Principles of seismic reinforcement

When the brick-concrete structure does not meet the requirements through the seismic appraisal, seismic reinforcement shall be carried out. The seismic reinforcement plan should be determined after comprehensive analysis based on the seismic appraisal results, and the comprehensive seismic capacity of the house should be improved through overall reinforcement, section reinforcement or component reinforcement. The following points need special attention:

1. In the same floor, since the self-supporting wall only bears its own gravity, the seismic force it bears is much smaller than that of the load-bearing wall. Therefore, the load-bearing wall should be considered first when strengthening, to avoid the situation that the seismic capacity of the self-supporting wall after reinforcement is higher than that of the load-bearing wall.

2. For houses with a non-rigid structure system, an anti-seismic reinforcement scheme should be used to change the non-rigid structure system to a rigid structure system, such as a superimposed layer of cast-in-place concrete on the roof of the building, and additional seismic walls. When only other reinforcement measures that maintain a non-rigid structure system can be used, the displacement between floors should be controlled to improve the deformation capacity of the structure.

3. In the same floor, the strength of the reinforced wall section should be uniform to prevent the structure from breaking down and causing serious damage after individual components fail. The stairwell is the main escape route for people in the earthquake. When the section reinforcement scheme is selected, the wall of the stairwell should be strengthened.

4. The seismic bearing capacity of the reinforced house should be more evenly distributed along the floors to prevent the large difference in seismic bearing capacity between adjacent floors and weak layers. If the seismic bearing capacity of this layer exceeds 20% of the next floor, the next floor needs to be reinforced.

Seismic reinforcement method

Specific reinforcement methods should also be selected in a targeted manner based on the results of seismic appraisal.

1. When the height and number of floors of a brick-concrete structure exceeds the specified limit, the following seismic reinforcement methods should be adopted:

When the total height of the house exceeds the regulation and the number of floors does not exceed the regulation limit, effective measures that are higher than the bearing capacity of the general house and strengthen the wall restraint should be taken. When the number of floors of a house exceeds the prescribed limit, the structural system can be changed or the number of floors can be reduced to meet the requirements, and the requirements for seismic fortification classification can also be reduced by changing the use, so that the number of floors can meet the requirements. When adopting a reinforcement scheme that changes the structural system, the double-sided reinforced concrete slab wall in the traditional reinforcement method can be selected, and the brick-concrete wall can be replaced by a reinforced concrete shear wall.

When a Type C fortified house with fewer horizontal walls exceeds the prescribed limit for one storey and within 3m, reinforcement methods such as increasing the bearing capacity of the wall and adding ring beams and structural columns can also be adopted. Meet the current national standards for houses with fewer horizontal walls, without reducing the number of floors and height.

2. When the seismic bearing capacity of the house cannot meet the requirements, the following reinforcement methods can be selected:

For the original walls with too low strength or severe damage and the walls with poor seismic performance, such as empty bucket walls, the method of demolishing and rebuilding is adopted. The materials for heavy masonry and additional seismic walls can be bricks or blocks, light aggregate concrete or ordinary concrete, to minimize the impact on the substructure and foundation. When dismantling, reliable support and protective measures should be taken.

For cracked walls, local grouting can be used for reinforcement, and for walls with poor masonry mortar fullness or low strength of masonry mortar, full wall grouting can be used for reinforcement.

For brick walls whose bearing capacity does not meet the requirements, the vertical unbonded prestressed tendons are arranged symmetrically along the two sides of the wall at the design interval and prestress is applied for reinforcement. It can also be reinforced with cement mortar surface layer, steel mesh mortar surface layer, steel strand mesh polymer mortar surface layer or sprayed concrete slab wall on one or both sides.

Use cast-in-place reinforced concrete structural columns to reinforce the wall junctions. The columns should be integrated with ring beams and tie rods, or be reliably connected with cast-in-place reinforced concrete buildings and roofs.

Use section steel or reinforced concrete to wrap corners or borders on columns, wall corners or door and window openings; columns and wall stacks can also be reinforced with cast-in-place reinforced concrete sleeves.

Set up a seismic isolation layer on the foundation of the building for seismic isolation and reinforcement to reduce the seismic response of the building.

3. When the integrity of the house does not meet the requirements, the following reinforcement methods should be selected:

When the wall is not closed in the plane, wall sections can be added or a cast-in-place reinforced concrete frame can be added at the opening to close the wall. When the vertical and horizontal walls are poorly connected, steel tie rods, long anchor rods, extra columns or extra ring beams can be used for reinforcement.

When the supporting length of the building and roof components does not meet the requirements, additional joists can be added or measures to enhance the integrity of the building and roof can be taken. When the configuration of the structure column or the core column does not meet the appraisal requirements, additional columns should be added. When the wall is reinforced with a double-sided steel mesh mortar surface layer or a reinforced concrete slab wall, and a mutually reliable reinforcement belt is added at the wall junction, no additional structural column is required. When the ring beam setting does not meet the appraisal requirements, a ring beam should be added. The outer wall ring beam should be cast-in-place reinforced concrete, and the inner wall ring beam can be replaced by steel tie rods or anchor rods at the end of the deep beam. When the double-sided steel mesh mortar surface layer or reinforced concrete slab wall is used for reinforcement, and the upper and lower ends are added with reinforcement belts, no additional ring beams are required. When prefabricated buildings and roofs do not meet the requirements of seismic appraisal, additional cast-in-place reinforced concrete layers or joists can be added to reinforce the buildings and roofs.