Design of Prefabricated Structures in Old Houses

The design of prefabricated structures in old houses primarily involves buildings constructed with prefabricated panels as the main components, covering their design characteristics, existing issues, and reinforcement methods:

Prefabricated panel houses originated in the early 20th century. In China, residential buildings constructed before 1985 often adopted this type of structure, which was widely used in factory and residential construction during the early stages of urbanization when resources were scarce, effectively addressing the housing shortage. Prefabricated panels are factory-made cement components, available in solid and hollow types, and form the floor structure by simply resting on load-bearing walls.

Existing prefabricated panel houses commonly suffer from structural defects such as weak earthquake resistance and poor sound and thermal insulation, with the core issue being insufficient integrity. There is a lack of effective connection between the prefabricated panels and load-bearing walls, as they are merely combined through resting, making the houses prone to separation or collapse under external forces such as earthquakes. Additionally, the lifespan of prefabricated panels is approximately 30-50 years, and material aging over time further reduces their load-bearing capacity.

Reinforcement of prefabricated panel houses should be tailored to specific issues:

• Floor reinforcement: If the foundation structure is sound, carbon fiber sheet粘贴（此处英文用adhering更合适） adhering can be used to enhance tensile strength and prevent crack propagation; if the load-bearing capacity has significantly declined, the section enlargement method can be adopted, involving the laying of steel mesh on the original floor surface and pouring new concrete to improve overall integrity and earthquake resistance; for large-span living rooms, steel beam supports can be added beneath the floor to distribute pressure. Another effective method is to pour a reinforced concrete 'composite layer', which involves cleaning the surface of the prefabricated panels, laying a steel mesh with a diameter of 6 mm and a spacing of 20 cm, and then pouring 5-8 cm thick fine aggregate concrete with a grade not lower than C25 to significantly enhance roof rigidity.
• Wall reinforcement: For brick walls with aging mortar and reduced load-bearing capacity, reinforced concrete夹板（英文用jacket更合适） jackets can be added to both the interior and exterior of the walls, forming a composite structure with the original walls through the new concrete layer to improve wall stability and earthquake resistance.

Reinforcement construction must strictly adhere to specifications, ensuring material quality and workmanship precision. At the same time, a professional assessment should be conducted based on the actual condition of the house to avoid excessive modification or overlooking key nodes.