Load-Bearing Capacity of Prefabricated Blocks in Old Houses

The load-bearing capacity of prefabricated slabs in old houses varies significantly depending on the era, type, and specifications, requiring comprehensive assessment based on specific parameters.

I. Load-Bearing Standards for Prefabricated Slabs in Different Eras

From the 1970s to the 1980s, the design standard for live loads in residential buildings was 150 kilograms per square meter, with a safety factor of 1.2 to 1.4 considered, potentially resulting in higher actual load-bearing capacities. In the 1990s, the national standard was raised to approximately 200 kilograms per square meter, though specific values varied based on the grade of the prefabricated slab. For instance, Grade IV slabs (common in modern residences) can bear up to 500 kilograms per square meter.

II. Load-Bearing Capacities of Different Types of Prefabricated Slabs

1. Concrete Hollow Prefabricated Slabs: The national standard specifies a load-bearing capacity of 200-250 kilograms per square meter, suitable for floor loads in ordinary residences.
2. Solid Prefabricated Slabs: Due to their denser structure, these slabs outperform hollow slabs in load-bearing capacity, reaching 250-300 kilograms per square meter. If produced by major manufacturers like Jianhua Construction Materials or China Railway 14th Bureau Group, with sufficient reinforcement and a concrete grade of C30 or higher, the load-bearing capacity can further increase to 300 kilograms per square meter.
3. Prestressed Prefabricated Slabs: A common type in modern new constructions. For spans within 3 meters, the load-bearing capacity is 300-400 kilograms per square meter; for spans exceeding 4 meters, the capacity decreases to 250-300 kilograms per square meter.

III. Key Factors Affecting Load-Bearing Capacity

1. Span and Thickness: Shorter and thicker prefabricated slabs exhibit stronger load-bearing capacities. For example, short-span prestressed slabs perform better in load-bearing due to more uniform stress distribution compared to long-span slabs.
2. Reinforcement and Concrete Strength: The amount of reinforcement directly influences bending resistance; larger steel bar diameters and smaller spacings result in higher load-bearing capacities. Higher concrete grades (e.g., C30) enhance compressive strength.
3. Load Type: Prefabricated slabs are sensitive to 'concentrated loads'; stacking heavy objects in one area may cause local cracking, whereas uniformly distributed loads (e.g., furniture, crowds) have less impact.

IV. Usage Recommendations

To assess the load-bearing safety of prefabricated slabs in old houses, it is essential to determine their production era, type, span, and reinforcement details. For houses that are old or have unclear structures, it is advisable to commission a professional institution to conduct load testing to avoid safety hazards caused by overloading.