor and the newly-added concrete strength utilization factor are used to reduce the calculated performance after reinforcement. The performance of each method of strengthening concrete structures after earthquake damage is precisely what the specification needs to guide, and it is also the most important consideration for engineers and technicians when selecting reinforcement methods.
Research progress abroad
In the 1980s, as an earthquake-prone Japan, began to study the shear wall structure damaged by earthquakes. In view of the possible bending failure and shear failure of the shear wall, researchers adopted different reinforcement methods. And studied the repair effect after reinforcement. After the great earthquake in Mexico in 1985, the country’s scientific researchers did a great deal of research on the post-earthquake restoration of concrete structures during the reconstruction process. Mainly for high-rise reinforced concrete structures that were severely damaged in the earthquake. The structural inspection and evaluation methods after the earthquake damage and the addition of pillars and support reinforcement technology have been extensively studied. In the 1990s, American researchers also did some experiments on earthquake-damaged structures, such as earthquake-resistant repair and reinforcement of severely damaged concrete frames. At the same time, Saudi researchers in the Middle East adopted the bonded steel sheet method and glass fiber board to strengthen the seismically damaged beams. It is concluded that the flexural strength of the reinforced concrete beams strengthened by the glass fiber board after the earthquake is increased by about 60%, and the shear strength is increased by about 26% -32%.
After entering the 21st century, the reinforcement performance of earthquake-damaged concrete structures has been valued by scientists from all over the world, and new reinforcement methods for different components have been studied. For example, researchers in Singapore conducted research on the repair performance of reinforced concrete beam-column joints and beam-wall joints reinforced with FRP after earthquake damage. Italian researchers studied the static and dynamic responses of reinforced concrete beams strengthened with CFRP after damage. Nanyang Technological University in Singapore studied the performance of reinforced concrete shear walls reinforced with FRP after earthquake damage. The shear wall was first damaged under axial compression and lateral cyclic loading, and then reinforced with FRP and loaded again. In the end, the strength of the reinforced damaged shear wall is increased by about 10%-20%, the damaged cracks are well controlled, and the structural performance is greatly improved.
Research progress in China
Compared with foreign countries, the research on the reinforcement of earthquake-damaged structures in my country started late. After 2000, my country's scientific researchers began to conduct research in this area. The Institute of Structural Engineering and Disaster Prevention of Tongji University conducted an in-depth study on the seismic performance of seismically damaged concrete frame joints reinforced by basalt fiber method. Zhou Yunyu and others conducted experiments based on three-dimensional reinforced concrete frame joints to study the reinforcement effect of basalt fiber on earthquake-damaged reinforced concrete frame joints. The experimental phenomena and data analysis show that the three-dimensional reinforced concrete frame joints strengthened by basalt have achieved the design goal of "strong column and weak beam". The failure modes are all beam bending failure, the ultimate bearing capacity and displacement ductility are improved, and the seismic performance of the structure is greatly improved. Moreover, the bearing capacity and stiffness of the undamaged joints are higher than those after damage, and the effect of the filling joints on the ultimate bearing capacity is not obvious. Wang Jialei of Southeast University and others have studied the seismic performance of CFRP-strengthened reinforced concrete columns damaged by earthquakes. The formula for the bearing capacity of the normal section of the damaged reinforced concrete column strengthened by the CFRP method in the transverse direction and the damaged reinforced concrete column strengthened in the vertical and horizontal directions is deduced and verified with the test results. Research shows that the ultimate bearing capacity of reinforced columns after damage is degraded compared to before damage, the bearing capacity recovery is about 60% -70%, and it can be restored to 118.3% of the ultimate bearing capacity at most, meeting the requirements of reinforcement design.
Zhao Gentian et al. designed four specimens of reinforced concrete short columns to simulate the performance of reinforcement methods after the shear failure of reinforced concrete short columns in earthquakes. The test results show that after the damaged and cracked reinforced concrete short columns are reinforced with CFRP, the ultimate bearing capacity is increased and brittle failure is avoided. Xiao Xiaoling et al. used a glass fiber reinforced plastic manual paste method to reinforce the four-rod frame joints with varying degrees of seismic damage. After tests under repeated low-cycle loads, it is found that the load-bearing capacity of the damaged structure can reach or exceed the level before the damage, which significantly improves the ductility of the structure and greatly increases the seismic energy consumption capacity.
Research at home and abroad shows that the rigidity, bearing capacity and ductility of structural members strengthened after earthquake damage have been partially improved. As long as the design is reasonable, it can meet the requirements of continued use and seismic resistance of the building structure. However, the current specifications have not yet given a quantitative conclusion on the problem of local performance recovery and reinforcement after various reinforcement methods have been adopted for large sting damage to the structure. The research on the post-earthquake reinforcement performance of the structure is urgently needed.
Conclusion
After earthquake-damaged structural members are reinforced by different methods, the existing cracks and other defects can indeed be controlled. After reasonable design, it can also meet the seismic demand under various fortification intensity. After the earthquake occurred, the engineers made a comprehensive consideration to select the reinforcement method based on the damage of the reinforced structure, the reinforcement cost budget, and the construction period. In the case of sufficient budget and tight construction period, CFRP, glass fiber polymer and other bonded fiber reinforced composite materials can be used to strengthen the method. According to the current scientific research conclusions, these methods have the advantages of fast construction progress and obvious performance improvement. In the case of economic stress, methods such as increasing the section method and sticking steel plate method can also be used.
Language: English
