Building reinforcement methods and classifications I. Direct reinforcement is a method to directly improve the bearing capacity and stiffness of members through some reinforcement measures. In engineering, the following methods are often used: strengthening crack-resistant fibers

1. Reinforcement with Increased Section

The construction technology of this method is simple, adaptable and has mature design and construction experience.

The reinforcement of building structure can be divided into direct reinforcement and indirect reinforcement. Appropriate methods and matching technologies can be selected according to actual conditions and application requirements in design.

First, the direct reinforcement method is a method to directly improve the bearing capacity and stiffness of the member section through some reinforcement measures. The following methods are commonly used in engineering:

1. Reinforcement with Increased Section

The construction technology of this method is simple, adaptable, and has mature design and construction experience. It is suitable for concrete reinforcement of beams, slabs, columns, walls and general structures. But the wet operation time of field construction is long, which has a certain impact on production and life, and the clearance of reinforced buildings is reduced to a certain extent.

2. Reinforcement of Replacement Concrete

The advantages of this method are similar to those of the enlarged section method, and it does not affect the clearance of the building after reinforcement, but it also has the disadvantages of long wet operation time in construction. It is suitable for the reinforcement of concrete bearing components such as beams and columns with low strength or serious defects in the compression zone.

3. Reinforcement Method of Bonded Outwrapped Profile Steel

This method is also called wet encased steel reinforcement method, which is reliable in force, simple in construction and less in-situ workload, but with a large amount of steel, and is not suitable for use in high temperature places above 600C without protection. It is suitable for use of concrete structures that do not allow significant increase in the cross-section size of original members, but also require a substantial increase in their bearing capacity.

4. Reinforcement by Sticking Steel Plate

The method is fast in construction, no wet operation on site or only plastering with a small amount of wet operation, 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, but the reinforcement effect largely depends on the adhesive technology and operation level; it is suitable for the reinforcement of bending or tension members under static action and in normal humidity environment.

5. Reinforcement with Fiber Reinforced Plastics

In addition to the similar 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, but requires special fire protection treatment, which is suitable for concrete structural components and general structures of various mechanical properties.

6. Wire winding

The advantage and disadvantage of this method are similar to that of enlarging section method, and it is suitable for reinforcement of insufficient bearing capacity of oblique section of concrete structural members or for application of transverse restraint to compressive members.

7. Anchor bolt anchoring method

This method is suitable for the retrofit and reinforcement of concrete load-bearing structures with concrete strength grades of C20 ~ C60, but not for those structures and lightweight structures which have been severely weathered.

II. Indirect reinforcement

Indirect reinforcement is to change the way of force acting on the original structure, reduce the load effect and exert the potential of the components through some components and local measures, so as to reduce the probability of structural failure and reinforce the structure. The commonly used methods in engineering are:

1. Additional Component Method

Additional component method is to add a new component between the components of the original structure (such as a new roof truss between two roof trusses, a new beam between two beams, a new column between columns and networks, etc.). In order to reduce the load acting on the original members and reinforce the structure, this method is generally applicable to single-storey industrial factory buildings or to the strengthening of floor beams and columns of multi-storey buildings without affecting the use requirements after adding new members. This method does not damage the original structure in construction, so the construction is safe.

2. Additional fulcrum method

The method of adding fulcrum is to add fulcrum on beams, slabs and columns to reduce the calculation span of the structure, to reduce the load effect, to exert the potential of components, to improve the bearing capacity and to reinforce the structure. According to the mechanical performance of the supporting structure, the reinforcement method with additional fulcrums is divided into rigid fulcrum method and elastic fulcrum method. The rigid fulcrum method transfers the load directly to other bearing components of the foundation through the axial compression of the supporting members. At this time, the deformation of the fulcrum is very small and negligible relative to the deflection of the strengthened beam. Elastic fulcrum reinforcement method transfers load indirectly by bending or truss action of supporting member. At this time, the deformation of fulcrum can not be ignored. The method of column support reinforcement can adopt the method of transverse support between columns. The method of adding fulcrum is suitable for the reinforcement of long-span beams, slabs or columns with high clearance.

3. Increasing the Integral Reinforcement Method of Structures

Increasing the integrality of the structure reinforcement method is to make multiple components form a spatial whole by adding support, and work together. Because the probability of overall failure is less than that of single component failure, the reliability of the structure is improved without strengthening any of the components.

4. Reinforcement by changing stiffness ratio

In the building structure, changing the stiffness ratio of components, adjusting the internal force distribution of the original structure, improving the stress condition of the structure can also achieve the purpose of structural reinforcement. This method is mostly used to improve the horizontal resistance of the structure.

Reinforcement classification

Reinforcement works can be classified into four categories according to the reinforcement materials used.

1. Steel

In order to ensure that steel skeleton connection, section steel frame connection and prestressing reinforcement are constructed by transverse tension, which is beneficial to the welding of reinforcing steel bar, section steel and steel plate, the first and second grade steel bars should be used for concrete structure reinforcement, and the third or 16 manganese steel bars should be used for section steel, steel plate, flat steel and steel pipe reinforcement. In the long-span pre-stressed reinforcement method, three or four grades of steel bars, carbon steel wires or strands with higher strength can also be reasonably selected according to the actual situation of the structure, and Jack tension should be adopted.

2, concrete

In order to strengthen the combination of new and old concrete members, and considering that the strength of original concrete is generally lower, the strength grade of concrete used for strengthening concrete structures should be higher than that of original structures and components in design. When the strength of original concrete members is higher, the same strength grade of concrete as that of original components can be generally adopted. However, technical measures should be taken to ensure adequate bonding strength between new and old concrete. To speed up the construction progress, reduce the impact on use and ensure the reinforcement effect, early-strength concrete should be adopted.

3. Soft Materials

Soft materials are mainly soft materials represented by cloth.

Characteristic is: 1. Stable performance, generally no corrosion problem. 2. Light weight without increasing static load. 3. High strength. 4. It is easy to operate by hand without special mechanical equipment. 5. Construction is free from dust and noise pollution, and can be operated uninterruptedly.

The use of carbon fiber reinforced concrete short columns can prevent the occurrence of inclined cracks or limit the development of inclined cracks, and significantly improve the shear capacity of columns. The failure of CFRP reinforced concrete columns is sudden, but there is a sound warning before the failure, which makes the damage predictable. The restraint of carbon fibers on the column is more effective and the shear strength of the column is greatly improved by wrapping carbon fibers first and adding axial force. The load-displacement hysteretic curve of reinforced concrete short columns under repeated loads is stable. Compared with ordinary concrete columns, reinforced concrete short columns have better energy dissipation capacity and smaller strength degradation.

4. Connecting Materials

When using chemical grouting connection, it is advisable to use grouting fluid with good grouting ability, small shrinkage, high bonding strength, adjustable curing time, good durability and non-toxicity. The bond strength between cement paste and concrete after solidification should be higher than the tensile and shear strength of bonded concrete.