Reinforced concrete structures will involve structural reinforcement due to the decline in durability over time or changes in performance. So, what concrete things should we do in the reinforcement phase?

1. Identify first and then reinforce

Whether the structure needs reinforcement and the degree of reinforcement shall be confirmed through structural reliability appraisal. Before carrying out the structural reinforcement design design, the existing structure must be inspected and appraised, and the material properties, structure structure and structural system of the existing structure must be fully understood, as well as structural problems and damages. Analyze the current force status and strength level of the structure to lay the foundation for the determination of the reinforcement plan.

2. Consider the overall effect of the structure

The structure is a system that is subjected to overall forces, and the reinforcement measures may affect the local stiffness or restraint deformation, thereby affecting the structure. Therefore, full consideration should be given to:

2.1. The relationship between component reinforcement and structural system reinforcement. From the perspective of structural system reinforcement, pay attention to the relationship between the reinforcement of individual components and the reinforcement of the structural system. From the perspective of the safety of the entire structural system, consider the influence of the reinforcement of structural members and the connections between structural members on the integrity of the structure.

2.2. The relationship between local and overall reinforcement. When individual members are reinforced without affecting the force-bearing performance of the entire structural system, local reinforcement can be performed.

2.3. The relationship between temporary reinforcement and long-term reinforcement. Relative to long-term reinforcement, the requirements for temporary reinforcement can be appropriately reduced.

3. Remove as little as possible and do not replace the original components

In consideration of the protection of the original components and the overall safety of the structure, the load-bearing capacity of the original structure should be used as much as possible during reinforcement to reduce the removal and replacement of the original structure or components. On the other hand, the demolition workload is large and there are many unsafe factors. Excessive demolition is not economical and may leave hidden dangers to the reinforced structure.

4. Optimize the reinforcement plan

Due to the various problems and damages of the reinforced structure itself, its reliability is low, and it is also possible that the load-bearing capacity of the structure is insufficient due to the increased load. Therefore, in the reinforcement design, the reinforcement plan is often not constant, and which reinforcement design plan is finally selected should be determined according to the principle of optimization.

5. Selection of reinforcement materials and strength values

5.1. When the reinforcement design is carried out, the material strength of the original structure shall be selected as follows:

1) When the original design document is valid, and there is no doubt that the structure has serious performance degradation, the standard value of the original design can be used;

2) When the structural reliability appraisal considers that the on-site inspection should be performed again, the standard value deduced by the inspection result shall be adopted;

3) When the testing of the original structure's concrete strength level is restricted by actual conditions and it is impossible to take the core, the rebound method can be used for testing, but the strength conversion value should be corrected by age, and it can only be used for structural reinforcement design.

5.2. The selection and strength of reinforcement materials are selected as follows:

Reinforcing materials should be selected as far as possible to be lightweight, high-strength, and good working performance with the original structural materials. The design strength of the reinforcement material is selected by comprehensively considering factors such as the reliability of the reinforcement structure, the reinforcement method and the material characteristics.

6. Checking calculation of bearing capacity

When carrying out the calculation of the bearing capacity before reinforcement, the calculation diagram of the structure should be determined according to the actual stress condition of the structure, the measured size of the structural member and the strength level of the material. The cross-sectional area of the component should be the actual effective cross-sectional area before reinforcement, that is, the adverse effects caused by structural damage, problems, rust, etc. should be considered. The check calculation should consider the actual strength of the structure during reinforcement, the hysteresis characteristics of the reinforced part, and the degree of cooperation between the reinforced part and the original structure. The material strength design value of the reinforced part should be appropriately reduced, and additional internal forces caused by actual load eccentricity, structural deformation, local damage, and temperature effects should also be considered. If the load of the structure changes after reinforcement, the relevant structure and foundation should also be checked.

7. Do a good job in seismic reinforcement design

my country is a country with many earthquakes. In order to make these structures have corresponding safety guarantees when they encounter earthquakes, it is necessary to formulate reinforcement treatment plans for bearing capacity and durability in combination with seismic reinforcement.

Also pay attention to the following issues in the seismic reinforcement design:

1). The stiffness and strength of the structure should be evenly distributed to avoid new weak layers;

2). Vertical components should be continuous to ensure clear, simple and direct force transmission methods;

3). The possibility of reducing the torsion effect of the entire structure should be considered when reinforcing members or strengthening the original members;

4). Strengthen the seismic structure of weak parts;

5). To make the stress state of the structure more reasonable, prevent brittle failure of components, and reduce unfavorable stress conditions such as strong beams, weak columns, and weak nodes of strong members that are not conducive to earthquake resistance;

6). Consider the impact of the construction site;

7). The reinforced structure should choose a structural system with low seismic response;

8). The original unreasonable structure system and the way of force transmission should be improved as far as possible.