Industrial Warehouse Mezzanine Slab in Pune Inland Zone
Engineering Case Study
Case Study 2: Industrial Warehouse Mezzanine Slab in Pune Inland Zone
Scenario
A logistics warehouse in Chakan, Pune requires a 5 m × 15 m mezzanine floor to house office and sorting operations. The slab is supported on steel beams (simulating simply supported two-way action with dominant short-span bending). Constraints include: low headroom (max slab thickness 180 mm), need for rapid installation (prefab deck system compatibility), and live load spikes up to 10 kPa during pallet racking installation. No seismic or fire-rating requirements beyond standard IS 875.
Given Data
- Slab Thickness: 180 mm (minimum feasible for duct routing and weight reduction)
- Span Length: 5.0 m (critical short-direction span)
- Live Load: 10.0 kPa (for temporary equipment staging)
- Concrete Strength: 25 MPa (standard M25, locally sourced OPC)
- Steel Yield Strength: 415 MPa (Fe415 TMT bars — cost-optimized and widely available)
Calculation
Using the Rebar Design Calculator:
- Inputs:
slab_thickness=180,span_length=5.0,live_load=10.0,concrete_strength=25,steel_yield_strength=415. - Tool computes factored moment assuming DL = 180 mm × 25 kN/m³ = 4.5 kPa → $w_u = 1.5(4.5 + 10.0) = 21.75\ \text{kPa}$.
- $M_u = \frac{21.75 \times 5.0^2}{8} = 67.97\ \text{kN·m/m}$.
- Effective depth $d = 180 - 25 = 155\ \text{mm}$ (25 mm cover per IS 456 for moderate exposure).
- $R_n = 67.97 \times 10^6 / (0.9 \times 1000 \times 155^2) = 3.19\ \text{MPa}$.
- Solving for $\rho$: $\rho = \frac{0.85 \times 25}{415} \left[1 - \sqrt{1 - \frac{2 \times 3.19}{0.85 \times 25}}\right] \approx 0.0083$.
- $A_s = 0.0083 \times 1000 \times 155 = 1287\ \text{mm}^2/\text{m}$.
- For 16 mm Ø bars ($A_{bar} = 201\ \text{mm}^2$): $s = \frac{1000 \times 201}{1287} \approx 156.2\ \text{mm}$ → rounded to 150 mm c/c (next practical increment; also satisfies IS 456 max spacing = $3d = 465\ \text{mm}$ and min bar count ≥ 3/m).
Result and Decision
The calculator outputs:
- Rebar Area: 1286.8 mm²/m
- Rebar Spacing: 156.2 mm → adopted as 16 mm Ø @ 150 mm c/c, single layer (bottom only), with 10 mm Ø @ 250 mm c/c top mesh for shrinkage. Confirmed via manual check that $A_s > A_{s,min} = 0.85 f'_c / f_y \cdot b \cdot d = 0.78\ \text{mm}^2/\text{m}$ — well satisfied.
Lesson
When slab thickness is constrained, even modest increases in live load dramatically increase required steel area — often necessitating larger bar diameters and tighter spacing. Always validate minimum steel ratio and spacing against code-specified lower bounds; here, 16 mm @ 150 mm met both strength and ductility requirements without compromising constructability.