The load calculation for the reinforced concrete cover of a ditch is based on standard design specifications for gutter covers. The maximum deflection, Dmax, should be less than or equal to L/200, and also not exceed 10mm (where L represents the span). For steel grating structures, the primary design condition involves determining the allowable bending stress [σ]. For Q235 carbon steel, the yield strength σS is 235 N/mm², and the ultimate tensile strength σb is 375 N/mm².
According to Article 9.1 of the relevant standard, the allowable stress [σ] must satisfy two key conditions:
1. When the design load is multiplied by 1.5, the steel grating should not undergo permanent deformation.
2. When the design load is multiplied by 3, the steel grating should not crack.
In practice, for Q235 carbon steel, an appropriate allowable bending stress [σ] is typically set at 120 N/mm². When the span L is small, the safety load capacity is generally governed by the strength condition. This means that the allowable load (including both uniform load Pu and line load PL) is calculated based on the allowable stress [σ], while also ensuring that the deflection remains below L/200 and does not exceed 10mm.
As the span increases, the deflection becomes a more critical factor in the design. According to reference data from , when the deflection D ≥ L/200 and D ≥ 10mm, the bearing capacity should be determined by the stiffness condition rather than strength. In such cases, the values of Pu and PL derived from the stiffness requirement will inherently meet the strength requirements, including the bending stress [σ].
The safety loads Pu and PL calculated using this method are therefore compliant with the provisions of Article 9.1 of the standard. Additionally, it's worth noting that the YB/T 4001-1998 standard for steel grating boards includes some data issues as outlined in Appendix B.
This detailed approach ensures that the steel grating structure is both safe and efficient, meeting all necessary engineering standards and performance criteria.
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