Industrial Warehouse Roof Cladding in Arid Rajasthan

Case Study 2: Industrial Warehouse Roof Cladding in Arid Rajasthan

Scenario A single-storey, 120 m × 80 m pre-engineered steel warehouse is being constructed near Jodhpur, Rajasthan (Zone III per IS 875). The structure features a 10° pitched roof with exposed purlins and trapezoidal profile metal sheeting. Site context includes open desert terrain with negligible surrounding obstructions but frequent dust storms generating high-frequency gusts. Constraints include: budget sensitivity, need for rapid erection, and avoidance of secondary bracing — requiring cladding fasteners and sheet thickness to carry full wind uplift directly.

Given Data

• Basic Wind Speed (Vz): 35 m/s (Zone III, 50-year return)
• Probability Factor (Cp): 1.0
• Seasonal Variation Factor (Cst): 1.0 (uniform wind climate year-round)
• Topography Factor (Cs): 1.12 (minor escarpment 2 km west increases local wind speed)
• Height Factor (Cz): 1.05 (roof apex at 12.4 m; interpolated from IS 875 Table 5)
• Air Density (ρ): 1.15 kg/m³ (elevated elevation ~220 m ASL + hot, dry air)
• Dynamic Pressure Coefficient (K): 1.0
• Gust Effect Factor (G): 1.30 (dust-laden turbulent flow amplifies peak gusts)
• External Pressure Coefficient (Cpe): −0.9 (uplift on windward roof slope, per IS 875 Fig. 6)

Calculation Using the same formula:

Pd = 0.613 × Vz² × Cp × Cst × Cs × Cz × ρ × K × G × |Cpe|

• 0.613 × (35)² = 0.613 × 1225 = 750.925
• × Cp (1.0) = 750.925
• × Cst (1.0) = 750.925
• × Cs (1.12) = 841.036
• × Cz (1.05) = 883.088
• × ρ (1.15) = 1015.55
• × K (1.0) = 1015.55
• × G (1.30) = 1320.22
• × |Cpe| (0.9) = 1188.20 Pa = 1.19 kN/m²

Result and Decision The computed design wind pressure of 1.19 kN/m² fell within the capacity of the baseline 0.6 mm thick trapezoidal sheet (rated to 1.3 kN/m²), but uplift at eaves and ridges required localized reinforcement. Instead of upgrading entire roof sheets, engineers specified enhanced fastener patterns: 4 fasteners/m² (vs. standard 2.5) at perimeter zones (first 2.5 m from edges), using self-drilling screws with EPDM washers and increased penetration depth (≥ 32 mm into purlins). Structural analysis confirmed this solution met serviceability and ultimate limit states without cost-prohibitive material changes.

Lesson For low-rise industrial buildings, localized pressure intensification (e.g., at eaves, ridges, corners) often governs design—not the average Pd. Always apply Cpe values specific to zone and surface orientation (per IS 875 Cl. 7.3.3), and never assume uniform pressure distribution across the entire roof.