Standard Values of Strength for Prefabricated Slab Houses
The standard values of strength for prefabricated slab houses cover multiple aspects such as concrete compressive strength, steel bar configuration, load performance, and durability. The specific standards are as follows:
Concrete Compressive Strength: The commonly used concrete strength grades for prefabricated floor slabs range from C25 to C50, with C30 being the most prevalent. The 28-day compressive strength of C30 concrete must be ≥30 MPa. Taking C30 as an example, the standard value of cube compressive strength (fcu,k) is 30 N/mm², the standard value of axial compressive strength (fck) is 20.1 N/mm², and the standard value of axial tensile strength (ftk) is 2.01 N/mm². For ordinary residential floor slabs, a strength of 30 MPa can meet daily load-bearing requirements, while industrial plants may require high-strength prefabricated slabs with a strength of over 40 MPa. Additionally, the strength grade of ordinary prefabricated base slabs must be ≥C30, that of prestressed concrete base slabs must be ≥C40, and that of the post-poured layer must be ≥C25.
Steel Bar Configuration Standards: Main reinforcement bars typically use HRB400 grade steel bars (yield strength ≥400 MPa) with diameters ranging from 8 to 16 mm and spacings of 100 to 200 mm. Distribution bars use HPB300 grade steel bars (yield strength ≥300 MPa) with diameters ranging from 6 to 10 mm to ensure crack resistance. Regarding the thickness of the concrete cover, when the slab thickness is ≤100 mm, the cover thickness should not be less than 15 mm; when the slab thickness is >100 mm, it should not be less than 20 mm. The spacing of steel bars needs to be adjusted according to their diameters. For example, the spacing of HPB300 steel bars with a diameter of 8 mm should not exceed 200 mm, and the spacing of HRB400 steel bars with a diameter of 10 mm is usually 150 to 200 mm.
Load Performance Requirements: The standard value of uniformly distributed live load for residential floor slabs is 2 kN/m², while that for commercial floor slabs must be ≥3.5 kN/m². Concentrated loads require separate verification (e.g., local compression from furniture weighing 1.5 kN). Regarding short-term load test values, prefabricated slabs for residential floors must reach 2.0 kN/m², with a long-term load test value of 1.5 kN/m², and the deflection value should not exceed 1/200 of the calculated span. For industrial plant prefabricated slabs, the short-term load test value can be increased to 3.5 kN/m², with a long-term load test value of 2.5 kN/m², and the deflection value should not exceed 1/250 of the calculated span.
Durability Standards: Prefabricated slabs must meet durability requirements within their design service life (usually 50 years), including impermeability (Grade P6, withstanding a water pressure of 0.6 MPa without leakage) and frost resistance (Grade F150, with a mass loss of ≤5% and a strength loss of ≤25% after 150 freeze-thaw cycles). Additionally, the design must consider the impact of factors such as concrete carbonation and steel bar corrosion on long-term performance.
