The document discusses wind load calculation according to the Bangladesh National Building Code of 1993. It defines three terrain exposures and provides the formula for calculating sustained wind pressure which considers velocity, pressure conversion, structure importance, height, and exposure coefficients. It also discusses determining design wind pressure using a gust coefficient and pressure coefficient. Finally, it presents two methods - surface area and projected area - for calculating total design wind load on a structure.

1. Wind Load Calculation
(BNBC 1993)
Shihab Ahammed

2. Terrain Exposure
Exposure A- Urban and Sub urban areas, industrial areas, wooded
areas
Exposure B- Open terrain with scattered obstructions
Exposure C- Flat and Unobstructed open terrain

3. Sustained Wind Pressure
• 𝑞𝑧 = 𝐶𝐶𝐶𝐼𝐶𝑍𝑉𝑏
2
Here,
𝑞𝑧= sustained wind pressure (KN/m^2)
𝐶𝐶=velocity to pressure conversion coefficient= 47.2*10^-6
𝐶𝐼= structure importance co-efficient
𝑉𝑏 = basic wind speed (km/h)
𝐶𝑍= combined height and exposure co-efficient

4. Structure Importance Co-efficient 𝐶𝐼

5. Basic Wind Speed, Vb (km/h)

6. Combined Height and Exposure Co-efficient,
Cz

7. Design Wind Pressure
• Pz = 𝐶𝐺𝐶𝑝𝑞𝑧 (𝑘𝑁/𝑚^2)
• Here,
𝐶𝐺= Gust Co-efficient
𝐶𝑝= Pressure co-efficient for structures
𝑞𝑧= sustained wind pressure

8. Gust Co-efficient, 𝐶𝐺

9. Pressure co-efficient for structures, 𝐶𝑝

10. Design Wind Load
Surface Area
Method
Projected
Area Method

11. Projected Area Method
𝐹𝑧 = 𝑃𝑧𝐴𝑧
Here,
𝐹𝑧= total wind force on the framed system (KN)
𝑃𝑧= design wind pressure (KN/m^2)
𝐴𝑧= projected frontal area normal to wind tributary (m^2)