Load-Bearing Safety Value of Prefabricated House Slabs

The load-bearing safety value of prefabricated house slabs is not a fixed value and needs to be comprehensively determined based on factors such as the purpose of the house, the type, specifications, and span of the prefabricated slabs. Here is a detailed analysis:

I. Common Design Live Load Standard Values According to national standards (such as GB 50009 'Building Structure Load Code'), the design live load standard values for prefabricated slabs in buildings with different purposes are as follows:

1. Residential buildings (such as houses, dormitories, and hotels): The standard value of the uniformly distributed live load on the floor is generally 2.0 kN/m² (about 200 kg/m²). For example, a commonly used 3.6-meter-span, 12-centimeter-thick hollow prefabricated slab in rural self-built houses has a uniformly distributed load of 200 kg/m².
2. Public buildings (such as offices, classrooms, and conference rooms): The standard value is usually 2.0-2.5 kN/m² (200-250 kg/m²).
3. Special-function rooms (such as hospital wards, laboratories, and rooms with heavy equipment): They may need to reach 3.5 kN/m² (350 kg/m²) or even higher.
4. Storage or vehicle passage areas (such as warehouses and garages): Light truck passages may need to be designed according to 10-20 kN/m².

II. Key Factors Affecting Load-Bearing Capacity

1. Span: The shorter the span of the prefabricated slab, the stronger its load-bearing capacity. For example, a 2.4-meter-span hollow slab can bear 250 kg per square meter, a 3.6-meter-span slab drops to 200 kg per square meter, and slabs with a span of over 4.2 meters may only be able to bear 150-180 kg per square meter.
2. Thickness and reinforcement: A 10-centimeter-thick prefabricated slab has stronger load-bearing capacity than an 8-centimeter-thick one; slabs with thicker and more densely spaced steel bars (such as 8-millimeter steel bars with a spacing of 15 centimeters) have better load-bearing capacity.
3. Load type: Prefabricated slabs are sensitive to 'concentrated loads'. For example, a prefabricated slab with a uniformly distributed load of 200 kg/m² can withstand uniformly laid 200 kg of sand, but if a 300 kg safe is placed within 1 square meter, it may crack the floor slab.

III. Special Cases

1. Old houses: Residential houses built in the 1970s and 1980s had a designed live load value of 150 kg per square meter, taking into account a safety factor of 1.2-1.4.
2. Solid prefabricated slabs: They are often used in areas with relatively large loads such as kitchens and bathrooms, and can bear 250-300 kg per square meter.
3. Prestressed prefabricated slabs: By applying tension to generate prestress, they have stronger crack resistance and load-bearing capacity. For spans within 3 meters, they can bear 300-400 kg per square meter; for spans over 4 meters, the load-bearing capacity remains at 250-300 kg per square meter.

IV. Precautions

1. It is strictly prohibited to add partition walls, install large fish tanks, or place heavy mechanical equipment on prefabricated floor slabs without professional structural calculations.
2. When renovating or adding floors to old houses, it is necessary to entrust a qualified testing agency to evaluate the remaining load-bearing capacity of the original prefabricated slabs and formulate a reinforcement plan.