Strength Standards for Prefabricated Slab Houses

The strength standards for prefabricated slab houses cover various aspects such as concrete compressive strength, steel bar configuration, load performance, deflection, and crack width, as detailed below:

Concrete Compressive Strength: The commonly used concrete strength grades for prefabricated floor slabs range from C25 to C50 (in accordance with GB/T 51231 - 2017), with C30 being the most prevalent. Its 28-day compressive strength must be ≥30 MPa. High-strength concrete (e.g., C50) is often used for large-span floor slabs, allowing for a 10% - 15% reduction in thickness while ensuring load-bearing capacity and optimizing structural efficiency.

Steel Bar Configuration Standards: Main reinforcement typically employs HRB400-grade steel bars (with a yield strength ≥400 MPa), with diameters ranging from 8 to 16 mm and spacing of 100 to 200 mm, providing primary flexural resistance. Distribution reinforcement uses HPB300-grade steel bars (with a yield strength ≥300 MPa), with diameters of 6 to 10 mm, enhancing the floor slab's crack resistance through uniform distribution and preventing cracks caused by temperature changes or shrinkage.

Load Performance Requirements: Depending on the usage scenario, the uniformly distributed live load standard for residential floor slabs is 2 kN/m² (GB 50009 - 2012), while commercial floor slabs require ≥3.5 kN/m². Additionally, concentrated loads must be calculated separately, such as the local bearing of 1.5 kN from furniture, ensuring the floor slab does not fail under localized heavy loads.

Deflection and Crack Width: Chinese standards (GB/T 51231) require that the floor slab's deflection be ≤l/250 (where l is the span), meaning the maximum deformation under load must not exceed 1/250 of the span to ensure comfort. The crack width must be ≤0.3 mm to prevent structural durability issues due to crack propagation.

Strength Differences Among Various Types of Prefabricated Slabs: Cement prefabricated slabs (e.g., products from Qingzhou Xinwang Cement Products Business Department) can have a compressive strength of up to 108.4 MPa, suitable for residential and factory buildings. Truss floor decks (e.g., products from Tianjin Lvheng Energy Technology Development Co., Ltd.) have a compressive strength of 20 MPa but enhance overall stability through truss structures, offering good seismic performance and are suitable for buildings and factories with high dynamic load requirements.

Comparison Between Prefabricated and Cast-in-Place Slabs: Prefabricated slabs are produced in factories with standardized processes, typically using concrete strength grades of C30 to C40, comparable to cast-in-place concrete. Prestressed prefabricated slabs (e.g., SP slabs) use pre-stressing techniques to offset some of the tensile stresses generated by loads in advance, potentially offering better crack resistance and load-bearing capacity than ordinary cast-in-place slabs, especially for large-span or high-load scenarios.