Volume Calculation
Concrete volume calculation is essential for accurate material estimation and cost planning. For rectangular slabs, the volume is simply length × width × thickness. Circular slabs require calculating the area using πr² before multiplying by thickness. Irregular shapes like L-shaped slabs or custom polygons need more complex area calculations before volume determination.
Maximum Span Length
The maximum span of a concrete slab is governed by both strength and serviceability requirements. Strength considerations include moment capacity and shear capacity, while serviceability focuses on deflection limits and crack control. The design follows the formula:
Mu = φ × Mn ≥ w × L² / 8 (for simply supported)
Where φ is the strength reduction factor, Mn is the nominal moment capacity, w is the factored load, and L is the span length.
Wall Load Capacity
When designing slabs to support walls, engineers must consider both the self-weight of the wall and any additional live loads. The slab must have adequate moment and shear capacity to resist these loads without excessive deflection or cracking. The wall load is typically distributed over a width equal to the effective width of the slab that participates in resisting the load.
Reinforcement Design
Proper reinforcement is critical for concrete slabs. The minimum reinforcement ratio is typically 0.13% for slabs up to 150mm thick. Maximum spacing should not exceed 3 times the slab thickness or 300mm, whichever is smaller. Development length must be provided to ensure proper bond between concrete and steel.
Deflection Control
Deflection limits are specified as a fraction of the span (L/Δ). Typical values are L/250 for roofs, L/360 for floors supporting non-structural elements, and L/480 for floors supporting brittle partitions. Instantaneous deflection is calculated using the effective moment of inertia, while long-term deflection considers creep effects.