Current methods for strengthening steel structures can be summarized as follows:

 

　　1) Increasing the member section (such as the steel bonding method);

 

　　2) Improving the structural force system (such as adding beams and columns);

 

　　3) Prestressed technology strengthening method.

 

　　Common methods for increasing the section size include: increasing the section height, thickening the flange plate, and changing the section shape to a box section. The main strengthening methods for increasing the steel structure section are steel bonding or carbon fiber cloth pasting. These two methods cause relatively little damage to the structure itself, and their development in China has been relatively rapid in recent years, with increasing applications. However, their application in steel structure buildings is relatively limited, especially concerning their service life under normal use conditions. Moreover, the construction of steel bonding or carbon fiber is relatively difficult, requiring the surface of the original structure to be treated, ground, and smoothed before bonding. Delamination may occur when the structure is subjected to dynamic loads or high temperatures.

 

　　Adding beams and columns to improve the structural force system can effectively and significantly reduce the load effect on the structure, thus ensuring that the load-bearing capacity of the structure meets the requirements. This method has a low investment and excellent economic benefits. When the building structure has no special requirements, this method is highly feasible, but it is not suitable for structures requiring large spaces.

 

　　The external prestressing technology strengthening method refers to arranging prestressing tendons outside the section of the structure to be strengthened. By changing the force transmission path of the structure, the load effect on the member is reduced, while simultaneously improving the load-bearing capacity of the structure based on its original foundation, improving its deformation performance, and reducing stress in the members. This method can restore the damaged engineering structure to its original technical functions, thus meeting the requirements of new load-bearing conditions and usage functions. The structure consists of components such as prestressing tendons, pipes, anticorrosion materials, turning blocks, and anchoring systems.

 

　　Although the external prestressing method for strengthening steel beams has advantages in operability, economy, and safety, there is currently limited research experience and engineering practice in this area, and its significant economic and social benefits require further research.