1 The main method of concrete structural strengthening reinforcement

1.1 Direct reinforcement method

The reinforcement of concrete structures is divided into two types: direct reinforcement and indirect reinforcement. Appropriate methods and supporting technologies can be selected according to actual conditions and requirements during design. The direct reinforcement method includes

1.1.1 Enlarged section reinforcement method

This method has simple construction technology, strong adaptability, and mature design and construction experience. It is suitable for concrete reinforcement of beams, slabs, columns, walls and general structures. However, the wet work on site construction takes a long time, which will have a certain impact on production and life, and the headroom of the reinforced building will be reduced to a certain extent.

1.1.2 Replacement concrete reinforcement method

The advantages of this method are similar to those of the enlarged section method, and the clearance of the building will not be affected after reinforcement. However, it also has the disadvantage of long wet working time. It is suitable for the reinforcement of concrete load-bearing members such as beams and columns with low concrete strength or serious defects in the compression zone.

1.1.3 Reinforcement method with bonded outer profile steel

This method is also called wet-clad steel reinforcement method, which is reliable in force, simple in construction, and less on-site workload. However, the amount of steel used is relatively large, and it is not suitable to be used in high humidity places above 600°C without protection. It is suitable for use and does not allow significant increase in the original structure. This method is also called wet-clad steel reinforcement method. The force is reliable, the construction is simple, and the on-site workload is small. However, the amount of steel used is relatively large, and it is not suitable to be used in high humidity places above 600°C without protection. It is suitable for use and it is not allowed to significantly increase the original structure.

1.1.4 Sticking steel plate reinforcement method

This method has fast construction, no wet work on site or only a small amount of wet work such as plastering, which has little impact on production and life, and has no significant impact on the appearance of the original structure and the original clearance after reinforcement. However, the reinforcement effect depends to a large extent on the bonding process and the level of operation. It is suitable for the reinforcement of bending or tension members that are subjected to static forces and are in a normal temperature environment.

1.1.5 Pasting fiber reinforced plastic reinforcement method

In addition to the advantages of sticking steel plates, it also has the advantages of corrosion resistance, moisture resistance, almost no increase in structural weight, durability, and low maintenance costs. However, special fire prevention treatment is required, which is suitable for concrete structural members and general structures with various stress properties.

1.2 Indirect reinforcement method

1.2.1 Prestressed reinforcement method

This method can reduce the stress level of the reinforced component, not only has a good reinforcement effect, but also can greatly increase the overall bearing capacity of the structure. However, after reinforcement, it will have a certain impact on the appearance of the original structure. It is suitable for the reinforcement of large-span or heavy structures and the restoration of concrete members under high stress and high strain. However, without protection, it cannot be used in an environment with a temperature above 600°C, and it is not suitable for structures with large shrinkage and creep of concrete.

1.2.2 Add support reinforcement method

This method is simple and reliable, but it is easy to damage the original appearance and use function of the building, and may reduce the use space. It is suitable for concrete structure reinforcement where specific conditions permit.

2. Selection of structural reinforcement plan

The selection of reinforcement projects should be targeted, and corresponding reinforcement measures should be taken for different reinforcement projects. The plan needs to show the scientific and advanced nature of its technology while performing price, performance, and quality ratios. Such a reinforcement plan is an excellent reinforcement plan.

(1) Take the reinforcement of frame beams as an example

The author believes that the more reasonable, economical, and technologically advanced reinforcement schemes are the bonded steel anchor method and the carbon fiber reinforcement method. The former is characterized by low cost, simple construction, small space occupation, and good reinforcement effect, which is obviously better than the enlarged section method and the prestressed reinforcement method. In addition to the high cost of materials, the latter has various advantages. It is mainly manifested in the light weight, the material itself hardly increases the weight, and the strength is high. After curing, the strength of carbon fiber is as high as ten times that of steel. The labor intensity is small, and only one working surface needs to be operated by two people. The construction period is short, and each skilled worker can complete nearly 200 per day. However, it is not as good as the performance of steel plate when it is used to strengthen the negative moment.

(2) Take the reinforcement of frame columns as an example

The more common reinforcement method is the steel-clad reinforcement method, which is reinforced by wrapping steel around the concrete column. In this way, the size of the concrete cross-section is not increased, and the bearing capacity of the concrete column is greatly improved. The specific method is divided into two forms: dry operation method and wet operation method. The dry reinforcement method is to wrap the section steel (generally an angle steel) directly around the concrete column that needs to be reinforced. There is no connection between the section steel and the concrete, and because it does not form a whole with the concrete, it cannot ensure that the joint surface transmits shear force. Wet reinforcement method-is to use latex cement paste or epoxy resin chemical grouting and other materials to paste the angle steel on the concrete column. The second is to leave a certain distance between the angle steel and the concrete, and pour concrete in the middle to achieve the combination of outer steel and concrete. Comparing the two methods of operation, the dry operation method is simpler, cheaper, and shorter in construction time, but its bearing capacity is not as good as the wet method. When selecting a plan, a reasonable plan should be selected for reinforcement according to the reinforcement requirements and the original component conditions. For example, due to functional changes in a hotel, the original design of the first-floor column adopts a dry reinforcement scheme. The L100 x 6 angle steel is wrapped around the column and connected with strips, which fully meets the reinforcement requirements. On the 4th and 5th floors of a mechanical and electrical engineering school, due to the corrosion of the built-in steel bars, the concrete columns were cracked. The wet reinforcement scheme was adopted. The high-grade cement mortar and epoxy mortar configured with quartz sand were used for the local column angles. The angle steel is pasted around the concrete column to achieve the purpose of overall reinforcement. Both reinforcement methods have achieved good results.

3. Conclusion

Concrete structures need to be reinforced due to functional changes, such as connection construction, increased load, etc., or quality problems, such as insufficient reinforcement, post-disaster repair, insufficient concrete strength, etc. The reinforcement construction and the formulation of reinforcement plans are particularly important. For structures that need to be reinforced, different reinforcement plans should be formulated according to the different conditions of the structure. The determination of the plan should follow the principles of safety, economy, speed, and ease of construction. Only in this way can the reinforcement project receive good social and economic benefits.