Secondary Structure Prefabricated Panel House

A secondary structure prefabricated panel house is a building form that takes non-load-bearing prefabricated components as the core and combines secondary structures to enhance overall integrity, but it has hidden dangers such as poor earthquake resistance and fragile connections.

Definition and Role of Secondary Structures

Secondary structures refer to non-load-bearing parts in a house that do not directly bear vertical loads, including constructional columns, lintels, steps, and waterproof counter-beams. Their core role is to enhance the overall integrity and stability of the house: for example, constructional columns and ring beams form a 'frame-restraint' system, reducing the risk of collapse by tying the walls together during earthquakes; lintels disperse the concentrated loads above door and window openings, preventing local damage.

Application Forms of Prefabricated Panels in Secondary Structures

Prefabricated panels are produced through standardized factory production and are mainly applied in the following parts of secondary structures:

1. Floor Systems: Steel floor panels without formwork support, ALC (autoclaved aerated concrete) prefabricated panels, etc., are used to form horizontal load-bearing surfaces through mortise-and-tenon or bolt connections. ALC panels have characteristics such as light weight (density approximately 500kg/m³) and fire resistance (fire endurance limit ≥ 3 hours), and their construction efficiency is more than 50% higher than that of traditional cast-in-place methods.
2. Partition Wall Systems: Cement fiber panels (thickness 9-12mm) are used for non-load-bearing partition walls. Their impact resistance is three times that of ordinary gypsum boards, and they have a Class A non-combustible performance.
3. Special Components: Prefabricated stairs, balcony panels, etc., are connected to the main structure through embedded parts, reducing on-site wet work.

Core Hidden Dangers of Prefabricated Panel Houses

1. Earthquake Resistance Defects: Prefabricated panels rely on splicing to form an overall structure, and the joints are only connected by mortar or a small amount of steel bars. During earthquakes, the joints are prone to cracking due to inertial forces. Experimental data shows that the inter-story displacement angle limit (1/120) of a prefabricated panel house in a 7-degree seismic fortification area is only one-third of that of a cast-in-place structure, significantly increasing the risk of collapse.
2. Fragility of Connection Joints: When there is uneven settlement of the foundation or cracking of the walls, misalignment is prone to occur at the joints of the prefabricated panels. For example, a prefabricated panel residential building constructed in 2000 experienced a maximum floor misalignment of 8cm due to foundation settlement, causing rainwater leakage and structural safety hazards.
3. Material Quality Risks: Some projects use low-grade concrete or reduce reinforcement to reduce costs, resulting in increased brittleness of the prefabricated panels. A testing case shows that the flexural bearing capacity of a shoddy prefabricated panel is only 62% of the designed value, and it may suddenly break under overload conditions.
4. Durability Issues: The joints of prefabricated panels are prone to becoming water infiltration channels, accelerating steel bar corrosion; at the same time, their thermal insulation performance (heat transfer coefficient approximately 1.5W/(m²·K)) is much lower than that of cast-in-place structures, leading to a more than 30% increase in winter energy consumption. The design service life of prefabricated panel houses is required to be 30-40 years by regulations, which is about 20 years shorter than that of cast-in-place structures.