Wind Load (structural)
Wind load in structural engineering refers to the force exerted by wind on a structure, calculated as a pressure applied to the exposed surfaces of buildings, towers, bridges, and other structures. Because wind pressure increases with the square of wind speed, even moderate increases in wind speed produce significantly larger forces. Structural design must account for both windward positive pressure and leeward suction, as well as internal pressures through openings; the relevant Indian standard is IS 875 (Part 3).
Key Formula
pz = 0.6 × Vz²
LaTeX: p_z = 0.6 \, V_z^2
| Symbol | Meaning | Unit |
|---|---|---|
| p_z | Design wind pressure at height z | N/m² |
| V_z | Design wind speed at height z = Vb × k1 × k2 × k3 | m/s |
| V_b | Basic wind speed (3-second gust, 50-year return period) | m/s |
| k_1 | Probability (risk) factor | dimensionless |
| k_2 | Terrain, height, and structure size factor | dimensionless |
| k_3 | Topography factor | dimensionless |
Worked Example
Problem
A building in Mumbai (basic wind speed Vb = 44 m/s per IS 875) is 30 m tall. Given k1 = 1.0, k2 = 1.05 (Terrain Category 2, class B), k3 = 1.0, find the design wind pressure pz at 30 m height.
Solution
Design wind speed: Vz = Vb × k1 × k2 × k3 = 44 × 1.0 × 1.05 × 1.0 = 46.2 m/s. Design wind pressure: pz = 0.6 × Vz² = 0.6 × (46.2)² = 0.6 × 2134.44 = 1280.7 N/m².
Answer
pz ≈ 1281 N/m² ≈ 1.28 kN/m² at 30 m height
Basic Wind Speeds (Vb) for Selected Indian Cities per IS 875 (Part 3)
| City | Basic Wind Speed Vb (m/s) | Wind Zone | Notes |
|---|---|---|---|
| Delhi | 47 | Zone IV | High wind zone |
| Mumbai | 44 | Zone III | Cyclone-prone coast |
| Chennai | 50 | Zone V | Highest risk coastal |
| Kolkata | 50 | Zone V | Cyclone-prone |
| Bengaluru | 33 | Zone II | Inland, lower risk |
| Bhubaneswar | 50 | Zone V | Odisha cyclone belt |
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Related Terms
Seismic Design
Seismic design is the process of designing structures to resist the dynamic forces imposed by earthquakes, ensuring they do not collapse and allow safe evacuation even under strong ground shaking. It involves determining design seismic forces based on a site's seismic zone, soil type, and building importance; modelling dynamic structural response; and detailing ductile connections and structural systems that can absorb and dissipate seismic energy. In India, seismic design follows IS 1893 (Part 1), which classifies the country into four seismic zones (II–V) of increasing hazard.
Steel Structure
A steel structure is a construction system in which the primary load-carrying framework is made from structural steel sections such as I-beams, channels, angles, and hollow sections connected by bolts, rivets, or welds. Steel structures offer high strength-to-weight ratios, predictable material properties, rapid erection, and the ability to span large distances, making them ideal for high-rise buildings, industrial sheds, bridges, and towers. Design follows limit-state or allowable-stress methods specified by standards such as IS 800 (India) or AISC (USA).
Bridge Design
Bridge design is the engineering discipline concerned with planning, analysing, and sizing all structural and non-structural components of a bridge to carry specified traffic, wind, seismic, and thermal loads safely and economically over its design life. The process involves selection of bridge type (beam, arch, truss, cable-stayed, suspension), site investigation, load calculations to relevant codes (IRC in India, AASHTO in the USA), structural analysis, material design, and consideration of aesthetics, constructability, and durability. Bridge design integrates structural mechanics, geotechnical engineering, hydraulics, and materials science.
The word 'wind' is from Old English 'wind', from Proto-Germanic 'windaz', related to Latin 'ventus' and Sanskrit 'vata'. 'Load' is from Old English 'lad' (way, course, support). The systematic study of wind forces on structures was pioneered by John Smeaton in the 18th century, and formalised by Osborne Reynolds and later engineers following disasters like the Tay Bridge collapse (1879) caused by underestimated wind loading.