India's Wind Zone Map
IS 875 Part 3 divides India into wind zones based on basic wind speed (50-year return period): Zone I (Vb ≤ 33 m/s): central India - Madhya Pradesh, southern Rajasthan, interior Maharashtra. Zone II (Vb = 39 m/s): most of India - Nashik, Pune, Aurangabad, Delhi, Bengaluru. Zone III (Vb = 44 m/s): coastal and eastern India - Mumbai coast, AP coast, Odisha interior. Zone IV (Vb = 47 m/s): coastal Maharashtra Konkan, Tamil Nadu coast, West Bengal coast. Zone V (Vb = 50 m/s): Andaman & Nicobar, parts of northeast India. Zone VI (Vb = 55 m/s): cyclone-prone coastal areas - some Odisha and AP coast districts. Check the IS 875 Part 3 wind zone map for your project location before specifying poles.
How Wind Load is Calculated
Design wind pressure (pd) = 0.6 × Vd² (in N/m²), where Vd is design wind speed. Design wind speed Vd = Vb × k1 × k2 × k3. k1 = risk factor (1.0 for normal structures). k2 = terrain factor (varies by category - open terrain = higher k2 than urban with buildings). k3 = topography factor (1.0 for flat terrain, higher for hilltops). Wind force on pole: F = Cf × A × pd. Cf = force coefficient (approximately 0.8 for circular poles, 1.3 for square). A = projected area of pole (diameter × height). For a 6m circular GI pole with 0.076m diameter in Wind Zone II: A = 0.076 × 6 = 0.456 m². pd at Vb = 39 m/s = 0.6 × 39² ≈ 912 N/m². F = 0.8 × 0.456 × 912 ≈ 333N. This force creates a bending moment at the base that the pole and foundation must resist.
Practical Implications for Specification
The wind load drives: pole wall thickness (thicker wall = more bending resistance). Foundation depth and diameter. Arm design (longer arms = greater overturning moment). For solar street lights: the solar panel adds significant wind area at the top of the pole - a 40W panel (approximately 0.5m × 0.5m) adds 0.25 m² of projected area at the most critical point (maximum moment arm). In Zone IV–V (Konkan, cyclone coast): a solar panel at 6m height creates substantially more wind force than the pole itself. Use structural calculations from a civil/structural engineer for solar poles in Zone IV–V. Xera Tech provides wind load calculations and structural drawings for poles supplied in high-wind zones.
